Edge gradients evaluation for 2D hybrid finite volume method model

USDA-ARS?s Scientific Manuscript database

In this study, a two-dimensional depth-integrated hydrodynamic model was developed using FVM on a hybrid unstructured collocated mesh system. To alleviate the negative effects of mesh irregularity and non-uniformity, a conservative evaluation method for edge gradients based on the second-order Tayl...

Gradient Calculation Methods on Arbitrary Polyhedral Unstructured Meshes for Cell-Centered CFD Solvers

NASA Technical Reports Server (NTRS)

Sozer, Emre; Brehm, Christoph; Kiris, Cetin C.

2014-01-01

A survey of gradient reconstruction methods for cell-centered data on unstructured meshes is conducted within the scope of accuracy assessment. Formal order of accuracy, as well as error magnitudes for each of the studied methods, are evaluated on a complex mesh of various cell types through consecutive local scaling of an analytical test function. The tests highlighted several gradient operator choices that can consistently achieve 1st order accuracy regardless of cell type and shape. The tests further offered error comparisons for given cell types, leading to the observation that the "ideal" gradient operator choice is not universal. Practical implications of the results are explored via CFD solutions of a 2D inviscid standing vortex, portraying the discretization error properties. A relatively naive, yet largely unexplored, approach of local curvilinear stencil transformation exhibited surprisingly favorable properties

Optimal integration strategies for a syngas fuelled SOFC and gas turbine hybrid

NASA Astrophysics Data System (ADS)

Zhao, Yingru; Sadhukhan, Jhuma; Lanzini, Andrea; Brandon, Nigel; Shah, Nilay

This article aims to develop a thermodynamic modelling and optimization framework for a thorough understanding of the optimal integration of fuel cell, gas turbine and other components in an ambient pressure SOFC-GT hybrid power plant. This method is based on the coupling of a syngas-fed SOFC model and an associated irreversible GT model, with an optimization algorithm developed using MATLAB to efficiently explore the range of possible operating conditions. Energy and entropy balance analysis has been carried out for the entire system to observe the irreversibility distribution within the plant and the contribution of different components. Based on the methodology developed, a comprehensive parametric analysis has been performed to explore the optimum system behavior, and predict the sensitivity of system performance to the variations in major design and operating parameters. The current density, operating temperature, fuel utilization and temperature gradient of the fuel cell, as well as the isentropic efficiencies and temperature ratio of the gas turbine cycle, together with three parameters related to the heat transfer between subsystems are all set to be controllable variables. Other factors affecting the hybrid efficiency have been further simulated and analysed. The model developed is able to predict the performance characteristics of a wide range of hybrid systems potentially sizing from 2000 to 2500 W m -2 with efficiencies varying between 50% and 60%. The analysis enables us to identify the system design tradeoffs, and therefore to determine better integration strategies for advanced SOFC-GT systems.

Correlation-based regularization and gradient operators for (joint) inversion on unstructured meshes

NASA Astrophysics Data System (ADS)

Jordi, Claudio; Doetsch, Joseph; Günther, Thomas; Schmelzbach, Cedric; Robertsson, Johan

2017-04-01

When working with unstructured meshes for geophysical inversions, special attention should be paid to the design of the operators that are used for regularizing the inverse problem and coupling of different property models in joint inversions. Regularization constraints for inversions on unstructured meshes are often defined in a rather ad-hoc manner and usually only involve the cell to which the operator is applied and its direct neighbours. Similarly, most structural coupling operators for joint inversion, such as the popular cross-gradients operator, are only defined in the direct neighbourhood of a cell. As a result, the regularization and coupling length scales and strength of these operators depend on the discretization as well as cell sizes and shape. Especially for unstructured meshes, where the cell sizes vary throughout the model domain, the dependency of the operator on the discretization may lead to artefacts. Designing operators that are based on a spatial correlation model allows to define correlation length scales over which an operator acts (called footprint), reducing the dependency on the discretization and the effects of variable cell sizes. Moreover, correlation-based operators can accommodate for expected anisotropy by using different length scales in horizontal and vertical directions. Correlation-based regularization operators also known as stochastic regularization operators have already been successfully applied to inversions on regular grids. Here, we formulate stochastic operators for unstructured meshes and apply them in 2D surface and 3D cross-well electrical resistivity tomography data inversion examples of layered media. Especially for the synthetic cross-well example, improved inversion results are achieved when stochastic regularization is used instead of a classical smoothness constraint. For the case of cross-gradients operators for joint inversion, the correlation model is used to define the footprint of the operator and weigh the contributions of the property values that are used to calculate the cross-gradients. In a first series of synthetic-data tests, we examined the mesh dependency of the cross-gradients operators. Compared to operators that are only defined in the direct neighbourhood of a cell, the dependency on the cell size of the cross-gradients calculation is markedly reduced when using operators with larger footprints. A second test with synthetic models focussed on the effect of small-scale variabilities of the parameter value on the cross-gradients calculation. Small-scale variabilities that are superimposed on a global trend of the property value can potentially degrade the cross-gradients calculation and destabilize joint inversion. We observe that the cross-gradients from operators with footprints larger than the length scale of the variabilities are less affected compared to operators with a small footprint. In joint inversions on unstructured meshes, we thus expect the correlation-based coupling operators to ensure robust coupling on a physically meaningful scale.

Grid adaption using Chimera composite overlapping meshes

NASA Technical Reports Server (NTRS)

Kao, Kai-Hsiung; Liou, Meng-Sing; Chow, Chuen-Yen

1993-01-01

The objective of this paper is to perform grid adaptation using composite over-lapping meshes in regions of large gradient to capture the salient features accurately during computation. The Chimera grid scheme, a multiple overset mesh technique, is used in combination with a Navier-Stokes solver. The numerical solution is first converged to a steady state based on an initial coarse mesh. Solution-adaptive enhancement is then performed by using a secondary fine grid system which oversets on top of the base grid in the high-gradient region, but without requiring the mesh boundaries to join in any special way. Communications through boundary interfaces between those separated grids are carried out using tri-linear interpolation. Applications to the Euler equations for shock reflections and to a shock wave/boundary layer interaction problem are tested. With the present method, the salient features are well resolved.

Grid adaptation using chimera composite overlapping meshes

NASA Technical Reports Server (NTRS)

Kao, Kai-Hsiung; Liou, Meng-Sing; Chow, Chuen-Yen

1994-01-01

The objective of this paper is to perform grid adaptation using composite overlapping meshes in regions of large gradient to accurately capture the salient features during computation. The chimera grid scheme, a multiple overset mesh technique, is used in combination with a Navier-Stokes solver. The numerical solution is first converged to a steady state based on an initial coarse mesh. Solution-adaptive enhancement is then performed by using a secondary fine grid system which oversets on top of the base grid in the high-gradient region, but without requiring the mesh boundaries to join in any special way. Communications through boundary interfaces between those separated grids are carried out using trilinear interpolation. Application to the Euler equations for shock reflections and to shock wave/boundary layer interaction problem are tested. With the present method, the salient features are well-resolved.

Grid adaptation using Chimera composite overlapping meshes

NASA Technical Reports Server (NTRS)

Kao, Kai-Hsiung; Liou, Meng-Sing; Chow, Chuen-Yen

1993-01-01

The objective of this paper is to perform grid adaptation using composite over-lapping meshes in regions of large gradient to capture the salient features accurately during computation. The Chimera grid scheme, a multiple overset mesh technique, is used in combination with a Navier-Stokes solver. The numerical solution is first converged to a steady state based on an initial coarse mesh. Solution-adaptive enhancement is then performed by using a secondary fine grid system which oversets on top of the base grid in the high-gradient region, but without requiring the mesh boundaries to join in any special way. Communications through boundary interfaces between those separated grids are carried out using tri-linear interpolation. Applications to the Euler equations for shock reflections and to a shock wave/boundary layer interaction problem are tested. With the present method, the salient features are well resolved.

Parallel, Gradient-Based Anisotropic Mesh Adaptation for Re-entry Vehicle Configurations

NASA Technical Reports Server (NTRS)

Bibb, Karen L.; Gnoffo, Peter A.; Park, Michael A.; Jones, William T.

2006-01-01

Two gradient-based adaptation methodologies have been implemented into the Fun3d refine GridEx infrastructure. A spring-analogy adaptation which provides for nodal movement to cluster mesh nodes in the vicinity of strong shocks has been extended for general use within Fun3d, and is demonstrated for a 70 sphere cone at Mach 2. A more general feature-based adaptation metric has been developed for use with the adaptation mechanics available in Fun3d, and is applicable to any unstructured, tetrahedral, flow solver. The basic functionality of general adaptation is explored through a case of flow over the forebody of a 70 sphere cone at Mach 6. A practical application of Mach 10 flow over an Apollo capsule, computed with the Felisa flow solver, is given to compare the adaptive mesh refinement with uniform mesh refinement. The examples of the paper demonstrate that the gradient-based adaptation capability as implemented can give an improvement in solution quality.

Effects of Mesh Irregularities on Accuracy of Finite-Volume Discretization Schemes

NASA Technical Reports Server (NTRS)

Diskin, Boris; Thomas, James L.

2012-01-01

The effects of mesh irregularities on accuracy of unstructured node-centered finite-volume discretizations are considered. The focus is on an edge-based approach that uses unweighted least-squares gradient reconstruction with a quadratic fit. For inviscid fluxes, the discretization is nominally third order accurate on general triangular meshes. For viscous fluxes, the scheme is an average-least-squares formulation that is nominally second order accurate and contrasted with a common Green-Gauss discretization scheme. Gradient errors, truncation errors, and discretization errors are separately studied according to a previously introduced comprehensive methodology. The methodology considers three classes of grids: isotropic grids in a rectangular geometry, anisotropic grids typical of adapted grids, and anisotropic grids over a curved surface typical of advancing layer grids. The meshes within the classes range from regular to extremely irregular including meshes with random perturbation of nodes. Recommendations are made concerning the discretization schemes that are expected to be least sensitive to mesh irregularities in applications to turbulent flows in complex geometries.

High-Fidelity Geometric Modeling and Mesh Generation for Mechanics Characterization of Polycrystalline Materials

DTIC Science & Technology

2015-01-07

and anisotropic quadrilateral meshes, which can be used as the control mesh for high-order T- spline surface modeling. Archival publications (published...anisotropic T-meshes for the further T- spline surface construction. Finally, a gradient flow-based method is developed to improve the T-mesh quality...shade-off. Halos are bright or dark thin regions around the boundary of the sample. These false edges around the object make many segmentation

Generating a Simulated Fluid Flow over a Surface Using Anisotropic Diffusion

NASA Technical Reports Server (NTRS)

Rodriguez, David L. (Inventor); Sturdza, Peter (Inventor)

2016-01-01

A fluid-flow simulation over a computer-generated surface is generated using a diffusion technique. The surface is comprised of a surface mesh of polygons. A boundary-layer fluid property is obtained for a subset of the polygons of the surface mesh. A gradient vector is determined for a selected polygon, the selected polygon belonging to the surface mesh but not one of the subset of polygons. A maximum and minimum diffusion rate is determined along directions determined using the gradient vector corresponding to the selected polygon. A diffusion-path vector is defined between a point in the selected polygon and a neighboring point in a neighboring polygon. An updated fluid property is determined for the selected polygon using a variable diffusion rate, the variable diffusion rate based on the minimum diffusion rate, maximum diffusion rate, and the gradient vector.

Discontinuous Skeletal Gradient Discretisation methods on polytopal meshes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Di Pietro, Daniele A.; Droniou, Jérôme; Manzini, Gianmarco

Here, in this work we develop arbitrary-order Discontinuous Skeletal Gradient Discretisations (DSGD) on general polytopal meshes. Discontinuous Skeletal refers to the fact that the globally coupled unknowns are broken polynomials on the mesh skeleton. The key ingredient is a high-order gradient reconstruction composed of two terms: (i) a consistent contribution obtained mimicking an integration by parts formula inside each element and (ii) a stabilising term for which sufficient design conditions are provided. An example of stabilisation that satisfies the design conditions is proposed based on a local lifting of high-order residuals on a Raviart–Thomas–Nédélec subspace. We prove that the novelmore » DSGDs satisfy coercivity, consistency, limit-conformity, and compactness requirements that ensure convergence for a variety of elliptic and parabolic problems. Lastly, links with Hybrid High-Order, non-conforming Mimetic Finite Difference and non-conforming Virtual Element methods are also studied. Numerical examples complete the exposition.« less

Generating a Simulated Fluid Flow Over an Aircraft Surface Using Anisotropic Diffusion

NASA Technical Reports Server (NTRS)

Rodriguez, David L. (Inventor); Sturdza, Peter (Inventor)

2013-01-01

A fluid-flow simulation over a computer-generated aircraft surface is generated using a diffusion technique. The surface is comprised of a surface mesh of polygons. A boundary-layer fluid property is obtained for a subset of the polygons of the surface mesh. A pressure-gradient vector is determined for a selected polygon, the selected polygon belonging to the surface mesh but not one of the subset of polygons. A maximum and minimum diffusion rate is determined along directions determined using a pressure gradient vector corresponding to the selected polygon. A diffusion-path vector is defined between a point in the selected polygon and a neighboring point in a neighboring polygon. An updated fluid property is determined for the selected polygon using a variable diffusion rate, the variable diffusion rate based on the minimum diffusion rate, maximum diffusion rate, and angular difference between the diffusion-path vector and the pressure-gradient vector.

Discontinuous Skeletal Gradient Discretisation methods on polytopal meshes

DOE PAGES

Di Pietro, Daniele A.; Droniou, Jérôme; Manzini, Gianmarco

2017-11-21

Here, in this work we develop arbitrary-order Discontinuous Skeletal Gradient Discretisations (DSGD) on general polytopal meshes. Discontinuous Skeletal refers to the fact that the globally coupled unknowns are broken polynomials on the mesh skeleton. The key ingredient is a high-order gradient reconstruction composed of two terms: (i) a consistent contribution obtained mimicking an integration by parts formula inside each element and (ii) a stabilising term for which sufficient design conditions are provided. An example of stabilisation that satisfies the design conditions is proposed based on a local lifting of high-order residuals on a Raviart–Thomas–Nédélec subspace. We prove that the novelmore » DSGDs satisfy coercivity, consistency, limit-conformity, and compactness requirements that ensure convergence for a variety of elliptic and parabolic problems. Lastly, links with Hybrid High-Order, non-conforming Mimetic Finite Difference and non-conforming Virtual Element methods are also studied. Numerical examples complete the exposition.« less

The lowest-order weak Galerkin finite element method for the Darcy equation on quadrilateral and hybrid meshes

NASA Astrophysics Data System (ADS)

Liu, Jiangguo; Tavener, Simon; Wang, Zhuoran

2018-04-01

This paper investigates the lowest-order weak Galerkin finite element method for solving the Darcy equation on quadrilateral and hybrid meshes consisting of quadrilaterals and triangles. In this approach, the pressure is approximated by constants in element interiors and on edges. The discrete weak gradients of these constant basis functions are specified in local Raviart-Thomas spaces, specifically RT0 for triangles and unmapped RT[0] for quadrilaterals. These discrete weak gradients are used to approximate the classical gradient when solving the Darcy equation. The method produces continuous normal fluxes and is locally mass-conservative, regardless of mesh quality, and has optimal order convergence in pressure, velocity, and normal flux, when the quadrilaterals are asymptotically parallelograms. Implementation is straightforward and results in symmetric positive-definite discrete linear systems. We present numerical experiments and comparisons with other existing methods.

Diesel Fueled SOFC for Class 7/Class 8 On-Highway Truck Auxiliary Power

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vesely, Charles John-Paul; Fuchs, Benjamin S.; Booten, Chuck W.

2010-03-31

The following report documents the progress of the Cummins Power Generation (CPG) Diesel Fueled SOFC for Class 7/Class 8 On-Highway Truck Auxiliary Power (SOFC APU) development and final testing under the U.S. Department of Energy (DOE) Energy Efficiency and Renewable Energy (EERE) contract DE-FC36-04GO14318. This report overviews and summarizes CPG and partner development leading to successful demonstration of the SOFC APU objectives and significant progress towards SOFC commercialization. Significant SOFC APU Milestones: Demonstrated: Operation meeting SOFC APU requirements on commercial Ultra Low Sulfur Diesel (ULSD) fuel. SOFC systems operating on dry CPOX reformate. Successful start-up and shut-down of SOFC APUmore » system without inert gas purge. Developed: Low cost balance of plant concepts and compatible systems designs. Identified low cost, high volume components for balance of plant systems. Demonstrated efficient SOFC output power conditioning. Demonstrated SOFC control strategies and tuning methods.« less

Probing and mapping electrode surfaces in solid oxide fuel cells.

PubMed

Blinn, Kevin S; Li, Xiaxi; Liu, Mingfei; Bottomley, Lawrence A; Liu, Meilin

2012-09-20

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen (1-7). The performance of SOFCs and the rates of many chemical and energy transformation processes in energy storage and conversion devices in general are limited primarily by charge and mass transfer along electrode surfaces and across interfaces. Unfortunately, the mechanistic understanding of these processes is still lacking, due largely to the difficulty of characterizing these processes under in situ conditions. This knowledge gap is a chief obstacle to SOFC commercialization. The development of tools for probing and mapping surface chemistries relevant to electrode reactions is vital to unraveling the mechanisms of surface processes and to achieving rational design of new electrode materials for more efficient energy storage and conversion(2). Among the relatively few in situ surface analysis methods, Raman spectroscopy can be performed even with high temperatures and harsh atmospheres, making it ideal for characterizing chemical processes relevant to SOFC anode performance and degradation(8-12). It can also be used alongside electrochemical measurements, potentially allowing direct correlation of electrochemistry to surface chemistry in an operating cell. Proper in situ Raman mapping measurements would be useful for pin-pointing important anode reaction mechanisms because of its sensitivity to the relevant species, including anode performance degradation through carbon deposition(8, 10, 13, 14) ("coking") and sulfur poisoning(11, 15) and the manner in which surface modifications stave off this degradation(16). The current work demonstrates significant progress towards this capability. In addition, the family of scanning probe microscopy (SPM) techniques provides a special approach to interrogate the electrode surface with nanoscale resolution. Besides the surface topography that is routinely collected by AFM and STM, other properties such as local electronic states, ion diffusion coefficient and surface potential can also be investigated(17-22). In this work, electrochemical measurements, Raman spectroscopy, and SPM were used in conjunction with a novel test electrode platform that consists of a Ni mesh electrode embedded in an yttria-stabilized zirconia (YSZ) electrolyte. Cell performance testing and impedance spectroscopy under fuel containing H2S was characterized, and Raman mapping was used to further elucidate the nature of sulfur poisoning. In situ Raman monitoring was used to investigate coking behavior. Finally, atomic force microscopy (AFM) and electrostatic force microscopy (EFM) were used to further visualize carbon deposition on the nanoscale. From this research, we desire to produce a more complete picture of the SOFC anode.

Probing and Mapping Electrode Surfaces in Solid Oxide Fuel Cells

PubMed Central

Blinn, Kevin S.; Li, Xiaxi; Liu, Mingfei; Bottomley, Lawrence A.; Liu, Meilin

2012-01-01

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen 1-7. The performance of SOFCs and the rates of many chemical and energy transformation processes in energy storage and conversion devices in general are limited primarily by charge and mass transfer along electrode surfaces and across interfaces. Unfortunately, the mechanistic understanding of these processes is still lacking, due largely to the difficulty of characterizing these processes under in situ conditions. This knowledge gap is a chief obstacle to SOFC commercialization. The development of tools for probing and mapping surface chemistries relevant to electrode reactions is vital to unraveling the mechanisms of surface processes and to achieving rational design of new electrode materials for more efficient energy storage and conversion2. Among the relatively few in situ surface analysis methods, Raman spectroscopy can be performed even with high temperatures and harsh atmospheres, making it ideal for characterizing chemical processes relevant to SOFC anode performance and degradation8-12. It can also be used alongside electrochemical measurements, potentially allowing direct correlation of electrochemistry to surface chemistry in an operating cell. Proper in situ Raman mapping measurements would be useful for pin-pointing important anode reaction mechanisms because of its sensitivity to the relevant species, including anode performance degradation through carbon deposition8, 10, 13, 14 ("coking") and sulfur poisoning11, 15 and the manner in which surface modifications stave off this degradation16. The current work demonstrates significant progress towards this capability. In addition, the family of scanning probe microscopy (SPM) techniques provides a special approach to interrogate the electrode surface with nanoscale resolution. Besides the surface topography that is routinely collected by AFM and STM, other properties such as local electronic states, ion diffusion coefficient and surface potential can also be investigated17-22. In this work, electrochemical measurements, Raman spectroscopy, and SPM were used in conjunction with a novel test electrode platform that consists of a Ni mesh electrode embedded in an yttria-stabilized zirconia (YSZ) electrolyte. Cell performance testing and impedance spectroscopy under fuel containing H2S was characterized, and Raman mapping was used to further elucidate the nature of sulfur poisoning. In situ Raman monitoring was used to investigate coking behavior. Finally, atomic force microscopy (AFM) and electrostatic force microscopy (EFM) were used to further visualize carbon deposition on the nanoscale. From this research, we desire to produce a more complete picture of the SOFC anode. PMID:23023264

An optimization-based framework for anisotropic simplex mesh adaptation

NASA Astrophysics Data System (ADS)

Yano, Masayuki; Darmofal, David L.

2012-09-01

We present a general framework for anisotropic h-adaptation of simplex meshes. Given a discretization and any element-wise, localizable error estimate, our adaptive method iterates toward a mesh that minimizes error for a given degrees of freedom. Utilizing mesh-metric duality, we consider a continuous optimization problem of the Riemannian metric tensor field that provides an anisotropic description of element sizes. First, our method performs a series of local solves to survey the behavior of the local error function. This information is then synthesized using an affine-invariant tensor manipulation framework to reconstruct an approximate gradient of the error function with respect to the metric tensor field. Finally, we perform gradient descent in the metric space to drive the mesh toward optimality. The method is first demonstrated to produce optimal anisotropic meshes minimizing the L2 projection error for a pair of canonical problems containing a singularity and a singular perturbation. The effectiveness of the framework is then demonstrated in the context of output-based adaptation for the advection-diffusion equation using a high-order discontinuous Galerkin discretization and the dual-weighted residual (DWR) error estimate. The method presented provides a unified framework for optimizing both the element size and anisotropy distribution using an a posteriori error estimate and enables efficient adaptation of anisotropic simplex meshes for high-order discretizations.

Adjoint Sensitivity Computations for an Embedded-Boundary Cartesian Mesh Method and CAD Geometry

NASA Technical Reports Server (NTRS)

Nemec, Marian; Aftosmis,Michael J.

2006-01-01

Cartesian-mesh methods are perhaps the most promising approach for addressing the issues of flow solution automation for aerodynamic design problems. In these methods, the discretization of the wetted surface is decoupled from that of the volume mesh. This not only enables fast and robust mesh generation for geometry of arbitrary complexity, but also facilitates access to geometry modeling and manipulation using parametric Computer-Aided Design (CAD) tools. Our goal is to combine the automation capabilities of Cartesian methods with an eficient computation of design sensitivities. We address this issue using the adjoint method, where the computational cost of the design sensitivities, or objective function gradients, is esseutially indepeudent of the number of design variables. In previous work, we presented an accurate and efficient algorithm for the solution of the adjoint Euler equations discretized on Cartesian meshes with embedded, cut-cell boundaries. Novel aspects of the algorithm included the computation of surface shape sensitivities for triangulations based on parametric-CAD models and the linearization of the coupling between the surface triangulation and the cut-cells. The objective of the present work is to extend our adjoint formulation to problems involving general shape changes. Central to this development is the computation of volume-mesh sensitivities to obtain a reliable approximation of the objective finction gradient. Motivated by the success of mesh-perturbation schemes commonly used in body-fitted unstructured formulations, we propose an approach based on a local linearization of a mesh-perturbation scheme similar to the spring analogy. This approach circumvents most of the difficulties that arise due to non-smooth changes in the cut-cell layer as the boundary shape evolves and provides a consistent approximation tot he exact gradient of the discretized abjective function. A detailed gradient accurace study is presented to verify our approach. Thereafter, we focus on a shape optimization problem for an Apollo-like reentry capsule. The optimization seeks to enhance the lift-to-drag ratio of the capsule by modifyjing the shape of its heat-shield in conjunction with a center-of-gravity (c.g.) offset. This multipoint and multi-objective optimization problem is used to demonstrate the overall effectiveness of the Cartesian adjoint method for addressing the issues of complex aerodynamic design. This abstract presents only a brief outline of the numerical method and results; full details will be given in the final paper.

Cycle Analysis of Two-stage Planar SOFC Power Generation by Series Connection of Low and High Temperature SOFCs

NASA Astrophysics Data System (ADS)

Ohba, Takahiro; Takezawa, Shinya; Araki, Takuto; Onda, Kazuo; Sakaki, Yoshinori

Solid Oxide Fuel Cell (SOFC) can be composed by solid components, and high power generation efficiency of a whole cycle is obtained by using high temperature exhaust heat for fuel reforming and bottoming power generation. Recently, the low temperature SOFC, which runs in the temperature range of around 600°C or above, has been developed with the high efficiency of power generation. On the other hand, multi-stage power generation system has been proposed by the United States DOE. In this study, a power generation system of two-stage SOFC by series connection of low and high temperature SOFCs has been studied. Overpotential data for low-temperature SOFC used in this study are based on recent published data, and those for high temperature SOFC arhaihe based on our previous study. The analytical results show the two-stage SOFC power generation efficiency of 50.3% and the total power generation efficiency of 56.1% under a standard operating condition.

Cycle analysis of planar SOFC power generation with serial connection of low and high temperature SOFCs

NASA Astrophysics Data System (ADS)

Araki, Takuto; Ohba, Takahiro; Takezawa, Shinya; Onda, Kazuo; Sakaki, Yoshinori

Solid oxide fuel cells (SOFCs) can be composed of solid components for stable operation, and high power generation efficiency is obtained by using high temperature exhaust heat for fuel reforming and bottoming power generation by a gas turbine. Recently, low-temperature SOFCs, which run in the temperature range of around 600 °C or above and give high power generation efficiency, have been developed. On the other hand, a power generation system with multi-staged fuel cells has been proposed by the United States DOE to obtain high efficiency. In our present study, a power generation system consisting of two-staged SOFCs with serial connection of low and high temperature SOFCs was investigated. Overpotential data for the low-temperature SOFC used in this study are based on recently published data, while data for high-temperature SOFC are based on our previous study. The numerical results show that the power generation efficiency of the two-staged SOFCs is 50.3% and the total efficiency of power generation with gas turbine is 56.1% under standard operating conditions. These efficiencies are a little higher than those by high-temperature SOFC only.

A matrix-form GSM-CFD solver for incompressible fluids and its application to hemodynamics

NASA Astrophysics Data System (ADS)

Yao, Jianyao; Liu, G. R.

2014-10-01

A GSM-CFD solver for incompressible flows is developed based on the gradient smoothing method (GSM). A matrix-form algorithm and corresponding data structure for GSM are devised to efficiently approximate the spatial gradients of field variables using the gradient smoothing operation. The calculated gradient values on various test fields show that the proposed GSM is capable of exactly reproducing linear field and of second order accuracy on all kinds of meshes. It is found that the GSM is much more robust to mesh deformation and therefore more suitable for problems with complicated geometries. Integrated with the artificial compressibility approach, the GSM is extended to solve the incompressible flows. As an example, the flow simulation of carotid bifurcation is carried out to show the effectiveness of the proposed GSM-CFD solver. The blood is modeled as incompressible Newtonian fluid and the vessel is treated as rigid wall in this paper.

Numeric Design and Performance Analysis of Solid Oxide Fuel Cell -- Gas Turbine Hybrids on Aircraft

NASA Astrophysics Data System (ADS)

Hovakimyan, Gevorg

The aircraft industry benefits greatly from small improvements in aircraft component design. One possible area of improvement is in the Auxiliary Power Unit (APU). Modern aircraft APUs are gas turbines located in the tail section of the aircraft that generate additional power when needed. Unfortunately the efficiency of modern aircraft APUs is low. Solid Oxide Fuel Cell/Gas Turbine (SOFC/GT) hybrids are one possible alternative for replacing modern gas turbine APUs. This thesis investigates the feasibility of replacing conventional gas turbine APUs with SOFC/GT APUs on aircraft. An SOFC/GT design algorithm was created in order to determine the specifications of an SOFC/GT APU. The design algorithm is comprised of several integrated modules which together model the characteristics of each component of the SOFC/GT system. Given certain overall inputs, through numerical analysis, the algorithm produces an SOFC/GT APU, optimized for specific power and efficiency, capable of performing to the required specifications. The SOFC/GT design is then input into a previously developed quasi-dynamic SOFC/GT model to determine its load following capabilities over an aircraft flight cycle. Finally an aircraft range study is conducted to determine the feasibility of the SOFC/GT APU as a replacement for the conventional gas turbine APU. The design results show that SOFC/GT APUs have lower specific power than GT systems, but have much higher efficiencies. Moreover, the dynamic simulation results show that SOFC/GT APUs are capable of following modern flight loads. Finally, the range study determined that SOFC/GT APUs are more attractive over conventional APUs for longer range aircraft.

The modeling of a standalone solid-oxide fuel cell auxiliary power unit

NASA Astrophysics Data System (ADS)

Lu, N.; Li, Q.; Sun, X.; Khaleel, M. A.

In this research, a Simulink model of a standalone vehicular solid-oxide fuel cell (SOFC) auxiliary power unit (APU) is developed. The SOFC APU model consists of three major components: a controller model; a power electronics system model; and an SOFC plant model, including an SOFC stack module, two heat exchanger modules, and a combustor module. This paper discusses the development of the nonlinear dynamic models for the SOFC stacks, the heat exchangers and the combustors. When coupling with a controller model and a power electronic circuit model, the developed SOFC plant model is able to model the thermal dynamics and the electrochemical dynamics inside the SOFC APU components, as well as the transient responses to the electric loading changes. It has been shown that having such a model for the SOFC APU will help design engineers to adjust design parameters to optimize the performance. The modeling results of the SOFC APU heat-up stage and the output voltage response to a sudden load change are presented in this paper. The fuel flow regulation based on fuel utilization is also briefly discussed.

Dynamic mesh for TCAD modeling with ECORCE

NASA Astrophysics Data System (ADS)

Michez, A.; Boch, J.; Touboul, A.; Saigné, F.

2016-08-01

Mesh generation for TCAD modeling is challenging. Because densities of carriers can change by several orders of magnitude in thin areas, a significant change of the solution can be observed for two very similar meshes. The mesh must be defined at best to minimize this change. To address this issue, a criterion based on polynomial interpolation on adjacent nodes is proposed that adjusts accurately the mesh to the gradients of Degrees of Freedom. Furthermore, a dynamic mesh that follows changes of DF in DC and transient mode is a powerful tool for TCAD users. But, in transient modeling, adding nodes to a mesh induces oscillations in the solution that appears as spikes at the current collected at the contacts. This paper proposes two schemes that solve this problem. Examples show that using these techniques, the dynamic mesh generator of the TCAD tool ECORCE handle semiconductors devices in DC and transient mode.

Unstructured and adaptive mesh generation for high Reynolds number viscous flows

NASA Technical Reports Server (NTRS)

Mavriplis, Dimitri J.

1991-01-01

A method for generating and adaptively refining a highly stretched unstructured mesh suitable for the computation of high-Reynolds-number viscous flows about arbitrary two-dimensional geometries was developed. The method is based on the Delaunay triangulation of a predetermined set of points and employs a local mapping in order to achieve the high stretching rates required in the boundary-layer and wake regions. The initial mesh-point distribution is determined in a geometry-adaptive manner which clusters points in regions of high curvature and sharp corners. Adaptive mesh refinement is achieved by adding new points in regions of large flow gradients, and locally retriangulating; thus, obviating the need for global mesh regeneration. Initial and adapted meshes about complex multi-element airfoil geometries are shown and compressible flow solutions are computed on these meshes.

Online estimation of internal stack temperatures in solid oxide fuel cell power generating units

NASA Astrophysics Data System (ADS)

Dolenc, B.; Vrečko, D.; Juričić, Ɖ.; Pohjoranta, A.; Pianese, C.

2016-12-01

Thermal stress is one of the main factors affecting the degradation rate of solid oxide fuel cell (SOFC) stacks. In order to mitigate the possibility of fatal thermal stress, stack temperatures and the corresponding thermal gradients need to be continuously controlled during operation. Due to the fact that in future commercial applications the use of temperature sensors embedded within the stack is impractical, the use of estimators appears to be a viable option. In this paper we present an efficient and consistent approach to data-driven design of the estimator for maximum and minimum stack temperatures intended (i) to be of high precision, (ii) to be simple to implement on conventional platforms like programmable logic controllers, and (iii) to maintain reliability in spite of degradation processes. By careful application of subspace identification, supported by physical arguments, we derive a simple estimator structure capable of producing estimates with 3% error irrespective of the evolving stack degradation. The degradation drift is handled without any explicit modelling. The approach is experimentally validated on a 10 kW SOFC system.

Anisotropic diffusion in mesh-free numerical magnetohydrodynamics

NASA Astrophysics Data System (ADS)

Hopkins, Philip F.

2017-04-01

We extend recently developed mesh-free Lagrangian methods for numerical magnetohydrodynamics (MHD) to arbitrary anisotropic diffusion equations, including: passive scalar diffusion, Spitzer-Braginskii conduction and viscosity, cosmic ray diffusion/streaming, anisotropic radiation transport, non-ideal MHD (Ohmic resistivity, ambipolar diffusion, the Hall effect) and turbulent 'eddy diffusion'. We study these as implemented in the code GIZMO for both new meshless finite-volume Godunov schemes (MFM/MFV). We show that the MFM/MFV methods are accurate and stable even with noisy fields and irregular particle arrangements, and recover the correct behaviour even in arbitrarily anisotropic cases. They are competitive with state-of-the-art AMR/moving-mesh methods, and can correctly treat anisotropic diffusion-driven instabilities (e.g. the MTI and HBI, Hall MRI). We also develop a new scheme for stabilizing anisotropic tensor-valued fluxes with high-order gradient estimators and non-linear flux limiters, which is trivially generalized to AMR/moving-mesh codes. We also present applications of some of these improvements for SPH, in the form of a new integral-Godunov SPH formulation that adopts a moving-least squares gradient estimator and introduces a flux-limited Riemann problem between particles.

Minimizing finite-volume discretization errors on polyhedral meshes

NASA Astrophysics Data System (ADS)

Mouly, Quentin; Evrard, Fabien; van Wachem, Berend; Denner, Fabian

2017-11-01

Tetrahedral meshes are widely used in CFD to simulate flows in and around complex geometries, as automatic generation tools now allow tetrahedral meshes to represent arbitrary domains in a relatively accessible manner. Polyhedral meshes, however, are an increasingly popular alternative. While tetrahedron have at most four neighbours, the higher number of neighbours per polyhedral cell leads to a more accurate evaluation of gradients, essential for the numerical resolution of PDEs. The use of polyhedral meshes, nonetheless, introduces discretization errors for finite-volume methods: skewness and non-orthogonality, which occur with all sorts of unstructured meshes, as well as errors due to non-planar faces, specific to polygonal faces with more than three vertices. Indeed, polyhedral mesh generation algorithms cannot, in general, guarantee to produce meshes free of non-planar faces. The presented work focuses on the quantification and optimization of discretization errors on polyhedral meshes in the context of finite-volume methods. A quasi-Newton method is employed to optimize the relevant mesh quality measures. Various meshes are optimized and CFD results of cases with known solutions are presented to assess the improvements the optimization approach can provide.

Method and apparatus for assembling solid oxide fuel cells

DOEpatents

Szreders, B.E.; Campanella, N.

1988-05-11

This invention relates generally to solid oxide fuel power generators and is particularly directed to improvements in the assembly and coupling of solid oxide fuel cell modules. A plurality of jet air tubes are supported and maintained in a spaced matrix array by a positioning/insertion assembly for insertion in respective tubes of a solid oxide fuel cell (SOFC) in the assembly of an SOFC module. The positioning/insertion assembly includes a plurality of generally planar, elongated, linear vanes which are pivotally mounted at each end thereof to a support frame. A rectangular compression assembly of adjustable size is adapted to receive and squeeze a matrix of SOFC tubes so as to compress the inter-tube nickel felt conductive pads which provide series/parallel electrical connection between adjacent SOFCs, with a series of increasingly larger retainer frames used to maintain larger matrices of SOFC tubes in position. Expansion of the SOFC module housing at the high operating temperatures of the SOFC is accommodated by conductive, flexible, resilient expansion, connector bars which provide support and electrical coupling at the top and bottom of the SOFC module housing. 17 figs.

Method and apparatus for assembling solid oxide fuel cells

DOEpatents

Szreders, Bernard E.; Campanella, Nicholas

1989-01-01

A plurality of jet air tubes are supported and maintained in a spaced matrix array by a positioning/insertion assembly for insertion in respective tubes of a solid oxide fuel cell (SOFC) in the assembly of an SOFC module. The positioning/insertion assembly includes a plurality of generally planar, elongated, linear vanes which are pivotally mounted at each end thereof to a support frame. The vanes, which each include a plurality of spaced slots along the facing edges thereof, may be pivotally displaced from a generally vertical orientation, wherein each jet air tube is positioned within and engaged by the aligned slots of a plurality of paired upper and lower vanes to facilitate their insertion in respective aligned SOFC tubes arranged in a matrix array, to an inclined orientation, wherein the jet air tubes may be removed from the positioning/insertion assembly after being inserted in the SOFC tubes. A rectangular compression assembly of adjustable size is adapted to receive and squeeze a matrix of SOFC tubes so as to compress the inter-tube nickel felt conductive pads which provide series/parallel electrical connection between adjacent SOFCs, with a series of increasingly larger retainer frames used to maintain larger matrices of SOFC tubes in position. Expansion of the SOFC module housing at the high operating temperatures of the SOFC is accommodated by conductive, flexible, resilient expansion, connector bars which provide support and electrical coupling at the top and bottom of the SOFC module housing.

Direct methane solid oxide fuel cells and their related applications

NASA Astrophysics Data System (ADS)

Lin, Yuanbo

Solid oxide fuel cells (SOFCs), renowned for their high electrical generation efficiency with low pollutant production, are promising for reducing global energy and environmental concerns. However, there are major barriers for SOFC commercialization. A primary challenge is reducing the capital cost of SOFC power plants to levels that can compete with other generation methods. While the focus of this thesis research was on operation of SOFCs directly with methane fuel, the underlying motivation was to make SOFCs more competitive by reducing their cost. This can be achieved by making SOFCs that reduce the size and complexity of the required "balance of plant". Firstly, direct operation of SOFCs on methane is desirable since it can eliminate the external reformer. However, effective means must be found to suppress deleterious anode coking in methane. In this thesis, the operating conditions under which SOFCs can operate stably and without anode coking were investigated in detail, and the underlying mechanisms of coking and degradation were determined. Furthermore, a novel design utilizing an inert anode barrier layer was developed and shown to substantially improve stability against coking. Secondly, the direct methane SOFCs were investigated for use as electrochemical partial oxidation (EPOx) reactors that can co-generate electricity and synthesis gas (CO+H2) from methane. The results indicated that conventional SOFCs work quite well as methane partial oxidation reactors, producing syngas at relatively high rates. While this approach would not decrease the cost of SOFC power plant, it would improve prospects for commercialization by increasing the value of the power plant, because two products, electricity and syngas, can be sold. Thirdly, SOFCs utilizing thin (La,Sr)(Ga,Mg)O3 electrolytes were demonstrated. This highly conductive material allows lower SOFC operation temperature, leading to the use of lower-cost materials for sealing, interconnection, and balance of plant. Deleterious electrolyte/electrode reactions and electrolyte La loss were avoided during high-temperature co-firing by using thin La-doped ceria barrier layers, allowing very high power densities at moderate operating temperatures. (La,Sr)(Ga,Mg)O3-(La,Sr)(Fe,Co)O3 composite cathodes were investigated and optimal processing parameters that yield low interfacial polarization resistance at intermediate temperature were determined.

On the electromagnetic scattering from infinite rectangular grids with finite conductivity

NASA Technical Reports Server (NTRS)

Christodoulou, C. G.; Kauffman, J. F.

1986-01-01

A variety of methods can be used in constructing solutions to the problem of mesh scattering. However, each of these methods has certain drawbacks. The present paper is concerned with a new technique which is valid for all spacings. The new method involved, called the fast Fourier transform-conjugate gradient method (FFT-CGM), represents an iterative technique which employs the conjugate gradient method to improve upon each iterate, utilizing the fast Fourier transform. The FFT-CGM method provides a new accurate model which can be extended and applied to the more difficult problems of woven mesh surfaces. The formulation of the FFT-conjugate gradient method for aperture fields and current densities for a planar periodic structure is considered along with singular operators, the formulation of the FFT-CG method for thin wires with finite conductivity, and reflection coefficients.

Evaluation of solid oxide fuel cell systems for electricity generation

NASA Technical Reports Server (NTRS)

Somers, E. V.; Vidt, E. J.; Grimble, R. E.

1982-01-01

Air blown (low BTU) gasification with atmospheric pressure Solid Electrolyte Fuel Cells (SOFC) and Rankine bottoming cycle, oxygen blown (medium BTU) gasification with atmospheric pressure SOFC and Rankine bottoming cycle, air blown gasification with pressurized SOFC and combined Brayton/Rankine bottoming cycle, oxygen blown gasification with pressurized SOFC and combined Brayton/Rankine bottoming cycle were evaluated.

Predicting mesh density for adaptive modelling of the global atmosphere.

PubMed

Weller, Hilary

2009-11-28

The shallow water equations are solved using a mesh of polygons on the sphere, which adapts infrequently to the predicted future solution. Infrequent mesh adaptation reduces the cost of adaptation and load-balancing and will thus allow for more accurate mapping on adaptation. We simulate the growth of a barotropically unstable jet adapting the mesh every 12 h. Using an adaptation criterion based largely on the gradient of the vorticity leads to a mesh with around 20 per cent of the cells of a uniform mesh that gives equivalent results. This is a similar proportion to previous studies of the same test case with mesh adaptation every 1-20 min. The prediction of the mesh density involves solving the shallow water equations on a coarse mesh in advance of the locally refined mesh in order to estimate where features requiring higher resolution will grow, decay or move to. The adaptation criterion consists of two parts: that resolved on the coarse mesh, and that which is not resolved and so is passively advected on the coarse mesh. This combination leads to a balance between resolving features controlled by the large-scale dynamics and maintaining fine-scale features.

Development of Anode-Supported Single Cells and Small Stacks for Intermediate Temperature Sofc at Kepri

NASA Astrophysics Data System (ADS)

Yoo, Y.-S.; Park, J.-W.; Park, J.-K.; Lim, H.-C.; Oh, J.-M.; Bae, J.-M.

Recent results on intermediate temperature-operating solid oxide fuel cells (IT-SOFC) are mainly focused on getting the higher performance of single cell at lower operating temperature, especially using planar type. We have started a project to develop 1 kW-class SOFC system for Residential Power Generation(RPG) application. For a 1 kW-class SOFC stack that can be operated at intermediate temperatures, we have developed anode-supported, planar type SOFC to have advantages for commercialization of SOFCs considering mass production and using cost-effective interconnects such as ferritic stainless steels. At higher temperature, performance of SOFC can be increased due to higher electrochemical activity of electrodes and lower ohmic losses, but the surface of metallic interconnects at cathode side is rapidly oxidized into resistive oxide scale. For efficient operation of SOFC at reduced temperature at, firstly we have developed alternative cathode materials of LSCF instead of LSM to get higher performance of electrodes, and secondly introduced functional-layered structure at anode side. The I-V and AC impedance characteristics of improved single cells and small stacks were evaluated at intermediate temperatures (650°C and 750°C) using hydrogen gas as a fuel.

A Moving Mesh Finite Element Algorithm for Singular Problems in Two and Three Space Dimensions

NASA Astrophysics Data System (ADS)

Li, Ruo; Tang, Tao; Zhang, Pingwen

2002-04-01

A framework for adaptive meshes based on the Hamilton-Schoen-Yau theory was proposed by Dvinsky. In a recent work (2001, J. Comput. Phys.170, 562-588), we extended Dvinsky's method to provide an efficient moving mesh algorithm which compared favorably with the previously proposed schemes in terms of simplicity and reliability. In this work, we will further extend the moving mesh methods based on harmonic maps to deal with mesh adaptation in three space dimensions. In obtaining the variational mesh, we will solve an optimization problem with some appropriate constraints, which is in contrast to the traditional method of solving the Euler-Lagrange equation directly. The key idea of this approach is to update the interior and boundary grids simultaneously, rather than considering them separately. Application of the proposed moving mesh scheme is illustrated with some two- and three-dimensional problems with large solution gradients. The numerical experiments show that our methods can accurately resolve detail features of singular problems in 3D.

Accuracy of Gradient Reconstruction on Grids with High Aspect Ratio

NASA Technical Reports Server (NTRS)

Thomas, James

2008-01-01

Gradient approximation methods commonly used in unstructured-grid finite-volume schemes intended for solutions of high Reynolds number flow equations are studied comprehensively. The accuracy of gradients within cells and within faces is evaluated systematically for both node-centered and cell-centered formulations. Computational and analytical evaluations are made on a series of high-aspect-ratio grids with different primal elements, including quadrilateral, triangular, and mixed element grids, with and without random perturbations to the mesh. Both rectangular and cylindrical geometries are considered; the latter serves to study the effects of geometric curvature. The study shows that the accuracy of gradient reconstruction on high-aspect-ratio grids is determined by a combination of the grid and the solution. The contributors to the error are identified and approaches to reduce errors are given, including the addition of higher-order terms in the direction of larger mesh spacing. A parameter GAMMA characterizing accuracy on curved high-aspect-ratio grids is discussed and an approximate-mapped-least-square method using a commonly-available distance function is presented; the method provides accurate gradient reconstruction on general grids. The study is intended to be a reference guide accompanying the construction of accurate and efficient methods for high Reynolds number applications

High-temperature Raman spectroscopy of solid oxide fuel cell materials and processes.

PubMed

Pomfret, Michael B; Owrutsky, Jeffrey C; Walker, Robert A

2006-09-07

Chemical and material processes occurring in high temperature environments are difficult to quantify due to a lack of experimental methods that can probe directly the species present. In this letter, Raman spectroscopy is shown to be capable of identifying in-situ and noninvasively changes in material properties as well as the formation and disappearance of molecular species on surfaces at temperatures of 715 degrees C. The material, yttria-stabilized zirconia or YSZ, and the molecular species, Ni/NiO and nanocrystalline graphite, factor prominently in the chemistry of solid oxide fuel cells (SOFCs). Experiments demonstrate the ability of Raman spectroscopy to follow reversible oxidation/reduction kinetics of Ni/NiO as well as the rate of carbon disappearance when graphite, formed in-situ, is exposed to a weakly oxidizing atmosphere. In addition, the Raman active phonon mode of YSZ shows a temperature dependent shift that correlates closely with the expansion of the lattice parameter, thus providing a convenient internal diagnostic for identifying thermal gradients in high temperature systems. These findings provide direct insight into processes likely to occur in operational SOFCs and motivate the use of in-situ Raman spectroscopy to follow chemical processes in these high-temperature, electrochemically active environments.

In-Situ Optical Studies of Oxidation/Reduction Kinetics on SOFC Cermet Anodes

DTIC Science & Technology

2010-12-28

DATES COVERED (From - To) 1/29/10-9/30/10 4. TITLE AND SUBTITLE In situ optical studies of oxidation/reduction kinetics on SOFC cermet anodes 5a...0572 In-situ Optical Studies of Oxidation/Reduction Kinetics on SOFC Cermet Anodes Department of Chemistry and Biochemistry Montana State University...of Research In-situ Optical Studies of Oxidation/Reduction Kinetics on SOFC Cermet Anodes Principal Investigator Robert Walker Organization

A PDE Sensitivity Equation Method for Optimal Aerodynamic Design

NASA Technical Reports Server (NTRS)

Borggaard, Jeff; Burns, John

1996-01-01

The use of gradient based optimization algorithms in inverse design is well established as a practical approach to aerodynamic design. A typical procedure uses a simulation scheme to evaluate the objective function (from the approximate states) and its gradient, then passes this information to an optimization algorithm. Once the simulation scheme (CFD flow solver) has been selected and used to provide approximate function evaluations, there are several possible approaches to the problem of computing gradients. One popular method is to differentiate the simulation scheme and compute design sensitivities that are then used to obtain gradients. Although this black-box approach has many advantages in shape optimization problems, one must compute mesh sensitivities in order to compute the design sensitivity. In this paper, we present an alternative approach using the PDE sensitivity equation to develop algorithms for computing gradients. This approach has the advantage that mesh sensitivities need not be computed. Moreover, when it is possible to use the CFD scheme for both the forward problem and the sensitivity equation, then there are computational advantages. An apparent disadvantage of this approach is that it does not always produce consistent derivatives. However, for a proper combination of discretization schemes, one can show asymptotic consistency under mesh refinement, which is often sufficient to guarantee convergence of the optimal design algorithm. In particular, we show that when asymptotically consistent schemes are combined with a trust-region optimization algorithm, the resulting optimal design method converges. We denote this approach as the sensitivity equation method. The sensitivity equation method is presented, convergence results are given and the approach is illustrated on two optimal design problems involving shocks.

Anode protection system for shutdown of solid oxide fuel cell system

DOEpatents

Li, Bob X; Grieves, Malcolm J; Kelly, Sean M

2014-12-30

An Anode Protection Systems for a SOFC system, having a Reductant Supply and safety subsystem, a SOFC anode protection subsystem, and a Post Combustion and slip stream control subsystem. The Reductant Supply and safety subsystem includes means for generating a reducing gas or vapor to prevent re-oxidation of the Ni in the anode layer during the course of shut down of the SOFC stack. The underlying ammonia or hydrogen based material used to generate a reducing gas or vapor to prevent the re-oxidation of the Ni can be in either a solid or liquid stored inside a portable container. The SOFC anode protection subsystem provides an internal pressure of 0.2 to 10 kPa to prevent air from entering into the SOFC system. The Post Combustion and slip stream control subsystem provides a catalyst converter configured to treat any residual reducing gas in the slip stream gas exiting from SOFC stack.

Adaptive and dynamic meshing methods for numerical simulations

NASA Astrophysics Data System (ADS)

Acikgoz, Nazmiye

For the numerical simulation of many problems of engineering interest, it is desirable to have an automated mesh adaption tool capable of producing high quality meshes with an affordably low number of mesh points. This is important especially for problems, which are characterized by anisotropic features of the solution and require mesh clustering in the direction of high gradients. Another significant issue in meshing emerges in the area of unsteady simulations with moving boundaries or interfaces, where the motion of the boundary has to be accommodated by deforming the computational grid. Similarly, there exist problems where current mesh needs to be adapted to get more accurate solutions because either the high gradient regions are initially predicted inaccurately or they change location throughout the simulation. To solve these problems, we propose three novel procedures. For this purpose, in the first part of this work, we present an optimization procedure for three-dimensional anisotropic tetrahedral grids based on metric-driven h-adaptation. The desired anisotropy in the grid is dictated by a metric that defines the size, shape, and orientation of the grid elements throughout the computational domain. Through the use of topological and geometrical operators, the mesh is iteratively adapted until the final mesh minimizes a given objective function. In this work, the objective function measures the distance between the metric of each simplex and a target metric, which can be either user-defined (a-priori) or the result of a-posteriori error analysis. During the adaptation process, one tries to decrease the metric-based objective function until the final mesh is compliant with the target within a given tolerance. However, in regions such as corners and complex face intersections, the compliance condition was found to be very difficult or sometimes impossible to satisfy. In order to address this issue, we propose an optimization process based on an ad-hoc application of the simulated annealing technique, which improves the likelihood of removing poor elements from the grid. Moreover, a local implementation of the simulated annealing is proposed to reduce the computational cost. Many challenging multi-physics and multi-field problems that are unsteady in nature are characterized by moving boundaries and/or interfaces. When the boundary displacements are large, which typically occurs when implicit time marching procedures are used, degenerate elements are easily formed in the grid such that frequent remeshing is required. To deal with this problem, in the second part of this work, we propose a new r-adaptation methodology. The new technique is valid for both simplicial (e.g., triangular, tet) and non-simplicial (e.g., quadrilateral, hex) deforming grids that undergo large imposed displacements at their boundaries. A two- or three-dimensional grid is deformed using a network of linear springs composed of edge springs and a set of virtual springs. The virtual springs are constructed in such a way as to oppose element collapsing. This is accomplished by confining each vertex to its ball through springs that are attached to the vertex and its projection on the ball entities. The resulting linear problem is solved using a preconditioned conjugate gradient method. The new method is compared with the classical spring analogy technique in two- and three-dimensional examples, highlighting the performance improvements achieved by the new method. Meshes are an important part of numerical simulations. Depending on the geometry and flow conditions, the most suitable mesh for each particular problem is different. Meshes are usually generated by either using a suitable software package or solving a PDE. In both cases, engineering intuition plays a significant role in deciding where clusterings should take place. In addition, for unsteady problems, the gradients vary for each time step, which requires frequent remeshing during simulations. Therefore, in order to minimize user intervention and prevent frequent remeshings, we conclude this work by defining a novel mesh adaptation technique that integrates metric based target mesh definitions with the ball-vertex mesh deformation method. In this new approach, the entire mesh is deformed based on either an a-priori or an a-posteriori error estimator. In other words, nodal points are repositioned upon application of a force field in order to comply with the target mesh or to get more accurate solutions. The method has been tested for two-dimensional problems of a-priori metric definitions as well as for oblique shock clusterings.

A conceptual design of catalytic gasification fuel cell hybrid power plant with oxygen transfer membrane

NASA Astrophysics Data System (ADS)

Shi, Wangying; Han, Minfang

2017-09-01

A hybrid power generation system integrating catalytic gasification, solid oxide fuel cell (SOFC), oxygen transfer membrane (OTM) and gas turbine (GT) is established and system energy analysis is performed. In this work, the catalytic gasifier uses steam, recycled anode off-gas and pure oxygen from OTM system to gasify coal, and heated by hot cathode off-gas at the same time. A zero-dimension SOFC model is applied and verified by fitting experimental data. Thermodynamic analysis is performed to investigate the integrated system performance, and system sensitivities on anode off-gas back flow ratio, SOFC fuel utilization, temperature and pressure are discussed. Main conclusions are as follows: (1) System overall electricity efficiency reaches 60.7%(HHV) while the gasifier operates at 700 °C and SOFC at 850 °C with system pressure at 3.04 bar; (2) oxygen enriched combustion simplify the carbon-dioxide capture process, which derives CO2 of 99.2% purity, but results in a penalty of 6.7% on system electricity efficiency; (3) with SOFC fuel utilization or temperature increasing, the power output of SOFC increases while GT power output decreases, and increasing system pressure can improve both the performance of SOFC and GT.

A critical analysis of some popular methods for the discretisation of the gradient operator in finite volume methods

NASA Astrophysics Data System (ADS)

Syrakos, Alexandros; Varchanis, Stylianos; Dimakopoulos, Yannis; Goulas, Apostolos; Tsamopoulos, John

2017-12-01

Finite volume methods (FVMs) constitute a popular class of methods for the numerical simulation of fluid flows. Among the various components of these methods, the discretisation of the gradient operator has received less attention despite its fundamental importance with regards to the accuracy of the FVM. The most popular gradient schemes are the divergence theorem (DT) (or Green-Gauss) scheme and the least-squares (LS) scheme. Both are widely believed to be second-order accurate, but the present study shows that in fact the common variant of the DT gradient is second-order accurate only on structured meshes whereas it is zeroth-order accurate on general unstructured meshes, and the LS gradient is second-order and first-order accurate, respectively. This is explained through a theoretical analysis and is confirmed by numerical tests. The schemes are then used within a FVM to solve a simple diffusion equation on unstructured grids generated by several methods; the results reveal that the zeroth-order accuracy of the DT gradient is inherited by the FVM as a whole, and the discretisation error does not decrease with grid refinement. On the other hand, use of the LS gradient leads to second-order accurate results, as does the use of alternative, consistent, DT gradient schemes, including a new iterative scheme that makes the common DT gradient consistent at almost no extra cost. The numerical tests are performed using both an in-house code and the popular public domain partial differential equation solver OpenFOAM.

Fuel Cell Airframe Integration Study for Short-Range Aircraft. Volume 1; Aircraft Propulsion and Subsystems Integration Evaluation

NASA Technical Reports Server (NTRS)

Gummalla, Mallika; Pandy, Arun; Braun, Robert; Carriere, Thierry; Yamanis, Jean; Vanderspurt, Thomas; Hardin, Larry; Welch, Rick

2006-01-01

The objective of this study is to define the functionality and evaluate the propulsion and power system benefits derived from a Solid Oxide Fuel Cell (SOFC) based Auxiliary Power Unit (APU) for a future short range commercial aircraft, and to define the technology gaps to enable such a system. United Technologies Corporation (UTC) Integrated Total Aircraft Power System (ITAPS) methodologies were used to evaluate a baseline aircraft and several SOFC architectures. The technology benefits were captured as reductions of the mission fuel burn, life cycle cost, noise and emissions. As a result of the study, it was recognized that system integration is critical to maximize benefits from the SOFC APU for aircraft application. The mission fuel burn savings for the two SOFC architectures ranged from 4.7 percent for a system with high integration to 6.7 percent for a highly integrated system with certain technological risks. The SOFC APU itself produced zero emissions. The reduction in engine fuel burn achieved with the SOFC systems also resulted in reduced emissions from the engines for both ground operations and in flight. The noise level of the baseline APU with a silencer is 78 dBA, while the SOFC APU produced a lower noise level. It is concluded that a high specific power SOFC system is needed to achieve the benefits identified in this study. Additional areas requiring further development are the processing of the fuel to remove sulfur, either on board or on the ground, and extending the heat sink capability of the fuel to allow greater waste heat recovery, resolve the transient electrical system integration issues, and identification of the impact of the location of the SOFC and its size on the aircraft.

Towards the next generation of solid oxide fuel cells operating below 600 °c with chemically stable proton-conducting electrolytes.

PubMed

Fabbri, Emiliana; Bi, Lei; Pergolesi, Daniele; Traversa, Enrico

2012-01-10

The need for reducing the solid oxide fuel cell (SOFC) operating temperature below 600 °C is imposed by cost reduction, which is essential for widespread SOFC use, but might also disclose new applications. To this aim, high-temperature proton-conducting (HTPC) oxides have gained widespread interest as electrolyte materials alternative to oxygen-ion conductors. This Progress Report describes recent developments in electrolyte, anode, and cathode materials for protonic SOFCs, addressing the issue of chemical stability, processability, and good power performance below 600 °C. Different fabrication methods are reported for anode-supported SOFCs, obtained using state-of-the-art, chemically stable proton-conducting electrolyte films. Recent findings show significant improvements in the power density output of cells based on doped barium zirconate electrolytes, pointing out towards the feasibility of the next generation of protonic SOFCs, including a good potential for the development of miniaturized SOFCs as portable power supplies. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thermodynamic analysis of Direct Urea Solid Oxide Fuel Cell in combined heat and power applications

NASA Astrophysics Data System (ADS)

Abraham, F.; Dincer, I.

2015-12-01

This paper presents a comprehensive steady state modelling and thermodynamic analysis of Direct Urea Solid Oxide Fuel Cell integrated with Gas Turbine power cycle (DU-SOFC/GT). The use of urea as direct fuel mitigates public health and safety risks associated with the use of hydrogen and ammonia. The integration scheme in this study covers both oxygen ion-conducting solid oxide fuel cells (SOFC-O) and hydrogen proton-conducting solid oxide fuel cells (SOFC-H). Parametric case studies are carried out to investigate the effects of design and operating parameters on the overall performance of the system. The results reveal that the fuel cell exhibited the highest level of exergy destruction among other system components. Furthermore, the SOFC-O based system offers better overall performance than that with the SOFC-H option mainly due to the detrimental reverse water-gas shift reaction at the SOFC anode as well as the unique configuration of the system.

Commercial sector solid oxide fuel cell business assessment. Interim report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schafer, P.

Estimates for the commercial potential of solid oxide fuel cells (SOFCs) from the year 2001 to 2015 is 4 billion MWh. Their quiet operation, low cost, efficiency, and small size could make SOFCs ideal power sources for commercial customers. To better understand the market, this study had three main objectives: (1) identify the extent of the commercial market potential; (2) describe the most likely commercial segments and locations for SOFCs to be competitive; and, (3) determine the most appropriate product sizes. To profile commercial sectors by energy use, investigators conducted a market segmentation analysis. They classified markets within sectors asmore » cogeneration and electric-only applications. Investigators then performed a market analysis to estimate the cost competitiveness of SOFC energy production by state, segment, and operating mode (cogeneration or electric-only). To determine which locations and sectors would be competitive with current utility retail rates, they used the cost per kWh of electrical energy produced by SOFC technology. Study results indicated that three sizes of SOFCs would meet most market capacity requirements: 20, 100, and 250 kW. The largest number of potential SOFC building applications fell into these sectors: education, health care, food service, and skilled nursing. In terms of competitive building applications, California, New York, Illinois, Texas, and Michigan were the top states. The potential market for SOFCs, however, could be much smaller if the pressures of deregulation decrease commercial retail rates or if the rates themselves increase more slowly than expected.« less

Fundamental researches of SOFC in Russia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Demin, A.K.; Neuimin, A.D.; Perfiliev, M.V.

1996-04-01

The main results of research on ZrO{sub 2}-based solid electrolytes, electrodes and interconnects are reviewed. The mathematical models of the processes in SOFC are considered. Two types of SOFC stacks composed of tubular and block cells, as well the results of their tests are described.

Adjoint Algorithm for CAD-Based Shape Optimization Using a Cartesian Method

NASA Technical Reports Server (NTRS)

Nemec, Marian; Aftosmis, Michael J.

2004-01-01

Adjoint solutions of the governing flow equations are becoming increasingly important for the development of efficient analysis and optimization algorithms. A well-known use of the adjoint method is gradient-based shape optimization. Given an objective function that defines some measure of performance, such as the lift and drag functionals, its gradient is computed at a cost that is essentially independent of the number of design variables (geometric parameters that control the shape). More recently, emerging adjoint applications focus on the analysis problem, where the adjoint solution is used to drive mesh adaptation, as well as to provide estimates of functional error bounds and corrections. The attractive feature of this approach is that the mesh-adaptation procedure targets a specific functional, thereby localizing the mesh refinement and reducing computational cost. Our focus is on the development of adjoint-based optimization techniques for a Cartesian method with embedded boundaries.12 In contrast t o implementations on structured and unstructured grids, Cartesian methods decouple the surface discretization from the volume mesh. This feature makes Cartesian methods well suited for the automated analysis of complex geometry problems, and consequently a promising approach to aerodynamic optimization. Melvin et developed an adjoint formulation for the TRANAIR code, which is based on the full-potential equation with viscous corrections. More recently, Dadone and Grossman presented an adjoint formulation for the Euler equations. In both approaches, a boundary condition is introduced to approximate the effects of the evolving surface shape that results in accurate gradient computation. Central to automated shape optimization algorithms is the issue of geometry modeling and control. The need to optimize complex, "real-life" geometry provides a strong incentive for the use of parametric-CAD systems within the optimization procedure. In previous work, we presented an effective optimization framework that incorporates a direct-CAD interface. In this work, we enhance the capabilities of this framework with efficient gradient computations using the discrete adjoint method. We present details of the adjoint numerical implementation, which reuses the domain decomposition, multigrid, and time-marching schemes of the flow solver. Furthermore, we explain and demonstrate the use of CAD in conjunction with the Cartesian adjoint approach. The final paper will contain a number of complex geometry, industrially relevant examples with many design variables to demonstrate the effectiveness of the adjoint method on Cartesian meshes.

The resolution sensitivity of the Asian summer monsoon and its inter-model comparison between MRI-AGCM and MetUM

NASA Astrophysics Data System (ADS)

Ogata, Tomomichi; Johnson, Stephanie J.; Schiemann, Reinhard; Demory, Marie-Estelle; Mizuta, Ryo; Yoshida, Kohei; Osamu Arakawa

2017-11-01

In this study, we compare the resolution sensitivity of the Asian Summer Monsoon (ASM) in two Atmospheric General Circulation Models (AGCMs): the MRI-AGCM and the MetUM. We analyze the MetUM at three different resolutions, N96 (approximately 200-km mesh on the equator), N216 (90-km mesh) and N512 (40-km mesh), and the MRI-AGCM at TL95 (approximately 180-km mesh on the equator), TL319 (60-km mesh), and TL959 (20-km mesh). The MRI-AGCM and the MetUM both show decreasing precipitation over the western Pacific with increasing resolution, but their precipitation responses differ over the Indian Ocean. In MRI-AGCM, a large precipitation increase appears off the equator (5-20°N). In MetUM, this off-equatorial precipitation increase is less significant and precipitation decreases over the equator. Moisture budget analysis demonstrates that a changing in moisture flux convergence at higher resolution is related to the precipitation response. Orographic effects, intra-seasonal variability and the representation of the meridional thermal gradient are explored as possible causes of the resolution sensitivity. Both high-resolution AGCMs (TL959 and N512) can represent steep topography, which anchors the rainfall pattern over south Asia and the Maritime Continent. In MRI-AGCM, representation of low pressure systems in TL959 also contributes to the rainfall pattern. Furthermore, the seasonal evolution of the meridional thermal gradient appears to be more accurate at higher resolution, particularly in the MRI-AGCM. These findings emphasize that the impact of resolution is only robust across the two AGCMs for some features of the ASM, and highlights the importance of multi-model studies of GCM resolution sensitivity.

Development of Residential SOFC Cogeneration System

NASA Astrophysics Data System (ADS)

Ono, Takashi; Miyachi, Itaru; Suzuki, Minoru; Higaki, Katsuki

2011-06-01

Since 2001 Kyocera has been developing 1kW class Solid Oxide Fuel Cell (SOFC) for power generation system. We have developed a cell, stack, module and system. Since 2004, Kyocera and Osaka Gas Co., Ltd. have been developed SOFC residential co-generation system. From 2007, we took part in the "Demonstrative Research on Solid Oxide Fuel Cells" Project conducted by New Energy Foundation (NEF). Total 57 units of 0.7kW class SOFC cogeneration systems had been installed at residential houses. In spite of residential small power demand, the actual electric efficiency was about 40%(netAC,LHV), and high CO2 reduction performance was achieved by these systems. Hereafter, new joint development, Osaka Gas, Toyota Motors, Kyocera and Aisin Seiki, aims early commercialization of residential SOFC CHP system.

Exergy & economic analysis of biogas fueled solid oxide fuel cell systems

NASA Astrophysics Data System (ADS)

Siefert, Nicholas S.; Litster, Shawn

2014-12-01

We present an exergy and an economic analysis of a power plant that uses biogas produced from a thermophilic anaerobic digester (AD) to fuel a solid oxide fuel cell (SOFC). We performed a 4-variable parametric analysis of the AD-SOFC system in order to determine the optimal design operation conditions, depending on the objective function of interest. We present results on the exergy efficiency (%), power normalized capital cost ( kW-1), and the internal rate of return on investment, IRR, (% yr-1) as a function of the current density, the stack pressure, the fuel utilization, and the total air stoichiometric ratio. To the authors' knowledge, this is the first AD-SOFC paper to include the cost of the AD when conducting economic optimization of the AD-SOFC plant. Our calculations show that adding a new AD-SOFC system to an existing waste water treatment (WWT) plant could yield positives values of IRR at today's average electricity prices and could significantly out-compete other options for using biogas to generate electricity. AD-SOFC systems could likely convert WWT plants into net generators of electricity rather than net consumers of electricity while generating economically viable rates of return on investment if the costs of SOFC systems are within a factor of two of the DOE/SECA cost targets.

On the implementation of an accurate and efficient solver for convection-diffusion equations

NASA Astrophysics Data System (ADS)

Wu, Chin-Tien

In this dissertation, we examine several different aspects of computing the numerical solution of the convection-diffusion equation. The solution of this equation often exhibits sharp gradients due to Dirichlet outflow boundaries or discontinuities in boundary conditions. Because of the singular-perturbed nature of the equation, numerical solutions often have severe oscillations when grid sizes are not small enough to resolve sharp gradients. To overcome such difficulties, the streamline diffusion discretization method can be used to obtain an accurate approximate solution in regions where the solution is smooth. To increase accuracy of the solution in the regions containing layers, adaptive mesh refinement and mesh movement based on a posteriori error estimations can be employed. An error-adapted mesh refinement strategy based on a posteriori error estimations is also proposed to resolve layers. For solving the sparse linear systems that arise from discretization, goemetric multigrid (MG) and algebraic multigrid (AMG) are compared. In addition, both methods are also used as preconditioners for Krylov subspace methods. We derive some convergence results for MG with line Gauss-Seidel smoothers and bilinear interpolation. Finally, while considering adaptive mesh refinement as an integral part of the solution process, it is natural to set a stopping tolerance for the iterative linear solvers on each mesh stage so that the difference between the approximate solution obtained from iterative methods and the finite element solution is bounded by an a posteriori error bound. Here, we present two stopping criteria. The first is based on a residual-type a posteriori error estimator developed by Verfurth. The second is based on an a posteriori error estimator, using local solutions, developed by Kay and Silvester. Our numerical results show the refined mesh obtained from the iterative solution which satisfies the second criteria is similar to the refined mesh obtained from the finite element solution.

3D level set methods for evolving fronts on tetrahedral meshes with adaptive mesh refinement

DOE PAGES

Morgan, Nathaniel Ray; Waltz, Jacob I.

2017-03-02

The level set method is commonly used to model dynamically evolving fronts and interfaces. In this work, we present new methods for evolving fronts with a specified velocity field or in the surface normal direction on 3D unstructured tetrahedral meshes with adaptive mesh refinement (AMR). The level set field is located at the nodes of the tetrahedral cells and is evolved using new upwind discretizations of Hamilton–Jacobi equations combined with a Runge–Kutta method for temporal integration. The level set field is periodically reinitialized to a signed distance function using an iterative approach with a new upwind gradient. We discuss themore » details of these level set and reinitialization methods. Results from a range of numerical test problems are presented.« less

Polyhedral shape model for terrain correction of gravity and gravity gradient data based on an adaptive mesh

NASA Astrophysics Data System (ADS)

Guo, Zhikui; Chen, Chao; Tao, Chunhui

2016-04-01

Since 2007, there are four China Da yang cruises (CDCs), which have been carried out to investigate polymetallic sulfides in the southwest Indian ridge (SWIR) and have acquired both gravity data and bathymetry data on the corresponding survey lines(Tao et al., 2014). Sandwell et al. (2014) published a new global marine gravity model including the free air gravity data and its first order vertical gradient (Vzz). Gravity data and its gradient can be used to extract unknown density structure information(e.g. crust thickness) under surface of the earth, but they contain all the mass effect under the observation point. Therefore, how to get accurate gravity and its gradient effect of the existing density structure (e.g. terrain) has been a key issue. Using the bathymetry data or ETOPO1 (http://www.ngdc.noaa.gov/mgg/global/global.html) model at a full resolution to calculate the terrain effect could spend too much computation time. We expect to develop an effective method that takes less time but can still yield the desired accuracy. In this study, a constant-density polyhedral model is used to calculate the gravity field and its vertical gradient, which is based on the work of Tsoulis (2012). According to gravity field attenuation with distance and variance of bathymetry, we present an adaptive mesh refinement and coarsening strategies to merge both global topography data and multi-beam bathymetry data. The local coarsening or size of mesh depends on user-defined accuracy and terrain variation (Davis et al., 2011). To depict terrain better, triangular surface element and rectangular surface element are used in fine and coarse mesh respectively. This strategy can also be applied to spherical coordinate in large region and global scale. Finally, we applied this method to calculate Bouguer gravity anomaly (BGA), mantle Bouguer anomaly(MBA) and their vertical gradient in SWIR. Further, we compared the result with previous results in the literature. Both synthetic model tests and field applications indicate that the adaptive terrain correction method can be adopted as a rapid and accurate tool of marine gravity data processing. References Davis, K. &Kass, M.A. & Li, Y., 2011. Rapid gravity and gravity gradiometry terrain corrections via an adaptive quadtree mesh discretization, EXPLOR GEOPHYS, 42, 88-97. Sandwell, D.T., Müller, R.D., Smith, W.H., Garcia, E. & Francis, R., 2014. New global marine gravity model from CryoSat-2 and Jason-1 reveals buried tectonic structure, SCIENCE, 346, 65-67. Tao, C., Li, H., Jin, X., Zhou, J., Wu, T., He, Y., Deng, X., Gu, C., Zhang, G. & Liu, W., 2014. Seafloor hydrothermal activity and polymetallic sulfide exploration on the southwest Indian ridge, CHINESE SCI BULL, 59, 2266-2276. Tsoulis, D., 2012. Analytical computation of the full gravity tensor of a homogeneous arbitrarily shaped polyhedral source using line integrals, GEOPHYSICS, 77, F1-F11.

Effects of fuel processing methods on industrial scale biogas-fuelled solid oxide fuel cell system for operating in wastewater treatment plants

NASA Astrophysics Data System (ADS)

Farhad, Siamak; Yoo, Yeong; Hamdullahpur, Feridun

The performance of three solid oxide fuel cell (SOFC) systems, fuelled by biogas produced through anaerobic digestion (AD) process, for heat and electricity generation in wastewater treatment plants (WWTPs) is studied. Each system has a different fuel processing method to prevent carbon deposition over the anode catalyst under biogas fuelling. Anode gas recirculation (AGR), steam reforming (SR), and partial oxidation (POX) are the methods employed in systems I-III, respectively. A planar SOFC stack used in these systems is based on the anode-supported cells with Ni-YSZ anode, YSZ electrolyte and YSZ-LSM cathode, operated at 800 °C. A computer code has been developed for the simulation of the planar SOFC in cell, stack and system levels and applied for the performance prediction of the SOFC systems. The key operational parameters affecting the performance of the SOFC systems are identified. The effect of these parameters on the electrical and CHP efficiencies, the generated electricity and heat, the total exergy destruction, and the number of cells in SOFC stack of the systems are studied. The results show that among the SOFC systems investigated in this study, the AGR and SR fuel processor-based systems with electrical efficiency of 45.1% and 43%, respectively, are suitable to be applied in WWTPs. If the entire biogas produced in a WWTP is used in the AGR or SR fuel processor-based SOFC system, the electricity and heat required to operate the WWTP can be completely self-supplied and the extra electricity generated can be sold to the electrical grid.

Applications of Space-Filling-Curves to Cartesian Methods for CFD

NASA Technical Reports Server (NTRS)

Aftosmis, Michael J.; Berger, Marsha J.; Murman, Scott M.

2003-01-01

The proposed paper presents a variety novel uses of Space-Filling-Curves (SFCs) for Cartesian mesh methods in 0. While these techniques will be demonstrated using non-body-fitted Cartesian meshes, most are applicable on general body-fitted meshes -both structured and unstructured. We demonstrate the use of single O(N log N) SFC-based reordering to produce single-pass (O(N)) algorithms for mesh partitioning, multigrid coarsening, and inter-mesh interpolation. The intermesh interpolation operator has many practical applications including warm starts on modified geometry, or as an inter-grid transfer operator on remeshed regions in moving-body simulations. Exploiting the compact construction of these operators, we further show that these algorithms are highly amenable to parallelization. Examples using the SFC-based mesh partitioner show nearly linear speedup to 512 CPUs even when using multigrid as a smoother. Partition statistics are presented showing that the SFC partitions are, on-average, within 10% of ideal even with only around 50,000 cells in each subdomain. The inter-mesh interpolation operator also has linear asymptotic complexity and can be used to map a solution with N unknowns to another mesh with M unknowns with O(max(M,N)) operations. This capability is demonstrated both on moving-body simulations and in mapping solutions to perturbed meshes for finite-difference-based gradient design methods.

Cold start dynamics and temperature sliding observer design of an automotive SOFC APU

NASA Astrophysics Data System (ADS)

Lin, Po-Hsu; Hong, Che-Wun

This paper presents a dynamic model for studying the cold start dynamics and observer design of an auxiliary power unit (APU) for automotive applications. The APU is embedded with a solid oxide fuel cell (SOFC) stack which is a quiet and pollutant-free electric generator; however, it suffers from slow start problem from ambient conditions. The SOFC APU system equips with an after-burner to accelerate the start-up transient in this research. The combustion chamber burns the residual fuel (and air) left from the SOFC to raise the exhaust temperature to preheat the SOFC stack through an energy recovery unit. Since thermal effect is the dominant factor that influences the SOFC transient and steady performance, a nonlinear real-time sliding observer for stack temperature was implemented into the system dynamics to monitor the temperature variation for future controller design. The simulation results show that a 100 W APU system in this research takes about 2 min (in theory) for start-up without considering the thermal limitation of the cell fracture.

Data-driven simultaneous fault diagnosis for solid oxide fuel cell system using multi-label pattern identification

NASA Astrophysics Data System (ADS)

Li, Shuanghong; Cao, Hongliang; Yang, Yupu

2018-02-01

Fault diagnosis is a key process for the reliability and safety of solid oxide fuel cell (SOFC) systems. However, it is difficult to rapidly and accurately identify faults for complicated SOFC systems, especially when simultaneous faults appear. In this research, a data-driven Multi-Label (ML) pattern identification approach is proposed to address the simultaneous fault diagnosis of SOFC systems. The framework of the simultaneous-fault diagnosis primarily includes two components: feature extraction and ML-SVM classifier. The simultaneous-fault diagnosis approach can be trained to diagnose simultaneous SOFC faults, such as fuel leakage, air leakage in different positions in the SOFC system, by just using simple training data sets consisting only single fault and not demanding simultaneous faults data. The experimental result shows the proposed framework can diagnose the simultaneous SOFC system faults with high accuracy requiring small number training data and low computational burden. In addition, Fault Inference Tree Analysis (FITA) is employed to identify the correlations among possible faults and their corresponding symptoms at the system component level.

A framework for developing a mimetic tensor artificial viscosity for Lagrangian hydrocodes on arbitrary polygonal and polyhedral meshes (u)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lipnikov, Konstantin; Shashkov, Mikhail

2011-01-11

We construct a new mimetic tensor artificial viscosity on general polygonal and polyhedral meshes. The tensor artificial viscosity is based on a mimetic discretization of coordinate invariant operators, divergence of a tensor and gradient of a vector. The focus of this paper is on the symmetric form, div ({mu},{var_epsilon}(u)), of the tensor artificial viscosity where {var_epsilon}(u) is the symmetrized gradient of u and {mu}, is a tensor. The mimetic discretizations of this operator is derived for the case of a full tensor coefficient {mu}, that may reflect a shock direction. We demonstrate performance of the new viscosity for the Nohmore » implosion, Sedov explosion and Saltzman piston problems in both Cartesian and axisymmetric coordinate systems.« less

LaNi0.6Co0 4O3-δ dip-coated on Fe-Cr mesh as a composite cathode contact material on intermediate solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Morán-Ruiz, Aroa; Vidal, Karmele; Larrañaga, Aitor; Laguna-Bercero, Miguel Angel; Porras-Vázquez, Jose Manuel; Slater, Peter Raymond; Arriortua, María Isabel

2014-12-01

The feasibility of using Crofer22APU mesh dip coated with LaNi0.6Co0.4O3-δ (LNC) ceramic paste as a uniform contact layer on a Crofer22APU channeled interconnect was studied. The control of LNC dip coating thickness on Fe-Cr mesh was carried out by rheological measurements of the suspension. SEM cross-section of formed composite contact material showed good adherence between ceramic and metallic components. The measured area specific resistance (ASR) value at 800 °C was 0.46 ± 0.01 mΩ cm2, indicating low contact resistance itself. The long term stability of metallic/ceramic composite was also studied. The contact resistance, when composite contact material was adhered to channeled Crofer22APU interconnect, was 5.40 ± 0.01 mΩ cm2, which is a suitable value for the performance of IT-SOFC stack. The stability of the system after treating at 800 °C for 1000 h was characterized using X-ray Micro-Diffraction (XRMD), Scanning Electron Microscope equipped with an Energy Dispersive X-ray analyzer (SEM-EDX) and X-ray Photoelectron Spectroscopy (XPS) techniques. The oxidation rate of the alloy and Fe3O4 phase formation were enhanced on the channels of the interconnect. Thus, the formation of CrO3 (g) and CrO2(OH)2 (g) species was accelerated on the composite surface under the channel. Through XRMD and XPS analysis the coexistence of two perovskite phases (initial LNC and Cr-perovskite) was observed.

On direct internal methane steam reforming kinetics in operating solid oxide fuel cells with nickel-ceria anodes

NASA Astrophysics Data System (ADS)

Thallam Thattai, A.; van Biert, L.; Aravind, P. V.

2017-12-01

Major operating challenges remain to safely operate methane fuelled solid oxide fuel cells due to undesirable temperature gradients across the porous anode and carbon deposition. This article presents an experimental study on methane steam reforming (MSR) global kinetics for single operating SOFCs with Ni-GDC (gadolinium doped ceria) anodes for low steam to carbon (S/C) ratios and moderate current densities. The study points out the hitherto insufficient research on MSR global and intrinsic kinetics for operating SOFCs with complete Ni-ceria anodes. Further, it emphasizes the need to develop readily applicable global kinetic models as a subsequent step from previously reported state-of-art and complex intrinsic models. Two rate expressions of the Power law (PL) and Langmuir-Hinshelwood (LH) type have been compared and based on the analysis, limitations of using previously proposed rate expressions for Ni catalytic beds to study MSR kinetics for complete cermet anodes have been identified. Firstly, it has been shown that methane reforming on metallic (Ni) current collectors may not be always negligible, contrary to literature reports. Both PL and LH kinetic models predict significantly different local MSR reaction rate and species partial pressure distributions along the normalized reactor length, indicating a strong need for further experimental verifications.

Electron beam physical vapor deposition of YSZ electrolyte coatings for SOFCs

NASA Astrophysics Data System (ADS)

He, Xiaodong; Meng, Bin; Sun, Yue; Liu, Bochao; Li, Mingwei

2008-09-01

YSZ electrolyte coatings were prepared by electron beam physical vapor deposition (EB-PVD) at a high deposition rate of up to 1 μm/min. The YSZ coating consisted of a single cubic phase and no phase transformation occurred after annealing treatment at 1000 °C. A typical columnar structure was observed in this coating by SEM and feather-like characteristics appeared in every columnar grain. In columnar grain boundaries there were many micron-sized gaps and pores. In TEM image, many white lines were found, originating from the alignment of nanopores existing within feather-like columnar grains. The element distribution along the cross-section of the coating was homogeneous except Zr with a slight gradient. The coating exhibited a characteristic anisotropic behavior in electrical conductivity. In the direction perpendicular to coating surface the electrical conductivity was remarkably higher than that in the direction parallel to coating surface. This mainly attributed to the typical columnar structure for EB-PVD coating and the existence of many grain boundaries along the direction parallel to coating surface. For as-deposited coating, the gas permeability coefficient of 9.78 × 10 -5 cm 4 N -1 s -1 was obtained and this value was close to the critical value of YSZ electrolyte layer required for solid oxide fuel cell (SOFC) operation.

Poisoning of Ni-Based anode for proton conducting SOFC by H2S, CO2, and H2O as fuel contaminants

NASA Astrophysics Data System (ADS)

Sun, Shichen; Awadallah, Osama; Cheng, Zhe

2018-02-01

It is well known that conventional solid oxide fuel cells (SOFCs) based on oxide ion conducting electrolyte (e.g., yttria-stabilized zirconia, YSZ) and nickel (Ni) - ceramic cermet anodes are susceptible to poisoning by trace amount of hydrogen sulfide (H2S) while not significantly impacted by the presence of carbon dioxide (CO2) and moisture (H2O) in the fuel stream unless under extreme operating conditions. In comparison, the impacts of H2S, CO2, and H2O on proton-conducting SOFCs remain largely unexplored. This study aims at revealing the poisoning behaviors caused by H2S, CO2, and H2O for proton-conducting SOFCs. Anode-supported proton-conducting SOFCs with BaZe0.1Ce0.7Y0.1Yb0.1O3 (BZCYYb) electrolyte and Ni-BZCYYb anode and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode as well as Ni-BZCYYb/BZCYYb/Ni-BZCYYb anode symmetrical cells were subjected to low ppm-level H2S or low percentage-level CO2 or H2O in the hydrogen fuel, and the responses in cell electrochemical behaviors were recorded. The results suggest that, contrary to conventional SOFCs that show sulfur poisoning and CO2 and H2O tolerance, such proton-conducting SOFCs with Ni-BZCYYb cermet anode seem to be poisoned by all three types of "contaminants". Beyond that, the implications of the experimental observations on understanding the fundamental mechanism of anode hydrogen electrochemical oxidation reaction in proton conducting SOFCs are also discussed.

Fuel Cell Auxiliary Power Study Volume 1: RASER Task Order 5

NASA Technical Reports Server (NTRS)

Mak, Audie; Meier, John

2007-01-01

This study evaluated the feasibility of a hybrid solid oxide fuel cell (SOFC) auxiliary power unit (APU) and the impact in a 90-passenger More-Electric Regional Jet application. The study established realistic hybrid SOFC APU system weight and system efficiencies, and evaluated the impact on the aircraft total weight, fuel burn, and emissions from the main engine and the APU during cruise, landing and take-off (LTO) cycle, and at the gate. Although the SOFC APU may be heavier than the current conventional APU, its weight disadvantage can be offset by fuel savings in the higher SOFC APU system efficiencies against the main engine bleed and extraction during cruise. The higher SOFC APU system efficiency compared to the conventional APU on the ground can also provide considerable fuel saving and emissions reduction, particularly at the gate, but is limited by the fuel cell stack thermal fatigue characteristic.

Electrically Conductive and Protective Coating for Planar SOFC Stacks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, Jung-Pyung; Stevenson, Jeffry W.

Ferritic stainless steels are preferred interconnect materials for intermediate temperature SOFCs because of their resistance to oxidation, high formability and low cost. However, their protective oxide layer produces Cr-containing volatile species at SOFC operating temperatures and conditions, which can cause cathode poisoning. Electrically conducting spinel coatings have been developed to prevent cathode poisoning and to maintain an electrically conductive pathway through SOFC stacks. However, this coating is not compatible with the formation of stable, hermetic seals between the interconnect frame component and the ceramic cell. Thus, a new aluminizing process has been developed by PNNL to enable durable sealing, preventmore » Cr evaporation, and maintain electrical insulation between stack repeat units. Hence, two different types of coating need to have stable operation of SOFC stacks. This paper will focus on the electrically conductive coating process. Moreover, an advanced coating process, compatible with a non-electrically conductive coating will be« less

Triple-conducting layered perovskites as cathode materials for proton-conducting solid oxide fuel cells.

PubMed

Kim, Junyoung; Sengodan, Sivaprakash; Kwon, Goeun; Ding, Dong; Shin, Jeeyoung; Liu, Meilin; Kim, Guntae

2014-10-01

We report on an excellent anode-supported H(+) -SOFC material system using a triple conducting (H(+) /O(2-) /e(-) ) oxide (TCO) as a cathode material for H(+) -SOFCs. Generally, mixed ionic (O(2-) ) and electronic conductors (MIECs) have been selected as the cathode material of H(+) -SOFCs. In an H(+) -SOFC system, however, MIEC cathodes limit the electrochemically active sites to the interface between the proton conducting electrolyte and the cathode. New approaches to the tailoring of cathode materials for H(+) -SOFCs should therefore be considered. TCOs can effectively extend the electrochemically active sites from the interface between the cathode and the electrolyte to the entire surface of the cathode. The electrochemical performance of NBSCF/BZCYYb/BZCYYb-NiO shows excellent long term stability for 500 h at 1023 K with high power density of 1.61 W cm(-2) . © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A finite element method with overlapping meshes for free-boundary axisymmetric plasma equilibria in realistic geometries

NASA Astrophysics Data System (ADS)

Heumann, Holger; Rapetti, Francesca

2017-04-01

Existing finite element implementations for the computation of free-boundary axisymmetric plasma equilibria approximate the unknown poloidal flux function by standard lowest order continuous finite elements with discontinuous gradients. As a consequence, the location of critical points of the poloidal flux, that are of paramount importance in tokamak engineering, is constrained to nodes of the mesh leading to undesired jumps in transient problems. Moreover, recent numerical results for the self-consistent coupling of equilibrium with resistive diffusion and transport suggest the necessity of higher regularity when approximating the flux map. In this work we propose a mortar element method that employs two overlapping meshes. One mesh with Cartesian quadrilaterals covers the vacuum chamber domain accessible by the plasma and one mesh with triangles discretizes the region outside. The two meshes overlap in a narrow region. This approach gives the flexibility to achieve easily and at low cost higher order regularity for the approximation of the flux function in the domain covered by the plasma, while preserving accurate meshing of the geometric details outside this region. The continuity of the numerical solution in the region of overlap is weakly enforced by a mortar-like mapping.

Application of SOFC for electric vehicle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamada, K.; Mizusaki, J.; Sasaki, H.

1995-12-31

Changing from gasoline powered vehicles to electric vehicles (EVs) will provide positive environmental effects. A present disadvantage of EVs with secondary battery systems is a short driving range. This can be improved by the application of a hybrid system of SOFCs and batteries. For that system, both tubular and planer types of SOFCs having 10kW power are designed which can be used for passenger cars with naphtha as fuel operated at 880--850 C . The tubular type has 106 liters in volume and 100kg in weight, and were smaller and lighter than the planer type. Subjects to be investigated onmore » SOFCs for EVs are described.« less

Investigation of aluminosilicate refractory for solid oxide fuel cell applications

NASA Astrophysics Data System (ADS)

Gentile, Paul Steven

Stationary solid oxide fuel cells (SOFCs) have been demonstrated to provide clean and reliable electricity through electro-chemical conversion of various fuel sources (CH4 and other light hydrocarbons). To become a competitive conversion technology the costs of SOFCs must be reduced to less than $400/kW. Aluminosilicate represents a potential low cost alternative to high purity alumina for SOFC refractory applications. The objectives of this investigation are to: (1) study changes of aluminosilicate chemistry and morphology under SOFC conditions, (2) identify volatile silicon species released by aluminosilicates, (3) identify the mechanisms of aluminosilicate vapor deposition on SOFC materials, and (4) determine the effects of aluminosilicate vapors on SOFC electrochemical performance. It is shown thermodynamically and empirically that low cost aluminosilicate refractory remains chemically and thermally unstable under SOFC operating conditions between 800°C and 1000°C. Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) of the aluminosilicate bulk and surface identified increased concentrations of silicon at the surface after exposure to SOFC gases at 1000°C for 100 hours. The presence of water vapor accelerated surface diffusion of silicon, creating a more uniform distribution. Thermodynamic equilibrium modeling showed aluminosilicate remains stable in dry air, but the introduction of water vapor indicative of actual SOFC gas streams creates low temperature (<1000°C) silicon instability due to the release of Si(OH)4 and SiO(OH) 2. Thermal gravimetric analysis and transpiration studies identified a discrete drop in the rate of silicon volatility before reaching steady state conditions after 100-200 hours. Electron microscopy observed the preferential deposition of vapors released from aluminosilicate on yttria stabilized zirconia (YSZ) over nickel. The adsorbent consisted of alumina rich clusters enclosed in an amorphous siliceous layer. Silicon penetrated the YSZ along grain boundaries, isolating grains in an insulating glassy phase. XPS did not detect spectra shifts or peak broadening associated with formation of new Si-Zr-Y-O phases. SOFC electrochemical performance testing at 800-1000°C attributed rapid degradation (0.1% per hour) of cells exposed to aluminosilicate vapors in the fuel stream predominately to ohmic polarization. EDS identified silicon concentrations above impurity levels at the electrolyte/active anode interface.

Study of catalysis for solid oxide fuel cells and direct methanol fuel cells

NASA Astrophysics Data System (ADS)

Jiang, Xirong

Fuel cells offer the enticing promise of cleaner electricity with lower environmental impact than traditional energy conversion technologies. Driven by the interest in power sources for portable electronics, and distributed generation and automotive propulsion markets, active development efforts in the technologies of both solid oxide fuel cell (SOFC) and direct methanol fuel cell (DMFC) devices have achieved significant progress. However, current catalysts for fuel cells are either of low catalytic activity or extremely expensive, presenting a key barrier toward the widespread commercialization of fuel cell devices. In this thesis work, atomic layer deposition (ALD), a novel thin film deposition technique, was employed to apply catalytic Pt to SOFC, and investigate both Pt skin catalysts and Pt-Ru catalysts for methanol oxidation, a very important reaction for DMFC, to increase the activity and utilization levels of the catalysts while simultaneously reducing the catalyst loading. For SOFCs, we explored the use of ALD for the fabrication of electrode components, including an ultra-thin Pt film for use as the electrocatalyst, and a Pt mesh structure for a current collector for SOFCs, aiming for precise control over the catalyst loading and catalyst geometry, and enhancement in the current collect efficiency. We choose Pt since it has high chemical stability and excellent catalytic activity for the O2 reduction reaction and the H2 oxidation reaction even at low operating temperatures. Working SOFC fuel cells were fabricated with ALD-deposited Pt thin films as an electrode/catalyst layer. The measured fuel cell performance reveals that comparable peak power densities were achieved for ALD-deposited Pt anodes with only one-fifth of the Pt loading relative to a DC-sputtered counterpart. In addition to the continuous electrocatalyst layer, a micro-patterned Pt structure was developed via the technique of area selective ALD. By coating yttria-stabilized zirconia, a typical solid oxide electrolyte, with patterned (octadecyltrichlorosilane) ODTS self-assembled monolayers (SAMs), Pt thin films were grown selectively on the SAM-free surface regions. Features with sizes as small as 2 mum were deposited by this combined ALD-muCP method. The micro-patterned Pt structure deposited by area selective ALD was applied to SOFCs as a current collector grid/patterned catalyst. An improvement in the fuel cell performance by a factor of 10 was observed using the Pt current collector grids/patterned catalyst integrated onto cathodic La0.6Sr 0.4Co0.2Fe0.8O3-delta. For possible catalytic anodes in DMFCs employing a 1:1 stoichiometric methanol-water reforming mixture, two strategies were employed in this thesis. One approach is to fabricate skin catalysts, where ALD Pt films of various thicknesses were used to coat sputtered Ru films forming Pt skin catalysts for study of methanol oxidation. Another strategy is to replace or alloy Pt with Ru; for this effort, both dc-sputtering and atomic layer deposition were employed to fabricate Pt-Ru catalysts of various Ru contents. The electrochemical behavior of all of the Pt skin catalysts, the DC co-sputtered Pt-Ru catalysts and the ALD co-deposited Pt-Ru catalysts were evaluated at room temperature for methanol oxidation using cyclic voltammetry and chronoamperometry in highly concentrated 16.6 M MeOH, which corresponds to the stoichiometric fuel that will be employed in next generation DMFCs that are designed to minimize or eliminate methanol crossover. The catalytic activity of sputtered Ru catalysts toward methanol oxidation is strongly enhanced by the ALD Pt overlayer, with such skin layer catalysts displaying superior catalytic activity over pure Pt. For both the DC co-sputtered catalysts and ALD co-deposited catalysts, the electrochemical studies illustrate that the optimal stoichiometry ratio for Pt to Ru is approximately 1:1, which is in good agreement with most literature.

The Turbo-Fuel-Cell 1.0 - family concept

NASA Astrophysics Data System (ADS)

Berg, H. P.; Himmelberg, A.; Lehmann, M.; Dückershoff, R.; Neumann, M.

2018-01-01

The “Turbo-Fuel-Cell-Technology” has been described as a MGT-SOFC hybrid system consisting of a recuperated micro gas turbine (MGT) process with an embedded solid oxide fuel cell (SOFC) subsystem. SOFC stacks are connected to “SOFC stack grapes” and are equipped with the so called HEXAR-Module. This module is composed of a high-temperature heat exchanger (HEX), an afterburner (A) and a steam reformer (R). The MGT-concept is based on a generator driven directly by the turbomachine and a recuperator, which returns the exhaust heat to the pressurized compressor outlet air. This provides the necessary base for a highly effective, pure MGT process and the “MGT-SOFC-high-efficiency process”. This paper describes the concept and the thermodynamic background of a highly effective and compact design of the “Turbo-Fuel-Cell 1.0-Family” in the electrical performance class from 100 to 500 kW. The technological state of the system is shown and a rating of the system with comparative parameters is discussed. It becomes visible that all necessary basic technologies should be available and that the technology (for stationary applications) can have the “entry into services (E.I.S.)” in the next 10 years. The MGT-SOFC performance map under different operation conditions is discussed. This article also provides an overview of the research on MGT-SOFC-Systems and the scenario of an energy supply network and a mobile energy conversion of the future introduction.

Nondestructive cell evaluation techniques in SOFC stack manufacturing

NASA Astrophysics Data System (ADS)

Wunderlich, C.

2016-04-01

Independent from the specifics of the application, a cost efficient manufacturing of solid oxide fuel cells (SOFC), its electrolyte membranes and other stack components, leading to reliable long-life stacks is the key for the commercial viability of this fuel cell technology. Tensile and shear stresses are most critical for ceramic components and especially for thin electrolyte membranes as used in SOFC cells. Although stack developers try to reduce tensile stresses acting on the electrolyte by either matching CTE of interconnects and electrolytes or by putting SOFC cells under some pressure - at least during transient operation of SOFC stacks ceramic cells will experience some tensile stresses. Electrolytes are required to have a high Weibull characteristic fracture strength. Practical experiences in stack manufacturing have shown that statistical fracture strength data generated by tests of electrolyte samples give limited information on electrolyte or cell quality. In addition, the cutting process of SOFC electrolytes has a major influence on crack initiation. Typically, any single crack in one the 30 to 80 cells in series connection will lead to a premature stack failure drastically reducing stack service life. Thus, for statistical reasons only 100% defect free SOFC cells must be assembled in stacks. This underlines the need for an automated inspection. So far, only manual processes of visual or mechanical electrolyte inspection are established. Fraunhofer IKTS has qualified the method of optical coherence tomography for an automated high throughput inspection. Alternatives like laser speckle photometry and acoustical methods are still under investigation.

Error driven remeshing strategy in an elastic-plastic shakedown problem

NASA Astrophysics Data System (ADS)

Pazdanowski, Michał J.

2018-01-01

A shakedown based approach has been for many years successfully used to calculate the distributions of residual stresses in bodies made of elastic-plastic materials and subjected to cyclic loads exceeding their bearing capacity. The calculations performed indicated the existence of areas characterized by extremely high gradients and rapid changes of sign over small areas in the stress field sought. In order to account for these changes in sign, relatively dense nodal meshes had to be used during calculations in disproportionately large parts of considered bodies, resulting in unnecessary expenditure of computer resources. Therefore the effort was undertaken to limit the areas of high mesh densities and drive the mesh regeneration algorithm by selected error indicators.

Applications of Space-Filling-Curves to Cartesian Methods for CFD

NASA Technical Reports Server (NTRS)

Aftosmis, M. J.; Murman, S. M.; Berger, M. J.

2003-01-01

This paper presents a variety of novel uses of space-filling-curves (SFCs) for Cartesian mesh methods in CFD. While these techniques will be demonstrated using non-body-fitted Cartesian meshes, many are applicable on general body-fitted meshes-both structured and unstructured. We demonstrate the use of single theta(N log N) SFC-based reordering to produce single-pass (theta(N)) algorithms for mesh partitioning, multigrid coarsening, and inter-mesh interpolation. The intermesh interpolation operator has many practical applications including warm starts on modified geometry, or as an inter-grid transfer operator on remeshed regions in moving-body simulations Exploiting the compact construction of these operators, we further show that these algorithms are highly amenable to parallelization. Examples using the SFC-based mesh partitioner show nearly linear speedup to 640 CPUs even when using multigrid as a smoother. Partition statistics are presented showing that the SFC partitions are, on-average, within 15% of ideal even with only around 50,000 cells in each sub-domain. The inter-mesh interpolation operator also has linear asymptotic complexity and can be used to map a solution with N unknowns to another mesh with M unknowns with theta(M + N) operations. This capability is demonstrated both on moving-body simulations and in mapping solutions to perturbed meshes for control surface deflection or finite-difference-based gradient design methods.

Methanethiol Concentrations and Sea-Air Fluxes in the Subarctic NE Pacific Ocean

NASA Astrophysics Data System (ADS)

Kiene, R. P.; Williams, T. E.; Esson, K.; Tortell, P. D.; Dacey, J. W. H.

2017-12-01

Exchange of volatile organic sulfur from the ocean to the atmosphere impacts the global sulfur cycle and the climate system and is thought to occur mainly via the gas dimethylsulfide (DMS). DMS is produced during degradation of the abundant phytoplankton osmolyte dimethylsulfoniopropionate (DMSP) but bacteria can also convert dissolved DMSP into the sulfur gas methanethiol (MeSH). MeSH has been difficult to measure in seawater because of its high chemical and biological reactivity and, thus, information on MeSH concentrations, distribution and sea-air fluxes is limited. We measured MeSH in the northeast subarctic Pacific Ocean in July 2016, along transects with strong phytoplankton abundance gradients. Water samples obtained with Niskin bottles were analyzed for MeSH by purge-and-trap gas chromatography. Depth profiles showed that MeSH concentrations were high near the surface and declined with depth. Surface waters (5 m depth) had an average MeSH concentration of 0.75 nM with concentrations reaching up to 3nM. MeSH concentrations were correlated (r = 0.47) with microbial turnover of dissolved DMSP which ranged up to 236 nM per day. MeSH was also correlated with total DMSP (r = 0.93) and dissolved DMS (r = 0.63), supporting the conclusion that DMSP was a major precursor of MeSH. Surface water MeSH:DMS concentration ratios averaged 0.19 and ranged up to 0.50 indicating that MeSH was a significant fraction of the volatile sulfur pool in surface waters. Sea-air fluxes of MeSH averaged 15% of the combined DMS+MeSH flux, therefore MeSH contributed an important fraction of the sulfur emitted to the atmosphere from the subarctic NE Pacific Ocean.

Recent Development of SOFC Metallic Interconnect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu JW, Liu XB

2010-04-01

Interest in solid oxide fuel cells (SOFC) stems from their higher e±ciencies and lower levels of emitted pollu- tants, compared to traditional power production methods. Interconnects are a critical part in SOFC stacks, which connect cells in series electrically, and also separate air or oxygen at the cathode side from fuel at the anode side. Therefore, the requirements of interconnects are the most demanding, i:e:, to maintain high elec- trical conductivity, good stability in both reducing and oxidizing atmospheres, and close coe±cient of thermal expansion (CTE) match and good compatibility with other SOFC ceramic components. The paper reviewed the interconnectmore » materials, and coatings for metallic interconnect materials.« less

An open-source library for the numerical modeling of mass-transfer in solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Novaresio, Valerio; García-Camprubí, María; Izquierdo, Salvador; Asinari, Pietro; Fueyo, Norberto

2012-01-01

The generation of direct current electricity using solid oxide fuel cells (SOFCs) involves several interplaying transport phenomena. Their simulation is crucial for the design and optimization of reliable and competitive equipment, and for the eventual market deployment of this technology. An open-source library for the computational modeling of mass-transport phenomena in SOFCs is presented in this article. It includes several multicomponent mass-transport models ( i.e. Fickian, Stefan-Maxwell and Dusty Gas Model), which can be applied both within porous media and in porosity-free domains, and several diffusivity models for gases. The library has been developed for its use with OpenFOAM ®, a widespread open-source code for fluid and continuum mechanics. The library can be used to model any fluid flow configuration involving multicomponent transport phenomena and it is validated in this paper against the analytical solution of one-dimensional test cases. In addition, it is applied for the simulation of a real SOFC and further validated using experimental data. Program summaryProgram title: multiSpeciesTransportModels Catalogue identifier: AEKB_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEKB_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public License No. of lines in distributed program, including test data, etc.: 18 140 No. of bytes in distributed program, including test data, etc.: 64 285 Distribution format: tar.gz Programming language:: C++ Computer: Any x86 (the instructions reported in the paper consider only the 64 bit case for the sake of simplicity) Operating system: Generic Linux (the instructions reported in the paper consider only the open-source Ubuntu distribution for the sake of simplicity) Classification: 12 External routines: OpenFOAM® (version 1.6-ext) ( http://www.extend-project.de) Nature of problem: This software provides a library of models for the simulation of the steady state mass and momentum transport in a multi-species gas mixture, possibly in a porous medium. The software is particularly designed to be used as the mass-transport library for the modeling of solid oxide fuel cells (SOFC). When supplemented with other sub-models, such as thermal and charge-transport ones, it allows the prediction of the cell polarization curve and hence the cell performance. Solution method: Standard finite volume method (FVM) is used for solving all the conservation equations. The pressure-velocity coupling is solved using the SIMPLE algorithm (possibly adding a porous drag term if required). The mass transport can be calculated using different alternative models, namely Fick, Maxwell-Stefan or dusty gas model. The code adopts a segregated method to solve the resulting linear system of equations. The different regions of the SOFC, namely gas channels, electrodes and electrolyte, are solved independently, and coupled through boundary conditions. Restrictions: When extremely large species fluxes are considered, current implementation of the Neumann and Robin boundary conditions do not avoid negative values of molar and/or mass fractions, which finally end up with numerical instability. However this never happened in the documented runs. Eventually these boundary conditions could be reformulated to become more robust. Running time: From seconds to hours depending on the mesh size and number of species. For example, on a 64 bit machine with Intel Core Duo T8300 and 3 GBytes of RAM, the provided test run requires less than 1 second.

A novel concept of dielectrophoretic engine oil filter

NASA Astrophysics Data System (ADS)

Khusid, Boris; Shen, Yueyang; Elele, Ezinwa

2011-11-01

A novel concept of an alternating current (AC) dielectrophoretic filter with a three-dimensional electrode array is presented. A filter is constructed by winding into layers around the core tube two sheets of woven metal wire-mesh with several sheets of woven insulating wire-mesh sandwiched in between. Contrary to conventional dielectrophoretic devices, the proposed design of electrodes generates a high-gradient field over a large working volume by applying several hundred volts at a standard frequency of 60 Hz. The operating principle of filtration is based on our recently developed method of AC dielectrophoretic gating for microfluidics. The filtration efficiency is expressed in terms of two non-dimensional parameters which describe the combined influence of the particle polarizability and size, the oil viscosity and flow rate, and the field gradient on the particle captivity. The proof-of-concept is tested by measuring the single-pass performance of two filters on positively polarized particles dispersed in engine oil: spherical glass beads, fused aluminum oxide powder, and silicon metal powder, all smaller than the mesh opening. The results obtained provide critical design guidelines for the development of a filter based on the retention capability of challenge particles. The work was supported in part by ONR and NSF.

A cellular automaton - finite volume method for the simulation of dendritic and eutectic growth in binary alloys using an adaptive mesh refinement

NASA Astrophysics Data System (ADS)

Dobravec, Tadej; Mavrič, Boštjan; Šarler, Božidar

2017-11-01

A two-dimensional model to simulate the dendritic and eutectic growth in binary alloys is developed. A cellular automaton method is adopted to track the movement of the solid-liquid interface. The diffusion equation is solved in the solid and liquid phases by using an explicit finite volume method. The computational domain is divided into square cells that can be hierarchically refined or coarsened using an adaptive mesh based on the quadtree algorithm. Such a mesh refines the regions of the domain near the solid-liquid interface, where the highest concentration gradients are observed. In the regions where the lowest concentration gradients are observed the cells are coarsened. The originality of the work is in the novel, adaptive approach to the efficient and accurate solution of the posed multiscale problem. The model is verified and assessed by comparison with the analytical results of the Lipton-Glicksman-Kurz model for the steady growth of a dendrite tip and the Jackson-Hunt model for regular eutectic growth. Several examples of typical microstructures are simulated and the features of the method as well as further developments are discussed.

Liquid Oxygen/Liquid Methane Integrated Power and Propulsion

NASA Technical Reports Server (NTRS)

Banker, Brian; Ryan, Abigail

2016-01-01

The proposed paper will cover ongoing work at the National Aeronautics and Space Administration (NASA) Johnson Space Center (JSC) on integrated power and propulsion for advanced human exploration. Specifically, it will present findings of the integrated design, testing, and operational challenges of a liquid oxygen / liquid methane (LOx/LCH4) propulsion brassboard and Solid Oxide Fuel Cell (SOFC) system. Human-Mars architectures point to an oxygen-methane economy utilizing common commodities, scavenged from the planetary atmosphere and soil via In-Situ Resource Utilization (ISRU), and common commodities across sub-systems. Due to the enormous mass gear-ratio required for human exploration beyond low-earth orbit, (for every 1 kg of payload landed on Mars, 226 kg will be required on Earth) increasing commonality between spacecraft subsystems such as power and propulsion can result in tremendous launch mass and volume savings. Historically, propulsion and fuel cell power subsystems have had little interaction outside of the generation (fuel cell) and consumption (propulsion) of electrical power. This was largely due to a mismatch in preferred commodities (hypergolics for propulsion; oxygen & hydrogen for fuel cells). Although this stove-piped approach benefits from simplicity in the design process, it means each subsystem has its own tanks, pressurization system, fluid feed system, etc. increasing overall spacecraft mass and volume. A liquid oxygen / liquid methane commodities architecture across propulsion and power subsystems would enable the use of common tankage and associated pressurization and commodity delivery hardware for both. Furthermore, a spacecraft utilizing integrated power and propulsion could use propellant residuals - propellant which could not be expelled from the tank near depletion due to hydrodynamic considerations caused by large flow demands of a rocket engine - to generate power after all propulsive maneuvers are complete thus utilizing previously wasted mass. Such is the case for human and robotic planetary landers. Although many potential benefits through integrated power & propulsion exist, integrated operations have yet to be successfully demonstrated and many challenges have already been identified the most obvious of which is the large temperature gradient. SOFC chemistry is exothermic with operating temperatures in excess of 1,000 K; however, any shared commodities will be undoubtedly stored at cryogenic temperatures (90-112 K) for mass efficiency reasons. Spacecraft packaging will drive these two subsystems in close proximity thus heat leak into the commodity tankage must be minimized and/or mitigated. Furthermore, commodities must be gasified prior to consumption by the SOFC. Excess heat generated by the SOFC could be used to perform this phase change; however, this has yet to be demonstrated. A further identified challenge is the ability of the SOFC to handle the sudden power spikes created by the propulsion system. A power accumulator (battery) will likely be necessary to handle these sudden demands while the SOFC thermally adjusts. JSC's current SOFC test system consists of a 1 kW fuel cell designed by Delphi. The fuel cell is currently undergoing characterization testing at the NASA JSC Energy Systems Test Area (ESTA) after which a Steam Methane Reformer (SMR) will be integrated and the combined system tested in closed-loop. The propulsion brassboard is approximately the size of what could be flown on a sounding rocket. It consists of one 100 lbf thrust "main" engine developed for NASA by Aerojet and two 10 lbf thrusters to simulate a reaction control system developed at NASA JSC. This system is also under development and initial testing at ESTA. After initial testing, combined testing will occur which will provide data on the fuel cell's ability to sufficiently handle the power spikes created by the propulsion system. These two systems will also be modeled using General-Use Nodal Network Solver (GUNNS) software. Once anchored with test data, this model will be used to extrapolate onto other firing profiles and used to size the power accumulator.

Electrolyte bi-layering strategy to improve the performance of an intermediate temperature solid oxide fuel cell: A review

NASA Astrophysics Data System (ADS)

Shri Prakash, B.; Pavitra, R.; Senthil Kumar, S.; Aruna, S. T.

2018-03-01

Lowering of operation temperature has become one of the primary goals of solid oxide fuel (SOFC) research as reduced temperature improves the prospects for widespread commercialization of this energy system. Reduced operational temperature also mitigates the issues associated with high temperature SOFCs and paves way not only for the large scale stationary power generation but also makes SOFCs viable for portable and transport applications. However, there are issues with electrolyte and cathode materials at low temperatures, individually as well as in association with other components, which makes the performance of the SOFCs less satisfactory than expected at lowered temperatures. Bi-layering of electrolytes and impregnation of cathodes have emerged as two important strategies to overcome these issues and achieve higher performance at low temperatures. This review article provides the perspective on the strategy of bi-layering of electrolyte to achieve the desired high performance from SOFC at low to intermediate temperatures.

Adaptive finite-volume WENO schemes on dynamically redistributed grids for compressible Euler equations

NASA Astrophysics Data System (ADS)

Pathak, Harshavardhana S.; Shukla, Ratnesh K.

2016-08-01

A high-order adaptive finite-volume method is presented for simulating inviscid compressible flows on time-dependent redistributed grids. The method achieves dynamic adaptation through a combination of time-dependent mesh node clustering in regions characterized by strong solution gradients and an optimal selection of the order of accuracy and the associated reconstruction stencil in a conservative finite-volume framework. This combined approach maximizes spatial resolution in discontinuous regions that require low-order approximations for oscillation-free shock capturing. Over smooth regions, high-order discretization through finite-volume WENO schemes minimizes numerical dissipation and provides excellent resolution of intricate flow features. The method including the moving mesh equations and the compressible flow solver is formulated entirely on a transformed time-independent computational domain discretized using a simple uniform Cartesian mesh. Approximations for the metric terms that enforce discrete geometric conservation law while preserving the fourth-order accuracy of the two-point Gaussian quadrature rule are developed. Spurious Cartesian grid induced shock instabilities such as carbuncles that feature in a local one-dimensional contact capturing treatment along the cell face normals are effectively eliminated through upwind flux calculation using a rotated Hartex-Lax-van Leer contact resolving (HLLC) approximate Riemann solver for the Euler equations in generalized coordinates. Numerical experiments with the fifth and ninth-order WENO reconstructions at the two-point Gaussian quadrature nodes, over a range of challenging test cases, indicate that the redistributed mesh effectively adapts to the dynamic flow gradients thereby improving the solution accuracy substantially even when the initial starting mesh is non-adaptive. The high adaptivity combined with the fifth and especially the ninth-order WENO reconstruction allows remarkably sharp capture of discontinuous propagating shocks with simultaneous resolution of smooth yet complex small scale unsteady flow features to an exceptional detail.

Thermal coupling potential of Solid Oxide Fuel Cells with metal hydride tanks: Thermodynamic and design considerations towards integrated systems

NASA Astrophysics Data System (ADS)

Yiotis, Andreas G.; Kainourgiakis, Michael E.; Kosmidis, Lefteris I.; Charalambopoulou, Georgia C.; Stubos, Athanassios K.

2014-12-01

We study the thermal coupling potential between a high temperature metal hydride (MH) tank and a Solid Oxide Fuel Cell (SOFC) aiming towards the design of an efficient integrated system, where the thermal power produced during normal SOFC operation is redirected towards the MH tank in order to maintain H2 desorption without the use of external heating sources. Based on principles of thermodynamics, we calculate the energy balance in the SOFC/MH system and derive analytical expressions for both the thermal power produced during SOFC operation and the corresponding thermal power required for H2 desorption, as a function of the operating temperature, efficiency and fuel utilization ratio in the SOFC, and the MH enthalpy of desorption in the tank. Based on these calculations, we propose an integrated SOFC/MH design where heat is transferred primarily by radiation to the tank in order to maintain steady-state desorption conditions. We develop a mathematical model for this particular design that accounts for heat/mass transfer and desorption kinetics in the tank, and solve for the dynamics of the system assuming MgH2 as a storage material. Our results focus primarily on tank operating conditions, such as pressure, temperature and H2 saturation profiles vs operation time.

Experimental and modeling study of high performance direct carbon solid oxide fuel cell with in situ catalytic steam-carbon gasification reaction

NASA Astrophysics Data System (ADS)

Xu, Haoran; Chen, Bin; Zhang, Houcheng; Tan, Peng; Yang, Guangming; Irvine, John T. S.; Ni, Meng

2018-04-01

In this paper, 2D models for direct carbon solid oxide fuel cells (DC-SOFCs) with in situ catalytic steam-carbon gasification reaction are developed. The simulation results are found to be in good agreement with experimental data. The performance of DC-SOFCs with and without catalyst are compared at different operating potential, anode inlet gas flow rate and operating temperature. It is found that adding suitable catalyst can significantly speed up the in situ steam-carbon gasification reaction and improve the performance of DC-SOFC with H2O as gasification agent. The potential of syngas and electricity co-generation from the fuel cell is also evaluated, where the composition of H2 and CO in syngas can be adjusted by controlling the anode inlet gas flow rate. In addition, the performance DC-SOFCs and the percentage of fuel in the outlet gas are both increased with increasing operating temperature. At a reduced temperature (below 800 °C), good performance of DC-SOFC can still be obtained with in-situ catalytic carbon gasification by steam. The results of this study form a solid foundation to understand the important effect of catalyst and related operating conditions on H2O-assisted DC-SOFCs.

Feasibility study of solid oxide fuel cell engines integrated with sprinter gas turbines: Modeling, design and control

NASA Astrophysics Data System (ADS)

Jia, Zhenzhong; Sun, Jing; Dobbs, Herb; King, Joel

2015-02-01

Conventional recuperating solid oxide fuel cell (SOFC)/gas turbine (GT) system suffers from its poor dynamic capability and load following performance. To meet the fast, safe and efficient load following requirements for mobile applications, a sprinter SOFC/GT system concept is proposed in this paper. In the proposed system, an SOFC stack operating at fairly constant temperature provides the baseline power with high efficiency while the fast dynamic capability of the GT-generator is fully explored for fast dynamic load following. System design and control studies have been conducted by using an SOFC/GT system model consisting of experimentally-verified component models. In particular, through analysis of the steady-state simulation results, an SOFC operation strategy is proposed to maintain fairly constant SOFC power (less than 2% power variation) and temperature (less than 2 K temperature variation) over the entire load range. A system design procedure well-suited to the proposed system has also been developed to help determining component sizes and the reference steady-state operation line. In addition, control analysis has been studied for both steady-state and transient operations. Simulation results suggest that the proposed system holds the promise to achieve fast and safe transient operations by taking full advantage of the fast dynamics of the GT-generator.

Characterization of Cr poisoning in a solid oxide fuel cell cathode using a high-energy x-ray microbeam.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, D. J.; Almer, J.; Cruse, T.

2010-01-01

A key feature of planar solid oxide fuel cells (SOFCs) is the feasibility of using metallic interconnects made of high temperature ferritic stainless steels, which reduce system cost while providing excellent electric conductivity. Such interconnects, however, contain high levels of chromium, which has been found to be associated with SOFC cathode performance degradation at SOFC operating temperatures; a phenomenon known as Cr poisoning. Here, we demonstrate an accurate measurement of the phase and concentration distributions of Cr species in a degraded SOFC, as well as related properties including deviatoric strain, integrated porosity, and lattice parameter variation, using high energy microbeammore » X-ray diffraction and radiography. We unambiguously identify (MnCr){sub 3}O{sub 4} and Cr{sub 2}O{sub 3} as the two main contaminant phases and find that their concentrations correlate strongly with the cathode layer composition. Cr{sub 2}O{sub 3} deposition within the active cathode region reduces porosity and produces compressive residual strains, which hinders the reactant gas percolation and can cause structural breakdown of the SOFC cathode. The information obtained through this study can be used to better understand the Cr-poisoning mechanism and improve SOFC design.« less

Manifold, bus support and coupling arrangement for solid oxide fuel cells

DOEpatents

Parry, Gareth W.

1989-01-01

Individual, tubular solid oxide fuel cells (SOFCs) are assembled into bundles called a module within a housing, with a plurality of modules arranged end-to-end in a linear, stacked configuration called a string. A common set of piping comprised of a suitable high temperture resistant material (1) provides fuel and air to each module housing, (2) serves as electrically conducting buses, and (3) provides structural support for a string of SOFC modules. The piping thus forms a manfold for directing fuel and air to each module in a string and makes electrical contact with the module's anode and cathode to conduct the DC power generated by the SOFC. The piping also provides structureal support for each individual module and maintains each string of modules as a structurally integral unit for ensuring high strength in a large 3-dimensional array of SOFC modules. Ceramic collars are used to connect fuel and air inlet piping to each of the electrodes in an SOFC module and provide (1) electrical insulation for the current carrying bus bars and gas manifolds, (2) damping for the fuel and air inlet piping, and (3) proper spacing between the fuel and air inlet piping to prevent contact between these tubes and possible damage to the SOFC.

Reentry-Vehicle Shape Optimization Using a Cartesian Adjoint Method and CAD Geometry

NASA Technical Reports Server (NTRS)

Nemec, Marian; Aftosmis, Michael J.

2006-01-01

A DJOINT solutions of the governing flow equations are becoming increasingly important for the development of efficient analysis and optimization algorithms. A well-known use of the adjoint method is gradient-based shape. Given an objective function that defines some measure of performance, such as the lift and drag functionals, its gradient is computed at a cost that is essentially independent of the number of design variables (e.g., geometric parameters that control the shape). Classic aerodynamic applications of gradient-based optimization include the design of cruise configurations for transonic and supersonic flow, as well as the design of high-lift systems. are perhaps the most promising approach for addressing the issues of flow solution automation for aerodynamic design problems. In these methods, the discretization of the wetted surface is decoupled from that of the volume mesh. This not only enables fast and robust mesh generation for geometry of arbitrary complexity, but also facilitates access to geometry modeling and manipulation using parametric computer-aided design (CAD). In previous work on Cartesian adjoint solvers, Melvin et al. developed an adjoint formulation for the TRANAIR code, which is based on the full-potential equation with viscous corrections. More recently, Dadone and Grossman presented an adjoint formulation for the two-dimensional Euler equations using a ghost-cell method to enforce the wall boundary conditions. In Refs. 18 and 19, we presented an accurate and efficient algorithm for the solution of the adjoint Euler equations discretized on Cartesian meshes with embedded, cut-cell boundaries. Novel aspects of the algorithm were the computation of surface shape sensitivities for triangulations based on parametric-CAD models and the linearization of the coupling between the surface triangulation and the cut-cells. The accuracy of the gradient computation was verified using several three-dimensional test cases, which included design variables such as the free stream parameters and the planform shape of an isolated wing. The objective of the present work is to extend our adjoint formulation to problems involving general shape changes. Factors under consideration include the computation of mesh sensitivities that provide a reliable approximation of the objective function gradient, as well as the computation of surface shape sensitivities based on a direct-CAD interface. We present detailed gradient verification studies and then focus on a shape optimization problem for an Apollo-like reentry vehicle. The goal of the optimization is to enhance the lift-to-drag ratio of the capsule by modifying the shape of its heat-shield in conjunction with a center-of-gravity (c.g.) offset. This multipoint and multi-objective optimization problem is used to demonstrate the overall effectiveness of the Cartesian adjoint method for addressing the issues of complex aerodynamic design.

A multidimensional unified gas-kinetic scheme for radiative transfer equations on unstructured mesh

NASA Astrophysics Data System (ADS)

Sun, Wenjun; Jiang, Song; Xu, Kun

2017-12-01

In order to extend the unified gas kinetic scheme (UGKS) to solve radiative transfer equations in a complex geometry, a multidimensional asymptotic preserving implicit method on unstructured mesh is constructed in this paper. With an implicit formulation, the CFL condition for the determination of the time step in UGKS can be much relaxed, and a large time step is used in simulations. Differently from previous direction-by-direction UGKS on orthogonal structured mesh, on unstructured mesh the interface flux transport takes into account multi-dimensional effect, where gradients of radiation intensity and material temperature in both normal and tangential directions of a cell interface are included in the flux evaluation. The multiple scale nature makes the UGKS be able to capture the solutions in both optically thin and thick regions seamlessly. In the optically thick region the condition of cell size being less than photon's mean free path is fully removed, and the UGKS recovers a solver for diffusion equation in such a limit on unstructured mesh. For a distorted quadrilateral mesh, the UGKS goes to a nine-point scheme for the diffusion equation, and it naturally reduces to the standard five-point scheme for a orthogonal quadrilateral mesh. Numerical computations covering a wide range of transport regimes on unstructured and distorted quadrilateral meshes will be presented to validate the current approach.

Three-Dimensional Navier-Stokes Calculations Using the Modified Space-Time CESE Method

NASA Technical Reports Server (NTRS)

Chang, Chau-lyan

2007-01-01

The space-time conservation element solution element (CESE) method is modified to address the robustness issues of high-aspect-ratio, viscous, near-wall meshes. In this new approach, the dependent variable gradients are evaluated using element edges and the corresponding neighboring solution elements while keeping the original flux integration procedure intact. As such, the excellent flux conservation property is retained and the new edge-based gradients evaluation significantly improves the robustness for high-aspect ratio meshes frequently encountered in three-dimensional, Navier-Stokes calculations. The order of accuracy of the proposed method is demonstrated for oblique acoustic wave propagation, shock-wave interaction, and hypersonic flows over a blunt body. The confirmed second-order convergence along with the enhanced robustness in handling hypersonic blunt body flow calculations makes the proposed approach a very competitive CFD framework for 3D Navier-Stokes simulations.

A constrained Delaunay discretization method for adaptively meshing highly discontinuous geological media

NASA Astrophysics Data System (ADS)

Wang, Yang; Ma, Guowei; Ren, Feng; Li, Tuo

2017-12-01

A constrained Delaunay discretization method is developed to generate high-quality doubly adaptive meshes of highly discontinuous geological media. Complex features such as three-dimensional discrete fracture networks (DFNs), tunnels, shafts, slopes, boreholes, water curtains, and drainage systems are taken into account in the mesh generation. The constrained Delaunay triangulation method is used to create adaptive triangular elements on planar fractures. Persson's algorithm (Persson, 2005), based on an analogy between triangular elements and spring networks, is enriched to automatically discretize a planar fracture into mesh points with varying density and smooth-quality gradient. The triangulated planar fractures are treated as planar straight-line graphs (PSLGs) to construct piecewise-linear complex (PLC) for constrained Delaunay tetrahedralization. This guarantees the doubly adaptive characteristic of the resulted mesh: the mesh is adaptive not only along fractures but also in space. The quality of elements is compared with the results from an existing method. It is verified that the present method can generate smoother elements and a better distribution of element aspect ratios. Two numerical simulations are implemented to demonstrate that the present method can be applied to various simulations of complex geological media that contain a large number of discontinuities.

Modeling of gas turbine - solid oxide fuel cell systems for combined propulsion and power on aircraft

NASA Astrophysics Data System (ADS)

Waters, Daniel Francis

This dissertation investigates the use of gas turbine (GT) engine integrated solid oxide fuel cells (SOFCs) to reduce fuel burn in aircraft with large electrical loads like sensor-laden unmanned air vehicles (UAVs). The concept offers a number of advantages: the GT absorbs many SOFC balance of plant functions (supplying fuel, air, and heat to the fuel cell) thereby reducing the number of components in the system; the GT supplies fuel and pressurized air that significantly increases SOFC performance; heat and unreacted fuel from the SOFC are recaptured by the GT cycle offsetting system-level losses; good transient response of the GT cycle compensates for poor transient response of the SOFC. The net result is a system that can supply more electrical power more efficiently than comparable engine-generator systems with only modest (<10%) decrease in power density. Thermodynamic models of SOFCs, catalytic partial oxidation (CPOx) reactors, and three GT engine types (turbojet, combined exhaust turbofan, separate exhaust turbofan) are developed that account for equilibrium gas phase and electrochemical reaction, pressure losses, and heat losses in ways that capture `down-the-channel' effects (a level of fidelity necessary for making meaningful performance, mass, and volume estimates). Models are created in a NASA-developed environment called Numerical Propulsion System Simulation (NPSS). A sensitivity analysis identifies important design parameters and translates uncertainties in model parameters into uncertainties in overall performance. GT-SOFC integrations reduce fuel burn 3-4% in 50 kW systems on 35 kN rated engines (all types) with overall uncertainty <1%. Reductions of 15-20% are possible at the 200 kW power level. GT-SOFCs are also able to provide more electric power (factors >3 in some cases) than generator-based systems before encountering turbine inlet temperature limits. Aerodynamic drag effects of engine-airframe integration are by far the most important limiter of the combined propulsion/electrical generation concept. However, up to 100-200 kW can be produced in a bypass ratio = 8, overall pressure ratio = 40 turbofan with little or no drag penalty. This study shows that it is possible to create cooperatively integrated GT-SOFC systems for combined propulsion and power with better overall performance than stand-alone components.

A fuel cell balance of plant test facility

NASA Astrophysics Data System (ADS)

Dicks, A. L.; Martin, P. A.

Much attention is focused in the fuel cell community on the development of reliable stack technology, but to successfully exploit fuel cells, they must form part of integrated power generation systems. No universal test facilities exist to evaluate SOFC stacks and comparatively little research has been undertaken concerning the issues of the rest of the system, or balance of plant (BOP). BG, in collaboration with Eniricerche, has therefore recently designed and built a test facility to evaluate different configurations of the BOP equipment for a 1-5 kWe solid oxide fuel cell (SOFC) stack. Within this BOP project, integrated, dynamic models have been developed. These have shown that three characteristic response times exist when the stack load is changed and that three independent control loops are required to manage the almost instantaneous change in power output from an SOFC stack, maintain the fuel utilisation and control the stack temperature. Control strategies and plant simplifications, arising from the dynamic modelling, have also been implemented in the BOP test facility. An SOFC simulator was designed and integrated into the control system of the test rig to behave as a real SOFC stack, allowing the development of control strategies without the need for a real stack. A novel combustor has been specifically designed, built and demonstrated to be capable of burning the low calorific anode exhaust gas from an SOFC using the oxygen depleted cathode stream. High temperature, low cost, shell and tube heat exchangers have been shown to be suitable for SOFC systems. Sealing of high temperature anode recirculation fans has, however, been shown to be a major issue and identified as a key area for further investigation.

Solid State Energy Conversion Energy Alliance (SECA)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hennessy, Daniel; Sibisan, Rodica; Rasmussen, Mike

2011-09-12

The overall objective is to develop a Solid Oxide Fuel Cell (SOFC) stack that can be economically produced in high volumes and mass customized for different applications in transportation, stationary power generation, and military market sectors. In Phase I, work will be conducted on system design and integration, stack development, and development of reformers for natural gas and gasoline. Specifically, Delphi-Battelle will fabricate and test a 5 kW stationary power generation system consisting of a SOFC stack, a steam reformer for natural gas, and balance-of-plant (BOP) components, having an expected efficiency of ≥ 35 percent (AC/LHV). In Phase II andmore » Phase III, the emphasis will be to improve the SOFC stack, reduce start-up time, improve thermal cyclability, demonstrate operation on diesel fuel, and substantially reduce materials and manufacturing cost by integrating several functions into one component and thus reducing the number of components in the system. In Phase II, Delphi-Battelle will fabricate and demonstrate two SOFC systems: an improved stationary power generation system consisting of an improved SOFC stack with integrated reformation of natural gas, and the BOP components, with an expected efficiency of ≥ 40 percent (AC/LHV), and a mobile 5 kW system for heavy-duty trucks and military power applications consisting of an SOFC stack, reformer utilizing anode tailgate recycle for diesel fuel, and BOP components, with an expected efficiency of ≥ 30 percent (DC/LHV). Finally, in Phase III, Delphi-Battelle will fabricate and test a 5 kW Auxiliary Power Unit (APU) for mass-market automotive application consisting of an optimized SOFC stack, an optimized catalytic partial oxidation (CPO) reformer for gasoline, and BOP components, having an expected efficiency of ≥ 30 percent (DC/LHV) and a factory cost of ≤ $400/kW.« less

Solid State Energy Conversion Energy Alliance (SECA)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hennessy, Daniel; Sibisan, Rodica; Rasmussen, Mike

2011-09-12

The overall objective is to develop a solid oxide fuel cell (SOFC) stack that can be economically produced in high volumes and mass customized for different applications in transportation, stationary power generation, and military market sectors. In Phase I, work will be conducted on system design and integration, stack development, and development of reformers for natural gas and gasoline. Specifically, Delphi-Battelle will fabricate and test a 5 kW stationary power generation system consisting of a SOFC stack, a steam reformer for natural gas, and balance-of-plant (BOP) components, having an expected efficiency of 35 percent (AC/LHV). In Phase II and Phasemore » III, the emphasis will be to improve the SOFC stack, reduce start-up time, improve thermal cyclability, demonstrate operation on diesel fuel, and substantially reduce materials and manufacturing cost by integrating several functions into one component and thus reducing the number of components in the system. In Phase II, Delphi-Battelle will fabricate and demonstrate two SOFC systems: an improved stationary power generation system consisting of an improved SOFC stack with integrated reformation of natural gas, and the BOP components, with an expected efficiency of ≥40 percent (AC/LHV), and a mobile 5 kW system for heavy-duty trucks and military power applications consisting of an SOFC stack, reformer utilizing anode tailgate recycle for diesel fuel, and BOP components, with an expected efficiency of ≥30 percent (DC/LHV). Finally, in Phase III, Delphi-Battelle will fabricate and test a 5 kW Auxiliary Power Unit (APU) for mass-market automotive application consisting of an optimized SOFC stack, an optimized catalytic partial oxidation (CPO) reformer for gasoline, and BOP components, having an expected efficiency of 30 percent (DC/LHV) and a factory cost of ≤$400/kW.« less

A prefilter for mitigating PH 3 contamination of a Ni-YSZ anode

NASA Astrophysics Data System (ADS)

Xu, Chunchuan; Zondlo, John W.; Sabolsky, Edward M.

Ni-YSZ is used as the anode of a solid oxide fuel cell (SOFC) because it has excellent electrochemical performance for operation with coal-derived syngas. However, trace impurities, PH 3 H 2S AsH 3, and Sb in coal-syngas can cause SOFC degradation. Described here is a means of removing PH 3 impurity from syngas by using a Ni-based prefilter. In one test, a thin Ni-based filter was set upstream of a Ni-YSZ anode-supported SOFC. The SOFC was exposed to syngas with PH 3 under a constant current load at 800 °C. The filter decreased 20 ppm PH 3 in the feed to a level which did not degrade the SOFC for over 400 h until the filter became saturated. In another test, both H 2S and PH 3 were co-fed to the cell with Ni-based and Fe/Ni-based filters. The interaction between these two impurities did not significantly impact the filter performance with respect to PH 3 removal for both filter formulations. The cell performance was evaluated by current-voltage measurements and impedance spectroscopy. Post-mortem analyses of the cell and filter were performed by means of XRD, SEM/EDS and XPS. With proper filter design, the Ni-YSZ SOFC can operate on contaminated coal-syngas without degradation over a prescribed period of time.

Feasibility study for SOFC-GT hybrid locomotive power: Part I. Development of a dynamic 3.5 MW SOFC-GT FORTRAN model

NASA Astrophysics Data System (ADS)

Martinez, Andrew S.; Brouwer, Jacob; Samuelsen, G. Scott

2012-09-01

This work presents the development of a dynamic SOFC-GT hybrid system model applied to a long-haul freight locomotive in operation. Given the expectations of the rail industry, the model is used to develop a preliminary analysis of the proposed system's operational capability on conventional diesel fuel as well as natural gas and hydrogen as potential fuels in the future. It is found that operation of the system on all three of these fuels is feasible with favorable efficiencies and reasonable dynamic response. The use of diesel fuel reformate in the SOFC presents a challenge to the electrochemistry, especially as it relates to control and optimization of the fuel utilization in the anode compartment. This is found to arise from the large amount of carbon monoxide in diesel reformate that is fed to the fuel cell, limiting the maximum fuel utilization possible. This presents an opportunity for further investigations into carbon monoxide electrochemical oxidation and/or system integration studies where the efficiency of the fuel reformer can be balanced against the needs of the SOFC.

Cassette less SOFC stack and method of assembly

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meinhardt, Kerry D

2014-11-18

A cassette less SOFC assembly and a method for creating such an assembly. The SOFC stack is characterized by an electrically isolated stack current path which allows welded interconnection between frame portions of the stack. In one embodiment electrically isolating a current path comprises the step of sealing a interconnect plate to a interconnect plate frame with an insulating seal. This enables the current path portion to be isolated from the structural frame an enables the cell frame to be welded together.

Thermodynamic Modeling of a Solid Oxide Fuel Cell to Couple with an Existing Gas Turbine Engine Model

NASA Technical Reports Server (NTRS)

Brinson, Thomas E.; Kopasakis, George

2004-01-01

The Controls and Dynamics Technology Branch at NASA Glenn Research Center are interested in combining a solid oxide fuel cell (SOFC) to operate in conjunction with a gas turbine engine. A detailed engine model currently exists in the Matlab/Simulink environment. The idea is to incorporate a SOFC model within the turbine engine simulation and observe the hybrid system's performance. The fuel cell will be heated to its appropriate operating condition by the engine s combustor. Once the fuel cell is operating at its steady-state temperature, the gas burner will back down slowly until the engine is fully operating on the hot gases exhausted from the SOFC. The SOFC code is based on a steady-state model developed by The U.S. Department of Energy (DOE). In its current form, the DOE SOFC model exists in Microsoft Excel and uses Visual Basics to create an I-V (current-voltage) profile. For the project's application, the main issue with this model is that the gas path flow and fuel flow temperatures are used as input parameters instead of outputs. The objective is to create a SOFC model based on the DOE model that inputs the fuel cells flow rates and outputs temperature of the flow streams; therefore, creating a temperature profile as a function of fuel flow rate. This will be done by applying the First Law of Thermodynamics for a flow system to the fuel cell. Validation of this model will be done in two procedures. First, for a given flow rate the exit stream temperature will be calculated and compared to DOE SOFC temperature as a point comparison. Next, an I-V curve and temperature curve will be generated where the I-V curve will be compared with the DOE SOFC I-V curve. Matching I-V curves will suggest validation of the temperature curve because voltage is a function of temperature. Once the temperature profile is created and validated, the model will then be placed into the turbine engine simulation for system analysis.

Effect of Samarium Oxide on the Electrical Conductivity of Plasma-Sprayed SOFC Anodes

NASA Astrophysics Data System (ADS)

Panahi, S. N.; Samadi, H.; Nemati, A.

2016-10-01

Solid oxide fuel cells (SOFCs) are rapidly becoming recognized as a new alternative to traditional energy conversion systems because of their high energy efficiency. From an ecological perspective, this environmentally friendly technology, which produces clean energy, is likely to be implemented more frequently in the future. However, the current SOFC technology still cannot meet the demands of commercial applications due to temperature constraints and high cost. To develop a marketable SOFC, suppliers have tended to reduce the operating temperatures by a few hundred degrees. The overall trend for SOFC materials is to reduce their service temperature of electrolyte. Meanwhile, it is important that the other components perform at the same temperature. Currently, the anodes of SOFCs are being studied in depth. Research has indicated that anodes based on a perovskite structure are a more promising candidate in SOFCs than the traditional system because they possess more favorable electrical properties. Among the perovskite-type oxides, SrTiO3 is one of the most promising compositions, with studies demonstrating that SrTiO3 exhibits particularly favorable electrical properties in contrast with other perovskite-type oxides. The main purpose of this article is to describe our study of the effect of rare-earth dopants with a perovskite structure on the electrical behavior of anodes in SOFCs. Sm2O3-doped SrTiO3 synthesized by a solid-state reaction was coated on substrate by atmospheric plasma spray. To compare the effect of the dopant on the electrical conductivity of strontium titanate, different concentrations of Sm2O3 were used. The samples were then investigated by x-ray diffraction, four-point probe at various temperatures (to determine the electrical conductivity), and a scanning electron microscope. The study showed that at room temperature, nondoped samples have a higher electrical resistance than doped samples. As the temperature was increased, the electrical conductivity correspondingly increased. The optimum value of 1.1 S/cm was found at 340°C for samples with 1.5% mol Sm2O3.

Sulfur Tolerant Solid Oxide Fuel Cell for Coal Syngas Application: Experimental Study on Diverse Impurity Effects and Fundamental Modeling of Electrode Kinetics

NASA Astrophysics Data System (ADS)

Gong, Mingyang

With demand over green energy economy, fuel cells have been developed as a promising energy conversion technology with higher efficiency and less emission. Solid oxide fuel cells (SOFC) can utilize various fuels in addition to hydrogen including coal derived sygas, and thus are favored for future power generation due to dependence on coal in electrical industry. However impurities such as sulfur and phosphorous present in coal syngas in parts per million (p.p.m.) levels can severely poison SOFC anode typically made of Ni/yttria-stabilized-zirconia (Ni-YSZ) and limit SOFC applicability in economically derivable fuels. The focus of the research is to develop strategy for application of high performance SOFC in coal syngas with tolerance against trace impurities such as H2S and PH3. To realize the research goal, the experimental study on sulfur tolerant anode materials and examination of various fuel impurity effects on SOFC anode are combined with electrochemical modeling of SOFC cathode kinetics in order to benefit design of direct-coal-syngas SOFC. Tolerant strategy for SOFC anode against sulfur is studied by using alternative materials which can both mitigate sulfur poisoning and function as active anode components. The Ni-YSZ anode was modified by incorporation of lanthanum doped ceria (LDC) nano-coatings via impregnation. Cell test in coal syngas containing 20 ppm H2S indicated the impregnated LDC coatings inhibited on-set of sulfur poisoning by over 10hrs. Cell analysis via X-ray photon spectroscopy (XPS), X-ray diffraction (XRD) and electrochemistry revealed LDC coatings reacted with H2S via chemisorptions, resulting in less sulfur blocking triple--phase-boundary and minimized performance loss. Meanwhile the effects of PH3 impurity on SOFC anode is examined by using Ni-YSZ anode supported SOFC. Degradation of cell is found to be irreversible due to adsorption of PH3 on TPB and further reaction with Ni to form secondary phases with low melting point. The feasibility of mixed ionic and electronic conductive (MIEC) metal oxides with perovskite structure (ABO3) as alternative ceramic SOFC anodes in coal syngas has been examined by PH3 exposure test. The study found although perovskite anodes can be generally more tolerant against H2S, further examination on PH3 tolerance is indispensable before their extensive application in coal syngas. On the theoretical end it is this research's initiative that oxygen reduction reaction at mixed ionic and electronic conductive (MIEC) cathode is a key factor controlling SOFC performance at intermediate temperature (700˜850°C). It is generally recognized that the overall charge-transfer process could occur through both surface pathway at triple-phase boundary (3PB) and bulk pathway at electrolyte/cathode interface (2PB). A modified one-dimensional model is thus developed to predict defect evolution of MIEC cathode under overpotential by incorporating multi-step charge-transfer into the bi-pathway continuum model. Finite volume control method is applied to obtain solutions for the model. The simulation predicted kinetics transition from 3PB control to 2PB control as cathodic overpotential stepping from -0.2V to -0.4V, depending on the material properties parameters. Meanwhile significant activation behavior of the MIEC electrode was also observed as indicated by extension of reaction region towards gas-exposed oxide surface. This model addressed contribution from electrochemical-controlled rate-limiting steps (RLSs) on the reduction kinetics, and identified the role played by multiple material property parameters such as surface oxygen ion concentration and bulk vacancy concentration on the kinetics transition. Combined academic knowledge gained through experimental investigation and theoretical simulation in this research would benefit the future design, development and application strategy of high-performance SOFC in coal syngas fuels.

Thermo-Mechanical and Electrochemistry Modeling of Planar SOFC Stacks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khaleel, Mohammad A.; Recknagle, Kurtis P.; Lin, Zijing

2002-12-01

Modeling activities at PNNL support design and development of modular SOFC systems. The SOFC stack modeling capability at PNNL has developed to a level at which planar stack designs can be compared and optimized for startup performance. Thermal-fluids and stress modeling is being performed to predict the transient temperature distribution and to determine the thermal stresses based on the temperature distribution. Current efforts also include the development of a model for calculating current density, cell voltage, and heat production in SOFC stacks with hydrogen or other fuels. The model includes the heat generation from both Joule heating and chemical reactions.more » It also accounts for species production and destruction via mass balance. The model is being linked to the finite element code MARC to allow for the evaluation of temperatures and stresses during steady state operations.« less

Millimeter-wave irradiation heating for operation of doped CeO2 electrolyte-supported single solid oxide fuel cell

NASA Astrophysics Data System (ADS)

Che Abdullah, Salmie Suhana Binti; Teranishi, Takashi; Hayashi, Hidetaka; Kishimoto, Akira

2018-01-01

High operation temperature of solid oxide fuel cell (SOFC) results in high cell and operation cost, time consuming and fast cell degradation. Developing high performance SOFC that operates at lower temperature is required. Here we demonstrate 24 GHz microwave as a rapid heating source to replace conventional heating method for SOFC operation using 20 mol% Sm doped CeO2 electrolyte-supported single cell. The tested cell shows improvement of 62% in maximum power density at 630 °C under microwave heating. This improvement governs by bulk conductivity of the electrolyte. Investigation of ionic transference number reveals that the value is unchanged under microwave irradiation, confirming the charge carrier is dominated by oxygen ion species. This work shows a potential new concept of high performance as well as cost and energy effective SOFC.

Efficient electrochemical refrigeration power plant using natural gas with ∼100% CO2 capture

NASA Astrophysics Data System (ADS)

Al-musleh, Easa I.; Mallapragada, Dharik S.; Agrawal, Rakesh

2015-01-01

We propose an efficient Natural Gas (NG) based Solid Oxide Fuel Cell (SOFC) power plant equipped with ∼100% CO2 capture. The power plant uses a unique refrigeration based process to capture and liquefy CO2 from the SOFC exhaust. The capture of CO2 is carried out via condensation and purification using two rectifying columns operating at different pressures. The uncondensed gas mixture, comprising of relatively high purity unconverted fuel, is recycled to the SOFC and found to boost the power generation of the SOFC by 22%, when compared to a stand alone SOFC. If Liquefied Natural Gas (LNG) is available at the plant gate, then the refrigeration available from its evaporation is used for CO2 Capture and Liquefaction (CO2CL). If NG is utilized, then a Mixed Refrigerant (MR) vapor compression cycle is utilized for CO2CL. Alternatively, the necessary refrigeration can be supplied by evaporating the captured liquid CO2 at a lower pressure, which is then compressed to supercritical pressures for pipeline transportation. From rigorous simulations, the power generation efficiency of the proposed processes is found to be 70-76% based on lower heating value (LHV). The benefit of the proposed processes is evident when the efficiency of 73% for a conventional SOFC-Gas turbine power plant without CO2 capture is compared with an equivalent efficiency of 71.2% for the proposed process with CO2CL.

Coal-fuelled systems for peaking power with 100% CO2 capture through integration of solid oxide fuel cells with compressed air energy storage

NASA Astrophysics Data System (ADS)

Nease, Jake; Adams, Thomas A.

2014-04-01

In this study, a coal-fuelled integrated solid oxide fuel cell (SOFC) and compressed air energy storage (CAES) system in a load-following power production scenario is discussed. Sixteen SOFC-based plants with optional carbon capture and sequestration (CCS) and syngas shifting steps are simulated and compared to a state-of-the-art supercritical pulverised coal (SCPC) plant. Simulations are performed using a combination of MATLAB and Aspen Plus v7.3. It was found that adding CAES to a SOFC-based plant can provide load-following capabilities with relatively small effects on efficiencies (1-2% HHV depending on the system configuration) and levelized costs of electricity (∼0.35 ¢ kW-1 h-1). The load-following capabilities, as measured by least-squares metrics, show that this system may utilize coal and achieve excellent load-tracking that is not adversely affected by the inclusion of CCS. Adding CCS to the SOFC/CAES system reduces measurable direct CO2 emission to zero. A seasonal partial plant shutdown schedule is found to reduce fuel consumption by 9.5% while allowing for cleaning and maintenance windows for the SOFC stacks without significantly affecting the performance of the system (∼1% HHV reduction in efficiency). The SOFC-based systems with CCS are found to become economically attractive relative to SCPC above carbon taxes of 22 ton-1.

Mixed fuel strategy for carbon deposition mitigation in solid oxide fuel cells at intermediate temperatures.

PubMed

Su, Chao; Chen, Yubo; Wang, Wei; Ran, Ran; Shao, Zongping; Diniz da Costa, João C; Liu, Shaomin

2014-06-17

In this study, we propose and experimentally verified that methane and formic acid mixed fuel can be employed to sustain solid oxide fuel cells (SOFCs) to deliver high power outputs at intermediate temperatures and simultaneously reduce the coke formation over the anode catalyst. In this SOFC system, methane itself was one part of the fuel, but it also played as the carrier gas to deliver the formic acid to reach the anode chamber. On the other hand, the products from the thermal decomposition of formic acid helped to reduce the carbon deposition from methane cracking. In order to clarify the reaction pathways for carbon formation and elimination occurring in the anode chamber during the SOFC operation, O2-TPO and SEM analysis were carried out together with the theoretical calculation. Electrochemical tests demonstrated that stable and high power output at an intermediate temperature range was well-maintained with a peak power density of 1061 mW cm(-2) at 750 °C. With the synergic functions provided by the mixed fuel, the SOFC was running for 3 days without any sign of cell performance decay. In sharp contrast, fuelled by pure methane and tested at similar conditions, the SOFC immediately failed after running for only 30 min due to significant carbon deposition. This work opens a new way for SOFC to conquer the annoying problem of carbon deposition just by properly selecting the fuel components to realize their synergic effects.

On the role of ultra-thin oxide cathode synthesis on the functionality of micro-solid oxide fuel cells: Structure, stress engineering and in situ observation of fuel cell membranes during operation

NASA Astrophysics Data System (ADS)

Lai, Bo-Kuai; Kerman, Kian; Ramanathan, Shriram

Microstructure and stresses in dense La 0.6Sr 0.4Co 0.8Fe 0.2O 3 (LSCF) ultra-thin films have been investigated to increase the physical thickness of crack-free cathodes and active area of thermo-mechanically robust micro-solid oxide fuel cell (μSOFC) membranes. Processing protocols employ low deposition rates to create a highly granular nanocrystalline microstructure in LSCF thin films and high substrate temperatures to produce linear temperature-dependent stress evolution that is dominated by compressive stresses in μSOFC membranes. Insight and trade-off on the synthesis are revealed by probing microstructure evolution and electrical conductivity in LSCF thin films, in addition to in situ monitoring of membrane deformation while measuring μSOFC performance at varying temperatures. From these studies, we were able to successfully fabricate failure-resistant square μSOFC (LSCF/YSZ/Pt) membranes with width of 250 μm and crack-free cathodes with thickness of ∼70 nm. Peak power density of ∼120 mW cm -2 and open circuit voltage of ∼0.6 V at 560 °C were achieved on a μSOFC array chip containing ten such membranes. Mechanisms affecting fuel cell performance are discussed. Our results provide fundamental insight to pathways of microstructure and stress engineering of ultra-thin, dense oxide cathodes and μSOFC membranes.

Direction-aware Slope Limiter for 3D Cubic Grids with Adaptive Mesh Refinement

DOE PAGES

Velechovsky, Jan; Francois, Marianne M.; Masser, Thomas

2018-06-07

In the context of finite volume methods for hyperbolic systems of conservation laws, slope limiters are an effective way to suppress creation of unphysical local extrema and/or oscillations near discontinuities. We investigate properties of these limiters as applied to piecewise linear reconstructions of conservative fluid quantities in three-dimensional simulations. In particular, we are interested in linear reconstructions on Cartesian adaptively refined meshes, where a reconstructed fluid quantity at a face center depends on more than a single gradient component of the quantity. We design a new slope limiter, which combines the robustness of a minmod limiter with the accuracy ofmore » a van Leer limiter. The limiter is called Direction-Aware Limiter (DAL), because the combination is based on a principal flow direction. In particular, DAL is useful in situations where the Barth–Jespersen limiter for general meshes fails to maintain global linear functions, such as on cubic computational meshes with stencils including only faceneighboring cells. Here, we verify the new slope limiter on a suite of standard hydrodynamic test problems on Cartesian adaptively refined meshes. Lastly, we demonstrate reduced mesh imprinting; for radially symmetric problems such as the Sedov blast wave or the Noh implosion test cases, the results with DAL show better preservation of radial symmetry compared to the other standard methods on Cartesian meshes.« less

Direction-aware Slope Limiter for 3D Cubic Grids with Adaptive Mesh Refinement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Velechovsky, Jan; Francois, Marianne M.; Masser, Thomas

In the context of finite volume methods for hyperbolic systems of conservation laws, slope limiters are an effective way to suppress creation of unphysical local extrema and/or oscillations near discontinuities. We investigate properties of these limiters as applied to piecewise linear reconstructions of conservative fluid quantities in three-dimensional simulations. In particular, we are interested in linear reconstructions on Cartesian adaptively refined meshes, where a reconstructed fluid quantity at a face center depends on more than a single gradient component of the quantity. We design a new slope limiter, which combines the robustness of a minmod limiter with the accuracy ofmore » a van Leer limiter. The limiter is called Direction-Aware Limiter (DAL), because the combination is based on a principal flow direction. In particular, DAL is useful in situations where the Barth–Jespersen limiter for general meshes fails to maintain global linear functions, such as on cubic computational meshes with stencils including only faceneighboring cells. Here, we verify the new slope limiter on a suite of standard hydrodynamic test problems on Cartesian adaptively refined meshes. Lastly, we demonstrate reduced mesh imprinting; for radially symmetric problems such as the Sedov blast wave or the Noh implosion test cases, the results with DAL show better preservation of radial symmetry compared to the other standard methods on Cartesian meshes.« less

Polyhedral meshing in numerical analysis of conjugate heat transfer

NASA Astrophysics Data System (ADS)

Sosnowski, Marcin; Krzywanski, Jaroslaw; Grabowska, Karolina; Gnatowska, Renata

2018-06-01

Computational methods have been widely applied in conjugate heat transfer analysis. The very first and crucial step in such research is the meshing process which consists in dividing the analysed geometry into numerous small control volumes (cells). In Computational Fluid Dynamics (CFD) applications it is desirable to use the hexahedral cells as the resulting mesh is characterized by low numerical diffusion. Unfortunately generating such mesh can be a very time-consuming task and in case of complicated geometry - it may not be possible to generate cells of good quality. Therefore tetrahedral cells have been implemented into commercial pre-processors. Their advantage is the ease of its generation even in case of very complex geometry. On the other hand tetrahedrons cannot be stretched excessively without decreasing the mesh quality factor, so significantly larger number of cells has to be used in comparison to hexahedral mesh in order to achieve a reasonable accuracy. Moreover the numerical diffusion of tetrahedral elements is significantly higher. Therefore the polyhedral cells are proposed within the paper in order to combine the advantages of hexahedrons (low numerical diffusion resulting in accurate solution) and tetrahedrons (rapid semi-automatic generation) as well as to overcome the disadvantages of both the above mentioned mesh types. The major benefit of polyhedral mesh is that each individual cell has many neighbours, so gradients can be well approximated. Polyhedrons are also less sensitive to stretching than tetrahedrons which results in better mesh quality leading to improved numerical stability of the model. In addition, numerical diffusion is reduced due to mass exchange over numerous faces. This leads to a more accurate solution achieved with a lower cell count. Therefore detailed comparison of numerical modelling results concerning conjugate heat transfer using tetrahedral and polyhedral meshes is presented in the paper.

Analysis of Slope Limiters on Irregular Grids

NASA Technical Reports Server (NTRS)

Berger, Marsha; Aftosmis, Michael J.

2005-01-01

This paper examines the behavior of flux and slope limiters on non-uniform grids in multiple dimensions. Many slope limiters in standard use do not preserve linear solutions on irregular grids impacting both accuracy and convergence. We rewrite some well-known limiters to highlight their underlying symmetry, and use this form to examine the proper - ties of both traditional and novel limiter formulations on non-uniform meshes. A consistent method of handling stretched meshes is developed which is both linearity preserving for arbitrary mesh stretchings and reduces to common limiters on uniform meshes. In multiple dimensions we analyze the monotonicity region of the gradient vector and show that the multidimensional limiting problem may be cast as the solution of a linear programming problem. For some special cases we present a new directional limiting formulation that preserves linear solutions in multiple dimensions on irregular grids. Computational results using model problems and complex three-dimensional examples are presented, demonstrating accuracy, monotonicity and robustness.

A thermally self-sustained micro-power plant with integrated micro-solid oxide fuel cells, micro-reformer and functional micro-fluidic carrier

NASA Astrophysics Data System (ADS)

Scherrer, Barbara; Evans, Anna; Santis-Alvarez, Alejandro J.; Jiang, Bo; Martynczuk, Julia; Galinski, Henning; Nabavi, Majid; Prestat, Michel; Tölke, René; Bieberle-Hütter, Anja; Poulikakos, Dimos; Muralt, Paul; Niedermann, Philippe; Dommann, Alex; Maeder, Thomas; Heeb, Peter; Straessle, Valentin; Muller, Claude; Gauckler, Ludwig J.

2014-07-01

Low temperature micro-solid oxide fuel cell (micro-SOFC) systems are an attractive alternative power source for small-size portable electronic devices due to their high energy efficiency and density. Here, we report on a thermally self-sustainable reformer-micro-SOFC assembly. The device consists of a micro-reformer bonded to a silicon chip containing 30 micro-SOFC membranes and a functional glass carrier with gas channels and screen-printed heaters for start-up. Thermal independence of the device from the externally powered heater is achieved by exothermic reforming reactions above 470 °C. The reforming reaction and the fuel gas flow rate of the n-butane/air gas mixture controls the operation temperature and gas composition on the micro-SOFC membrane. In the temperature range between 505 °C and 570 °C, the gas composition after the micro-reformer consists of 12 vol.% to 28 vol.% H2. An open-circuit voltage of 1.0 V and maximum power density of 47 mW cm-2 at 565 °C is achieved with the on-chip produced hydrogen at the micro-SOFC membranes.

Oxidation Resistant, Cr Retaining, Electrically Conductive Coatings on Metallic Alloys for SOFC Interconnects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vladimir Gorokhovsky

2008-03-31

This report describes significant results from an on-going, collaborative effort to enable the use of inexpensive metallic alloys as interconnects in planar solid oxide fuel cells (SOFCs) through the use of advanced coating technologies. Arcomac Surface Engineering, LLC, under the leadership of Dr. Vladimir Gorokhovsky, is investigating filtered-arc and filtered-arc plasma-assisted hybrid coating deposition technologies to promote oxidation resistance, eliminate Cr volatility, and stabilize the electrical conductivity of both standard and specialty steel alloys of interest for SOFC metallic interconnect (IC) applications. Arcomac has successfully developed technologies and processes to deposit coatings with excellent adhesion, which have demonstrated a substantialmore » increase in high temperature oxidation resistance, stabilization of low Area Specific Resistance values and significantly decrease Cr volatility. An extensive matrix of deposition processes, coating compositions and architectures was evaluated. Technical performance of coated and uncoated sample coupons during exposures to SOFC interconnect-relevant conditions is discussed, and promising future directions are considered. Cost analyses have been prepared based on assessment of plasma processing parameters, which demonstrate the feasibility of the proposed surface engineering process for SOFC metallic IC applications.« less

Real-time thermal imaging of solid oxide fuel cell cathode activity in working condition.

PubMed

Montanini, Roberto; Quattrocchi, Antonino; Piccolo, Sebastiano A; Amato, Alessandra; Trocino, Stefano; Zignani, Sabrina C; Faro, Massimiliano Lo; Squadrito, Gaetano

2016-09-01

Electrochemical methods such as voltammetry and electrochemical impedance spectroscopy are effective for quantifying solid oxide fuel cell (SOFC) operational performance, but not for identifying and monitoring the chemical processes that occur on the electrodes' surface, which are thought to be strictly related to the SOFCs' efficiency. Because of their high operating temperature, mechanical failure or cathode delamination is a common shortcoming of SOFCs that severely affects their reliability. Infrared thermography may provide a powerful tool for probing in situ SOFC electrode processes and the materials' structural integrity, but, due to the typical design of pellet-type cells, a complete optical access to the electrode surface is usually prevented. In this paper, a specially designed SOFC is introduced, which allows temperature distribution to be measured over all the cathode area while still preserving the electrochemical performance of the device. Infrared images recorded under different working conditions are then processed by means of a dedicated image processing algorithm for quantitative data analysis. Results reported in the paper highlight the effectiveness of infrared thermal imaging in detecting the onset of cell failure during normal operation and in monitoring cathode activity when the cell is fed with different types of fuels.

Investigation of aluminosilicate as a solid oxide fuel cell refractory

NASA Astrophysics Data System (ADS)

Gentile, Paul S.; Sofie, Stephen W.

2011-05-01

Aluminosilicate represents a potential low cost alternative to alumina for solid oxide fuel cell (SOFC) refractory applications. The objectives of this investigation are to study: (1) changes of aluminosilicate chemistry and morphology under SOFC conditions, (2) deposition of aluminosilicate vapors on yttria stabilized zirconia (YSZ) and nickel, and (3) effects of aluminosilicate vapors on SOFC electrochemical performance. Thermal treatment of aluminosilicate under high temperature SOFC conditions is shown to result in increased mullite concentrations at the surface due to diffusion of silicon from the bulk. Water vapor accelerates the rate of surface diffusion resulting in a more uniform distribution of silicon. The high temperature condensation of volatile gases released from aluminosilicate preferentially deposit on YSZ rather than nickel. Silicon vapor deposited on YSZ consists primarily of aluminum rich clusters enclosed in an amorphous siliceous layer. Increased concentrations of silicon are observed in enlarged grain boundaries indicating separation of YSZ grains by insulating glassy phase. The presence of aluminosilicate powder in the hot zone of a fuel line supplying humidified hydrogen to an SOFC anode impeded peak performance and accelerated degradation. Energy dispersive X-ray spectroscopy detected concentrations of silicon at the interface between the electrolyte and anode interlayer above impurity levels.

The financial viability of an SOFC cogeneration system in single-family dwellings

NASA Astrophysics Data System (ADS)

Alanne, Kari; Saari, Arto; Ugursal, V. Ismet; Good, Joel

In the near future, fuel cell-based residential micro-CHP systems will compete with traditional methods of energy supply. A micro-CHP system may be considered viable if its incremental capital cost compared to its competitors equals to cumulated savings during a given period of time. A simplified model is developed in this study to estimate the operation of a residential solid oxide fuel cell (SOFC) system. A comparative assessment of the SOFC system vis-à-vis heating systems based on gas, oil and electricity is conducted using the simplified model for a single-family house located in Ottawa and Vancouver. The energy consumption of the house is estimated using the HOT2000 building simulation program. A financial analysis is carried out to evaluate the sensitivity of the maximum allowable capital cost with respect to system sizing, acceptable payback period, energy price and the electricity buyback strategy of an energy utility. Based on the financial analysis, small (1-2 kW e) SOFC systems seem to be feasible in the considered case. The present study shows also that an SOFC system is especially an alternative to heating systems based on oil and electrical furnaces.

Transient deformational properties of high temperature alloys used in solid oxide fuel cell stacks

NASA Astrophysics Data System (ADS)

Molla, Tesfaye Tadesse; Kwok, Kawai; Frandsen, Henrik Lund

2017-05-01

Stresses and probability of failure during operation of solid oxide fuel cells (SOFCs) is affected by the deformational properties of the different components of the SOFC stack. Though the overall stress relaxes with time during steady state operation, large stresses would normally appear through transients in operation including temporary shut downs. These stresses are highly affected by the transient creep behavior of metallic components in the SOFC stack. This study investigates whether a variation of the so-called Chaboche's unified power law together with isotropic hardening can represent the transient behavior of Crofer 22 APU, a typical iron-chromium alloy used in SOFC stacks. The material parameters for the model are determined by measurements involving relaxation and constant strain rate experiments. The constitutive law is implemented into commercial finite element software using a user-defined material model. This is used to validate the developed constitutive law to experiments with constant strain rate, cyclic and creep experiments. The predictions from the developed model are found to agree well with experimental data. It is therefore concluded that Chaboche's unified power law can be applied to describe the high temperature inelastic deformational behaviors of Crofer 22 APU used for metallic interconnects in SOFC stacks.

Optimal robust control strategy of a solid oxide fuel cell system

NASA Astrophysics Data System (ADS)

Wu, Xiaojuan; Gao, Danhui

2018-01-01

Optimal control can ensure system safe operation with a high efficiency. However, only a few papers discuss optimal control strategies for solid oxide fuel cell (SOFC) systems. Moreover, the existed methods ignore the impact of parameter uncertainty on system instantaneous performance. In real SOFC systems, several parameters may vary with the variation of operation conditions and can not be identified exactly, such as load current. Therefore, a robust optimal control strategy is proposed, which involves three parts: a SOFC model with parameter uncertainty, a robust optimizer and robust controllers. During the model building process, boundaries of the uncertain parameter are extracted based on Monte Carlo algorithm. To achieve the maximum efficiency, a two-space particle swarm optimization approach is employed to obtain optimal operating points, which are used as the set points of the controllers. To ensure the SOFC safe operation, two feed-forward controllers and a higher-order robust sliding mode controller are presented to control fuel utilization ratio, air excess ratio and stack temperature afterwards. The results show the proposed optimal robust control method can maintain the SOFC system safe operation with a maximum efficiency under load and uncertainty variations.

Direct Logistic Fuel JP-8 Conversion in a Liquid Tin Anode Solid Oxide Fuel Cell (LTA-SOFC)

DTIC Science & Technology

2008-04-09

GeSnOOSn sgl [1] As governed by the Nernst equation Open Circuit Voltage (OCV) is inversely proportional to temperature. The OCV of...inherently stable at 1,000°C. The LTA-SOFC electrochemical reaction is based on the following thermodynamic equation . C1000T kJ 311 42 o)(2... equation 1 is 0.8V at 1000°C, using an oxygen partial pressure of one. This equation gives the OCV for a LTA–SOFC functioning as a battery. The tin oxide

Measuring attitude with a gradiometer

NASA Technical Reports Server (NTRS)

Sonnabend, David; Born, George H.

1994-01-01

Static attitude estimation and dynamic attitude estimation are used to describe a gradiometer composed of a number of accelerometers that are used to measure a combination of the local gravity gradient and instrument rotation effects. After a series of measures to isolate the gradient, a global mesh of measurements can be obtained that determine the planetary external gravity potential. Orbital and spacecraft models are developed to determine if, when the gravity potential is known, the same measurements, unsupported by any other information can be used to infer the spacecraft attitude.

Phase-field modelling of ductile fracture: a variational gradient-extended plasticity-damage theory and its micromorphic regularization

PubMed Central

Teichtmeister, S.; Aldakheel, F.

2016-01-01

This work outlines a novel variational-based theory for the phase-field modelling of ductile fracture in elastic–plastic solids undergoing large strains. The phase-field approach regularizes sharp crack surfaces within a pure continuum setting by a specific gradient damage modelling. It is linked to a formulation of gradient plasticity at finite strains. The framework includes two independent length scales which regularize both the plastic response as well as the crack discontinuities. This ensures that the damage zones of ductile fracture are inside of plastic zones, and guarantees on the computational side a mesh objectivity in post-critical ranges. PMID:27002069

Innovative Self-Healing Seals for Solid Oxide Fuel Cells (SOFC)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raj Singh

Solid oxide fuel cell (SOFC) technology is critical to several national initiatives. Solid State Energy Conversion Alliance (SECA) addresses the technology needs through its comprehensive programs on SOFC. A reliable and cost-effective seal that works at high temperatures is essential to the long-term performance of the SOFC for 40,000 hours at 800°C. Consequently, seals remain an area of highest priority for the SECA program and its industry teams. An innovative concept based on self-healing glasses was advanced and successfully demonstrated through seal tests for 3000 hours and 300 thermal cycles to minimize internal stresses under both steady state and thermalmore » transients for making reliable seals for the SECA program. The self-healing concept requires glasses with low viscosity at the SOFC operating temperature of 800°C but this requirement may lead to excessive flow of the glass in areas forming the seal. To address this challenge, a modification to glass properties by addition of particulate fillers is pursued in the project. The underlying idea is that a non-reactive ceramic particulate filler is expected to form glass-ceramic composite and increase the seal viscosity thereby increasing the creep resistance of the glass-composite seals under load. The objectives of the program are to select appropriate filler materials for making glass-composite, fabricate glass-composites, measure thermal expansion behaviors, and determine stability of the glass-composites in air and fuel environments of a SOFC. Self-healing glass-YSZ composites are further developed and tested over a longer time periods under conditions typical of the SOFCs to validate the long-term stability up to 2000 hours. The new concepts of glass-composite seals, developed and nurtured in this program, are expected to be cost-effective as these are based on conventional processing approaches and use of the inexpensive materials.« less

The ways of SOFC systems efficiency increasing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Demin, A.K.; Timofeyeva, N.

1996-04-01

The efficiency of solid oxide fuel cells (SOFCs) is described. This paper considers methods to lift the fuel utilization and/or the average cell voltage with the goal of increasing the cell efficiency by improved cell designs.

Status of tubular SOFC field unit demonstrations

NASA Astrophysics Data System (ADS)

George, Raymond A.

Siemens Westinghouse is in the final stage of its tubular solid oxide fuel cell (SOFC) development program, and the program emphasis has shifted from basic technology development to cost reduction, scale-up and demonstration of pre-commercial power systems at customer sites. This paper describes our field unit demonstration program including the EDB/ELSAM 100-kW e combined heat and power (CHP) system, the Southern California Edison (SCE) 220-kW e pressurized SOFC/gas turbine (PSOFC/GT) power system, and the planned demonstrations of commercial prototype power systems. In the Spring of 1999, the EDB/ELSAM 100-kW e SOFC-CHP system produced 109 kW e net AC to the utility grid at 46% electrical efficiency and 65 kW t to the hot water district heating system, verifying the analytical predictions. The SCE 220-kW e PSOFC/GT power system will undergo factory startup in the Fall of 1999.

Modeling Methodologies for Design and Control of Solid Oxide Fuel Cell APUs

NASA Astrophysics Data System (ADS)

Pianese, C.; Sorrentino, M.

2009-08-01

Among the existing fuel cell technologies, Solid Oxide Fuel Cells (SOFC) are particularly suitable for both stationary and mobile applications, due to their high energy conversion efficiencies, modularity, high fuel flexibility, low emissions and noise. Moreover, the high working temperatures enable their use for efficient cogeneration applications. SOFCs are entering in a pre-industrial era and a strong interest for designing tools has growth in the last years. Optimal system configuration, components sizing, control and diagnostic system design require computational tools that meet the conflicting needs of accuracy, affordable computational time, limited experimental efforts and flexibility. The paper gives an overview on control-oriented modeling of SOFC at both single cell and stack level. Such an approach provides useful simulation tools for designing and controlling SOFC-APUs destined to a wide application area, ranging from automotive to marine and airplane APUs.

Modelling and control of solid oxide fuel cell generation system in microgrid

NASA Astrophysics Data System (ADS)

Zhou, Niancheng; Li, Chunyan; Sun, Fangqing; Wang, Qianggang

2017-11-01

Compared with other kinds of fuel cells, solid oxide fuel cell (SOFC) has been widely used in microgrids because of its higher efficiency and longer operation life. The weakness of SOFC lies in its slow response speed when grid disturbance occurs. This paper presents a control strategy that can promote the response speed and limit the fault current impulse for SOFC systems integrated into microgrids. First, the hysteretic control of the bidirectional DC-DC converter, which joins the SOFC and DC bus together, is explored. In addition, an improved droop control with limited current protection is applied in the DC-AC inverter, and the active synchronization control is applied to ensure a smooth transition of the microgrid between the grid-connected mode and the islanded mode. To validate the effectiveness of this control strategy, the control model was built and simulated in PSCAD/EMTDC.

Manifold, bus support and coupling arrangement for solid oxide fuel cells

DOEpatents

Parry, G.W.

1988-04-21

Individual, tubular solid oxide fuel cells (SOFCs) are assembled into bundles called a module within a housing, with a plurality of modules arranged end-to-end in a linear, stacked configuration called a string. A common set of piping comprised of a suitable high temperature resistant material (1) provides fuel and air to each module housing, (2) serves as electrically conducting buses, and (3) provides structural support for a string of SOFC modules. Ceramic collars are used to connect fuel and air inlet piping to each of the electrodes in an SOFC module and provide (1) electrical insulation for the current carrying bus bars and gas manifolds, (2) damping for the fuel and air inlet piping, and (3) proper spacing between the fuel and air inlet piping to prevent contact between these tubes and possible damage to the SOFC. 11 figs.

Commercialisation of Solid Oxide Fuel Cells - opportunities and forecasts

NASA Astrophysics Data System (ADS)

Dziurdzia, B.; Magonski, Z.; Jankowski, H.

2016-01-01

The paper presents the analysis of commercialisation possibilities of the SOFC stack designed at AGH. The paper reminds the final design of the stack, presented earlier at IMAPS- Poland conferences, its recent modifications and measurements. The stack consists of planar double-sided ceramic fuel cells which characterize by the special anode construction with embedded fuel channels. The stack features by a simple construction without metallic interconnectors and frames, lowered thermal capacity and quick start-up time. Predictions for the possible applications of the stack include portable generators for luxurious caravans, yachts, ships at berth. The SOFC stack operating as clean, quiet and efficient power source could replace on-board diesel generators. Market forecasts shows that there is also some room on a market for the SOFC stack as a standalone generator in rural areas far away from the grid. The paper presents also the survey of SOFC market in Europe USA, Australia and other countries.

Exergy analysis of a solid oxide fuel cell micropowerplant

NASA Astrophysics Data System (ADS)

Hotz, Nico; Senn, Stephan M.; Poulikakos, Dimos

In this paper, an analytical model of a micro solid oxide fuel cell (SOFC) system fed by butane is introduced and analyzed in order to optimize its exergetic efficiency. The micro SOFC system is equipped with a partial oxidation (POX) reformer, a vaporizer, two pre-heaters, and a post-combustor. A one-dimensional (1D) polarization model of the SOFC is used to examine the effects of concentration overpotentials, activation overpotentials, and ohmic resistances on cell performance. This 1D polarization model is extended in this study to a two-dimensional (2D) fuel cell model considering convective mass and heat transport along the fuel cell channel and from the fuel cell to the environment. The influence of significant operational parameters on the exergetic efficiency of the micro SOFC system is discussed. The present study shows the importance of an exergy analysis of the fuel cell as part of an entire thermodynamic system (transportable micropowerplant) generating electric power.

Study on dynamic performance of SOFC

NASA Astrophysics Data System (ADS)

Zhan, Haiyang; Liang, Qianchao; Wen, Qiang; Zhu, Runkai

2017-05-01

In order to solve the problem of real-time matching of load and fuel cell power, it is urgent to study the dynamic response process of SOFC in the case of load mutation. The mathematical model of SOFC is constructed, and its performance is simulated. The model consider the influence factors such as polarization effect, ohmic loss. It also takes the diffusion effect, thermal effect, energy exchange, mass conservation, momentum conservation. One dimensional dynamic mathematical model of SOFC is constructed by using distributed lumped parameter method. The simulation results show that the I-V characteristic curves are in good agreement with the experimental data, and the accuracy of the model is verified. The voltage response curve, power response curve and the efficiency curve are obtained by this way. It lays a solid foundation for the research of dynamic performance and optimal control in power generation system of high power fuel cell stack.

Real-time electrochemical impedance spectroscopy diagnosis of the solid oxide fuel cell for marine power applications

NASA Astrophysics Data System (ADS)

Nakajima, Hironori; Kitahara, Tatsumi

2017-11-01

We have investigated the behavior of an operating solid oxide fuel cell (SOFC) with supplying a simulated syngas to develop diagnosis method of the SOFC for marine power applications fueled with liquefied natural gas (LNG). We analyze the characteristics of a syngas-fueled intermediate temperature microtubular SOFC at 500 ∘C for accelerated deterioration by carbon deposition as a model case by electrochemical impedance spectroscopy (EIS) to in-situ find parameters useful for the real-time diagnosis. EIS analyses are performed by complex nonlinear least squares (CNLS) curve fitting to measured impedance spectra with an equivalent electric circuit model consisting of several resistances and capacitances attributed to the anode and cathode processes as well as Ohmic resistance of the cell. The characteristic changes of those circuit parameters by internal reforming and anode degradation are extracted, showing that they can be used for the real-time diagnosis of operating SOFCs.

Adaptive mesh strategies for the spectral element method

NASA Technical Reports Server (NTRS)

Mavriplis, Catherine

1992-01-01

An adaptive spectral method was developed for the efficient solution of time dependent partial differential equations. Adaptive mesh strategies that include resolution refinement and coarsening by three different methods are illustrated on solutions to the 1-D viscous Burger equation and the 2-D Navier-Stokes equations for driven flow in a cavity. Sharp gradients, singularities, and regions of poor resolution are resolved optimally as they develop in time using error estimators which indicate the choice of refinement to be used. The adaptive formulation presents significant increases in efficiency, flexibility, and general capabilities for high order spectral methods.

Effect of DEM mesh size on AnnAGNPS simulation and slope correction.

PubMed

Wang, Xiaoyan; Lin, Q

2011-08-01

The objective of this paper is to study the impact of the mesh size of the digital elevation model (DEM) on terrain attributes within an Annualized AGricultural NonPoint Source pollution (AnnAGNPS) Model simulation at watershed scale and provide a correction of slope gradient for low resolution DEMs. The effect of different grid sizes of DEMs on terrain attributes was examined by comparing eight DEMs (30, 40, 50, 60, 70, 80, 90, and 100 m). The accuracy of the AnnAGNPS stimulation on runoff, sediments, and nutrient loads is evaluated. The results are as follows: (1) Rnoff does not vary much with decrease of DEM resolution whereas soil erosion and total nitrogen (TN) load change prominently. There is little effect on runoff simulation of AnnAGNPS modeling by the amended slope using an adjusted 50 m DEM. (2) A decrease of sediment yield and TN load is observed with an increase of DEM mesh size from 30 to 60 m; a slight decrease of sediment and TN load with the DEM mesh size bigger than 60 m. There is similar trend for total phosphorus (TP) variation, but with less range of variation, the simulation of sediment, TN, and TP increase, in which sediment increase up to 1.75 times compared to the model using unadjusted 50 m DEM. In all, the amended simulation still has a large difference relative to the results using 30 m DEM. AnnAGNPS is less reliable for sediment loading prediction in a small hilly watershed. (3) Resolution of DEM has significant impact on slope gradient. The average, minimum, maximum of slope from the various DEMs reduced obviously with the decrease of DEM precision. For the grade of 0∼15°, the slopes at lower resolution DEM are generally bigger than those at higher resolution DEM. But for the grade bigger than 15°, the slopes at lower resolution DEM are generally smaller than those at higher resolution DEM. So it is necessary to adjust the slope with a fitting equation. A cubic model is used for correction of slope gradient from lower resolution to that from higher resolution. Results for Dage watershed showed that fine meshes are desired to avoid large underestimates of sediment and total nitrogen loads and moderate underestimates of total phosphorus loads even with the slopes for the 50 m DEM adjusted to be more similar to the slopes from the 30 m DEM. Decreasing the mesh size beyond this threshold does not substantially affect the computed runoff flux but generated prediction errors for nitrogen and sediment yields. So the appropriate DEM will control error and make simulation at acceptable level.

A modular approach to large-scale design optimization of aerospace systems

NASA Astrophysics Data System (ADS)

Hwang, John T.

Gradient-based optimization and the adjoint method form a synergistic combination that enables the efficient solution of large-scale optimization problems. Though the gradient-based approach struggles with non-smooth or multi-modal problems, the capability to efficiently optimize up to tens of thousands of design variables provides a valuable design tool for exploring complex tradeoffs and finding unintuitive designs. However, the widespread adoption of gradient-based optimization is limited by the implementation challenges for computing derivatives efficiently and accurately, particularly in multidisciplinary and shape design problems. This thesis addresses these difficulties in two ways. First, to deal with the heterogeneity and integration challenges of multidisciplinary problems, this thesis presents a computational modeling framework that solves multidisciplinary systems and computes their derivatives in a semi-automated fashion. This framework is built upon a new mathematical formulation developed in this thesis that expresses any computational model as a system of algebraic equations and unifies all methods for computing derivatives using a single equation. The framework is applied to two engineering problems: the optimization of a nanosatellite with 7 disciplines and over 25,000 design variables; and simultaneous allocation and mission optimization for commercial aircraft involving 330 design variables, 12 of which are integer variables handled using the branch-and-bound method. In both cases, the framework makes large-scale optimization possible by reducing the implementation effort and code complexity. The second half of this thesis presents a differentiable parametrization of aircraft geometries and structures for high-fidelity shape optimization. Existing geometry parametrizations are not differentiable, or they are limited in the types of shape changes they allow. This is addressed by a novel parametrization that smoothly interpolates aircraft components, providing differentiability. An unstructured quadrilateral mesh generation algorithm is also developed to automate the creation of detailed meshes for aircraft structures, and a mesh convergence study is performed to verify that the quality of the mesh is maintained as it is refined. As a demonstration, high-fidelity aerostructural analysis is performed for two unconventional configurations with detailed structures included, and aerodynamic shape optimization is applied to the truss-braced wing, which finds and eliminates a shock in the region bounded by the struts and the wing.

On configurational forces for gradient-enhanced inelasticity

NASA Astrophysics Data System (ADS)

Floros, Dimosthenis; Larsson, Fredrik; Runesson, Kenneth

2018-04-01

In this paper we discuss how configurational forces can be computed in an efficient and robust manner when a constitutive continuum model of gradient-enhanced viscoplasticity is adopted, whereby a suitably tailored mixed variational formulation in terms of displacements and micro-stresses is used. It is demonstrated that such a formulation produces sufficient regularity to overcome numerical difficulties that are notorious for a local constitutive model. In particular, no nodal smoothing of the internal variable fields is required. Moreover, the pathological mesh sensitivity that has been reported in the literature for a standard local model is no longer present. Numerical results in terms of configurational forces are shown for (1) a smooth interface and (2) a discrete edge crack. The corresponding configurational forces are computed for different values of the intrinsic length parameter. It is concluded that the convergence of the computed configurational forces with mesh refinement depends strongly on this parameter value. Moreover, the convergence behavior for the limit situation of rate-independent plasticity is unaffected by the relaxation time parameter.

The Simulation of Precipitation Evolutions and Mechanical Properties in Friction Stir Welding with Post-Weld Heat Treatments

NASA Astrophysics Data System (ADS)

Zhang, Z.; Wan, Z. Y.; Lindgren, L.-E.; Tan, Z. J.; Zhou, X.

2017-12-01

A finite element model of friction stir welding capable of re-meshing is used to simulate the temperature variations. Re-meshing of the finite element model is used to maintain a fine mesh resolving the gradients of the solution. The Kampmann-Wagner numerical model for precipitation is then used to study the relation between friction stir welds with post-weld heat treatment (PWHT) and the changes in mechanical properties. Results indicate that the PWHT holding time and PWHT holding temperature need to be optimally designed to obtain FSW with better mechanical properties. Higher precipitate number with lower precipitate sizes gives higher strength in the stirring zone after PWHT. The coarsening of precipitates in HAZ are the main reason to hinder the improvement of mechanical property when PWHT is used.

Design and fabrication of segmented-in-series solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Lai, Tammy S.

Segmented-in-series solid oxide fuel cells (SS-SOFC) consist of several thick film cells deposited onto a porous, flattened tubular substrate. SS-SOFCs have a reduced need for gas-tight seals relative to planar SOFCs and can have a short current path compared to tubular SOFCs, limiting electrode ohmic resistance. Like tubular SOFCs, SS-SOFCs are suitable for stationary power generation. Their potentially small cell size makes them candidates for portable applications as well. The goals of this thesis project were to develop SS-SOFCs with 1-2 mm cell lengths and to analyze the effects of cell geometry and support current shunting on performance. Standard SOFC materials were chosen for the active components: yttria stabilized zirconia (YSZ) electrolyte; Ni-YSZ cermet anode; and (La,Sr)MnO 3-based cathode. A Pt-YSZ cermet was used as the interconnect material. Screen printing was the deposition method for all layers due to its low cost and patterning ability. A power density of >900 mW/cm2 was achieved with a cathode sheet resistance of ≈3 O/□ (≈90 mum LSM thickness). A D-optimal study was conducted to find processing conditions yielding substrates with ≥30 vol% porosity and high strength. Uniaxially pressed partially stabilized zirconia (PSZ) with 15 wt% starch pore former met the requirements, though 20 wt% graphite pore former was later found to give a smoother surface that improved screen printed layer quality. Calculations presented in this thesis take into account losses due to cell resistances, electrode ohmic resistances, interconnect resistance, and shunting by a weakly-conductive support material. Power density was maximized at an optimal cell length---it decreased at larger cell lengths due to electrode lateral resistance loss and at smaller cell lengths due to a decreasing fraction of cell active area. Assuming dimensions expected for screen printing and typical area specific resistances (RAS), optimal cell lengths typically ranged from 1 to 3 mm. The calculated and experimental values for the array RAS (active and inactive areas) showed similar dependences on cathode sheet resistance. The impact of shunting current increased with decreasing cell lengths. Shunting current was predicted to decrease array current by ˜10% for a 1.5 mm active cell length, though experimental measurements suggest that the calculation may overestimate the shunting effect.

Advanced materials and design for low temperature SOFCs

DOEpatents

Wachsman, Eric D.; Yoon, Heesung; Lee, Kang Taek; Camaratta, Matthew; Ahn, Jin Soo

2016-05-17

Embodiments of the invention are directed to SOFC with a multilayer structure comprising a porous ceramic cathode, optionally a cathodic triple phase boundary layer, a bilayer electrolyte comprising a cerium oxide comprising layer and a bismuth oxide comprising layer, an anion functional layer, and a porous ceramic anode with electrical interconnects, wherein the SOFC displays a very high power density at temperatures below 700.degree. C. with hydrogen or hydrocarbon fuels. The low temperature conversion of chemical energy to electrical energy allows the fabrication of the fuel cells using stainless steel or other metal alloys rather than ceramic conductive oxides as the interconnects.

The main directions in technology investigation of soid oxide fuel cell in Russian Federal Research Center Institute of Physics & Power Engineering (IPPE)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ievleva, J.I.; Kolesnikov, V.P.; Mezhertisky, G.S.

1996-04-01

The main direction of science investigations for creation of efficient solid oxide fuel cells (SOFC) in IPPE are considered in this work. The development program of planar SOFC with thin-film electrolyte is shown. General design schemes of experimental SOFC units are presented. The flow design schemes of processes for initial materials and electrodes fabrication are shown. The results of investigations for creation thin-film solid oxide electrolyte at porous cathode by magnetron sputtering from complex metal target in oxidative environment are presented.

Engine-integrated solid oxide fuel cells for efficient electrical power generation on aircraft

NASA Astrophysics Data System (ADS)

Waters, Daniel F.; Cadou, Christopher P.

2015-06-01

This work investigates the use of engine-integrated catalytic partial oxidation (CPOx) reactors and solid oxide fuel cells (SOFCs) to reduce fuel burn in vehicles with large electrical loads like sensor-laden unmanned air vehicles. Thermodynamic models of SOFCs, CPOx reactors, and three gas turbine (GT) engine types (turbojet, combined exhaust turbofan, separate exhaust turbofan) are developed and checked against relevant data and source material. Fuel efficiency is increased by 4% and 8% in the 50 kW and 90 kW separate exhaust turbofan systems respectively at only modest cost in specific power (8% and 13% reductions respectively). Similar results are achieved in other engine types. An additional benefit of hybridization is the ability to provide more electric power (factors of 3 or more in some cases) than generator-based systems before encountering turbine inlet temperature limits. A sensitivity analysis shows that the most important parameters affecting the system's performance are operating voltage, percent fuel oxidation, and SOFC assembly air flows. Taken together, this study shows that it is possible to create a GT-SOFC hybrid where the GT mitigates balance of plant losses and the SOFC raises overall system efficiency. The result is a synergistic system with better overall performance than stand-alone components.

Extended Durability Testing of an External Fuel Processor for a Solid Oxide Fuel Cell (SOFC)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mark Perna; Anant Upadhyayula; Mark Scotto

2012-11-05

Durability testing was performed on an external fuel processor (EFP) for a solid oxide fuel cell (SOFC) power plant. The EFP enables the SOFC to reach high system efficiency (electrical efficiency up to 60%) using pipeline natural gas and eliminates the need for large quantities of bottled gases. LG Fuel Cell Systems Inc. (formerly known as Rolls-Royce Fuel Cell Systems (US) Inc.) (LGFCS) is developing natural gas-fired SOFC power plants for stationary power applications. These power plants will greatly benefit the public by reducing the cost of electricity while reducing the amount of gaseous emissions of carbon dioxide, sulfur oxides,more » and nitrogen oxides compared to conventional power plants. The EFP uses pipeline natural gas and air to provide all the gas streams required by the SOFC power plant; specifically those needed for start-up, normal operation, and shutdown. It includes a natural gas desulfurizer, a synthesis-gas generator and a start-gas generator. The research in this project demonstrated that the EFP could meet its performance and durability targets. The data generated helped assess the impact of long-term operation on system performance and system hardware. The research also showed the negative impact of ambient weather (both hot and cold conditions) on system operation and performance.« less

Online gas composition estimation in solid oxide fuel cell systems with anode off-gas recycle configuration

NASA Astrophysics Data System (ADS)

Dolenc, B.; Vrečko, D.; Juričić, Ð.; Pohjoranta, A.; Pianese, C.

2017-03-01

Degradation and poisoning of solid oxide fuel cell (SOFC) stacks are continuously shortening the lifespan of SOFC systems. Poisoning mechanisms, such as carbon deposition, form a coating layer, hence rapidly decreasing the efficiency of the fuel cells. Gas composition of inlet gases is known to have great impact on the rate of coke formation. Therefore, monitoring of these variables can be of great benefit for overall management of SOFCs. Although measuring the gas composition of the gas stream is feasible, it is too costly for commercial applications. This paper proposes three distinct approaches for the design of gas composition estimators of an SOFC system in anode off-gas recycle configuration which are (i.) accurate, and (ii.) easy to implement on a programmable logic controller. Firstly, a classical approach is briefly revisited and problems related to implementation complexity are discussed. Secondly, the model is simplified and adapted for easy implementation. Further, an alternative data-driven approach for gas composition estimation is developed. Finally, a hybrid estimator employing experimental data and 1st-principles is proposed. Despite the structural simplicity of the estimators, the experimental validation shows a high precision for all of the approaches. Experimental validation is performed on a 10 kW SOFC system.

A simplified approach to predict performance degradation of a solid oxide fuel cell anode

NASA Astrophysics Data System (ADS)

Khan, Muhammad Zubair; Mehran, Muhammad Taqi; Song, Rak-Hyun; Lee, Jong-Won; Lee, Seung-Bok; Lim, Tak-Hyoung

2018-07-01

The agglomeration of nickel (Ni) particles in a Ni-cermet anode is a significant degradation phenomenon for solid oxide fuel cells (SOFCs). This work aims to predict the performance degradation of SOFCs due to Ni grain growth by using a simplified approach. Accelerated aging of Ni-scandia stabilized zirconia (SSZ) as an SOFC anode is carried out at 900 °C and subsequent microstructural evolution is investigated every 100 h up to 1000 h using scanning electron microscopy (SEM). The resulting morphological changes are quantified using a two-dimensional image analysis technique that yields the particle size, phase proportion, and triple phase boundary (TPB) point distribution. The electrochemical properties of an anode-supported SOFC are characterized using electrochemical impedance spectroscopy (EIS). The changes of particle size and TPB length in the anode as a function of time are in excellent agreement with the power-law coarsening model. This model is further combined with an electrochemical model to predict the changes in the anode polarization resistance. The predicted polarization resistances are in good agreement with the experimentally obtained values. This model for prediction of anode lifetime provides deep insight into the time-dependent Ni agglomeration behavior and its impact on the electrochemical performance degradation of the SOFC anode.

Electrochemical Approach for Analyzing Electrolyte Transport Properties and Their Effect on Protonic Ceramic Fuel Cell Performance.

PubMed

Danilov, Nikolay; Lyagaeva, Julia; Vdovin, Gennady; Medvedev, Dmitry; Demin, Anatoly; Tsiakaras, Panagiotis

2017-08-16

The design and development of highly conductive materials with wide electrolytic domain boundaries are among the most promising means of enabling solid oxide fuel cells (SOFCs) to demonstrate outstanding performance across low- and intermediate-temperature ranges. While reducing the thickness of the electrolyte is an extensively studied means for diminishing the total resistance of SOFCs, approaches involving an improvement in the transport behavior of the electrolyte membranes have been less-investigated. In the present work, a strategy for analyzing the electrolyte properties and their effect on SOFC output characteristics is proposed. To this purpose, a SOFC based on a recently developed BaCe 0.5 Zr 0.3 Dy 0.2 O 3-δ proton-conducting ceramic material was fabricated and tested. The basis of the strategy consists of the use of traditional SOFC testing techniques combined with the current interruption method and electromotive force measurements with a modified polarization-correction assessment. This allows one to determine simultaneously such important parameters as maximal power density; ohmic and polarization resistances; average ion transport numbers; and total, ionic, and electronic film conductivities and their activation energies. The proposed experimental procedure is expected to expand both fundamental and applied basics that could be further adopted to improve the technology of electrochemical devices based on proton-conducting electrolytes.

Thermodynamic analysis of a combined gas turbine power plant with a solid oxide fuel cell for marine applications

NASA Astrophysics Data System (ADS)

Welaya, Yousri M. A.; Mosleh, M.; Ammar, Nader R.

2013-12-01

Strong restrictions on emissions from marine power plants (particularly SOx, NOx) will probably be adopted in the near future. In this paper, a combined solid oxide fuel cell (SOFC) and gas turbine fuelled by natural gas is proposed as an attractive option to limit the environmental impact of the marine sector. It includes a study of a heatrecovery system for 18 MW SOFC fuelled by natural gas, to provide the electric power demand onboard commercial vessels. Feasible heat-recovery systems are investigated, taking into account different operating conditions of the combined system. Two types of SOFC are considered, tubular and planar SOFCs, operated with either natural gas or hydrogen fuels. This paper includes a detailed thermodynamic analysis for the combined system. Mass and energy balances are performed, not only for the whole plant but also for each individual component, in order to evaluate the thermal efficiency of the combined cycle. In addition, the effect of using natural gas as a fuel on the fuel cell voltage and performance is investigated. It is found that a high overall efficiency approaching 70% may be achieved with an optimum configuration using SOFC system under pressure. The hybrid system would also reduce emissions, fuel consumption, and improve the total system efficiency.

Large size biogas-fed Solid Oxide Fuel Cell power plants with carbon dioxide management: Technical and economic optimization

NASA Astrophysics Data System (ADS)

Curletti, F.; Gandiglio, M.; Lanzini, A.; Santarelli, M.; Maréchal, F.

2015-10-01

This article investigates the techno-economic performance of large integrated biogas Solid Oxide Fuel Cell (SOFC) power plants. Both atmospheric and pressurized operation is analysed with CO2 vented or captured. The SOFC module produces a constant electrical power of 1 MWe. Sensitivity analysis and multi-objective optimization are the mathematical tools used to investigate the effects of Fuel Utilization (FU), SOFC operating temperature and pressure on the plant energy and economic performances. FU is the design variable that most affects the plant performance. Pressurized SOFC with hybridization with a gas turbine provides a notable boost in electrical efficiency. For most of the proposed plant configurations, the electrical efficiency ranges in the interval 50-62% (LHV biogas) when a trade-off of between energy and economic performances is applied based on Pareto charts obtained from multi-objective plant optimization. The hybrid SOFC is potentially able to reach an efficiency above 70% when FU is 90%. Carbon capture entails a penalty of more 10 percentage points in pressurized configurations mainly due to the extra energy burdens of captured CO2 pressurization and oxygen production and for the separate and different handling of the anode and cathode exhausts and power recovery from them.

Micro-tubular solid oxide fuel cell based on a porous yttria-stabilized zirconia support

NASA Astrophysics Data System (ADS)

Panthi, Dhruba; Tsutsumi, Atsushi

2014-08-01

Solid oxide fuel cells (SOFCs) are promising electrochemical energy conversion devices owing to their high power generation efficiency and environmentally benign operation. Micro-tubular SOFCs, which have diameters ranging from a few millimeters to the sub-millimeter scale, offer several advantages over competing SOFCs such as high volumetric power density, good endurance against thermal cycling, and flexible sealing between fuel and oxidant streams. Herein, we successfully realized a novel micro-tubular SOFC design based on a porous yttria-stabilized zirconia (YSZ) support using multi-step dip coating and co-sintering methods. The micro-tubular SOFC consisted of Ni-YSZ, YSZ, and strontium-doped lanthanum manganite (LSM)-YSZ as the anode, electrolyte, and cathode, respectively. In addition, to facilitate current collection from the anode and cathode, Ni and LSM were applied as an anode current collector and cathode current collector, respectively. Micro-crystalline cellulose was selected as a pore former to achieve better shrinkage behavior of the YSZ support so that the electrolyte layer could be densified at a co-sintering temperature of 1300°C. The developed micro-tubular design showed a promising electrochemical performance with maximum power densities of 525, 442, and 354 mW cm-2 at 850, 800, and 750°C, respectively.

Investigation of low temperature solid oxide fuel cells for air-independent UUV applications

NASA Astrophysics Data System (ADS)

Moton, Jennie Mariko

Unmanned underwater vehicles (UUVs) will benefit greatly from high energy density (> 500 Wh/L) power systems utilizing high-energy-density fuels and air-independent oxidizers. Current battery-based systems have limited energy densities (< 400 Wh/L), which motivate development of alternative power systems such as solid oxide fuel cells (SOFCs). SOFC-based power systems have the potential to achieve the required UUV energy densities, and the current study explores how SOFCs based on gadolinia-doped ceria (GDC) electrolytes with operating temperatures of 650°C and lower may operate in the unique environments of a promising UUV power plant. The plant would contain a H 2O2 decomposition reactor to supply humidified O2 to the SOFC cathode and exothermic aluminum/H2O combustor to provide heated humidified H2 fuel to the anode. To characterize low-temperature SOFC performance with these unique O2 and H2 source, SOFC button cells based on nickel/GDC (Gd0.1Ce0.9O 1.95) anodes, GDC electrolytes, and lanthanum strontium cobalt ferrite (La0.6Sr0.4Co0.2Fe0.8O3-δ or LSCF)/GDC cathodes were fabricated and tested for performance and stability with humidity on both the anode and the cathode. Cells were also tested with various reactant concentrations of H2 and O2 to simulate gas depletion down the channel of an SOFC stack. Results showed that anode performance depended primarily on fuel concentration and less on the concentration of the associated increase in product H2O. O 2 depletion with humidified cathode flows also caused significant loss in cell current density at a given voltage. With the humidified flows in either the anode or cathode, stability tests of the button cells at 650 °C showed stable voltage is maintained at low operating current (0.17 A/cm2) at up to 50 % by mole H2O, but at higher current densities (0.34 A/cm2), irreversible voltage degradation occurred at rates of 0.8-3.7 mV/hour depending on exposure time. From these button cell results, estimated average current densities over the length of a low-temperature SOFC stack were estimated and used to size a UUV power system based on Al/H 2O oxidation for fuel and H2O2 decomposition for O2. The resulting system design suggested that energy densities above 300 Wh/L may be achieved at neutral buoyancy with seawater if the cell is operated at high reactant utilizations in the SOFC stack for missions longer than 20 hours.

Bessel smoothing filter for spectral-element mesh

NASA Astrophysics Data System (ADS)

Trinh, P. T.; Brossier, R.; Métivier, L.; Virieux, J.; Wellington, P.

2017-06-01

Smoothing filters are extremely important tools in seismic imaging and inversion, such as for traveltime tomography, migration and waveform inversion. For efficiency, and as they can be used a number of times during inversion, it is important that these filters can easily incorporate prior information on the geological structure of the investigated medium, through variable coherent lengths and orientation. In this study, we promote the use of the Bessel filter to achieve these purposes. Instead of considering the direct application of the filter, we demonstrate that we can rely on the equation associated with its inverse filter, which amounts to the solution of an elliptic partial differential equation. This enhances the efficiency of the filter application, and also its flexibility. We apply this strategy within a spectral-element-based elastic full waveform inversion framework. Taking advantage of this formulation, we apply the Bessel filter by solving the associated partial differential equation directly on the spectral-element mesh through the standard weak formulation. This avoids cumbersome projection operators between the spectral-element mesh and a regular Cartesian grid, or expensive explicit windowed convolution on the finite-element mesh, which is often used for applying smoothing operators. The associated linear system is solved efficiently through a parallel conjugate gradient algorithm, in which the matrix vector product is factorized and highly optimized with vectorized computation. Significant scaling behaviour is obtained when comparing this strategy with the explicit convolution method. The theoretical numerical complexity of this approach increases linearly with the coherent length, whereas a sublinear relationship is observed practically. Numerical illustrations are provided here for schematic examples, and for a more realistic elastic full waveform inversion gradient smoothing on the SEAM II benchmark model. These examples illustrate well the efficiency and flexibility of the approach proposed.

Reflectance analysis of porosity gradient in nanostructured silicon layers

NASA Astrophysics Data System (ADS)

Jurečka, Stanislav; Imamura, Kentaro; Matsumoto, Taketoshi; Kobayashi, Hikaru

2017-12-01

In this work we study optical properties of nanostructured layers formed on silicon surface. Nanostructured layers on Si are formed in order to reach high suppression of the light reflectance. Low spectral reflectance is important for improvement of the conversion efficiency of solar cells and for other optoelectronic applications. Effective method of forming nanostructured layers with ultralow reflectance in a broad interval of wavelengths is in our approach based on metal assisted etching of Si. Si surface immersed in HF and H2O2 solution is etched in contact with the Pt mesh roller and the structure of the mesh is transferred on the etched surface. During this etching procedure the layer density evolves gradually and the spectral reflectance decreases exponentially with the depth in porous layer. We analyzed properties of the layer porosity by incorporating the porosity gradient into construction of the layer spectral reflectance theoretical model. Analyzed layer is splitted into 20 sublayers in our approach. Complex dielectric function in each sublayer is computed by using Bruggeman effective media theory and the theoretical spectral reflectance of modelled multilayer system is computed by using Abeles matrix formalism. Porosity gradient is extracted from the theoretical reflectance model optimized in comparison to the experimental values. Resulting values of the structure porosity development provide important information for optimization of the technological treatment operations.

A triangular prism solid and shell interactive mapping element for electromagnetic sheet metal forming process

NASA Astrophysics Data System (ADS)

Cui, Xiangyang; Li, She; Feng, Hui; Li, Guangyao

2017-05-01

In this paper, a novel triangular prism solid and shell interactive mapping element is proposed to solve the coupled magnetic-mechanical formulation in electromagnetic sheet metal forming process. A linear six-node "Triprism" element is firstly proposed for transient eddy current analysis in electromagnetic field. In present "Triprism" element, shape functions are given explicitly, and a cell-wise gradient smoothing operation is used to obtain the gradient matrices without evaluating derivatives of shape functions. In mechanical field analysis, a shear locking free triangular shell element is employed in internal force computation, and a data mapping method is developed to transfer the Lorentz force on solid into the external forces suffered by shell structure for dynamic elasto-plasticity deformation analysis. Based on the deformed triangular shell structure, a "Triprism" element generation rule is established for updated electromagnetic analysis, which means inter-transformation of meshes between the coupled fields can be performed automatically. In addition, the dynamic moving mesh is adopted for air mesh updating based on the deformation of sheet metal. A benchmark problem is carried out for confirming the accuracy of the proposed "Triprism" element in predicting flux density in electromagnetic field. Solutions of several EMF problems obtained by present work are compared with experiment results and those of traditional method, which are showing excellent performances of present interactive mapping element.

Cause and Cure - Deterioration in Accuracy of CFD Simulations with Use of High-Aspect-Ratio Triangular/Tetrahedral Grids

NASA Technical Reports Server (NTRS)

Chang, Sin-Chung; Chang, Chau-Lyan; Venkatachari, Balaji Shankar

2017-01-01

Traditionally high-aspect ratio triangular/tetrahedral meshes are avoided by CFD researchers in the vicinity of a solid wall, as it is known to reduce the accuracy of gradient computations in those regions. Although for certain complex geometries, the use of high-aspect ratio triangular/tetrahedral elements in the vicinity of a solid wall can be replaced by quadrilateral/prismatic elements, ability to use triangular/tetrahedral elements in such regions without any degradation in accuracy can be beneficial from a mesh generation point of view. The benefits also carry over to numerical frameworks such as the space-time conservation element and solution element (CESE), where simplex elements are the mandatory building blocks. With the requirement of the CESE method in mind, a rigorous mathematical framework that clearly identifies the reason behind the difficulties in use of such high-aspect ratio simplex elements is formulated using two different approaches and presented here. Drawing insights from the analysis, a potential solution to avoid that pitfall is also provided as part of this work. Furthermore, through the use of numerical simulations of practical viscous problems involving high-Reynolds number flows, how the gradient evaluation procedures of the CESE framework can be effectively used to produce accurate and stable results on such high-aspect ratio simplex meshes is also showcased.

Program of scientific investigations and development of solid-oxide fuel cells (SOFC) in VIITF proposals on scientific and technical collaboration and SOFC commercialization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kleschev, Yu.N.; Chulharev, V.F.

1996-04-01

Investigations being performed at VNIITF covers the whole cycle of solid oxide fuel cell manufacturing. This report describes the main directions of investigations in materials, technologies, and commercialization.

Universal ventricular coordinates: A generic framework for describing position within the heart and transferring data.

PubMed

Bayer, Jason; Prassl, Anton J; Pashaei, Ali; Gomez, Juan F; Frontera, Antonio; Neic, Aurel; Plank, Gernot; Vigmond, Edward J

2018-04-01

Being able to map a particular set of cardiac ventricles to a generic topologically equivalent representation has many applications, including facilitating comparison of different hearts, as well as mapping quantities and structures of interest between them. In this paper we describe Universal Ventricular Coordinates (UVC), which can be used to describe position within any biventricular heart. UVC comprise four unique coordinates that we have chosen to be intuitive, well defined, and relevant for physiological descriptions. We describe how to determine these coordinates for any volumetric mesh by illustrating how to properly assign boundary conditions and utilize solutions to Laplace's equation. Using UVC, we transferred scalar, vector, and tensor data between four unstructured ventricular meshes from three different species. Performing the mappings was very fast, on the order of a few minutes, since mesh nodes were searched in a KD tree. Distance errors in mapping mesh nodes back and forth between meshes were less than the size of an element. Analytically derived fiber directions were also mapped across meshes and compared, showing  < 5° difference over most of the ventricles. The ability to transfer gradients was also demonstrated. Topologically variable structures, like papillary muscles, required further definition outside of the UVC framework. In conclusion, UVC can aid in transferring many types of data between different biventricular geometries. Copyright © 2018 The Author(s). Published by Elsevier B.V. All rights reserved.

Tailored Core Shell Cathode Powders for Solid Oxide Fuel Cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swartz, Scott

2015-03-23

In this Phase I SBIR project, a “core-shell” composite cathode approach was evaluated for improving SOFC performance and reducing degradation of lanthanum strontium cobalt ferrite (LSCF) cathode materials, following previous successful demonstrations of infiltration approaches for achieving the same goals. The intent was to establish core-shell cathode powders that enabled high performance to be obtained with “drop-in” process capability for SOFC manufacturing (i.e., rather than adding an infiltration step to the SOFC manufacturing process). Milling, precipitation and hetero-coagulation methods were evaluated for making core-shell composite cathode powders comprised of coarse LSCF “core” particles and nanoscale “shell” particles of lanthanum strontiummore » manganite (LSM) or praseodymium strontium manganite (PSM). Precipitation and hetero-coagulation methods were successful for obtaining the targeted core-shell morphology, although perfect coverage of the LSCF core particles by the LSM and PSM particles was not obtained. Electrochemical characterization of core-shell cathode powders and conventional (baseline) cathode powders was performed via electrochemical impedance spectroscopy (EIS) half-cell measurements and single-cell SOFC testing. Reliable EIS testing methods were established, which enabled comparative area-specific resistance measurements to be obtained. A single-cell SOFC testing approach also was established that enabled cathode resistance to be separated from overall cell resistance, and for cathode degradation to be separated from overall cell degradation. The results of these EIS and SOFC tests conclusively determined that the core-shell cathode powders resulted in significant lowering of performance, compared to the baseline cathodes. Based on the results of this project, it was concluded that the core-shell cathode approach did not warrant further investigation.« less

Multi-Phase Field Models and Microstructural Evolution with Applications in Fuel Cell Technology

NASA Astrophysics Data System (ADS)

Davis, Ryan Scott

The solid oxide fuel cell (SOFC) has shown tremendous potential as an efficient energy conversion device that may be instrumental in the transition to renewable resources. However, commercialization is hindered by many degradation mechanisms that plague long term stability. In this dissertation, computation methods are used to explore the relationship between the microstructure of the fuel cell anode and performance critical metrics. The phase field method and standard modeling procedures are introduced using a classic model of spinodal decomposition. This is further developed into a complete, multi-phase modeling framework designed for the complex microstructural evolution of SOFC anode systems. High-temperature coarsening of the metallic phase in the state-of-the-art SOFC cermet anode is investigated using our phase field model. A systematic study into the effects of interface properties on microstructural evolution is accomplished by altering the contact angle between constituent phases. It is found that metrics of catalytic activity and conductivity display undesirable minima near the contact angle of conventional SOFC materials. These results suggest that tailoring the interface properties of the constituent phases could lead to a significant increase in the performance and lifetime of SOFCs. Supported-metal catalyst systems are investigated in the first detailed study of their long-term stability and application to SOFC anode design. Porous support structures are numerically sintered to mimic specific fabrication techniques, and these structures are then infiltrated with a nanoscale catalyst phase ranging from 2% to 21% loading. Initially, these systems exhibit enhanced potential for catalytic activity relative to conventional cells. However, extended evolution results in severe degradation, and we show that Ostwald ripening and particle migration are key kinetic processes. Strong geometric heterogeneity in the support structure via a novel approach to nanopore formation is proposed as a potential solution for catalyst stabilization.

Use of wastewater treatment plant biogas for the operation of Solid Oxide Fuel Cells (SOFCs).

PubMed

Lackey, Jillian; Champagne, Pascale; Peppley, Brant

2017-12-01

Solid Oxide Fuel Cells (SOFCs) perform well on light hydrocarbon fuels, and the use of biogas derived from the anaerobic digestion (AD) of municipal wastewater sludges could provide an opportunity for the CH 4 produced to be used as a renewable fuel. Greenhouse gas (GHG), NO x , SO x , and hydrocarbon pollutant emissions would also be reduced. In this study, SOFCs were operated on AD derived biogas. Initially, different H 2 dilutions were tested (N 2 , Ar, CO 2 ) to examine the performance of tubular SOFCs. With inert gases as diluents, a decrease in cell performance was observed, however, the use of CO 2 led to a higher decrease in performance as it promoted the reverse water-gas shift (WGS) reaction, reducing the H 2 partial pressure in the gas mixture. A model was developed to predict system efficiency and GHG emissions. A higher electrical system efficiency was noted for a steam:carbon ratio of 2 compared to 1 due to the increased H 2 partial pressure in the reformate resulting from higher H 2 O concentration. Reductions in GHG emissions were estimated at 2400 tonnes CO 2 , 60 kg CH 4 and 18 kg N 2 O. SOFCs were also tested using a simulated biogas reformate mixture (66.7% H 2 , 16.1% CO, 16.5% CO 2 , 0.7% N 2 , humidified to 2.3 or 20 mol% H 2 O). Higher humidification yielded better performance as the WGS reaction produced more H 2 with additional H 2 O. It was concluded that AD-derived biogas, when cleaned to remove H 2 S, Si compounds, halides and other contaminants, could be reformed to provide a clean, renewable fuel for SOFCs. Copyright © 2016 Elsevier Ltd. All rights reserved.

Phase-field modelling of ductile fracture: a variational gradient-extended plasticity-damage theory and its micromorphic regularization.

PubMed

Miehe, C; Teichtmeister, S; Aldakheel, F

2016-04-28

This work outlines a novel variational-based theory for the phase-field modelling of ductile fracture in elastic-plastic solids undergoing large strains. The phase-field approach regularizes sharp crack surfaces within a pure continuum setting by a specific gradient damage modelling. It is linked to a formulation of gradient plasticity at finite strains. The framework includes two independent length scales which regularize both the plastic response as well as the crack discontinuities. This ensures that the damage zones of ductile fracture are inside of plastic zones, and guarantees on the computational side a mesh objectivity in post-critical ranges. © 2016 The Author(s).

Method for in situ carbon deposition measurement for solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Kuhn, J.; Kesler, O.

2014-01-01

Previous methods to measure carbon deposition in solid oxide fuel cell (SOFC) anodes do not permit simultaneous electrochemical measurements. Electrochemical measurements supplemented with carbon deposition quantities create the opportunity to further understand how carbon affects SOFC performance and electrochemical impedance spectra (EIS). In this work, a method for measuring carbon in situ, named here as the quantification of gasified carbon (QGC), was developed. TGA experiments showed that carbon with a 100 h residence time in the SOFC was >99.8% gasified. Comparison of carbon mass measurements between the TGA and QGC show good agreement. In situ measurements of carbon deposition in SOFCs at varying molar steam/carbon ratios were performed to further validate the QGC method, and suppression of carbon deposition with increasing steam concentration was observed, in agreement with previous studies. The technique can be used to investigate in situ carbon deposition and gasification behavior simultaneously with electrochemical measurements for a variety of fuels and operating conditions, such as determining conditions under which incipient carbon deposition is reversible.

Rational design of novel cathode materials in solid oxide fuel cells using first-principles simulations

NASA Astrophysics Data System (ADS)

Choi, YongMan; Lin, M. C.; Liu, Meilin

The search for clean and renewable sources of energy represents one of the most vital challenges facing us today. Solid oxide fuel cells (SOFCs) are among the most promising technologies for a clean and secure energy future due to their high energy efficiency and excellent fuel flexibility (e.g., direct utilization of hydrocarbons or renewable fuels). To make SOFCs economically competitive, however, development of new materials for low-temperature operation is essential. Here we report our results on a computational study to achieve rational design of SOFC cathodes with fast oxygen reduction kinetics and rapid ionic transport. Results suggest that surface catalytic properties are strongly correlated with the bulk transport properties in several material systems with the formula of La 0.5Sr 0.5BO 2.75 (where B = Cr, Mn, Fe, or Co). The predictions seem to agree qualitatively with available experimental results on these materials. This computational screening technique may guide us to search for high-efficiency cathode materials for a new generation of SOFCs.

Barium oxide, calcium oxide, magnesia, and alkali oxide free glass

DOEpatents

Lu, Peizhen Kathy; Mahapatra, Manoj Kumar

2013-09-24

A glass composition consisting essentially of about 10-45 mole percent of SrO; about 35-75 mole percent SiO.sub.2; one or more compounds from the group of compounds consisting of La.sub.2O.sub.3, Al.sub.2O.sub.3, B.sub.2O.sub.3, and Ni; the La.sub.2O.sub.3 less than about 20 mole percent; the Al.sub.2O.sub.3 less than about 25 mole percent; the B.sub.2O.sub.3 less than about 15 mole percent; and the Ni less than about 5 mole percent. Preferably, the glass is substantially free of barium oxide, calcium oxide, magnesia, and alkali oxide. Preferably, the glass is used as a seal in a solid oxide fuel/electrolyzer cell (SOFC) stack. The SOFC stack comprises a plurality of SOFCs connected by one or more interconnect and manifold materials and sealed by the glass. Preferably, each SOFC comprises an anode, a cathode, and a solid electrolyte.

Failure of Anisotropic Unstructured Mesh Adaption Based on Multidimensional Residual Minimization

NASA Technical Reports Server (NTRS)

Wood, William A.; Kleb, William L.

2003-01-01

An automated anisotropic unstructured mesh adaptation strategy is proposed, implemented, and assessed for the discretization of viscous flows. The adaption criteria is based upon the minimization of the residual fluctuations of a multidimensional upwind viscous flow solver. For scalar advection, this adaption strategy has been shown to use fewer grid points than gradient based adaption, naturally aligning mesh edges with discontinuities and characteristic lines. The adaption utilizes a compact stencil and is local in scope, with four fundamental operations: point insertion, point deletion, edge swapping, and nodal displacement. Evaluation of the solution-adaptive strategy is performed for a two-dimensional blunt body laminar wind tunnel case at Mach 10. The results demonstrate that the strategy suffers from a lack of robustness, particularly with regard to alignment of the bow shock in the vicinity of the stagnation streamline. In general, constraining the adaption to such a degree as to maintain robustness results in negligible improvement to the solution. Because the present method fails to consistently or significantly improve the flow solution, it is rejected in favor of simple uniform mesh refinement.

Ab initio study of perovskite type oxide materials for solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Lee, Yueh-Lin

2011-12-01

Perovskite type oxides form a family of materials of significant interest for cathodes and electrolytes of solid oxide fuel cells (SOFCs). These perovskites not only are active catalysts for surface oxygen reduction (OR) reactions but also allow incorporating the spilt oxygen monomers into their bulk, an unusual and poorly understood catalytic mechanism that couples surface and bulk properties. The OR mechanisms can be influenced strongly by defects in perovskite oxides, composition, and surface defect structures. This thesis work initiates a first step in developing a general strategy based on first-principles calculations for detailed control of oxygen vacancy content, transport rates of surface and bulk oxygen species, and surface/interfacial reaction kinetics. Ab initio density functional theory methods are used to model properties relevant for the OR reactions on SOFC cathodes. Three main research thrusts, which focus on bulk defect chemistry, surface defect structures and surface energetics, and surface catalytic properties, are carried to investigate different level of material chemistry for improved understanding of key physics/factors that govern SOFC cathode OR activity. In the study of bulk defect chemistry, an ab initio based defect model is developed for modeling defect chemistry of LaMnO 3 under SOFC conditions. The model suggests an important role for defect interactions, which are typically excluded in previous defect models. In the study of surface defect structures and surface energetics, it is shown that defect energies change dramatically (1˜2 eV lower) from bulk values near surfaces. Based on the existing bulk defect model with the calculated ab initio surface defect energetics, we predict the (001) MnO 2 surface oxygen vacancy concentration of (La0.9Sr0.1 )MnO3 is about 5˜6 order magnitude higher than that of the bulk under typical SOFC conditions. Finally, for surface catalytic properties, we show that area specific resistance, oxygen exchange rates, and key OR energetics of the SOFC cathode perovskites, can be described by a single descriptor, either the bulk O p-band or the bulk oxygen vacancy formation energy. These simple descriptors will further enable first-principles optimization/design of new SOFC cathodes.

A novel approach in formulation of special transition elements: Mesh interface elements

NASA Technical Reports Server (NTRS)

Sarigul, Nesrin

1991-01-01

The objective of this research program is in the development of more accurate and efficient methods for solution of singular problems encountered in various branches of mechanics. The research program can be categorized under three levels. The first two levels involve the formulation of a new class of elements called 'mesh interface elements' (MIE) to connect meshes of traditional elements either in three dimensions or in three and two dimensions. The finite element formulations are based on boolean sum and blending operators. MEI are being formulated and tested in this research to account for the steep gradients encountered in aircraft and space structure applications. At present, the heat transfer and structural analysis problems are being formulated from uncoupled theory point of view. The status report: (1) summarizes formulation for heat transfer and structural analysis; (2) explains formulation of MEI; (3) examines computational efficiency; and (4) shows verification examples.

Spatial adaptation procedures on tetrahedral meshes for unsteady aerodynamic flow calculations

NASA Technical Reports Server (NTRS)

Rausch, Russ D.; Batina, John T.; Yang, Henry T. Y.

1993-01-01

Spatial adaptation procedures for the accurate and efficient solution of steady and unsteady inviscid flow problems are described. The adaptation procedures were developed and implemented within a three-dimensional, unstructured-grid, upwind-type Euler code. These procedures involve mesh enrichment and mesh coarsening to either add points in high gradient regions of the flow or remove points where they are not needed, respectively, to produce solutions of high spatial accuracy at minimal computational cost. A detailed description of the enrichment and coarsening procedures are presented and comparisons with experimental data for an ONERA M6 wing and an exact solution for a shock-tube problem are presented to provide an assessment of the accuracy and efficiency of the capability. Steady and unsteady results, obtained using spatial adaptation procedures, are shown to be of high spatial accuracy, primarily in that discontinuities such as shock waves are captured very sharply.

Spatial adaptation procedures on tetrahedral meshes for unsteady aerodynamic flow calculations

NASA Technical Reports Server (NTRS)

Rausch, Russ D.; Batina, John T.; Yang, Henry T. Y.

1993-01-01

Spatial adaptation procedures for the accurate and efficient solution of steady and unsteady inviscid flow problems are described. The adaptation procedures were developed and implemented within a three-dimensional, unstructured-grid, upwind-type Euler code. These procedures involve mesh enrichment and mesh coarsening to either add points in high gradient regions of the flow or remove points where they are not needed, respectively, to produce solutions of high spatial accuracy at minimal computational cost. The paper gives a detailed description of the enrichment and coarsening procedures and presents comparisons with experimental data for an ONERA M6 wing and an exact solution for a shock-tube problem to provide an assessment of the accuracy and efficiency of the capability. Steady and unsteady results, obtained using spatial adaptation procedures, are shown to be of high spatial accuracy, primarily in that discontinuities such as shock waves are captured very sharply.

A finite element conjugate gradient FFT method for scattering

NASA Technical Reports Server (NTRS)

Collins, Jeffery D.; Ross, Dan; Jin, J.-M.; Chatterjee, A.; Volakis, John L.

1991-01-01

Validated results are presented for the new 3D body of revolution finite element boundary integral code. A Fourier series expansion of the vector electric and mangnetic fields is employed to reduce the dimensionality of the system, and the exact boundary condition is employed to terminate the finite element mesh. The mesh termination boundary is chosen such that is leads to convolutional boundary operatores of low O(n) memory demand. Improvements of this code are discussed along with the proposed formulation for a full 3D implementation of the finite element boundary integral method in conjunction with a conjugate gradiant fast Fourier transformation (CGFFT) solution.

Functionally Graded Bismuth Oxide/Zirconia Bilayer Electrolytes for High-Performance Intermediate-Temperature Solid Oxide Fuel Cells (IT-SOFCs).

PubMed

Joh, Dong Woo; Park, Jeong Hwa; Kim, Doyeub; Wachsman, Eric D; Lee, Kang Taek

2017-03-15

A functionally graded Bi 1.6 Er 0.4 O 3 (ESB)/Y 0.16 Zr 0.84 O 1.92 (YSZ) bilayer electrolyte is successfully developed via a cost-effective screen printing process using nanoscale ESB powders on the tape-cast NiO-YSZ anode support. Because of the highly enhanced oxygen incorporation process at the cathode/electrolyte interface, a novel bilayer solid oxide fuel cell (SOFC) yields extremely high power density of ∼2.1 W cm -2 at 700 °C, which is a 2.4 times increase compared to that of the YSZ single electrolyte SOFC.

XPS studies of Mg doped GDC (Ce0.8Gd0.2O2-δ) for IT-SOFC

NASA Astrophysics Data System (ADS)

Tyagi, Deepak; Rao, P. Koteswara; Wani, B. N.

2018-04-01

Fuel Cells have gained much attention as efficient and environment friendly device for both stationary as well as mobile applications. For intermediate temperature SOFC (IT-SOFC), ceria based electrolytes are the most promising one, due to their higher ionic conductivity at relatively lower temperatures. Gd doped ceria is reported to be having the highest ionic conductivity. In the present work, Mg is codoped along with Gd and the electronic structure of the constituents is studied by XPS. XPS confirm that the Cerium is present in +4 oxidation state only which indicates that electronic conduction can be completely avoided.

Final Progress Report, Renewable and Logistics Fuels for Fuel Cells at the Colorado School of Mines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sullivan, Neal P.

The objective of this program is to advance the current state of technology of solid-oxide fuel cells (SOFCs) to improve performance when operating on renewable and logistics hydrocarbon fuel streams. Outcomes will include: 1.) new SOFC materials and architectures that address the technical challenges associated with carbon-deposit formation and sulfur poisoning; 2.) new integration strategies for combining fuel reformers with SOFCs; 3.) advanced modeling tools that bridge the scales of fundamental charge-transfer chemistry to system operation and control; and 4.) outreach through creation of the Distinguished Lecturer Series to promote nationwide collaboration with fuel-cell researchers and scientists.

Development of a Novel Efficient Solid-Oxide Hybrid for Co-generation of Hydrogen and Electricity Using Nearby Resources for Local Application

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tao, Greg, G.; Virkar, Anil, V.; Bandopadhyay, Sukumar

2009-06-30

Developing safe, reliable, cost-effective, and efficient hydrogen-electricity co-generation systems is an important step in the quest for national energy security and minimized reliance on foreign oil. This project aimed to, through materials research, develop a cost-effective advanced technology cogenerating hydrogen and electricity directly from distributed natural gas and/or coal-derived fuels. This advanced technology was built upon a novel hybrid module composed of solid-oxide fuel-assisted electrolysis cells (SOFECs) and solid-oxide fuel cells (SOFCs), both of which were in planar, anode-supported designs. A SOFEC is an electrochemical device, in which an oxidizable fuel and steam are fed to the anode and cathode,more » respectively. Steam on the cathode is split into oxygen ions that are transported through an oxygen ion-conducting electrolyte (i.e. YSZ) to oxidize the anode fuel. The dissociated hydrogen and residual steam are exhausted from the SOFEC cathode and then separated by condensation of the steam to produce pure hydrogen. The rationale was that in such an approach fuel provides a chemical potential replacing the external power conventionally used to drive electrolysis cells (i.e. solid oxide electrolysis cells). A SOFC is similar to the SOFEC by replacing cathode steam with air for power generation. To fulfill the cogeneration objective, a hybrid module comprising reversible SOFEC stacks and SOFC stacks was designed that planar SOFECs and SOFCs were manifolded in such a way that the anodes of both the SOFCs and the SOFECs were fed the same fuel, (i.e. natural gas or coal-derived fuel). Hydrogen was produced by SOFECs and electricity was generated by SOFCs within the same hybrid system. A stand-alone 5 kW system comprising three SOFEC-SOFC hybrid modules and three dedicated SOFC stacks, balance-of-plant components (including a tailgas-fired steam generator and tailgas-fired process heaters), and electronic controls was designed, though an overall integrated system assembly was not completed because of limited resources. An inexpensive metallic interconnects fabrication process was developed in-house. BOP components were fabricated and evaluated under the forecasted operating conditions. Proof-of-concept demonstration of cogenerating hydrogen and electricity was performed, and demonstrated SOFEC operational stability over 360 hours with no significant degradation. Cost analysis was performed for providing an economic assessment of the cost of hydrogen production using the targeted hybrid technology, and for guiding future research and development.« less

Predicting the ultimate potential of natural gas SOFC power cycles with CO2 capture - Part B: Applications

NASA Astrophysics Data System (ADS)

Campanari, Stefano; Mastropasqua, Luca; Gazzani, Matteo; Chiesa, Paolo; Romano, Matteo C.

2016-09-01

An important advantage of solid oxide fuel cells (SOFC) as future systems for large scale power generation is the possibility of being efficiently integrated with processes for CO2 capture. Focusing on natural gas power generation, Part A of this work assessed the performances of advanced pressurised and atmospheric plant configurations (SOFC + GT and SOFC + ST, with fuel cell integration within a gas turbine or a steam turbine cycle) without CO2 separation. This Part B paper investigates such kind of power cycles when applied to CO2 capture, proposing two ultra-high efficiency plant configurations based on advanced intermediate-temperature SOFCs with internal reforming and low temperature CO2 separation process. The power plants are simulated at the 100 MW scale with a set of realistic assumptions about FC performances, main components and auxiliaries, and show the capability of exceeding 70% LHV efficiency with high CO2 capture (above 80%) and a low specific primary energy consumption for the CO2 avoided (1.1-2.4 MJ kg-1). Detailed results are presented in terms of energy and material balances, and a sensitivity analysis of plant performance is developed vs. FC voltage and fuel utilisation to investigate possible long-term improvements. Options for further improvement of the CO2 capture efficiency are also addressed.

The surface evolution of La0.4Sr0.6TiO3+δ anode in solid oxide fuel cells: Understanding the sulfur-promotion effect

NASA Astrophysics Data System (ADS)

Yan, Ning; Zanna, Sandrine; Klein, Lorena H.; Roushanafshar, Milad; Amirkhiz, Babak S.; Zeng, Yimin; Rothenberg, Gadi; Marcus, Philippe; Luo, Jing-Li

2017-03-01

The ideal solid oxide fuel cells (SOFCs) can be powered by readily available hydrocarbon fuels containing impurities. While this is commonly recognized as a key advantage of SOFC, it also, together with the elevated operating temperature, becomes the main barrier impeding the in-situ or operando investigations of the anode surface chemistry. Here, using a well-designed quenching experiment, we managed to characterize the near-surface structure of La0.4Sr0.6TiO3+δ (LST) anode in SOFCs fuelled by H2S-containing methane. This new method enabled us to clearly observe the surface amorphization and sulfidation of LST under simulated SOFC operating conditions. The ∼1 nm-thick two dimensional sulfur-adsorbed layer was on top of the disordered LST, containing -S, -SH and elemental sulfur species. In SOFC test, such "poisoned" anode showed increased performances: a ten-fold enhanced power density enhancement (up to 30 mW cm-2) and an improved open circuit voltage (from 0.69 V to 1.17 V). Moreover, its anodic polarization resistance in methane decreased to 21.53 Ω cm2, a difference of 95% compared with the sulfur-free anode. Control experiments confirmed that once the adsorbed sulfur species were removed electrochemically, methane conversion slowed down simultaneously till full stop.

Mesh-free data transfer algorithms for partitioned multiphysics problems: Conservation, accuracy, and parallelism

DOE PAGES

Slattery, Stuart R.

2015-12-02

In this study we analyze and extend mesh-free algorithms for three-dimensional data transfer problems in partitioned multiphysics simulations. We first provide a direct comparison between a mesh-based weighted residual method using the common-refinement scheme and two mesh-free algorithms leveraging compactly supported radial basis functions: one using a spline interpolation and one using a moving least square reconstruction. Through the comparison we assess both the conservation and accuracy of the data transfer obtained from each of the methods. We do so for a varying set of geometries with and without curvature and sharp features and for functions with and without smoothnessmore » and with varying gradients. Our results show that the mesh-based and mesh-free algorithms are complementary with cases where each was demonstrated to perform better than the other. We then focus on the mesh-free methods by developing a set of algorithms to parallelize them based on sparse linear algebra techniques. This includes a discussion of fast parallel radius searching in point clouds and restructuring the interpolation algorithms to leverage data structures and linear algebra services designed for large distributed computing environments. The scalability of our new algorithms is demonstrated on a leadership class computing facility using a set of basic scaling studies. Finally, these scaling studies show that for problems with reasonable load balance, our new algorithms for both spline interpolation and moving least square reconstruction demonstrate both strong and weak scalability using more than 100,000 MPI processes with billions of degrees of freedom in the data transfer operation.« less

Auxiliary power unit based on a solid oxide fuel cell and fuelled with diesel

NASA Astrophysics Data System (ADS)

Lawrence, Jeremy; Boltze, Matthias

An auxiliary power unit (APU) is presented that is fuelled with diesel, thermally self-sustaining, and based on a solid oxide fuel cell (SOFC). The APU is rated at 1 kW electrical, and can generate electrical power after a 3 h warm-up phase. System features include a "dry" catalytic partial oxidation (CPOX) diesel reformer, a 30 cell SOFC stack with an open cathode, and a porous-media afterburner. The APU does not require a supply of external water. The SOFC stack is an outcome of a development partnership with H.C. Starck GmbH and Fraunhofer IKTS, and is discussed in detail in an accompanying paper.

Solid State Energy Conversion Alliance Delphi SOFC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steven Shaffer; Gary Blake; Sean Kelly

2006-12-31

The following report details the results under the DOE SECA program for the period July 2006 through December 2006. Developments pertain to the development of a 3 to 5 kW Solid Oxide Fuel Cell power system for a range of fuels and applications. This report details technical results of the work performed under the following tasks for the SOFC Power System: Task 1 SOFC System Development; Task 2 Solid Oxide Fuel Cell Stack Developments; Task 3 Reformer Developments; Task 4 Development of Balance of Plant Components; Task 5 Project Management; and Task 6 System Modeling & Cell Evaluation for Highmore » Efficiency Coal-Based Solid Oxide Fuel Cell Gas Turbine Hybrid System.« less

Strong, Tough Glass Composites Developed for Solid Oxide Fuel Cell Seals

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Choi, Sung R.

2005-01-01

A fuel cell is an electrochemical device that continuously converts the chemical energy of a fuel directly into electrical energy. It consists of an electrolyte, an anode, and a cathode. Various types of fuel cells are available, such as direct methanol fuel cells, alkaline fuel cells, proton-exchange-membrane fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, and solid oxide fuel cells (SOFCs). The salient features of an SOFC are all solid construction and high-temperature electrochemical-reaction-based operation, resulting in clean, efficient power generation from a variety of fuels. SOFCs are being developed for a broad range of applications, such as portable electronic devices, automobiles, power generation, and aeronautics.

Design and operation of interconnectors for solid oxide fuel cell stacks

NASA Astrophysics Data System (ADS)

Winkler, W.; Koeppen, J.

Highly efficient combined cycles with solid oxide fuel cell (SOFC) need an integrated heat exchanger in the stack to reach efficiencies of about 80%. The stack costs must be lower than 1000 DM/kW. A newly developed welded metallic (Haynes HA 230) interconnector with a free stretching planar SOFC and an integrated heat exchanger was tested in thermal cycling operation. The design allowed a cycling of the SOFC without mechanical damage of the electrolyte in several tests. However, more tests and a further design optimization will be necessary. These results could indicate that commercial high-temperature alloys can be used as interconnector material in order to fullfil the cost requirements.

Improvement of capabilities of the Distributed Electrochemistry Modeling Tool for investigating SOFC long term performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gonzalez Galdamez, Rinaldo A.; Recknagle, Kurtis P.

2012-04-30

This report provides an overview of the work performed for Solid Oxide Fuel Cell (SOFC) modeling during the 2012 Winter/Spring Science Undergraduate Laboratory Internship at Pacific Northwest National Laboratory (PNNL). A brief introduction on the concept, operation basics and applications of fuel cells is given for the general audience. Further details are given regarding the modifications and improvements of the Distributed Electrochemistry (DEC) Modeling tool developed by PNNL engineers to model SOFC long term performance. Within this analysis, a literature review on anode degradation mechanisms is explained and future plans of implementing these into the DEC modeling tool are alsomore » proposed.« less

A fully consistent and conservative vertically adaptive coordinate system for SLIM 3D v0.4 with an application to the thermocline oscillations of Lake Tanganyika

NASA Astrophysics Data System (ADS)

Delandmeter, Philippe; Lambrechts, Jonathan; Legat, Vincent; Vallaeys, Valentin; Naithani, Jaya; Thiery, Wim; Remacle, Jean-François; Deleersnijder, Eric

2018-03-01

The discontinuous Galerkin (DG) finite element method is well suited for the modelling, with a relatively small number of elements, of three-dimensional flows exhibiting strong velocity or density gradients. Its performance can be highly enhanced by having recourse to r-adaptivity. Here, a vertical adaptive mesh method is developed for DG finite elements. This method, originally designed for finite difference schemes, is based on the vertical diffusion of the mesh nodes, with the diffusivity controlled by the density jumps at the mesh element interfaces. The mesh vertical movement is determined by means of a conservative arbitrary Lagrangian-Eulerian (ALE) formulation. Though conservativity is naturally achieved, tracer consistency is obtained by a suitable construction of the mesh vertical velocity field, which is defined in such a way that it is fully compatible with the tracer and continuity equations at a discrete level. The vertically adaptive mesh approach is implemented in the three-dimensional version of the geophysical and environmental flow Second-generation Louvain-la-Neuve Ice-ocean Model (SLIM 3D; www.climate.be/slim). Idealised benchmarks, aimed at simulating the oscillations of a sharp thermocline, are dealt with. Then, the relevance of the vertical adaptivity technique is assessed by simulating thermocline oscillations of Lake Tanganyika. The results are compared to measured vertical profiles of temperature, showing similar stratification and outcropping events.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Slattery, Stuart R.

In this study we analyze and extend mesh-free algorithms for three-dimensional data transfer problems in partitioned multiphysics simulations. We first provide a direct comparison between a mesh-based weighted residual method using the common-refinement scheme and two mesh-free algorithms leveraging compactly supported radial basis functions: one using a spline interpolation and one using a moving least square reconstruction. Through the comparison we assess both the conservation and accuracy of the data transfer obtained from each of the methods. We do so for a varying set of geometries with and without curvature and sharp features and for functions with and without smoothnessmore » and with varying gradients. Our results show that the mesh-based and mesh-free algorithms are complementary with cases where each was demonstrated to perform better than the other. We then focus on the mesh-free methods by developing a set of algorithms to parallelize them based on sparse linear algebra techniques. This includes a discussion of fast parallel radius searching in point clouds and restructuring the interpolation algorithms to leverage data structures and linear algebra services designed for large distributed computing environments. The scalability of our new algorithms is demonstrated on a leadership class computing facility using a set of basic scaling studies. Finally, these scaling studies show that for problems with reasonable load balance, our new algorithms for both spline interpolation and moving least square reconstruction demonstrate both strong and weak scalability using more than 100,000 MPI processes with billions of degrees of freedom in the data transfer operation.« less

Program of scientific investigations and development of solid-oxide fuel cells (SOFC) in VNIITF. Proposals on scientific and technical collaboration and SOFC commercialization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kleschev, Yu.N.; Chukharev, V.F.

1996-04-01

This paper describes proposals on scientific and technical collaborations pertaining to solid oxide fuel cell commercialization. Topics included for discussion are: materials research and manufacture; market estimation and cost; directions of collaboration; and project of proposals on joint enterprise creation.

Review of Fuel Cell Technologies for Military Land Vehicles

DTIC Science & Technology

2014-09-01

fuel cell technologies for APUs are Proton Exchange Membrane Fuel Cells ( PEMFC ), direct methanol fuel cells and Solid Oxide Fuel Cells (SOFC). The...6 4.2 Proton Exchange Membrane Fuel Cells ( PEMFC ...OEM Original Equipment Manufacturer PEM Proton Exchange Membrane PEMFC Proton Exchange Membrane Fuel Cell SOFC Solid Oxide Fuel Cell TRL Technical

The calibration of a model for simulating the thermal and electrical performance of a 2.8 kW AC solid-oxide fuel cell micro-cogeneration device

NASA Astrophysics Data System (ADS)

Beausoleil-Morrison, Ian; Lombardi, Kathleen

The concurrent production of heat and electricity within residential buildings using solid-oxide fuel cell (SOFC) micro-cogeneration devices has the potential to reduce primary energy consumption, greenhouse gas emissions, and air pollutants. A realistic assessment of this emerging technology requires the accurate simulation of the thermal and electrical production of SOFC micro-cogeneration devices concurrent with the simulation of the building, its occupants, and coupled plant components. The calibration of such a model using empirical data gathered from experiments conducted with a 2.8 kW AC SOFC micro-cogeneration device is demonstrated. The experimental configuration, types of instrumentation employed, and the operating scenarios examined are treated. The propagation of measurement uncertainty into the derived quantities that are necessary for model calibration are demonstrated by focusing upon the SOFC micro-cogeneration system's gas-to-water heat exchanger. The calibration coefficients necessary to accurately simulate the thermal and electrical performance of this prototype device are presented and the types of analyses enabled to study the potential of the technology are demonstrated.

Linking Initial Microstructure to ORR Related Property Degradation in SOFC Cathode: A Phase Field Simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lei, Y.; Cheng, T. -L.; Wen, Y. H.

Microstructure evolution driven by thermal coarsening is an important factor for the loss of oxygen reduction reaction rates in SOFC cathode. In this work, the effect of an initial microstructure on the microstructure evolution in SOFC cathode is investigated using a recently developed phase field model. Specifically, we tune the phase fraction, the average grain size, the standard deviation of the grain size and the grain shape in the initial microstructure, and explore their effect on the evolution of the grain size, the density of triple phase boundary, the specific surface area and the effective conductivity in LSM-YSZ cathodes. Itmore » is found that the degradation rate of TPB density and SSA of LSM is lower with less LSM phase fraction (with constant porosity assumed) and greater average grain size, while the degradation rate of effective conductivity can also be tuned by adjusting the standard deviation of grain size distribution and grain aspect ratio. The implication of this study on the designing of an optimal initial microstructure of SOFC cathodes is discussed.« less

Linking Initial Microstructure to ORR Related Property Degradation in SOFC Cathode: A Phase Field Simulation

DOE PAGES

Lei, Y.; Cheng, T. -L.; Wen, Y. H.

2017-07-05

Microstructure evolution driven by thermal coarsening is an important factor for the loss of oxygen reduction reaction rates in SOFC cathode. In this work, the effect of an initial microstructure on the microstructure evolution in SOFC cathode is investigated using a recently developed phase field model. Specifically, we tune the phase fraction, the average grain size, the standard deviation of the grain size and the grain shape in the initial microstructure, and explore their effect on the evolution of the grain size, the density of triple phase boundary, the specific surface area and the effective conductivity in LSM-YSZ cathodes. Itmore » is found that the degradation rate of TPB density and SSA of LSM is lower with less LSM phase fraction (with constant porosity assumed) and greater average grain size, while the degradation rate of effective conductivity can also be tuned by adjusting the standard deviation of grain size distribution and grain aspect ratio. The implication of this study on the designing of an optimal initial microstructure of SOFC cathodes is discussed.« less

Hybrid Solid Oxide Fuel Cell/Gas Turbine System Design for High Altitude Long Endurance Aerospace Missions

NASA Technical Reports Server (NTRS)

Himansu, Ananda; Freeh, Joshua E.; Steffen, Christopher J., Jr.; Tornabene, Robert T.; Wang, Xiao-Yen J.

2006-01-01

A system level analysis, inclusive of mass, is carried out for a cryogenic hydrogen fueled hybrid solid oxide fuel cell and bottoming gas turbine (SOFC/GT) power system. The system is designed to provide primary or secondary electrical power for an unmanned aerial vehicle (UAV) over a high altitude, long endurance mission. The net power level and altitude are parametrically varied to examine their effect on total system mass. Some of the more important technology parameters, including turbomachinery efficiencies and the SOFC area specific resistance, are also studied for their effect on total system mass. Finally, two different solid oxide cell designs are compared to show the importance of the individual solid oxide cell design on the overall system. We show that for long mission durations of 10 days or more, the fuel mass savings resulting from the high efficiency of a SOFC/GT system more than offset the larger powerplant mass resulting from the low specific power of the SOFC/GT system. These missions therefore favor high efficiency, low power density systems, characteristics typical of fuel cell systems in general.

Solid Oxide Fuel Cells Operating on Alternative and Renewable Fuels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xiaoxing; Quan, Wenying; Xiao, Jing

2014-09-30

This DOE project at the Pennsylvania State University (Penn State) initially involved Siemens Energy, Inc. to (1) develop new fuel processing approaches for using selected alternative and renewable fuels – anaerobic digester gas (ADG) and commercial diesel fuel (with 15 ppm sulfur) – in solid oxide fuel cell (SOFC) power generation systems; and (2) conduct integrated fuel processor – SOFC system tests to evaluate the performance of the fuel processors and overall systems. Siemens Energy Inc. was to provide SOFC system to Penn State for testing. The Siemens work was carried out at Siemens Energy Inc. in Pittsburgh, PA. Themore » unexpected restructuring in Siemens organization, however, led to the elimination of the Siemens Stationary Fuel Cell Division within the company. Unfortunately, this led to the Siemens subcontract with Penn State ending on September 23rd, 2010. SOFC system was never delivered to Penn State. With the assistance of NETL project manager, the Penn State team has since developed a collaborative research with Delphi as the new subcontractor and this work involved the testing of a stack of planar solid oxide fuel cells from Delphi.« less

Performance Impact Associated with Ni-Based SOFCs Fueled with Higher Hydrocarbon-Doped Coal Syngas

NASA Astrophysics Data System (ADS)

Hackett, Gregory A.; Gerdes, Kirk; Chen, Yun; Song, Xueyan; Zondlo, John

2015-03-01

Energy generation strategies demonstrating high efficiency and fuel flexibility are desirable in the contemporary energy market. When integrated with a gasification process, a solid oxide fuel cell (SOFC) can produce electricity at efficiencies exceeding 50 pct by consuming fuels such as coal, biomass, municipal solid waste, or other opportunity wastes. The synthesis gas derived from such fuel may contain trace species (including arsenic, lead, cadmium, mercury, phosphorus, sulfur, and tars) and low concentration organic species that adversely affect the SOFC performance. This work demonstrates the impact of exposure of the hydrocarbons ethylene, benzene, and naphthalene at various concentrations. The cell performance degradation rate is determined for tests exceeding 500 hours at 1073 K (800 °C). Cell performance is evaluated during operation with electrochemical impedance spectroscopy, and exposed samples are post-operationally analyzed by scanning electron microscopy/energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The short-term performance is modeled to predict performances to the desired 40,000-hours operational lifetime for SOFCs. Possible hydrocarbon interactions with the nickel anode are postulated, and acceptable hydrocarbon exposure limits are discussed.

Is it possible to design a portable power generator based on micro-solid oxide fuel cells? A finite volume analysis

NASA Astrophysics Data System (ADS)

Pla, D.; Sánchez-González, A.; Garbayo, I.; Salleras, M.; Morata, A.; Tarancón, A.

2015-10-01

The inherent limited capacity of current battery technology is not sufficient for covering the increasing power requirements of widely extended portable devices. Among other promising alternatives, recent advances in the field of micro-Solid Oxide Fuel Cells (μ-SOFCs) converted this disruptive technology into a serious candidate to power next generations of portable devices. However, the implementation of single cells in real devices, i.e. μ-SOFC stacks coupled to the required balance-of-plant elements like fuel reformers or post combustors, still remains unexplored. This work aims addressing this system-level research by proposing a new compact design of a vertically stacked device fuelled with ethanol. The feasibility and design optimization for achieving a thermally self-sustained regime and a rapid and low-power consuming start-up is studied by finite volume analysis. An optimal thermal insulation strategy is defined to maintain the steady-state operation temperature of the μ-SOFC at 973 K and an external temperature lower than 323 K. A hybrid start-up procedure, based on heaters embedded in the μ-SOFCs and heat released by chemical reactions in the post-combustion unit, is analyzed allowing start-up times below 1 min and energy consumption under 500 J. These results clearly demonstrate the feasibility of high temperature μ-SOFC power systems fuelled with hydrocarbons for portable applications, therefore, anticipating a new family of mobile and uninterrupted power generators.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morgan, Nathaniel Ray; Waltz, Jacob I.

The level set method is commonly used to model dynamically evolving fronts and interfaces. In this work, we present new methods for evolving fronts with a specified velocity field or in the surface normal direction on 3D unstructured tetrahedral meshes with adaptive mesh refinement (AMR). The level set field is located at the nodes of the tetrahedral cells and is evolved using new upwind discretizations of Hamilton–Jacobi equations combined with a Runge–Kutta method for temporal integration. The level set field is periodically reinitialized to a signed distance function using an iterative approach with a new upwind gradient. We discuss themore » details of these level set and reinitialization methods. Results from a range of numerical test problems are presented.« less

The Evolution of Solid Oxide Fuel Cell Nickel-Yttria Stabilized Zirconia Anodes Studied Using Electrochemical and Three-Dimensional Microstructural Characterizations

NASA Astrophysics Data System (ADS)

Kennouche, David O.

This thesis focuses on Solid Oxide Fuel Cells (SOFCs). The 21st century will see major changes in the way energy is produced, stored, and used around the world. SOFCs, which provide an efficient, scalable, and low-pollution alternative method for electricity generation, are expected to play an important role. SOFCs can also be operated in electrolysis mode for energy storage, important since health and economic reasons are causing a shift towards intermittent renewable energy resources. However, multiple limitations mainly linked to cost and durability have prevented the expansion of this technology to mass markets. This work focuses on the Nickel - Yttria Stabilized Zirconia (Ni-YSZ) anode that is widely used in SOFCs. Coarsening of Ni in the Ni-YSZ anode has been widely cited as a primary cause of long-term SOFC degradation. While there have been numerous studies of Ni coarsening reported, these have typically only tracked the evolution of Ni particle size, not the entire microstructure, and have typically not been correlated directly with electrochemical performance. In this thesis, the advanced tomography techniques Focused Ion Beam - Scanning Electron Microscopy (FIB-SEM) tomography and Trans- mission X-ray Microscopy (TXM) have been utilized to enable insight into the evolution of Ni-YSZ structure and how it relates to performance degradation. Extensive anode aging studies were done for relatively short times using temperatures higher than in normal SOFC operation in order to accelerate microstructural evolution. In addition the microstructure changes were correlated with changes in anode polarization resistance. While most of the measurements were done by comparing different anodes aged under different conditions, the first example of a "pseudo in situ" measurement where the same anode was 3D imaged repeatedly with intervening aging steps, was also demonstrated. A microstructural evolution model that focuses on the active three-phase boundary density was fitted to the experimental data, and subsequently used to predict the change in anode three-phase boundary density and average particle size for extended times under normal SOFC conditions. Characterization of other anodes (pulsed-laser deposited and micro-tubular geometries) produced by international collaborators is also presented. Finally, a testing setup and protocol for anode life testing with current density and overpotential has been developed and implemented. Early test results are presented.

A consortium approach to commercialized Westinghouse solid oxide fuel cell technology

NASA Astrophysics Data System (ADS)

Casanova, Allan

Westinghouse is developing its tubular solid oxide fuel cells (SOFCs) for a variety of applications in stationary power generation markets. By pressurizing a SOFC and integrating it with a gas turbine (GT), power systems with efficiencies as high as 70-75% can be obtained. The first such system will be tested in 1998. Because of their extraordinarily high efficiency (60-70%) even in small sizes the first SOFC products to be offered are expected to be integrated SOFC/GT power systems in the 1-7 MW range, for use in the emerging distributed generation (DG) market segment. Expansion into larger sizes will follow later. Because of their modularity, environmental friendliness and expected cost effectiveness, and because of a worldwide thrust towards utility deregulation, a ready market is forecasted for baseload distributed generation. Assuming Westinghouse can complete its technology development and reach its cost targets, the integrated SOFC/GT power system is seen as a product with tremendous potential in the emerging distributed generation market. While Westinghouse has been a leader in the development of power generation technology for over a century, it does not plan to manufacture small gas turbines. However, GTs small enough to integrate with SOFCs and address the 1-7 MW market are generally available from various manufacturers. Westinghouse will need access to a new set of customers as it brings baseload plants to the present small market mix of emergency and peaking power applications. Small cogeneration applications, already strong in some parts of the world, are also gaining ground everywhere. Small GT manufacturers already serve this market, and alliances and partnerships can enhance SOFC commercialization. Utilities also serve the DG market, especially those that have set up energy service companies and seek to grow beyond the legal and geographical confines of their current regulated business. Because fuel cells in general are a new product, because small baseload applications are a new segment, and because deregulation will continue to shake up the mature traditional power generation market, the commercial risks of launching a new product at this time are unique and considerable. Hence, a collaborative approach to commercialization is deemed desirable and appropriate, and collaboration with GT manufacturers and utilities will be addressed in this paper.

A metallic interconnect for a solid oxide fuel cell stack

NASA Astrophysics Data System (ADS)

England, Diane Mildred

A solid oxide fuel cell (SOFC) electrochemically converts the chemical energy of reaction into electrical energy. The commercial success of planar, SOFC stack technology has a number of challenges, one of which is the interconnect that electrically and physically connects the cathode of one cell to the anode of an adjacent cell in the SOFC stack and in addition, separates the anodic and cathodic gases. An SOFC stack operating at intermediate temperatures, between 600°C and 800°C, can utilize a metallic alloy as an interconnect material. Since the interconnect of an SOFC stack must operate in both air and fuel environments, the oxidation kinetics, adherence and electronic resistance of the oxide scales formed on commercial alloys were investigated in air and wet hydrogen under thermal cycling conditions to 800°C. The alloy, Haynes 230, exhibited the slowest oxidation kinetics and the lowest area-specific resistance as a function of oxidation time of all the alloys in air at 800°C. However, the area-specific resistance of the oxide scale formed on Haynes 230 in wet hydrogen was unacceptably high after only 500 hours of oxidation, which was attributed to the high resistivity of Cr2O3 in a reducing atmosphere. A study of the electrical conductivity of the minor phase manganese chromite, MnXCr3-XO4, in the oxide scale of Haynes 230, revealed that a composition closer to Mn2CrO4 had significantly higher electrical conductivity than that closer to MnCr 2O4. Haynes 230 was coated with Mn to form a phase closer to the Mn2CrO4 composition for application on the fuel side of the interconnect. U.S. Patent No. 6,054,231 is pending. Although coating a metallic alloy is inexpensive, the stringent economic requirements of SOFC stack technology required an alloy without coating for production applications. As no commercially available alloy, among the 41 alloys investigated, performed to the specifications required, a new alloy was created and designated DME-A2. The oxide scale formed on DME-A2 at 800°C exhibited extremely high electrical conductivity with respect to the commercially available alloys studied. This new alloy shows great promise for use as an interconnect material for a planar SOFC stack operating at intermediate temperatures.

Fuel Cell Power Plant Initiative. Volume 2; Preliminary Design of a Fixed-Base LFP/SOFC Power System

NASA Technical Reports Server (NTRS)

Veyo, S.E.

1997-01-01

This report documents the preliminary design for a military fixed-base power system of 3 MWe nominal capacity using Westinghouse's tubular Solid Oxide Fuel Cell [SOFC] and Haldor Topsoe's logistic fuels processor [LFP]. The LFP provides to the fuel cell a methane rich sulfur free fuel stream derived from either DF-2 diesel fuel, or JP-8 turbine fuel. Fuel cells are electrochemical devices that directly convert the chemical energy contained in fuels such as hydrogen, natural gas, or coal gas into electricity at high efficiency with no intermediate heat engine or dynamo. The SOFC is distinguished from other fuel cell types by its solid state ceramic structure and its high operating temperature, nominally 1000'C. The SOFC pioneered by Westinghouse has a tubular geometry closed at one end. A power generation stack is formed by aggregating many cells in an ordered array. The Westinghouse stack design is distinguished from other fuel cell stacks by the complete absence of high integrity seals between cell elements, cells, and between stack and manifolds. Further, the reformer for natural gas [predominantly methane] and the stack are thermally and hydraulically integrated with no requirement for process water. The technical viability of combining the tubular SOFC and a logistic fuels processor was demonstrated at 27 kWe scale in a test program sponsored by the Advanced Research Projects Agency [ARPA) and carried out at the Southern California Edison's [SCE] Highgrove generating station near San Bernardino, California in 1994/95. The LFP was a breadboard design supplied by Haldor Topsoe, Inc. under subcontract to Westinghouse. The test program was completely successful. The LFP fueled the SOFC for 766 hours on JP-8 and 1555 hours of DF-2. In addition, the fuel cell operated for 3261 hours on pipeline natural gas. Over the 5582 hours of operation, the SOFC generated 118 MVVH of electricity with no perceptible degradation in performance. The LFP processed military specification JP-8 and DF-2 removing the sulfur and reforming these liquid fuels to a methane rich gaseous fuel. Results of this program are documented in a companion report titled 'Final Report-Solid Oxide Fuel Cell/ Logistic Fuels Processor 27 kWe Power System'.

Application of adaptive gridding to magnetohydrodynamic flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schnack, D.D.; Lotatti, I.; Satyanarayana, P.

1996-12-31

The numerical simulation of the primitive, three-dimensional, time-dependent, resistive MHD equations on an unstructured, adaptive poloidal mesh using the TRIM code has been reported previously. The toroidal coordinate is approximated pseudo-spectrally with finite Fourier series and Fast-Fourier Transforms. The finite-volume algorithm preserves the magnetic field as solenoidal to round-off error, and also conserves mass, energy, and magnetic flux exactly. A semi-implicit method is used to allow for large time steps on the unstructured mesh. This is important for tokamak calculations where the relevant time scale is determined by the poloidal Alfven time. This also allows the viscosity to be treatedmore » implicitly. A conjugate-gradient method with pre-conditioning is used for matrix inversion. Applications to the growth and saturation of ideal instabilities in several toroidal fusion systems has been demonstrated. Recently we have concentrated on the details of the mesh adaption algorithm used in TRIM. We present several two-dimensional results relating to the use of grid adaptivity to track the evolution of hydrodynamic and MHD structures. Examples of plasma guns, opening switches, and supersonic flow over a magnetized sphere are presented. Issues relating to mesh adaption criteria are discussed.« less

Fully anisotropic goal-oriented mesh adaptation for 3D steady Euler equations

NASA Astrophysics Data System (ADS)

Loseille, A.; Dervieux, A.; Alauzet, F.

2010-04-01

This paper studies the coupling between anisotropic mesh adaptation and goal-oriented error estimate. The former is very well suited to the control of the interpolation error. It is generally interpreted as a local geometric error estimate. On the contrary, the latter is preferred when studying approximation errors for PDEs. It generally involves non local error contributions. Consequently, a full and strong coupling between both is hard to achieve due to this apparent incompatibility. This paper shows how to achieve this coupling in three steps. First, a new a priori error estimate is proved in a formal framework adapted to goal-oriented mesh adaptation for output functionals. This estimate is based on a careful analysis of the contributions of the implicit error and of the interpolation error. Second, the error estimate is applied to the set of steady compressible Euler equations which are solved by a stabilized Galerkin finite element discretization. A goal-oriented error estimation is derived. It involves the interpolation error of the Euler fluxes weighted by the gradient of the adjoint state associated with the observed functional. Third, rewritten in the continuous mesh framework, the previous estimate is minimized on the set of continuous meshes thanks to a calculus of variations. The optimal continuous mesh is then derived analytically. Thus, it can be used as a metric tensor field to drive the mesh adaptation. From a numerical point of view, this method is completely automatic, intrinsically anisotropic, and does not depend on any a priori choice of variables to perform the adaptation. 3D examples of steady flows around supersonic and transsonic jets are presented to validate the current approach and to demonstrate its efficiency.

Multiphase flow modelling of volcanic ash particle settling in water using adaptive unstructured meshes

NASA Astrophysics Data System (ADS)

Jacobs, C. T.; Collins, G. S.; Piggott, M. D.; Kramer, S. C.; Wilson, C. R. G.

2013-02-01

Small-scale experiments of volcanic ash particle settling in water have demonstrated that ash particles can either settle slowly and individually, or rapidly and collectively as a gravitationally unstable ash-laden plume. This has important implications for the emplacement of tephra deposits on the seabed. Numerical modelling has the potential to extend the results of laboratory experiments to larger scales and explore the conditions under which plumes may form and persist, but many existing models are computationally restricted by the fixed mesh approaches that they employ. In contrast, this paper presents a new multiphase flow model that uses an adaptive unstructured mesh approach. As a simulation progresses, the mesh is optimized to focus numerical resolution in areas important to the dynamics and decrease it where it is not needed, thereby potentially reducing computational requirements. Model verification is performed using the method of manufactured solutions, which shows the correct solution convergence rates. Model validation and application considers 2-D simulations of plume formation in a water tank which replicate published laboratory experiments. The numerically predicted settling velocities for both individual particles and plumes, as well as instability behaviour, agree well with experimental data and observations. Plume settling is clearly hindered by the presence of a salinity gradient, and its influence must therefore be taken into account when considering particles in bodies of saline water. Furthermore, individual particles settle in the laminar flow regime while plume settling is shown (by plume Reynolds numbers greater than unity) to be in the turbulent flow regime, which has a significant impact on entrainment and settling rates. Mesh adaptivity maintains solution accuracy while providing a substantial reduction in computational requirements when compared to the same simulation performed using a fixed mesh, highlighting the benefits of an adaptive unstructured mesh approach.

Jet fuel based high pressure solid oxide fuel cell system

NASA Technical Reports Server (NTRS)

Gummalla, Mallika (Inventor); Yamanis, Jean (Inventor); Olsommer, Benoit (Inventor); Dardas, Zissis (Inventor); Bayt, Robert (Inventor); Srinivasan, Hari (Inventor); Dasgupta, Arindam (Inventor); Hardin, Larry (Inventor)

2013-01-01

A power system for an aircraft includes a solid oxide fuel cell system which generates electric power for the aircraft and an exhaust stream; and a heat exchanger for transferring heat from the exhaust stream of the solid oxide fuel cell to a heat requiring system or component of the aircraft. The heat can be transferred to fuel for the primary engine of the aircraft. Further, the same fuel can be used to power both the primary engine and the SOFC. A heat exchanger is positioned to cool reformate before feeding to the fuel cell. SOFC exhaust is treated and used as inerting gas. Finally, oxidant to the SOFC can be obtained from the aircraft cabin, or exterior, or both.

The Design of Connection Solid Oxide Fuel Cell (SOFC) Integrated Grid with Three-Phase Inverter

NASA Astrophysics Data System (ADS)

Darjat; Sulistyo; Triwiyatno, Aris; Thalib, Humaid

2018-03-01

Fuel cell technology is a relatively new energy-saving technology that has the potential to replace conventional energy technologies. Among the different types of generation technologies, fuel cells is the generation technologies considered as a potential source of power generation because it is flexible and can be placed anywhere based distribution system. Modeling of SOFC is done by using Nernst equation. The output power of the fuel cell can be controlled by controlling the flow rate of the fuels used in the process. Three-phase PWM inverter is used to get the form of three-phase voltage which same with the grid. In this paper, the planning and design of the SOFC are connected to the grid.

High power density solid oxide fuel cells

DOEpatents

Pham, Ai Quoc; Glass, Robert S.

2004-10-12

A method for producing ultra-high power density solid oxide fuel cells (SOFCs). The method involves the formation of a multilayer structure cells wherein a buffer layer of doped-ceria is deposited intermediate a zirconia electrolyte and a cobalt iron based electrode using a colloidal spray deposition (CSD) technique. For example, a cobalt iron based cathode composed of (La,Sr)(Co,Fe)O (LSCF) may be deposited on a zirconia electrolyte via a buffer layer of doped-ceria deposited by the CSD technique. The thus formed SOFC have a power density of 1400 mW/cm.sup.2 at 600.degree. C. and 900 mW/cm.sup.2 at 700.degree. C. which constitutes a 2-3 times increased in power density over conventionally produced SOFCs.

Electrode materials: a challenge for the exploitation of protonic solid oxide fuel cells

PubMed Central

Fabbri, Emiliana; Pergolesi, Daniele; Traversa, Enrico

2010-01-01

High temperature proton conductor (HTPC) oxides are attracting extensive attention as electrolyte materials alternative to oxygen-ion conductors for use in solid oxide fuel cells (SOFCs) operating at intermediate temperatures (400–700 °C). The need to lower the operating temperature is dictated by cost reduction for SOFC pervasive use. The major stake for the deployment of this technology is the availability of electrodes able to limit polarization losses at the reduced operation temperature. This review aims to comprehensively describe the state-of-the-art anode and cathode materials that have so far been tested with HTPC oxide electrolytes, offering guidelines and possible strategies to speed up the development of protonic SOFCs. PMID:27877342

Jet Fuel Based High Pressure Solid Oxide Fuel Cell System

NASA Technical Reports Server (NTRS)

Srinivasan, Hari (Inventor); Hardin, Larry (Inventor); Gummalla, Mallika (Inventor); Yamanis, Jean (Inventor); Olsommer, Benoit (Inventor); Dardas, Zissis (Inventor); Dasgupta, Arindam (Inventor); Bayt, Robert (Inventor)

2015-01-01

A power system for an aircraft includes a solid oxide fuel cell system which generates electric power for the aircraft and an exhaust stream; and a heat exchanger for transferring heat from the exhaust stream of the solid oxide fuel cell to a heat requiring system or component of the aircraft. The heat can be transferred to fuel for the primary engine of the aircraft. Further, the same fuel can be used to power both the primary engine and the SOFC. A heat exchanger is positioned to cool reformate before feeding to the fuel cell. SOFC exhaust is treated and used as inerting gas. Finally, oxidant to the SOFC can be obtained from the aircraft cabin, or exterior, or both.

THE RELATIVE IMPORTANCE OF NUTRIENT ENRICHMENT AND HERBIVORY ON MACROALGAL COMMUNITIES NEAR NORMAN'S POND CAY, EXUMAS CAYS, BAHAMAS: A "NATURAL" ENRICHMENT EXPERIMENT. (R830414)

EPA Science Inventory

The simultaneous effects of grazing and nutrient enrichment on macroalgal communities were experimentally investigated using plastic mesh enclosure/exclosure cages along a natural nutrient (DIN, SRP) gradient from the discharge of a tidal mangrove creek on the west side of Nor...

Full-Carpet Design of a Low-Boom Demonstrator Concept

NASA Technical Reports Server (NTRS)

Ordaz, Irian; Wintzer, Mathias; Rallabhandi, Sriram K.

2015-01-01

The Cart3D adjoint-based design framework is used to mitigate the undesirable o -track sonic boom properties of a demonstrator concept designed for low-boom directly under the flight path. First, the requirements of a Cart3D design mesh are determined using a high-fidelity mesh adapted to minimize the discretization error of the CFD analysis. Low-boom equivalent area targets are then generated at the under-track and one off-track azimuthal position for the baseline configuration. The under-track target is generated using a trim- feasible low-boom target generation process, ensuring that the final design is not only low-boom, but also trimmed at the specified flight condition. The o -track equivalent area target is generated by minimizing the A-weighted loudness using an efficient adjoint-based approach. The configuration outer mold line is then parameterized and optimized to match the off-body pressure distributions prescribed by the low-boom targets. The numerical optimizer uses design gradients which are calculated using the Cart3D adjoint- based design capability. Optimization constraints are placed on the geometry to satisfy structural feasibility. The low-boom properties of the final design are verified using the adaptive meshing approach. This analysis quantifies the error associated with the CFD mesh that is used for design. Finally, an alternate mesh construction and target positioning approach offering greater computational efficiency is demonstrated and verified.

Spatial adaption procedures on unstructured meshes for accurate unsteady aerodynamic flow computation

NASA Technical Reports Server (NTRS)

Rausch, Russ D.; Batina, John T.; Yang, Henry T. Y.

1991-01-01

Spatial adaption procedures for the accurate and efficient solution of steady and unsteady inviscid flow problems are described. The adaption procedures were developed and implemented within a two-dimensional unstructured-grid upwind-type Euler code. These procedures involve mesh enrichment and mesh coarsening to either add points in a high gradient region or the flow or remove points where they are not needed, respectively, to produce solutions of high spatial accuracy at minimal computational costs. A detailed description is given of the enrichment and coarsening procedures and comparisons with alternative results and experimental data are presented to provide an assessment of the accuracy and efficiency of the capability. Steady and unsteady transonic results, obtained using spatial adaption for the NACA 0012 airfoil, are shown to be of high spatial accuracy, primarily in that the shock waves are very sharply captured. The results were obtained with a computational savings of a factor of approximately fifty-three for a steady case and as much as twenty-five for the unsteady cases.

3D hierarchical interface-enriched finite element method: Implementation and applications

NASA Astrophysics Data System (ADS)

Soghrati, Soheil; Ahmadian, Hossein

2015-10-01

A hierarchical interface-enriched finite element method (HIFEM) is proposed for the mesh-independent treatment of 3D problems with intricate morphologies. The HIFEM implements a recursive algorithm for creating enrichment functions that capture gradient discontinuities in nonconforming finite elements cut by arbitrary number and configuration of materials interfaces. The method enables the mesh-independent simulation of multiphase problems with materials interfaces that are in close proximity or contact while providing a straightforward general approach for evaluating the enrichments. In this manuscript, we present a detailed discussion on the implementation issues and required computational geometry considerations associated with the HIFEM approximation of thermal and mechanical responses of 3D problems. A convergence study is provided to investigate the accuracy and convergence rate of the HIFEM and compare them with standard FEM benchmark solutions. We will also demonstrate the application of this mesh-independent method for simulating the thermal and mechanical responses of two composite materials systems with complex microstructures.

Spatial adaption procedures on unstructured meshes for accurate unsteady aerodynamic flow computation

NASA Technical Reports Server (NTRS)

Rausch, Russ D.; Yang, Henry T. Y.; Batina, John T.

1991-01-01

Spatial adaption procedures for the accurate and efficient solution of steady and unsteady inviscid flow problems are described. The adaption procedures were developed and implemented within a two-dimensional unstructured-grid upwind-type Euler code. These procedures involve mesh enrichment and mesh coarsening to either add points in high gradient regions of the flow or remove points where they are not needed, respectively, to produce solutions of high spatial accuracy at minimal computational cost. The paper gives a detailed description of the enrichment and coarsening procedures and presents comparisons with alternative results and experimental data to provide an assessment of the accuracy and efficiency of the capability. Steady and unsteady transonic results, obtained using spatial adaption for the NACA 0012 airfoil, are shown to be of high spatial accuracy, primarily in that the shock waves are very sharply captured. The results were obtained with a computational savings of a factor of approximately fifty-three for a steady case and as much as twenty-five for the unsteady cases.

Rational Design of a Water-Storable Hierarchical Architecture Decorated with Amorphous Barium Oxide and Nickel Nanoparticles as a Solid Oxide Fuel Cell Anode with Excellent Sulfur Tolerance.

PubMed

Song, Yufei; Wang, Wei; Ge, Lei; Xu, Xiaomin; Zhang, Zhenbao; Julião, Paulo Sérgio Barros; Zhou, Wei; Shao, Zongping

2017-11-01

Solid oxide fuel cells (SOFCs), which can directly convert chemical energy stored in fuels into electric power, represent a useful technology for a more sustainable future. They are particularly attractive given that they can be easily integrated into the currently available fossil fuel infrastructure to realize an ideal clean energy system. However, the widespread use of the SOFC technology is hindered by sulfur poisoning at the anode caused by the sulfur impurities in fossil fuels. Therefore, improving the sulfur tolerance of the anode is critical for developing SOFCs for use with fossil fuels. Herein, a novel, highly active, sulfur-tolerant anode for intermediate-temperature SOFCs is prepared via a facile impregnation and limited reaction protocol. During synthesis, Ni nanoparticles, water-storable BaZr 0.4 Ce 0.4 Y 0.2 O 3- δ (BZCY) perovskite, and amorphous BaO are formed in situ and deposited on the surface of a Sm 0.2 Ce 0.8 O 1.9 (SDC) scaffold. More specifically, a porous SDC scaffold is impregnated with a well-designed proton-conducting perovskite oxide liquid precursor with the nominal composition of Ba(Zr 0.4 Ce 0.4 Y 0.2 ) 0.8 Ni 0.2 O 3- δ (BZCYN), calcined and reduced in hydrogen. The as-synthesized hierarchical architecture exhibits high H 2 electro-oxidation activity, excellent operational stability, superior sulfur tolerance, and good thermal cyclability. This work demonstrates the potential of combining nanocatalysts and water-storable materials in advanced electrocatalysts for SOFCs.

Performance and long term degradation of 7 W micro-tubular solid oxide fuel cells for portable applications

NASA Astrophysics Data System (ADS)

Torrell, M.; Morata, A.; Kayser, P.; Kendall, M.; Kendall, K.; Tarancón, A.

2015-07-01

Micro-tubular SOFCs have shown an astonishing thermal shock resistance, many orders of magnitude larger than planar SOFCs, opening the possibility of being used in portable applications. However, only few studies have been devoted to study the degradation of large-area micro-tubular SOFCs. This work presents microstructural, electrochemical and long term degradation studies of single micro-tubular cells fabricated by high shear extrusion, operating in the intermediate range of temperatures (T∼700 °C). A maximum power of 7 W per cell has been measured in a wide range of fuel utilizations between 10% and 60% at 700 °C. A degradation rate of 360 mW/1000 h (8%) has been observed for cells operated over more than 1500 h under fuel utilizations of 40%. Higher fuel utilizations lead to strong degradations associated to nickel oxidation/reduction processes. Quick thermal cycling with heating ramp rates of 30 °C /min yielded degradation rates of 440 mW/100 cycles (9%). These reasonable values of degradation under continuous and thermal cycling operation approach the requirements for many portable applications including auxiliary power units or consumer electronics opening this typically forbidden market to the SOFC technology.

MECHANICAL PROPERTY CHARACTERIZATIONS AND PERFORMANCE MODELING OF SOFC SEALS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koeppel, Brian J.; Vetrano, John S.; Nguyen, Ba Nghiep

2008-03-26

This study provides modeling tools for the design of reliable seals for SOFC stacks. The work consists of 1) experimental testing to determine fundamental properties of SOFC sealing materials, and 2) numerical modeling of stacks and sealing systems. The material tests capture relevant temperature-dependent physical and mechanical data needed by the analytical models such as thermal expansion, strength, fracture toughness, and relaxation behavior for glass-ceramic seals and other materials. Testing has been performed on both homogenous specimens and multiple material assemblies to investigate the effect of interfacial reactions. A viscoelastic continuum damage model for a glass-ceramic seal was developed tomore » capture the nonlinear behavior of this material at high temperatures. This model was implemented in the MSC MARC finite element code and was used for a detailed analysis of a planar SOFC stack under thermal cycling conditions. Realistic thermal loads for the stack were obtained using PNNL’s in-house multiphysics solver. The accumulated seal damage and component stresses were evaluated for multiple thermal loading cycles, and regions of high seal damage susceptible to cracking were identified. Selected test results, numerical model development, and analysis results will be presented.« less

Predicting the ultimate potential of natural gas SOFC power cycles with CO2 capture - Part A: Methodology and reference cases

NASA Astrophysics Data System (ADS)

Campanari, Stefano; Mastropasqua, Luca; Gazzani, Matteo; Chiesa, Paolo; Romano, Matteo C.

2016-08-01

Driven by the search for the highest theoretical efficiency, in the latest years several studies investigated the integration of high temperature fuel cells in natural gas fired power plants, where fuel cells are integrated with simple or modified Brayton cycles and/or with additional bottoming cycles, and CO2 can be separated via chemical or physical separation, oxy-combustion and cryogenic methods. Focusing on Solid Oxide Fuel Cells (SOFC) and following a comprehensive review and analysis of possible plant configurations, this work investigates their theoretical potential efficiency and proposes two ultra-high efficiency plant configurations based on advanced intermediate-temperature SOFCs integrated with a steam turbine or gas turbine cycle. The SOFC works at atmospheric or pressurized conditions and the resulting power plant exceeds 78% LHV efficiency without CO2 capture (as discussed in part A of the work) and 70% LHV efficiency with substantial CO2 capture (part B). The power plants are simulated at the 100 MW scale with a complete set of realistic assumptions about fuel cell (FC) performance, plant components and auxiliaries, presenting detailed energy and material balances together with a second law analysis.

Nickel-based anode with water storage capability to mitigate carbon deposition for direct ethanol solid oxide fuel cells.

PubMed

Wang, Wei; Su, Chao; Ran, Ran; Zhao, Bote; Shao, Zongping; Tade, Moses O; Liu, Shaomin

2014-06-01

The potential to use ethanol as a fuel places solid oxide fuel cells (SOFCs) as a sustainable technology for clean energy delivery because of the renewable features of ethanol versus hydrogen. In this work, we developed a new class of anode catalyst exemplified by Ni+BaZr0.4Ce0.4Y0.2O3 (Ni+BZCY) with a water storage capability to overcome the persistent problem of carbon deposition. Ni+BZCY performed very well in catalytic efficiency, water storage capability and coking resistance tests. A stable and high power output was well maintained with a peak power density of 750 mW cm(-2) at 750 °C. The SOFC with the new robust anode performed for seven days without any sign of performance decay, whereas SOFCs with conventional anodes failed in less than 2 h because of significant carbon deposition. Our findings indicate the potential applications of these water storage cermets as catalysts in hydrocarbon reforming and as anodes for SOFCs that operate directly on hydrocarbons. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Reversible operation of microtubular solid oxide cells using La0.6Sr0.4Co0.2Fe0.8O3-δ-Ce0.9Gd0.1O2-δ oxygen electrodes

NASA Astrophysics Data System (ADS)

López-Robledo, M. J.; Laguna-Bercero, M. A.; Larrea, A.; Orera, V. M.

2018-02-01

Yttria stabilized zirconia (YSZ) based microtubular solid oxide fuel cells (mT-SOFCs) using La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and Ce0.9Gd0.1O2-δ (GDC) as the oxygen electrode, along with a porous GDC electrolyte-electrode barrier layer, were fabricated and characterized in both fuel cell (SOFC) and electrolysis (SOEC) operation modes. The cells were anode-supported, the NiO-YSZ microtubular supports being made by Powder Extrusion Moulding (PEM). The cells showed power densities of 695 mW cm-2 at 800 °C and 0.7 V in SOFC mode, and of 845 mA cm-2 at 800 °C and 1.3 V in SOEC mode. AC impedance experiments performed under different potential loads demonstrated the reversibility of the cells. These results showed that these cells, prepared with a method suitable for using on an industrial scale, are highly reproducible and reliable, as well as very competitive as reversible SOFC-SOEC devices operating at intermediate temperatures.

Influence of the charge double layer on solid oxide fuel cell stack behavior

NASA Astrophysics Data System (ADS)

Whiston, Michael M.; Bilec, Melissa M.; Schaefer, Laura A.

2015-10-01

While the charge double layer effect has traditionally been characterized as a millisecond phenomenon, longer timescales may be possible under certain operating conditions. This study simulates the dynamic response of a previously developed solid oxide fuel cell (SOFC) stack model that incorporates the charge double layer via an equivalent circuit. The model is simulated under step load changes. Baseline conditions are first defined, followed by consideration of minor and major deviations from the baseline case. This study also investigates the behavior of the SOFC stack with a relatively large double layer capacitance value, as well as operation of the SOFC stack under proportional-integral (PI) control. Results indicate that the presence of the charge double layer influences the SOFC stack's settling time significantly under the following conditions: (i) activation and concentration polarizations are significantly increased, or (ii) a large value of the double layer capacitance is assumed. Under normal (baseline) operation, on the other hand, the charge double layer effect diminishes within milliseconds, as expected. It seems reasonable, then, to neglect the charge double layer under normal operation. However, careful consideration should be given to potential variations in operation or material properties that may give rise to longer electrochemical settling times.

Optimal fault-tolerant control strategy of a solid oxide fuel cell system

NASA Astrophysics Data System (ADS)

Wu, Xiaojuan; Gao, Danhui

2017-10-01

For solid oxide fuel cell (SOFC) development, load tracking, heat management, air excess ratio constraint, high efficiency, low cost and fault diagnosis are six key issues. However, no literature studies the control techniques combining optimization and fault diagnosis for the SOFC system. An optimal fault-tolerant control strategy is presented in this paper, which involves four parts: a fault diagnosis module, a switching module, two backup optimizers and a controller loop. The fault diagnosis part is presented to identify the SOFC current fault type, and the switching module is used to select the appropriate backup optimizer based on the diagnosis result. NSGA-II and TOPSIS are employed to design the two backup optimizers under normal and air compressor fault states. PID algorithm is proposed to design the control loop, which includes a power tracking controller, an anode inlet temperature controller, a cathode inlet temperature controller and an air excess ratio controller. The simulation results show the proposed optimal fault-tolerant control method can track the power, temperature and air excess ratio at the desired values, simultaneously achieving the maximum efficiency and the minimum unit cost in the case of SOFC normal and even in the air compressor fault.

Energy analysis of a combined solid oxide fuel cell with a steam turbine power plant for marine applications

NASA Astrophysics Data System (ADS)

Welaya, Yousri M. A.; Mosleh, M.; Ammar, Nader R.

2013-12-01

Strong restrictions on emissions from marine power plants (particularly SO x , NO x ) will probably be adopted in the near future. In this paper, a combined solid oxide fuel cell (SOFC) and steam turbine fuelled by natural gas is proposed as an attractive option to limit the environmental impact of the marine sector. The analyzed variant of the combined cycle includes a SOFC operated with natural gas fuel and a steam turbine with a single-pressure waste heat boiler. The calculations were performed for two types of tubular and planar SOFCs, each with an output power of 18 MW. This paper includes a detailed energy analysis of the combined system. Mass and energy balances are performed not only for the whole plant but also for each component in order to evaluate the thermal efficiency of the combined cycle. In addition, the effects of using natural gas as a fuel on the fuel cell voltage and performance are investigated. It has been found that a high overall efficiency approaching 60% may be achieved with an optimum configuration using the SOFC system. The hybrid system would also reduce emissions, fuel consumption, and improve the total system efficiency.

On the Nonlinear Behavior of a Glass-Ceramic Seal and its Application in Planar SOFC Systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Ba Nghiep; Koeppel, Brian J.; Vetrano, John S.

2006-06-01

This paper studies the nonlinear behavior of a glass-ceramic seal used in planar solid oxide fuel cells (SOFCs). To this end, a viscoelastic damage model has been developed that can capture the nonlinear material response due to both progressive damage in the glass-ceramic material and viscous flow of the residual glass in this material. The model has been implemented in the MSC MARC finite element code, and its validation has been carried out using the experimental relaxation test data obtained for this material at 700oC, 750oC, and 800oC. Finally, it has been applied to the simulation of a SOFC stackmore » under thermal cycling conditions. The areas of potential damage have been predicted.« less

Determination of interfacial adhesion strength between oxide scale and substrate for metallic SOFC interconnects

NASA Astrophysics Data System (ADS)

Sun, X.; Liu, W. N.; Stephens, E.; Khaleel, M. A.

The interfacial adhesion strength between the oxide scale and the substrate is crucial to the reliability and durability of metallic interconnects in solid oxide fuel cell (SOFC) operating environments. It is necessary, therefore, to establish a methodology to quantify the interfacial adhesion strength between the oxide scale and the metallic interconnect substrate, and furthermore to design and optimize the interconnect material as well as the coating materials to meet the design life of an SOFC system. In this paper, we present an integrated experimental/analytical methodology for quantifying the interfacial adhesion strength between the oxide scale and a ferritic stainless steel interconnect. Stair-stepping indentation tests are used in conjunction with subsequent finite element analyses to predict the interfacial strength between the oxide scale and Crofer 22 APU substrate.

Method of Fabrication of High Power Density Solid Oxide Fuel Cells

DOEpatents

Pham, Ai Quoc; Glass, Robert S.

2008-09-09

A method for producing ultra-high power density solid oxide fuel cells (SOFCs). The method involves the formation of a multilayer structure cells wherein a buffer layer of doped-ceria is deposited intermediate a zirconia electrolyte and a cobalt iron based electrode using a colloidal spray deposition (CSD) technique. For example, a cobalt iron based cathode composed of (La,Sr)(Co,Fe)O(LSCF) may be deposited on a zirconia electrolyte via a buffer layer of doped-ceria deposited by the CSD technique. The thus formed SOFC have a power density of 1400 mW/cm.sup.2 at 600.degree. C. and 900 mW/cm.sup.2 at 700.degree. C. which constitutes a 2-3 times increased in power density over conventionally produced SOFCs.

Recent work on material interface reconstruction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mosso, S.J.; Swartz, B.K.

1997-12-31

For the last 15 years, many Eulerian codes have relied on a series of piecewise linear interface reconstruction algorithms developed by David Youngs. In a typical Youngs` method, the material interfaces were reconstructed based upon nearly cell values of volume fractions of each material. The interfaces were locally represented by linear segments in two dimensions and by pieces of planes in three dimensions. The first step in such reconstruction was to locally approximate an interface normal. In Youngs` 3D method, a local gradient of a cell-volume-fraction function was estimated and taken to be the local interface normal. A linear interfacemore » was moved perpendicular to the now known normal until the mass behind it matched the material volume fraction for the cell in question. But for distorted or nonorthogonal meshes, the gradient normal estimate didn`t accurately match that of linear material interfaces. Moreover, curved material interfaces were also poorly represented. The authors will present some recent work in the computation of more accurate interface normals, without necessarily increasing stencil size. Their estimate of the normal is made using an iterative process that, given mass fractions for nearby cells of known but arbitrary variable density, converges in 3 or 4 passes in practice (and quadratically--like Newton`s method--in principle). The method reproduces a linear interface in both orthogonal and nonorthogonal meshes. The local linear approximation is generally 2nd-order accurate, with a 1st-order accurate normal for curved interfaces in both two and three dimensional polyhedral meshes. Recent work demonstrating the interface reconstruction for curved surfaces will /be discussed.« less

A family of position- and orientation-independent embedded boundary methods for viscous flow and fluid-structure interaction problems

NASA Astrophysics Data System (ADS)

Huang, Daniel Z.; De Santis, Dante; Farhat, Charbel

2018-07-01

The Finite Volume method with Exact two-material Riemann Problems (FIVER) is both a computational framework for multi-material flows characterized by large density jumps, and an Embedded Boundary Method (EBM) for computational fluid dynamics and highly nonlinear Fluid-Structure Interaction (FSI) problems. This paper deals with the EBM aspect of FIVER. For FSI problems, this EBM has already demonstrated the ability to address viscous effects along wall boundaries, and large deformations and topological changes of such boundaries. However, like for most EBMs - also known as immersed boundary methods - the performance of FIVER in the vicinity of a wall boundary can be sensitive with respect to the position and orientation of this boundary relative to the embedding mesh. This is mainly due to ill-conditioning issues that arise when an embedded interface becomes too close to a node of the embedding mesh, which may lead to spurious oscillations in the computed solution gradients at the wall boundary. This paper resolves these issues by introducing an alternative definition of the active/inactive status of a mesh node that leads to the removal of all sources of potential ill-conditioning from all spatial approximations performed by FIVER in the vicinity of a fluid-structure interface. It also makes two additional contributions. The first one is a new procedure for constructing the fluid-structure half Riemann problem underlying the semi-discretization by FIVER of the convective fluxes. This procedure eliminates one extrapolation from the conventional treatment of the wall boundary conditions and replaces it by an interpolation, which improves robustness. The second contribution is a post-processing algorithm for computing quantities of interest at the wall that achieves smoothness in the computed solution and its gradients. Lessons learned from these enhancements and contributions that are triggered by the new definition of the status of a mesh node are then generalized and exploited to eliminate from the original version of the FIVER method its sensitivities with respect to both of the position and orientation of the wall boundary relative to the embedding mesh, while maintaining the original definition of the status of a mesh node. This leads to a family of second-generation FIVER methods whose performance is illustrated in this paper for several flow and FSI problems. These include a challenging flow problem over a bird wing characterized by a feather-induced surface roughness, and a complex flexible flapping wing problem for which experimental data is available.

Direct energy conversion bottoming cycles for solid oxide fuel cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paramonov, D.V.; Carelli, M.D.

1998-07-01

Besides high conversion efficiency, advantages of Solid Oxide Fuel Cell (SOFC) include ability of low pressure operation, absence of moving parts and resulting inherently low maintenance requirements, modularity, long lifetime and unattended operation. A further increase in the conversion efficiency, without compromising the advantages inherent with static devices, can be achieved by employing a direct energy conversion bottoming cycle. The biggest challenges in the integration of direct energy conversion devices with SOFC are: (a) the need to preheat the SOFC feed air while maximizing the bottoming cycle power, and (b) limited temperature of the SOFC exhaust. These restrictions limit themore » choice to the Alkali Metal Thermal to Electric Conversion (AMTEC) and Thermoelectric (TE) technologies while eliminating thermionics and thermophotovoltaics. In addition to the aforementioned advantages, the SOFC-AMTEC and SOFC-TE cycles are attractive for certain applications such as cogeneration and power supplies for remote locations where the use of higher efficiency dynamic bottoming cycles might be undesirable due to maintenance and noise restrictions. A preliminary feasibility assessment of AMTEC and TE bottoming of SOFC power systems has been performed. Five SOFC bottoming cycle concepts were considered. They include: TE bottoming with cogeneration capability, TE bottoming with additional heat recovery, TE bottoming with uncoupled TE converter and air preheater, AMTEC bottoming, and Cascaded AMTEC-TE bottoming. The cascaded AMTEC-TE bottoming cycle increases the overall cycle efficiency by 4.7 percentage points. TE bottoming cycle with additional heat recovery adds 3.8 percentage points, and the other concepts are between 3 and 3.5 percentage points. The results are also compared with results of similar studies reported in literature. The AMTEC-TE cascade has the largest potential, however, development of both AMTEC and TE components would be required. The second best option from the efficiency point of view is the TE bottoming with additional heat recovery which would require development of only the TE component. Despite that fact that AMTEC is generally perceived as more efficient than thermoelectrics, efficiencies of the considered AMTEC and TE bottoming cycles are almost equal. The reason is that the somewhat more efficient AMTEC requires relatively high hot side temperature ({gt}850--900 K) and, at the same time, air has to be preheated to 973 K. (This is equally true for a high efficiency TE converter operating at the highest hot side to cold side temperature difference possible). As a result, only a small fraction ({lt}30 %) of the total heat available is directed to the bottoming cycle where it is converted with relatively high efficiency. When a TE converter operating in a wider hot side temperature range, but at a smaller hot side--cold side temperature difference is employed, its lower efficiency is offset by its larger thermal power and the overall bottoming cycle efficiency changes insignificantly.« less

Solving of the coefficient inverse problems for a nonlinear singularly perturbed reaction-diffusion-advection equation with the final time data

NASA Astrophysics Data System (ADS)

Lukyanenko, D. V.; Shishlenin, M. A.; Volkov, V. T.

2018-01-01

We propose the numerical method for solving coefficient inverse problem for a nonlinear singularly perturbed reaction-diffusion-advection equation with the final time observation data based on the asymptotic analysis and the gradient method. Asymptotic analysis allows us to extract a priory information about interior layer (moving front), which appears in the direct problem, and boundary layers, which appear in the conjugate problem. We describe and implement the method of constructing a dynamically adapted mesh based on this a priory information. The dynamically adapted mesh significantly reduces the complexity of the numerical calculations and improve the numerical stability in comparison with the usual approaches. Numerical example shows the effectiveness of the proposed method.

Thermodynamic stability of perovskite and lanthanum nickelate-type cathode materials for solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Cetin, Deniz

The need for cleaner and more efficient alternative energy sources is becoming urgent as concerns mount about climate change wrought by greenhouse gas emissions. Solid oxide fuel cells (SOFCs) are one of the most efficient options if the goal is to reduce emissions while still operating on fossil energy resources. One of the foremost problems in SOFCs that causes efficiency loss is the polarization resistance associated with the oxygen reduction reaction(ORR) at the cathodes. Hence, improving the cathode design will greatly enhance the overall performance of SOFCs. Lanthanum nickelate, La2NiO4+delta (LNO), is a mixed ionic and electronic conductor that has competitive surface oxygen exchange and transport properties and excellent electrical conductivity compared to perovskite-type oxides. This makes it an excellent candidate for solid oxide fuel cell (SOFC) applications. It has been previously shown that composites of LNO with Sm0.2Ce0.8O2-delta (SDC20) as cathode materials lead to higher performance than standalone LNO. However, in contact with lanthanide-doped ceria, LNO decomposes resulting in free NiO and ceria with higher lanthanide dopant concentration. In this study, the aforementioned instability of LNO has been addressed by compositional tailoring of LNO: lanthanide doped ceria (LnxCe 1-xO2,LnDC)composite. By increasing the lanthanide dopant concentration in the ceria phase close to its solubility limit, the LNO phase has been stabilized in the LNO:LnDC composites. Electrical conductivity of the composites as a function of LNO volume fraction and temperature has been measured, and analyzed using a resistive network model which allows the identification of a percolation threshold for the LNO phase. The thermomechanical compatibility of these composites has been investigated with SOFC systems through measurement of the coefficients of thermal expansion. LNO:LDC40 composites containing LNO lower than 50 vol%and higher than 40 vol% were identified as being suitable to incorporate into full button cell configuration from the standpoint of thermomechanical stability and adequate electrical conductivity. Proof-of-concept performance comparison for SOFC button cells manufactured using LNO: La 0.4Ce0.6O2-delta composite to the conventional composite cathode materials has also been provided. This thermodynamics-based phase stabilization strategy can be applied to a wider range of materials in the same crystallographic family, thus providing the SOFC community with alternate material options for high performance devices.

Asynchronous variational integration using continuous assumed gradient elements.

PubMed

Wolff, Sebastian; Bucher, Christian

2013-03-01

Asynchronous variational integration (AVI) is a tool which improves the numerical efficiency of explicit time stepping schemes when applied to finite element meshes with local spatial refinement. This is achieved by associating an individual time step length to each spatial domain. Furthermore, long-term stability is ensured by its variational structure. This article presents AVI in the context of finite elements based on a weakened weak form (W2) Liu (2009) [1], exemplified by continuous assumed gradient elements Wolff and Bucher (2011) [2]. The article presents the main ideas of the modified AVI, gives implementation notes and a recipe for estimating the critical time step.

Molybdenum dioxide-based anode for solid oxide fuel cell applications

NASA Astrophysics Data System (ADS)

Kwon, Byeong Wan; Ellefson, Caleb; Breit, Joe; Kim, Jinsoo; Grant Norton, M.; Ha, Su

2013-12-01

The present paper describes the fabrication and performance of a molybdenum dioxide (MoO2)-based anode for liquid hydrocarbon/oxygenated hydrocarbon-fueled solid oxide fuel cells (SOFCs). These fuel cells first internally reform the complex liquid fuel into carbon fragments and hydrogen, which are then electrochemically oxidized to produce electrical energy without external fuel processors. The MoO2-based anode was fabricated on to an yttria-stabilized zirconia (YSZ) electrolyte via combined electrostatic spray deposition (ESD) and direct painting methods. The cell performance was measured by directly feeding liquid fuels such as n-dodecane (i.e., a model diesel/kerosene fuel) or biodiesel (i.e., a future biomass-based liquid fuel) to the MoO2-based anode at 850 °C. The maximum initial power densities obtained from our MoO2-based SOFC were 34 mW cm-2 and 45 mW cm-2 using n-dodecane and biodiesel, respectively. The initial power density of the MoO2-based SOFC was improved up to 2500 mW cm-2 by optimizing the porosity of the MoO2-based anode. To test the long-term stability of the MoO2-based anode SOFC against coking, n-dodecane was continuously fed into the cell for 24 h at the open circuit voltage (OCV). During long-term testing, voltage-current density (V-I) plots were periodically obtained and they showed no significant changes over the operation time. Microstructural examination of the tested cells indicated that the MoO2-based anode displayed negligible coke formation, which explains its stability. On the other hand, SOFCs with conventional nickel (Ni)-based anodes under the same operating conditions showed a significant amount of coke formation on the metal surface, which led to a rapid drop in cell performance. Hence, the present work demonstrates that MoO2-based anodes exhibit outstanding tolerance to coke formation. This result opens up the opportunity for more efficiently generating electrical energy from both existing transportation and next generation biomass-derived liquid fuels using liquid hydrocarbon/oxygenated hydrocarbon-fueled SOFCs.

Electric terminal performance and characterization of solid oxide fuel cells and systems

NASA Astrophysics Data System (ADS)

Lindahl, Peter Allan

Solid Oxide Fuel Cells (SOFCs) are electrochemical devices which can effect efficient, clean, and quiet conversion of chemical to electrical energy. In contrast to conventional electricity generation systems which feature multiple discrete energy conversion processes, SOFCs are direct energy conversion devices. That is, they feature a fully integrated chemical to electrical energy conversion process where the electric load demanded of the cell intrinsically drives the electrochemical reactions and associated processes internal to the cell. As a result, the cell's electric terminals provide a path for interaction between load side electric demand and the conversion side processes. The implication of this is twofold. First, the magnitude and dynamic characteristics of the electric load demanded of the cell can directly impact the long-term efficacy of the cell's chemical to electrical energy conversion. Second, the electric terminal response to dynamic loads can be exploited for monitoring the cell's conversion side processes and used in diagnostic analysis and degradation-mitigating control schemes. This dissertation presents a multi-tier investigation into this electric terminal based performance characterization of SOFCs through the development of novel test systems, analysis techniques and control schemes. First, a reference-based simulation system is introduced. This system scales up the electric terminal performance of a prototype SOFC system, e.g. a single fuel cell, to that of a full power-level stack. This allows realistic stack/load interaction studies while maintaining explicit ability for post-test analysis of the prototype system. Next, a time-domain least squares fitting method for electrochemical impedance spectroscopy (EIS) is developed for reduced-time monitoring of the electrochemical and physicochemical mechanics of the fuel cell through its electric terminals. The utility of the reference-based simulator and the EIS technique are demonstrated through their combined use in the performance testing of a hybrid-source power management (HSPM) system designed to allow in-situ EIS monitoring of a stack under dynamic loading conditions. The results from the latter study suggest that an HSPM controller allows an opportunity for in-situ electric terminal monitoring and control-based mitigation of SOFC degradation. As such, an exploration of control-based SOFC degradation mitigation is presented and ideas for further work are suggested.

Fertilization capacity of cryopreserved Iberian ibex epididymal sperm in a heterologous in vitro fertilization assay.

PubMed

López-Saucedo, J; Santiago-Moreno, J; Fierro, R; Izquierdo, D; Coloma, M A; Catalá, M G; Jiménez, I; Paramio, M T

2015-02-01

In vitro fertilization (IVF) can be used to assess the fertilization capacity of sperm. Heterologous IVF may be useful when assessing that of wild animals as it is often difficult to obtain adequate numbers of naturally corresponding oocytes. The aim of the present study was to assess the fertilization capacity of frozen-thawed ibex epididymal spermatozoa via heterologous IVF involving the oocytes of prepubertal domestic goats. The effect on fertilization and embryo development of adding oestrous sheep serum (ESS) to the fertilization medium was also examined. Cumulus-oocyte complexes (COCs) were matured in TCM-199 for 24-27 h at 38.5°C in a 5% CO2 in air atmosphere. Frozen-thawed epididymal spermatozoa were selected by density gradient centrifugation. After maturation, the oocytes were co-incubated with spermatozoa in synthetic oviductal fluid (SOF) with different concentrations of ESS: SOF-C (0%), SOF-2 (2%) and SOF-20 (20%). At 17 h post-insemination (hpi), zygotes with one female and one male pronucleus (2PN) were categorised as normal; zygotes with 3PN were recorded as polyspermic, and oocytes with 1PN as asynchronous. Cleavage and blastocyst development were assessed at 48 and 168 hpi respectively. The percentage of zygotes with 2PN was higher in the SOF-2 than in the SOF-20 treatment group (27.7% versus 2.9% P < 0.05). The percentage of blastocysts formed with the SOF-C, SOF-2 and SOF-20 treatments were 1.1%, 7.5% and 0% respectively. These results show that the presence of 2% ESS achieves better results than the use of no serum or the standard 20% concentration. Heterologous IVF may be an effective method for predicting the fertilization capacity of ibex spermatozoa, and therefore perhaps that of other wild mountain ungulates.

Compact Ceramic Microchannel Heat Exchangers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lewinsohn, Charles

The objective of the proposed work was to demonstrate the feasibility of a step change in power plant efficiency at a commercially viable cost, by obtaining performance data for prototype, compact, ceramic microchannel heat exchangers. By performing the tasks described in the initial proposal, all of the milestones were met. The work performed will advance the technology from Technology Readiness Level 3 (TRL 3) to Technology Readiness Level 4 (TRL 4) and validate the potential of using these heat exchangers for enabling high efficiency solid oxide fuel cell (SOFC) or high-temperature turbine-based power plants. The attached report will describe howmore » this objective was met. In collaboration with The Colorado School of Mines (CSM), specifications were developed for a high temperature heat exchanger for three commercial microturbines. Microturbines were selected because they are a more mature commercial technology than SOFC, they are a low-volume and high-value target for market entry of high-temperature heat exchangers, and they are essentially scaled-down versions of turbines used in utility-scale power plants. Using these specifications, microchannel dimensions were selected to meet the performance requirements. Ceramic plates were fabricated with microchannels of these dimensions. The plates were tested at room temperature and elevated temperature. Plates were joined together to make modular, heat exchanger stacks that were tested at a variety of temperatures and flow rates. Although gas flow rates equivalent to those in microturbines could not be achieved in the laboratory environment, the results showed expected efficiencies, robust operation under significant temperature gradients at high temperature, and the ability to cycle the stacks. Details of the methods and results are presented in this final report.« less

Practical implementation of tetrahedral mesh reconstruction in emission tomography

PubMed Central

Boutchko, R.; Sitek, A.; Gullberg, G. T.

2014-01-01

This paper presents a practical implementation of image reconstruction on tetrahedral meshes optimized for emission computed tomography with parallel beam geometry. Tetrahedral mesh built on a point cloud is a convenient image representation method, intrinsically three-dimensional and with a multi-level resolution property. Image intensities are defined at the mesh nodes and linearly interpolated inside each tetrahedron. For the given mesh geometry, the intensities can be computed directly from tomographic projections using iterative reconstruction algorithms with a system matrix calculated using an exact analytical formula. The mesh geometry is optimized for a specific patient using a two stage process. First, a noisy image is reconstructed on a finely-spaced uniform cloud. Then, the geometry of the representation is adaptively transformed through boundary-preserving node motion and elimination. Nodes are removed in constant intensity regions, merged along the boundaries, and moved in the direction of the mean local intensity gradient in order to provide higher node density in the boundary regions. Attenuation correction and detector geometric response are included in the system matrix. Once the mesh geometry is optimized, it is used to generate the final system matrix for ML-EM reconstruction of node intensities and for visualization of the reconstructed images. In dynamic PET or SPECT imaging, the system matrix generation procedure is performed using a quasi-static sinogram, generated by summing projection data from multiple time frames. This system matrix is then used to reconstruct the individual time frame projections. Performance of the new method is evaluated by reconstructing simulated projections of the NCAT phantom and the method is then applied to dynamic SPECT phantom and patient studies and to a dynamic microPET rat study. Tetrahedral mesh-based images are compared to the standard voxel-based reconstruction for both high and low signal-to-noise ratio projection datasets. The results demonstrate that the reconstructed images represented as tetrahedral meshes based on point clouds offer image quality comparable to that achievable using a standard voxel grid while allowing substantial reduction in the number of unknown intensities to be reconstructed and reducing the noise. PMID:23588373

Simulation of geothermal water extraction in heterogeneous reservoirs using dynamic unstructured mesh optimisation

NASA Astrophysics Data System (ADS)

Salinas, P.; Pavlidis, D.; Jacquemyn, C.; Lei, Q.; Xie, Z.; Pain, C.; Jackson, M.

2017-12-01

It is well known that the pressure gradient into a production well increases with decreasing distance to the well. To properly capture the local pressure drawdown into the well a high grid or mesh resolution is required; moreover, the location of the well must be captured accurately. In conventional simulation models, the user must interact with the model to modify grid resolution around wells of interest, and the well location is approximated on a grid defined early in the modelling process.We report a new approach for improved simulation of near wellbore flow in reservoir scale models through the use of dynamic mesh optimisation and the recently presented double control volume finite element method. Time is discretized using an adaptive, implicit approach. Heterogeneous geologic features are represented as volumes bounded by surfaces. Within these volumes, termed geologic domains, the material properties are constant. Up-, cross- or down-scaling of material properties during dynamic mesh optimization is not required, as the properties are uniform within each geologic domain. A given model typically contains numerous such geologic domains. Wells are implicitly coupled with the domain, and the fluid flows is modelled inside the wells. The method is novel for two reasons. First, a fully unstructured tetrahedral mesh is used to discretize space, and the spatial location of the well is specified via a line vector, ensuring its location even if the mesh is modified during the simulation. The well location is therefore accurately captured, the approach allows complex well trajectories and wells with many laterals to be modelled. Second, computational efficiency is increased by use of dynamic mesh optimization, in which an unstructured mesh adapts in space and time to key solution fields (preserving the geometry of the geologic domains), such as pressure, velocity or temperature, this also increases the quality of the solutions by placing higher resolution where required to reduce an error metric based on the Hessian of the field. This allows the local pressure drawdown to be captured without user¬ driven modification of the mesh. We demonstrate that the method has wide application in reservoir ¬scale models of geothermal fields, and regional models of groundwater resources.

Practical implementation of tetrahedral mesh reconstruction in emission tomography

NASA Astrophysics Data System (ADS)

Boutchko, R.; Sitek, A.; Gullberg, G. T.

2013-05-01

This paper presents a practical implementation of image reconstruction on tetrahedral meshes optimized for emission computed tomography with parallel beam geometry. Tetrahedral mesh built on a point cloud is a convenient image representation method, intrinsically three-dimensional and with a multi-level resolution property. Image intensities are defined at the mesh nodes and linearly interpolated inside each tetrahedron. For the given mesh geometry, the intensities can be computed directly from tomographic projections using iterative reconstruction algorithms with a system matrix calculated using an exact analytical formula. The mesh geometry is optimized for a specific patient using a two stage process. First, a noisy image is reconstructed on a finely-spaced uniform cloud. Then, the geometry of the representation is adaptively transformed through boundary-preserving node motion and elimination. Nodes are removed in constant intensity regions, merged along the boundaries, and moved in the direction of the mean local intensity gradient in order to provide higher node density in the boundary regions. Attenuation correction and detector geometric response are included in the system matrix. Once the mesh geometry is optimized, it is used to generate the final system matrix for ML-EM reconstruction of node intensities and for visualization of the reconstructed images. In dynamic PET or SPECT imaging, the system matrix generation procedure is performed using a quasi-static sinogram, generated by summing projection data from multiple time frames. This system matrix is then used to reconstruct the individual time frame projections. Performance of the new method is evaluated by reconstructing simulated projections of the NCAT phantom and the method is then applied to dynamic SPECT phantom and patient studies and to a dynamic microPET rat study. Tetrahedral mesh-based images are compared to the standard voxel-based reconstruction for both high and low signal-to-noise ratio projection datasets. The results demonstrate that the reconstructed images represented as tetrahedral meshes based on point clouds offer image quality comparable to that achievable using a standard voxel grid while allowing substantial reduction in the number of unknown intensities to be reconstructed and reducing the noise.

Strength and Fracture Toughness of Solid Oxide Fuel Cell Electrolyte Material Improved

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Choi, Sung R.

2002-01-01

Solid oxide fuel cells (SOFC) are being developed for various applications in the automobile, power-generation, and aeronautics industries. Recently, the NASA Glenn Research Center has been exploring the possibility of using SOFC's for aeropropulsion under its Zero Carbon Dioxide Emission Technology (ZCET) Program. 10-mol% yttriastabilized zirconia (10YSZ) is a very good anionic conductor at high temperatures and is, therefore, used as an oxygen solid electrolyte in SOFC. However, it has a high thermal expansion coefficient, low thermal shock resistance, low fracture toughness, and poor mechanical strength. For aeronautic applications, the thin ceramic electrolyte membrane of the SOFC needs to be strong and tough. Therefore, we have been investigating the possibility of enhancing the strength and fracture toughness of the 10YSZ electrolyte without degrading its electrical conductivity to an appreciable extent. We recently demonstrated that the addition of alumina to zirconia electrolyte increases its strength as well as its fracture toughness. Zirconia-alumina composites containing 0 to 30 mol% of alumina were fabricated by hot pressing. The hot pressing procedure was developed and various hot pressing parameters were optimized, resulting in dense, crackfree panels of composite materials. Cubic zirconia and a-alumina were the only phases detected, indicating that there was no chemical reaction between the constituents during hot pressing at elevated temperatures. Flexure strength sf and fracture toughness K(sub IC) of the various zirconia-alumina composites were measured at room temperature as well as at 1000 C in air. Both properties showed systematic improvement with increased alumina addition at room temperature and at 1000 C. Use of these modified electrolytes with improved strength and fracture toughness should prolong the life and enhance the performance of SOFC in aeronautics and other applications.

Micro solid oxide fuel cell fabricated on porous stainless steel: a new strategy for enhanced thermal cycling ability

PubMed Central

Kim, Kun Joong; Park, Byung Hyun; Kim, Sun Jae; Lee, Younki; Bae, Hongyeul; Choi, Gyeong Man

2016-01-01

Miniaturized solid oxide fuel cells (micro-SOFCs) are being extensively studied as a promising alternative to Li batteries for next generation portable power. A new micro-SOFC is designed and fabricated which shows enhanced thermal robustness by employing oxide-based thin-film electrode and porous stainless steel (STS) substrate. To deposit gas-tight thin-film electrolyte on STS, nano-porous composite oxide is proposed and applied as a new contact layer on STS. The micro-SOFC fabricated on composite oxide- STS dual layer substrate shows the peak power density of 560 mW cm−2 at 550 °C and maintains this power density during rapid thermal cycles. This cell may be suitable for portable electronic device that requires high power-density and fast thermal cycling. PMID:26928921

The thermomechanical stability of micro-solid oxide fuel cells fabricated on anodized aluminum oxide membranes

NASA Astrophysics Data System (ADS)

Kwon, Chang-Woo; Lee, Jae-Il; Kim, Ki-Bum; Lee, Hae-Weon; Lee, Jong-Ho; Son, Ji-Won

2012-07-01

The thermomechanical stability of micro-solid oxide fuel cells (micro-SOFCs) fabricated on an anodized aluminum oxide (AAO) membrane template is investigated. The full structure consists of the following layers: AAO membrane (600 nm)/Pt anode/YSZ electrolyte (900 nm)/porous Pt cathode. The utilization of a 600-nm-thick AAO membrane significantly improves the thermomechanical stability due to its well-known honeycomb-shaped nanopore structure. Moreover, the Pt anode layer deposited in between the AAO membrane and the YSZ electrolyte preserves its integrity in terms of maintaining the triple-phase boundary (TPB) and electrical conductivity during high-temperature operation. Both of these results guarantee thermomechanical stability of the micro-SOFC and extend the cell lifetime, which is one of the most critical issues in the fabrication of freestanding membrane-type micro-SOFCs.

Identification of a Methane Oxidation Intermediate on Solid Oxide Fuel Cell Anode Surfaces with Fourier Transform Infrared Emission.

PubMed

Pomfret, Michael B; Steinhurst, Daniel A; Owrutsky, Jeffrey C

2013-04-18

Fuel interactions on solid oxide fuel cell (SOFC) anodes are studied with in situ Fourier transform infrared emission spectroscopy (FTIRES). SOFCs are operated at 800 °C with CH4 as a representative hydrocarbon fuel. IR signatures of gas-phase oxidation products, CO2(g) and CO(g), are observed while cells are under load. A broad feature at 2295 cm(-1) is assigned to CO2 adsorbed on Ni as a CH4 oxidation intermediate during cell operation and while carbon deposits are electrochemically oxidized after CH4 operation. Electrochemical control provides confirmation of the assignment of adsorbed CO2. FTIRES has been demonstrated as a viable technique for the identification of fuel oxidation intermediates and products in working SOFCs, allowing for the elucidation of the mechanisms of fuel chemistry.

Micro solid oxide fuel cell fabricated on porous stainless steel: a new strategy for enhanced thermal cycling ability.

PubMed

Kim, Kun Joong; Park, Byung Hyun; Kim, Sun Jae; Lee, Younki; Bae, Hongyeul; Choi, Gyeong Man

2016-03-01

Miniaturized solid oxide fuel cells (micro-SOFCs) are being extensively studied as a promising alternative to Li batteries for next generation portable power. A new micro-SOFC is designed and fabricated which shows enhanced thermal robustness by employing oxide-based thin-film electrode and porous stainless steel (STS) substrate. To deposit gas-tight thin-film electrolyte on STS, nano-porous composite oxide is proposed and applied as a new contact layer on STS. The micro-SOFC fabricated on composite oxide- STS dual layer substrate shows the peak power density of 560 mW cm(-2) at 550 °C and maintains this power density during rapid thermal cycles. This cell may be suitable for portable electronic device that requires high power-density and fast thermal cycling.

Development of a Solid-Oxide Fuel Cell/Gas Turbine Hybrid System Model for Aerospace Applications

NASA Technical Reports Server (NTRS)

Freeh, Joshua E.; Pratt, Joseph W.; Brouwer, Jacob

2004-01-01

Recent interest in fuel cell-gas turbine hybrid applications for the aerospace industry has led to the need for accurate computer simulation models to aid in system design and performance evaluation. To meet this requirement, solid oxide fuel cell (SOFC) and fuel processor models have been developed and incorporated into the Numerical Propulsion Systems Simulation (NPSS) software package. The SOFC and reformer models solve systems of equations governing steady-state performance using common theoretical and semi-empirical terms. An example hybrid configuration is presented that demonstrates the new capability as well as the interaction with pre-existing gas turbine and heat exchanger models. Finally, a comparison of calculated SOFC performance with experimental data is presented to demonstrate model validity. Keywords: Solid Oxide Fuel Cell, Reformer, System Model, Aerospace, Hybrid System, NPSS

Large scale generation of micro-droplet array by vapor condensation on mesh screen piece

PubMed Central

Xie, Jian; Xu, Jinliang; He, Xiaotian; Liu, Qi

2017-01-01

We developed a novel micro-droplet array system, which is based on the distinct three dimensional mesh screen structure and sintering and oxidation induced thermal-fluid performance. Mesh screen was sintered on a copper substrate by bonding the two components. Non-uniform residue stress is generated along weft wires, with larger stress on weft wire top location than elsewhere. Oxidation of the sintered package forms micro pits with few nanograsses on weft wire top location, due to the stress corrosion mechanism. Nanograsses grow elsewhere to show hydrophobic behavior. Thus, surface-energy-gradient weft wires are formed. Cooling the structure in a wet air environment nucleates water droplets on weft wire top location, which is more “hydrophilic” than elsewhere. Droplet size is well controlled by substrate temperature, air humidity and cooling time. Because warp wires do not contact copper substrate and there is a larger conductive thermal resistance between warp wire and weft wire, warp wires contribute less to condensation but function as supporting structure. The surface energy analysis of drops along weft wires explains why droplet array can be generated on the mesh screen piece. Because the commercial material is used, the droplet system is cost effective and can be used for large scale utilization. PMID:28054635

Large scale generation of micro-droplet array by vapor condensation on mesh screen piece.

PubMed

Xie, Jian; Xu, Jinliang; He, Xiaotian; Liu, Qi

2017-01-05

We developed a novel micro-droplet array system, which is based on the distinct three dimensional mesh screen structure and sintering and oxidation induced thermal-fluid performance. Mesh screen was sintered on a copper substrate by bonding the two components. Non-uniform residue stress is generated along weft wires, with larger stress on weft wire top location than elsewhere. Oxidation of the sintered package forms micro pits with few nanograsses on weft wire top location, due to the stress corrosion mechanism. Nanograsses grow elsewhere to show hydrophobic behavior. Thus, surface-energy-gradient weft wires are formed. Cooling the structure in a wet air environment nucleates water droplets on weft wire top location, which is more "hydrophilic" than elsewhere. Droplet size is well controlled by substrate temperature, air humidity and cooling time. Because warp wires do not contact copper substrate and there is a larger conductive thermal resistance between warp wire and weft wire, warp wires contribute less to condensation but function as supporting structure. The surface energy analysis of drops along weft wires explains why droplet array can be generated on the mesh screen piece. Because the commercial material is used, the droplet system is cost effective and can be used for large scale utilization.

Large scale generation of micro-droplet array by vapor condensation on mesh screen piece

NASA Astrophysics Data System (ADS)

Xie, Jian; Xu, Jinliang; He, Xiaotian; Liu, Qi

2017-01-01

We developed a novel micro-droplet array system, which is based on the distinct three dimensional mesh screen structure and sintering and oxidation induced thermal-fluid performance. Mesh screen was sintered on a copper substrate by bonding the two components. Non-uniform residue stress is generated along weft wires, with larger stress on weft wire top location than elsewhere. Oxidation of the sintered package forms micro pits with few nanograsses on weft wire top location, due to the stress corrosion mechanism. Nanograsses grow elsewhere to show hydrophobic behavior. Thus, surface-energy-gradient weft wires are formed. Cooling the structure in a wet air environment nucleates water droplets on weft wire top location, which is more “hydrophilic” than elsewhere. Droplet size is well controlled by substrate temperature, air humidity and cooling time. Because warp wires do not contact copper substrate and there is a larger conductive thermal resistance between warp wire and weft wire, warp wires contribute less to condensation but function as supporting structure. The surface energy analysis of drops along weft wires explains why droplet array can be generated on the mesh screen piece. Because the commercial material is used, the droplet system is cost effective and can be used for large scale utilization.

An optimization-based approach for high-order accurate discretization of conservation laws with discontinuous solutions

NASA Astrophysics Data System (ADS)

Zahr, M. J.; Persson, P.-O.

2018-07-01

This work introduces a novel discontinuity-tracking framework for resolving discontinuous solutions of conservation laws with high-order numerical discretizations that support inter-element solution discontinuities, such as discontinuous Galerkin or finite volume methods. The proposed method aims to align inter-element boundaries with discontinuities in the solution by deforming the computational mesh. A discontinuity-aligned mesh ensures the discontinuity is represented through inter-element jumps while smooth basis functions interior to elements are only used to approximate smooth regions of the solution, thereby avoiding Gibbs' phenomena that create well-known stability issues. Therefore, very coarse high-order discretizations accurately resolve the piecewise smooth solution throughout the domain, provided the discontinuity is tracked. Central to the proposed discontinuity-tracking framework is a discrete PDE-constrained optimization formulation that simultaneously aligns the computational mesh with discontinuities in the solution and solves the discretized conservation law on this mesh. The optimization objective is taken as a combination of the deviation of the finite-dimensional solution from its element-wise average and a mesh distortion metric to simultaneously penalize Gibbs' phenomena and distorted meshes. It will be shown that our objective function satisfies two critical properties that are required for this discontinuity-tracking framework to be practical: (1) possesses a local minima at a discontinuity-aligned mesh and (2) decreases monotonically to this minimum in a neighborhood of radius approximately h / 2, whereas other popular discontinuity indicators fail to satisfy the latter. Another important contribution of this work is the observation that traditional reduced space PDE-constrained optimization solvers that repeatedly solve the conservation law at various mesh configurations are not viable in this context since severe overshoot and undershoot in the solution, i.e., Gibbs' phenomena, may make it impossible to solve the discrete conservation law on non-aligned meshes. Therefore, we advocate a gradient-based, full space solver where the mesh and conservation law solution converge to their optimal values simultaneously and therefore never require the solution of the discrete conservation law on a non-aligned mesh. The merit of the proposed method is demonstrated on a number of one- and two-dimensional model problems including the L2 projection of discontinuous functions, Burgers' equation with a discontinuous source term, transonic flow through a nozzle, and supersonic flow around a bluff body. We demonstrate optimal O (h p + 1) convergence rates in the L1 norm for up to polynomial order p = 6 and show that accurate solutions can be obtained on extremely coarse meshes.

In situ, simultaneous thermal imaging and infrared molecular emission studies of solid oxide fuel cell electrodes

NASA Astrophysics Data System (ADS)

Kirtley, J. D.; Qadri, S. N.; Steinhurst, D. A.; Owrutsky, J. C.

2016-12-01

Various in situ probes of solid oxide fuel cells (SOFCs) have advanced recently to provide detailed, real time data regarding materials and chemical processes that relate to device performance and degradation. These techniques offer insights into complex fuel chemistry at the anode in particular, especially in the context of model predictions. However, cell-to-cell variations can hinder mechanistic interpretations of measurements from separate, independent techniques. The present study describes an in situ technique that for the first time simultaneously measures surface temperature changes using near infrared thermal imaging and gas species using Fourier-transform infrared emission spectra at the anodes of operating SOFCs. Electrolyte-supported SOFCs with Ni-based anodes are operated at 700 °C with internal, dry-reformed methane at 75% maximum current and at open circuit voltage (OCV) while electrochemical and optical measurements are collected. At OCV, more cooling is observed coincident with more CO reforming products. Under load, CO decreases while the anode cools less, especially near the current collectors. The extent of cooling is more sensitive to polarization for electrolyte-supported cells because their anodes are thinner relative to anode-supported cells. This study exemplifies how this duplex technique can be a useful probe of electrochemical processes in SOFCs.

Anode regeneration following carbon depositions in an industrial-sized anode supported solid oxide fuel cell operating on synthetic diesel reformate

NASA Astrophysics Data System (ADS)

Subotić, Vanja; Schluckner, Christoph; Mathe, Jörg; Rechberger, Jürgen; Schroettner, Hartmuth; Hochenauer, Christoph

2015-11-01

Carbon deposition is a primary concern during operation of solid oxide fuel cells (SOFCs) fueled with carbon-containing fuels. It leads to cell degradation and thus reduces SOFC sustained operation and durability. This paper reports on an experimental investigation of carbon formation on the nickel/yttria-stabilized zirconia (Ni/YSZ) anode of an anode-supported SOFC and its regeneration. The cell was fueled with a synthetically produced diesel reformate to investigate and simulate the cell behavior under real operating conditions. For this purpose the cell was operated under load to determine the critical operating time. Rapid carbon generation, such as at open circuit voltage (OCV), can be prevented when the cell is under load. Carbon depositions were detected using scanning electron microscopy (SEM) and further analyzed by Raman spectroscopy. Industrial-size cells suitable for commercial applications were studied. This study proves the reversibility of carbon formation and the reproducibility of the regeneration process. It shows that carbon formations can be recognized and effectively, fully and cell-protecting regenerated. It indicates the excellent possibility of using SOFCs in the automotive industry as an auxiliary power unit (APU) or combined power-heat unit, operated with diesel reformate, without danger from cell degradation caused by carbon-containing fuels.

Performance and economic assessments of a solid oxide fuel cell system with a two-step ethanol-steam-reforming process using CaO sorbent

NASA Astrophysics Data System (ADS)

Tippawan, Phanicha; Arpornwichanop, Amornchai

2016-02-01

The hydrogen production process is known to be important to a fuel cell system. In this study, a carbon-free hydrogen production process is proposed by using a two-step ethanol-steam-reforming procedure, which consists of ethanol dehydrogenation and steam reforming, as a fuel processor in the solid oxide fuel cell (SOFC) system. An addition of CaO in the reformer for CO2 capture is also considered to enhance the hydrogen production. The performance of the SOFC system is analyzed under thermally self-sufficient conditions in terms of the technical and economic aspects. The simulation results show that the two-step reforming process can be run in the operating window without carbon formation. The addition of CaO in the steam reformer, which runs at a steam-to-ethanol ratio of 5, temperature of 900 K and atmospheric pressure, minimizes the presence of CO2; 93% CO2 is removed from the steam-reforming environment. This factor causes an increase in the SOFC power density of 6.62%. Although the economic analysis shows that the proposed fuel processor provides a higher capital cost, it offers a reducing active area of the SOFC stack and the most favorable process economics in term of net cost saving.

Dynamic modeling and evaluation of solid oxide fuel cell - combined heat and power system operating strategies

NASA Astrophysics Data System (ADS)

Nanaeda, Kimihiro; Mueller, Fabian; Brouwer, Jacob; Samuelsen, Scott

Operating strategies of solid oxide fuel cell (SOFC) combined heat and power (CHP) systems are developed and evaluated from a utility, and end-user perspective using a fully integrated SOFC-CHP system dynamic model that resolves the physical states, thermal integration and overall efficiency of the system. The model can be modified for any SOFC-CHP system, but the present analysis is applied to a hotel in southern California based on measured electric and heating loads. Analysis indicates that combined heat and power systems can be operated to benefit both the end-users and the utility, providing more efficient electric generation as well as grid ancillary services, namely dispatchable urban power. Design and operating strategies considered in the paper include optimal sizing of the fuel cell, thermal energy storage to dispatch heat, and operating the fuel cell to provide flexible grid power. Analysis results indicate that with a 13.1% average increase in price-of-electricity (POE), the system can provide the grid with a 50% operating range of dispatchable urban power at an overall thermal efficiency of 80%. This grid-support operating mode increases the operational flexibility of the SOFC-CHP system, which may make the technology an important utility asset for accommodating the increased penetration of intermittent renewable power.

Advances in catalysts for internal reforming in high temperature fuel cells

NASA Astrophysics Data System (ADS)

Dicks, A. L.

Catalytic steam reforming of natural gas is an attractive method of producing the hydrogen required by the present generation of fuel cells. The molten carbonate (MCFC) and solid oxide (SOFC) fuel cells operate at high enough temperatures for the endothermic steam reforming reaction to be carried out within the stack. For the MCFC, the conventional anodes have insufficient activity to catalyse the steam reforming of natural gas. For these cells, internal reforming can be achieved only with the addition of a separate catalyst, preferably located in close proximity to the anode. However, in the so-called `Direct Internal Reforming' configuration, attack from alkali in the MCFC may severely limit catalyst lifetime. In the case of the state-of-the-art SOFC, natural gas can be reformed directly on the nickel cermet anode. However, in the SOFC, temperature variations in the cell caused by the reforming reaction may limit the amount of internal reforming that can be allowed in practice. In addition, some external pre-reforming may be desirable to remove high molecular weight hydrocarbons from the fuel gas, which would otherwise crack to produce elemental carbon. Degradation of the SOFC anode may also be a problem when internal reforming is carried out. This has prompted several research groups to investigate the use of alternative anode materials.

On-line experimental validation of a model-based diagnostic algorithm dedicated to a solid oxide fuel cell system

NASA Astrophysics Data System (ADS)

Polverino, Pierpaolo; Esposito, Angelo; Pianese, Cesare; Ludwig, Bastian; Iwanschitz, Boris; Mai, Andreas

2016-02-01

In the current energetic scenario, Solid Oxide Fuel Cells (SOFCs) exhibit appealing features which make them suitable for environmental-friendly power production, especially for stationary applications. An example is represented by micro-combined heat and power (μ-CHP) generation units based on SOFC stacks, which are able to produce electric and thermal power with high efficiency and low pollutant and greenhouse gases emissions. However, the main limitations to their diffusion into the mass market consist in high maintenance and production costs and short lifetime. To improve these aspects, the current research activity focuses on the development of robust and generalizable diagnostic techniques, aimed at detecting and isolating faults within the entire system (i.e. SOFC stack and balance of plant). Coupled with appropriate recovery strategies, diagnosis can prevent undesired system shutdowns during faulty conditions, with consequent lifetime increase and maintenance costs reduction. This paper deals with the on-line experimental validation of a model-based diagnostic algorithm applied to a pre-commercial SOFC system. The proposed algorithm exploits a Fault Signature Matrix based on a Fault Tree Analysis and improved through fault simulations. The algorithm is characterized on the considered system and it is validated by means of experimental induction of faulty states in controlled conditions.

Fault Diagnosis Strategies for SOFC-Based Power Generation Plants

PubMed Central

Costamagna, Paola; De Giorgi, Andrea; Gotelli, Alberto; Magistri, Loredana; Moser, Gabriele; Sciaccaluga, Emanuele; Trucco, Andrea

2016-01-01

The success of distributed power generation by plants based on solid oxide fuel cells (SOFCs) is hindered by reliability problems that can be mitigated through an effective fault detection and isolation (FDI) system. However, the numerous operating conditions under which such plants can operate and the random size of the possible faults make identifying damaged plant components starting from the physical variables measured in the plant very difficult. In this context, we assess two classical FDI strategies (model-based with fault signature matrix and data-driven with statistical classification) and the combination of them. For this assessment, a quantitative model of the SOFC-based plant, which is able to simulate regular and faulty conditions, is used. Moreover, a hybrid approach based on the random forest (RF) classification method is introduced to address the discrimination of regular and faulty situations due to its practical advantages. Working with a common dataset, the FDI performances obtained using the aforementioned strategies, with different sets of monitored variables, are observed and compared. We conclude that the hybrid FDI strategy, realized by combining a model-based scheme with a statistical classifier, outperforms the other strategies. In addition, the inclusion of two physical variables that should be measured inside the SOFCs can significantly improve the FDI performance, despite the actual difficulty in performing such measurements. PMID:27556472

A new class of accurate, mesh-free hydrodynamic simulation methods

NASA Astrophysics Data System (ADS)

Hopkins, Philip F.

2015-06-01

We present two new Lagrangian methods for hydrodynamics, in a systematic comparison with moving-mesh, smoothed particle hydrodynamics (SPH), and stationary (non-moving) grid methods. The new methods are designed to simultaneously capture advantages of both SPH and grid-based/adaptive mesh refinement (AMR) schemes. They are based on a kernel discretization of the volume coupled to a high-order matrix gradient estimator and a Riemann solver acting over the volume `overlap'. We implement and test a parallel, second-order version of the method with self-gravity and cosmological integration, in the code GIZMO:1 this maintains exact mass, energy and momentum conservation; exhibits superior angular momentum conservation compared to all other methods we study; does not require `artificial diffusion' terms; and allows the fluid elements to move with the flow, so resolution is automatically adaptive. We consider a large suite of test problems, and find that on all problems the new methods appear competitive with moving-mesh schemes, with some advantages (particularly in angular momentum conservation), at the cost of enhanced noise. The new methods have many advantages versus SPH: proper convergence, good capturing of fluid-mixing instabilities, dramatically reduced `particle noise' and numerical viscosity, more accurate sub-sonic flow evolution, and sharp shock-capturing. Advantages versus non-moving meshes include: automatic adaptivity, dramatically reduced advection errors and numerical overmixing, velocity-independent errors, accurate coupling to gravity, good angular momentum conservation and elimination of `grid alignment' effects. We can, for example, follow hundreds of orbits of gaseous discs, while AMR and SPH methods break down in a few orbits. However, fixed meshes minimize `grid noise'. These differences are important for a range of astrophysical problems.

Temperature field analysis for PZT pyroelectric cells for thermal energy harvesting.

PubMed

Hsiao, Chun-Ching; Ciou, Jing-Chih; Siao, An-Shen; Lee, Chi-Yuan

2011-01-01

This paper proposes the idea of etching PZT to improve the temperature variation rate of a thicker PZT sheet in order to enhance the energy conversion efficiency when used as pyroelectric cells. A partially covered electrode was proven to display a higher output response than a fully covered electrode did. A mesh top electrode monitored the temperature variation rate and the electrode area. The mesh electrode width affected the distribution of the temperature variation rate in a thinner pyroelectric material. However, a pyroelectric cell with a thicker pyroelectric material was beneficial in generating electricity pyroelectrically. The PZT sheet was further etched to produce deeper cavities and a smaller electrode width to induce lateral temperature gradients on the sidewalls of cavities under homogeneous heat irradiation, enhancing the temperature variation rate.

Temperature Field Analysis for PZT Pyroelectric Cells for Thermal Energy Harvesting

PubMed Central

Hsiao, Chun-Ching; Ciou, Jing-Chih; Siao, An-Shen; Lee, Chi-Yuan

2011-01-01

This paper proposes the idea of etching PZT to improve the temperature variation rate of a thicker PZT sheet in order to enhance the energy conversion efficiency when used as pyroelectric cells. A partially covered electrode was proven to display a higher output response than a fully covered electrode did. A mesh top electrode monitored the temperature variation rate and the electrode area. The mesh electrode width affected the distribution of the temperature variation rate in a thinner pyroelectric material. However, a pyroelectric cell with a thicker pyroelectric material was beneficial in generating electricity pyroelectrically. The PZT sheet was further etched to produce deeper cavities and a smaller electrode width to induce lateral temperature gradients on the sidewalls of cavities under homogeneous heat irradiation, enhancing the temperature variation rate. PMID:22346652

A finite element conjugate gradient FFT method for scattering

NASA Technical Reports Server (NTRS)

Collins, Jeffery D.; Zapp, John; Hsa, Chang-Yu; Volakis, John L.

1990-01-01

An extension of a two dimensional formulation is presented for a three dimensional body of revolution. With the introduction of a Fourier expansion of the vector electric and magnetic fields, a coupled two dimensional system is generated and solved via the finite element method. An exact boundary condition is employed to terminate the mesh and the fast fourier transformation (FFT) is used to evaluate the boundary integrals for low O(n) memory demand when an iterative solution algorithm is used. By virtue of the finite element method, the algorithm is applicable to structures of arbitrary material composition. Several improvements to the two dimensional algorithm are also described. These include: (1) modifications for terminating the mesh at circular boundaries without distorting the convolutionality of the boundary integrals; (2) the development of nonproprietary mesh generation routines for two dimensional applications; (3) the development of preprocessors for interfacing SDRC IDEAS with the main algorithm; and (4) the development of post-processing algorithms based on the public domain package GRAFIC to generate two and three dimensional gray level and color field maps.

A versatile embedded boundary adaptive mesh method for compressible flow in complex geometry

NASA Astrophysics Data System (ADS)

Al-Marouf, M.; Samtaney, R.

2017-05-01

We present an embedded ghost fluid method for numerical solutions of the compressible Navier Stokes (CNS) equations in arbitrary complex domains. A PDE multidimensional extrapolation approach is used to reconstruct the solution in the ghost fluid regions and imposing boundary conditions on the fluid-solid interface, coupled with a multi-dimensional algebraic interpolation for freshly cleared cells. The CNS equations are numerically solved by the second order multidimensional upwind method. Block-structured adaptive mesh refinement, implemented with the Chombo framework, is utilized to reduce the computational cost while keeping high resolution mesh around the embedded boundary and regions of high gradient solutions. The versatility of the method is demonstrated via several numerical examples, in both static and moving geometry, ranging from low Mach number nearly incompressible flows to supersonic flows. Our simulation results are extensively verified against other numerical results and validated against available experimental results where applicable. The significance and advantages of our implementation, which revolve around balancing between the solution accuracy and implementation difficulties, are briefly discussed as well.

Finite element modeling of mass transport in high-Péclet cardiovascular flows

NASA Astrophysics Data System (ADS)

Hansen, Kirk; Arzani, Amirhossein; Shadden, Shawn

2016-11-01

Mass transport plays an important role in many important cardiovascular processes, including thrombus formation and atherosclerosis. These mass transport problems are characterized by Péclet numbers of up to 108, leading to several numerical difficulties. The presence of thin near-wall concentration boundary layers requires very fine mesh resolution in these regions, while large concentration gradients within the flow cause numerical stabilization issues. In this work, we will discuss some guidelines for solving mass transport problems in cardiovascular flows using a stabilized Galerkin finite element method. First, we perform mesh convergence studies in a series of idealized and patient-specific geometries to determine the required near-wall mesh resolution for these types of problems, using both first- and second-order tetrahedral finite elements. Second, we investigate the use of several boundary condition types at outflow boundaries where backflow during some parts of the cardiac cycle can lead to convergence issues. Finally, we evaluate the effect of reducing Péclet number by increasing mass diffusivity as has been proposed by some researchers. This work was supported by the NSF GRFP and NSF Career Award #1354541.

Growth morphologies of wax in the presence of kinetic inhibitors

NASA Astrophysics Data System (ADS)

Tetervak, Alexander A.

Driven by the need to prevent crystallization of normal alkanes from diesel fuels in cold climates, the petroleum industry has developed additives to slow the growth of these crystals and alter their morphologies. Although the utility of these kinetic inhibitors has been well demonstrated in the field, few studies have directly monitored their effect at microscopic morphology, and the mechanisms by which they act remain poorly understood. Here we present a study of the effects of such additives on the crystallization of long-chain n-alkanes from solution. The additives change the growth morphology from plate-like crystals to a microcrystalline mesh. When we impose a front velocity by moving the sample through a temperature gradient, the mesh growth may form a macroscopic banded pattern and also exhibit a burst-crystallization behavior. In this study, we characterize these crystallization phenomena and also two growth models: a continuum model that demonstrates the essential behavior of the banded crystallization, and a simple qualitative cellular automata model that captures basics of the burst-crystallization process. Keywords: solidification; mesh crystallization; kinetic inhibitor; burst growth.

Structures and fabrication techniques for solid state electrochemical devices

DOEpatents

Visco, Steven J.; Jacobson, Craig P.; DeJonghe, Lutgard C.

2012-10-09

Porous substrates and associated structures for solid-state electrochemical devices, such as solid-oxide fuel cells (SOFCs), are low-cost, mechanically strong and highly electronically conductive. Some preferred structures have a thin layer of an electrocatalytically active material (e.g., Ni--YSZ) coating a porous high-strength alloy support (e.g., SS-430) to form a porous SOFC fuel electrode. Electrode/electrolyte structures can be formed by co-firing or constrained sintering processes.

Structures and fabrication techniques for solid state electrochemical devices

DOEpatents

Visco, Steven J.; Jacobson, Craig P.; DeJonghe, Lutgard C.

2008-04-01

Porous substrates and associated structures for solid-state electrochemical devices, such as solid-oxide fuel cells (SOFCs), are low-cost, mechanically strong and highly electronically conductive. Some preferred structures have a thin layer of an electrocatalytically active material (e.g., Ni--YSZ) coating a porous high-strength alloy support (e.g., SS-430) to form a porous SOFC fuel electrode. Electrode/electrolyte structures can be formed by co-firing or constrained sintering processes.

A Hybrid Approach to Tactical Vehicles

DTIC Science & Technology

2011-09-01

membrane fuel cell ( PEMFC ), molten carbonate fuel cell (MCFC), solid oxide fuel cell (SOFC), phosphoric acid fuel cell (PAFC), alkaline fuel cell (AFC...and the direct methanol fuel cell (DMFC) (Ehsani, Gao, & Emadi, 2010). Of the six major types of fuel cells; the PEMFC , SOFC, and AFC are... PEMFC (21st Century Truck Program, 2000). There are a number of advantages of using a fuel cell as the primary power source for a vehicle. All fuel

Diffusion in energy materials: Governing dynamics from atomistic modelling

NASA Astrophysics Data System (ADS)

Parfitt, D.; Kordatos, A.; Filippatos, P. P.; Chroneos, A.

2017-09-01

Understanding diffusion in energy materials is critical to optimising the performance of solid oxide fuel cells (SOFCs) and batteries both of which are of great technological interest as they offer high efficiency for cleaner energy conversion and storage. In the present review, we highlight the insights offered by atomistic modelling of the ionic diffusion mechanisms in SOFCs and batteries and how the growing predictive capability of high-throughput modelling, together with our new ability to control compositions and microstructures, will produce advanced materials that are designed rather than chosen for a given application. The first part of the review focuses on the oxygen diffusion mechanisms in cathode and electrolyte materials for SOFCs and in particular, doped ceria and perovskite-related phases with anisotropic structures. The second part focuses on disordered oxides and two-dimensional materials as these are very promising systems for battery applications.

Development and Validation of an NPSS Model of a Small Turbojet Engine

NASA Astrophysics Data System (ADS)

Vannoy, Stephen Michael

Recent studies have shown that integrated gas turbine engine (GT)/solid oxide fuel cell (SOFC) systems for combined propulsion and power on aircraft offer a promising method for more efficient onboard electrical power generation. However, it appears that nobody has actually attempted to construct a hybrid GT/SOFC prototype for combined propulsion and electrical power generation. This thesis contributes to this ambition by developing an experimentally validated thermodynamic model of a small gas turbine (˜230 N thrust) platform for a bench-scale GT/SOFC system. The thermodynamic model is implemented in a NASA-developed software environment called Numerical Propulsion System Simulation (NPSS). An indoor test facility was constructed to measure the engine's performance parameters: thrust, air flow rate, fuel flow rate, engine speed (RPM), and all axial stage stagnation temperatures and pressures. The NPSS model predictions are compared to the measured performance parameters for steady state engine operation.

Atomic layer deposition of ultrathin blocking layer for low-temperature solid oxide fuel cell on nanoporous substrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Wonjong; Cho, Gu Young; Noh, Seungtak

2015-01-15

An ultrathin yttria-stabilized zirconia (YSZ) blocking layer deposited by atomic layer deposition (ALD) was utilized for improving the performance and reliability of low-temperature solid oxide fuel cells (SOFCs) supported by an anodic aluminum oxide substrate. Physical vapor-deposited YSZ and gadolinia-doped ceria (GDC) electrolyte layers were deposited by a sputtering method. The ultrathin ALD YSZ blocking layer was inserted between the YSZ and GDC sputtered layers. To investigate the effects of an inserted ultrathin ALD blocking layer, SOFCs with and without an ultrathin ALD blocking layer were electrochemically characterized. The open circuit voltage (1.14 V) of the ALD blocking-layered SOFC was visiblymore » higher than that (1.05 V) of the other cell. Furthermore, the ALD blocking layer augmented the power density and improved the reproducibility.« less

Electrolytes for solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Fergus, Jeffrey W.

The high operating temperature of solid oxide fuel cells (SOFCs), as compared to polymer electrolyte membrane fuel cells (PEMFCs), improves tolerance to impurities in the fuel, but also creates challenges in the development of suitable materials for the various fuel cell components. In response to these challenges, intermediate temperature solid oxide fuel cells (IT-SOFCs) are being developed to reduce high-temperature material requirements, which will extend useful lifetime, improve durability and reduce cost, while maintaining good fuel flexibility. A major challenge in reducing the operating temperature of SOFCs is the development of solid electrolyte materials with sufficient conductivity to maintain acceptably low ohmic losses during operation. In this paper, solid electrolytes being developed for solid oxide fuel cells, including zirconia-, ceria- and lanthanum gallate-based materials, are reviewed and compared. The focus is on the conductivity, but other issues, such as compatibility with electrode materials, are also discussed.

Clad metals, roll bonding and their applications for SOFC interconnects

NASA Astrophysics Data System (ADS)

Chen, Lichun; Yang, Zhenguo; Jha, Bijendra; Xia, Guanguang; Stevenson, Jeffry W.

Metallic interconnects have been becoming an increasingly interesting topic in the development in intermediate temperature solid oxide fuel cells (SOFC). High temperature oxidation resistant alloys are currently considered as candidate materials. Among these alloys however, different groups of alloys demonstrate different advantages and disadvantages, and few if any can completely satisfy the stringent requirements for the application. To integrate the advantages and avoid the disadvantages of different groups of alloys, clad metal has been proposed for SOFC interconnect applications and interconnect structures. This paper gives a brief overview of the cladding approach and its applications, and discuss the viability of this technology to fabricate the metallic layered-structure interconnects. To examine the feasibility of this approach, the austenitic Ni-base alloy Haynes 230 and the ferritic stainless steel AL 453 were selected as examples and manufactured into a clad metal. Its suitability as an interconnect construction material was investigated.

Effect of load transients on SOFC operation—current reversal on loss of load

NASA Astrophysics Data System (ADS)

Gemmen, Randall S.; Johnson, Christopher D.

The dynamics of solid oxide fuel cell (SOFC) operation have been considered previously, but mainly through the use of one-dimensional codes applied to co-flow fuel cell systems. In this paper several geometries are considered, including cross-flow, co-flow, and counter-flow. The details of the model are provided, and the model is compared with some initial experimental data. For parameters typical of SOFC operation, a variety of transient cases are investigated, including representative load increase and decrease and system shutdown. Of particular note for large load decrease conditions (e.g., shutdown) is the occurrence of reverse current over significant portions of the cell, starting from the moment of load loss up to the point where equilibrated conditions again provide positive current. Consideration is given as to when such reverse current conditions might most significantly impact the reliability of the cell.

Computational analysis of species transport and electrochemical characteristics of a MOLB-type SOFC

NASA Astrophysics Data System (ADS)

Hwang, J. J.; Chen, C. K.; Lai, D. Y.

A multi-physics model coupling electrochemical kinetics with fluid dynamics has been developed to simulate the transport phenomena in mono-block-layer built (MOLB) solid oxide fuel cells (SOFC). A typical MOLB module is composed of trapezoidal flow channels, corrugated positive electrode-electrolyte-negative electrode (PEN) plates, and planar inter-connecters. The control volume-based finite difference method is employed for calculation, which is based on the conservation of mass, momentum, energy, species, and electric charge. In the porous electrodes, the flow momentum is governed by a Darcy model with constant porosity and permeability. The diffusion of reactants follows the Bruggman model. The chemistry within the plates is described via surface reactions with a fixed surface-to-volume ratio, tortuosity and average pore size. Species transports as well as the local variations of electrochemical characteristics, such as overpotential and current density distributions in the electrodes of an MOLB SOFC, are discussed in detail.

Preconditioned conjugate gradient methods for the compressible Navier-Stokes equations

NASA Technical Reports Server (NTRS)

Venkatakrishnan, V.

1990-01-01

The compressible Navier-Stokes equations are solved for a variety of two-dimensional inviscid and viscous problems by preconditioned conjugate gradient-like algorithms. Roe's flux difference splitting technique is used to discretize the inviscid fluxes. The viscous terms are discretized by using central differences. An algebraic turbulence model is also incorporated. The system of linear equations which arises out of the linearization of a fully implicit scheme is solved iteratively by the well known methods of GMRES (Generalized Minimum Residual technique) and Chebyschev iteration. Incomplete LU factorization and block diagonal factorization are used as preconditioners. The resulting algorithm is competitive with the best current schemes, but has wide applications in parallel computing and unstructured mesh computations.

SEEK: A FORTRAN optimization program using a feasible directions gradient search

NASA Technical Reports Server (NTRS)

Savage, M.

1995-01-01

This report describes the use of computer program 'SEEK' which works in conjunction with two user-written subroutines and an input data file to perform an optimization procedure on a user's problem. The optimization method uses a modified feasible directions gradient technique. SEEK is written in ANSI standard Fortran 77, has an object size of about 46K bytes, and can be used on a personal computer running DOS. This report describes the use of the program and discusses the optimizing method. The program use is illustrated with four example problems: a bushing design, a helical coil spring design, a gear mesh design, and a two-parameter Weibull life-reliability curve fit.

A gradient enhanced plasticity-damage microplane model for concrete

NASA Astrophysics Data System (ADS)

Zreid, Imadeddin; Kaliske, Michael

2018-03-01

Computational modeling of concrete poses two main types of challenges. The first is the mathematical description of local response for such a heterogeneous material under all stress states, and the second is the stability and efficiency of the numerical implementation in finite element codes. The paper at hand presents a comprehensive approach addressing both issues. Adopting the microplane theory, a combined plasticity-damage model is formulated and regularized by an implicit gradient enhancement. The plasticity part introduces a new microplane smooth 3-surface cap yield function, which provides a stable numerical solution within an implicit finite element algorithm. The damage part utilizes a split, which can describe the transition of loading between tension and compression. Regularization of the model by the implicit gradient approach eliminates the mesh sensitivity and numerical instabilities. Identification methods for model parameters are proposed and several numerical examples of plain and reinforced concrete are carried out for illustration.

Mixed ionic-electronic conductors for electrodes of barium cerate-based SOFCS

NASA Astrophysics Data System (ADS)

Wu, Zhonglin

Gadolinium doped barium cerates (BCGs) have been identified as promising electrolyte materials for intermediate-temperature solid oxide fuel cells (SOFCs). It is crucial to develop compatible electrode materials for such electrolytes. Mixed ionic-electronic conductor (MIEC) electrode materials developed for SOFCs based on yttrium-stabilized zirconia (YSZ) may be used as electrode materials for BCG-based SOFCs; but a careful re-evaluation is required due to the intrinsic differences between BCG and YSZ. The performance of these electrode materials depends critically the transport of ionic and electronic species as well as gas. Accordingly, a profound understanding of transport in MIEC electrodes is imperative to effective design of high performance SOFCs. In this thesis, ambipolar transport in composite MIEC electrodes has been modeled using percolation theory to predict the effect of volume fractions of constituent phases and porosity on ambipolar conductivity. Transport and electrode kinetics of homogeneous MIEC electrodes have also been formulated under a steady-state condition to predict the distributions of ionic defects and current carried by each defect in such electrodes. Effects of catalytic properties, transport properties, and microstructure of porous electrodes and interfaces on the electrode performance are investigated. Under the guidelines of the theoretical modeling, several MIEC electrode materials are developed. Lasb{1-x}Srsb{x}Cosb{1-x}Fesb{y}Osb{3-delta} homogeneous materials are studied as cathode materials. However, the interfacial resistance seems too high due to the lack of catalytic activity at intermediate temperatures. Results indicate that Ag-Bisb{1.5}Ysb{0.5}Osb3 composite MIECs are good cathode materials when the volume fractions of constituent phases and porosity are carefully controlled. Such electrodes have low interfacial resistance, better binding strength, and smaller thermal mismatch with the BCG electrolyte, compared to other metal electrodes (such as Pt and Ag). Ni-BCG composite MIECs are studied as anode materials. It is found that electrodes prepared from NiO and reduced to Ni in situ is not catalytically active because of diffusion of NiO into BCG, which forms a resistive layer. Electrodes prepared from Ni metal and fired in an inert or reducing atmosphere exhibit low interfacial resistance and good compatibility with BCG electrolyte. Stability of these developed electrode materials is investigated under conditions pertinent to SOFCs.

Cause and Cure - Deterioration in Accuracy of CFD Simulations With Use of High-Aspect-Ratio Triangular Tetrahedral Grids

NASA Technical Reports Server (NTRS)

Chang, Sin-Chung; Chang, Chau-Lyan; Venkatachari, Balaji Shankar

2017-01-01

Traditionally high-aspect ratio triangular/tetrahedral meshes are avoided by CFD re-searchers in the vicinity of a solid wall, as it is known to reduce the accuracy of gradient computations in those regions and also cause numerical instability. Although for certain complex geometries, the use of high-aspect ratio triangular/tetrahedral elements in the vicinity of a solid wall can be replaced by quadrilateral/prismatic elements, ability to use triangular/tetrahedral elements in such regions without any degradation in accuracy can be beneficial from a mesh generation point of view. The benefits also carry over to numerical frameworks such as the space-time conservation element and solution element (CESE), where triangular/tetrahedral elements are the mandatory building blocks. With the requirement of the CESE method in mind, a rigorous mathematical framework that clearly identities the reason behind the difficulties in use of such high-aspect ratio triangular/tetrahedral elements is presented here. As will be shown, it turns out that the degree of accuracy deterioration of gradient computation involving a triangular element is hinged on the value of its shape factor Gamma def = sq sin Alpha1 + sq sin Alpha2 + sq sin Alpha3, where Alpha1; Alpha2 and Alpha3 are the internal angles of the element. In fact, it is shown that the degree of accuracy deterioration increases monotonically as the value of Gamma decreases monotonically from its maximal value 9/4 (attained by an equilateral triangle only) to a value much less than 1 (associated with a highly obtuse triangle). By taking advantage of the fact that a high-aspect ratio triangle is not necessarily highly obtuse, and in fact it can have a shape factor whose value is close to the maximal value 9/4, a potential solution to avoid accuracy deterioration of gradient computation associated with a high-aspect ratio triangular grid is given. Also a brief discussion on the extension of the current mathematical framework to the tetrahedral-grid case along with some of the practical results of this extension is also provided. Furthermore, through the use of numerical simulations of practical viscous problems involving high-Reynolds number flows, the effectiveness of the gradient evaluation procedures within the CESE framework (that have their basis on the analysis presented here) to produce accurate and stable results on such high-aspect ratio meshes is also showcased.

Conceptual study of a 250 kW planar SOFC system for CHP application

NASA Astrophysics Data System (ADS)

Fontell, E.; Kivisaari, T.; Christiansen, N.; Hansen, J.-B.; Pålsson, J.

In August 2002, Wärtsilä Corporation and Haldor Topsøe A/S entered into a co-operation agreement to start joint development program within the planar SOFC technology. The development program aims to bring to the market highly efficient, clean and cost competitive fuel cell systems with power outputs above 200 kW for distributed power generation with CHP and for marine applications. In this study, the product concept for a 250 kW natural gas-fuelled atmospheric SOFC plant has been studied. The process has been calculated and optimised for high electrical efficiency. In the calculations, system efficiencies more than 55-85% (electrical co-generation) have been reached. The necessary balance of plant (BoP) components have been identified and the concept for grid connection has been defined. The BoP includes fuel and air supply, anode re-circulation, start-up steam, purge gas, exhaust gas heat recovery, back-up power, power electronics and control system. Based on the analysed system and component information, a conceptual design and cost break down structure for the product have been made. The cost breakdown shows that the stack, system control and power electronics are the major cost factors, while the remaining BoP equipment stands for a minor share of the manufacturing cost. Finally, the feasibility of the SOFC plants has been compared to gas engines.

Mitigation of Sulfur Poisoning of Ni/Zirconia SOFC Anodes by Antimony and Tin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marina, Olga A.; Coyle, Christopher A.; Engelhard, Mark H.

2011-02-28

Surface Ni/Sb and Ni/Sb alloys were found to efficiently minimize the negative effects of sulfur on the performance of Ni/zirconia anode-supported solid oxide fuel cells (SOFC). Prior to operating on fuel gas containing low concentrations of H2S, the nickel/zirconia anodes were briefly exposed to antimony or tin vapor, which only slightly affected the SOFC performance. During the subsequent exposures to 1 and 5 ppm H2S, increases in anodic polarization losses were minimal compared to those observed for the standard nickel/zirconia anodes. Post-test XPS analyses showed that Sb and Sn tended to segregate to the surface of Ni particles, and furthermore » confirmed a significant reduction of adsorbed sulfur on the Ni surface in Ni/Sn and Ni/Sb samples compared to the Ni. The effect may be the result of weaker sulfur adsorption on bimetallic surfaces, adsorption site competition between sulfur and Sb or Sn on Ni, or other factors. The use of dilute binary alloys of Ni-Sb or Ni-Sn in the place of Ni, or brief exposure to Sb or Sn vapor, may be effective means to counteract the effects of sulfur poisoning in SOFC anodes and Ni catalysts. Other advantages, including suppression of coking or tailoring the anode composition for the internal reforming, are also expected.« less

Simultaneous NOx and hydrocarbon emissions control for lean-burn engines using low-temperature solid oxide fuel cell at open circuit.

PubMed

Huang, Ta-Jen; Hsu, Sheng-Hsiang; Wu, Chung-Ying

2012-02-21

The high fuel efficiency of lean-burn engines is associated with high temperature and excess oxygen during combustion and thus is associated with high-concentration NO(x) emission. This work reveals that very high concentration of NO(x) in the exhaust can be reduced and hydrocarbons (HCs) can be simultaneously oxidized using a low-temperature solid oxide fuel cell (SOFC). An SOFC unit is constructed with Ni-YSZ as the anode, YSZ as the electrolyte, and La(0.6)Sr(0.4)CoO(3) (LSC)-Ce(0.9)Gd(0.1)O(1.95) as the cathode, with or without adding vanadium to LSC. SOFC operation at 450 °C and open circuit can effectively treat NO(x) over the cathode at a very high concentration in the simulated exhaust. Higher NO(x) concentration up to 5000 ppm can result in a larger NO(x) to N(2) rate. Moreover, a higher oxygen concentration promotes NO conversion. Complete oxidation of HCs can be achieved by adding silver to the LSC current collecting layer. The SOFC-based emissions control system can treat NO(x) and HCs simultaneously, and can be operated without consuming the anode fuel (a reductant) at near the engine exhaust temperature to eliminate the need for reductant refilling and extra heating.

Electrochemical enhancement of nitric oxide removal from simulated lean-burn engine exhaust via solid oxide fuel cells.

PubMed

Huang, Ta-Jen; Wu, Chung-Ying; Lin, Yu-Hsien

2011-07-01

A solid oxide fuel cell (SOFC) unit is constructed with Ni-YSZ as the anode, YSZ as the electrolyte, and La(0.6)Sr(0.4)CoO(3)-Ce(0.9)Gd(0.1)O(1.95) as the cathode. The SOFC operation is performed at 600 °C with a cathode gas simulating the lean-burn engine exhaust and at various fixed voltage, at open-circuit voltage, and with an inert gas flowing over the anode side, respectively. Electrochemical enhancement of NO decomposition occurs when an operating voltage is generated; higher O(2) concentration leads to higher enhancement. Smaller NO concentration results in larger NO conversion. Higher operating voltage and higher O(2) concentration can lead to both higher NO conversion and lower fuel consumption. The molar rate of the consumption of the anode fuel can be very much smaller than that of NO to N(2) conversion. This makes the anode fuel consumed in the SOFC-DeNO(x) process to be much less than the equivalent amount of ammonia consumed in the urea-based selective catalytic reduction process. Additionally, the NO conversion increases with the addition of propylene and SO(2) into the cathode gas. These are beneficial for the application of the SOFC-DeNO(x) technology on treating diesel and other lean-burn engine exhausts.

An 8-node tetrahedral finite element suitable for explicit transient dynamic simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Key, S.W.; Heinstein, M.W.; Stone, C.M.

1997-12-31

Considerable effort has been expended in perfecting the algorithmic properties of 8-node hexahedral finite elements. Today the element is well understood and performs exceptionally well when used in modeling three-dimensional explicit transient dynamic events. However, the automatic generation of all-hexahedral meshes remains an elusive achievement. The alternative of automatic generation for all-tetrahedral finite element is a notoriously poor performer, and the 10-node quadratic tetrahedral finite element while a better performer numerically is computationally expensive. To use the all-tetrahedral mesh generation extant today, the authors have explored the creation of a quality 8-node tetrahedral finite element (a four-node tetrahedral finite elementmore » enriched with four midface nodal points). The derivation of the element`s gradient operator, studies in obtaining a suitable mass lumping and the element`s performance in applications are presented. In particular, they examine the 80node tetrahedral finite element`s behavior in longitudinal plane wave propagation, in transverse cylindrical wave propagation, and in simulating Taylor bar impacts. The element only samples constant strain states and, therefore, has 12 hourglass modes. In this regard, it bears similarities to the 8-node, mean-quadrature hexahedral finite element. Given automatic all-tetrahedral meshing, the 8-node, constant-strain tetrahedral finite element is a suitable replacement for the 8-node hexahedral finite element and handbuilt meshes.« less

Hardware simulation of fuel cell/gas turbine hybrids

NASA Astrophysics Data System (ADS)

Smith, Thomas Paul

Hybrid solid oxide fuel cell/gas turbine (SOFC/GT) systems offer high efficiency power generation, but face numerous integration and operability challenges. This dissertation addresses the application of hardware-in-the-loop simulation (HILS) to explore the performance of a solid oxide fuel cell stack and gas turbine when combined into a hybrid system. Specifically, this project entailed developing and demonstrating a methodology for coupling a numerical SOFC subsystem model with a gas turbine that has been modified with supplemental process flow and control paths to mimic a hybrid system. This HILS approach was implemented with the U.S. Department of Energy Hybrid Performance Project (HyPer) located at the National Energy Technology Laboratory. By utilizing HILS the facility provides a cost effective and capable platform for characterizing the response of hybrid systems to dynamic variations in operating conditions. HILS of a hybrid system was accomplished by first interfacing a numerical model with operating gas turbine hardware. The real-time SOFC stack model responds to operating turbine flow conditions in order to predict the level of thermal effluent from the SOFC stack. This simulated level of heating then dynamically sets the turbine's "firing" rate to reflect the stack output heat rate. Second, a high-speed computer system with data acquisition capabilities was integrated with the existing controls and sensors of the turbine facility. In the future, this will allow for the utilization of high-fidelity fuel cell models that infer cell performance parameters while still computing the simulation in real-time. Once the integration of the numeric and the hardware simulation components was completed, HILS experiments were conducted to evaluate hybrid system performance. The testing identified non-intuitive transient responses arising from the large thermal capacitance of the stack that are inherent to hybrid systems. Furthermore, the tests demonstrated the capabilities of HILS as a research tool for investigating the dynamic behavior of SOFC/GT hybrid power generation systems.

Structural analysis of nickel doped cerium oxide catalysts for fuel reforming in solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Cavendish, Rio

As world energy demands increase, research into more efficient energy production methods has become imperative. Heterogeneous catalysis and nanoscience are used to promote chemical transformations important for energy production. These concepts are important in solid oxide fuel cells (SOFCs) which have attracted attention because of their potential to provide an efficient and environmentally favorable power generation system. The SOFC is also fuel-flexible with the ability to run directly on many fuels other than hydrogen. Internal fuel reforming directly in the anode of the SOFC would greatly reduce the cost and complexity of the device. Methane is the simplest hydrocarbon and a main component in natural gas, making it useful when testing catalysts on the laboratory scale. Nickel (Ni) and gadolinium (Gd) doped ceria (CeO 2) catalysts for potential use in the SOFC anode were synthesized with a spray drying method and tested for catalytic performance using partial oxidation of methane and steam reforming. The relationships between catalytic performance and structure were then investigated using X-ray diffraction, transmission electron microscopy, and environmental transmission electron microscopy. The possibility of solid solutions, segregated phases, and surface layers of Ni were explored. Results for a 10 at.% Ni in CeO2 catalyst reveal a poor catalytic behavior while a 20 at.% Ni in CeO2 catalyst is shown to have superior activity. The inclusion of both 10 at.% Gd and 10 at.% Ni in CeO2 enhances the catalytic performance. Analysis of the presence of Ni in all 3 samples reveals Ni heterogeneity and little evidence for extensive solid solution doping. Ni is found in small domains throughout CeO2 particles. In the 20 at.% Ni sample a segregated, catalytically active NiO phase is observed. Overall, it is found that significant interaction between Ni and CeO2 occurs that could affect the synthesis and functionality of the SOFC anode.

Studies of Plasma Instabilities using Unstructured Discontinuous Galerkin Method with the Two-Fluid Plasma Model

NASA Astrophysics Data System (ADS)

Song, Yang; Srinivasan, Bhuvana

2017-10-01

The discontinuous Galerkin (DG) method has the advantage of resolving shocks and sharp gradients that occur in neutral fluids and plasmas. An unstructured DG code has been developed in this work to study plasma instabilities using the two-fluid plasma model. Unstructured meshes are known to produce small and randomized grid errors compared to traditional structured meshes. Computational tests for Rayleigh-Taylor instabilities in radially-converging flows are performed using the MHD model. Choice of grid geometry is not obvious for simulations of instabilities in these circular configurations. Comparisons of the effects for different grids are made. A 2D magnetic nozzle simulation using the two-fluid plasma model is also performed. A vacuum boundary condition technique is applied to accurately solve the Riemann problem on the edge of the plume.

Progress in the planar CPn SOFC system design verification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elangovan, S.; Hartvigsen, J.; Khandkar, A.

1996-04-01

SOFCo is developing a high efficiency, modular and scaleable planar SOFC module termed the CPn design. This design has been verified in a 1.4 kW module test operated directly on pipeline natural gas. The design features multistage oxidation of fuel wherein the fuel is consumed incrementally over several stages. High efficiency is achieved by uniform current density distribution per stage, which lowers the stack resistance. Additional benefits include thermal regulation and compactness. Test results from stack modules operating in pipeline natural gas are presented.

Energy Conversion Efficiency Potential for Forward-Deployed Generation Using Direct Carbon Fuel Cells

DTIC Science & Technology

2012-05-01

fuel cells vs. DCFCs. PEMFC PAFC MCFC SOFC DCFC Electrolyte Polymer Phosphoric acid Molten car- bonate salt Ceramic Fused KNO3 Operating...air O2/air CO2/O2/air O2/air Humidified air Efficiency (Higher Heating Value [HHV]) 30–35% 40–50% 50–60% 45–55% 80% PEMFC : Proton Exchange... PEMFC proton-exchange membrane fuel cell SOFC solid oxide fuel cell SRI Statistical Research, Inc. TR technical report TRL technology readiness level

Synthesis, Characterization, and Optimization of Novel Solid Oxide Fuel Cell Anodes

NASA Astrophysics Data System (ADS)

Miller, Elizabeth C.

This dissertation presents research on the development of novel materials and fabrication procedures for solid oxide fuel cell (SOFC) anodes. The work discussed here is divided into three main categories: all-oxide anodes, catalyst exsolution oxide anodes, and Ni-infiltrated anodes. The all-oxide and catalyst exsolution anodes presented here are further classi?ed as Ni-free anodes operating at the standard 700-800°C SOFC temperature while the Ni-infiltrated anodes operate at intermediate temperatures (≤650°C). Compared with the current state-of-the-art Ni-based cermets, all-oxide, Ni-free SOFC anodes offer fewer coking issues in carbon-containing fuels, reduced degradation due to fuel contaminants, and improved stability during redox cycling. However, electrochemical performance has proven inferior to Ni-based anodes. The perovskite oxide Fe-substituted strontium titanate (STF) has shown potential as an anode material both as a single phase electrode and when combined with Gd-doped ceria (GDC) in a composite electrode. In this work, STF is synthesized using a modified Pechini processes with the aim of reducing STF particle size and increasing the electrochemically active area in the anode. The Pechini method produced particles ? 750 nm in diameter, which is signi°Cantly smaller than the typically micron-sized solid state reaction powder. In the first iteration of anode fabrication with the Pechini powder, issues with over-sintering of the small STF particles limited gas di?usion in the anode. However, after modifying the anode firing temperature, the Pechini cells produced power density comparable to solid state reaction based cells from previous work by Cho et al. Catalyst exsolution anodes, in which metal cations exsolve out of the lattice under reducing conditions and form nanoparticles on the oxide surface, are another Ni-free option for standard operating temperature SOFCs. Little information is known about the onset of nanoparticle formation, which presents opportunities for the new kinds of ex situ and in situ experiments performed in this thesis. Ex situ experiments involved reducing powder samples at SOFC operating temperatures under hydrogen gas and characterizing them via electron microscopy and X-ray diffraction (XRD). For the in situ experiments, powders were heated, then reduced at temperature, and catalyst exsolution was observed in real-time. Pechini-synthesized cerium oxide substituted with 2-5 mol% Pd was studied using in situ X-ray heating experiments at Argonne National Laboratory's Advanced Photon Source. In these experiments, the powder was subjected to several cycles of reduction and oxidation at 800°C, and Pd metal formation was confirmed through the appearance of Pd peaks in the X-ray spectra. Next, Fe- and Ru-substituted lanthanum strontium chromite (LSCrFeRu14) synthesized by solid state reaction was characterized with ex situ and in situ microscopy. Transmission electron microscopy (TEM) in situ heating experiments were conducted to observe Ru nanoparticle evolution under the reducing conditions of the TEM vacuum chamber. LSCrFeRu14 was heated to 750°C and observed over ˜ 90 min at temperature during which time nanoparticle formation, coarsening, and di?usion were observed. Experiments on both materials sought to understand the conditions and timing of nanoparticle formation in the anode, which is not necessarily apparent from electrochemical data. Reducing the operating temperature of SOFCs from the current state-of-the-art range of 700-800°C to ≤ 650°C has many advantages, among them increased long-term stability, reduced balance of plant costs, fewer interconnect/seal material issues, and decreased start-up times. In order to maintain good performance at reduced temperature, these intermediate temperature SOFCs require new materials including highly active alternatives to micron-scale Ni-YSZ composite anodes. The present work focuses on the development of IT-SOFCs with Sr0.8La 0.2TiO3 (SLT) anode supports, thin La1--xSr x Ga0.8Mg0.2O3 (x = 0.1, 0.2) dense electrolytes, and porous LSGM anode functional layers. The SLT support and the LSGM functional layer are infiltrated with nanoscale Ni, creating extensive electrochemically active triple phase boundary area. The scope of the work presented here encompasses every step of cell development including powder synthesis, optimization of firing conditions, and long-term stability testing. Using an optimized fabrication process, cells with power density > 1.2 W cm-2 were fabricated. Dry pressing and colloidal de-position were used to make the first generation of these cells, and once suitable times and temperatures were determined, the process was shifted to tape casting to make larger batches of uniform cells. After obtaining initial results of low anode polarization resistance and high power density, the long-term stability of the Ni-infiltrated anodes was examined. A coarsening model was developed using the data from accelerated degradation tests to predict cell performance over a typical device lifetime. This thesis encompasses a broad range of novel SOFC anode materials, each of which has its own strengths and weaknesses. Presenting several possible avenues for SOFC development provides a complete picture of the ?eld and its current focuses. The wide scope of this work offers multiple solutions for the SOFC community and demonstrates that SOFCs are a strong candidate for meeting the United States' need for energy conversion and storage.

Groundwater biofilm dynamics grown in situ along a nutrient gradient.

PubMed

Williamson, Wendy M; Close, Murray E; Leonard, Margaret M; Webber, Judith B; Lin, Susan

2012-01-01

This paper describes the in situ response of groundwater biofilms in an alluvial gravel aquifer system on the Canterbury Plains, New Zealand. Biofilms were developed on aquifer gravel, encased in fine mesh bags and suspended in protective columns in monitoring wells for at least 20 weeks. Four sites were selected in the same groundwater system where previous analyses indicated a gradient of increasing nitrate down the hydraulic gradient from Sites 1 to 4. Measurements during the current study classified the groundwater as oligotrophic. Biofilm responses to the nutrient gradients were assessed using bioassays, with biomass determined using protein and cellular and nucleic acid staining and biofilm activity using enzyme assays for lipid, carbohydrate, phosphate metabolism, and cell viability. In general, biofilm activity decreased as nitrate levels increased from Sites 1 to 4, with the opposite relationship for carbon and phosphorus concentrations. These results showed that the groundwater system supported biofilm growth and that the upper catchment supported efficient and productive biofilms (high ratio of activity per unit biomass). © 2012, Institute of Environmental Science & Research Ltd (ESR). Ground Water © 2012, National Ground Water Association.

Prediction of SOFC Performance with or without Experiments: A Study on Minimum Requirements for Experimental Data

DOE PAGES

Yang, Tao; Sezer, Hayri; Celik, Ismail B.; ...

2015-06-02

In the present paper, a physics-based procedure combining experiments and multi-physics numerical simulations is developed for overall analysis of SOFCs operational diagnostics and performance predictions. In this procedure, essential information for the fuel cell is extracted first by utilizing empirical polarization analysis in conjunction with experiments and refined by multi-physics numerical simulations via simultaneous analysis and calibration of polarization curve and impedance behavior. The performance at different utilization cases and operating currents is also predicted to confirm the accuracy of the proposed model. It is demonstrated that, with the present electrochemical model, three air/fuel flow conditions are needed to producemore » a set of complete data for better understanding of the processes occurring within SOFCs. After calibration against button cell experiments, the methodology can be used to assess performance of planar cell without further calibration. The proposed methodology would accelerate the calibration process and improve the efficiency of design and diagnostics.« less

Biomass-to-electricity: analysis and optimization of the complete pathway steam explosion--enzymatic hydrolysis--anaerobic digestion with ICE vs SOFC as biogas users.

PubMed

Santarelli, M; Barra, S; Sagnelli, F; Zitella, P

2012-11-01

The paper deals with the energy analysis and optimization of a complete biomass-to-electricity energy pathway, starting from raw biomass towards the production of renewable electricity. The first step (biomass-to-biogas) is based on a real pilot plant located in Environment Park S.p.A. (Torino, Italy) with three main steps ((1) impregnation; (2) steam explosion; (3) enzymatic hydrolysis), completed by a two-step anaerobic fermentation. In the second step (biogas-to-electricity), the paper considers two technologies: internal combustion engines and a stack of solid oxide fuel cells. First, the complete pathway has been modeled and validated through experimental data. After, the model has been used for an analysis and optimization of the complete thermo-chemical and biological process, with the objective function of maximization of the energy balance at minimum consumption. The comparison between ICE and SOFC shows the better performance of the integrated plants based on SOFC. Copyright © 2012 Elsevier Ltd. All rights reserved.

High-performance low-temperature solid oxide fuel cell with novel BSCF cathode

NASA Astrophysics Data System (ADS)

Liu, Q. L.; Khor, K. A.; Chan, S. H.

An anode-supported solid oxide fuel cell (SOFC), consisting of a dense 10 μm Gd 0.1Ce 0.9O 1.95 (GDC) electrolyte, a porous Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3- δ (BSCF) cathode and a porous Ni-GDC cermet anode, is successfully assembled and electrochemically characterized. With humidified (3% water vapour) hydrogen as the fuel and air as the oxidant, the cell exhibits open-circuit voltages of 0.903 and 0.984 V when operating at 600 and 500 °C, respectively. The cell produces peak power densities of 1329, 863, 454, 208 and 83 mW cm -2 at 600, 550, 500, 450 and 400 °C, respectively. These results are impressive and demonstrate the potential of BSCF for use as the cathode material in new-generation SOFCs with GDC as the electrolyte. In addition, the sustained performance at temperatures below 600 °C warrants commercial exploitation of this SOFC in stationary and mobile applications.

Atmospheric Plasma Spraying Low-Temperature Cathode Materials for Solid Oxide Fuel Cells

NASA Astrophysics Data System (ADS)

Harris, J.; Kesler, O.

2010-01-01

Atmospheric plasma spraying (APS) is attractive for manufacturing solid oxide fuel cells (SOFCs) because it allows functional layers to be built rapidly with controlled microstructures. The technique allows SOFCs that operate at low temperatures (500-700 °C) to be fabricated by spraying directly onto robust and inexpensive metallic supports. However, standard cathode materials used in commercial SOFCs exhibit high polarization resistances at low operating temperatures. Therefore, alternative cathode materials with high performance at low temperatures are essential to facilitate the use of metallic supports. Coatings of lanthanum strontium cobalt ferrite (LSCF) were fabricated on steel substrates using axial-injection APS. The thickness and microstructure of the coating layers were evaluated, and x-ray diffraction analysis was performed on the coatings to detect material decomposition and the formation of undesired phases in the plasma. These results determined the envelope of plasma spray parameters in which coatings of LSCF can be manufactured, and the range of conditions in which composite cathode coatings could potentially be manufactured.

Development and Application of HVOF Sprayed Spinel Protective Coating for SOFC Interconnects

NASA Astrophysics Data System (ADS)

Thomann, O.; Pihlatie, M.; Rautanen, M.; Himanen, O.; Lagerbom, J.; Mäkinen, M.; Varis, T.; Suhonen, T.; Kiviaho, J.

2013-06-01

Protective coatings are needed for metallic interconnects used in solid oxide fuel cell (SOFC) stacks to prevent excessive high-temperature oxidation and evaporation of chromium species. These phenomena affect the lifetime of the stacks by increasing the area-specific resistance (ASR) and poisoning of the cathode. Protective MnCo2O4 and MnCo1.8Fe0.2O4 coatings were applied on ferritic steel interconnect material (Crofer 22 APU) by high velocity oxy fuel spraying. The substrate-coating systems were tested in long-term exposure tests to investigate their high-temperature oxidation behavior. Additionally, the ASRs were measured at 700 °C for 1000 h. Finally, a real coated interconnect was used in a SOFC single-cell stack for 6000 h. Post-mortem analysis was carried out with scanning electron microscopy. The deposited coatings reduced significantly the oxidation of the metal, exhibited low and stable ASR and reduced effectively the migration of chromium.

Direct Internal Reformation and Mass Transport in the Solid Oxide Fuel Cell Anode: A Pore-Scale Lattice Boltzmann Study with Detailed Reaction Kinetics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grew, Kyle N.; Joshi, Abhijit S.; Chiu, W. K. S.

2010-11-30

The solid oxide fuel cell (SOFC) allows the conversion of chemical energy that is stored in a given fuel, including light hydrocarbons, to electrical power. Hydrocarbon fuels, such as methane, are logistically favourable and provide high energy densities. However, the use of these fuels often results in a decreased efficiency and life. An improved understanding of the reactive flow in the SOFC anode can help address these issues. In this study, the transport and heterogeneous internal reformation of a methane based fuel is addressed. The effect of the SOFC anode's complex structure on transport and reactions is shown to exhibitmore » a complicated interplay between the local molar concentrations and the anode structure. Strong coupling between the phenomenological microstructures and local reformation reaction rates are recognised in this study, suggesting the extension to actual microstructures may provide new insights into the reformation processes.« less

Structural analysis of PrBaMn2O5+δ under SOFC anode conditions by in-situ neutron powder diffraction

NASA Astrophysics Data System (ADS)

Tomkiewicz, Alex C.; Tamimi, Mazin A.; Huq, Ashfia; McIntosh, Steven

2016-10-01

The crystal structure and oxygen stoichiometry of the proposed double perovskite solid oxide fuel cell (SOFC) anode material PrBaMn2O5+δ were determined under SOFC anode conditions via in-situ neutron diffraction. Measurements were performed in reducing atmospheres between 692 K and 984 K. The structure was fit to a tetragonal (space group P4/mmm) layered double perovskite structure with alternating Pr and Ba A-site cation layers. Under all conditions examined, the oxygen sites in the Ba and Mn layers were fully occupied, while the sites in the Pr layer were close to completely vacant. The results of the neutron diffraction experiments are compared to previous thermogravimetric analysis experiments to verify the accuracy of both experiments. PrBaMn2O5+δ was shown to be stable over a wide range of reducing atmospheres similar to anode operating conditions in solid oxide fuel cells without significant structural changes.

Tracking Oxygen Vacancies in Thin Film SOFC Cathodes

NASA Astrophysics Data System (ADS)

Leonard, Donovan; Kumar, Amit; Jesse, Stephen; Kalinin, Sergei; Shao-Horn, Yang; Crumlin, Ethan; Mutoro, Eva; Biegalski, Michael; Christen, Hans; Pennycook, Stephen; Borisevich, Albina

2011-03-01

Oxygen vacancies have been proposed to control the rate of the oxygen reduction reaction and ionic transport in complex oxides used as solid oxide fuel cell (SOFC) cathodes [1,2]. In this study oxygen vacancies were tracked, both dynamically and statically, with the combined use of scanned probe microscopy (SPM) and scanning transmission electron microscopy (STEM). Epitaxial films of La 0.8 Sr 0.2 Co O3 (L SC113) and L SC113 / LaSrCo O4 (L SC214) on a GDC/YSZ substrate were studied, where the latter showed increased electrocatalytic activity at moderate temperature. At atomic resolution, high angle annular dark field STEM micrographs revealed vacancy ordering in L SC113 as evidenced by lattice parameter modulation and EELS studies. The evolution of oxygen vacancy concentration and ordering with applied bias and the effects of bias cycling on the SOFC cathode performance will be discussed. Research is sponsored by the of Materials Sciences and Engineering Division, U.S. DOE.

Solid oxide fuel cell simulation and design optimization with numerical adjoint techniques

NASA Astrophysics Data System (ADS)

Elliott, Louie C.

This dissertation reports on the application of numerical optimization techniques as applied to fuel cell simulation and design. Due to the "multi-physics" inherent in a fuel cell, which results in a highly coupled and non-linear behavior, an experimental program to analyze and improve the performance of fuel cells is extremely difficult. This program applies new optimization techniques with computational methods from the field of aerospace engineering to the fuel cell design problem. After an overview of fuel cell history, importance, and classification, a mathematical model of solid oxide fuel cells (SOFC) is presented. The governing equations are discretized and solved with computational fluid dynamics (CFD) techniques including unstructured meshes, non-linear solution methods, numerical derivatives with complex variables, and sensitivity analysis with adjoint methods. Following the validation of the fuel cell model in 2-D and 3-D, the results of the sensitivity analysis are presented. The sensitivity derivative for a cost function with respect to a design variable is found with three increasingly sophisticated techniques: finite difference, direct differentiation, and adjoint. A design cycle is performed using a simple optimization method to improve the value of the implemented cost function. The results from this program could improve fuel cell performance and lessen the world's dependence on fossil fuels.

Development of planar solid oxide fuel cells for power generation applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Minh, N.Q.

1996-04-01

Planar solid oxide fuel cells (SOFCs) are presently being developed for a variety of electric power generation application. The planar design offers simple cell geometry, high power density, and multiple fabrication and gas manifolding options. Planar SOFC technology has received much attention recently, and significant progress has been made in this area. Recent effort at AlliedSignal has focused on the development of high-performance, lightweight planar SOFCs, having thin-electrolyte films, that can be operated efficiently at reduced temperatures (< 1000{degrees}C). The advantages of reduced-temperature operation include wider material choice (including use of metallic interconnects), expected longer cell life, reduced thermal stress,more » improved reliability, and reduced fuel cell cost. The key aspect in the development of thin-film SIFCs is to incorporate the thin electrolyte layer into the desired structure of cells in a manner that yields the required characteristics. AlliedSignal has developed a simple and cost-effective method based on tape calendering for the fabrication of thin-electrolyte SOFCs. Thin-electrolyte cells made by tape calendering have shown extraordinary performance, e.g., producing more than 500mW/cm{sup 2} at 700{degrees}C and 800mW/cm{sup 2} at 800{degrees}C with hydrogen as fuel and air is oxidant. thin-electrolyte single cells have been incorporated into a compliant metallic stack structure and operated at reduced and operated at reduced-temperature conditions.« less

From macro- to micro-single chamber solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Buergler, B. E.; Ochsner, M.; Vuillemin, S.; Gauckler, L. J.

Single chamber solid oxide fuel cells (SC-SOFCs) with interdigitating electrodes were prepared and operated in CH 4/air mixtures. Both electrodes (Ni-Ce 0.8Gd 0.2O 1.9 cermet and Sm 0.5Sr 0.5CoO 3- δ perovskite) were placed on the same side of a Ce 0.8Gd 0.1O 1.95 electrolyte disc. The separating gap between the electrodes was varied from 1.2 to 0.27 mm and finally down to 10 μm. Screen-printing was used for the preparation of the cells with a gap in the millimetre range, whereas micromolding in capillaries (MIMIC) was used for the preparation of the micro-SC-SOFCs. The prepared micro-SC-SOFCs consisted of an array of 19 individual cells that were connected in parallel having 100 μm wide electrodes. An open circuit voltage of 0.65-0.75 V was measured in flowing mixtures of methane and air. The maximum power density of 17 mW cm -2 was limited by the ohmic resistance of the long conduction paths along the thin electrodes to the active sites of the individual cells. The feasibility of the micro-cell was demonstrated by comparing the performance with the performance of the cells having feature sizes in the millimetre range. The cell resistance of micro-SC-SOFCs may be significantly reduced when connecting the cells in series using interconnections between anode and cathodes of adjacent cells.

Direct modeling of the electrochemistry in the three-phase boundary of solid oxide fuel cell anodes by density functional theory: a critical overview.

PubMed

Shishkin, M; Ziegler, T

2014-02-07

The first principles modeling of electrochemical reactions has proven useful for the development of efficient, durable and low cost solid oxide full cells (SOFCs). In this account we focus on recent advances in modeling of structural, electronic and catalytic properties of the SOFC anodes based on density functional theory (DFT) first principle calculations. As a starting point, we highlight that the adequate analysis of cell electrochemistry generally requires modeling of chemical reactions at the metal/oxide interface rather than on individual metal or oxide surfaces. The atomic models of Ni/YSZ and Ni/CeO2 interfaces, required for DFT simulations of reactions on SOFC anodes are discussed next, together with the analysis of the electronic structure of these interfaces. Then we proceed to DFT-based findings on charge transfer mechanisms during redox reactions on these two anodes. We provide a comparison of the electronic properties of Ni/YSZ and Ni/CeO2 interfaces and present an interpretation of their different chemical performances. Subsequently we discuss the computed energy pathways of fuel oxidation mechanisms, obtained by various groups to date. We also discuss the results of DFT studies combined with microkinetic modeling as well as the results of kinetic Monte Carlo simulations. In conclusion we summarize the key findings of DFT modeling of metal/oxide interfaces to date and highlight possible directions in the future modeling of SOFC anodes.

Solid oxide fuel cell matrix and modules

DOEpatents

Riley, Brian

1990-01-01

Porous refractory ceramic blocks arranged in an abutting, stacked configuration and forming a three dimensional array provide a support structure and coupling means for a plurality of solid oxide fuel cells (SOFCs). Each of the blocks includes a square center channel which forms a vertical shaft when the blocks are arranged in a stacked array. Positioned within the channel is a SOFC unit cell such that a plurality of such SOFC units disposed within a vertical shaft form a string of SOFC units coupled in series. A first pair of facing inner walls of each of the blocks each include an interconnecting channel hole cut horizontally and vertically into the block walls to form gas exit channels. A second pair of facing lateral walls of each block further include a pair of inner half circular grooves which form sleeves to accommodate anode fuel and cathode air tubes. The stack of ceramic blocks is self-supporting, with a plurality of such stacked arrays forming a matrix enclosed in an insulating refractory brick structure having an outer steel layer. The necessary connections for air, fuel, burnt gas, and anode and cathode connections are provided through the brick and steel outer shell. The ceramic blocks are so designed with respect to the strings of modules that by simple and logical design the strings could be replaced by hot reloading if one should fail. The hot reloading concept has not been included in any previous designs.

Solid oxide fuel cells with apatite-type lanthanum silicate-based electrolyte films deposited by radio frequency magnetron sputtering

NASA Astrophysics Data System (ADS)

Liu, Yi-Xin; Wang, Sea-Fue; Hsu, Yung-Fu; Wang, Chi-Hua

2018-03-01

In this study, solid oxide fuel cells (SOFCs) containing high-quality apatite-type magnesium doped lanthanum silicate-based electrolyte films (LSMO) deposited by RF magnetron sputtering are successfully fabricated. The LSMO film deposited at an Ar:O2 ratio of 6:4 on an anode supported NiO/Sm0.2Ce0·8O2-δ (SDC) substrate followed by post-annealing at 1000 °C reveals a uniform and dense c-axis oriented polycrystalline structure, which is well adhered to the anode substrate. A composite SDC/La0·6Sr0·4Co0·2Fe0·8O3-δ cathode layer is subsequently screen-printed on the LSMO deposited anode substrate and fired. The SOFC fabricated with the LSMO film exhibits good mechanical integrity. The single cell with the LSMO layer of ≈2.8 μm thickness reports a total cell resistance of 1.156 and 0.163 Ωcm2, open circuit voltage of 1.051 and 0.982 V, and maximum power densities of 0.212 and 1.490 Wcm-2 at measurement temperatures of 700 and 850 °C, respectively, which are comparable or superior to those of previously reported SOFCs with yttria stabilized zirconia electrolyte films. The results of the present study demonstrate the feasibility of deposition of high-quality LSMO films by RF magnetron sputtering on NiO-SDC anode substrates for the fabrication of SOFCs with good cell performance.

Novel solid oxide cells with SrCo0.8Fe0.1Ga0.1O3-δ oxygen electrode for flexible power generation and hydrogen production

NASA Astrophysics Data System (ADS)

Meng, Xiuxia; Shen, Yichi; Xie, Menghan; Yin, Yimei; Yang, Naitao; Ma, Zi-Feng; Diniz da Costa, João C.; Liu, Shaomin

2016-02-01

This work investigates the performance of solid oxide cells as fuel cells (SOFCs) for power production and also as electrolysis cells (SOECs) for hydrogen production. In order to deliver this dual mode flexible operation system, a novel perovskite oxide based on Ga3+ doped SrCo0.8Fe0.1Ga0.1O3-δ (SCFG) is synthesized via a sol-gel method. Its performance for oxygen electrode catalyst was then evaluated. Single solid oxide cell in the configuration of Ni-YSZ|YSZ|GDC|SCFG is assembled and tested in SOFC or SOEC modes from 550 to 850 °C with hydrogen as the fuel or as the product, respectively. GDC is used to avoid the reaction between the electrolyte YSZ and the cobalt-based electrode. Under SOFC mode, a maximum power density of 1044 mW cm-2 is obtained at 750 °C. Further, the cell delivers a stable power output of 650 mW cm-2 up to 125 h at 0.7 V. In the electrolysis mode, when the applied voltage is controlled at 2 V, the electrolysis current density reaches 3.33 A cm-2 at 850 °C with the hydrogen production rate up to 22.9 mL min-1 cm-2 (STP). These results reveal that SCFG is a very promising oxygen electrode material for application in both SOFC and SOEC.

Helium Ion Microscopy: A Promising Tool for Probing Biota-Mineral Interfaces

NASA Astrophysics Data System (ADS)

Lybrand, R.; Zaharescu, D. G.; Gallery, R. E.

2017-12-01

The study of biogeochemical interfaces in soil requires powerful technologies that can enhance our ability to characterize mineral surfaces and interacting organisms at micro- to nanoscale resolutions. We aim to demonstrate potential applications of Helium Ion Microscopy in the earth and ecological sciences using, as an example, samples from a field experiment. We assessed samples deployed for one year along climatic and topographic gradients in two Critical Zone Observatories (CZOs): a desert to mixed conifer forest gradient (Catalina CZO) and a humid hardwood forest (Calhoun CZO). Sterile ground rock (basalt, quartz, and granite; 53-250 µm) was sealed into nylon mesh bags and buried in the surface soils of both CZOs. We employed helium ion and scanning electron microscopies to compare retrieved ground rock samples with sterile unreacted mineral controls in conjunction with the Environmental Molecular Sciences Laboratory at Pacific Northwest National Laboratory, USA. Our work showed early colonization of mesh bag materials by fungal and bacterial organisms from the field systems and identified morphological changes in mineral grains following exposure to the soil environment. Biological specimens observed on grain surfaces exhibited contrasting features depending on mineral type and ecosystem location, including fungal hyphae that varied in length, diameter, and surface morphologies. We also present imagery that provides evidence for incipient stages of mineral transformation at the fungal-mineral interface. Our findings demonstrate that helium ion microscopy can be successfully used to characterize grain features and biological agents of weathering in experimental field samples, representing a promising avenue for research in the biogeosciences. Future directions of this work will couple high resolution imaging with measures of aqueous and solid geochemistry, fungal morphological characterization, and microbial profiling to better understand mineral transformation along gradients of climate and topography.

An efficient fully-implicit multislope MUSCL method for multiphase flow with gravity in discrete fractured media

NASA Astrophysics Data System (ADS)

Jiang, Jiamin; Younis, Rami M.

2017-06-01

The first-order methods commonly employed in reservoir simulation for computing the convective fluxes introduce excessive numerical diffusion leading to severe smoothing of displacement fronts. We present a fully-implicit cell-centered finite-volume (CCFV) framework that can achieve second-order spatial accuracy on smooth solutions, while at the same time maintain robustness and nonlinear convergence performance. A novel multislope MUSCL method is proposed to construct the required values at edge centroids in a straightforward and effective way by taking advantage of the triangular mesh geometry. In contrast to the monoslope methods in which a unique limited gradient is used, the multislope concept constructs specific scalar slopes for the interpolations on each edge of a given element. Through the edge centroids, the numerical diffusion caused by mesh skewness is reduced, and optimal second order accuracy can be achieved. Moreover, an improved smooth flux-limiter is introduced to ensure monotonicity on non-uniform meshes. The flux-limiter provides high accuracy without degrading nonlinear convergence performance. The CCFV framework is adapted to accommodate a lower-dimensional discrete fracture-matrix (DFM) model. Several numerical tests with discrete fractured system are carried out to demonstrate the efficiency and robustness of the numerical model.

Process Developed for Generating Ceramic Interconnects With Low Sintering Temperatures for Solid Oxide Fuel Cells

NASA Technical Reports Server (NTRS)

Zhong, Zhi-Min; Goldsby, Jon C.

2005-01-01

Solid oxide fuel cells (SOFCs) have been considered as premium future power generation devices because they have demonstrated high energy-conversion efficiency, high power density, and extremely low pollution, and have the flexibility of using hydrocarbon fuel. The Solid-State Energy Conversion Alliance (SECA) initiative, supported by the U.S. Department of Energy and private industries, is leading the development and commercialization of SOFCs for low-cost stationary and automotive markets. The targeted power density for the initiative is rather low, so that the SECA SOFC can be operated at a relatively low temperature (approx. 700 C) and inexpensive metallic interconnects can be utilized in the SOFC stack. As only NASA can, the agency is investigating SOFCs for aerospace applications. Considerable high power density is required for the applications. As a result, the NASA SOFC will be operated at a high temperature (approx. 900 C) and ceramic interconnects will be employed. Lanthanum chromite-based materials have emerged as a leading candidate for the ceramic interconnects. The interconnects are expected to co-sinter with zirconia electrolyte to mitigate the interface electric resistance and to simplify the processing procedure. Lanthanum chromites made by the traditional method are sintered at 1500 C or above. They react with zirconia electrolytes (which typically sinter between 1300 and 1400 C) at the sintering temperature of lanthanum chromites. It has been envisioned that lanthanum chromites with lower sintering temperatures can be co-fired with zirconia electrolyte. Nonstoichiometric lanthanum chromites can be sintered at lower temperatures, but they are unstable and react with zirconia electrolyte during co-sintering. NASA Glenn Research Center s Ceramics Branch investigated a glycine nitrate process to generate fine powder of the lanthanum-chromite-based materials. By simultaneously doping calcium on the lanthanum site, and cobalt and aluminum on the chromium site, we could sinter the materials below 1400 C. The doping concentrations were adjusted so that the thermal expansion coefficient matched that of the zirconia electrolyte. Also, the investigation was focused on stoichiometric compositions so that the materials would have better stability. Co-sintering and chemical compatibility with zirconia electrolyte were examined by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy (line scanning and dot map). The results showed that the materials bond well, but do not react, with zirconia electrolyte. The electric conductivity of the materials measured at 900 C in air was about 20 S/cm.

Measurement of heat conduction through stacked screens

NASA Technical Reports Server (NTRS)

Lewis, M. A.; Kuriyama, T.; Kuriyama, F.; Radebaugh, R.

1998-01-01

This paper describes the experimental apparatus for the measurement of heat conduction through stacked screens as well as some experimental results taken with the apparatus. Screens are stacked in a fiberglass-epoxy cylinder, which is 24.4 mm in diameter and 55 mm in length. The cold end of the stacked screens is cooled by a Gifford-McMahon (GM) cryocooler at cryogenic temperature, and the hot end is maintained at room temperature. Heat conduction through the screens is determined from the temperature gradient in a calibrated heat flow sensor mounted between the cold end of the stacked screens and the GM cryocooler. The samples used for these experiments consisted of 400-mesh stainless steel screens, 400-mesh phosphor bronze screens, and two different porosities of 325-mesh stainless steel screens. The wire diameter of the 400-mesh stainless steel and phosphor bronze screens was 25.4 micrometers and the 325-mesh stainless steel screen wire diameters were 22.9 micrometers and 27.9 micrometers. Standard porosity values were used for the experimental data with additional porosity values used on selected experiments. The experimental results showed that the helium gas between each screen enhanced the heat conduction through the stacked screens by several orders of magnitude compared to that in vacuum. The conduction degradation factor is the ratio of actual heat conduction to the heat conduction where the regenerator material is assumed to be a solid rod of the same cross sectional area as the metal fraction of the screen. This factor was about 0.1 for the stainless steel and 0.022 for the phosphor bronze, and almost constant for the temperature range of 40 to 80 K at the cold end.

Measurement of heat conduction through stacked screens.

PubMed

Lewis, M A; Kuriyama, T; Kuriyama, F; Radebaugh, R

1998-01-01

This paper describes the experimental apparatus for the measurement of heat conduction through stacked screens as well as some experimental results taken with the apparatus. Screens are stacked in a fiberglass-epoxy cylinder, which is 24.4 mm in diameter and 55 mm in length. The cold end of the stacked screens is cooled by a Gifford-McMahon (GM) cryocooler at cryogenic temperature, and the hot end is maintained at room temperature. Heat conduction through the screens is determined from the temperature gradient in a calibrated heat flow sensor mounted between the cold end of the stacked screens and the GM cryocooler. The samples used for these experiments consisted of 400-mesh stainless steel screens, 400-mesh phosphor bronze screens, and two different porosities of 325-mesh stainless steel screens. The wire diameter of the 400-mesh stainless steel and phosphor bronze screens was 25.4 micrometers and the 325-mesh stainless steel screen wire diameters were 22.9 micrometers and 27.9 micrometers. Standard porosity values were used for the experimental data with additional porosity values used on selected experiments. The experimental results showed that the helium gas between each screen enhanced the heat conduction through the stacked screens by several orders of magnitude compared to that in vacuum. The conduction degradation factor is the ratio of actual heat conduction to the heat conduction where the regenerator material is assumed to be a solid rod of the same cross sectional area as the metal fraction of the screen. This factor was about 0.1 for the stainless steel and 0.022 for the phosphor bronze, and almost constant for the temperature range of 40 to 80 K at the cold end.

Edge delamination of composite laminates subject to combined tension and torsional loading

NASA Technical Reports Server (NTRS)

Hooper, Steven J.

1990-01-01

Delamination is a common failure mode of laminated composite materials. Edge delamination is important since it results in reduced stiffness and strength of the laminate. The tension/torsion load condition is of particular significance to the structural integrity of composite helicopter rotor systems. Material coupons can easily be tested under this type of loading in servo-hydraulic tension/torsion test stands using techniques very similar to those used for the Edge Delamination Tensile Test (EDT) delamination specimen. Edge delamination of specimens loaded in tension was successfully analyzed by several investigators using both classical laminate theory and quasi-three dimensional (Q3D) finite element techniques. The former analysis technique can be used to predict the total strain energy release rate, while the latter technique enables the calculation of the mixed-mode strain energy release rates. The Q3D analysis is very efficient since it produces a three-dimensional solution to a two-dimensional domain. A computer program was developed which generates PATRAN commands to generate the finite element model. PATRAN is a pre- and post-processor which is commonly used with a variety of finite element programs such as MCS/NASTRAN. The program creates a sufficiently dense mesh at the delamination crack tips to support a mixed-mode fracture mechanics analysis. The program creates a coarse mesh in those regions where the gradients in the stress field are low (away from the delamination regions). A transition mesh is defined between these regions. This program is capable of generating a mesh for an arbitrarily oriented matrix crack. This program significantly reduces the modeling time required to generate these finite element meshes, thus providing a realistic tool with which to investigate the tension torsion problem.

Dose gradient curve: A new tool for evaluating dose gradient.

PubMed

Sung, KiHoon; Choi, Young Eun

2018-01-01

Stereotactic radiotherapy, which delivers an ablative high radiation dose to a target volume for maximum local tumor control, requires a rapid dose fall-off outside the target volume to prevent extensive damage to nearby normal tissue. Currently, there is no tool to comprehensively evaluate the dose gradient near the target volume. We propose the dose gradient curve (DGC) as a new tool to evaluate the quality of a treatment plan with respect to the dose fall-off characteristics. The average distance between two isodose surfaces was represented by the dose gradient index (DGI) estimated by a simple equation using the volume and surface area of isodose levels. The surface area was calculated by mesh generation and surface triangulation. The DGC was defined as a plot of the DGI of each dose interval as a function of the dose. Two types of DGCs, differential and cumulative, were generated. The performance of the DGC was evaluated using stereotactic radiosurgery plans for virtual targets. Over the range of dose distributions, the dose gradient of each dose interval was well-characterized by the DGC in an easily understandable graph format. Significant changes in the DGC were observed reflecting the differences in planning situations and various prescription doses. The DGC is a rational method for visualizing the dose gradient as the average distance between two isodose surfaces; the shorter the distance, the steeper the dose gradient. By combining the DGC with the dose-volume histogram (DVH) in a single plot, the DGC can be utilized to evaluate not only the dose gradient but also the target coverage in routine clinical practice.

MATERIALS SCIENCE: New Tigers in the Fuel Cell Tank.

PubMed

Service, R F

2000-06-16

After decades of incremental advances, a spurt of findings suggests that fuel cells that run on good old fossil fuels are almost ready for prime time. Although conventional ceramic cells, known as solid oxide fuel cells, require expensive heat-resistant materials, a new generation of SOFCs, including one featured on page 2031, converts hydrocarbons directly into electricity at lower temperatures. And a recent demonstration of a system of standard SOFCs large enough to light up more than 200 homes showed that it is the most efficient large-scale electrical generator ever designed.

Using Polymer Electrolyte Membrane Fuel Cells in a Hybrid Surface Ship Propulsion Plant to Increase Fuel Efficiency

DTIC Science & Technology

2010-06-01

cell ( PEMFC ), and the phosphoric acid fuel cell (PAFC). 2.3.1 Solid Oxide Fuel Cells (SOFC) The first type of fuel cell considered is the SOFC. This...durability issues for use within a given application. 2.3.2 Polymer Electrolyte Membrane Fuel Cells ( PEMFC ) The PEMFC operates by passing hydrogen that has...cells. Some advantages of PEMFC operating at such low temperatures is that the fuel cell doesn’t require as meticulous of a support system infrastructure

Direct ethanol solid oxide fuel cell operating in gradual internal reforming

NASA Astrophysics Data System (ADS)

Nobrega, S. D.; Galesco, M. V.; Girona, K.; de Florio, D. Z.; Steil, M. C.; Georges, S.; Fonseca, F. C.

2012-09-01

An electrolyte supported solid oxide fuel cell (SOFC) using standard electrodes, doped-lanthanum manganite cathode and Ni-cermet anode, was operated with direct (anhydrous) ethanol for more than 100 h, delivering essentially the same power output as running on hydrogen. A ceria-based layer provides the catalytic activity for the gradual internal reforming, which uses the steam formed by the electrochemical oxidation of hydrogen for the decomposition of ethanol. Such a concept opens up the way for multi-fuel SOFCs using standard components and a catalytic layer.

Design, integration and demonstration of a 50 W JP8/kerosene fueled portable SOFC power generator

NASA Astrophysics Data System (ADS)

Cheekatamarla, Praveen K.; Finnerty, Caine M.; Robinson, Charles R.; Andrews, Stanley M.; Brodie, Jonathan A.; Lu, Y.; DeWald, Paul G.

A man-portable solid oxide fuel cell (SOFC) system integrated with desulfurized JP8 partial oxidation (POX) reformer was demonstrated to supply a continuous power output of 50 W. This paper discusses some of the design paths chosen and challenges faced during the thermal integration of the stack and reformer in aiding the system startup and shutdown along with balance of plant and power management solutions. The package design, system capabilities, and test results of the prototype unit are presented.

Process Developed for Fabricating Engineered Pore Structures for High- Fuel-Utilization Solid Oxide Fuel Cells

NASA Technical Reports Server (NTRS)

Sofie, Stephen W.; Cable, Thomas L.; Salamone, Sam M.

2005-01-01

Solid oxide fuel cells (SOFCs) have tremendous commercial potential because of their high efficiency, high energy density, and flexible fuel capability (ability to use fossil fuels). The drive for high-power-utilizing, ultrathin electrolytes (less than 10 microns), has placed an increased demand on the anode to provide structural support, yet allow sufficient fuel entry for sustained power generation. Concentration polarization, a condition where the fuel demand exceeds the supply, is evident in all commercial-based anode-supported cells, and it presents a significant roadblock to SOFC commercialization.

Sensitivity analysis, approximate analysis, and design optimization for internal and external viscous flows

NASA Technical Reports Server (NTRS)

Taylor, Arthur C., III; Hou, Gene W.; Korivi, Vamshi M.

1991-01-01

A gradient-based design optimization strategy for practical aerodynamic design applications is presented, which uses the 2D thin-layer Navier-Stokes equations. The strategy is based on the classic idea of constructing different modules for performing the major tasks such as function evaluation, function approximation and sensitivity analysis, mesh regeneration, and grid sensitivity analysis, all driven and controlled by a general-purpose design optimization program. The accuracy of aerodynamic shape sensitivity derivatives is validated on two viscous test problems: internal flow through a double-throat nozzle and external flow over a NACA 4-digit airfoil. A significant improvement in aerodynamic performance has been achieved in both cases. Particular attention is given to a consistent treatment of the boundary conditions in the calculation of the aerodynamic sensitivity derivatives for the classic problems of external flow over an isolated lifting airfoil on 'C' or 'O' meshes.

The DANTE Boltzmann transport solver: An unstructured mesh, 3-D, spherical harmonics algorithm compatible with parallel computer architectures

DOE Office of Scientific and Technical Information (OSTI.GOV)

McGhee, J.M.; Roberts, R.M.; Morel, J.E.

1997-06-01

A spherical harmonics research code (DANTE) has been developed which is compatible with parallel computer architectures. DANTE provides 3-D, multi-material, deterministic, transport capabilities using an arbitrary finite element mesh. The linearized Boltzmann transport equation is solved in a second order self-adjoint form utilizing a Galerkin finite element spatial differencing scheme. The core solver utilizes a preconditioned conjugate gradient algorithm. Other distinguishing features of the code include options for discrete-ordinates and simplified spherical harmonics angular differencing, an exact Marshak boundary treatment for arbitrarily oriented boundary faces, in-line matrix construction techniques to minimize memory consumption, and an effective diffusion based preconditioner formore » scattering dominated problems. Algorithm efficiency is demonstrated for a massively parallel SIMD architecture (CM-5), and compatibility with MPP multiprocessor platforms or workstation clusters is anticipated.« less

Vectorization, threading, and cache-blocking considerations for hydrocodes on emerging architectures

DOE PAGES

Fung, J.; Aulwes, R. T.; Bement, M. T.; ...

2015-07-14

This work reports on considerations for improving computational performance in preparation for current and expected changes to computer architecture. The algorithms studied will include increasingly complex prototypes for radiation hydrodynamics codes, such as gradient routines and diffusion matrix assembly (e.g., in [1-6]). The meshes considered for the algorithms are structured or unstructured meshes. The considerations applied for performance improvements are meant to be general in terms of architecture (not specifically graphical processing unit (GPUs) or multi-core machines, for example) and include techniques for vectorization, threading, tiling, and cache blocking. Out of a survey of optimization techniques on applications such asmore » diffusion and hydrodynamics, we make general recommendations with a view toward making these techniques conceptually accessible to the applications code developer. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.« less

Diffusion of Zonal Variables Using Node-Centered Diffusion Solver

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, T B

2007-08-06

Tom Kaiser [1] has done some preliminary work to use the node-centered diffusion solver (originally developed by T. Palmer [2]) in Kull for diffusion of zonal variables such as electron temperature. To avoid numerical diffusion, Tom used a scheme developed by Shestakov et al. [3] and found their scheme could, in the vicinity of steep gradients, decouple nearest-neighbor zonal sub-meshes leading to 'alternating-zone' (red-black mode) errors. Tom extended their scheme to couple the sub-meshes with appropriate chosen artificial diffusion and thereby solved the 'alternating-zone' problem. Because the choice of the artificial diffusion coefficient could be very delicate, it is desirablemore » to use a scheme that does not require the artificial diffusion but still able to avoid both numerical diffusion and the 'alternating-zone' problem. In this document we present such a scheme.« less

Tempest: Mesoscale test case suite results and the effect of order-of-accuracy on pressure gradient force errors

NASA Astrophysics Data System (ADS)

Guerra, J. E.; Ullrich, P. A.

2014-12-01

Tempest is a new non-hydrostatic atmospheric modeling framework that allows for investigation and intercomparison of high-order numerical methods. It is composed of a dynamical core based on a finite-element formulation of arbitrary order operating on cubed-sphere and Cartesian meshes with topography. The underlying technology is briefly discussed, including a novel Hybrid Finite Element Method (HFEM) vertical coordinate coupled with high-order Implicit/Explicit (IMEX) time integration to control vertically propagating sound waves. Here, we show results from a suite of Mesoscale testing cases from the literature that demonstrate the accuracy, performance, and properties of Tempest on regular Cartesian meshes. The test cases include wave propagation behavior, Kelvin-Helmholtz instabilities, and flow interaction with topography. Comparisons are made to existing results highlighting improvements made in resolving atmospheric dynamics in the vertical direction where many existing methods are deficient.

3-D direct current resistivity anisotropic modelling by goal-oriented adaptive finite element methods

NASA Astrophysics Data System (ADS)

Ren, Zhengyong; Qiu, Lewen; Tang, Jingtian; Wu, Xiaoping; Xiao, Xiao; Zhou, Zilong

2018-01-01

Although accurate numerical solvers for 3-D direct current (DC) isotropic resistivity models are current available even for complicated models with topography, reliable numerical solvers for the anisotropic case are still an open question. This study aims to develop a novel and optimal numerical solver for accurately calculating the DC potentials for complicated models with arbitrary anisotropic conductivity structures in the Earth. First, a secondary potential boundary value problem is derived by considering the topography and the anisotropic conductivity. Then, two a posteriori error estimators with one using the gradient-recovery technique and one measuring the discontinuity of the normal component of current density are developed for the anisotropic cases. Combing the goal-oriented and non-goal-oriented mesh refinements and these two error estimators, four different solving strategies are developed for complicated DC anisotropic forward modelling problems. A synthetic anisotropic two-layer model with analytic solutions verified the accuracy of our algorithms. A half-space model with a buried anisotropic cube and a mountain-valley model are adopted to test the convergence rates of these four solving strategies. We found that the error estimator based on the discontinuity of current density shows better performance than the gradient-recovery based a posteriori error estimator for anisotropic models with conductivity contrasts. Both error estimators working together with goal-oriented concepts can offer optimal mesh density distributions and highly accurate solutions.

A finite element: Boundary integral method for electromagnetic scattering. Ph.D. Thesis Technical Report, Feb. - Sep. 1992

NASA Technical Reports Server (NTRS)

Collins, J. D.; Volakis, John L.

1992-01-01

A method that combines the finite element and boundary integral techniques for the numerical solution of electromagnetic scattering problems is presented. The finite element method is well known for requiring a low order storage and for its capability to model inhomogeneous structures. Of particular emphasis in this work is the reduction of the storage requirement by terminating the finite element mesh on a boundary in a fashion which renders the boundary integrals in convolutional form. The fast Fourier transform is then used to evaluate these integrals in a conjugate gradient solver, without a need to generate the actual matrix. This method has a marked advantage over traditional integral equation approaches with respect to the storage requirement of highly inhomogeneous structures. Rectangular, circular, and ogival mesh termination boundaries are examined for two-dimensional scattering. In the case of axially symmetric structures, the boundary integral matrix storage is reduced by exploiting matrix symmetries and solving the resulting system via the conjugate gradient method. In each case several results are presented for various scatterers aimed at validating the method and providing an assessment of its capabilities. Important in methods incorporating boundary integral equations is the issue of internal resonance. A method is implemented for their removal, and is shown to be effective in the two-dimensional and three-dimensional applications.

Ionic Conductivity and its Role in Oxidation Reactions

NASA Astrophysics Data System (ADS)

Tamimi, Mazin Abdulla

In the field of solid oxide fuel cells (SOFCs), a substantial portion of research is focused on the ability of some oxide materials to conduct oxygen anions through their structure. For electrolytes, the benefits of improving bulk transport of ions are obvious: decrease the resistive losses of the electrolyte, and device efficiency goes up and higher power densities are possible. Even for cathode materials, better bulk ion transport leads to an increase in the oxygen exchange rate at the cathode surface, and the oxygen reduction reaction at the cathode surface is the rate limiting step for SOFC operation at intermediate temperatures (500-700ºC). As operation in this regime is a key step towards lowering the manufacturing cost and increasing the lifetime of devices, much effort is spent searching for new, more conductive materials, and analyzing existing materials to discover the structure-activity relationships that influence ionic conductivity. In the first part of this work, an overview is given of the neutron powder diffraction (NPD) techniques that are used to probe the structure of the materials in later parts. In the second part, NPD was used to analyze the structures of perovskite-type cathode materials, and show that increases in bulk conductivity led to increases in the surface oxygen exchange rate of these materials. In the final part, the methods used for SOFC cathode design were applied towards the design of oxide catalysts used for certain hydrocarbon partial oxidation reactions. The reactions studied follow the Mars van Krevelen mechanism, where oxygen atoms in the catalyst are consumed as part of the reaction and are subsequently replenished by oxygen in the gas phase. Similar to SOFC cathode operation, these processes include an oxygen reduction step, so it was hypothesized that increasing the ionic conductivity of the catalysts would improve their performance, just as it does for SOFC cathode materials. While the results are preliminary, the combination of a reference catalyst for the oxidative coupling of methane with a support with very high oxygen conductivity demonstrated a small increase in performance at low temperatures.

Operation of a solid oxide fuel cell on biodiesel with a partial oxidation reformer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siefert, N, Shekhawat, D.; Gemmen, R.; Berry, D.

The National Energy Technology Laboratory’s Office of Research & Development (NETL/ORD) has successfully demonstrated the operation of a solid oxide fuel cell (SOFC) using reformed biodiesel. The biodiesel for the project was produced and characterized by West Virginia State University (WVSU). This project had two main aspects: 1) demonstrate a catalyst formulation on monolith for biodiesel fuel reforming; and 2) establish SOFC stack test stand capabilities. Both aspects have been completed successfully. For the first aspect, in–house patented catalyst specifications were developed, fabricated and tested. Parametric reforming studies of biofuels provided data on fuel composition, catalyst degradation, syngas composition, andmore » operating parameters required for successful reforming and integration with the SOFC test stand. For the second aspect, a stack test fixture (STF) for standardized testing, developed by Pacific Northwest National Laboratory (PNNL) and Lawrence Berkeley National Laboratory (LBNL) for the Solid Energy Conversion Alliance (SECA) Program, was engineered and constructed at NETL. To facilitate the demonstration of the STF, NETL employed H.C. Starck Ceramics GmbH & Co. (Germany) anode supported solid oxide cells. In addition, anode supported cells, SS441 end plates, and cell frames were transferred from PNNL to NETL. The stack assembly and conditioning procedures, including stack welding and sealing, contact paste application, binder burn-out, seal-setting, hot standby, and other stack assembly and conditioning methods were transferred to NETL. In the future, fuel cell stacks provided by SECA or other developers could be tested at the STF to validate SOFC performance on various fuels. The STF operated on hydrogen for over 1000 hrs before switching over to reformed biodiesel for 100 hrs of operation. Combining these first two aspects led to demonstrating the biodiesel syngas in the STF. A reformer was built and used to convert 0.5 ml/min of biodiesel into mostly hydrogen and carbon monoxide (syngas.) The syngas was fed to the STF and fuel cell stack. The results presented in this experimental report document one of the first times a SOFC has been operated on syngas from reformed biodiesel.« less

Solid oxide fuel cell electrolytes produced via very low pressure suspension plasma spray and electrophoretic deposition

NASA Astrophysics Data System (ADS)

Fleetwood, James D.

Solid oxide fuel cells (SOFCs) are a promising element of comprehensive energy policies due to their direct mechanism for converting the oxidization of fuel, such as hydrogen, into electrical energy. Both very low pressure plasma spray and electrophoretic deposition allow working with high melting temperature SOFC suspension based feedstock on complex surfaces, such as in non-planar SOFC designs. Dense, thin electrolytes of ideal composition for SOFCs can be fabricated with each of these processes, while compositional control is achieved with dissolved dopant compounds that are incorporated into the coating during deposition. In the work reported, sub-micron 8 mole % Y2O3-ZrO2 (YSZ) and gadolinia-doped ceria (GDC), powders, including those in suspension with scandium-nitrate dopants, were deposited on NiO-YSZ anodes, via very low pressure suspension plasma spray (VLPSPS) at Sandia National Laboratories' Thermal Spray Research Laboratory and electrophoretic deposition (EPD) at Purdue University. Plasma spray was carried out in a chamber held at 320 - 1300 Pa, with the plasma composed of argon, hydrogen, and helium. EPD was characterized utilizing constant current deposition at 10 mm electrode separation, with deposits sintered from 1300 -- 1500 °C for 2 hours. The role of suspension constituents in EPD was analyzed based on a parametric study of powder loading, powder specific surface area, polyvinyl butyral (PVB) content, polyethyleneimine (PEI) content, and acetic acid content. Increasing PVB content and reduction of particle specific surface area were found to eliminate the formation of cracks when drying. PEI and acetic acid content were used to control suspension stability and the adhesion of deposits. Additionally, EPD was used to fabricate YSZ/GDC bilayer electrolyte systems. The resultant YSZ electrolytes were 2-27 microns thick and up to 97% dense. Electrolyte performance as part of a SOFC system with screen printed LSCF cathodes was evaluated with peak power densities as high as 520 mW/cm2 at 800 °C for YSZ and 350 mW/cm 2 at 800 °C for YSZ/GDC bilayer electrolytes.

Promotion of Oxygen Reduction by Exsolved Silver Nanoparticles on a Perovskite Scaffold for Low-Temperature Solid Oxide Fuel Cells.

PubMed

Zhu, Yinlong; Zhou, Wei; Ran, Ran; Chen, Yubo; Shao, Zongping; Liu, Meilin

2016-01-13

Solid oxide fuel cells (SOFCs) have potential to be the cleanest and most efficient electrochemical energy conversion devices with excellent fuel flexibility. To make SOFC systems more durable and economically competitive, however, the operation temperature must be significantly reduced, which depends sensitively on the development of highly active electrocatalysts for oxygen reduction reaction (ORR) at low temperatures. Here we report a novel silver nanoparticle-decorated perovskite oxide, prepared via a facile exsolution process from a Sr0.95Ag0.05Nb0.1Co0.9O3-δ (SANC) perovskite precursor, as a highly active and robust ORR electrocatalyst for low-temperature SOFCs. The exsolved Sr0.95Ag0.05Nb0.1Co0.9O3-δ (denoted as e-SANC) electrode is very active for ORR, achieving a very low area specific resistance (∼0.214 Ω cm(2) at 500 °C). An anode-supported cell with the new heterostructured cathode demonstrates very high peak power density (1116 mW cm(-2) at 500 °C) and stable operation for 140 h at a current density of 625 mA cm(-2). The superior ORR activity and stability are attributed to the fast oxygen surface exchange kinetics and the firm adhesion of the Ag nanoparticles to the Sr0.95Nb0.1Co0.9O3-δ (SNC0.95) support. Moreover, the e-SANC cathode displays improved tolerance to CO2. These unique features make the new heterostructured material a highly promising cathode for low-temperature SOFCs.

Techno-economic analysis of sorption-enhanced steam methane reforming in a fixed bed reactor network integrated with fuel cell

NASA Astrophysics Data System (ADS)

Diglio, Giuseppe; Hanak, Dawid P.; Bareschino, Piero; Mancusi, Erasmo; Pepe, Francesco; Montagnaro, Fabio; Manovic, Vasilije

2017-10-01

Sorption-enhanced steam methane reforming (SE-SMR) is a promising alternative for H2 production with inherent CO2 capture. This study evaluates the techno-economic performance of SE-SMR in a network of fixed beds and its integration with a solid oxide fuel cell (SE-SMR-SOFC) for power generation. The analysis revealed that both proposed systems are characterised by better economic performance than the reference systems. In particular, for SE-SMR the levelised cost of hydrogen is 1.6 €ṡkg-1 and the cost of CO2 avoided is 29.9 €ṡtCO2-1 (2.4 €ṡkg-1 and 50 €ṡtCO2-1, respectively, for SMR with CO2 capture) while for SE-SMR-SOFC the levelised cost of electricity is 0.078 €ṡkWh-1 and the cost of CO2 avoided is 36.9 €ṡtCO2-1 (0.080 €ṡkWh-1 and 80 €ṡtCO2-1, respectively, for natural gas-fired power plant with carbon capture). The sensitivity analysis showed that the specific cost of fuel and the capital cost of fuel cell mainly affect the economic performance of SE-SMR and SE-SMR-SOFC, respectively. The daily revenue of the SE-SMR-SOFC system is higher than that of the natural gas-fired power plant if the difference between the carbon tax and the CO2 transport and storage cost is > 6 €ṡtCO2-1.

Emerging Fuel Cell Technology Being Developed: Offers Many Benefits to Air Vehicles

NASA Technical Reports Server (NTRS)

Walker, James F.; Civinskas, Kestutis C.

2004-01-01

Fuel cells, which have recently received considerable attention for terrestrial applications ranging from automobiles to stationary power generation, may enable new aerospace missions as well as offer fuel savings, quiet operations, and reduced emissions for current and future aircraft. NASA has extensive experience with fuel cells, having used them on manned space flight systems over four decades. Consequently, the NASA Glenn Research Center has initiated an effort to investigate and develop fuel cell technologies for multiple aerospace applications. Two promising fuel cell types are the proton exchange membrane (PEM) and solid oxide fuel cell (SOFC). PEM technology, first used on the Gemini spacecraft in the sixties, remained unutilized thereafter until the automotive industry recently recognized the potential. PEM fuel cells are low-temperature devices offering quick startup time but requiring relatively pure hydrogen fuel. In contrast, SOFCs operate at high temperatures and tolerate higher levels of impurities. This flexibility allows SOFCs to use hydrocarbon fuels, which is an important factor considering our current liquid petroleum infrastructure. However, depending on the specific application, either PEM or SOFC can be attractive. As only NASA can, the Agency is pursuing fuel cell technology for civil uninhabited aerial vehicles (UAVs) because it offers enhanced scientific capabilities, including enabling highaltitude, long-endurance missions. The NASA Helios aircraft demonstrated altitudes approaching 100,000 ft using solar power in 2001, and future plans include the development of a regenerative PEM fuel cell to provide nighttime power. Unique to NASA's mission, the high-altitude aircraft application requires the PEM fuel cell to operate on pure oxygen, instead of the air typical of terrestrial applications.

Degradation analysis of anode-supported intermediate temperature-solid oxide fuel cells under various failure modes

NASA Astrophysics Data System (ADS)

Lee, Tae-Hee; Park, Ka-Young; Kim, Ji-Tae; Seo, Yongho; Kim, Ki Buem; Song, Sun-Ju; Park, Byoungnam; Park, Jun-Young

2015-02-01

This study focuses on mechanisms and symptoms of several simulated failure modes, which may have significant influences on the long-term durability and operational stability of intermediate temperature-solid oxide fuel cells (IT-SOFCs), including fuel/oxidation starvation by breakdown of fuel/air supply components and wet and dry cycling atmospheres. Anode-supported IT-SOFCs consisting of a Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF)-Nd0.1Ce0.9O2-δ (NDC) composite cathode with an NDC electrolyte on a Ni-NDC anode substrate are fabricated via dry-pressings followed by the co-firing method. Comprehensive and systematic research based on the failure mode and effect analysis (FMEA) of anode-supported IT-SOFCs is conducted using various electrochemical and physiochemical analysis techniques to extend our understanding of the major mechanisms of performance deterioration under SOFC operating conditions. The fuel-starvation condition in the fuel-pump failure mode causes irreversible mechanical degradation of the electrolyte and cathode interface by the dimensional expansion of the anode support due to the oxidation of Ni metal to NiO. In contrast, the BSCF cathode shows poor stability under wet and dry cycling modes of cathode air due to the strong electroactivity of SrO with H2O. On the other hand, the air-depletion phenomena under air-pump failure mode results in the recovery of cell performance during the long-term operation without the visible microstructural transformation through the reduction of anode overvoltage.

Multi-Dimensional Quantum Effect Simulation Using a Density-Gradient Model and Script-Level Programming Techniques

NASA Technical Reports Server (NTRS)

Rafferty, Connor S.; Biegel, Bryan A.; Yu, Zhi-Ping; Ancona, Mario G.; Bude, J.; Dutton, Robert W.; Saini, Subhash (Technical Monitor)

1998-01-01

A density-gradient (DG) model is used to calculate quantum-mechanical corrections to classical carrier transport in MOS (Metal Oxide Semiconductor) inversion/accumulation layers. The model is compared to measured data and to a fully self-consistent coupled Schrodinger and Poisson equation (SCSP) solver. Good agreement is demonstrated for MOS capacitors with gate oxide as thin as 21 A. It is then applied to study carrier distribution in ultra short MOSFETs (Metal Oxide Semiconductor Field Effect Transistor) with surface roughness. This work represents the first implementation of the DG formulation on multidimensional unstructured meshes. It was enabled by a powerful scripting approach which provides an easy-to-use and flexible framework for solving the fourth-order PDEs (Partial Differential Equation) of the DG model.

SAGE: The Self-Adaptive Grid Code. 3

NASA Technical Reports Server (NTRS)

Davies, Carol B.; Venkatapathy, Ethiraj

1999-01-01

The multi-dimensional self-adaptive grid code, SAGE, is an important tool in the field of computational fluid dynamics (CFD). It provides an efficient method to improve the accuracy of flow solutions while simultaneously reducing computer processing time. Briefly, SAGE enhances an initial computational grid by redistributing the mesh points into more appropriate locations. The movement of these points is driven by an equal-error-distribution algorithm that utilizes the relationship between high flow gradients and excessive solution errors. The method also provides a balance between clustering points in the high gradient regions and maintaining the smoothness and continuity of the adapted grid, The latest version, Version 3, includes the ability to change the boundaries of a given grid to more efficiently enclose flow structures and provides alternative redistribution algorithms.

Weak Galerkin finite element methods for Darcy flow: Anisotropy and heterogeneity

NASA Astrophysics Data System (ADS)

Lin, Guang; Liu, Jiangguo; Mu, Lin; Ye, Xiu

2014-11-01

This paper presents a family of weak Galerkin finite element methods (WGFEMs) for Darcy flow computation. The WGFEMs are new numerical methods that rely on the novel concept of discrete weak gradients. The WGFEMs solve for pressure unknowns both in element interiors and on the mesh skeleton. The numerical velocity is then obtained from the discrete weak gradient of the numerical pressure. The new methods are quite different than many existing numerical methods in that they are locally conservative by design, the resulting discrete linear systems are symmetric and positive-definite, and there is no need for tuning problem-dependent penalty factors. We test the WGFEMs on benchmark problems to demonstrate the strong potential of these new methods in handling strong anisotropy and heterogeneity in Darcy flow.

Promotion of water-mediated carbon removal by nanostructured barium oxide/nickel interfaces in solid oxide fuel cells.

PubMed

Yang, Lei; Choi, YongMan; Qin, Wentao; Chen, Haiyan; Blinn, Kevin; Liu, Mingfei; Liu, Ping; Bai, Jianming; Tyson, Trevor A; Liu, Meilin

2011-06-21

The existing Ni-yttria-stabilized zirconia anodes in solid oxide fuel cells (SOFCs) perform poorly in carbon-containing fuels because of coking and deactivation at desired operating temperatures. Here we report a new anode with nanostructured barium oxide/nickel (BaO/Ni) interfaces for low-cost SOFCs, demonstrating high power density and stability in C(3)H(8), CO and gasified carbon fuels at 750°C. Synchrotron-based X-ray analyses and microscopy reveal that nanosized BaO islands grow on the Ni surface, creating numerous nanostructured BaO/Ni interfaces that readily adsorb water and facilitate water-mediated carbon removal reactions. Density functional theory calculations predict that the dissociated OH from H(2)O on BaO reacts with C on Ni near the BaO/Ni interface to produce CO and H species, which are then electrochemically oxidized at the triple-phase boundaries of the anode. This anode offers potential for ushering in a new generation of SOFCs for efficient, low-emission conversion of readily available fuels to electricity.

Effect of Gd2O3 doping on structure and boron volatility of borosilicate glass sealants in solid oxide fuel cells-A study on the La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode

NASA Astrophysics Data System (ADS)

Zhang, Qi; Tan, Shengwei; Ren, Mengyuan; Yang, Hsiwen; Tang, Dian; Chen, Kongfa; Zhang, Teng; Jiang, San Ping

2018-04-01

Boron volatility is one of the most important properties of borosilicate-based glass sealants in solid oxide fuel cells (SOFCs), as boron contaminants react with lanthanum-containing cathodes, forming LaBO3 and degrading the activity of SOFCs. Here, we report that the reaction between the volatile boron and a La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode during polarization can be significantly reduced by doping aluminoborosilicate glass with Gd2O3. Specifically, the Gd cations in glass with 2 mol.% Gd2O3 dissolve preferentially in the borate-rich environment to form more Gd-metaborate structures and promote the formation of calcium metaborate (CaB2O4); they also condense the B-O network after heat treatment, which suppresses poisoning by boron contaminants on the LSCF cathode. The results provide insights into design and development of a reliable sealing glass for SOFC applications.

Why solid oxide cells can be reversibly operated in solid oxide electrolysis cell and fuel cell modes?

PubMed

Chen, Kongfa; Liu, Shu-Sheng; Ai, Na; Koyama, Michihisa; Jiang, San Ping

2015-12-14

High temperature solid oxide cells (SOCs) are attractive for storage and regeneration of renewable energy by operating reversibly in solid oxide electrolysis cell (SOEC) and solid oxide fuel cell (SOFC) modes. However, the stability of SOCs, particularly the deterioration of the performance of oxygen electrodes in the SOEC operation mode, is the most critical issue in the development of high performance and durable SOCs. In this study, we investigate in detail the electrochemical activity and stability of La0.8Sr0.2MnO3 (LSM) oxygen electrodes in cyclic SOEC and SOFC modes. The results show that the deterioration of LSM oxygen electrodes caused by anodic polarization can be partially or completely recovered by subsequent cathodic polarization. Using in situ assembled LSM electrodes without pre-sintering, we demonstrate that the deteriorated LSM/YSZ interface can be repaired and regenerated by operating the cells under cathodic polarization conditions. This study for the first time establishes the foundation for the development of truly reversible and stable SOCs for hydrogen fuel production and electricity generation in cyclic SOEC and SOFC operation modes.

Thermal Modeling and Management of Solid Oxide Fuel Cells Operating with Internally Reformed Methane

NASA Astrophysics Data System (ADS)

Wu, Yiyang; Shi, Yixiang; Cai, Ningsheng; Ni, Meng

2018-06-01

A detailed three-dimensional mechanistic model of a large-scale solid oxide fuel cell (SOFC) unit running on partially pre-reformed methane is developed. The model considers the coupling effects of chemical and electrochemical reactions, mass transport, momentum and heat transfer in the SOFC unit. After model validation, parametric simulations are conducted to investigate how the methane pre-reforming ratio affects the transport and electrochemistry of the SOFC unit. It is found that the methane steam reforming reaction has a "smoothing effect", which can achieve more uniform distributions of gas compositions, current density and temperature among the cell plane. In the case of 1500 W/m2 power density output, adding 20% methane absorbs 50% of internal heat production inside the cell, reduces the maximum temperature difference inside the cell from 70 K to 22 K and reduces the cathode air supply by 75%, compared to the condition of completely pre-reforming of methane. Under specific operating conditions, the pre-reforming ratio of methane has an optimal range for obtaining a good temperature distribution and good cell performance.

Proton-conducting Micro-solid Oxide Fuel Cells with Improved Cathode Reactions by a Nanoscale Thin Film Gadolinium-doped Ceria Interlayer

PubMed Central

Li, Yong; Wang, Shijie; Su, Pei-Chen

2016-01-01

An 8 nm-thick gadolinium-doped ceria (GDC) layer was inserted as a cathodic interlayer between the nanoscale proton-conducting yttrium-doped barium zirconate (BZY) electrolyte and the porous platinum cathode of a micro-solid oxide fuel cell (μ-SOFC), which has effectively improved the cathode reaction kinetics and rendered high cell power density. The addition of the GDC interlayer significantly reduced the cathodic activation loss and increased the peak power density of the μ-SOFC by 33% at 400 °C. The peak power density reached 445 mW/cm2 at 425 °C, which is the highest among the reported μ-SOFCs using proton-conducting electrolytes. The impressive performance was attributed to the mixed protonic and oxygen ionic conducting properties of the nano-granular GDC, and also to the high densities of grain boundaries and lattice defects in GDC interlayer that favored the oxygen incorporation and transportation during the oxygen reduction reaction (ORR) and the water evolution reaction at cathode. PMID:26928192

Palliative effects of H2 on SOFCs operating with carbon containing fuels

NASA Astrophysics Data System (ADS)

Reeping, Kyle W.; Bohn, Jessie M.; Walker, Robert A.

2017-12-01

Chlorine can accelerate degradation of solid oxide fuel cell (SOFC) Ni-based anodes operating on carbon containing fuels through several different mechanisms. However, supplementing the fuel with a small percentage of excess molecular hydrogen effectively masks the degradation to the catalytic activity of the Ni and carbon fuel cracking reaction reactions. Experiments described in this work explore the chemistry behind the "palliative" effect of hydrogen on SOFCs operating with chlorine-contaminated, carbon-containing fuels using a suite of independent, complementary techniques. Operando Raman spectroscopy is used to monitor carbon accumulation and, by inference, Ni catalytic activity while electrochemical techniques including electrochemical impedance spectroscopy and voltammetry are used to monitor overall cell performance. Briefly, hydrogen not only completely hides degradation observed with chlorine-contaminated carbon-containing fuels, but also actively removes adsorbed chlorine from the surface of the Ni, allowing for the methane cracking reaction to continue, albeit at a slower rate. When hydrogen is removed from the fuel stream the cell fails immediately due to chlorine occupation of methane/biogas reaction sites.

Promotion of water-mediated carbon removal by nanostructured barium oxide/nickel interfaces in solid oxide fuel cells

PubMed Central

Yang, Lei; Choi, YongMan; Qin, Wentao; Chen, Haiyan; Blinn, Kevin; Liu, Mingfei; Liu, Ping; Bai, Jianming; Tyson, Trevor A.; Liu, Meilin

2011-01-01

The existing Ni-yttria-stabilized zirconia anodes in solid oxide fuel cells (SOFCs) perform poorly in carbon-containing fuels because of coking and deactivation at desired operating temperatures. Here we report a new anode with nanostructured barium oxide/nickel (BaO/Ni) interfaces for low-cost SOFCs, demonstrating high power density and stability in C3H8, CO and gasified carbon fuels at 750°C. Synchrotron-based X-ray analyses and microscopy reveal that nanosized BaO islands grow on the Ni surface, creating numerous nanostructured BaO/Ni interfaces that readily adsorb water and facilitate water-mediated carbon removal reactions. Density functional theory calculations predict that the dissociated OH from H2O on BaO reacts with C on Ni near the BaO/Ni interface to produce CO and H species, which are then electrochemically oxidized at the triple-phase boundaries of the anode. This anode offers potential for ushering in a new generation of SOFCs for efficient, low-emission conversion of readily available fuels to electricity. PMID:21694705

Control of Co content and SOFC cathode performance in Y1-ySr2+yCu3-xCoxO7+δ

NASA Astrophysics Data System (ADS)

Šimo, F.; Payne, J. L.; Demont, A.; Sayers, R.; Li, Ming; Collins, C. M.; Pitcher, M. J.; Claridge, J. B.; Rosseinsky, M. J.

2014-11-01

The electrochemical performance of the layered perovskite YSr2Cu3-xCoxO7+δ, a potential solid oxide fuel cell (SOFC) cathode, is improved by increasing the Co content from x = 1.00 to a maximum of x = 1.30. Single phase samples with x > 1.00 are obtained by tuning the Y/Sr ratio, yielding the composition Y1-ySr2+yCu3-xCoxO7+δ (where y ≤ 0.05). The high temperature structure of Y0.95Sr2.05Cu1.7Co1.3O7+δ at 740 °C is characterised by powder neutron diffraction and the potential of this Co-enriched material as a SOFC cathode is investigated by combining AC impedance spectroscopy, four-probe DC conductivity and powder XRD measurements to determine its electrochemical properties along with its thermal stability and compatibility with a range of commercially available electrolytes. The material is shown to be compatible with doped ceria electrolytes at 900 °C.

Combined theoretical and experimental analysis of processes determining cathode performance in solid oxide fuel cells.

PubMed

Kuklja, M M; Kotomin, E A; Merkle, R; Mastrikov, Yu A; Maier, J

2013-04-21

Solid oxide fuel cells (SOFC) are under intensive investigation since the 1980's as these devices open the way for ecologically clean direct conversion of the chemical energy into electricity, avoiding the efficiency limitation by Carnot's cycle for thermochemical conversion. However, the practical development of SOFC faces a number of unresolved fundamental problems, in particular concerning the kinetics of the electrode reactions, especially oxygen reduction reaction. We review recent experimental and theoretical achievements in the current understanding of the cathode performance by exploring and comparing mostly three materials: (La,Sr)MnO3 (LSM), (La,Sr)(Co,Fe)O3 (LSCF) and (Ba,Sr)(Co,Fe)O3 (BSCF). Special attention is paid to a critical evaluation of advantages and disadvantages of BSCF, which shows the best cathode kinetics known so far for oxides. We demonstrate that it is the combined experimental and theoretical analysis of all major elementary steps of the oxygen reduction reaction which allows us to predict the rate determining steps for a given material under specific operational conditions and thus control and improve SOFC performance.

Superionic Conductivity of Sm3+, Pr3+, and Nd3+ Triple-Doped Ceria through Bulk and Surface Two-Step Doping Approach.

PubMed

Liu, Yanyan; Fan, Liangdong; Cai, Yixiao; Zhang, Wei; Wang, Baoyuan; Zhu, Bin

2017-07-19

Sufficiently high oxygen ion conductivity of electrolyte is critical for good performance of low-temperature solid oxide fuel cells (LT-SOFCs). Notably, material conductivity, reliability, and manufacturing cost are the major barriers hindering LT-SOFC commercialization. Generally, surface properties control the physical and chemical functionalities of materials. Hereby, we report a Sm 3+ , Pr 3+ , and Nd 3+ triple-doped ceria, exhibiting the highest ionic conductivity among reported doped-ceria oxides, 0.125 S cm -1 at 600 °C. It was designed using a two-step wet-chemical coprecipitation method to realize a desired doping for Sm 3+ at the bulk and Pr 3+ /Nd 3+ at surface domains (abbreviated as PNSDC). The redox couple Pr 3+ /Pr 4+ contributes to the extraordinary ionic conductivity. Moreover, the mechanism for ionic conductivity enhancement is demonstrated. The above findings reveal that a joint bulk and surface doping methodology for ceria is a feasible approach to develop new oxide-ion conductors with high impacts on advanced LT-SOFCs.

Slurry spin coating of thin film yttria stabilized zirconia/gadolinia doped ceria bi-layer electrolytes for solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Kim, Hyun Joong; Kim, Manjin; Neoh, Ke Chean; Han, Gwon Deok; Bae, Kiho; Shin, Jong Mok; Kim, Gyu-Tae; Shim, Joon Hyung

2016-09-01

Thin ceramic bi-layered membrane comprising yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (GDC) is fabricated by the cost-effective slurry spin coating technique, and it is evaluated as an electrolyte of solid oxide fuel cells (SOFCs). It is demonstrated that the slurry spin coating method is capable of fabricating porous ceramic films by adjusting the content of ethyl-cellulose binders in the source slurry. The porous GDC layer deposited by spin coating under an optimal condition functions satisfactorily as a cathode-electrolyte interlayer in the test SOFC stack. A 2-μm-thick electrolyte membrane of the spin-coated YSZ/GDC bi-layer is successfully deposited as a dense and stable film directly on a porous NiO-YSZ anode support without any interlayers, and the SOFC produces power output over 200 mW cm-2 at 600 °C, with an open circuit voltage close to 1 V. Electrochemical impedance spectra analysis is conducted to evaluate the performance of the fuel cell components in relation with the microstructure of the spin-coated layers.

Increasing the Thermal Stability of Aluminum Titanate for Solid Oxide Fuel Cell Anodes

NASA Technical Reports Server (NTRS)

Bender, Jeffrey B.

2004-01-01

Solid-oxide fuel cells (SOFCs) show great potential as a power source for future space exploration missions. Because SOFCs operate at temperatures significantly higher than other types of fuel cells, they can reach overall efficiencies of up to 60% and are able to utilize fossil fuels. The SOFC team at GRC is leading NASA's effort to develop a solid oxide fuel cell with a power density high enough to be used for aeronautics and space applications, which is approximately ten times higher than ground transport targets. layers must be able to operate as a single unit at temperatures upwards of 900'C for at least 40,000 hours with less than ten percent degradation. One key challenge to meeting this goal arises from the thermal expansion mismatch between different layers. The amount a material expands upon heating is expressed by its coefficient of thermal expansion (CTE). If the CTEs of adjacent layers are substantially different, thermal stresses will arise during the cell's fabrication and operation. These stresses, accompanied by thermal cycling, can fracture and destroy the cell. While this is not an issue at the electrolyte-cathode interface, it is a major concern at the electrolyte-anode interface, especially in high power anode-supported systems. electrolyte are nearly identical. Conventionally, this has been accomplished by varying the composition of the anode to match the CTE of the yittria-stabilized zirconia (YSZ) electrolyte (approx.10.8x10(exp -6/degC). A Ni/YSZ composite is typically used as a base material for the anode due to its excellent electrochemical properties, but its CTE is about 13.4x10(exp -6/degC). One potential way to lower the CTE of this anode is to add a small percentage of polycrystalline Al2TiO5, with a CTE of 0.68x10(exp -6/degC, to the Ni/YSZ base. However, Al2TiO5 is thermally unstable and loses its effectiveness as it decomposes to Al2O3 and TiO2 between 750 C and 1280 C. be used as additives to increase the thermal stability of Al2TiO5 in SOFC operating conditions without adversely affecting the electrochemical properties of the SOFC anode. Three candidate materials were chosen through an extensive literature review: MgO, Fe2O3, and ZrTiO4. Although all three have been shown to prevent Al2TiO5 decomposition under various conditions, their effectiveness in the temperature range and atmosphere of the SOFC has not yet been evaluated. Several batches of Al2TiO5 with varying amounts of additives were prepared, exposed to reducing and oxidizing atmospheres at elevated temperatures, and the resulting decomposition of Al2TiO5 was measured. The most promising additives were further evaluated with the goal of ultimately preparing low CTE anodes that are chemically compatible to current systems. Adding minor constituents to stabilize Al2TiO5 could ultimately preserve its low CTE for the life of the fuel cell and improve the cell's long-term performance without a drop in anode conductivity. Further, these low CTE filler additions could allow the use of new sulfur tolerant anode materials, improving the viability of SOFCs for future aeronautics and space applications. Every SOFC consists of a cathode and an anode separated by an electrolyte, These three One way to avoid this problem is to design the cell such that the CTEs of the anode and The objective of this summer research project was to evaluate several materials that could

Dose gradient curve: A new tool for evaluating dose gradient

PubMed Central

Choi, Young Eun

2018-01-01

Purpose Stereotactic radiotherapy, which delivers an ablative high radiation dose to a target volume for maximum local tumor control, requires a rapid dose fall-off outside the target volume to prevent extensive damage to nearby normal tissue. Currently, there is no tool to comprehensively evaluate the dose gradient near the target volume. We propose the dose gradient curve (DGC) as a new tool to evaluate the quality of a treatment plan with respect to the dose fall-off characteristics. Methods The average distance between two isodose surfaces was represented by the dose gradient index (DGI) estimated by a simple equation using the volume and surface area of isodose levels. The surface area was calculated by mesh generation and surface triangulation. The DGC was defined as a plot of the DGI of each dose interval as a function of the dose. Two types of DGCs, differential and cumulative, were generated. The performance of the DGC was evaluated using stereotactic radiosurgery plans for virtual targets. Results Over the range of dose distributions, the dose gradient of each dose interval was well-characterized by the DGC in an easily understandable graph format. Significant changes in the DGC were observed reflecting the differences in planning situations and various prescription doses. Conclusions The DGC is a rational method for visualizing the dose gradient as the average distance between two isodose surfaces; the shorter the distance, the steeper the dose gradient. By combining the DGC with the dose-volume histogram (DVH) in a single plot, the DGC can be utilized to evaluate not only the dose gradient but also the target coverage in routine clinical practice. PMID:29698471

Niobium-Matrix-Composite High-Temperature Turbine Blades

NASA Technical Reports Server (NTRS)

Kaplan, Richard B.; Tuffias, Robert H.; La Ferla, Raffaele; Heng, Sangvavann; Harding, John T.

1995-01-01

High-temperture composite-material turbine blades comprising mainly niobium matrices reinforced with refractory-material fibers being developed. Of refractory fibrous materials investigated, FP-AL(2)0(3), tungsten, and polymer-based SiC fibers most promising. Blade of this type hollow and formed in nearly net shape by wrapping mesh of reinforcing refractory fibers around molybdenum mandrel, then using thermal-gradient chemical-vapor infiltration (CVI) to fill interstices with niobium. CVI process controllable and repeatable, and kinetics of both deposition and infiltration well understood.

Power and Thermal Technologies for Air and Space. Delivery Order 0003: Development of High-Performance Solid Oxide Fuel Cell (SOFC) Technology for Remote Base Applications

DTIC Science & Technology

2007-08-01

In recent years, however, anode supported electrode conformations with thin film electrolytes have been heavily explored because they are capable ...further clarify relationship between interlayer morphology and cell performance will be a subject of a future study. Figure 2. SEM Images of SOFC...CPE B1B CPE B2B RB4B CPE B3B R1 R2 10 and R3, which also exhibited a constant slope over the test range, averaged 0.1 +/- 0.02 and 0.9 +/- 0.01

Mathematical modeling of solid oxide fuel cells

NASA Technical Reports Server (NTRS)

Lu, Cheng-Yi; Maloney, Thomas M.

1988-01-01

Development of predictive techniques, with regard to cell behavior, under various operating conditions is needed to improve cell performance, increase energy density, reduce manufacturing cost, and to broaden utilization of various fuels. Such technology would be especially beneficial for the solid oxide fuel cells (SOFC) at it early demonstration stage. The development of computer models to calculate the temperature, CD, reactant distributions in the tubular and monolithic SOFCs. Results indicate that problems of nonuniform heat generation and fuel gas depletion in the tubular cell module, and of size limitions in the monolithic (MOD 0) design may be encountered during FC operation.

Effect of Lanthanum-Strontium Cathode Current-Collecting Layer on the Performance of Anode Supported Type Planar Solid Oxide Fuel Cells

NASA Astrophysics Data System (ADS)

Park, Sun-Young; Ji, Ho-Il; Kim, Hae-Ryoung; Yoon, Kyung Joong; Son, Ji-Won; Lee, Hae-Weon; Lee, Jong-Ho

2013-07-01

We applied screen-printed (La,Sr)CoO3 as a current-collecting layer of planar type unit-cell for lower temperature operation of SOFCs. In this study the effects of the cathode current-collecting layer on the performance of unit cell and symmetric half cell were investigated via AC and DC polarization experiments. According to our investigation, appropriately controlled current collecting layer was very effective to enhance the unit cell performance by reducing not only the ohmic resistance but also the polarization losses of SOFC cathode.

Energetics of Intermediate Temperature Solid Oxide Fuel Cell Electrolytes: Singly and Doubly doped Ceria Systems

NASA Astrophysics Data System (ADS)

Buyukkilic, Salih

Solid oxide fuel cells (SOFCs) have potential to convert chemical energy directly to electrical energy with high efficiency, with only water vapor as a by-product. However, the requirement of extremely high operating temperatures (~1000 °C) limits the use of SOFCs to only in large scale stationary applications. In order to make SOFCs a viable energy solution, enormous effort has been focused on lowering the operating temperatures below 700 °C. A low temperature operation would reduce manufacturing costs by slowing component degradation, lessening thermal mismatch problems, and sharply reducing costs of operation. In order to optimize SOFC applications, it is critical to understand the thermodynamic stabilities of electrolytes since they directly influence device stability, sustainability and performance. Rare-earth doped ceria electrolytes have emerged as promising materials for SOFC applications due to their high ionic conductivity at the intermediate temperatures (500--700 °C). However there is a fundamental lack of understanding regarding their structure, thermodynamic stability and properties. Therefore, the enthalpies of formation from constituent oxides and ionic conductivities were determined to investigate a relationship between the stability, composition, structural defects and ionic conductivity in rare earth doped ceria systems. For singly doped ceria electrolytes, we investigated the solid solution phase of bulk Ce1-xLnxO2-0.5x where Ln = Sm and Nd (0 ≤ x ≤ 0.30) and analyzed their enthalpies of formation, mixing and association, and bulk ionic conductivities while considering cation size mismatch and defect associations. It was shown that for ambient temperatures in the dilute dopant region, the positive heat of formation reaches a maximum as the system becomes increasingly less stable due to size mismatch. In concentrated region, stabilization to a certain solubility limit was observed probably due to the defect association of trivalent cations with charge-balancing oxygen vacancies. At higher temperatures near 700 °C, maximum enthalpy of formation shifts toward higher dopant concentrations, as a result of defect disordering. This concentration coincides with that of maximum ionic conductivity, extending the correlation seen previously near room temperature. It is also possible to co-dope these systems with Sm and Nd to further enhance ionic conductivity. For doubly doped ceria electrolytes, the solid solution phase of Ce1-xSm0.5xNd0.5xO2-0.5x (0 ≤ x ≤ 0.30) was investigated. It has been shown that for doubly doped ceria, the maximum enthalpy of formation occurs towards higher dopant concentration than that of singly doped counterparts, with less exothermic association enthalpies. These studies provide insight into the structure-composition-property-stability relations and aid in the rational design of the future SOFCs electrolytes.

Experimental study on corrosion and precipitation in non-isothermal Pb-17Li system for development of liquid breeder blanket of fusion reactor

NASA Astrophysics Data System (ADS)

Kondo, Masatoshi; Ishii, Masaomi; Norimatsu, Takayoshi; Muroga, Takeo

2017-07-01

The corrosion characteristics of RAFM steel JLF-1 in a non-isothermal Pb-17Li flowing system were investigated by means of the corrosion test using a non-isothermal mixing pot. The corrosion test was performed at 739K with a temperature gradient of 14K for 500 hours. The corrosion tests at a static and a flowing conditions in an isothermal Pb-17Li system were also performed at the same temperature for the same duration with the non-isothermal test. Then, the effect of mass transfer both by the flow and the temperature gradient on the corrosion behaviors was featured by the comparison of these results. The corrosion was caused by the dissolution of Fe and Cr from the steel surface into the flowing Pb-17Li. The specimen surface revealed a fine granular microstructure after the corrosion tests. A large number of pebbleshaped protrusions were observed on the specimen surface. This microstructure was different from the original martensite microstructure of the steel, and might be formed by the influence of the reaction with Li component in the alloy. The formation of the granular microstructure was accelerated by the flow and the temperature gradient. Some pebble-shaped protrusions had gaps at their bases. The removal of these pebble-shaped granules by the flowing Pb-17Li might cause a small-scale corrosion-erosion. The results of metallurgical analysis indicated that a large-scale corrosion-erosion was also caused by their destruction of the corroded layer on the surface. The non-isothermal mixing pot equipped a cold trap by a metal mesh in the low temperature region. The metal elements of Fe and Cr were recovered as they precipitated on the surface of the metal mesh. It was found that a Fe-Cr binary intermetallic compound was formed in the precipitation procedure. The overall mass transfer coefficient for the dissolution type corrosion in the non-isothermal system was much bigger than that in the isothermal system. This model evaluation indicated that the temperature gradient accelerated the corrosion.

Hydrodynamic Modeling of Air Blast Propagation from the Humble Redwood Chemical High Explosive Detonations Using GEODYN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chipman, V D

Two-dimensional axisymmetric hydrodynamic models were developed using GEODYN to simulate the propagation of air blasts resulting from a series of high explosive detonations conducted at Kirtland Air Force Base in August and September of 2007. Dubbed Humble Redwood I (HR-1), these near-surface chemical high explosive detonations consisted of seven shots of varying height or depth of burst. Each shot was simulated numerically using GEODYN. An adaptive mesh refinement scheme based on air pressure gradients was employed such that the mesh refinement tracked the advancing shock front where sharp discontinuities existed in the state variables, but allowed the mesh to sufficientlymore » relax behind the shock front for runtime efficiency. Comparisons of overpressure, sound speed, and positive phase impulse from the GEODYN simulations were made to the recorded data taken from each HR-1 shot. Where the detonations occurred above ground or were shallowly buried (no deeper than 1 m), the GEODYN model was able to simulate the sound speeds, peak overpressures, and positive phase impulses to within approximately 1%, 23%, and 6%, respectively, of the actual recorded data, supporting the use of numerical simulation of the air blast as a forensic tool in determining the yield of an otherwise unknown explosion.« less

Experimentally simulated global warming and nitrogen enrichment effects on microbial litter decomposers in a marsh.

PubMed

Flury, Sabine; Gessner, Mark O

2011-02-01

Atmospheric warming and increased nitrogen deposition can lead to changes of microbial communities with possible consequences for biogeochemical processes. We used an enclosure facility in a freshwater marsh to assess the effects on microbes associated with decomposing plant litter under conditions of simulated climate warming and pulsed nitrogen supply. Standard batches of litter were placed in coarse-mesh and fine-mesh bags and submerged in a series of heated, nitrogen-enriched, and control enclosures. They were retrieved later and analyzed for a range of microbial parameters. Fingerprinting profiles obtained by denaturing gradient gel electrophoresis (DGGE) indicated that simulated global warming induced a shift in bacterial community structure. In addition, warming reduced fungal biomass, whereas bacterial biomass was unaffected. The mesh size of the litter bags and sampling date also had an influence on bacterial community structure, with the apparent number of dominant genotypes increasing from spring to summer. Microbial respiration was unaffected by any treatment, and nitrogen enrichment had no clear effect on any of the microbial parameters considered. Overall, these results suggest that microbes associated with decomposing plant litter in nutrient-rich freshwater marshes are resistant to extra nitrogen supplies but are likely to respond to temperature increases projected for this century.

Self-sustained operation of a kW e-class kerosene-reforming processor for solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Yoon, Sangho; Bae, Joongmyeon; Kim, Sunyoung; Yoo, Young-Sung

In this paper, fuel-processing technologies are developed for application in residential power generation (RPG) in solid oxide fuel cells (SOFCs). Kerosene is selected as the fuel because of its high hydrogen density and because of the established infrastructure that already exists in South Korea. A kerosene fuel processor with two different reaction stages, autothermal reforming (ATR) and adsorptive desulfurization reactions, is developed for SOFC operations. ATR is suited to the reforming of liquid hydrocarbon fuels because oxygen-aided reactions can break the aromatics in the fuel and steam can suppress carbon deposition during the reforming reaction. ATR can also be implemented as a self-sustaining reactor due to the exothermicity of the reaction. The kW e self-sustained kerosene fuel processor, including the desulfurizer, operates for about 250 h in this study. This fuel processor does not require a heat exchanger between the ATR reactor and the desulfurizer or electric equipment for heat supply and fuel or water vaporization because a suitable temperature of the ATR reformate is reached for H 2S adsorption on the ZnO catalyst beds in desulfurizer. Although the CH 4 concentration in the reformate gas of the fuel processor is higher due to the lower temperature of ATR tail gas, SOFCs can directly use CH 4 as a fuel with the addition of sufficient steam feeds (H 2O/CH 4 ≥ 1.5), in contrast to low-temperature fuel cells. The reforming efficiency of the fuel processor is about 60%, and the desulfurizer removed H 2S to a sufficient level to allow for the operation of SOFCs.

Comparative study of Ce0.80Sm0.20 Ba0.80Y0.20O3-δ (YB-SDC) electrolyte by various chemical synthesis routes

NASA Astrophysics Data System (ADS)

Tariq, Sana; Marium, Aniqa; Raza, Rizwan; Ashfaq Ahmad, M.; Ajmal Khan, M.; Abbas, Ghazanfar; Waseem Boota, M.; Khalid Imran, S.; Arshad, Sarfraz; Ikram, Muhammad

2018-03-01

Solid Oxide Fuel Cells is received a significant attention in recent years due to higher efficiency and fuel flexibility. The one of the main challenge for SOFC is to lower the operating temperature of SOFCs. Therefore, different strategies are used in order to enhance the ionic conduction of electrolyte, which can lower the overall SOFC operating temperature. The present work is focused on this strategy to enhance the electrolytic conductivity. Therefore, the ceria based composite electrolytes Ce0.80Sm0.20B0.80Y0.20O3-δ (YBSDC) are synthesized using three different approaches i.e. co-precipitation (YBSDC-1), sol-gel (YBSDC-2) and ball milling (YBSDC-3). Their crystal structures and surface morphologies are characterized through X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) techniques, respectively. The four-probe technique is employed to measure their dc conductivities in the temperature range (300-700) °C under air atmosphere. The open circuit voltage (OCV) and current are recorded with natural gas as fuel {flow rate kept at 100 ml min-1 at 1 atm pressure} over the temperature range (300-600) °C. The electrolyte (YBSDC-1) prepared by co-precipitation technique is shown better results as compare to other two electrolytes (YBSDC-2 and YBSDC-3). The electrolyte (YBSDC-1) having maximum dc conductivity (0.096 S/cm), peak power density 224 mW cm-2 and OCV 0.94 V at 600 °C. These results show that YBSDC-1electrolyte is potential candidate for low temperature SOFCs.

In situ transmission electron microscopic observations of redox cycling of a Ni-ScSZ cermet fuel cell anode.

PubMed

Matsuda, Junko; Kawasaki, Tatsuya; Futamura, Shotaro; Kawabata, Tsutomu; Taniguchi, Shunsuke; Sasaki, Kazunari

2018-05-19

In situ transmission electron microscopy (TEM) observations of a Ni(O)-Sc2O3-stabilized ZrO2 (ScSZ; 10 mol% Sc2O3, 1 mol% CeO2, 89 mol% ZrO2) anode in a solid oxide fuel cell (SOFC) have been performed at high temperatures under a hydrogen/oxygen gas atmosphere using an environmental transmission electron microscope (ETEM); the specimens were removed from cross-sections of the real SOFC by focused ion beam milling and lifting. When heating the NiO-ScSZ anode under a hydrogen atmosphere of 3 mbar in ETEM, nano-pores were formed at the grain boundaries and on the surface of NiO particles at around 400°C due to the volume shrinkage accompanying the reduction of NiO to Ni. Moreover, densification of Ni occurred when increasing the temperature from 600 to 700°C. High-magnification TEM images obtained in the early stages of NiO reduction revealed that the (111) planes of Ni grew almost parallel to the (111) planes of NiO. In the case of heating Ni-ScSZ under an oxygen atmosphere of 3 mbar in ETEM, oxidation of Ni starting from the surface of the particles occurred above 300°C. All Ni particles became polycrystalline NiO after the temperature was increased to 800°C. Volume expansion/contraction by mass transfer to the outside/inside of the Ni particles in the anode during repeated oxidation/reduction seems to result in the agglomeration of Ni catalysts during long-term SOFC operation. We emphasize that our in situ TEM observations will be applied to observe electrochemical reactions in SOFCs under applied electric fields.

Validating the technological feasibility of yttria-stabilized zirconia-based semiconducting-ionic composite in intermediate-temperature solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Cai, Yixiao; Wang, Baoyuan; Wang, Yi; Xia, Chen; Qiao, Jinli; van Aken, Peter A.; Zhu, Bin; Lund, Peter

2018-04-01

YSZ as the electrolyte of choice has dominated the progressive development of solid oxide fuel cell (SOFC) technologies for many years. To enable SOFCs operating at intermediate temperatures of 600 °C or below, major technical advances were built on a foundation of a thin-film YSZ electrolyte, NiO anode, and perovskite cathode, e.g. La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF). Inspired by functionalities in engineered heterostructure interfaces, the present work uses the components from state-of-the-art SOFCs, i.e, the anode NiO-YSZ and the cathode LSCF-YSZ, or the convergence of all three components, i.e., NiO-YSZ-LSCF, to fabricate semiconductor-ionic membranes (SIMs) and devices. A series of proof-of-concept fuel cell devices are designed by using each of the above SIMs sandwiched between two semiconducting Ni0.8Co0.15Al0.05LiO2-δ (NCAL) layers. We systematically compare these novel designs at 600 °C with two reference fuel cells: a commercial product of anode-supported YSZ electrolyte thin-film cell, and a lab-assembled fuel cell with a conventional configuration of NiO-YSZ (anode)/YSZ (electrolyte)/LSCF-YSZ (cathode). In comparison to the reference cells, the SIM device in a configuration of NCAL/NiO-YSZ-LSCF/NCAL reaches more than 3-fold enhancement of the maximum power output. By using spherical aberration-corrected transmission electron microscopy and spectroscopy approaches, this work offers insight into the mechanisms underlying SIM-associated SOFC performance enhancement.

Binder Jetting: A Novel Solid Oxide Fuel-Cell Fabrication Process and Evaluation

NASA Astrophysics Data System (ADS)

Manogharan, Guha; Kioko, Meshack; Linkous, Clovis

2015-03-01

With an ever-growing concern to find a more efficient and less polluting means of producing electricity, fuel cells have constantly been of great interest. Fuel cells electrochemically convert chemical energy directly into electricity and heat without resorting to combustion/mechanical cycling. This article studies the solid oxide fuel cell (SOFC), which is a high-temperature (100°C to 1000°C) ceramic cell made from all solid-state components and can operate under a wide range of fuel sources such as hydrogen, methanol, gasoline, diesel, and gasified coal. Traditionally, SOFCs are fabricated using processes such as tape casting, calendaring, extrusion, and warm pressing for substrate support, followed by screen printing, slurry coating, spray techniques, vapor deposition, and sputter techniques, which have limited control in substrate microstructure. In this article, the feasibility of engineering the porosity and configuration of an SOFC via an additive manufacturing (AM) method known as binder jet printing was explored. The anode, cathode and oxygen ion-conducting electrolyte layers were fabricated through AM sequentially as a complete fuel cell unit. The cell performance was measured in two modes: (I) as an electrolytic oxygen pump and (II) as a galvanic electricity generator using hydrogen gas as the fuel. An analysis on influence of porosity was performed through SEM studies and permeability testing. An additional study on fuel cell material composition was conducted to verify the effects of binder jetting through SEM-EDS. Electrical discharge of the AM fabricated SOFC and nonlinearity of permeability tests show that, with additional work, the porosity of the cell can be modified for optimal performance at operating flow and temperature conditions.

Apparatus for investigating the reactions of soft-bodied invertebrates to controlled humidity gradients

PubMed Central

Russell, Joshua; Pierce-Shimomura, Jonathan T.

2015-01-01

Background While many studies have assayed behavioral responses of animals to chemical, temperature and light gradients, fewer studies have assayed how animals respond to humidity gradients. Our novel humidity chamber has allowed us to study the neuromolecular basis of humidity sensation in the nematode Caenorhabditis elegans (Russell et al. 2014). New Method We describe an easy-to-construct, low-cost humidity chamber to assay the behavior of small animals, including soft-bodied invertebrates, in controlled humidity gradients. Results We show that our humidity-chamber design is amenable to soft-bodied invertebrates and can produce reliable gradients ranging 0.3–8% RH/cm across a 9-cm long x 7.5-cm wide gel-covered arena. Comparison with Existing Method(s) Previous humidity chambers relied on circulating dry and moist air to produce a steep humidity gradient in a small arena (e.g. Sayeed & Benzer, 1996). To remove the confound of moving air that may elicit mechanical responses independent of humidity responses, our chamber controlled the humidity gradient using reservoirs of hygroscopic materials. Additionally, to better observe the behavioral mechanisms for humidity responses, our chamber provided a larger arena. Although similar chambers have been described previously, these approaches were not suitable for soft-bodied invertebrates or for easy imaging of behavior because they required that animals move across wire or fabric mesh. Conclusion The general applicability of our humidity chamber overcomes limitations of previous designs and opens the door to observe the behavioral responses of soft-bodied invertebrates, including genetically powerful C. elegans and Drosophila larvae. PMID:25176025

Weak Galerkin finite element methods for Darcy flow: Anisotropy and heterogeneity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Guang; Liu, Jiangguo; Mu, Lin

2014-11-01

This paper presents a family of weak Galerkin finite element methods (WGFEMs) for Darcy flow computation. The WGFEMs are new numerical methods that rely on the novel concept of discrete weak gradients. The WGFEMs solve for pressure unknowns both in element interiors and on the mesh skeleton. The numerical velocity is then obtained from the discrete weak gradient of the numerical pressure. The new methods are quite different than many existing numerical methods in that they are locally conservative by design, the resulting discrete linear systems are symmetric and positive-definite, and there is no need for tuning problem-dependent penalty factors.more » We test the WGFEMs on benchmark problems to demonstrate the strong potential of these new methods in handling strong anisotropy and heterogeneity in Darcy flow.« less

A comparison of the primal and semi-dual variational formats of gradient-extended crystal inelasticity

NASA Astrophysics Data System (ADS)

Carlsson, Kristoffer; Runesson, Kenneth; Larsson, Fredrik; Ekh, Magnus

2017-10-01

In this paper we discuss issues related to the theoretical as well as the computational format of gradient-extended crystal viscoplasticity. The so-called primal format uses the displacements, the slip of each slip system and the dissipative stresses as the primary unknown fields. An alternative format is coined the semi-dual format, which in addition includes energetic microstresses among the primary unknown fields. We compare the primal and semi-dual variational formats in terms of advantages and disadvantages from modeling as well as numerical viewpoints. Finally, we perform a series of representative numerical tests to investigate the rate of convergence with finite element mesh refinement. In particular, it is shown that the commonly adopted microhard boundary condition poses a challenge in the special case that the slip direction is parallel to a grain boundary.

Development of high gradient magnetic separation system for removing the metallic wear debris to be present in highly viscous fluid

NASA Astrophysics Data System (ADS)

Hayashi, S.; Mishima, F.; Akiyama, Y.; Nishijima, S.

2010-11-01

In the industrial plants processing highly viscous fluid such as foods or industrial materials, there is an issue of contamination by metallic wear debris originating from pipe of manufacturing line. It is necessary to remove the metallic wear debris in highly viscous fluid, since these debris causes quality loss. In this study, we developed a high gradient magnetic separation system by using superconducting magnet to remove the metallic wear debris. The particle trajectory simulation and the magnetic separation experiment were conducted with polyvinyl alcohol as a model material. As a result, ca. 100% and 92.2% of the separation efficiency was achieved respectively for the highly viscous fluid of 1 Pa s and 6 Pa s in viscosity, with 14 and 30 mesh magnetic filters.

Thermofluid Modeling of Fuel Cells

NASA Astrophysics Data System (ADS)

Young, John B.

2007-01-01

Fuel cells offer the prospect of silent electrical power generation at high efficiency with near-zero pollutant emission. Many materials and fabrication problems have now been solved and attention has shifted toward system modeling, including the fluid flows that supply the cells with hydrogen and oxygen. This review describes the current thermofluid modeling capabilities for proton exchange membrane fuel cells (PEMFCs) and solid oxide fuel cells (SOFCs), the most promising candidates for commercial exploitation. Topics covered include basic operating principles and stack design, convective-diffusive flow in porous solids, special modeling issues for PEMFCs and SOFCs, and the use of computational fluid dynamics (CFD) methods.

Performance of planar single cell lanthanum gallate based solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Maffei, N.; Kuriakose, A. K.

A novel synthesis of high purity, single phase strontium-magnesium doped lanthanum gallate through a nitrate route is described. The prepared powder is formed into planar monolithic elements by uniaxial pressing followed by isostatic pressing and sintering. XRD analysis of the sintered elements reveal no detectable secondary phases. The performance of the electrolyte in solid oxide fuel cells (SOFC) with three different anode/cathode combinations tested at 700°C with respect to the J- V and power density is reported. The data show that the characteristics of this SOFC are strongly dependent on the particular anode/cathode system chosen.

Protective coatings for metal alloys and methods incorporating the same

DOEpatents

Seabaugh, Matthew M.; Ibanez, Sergio; Swartz, Scott L.

2015-06-09

An electrochemical device having one or more solid oxide fuel cells (SOFCs), each of the SOFCs including a cathode, an anode, and an electrolyte layer positioned between the cathode and anode; and at least one additional component comprising a metallic substrate having an electronically conductive, chromium-free perovskite coating deposited directly thereon. The perovskite coating has the formula ABO.sub.3, wherein A is a lanthanide element or Y, and B is a mixture of two or more transition elements, with the A site undoped by any alkaline earth element, and the perovskite coating exhibits limited or no ionic transport of oxygen.

Creep analysis of solid oxide fuel cell with bonded compliant seal design

NASA Astrophysics Data System (ADS)

Jiang, Wenchun; Zhang, Yucai; Luo, Yun; Gong, J. M.; Tu, S. T.

2013-12-01

Solid oxide fuel cell (SOFC) requires good sealant because it works in harsh conditions (high temperature, thermal cycle, oxidative and reducing gas environments). Bonded compliant seal (BCS) is a new sealing method for planar SOFC. It uses a thin foil metal to bond the window frame and cell, achieving the seal between window frame and cell. At high temperature, a comprehensive evaluation of its creep strength is essential for the adoption of BCS design. In order to characterize the creep behavior, the creep induced by thermal stresses in SOFC with BCS design is simulated by finite element method. The results show that the foil is compressed and large thermal stresses are generated. The initial peak thermal stress is located in the thin foil because the foil acts as a spring stores the thermal stresses by elastic and plastic deformation in itself. Serving at high temperature, initial thermal displacement is partially recovered because of the creep relaxation, which becomes a new discovered advantage for BCS design. It predicts that the failures are likely to happen in the middle of the cell edge and BNi-2 filler metal, because the maximum residual displacement and creep strain are located.

Preparation and properties of a MnCo2O4 for ceramic interconnect of solid oxide fuel cell via glycine nitrate process

NASA Astrophysics Data System (ADS)

Yoon, Mi Young; Lee, Eun Jung; Song, Rak Hyun; Hwang, Hae Jin

2011-12-01

MnCo2O4 powder was prepared by a wet chemistry method using metal nitrates and glycine in an aqueous solution. The phase stability, sintering behavior, thermal expansion and electrical conductivity were examined to characterize powder suitability as an interconnect material in solid oxide fuel cells (SOFCs). X-ray diffraction indicated that the MnCo2O4 spinel synthesized by the glycine nitrate process was stable until 1100 °C and it was possible to obtain a fully densified single phase spinel. On the other hand, the MnCo2O4 synthesized by a solid state reaction decomposed into a cubic spinel and CoO after being sintered at 1100 °C. This might be associated with the reduction of Co3+ in the octahedral site of the cubic spinel phase. MnCo2O4 showed a thermal expansion coefficient comparable to that of other SOFCs components, as well as good electrical conductivity. Therefore, MnCo2O4 is a potential candidate for the ceramic interconnects in SOFCs, provided the phase instability under reducing environments can be improved.

A techno-economic comparison of fuel processors utilizing diesel for solid oxide fuel cell auxiliary power units

NASA Astrophysics Data System (ADS)

Nehter, Pedro; Hansen, John Bøgild; Larsen, Peter Koch

Ultra-low sulphur diesel (ULSD) is the preferred fuel for mobile auxiliary power units (APU). The commercial available technologies in the kW-range are combustion engine based gensets, achieving system efficiencies about 20%. Solid oxide fuel cells (SOFC) promise improvements with respect to efficiency and emission, particularly for the low power range. Fuel processing methods i.e., catalytic partial oxidation, autothermal reforming and steam reforming have been demonstrated to operate on diesel with various sulphur contents. The choice of fuel processing method strongly affects the SOFC's system efficiency and power density. This paper investigates the impact of fuel processing methods on the economical potential in SOFC APUs, taking variable and capital cost into account. Autonomous concepts without any external water supply are compared with anode recycle configurations. The cost of electricity is very sensitive on the choice of the O/C ratio and the temperature conditions of the fuel processor. A sensitivity analysis is applied to identify the most cost effective concept for different economic boundary conditions. The favourite concepts are discussed with respect to technical challenges and requirements operating in the presence of sulphur.

On the nanostructuring and catalytic promotion of intermediate temperature solid oxide fuel cell (IT-SOFC) cathodes

NASA Astrophysics Data System (ADS)

Serra, José M.; Buchkremer, Hans-Peter

Solid oxide fuel cells (SOFCs) are highly efficient energy converters for both stationary and mobile purposes. However, their market introduction still demands the reduction of manufacture costs and one possible way to reach this goal is the decrease of the operating temperatures, which entails the improvement of the cathode electrocatalytic properties. An ideal cathode material may have mixed ionic and electronic conductivity as well as proper catalytic properties. Nanostructuring and catalytic promotion of mixed conducting perovskites (e.g. La 0.58Sr 0.4Fe 0.8Co 0.2O 3- δ) seem to be promising approaches to overcoming cathode polarization problems and are briefly illustrated here. The preparation of nanostructured cathodes with relatively high surface area and enough thermal stability enables to improve the oxygen exchange rate and therefore the overall SOFC performance. A similar effect was obtained by catalytic promoting the perovskite surface, allowing decoupling the catalytic and ionic-transport properties in the cathode design. Noble metal incorporation may improve the reversibility of the reduction cycles involved in the oxygen reduction. Under the cathode oxidizing conditions, Pd seems to be partially dissolved in the perovskite structure and as a result very well dispersed.

The effects of minor elements in La0.6Sr0.4Co0.2Fe0.8O3-δ cathodes on oxygen reduction reaction

NASA Astrophysics Data System (ADS)

Oishi, Junya; Otomo, Junichiro; Oshima, Yoshito; Koyama, Michihisa

2015-03-01

It is known that the minor elements affect the performance of solid oxide fuel cell (SOFC). In this study, we focus on the influence of minor elements on the SOFC cathode properties. The Ca, Ba, Al, and Si, which originate from raw materials and production processes for SOFC cathodes, are investigated as minor elements that may have effect on the properties of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode. To examine the effects of minor elements on the cathode properties, Ca, Ba, Al, and Si with a controlled concentration are added to the LSCF reference sample. Conductivity relaxation measurements are conducted to determine the chemical diffusion coefficient (Dchem) and surface exchange coefficient (ktr), which governs the overpotential characteristics of the LSCF cathode. The results show that Al and Si have negative effects on both Dchem and ktr while Ca and Ba do not alter Dchem and show weakly positive effects on ktr. The effects of Ca and Ba for the cathode properties are discussed on the basis of XPS measurements.

Solid Oxide Fuel Cell Hybrid System for Distributed Power Generation

DOE Office of Scientific and Technical Information (OSTI.GOV)

David Deangelis; Rich Depuy; Debashis Dey

2004-09-30

This report summarizes the work performed by Hybrid Power Generation Systems, LLC (HPGS) during the April to October 2004 reporting period in Task 2.3 (SOFC Scaleup for Hybrid and Fuel Cell Systems) under Cooperative Agreement DE-FC26-01NT40779 for the U. S. Department of Energy, National Energy Technology Laboratory (DOE/NETL), entitled ''Solid Oxide Fuel Cell Hybrid System for Distributed Power Generation''. This study analyzes the performance and economics of power generation systems for central power generation application based on Solid Oxide Fuel Cell (SOFC) technology and fueled by natural gas. The main objective of this task is to develop credible scale upmore » strategies for large solid oxide fuel cell-gas turbine systems. System concepts that integrate a SOFC with a gas turbine were developed and analyzed for plant sizes in excess of 20 MW. A 25 MW plant configuration was selected with projected system efficiency of over 65% and a factory cost of under $400/kW. The plant design is modular and can be scaled to both higher and lower plant power ratings. Technology gaps and required engineering development efforts were identified and evaluated.« less

Materials for low temperature SOFCs.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krumpelt, M.; Ralph, J.; Cruse, T.

2002-08-02

Solid oxide fuel cells (SOFCs) are one of the potentially most efficient and clean energy conversion technologies for electric utility applications. Laboratory cells have shown extraordinary durability, and actual utility-scale prototypes have worked very well. The main obstacle to commercialization has been the relatively high manufacturing cost. To reduce these costs, efforts have been underway for several years to adapt manufacturing technology from the semiconductor industry to the SOFCs; however, tape casting, screen printing and similar methods are more applicable to planar configurations than to the more proven tubular ones. In planar cells the bipolar plate and edge seals becomemore » more critical elements, and material selection may have repercussions for the other fuel cell components. Ferritic stainless steel bipolar plates may be a good choice for reducing the cost of the stacks, but ferritic steels oxidize rapidly at temperatures above 800 C. Inexorably, one is led to the conclusion that anodes, cathodes and electrolytes operating below 800 C need to be found. Another motivation for developing planar SOFCs operating at reduced temperature is the prospect of new non-utility applications. The U.S. Department of Energy has initiated the Solid State Energy Conversion Alliance (SECA) program for developing small modular stacks ranging in capacity from 5 to 10 kW{sup (1)}. This size range meets the power requirements of auxiliary power units for heavy and perhaps even light-duty vehicles, and also for remote stationary applications. In terms of electric capacity, the distributed electric utility market may well exceed the potential market for APUs, but the number of units produced could be higher for the latter, yielding cost benefits related to mass production. On the other hand, the fuel for use in transportation or remote stationary applications will consist of gasoline, diesel or propane, which contain higher sulfur levels than natural gas. Anodes with some resistance to sulfur poisoning would be desirable. Also, during the more frequent shutdowns and startups in these applications, the anodes may get exposed to air. Typical nickel-based SOFC anodes may not tolerate air exposure very well and may need to be modified. Argonne National Laboratory is engaged in developing new materials options for SECA applications, as discussed here.« less

Recent Development in the CESE Method for the Solution of the Navier-Stokes Equations Using Unstructured Triangular or Tetrahedral Meshes With High Aspect Ratio

NASA Technical Reports Server (NTRS)

Chang, Sin-Chung; Chang, Chau-Lyan; Yen, Joseph C.

2013-01-01

In the multidimensional CESE development, triangles and tetrahedra turn out to be the most natural building blocks for 2D and 3D spatial meshes. As such the CESE method is compatible with the simplest unstructured meshes and thus can be easily applied to solve problems with complex geometries. However, because the method uses space-time staggered stencils, solution decoupling may become a real nuisance in applications involving unstructured meshes. In this paper we will describe a simple and general remedy which, according to numerical experiments, has removed any possibility of solution decoupling. Moreover, in a real-world viscous flow simulation near a solid wall, one often encounters a case where a boundary with high curvature or sharp corner is surrounded by triangular/tetrahedral meshes of extremely high aspect ratio (up to 106). For such an extreme case, the spatial projection of a space-time compounded conservation element constructed using the original CESE design may become highly concave and thus its centroid (referred to as a spatial solution point) may lie far outside of the spatial projection. It could even be embedded beyond a solid wall boundary and causes serious numerical difficulties. In this paper we will also present a new procedure for constructing conservation elements and solution elements which effectively overcomes the difficulties associated with the original design. Another difficulty issue which was addressed more recently is the wellknown fact that accuracy of gradient computations involving triangular/tetrahedral grids deteriorates rapidly as the aspect ratio of grid cells increases. The root cause of this difficulty was clearly identified and several remedies to overcome it were found through a rigorous mathematical analysis. However, because of the length of the current paper and the complexity of mathematics involved, this new work will be presented in another paper.

Superconducting transition temperature of a boron nitride layer with a high niobium coverage.

NASA Astrophysics Data System (ADS)

Vazquez, Gerardo; Magana, Fernando

We explore the possibility of inducing superconductivity in a Boron Nitride (BN) sheet, by doping its surface with Nb atoms sitting on the center of the hexagons. We used first-principles density functional theory in the general gradient approximation. The Quantum-Espresso package was used with norm conserving pseudo potentials. The structure considered was relaxed to their minimum energy configuration. Phonon frequencies were calculated using the linear-response technique on several phonon wave-vector meshes. The electron-phonon coupling parameter was calculated for a number of k meshes. The superconducting critical temperature was estimated using the Allen-Dynes formula with μ* = 0.1 - 0.15. We note that Nb is a good candidate material to show a superconductor transition for the BN-metal system. We thank Dirección General de Asuntos del Personal Académico de la Universidad Nacional Autónoma de México, partial financial support by Grant IN-106514 and we also thank Miztli Super-Computing center the technical assistance.

Osteochondral tissue formation through adipose-derived stromal cell differentiation on biomimetic polycaprolactone nanofibrous scaffolds with graded insulin and Beta-glycerophosphate concentrations.

PubMed

Erisken, Cevat; Kalyon, Dilhan M; Wang, Hongjun; Ornek-Ballanco, Ceren; Xu, Jiahua

2011-05-01

The ability to fabricate tissue engineering scaffolds containing systematic gradients in the distributions of stimulators provides additional means for the mimicking of the important gradients observed in native tissues. Here the concentration distributions of two bioactive agents were varied concomitantly for the first time (one increasing, whereas the other decreasing monotonically) in between the two sides of a nanofibrous scaffold. This was achieved via the application of a new processing method, that is, the twin-screw extrusion and electrospinning method, to generate gradients of insulin, a stimulator of chondrogenic differentiation, and β-glycerophosphate (β-GP), for mineralization. The graded poly(ɛ-caprolactone) mesh was seeded with human adipose-derived stromal cells and cultured over 8 weeks. The resulting tissue constructs were analyzed for and revealed indications of selective differentiation of human adipose-derived stromal cells toward chondrogenic lineage and mineralization as functions of position as a result of the corresponding concentrations of insulin and β-GP. Chondrogenic differentiation of the stem cells increased at insulin-rich locations and mineralization increased at β-GP-rich locations.

Electrochemical degradation, kinetics & performance studies of solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Das, Debanjan

Linear and Non-linear electrochemical characterization techniques and equivalent circuit modelling were carried out on miniature and sub-commercial Solid Oxide Fuel Cell (SOFC) stacks as an in-situ diagnostic approach to evaluate and analyze their performance under the presence of simulated alternative fuel conditions. The main focus of the study was to track the change in cell behavior and response live, as the cell was generating power. Electrochemical Impedance Spectroscopy (EIS) was the most important linear AC technique used for the study. The distinct effects of inorganic components usually present in hydrocarbon fuel reformates on SOFC behavior have been determined, allowing identification of possible "fingerprint" impedance behavior corresponding to specific fuel conditions and reaction mechanisms. Critical electrochemical processes and degradation mechanisms which might affect cell performance were identified and quantified. Sulfur and siloxane cause the most prominent degradation and the associated electrochemical cell parameters such as Gerisher and Warburg elements are applied respectively for better understanding of the degradation processes. Electrochemical Frequency Modulation (EFM) was applied for kinetic studies in SOFCs for the very first time for estimating the exchange current density and transfer coefficients. EFM is a non-linear in-situ electrochemical technique conceptually different from EIS and is used extensively in corrosion work, but rarely used on fuel cells till now. EFM is based on exploring information obtained from non-linear higher harmonic contributions from potential perturbations of electrochemical systems, otherwise not obtained by EIS. The baseline fuel used was 3 % humidified hydrogen with a 5-cell SOFC sub-commercial planar stack to perform the analysis. Traditional methods such as EIS and Tafel analysis were carried out at similar operating conditions to verify and correlate with the EFM data and ensure the validity of the obtained information. The obtained values closely range from around 11 mA cm-2 - 16 mA cm -2 with reasonable repeatability and excellent accuracy. The potential advantages of EFM compared to traditional methods were realized and our primary aim at demonstrating this technique on a SOFC system are presented which can act as a starting point for future research efforts in this area. Finally, an approach based on in-situ State of Health tests by EIS was formulated and investigated to understand the most efficient fuel conditions for suitable long term operation of a solid oxide fuel cell stack under power generation conditions. The procedure helped to reflect the individual effects of three most important fuel characteristics CO/H2 volumetric ratio, S/C ratio and fuel utilization under the presence of a simulated alternative fuel at 0.4 A cm-2. Variation tests helped to identify corresponding electrochemical/chemical processes, narrow down the most optimum operating regimes considering practical behavior of simulated reformer-SOFC system arrangements. At the end, 8 different combinations of the optimized parameters were tested long term with the stack, and the most efficient blend was determined.

Dynamic, High-Temperature, Flexible Seal

NASA Technical Reports Server (NTRS)

Steinetz, Bruce M.; Sirocky, Paul J.

1989-01-01

New seal consists of multiple plies of braided ceramic sleeves filled with small ceramic balls. Innermost braided sleeve supported by high-temperature-wire-mesh sleeve that provides both springback and preload capabilities. Ceramic balls reduce effect of relatively high porosity of braided ceramic sleeves by acting as labyrinth flow path for gases and thereby greatly increasing pressure gradient seal can sustain. Dynamic, high-temperature, flexible seal employed in hypersonic engines, two-dimensional convergent/divergent and vectorized-thrust exhaust nozzles, reentry vehicle airframes, rocket-motor casings, high-temperature furnaces, and any application requiring non-asbestos high-temperature gaskets.

Using the GeoFEST Faulted Region Simulation System

NASA Technical Reports Server (NTRS)

Parker, Jay W.; Lyzenga, Gregory A.; Donnellan, Andrea; Judd, Michele A.; Norton, Charles D.; Baker, Teresa; Tisdale, Edwin R.; Li, Peggy

2004-01-01

GeoFEST (the Geophysical Finite Element Simulation Tool) simulates stress evolution, fault slip and plastic/elastic processes in realistic materials, and so is suitable for earthquake cycle studies in regions such as Southern California. Many new capabilities and means of access for GeoFEST are now supported. New abilities include MPI-based cluster parallel computing using automatic PYRAMID/Parmetis-based mesh partitioning, automatic mesh generation for layered media with rectangular faults, and results visualization that is integrated with remote sensing data. The parallel GeoFEST application has been successfully run on over a half-dozen computers, including Intel Xeon clusters, Itanium II and Altix machines, and the Apple G5 cluster. It is not separately optimized for different machines, but relies on good domain partitioning for load-balance and low communication, and careful writing of the parallel diagonally preconditioned conjugate gradient solver to keep communication overhead low. Demonstrated thousand-step solutions for over a million finite elements on 64 processors require under three hours, and scaling tests show high efficiency when using more than (order of) 4000 elements per processor. The source code and documentation for GeoFEST is available at no cost from Open Channel Foundation. In addition GeoFEST may be used through a browser-based portal environment available to approved users. That environment includes semi-automated geometry creation and mesh generation tools, GeoFEST, and RIVA-based visualization tools that include the ability to generate a flyover animation showing deformations and topography. Work is in progress to support simulation of a region with several faults using 16 million elements, using a strain energy metric to adapt the mesh to faithfully represent the solution in a region of widely varying strain.

Inverse modeling of rainfall infiltration with a dual permeability approach using different matrix-fracture coupling variants.

NASA Astrophysics Data System (ADS)

Blöcher, Johanna; Kuraz, Michal

2017-04-01

In this contribution we propose implementations of the dual permeability model with different inter-domain exchange descriptions and metaheuristic optimization algorithms for parameter identification and mesh optimization. We compare variants of the coupling term with different numbers of parameters to test if a reduction of parameters is feasible. This can reduce parameter uncertainty in inverse modeling, but also allow for different conceptual models of the domain and matrix coupling. The different variants of the dual permeability model are implemented in the open-source objective library DRUtES written in FORTRAN 2003/2008 in 1D and 2D. For parameter identification we use adaptations of the particle swarm optimization (PSO) and Teaching-learning-based optimization (TLBO), which are population-based metaheuristics with different learning strategies. These are high-level stochastic-based search algorithms that don't require gradient information or a convex search space. Despite increasing computing power and parallel processing, an overly fine mesh is not feasible for parameter identification. This creates the need to find a mesh that optimizes both accuracy and simulation time. We use a bi-objective PSO algorithm to generate a Pareto front of optimal meshes to account for both objectives. The dual permeability model and the optimization algorithms were tested on virtual data and field TDR sensor readings. The TDR sensor readings showed a very steep increase during rapid rainfall events and a subsequent steep decrease. This was theorized to be an effect of artificial macroporous envelopes surrounding TDR sensors creating an anomalous region with distinct local soil hydraulic properties. One of our objectives is to test how well the dual permeability model can describe this infiltration behavior and what coupling term would be most suitable.

Two-phase flow pattern measurements with a wire mesh sensor in a direct steam generating solar thermal collector

NASA Astrophysics Data System (ADS)

Berger, Michael; Mokhtar, Marwan; Zahler, Christian; Willert, Daniel; Neuhäuser, Anton; Schleicher, Eckhard

2017-06-01

At Industrial Solar's test facility in Freiburg (Germany), two phase flow patterns have been measured by using a wire mesh sensor from Helmholtz Zentrum Dresden-Rossendorf (HZDR). Main purpose of the measurements was to compare observed two-phase flow patterns with expected flow patterns from models. The two-phase flow pattern is important for the design of direct steam generating solar collectors. Vibrations should be avoided in the peripheral piping, and local dry-outs or large circumferential temperature gradients should be prevented in the absorber tubes. Therefore, the choice of design for operation conditions like mass flow and steam quality are an important step in the engineering process of such a project. Results of a measurement with the wire mesh sensor are the flow pattern and the plug or slug frequency at the given operating conditions. Under the assumption of the collector power, which can be assumed from previous measurements at the same collector and adaption with sun position and incidence angle modifier, also the slip can be evaluated for a wire mesh sensor measurement. Measurements have been performed at different mass flows and pressure levels. Transient behavior has been tested for flashing, change of mass flow, and sudden changes of irradiation (cloud simulation). This paper describes the measurements and the method of evaluation. Results are shown as extruded profiles in top view and in side view. Measurement and model are compared. The tests have been performed at low steam quality, because of the limits of the test facility. Conclusions and implications for possible future measurements at larger collectors are also presented in this paper.

Investigation of the stress distribution around a mode 1 crack with a novel strain gradient theory

NASA Astrophysics Data System (ADS)

Lederer, M.; Khatibi, G.

2017-01-01

Stress concentrations at the tip of a sharp crack have extensively been investigated in the past century. According to the calculations of Inglis, the stress ahead of a mode 1 crack shows the characteristics of a singularity. This solution is exact in the framework of linear elastic fracture mechanics (LEFM). From the viewpoint of multiscale modelling, however, it is evident that the stress at the tip of a stable crack cannot be infinite, because the strengths of atomic bonds are finite. In order to prevent the problem of this singularity, a new version of strain gradient elasticity is employed here. This theory is implemented in the commercial FEM code ABAQUS through user subroutine UEL. Convergence of the model is proved through consecutive mesh refinement. In consequence, the stresses ahead of a mode 1 crack become finite. Furthermore, the model predicts a size effect in the sense “smaller is stronger”.

A unified wall function for compressible turbulence modelling

NASA Astrophysics Data System (ADS)

Ong, K. C.; Chan, A.

2018-05-01

Turbulence modelling near the wall often requires a high mesh density clustered around the wall and the first cells adjacent to the wall to be placed in the viscous sublayer. As a result, the numerical stability is constrained by the smallest cell size and hence requires high computational overhead. In the present study, a unified wall function is developed which is valid for viscous sublayer, buffer sublayer and inertial sublayer, as well as including effects of compressibility, heat transfer and pressure gradient. The resulting wall function applies to compressible turbulence modelling for both isothermal and adiabatic wall boundary conditions with the non-zero pressure gradient. Two simple wall function algorithms are implemented for practical computation of isothermal and adiabatic wall boundary conditions. The numerical results show that the wall function evaluates the wall shear stress and turbulent quantities of wall adjacent cells at wide range of non-dimensional wall distance and alleviate the number and size of cells required.

Two-dimensional strain gradient damage modeling: a variational approach

NASA Astrophysics Data System (ADS)

Placidi, Luca; Misra, Anil; Barchiesi, Emilio

2018-06-01

In this paper, we formulate a linear elastic second gradient isotropic two-dimensional continuum model accounting for irreversible damage. The failure is defined as the condition in which the damage parameter reaches 1, at least in one point of the domain. The quasi-static approximation is done, i.e., the kinetic energy is assumed to be negligible. In order to deal with dissipation, a damage dissipation term is considered in the deformation energy functional. The key goal of this paper is to apply a non-standard variational procedure to exploit the damage irreversibility argument. As a result, we derive not only the equilibrium equations but, notably, also the Karush-Kuhn-Tucker conditions. Finally, numerical simulations for exemplary problems are discussed as some constitutive parameters are varying, with the inclusion of a mesh-independence evidence. Element-free Galerkin method and moving least square shape functions have been employed.

Gravity and thermal deformation of large primary mirror in space telescope

NASA Astrophysics Data System (ADS)

Wang, Xin; Jiang, Shouwang; Wan, Jinlong; Shu, Rong

2016-10-01

The technology of integrating mechanical FEA analysis with optical estimation is essential to simulate the gravity deformation of large main mirror and the thermal deformation such as static or temperature gradient of optical structure. We present the simulation results of FEA analysis, data processing, and image performance. Three kinds of support structure for large primary mirror which have the center holding structure, the edge glue fixation and back support, are designed and compared to get the optimal gravity deformation. Variable mirror materials Zerodur/SiC are chosen and analyzed to obtain the small thermal gradient distortion. The simulation accuracy is dependent on FEA mesh quality, the load definition of structure, the fitting error from discrete data to smooth surface. A main mirror with 1m diameter is designed as an example. The appropriate structure material to match mirror, the central supporting structure, and the key aspects of FEA simulation are optimized for space application.

Space-time adaptive solution of inverse problems with the discrete adjoint method

NASA Astrophysics Data System (ADS)

Alexe, Mihai; Sandu, Adrian

2014-08-01

This paper develops a framework for the construction and analysis of discrete adjoint sensitivities in the context of time dependent, adaptive grid, adaptive step models. Discrete adjoints are attractive in practice since they can be generated with low effort using automatic differentiation. However, this approach brings several important challenges. The space-time adjoint of the forward numerical scheme may be inconsistent with the continuous adjoint equations. A reduction in accuracy of the discrete adjoint sensitivities may appear due to the inter-grid transfer operators. Moreover, the optimization algorithm may need to accommodate state and gradient vectors whose dimensions change between iterations. This work shows that several of these potential issues can be avoided through a multi-level optimization strategy using discontinuous Galerkin (DG) hp-adaptive discretizations paired with Runge-Kutta (RK) time integration. We extend the concept of dual (adjoint) consistency to space-time RK-DG discretizations, which are then shown to be well suited for the adaptive solution of time-dependent inverse problems. Furthermore, we prove that DG mesh transfer operators on general meshes are also dual consistent. This allows the simultaneous derivation of the discrete adjoint for both the numerical solver and the mesh transfer logic with an automatic code generation mechanism such as algorithmic differentiation (AD), potentially speeding up development of large-scale simulation codes. The theoretical analysis is supported by numerical results reported for a two-dimensional non-stationary inverse problem.

Analyzing the Adaptive Mesh Refinement (AMR) Characteristics of a High-Order 2D Cubed-Sphere Shallow-Water Model

DOE PAGES

Ferguson, Jared O.; Jablonowski, Christiane; Johansen, Hans; ...

2016-11-09

Adaptive mesh refinement (AMR) is a technique that has been featured only sporadically in atmospheric science literature. This study aims to demonstrate the utility of AMR for simulating atmospheric flows. Several test cases are implemented in a 2D shallow-water model on the sphere using the Chombo-AMR dynamical core. This high-order finite-volume model implements adaptive refinement in both space and time on a cubed-sphere grid using a mapped-multiblock mesh technique. The tests consist of the passive advection of a tracer around moving vortices, a steady-state geostrophic flow, an unsteady solid-body rotation, a gravity wave impinging on a mountain, and the interactionmore » of binary vortices. Both static and dynamic refinements are analyzed to determine the strengths and weaknesses of AMR in both complex flows with small-scale features and large-scale smooth flows. The different test cases required different AMR criteria, such as vorticity or height-gradient based thresholds, in order to achieve the best accuracy for cost. The simulations show that the model can accurately resolve key local features without requiring global high-resolution grids. The adaptive grids are able to track features of interest reliably without inducing noise or visible distortions at the coarse–fine interfaces. Finally and furthermore, the AMR grids keep any degradations of the large-scale smooth flows to a minimum.« less

Analyzing the Adaptive Mesh Refinement (AMR) Characteristics of a High-Order 2D Cubed-Sphere Shallow-Water Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferguson, Jared O.; Jablonowski, Christiane; Johansen, Hans

Adaptive mesh refinement (AMR) is a technique that has been featured only sporadically in atmospheric science literature. This study aims to demonstrate the utility of AMR for simulating atmospheric flows. Several test cases are implemented in a 2D shallow-water model on the sphere using the Chombo-AMR dynamical core. This high-order finite-volume model implements adaptive refinement in both space and time on a cubed-sphere grid using a mapped-multiblock mesh technique. The tests consist of the passive advection of a tracer around moving vortices, a steady-state geostrophic flow, an unsteady solid-body rotation, a gravity wave impinging on a mountain, and the interactionmore » of binary vortices. Both static and dynamic refinements are analyzed to determine the strengths and weaknesses of AMR in both complex flows with small-scale features and large-scale smooth flows. The different test cases required different AMR criteria, such as vorticity or height-gradient based thresholds, in order to achieve the best accuracy for cost. The simulations show that the model can accurately resolve key local features without requiring global high-resolution grids. The adaptive grids are able to track features of interest reliably without inducing noise or visible distortions at the coarse–fine interfaces. Finally and furthermore, the AMR grids keep any degradations of the large-scale smooth flows to a minimum.« less

A review of integration strategies for solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Zhang, Xiongwen; Chan, S. H.; Li, Guojun; Ho, H. K.; Li, Jun; Feng, Zhenping

Due to increasing oil and gas demand, the depletion of fossil resources, serious global warming, efficient energy systems and new energy conversion processes are urgently needed. Fuel cells and hybrid systems have emerged as advanced thermodynamic systems with great promise in achieving high energy/power efficiency with reduced environmental loads. In particular, due to the synergistic effect of using integrated solid oxide fuel cell (SOFC) and classical thermodynamic cycle technologies, the efficiency of the integrated system can be significantly improved. This paper reviews different concepts/strategies for SOFC-based integration systems, which are timely transformational energy-related technologies available to overcome the threats posed by climate change and energy security.

Heat resistant alloys as interconnect materials of reduced temperature SOFCs

NASA Astrophysics Data System (ADS)

Jian, Li; Jian, Pu; Guangyuan, Xie; Shunxu, Wang; Jianzhong, Xiao

Heat-resistant alloys, Haynes 230 and SS310, were exposed to air and humidified H 2 at 750 °C for up to 1000 h, respectively, simulating the environments in reduced temperature solid oxide fuel cells (SOFCs). The oxidized samples were characterized by using SEM, EDS and X-ray diffraction to obtain the morphology, thickness, composition and crystal structure of the oxide scales. A mechanism for the formation of metallic Ni-rich nodules on top of the oxide scale in Haynes 230 sample oxidized in humidified H 2 was established. Thermodynamic analysis confirmed that MnCr 2O 4 is the favored spinel phase, together with Cr 2O 3, in the oxide scales.

Tuneable diode laser gas analyser for methane measurements on a large scale solid oxide fuel cell

NASA Astrophysics Data System (ADS)

Lengden, Michael; Cunningham, Robert; Johnstone, Walter

2011-10-01

A new in-line, real time gas analyser is described that uses tuneable diode laser spectroscopy (TDLS) for the measurement of methane in solid oxide fuel cells. The sensor has been tested on an operating solid oxide fuel cell (SOFC) in order to prove the fast response and accuracy of the technology as compared to a gas chromatograph. The advantages of using a TDLS system for process control in a large-scale, distributed power SOFC unit are described. In future work, the addition of new laser sources and wavelength modulation will allow the simultaneous measurement of methane, water vapour, carbon-dioxide and carbon-monoxide concentrations.

Evaluation of Cathode Air Flow Transients in a SOFC/GT Hybrid System Using Hardware in the Loop Simulation.

PubMed

Zhou, Nana; Yang, Chen; Tucker, David

2015-02-01

Thermal management in the fuel cell component of a direct fired solid oxide fuel cell gas turbine (SOFC/GT) hybrid power system can be improved by effective management and control of the cathode airflow. The disturbances of the cathode airflow were accomplished by diverting air around the fuel cell system through the manipulation of a hot-air bypass valve in open loop experiments, using a hardware-based simulation facility designed and built by the U.S. Department of Energy, National Energy Technology Laboratory (NETL). The dynamic responses of the fuel cell component and hardware component of the hybrid system were studied in this paper.

Novel approaches for fabrication of thin film layers for solid oxide electrolyte fuel cells

NASA Technical Reports Server (NTRS)

Murugesamoorthi, K. A.; Srinivasan, S.; Cocke, D. L.; Appleby, A. J.

1990-01-01

The main objectives of the SOFC (solid oxide fuel cell) project are to (1) identify viable and cost-effective techniques to prepare cell components for stable MSOFCs (monolithic SOFCs); (2) fabricate half and single cells; and (3) evaluate their performances. The approach used to fabricate stable MSOFCs is as follows: (1) the electrolyte layer is prepared in the form of a honeycomb structure by alloy oxidation and other cell components are deposited on it; (2) the electrolyte and anode layers are deposited on the cathode layer, which has a porous, honeycomb structure; and (3) the electrolyte and cathode layers are deposited on the anode layer. The current status of the project is reported.

On continuous and discontinuous approaches for modeling groundwater flow in heterogeneous media using the Numerical Manifold Method: Model development and comparison

NASA Astrophysics Data System (ADS)

Hu, Mengsu; Wang, Yuan; Rutqvist, Jonny

2015-06-01

One major challenge in modeling groundwater flow within heterogeneous geological media is that of modeling arbitrarily oriented or intersected boundaries and inner material interfaces. The Numerical Manifold Method (NMM) has recently emerged as a promising method for such modeling, in its ability to handle boundaries, its flexibility in constructing physical cover functions (continuous or with gradient jump), its meshing efficiency with a fixed mathematical mesh (covers), its convenience for enhancing approximation precision, and its integration precision, achieved by simplex integration. In this paper, we report on developing and comparing two new approaches for boundary constraints using the NMM, namely a continuous approach with jump functions and a discontinuous approach with Lagrange multipliers. In the discontinuous Lagrange multiplier method (LMM), the material interfaces are regarded as discontinuities which divide mathematical covers into different physical covers. We define and derive stringent forms of Lagrange multipliers to link the divided physical covers, thus satisfying the continuity requirement of the refraction law. In the continuous Jump Function Method (JFM), the material interfaces are regarded as inner interfaces contained within physical covers. We briefly define jump terms to represent the discontinuity of the head gradient across an interface to satisfy the refraction law. We then make a theoretical comparison between the two approaches in terms of global degrees of freedom, treatment of multiple material interfaces, treatment of small area, treatment of moving interfaces, the feasibility of coupling with mechanical analysis and applicability to other numerical methods. The newly derived boundary-constraint approaches are coded into a NMM model for groundwater flow analysis, and tested for precision and efficiency on different simulation examples. We first test the LMM for a Dirichlet boundary and then test both LMM and JFM for an idealized heterogeneous model, comparing the numerical results with analytical solutions. Then we test both approaches for a heterogeneous model and compare the results of hydraulic head and specific discharge. We show that both approaches are suitable for modeling material boundaries, considering high accuracy for the boundary constraints, the capability to deal with arbitrarily oriented or complexly intersected boundaries, and their efficiency using a fixed mathematical mesh.

Multi-length scale tomography for the determination and optimization of the effective microstructural properties in novel hierarchical solid oxide fuel cell anodes

NASA Astrophysics Data System (ADS)

Lu, Xuekun; Taiwo, Oluwadamilola O.; Bertei, Antonio; Li, Tao; Li, Kang; Brett, Dan J. L.; Shearing, Paul R.

2017-11-01

Effective microstructural properties are critical in determining the electrochemical performance of solid oxide fuel cells (SOFCs), particularly when operating at high current densities. A novel tubular SOFC anode with a hierarchical microstructure, composed of self-organized micro-channels and sponge-like regions, has been fabricated by a phase inversion technique to mitigate concentration losses. However, since pore sizes span over two orders of magnitude, the determination of the effective transport parameters using image-based techniques remains challenging. Pioneering steps are made in this study to characterize and optimize the microstructure by coupling multi-length scale 3D tomography and modeling. The results conclusively show that embedding finger-like micro-channels into the tubular anode can improve the mass transport by 250% and the permeability by 2-3 orders of magnitude. Our parametric study shows that increasing the porosity in the spongy layer beyond 10% enhances the effective transport parameters of the spongy layer at an exponential rate, but linearly for the full anode. For the first time, local and global mass transport properties are correlated to the microstructure, which is of wide interest for rationalizing the design optimization of SOFC electrodes and more generally for hierarchical materials in batteries and membranes.

Solid oxide fuel cell short stack performance testing - Part A: Experimental analysis and μ-combined heat and power unit comparison

NASA Astrophysics Data System (ADS)

Mastropasqua, L.; Campanari, S.; Brouwer, J.

2017-12-01

The need to experimentally understand the detailed performance of SOFC stacks under operating conditions typical of commercial SOFC systems has prompted this two-part study. The steady state performance of a 6-cell short stack of yttria (Y2O3) stabilised zirconia (YSZ) with Ni/YSZ anodes and composite Sr-doped lanthanum manganite (LaMnO3, LSM)/YSZ cathodes is experimentally evaluated. In Part A, the stack characterisation is carried out by means of sensitivity analyses on the fuel utilisation factor and the steam-to-carbon ratio. Electrical and environmental performances are assessed and the results are compared with a commercial full-scale micro-CHP system, which comprises the same cells. The results show that the measured temperature dynamics of the short stack in a test stand environment are on the order of many minutes; therefore, one cannot neglect temperature dynamics for a precise measurement of the steady state polarisation behaviour. The overall polarisation performance is comparable to that of the full stack employed in the micro-CHP system, confirming the good representation that short-stack analyses can give of the entire SOFC module. The environmental performance is measured verifying the negligible values of NO emissions (<10 ppb) across the whole polarisation curve.

Numerical analysis on effect of aspect ratio of planar solid oxide fuel cell fueled with decomposed ammonia

NASA Astrophysics Data System (ADS)

Tan, Wee Choon; Iwai, Hiroshi; Kishimoto, Masashi; Brus, Grzegorz; Szmyd, Janusz S.; Yoshida, Hideo

2018-04-01

Planar solid oxide fuel cells (SOFCs) with decomposed ammonia are numerically studied to investigate the effect of the cell aspect ratio. The ammonia decomposer is assumed to be located next to the SOFCs, and the heat required for the endothermic decomposition reaction is supplied by the thermal radiation from the SOFCs. Cells with aspect ratios (ratios of the streamwise length to the spanwise width) between 0.130 and 7.68 are provided with the reactants at a constant mass flow rate. A parametric study is conducted by varying the cell temperature and fuel utility factor to investigate their effects on the cell performance in terms of the voltage efficiency. The effect of the heat supply to the ammonia decomposer is also studied. The developed model shows good agreement, in terms of the current-voltage curve, with the experimental data obtained from a short stack without parameter tuning. The simulation study reveals that the cell with the highest aspect ratio achieves the highest performance under furnace operation. On the other hand, the 0.750 aspect ratio cell with the highest voltage efficiency of 0.67 is capable of thermally sustaining the ammonia decomposers at a fuel utility of 0.80 using the thermal radiation from both sidewalls.

Micro solid oxide fuel cells: a new generation of micro-power sources for portable applications

NASA Astrophysics Data System (ADS)

Chiabrera, Francesco; Garbayo, Iñigo; Alayo, Nerea; Tarancón, Albert

2017-06-01

Portable electronic devices are already an indispensable part of our daily life; and their increasing number and demand for higher performance is becoming a challenge for the research community. In particular, a major concern is the way to efficiently power these energy-demanding devices, assuring long grid independency with high efficiency, sustainability and cheap production. In this context, technologies beyond Li-ion are receiving increasing attention, among which the development of micro solid oxide fuel cells (μSOFC) stands out. In particular, μSOFC provides a high energy density, high efficiency and opens the possibility to the use of different fuels, such as hydrocarbons. Yet, its high operating temperature has typically hindered its application as miniaturized portable device. Recent advances have however set a completely new range of lower operating temperatures, i.e. 350-450°C, as compared to the typical <900°C needed for classical bulk SOFC systems. In this work, a comprehensive review of the status of the technology is presented. The main achievements, as well as the most important challenges still pending are discussed, regarding (i.) the cell design and microfabrication, and (ii.) the integration of functional electrolyte and electrode materials. To conclude, the different strategies foreseen for a wide deployment of the technology as new portable power source are underlined.

Air plasma spray processing and electrochemical characterization of SOFC composite cathodes

NASA Astrophysics Data System (ADS)

White, B. D.; Kesler, O.; Rose, Lars

Air plasma spraying has been used to produce porous composite cathodes containing (La 0.8Sr 0.2) 0.98MnO 3- y (LSM) and yttria-stabilized zirconia (YSZ) for use in solid oxide fuel cells (SOFCs). Preliminary investigations focused on determining the range of plasma conditions under which each of the individual materials could be successfully deposited. A range of conditions was thereby determined that was suitable for the deposition of a composite cathode from pre-mixed LSM and YSZ powders. A number of composite cathodes were produced using different combinations of parameter values within the identified range according to a Uniform Design experimental grid. Coatings were then characterized for composition and microstructure using EDX and SEM. As a result of these tests, combinations of input parameter values were identified that are best suited to the production of coatings with microstructures appropriate for use in SOFC composite cathodes. A selection of coatings representative of the types of observed microstructures were then subjected to electrochemical testing to evaluate the performance of these cathodes. From these tests, it was found that, in general, the coatings that appeared to have the most suitable microstructures also had the highest electrochemical performances, provided that the deposition efficiency of both phases was sufficiently high.

Thermodynamic analysis of biofuels as fuels for high temperature fuel cells

NASA Astrophysics Data System (ADS)

Milewski, Jarosław; Bujalski, Wojciech; Lewandowski, Janusz

2011-11-01

Based on mathematical modeling and numerical simulations, applicativity of various biofuels on high temperature fuel cell performance are presented. Governing equations of high temperature fuel cell modeling are given. Adequate simulators of both solid oxide fuel cell (SOFC) and molten carbonate fuel cell (MCFC) have been done and described. Performance of these fuel cells with different biofuels is shown. Some characteristics are given and described. Advantages and disadvantages of various biofuels from the system performance point of view are pointed out. An analysis of various biofuels as potential fuels for SOFC and MCFC is presented. The results are compared with both methane and hydrogen as the reference fuels. The biofuels are characterized by both lower efficiency and lower fuel utilization factors compared with methane. The presented results are based on a 0D mathematical model in the design point calculation. The governing equations of the model are also presented. Technical and financial analysis of high temperature fuel cells (SOFC and MCFC) are shown. High temperature fuel cells can be fed by biofuels like: biogas, bioethanol, and biomethanol. Operational costs and possible incomes of those installation types were estimated and analyzed. A comparison against classic power generation units is shown. A basic indicator net present value (NPV) for projects was estimated and commented.

Thermodynamic analysis of biofuels as fuels for high temperature fuel cells

NASA Astrophysics Data System (ADS)

Milewski, Jarosław; Bujalski, Wojciech; Lewandowski, Janusz

2013-02-01

Based on mathematical modeling and numerical simulations, applicativity of various biofuels on high temperature fuel cell performance are presented. Governing equations of high temperature fuel cell modeling are given. Adequate simulators of both solid oxide fuel cell (SOFC) and molten carbonate fuel cell (MCFC) have been done and described. Performance of these fuel cells with different biofuels is shown. Some characteristics are given and described. Advantages and disadvantages of various biofuels from the system performance point of view are pointed out. An analysis of various biofuels as potential fuels for SOFC and MCFC is presented. The results are compared with both methane and hydrogen as the reference fuels. The biofuels are characterized by both lower efficiency and lower fuel utilization factors compared with methane. The presented results are based on a 0D mathematical model in the design point calculation. The governing equations of the model are also presented. Technical and financial analysis of high temperature fuel cells (SOFC and MCFC) are shown. High temperature fuel cells can be fed by biofuels like: biogas, bioethanol, and biomethanol. Operational costs and possible incomes of those installation types were estimated and analyzed. A comparison against classic power generation units is shown. A basic indicator net present value (NPV) for projects was estimated and commented.

Liquid-fueled SOFC power sources for transportation

NASA Astrophysics Data System (ADS)

Myles, K. M.; Doshi, R.; Kumar, R.; Krumpelt, M.

Traditionally, fuel cells have been developed for space or stationary terrestrial applications. As the first commercial 200-kW systems were being introduced by ONSI and Fuji Electric, the potentially much larger, but also more challenging, application in transportation was beginning to be addressed. As a result, fuel cell-powered buses have been designed and built, and R&D programs for fuel cell-powered passenger cars have been initiated. The engineering challenge of eventually replacing the internal combustion engine in buses, trucks, and passenger cars with fuel cell systems is to achieve much higher power densities and much lower costs than obtainable in systems designed for stationary applications. At present, the leading fuel cell candidate for transportation applications is, without question, the polymer electrolyte fuel cell (PEFC). Offering ambient temperature start-up and the potential for a relatively high power density, the polymer technology has attracted the interest of automotive manufacturers worldwide. But the difficulties of fuel handling for the PEFC have led to a growing interest in exploring the prospects for solid oxide fuel cells (SOFCs) operating on liquid fuels for transportation applications. Solid oxide fuel cells are much more compatible with liquid fuels (methanol or other hydrocarbons) and are potentially capable of power densities high enough for vehicular use. Two SOFC options for such use are discussed in this report.

Conformal bi-layered perovskite/spinel coating on a metallic wire network for solid oxide fuel cells via an electrodeposition-based route

NASA Astrophysics Data System (ADS)

Park, Beom-Kyeong; Song, Rak-Hyun; Lee, Seung-Bok; Lim, Tak-Hyoung; Park, Seok-Joo; Jung, WooChul; Lee, Jong-Won

2017-04-01

Solid oxide fuel cells (SOFCs) require low-cost metallic components for current collection from electrodes as well as electrical connection between unit cells; however, the degradation of their electrical properties and surface stability associated with high-temperature oxidation is of great concern. It is thus important to develop protective conducting oxide coatings capable of mitigating the degradation of metallic components under SOFC operating conditions. Here, we report a conformal bi-layered coating composed of perovskite and spinel oxides on a metallic wire network fabricated by a facile electrodeposition-based route. A highly dense, crack-free, and adhesive bi-layered LaMnO3/Co3O4 coating of ∼1.2 μm thickness is conformally formed on the surfaces of wires with ∼100 μm diameter. We demonstrate that the bi-layered LaMnO3/Co3O4 coating plays a key role in improving the power density and durability of a tubular SOFC by stabilizing the surface of the metallic wire network used as a cathode current collector. The electrodeposition-based technique presented in this study offers a low-cost and scalable process to fabricate conformal multi-layered coatings on various metallic structures.

Performance evaluation of GDC-SrMoO4-YSZ SOFCs prepared with different pore formers

NASA Astrophysics Data System (ADS)

Hongxin, You; Lian, Peng; Xiaojuan, Wang; Cong, Zhao; Yajun, Guan; Tao, Yu; Lijun, Xu; Abuliti

2018-04-01

The paper aims to evaluate the performance of anodes prepared with different pore formers. Anodic precursor material SrMoO4 was prepared by hard template method. Gd0.2Ce0.8O1.9 (GDC) was introduced to the precursor to prepare composite anode material GDC-SrMoO4-YSZ by wet impregnation method. Cotton-fibers, graphite powder, flour and activated carbon fibers (ACF) were added as pore formers to the anode to prepare the corresponding solid oxide fuel cell (SOFC), respectively. The electrical performance testing was conducted under the methane environment at 800°C. The result showed that the single cell with 5wt% cotton-fibers as anode pore-former performed best with the maximum power density (464.49 mW.cm2). The cross section samples of the test cells indicated that the anode was left with a plenty of continuous long channels because of the burning of cotton-fibers. Thus, the influence of the amount of cotton-fibers (2wt%, 4wt%, 5wt%, 7wt%, 10wt%) of the anode on the performance of SOFC was tested and further analyzed by the scanning electron microscope (SEM). It was indicated that the optimum adding amount of cotton-fibers was 5wt%.

Solid State Energy Conversion Alliance Delphi SOFC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steven Shaffer; Sean Kelly; Larry Chick

2003-05-20

The objective of Phase I under this project is to develop a 5 kW SOFC power system for a range of fuels and applications. During Phase I, the following will be accomplished: 1. Develop and demonstrate technology transfer efforts on a 5 kW stationary distributed power generation system that incorporates steam reforming of natural gas with piped-in water (Demonstration System A). 2. Initiate development of a 5 kW system for later mass-market automotive auxiliary power unit application, which will incorporate catalytic partial oxidation (CPO) reforming of gasoline, with anode exhaust gas injected into an ultra-lean burn internal combustion engine. Thismore » topical report covers work performed by Delphi Automotive Systems from January through June 2002 under DOE Cooperative Agreement DE-FC-02NT41246 for the 5 kW mass-market automotive (gasoline) auxiliary power unit. This report highlights technical results of the work performed under the following tasks for the automotive 5 kW system: 1. System Design and Integration 2. SOFC Stack Development 3. Reformer Development The next anticipated Technical Progress Report will be submitted January 30, 2003 and will include tasks contained within the cooperative agreement including development work on the Demonstration System A, if available.« less

Influence of the Crystal Structure of Titanium Oxide on the Catalytic Activity of Rh/TiO2 in Steam Reforming of Propane at Low Temperature.

PubMed

Yu, Lin; Sato, Katsutoshi; Toriyama, Takaaki; Yamamoto, Tomokazu; Matsumura, Syo; Nagaoka, Katsutoshi

2018-06-21

Solid oxide fuel cells (SOFCs) with liquefied petroleum gas (LPG) reduce CO 2 emissions due to their high-energy-conversion efficiency. Although SOFCs can convert LPG directly, coking occurs easily by decomposition of hydrocarbons, including C-C bonds on the electrode of fuel cell stacks. It is therefore necessary to develop an active steam pre-reforming catalyst that eliminates the hydrocarbons at low temperature, in which waste heat of SOFCs is used. Herein, we show that the crystal structure of the TiO 2 that anchors Rh particles is crucial for catalytic activity of Rh/TiO 2 catalysts for propane pre-reforming. Our experimental results revealed that strong metal support interaction (SMSI) induced during H 2 pre-reduction were optimized over Rh/TiO 2 with a rutile structure; this catalyst catalyzed the reaction much more effectively than conventional Rh/γ-Al 2 O 3 . In contrast, the SMSI was too strong for Rh/TiO 2 with an anatase structure, and the surface of the Rh particles was therefore covered mostly with partially reduced TiO 2 . The result was very low activity. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Modeling cascading diffusion of new energy technologies: case study of residential solid oxide fuel cells in the US and internationally.

PubMed

Herron, Seth; Williams, Eric

2013-08-06

Subsidy programs for new energy technologies are motivated by the experience curve: increased adoption of a technology leads to learning and economies of scale that lower costs. Geographic differences in fuel prices and climate lead to large variability in the economic performance of energy technologies. The notion of cascading diffusion is that regions with favorable economic conditions serve as the basis to build scale and reduce costs so that the technology becomes attractive in new regions. We develop a model of cascading diffusion and implement via a case study of residential solid oxide fuel cells (SOFCs) for combined heating and power. We consider diffusion paths within the U.S. and internationally. We construct market willingness-to-pay curves and estimate future manufacturing costs via an experience curve. Combining market and cost results, we find that for rapid cost reductions (learning rate = 25%), a modest public subsidy can make SOFC investment profitable for 20-160 million households. If cost reductions are slow however (learning rate = 15%), residential SOFCs may not become economically competitive. Due to higher energy prices in some countries, international diffusion is more favorable than domestic, mitigating much of the uncertainty in the learning rate.

Efficiency gain of solid oxide fuel cell systems by using anode offgas recycle - Results for a small scale propane driven unit

NASA Astrophysics Data System (ADS)

Dietrich, Ralph-Uwe; Oelze, Jana; Lindermeir, Andreas; Spitta, Christian; Steffen, Michael; Küster, Torben; Chen, Shaofei; Schlitzberger, Christian; Leithner, Reinhard

The transfer of high electrical efficiencies of solid oxide fuel cells (SOFC) into praxis requires appropriate system concepts. One option is the anode-offgas recycling (AOGR) approach, which is based on the integration of waste heat using the principle of a chemical heat pump. The AOGR concept allows a combined steam- and dry-reforming of hydrocarbon fuel using the fuel cell products steam and carbon dioxide. SOFC fuel gas of higher quantity and quality results. In combination with internal reuse of waste heat the system efficiency increases compared to the usual path of partial oxidation (POX). The demonstration of the AOGR concept with a 300 Wel-SOFC stack running on propane required: a combined reformer/burner-reactor operating in POX (start-up) and AOGR modus; a hotgas-injector for anode-offgas recycling to the reformer; a dynamic process model; a multi-variable process controller; full system operation for experimental proof of the efficiency gain. Experimental results proof an efficiency gain of 18 percentage points (η·POX = 23%, η·AOGR = 41%) under idealized lab conditions. Nevertheless, further improvements of injector performance, stack fuel utilization and additional reduction of reformer reformer O/C ratio and system pressure drop are required to bring this approach into self-sustaining operation.

Electrochemical characterization of B-site cation-excess Pr 2Ni 0.75Cu 0.25Ga 0.05O 4+δ cathode for IT-SOFCs

DOE PAGES

Meng, Xiangwei; Lü, Shiquan; Liu, Shouxiu; ...

2015-06-15

In this paper, the B-site cation-excess K 2NiF 4-type structure oxide, Pr 2Ni 0.75Cu 0.25Ga 0.05O 4+δ (PNCG) is investigated as a cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). XRD result shows that PNCG cathode is chemically compatible with the electrolyte Gd 0.1Ce 0.9O 2-δ (GDC) at 900 °C for 5 h. The PNCG material exhibits a semiconductor to metal transition around 425 °C. The thermal expansion coefficient (TEC) of the PNCG sample is 12.72×10 -6 K -1 between 30 and 850 °C in air. The polarization resistance (R p) of PNCG cathode on GDC electrolyte is 0.105, 0.197more » and 0.300 Ω cm 2 at 800, 750, 700 °C, respectively. A maximum power density of 371 mW cm -2 is obtained at 800 °C for single-cell with 300 μm thick GDC electrolyte and PNCG cathode. Finally, the results of this study demonstrate that PNCG can be a promising cathode material for IT-SOFCs.« less

Observations on the oxidation of Mn-modified Ni-base Haynes 230 alloy under SOFC exposure conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Z Gary; Xia, Gordon; Stevenson, Jeffry W.

2005-07-01

The commercial Ni-base Haynes 230 alloy (Ni-Cr-Mo-W-Mn) was modified with two increased levels of Mn (1 and 2 wt per cent) and evaluated for its oxidation resistance under simulated SOFC interconnect exposure conditions. Oxidation rate, oxide morphology, oxide conductivity and thermal expansion were measured and compared with commercial Haynes 230. It was observed that additions of higher levels of Mn to the bulk alloy facilitated the formation of a bi-layered oxide scale that was comprised of an outer M3O4 (M=Mn, Cr, Ni) spinel-rich layer at the oxide – gas interface over a Cr2O3-rich sub-layer at the metal – oxide interface.more » The modified alloys showed higher oxidation rates and the formation of thicker oxide scales compared to the base alloy. The formation of a spinel-rich top layer improved the scale conductivity, especially during the early stages of the oxidation, but the higher scale growth rate resulted in an increase in the area-specific electrical resistance over time. Due to their face-centered cubic crystal structure, both commercial and modified alloys demonstrated a coefficient of thermal expansion that was higher than that of typical anode-supported and electrolyte-supported SOFCs.« less

Solid oxide fuel cell systems for residential micro-combined heat and power in the UK: Key economic drivers

NASA Astrophysics Data System (ADS)

Hawkes, Adam; Leach, Matthew

The ability of combined heat and power (CHP) to meet residential heat and power demands efficiently offers potentially significant financial and environmental advantages over centralised power generation and heat-provision through natural-gas fired boilers. A solid oxide fuel cell (SOFC) can operate at high overall efficiencies (heat and power) of 80-90%, offering an improvement over centralised generation, which is often unable to utilise waste heat. This paper applies an equivalent annual cost (EAC) minimisation model to a residential solid oxide fuel cell CHP system to determine what the driving factors are behind investment in this technology. We explore the performance of a hypothetical SOFC system—representing expectations of near to medium term technology development—under present UK market conditions. We find that households with small to average energy demands do not benefit from installation of a SOFC micro-CHP system, but larger energy demands do benefit under these conditions. However, this result is sensitive to a number of factors including stack capital cost, energy import and export prices, and plant lifetime. The results for small and average dwellings are shown to reverse under an observed change in energy import prices, an increase in electricity export price, a decrease in stack capital costs, or an improvement in stack lifetime.

Influence of Electrode Design and Contacting Layers on Performance of Electrolyte Supported SOFC/SOEC Single Cells.

PubMed

Kusnezoff, Mihails; Trofimenko, Nikolai; Müller, Martin; Michaelis, Alexander

2016-11-08

The solid oxide cell is a basis for highly efficient and reversible electrochemical energy conversion. A single cell based on a planar electrolyte substrate as support (ESC) is often utilized for SOFC/SOEC stack manufacturing and fulfills necessary requirements for application in small, medium and large scale fuel cell and electrolysis systems. Thickness of the electrolyte substrate, and its ionic conductivity limits the power density of the ESC. To improve the performance of this cell type in SOFC/SOEC mode, alternative fuel electrodes, on the basis of Ni/CGO as well as electrolytes with reduced thickness, have been applied. Furthermore, different interlayers on the air side have been tested to avoid the electrode delamination and to reduce the cell degradation in electrolysis mode. Finally, the influence of the contacting layer on cell performance, especially for cells with an ultrathin electrolyte and thin electrode layers, has been investigated. It has been found that Ni/CGO outperform traditional Ni/8YSZ electrodes and the introduction of a ScSZ interlayer substantially reduces the degradation rate of ESC in electrolysis mode. Furthermore, it was demonstrated that, for thin electrodes, the application of contacting layers with good conductivity and adhesion to current collectors improves performance significantly.

Experimental study on the 300W class planar type solid oxide fuel cell stack: Investigation for appropriate fuel provision control and the transient capability of the cell performance

NASA Astrophysics Data System (ADS)

Komatsu, Y.; Brus, G.; Kimijima, S.; Szmyd, J. S.

2012-11-01

The present paper reports the experimental study on the dynamic behavior of a solid oxide fuel cell (SOFC). The cell stack consists of planar type cells with standard power output 300W. A Major subject of the present study is characterization of the transient response to the electric current change, assuming load-following operation. The present studies particularly focus on fuel provision control to the load change. Optimized fuel provision improves power generation efficiency. However, the capability of SOFC must be restricted by a few operative parameters. Fuel utilization factor, which is defined as the ratio of the consumed fuel to the supplied fuel is adopted for a reference in the control scheme. The fuel flow rate was regulated to keep the fuel utilization at 50%, 60% and 70% during the current ramping. Lower voltage was observed with the higher fuel utilization, but achieved efficiency was higher. The appropriate mass flow control is required not to violate the voltage transient behavior. Appropriate fuel flow manipulation can contribute to moderate the overshoot on the voltage that may appear to the current change. The overshoot on the voltage response resulted from the gradual temperature behavior in the SOFC stack module.

Robust adaptive control for a hybrid solid oxide fuel cell system

NASA Astrophysics Data System (ADS)

Snyder, Steven

2011-12-01

Solid oxide fuel cells (SOFCs) are electrochemical energy conversion devices. They offer a number of advantages beyond those of most other fuel cells due to their high operating temperature (800-1000°C), such as internal reforming, heat as a byproduct, and faster reaction kinetics without precious metal catalysts. Mitigating fuel starvation and improving load-following capabilities of SOFC systems are conflicting control objectives. However, this can be resolved by the hybridization of the system with an energy storage device, such as an ultra-capacitor. In this thesis, a steady-state property of the SOFC is combined with an input-shaping method in order to address the issue of fuel starvation. Simultaneously, an overall adaptive system control strategy is employed to manage the energy sharing between the elements as well as to maintain the state-of-charge of the energy storage device. The adaptive control method is robust to errors in the fuel cell's fuel supply system and guarantees that the fuel cell current and ultra-capacitor state-of-charge approach their target values and remain uniformly, ultimately bounded about these target values. Parameter saturation is employed to guarantee boundedness of the parameters. The controller is validated through hardware-in-the-loop experiments as well as computer simulations.

Challenge for lowering concentration polarization in solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Shimada, Hiroyuki; Suzuki, Toshio; Yamaguchi, Toshiaki; Sumi, Hirofumi; Hamamoto, Koichi; Fujishiro, Yoshinobu

2016-01-01

In the scope of electrochemical phenomena, concentration polarization at electrodes is theoretically inevitable, and lowering the concentration overpotential to improve the performance of electrochemical cells has been a continuing challenge. Electrodes with highly controlled microstructure, i.e., high porosity and uniform large pores are therefore essential to achieve high performance electrochemical cells. In this study, state-of-the-art technology for controlling the microstructure of electrodes has been developed for realizing high performance support electrodes of solid oxide fuel cells (SOFCs). The key is controlling the porosity and pore size distribution to improve gas diffusion, while maintaining the integrity of the electrolyte and the structural strength of actual sized electrode supports needed for the target application. Planar anode-supported SOFCs developed in this study realize 5 μm thick dense electrolyte (yttria-stabilized zirconia: YSZ) and the anode substrate (Ni-YSZ) of 53.6 vol.% porosity with a large median pore diameter of 0.911 μm. Electrochemical measurements reveal that the performance of the anode-supported SOFCs improves with increasing anode porosity. This Ni-YSZ anode minimizes the concentration polarization, resulting in a maximum power density of 3.09 W cm-2 at 800 °C using humidified hydrogen fuel without any electrode functional layers.

Meshless Method for Simulation of Compressible Flow

NASA Astrophysics Data System (ADS)

Nabizadeh Shahrebabak, Ebrahim

In the present age, rapid development in computing technology and high speed supercomputers has made numerical analysis and computational simulation more practical than ever before for large and complex cases. Numerical simulations have also become an essential means for analyzing the engineering problems and the cases that experimental analysis is not practical. There are so many sophisticated and accurate numerical schemes, which do these simulations. The finite difference method (FDM) has been used to solve differential equation systems for decades. Additional numerical methods based on finite volume and finite element techniques are widely used in solving problems with complex geometry. All of these methods are mesh-based techniques. Mesh generation is an essential preprocessing part to discretize the computation domain for these conventional methods. However, when dealing with mesh-based complex geometries these conventional mesh-based techniques can become troublesome, difficult to implement, and prone to inaccuracies. In this study, a more robust, yet simple numerical approach is used to simulate problems in an easier manner for even complex problem. The meshless, or meshfree, method is one such development that is becoming the focus of much research in the recent years. The biggest advantage of meshfree methods is to circumvent mesh generation. Many algorithms have now been developed to help make this method more popular and understandable for everyone. These algorithms have been employed over a wide range of problems in computational analysis with various levels of success. Since there is no connectivity between the nodes in this method, the challenge was considerable. The most fundamental issue is lack of conservation, which can be a source of unpredictable errors in the solution process. This problem is particularly evident in the presence of steep gradient regions and discontinuities, such as shocks that frequently occur in high speed compressible flow problems. To solve this discontinuity problem, this research study deals with the implementation of a conservative meshless method and its applications in computational fluid dynamics (CFD). One of the most common types of collocating meshless method the RBF-DQ, is used to approximate the spatial derivatives. The issue with meshless methods when dealing with highly convective cases is that they cannot distinguish the influence of fluid flow from upstream or downstream and some methodology is needed to make the scheme stable. Therefore, an upwinding scheme similar to one used in the finite volume method is added to capture steep gradient or shocks. This scheme creates a flexible algorithm within which a wide range of numerical flux schemes, such as those commonly used in the finite volume method, can be employed. In addition, a blended RBF is used to decrease the dissipation ensuing from the use of a low shape parameter. All of these steps are formulated for the Euler equation and a series of test problems used to confirm convergence of the algorithm. The present scheme was first employed on several incompressible benchmarks to validate the framework. The application of this algorithm is illustrated by solving a set of incompressible Navier-Stokes problems. Results from the compressible problem are compared with the exact solution for the flow over a ramp and compared with solutions of finite volume discretization and the discontinuous Galerkin method, both requiring a mesh. The applicability of the algorithm and its robustness are shown to be applied to complex problems.

A constrained-gradient method to control divergence errors in numerical MHD

NASA Astrophysics Data System (ADS)

Hopkins, Philip F.

2016-10-01

In numerical magnetohydrodynamics (MHD), a major challenge is maintaining nabla \\cdot {B}=0. Constrained transport (CT) schemes achieve this but have been restricted to specific methods. For more general (meshless, moving-mesh, ALE) methods, `divergence-cleaning' schemes reduce the nabla \\cdot {B} errors; however they can still be significant and can lead to systematic errors which converge away slowly. We propose a new constrained gradient (CG) scheme which augments these with a projection step, and can be applied to any numerical scheme with a reconstruction. This iteratively approximates the least-squares minimizing, globally divergence-free reconstruction of the fluid. Unlike `locally divergence free' methods, this actually minimizes the numerically unstable nabla \\cdot {B} terms, without affecting the convergence order of the method. We implement this in the mesh-free code GIZMO and compare various test problems. Compared to cleaning schemes, our CG method reduces the maximum nabla \\cdot {B} errors by ˜1-3 orders of magnitude (˜2-5 dex below typical errors if no nabla \\cdot {B} cleaning is used). By preventing large nabla \\cdot {B} at discontinuities, this eliminates systematic errors at jumps. Our CG results are comparable to CT methods; for practical purposes, the nabla \\cdot {B} errors are eliminated. The cost is modest, ˜30 per cent of the hydro algorithm, and the CG correction can be implemented in a range of numerical MHD methods. While for many problems, we find Dedner-type cleaning schemes are sufficient for good results, we identify a range of problems where using only Powell or `8-wave' cleaning can produce order-of-magnitude errors.

Optimization of La 2O 3-containing diopside based glass-ceramic sealants for fuel cell applications

NASA Astrophysics Data System (ADS)

Goel, Ashutosh; Tulyaganov, Dilshat U.; Kharton, Vladislav V.; Yaremchenko, Aleksey A.; Eriksson, Sten; Ferreira, José M. F.

We report on the optimization of La 2O 3-containing diopside based glass-ceramics (GCs) for sealant applications in solid oxide fuel cells (SOFC). Seven glass compositions were prepared by modifying the parent glass composition, Ca 0.8Ba 0.1MgAl 0.1La 0.1Si 1.9O 6. First five glasses were prepared by the addition of different amounts of B 2O 3 in a systematic manner (i.e. 2, 5, 10, 15, 20 wt.%) to the parent glass composition while the remaining two glasses were derived by substituting SrO for BaO in the glasses containing 2 wt.% and 5 wt.% B 2O 3. Structural and thermal behavior of the glasses was investigated by infrared spectroscopy (FTIR), density measurements, dilatometry and differential thermal analysis (DTA). Liquid-liquid amorphous phase separation was observed in B 2O 3-containing glasses. Sintering and crystallization behavior, microstructure, and properties of the GCs were investigated under different heat treatment conditions (800 and 850 °C; 1-300 h). The GCs with ≥5 wt.% B 2O 3 showed an abnormal thermal expansion behavior above 600 °C. The chemical interaction behavior of the glasses with SOFC electrolyte and metallic interconnects, has been investigated in air atmosphere at SOFC operating temperature. Thermal shock resistance and gas-tightness of GC sealants in contact with 8YSZ was evaluated in air and water. The total electrical resistance of a model cell comprising Crofer 22 APU and 8YSZ plates joined by a GC sealant has been examined by the impedance spectroscopy. Good matching of thermal expansion coefficients (CTE) and strong, but not reactive, adhesion to electrolyte and interconnect, in conjunction with a low level of electrical conductivity, indicate that the investigated GCs are suitable candidates for further experimentation as SOFC sealants.

Interaction of nickel-based SOFC anodes with trace contaminants from coal-derived synthesis gas

NASA Astrophysics Data System (ADS)

Hackett, Gregory Allen

New and efficient methods of producing electrical energy from natural resources have become an important topic for researchers. Integrated gasification and fuel cell (IGFC) systems offer a fuel-flexible, high-efficiency method of energy generation. Specifically, in coal gasification processes, coal can be changed into a high-quality gaseous fuel suitable for feeding solid oxide fuel cells (SOFCs). However, trace species found in coal synthesis gas (syngas) may have a deleterious effect on the performance of nickel-based SOFC anodes. Generally, the cost of removing these species down to parts per million (ppm) levels is high. The purpose of this research is to determine the highest amount of contaminant that results in a low rate (˜1% per 1000 h) of cell performance degradation, allowing the SOFC to produce usable power for 40,000 hours. The cell performance degradation rate was determined for benzene, naphthalene, and mercury-doped syngas based on species concentration. Experimental data are fitted with degradation models to predict cell lifetime behavior. From these results, the minimum coal syngas cleanup required for these trace materials is determined. It is found that for a final cell voltage of 0.6 V, naphthalene and benzene must be cleaned to 360 ppm and less than 150 ppm, respectively. No additional cleaning is required for mercury beyond established environmental standards. Additionally, a detailed attack and recovery mechanism is proposed for the hydrocarbon species and their interaction with the fuel cell. This mechanism is proposed by considering the type of degradation models predicted and how carbon would interact with the Ni-YSZ anode to justify those models. The mechanism postulates that carbon is diffusing into the nickel structure, creating a metal solution. Once the nickel is saturated, the carbon begins to deposit on the nickel surface, reducing the electrode active area. The formation of metal solutions and the deposition of carbon results in reduced cell productivity.

Regenerative Performance of the NASA Symmetrical Solid Oxide Fuel Cell Design

NASA Technical Reports Server (NTRS)

Cable, Thomas L.; Setlock, John A.; Farmer, Serene C.; Eckel, Andy J.

2009-01-01

The NASA Glenn Research Center is developing both a novel cell design (BSC) and a novel ceramic fabrication technique to produce fuel cells predicted to exceed a specific power density of 1.0 kW/kg. The NASA Glenn cell design has taken a completely different approach among planar designs by removing the metal interconnect and returning to the use of a thin, doped LaCrO3 interconnect. The cell is structurally symmetrical. Both electrodes support the thin electrolyte and contain micro-channels for gas flow-- a geometry referred to as a bi-electrode supported cell or BSC. The cell characteristics have been demonstrated under both SOFC and SOE conditions. Electrolysis tests verify that this cell design operates at very high electrochemical voltage efficiencies (EVE) and high H2O conversion percentages, even at the low flow rates predicted for closed loop systems encountered in unmanned aerial vehicle (UAV) applications. For UAVs the volume, weight and the efficiency are critical as they determine the size of the water tank, the solar panel size, and other system requirements. For UAVs, regenerative solid oxide fuel cell stacks (RSOFC) use solar panels during daylight to generate power for electrolysis and then operate in fuel cell mode during the night to power the UAV and electronics. Recent studies, performed by NASA for a more electric commercial aircraft, evaluated SOFCs for auxiliary power units (APUs). System studies were also conducted for regenerative RSOFC systems. One common requirement for aerospace SOFCs and RSOFCs, determined independently in each application study, was the need for high specific power density and volume density, on the order of 1.0 kW/kg and greater than 1.0 kW/L. Until recently the best reported performance for SOFCs was 0.2 kW/kg or less for stacks. NASA Glenn is working to prototype the light weight, low volume BSC design for such high specific power aerospace applications.

Optimal design and operation of solid oxide fuel cell systems for small-scale stationary applications

NASA Astrophysics Data System (ADS)

Braun, Robert Joseph

The advent of maturing fuel cell technologies presents an opportunity to achieve significant improvements in energy conversion efficiencies at many scales; thereby, simultaneously extending our finite resources and reducing "harmful" energy-related emissions to levels well below that of near-future regulatory standards. However, before realization of the advantages of fuel cells can take place, systems-level design issues regarding their application must be addressed. Using modeling and simulation, the present work offers optimal system design and operation strategies for stationary solid oxide fuel cell systems applied to single-family detached dwellings. A one-dimensional, steady-state finite-difference model of a solid oxide fuel cell (SOFC) is generated and verified against other mathematical SOFC models in the literature. Fuel cell system balance-of-plant components and costs are also modeled and used to provide an estimate of system capital and life cycle costs. The models are used to evaluate optimal cell-stack power output, the impact of cell operating and design parameters, fuel type, thermal energy recovery, system process design, and operating strategy on overall system energetic and economic performance. Optimal cell design voltage, fuel utilization, and operating temperature parameters are found using minimization of the life cycle costs. System design evaluations reveal that hydrogen-fueled SOFC systems demonstrate lower system efficiencies than methane-fueled systems. The use of recycled cell exhaust gases in process design in the stack periphery are found to produce the highest system electric and cogeneration efficiencies while achieving the lowest capital costs. Annual simulations reveal that efficiencies of 45% electric (LHV basis), 85% cogenerative, and simple economic paybacks of 5--8 years are feasible for 1--2 kW SOFC systems in residential-scale applications. Design guidelines that offer additional suggestions related to fuel cell-stack sizing and operating strategy (base-load or load-following and cogeneration or electric-only) are also presented.

Fundamental Impact of Humidity on SOFC Cathode ORR

DOE PAGES

Huang, Y. L.; Pellegrinelli, C.; Wachsman, E. D.

2015-12-17

Although solid oxide fuel cells (SOFC) have demonstrated excellent performance, the durability of SOFCs under real working conditions is still an issue for commercial deployment. In particular cathode exposure to atmospheric air contaminants, such as humidity, can result in long-term performance degradation issues. Therefore, a fundamental understanding of the interaction between water molecules and cathodes is essential to resolve this issue and further enhance cathode durability. In order to study the effects of humidity on the oxygen reduction reaction (ORR), we used in-situ 18O isotope exchange techniques to probe the exchange of water with two of themost common SOFC cathodemore » materials, (La 0.8Sr 0.2) 0.95MnO 3±δ (LSM) and La 0.6Sr 0.4Co 0.2Fe 0.8O 3-δ (LSCF). In this experiment, heavy water, D 2O (with a mass/charge ratio of m/z = 20), is used to avoid the overlapping of H 2O and the 18O 2 cracking fraction, which both provide a peak at m/z = 18. A series of temperature programmed isotope exchange measurements were performed to comprehensively study the interaction of water with the cathode surface as a function of temperature, oxygen partial pressure, and water vapor concentration. The results suggest that water and O 2 share the same surface exchange sites, leading to competitive adsorption. Our findings show that water prefers to exchange with LSCF at lower temperatures, around 300–450°C. For LSM, O 2 is more favorable than water to be adsorbed on the surface and the presence of O 2 limits water exchange. The experimental data are summarized in a Temperature-PO 2 diagram to help visualize how the exchange of water on each material depends on the operating conditions.« less

Effectiveness of paper-structured catalyst for the operation of biodiesel-fueled solid oxide fuel cell

NASA Astrophysics Data System (ADS)

Quang-Tuyen, Tran; Kaida, Taku; Sakamoto, Mio; Sasaki, Kazunari; Shiratori, Yusuke

2015-06-01

Mg/Al-hydrotalcite (HDT)-dispersed paper-structured catalyst (PSC) was prepared by a simple paper-making process. The PSC exhibited excellent catalytic activity for the steam reforming of model biodiesel fuel (BDF), pure oleic acid methyl ester (oleic-FAME, C19H36O2) which is a mono-unsaturated component of practical BDFs. The PSC exhibited fuel conversion comparable to a pelletized catalyst material, here, conventional Ni-zirconia cermet anode for solid oxide fuel cell (SOFC) with less than one-hundredth Ni weight. Performance of electrolyte-supported cell connected with the PSC was evaluated in the feed of oleic-FAME, and stable operation was achieved. After 60 h test, coking was not observed in both SOFC anode and PSC.

Structural design considerations for micromachined solid-oxide fuel cells

NASA Astrophysics Data System (ADS)

Srikar, V. T.; Turner, Kevin T.; Andrew Ie, Tze Yung; Spearing, S. Mark

Micromachined solid-oxide fuel cells (μSOFCs) are among a class of devices being investigated for portable power generation. Optimization of the performance and reliability of such devices requires robust, scale-dependent, design methodologies. In this first analysis, we consider the structural design of planar, electrolyte-supported, μSOFCs from the viewpoints of electrochemical performance, mechanical stability and reliability, and thermal behavior. The effect of electrolyte thickness on fuel cell performance is evaluated using a simple analytical model. Design diagrams that account explicitly for thermal and intrinsic residual stresses are presented to identify geometries that are resistant to fracture and buckling. Analysis of energy loss due to in-plane heat conduction highlights the importance of efficient thermal isolation in microscale fuel cell design.

Strategies for Carbon and Sulfur Tolerant Solid Oxide Fuel Cell Materials, Incorporating Lessons from Heterogeneous Catalysis.

PubMed

Boldrin, Paul; Ruiz-Trejo, Enrique; Mermelstein, Joshua; Bermúdez Menéndez, José Miguel; Ramı Rez Reina, Tomás; Brandon, Nigel P

2016-11-23

Solid oxide fuel cells (SOFCs) are a rapidly emerging energy technology for a low carbon world, providing high efficiency, potential to use carbonaceous fuels, and compatibility with carbon capture and storage. However, current state-of-the-art materials have low tolerance to sulfur, a common contaminant of many fuels, and are vulnerable to deactivation due to carbon deposition when using carbon-containing compounds. In this review, we first study the theoretical basis behind carbon and sulfur poisoning, before examining the strategies toward carbon and sulfur tolerance used so far in the SOFC literature. We then study the more extensive relevant heterogeneous catalysis literature for strategies and materials which could be incorporated into carbon and sulfur tolerant fuel cells.

Energy approach to brittle fracture in strain-gradient modelling.

PubMed

Placidi, Luca; Barchiesi, Emilio

2018-02-01

In this paper, we exploit some results in the theory of irreversible phenomena to address the study of quasi-static brittle fracture propagation in a two-dimensional isotropic continuum. The elastic strain energy density of the body has been assumed to be geometrically nonlinear and to depend on the strain gradient. Such generalized continua often arise in the description of microstructured media. These materials possess an intrinsic length scale, which determines the size of internal boundary layers. In particular, the non-locality conferred by this internal length scale avoids the concentration of deformations, which is usually observed when dealing with local models and which leads to mesh dependency. A scalar Lagrangian damage field, ranging from zero to one, is introduced to describe the internal state of structural degradation of the material. Standard Lamé and second-gradient elastic coefficients are all assumed to decrease as damage increases and to be locally zero if the value attained by damage is one. This last situation is associated with crack formation and/or propagation. Numerical solutions of the model are provided in the case of an obliquely notched rectangular specimen subjected to monotonous tensile and shear loading tests, and brittle fracture propagation is discussed.

Direct Coupling Method for Time-Accurate Solution of Incompressible Navier-Stokes Equations

NASA Technical Reports Server (NTRS)

Soh, Woo Y.

1992-01-01

A noniterative finite difference numerical method is presented for the solution of the incompressible Navier-Stokes equations with second order accuracy in time and space. Explicit treatment of convection and diffusion terms and implicit treatment of the pressure gradient give a single pressure Poisson equation when the discretized momentum and continuity equations are combined. A pressure boundary condition is not needed on solid boundaries in the staggered mesh system. The solution of the pressure Poisson equation is obtained directly by Gaussian elimination. This method is tested on flow problems in a driven cavity and a curved duct.

Low eddy current RF shielding enclosure designs for 3T MR applications.

PubMed

Lee, Brian J; Watkins, Ronald D; Chang, Chen-Ming; Levin, Craig S

2018-03-01

Magnetic resonance-compatible medical devices operate within the MR environment while benefitting from the superior anatomic information of MRI. Avoiding electromagnetic interference between such instrumentation and the MR system is crucial. In this work, various shielding configurations for positron emission tomography (PET) detectors were studied and analyzed regarding radiofrequency (RF) shielding effectiveness and gradient-induced eddy current performances. However, the results of this work apply to shielding considerations for any MR-compatible devices. Six shielding enclosure configurations with various thicknesses, patterns, and materials were designed: solid and segmented copper, phosphor bronze mesh (PBM), and carbon fiber composite (CFC). A series of tests was performed on RF shielding effectiveness and the gradient-induced eddy current. For the shielding effectiveness, the solid copper with various thickness and PBM configurations yield significantly better shielding effectiveness (>15 dB) compared with CFC and segmented configurations. For the gradient-induced eddy current performance, the solid copper shielding configurations with different thicknesses showed significantly worse results, up to a factor of 3.89 dB, compared with the segmented copper, PBM, and the CFC configurations. We evaluated the RF shielding effectiveness and the gradient-induced eddy current artifacts of several shielding designs, and only the PBM showed positive outcomes for both aspects. Magn Reson Med 79:1745-1752, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Mathematical and computational studies of equilibrium capillary free surfaces

NASA Technical Reports Server (NTRS)

Albright, N.; Chen, N. F.; Concus, P.; Finn, R.

1977-01-01

The results of several independent studies are presented. The general question is considered of whether a wetting liquid always rises higher in a small capillary tube than in a larger one, when both are dipped vertically into an infinite reservoir. An analytical investigation is initiated to determine the qualitative behavior of the family of solutions of the equilibrium capillary free-surface equation that correspond to rotationally symmetric pendent liquid drops and the relationship of these solutions to the singular solution, which corresponds to an infinite spike of liquid extending downward to infinity. The block successive overrelaxation-Newton method and the generalized conjugate gradient method are investigated for solving the capillary equation on a uniform square mesh in a square domain, including the case for which the solution is unbounded at the corners. Capillary surfaces are calculated on the ellipse, on a circle with reentrant notches, and on other irregularly shaped domains using JASON, a general purpose program for solving nonlinear elliptic equations on a nonuniform quadrilaterial mesh. Analytical estimates for the nonexistence of solutions of the equilibrium capillary free-surface equation on the ellipse in zero gravity are evaluated.

Aerodynamic Shape Optimization of a Dual-Stream Supersonic Plug Nozzle

NASA Technical Reports Server (NTRS)

Heath, Christopher M.; Gray, Justin S.; Park, Michael A.; Nielsen, Eric J.; Carlson, Jan-Renee

2015-01-01

Aerodynamic shape optimization was performed on an isolated axisymmetric plug nozzle sized for a supersonic business jet. The dual-stream concept was tailored to attenuate nearfield pressure disturbances without compromising nozzle performance. Adjoint-based anisotropic mesh refinement was applied to resolve nearfield compression and expansion features in the baseline viscous grid. Deformed versions of the adapted grid were used for subsequent adjoint-driven shape optimization. For design, a nonlinear gradient-based optimizer was coupled to the discrete adjoint formulation of the Reynolds-averaged Navier- Stokes equations. All nozzle surfaces were parameterized using 3rd order B-spline interpolants and perturbed axisymmetrically via free-form deformation. Geometry deformations were performed using 20 design variables shared between the outer cowl, shroud and centerbody nozzle surfaces. Interior volume grid deformation during design was accomplished using linear elastic mesh morphing. The nozzle optimization was performed at a design cruise speed of Mach 1.6, assuming core and bypass pressure ratios of 6.19 and 3.24, respectively. Ambient flight conditions at design were commensurate with 45,000-ft standard day atmosphere.

Well-balanced compressible cut-cell simulation of atmospheric flow.

PubMed

Klein, R; Bates, K R; Nikiforakis, N

2009-11-28

Cut-cell meshes present an attractive alternative to terrain-following coordinates for the representation of topography within atmospheric flow simulations, particularly in regions of steep topographic gradients. In this paper, we present an explicit two-dimensional method for the numerical solution on such meshes of atmospheric flow equations including gravitational sources. This method is fully conservative and allows for time steps determined by the regular grid spacing, avoiding potential stability issues due to arbitrarily small boundary cells. We believe that the scheme is unique in that it is developed within a dimensionally split framework, in which each coordinate direction in the flow is solved independently at each time step. Other notable features of the scheme are: (i) its conceptual and practical simplicity, (ii) its flexibility with regard to the one-dimensional flux approximation scheme employed, and (iii) the well-balancing of the gravitational sources allowing for stable simulation of near-hydrostatic flows. The presented method is applied to a selection of test problems including buoyant bubble rise interacting with geometry and lee-wave generation due to topography.

Marine Controlled-Source Electromagnetic 2D Inversion for synthetic models.

NASA Astrophysics Data System (ADS)

Liu, Y.; Li, Y.

2016-12-01

We present a 2D inverse algorithm for frequency domain marine controlled-source electromagnetic (CSEM) data, which is based on the regularized Gauss-Newton approach. As a forward solver, our parallel adaptive finite element forward modeling program is employed. It is a self-adaptive, goal-oriented grid refinement algorithm in which a finite element analysis is performed on a sequence of refined meshes. The mesh refinement process is guided by a dual error estimate weighting to bias refinement towards elements that affect the solution at the EM receiver locations. With the use of the direct solver (MUMPS), we can effectively compute the electromagnetic fields for multi-sources and parametric sensitivities. We also implement the parallel data domain decomposition approach of Key and Ovall (2011), with the goal of being able to compute accurate responses in parallel for complicated models and a full suite of data parameters typical of offshore CSEM surveys. All minimizations are carried out by using the Gauss-Newton algorithm and model perturbations at each iteration step are obtained by using the Inexact Conjugate Gradient iteration method. Synthetic test inversions are presented.

On the electromagnetic scattering from infinite rectangular conducting grids

NASA Technical Reports Server (NTRS)

Christodoulou, C.

1985-01-01

The study and development of two numerical techniques for the analysis of electromagnetic scattering from a rectangular wire mesh are described. Both techniques follow from one basic formulation and they are both solved in the spectral domain. These techniques were developed as a result of an investigation towards more efficient numerical computation for mesh scattering. These techniques are efficient for the following reasons: (a1) make use of the Fast Fourier Transform; (b2) they avoid any convolution problems by converting integrodifferential equations into algebraic equations; and (c3) they do not require inversions of any matrices. The first method, the SIT or Spectral Iteration Technique, is applied for regions where the spacing between wires is not less than two wavelengths. The second method, the SDCG or Spectral Domain Conjugate Gradient approach, can be used for any spacing between adjacent wires. A study of electromagnetic wave properties, such as reflection coefficient, induced currents and aperture fields, as functions of frequency, angle of incidence, polarization and thickness of wires is presented. Examples and comparisons or results with other methods are also included to support the validity of the new algorithms.

Parallel numerical modeling of hybrid-dimensional compositional non-isothermal Darcy flows in fractured porous media

NASA Astrophysics Data System (ADS)

Xing, F.; Masson, R.; Lopez, S.

2017-09-01

This paper introduces a new discrete fracture model accounting for non-isothermal compositional multiphase Darcy flows and complex networks of fractures with intersecting, immersed and non-immersed fractures. The so called hybrid-dimensional model using a 2D model in the fractures coupled with a 3D model in the matrix is first derived rigorously starting from the equi-dimensional matrix fracture model. Then, it is discretized using a fully implicit time integration combined with the Vertex Approximate Gradient (VAG) finite volume scheme which is adapted to polyhedral meshes and anisotropic heterogeneous media. The fully coupled systems are assembled and solved in parallel using the Single Program Multiple Data (SPMD) paradigm with one layer of ghost cells. This strategy allows for a local assembly of the discrete systems. An efficient preconditioner is implemented to solve the linear systems at each time step and each Newton type iteration of the simulation. The numerical efficiency of our approach is assessed on different meshes, fracture networks, and physical settings in terms of parallel scalability, nonlinear convergence and linear convergence.

Subgrid-scale models for large-eddy simulation of rotating turbulent flows

NASA Astrophysics Data System (ADS)

Silvis, Maurits; Trias, Xavier; Abkar, Mahdi; Bae, Hyunji Jane; Lozano-Duran, Adrian; Verstappen, Roel

2016-11-01

This paper discusses subgrid models for large-eddy simulation of anisotropic flows using anisotropic grids. In particular, we are looking into ways to model not only the subgrid dissipation, but also transport processes, since these are expected to play an important role in rotating turbulent flows. We therefore consider subgrid-scale models of the form τ = - 2νt S +μt (SΩ - ΩS) , where the eddy-viscosity νt is given by the minimum-dissipation model, μt represents a transport coefficient; S is the symmetric part of the velocity gradient and Ω the skew-symmetric part. To incorporate the effect of mesh anisotropy the filter length is taken in such a way that it minimizes the difference between the turbulent stress in physical and computational space, where the physical space is covered by an anisotropic mesh and the computational space is isotropic. The resulting model is successfully tested for rotating homogeneous isotropic turbulence and rotating plane-channel flows. The research was largely carried out during the CTR SP 2016. M.S, and R.V. acknowledge the financial support to attend this Summer Program.

First principles calculation of thermo-mechanical properties of thoria using Quantum ESPRESSO

NASA Astrophysics Data System (ADS)

Malakkal, Linu; Szpunar, Barbara; Zuniga, Juan Carlos; Siripurapu, Ravi Kiran; Szpunar, Jerzy A.

2016-05-01

In this work, we have used Quantum ESPRESSO (QE), an open source first principles code, based on density-functional theory, plane waves, and pseudopotentials, along with quasi-harmonic approximation (QHA) to calculate the thermo-mechanical properties of thorium dioxide (ThO2). Using Python programming language, our group developed qe-nipy-advanced, an interface to QE, which can evaluate the structural and thermo-mechanical properties of materials. We predicted the phonon contribution to thermal conductivity (kL) using the Slack model. We performed the calculations within local density approximation (LDA) and generalized gradient approximation (GGA) with the recently proposed version for solids (PBEsol). We employed a Monkhorst-Pack 5 × 5 × 5 k-points mesh in reciprocal space with a plane wave cut-off energy of 150 Ry to obtain the convergence of the structure. We calculated the dynamical matrices of the lattice on a 4 × 4 × 4 mesh. We have predicted the heat capacity, thermal expansion and the phonon contribution to thermal conductivity, as a function of temperature up to 1400K, and compared them with the previous work and known experimental results.

Gas stripping and mixing in galaxy clusters: a numerical comparison study

NASA Astrophysics Data System (ADS)

Heß, Steffen; Springel, Volker

2012-11-01

The ambient hot intrahalo gas in clusters of galaxies is constantly fed and stirred by infalling galaxies, a process that can be studied in detail with cosmological hydrodynamical simulations. However, different numerical methods yield discrepant predictions for crucial hydrodynamical processes, leading for example to different entropy profiles in clusters of galaxies. In particular, the widely used Lagrangian smoothed particle hydrodynamics (SPH) scheme is suspected to strongly damp fluid instabilities and turbulence, which are both crucial to establish the thermodynamic structure of clusters. In this study, we test to which extent our recently developed Voronoi particle hydrodynamics (VPH) scheme yields different results for the stripping of gas out of infalling galaxies and for the bulk gas properties of cluster. We consider both the evolution of isolated galaxy models that are exposed to a stream of intracluster medium or are dropped into cluster models, as well as non-radiative cosmological simulations of cluster formation. We also compare our particle-based method with results obtained with a fundamentally different discretization approach as implemented in the moving-mesh code AREPO. We find that VPH leads to noticeably faster stripping of gas out of galaxies than SPH, in better agreement with the mesh-code than with SPH. We show that despite the fact that VPH in its present form is not as accurate as the moving mesh code in our investigated cases, its improved accuracy of gradient estimates makes VPH an attractive alternative to SPH.

HFEM3D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weiss, Chester J

Software solves the three-dimensional Poisson equation div(k(grad(u)) = f, by the finite element method for the case when material properties, k, are distributed over hierarchy of edges, facets and tetrahedra in the finite element mesh. Method is described in Weiss, CJ, Finite element analysis for model parameters distributed on a hierarchy of geometric simplices, Geophysics, v82, E155-167, doi:10.1190/GEO2017-0058.1 (2017). A standard finite element method for solving Poisson’s equation is augmented by including in the 3D stiffness matrix additional 2D and 1D stiffness matrices representing the contributions from material properties associated with mesh faces and edges, respectively. The resulting linear systemmore » is solved iteratively using the conjugate gradient method with Jacobi preconditioning. To minimize computer storage for program execution, the linear solver computes matrix-vector contractions element-by-element over the mesh, without explicit storage of the global stiffness matrix. Program output vtk compliant for visualization and rendering by 3rd party software. Program uses dynamic memory allocation and as such there are no hard limits on problem size outside of those imposed by the operating system and configuration on which the software is run. Dimension, N, of the finite element solution vector is constrained by the the addressable space in 32-vs-64 bit operating systems. Total storage requirements for the problem. Total working space required for the program is approximately 13*N double precision words.« less

Predicting Young’s Modulus of Glass/Ceramic Sealant for Solid Oxide Fuel Cell Considering the Combined Effects of Aging, Micro-Voids and Self-Healing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Wenning N.; Sun, Xin; Khaleel, Mohammad A.

We study the temperature dependent Young’s modulus for the glass/ceramic seal material used in Solid Oxide Fuel Cells (SOFCs). With longer heat treatment or aging time during operation, further devitrification may reduce the residual glass content in the seal material while boosting the ceramic crystalline content. In the meantime, micro-voids induced by the cooling process from the high operating temperature to room temperature can potentially degrade the mechanical properties of the glass/ceramic sealant. Upon reheating to the SOFC operating temperature, possible self-healing phenomenon may occur in the glass/ceramic sealant which can potentially restore some of its mechanical properties. A phenomenologicalmore » model is developed to model the temperature dependent Young’s modulus of glass/ceramic seal considering the combined effects of aging, micro-voids, and possible self-healing. An aging-time-dependent crystalline content model is first developed to describe the increase of the crystalline content due to the continuing devitrification under high operating temperature. A continuum damage mechanics (CDM) model is then adapted to model the effects of both cooling induced micro-voids and reheating induced self-healing. This model is applied to model the glass-ceramic G18, a candidate SOFC seal material previously developed at PNNL. Experimentally determined temperature dependent Young’s modulus is used to validate the model predictions« less

A High-Performing Sulfur-Tolerant and Redox-Stable Layered Perovskite Anode for Direct Hydrocarbon Solid Oxide Fuel Cells

PubMed Central

Ding, Hanping; Tao, Zetian; Liu, Shun; Zhang, Jiujun

2015-01-01

Development of alternative ceramic oxide anode materials is a key step for direct hydrocarbon solid oxide fuel cells (SOFCs). Several lanthanide based layered perovskite-structured oxides demonstrate outstanding oxygen diffusion rate, favorable electronic conductivity, and good oxygen surface exchange kinetics, owing to A-site ordered structure in which lanthanide and alkali-earth ions occupy alternate (001) layers and oxygen vacancies are mainly located in [LnOx] planes. Here we report a nickel-free cation deficient layered perovskite, (PrBa)0.95(Fe0.9Mo0.1)2O5 + δ (PBFM), for SOFC anode, and this anode shows an outstanding performance with high resistance against both carbon build-up and sulfur poisoning in hydrocarbon fuels. At 800 °C, the layered PBFM showed high electrical conductivity of 59.2 S cm−1 in 5% H2 and peak power densities of 1.72 and 0.54 W cm−2 using H2 and CH4 as fuel, respectively. The cell exhibits a very stable performance under a constant current load of 1.0 A cm−2. To our best knowledge, this is the highest performance of ceramic anodes operated in methane. In addition, the anode is structurally stable at various fuel and temperature conditions, suggesting that it is a feasible material candidate for high-performing SOFC anode. PMID:26648509

Evaluation of Ni-Cr-base alloys for SOFC interconnect applications

NASA Astrophysics Data System (ADS)

Yang, Zhenguo; Xia, Guan-Guang; Stevenson, Jeffry W.

To further understand the suitability of Ni-Cr-base alloys for solid oxide fuel cell (SOFC) interconnect applications, three commercial Ni-Cr-base alloys, Haynes 230, Hastelloy S and Haynes 242 were selected and evaluated for oxidation behavior under different exposure conditions, scale conductivity and thermal expansion. Haynes 230 and Hastelloy S, which have a relatively high Cr content, formed a thin scale mainly comprised of Cr 2O 3 and (Mn,Cr,Ni) 3O 4 spinels under SOFC operating conditions, demonstrating excellent oxidation resistance and a high scale electrical conductivity. In contrast, a thick double-layer scale with a NiO outer layer above a chromia-rich substrate was grown on Haynes 242 in moist air or at the air side of dual exposure samples, indicating limited oxidation resistance for the interconnect application. With a face-centered-cubic (FCC) substrate, all three alloys possess a coefficient of thermal expansion (CTE) that is higher than that of candidate ferritic stainless steels, e.g. Crofer22 APU. Among the three alloys, Haynes 242, which is heavily alloyed with W and Mo and contains a low Cr content, demonstrated the lowest average CTE at 13.1 × 10 -6 K -1 from room temperature to 800 °C, but it was also observed that the CTE behavior of Haynes 242 was very non-linear.

Development of Ni-Ba(Zr,Y)O3 cermet anodes for direct ammonia-fueled solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Miyazaki, Kazunari; Okanishi, Takeou; Muroyama, Hiroki; Matsui, Toshiaki; Eguchi, Koichi

2017-10-01

In this study, the availability of Ni-Ba(Zr,Y)O3-δ (BZY) cermet for the anode of direct ammonia-fueled solid oxide fuel cells (SOFCs) is evaluated. In this device, the anodes need to be active for the catalytic ammonia decomposition as well as the electrochemical hydrogen oxidation. In the catalytic activity test, ammonia decomposes completely over Ni-BZY at ca. 600 °C, while higher temperature is required to accomplish the complete decomposition over the conventional SOFC anode of Ni-yttria-stabilized zirconia cermet. The high activity of Ni-BZY is attributed to the high basicity of BZY and the high resistance to hydrogen poisoning effect. The electrochemical property of Ni-BZY anode is also evaluated with the anode-supported cell of Ni-BZY|BZY|Pt at 600-700 °C with feeding ammonia or hydrogen as a fuel. Since the residence time of ammonia fuel in the thick Ni-BZY anode is long, the difference in the cell performance between two fuels is relatively small. Furthermore, it is proved that the steam concentration in the fuel strongly affects the cell performance. We find that this factor is important to satisfy the above mentioned requirements for the anode of direct ammonia-fueled SOFCs. Throughout this study, it is concluded that Ni-BZY cermet will be a promising anode.

Stall/surge dynamics of a multi-stage air compressor in response to a load transient of a hybrid solid oxide fuel cell-gas turbine system

NASA Astrophysics Data System (ADS)

Azizi, Mohammad Ali; Brouwer, Jacob

2017-10-01

A better understanding of turbulent unsteady flows in gas turbine systems is necessary to design and control compressors for hybrid fuel cell-gas turbine systems. Compressor stall/surge analysis for a 4 MW hybrid solid oxide fuel cell-gas turbine system for locomotive applications is performed based upon a 1.7 MW multi-stage air compressor. Control strategies are applied to prevent operation of the hybrid SOFC-GT beyond the stall/surge lines of the compressor. Computational fluid dynamics tools are used to simulate the flow distribution and instabilities near the stall/surge line. The results show that a 1.7 MW system compressor like that of a Kawasaki gas turbine is an appropriate choice among the industrial compressors to be used in a 4 MW locomotive SOFC-GT with topping cycle design. The multi-stage radial design of the compressor enhances the ability of the compressor to maintain air flow rate during transient step-load changes. These transient step-load changes are exhibited in many potential applications for SOFC/GT systems. The compressor provides sustained air flow rate during the mild stall/surge event that occurs due to the transient step-load change that is applied, indicating that this type of compressor is well-suited for this hybrid application.

High-Performanced Cathode with a Two-Layered R-P Structure for Intermediate Temperature Solid Oxide Fuel Cells.

PubMed

Huan, Daoming; Wang, Zhiquan; Wang, Zhenbin; Peng, Ranran; Xia, Changrong; Lu, Yalin

2016-02-01

Driven by the mounting concerns on global warming and energy crisis, intermediate temperature solid-oxide fuel cells (IT-SOFCs) have attracted special attention for their high fuel efficiency, low toxic gas emission, and great fuel flexibility. A key obstacle to the practical operation of IT-SOFCs is their sluggish oxygen reduction reaction (ORR) kinetics. In this work, we applied a new two-layered Ruddlesden-Popper (R-P) oxide, Sr3Fe2O7-δ (SFO), as the material for oxygen ion conducting IT-SOFCs. Density functional theory calculation suggested that SFO has extremely low oxygen ion formation energy and considerable energy barrier for O(2-) diffusion. Unfortunately, the stable SrO surface of SFO was demonstrated to be inert to O2 adsorption and dissociation reaction, and thus restricts its catalytic activity toward ORR. Based on this observation, Co partially substituted SFO (SFCO) was then synthesized and applied to improve its surface vacancy concentration to accelerate the oxygen adsorptive reduction reaction rate. Electrochemical performance results suggested that the cell using the SFCO single phase cathode has a peak power density of 685 mW cm(-2) at 650 °C, about 15% higher than those when using LSCF cathode. Operating at 200 mA cm(-2), the new cell using SFCO is quite stable within the 100-h' test.

Mathematical modeling of synthesis gas fueled electrochemistry and transport including H2/CO co-oxidation and surface diffusion in solid oxide fuel cell

NASA Astrophysics Data System (ADS)

Bao, Cheng; Jiang, Zeyi; Zhang, Xinxin

2015-10-01

Fuel flexibility is a significant advantage of solid oxide fuel cell (SOFC). A comprehensive macroscopic framework is proposed for synthesis gas (syngas) fueled electrochemistry and transport in SOFC anode with two main novelties, i.e. analytical H2/CO electrochemical co-oxidation, and correction of gas species concentration at triple phase boundary considering competitive absorption and surface diffusion. Staring from analytical approximation of the decoupled charge and mass transfer, we present analytical solutions of two defined variables, i.e. hydrogen current fraction and enhancement factor. Giving explicit answer (rather than case-by-case numerical calculation) on how many percent of the current output contributed by H2 or CO and on how great the water gas shift reaction plays role on, this approach establishes at the first time an adaptive superposition mechanism of H2-fuel and CO-fuel electrochemistry for syngas fuel. Based on the diffusion equivalent circuit model, assuming series-connected resistances of surface diffusion and bulk diffusion, the model predicts well at high fuel utilization by keeping fixed porosity/tortuosity ratio. The model has been validated by experimental polarization behaviors in a wide range of operation on a button cell for H2-H2O-CO-CO2-N2 fuel systems. The framework could be helpful to narrow the gap between macro-scale and meso-scale SOFC modeling.

Curvature in solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Li, Wenxia; Hasinska, Kathy; Seabaugh, Matt; Swartz, Scott; Lannutti, John

At this point in history, curvature is inherent to the laminated components that comprise solid oxide fuel cells (SOFCs). Surprisingly, however, this fact has never been previously quantified in the literature. In addition, potential curvature changes associated with NiO reduction and re-oxidation during operation have not been investigated. In this report, an optical profilometer was employed to non-destructively quantify the surface curvature or cracking behavior observed on a large scale in industrially manufactured cells. This provides insights into the challenges that the component materials face as well as additional appreciation for why, in spite of a concerted effort to commercialize SOFC power generation, all currently manufactured SOFC stacks fail. Our results demonstrate that cracked electrolyte areas (caused by differential sintering) are flatter than uncracked regions. The height of the electrolyte surface ranged from 86 to 289 μm above the baseline following sintering. Reduction typically results in increases in curvature of up to 214 μm. Initial crack density appears to affect curvature evolution during reduction; the higher the crack density, the smaller the curvature increase following reduction at 600 °C. In general, however, we observed that the electrolyte layer is remarkably resistant to further cracking during these typographic changes. Following oxidation at 750 °C, large changes in curvature (up to 280 μm) are noted that appear to be related to the strength of the bond between the electrolyte and the underlying anode.

Quantifying intermediate-frequency heterogeneities of SOFC electrodes using X-ray computed tomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Epting, William K.; Mansley, Zachary; Menasche, David B.

2017-03-03

The electrodes in solid oxide fuel cells (SOFCs) consist of three phases interconnected in three dimensions. The volume needed to describe quantitatively such microstructures depends on several lengths scales, which are functions of materials properties and fabrication methods. This work focuses on quantifying the volume needed to represent “intermediate frequency” heterogeneities in electrodes of a commercial SOFC using X-ray computed tomography (CT) over two different length scales. Electrode volumes of 150 x 150 x 9 μm 3 were extracted from a synchrotron-based micro-CT data set, with 13 μm 3 voxels. 13.6 x 19.8 x 19.4 μm 3 of the cathodemore » and 26.3 x 24.8 x 15.7 μm 3 of the anode were extracted from laboratory nano-CT data sets, both with 65 3 nm 3 voxels. After comparing the variation across sub-regions for the greyscale values from the micro-CT, and for the phase fractions and triple phase boundary densities from the nano-CT, it was found that the sub-region length scales needed to yield statistically similar average values were an order of magnitude larger than those expected to capture the “high frequency” heterogeneity related to the discrete nature of the three phases in electrodes. In conclusion, the challenge of quantifying such electrodes using available experimental methods is discussed.« less

A High-Performing Sulfur-Tolerant and Redox-Stable Layered Perovskite Anode for Direct Hydrocarbon Solid Oxide Fuel Cells

NASA Astrophysics Data System (ADS)

Ding, Hanping; Tao, Zetian; Liu, Shun; Zhang, Jiujun

2015-12-01

Development of alternative ceramic oxide anode materials is a key step for direct hydrocarbon solid oxide fuel cells (SOFCs). Several lanthanide based layered perovskite-structured oxides demonstrate outstanding oxygen diffusion rate, favorable electronic conductivity, and good oxygen surface exchange kinetics, owing to A-site ordered structure in which lanthanide and alkali-earth ions occupy alternate (001) layers and oxygen vacancies are mainly located in [LnOx] planes. Here we report a nickel-free cation deficient layered perovskite, (PrBa)0.95(Fe0.9Mo0.1)2O5 + δ (PBFM), for SOFC anode, and this anode shows an outstanding performance with high resistance against both carbon build-up and sulfur poisoning in hydrocarbon fuels. At 800 °C, the layered PBFM showed high electrical conductivity of 59.2 S cm-1 in 5% H2 and peak power densities of 1.72 and 0.54 W cm-2 using H2 and CH4 as fuel, respectively. The cell exhibits a very stable performance under a constant current load of 1.0 A cm-2. To our best knowledge, this is the highest performance of ceramic anodes operated in methane. In addition, the anode is structurally stable at various fuel and temperature conditions, suggesting that it is a feasible material candidate for high-performing SOFC anode.

A High-Performing Sulfur-Tolerant and Redox-Stable Layered Perovskite Anode for Direct Hydrocarbon Solid Oxide Fuel Cells.

PubMed

Ding, Hanping; Tao, Zetian; Liu, Shun; Zhang, Jiujun

2015-12-09

Development of alternative ceramic oxide anode materials is a key step for direct hydrocarbon solid oxide fuel cells (SOFCs). Several lanthanide based layered perovskite-structured oxides demonstrate outstanding oxygen diffusion rate, favorable electronic conductivity, and good oxygen surface exchange kinetics, owing to A-site ordered structure in which lanthanide and alkali-earth ions occupy alternate (001) layers and oxygen vacancies are mainly located in [LnOx] planes. Here we report a nickel-free cation deficient layered perovskite, (PrBa)0.95(Fe0.9Mo0.1)2O5 + δ (PBFM), for SOFC anode, and this anode shows an outstanding performance with high resistance against both carbon build-up and sulfur poisoning in hydrocarbon fuels. At 800 °C, the layered PBFM showed high electrical conductivity of 59.2 S cm(-1) in 5% H2 and peak power densities of 1.72 and 0.54 W cm(-2) using H2 and CH4 as fuel, respectively. The cell exhibits a very stable performance under a constant current load of 1.0 A cm(-2). To our best knowledge, this is the highest performance of ceramic anodes operated in methane. In addition, the anode is structurally stable at various fuel and temperature conditions, suggesting that it is a feasible material candidate for high-performing SOFC anode.

Parameter setting and analysis of a dynamic tubular SOFC model

NASA Astrophysics Data System (ADS)

Jiang, Wei; Fang, Ruixian; Khan, Jamil A.; Dougal, Roger A.

An improved one-dimensional dynamic model of a tubular SOFC stack capable of system simulation in the virtual test bed (VTB) simulation environment is presented in this paper. This model is based on the electrochemical and thermal modeling, accounting for the voltage losses and temperature dynamics. The modeling of an external reformer is also included in this study. A detailed parametric analysis of working conditions and cell configuration of the solid oxide fuel cell (SOFC) stack is the main focus of this paper. The following operating parameters are investigated: pressure ratio, temperature, mass flow rate, external reforming degree and stream to carbon (S/C) ratio. The cell geometric parameters studied include cell diameter and cell length. Elevated operating pressure improves the cell performance. Whereas, higher operating temperature decreases both the Nernst potential and the irreversible losses, resulting in an initial increase then a decrease in cell efficiency. It was found that a higher S/C ratio yields a lower H 2 concentration and partial pressure, which has a negative effect on the Nernst potential. Increased cell diameter is found to increase the power due to a larger activation area at the same time and due to longer current path length there is an increase in the ohmic loss. Increased length of the cell has the undesired affect of an increased pressure drop.

Extremely fine structured cathode for solid oxide fuel cells using Sr-doped LaMnO3 and Y2O3-stabilized ZrO2 nano-composite powder synthesized by spray pyrolysis

NASA Astrophysics Data System (ADS)

Shimada, Hiroyuki; Yamaguchi, Toshiaki; Sumi, Hirofumi; Nomura, Katsuhiro; Yamaguchi, Yuki; Fujishiro, Yoshinobu

2017-02-01

A solid oxide fuel cell (SOFC) for high power density operation was developed with a microstructure-controlled cathode using a nano-composite powder of Sr-doped LaMnO3 (LSM) and Y2O3-stabilized ZrO2 (YSZ) synthesized by spray pyrolysis. The individual LSM-YSZ nano-composite particles, formed by crystalline and amorphous nano-size LSM and YSZ particles, showed spherical morphology with uniform particle size. The use of this powder for cathode material led to an extremely fine microstructure, in which all the LSM and YSZ grains (approximately 100-200 nm) were highly dispersed and formed their own network structures. This microstructure was due to the two phase electrode structure control using the powder, namely, nano-order level in each particle and micro-order level between particles. An anode-supported SOFC with the LSM-YSZ cathode using humidified H2 as fuel and ambient air as oxidant exhibited high power densities, such as 1.29 W cm-2 under a voltage of 0.75 V and a maximum power density of 2.65 W cm-2 at 800 °C. Also, the SOFC could be stably operated for 250 h with no degradation, even at a high temperature of 800 °C.

Density functional theory study for the enhanced sulfur tolerance of Ni catalysts by surface alloying

NASA Astrophysics Data System (ADS)

Hwang, Bohyun; Kwon, Hyunguk; Ko, Jeonghyun; Kim, Byung-Kook; Han, Jeong Woo

2018-01-01

Sulfur compounds in fuels deactivate the surface of anode materials in solid oxide fuel cells (SOFCs), which adversely affect the long-term durability. To solve this issue, it is important to design new SOFC anode materials with high sulfur tolerance. Unfortunately, it is difficult to completely replace the traditional Ni anode owing to its outstanding reactivity with low cost. As an alternative, alloying Ni with transition metals is a practical strategy to enhance the sulfur resistance while taking advantage of Ni metal. Therefore, in this study, we examined the effects of transition metal (Cu, Rh, Pd, Ag, Pt, and Au) doping into a Ni catalyst on not only the adsorption of H2S, HS, S, and H but also H2S decomposition using density functional theory (DFT) calculations. The dopant metals were selected rationally by considering the stability of the Ni-based binary alloys. The interactions between sulfur atoms produced by H2S dissociation and the surface are weakened by the dopant metals at the topmost layer. In addition, the findings show that H2S dissociation can be suppressed by doping transition metals. It turns out that these effects are maximized in the Au-doped Ni catalyst. Our DFT results will provide useful insights into the design of sulfur-tolerant SOFC anode materials.

Implicit mesh discontinuous Galerkin methods and interfacial gauge methods for high-order accurate interface dynamics, with applications to surface tension dynamics, rigid body fluid-structure interaction, and free surface flow: Part I

NASA Astrophysics Data System (ADS)

Saye, Robert

2017-09-01

In this two-part paper, a high-order accurate implicit mesh discontinuous Galerkin (dG) framework is developed for fluid interface dynamics, facilitating precise computation of interfacial fluid flow in evolving geometries. The framework uses implicitly defined meshes-wherein a reference quadtree or octree grid is combined with an implicit representation of evolving interfaces and moving domain boundaries-and allows physically prescribed interfacial jump conditions to be imposed or captured with high-order accuracy. Part one discusses the design of the framework, including: (i) high-order quadrature for implicitly defined elements and faces; (ii) high-order accurate discretisation of scalar and vector-valued elliptic partial differential equations with interfacial jumps in ellipticity coefficient, leading to optimal-order accuracy in the maximum norm and discrete linear systems that are symmetric positive (semi)definite; (iii) the design of incompressible fluid flow projection operators, which except for the influence of small penalty parameters, are discretely idempotent; and (iv) the design of geometric multigrid methods for elliptic interface problems on implicitly defined meshes and their use as preconditioners for the conjugate gradient method. Also discussed is a variety of aspects relating to moving interfaces, including: (v) dG discretisations of the level set method on implicitly defined meshes; (vi) transferring state between evolving implicit meshes; (vii) preserving mesh topology to accurately compute temporal derivatives; (viii) high-order accurate reinitialisation of level set functions; and (ix) the integration of adaptive mesh refinement. In part two, several applications of the implicit mesh dG framework in two and three dimensions are presented, including examples of single phase flow in nontrivial geometry, surface tension-driven two phase flow with phase-dependent fluid density and viscosity, rigid body fluid-structure interaction, and free surface flow. A class of techniques known as interfacial gauge methods is adopted to solve the corresponding incompressible Navier-Stokes equations, which, compared to archetypical projection methods, have a weaker coupling between fluid velocity, pressure, and interface position, and allow high-order accurate numerical methods to be developed more easily. Convergence analyses conducted throughout the work demonstrate high-order accuracy in the maximum norm for all of the applications considered; for example, fourth-order spatial accuracy in fluid velocity, pressure, and interface location is demonstrated for surface tension-driven two phase flow in 2D and 3D. Specific application examples include: vortex shedding in nontrivial geometry, capillary wave dynamics revealing fine-scale flow features, falling rigid bodies tumbling in unsteady flow, and free surface flow over a submersed obstacle, as well as high Reynolds number soap bubble oscillation dynamics and vortex shedding induced by a type of Plateau-Rayleigh instability in water ripple free surface flow. These last two examples compare numerical results with experimental data and serve as an additional means of validation; they also reveal physical phenomena not visible in the experiments, highlight how small-scale interfacial features develop and affect macroscopic dynamics, and demonstrate the wide range of spatial scales often at play in interfacial fluid flow.

Implicit mesh discontinuous Galerkin methods and interfacial gauge methods for high-order accurate interface dynamics, with applications to surface tension dynamics, rigid body fluid-structure interaction, and free surface flow: Part II

NASA Astrophysics Data System (ADS)

Saye, Robert

2017-09-01

In this two-part paper, a high-order accurate implicit mesh discontinuous Galerkin (dG) framework is developed for fluid interface dynamics, facilitating precise computation of interfacial fluid flow in evolving geometries. The framework uses implicitly defined meshes-wherein a reference quadtree or octree grid is combined with an implicit representation of evolving interfaces and moving domain boundaries-and allows physically prescribed interfacial jump conditions to be imposed or captured with high-order accuracy. Part one discusses the design of the framework, including: (i) high-order quadrature for implicitly defined elements and faces; (ii) high-order accurate discretisation of scalar and vector-valued elliptic partial differential equations with interfacial jumps in ellipticity coefficient, leading to optimal-order accuracy in the maximum norm and discrete linear systems that are symmetric positive (semi)definite; (iii) the design of incompressible fluid flow projection operators, which except for the influence of small penalty parameters, are discretely idempotent; and (iv) the design of geometric multigrid methods for elliptic interface problems on implicitly defined meshes and their use as preconditioners for the conjugate gradient method. Also discussed is a variety of aspects relating to moving interfaces, including: (v) dG discretisations of the level set method on implicitly defined meshes; (vi) transferring state between evolving implicit meshes; (vii) preserving mesh topology to accurately compute temporal derivatives; (viii) high-order accurate reinitialisation of level set functions; and (ix) the integration of adaptive mesh refinement. In part two, several applications of the implicit mesh dG framework in two and three dimensions are presented, including examples of single phase flow in nontrivial geometry, surface tension-driven two phase flow with phase-dependent fluid density and viscosity, rigid body fluid-structure interaction, and free surface flow. A class of techniques known as interfacial gauge methods is adopted to solve the corresponding incompressible Navier-Stokes equations, which, compared to archetypical projection methods, have a weaker coupling between fluid velocity, pressure, and interface position, and allow high-order accurate numerical methods to be developed more easily. Convergence analyses conducted throughout the work demonstrate high-order accuracy in the maximum norm for all of the applications considered; for example, fourth-order spatial accuracy in fluid velocity, pressure, and interface location is demonstrated for surface tension-driven two phase flow in 2D and 3D. Specific application examples include: vortex shedding in nontrivial geometry, capillary wave dynamics revealing fine-scale flow features, falling rigid bodies tumbling in unsteady flow, and free surface flow over a submersed obstacle, as well as high Reynolds number soap bubble oscillation dynamics and vortex shedding induced by a type of Plateau-Rayleigh instability in water ripple free surface flow. These last two examples compare numerical results with experimental data and serve as an additional means of validation; they also reveal physical phenomena not visible in the experiments, highlight how small-scale interfacial features develop and affect macroscopic dynamics, and demonstrate the wide range of spatial scales often at play in interfacial fluid flow.

Evaluation of Ca3Co2O6 as cathode material for high-performance solid-oxide fuel cell

PubMed Central

Wei, Tao; Huang, Yun-Hui; Zeng, Rui; Yuan, Li-Xia; Hu, Xian-Luo; Zhang, Wu-Xing; Jiang, Long; Yang, Jun-You; Zhang, Zhao-Liang

2013-01-01

A cobalt-based thermoelectric compound Ca3Co2O6 (CCO) has been developed as new cathode material with superior performance for intermediate-temperature (IT) solid-oxide fuel cell (SOFC). Systematic evaluation has been carried out. Measurement of thermal expansion coefficient (TEC), thermal-stress (σ) and interfacial shearing stress (τ) with the electrolyte show that CCO matches well with several commonly-used IT electrolytes. Maximum power density as high as 1.47 W cm−2 is attained at 800°C, and an additional thermoelectric voltage of 11.7 mV is detected. The superior electrochemical performance, thermoelectric effect, and comparable thermal and mechanical behaviors with the electrolytes make CCO to be a promising cathode material for SOFC. PMID:23350032

An Aurivillius Oxide Based Cathode with Excellent CO2 Tolerance for Intermediate-Temperature Solid Oxide Fuel Cells.

PubMed

Zhu, Yinlong; Zhou, Wei; Chen, Yubo; Shao, Zongping

2016-07-25

The Aurivillius oxide Bi2 Sr2 Nb2 MnO12-δ (BSNM) was used as a cobalt-free cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). To the best of our knowledge, the BSNM oxide is the only alkaline-earth-containing cathode material with complete CO2 tolerance that has been reported thus far. BSNM not only shows favorable activity in the oxygen reduction reaction (ORR) at intermediate temperatures but also exhibits a low thermal expansion coefficient, excellent structural stability, and good chemical compatibility with the electrolyte. These features highlight the potential of the new BSNM material as a highly promising cathode material for IT-SOFCs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

An afterburner-powered methane/steam reformer for a solid oxide fuel cells application

NASA Astrophysics Data System (ADS)

Mozdzierz, Marcin; Chalusiak, Maciej; Kimijima, Shinji; Szmyd, Janusz S.; Brus, Grzegorz

2018-04-01

Solid oxide fuel cell (SOFC) systems can be fueled by natural gas when the reforming reaction is conducted in a stack. Due to its maturity and safety, indirect internal reforming is usually used. A strong endothermic methane/steam reforming process needs a large amount of heat, and it is convenient to provide thermal energy by burning the remainders of fuel from a cell. In this work, the mathematical model of afterburner-powered methane/steam reformer is proposed. To analyze the effect of a fuel composition on SOFC performance, the zero-dimensional model of a fuel cell connected with a reformer is formulated. It is shown that the highest efficiency of a solid oxide fuel cell is achieved when the steam-to-methane ratio at the reforming reactor inlet is high.

Dense Membranes for Anode Supported all Perovskite IT-SOFCs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rambabu Bobba

2006-09-14

During this first year of the project, a post doctoral fellow (Dr. Hrudananda Jena), and two graduate students (Mr. Vinay B. V. Sivareddy, Aswin Somuru), were supported through this project funds. Also, partial support was provided to three undergraduate students (Jonthan Dooley, India Snowden, Jeremy Gilmore) majoring in Chemistry, Physics, and Engineering disciplines. Various wet chemical methods of synthesis have been attempted to prepare perovskite oxide powders with a hope to improve and engineer its properties to meet the requirements of Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFCs) components. Various compounds were synthesized, characterized by XRD, TEM, SEM, XPS, electronmore » microprobe and their electrical transport properties were measured by EIS at elevated temperatures and compared. Sonochemical technique (power of ultra sonic probe 750 watt) combined with hydrothermal treatment of precursors for the preparation of calcium hydroxy apatites (Ca-HAp) was used for the first time. Ca-HAp was substituted with Sr and Mg (50% replacement of Ca in Ca-HAp) to study the effect of substitution on Ca-HAp. Calcium hydroxy apatite is a bioceramic and has potential applications as artificial bone, enamel materials. In this study we tried to investigate its use as proton conductors in PC-SOFC. The properties like electrical conductivity, crystal structure, compositions of CaHAp were studied and compared with the natural bone material. The comparison found to be excellent indicating the efficiency of the preparation techniques. The typical value of conductivity measured is 0.091 x 10{sup -6} Scm{sup -1} at 25 C and 19.26 x 10{sup -6} Scm{sup -1} at 850 C with an applied frequency of 100 kHz. The conductivity increases on increasing frequency and temperature and reaches 0.05mS/cm at 500 C. The crystal structure and phase stability of perovskites as well as apatites were investigated with respect to substitution of various iso-valent and alivalent ions to determine the % of solubility in the crystal lattice of perovskite, apatites. Various electrode and electrolyte material compositions were prepared and characterized by XRD, SEM, XPS and electron microprobe. The material compositions were selected based on their thermo-physical properties to achieve compatibility with each other in ideal fuel cell operating conditions. The series of electrode materials investigated are LaGa{sub 1-x}M{sub x}O{sub 3} (M = Mn, Mg, x = 0.1), LaCr{sub 1-x}M{sub x}O{sub 3} (M = Mn, Mg, Co, x=0.1), LaNi{sub 1-x}Fe{sub x}O{sub 3} (0 < x < 0.6) and Gd{sub 1-x}M{sub x}CoO{sub 3} (M=Ca, x=0.1). Attempts were made to prepare proton-conducting perovskites of SrCe{sub 1-x} M{sub x}O{sub 3} (M= Dy, Eu, Er, Tb, x=0.1) by using sonochemical and hydrothermal technique followed by microwave sintering processes. These compositions were prepared characterized by XRD, TEM, SEM and electrical conductivity of the pellets was measured. The interest of low temperature proton conducting electrolyte is to replace the well known oxide ion conducting solid electrolyte in SOFCs, thereby reducing the operating temperature of SOFC to lower temperature (i.e 400-600 C) and named it as PC-SOFC (proton conducting-solid oxide fuel cell).« less

Development of a Microchannel High Temperature Recuperator for Fuel Cell Systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lukas, Michael

This report summarizes the progress made in development of microchannel recuperators for high temperature fuel cell/turbine hybrid systems for generation of clean power at very high efficiencies. Both Solid Oxide Fuel Cell/Turbine (SOFC/T) and Direct FuelCell/Turbine (DFC/T) systems employ an indirectly heated Turbine Generator to supplement fuel cell generated power. The concept extends the high efficiency of the fuel cell by utilizing the fuel cell’s byproduct heat in a Brayton cycle. Features of the SOFC/T and DFC/T systems include: electrical efficiencies of up to 65% on natural gas, minimal emissions, reduced carbon dioxide release to the environment, simplicity in design,more » and potential cost competitiveness with existing combined cycle power plants. Project work consisted of candidate material selection from FuelCell Energy (FCE) and Pacific Northwest National Laboratory (PNNL) institutional databases as well as from industrial and academic literature. Candidate materials were then downselected and actual samples were tested under representative environmental conditions resulting in further downselection. A microchannel thermal-mechanical model was developed to calculate overall device cost to be later used in developing a final Tier 1 material candidate list. Specifications and operating conditions were developed for both SOFC/T and DFC/T systems. This development included system conceptualization and progression to process flow diagrams (PFD’s) including all major equipment. Material and energy balances were then developed for the two types of systems which were then used for extensive sensitivity studies that used high temperature recuperator (HTR) design parameters (e.g., operating temperature) as inputs and calculated overall system parameters (e.g., system efficiency). The results of the sensitivity studies determined the final HTR design temperatures, pressure drops, and gas compositions. The results also established operating conditions and specifications for all equipment in the SOFC/T and DFC/T systems. Capital cost and Cost of Electricity (COE) sensitivity analyses have been completed for MW-scale SOFC/T and DFC/T systems. Environmental testing consisted of 1000-hour and 2000-hour dry air oxidation testing on leading candidate materials, used to rank order and, in part, develop a final Tier 1 material candidate list. A thermal-mechanical model was subsequently used to provide material and manufacturing cost estimations for microchannel HTR’s to further refine the Tier 1 candidates. A capital cost and 20-year levelized cost of electricity (COE) was developed for a MW-scale version of the SOFC/T system concept as well as for a MW-scale version of the DFC/T system concept. Test frameworks were established for subsequent long-term materials stability testing, including oxidation resistance and mechanical strength. Mechanical strength testing was then carried out by a third-party test laboratory. Technology demonstration vehicles (TDV’s) were designed and fabricated. Several iterations of TDV’s were fabricated, each improved over the previous build as far as fabrication techniques. Two of three fabricated TDV’s were integrated with the TDV Test Facility for hot-testing at simulated operating conditions. The second of these two was successfully hot-tested for over 1000 hours at simulated temperature and pressure. Post-test leakdown assessment showed negligible leakage at benchtop conditions of 30 psig, a considerable improvement over the previous TDV’s.« less

2D Seismic Imaging of Elastic Parameters by Frequency Domain Full Waveform Inversion

NASA Astrophysics Data System (ADS)

Brossier, R.; Virieux, J.; Operto, S.

2008-12-01

Thanks to recent advances in parallel computing, full waveform inversion is today a tractable seismic imaging method to reconstruct physical parameters of the earth interior at different scales ranging from the near- surface to the deep crust. We present a massively parallel 2D frequency-domain full-waveform algorithm for imaging visco-elastic media from multi-component seismic data. The forward problem (i.e. the resolution of the frequency-domain 2D PSV elastodynamics equations) is based on low-order Discontinuous Galerkin (DG) method (P0 and/or P1 interpolations). Thanks to triangular unstructured meshes, the DG method allows accurate modeling of both body waves and surface waves in case of complex topography for a discretization of 10 to 15 cells per shear wavelength. The frequency-domain DG system is solved efficiently for multiple sources with the parallel direct solver MUMPS. The local inversion procedure (i.e. minimization of residuals between observed and computed data) is based on the adjoint-state method which allows to efficiently compute the gradient of the objective function. Applying the inversion hierarchically from the low frequencies to the higher ones defines a multiresolution imaging strategy which helps convergence towards the global minimum. In place of expensive Newton algorithm, the combined use of the diagonal terms of the approximate Hessian matrix and optimization algorithms based on quasi-Newton methods (Conjugate Gradient, LBFGS, ...) allows to improve the convergence of the iterative inversion. The distribution of forward problem solutions over processors driven by a mesh partitioning performed by METIS allows to apply most of the inversion in parallel. We shall present the main features of the parallel modeling/inversion algorithm, assess its scalability and illustrate its performances with realistic synthetic case studies.

Improved algorithm of ray tracing in ICF cryogenic targets

NASA Astrophysics Data System (ADS)

Zhang, Rui; Yang, Yongying; Ling, Tong; Jiang, Jiabin

2016-10-01

The high precision ray tracing inside inertial confinement fusion (ICF) cryogenic targets plays an important role in the reconstruction of the three-dimensional density distribution by algebraic reconstruction technique (ART) algorithm. The traditional Runge-Kutta methods, which is restricted by the precision of the grid division and the step size of ray tracing, cannot make an accurate calculation in the case of refractive index saltation. In this paper, we propose an improved algorithm of ray tracing based on the Runge-Kutta methods and Snell's law of refraction to achieve high tracing precision. On the boundary of refractive index, we apply Snell's law of refraction and contact point search algorithm to ensure accuracy of the simulation. Inside the cryogenic target, the combination of the Runge-Kutta methods and self-adaptive step algorithm are employed for computation. The original refractive index data, which is used to mesh the target, can be obtained by experimental measurement or priori refractive index distribution function. A finite differential method is performed to calculate the refractive index gradient of mesh nodes, and the distance weighted average interpolation methods is utilized to obtain refractive index and gradient of each point in space. In the simulation, we take ideal ICF target, Luneberg lens and Graded index rod as simulation model to calculate the spot diagram and wavefront map. Compared the simulation results to Zemax, it manifests that the improved algorithm of ray tracing based on the fourth-order Runge-Kutta methods and Snell's law of refraction exhibits high accuracy. The relative error of the spot diagram is 0.2%, and the peak-to-valley (PV) error and the root-mean-square (RMS) error of the wavefront map is less than λ/35 and λ/100, correspondingly.

Mountainous Ecosystem Sensor Array (MESA): a mesh sensor network for climate change research in remote mountainous environments

NASA Astrophysics Data System (ADS)

Robinson, P. W.; Neal, D.; Frome, D.; Kavanagh, K.; Davis, A.; Gessler, P. E.; Hess, H.; Holden, Z. A.; Link, T. E.; Newingham, B. A.; Smith, A. M.

2013-12-01

Developing sensor networks robust enough to perform unattended in the world's remote regions is critical since these regions serve as important benchmarks that lack anthropogenic influence. Paradoxically, the factors that make these remote, natural sites challenging for sensor networking are often what make them indispensable for climate change research. The MESA (Mountainous Ecosystem Sensor Array) project has faced these challenges and developed a wireless mesh sensor network across a 660 m topoclimatic gradient in a wilderness area in central Idaho. This sensor array uses advances in sensing, networking, and power supply technologies to provide near real-time synchronized data covering a suite of biophysical parameters used in ecosystem process models. The 76 sensors in the network monitor atmospheric carbon dioxide concentration, humidity, air and soil temperature, soil water content, precipitation, incoming and outgoing shortwave and longwave radiation, snow depth, wind speed and direction, and leaf wetness at synchronized time intervals ranging from two minutes to two hours and spatial scales from a few meters to two kilometers. We present our novel methods of placing sensors and network nodes above, below, and throughout the forest canopy without using meteorological towers. In addition, we explain our decision to use different forms of power (wind and solar) and the equipment we use to control and integrate power harvesting. Further, we describe our use of the network to sense and quantify its own power use. Using examples of environmental data from the project, we discuss how these data may be used to increase our understanding of the effects of climate change on ecosystem processes in mountainous environments. MESA sensor locations across a 700 m topoclimatic gradient at the University of Idaho Taylor Wilderness Research Station.

The Role of Cosmic-Ray Pressure in Accelerating Galactic Outflows

NASA Astrophysics Data System (ADS)

Simpson, Christine M.; Pakmor, Rüdiger; Marinacci, Federico; Pfrommer, Christoph; Springel, Volker; Glover, Simon C. O.; Clark, Paul C.; Smith, Rowan J.

2016-08-01

We study the formation of galactic outflows from supernova (SN) explosions with the moving-mesh code AREPO in a stratified column of gas with a surface density similar to the Milky Way disk at the solar circle. We compare different simulation models for SN placement and energy feedback, including cosmic rays (CRs), and find that models that place SNe in dense gas and account for CR diffusion are able to drive outflows with similar mass loading as obtained from a random placement of SNe with no CRs. Despite this similarity, CR-driven outflows differ in several other key properties including their overall clumpiness and velocity. Moreover, the forces driving these outflows originate in different sources of pressure, with the CR diffusion model relying on non-thermal pressure gradients to create an outflow driven by internal pressure and the random-placement model depending on kinetic pressure gradients to propel a ballistic outflow. CRs therefore appear to be non-negligible physics in the formation of outflows from the interstellar medium.

THE ROLE OF COSMIC-RAY PRESSURE IN ACCELERATING GALACTIC OUTFLOWS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simpson, Christine M.; Pakmor, Rüdiger; Pfrommer, Christoph

We study the formation of galactic outflows from supernova (SN) explosions with the moving-mesh code AREPO in a stratified column of gas with a surface density similar to the Milky Way disk at the solar circle. We compare different simulation models for SN placement and energy feedback, including cosmic rays (CRs), and find that models that place SNe in dense gas and account for CR diffusion are able to drive outflows with similar mass loading as obtained from a random placement of SNe with no CRs. Despite this similarity, CR-driven outflows differ in several other key properties including their overallmore » clumpiness and velocity. Moreover, the forces driving these outflows originate in different sources of pressure, with the CR diffusion model relying on non-thermal pressure gradients to create an outflow driven by internal pressure and the random-placement model depending on kinetic pressure gradients to propel a ballistic outflow. CRs therefore appear to be non-negligible physics in the formation of outflows from the interstellar medium.« less

Microstructurally tailored ceramics for advanced energy applications by thermoreversible gelcasting

NASA Astrophysics Data System (ADS)

Shanti, Noah Omar

Thermoreversible gelcasting (TRG) is an advantageous technique for rapidly producing bulk, net-shape ceramics and laminates. In this method, ceramic powder is suspended in warm acrylate triblock copolymer/alcohol solutions that reversibly gel upon cooling by the formation of endblock aggregates, to produce slurries which are cast into molds. Gel properties can be tailored by controlling the endblock and midblock lengths of the copolymer network-former and selecting an appropriate alcohol solvent. This research focuses on expanding and improving TRG techniques, focusing specifically on advanced energy applications including the solid oxide fuel cell (SOFC). Rapid drying of filled gels can lead to warping and cracking caused by high differential capillary stresses. A new drying technique using concentrated, alcohol-based solutions as liquid desiccants (LDs) to greatly reduce warping is introduced. The optimal LD is a poly(tert-butyl acrylate)/isopropyl alcohol solution with 5 mol% tert-butyl acrylate units. Alcohol emissions during drying are completely eliminated by combining initial drying in an LD with final stage drying in a vacuum oven having an in-line solvent trap. Porous ceramics are important structures for many applications, including SOFCs. Pore network geometries are tailored by the addition of fugitive fillers to TRG slurries. Uniform spherical, bimodal spherical and uniform fibrous fillers are used. Three-dimensional pore structures are visualized by X-ray computed tomography, allowing for direct measurements of physical parameters such as concentration and morphology as well as transport properties such as tortuosity. Tortuosity values as low as 1.52 are achieved when 60 vol% of solids are uniform spherical filler. Functionally graded laminates with layers ranging from 10 mum to > 1 mm thick are produced with a new technique that combines TRG with tape casting. Gels used for bulk casting are not suitable for use with tape casting, and appropriate base gels are selected for this technique. Each layer is cast in a single pass, and the layers are directly laminated. The anode support, anode functional layer, and electrolyte of anode-supported SOFCs are produced using this technique. The performance of SOFCs produced this way is not yet equal to that of traditionally processed cells, but shows the promise of this technique.

High temperature tubular solid oxide fuel cell development

NASA Astrophysics Data System (ADS)

Ray, E. R.

Important to the development commercialization of any new technology is a field test program. This is a mutually beneficial program for both the developer and the prospective user. The developer is able to acquire valuable field operating experience that is not available in a laboratory while the user has the opportunity to become familiar with the new technology and gains a working knowledge of it through hands-on experience. Westinghouse, recognizing these benefits, initiated a program in 1986 by supplying a 400 W SOFC generator to Tennessee Valley Authority. This generator operated for approximately 1,760 hours and was constructed of twenty-four 30 cm thick-wall PST cells. In 1987, three, 3 kW SOFC generators were installed and operated at the facilities of the Tokyo Gas Company and the Osaka Gas Company. At Osaka Gas, two generators were used. First a training generator, operated for 2900 hours before it was replaced on a preplanned schedule with the second generator. The second generator operated for 3,600 hours. Tokyo Gas generator was operated for 4,900 hours. These generators had a 98 percent availability and measured NO(x) levels of less than 1.3 ppm. The 3 kW SOFC generators were constructed of 144 36 cm thick-wall PST cells. The 3 kW generators, as was the TVA generator, were fueled with hydrogen and carbon monoxide. The next major milestone in the field unit program was reached in early 1992 with the delivery to the UTILITIES, a consortium of the Kansai Electric Power company, the Tokyo Gas Company, and the Osaka Gas Company, of a natural gas fueled all electric SOFC system. This system is rated at a nominal 25 kW dc with a peak capacity of 40 kW dc. The NO(x) was measured at less than 0.3 ppM (corrected to 15 percent oxygen). The system consists of 1152 cells (thin-wall PST) of 50 cm active length, manufactured at the PPMF. Cells are contained in two independently controlled and operated generators.

Navier-Stokes Aerodynamic Simulation of the V-22 Osprey on the Intel Paragon MPP

NASA Technical Reports Server (NTRS)

Vadyak, Joseph; Shrewsbury, George E.; Narramore, Jim C.; Montry, Gary; Holst, Terry; Kwak, Dochan (Technical Monitor)

1995-01-01

The paper will describe the Development of a general three-dimensional multiple grid zone Navier-Stokes flowfield simulation program (ENS3D-MPP) designed for efficient execution on the Intel Paragon Massively Parallel Processor (MPP) supercomputer, and the subsequent application of this method to the prediction of the viscous flowfield about the V-22 Osprey tiltrotor vehicle. The flowfield simulation code solves the thin Layer or full Navier-Stoke's equation - for viscous flow modeling, or the Euler equations for inviscid flow modeling on a structured multi-zone mesh. In the present paper only viscous simulations will be shown. The governing difference equations are solved using a time marching implicit approximate factorization method with either TVD upwind or central differencing used for the convective terms and central differencing used for the viscous diffusion terms. Steady state or Lime accurate solutions can be calculated. The present paper will focus on steady state applications, although time accurate solution analysis is the ultimate goal of this effort. Laminar viscosity is calculated using Sutherland's law and the Baldwin-Lomax two layer algebraic turbulence model is used to compute the eddy viscosity. The Simulation method uses an arbitrary block, curvilinear grid topology. An automatic grid adaption scheme is incorporated which concentrates grid points in high density gradient regions. A variety of user-specified boundary conditions are available. This paper will present the application of the scalable and superscalable versions to the steady state viscous flow analysis of the V-22 Osprey using a multiple zone global mesh. The mesh consists of a series of sheared cartesian grid blocks with polar grids embedded within to better simulate the wing tip mounted nacelle. MPP solutions will be shown in comparison to equivalent Cray C-90 results and also in comparison to experimental data. Discussions on meshing considerations, wall clock execution time, load balancing, and scalability will be provided.

jInv: A Modular and Scalable Framework for Electromagnetic Inverse Problems

NASA Astrophysics Data System (ADS)

Belliveau, P. T.; Haber, E.

2016-12-01

Inversion is a key tool in the interpretation of geophysical electromagnetic (EM) data. Three-dimensional (3D) EM inversion is very computationally expensive and practical software for inverting large 3D EM surveys must be able to take advantage of high performance computing (HPC) resources. It has traditionally been difficult to achieve those goals in a high level dynamic programming environment that allows rapid development and testing of new algorithms, which is important in a research setting. With those goals in mind, we have developed jInv, a framework for PDE constrained parameter estimation problems. jInv provides optimization and regularization routines, a framework for user defined forward problems, and interfaces to several direct and iterative solvers for sparse linear systems. The forward modeling framework provides finite volume discretizations of differential operators on rectangular tensor product meshes and tetrahedral unstructured meshes that can be used to easily construct forward modeling and sensitivity routines for forward problems described by partial differential equations. jInv is written in the emerging programming language Julia. Julia is a dynamic language targeted at the computational science community with a focus on high performance and native support for parallel programming. We have developed frequency and time-domain EM forward modeling and sensitivity routines for jInv. We will illustrate its capabilities and performance with two synthetic time-domain EM inversion examples. First, in airborne surveys, which use many sources, we achieve distributed memory parallelism by decoupling the forward and inverse meshes and performing forward modeling for each source on small, locally refined meshes. Secondly, we invert grounded source time-domain data from a gradient array style induced polarization survey using a novel time-stepping technique that allows us to compute data from different time-steps in parallel. These examples both show that it is possible to invert large scale 3D time-domain EM datasets within a modular, extensible framework written in a high-level, easy to use programming language.

Numerical simulation of tides in Ontario Lacus

NASA Astrophysics Data System (ADS)

Vincent, David; Karatekin, Ozgür

2015-04-01

Hydrocarbons liquid filled lakes has been recently detected on Titan's surface. Most of these lakes are located in the northern latitudes but there is a substantial lake in the southern latitudes: Ontario Lacus. This lake gets our attention because of possible shoreline changes suggested by Cassini flybys over Ontario Lacus between September 2005 (T7) et January 2010 (T65). The shoreline changes could be due to evaporation-precipitation processes but could also be a consequence of tides. Previous studies showed that the maximal tidal amplitudes of Ontario Lacus would be about 0.2m (for an uniform bathymetry of 20m). In this study we simulate tidal amplitude and currents with SLIM (Second-generation Louvain-la-Neuve Ice-ocean Model, http://sites.uclouvain.be/slim/ ) which resolves 2D shallow water equation on an unstructured mesh. Unstructured mesh prevents problems like mesh discontinuities at poles and allows higher accuracy at some place like coast or straits without drastically increasing computing costs. The tide generating force modeled in this work is the gradient of tidal potential due to titan's obliquity and titan's orbital eccentricity around Saturn (other contribution such as sun tide generating force are unheeded). The uncertain input parameters such as the wind direction and amplitude, bottom friction and thermo-physical properties of hydrocarbons liquids are varied within their expected ranges. SAR data analysis can result in different bathymetry according to the method. We proceed simulations for different bathymetries: tidal amplitudes doesn't change but this is not the case for tidal currents. Using a recent bathymetry deduced from most recent RADAR/SAR observations and a finer mesh, the peak-to peak tidal amplitudes are calculated to be up to 0.6 m. which is more than a factor two larger than the previous results. The maximal offshore tidal currents magnitude is about 0.06 m/s.

Fabrication and characterization of anode-supported micro-tubular solide oxide fuel cell by phase inversion method

NASA Astrophysics Data System (ADS)

Ren, Cong

Nowadays, the micro-tubular solid oxide fuel cells (MT-SOFCs), especially the anode supported MT-SOFCs have been extensively developed to be applied for SOFC stacks designation, which can be potentially used for portable power sources and vehicle power supply. To prepare MT-SOFCs with high electrochemical performance, one of the main strategies is to optimize the microstructure of the anode support. Recently, a novel phase inversion method has been applied to prepare the anode support with a unique asymmetrical microstructure, which can improve the electrochemical performance of the MT-SOFCs. Since several process parameters of the phase inversion method can influence the pore formation mechanism and final microstructure, it is essential and necessary to systematically investigate the relationship between phase inversion process parameters and final microstructure of the anode supports. The objective of this study is aiming at correlating the process parameters and microstructure and further preparing MT-SOFCs with enhanced electrochemical performance. Non-solvent, which is used to trigger the phase separation process, can significantly influence the microstructure of the anode support fabricated by phase inversion method. To investigate the mechanism of non-solvent affecting the microstructure, water and ethanol/water mixture were selected for the NiO-YSZ anode supports fabrication. The presence of ethanol in non-solvent can inhibit the growth of the finger-like pores in the tubes. With the increasing of the ethanol concentration in the non-solvent, a relatively dense layer can be observed both in the outside and inside of the tubes. The mechanism of pores growth and morphology obtained by using non-solvent with high concentration ethanol was explained based on the inter-diffusivity between solvent and non-solvent. Solvent and non-solvent pair with larger Dm value is benefit for the growth of finger-like pores. Three cells with different anode geometries was prepared, La0.85Sr0.15MnO 3 (LSM) was selected as the cathode. Cells were tested at 800°C using humidified H2 as fuel. Cell with anode prepared by using pure water as non-solvent shows a maximum power density up to 437mW/cm 2. By comparing the anode geometry and electrochemical performance, it indicated that microstructure with longer finger-like pores and thinner macrovoid free layer close to the inner side of the tube is benefit to cell performance. Another factor that can affect the microstructure of anode support is the ratio of solvent and polymer binder. In this research, anode-supported MT-SOFCs have been fabricated by phase inversion method. The effect of the viscosity of the casting slurry on the microstructure of YSZ-NiO anode support has been investigated. The microstructure of the YSZ-NiO support can be effectively controlled by varying the slurry composition with different solvent and polymer binder content. Gas permeation and mechanical strength of the YSZ-NiO support have been measured and four YSZ-NiO anode supports have been chosen for subsequent cell fabrication. The effective conductivity of the different anode supports has been measured at room temperature after reduced. Anode-supported single cells with YSZ electrolyte and LSM/YSZ cathode are fabricated and tested. Maximum cell power densities of 606 mWcm-2, 449 mWcm -2, 339 mWcm-2 and 253 mWcm-2 have been obtained respectively at 750 °C with humidified hydrogen as fuel and ambient air as oxidant. The correlation between the cell electrochemical performance and anode microstructures has been discussed. Adjusting the slurry composition by introducing additive is also an effective approach to tailor the microstructure of the anode support. Poly(ethylene glycol) (PEG), which is a common applied polymer additive, was selected to fabricate the YSZ-NiO anode supports. The effect of molecular weight and amount of PEG additive on the thermodynamics of the casting solutions was characterized by measuring the coagulation value. Viscosity of the casting slurries was also measured and the influence of PEG additive on viscosity was studied and discussed. The presence of PEG in the casting slurry can greatly influence the final anode support microstructure. Based on the microstructure result and the measured gas permeation value, two anode supports were selected for cell fabrication. For cell with the anode support fabricated using slurry with PEG additive, a maximum cell power density of 704 mWcm-2 is obtained at 750 oC with humidified hydrogen as fuel and ambient air as oxidant; cell fabricated without any PEG additive shows the peak cell power density of 331 mWcm-2. The relationship between anode microstructure and cell performance was discussed. Anode-supported micro-tubular solid oxide fuel cells (MT-SOFCs) based on BaZr0.1Ce0.7Y0.1Yb0.1O 3-delta (BZCYYb) proton-conducting electrolyte have been prepared using a phase inversion method. Three sulfur-free polymer binder candidates ethyl cellulose (EC), polyvinylidene fluoride (PVDF), polyetherimide (PEI) and sulfur-containing polythersulfone (PESf) were used as polymer binders to fabricate NiO-BZCYYb anode. The overall influence of polymer binder on the anode supports was evaluated. Sulfide impurity generated from PESf was revealed by XRD and X-ray photoelectron spectroscopy (XPS). The difference in the anode microstructure for samples fabricated by different polymer binders was examined by scanning electron microscope (SEM) and analyzed by measuring the gas permeation data of the reduced samples. Single cells based on different anode supports were characterized in anode-supported MT-SOFCs with the cell configuration of Ni-BZCYYb anode, BZCYYb electrolyte and La0.6Sr 0.4Co0.2Fe0.8O3-delta (LSCF)-BZCYYb cathode at 650 °C using hydrogen as fuel and ambient air as oxidant. MT-SOFCs of the anode fabricated using PEI show maximum power density of 0.45 Wcm -2 compared with 0.35 Wcm-2 for cells fabricated with PESf. The difference in cell performance was attributed to the phase purity of the anode fabricated by different polymer binders. Sulfur-free polymer binder PEI exhibits advantages over the commonly applied PESf and other sulfur-free polymer binder candidates. To eliminate the skin layer formed close to the inner side of the tubular sample when using the phase inversion method. Polyethersulfone (PESf)-polyethylenimine (PEI) blend was employed as the polymer binder to fabricate the micro-tubular solid oxide fuel cells (MT-SOFCs). The potential impurity introduced in the anode support by the polymer binder was examined by XPS and the resulting novel microstructure was analyzed based on the backscattered electron (BSE) images. Cells fabricated with blend polymer binder showed significantly enhanced power output compared with those cells only fabricated with PEI or PESf. The improved cell performance demonstrated that using blend polymer as binder is a promising and versatile approach for MT-SOFC fabrication via phase inversion method. Finally, to investigate the effect of the anode microstructure on the total cell performance, two types of anode support with different microstructure were prepared via the phase inversion method at different temperature. Cells fabricated based on these two anode supports were tested at 750 °C with hydrogen or hydrogen mixture with fuel gas. The measured current density-voltage (I-V) curves were fitted by a polarization model, and several parameters were archived through the modeling process. The influence of the anode support on the total cell performance was discussed based on the calculated result.

Finite elements: Theory and application

NASA Technical Reports Server (NTRS)

Dwoyer, D. L. (Editor); Hussaini, M. Y. (Editor); Voigt, R. G. (Editor)

1988-01-01

Recent advances in FEM techniques and applications are discussed in reviews and reports presented at the ICASE/LaRC workshop held in Hampton, VA in July 1986. Topics addressed include FEM approaches for partial differential equations, mixed FEMs, singular FEMs, FEMs for hyperbolic systems, iterative methods for elliptic finite-element equations on general meshes, mathematical aspects of FEMS for incompressible viscous flows, and gradient weighted moving finite elements in two dimensions. Consideration is given to adaptive flux-corrected FEM transport techniques for CFD, mixed and singular finite elements and the field BEM, p and h-p versions of the FEM, transient analysis methods in computational dynamics, and FEMs for integrated flow/thermal/structural analysis.

Aerodynamic Design Optimization on Unstructured Meshes Using the Navier-Stokes Equations

NASA Technical Reports Server (NTRS)

Nielsen, Eric J.; Anderson, W. Kyle

1998-01-01

A discrete adjoint method is developed and demonstrated for aerodynamic design optimization on unstructured grids. The governing equations are the three-dimensional Reynolds-averaged Navier-Stokes equations coupled with a one-equation turbulence model. A discussion of the numerical implementation of the flow and adjoint equations is presented. Both compressible and incompressible solvers are differentiated and the accuracy of the sensitivity derivatives is verified by comparing with gradients obtained using finite differences. Several simplifying approximations to the complete linearization of the residual are also presented, and the resulting accuracy of the derivatives is examined. Demonstration optimizations for both compressible and incompressible flows are given.

Comparison of phase-contrast MR and flow simulations for the study of CSF dynamics in the cervical spine.

PubMed

Lindstrøm, Erika Kristina; Schreiner, Jakob; Ringstad, Geir Andre; Haughton, Victor; Eide, Per Kristian; Mardal, Kent-Andre

2018-06-01

Background Investigators use phase-contrast magnetic resonance (PC-MR) and computational fluid dynamics (CFD) to assess cerebrospinal fluid dynamics. We compared qualitative and quantitative results from the two methods. Methods Four volunteers were imaged with a heavily T2-weighted volume gradient echo scan of the brain and cervical spine at 3T and with PC-MR. Velocities were calculated from PC-MR for each phase in the cardiac cycle. Mean pressure gradients in the PC-MR acquisition through the cardiac cycle were calculated with the Navier-Stokes equations. Volumetric MR images of the brain and upper spine were segmented and converted to meshes. Models of the subarachnoid space were created from volume images with the Vascular Modeling Toolkit. CFD simulations were performed with a previously verified flow solver. The flow patterns, velocities and pressures were compared in PC-MR and CFD flow images. Results PC-MR images consistently revealed more inhomogeneous flow patterns than CFD, especially in the anterolateral subarachnoid space where spinal nerve roots are located. On average, peak systolic and diastolic velocities in PC-MR exceeded those in CFD by 31% and 41%, respectively. On average, systolic and diastolic pressure gradients calculated from PC-MR exceeded those of CFD by 11% and 39%, respectively. Conclusions PC-MR shows local flow disturbances that are not evident in typical CFD. The velocities and pressure gradients calculated from PC-MR are systematically larger than those calculated from CFD.

Structural and electrochemical characterisation of Pr 0.7Ca 0.3Cr 1- yMn yO 3- δ as symmetrical solid oxide fuel cell electrodes

NASA Astrophysics Data System (ADS)

El-Himri, Abdelouhad; Marrero-López, David; Ruiz-Morales, Juan Carlos; Peña-Martínez, Juan; Núñez, Pedro

A series of compounds with composition Pr 0.7Ca 0.3Cr 1- yMn yO 3- δ (y = 0.2, 0.4, 0.6, 0.8) were prepared from an alternative freeze-drying precursor method to obtain polycrystalline powders at relatively low temperature. These perovskite-type materials were tested simultaneously as both anode and cathode in a symmetrical SOFC. The effect of the ratio Mn/Cr on the structure, microstructure and electrochemical properties was studied. The performance is rather modest at low temperature and only interesting values were obtained at high temperatures. An assembled symmetrical SOFC rendered performances of 250 and 160 mW cm -2, at 950 °C, under humidified H 2 and CH 4 respectively.

Evaluation of SmCo and SmCoN magnetron sputtering coatings for SOFC interconnect applications

NASA Astrophysics Data System (ADS)

Wu, Junwei; Li, Chengming; Johnson, Christopher; Liu, Xingbo

Cobalt or cobalt containing coatings are promising for SOFC interconnect applications because of their high conductivity. We have investigated SmCo and SmCoN coatings deposited by magnetron sputtering from a SmCo (5% Sm) target on to Crofer 22 APU substrates. The composition, structure, surface morphology, and electrical conductivity of the coated substrates were characterized by SEM/EDX, XRD and ASR measurements. Addition of Sm enhances the oxidation resistance and the Cr retention capability of the coatings. The use of nitride as a precursor stabilizes Sm during oxidation of the films, thus inhibiting diffusion of Fe, resulting in a more compact coating and lowering ASR. The combined advantages of Sm addition to cobalt and the use of a nitride as a precursor, makes SmCoN coatings a promising new interconnect coating material.

Nanoporous palladium anode for direct ethanol solid oxide fuel cells with nanoscale proton-conducting ceramic electrolyte

NASA Astrophysics Data System (ADS)

Li, Yong; Wong, Lai Mun; Xie, Hanlin; Wang, Shijie; Su, Pei-Chen

2017-02-01

In this work, we demonstrate the operation of micro-solid oxide fuel cells (μ-SOFCs) with nanoscale proton-conducting Y-BaZrO3 (BZY) electrolyte to avoid the fuel crossover problem for direct ethanol fuel cells (DEFCs). The μ-SOFCs are operated with the direct utilisation of ethanol vapour as a fuel and Pd as anode at the temperature range of 300-400 °C. The nanoporous Pd anode is achieved by DC sputtering at high Ar pressure of 80 mTorr. The Pd-anode/BYZ-electrolyte/Pt-cathode cell show peak power densities of 72.4 mW/cm2 using hydrogen and 15.3 mW/cm2 using ethanol at 400 °C. No obvious carbon deposition is seen from XPS analysis after fuel cell test with ethanol fuel.

Mosaic-shaped cathode for highly durable solid oxide fuel cell under thermal stress

NASA Astrophysics Data System (ADS)

Joo, Jong Hoon; Jeong, Jaewon; Kim, Se Young; Yoo, Chung-Yul; Jung, Doh Won; Park, Hee Jung; Kwak, Chan; Yu, Ji Haeng

2014-02-01

In this study, we propose a novel "mosaic structure" for a SOFC (solid oxide fuel cell) cathode with high thermal expansion to improve the stability against thermal stress. Self-organizing mosaic-shaped cathode has been successfully achieved by controlling the amount of binder in the dip-coating solution. The anode-supported cell with mosaic-shaped cathode shows itself to be highly durable performance for rapid thermal cycles, however, the performance of the cell with a non-mosaic cathode exhibits severe deterioration originated from the delamination at the cathode/electrolyte interface after 7 thermal cycles. The thermal stability of an SOFC cathode can be evidently improved by controlling the surface morphology. In view of the importance of the thermal expansion properties of the cathode, the effects of cathode morphology on the thermal stress stability are discussed.

Use of La 0.75Sr 0.25Cr 0.5Mn 0.5O 3 materials in composite anodes for direct ethanol solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Ye, Xiao-Feng; Wang, S. R.; Wang, Z. R.; Hu, Q.; Sun, X. F.; Wen, T. L.; Wen, Z. Y.

The perovskite system La 1- xSr xCr 1- yM yO 3- δ (M, Mn, Fe and V) has recently attracted much attention as a candidate material for the fabrication of solid oxide fuel cells (SOFCs) due to its stability in both H 2 and CH 4 atmospheres at temperatures up to 1000 °C. In this paper, we report the synthesis of La 0.75Sr 0.25Cr 0.5Mn 0.5O 3 (LSCM) by solid-state reaction and its employment as an alternative anode material for anode-supported SOFCs. Because LSCM shows a greatly decreased electronic conductivity in a reducing atmosphere compared to that in air, we have fabricated Cu-LSCM-ScSZ (scandia-stabilized zirconia) composite anodes by tape-casting and a wet-impregnation method. Additionally, a composite structure (support anode, functional anode and electrolyte) structure with a layer of Cu-LSCM-YSZ (yttria-stabilized zirconia) on the supported anode surface has been manufactured by tape-casting and screen-printing. Single cells with these two kinds of anodes have been fabricated, and their performance characteristics using hydrogen and ethanol have been measured. In the operation period, no obvious carbon deposition was observed when these cells were operated on ethanol. These results demonstrate the stability of LSCM in an ethanol atmosphere and its potential utilization in anode-supported SOFCs.

Elementary reaction modeling of reversible CO/CO2 electrochemical conversion on patterned nickel electrodes

NASA Astrophysics Data System (ADS)

Luo, Yu; Shi, Yixiang; Li, Wenying; Cai, Ningsheng

2018-03-01

CO/CO2 are the major gas reactant/product in the fuel electrode of reversible solid oxide cells (RSOC). This study proposes a two-charge-transfer-step mechanism to describe the reaction and transfer processes of CO-CO2 electrochemical conversion on a patterned Ni electrode of RSOC. An elementary reaction model is developed to couple two charge transfer reactions, C(Ni)+O2-(YSZ) ↔ CO(Ni)+(YSZ) +2e- and CO(Ni)+O2-(YSZ) ↔ CO2(Ni)+(YSZ)+2e-, with adsorption/desorption, surface chemical reactions and surface diffusion. This model well validates in both solid oxide electrolysis cell (SOEC) and solid oxide fuel cell (SOFC) modes by the experimental data from a patterned Ni electrode with 10 μm stripe width at different pCO (0-0.25 atm), pCO2 (0-0.35 atm) and operating temperature (600-700 °C). This model indicates SOEC mode is dominated by charge transfer step C(Ni)+O2-(YSZ)↔CO(Ni)+(YSZ) +2e-, while SOFC mode by CO(Ni)+ O2-(YSZ)↔CO2(Ni)+(YSZ)+2e- on the patterned Ni electrode. The sensitivity analysis shows charge transfer step is the major rate-determining step for RSOC, besides, surface diffusion of CO and CO2 as well as CO2 adsorption also plays a significant role in the electrochemical reaction of SOEC while surface diffusion of CO and CO2 desorption could be co-limiting in SOFC.

Unraveling the Role of Transport, Electrocatalysis, and Surface Science in the Solid Oxide Fuel Cell Cathode Oxygen Reduction Reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gopalan, Srikanth

2017-04-06

This final report for project FE0009656 covers the period from 10/01/2012 to 09/30/2015 and covers research accomplishments on the effects of carbon dioxide on the surface composition and structure of cathode materials for solid oxide fuel cells (SOFCs), specifically La1-xSrxFeyCo1- yO3-δ (LSCF). Epitaxially deposited thin films of LSCF on various single-crystal substrates have revealed the selective segregation of strontium to the surface thereby resulting in a surface enrichment of strontium. The near surface compositional profile in the films have been measured using total x-ray fluorescence (TXRF), and show that the kinetics of strontium segregation are higher at higher partial pressuresmore » of carbon dioxide. Once the strontium segregates to the surface, it leads to the formation of precipitates of SrO which convert to SrCO3 in the presence of even modest concentrations of carbon dioxide in the atmosphere. This has important implications for the performance of SOFCs which is discussed in this report. These experimental observations have also been verified by Density Functional Theory calculations (DFT) which predict the conditions under which SrO and SrCO3 can occur in LSCF. Furthermore, a few cathode compositions which have received attention in the literature as alternatives to LSCF cathodes have been studied in this work and shown to be thermodynamically unstable under the operating conditions of the SOFCs.« less

Investigation of the stability of Co-doped apatite ionic conductors in NH 3

NASA Astrophysics Data System (ADS)

Headspith, D. A.; Orera, A.; Slater, P. R.; Young, N. A.; Francesconi, M. G.

2010-12-01

Hydrogen powered solid oxide fuel cells (SOFCs) are of enormous interest as devices for the efficient and clean production of electrical energy. However, a number of problems linked to hydrogen production, storage and transportation are slowing down the larger scale use of SOFCs. Identifying alternative fuel sources to act as intermediate during the transition to the full use of hydrogen is, therefore, of importance. One excellent alternative is ammonia, which is produced on a large scale, is relatively cheap and has the infrastructure for storage and transportation already in place. However, considering that SOFCs operate at temperatures higher than 500 °C, a potential problem is the interaction of gaseous ammonia with the materials in the cathode, anode and solid electrolyte. In this paper, we extend earlier work on high temperature reactions of apatite electrolytes with NH 3 to the transition metal (Co) doped systems, La 9.67Si 5CoO 26 and La 10(Si/Ge) 5CoO 26.5. A combination of PXRD, TGA and XAFS spectroscopy data showed a better structural stability for the silicate systems. Apatite silicates and germanates not containing transition metals tend to substitute nitride anions for their interstitial oxide anions, when reacted with NH 3 at high temperature and, consequentially, lower the interstitial oxide content. In La 9.67Si 5CoO 26 and La 10(Si/Ge) 5CoO 26.5 reduction of Co occurs as a competing process, favouring lower levels of nitride-oxide substitution.