A generalized kinetic model for heterogeneous gas-solid reactions.
Xu, Zhijie; Sun, Xin; Khaleel, Mohammad A
2012-08-21
We present a generalized kinetic model for gas-solid heterogeneous reactions taking place at the interface between two phases. The model studies the reaction kinetics by taking into account the reactions at the interface, as well as the transport process within the product layer. The standard unreacted shrinking core model relies on the assumption of quasi-static diffusion that results in a steady-state concentration profile of gas reactant in the product layer. By relaxing this assumption and resolving the entire problem, general solutions can be obtained for reaction kinetics, including the reaction front velocity and the conversion (volume fraction of reacted solid). The unreacted shrinking core model is shown to be accurate and in agreement with the generalized model for slow reaction (or fast diffusion), low concentration of gas reactant, and small solid size. Otherwise, a generalized kinetic model should be used. PMID:22920132
A generalized kinetic model for heterogeneous gas-solid reactions
NASA Astrophysics Data System (ADS)
Xu, Zhijie; Sun, Xin; Khaleel, Mohammad A.
2012-08-01
We present a generalized kinetic model for gas-solid heterogeneous reactions taking place at the interface between two phases. The model studies the reaction kinetics by taking into account the reactions at the interface, as well as the transport process within the product layer. The standard unreacted shrinking core model relies on the assumption of quasi-static diffusion that results in a steady-state concentration profile of gas reactant in the product layer. By relaxing this assumption and resolving the entire problem, general solutions can be obtained for reaction kinetics, including the reaction front velocity and the conversion (volume fraction of reacted solid). The unreacted shrinking core model is shown to be accurate and in agreement with the generalized model for slow reaction (or fast diffusion), low concentration of gas reactant, and small solid size. Otherwise, a generalized kinetic model should be used.
Turbulence modeling of gas-solid suspension flows
NASA Technical Reports Server (NTRS)
Chen, C. P.
1988-01-01
The purpose here is to discuss and review advances in two-phase turbulent modeling techniques and their applications in various gas-solid suspension flow situations. In addition to the turbulence closures, heat transfer effect, particle dispersion and wall effects are partially covered.
Gas-solid flow in vertical tubes
Pita, J.A.; Sundaresan, S. )
1991-07-01
This paper reports on a computational study of fully-developed flow of gas-particle suspensions in vertical pipes which was carried out, using the model proposed recently by Sinclair and Jackson, to understand the predicted scale-up characteristics. It was shown that the model can capture the existence of steady-state multiplicity wherein different pressure gradients can be obtained for the same gas and solids fluxes. A pronounced and nonmonotonic variation of the pressure gradient required to achieve desired fluxes of solid and gas with tube diameter was predicted by the model, and this is explained on a physical basis. The computed results were compared with the experimental data. The model manifests an unsatisfactory degree of sensitivity to the inelasticity of the particle-particle collisions and the damping of particle-phase fluctuating motion by the gas.
Gas-solid flow characteristics in high-density CFB
NASA Astrophysics Data System (ADS)
Wang, Xue-yao; Fan, Bao-guo; Wang, Sheng-dian; Xu, Xiang; Xiao, Yun-han
2012-08-01
The gas-solid flow characteristics in the riser of a high density CFB of square (0.27 m×0.27 m×10.4 m) or circular ( ϕ 0.187m×10.4 m) cross section, using Geldart B particles (quartz sand), was investigated experimentally. The influence of riser structure on the hydrodynamic behaviors of a high-density circulating fluidized bed was investigated. The solid circulation rate was up to 321 kg/(m2s) with the circular cross-section under the operating conditions of the main bed air velocity 12.1 m/s and loosen wind and back-feed wind flow 25.1 m3/h. Different operating conditions on realizing high density circulation was analyzed, while both solids circulation rate and particle holdup depended highly on operating conditions. The circulating gas-solid flow was accompanied by an evidently-dense character in the riser's bottom zone and became fully developed in the middle and upper zones.
A new model for gas/solid pipe flow
Wu, Bangxian; Chang, S.L.; Lottes, S.A.; Petrick, M.
1995-12-31
A new model of particle turbulent dispersion in vertical gas/solid pipe flow is presented in this paper. The essence of the model is to pay more attention to the active and discrete behavior of particles in the dispersion process in non-homogeneous turbulent vertical pipe flows using two-fluid approaches. In the new model, a non-gradient type of diffusion term is included in the expression of radial particle dispersion flux; the transport equation for particle turbulent kinetic energy (PTKE) is developed and solved for its distribution; the effect of intra-particle collision is considered for the generation and dissipation of PTKE; turbulence modulation due to particle presence is taken into account. Preliminary numerical results based on this new model are also presented in this paper.
DEVELOPMENT OF LOW-DIFFUSION FLUX-SPLITTING METHODS FOR DENSE GAS-SOLID FLOWS
The development of a class of low-diffusion upwinding methods for computing dense gas-solid flows is presented in this work. An artificial compressibility/low-Mach preconditioning strategy is developed for a hyperbolic two-phase flow equation system consisting of separate solids ...
Particle-Resolved Direct Numerical Simulation for Gas-Solid Flow Model Development
NASA Astrophysics Data System (ADS)
Tenneti, Sudheer; Subramaniam, Shankar
2014-01-01
Gas-solid flows in nature and industrial applications are characterized by multiscale and nonlinear interactions that manifest as rich flow physics and pose unique modeling challenges. In this article, we review particle-resolved direct numerical simulation (PR-DNS) of the microscale governing equations for understanding gas-solid flow physics and obtaining quantitative information for model development. A clear connection between a microscale realization and meso/macroscale representation is necessary for PR-DNS to be used effectively for model development at the meso- and macroscale. Furthermore, the design of PR-DNS must address the computational challenges of parameterizing models in a high-dimensional parameter space and obtaining accurate statistics of flow properties from a finite number of realizations at acceptable grid resolution. This review also summarizes selected recent insights into the physics of momentum, kinetic energy, and heat transfer in gas-solid flows obtained from PR-DNS. Promising future applications of PR-DNS include the study of the effect of number fluctuations on hydrodynamics, instabilities in gas-solid flow, and wall-bounded flows.
Fictitious domain method for fully resolved reacting gas-solid flow simulation
NASA Astrophysics Data System (ADS)
Zhang, Longhui; Liu, Kai; You, Changfu
2015-10-01
Fully resolved simulation (FRS) for gas-solid multiphase flow considers solid objects as finite sized regions in flow fields and their behaviours are predicted by solving equations in both fluid and solid regions directly. Fixed mesh numerical methods, such as fictitious domain method, are preferred in solving FRS problems and have been widely researched. However, for reacting gas-solid flows no suitable fictitious domain numerical method has been developed. This work presents a new fictitious domain finite element method for FRS of reacting particulate flows. Low Mach number reacting flow governing equations are solved sequentially on a regular background mesh. Particles are immersed in the mesh and driven by their surface forces and torques integrated on immersed interfaces. Additional treatments on energy and surface reactions are developed. Several numerical test cases validated the method and a burning carbon particles array falling simulation proved the capability for solving moving reacting particle cluster problems.
A study of pneumatic conveying of gas-solid flow for industrial application
NASA Astrophysics Data System (ADS)
Al-Khateeb, Khalid A. S.; Tasnim, Rumana; Khan, Sheroz; Mohammod, Musse; Arshad, Atika; Shobaki, Mohammed M.; Haider, Samnan; Saquib, Nazmus; Rahman, Tawfilur
2013-12-01
The complicated nature of gas-solids' physical properties have challenged the researchers over past decades who have led their efforts in developing its' flow sensing and measurement methods. The term 'gas-solid flow' signifies dilute- or dense-phase flow with a very little concentration of solids. For conducting such flow measurement, generally velocity profile and volumetric concentration of the flow particles being conveyed are needed to be measured. An important application of gas-solid flow has taken root in the form of biomass flow in pneumatic conveying systems, and its' online measurement has proven to be an exigent research pursuit. Additionally the other applications have been explored in power plants, food, chemical and automobiles industries as well. This paper aims at exploring the evolution of flow measurement methods along with a brief explanation on existing fundamental sensing techniques. Furthermore, the most recent patents developed for such measurements in pneumatic conveying pipelines are scrutinized along with their concomitant pros and cons.
Open-source MFIX-DEM software for gas-solids flows: Part II Validation studies
Li, Tingwen; Garg, Rahul; Galvin, Janine; Pannala, Sreekanth
2012-01-01
With rapid advancements in computer hardware and numerical algorithms, computational fluid dynamics (CFD) has been increasingly employed as a useful tool for investigating the complex hydrodynamics inherent in multiphase flows. An important step during the development of a CFD model and prior to its application is conducting careful and comprehensive verification and validation studies. Accordingly, efforts to verify and validate the open-source MFIX-DEM software, which can be used for simulating the gas solids flow using an Eulerian reference frame for the continuum fluid and a Lagrangian discrete framework (Discrete Element Method) for the particles, have been made at the National Energy Technology Laboratory (NETL). In part I of this paper, extensive verification studies were presented and in this part, detailed validation studies of MFIX-DEM are presented. A series of test cases covering a range of gas solids flow applications were conducted. In particular the numerical results for the random packing of a binary particle mixture, the repose angle of a sandpile formed during a side charge process, velocity, granular temperature, and voidage profiles from a bounded granular shear flow, lateral voidage and velocity profiles from a monodisperse bubbling fluidized bed, lateral velocity profiles from a spouted bed, and the dynamics of segregation of a binary mixture in a bubbling bed were compared with available experimental data, and in some instances with empirical correlations. In addition, sensitivity studies were conducted for various parameters to quantify the error in the numerical simulation.
Characteristics of dilute gas-solids suspensions in drag reducing flow
NASA Technical Reports Server (NTRS)
Kane, R. S.; Pfeffer, R.
1973-01-01
Measurements were performed on dilute flowing gas-solids suspensions and included data, with particles present, on gas friction factors, velocity profiles, turbulence intensity profiles, turbulent spectra, and particle velocity profiles. Glass beads of 10 to 60 micron diameter were suspended in air at Reynolds numbers of 10,000 to 25,000 and solids loading ratios from 0 to 4. Drag reduction was achieved for all particle sizes in vertical flow and for the smaller particle sizes in horizontal flow. The profile measurements in the vertical tube indicated that the presence of particles thickened the viscous sublayer. A quantitative theory based on particle-eddy interaction and viscous sublayer thickening has been proposed.
Open source development experience with a computational gas-solids flow code
Syamlal, M; O'Brien, T. J.; Benyahia, Sofiane; Gel, Aytekin; Pannala, Sreekanth
2008-01-01
A case study on the use of open source (OS) software development in chemical engineering research and education is presented here. The multiphase computational fluid dynamics software MFIX is the object of the case study. The verification and validation steps required for constructing modern computational software and the advantages of OS development in those steps are discussed. The infrastructure used for enabling the OS development of MFIX is described. The impact of OS development on computational research and education in gas-solids flow and the dissemination of information to other areas such as geotechnical and volcanology research are demonstrated. It is shown that the advantages of OS development methodology were realized: verification by many users, which enhances software quality; the use of software as a means for accumulating and exchanging information; and the facilitation of peer review of the results of computational research.
Numerical simulation of gas-solid two-phase flow in U-beam separator
NASA Astrophysics Data System (ADS)
Zhou, X. Y.; Zhang, H. Z.; Chen, X. P.; Ruan, J. M.; Dou, H. S.
2015-01-01
Numerical simulation is carried out for gas-solid two-phase flow in a U-beam separator. In this study, the U-beam is altered with the inlet fins in order to improve the performance of the separator. The inlet fin angle of the separator are 30°, 35°, 40°, 45°, 50°, 55 ° and 60°. The governing equations are the Reynolds-Averaged Navier-Stokes equation with the standard k-epsilon model and the discrete phase model (DPM) describing the discrete two - phase flow as well as stochastic tracking model. Results show that the pressure drop deviation with fins is within 3% from those without fins. It is found that there is a maximum separation efficiency at the fin angle of 35°. Fin induces generation of a stagnation region which could collect particles and lead to change of vortical structures. The fin induced flow also causes the turbulent intensity inside the baffle to decrease to facilitate separation.
Modeling blood flow heterogeneity.
King, R B; Raymond, G M; Bassingthwaighte, J B
1996-01-01
It has been known for some time that regional blood flows within an organ are not uniform. Useful measures of heterogeneity of regional blood flows are the standard deviation and coefficient of variation or relative dispersion of the probability density function (PDF) of regional flows obtained from the regional concentrations of tracers that are deposited in proportion to blood flow. When a mathematical model is used to analyze dilution curves after tracer solute administration, for many solutes it is important to account for flow heterogeneity and the wide range of transit times through multiple pathways in parallel. Failure to do so leads to bias in the estimates of volumes of distribution and membrane conductances. Since in practice the number of paths used should be relatively small, the analysis is sensitive to the choice of the individual elements used to approximate the distribution of flows or transit times. Presented here is a method for modeling heterogeneous flow through an organ using a scheme that covers both the high flow and long transit time extremes of the flow distribution. With this method, numerical experiments are performed to determine the errors made in estimating parameters when flow heterogeneity is ignored, in both the absence and presence of noise. The magnitude of the errors in the estimates depends upon the system parameters, the amount of flow heterogeneity present, and whether the shape of the input function is known. In some cases, some parameters may be estimated to within 10% when heterogeneity is ignored (homogeneous model), but errors of 15-20% may result, even when the level of heterogeneity is modest. In repeated trials in the presence of 5% noise, the mean of the estimates was always closer to the true value with the heterogeneous model than when heterogeneity was ignored, but the distributions of the estimates from the homogeneous and heterogeneous models overlapped for some parameters when outflow dilution curves were
Research of the gas-solid flow character based on the DEM method
NASA Astrophysics Data System (ADS)
Wang, Xueyao; Xiao, Yunhan
2011-12-01
Numerical simulation of gas-solid flow behaviors in a rectangular fluidized bed is carried out three dimensionally by the discrete element method (DEM). Euler method and Lagrange method are employed to deal with the gas phase and solid phase respectively. The collided force among particles, striking force between particle and wall, drag force, gravity, Magnus lift force and Saffman lift force are considered when establishing the mathematic models. Soft-sphere model is used to describe the collision of particles. In addition, the Euler method is also used for modeling the solid phase to compare with the results of DEM. The flow patterns, particle mean velocities, particles' diffusion and pressure drop of the bed under typical operating conditions are obtained. The results show that the DEM method can describe the detailed information among particles, while the Euler-Euler method cannot capture the micro-scale character. No matter which method is used, the diffusion of particles increases with the increase of gas velocity. But the gathering and crushing of particles cannot be simulated, so the energy loss of particles' collision cannot be calculated and the diffusion by using the Euler-Euler method is larger. In addition, it is shown by DEM method, with strengthening of the carrying capacity, more and more particles can be schlepped upward and the dense suspension upflow pattern can be formed. However, the results given by the Euler-Euler method are not consistent with the real situation.
High-Resolution Simulations of Gas-Solids Jet Penetration Into a High Density Riser Flow
Li, Tingwen
2011-05-01
High-resolution simulations of a gas-solids jet in a 0.3 m diameter and 15.9 m tall circulating fluidized bed (CFB) riser were conducted with the open source software-MFIX. In the numerical simulations, both gas and solids injected through a 1.6 cm diameter radial-directed tube 4.3 m above the bottom distributor were tracked as tracers, which enable the analysis of the characteristics of a two-phase jet. Two jetting gas velocities of 16.6 and 37.2 m/s were studied with the other operating conditions fixed. Reasonable flow hydrodynamics with respect to overall pressure drop, voidage, and solids velocity distributions were predicted. Due to the different dynamic responses of gas and particles to the crossflow, a significant separation of gas and solids within the jet region was predicted for both cases. In addition, the jet characteristics based on tracer concentration and tracer mass fraction profiles at different downstream levels are discussed. Overall, the numerical predictions compare favorably to the experimental measurements made at NETL.
Flow Mapping in a Gas-Solid Riser via Computer Automated Radioactive Particle Tracking (CARPT)
Muthanna Al-Dahhan; Milorad P. Dudukovic; Satish Bhusarapu; Timothy J. O'hern; Steven Trujillo; Michael R. Prairie
2005-06-04
Statement of the Problem: Developing and disseminating a general and experimentally validated model for turbulent multiphase fluid dynamics suitable for engineering design purposes in industrial scale applications of riser reactors and pneumatic conveying, require collecting reliable data on solids trajectories, velocities ? averaged and instantaneous, solids holdup distribution and solids fluxes in the riser as a function of operating conditions. Such data are currently not available on the same system. Multiphase Fluid Dynamics Research Consortium (MFDRC) was established to address these issues on a chosen example of circulating fluidized bed (CFB) reactor, which is widely used in petroleum and chemical industry including coal combustion. This project addresses the problem of lacking reliable data to advance CFB technology. Project Objectives: The objective of this project is to advance the understanding of the solids flow pattern and mixing in a well-developed flow region of a gas-solid riser, operated at different gas flow rates and solids loading using the state-of-the-art non-intrusive measurements. This work creates an insight and reliable database for local solids fluid-dynamic quantities in a pilot-plant scale CFB, which can then be used to validate/develop phenomenological models for the riser. This study also attempts to provide benchmark data for validation of Computational Fluid Dynamic (CFD) codes and their current closures. Technical Approach: Non-Invasive Computer Automated Radioactive Particle Tracking (CARPT) technique provides complete Eulerian solids flow field (time average velocity map and various turbulence parameters such as the Reynolds stresses, turbulent kinetic energy, and eddy diffusivities). It also gives directly the Lagrangian information of solids flow and yields the true solids residence time distribution (RTD). Another radiation based technique, Computed Tomography (CT) yields detailed time averaged local holdup profiles at
FORCE2: A multidimensional flow program for gas solids flow user`s guide
Burge, S.W.
1991-05-01
This report describes the FORCE2 flow program input, output, and the graphical post-processor. The manual describes the steps for creating the model, executing the programs and processing the results into graphical form. The FORCE2 post-processor was developed as an interactive program written in FORTRAN-77. It uses the Graphical Kernel System (GKS) graphics standard recently adopted by International Organization for Standardization, ISO, and American National Standards Institute, ANSI, and, therefore, can be used with many terminals. The post-processor vas written with Calcomp subroutine calls and is compatible with Tektkonix terminals and Calcomp and Nicolet pen plotters. B&W has been developing the FORCE2 code as a general-purpose tool for flow analysis of B&W equipment. The version of FORCE2 described in this manual was developed under the sponsorship of ASEA-Babcock as part of their participation in the joint R&D venture, ``Erosion of FBC Heat Transfer Tubes,`` and is applicable to the analyses of bubbling fluid beds. This manual is the principal documentation for program usage and is segmented into several sections to facilitate usage. In Section 2.0 the program is described, including assumptions, capabilities, limitations and uses, program status and location, related programs and program hardware and software requirements. Section 3.0 is a quick user`s reference guide for preparing input, executing FORCE2, and using the post-processor. Section 4.0 is a detailed description of the FORCE2 input. In Section 5.0, FORCE2 output is summarized. Section 6.0 contains a sample application, and Section 7.0 is a detailed reference guide.
Clustering Instability in Sedimenting Gas-Solid Suspensions and its Influence on Flow Properties.
NASA Astrophysics Data System (ADS)
Li, Xiaoqi; Yin, Xiaolong; Liu, Guodong
2015-11-01
It is well known that sedimentation or fluidization of solid particles through gas is unstable. Instability is usually recognized as particle clusters when the solid fraction is low, or as void `bubbles' when the solid volume fraction is high. Using particle-resolved numerical simulations, we studied cluster formation in gas-solid systems with gas-to-solid density ratio being 0.01 and 0.001. The particles are uniformly sized spheres with a terminal Re of 30. The solid fraction is 0.25. Up to 4808 particles were used such that the clustering phenomena can be adequately examined. In periodic computational domains whose lateral dimension is about eight particle diameters, nucleated particle clusters quickly coalesce and grow into traveling waves that span the entire width of the domain. Consequently, gas-solid drag is significantly increased compared to that in a homogeneous liquid-solid suspension, the lateral velocity variance is suppressed, and the particle velocity distributions are strongly non-Gaussian. When lateral dimension is increased to about thirty particle diameters, particle clusters never turn into width-spanning traveling waves. As results, the drag is similar to that in a homogeneous suspension, the lateral velocity variance is strongly enhanced and the vertical variance reduced, and particle velocity distributions are nearly Gaussian. These results suggest that the effect of particle clusters should be examined in domains with large lateral dimensions.
NASA Astrophysics Data System (ADS)
Subramaniam, Shankar; Sun, Bo
2015-11-01
The presence of solid particles in a steady laminar flow generates velocity fluctuations with respect to the mean fluid velocity that are termed pseudo-turbulence. The level of these pseudo-turbulent velocity fluctuations has been characterized in statistically homogeneous fixed particle assemblies and freely evolving suspensions using particle-resolved direct numerical simulation (PR-DNS) by Mehrabadi et al. (JFM, 2015), and it is found to be a significant contribution to the total kinetic energy associated with the flow. The correlation of these velocity fluctuations with temperature (or a passive scalar) generates a flux term that appears in the transport equation for the average fluid temperature (or average scalar concentration). The magnitude of this transport of temperature-velocity covariance is quantified using PR-DNS of thermally fully developed flow past a statistically homogeneous fixed assembly of particles, and the budget of the average fluid temperature equation is presented. The relation of this transport term to the axial dispersion coefficient (Brenner, Phil. Trans. Roy. Soc. A, 1980) is established. The simulation results are then interpreted in the context of our understanding of axial dispersion in gas-solid flow. NSF CBET 1336941.
NASA Astrophysics Data System (ADS)
Lin, Zhe; Zhu, Linhang; Cui, Baoling; Li, Yi; Ruan, Xiaodong
2014-12-01
Gate valve has various placements in the practical usages. Due to the effect of gravity, particle trajectories and erosions are distinct between placements. Thus in this study, gas-solid flow properties and erosion in gate valve for horizontal placement and vertical placement are discussed and compared by using Euler-Lagrange simulation method. The structure of a gate valve and a simplified structure are investigated. The simulation procedure is validated in our published paper by comparing with the experiment data of a pipe and an elbow. The results show that for all investigated open degrees and Stokes numbers (St), there are little difference of gas flow properties and flow coefficients between two placements. It is also found that the trajectories of particles for two placements are mostly identical when St « 1, making the erosion independent of placement. With the increase of St, the distinction of trajectories between placements becomes more obvious, leading to an increasing difference of the erosion distributions. Besides, the total erosion ratio of surface T for horizontal placement is two orders of magnitudes larger than that for vertical placement when the particle diameter is 250μm.
A CFD study of gas-solid jet in a CFB riser flow
Li, Tingwen; Guenther, Chris
2012-03-01
Three-dimensional high-resolution numerical simulations of a gas–solid jet in a high-density riser flow were conducted. The impact of gas–solid injection on the riser flow hydrodynamics was investigated with respect to voidage, tracer mass fractions, and solids velocity distribution. The behaviors of a gas–solid jet in the riser crossflow were studied through the unsteady numerical simulations. Substantial separation of the jetting gas and solids in the riser crossflow was observed. Mixing of the injected gas and solids with the riser flow was investigated and backmixing of gas and solids was evaluated. In the current numerical study, both the overall hydrodynamics of riser flow and the characteristics of gas–solid jet were reasonably predicted compared with the experimental measurements made at NETL.
Cartesian grid simulations of gas-solids flow systems with complex geometry
Dietiker, Jean-Francois; Li, Tingwen; Garg, Rahul; Shahnam, Mehrdad
2013-02-01
Complex geometries encountered in many applications of gas–solids flow need special treatment in most legacy multiphase flow solvers with Cartesian numerical grid. This paper briefly outlines the implementation of a cut cell technique in the open-source multiphase flow solver—MFIX for accurate representation of complex geometries. Specifically, applications of the Cartesian cut cell method to different gas–solids fluidization systems including a small scale bubbling fluidized bed with submerged tube bundle and a complete pilot-scale circulating fluidized bed will be presented. In addition to qualitative predictions on the general flow behaviors inside each system, quantitative comparison with the available experimental data will be presented. Furthermore, some results on extending the current cut-cell technique to Lagrangian–Eulerian simulations will be presented.
A Study of the Influence of Numerical Diffusion on Gas-Solid Flow Predictions in Fluidized Beds
NASA Astrophysics Data System (ADS)
Ghandriz, Ronak; Sheikhi, Reza
2015-11-01
In this work, an investigation is made of the influence of numerical diffusion on the accuracy of gas-solid flow predictions in fluidized beds. This is an important issue particularly in bubbling fluidized beds since numerical error greatly affects the dynamics of bubbles and their associated mixing process. A bed of coal (classified as Geldart A) is considered which becomes fluidized as the velocity of nitrogen stream into the reactor is gradually increased. The fluidization process is simulated using various numerical schemes as well as grid resolutions. Simulations involve Eulerian-Eulerian two-phase flow modeling approach and results are compared with experimental data. It is shown that higher order schemes equipped with flux limiter give favorable prediction of bubble and particle dynamics and hence, the mixing process within the reactor. The excessive numerical diffusion associated with lower order schemes results in unrealistic prediction of bubble shapes and bed height. Comparison is also made of computational efficiency of various schemes. It is shown that the Monotonized Central scheme with down wind factor results in the shortest simulation time because of its efficient parallelization on distributed memory platforms.
Fine-grid simulations of gas-solids flow in a circulating fluidized bed
Benyahia, S.
2012-01-01
This research note demonstrates that more accurate predictions of a two-fluid model for the riser section of a circulating fluidized bed are obtained as the grid size is equally refined along all the directions of the gas-particle flow. However, two-fluid simulations of large-scale fluidized beds with such a fine mesh are currently computationally prohibitive. Alternatively,subgrid models can significantly reduce the simulation time of multiphase flow by using coarse mesh, whereas maintaining a high level of accuracy.
GAS-SOLID TWO-PHASE FLOW IN A TRIPLE BIFURCATION LUNG AIRWAY MODEL
Laminar oscillatory flow as well as micron-particle transport and wall deposition in a triple bifurcation airway model have been simulated using a validated finite-volume code with user-enhanced programs. Three realistic breathing patterns, i.e., resting, light, acitvity and mod...
Open-Source MFIX-DEM Software for Gas-Solids Flows: Part II - Validation Studies
Li, Tingwen
2012-04-01
With rapid advancements in computer hardware and numerical algorithms, computational fluid dynamics (CFD) has been increasingly employed as a useful tool for investigating the complex hydrodynamics inherent in multiphase flows. An important step during the development of a CFD model and prior to its application is conducting careful and comprehensive verification and validation studies. Accordingly, efforts to verify and validate the open-source MFIX-DEM software, which can be used for simulating the gas–solids flow using an Eulerian reference frame for the continuum fluid and a Lagrangian discrete framework (Discrete Element Method) for the particles, have been made at the National Energy Technology Laboratory (NETL). In part I of this paper, extensive verification studies were presented and in this part, detailed validation studies of MFIX-DEM are presented. A series of test cases covering a range of gas–solids flow applications were conducted. In particular the numerical results for the random packing of a binary particle mixture, the repose angle of a sandpile formed during a side charge process, velocity, granular temperature, and voidage profiles from a bounded granular shear flow, lateral voidage and velocity profiles from a monodisperse bubbling fluidized bed, lateral velocity profiles from a spouted bed, and the dynamics of segregation of a binary mixture in a bubbling bed were compared with available experimental data, and in some instances with empirical correlations. In addition, sensitivity studies were conducted for various parameters to quantify the error in the numerical simulation.
In Situ Control of Gas Flow by Modification of Gas-Solid Interactions
NASA Astrophysics Data System (ADS)
Seo, Dongjin; Ducker, William A.
2013-10-01
The boundary condition for gas flow at the solid-gas interface can be altered by in situ control of the state of a thin film adsorbed to the solid. A monolayer of ocatadecyltrichlorosilane (OTS) reversibly undergoes a meltinglike transition. When the temperature of an OTS-coated particle and plate is moved through the range of OTS “melting” temperatures, there is a change in the lubrication force between the particle and plate in 1 atm of nitrogen gas. This change is interpreted in terms of a change in the flow of gas mediated by the slip length and tangential momentum accommodation coefficient (TMAC). There is a minimum in slip length (290 nm) at 18°C, which corresponds to a maximum in TMAC (0.44). The slip length increases to 590 nm at 40°C which corresponds to a TMAC of 0.25. We attribute the decrease in TMAC with increasing temperature to a decrease in roughness of the monolayer on melting, which allows a higher fraction of specular gas reflections, thereby conserving tangential gas momentum. The importance of this work is that it demonstrates the ability to control gas flow simply by altering the interface for fixed geometry and gas properties.
NASA Astrophysics Data System (ADS)
Wang, Chao; Zhang, Jingyu; Gao, Wenbin; Ding, Hongbing; Wu, Weiping
2015-11-01
The gas-solid two-phase flow has been widely applied in the power, chemical and metallurgical industries. It is of great significance in the research of gas-solid two-phase flow to measure particle velocity at different locations in the pipeline. Thus, an electrostatic sensor array comprising eight arc-shaped electrodes was designed. The relationship between the cross-correlation (CC) velocity and the distribution of particle velocity, charge density and electrode spatial sensitivity was analysed. Then the CC sensitivity and its calculation method were proposed. According to the distribution of CC sensitivity, it was found that, between different electrode pairs, it had different focus areas. The CC focus method was proposed for particle velocity measurement at different locations and validated by a belt-style electrostatic induction experiment facility. Finally, the particle velocities at different locations with different flow conditions were measured to research the particle velocity distribution in a dilute horizontal pneumatic conveying pipeline.
The kinetics of mercury chlorination (with HC1) were studied using a flow reactor system with an on-line Hg analyzer and spciation sampling using a set of impingers. Kinetic parameters, such as reaction order (a), activation energy (Eu) and the overall rate constant (k') were es...
Fort, James A.; Pfund, David M.; Sheen, David M.; Pappas, Richard A.; Morgen, Gerald P.
2007-04-01
The MFDRC was formed in 1998 to advance the state-of-the-art in simulating multiphase turbulent flows by developing advanced computational models for gas-solid flows that are experimentally validated over a wide range of industrially relevant conditions. The goal was to transfer the resulting validated models to interested US commercial CFD software vendors, who would then propagate the models as part of new code versions to their customers in the US chemical industry. Since the lack of detailed data sets at industrially relevant conditions is the major roadblock to developing and validating multiphase turbulence models, a significant component of the work involved flow measurements on an industrial-scale riser contributed by Westinghouse, which was subsequently installed at SNL. Model comparisons were performed against these datasets by LANL. A parallel Office of Industrial Technology (OIT) project within the consortium made similar comparisons between riser measurements and models at NETL. Measured flow quantities of interest included volume fraction, velocity, and velocity-fluctuation profiles for both gas and solid phases at various locations in the riser. Some additional techniques were required for these measurements beyond what was currently available. PNNL’s role on the project was to work with the SNL experimental team to develop and test two new measurement techniques, acoustic tomography and millimeter-wave velocimetry. Acoustic tomography is a promising technique for gas-solid flow measurements in risers and PNNL has substantial related experience in this area. PNNL is also active in developing millimeter wave imaging techniques, and this technology presents an additional approach to make desired measurements. PNNL supported the advanced diagnostics development part of this project by evaluating these techniques and then by adapting and developing the selected technology to bulk gas-solids flows and by implementing them for testing in the SNL riser
Wu, Yingchun; Wu, Xuecheng; Yao, Longchao; Gréhan, Gérard; Cen, Kefa
2015-03-20
The 3D measurement of the particles in a gas-solid pipe flow is of great interest, but remains challenging due to curved pipe walls in various engineering applications. Because of the astigmatism induced by the pipe, concentric ellipse fringes in the hologram of spherical particles are observed in the experiments. With a theoretical analysis of the particle holography by an ABCD matrix, the in-focus particle image can be reconstructed by the modified convolution method and fractional Fourier transform. Thereafter, the particle size, 3D position, and velocity are simultaneously measured by digital holographic particle tracking velocimetry (DHPTV). The successful application of DHPTV to the particle size and 3D velocity measurement in a glass pipe's flow can facilitate its 3D diagnostics. PMID:25968543
Cheng, Cheng; Zhang, Xiaobing
2013-05-01
In conventional models for two-phase reactive flow of interior ballistic, the dynamic collision phenomenon of particles is neglected or empirically simplified. However, the particle collision between particles may play an important role in dilute two-phase flow because the distribution of particles is extremely nonuniform. The collision force may be one of the key factors to influence the particle movement. This paper presents the CFD-DEM approach for simulation of interior ballistic two-phase flow considering the dynamic collision process. The gas phase is treated as a Eulerian continuum and described by a computational fluid dynamic method (CFD). The solid phase is modeled by discrete element method (DEM) using a soft sphere approach for the particle collision dynamic. The model takes into account grain combustion, particle-particle collisions, particle-wall collisions, interphase drag and heat transfer between gas and solid phases. The continuous gas phase equations are discretized in finite volume form and solved by the AUSM+-up scheme with the higher order accurate reconstruction method. Translational and rotational motions of discrete particles are solved by explicit time integrations. The direct mapping contact detection algorithm is used. The multigrid method is applied in the void fraction calculation, the contact detection procedure, and CFD solving procedure. Several verification tests demonstrate the accuracy and reliability of this approach. The simulation of an experimental igniter device in open air shows good agreement between the model and experimental measurements. This paper has implications for improving the ability to capture the complex physics phenomena of two-phase flow during the interior ballistic cycle and to predict dynamic collision phenomena at the individual particle scale. PMID:24891728
NASA Astrophysics Data System (ADS)
Kou, Mingyin; Wu, Shengli; Du, Kaiping; Shen, Wei; Ma, Xiaodong; Chen, Mao; Zhao, Baojun
2015-02-01
The COREX shaft furnace is of great importance to the whole C-3000 process. There are many problems with the operation of the COREX shaft furnace, especially with gas and burden distribution, that have as yet been little studied. The present work establishes a three-dimensional quarter model. After validation by operating data in Baosteel, the model is used to investigate the gas utilization rate and the metallization rate of the COREX shaft furnace. The parameters, including the reducing gas flow, the volume fraction of gas phase, and the multilayered burden, are systematically investigated. The results show that the reducing gas flow has a great influence on the gas utilization rate and the metallization rate, while the volume fraction of gas phase has a more significant effect on the metallization rate than on the gas utilization rate. In order to obtain a higher metallization rate, the reducing gas flow needs to be adjusted step by step and the volume fraction of gas phase needs to be increased. In addition, ore and coke need to be discharged separately in order to increase the solid metallization rate.
NASA Astrophysics Data System (ADS)
Ukhov, Alexander; Borisov, Sergey; Porodnov, Boris
2011-05-01
On the basis of classical knowledge about movement of atoms and lattice theory of F. Goodman and G. Wachman the program modeling helium atom interaction with a three-dimensional crystal tungsten lattice taking into account partial surface covering by chemisorbed oxygen atoms is developed. An efficiency of molecular heat exchange of helium for pure and partially chemisorbed tungsten surface is calculated for different temperatures. Similar model of the surface and procedure of calculations have been applied for description of free-molecular gas flow in long cylindrical channel with clean and fully chemisorbed metal surface. Within the limits of the developed approach the results of calculations for both problems agree well with available experiments with surface contamination control.
Kwon, Kyung; Fan, Liang-Shih; Zhou, Qiang; Yang, Hui
2014-09-30
A new and efficient direct numerical method with second-order convergence accuracy was developed for fully resolved simulations of incompressible viscous flows laden with rigid particles. The method combines the state-of-the-art immersed boundary method (IBM), the multi-direct forcing method, and the lattice Boltzmann method (LBM). First, the multi-direct forcing method is adopted in the improved IBM to better approximate the no-slip/no-penetration (ns/np) condition on the surface of particles. Second, a slight retraction of the Lagrangian grid from the surface towards the interior of particles with a fraction of the Eulerian grid spacing helps increase the convergence accuracy of the method. An over-relaxation technique in the procedure of multi-direct forcing method and the classical fourth order Runge-Kutta scheme in the coupled fluid-particle interaction were applied. The use of the classical fourth order Runge-Kutta scheme helps the overall IB-LBM achieve the second order accuracy and provides more accurate predictions of the translational and rotational motion of particles. The preexistent code with the first-order convergence rate is updated so that the updated new code can resolve the translational and rotational motion of particles with the second-order convergence rate. The updated code has been validated with several benchmark applications. The efficiency of IBM and thus the efficiency of IB-LBM were improved by reducing the number of the Lagragian markers on particles by using a new formula for the number of Lagrangian markers on particle surfaces. The immersed boundary-lattice Boltzmann method (IBLBM) has been shown to predict correctly the angular velocity of a particle. Prior to examining drag force exerted on a cluster of particles, the updated IB-LBM code along with the new formula for the number of Lagrangian markers has been further validated by solving several theoretical problems. Moreover, the unsteadiness of the drag force is examined when a
Information flow in heterogeneously interacting systems.
Yamaguti, Yutaka; Tsuda, Ichiro; Takahashi, Yoichiro
2014-02-01
Motivated by studies on the dynamics of heterogeneously interacting systems in neocortical neural networks, we studied heterogeneously-coupled chaotic systems. We used information-theoretic measures to investigate directions of information flow in heterogeneously coupled Rössler systems, which we selected as a typical chaotic system. In bi-directionally coupled systems, spontaneous and irregular switchings of the phase difference between two chaotic oscillators were observed. The direction of information transmission spontaneously switched in an intermittent manner, depending on the phase difference between the two systems. When two further oscillatory inputs are added to the coupled systems, this system dynamically selects one of the two inputs by synchronizing, selection depending on the internal phase differences between the two systems. These results indicate that the effective direction of information transmission dynamically changes, induced by a switching of phase differences between the two systems. PMID:24465282
NASA Astrophysics Data System (ADS)
Minier, Jean-Pierre; Peirano, Eric; Chibbaro, Sergio
2004-07-01
The aim of the paper is to discuss the main characteristics of a complete theoretical and numerical model for turbulent polydispersed two-phase flows, pointing out some specific issues. The theoretical details of the model have already been presented [Minier and Peirano, Phys. Rep. 352, 1 (2001)]. Consequently, the present work is mainly focused on complementary aspects that are often overlooked and that require particular attention. In particular, the following points are analyzed: the necessity to add an extra term in the equation for the velocity of the fluid seen in the case of two-way coupling, the theoretical and numerical evaluations of particle averages and the fulfillment of the particle mass-continuity constraint. The theoretical model is developed within the probability density function (PDF) formalism. The important physical choice of the state vector variables is first discussed and the model is then expressed as a stochastic differential equation written in continuous time (Langevin equations) for the velocity of the fluid seen. The interests and limitations of Langevin equations, compared to the single-phase case, are reviewed. From the numerical point of view, the model corresponds to a hybrid Eulerian/Lagrangian approach where the fluid and particle phases are simulated by different methods. Important aspects of the Monte Carlo particle/mesh numerical method are emphasized. Finally, the complete model is validated and its performance is assessed by simulating a bluff-body case with an important recirculation zone and in which two-way coupling is noticeable.
Heterogeneity and Flow in the Deep Earth
NASA Astrophysics Data System (ADS)
Cottaar, Sanne
Over the past half century, study of deep regions in the Earth has revealed them to be complex and dynamic. Much of our knowledge comes from seismological data, and ultimately these observations need to be linked to results from geodynamics and mineral physics in order to make inferences about compositional heterogeneities and flow. One example of a strongly-heterogeneous region is the lower thermal boundary layer of the mantle, i.e. the layer of several hundred kilometers thickness above the core-mantle boundary, commonly referred to as D″. This region appears to be characterized by two large provinces of distinctive slow shear velocities, 4000-5000 km across, one beneath the Pacific and one beneath Africa. Surrounding these regions, seismic velocities are faster, and often interpreted as corresponding to a graveyard of slabs. A recently discovered phase transition from perovskite to postperovskite may also occur in this depth range and has been associated with an intermittently observed seismic discontinuity at the top of D″. This study adds to the seismological evidence for complexities both in isotropic seismic velocities as well as in anisotropic velocities and how those can be linked to flow of material. We map a distinctive small "pile" of slow shear velocity beneath Russia through direct waveform evidence. This "pile" is less than 1000 km across, and thus much smaller than the Pacific and African provinces. Its height is several hundreds of kilometers and its velocity reduction suggests it is composed of the same material as the large provinces of slow shear velocity. Beneath Hawaii, at the northern edge of the Pacific province, we find an extended thin zone of ultra-low velocities. This is the first time the three-dimensional extent of such a zone is constrained with some accuracy. The constraints on its morphology come from the presence of strong postcursors to shear waves diffracted along the core-mantle boundary, delayed by 30 to 50 seconds with
Real-Time Monitoring of Heterogeneous Catalysis with Mass Spectrometry
ERIC Educational Resources Information Center
Young, Mark A.
2009-01-01
Heterogeneous, gas-solid processes constitute an important class of catalytic reactions that play a key role in a variety of applications, such as industrial processing and environmental controls. Heterogeneous catalytic chemistry can be demonstrated in a simple heated flow reactor containing a fragment of the catalytic converter from a vehicular…
Godunov Method for Calculating Multicomponent Heterogeneous Medium Flows
NASA Astrophysics Data System (ADS)
Surov, V. S.
2014-03-01
The modified Godunov method intended for integrating the nondivergent systems that describe a multivelocity heterogeneous mixture flow is presented. The linearized Riemann solver has been used in solving the Riemann problems.
Harmonically Perturbed Gas-Solid Fluidized System
NASA Astrophysics Data System (ADS)
Nix, S. T.; Muller, M. R.
1996-11-01
Experiments were performed on a harmonically perturbed gas-solid fluidized system, to determine the extent to which the total system behaved as a liquid in regards to the aspects of resonant frequency, wave shapes, and damping effects. The fluidized system consists of a cylindrical alumina oxide/air fluidized bed which is vertically perturbed in a symmetrical fashion by externally vibrating the entire vessel. The external vibrations were carried out over various flow rates, amplitudes, and frequencies. The results obtained could then be compared to the natural frequencies of water for the same governing parameters by analytical means. The effects of excitations on the formation of voidage disturbances or "gas bubbles" was also investigated. Data acquisition enabled the determination of both the amplitude and frequency of the waves generated in the bath. Results indicate that external vertical vibration caused the mean surface level of the bed to drop. This can be attributed to a closer packing of the particles along with a decrease in the number and size of gas bubbles in the bed.
Heterogeneous scalable framework for multiphase flows.
Morris, Karla Vanessa
2013-09-01
Two categories of challenges confront the developer of computational spray models: those related to the computation and those related to the physics. Regarding the computation, the trend towards heterogeneous, multi- and many-core platforms will require considerable re-engineering of codes written for the current supercomputing platforms. Regarding the physics, accurate methods for transferring mass, momentum and energy from the dispersed phase onto the carrier fluid grid have so far eluded modelers. Significant challenges also lie at the intersection between these two categories. To be competitive, any physics model must be expressible in a parallel algorithm that performs well on evolving computer platforms. This work created an application based on a software architecture where the physics and software concerns are separated in a way that adds flexibility to both. The develop spray-tracking package includes an application programming interface (API) that abstracts away the platform-dependent parallelization concerns, enabling the scientific programmer to write serial code that the API resolves into parallel processes and threads of execution. The project also developed the infrastructure required to provide similar API's to other application. The API allow object-oriented Fortran applications direct interaction with Trilinos to support memory management of distributed objects in central processing units (CPU) and graphic processing units (GPU) nodes for applications using C++.
Relationship between beta-adrenoceptors and coronary blood flow heterogeneity
Upsher, M.E.; Weiss, H.R.
1989-01-01
The purpose of this study was to investigate the hypothesis that the heterogeneous distribution of ..beta.. adrenoceptors contributes to the control of flow heterogeneity in the canine myocardium. ..beta.. adrenoceptor density and affinity were measured simultaneously with coronary blood flow in multiple sections of the left ventricle of 14 anesthetized open chest dogs. Radioactive microspheres were used for the measurement of blood flow. Receptor density (Bmax) and dissociation constant (Kd) were measured using (/sup 125/I)- iodopindolol. The average control myocardial blood flow (MBF) was 86/+-/15 ml/min/100 g. Isoproterenol increased MBF by 82%, whereas propranolol reduced MBF by 13%. The mean value of Bmax was unaltered by either treatment. Under control conditions, a significant positive positive correlation was observed between Bmax and blood flow. In the isoproterenol treatment group, this correlation was enhanced. Beta adrenoceptor blockade led to a negative correlation. Kd showed no overall correlation with blood flow. Kd but not Bmax was significantly higher in the EPI than in the ENDO and in the base compared to the apex. There appears to be a direct linear relationship between the distribution of beta adrenoceptors and MBF distribution which is enhanced under conditions of high beta adrenergic activity. There is a correlation between beta adrenoceptor activity and blood flow distribution in the canine myocardium.
Analytical studies on the instabilities of heterogeneous intelligent traffic flow
NASA Astrophysics Data System (ADS)
Ngoduy, D.
2013-10-01
It has been widely reported in literature that a small perturbation in traffic flow such as a sudden deceleration of a vehicle could lead to the formation of traffic jams without a clear bottleneck. These traffic jams are usually related to instabilities in traffic flow. The applications of intelligent traffic systems are a potential solution to reduce the amplitude or to eliminate the formation of such traffic instabilities. A lot of research has been conducted to theoretically study the effect of intelligent vehicles, for example adaptive cruise control vehicles, using either computer simulation or analytical method. However, most current analytical research has only applied to single class traffic flow. To this end, the main topic of this paper is to perform a linear stability analysis to find the stability threshold of heterogeneous traffic flow using microscopic models, particularly the effect of intelligent vehicles on heterogeneous (or multi-class) traffic flow instabilities. The analytical results will show how intelligent vehicle percentages affect the stability of multi-class traffic flow.
Effects of incomplete mixing on chemical reactions under flow heterogeneities.
NASA Astrophysics Data System (ADS)
Perez, Lazaro; Hidalgo, Juan J.; Dentz, Marco
2016-04-01
Evaluation of the mixing process in aquifers is of primary importance when assessing attenuation of pollutants. In aquifers different hydraulic and chemical properties can increase mixing and spreading of the transported species. Mixing processes control biogeochemical transformations such as precipitation/dissolution reactions or degradation reactions that are fast compared to mass transfer processes. Reactions are local phenomena that fluctuate at the pore scale, but predictions are often made at much larger scales. However, aquifer heterogeities are found at all scales and generates flow heterogeneities which creates complex concentration distributions that enhances mixing. In order to assess the impact of spatial flow heterogeneities at pore scale we study concentration profiles, gradients and reaction rates using a random walk particle tracking (RWPT) method and kernel density estimators to reconstruct concentrations and gradients in two setups. First, we focus on a irreversible bimolecular reaction A+B → C under homogeneous flow to distinguish phenomena of incomplete mixing of reactants from finite-size sampling effects. Second, we analise a fast reversible bimolecular chemical reaction A+B rightleftharpoons C in a laminar Poiseuille flow reactor to determine the difference between local and global reaction rates caused by the incomplete mixing under flow heterogeneities. Simulation results for the first setup differ from the analytical solution of the continuum scale advection-dispersion-reaction equation studied by Gramling et al. (2002), which results in an overstimation quantity of reaction product (C). In the second setup, results show that actual reaction rates are bigger than the obtained from artificially mixing the system by averaging the concentration vertically. - LITERATURE Gramling, C. M.,Harvey, C. F., Meigs, and L. C., (2002). Reactive transport in porous media: A comparison of model prediction with laboratory visualization, Environ. Sci
Adaptive multiresolution modeling of groundwater flow in heterogeneous porous media
NASA Astrophysics Data System (ADS)
Malenica, Luka; Gotovac, Hrvoje; Srzic, Veljko; Andric, Ivo
2016-04-01
Proposed methodology was originally developed by our scientific team in Split who designed multiresolution approach for analyzing flow and transport processes in highly heterogeneous porous media. The main properties of the adaptive Fup multi-resolution approach are: 1) computational capabilities of Fup basis functions with compact support capable to resolve all spatial and temporal scales, 2) multi-resolution presentation of heterogeneity as well as all other input and output variables, 3) accurate, adaptive and efficient strategy and 4) semi-analytical properties which increase our understanding of usually complex flow and transport processes in porous media. The main computational idea behind this approach is to separately find the minimum number of basis functions and resolution levels necessary to describe each flow and transport variable with the desired accuracy on a particular adaptive grid. Therefore, each variable is separately analyzed, and the adaptive and multi-scale nature of the methodology enables not only computational efficiency and accuracy, but it also describes subsurface processes closely related to their understood physical interpretation. The methodology inherently supports a mesh-free procedure, avoiding the classical numerical integration, and yields continuous velocity and flux fields, which is vitally important for flow and transport simulations. In this paper, we will show recent improvements within the proposed methodology. Since "state of the art" multiresolution approach usually uses method of lines and only spatial adaptive procedure, temporal approximation was rarely considered as a multiscale. Therefore, novel adaptive implicit Fup integration scheme is developed, resolving all time scales within each global time step. It means that algorithm uses smaller time steps only in lines where solution changes are intensive. Application of Fup basis functions enables continuous time approximation, simple interpolation calculations across
Numerical simulation on the reduction of flow heterogeneity in the biofilter media
NASA Astrophysics Data System (ADS)
Yan, Weiwei; Liu, Xingli; Wu, Jie; Wei, Yikun; Xu, Peng
2016-02-01
The biofilters are the ideal solutions for the biological treatment of air pollutants. However, there exists strong flow heterogeneity in porous media that degrades the removal efficiency of biofilters. Thus, the effects of Darcy number, Reynolds number and porosity of porous media on the reduction of flow heterogeneity in three biofilter models were numerically studied by the lattice Boltzmann method. The simulation results lead to three conclusions: (1) The Darcy number has dominant influence on the flow heterogeneity in the biofilters. The reduction of flow heterogeneity can be realized by designing a comparatively low Darcy number. (2) The Reynolds number has obvious effect on the flow heterogeneity in the biofilters. However, the reduction of flow heterogeneity cannot be effectively established by regulating the Reynolds number. (3) The property of porous media greatly influences the flow heterogeneity in the biofilters. The present results are helpful for the optimized design of practical biofilter models.
Scaling of flow and transport behavior in heterogeneous groundwater systems
NASA Astrophysics Data System (ADS)
Scheibe, Timothy; Yabusaki, Steven
1998-11-01
Three-dimensional numerical simulations using a detailed synthetic hydraulic conductivity field developed from geological considerations provide insight into the scaling of subsurface flow and transport processes. Flow and advective transport in the highly resolved heterogeneous field were modeled using massively parallel computers, providing a realistic baseline for evaluation of the impacts of parameter scaling. Upscaling of hydraulic conductivity was performed at a variety of scales using a flexible power law averaging technique. A series of tests were performed to determine the effects of varying the scaling exponent on a number of metrics of flow and transport behavior. Flow and transport simulation on high-performance computers and three-dimensional scientific visualization combine to form a powerful tool for gaining insight into the behavior of complex heterogeneous systems. Many quantitative groundwater models utilize upscaled hydraulic conductivity parameters, either implicitly or explicitly. These parameters are designed to reproduce the bulk flow characteristics at the grid or field scale while not requiring detailed quantification of local-scale conductivity variations. An example from applied groundwater modeling is the common practice of calibrating grid-scale model hydraulic conductivity or transmissivity parameters so as to approximate observed hydraulic head and boundary flux values. Such parameterizations, perhaps with a bulk dispersivity imposed, are then sometimes used to predict transport of reactive or non-reactive solutes. However, this work demonstrates that those parameters that lead to the best upscaling for hydraulic conductivity and head do not necessarily correspond to the best upscaling for prediction of a variety of transport behaviors. This result reflects the fact that transport is strongly impacted by the existence and connectedness of extreme-valued hydraulic conductivities, in contrast to bulk flow which depends more strongly on
Flow heterogeneity following global no-flow ischemia in isolated rabbit heart
Marshall, Robert C.; Powers-Risius, Patricia; Reutter, Bryan W.; Schustz, Amy M.; Kuo, Chaincy; Huesman, Michelle K.; Huesman, Ronald H.
2003-02-01
The purpose of this study was to evaluate flow heterogeneity and impaired reflow during reperfusion following 60 min global no-flow ischemia in the isolated rabbit heart. Radiolabeled microspheres were used to measure relative flow in small left ventricular (LV) segments in five ischemia + reperfused hearts and in five non-ischemic controls. Although variable in the post-ischemic hearts, flow heterogeneity was increased relative to pre-ischemia for the whole LV (0.92 plus or minus 0.41 vs. 0.37 plus or minus 0.07, P < 0.05) as well as the subendocardium (Endo) and subepicardium (Epi) considered separately (endo: 1.28 plus or minus 0.74 vs. 0.30 plus or minus 0.09; epi: 0.69 plus or minus 0.22 vs. 0.38 plus or minus 0.08; P < 0.05 for both comparisons) during early reperfusion. There were also segments with abnormally reduced reflow. The number of segments with abnormally reduced reflow increased as flow heterogeneity increased. Abnormally reduced reflow indicates that regional ischemia can persist despite restoration of normal global flow. In addition, the relationship between regional and global flow is altered and venous outflow is derived from regions with continued perfusion and not the whole LV. These observations emphasize the need to quantify regional reflow during reperfusion following sustained no-flow ischemia in the isolated rabbit heart.
Small scale flow processes in aqueous heterogeneous porous media
Rashidi, M.; Dickenson, E.
1996-04-01
Small scale flow processes in aqueous heterogeneous porous systems have been studied experimentally via novel nonintrusive fluorescence imaging techniques. The techniques involve 3D visualization and quantification of flow fields within a refractive index-matched transparent porous column. The refractive index-matching yields a transparent porous medium, free from any scattering and refraction at the solid-liquid interfaces, as a result allowing direct optical probing at any point within the porous system. By illuminating the porous regions within the column with a planar sheet of laser beam, flow processes through the porous medium can be observed microscopically, and qualitative and quantitative in-pore transport information can be obtained at a good resolution and a good accuracy. A CCD camera is used to record the fluorescent images at every vertical plane location while sweeping back and forth across the column. These digitized flow images are then analyzed and accumulated over a 3D volume within the column. Series of flow experiments in aqueous, refractive index-matched, porous systems packed with natural mineral particles have been performed successfully in these laboratories.
Modeling flow in a pressure-sensitive, heterogeneous medium
Vasco, Donald W.; Minkoff, Susan E.
2009-06-01
Using an asymptotic methodology, including an expansion in inverse powers of {radical}{omega}, where {omega} is the frequency, we derive a solution for flow in a medium with pressure dependent properties. The solution is valid for a heterogeneous medium with smoothly varying properties. That is, the scale length of the heterogeneity must be significantly larger then the scale length over which the pressure increases from it initial value to its peak value. The resulting asymptotic expression is similar in form to the solution for pressure in a medium in which the flow properties are not functions of pressure. Both the expression for pseudo-phase, which is related to the 'travel time' of the transient pressure disturbance, and the expression for pressure amplitude contain modifications due to the pressure dependence of the medium. We apply the method to synthetic and observed pressure variations in a deforming medium. In the synthetic test we model one-dimensional propagation in a pressure-dependent medium. Comparisons with both an analytic self-similar solution and the results of a numerical simulation indicate general agreement. Furthermore, we are able to match pressure variations observed during a pulse test at the Coaraze Laboratory site in France.
Skeletal muscle blood flow and flow heterogeneity during dynamic and isometric exercise in humans.
Laaksonen, Marko S; Kalliokoski, Kari K; Kyröläinen, Heikki; Kemppainen, Jukka; Teräs, Mika; Sipilä, Hannu; Nuutila, Pirjo; Knuuti, Juhani
2003-03-01
The effects of dynamic and intermittent isometric knee extension exercises on skeletal muscle blood flow and flow heterogeneity were studied in seven healthy endurance-trained men. Regional muscle blood flow was measured using positron emission tomography (PET) and an [(15)O]H(2)O tracer, and electromyographic (EMG) activity was recorded in the quadriceps femoris (QF) muscle during submaximal intermittent isometric and dynamic exercises. QF blood flow was 61% (P = 0.002) higher during dynamic exercise. Interestingly, flow heterogeneity was 13% (P = 0.024) lower during dynamic compared with intermittent isometric exercise. EMG activity was significantly higher (P < 0.001) during dynamic exercise, and the change in EMG activity from isometric to dynamic exercise was tightly related to the change in blood flow in the vastus lateralis muscle (r = 0.98, P < 0.001) but not in the rectus femoris muscle (r = -0.09, P = 0.942). In conclusion, dynamic exercise causes higher and less heterogeneous blood flow than intermittent isometric exercise at the same exercise intensity. These responses are, at least partly, related to the increased EMG activity. PMID:12446282
Ambient Flow and Heterogeneity in Multi-Aquifer Wells
NASA Astrophysics Data System (ADS)
Hart, D. J.; Gotkowitz, M. B.; Luczaj, J. A.
2009-12-01
Multi-aquifers wells, those wells that are open to more than one aquifer, have the potential to allow large quantities of flow between aquifers. Observed rates and direction of intra-borehole flow are often complex, reflecting the heterogeneity of the aquifers and variation of farfield heads. Spinner flow logs collected from several multi-aquifer wells in southern and eastern Wisconsin indicate the importance of flows through these wells in groundwater flow systems. The Paleozoic geology of Wisconsin, composed of more-or-less flat-lying sandstones, dolomites, and shales, gives rise to layered aquifer-aquitard systems where multi-aquifer wells are relatively common. A comparison of the flows in three multi-aquifer wells that cross the Wisconsin’s Paleozoic units showed heterogeniety in aquifers commonly thought to be homogeneous. Variation of the intra-borehole flow in a well gives an indication of heterogeneity and farfield heads in the aquifers. In the first example, the system was relatively simple, consisting of an aquitard (Eau Claire shale) between an upper aquifer (Wonewoc sandstone) and a lower aquifer (Mt Simon sandstone). Heads in the upper aquifer are higher than those in the lower aquifer. In this well, flows gradually increased with depth in the upper aquifer, remained constant in the aquitard, and then gradually decreased with depth in the lower aquifer. The gradual changes indicate relatively homogenous upper and lower aquifers. In the second example, the system also consisted of an aquitard (Tunnel City Group) between an upper aquifer (Sinnipee dolomite and the St. Peter sandstone) and a lower aquifer (Elk Mound Ground). As in the first example, heads in the upper aquifer are greater than those in the lower sandstone aquifer. In contrast to the first example, there were abrupt changes in intra-borehole flow in the upper aquifer, sometimes of more than 180 liters/minute over an interval of less than a meter. Caliper and television logging showed
Macrodispersion by diverging radial flows in randomly heterogeneous porous media
NASA Astrophysics Data System (ADS)
Severino, Gerardo; Santini, Alessandro; Sommella, Angelo
2011-04-01
Radial flow takes place in a heterogeneous porous formation where the transmissivity T is modelled as a stationary random space function ( RSF). The steady flow is driven by a given rate, and the mean velocity is radial. A pulse-like of a tracer is injected in the porous formation, and the thin plume spreads due to the fluctuations of the velocity which results a RSF as well. Transport is characterized by the mean front, and by the second spatial moment of the plume. We are primarily interested in tracer macrodispersion modelling. With the neglect of pore-scale dispersion, macrodispersion coefficients are computed at the second order of approximation, without neglecting the head-gradient fluctuations. Although transport is non-ergodic at the source, it is shown that ergodicity is achieved at small distances from the source. This is due to the fact that close to the source local velocities are quite large, and therefore solute particles become uncorrelated very soon. Under ergodic conditions, we compare macrodispersion mechanism in radial flows with that occurring in mean uniform flows. At short distances the spreading effect is highly enhanced by the large variability of the flow field, whereas at large distances transport exhibits a lesser dispersion due to the reduction of velocities. This supports the explanation provided by Indelman and Dagan (1999) to justify why the macrodispersivity is found smaller than that pertaining to mean uniform flows. The model is tested against a tracer transport experiment (Fernàndez-Garcia et al., 2004) by comparing the theoretical and experimental breakthrough curves. The accordance with real data, that is achieved without any fitting to concentration values, strengthens the capability of the proposed model to grasp the main features of such an experiment, the approximations as well as experimental uncertainties notwithstanding.
Multiscale modeling of metabolism, flows, and exchanges in heterogeneous organs
Bassingthwaighte, James B.; Raymond, Gary M.; Butterworth, Erik; Alessio, Adam; Caldwell, James H.
2010-01-01
Large-scale models accounting for the processes supporting metabolism and function in an organ or tissue with a marked heterogeneity of flows and metabolic rates are computationally complex and tedious to compute. Their use in the analysis of data from positron emission tomography (PET) and magnetic resonance imaging (MRI) requires model reduction since the data are composed of concentration–time curves from hundreds of regions of interest (ROI) within the organ. Within each ROI, one must account for blood flow, intracapillary gradients in concentrations, transmembrane transport, and intracellular reactions. Using modular design, we configured a whole organ model, GENTEX, to allow adaptive usage for multiple reacting molecular species while omitting computation of unused components. The temporal and spatial resolution and the number of species are adaptable and the numerical accuracy and computational speed is adjustable during optimization runs, which increases accuracy and spatial resolution as convergence approaches. An application to the interpretation of PET image sequences after intravenous injection of 13NH3 provides functional image maps of regional myocardial blood flows. PMID:20201893
Uncertainty quantification for flow in highly heterogeneous porous media
Tartakovsky, D. M.; Xiu, D.
2004-01-01
Natural porous media are highly heterogeneous and characterized by parameters that are often uncertain due to the lack of sufficient data. This uncertainty (randomness) occurs on a multiplicity of scales. We focus on geologic formations with the two dominant scales of uncertainty: a large-scale uncertainty in the spatial arrangement of geologic facies and a small-scale uncertainty in the parameters within each facies. We propose an approach that combines random domain decompositions (RDD) and polynomial chaos expansions (PCE) to account for the large- and small-scales of uncertainty, respectively. We present a general framework and use a one-dimensional flow example to demonstrate that our combined approach provides robust, non-perturbative approximations for the statistics of the system states.
On fluid flow in a heterogeneous medium under nonisothermal conditions
D.W., Vasco
2010-11-01
An asymptotic technique, valid in the presence of smoothly-varying heterogeneity, provides explicit expressions for the velocity of a propagating pressure and temperature disturbance. The governing equations contain nonlinear terms due to the presence of temperature-dependent coefficients and due to the advection of fluids with differing temperatures. Two cases give well-defined expressions in terms of the parameters of the porous medium: the uncoupled propagation of a pressure disturbance and the propagation of a fully coupled temperature and pressure disturbance. The velocity of the coupled disturbance or front, depends upon the medium parameters and upon the change in temperature and pressure across the front. For uncoupled flow, the semi-analytic expression for the front velocity reduces to that associated with a linear diffusion equation. A comparison of the asymptotic travel time estimates with calculations from a numerical simulator indicates reasonably good agreement for both uncoupled and coupled disturbances.
Strategy for understanding gas-solid riser hydrodynamics and other LANL status items
Kashiwa, B. A.
2002-01-01
The talk presents the status of work in progress in the area of momentum transport theory in turbulent gas-solid multiphase flow. Previous installments have reported details of the theory, and validation results. This talk provides a grand overview of how the details of dynamic simulations in 3D, 2D, 1D and 0D, all fit together to form a consistent strategy for understanding gas-solid riser hydrodynamics. The circulating fluidized bed is the canonical example for showing how the strategy works. Performance of the procedure is shown by comparison to data recently obtained by Sandia National Laboratory. Status of other LANL efforts is also mentioned.
Metalized Heterogeneous Detonation and Dense Reactive Particle Flow
NASA Astrophysics Data System (ADS)
Zhang, Fan
2011-06-01
A metalized explosive system comprises a condensed-phase explosive and a large quantity of reactive metal particles, in an attempt to exploit the high energy content of the particles through their rapid combustion. Detonation in such heterogeneous matter and subsequent reaction of the metal particles under strong shock conditions constitute a new area in the dynamics and combustion of dense particle flow, which is characterized by a large number of particle interactions through shocked interstitial fluid or direct inelastic collisions. Progress in the fundamentals of this field is reviewed with an emphasis on particle aspects in three parts: detonation-particle interactions, particle ignition and reaction, and dynamic instabilities of particles. The paper begins with the unique characteristics of the subject heterogeneous detonation including the breakdown of the CJ detonation and detonation shock interaction effects on wave velocity, critical failure diameter, momentum transfer and morphology of particles. Secondly, the concept of a critical diameter for particle ignition, shocked particle reaction mechanism, multiple heat release history and aerodynamic secondary fragmentation combustion are described. Thirdly, particle dynamic instabilities lead to clustering, collisions and coherent jet structure and influence not only the aerodynamic trajectories but also the particle-gas mixing and subsequent energy release. Their mechanisms are revealed through the role of stochastic particle interactions with shock waves and fluid vorticity and turbulence on the formation of the trajectory instabilities of the particles. A hybrid detonation mode is finally invoked to exploit the energy release limit of metal particles. The paper is portrayed in a large number of experiments combined with meso-scale modeling and theoretical explanation.
Effective parameters for two-phase flow in a porous medium with periodic heterogeneities
NASA Astrophysics Data System (ADS)
Ataie-Ashtiani, B.; Hassanizadeh, S. M.; Oostrom, M.; Celia, M. A.; White, M. D.
2001-05-01
Computational simulations of two-phase flow in porous media are used to investigate the feasibility of replacing a porous medium containing heterogeneities with an equivalent homogeneous medium. Simulations are performed for the case of infiltration of a dense nonaqueous phase liquid (DNAPL) in a water-saturated, heterogeneous porous medium. For two specific porous media, with periodic and rather simple heterogeneity patterns, the existence of a representative elementary volume (REV) is studied. Upscaled intrinsic permeabilities and upscaled nonlinear constitutive relationships for two-phase flow systems are numerically calculated and the effects of heterogeneities are evaluated. Upscaled capillary pressure-saturation curves for drainage are found to be distinctly different from the lower-scale curves for individual regions of heterogeneity. Irreducible water saturation for the homogenized medium is found to be much larger than the corresponding lower-scale values. Numerical simulations for both heterogeneous and homogeneous representations of the considered porous media are carried out. Although the homogenized model simulates the spreading behavior of DNAPL reasonably well, it still fails to match completely the results form the heterogeneous simulations. This seems to be due, in part, to the nonlinearities inherent to multiphase flow systems. Although we have focussed on a periodic heterogeneous medium in this study, our methodology is applicable to other forms of heterogeneous media. In particular, the procedure for identification of a REV, and associated upscaled constitutive relations, can be used for randomly heterogeneous or layered media as well.
A novel planar flow cell for studies of biofilm heterogeneity and flow-biofilm interactions
Zhang, Wei; Sileika, Tadas S.; Chen, Cheng; Liu, Yang; Lee, Jisun; Packman, Aaron I.
2012-01-01
Biofilms are microbial communities growing on surfaces, and are ubiquitous in nature, in bioreactors, and in human infection. Coupling between physical, chemical, and biological processes is known to regulate the development of biofilms; however, current experimental systems do not provide sufficient control of environmental conditions to enable detailed investigations of these complex interactions. We developed a novel planar flow cell that supports biofilm growth under complex two-dimensional fluid flow conditions. This device provides precise control of flow conditions and can be used to create well-defined physical and chemical gradients that significantly affect biofilm heterogeneity. Moreover, the top and bottom of the flow chamber are transparent, so biofilm growth and flow conditions are fully observable using non-invasive confocal microscopy and high-resolution video imaging. To demonstrate the capability of the device, we observed the growth of Pseudomonas aeruginosa biofilms under imposed flow gradients. We found a positive relationship between patterns of fluid velocity and biofilm biomass because of faster microbial growth under conditions of greater local nutrient influx, but this relationship eventually reversed because high hydrodynamic shear leads to the detachment of cells from the surface. These results reveal that flow gradients play a critical role in the development of biofilm communities. By providing new capability for observing biofilm growth, solute and particle transport, and net chemical transformations under user-specified environmental gradients, this new planar flow cell system has broad utility for studies of environmental biotechnology and basic biofilm microbiology, as well as applications in bioreactor design, environmental engineering, biogeochemistry, geomicrobiology, and biomedical research. PMID:21656713
NASA Astrophysics Data System (ADS)
Kang, P. K.; Le Borgne, T.; Dentz, M.; Bour, O.; Juanes, R.
2014-12-01
Quantitative modeling of flow and transport through fractured geological media is challenging due to the inaccessibility of the underlying medium properties and the complex interplay between heterogeneity and small scale transport processes such as heterogeneous advection, matrix diffusion, hydrodynamic dispersion and adsorption. This complex interplay leads to anomalous (non-Fickian) transport behavior, the origin of which remains a matter of debate: whether it arises from variability in fracture permeability (velocity heterogeneity), connectedness in the fracture network (velocity correlation), or interaction between fractures and matrix. Here we show that this uncertainty of heterogeneity- vs. correlation-controlled transport can be resolved by combining convergent and push-pull tracer tests because flow reversibility is strongly dependent on correlation, whereas late-time scaling of breakthrough curves is mainly controlled by heterogeneity. We build on this insight, and propose a Lagrangian statistical model that takes the form of a continuous time random walk (CTRW) with correlated particle velocities. In this framework, flow heterogeneity and flow correlation are quantified by a Markov process of particle transition times that is characterized by a distribution function and a transition probability. Our transport model captures the anomalous behavior in the breakthrough curves for both push-pull and convergent flow geometries, with the same set of parameters. We validate our model in the Ploemeur observatory in France. Thus, the proposed correlated CTRW modeling approach provides a simple yet powerful framework for characterizing the impact of flow correlation and heterogeneity on transport in fractured media.
ADAPTIVE-GRID SIMULATION OF GROUNDWATER FLOW IN HETEROGENEOUS AQUIFERS. (R825689C068)
The prediction of contaminant transport in porous media requires the computation of the flow velocity. This work presents a methodology for high-accuracy computation of flow in a heterogeneous isotropic formation, employing a dual-flow formulation and adaptive...
Evaluation of wall boundary condition parameters for gas-solids fluidized bed simulations
Li, Tingwen; Benyahia, Sofiane
2013-10-01
Wall boundary conditions for the solids phase have significant effects on numerical predictions of various gas-solids fluidized beds. Several models for the granular flow wall boundary condition are available in the open literature for numerical modeling of gas-solids flow. In this study, a model for specularity coefficient used in Johnson and Jackson boundary conditions by Li and Benyahia (AIChE Journal, 2012, 58, 2058-2068) is implemented in the open-source CFD code-MFIX. The variable specularity coefficient model provides a physical way to calculate the specularity coefficient needed by the partial-slip boundary conditions for the solids phase. Through a series of 2-D numerical simulations of bubbling fluidized bed and circulating fluidized bed riser, the model predicts qualitatively consistent trends to the previous studies. Furthermore, a quantitative comparison is conducted between numerical results of variable and constant specularity coefficients to investigate the effect of spatial and temporal variations in specularity coefficient.
Nelson, R.W.
1990-11-01
Groundwater theory that applies to only homogeneous systems is often too restricted to adequately solve actual groundwater pollution problems. For adequate solutions, the more general theory for heterogeneous porous systems is needed. However, the present dynamic and kinematic descriptions in heterogeneous materials have evolved largely from the restricted and less general homogeneous theory. These descriptions are inadequate because they fail to account for all the energy dissipation in the system. The basic distinguishing dynamic feature of heterogeneous flow theory from the less general homogeneous-based theory is the macroscopic rotational flow component. Specifically, existence of rotational flow components and their independence from the translational flow components are the necessary and sufficient conditions that completely differentiate between the complex lamellar heterogeneous flow theory and the simpler lamellar flow of homogeneous theory. This paper proposes a more general dynamic form of the flow equation to include the added rotational dissipation that is missing from the present Darcian description of flow in heterogeneous media. 31 refs.
Flow channeling in strongly heterogeneous porous media: A numerical study
Moreno, L.; Tsang, C.F.
1994-05-01
The variation of hydraulic conductivity in a porous medium causes the fluids flowing through it to have nonuniform velocities. Variation in fluid velocity is one of the main contributors to solute dispersion, causing a part of the contaminants dissolved in the fluid to be transported with greater than average velocities. In practical problems concerning transport of radioactive or toxic wastes, the velocity of contaminant flow may be of vital importance. This paper examines a three dimensional case, considering also the similarities and differences between parallel flow and convergent/divergent flow. Fluid flow in a porous medium is shown to perfer the most conductive paths. For a medium with strongly variable permeability this effect can be very pronounced. This paper discusses the impact of this flow distribution upon solute transport. 28 refs., 11 figs., 2 tabs.
Homogeneous-heterogeneous reactions in peristaltic flow with convective conditions.
Hayat, Tasawar; Tanveer, Anum; Yasmin, Humaira; Alsaedi, Ahmed
2014-01-01
This article addresses the effects of homogeneous-heterogeneous reactions in peristaltic transport of Carreau fluid in a channel with wall properties. Mathematical modelling and analysis have been carried out in the presence of Hall current. The channel walls satisfy the more realistic convective conditions. The governing partial differential equations along with long wavelength and low Reynolds number considerations are solved. The results of temperature and heat transfer coefficient are analyzed for various parameters of interest. PMID:25460608
Homogeneous-Heterogeneous Reactions in Peristaltic Flow with Convective Conditions
Hayat, Tasawar; Tanveer, Anum; Yasmin, Humaira; Alsaedi, Ahmed
2014-01-01
This article addresses the effects of homogeneous-heterogeneous reactions in peristaltic transport of Carreau fluid in a channel with wall properties. Mathematical modelling and analysis have been carried out in the presence of Hall current. The channel walls satisfy the more realistic convective conditions. The governing partial differential equations along with long wavelength and low Reynolds number considerations are solved. The results of temperature and heat transfer coefficient are analyzed for various parameters of interest. PMID:25460608
On the Mean Flow Behaviour in the Presence of Regional-Scale Surface Roughness Heterogeneity
NASA Astrophysics Data System (ADS)
Yang, Xiang I. A.
2016-05-01
A suite of large-eddy simulations of the neutral atmospheric boundary layer is conducted to study the mean flow response to the presence of surface roughness heterogeneity at regional scales (surface roughness heterogeneity on the scale of several boundary-layer heights). The roughness heterogeneity is imposed using alternating rough wall patches with numerically resolved rectangular roughness elements of different packing densities. The flow near the surface is found to adjust rapidly, reaching equilibrium conditions at distances on the order of a single inter-roughness element spacing. Despite the regional heterogeneity in surface roughness, it is often desirable to parametrize the entire rough wall using one single effective roughness height. To develop such a parametrization the model of Bou-Zeid et al. [Water Resources Research 40(2):1, 2004] is extended to incorporate the displacement height, d. Predictions from this parametrization are compared with the simulations, with reasonably good agreement.
NASA Astrophysics Data System (ADS)
Antonellini, Marco; Nella Mollema, Pauline
2016-04-01
Surface outcrops provide natural analogs for aquifers and they offer an opportunity to study the geometry of geologic heterogeneities in three dimensions over a range of scales. We show photographs, maps, quantitative field data of rock fractures and sedimentary features in outcrops exposed in a unique collection of many different settings. These include small-scale sedimentary structures, carbonate nodules, faults, and other fractures as documented in outcrops of porous sandstone (Utah, USA and Italy), tight sandstones (Bolivia), dolomite (Northern Italy), and carbonates (Central Italy). We simulate the geometries observed in outcrops with simple conceptual and numerical models of flow to show how important it is to recognize the appropriate attributes for the description and the process responsible for the formation of geologic heterogeneities. For example, knowing the type of structural heterogeneities (fault, joint, compaction band, stylolite, and vein) and their development mechanics helps to predict the distribution and preferential orientation of these features within an aquifer. This knowledge is particularly important for modeling of fluid flow where geophysical or borehole data are lacking. Geologic heterogeneities of sedimentary, structural or diagenetic (chemical) nature influence the fluid flow properties in many aquifers and reservoirs at scales varying over several orders of magnitude and with a spatial variability ranging from mm to tens of meters. Heterogeneities may enhance or degrade porosity and permeability, they impart anisotropy to permeability and dispersion and affect mass transport-related processes in groundwater. Furthermore, aquifer heterogeneities control aquifer continuity and compartmentalization. In fractured aquifers, geologic and diagenetic heterogeneities may affect connectivity, aperture of the flow channels or the distribution of permeability buffers, barriers and seals. Also variations in layer thickness and lithology within a
The stationary flow in a heterogeneous compliant vessel network
NASA Astrophysics Data System (ADS)
Filoche, Marcel; Florens, Magali
2011-09-01
We introduce a mathematical model of the hydrodynamic transport into systems consisting in a network of connected flexible pipes. In each pipe of the network, the flow is assumed to be steady and one-dimensional. The fluid-structure interaction is described through tube laws which relate the pipe diameter to the pressure difference across the pipe wall. We show that the resulting one-dimensional differential equation describing the flow in the pipe can be exactly integrated if one is able to estimate averages of the Reynolds number along the pipe. The differential equation is then transformed into a non linear scalar equation relating pressures at both ends of the pipe and the flow rate in the pipe. These equations are coupled throughout the network with mass conservation equations for the flow and zero pressure losses at the branching points of the network. This allows us to derive a general model for the computation of the flow into very large inhomogeneous networks consisting of several thousands of flexible pipes. This model is then applied to perform numerical simulations of the human lung airway system at exhalation. The topology of the system and the tube laws are taken from morphometric and physiological data in the literature. We find good qualitative and quantitative agreement between the simulation results and flow-volume loops measured in real patients. In particular, expiratory flow limitation which is an essential characteristic of forced expiration is found to be well reproduced by our simulations. Finally, a mathematical model of a pathology (Chronic Obstructive Pulmonary Disease) is introduced which allows us to quantitatively assess the influence of a moderate or severe alteration of the airway compliances.
Reducing Spatial Heterogeneity of MALDI Samples with Marangoni Flows During Sample Preparation.
Lai, Yin-Hung; Cai, Yi-Hong; Lee, Hsun; Ou, Yu-Meng; Hsiao, Chih-Hao; Tsao, Chien-Wei; Chang, Huan-Tsung; Wang, Yi-Sheng
2016-08-01
This work demonstrates a method to prepare homogeneous distributions of analytes to improve data reproducibility in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS). Natural-air drying processes normally result in unwanted heterogeneous spatial distributions of analytes in MALDI crystals and make quantitative analysis difficult. This study demonstrates that inducing Marangoni flows within drying droplets can significantly reduce the heterogeneity problem. The Marangoni flows are accelerated by changing substrate temperatures to create temperature gradients across droplets. Such hydrodynamic flows are analyzed semi-empirically. Using imaging mass spectrometry, changes of heterogeneity of molecules with the change of substrate temperature during drying processes are demonstrated. The observed heterogeneities of the biomolecules reduce as predicted Marangoni velocities increase. In comparison to conventional methods, drying droplets on a 5 °C substrate while keeping the surroundings at ambient conditions typically reduces the heterogeneity of biomolecular ions by 65%-80%. The observation suggests that decreasing substrate temperature during droplet drying processes is a simple and effective means to reduce analyte heterogeneity for quantitative applications. Graphical Abstract ᅟ. PMID:27126469
Reducing Spatial Heterogeneity of MALDI Samples with Marangoni Flows During Sample Preparation
NASA Astrophysics Data System (ADS)
Lai, Yin-Hung; Cai, Yi-Hong; Lee, Hsun; Ou, Yu-Meng; Hsiao, Chih-Hao; Tsao, Chien-Wei; Chang, Huan-Tsung; Wang, Yi-Sheng
2016-04-01
This work demonstrates a method to prepare homogeneous distributions of analytes to improve data reproducibility in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS). Natural-air drying processes normally result in unwanted heterogeneous spatial distributions of analytes in MALDI crystals and make quantitative analysis difficult. This study demonstrates that inducing Marangoni flows within drying droplets can significantly reduce the heterogeneity problem. The Marangoni flows are accelerated by changing substrate temperatures to create temperature gradients across droplets. Such hydrodynamic flows are analyzed semi-empirically. Using imaging mass spectrometry, changes of heterogeneity of molecules with the change of substrate temperature during drying processes are demonstrated. The observed heterogeneities of the biomolecules reduce as predicted Marangoni velocities increase. In comparison to conventional methods, drying droplets on a 5 °C substrate while keeping the surroundings at ambient conditions typically reduces the heterogeneity of biomolecular ions by 65%-80%. The observation suggests that decreasing substrate temperature during droplet drying processes is a simple and effective means to reduce analyte heterogeneity for quantitative applications.
Reducing Spatial Heterogeneity of MALDI Samples with Marangoni Flows During Sample Preparation
NASA Astrophysics Data System (ADS)
Lai, Yin-Hung; Cai, Yi-Hong; Lee, Hsun; Ou, Yu-Meng; Hsiao, Chih-Hao; Tsao, Chien-Wei; Chang, Huan-Tsung; Wang, Yi-Sheng
2016-08-01
This work demonstrates a method to prepare homogeneous distributions of analytes to improve data reproducibility in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS). Natural-air drying processes normally result in unwanted heterogeneous spatial distributions of analytes in MALDI crystals and make quantitative analysis difficult. This study demonstrates that inducing Marangoni flows within drying droplets can significantly reduce the heterogeneity problem. The Marangoni flows are accelerated by changing substrate temperatures to create temperature gradients across droplets. Such hydrodynamic flows are analyzed semi-empirically. Using imaging mass spectrometry, changes of heterogeneity of molecules with the change of substrate temperature during drying processes are demonstrated. The observed heterogeneities of the biomolecules reduce as predicted Marangoni velocities increase. In comparison to conventional methods, drying droplets on a 5 °C substrate while keeping the surroundings at ambient conditions typically reduces the heterogeneity of biomolecular ions by 65%-80%. The observation suggests that decreasing substrate temperature during droplet drying processes is a simple and effective means to reduce analyte heterogeneity for quantitative applications.
Multistep continuous-flow synthesis of (R)- and (S)-rolipram using heterogeneous catalysts
NASA Astrophysics Data System (ADS)
Tsubogo, Tetsu; Oyamada, Hidekazu; Kobayashi, Shū
2015-04-01
Chemical manufacturing is conducted using either batch systems or continuous-flow systems. Flow systems have several advantages over batch systems, particularly in terms of productivity, heat and mixing efficiency, safety, and reproducibility. However, for over half a century, pharmaceutical manufacturing has used batch systems because the synthesis of complex molecules such as drugs has been difficult to achieve with continuous-flow systems. Here we describe the continuous-flow synthesis of drugs using only columns packed with heterogeneous catalysts. Commercially available starting materials were successively passed through four columns containing achiral and chiral heterogeneous catalysts to produce (R)-rolipram, an anti-inflammatory drug and one of the family of γ-aminobutyric acid (GABA) derivatives. In addition, simply by replacing a column packed with a chiral heterogeneous catalyst with another column packed with the opposing enantiomer, we obtained antipole (S)-rolipram. Similarly, we also synthesized (R)-phenibut, another drug belonging to the GABA family. These flow systems are simple and stable with no leaching of metal catalysts. Our results demonstrate that multistep (eight steps in this case) chemical transformations for drug synthesis can proceed smoothly under flow conditions using only heterogeneous catalysts, without the isolation of any intermediates and without the separation of any catalysts, co-products, by-products, and excess reagents. We anticipate that such syntheses will be useful in pharmaceutical manufacturing.
Multistep continuous-flow synthesis of (R)- and (S)-rolipram using heterogeneous catalysts.
Tsubogo, Tetsu; Oyamada, Hidekazu; Kobayashi, Shū
2015-04-16
Chemical manufacturing is conducted using either batch systems or continuous-flow systems. Flow systems have several advantages over batch systems, particularly in terms of productivity, heat and mixing efficiency, safety, and reproducibility. However, for over half a century, pharmaceutical manufacturing has used batch systems because the synthesis of complex molecules such as drugs has been difficult to achieve with continuous-flow systems. Here we describe the continuous-flow synthesis of drugs using only columns packed with heterogeneous catalysts. Commercially available starting materials were successively passed through four columns containing achiral and chiral heterogeneous catalysts to produce (R)-rolipram, an anti-inflammatory drug and one of the family of γ-aminobutyric acid (GABA) derivatives. In addition, simply by replacing a column packed with a chiral heterogeneous catalyst with another column packed with the opposing enantiomer, we obtained antipole (S)-rolipram. Similarly, we also synthesized (R)-phenibut, another drug belonging to the GABA family. These flow systems are simple and stable with no leaching of metal catalysts. Our results demonstrate that multistep (eight steps in this case) chemical transformations for drug synthesis can proceed smoothly under flow conditions using only heterogeneous catalysts, without the isolation of any intermediates and without the separation of any catalysts, co-products, by-products, and excess reagents. We anticipate that such syntheses will be useful in pharmaceutical manufacturing. PMID:25877201
Analysis of hydrodynamic conditions in adjacent free and heterogeneous porous flow domains
NASA Astrophysics Data System (ADS)
Das, D. B.; Hanspal, N. S.; Nassehi, V.
2005-09-01
The existence of a free-flow domain (e.g. a liquid layer) adjacent to a porous medium is a common occurrence in many environmental and petroleum engineering problems. The porous media may often contain various forms of heterogeneity, e.g. layers, fractures, micro-scale lenses, etc. These heterogeneities affect the pressure distribution within the porous domain. This may influence the hydrodynamic conditions at the free-porous domain interface and, hence, the combined flow behaviour. Under steady-state conditions, the heterogeneities are known to have negligible effects on the coupled flow behaviour. However, the significance of the heterogeneity effects on coupled free and porous flow under transient conditions is not certain. In this study, numerical simulations have been carried out to investigate the effects of heterogeneous (layered) porous media on the hydrodynamics conditions in determining the behaviour of combined free and porous regimes. Heterogeneity in the porous media is introduced by defining a domain composed of two layers of porous media with different values of intrinsic permeability. The coupling of the governing equations of motion in free and porous domains has been achieved through the well-known Beavers and Joseph interfacial condition. Of special interest in this work are porous domains with flow-through ends. They represent the general class of problems where large physical domains are truncated to smaller sections for ease of mathematical analysis. However, this causes a practical difficulty in modelling such systems. This is because the information on flow behaviour, i.e. boundary conditions at the truncated sections, is usually not available. Use of artificial boundary conditions to solve these problems effectively implies the imposition of conditions that do not necessarily match with the solutions required for the interior of the domain. This difficulty is resolved in this study by employing stress-free boundary conditions at the open
Enriched boundary layers for heterogeneous reaction in stirred microfluidic flows
NASA Astrophysics Data System (ADS)
Kirtland, Joseph; Stroock, Abraham
2008-11-01
The rate of transport of a scalar from a fluid stream to a reactive surface depends on both the character of the flow and the scalar concentration profile incident on the surface. Uniaxial flows tend to form thick regions of low concentration near the reactive surface, leading to decreased rates of scalar transport. For irreversible reactions, this effect can be mitigated through efficient mixing of the bulk. This ensures that the average concentration is incident on the reactive surface, and that concentration boundary layers are kept thin. Coupled reversible reactions, such as those occurring at the electrodes of an electrochemical cell, can complicate the analysis of such a system. In a stirred microfluidic electrochemical cell, depletion of the reactant of the forward reaction implies enrichment of the reactant of the reverse reaction. This enriched fluid can bypass the well mixed bulk, leading to increased scaling of the overall transport process with the Péclet number Pe, even in cases of efficient bulk mixing. We present numerical and experimental results in several such flows and discuss situations where this enrichment can be beneficial (amplification in sensors) or detrimental (quantitative concentration measurement). J. Kirtland, G. McGraw, A. Stroock. Physics of Fluids 18, 073602 (2006).
Apaydin, Osman G.; Bertin, Henri; Castanier, Louis M.; Kovscek, Anthony R.
1999-08-09
Foam is used to reduce the high mobility of gas-drive fluids and improve the contact between oil and these injected fluids. We require a better understanding of the effect of surfactant concentration on foam flow in porous media. Besides this, the literature on foam flow and transport in heterogeneous systems is sparse although the field situation is primarily heterogeneous and multidimensional. In this study, foam flow experiments were conducted first in homogeneous sand packs to investigate the effect of surfactant concentration on foam flow and then a heterogeneous experimental setup was prepared to observe heterogeneity and multidimensional flow effects on foam propagation. The homogeneous core experiments were conducted in a cylindrical aluminum core holder that was packed with a uniform Ottawa sand. Sand permeability is about 7.0 Darcy. The experiments were interpreted in terms of evolution of in-situ water saturation as a function of time by the usage of CT scanner, cumulative water, and pressure drop across the core. At very low surfactant concentration, no significant benefit was observed. But when stable foam generation started sweep efficiency (water recovery), breakthrough time, and pressure drop increased as surfactant concentration increased.
Non-Newtonian fluid flow over a heterogeneously slippery surface
NASA Astrophysics Data System (ADS)
Haase, A. Sander; Wood, Jeffery A.; Sprakel, Lisette M. J.; Lammertink, Rob G. H.
2015-11-01
The no-slip boundary condition does not always hold. In the past, we have investigated the influence of effective wall slip on interfacial transport for a bubble mattress - a superhydrophobic surface consisting of an array of transverse gas-filled grooves. We proved experimentally that the amount of effective wall slip depends on the bubble protrusion angle and the surface porosity (Karatay et al., PNAS 110, 2013), and predicted that mass transport can be enhanced significantly (Haase et al., Soft Matter 9, 2013). Both studies involve the flow of water. In practise, however, many liquids encountered are non-Newtonian, like blood and polymer solutions. This raises some interesting questions. How does interfacial transport depend on the rheological properties of the liquid? Does the time-scale of the experiment matter? A bubble mattress is a suitable platform to investigate this, due to local variations in shear rate. We predict that for shear-thinning liquids, compared to water, the amount of wall slip can be enhanced considerably, although this depends on the applied flow rate. Experiments are performed to proof this behaviour. Simulations are used to assess what will happen when the characteristic time-scale of the system matches the relaxation time of the visco-elastic liquid. R.G.H.L. acknowledges the European Research Council for the ERC starting grant 307342-TRAM.
Method for improved gas-solids separation
Kusik, Charles L.; He, Bo X.
1990-01-01
Methods are disclosed for the removal of particulate solids from a gas stream at high separation efficiency, including the removal of submicron size particles. The apparatus includes a cyclone separator type of device which contains an axially mounted perforated cylindrical hollow rotor. The rotor is rotated at high velocity in the same direction as the flow of an input particle-laden gas stream to thereby cause enhanced separation of particulate matter from the gas stream in the cylindrical annular space between the rotor and the sidewall of the cyclone vessel. Substantially particle-free gas passes through the perforated surface of the spinning rotor and into the hollow rotor, from when it is discharged out of the top of the apparatus. Separated particulates are removed from the bottom of the vessel.
Method for improved gas-solids separation
Kusik, C.L.; He, B.X.
1990-11-13
Methods are disclosed for the removal of particulate solids from a gas stream at high separation efficiency, including the removal of submicron size particles. The apparatus includes a cyclone separator type of device which contains an axially mounted perforated cylindrical hollow rotor. The rotor is rotated at high velocity in the same direction as the flow of an input particle-laden gas stream to thereby cause enhanced separation of particulate matter from the gas stream in the cylindrical annular space between the rotor and the sidewall of the cyclone vessel. Substantially particle-free gas passes through the perforated surface of the spinning rotor and into the hollow rotor, from where it is discharged out of the top of the apparatus. Separated particulates are removed from the bottom of the vessel. 4 figs.
A Multidimensional Eulerian Model for Simulating Gas-Solids Flow
Energy Science and Technology Software Center (ESTSC)
1993-12-13
FORCE2 is a fundamentally based three-dimensional numerical model for simulating fluid-bed hydrodynamics for a wide range of fluid beds, from laboratory to plant scale. It is based upon the ''two-fluid'' modeling approach and includes surface permeabilities, volume porosities, and distributed resistances.
Sott, Kristin; Gebäck, Tobias; Pihl, Maria; Lorén, Niklas; Hermansson, Anne-Marie; Heintz, Alexei; Rasmuson, Anders
2013-05-15
A methodology for studying flow in heterogeneous soft microstructures has been developed. The methodology includes: (1) model fractal or random heterogeneous microstructures fabricated in PDMS and characterised using CLSM; (2) μPIV measurements; (3) Lattice-Boltzmann simulations of flow. It has been found that the flow behaviour in these model materials is highly dependent on pore size as well as on the connectivity and occurrence of dead ends. The experimental flow results show good agreement with predictions from the Lattice-Boltzmann modelling. These simulations were performed in geometries constructed from 3D CLSM images of the actual PDMS structures. Given these results, mass transport behaviour may be predicted for even more complex structures, like gels or composite material in, e.g., food or biomaterials. This is a step in the direction towards predictive science with regards to tailoring soft biomaterials for specific mass transport properties. PMID:23489610
NASA Astrophysics Data System (ADS)
Fox, Aryeh; Laube, Gerrit; Schmidt, Christian; Fleckenstein, Jan H.; Arnon, Shai
2015-04-01
Biogeochemical processes in streams are affected by water exchange between the surface and subsurface environments (e.g. hyporheic exchange). It has previously been shown that hyporheic exchange is strongly affected by the local morphology of the streambed and the flow conditions, including overlying water velocity and losing or gaining fluxes. The objectives of this work were to evaluate how the streambed heterogeneity is affecting hyporheic exchange. In addition, we tested how losing or gaining flow conditions are affecting the hyporheic exchange fluxes and the spatial distribution of the flow paths within the streambed. Experiments measuring the combined effect of streambed heterogeneity and losing and gaining flow conditions on hyporheic exchange were conducted in a laboratory flume system (640 cm long and 30 cm wide). The flow in the flume is fully controlled including gaining or losing fluxes, and it was packed with heterogeneous sediments. An estimate of the solute exchange between the stream and the sediment was obtained from the analysis of a salt tracer (NaCl) injection into the overlying water, which then was monitored by an electrical conductivity meter. In addition, dye injections into the overlying water were used to visualize the effect of sediment heterogeneity on the flow paths in the streambed. Experimental results showed that increasing losing and gaining fluxes resulted in a similar decline in the hyporheic exchange flux as previously observed for a homogenous streambed. However the location in which the hyporheic exchange takes place is different and is strongly influenced by the sediment heterogeneity. The spatial distribution of hyporheic exchange within the streambed will be discussed in light of the distribution of the local, horizontal and vertical hydraulic conductivities.
River-aquifer interactions, geologic heterogeneity, and low-flow management
Fleckenstein, J.H.; Niswonger, R.G.; Fogg, G.E.
2006-01-01
Low river flows are commonly controlled by river-aquifer exchange, the magnitude of which is governed by hydraulic properties of both aquifer and aquitard materials beneath the river. Low flows are often important ecologically. Numerical simulations were used to assess how textural heterogeneity of an alluvial system influences river seepage and low flows. The Cosumnes River in California was used as a test case. Declining fall flows in the Cosumnes River have threatened Chinook salmon runs. A ground water-surface water model for the lower river basin was developed, which incorporates detailed geostatistical simulations of aquifer heterogeneity. Six different realizations of heterogeneity and a homogenous model were run for a 3-year period. Net annual seepage from the river was found to be similar among the models. However, spatial distribution of seepage along the channel, water table configuration and the level of local connection, and disconnection between the river and aquifer showed strong variations among the different heterogeneous models. Most importantly, the heterogeneous models suggest that river seepage losses can be reduced by local reconnections, even when the regional water table remains well below the riverbed. The percentage of river channel responsible for 50% of total river seepage ranged from 10% to 26% in the heterogeneous models as opposed to 23% in the homogeneous model. Differences in seepage between the models resulted in up to 13 d difference in the number of days the river was open for salmon migration during the critical fall months in one given year. Copyright ?? 2006 The Author(s).
A disaggregation theory for predicting concentration gradient distributions in heterogeneous flows
NASA Astrophysics Data System (ADS)
Le Borgne, Tanguy; Huck, Peter; Dentz, Marco; Villermaux, Emmanuel
2016-04-01
Many transport processes occurring in fluid flows depend on concentration gradients, including a wide range of chemical reactions, such as mixing-driven precipitation, and biological processes, such as chemotaxis. A general framework for predicting the distribution of concentration gradients in heterogeneous flow fields is proposed based on a disaggregation theory. The evolution of concentration fields under the combined action of heterogeneous advection and diffusion is quantified from the analysis of the development and aggregation of elementary lamellar structures, which naturally form under the stretching action of flow fields. Therefore spatial correlations in concentrations can be estimated based on the understanding of the lamellae aggregation process that determine the concentration levels at neighboring spatial locations. Using this principle we quantify the temporal evolution of the concentration gradient Probability Density Functions in heterogeneous Darcy fields for arbitrary Peclet numbers. This approach is shown to provide accurate predictions of concentration gradient distributions for a range of flow systems, including turbulent flows and low Reynolds number porous media flows, for confined and dispersing mixtures.
Transport phenomena of reactive fluid flow in heterogeneous combustion processes.
NASA Technical Reports Server (NTRS)
Hung, W. S. Y.; Chen, C. S.; Haviland, J. K.
1972-01-01
A previously developed computer program was used to model two transient hybrid combustion processes involving tubes of solid Plexiglas. In the first study, representing combustion of a hybrid rocket, the oxidizing gas was oxygen, and calculations were continued sufficiently long to obtain steady-state values. Systematic variations were made in reaction rate constant, mass flow rate, and pressure, alternatively using constant and temperature dependent regression rate models for the fuel surface. Consistent results were obtained, as is evidenced by the values for the mass function of the reaction product and the flame temperature, for which plots are supplied. In the second study, fire initiation in a duct was studied, with an air mixture as the oxidizing gas. It was demonstrated that a satisfactory flame spread mechanism could be reproduced on the computer. In both of the above applications, the general, transient, two-dimensional conservation equations were represented, together with chemical reactions, solid-fuel interface conditions, and heat conduction in the solid fuel.
Correlation velocities in heterogeneous bidirectional cellular automata traffic flow
NASA Astrophysics Data System (ADS)
Lakouari, N.; Bentaleb, K.; Ez-Zahraouy, H.; Benyoussef, A.
2015-12-01
Traffic flow behavior and velocity correlation in a bidirectional two lanes road are studied using Cellular Automata (CA) model within a mixture of fast and slow vehicles. The behaviors of the Inter-lane and Intra-lane Velocity Correlation Coefficients (V.C.C.) due to the interactions between vehicles in the same lane and the opposite lane as a function of the density are investigated. It is shown that high densities in one lane lead to large cluster in the second one, which decreases the Intra-lane velocity correlations and thereby form clusters in the opposite lane. Moreover, we have found that there is a critical density over which the Inter-lane V.C.C. occurs, but below which no Inter-lane V.C.C. happens. The spatiotemporal diagrams correspond to those regions are derived numerically. Furthermore, the effect of the overtaking probability in one lane on the Intra-lane V.C.C. in the other lane is also investigated. It is shown that the decrease of the overtaking probability in one lane decreases slightly the Intra-lane V.C.C. at intermediate density regimes in the other lane, which improves the current, as well as the Inter-lane V.C.C. decreases.
NASA Astrophysics Data System (ADS)
Chang, Ching-Min; Yeh, Hund-Der
2009-01-01
This paper describes a stochastic analysis of steady state flow in a bounded, partially saturated heterogeneous porous medium subject to distributed infiltration. The presence of boundary conditions leads to non-uniformity in the mean unsaturated flow, which in turn causes non-stationarity in the statistics of velocity fields. Motivated by this, our aim is to investigate the impact of boundary conditions on the behavior of field-scale unsaturated flow. Within the framework of spectral theory based on Fourier-Stieltjes representations for the perturbed quantities, the general expressions for the pressure head variance, variance of log unsaturated hydraulic conductivity and variance of the specific discharge are presented in the wave number domain. Closed-form expressions are developed for the simplified case of statistical isotropy of the log hydraulic conductivity field with a constant soil pore-size distribution parameter. These expressions allow us to investigate the impact of the boundary conditions, namely the vertical infiltration from the soil surface and a prescribed pressure head at a certain depth below the soil surface. It is found that the boundary conditions are critical in predicting uncertainty in bounded unsaturated flow. Our analytical expression for the pressure head variance in a one-dimensional, heterogeneous flow domain, developed using a nonstationary spectral representation approach [Li S-G, McLaughlin D. A nonstationary spectral method for solving stochastic groundwater problems: unconditional analysis. Water Resour Res 1991;27(7):1589-605; Li S-G, McLaughlin D. Using the nonstationary spectral method to analyze flow through heterogeneous trending media. Water Resour Res 1995; 31(3):541-51], is precisely equivalent to the published result of Lu et al. [Lu Z, Zhang D. Analytical solutions to steady state unsaturated flow in layered, randomly heterogeneous soils via Kirchhoff transformation. Adv Water Resour 2004;27:775-84].
NASA Astrophysics Data System (ADS)
Ben Slimene, Erij; Lassabatere, Laurent; Winiarski, Thierry; Gourdon, Remy
2016-04-01
The understanding of the fate of pollutants in the vadose zone is a prerequisite to manage soil and groundwater quality. Water infiltrates into the soil and carries a large amount of pollutants (heavy metals, organic compounds, etc.). The quality of groundwater depends on the capability of soils to remove pollutants while water infiltrates. The capability of soils to remove pollutants depends not only on their geochemical properties and affinity with pollutants but also on the quality of the contact between the reactive particles of the soil and pollutants. In such a context, preferential flows are the worst scenario since they prevent pollutants from reaching large parts of the soil including reactive zones that could serve for pollutant removal. The negative effects of preferential flow have already been pointed out by several studies. In this paper, we investigate numerically the effect of the establishment of preferential flow in a numerical section (13.5m long and 2.5m deep) that mimics a strongly heterogeneous deposit. The modelled deposit is made of several lithofacies with contrasting hydraulic properties. The numerical study proves that this strong contrast in hydraulic properties triggers the establishment of preferential flow (capillary barriers and funneled flow). Preferential flow develops mainly for low initial water contents and low fluxes imposed at the soil surface. The impact of these flows on solute transfer is also investigated as a function of solute reactivity and affinity to soil sorption sites. Modeled results clearly show that solute transport is greatly impacted by flow heterogeneity. Funneled flows have the same impacts as water fractionation into mobile and immobile transfer with a fast transport of solutes by preferential flow and solute diffusion to zones where the flow is slower. Such a pattern greatly impacts retention and reduces the access of pollutants into large parts of the soil. Retention is thus greatly reduced at the section
Grayscale lattice Boltzmann model for multiphase heterogeneous flow through porous media
NASA Astrophysics Data System (ADS)
Pereira, Gerald G.
2016-06-01
The grayscale lattice Boltzmann (LB) model has been recently developed to model single-phase fluid flow through heterogeneous porous media. Flow is allowed in each voxel but the degree of flow depends on that voxel's resistivity to fluid motion. Here we extend the grayscale LB model to multiphase, immiscible flow. The new model is outlined and then applied to a number of test cases, which show good agreement with theory. This method is subsequently used to model the important case where each voxel may have a different resistance to each particular fluid that is passing through it. Finally, the method is applied to model fluid flow through real porous media to demonstrate its capability. Both the capillary and viscous flow regimes are recovered in these simulations.
Grayscale lattice Boltzmann model for multiphase heterogeneous flow through porous media.
Pereira, Gerald G
2016-06-01
The grayscale lattice Boltzmann (LB) model has been recently developed to model single-phase fluid flow through heterogeneous porous media. Flow is allowed in each voxel but the degree of flow depends on that voxel's resistivity to fluid motion. Here we extend the grayscale LB model to multiphase, immiscible flow. The new model is outlined and then applied to a number of test cases, which show good agreement with theory. This method is subsequently used to model the important case where each voxel may have a different resistance to each particular fluid that is passing through it. Finally, the method is applied to model fluid flow through real porous media to demonstrate its capability. Both the capillary and viscous flow regimes are recovered in these simulations. PMID:27415381
NASA Astrophysics Data System (ADS)
Li, Qi-Lang; Wong, S. C.; Min, Jie; Tian, Shuo; Wang, Bing-Hong
2016-08-01
This study examines the cellular automata traffic flow model, which considers the heterogeneity of vehicle acceleration and the delay probability of vehicles. Computer simulations are used to identify three typical phases in the model: free-flow, synchronized flow, and wide moving traffic jam. In the synchronized flow region of the fundamental diagram, the low and high velocity vehicles compete with each other and play an important role in the evolution of the system. The analysis shows that there are two types of bistable phases. However, in the original Nagel and Schreckenberg cellular automata traffic model, there are only two kinds of traffic conditions, namely, free-flow and traffic jams. The synchronized flow phase and bistable phase have not been found.
Bortolini, Olga; Cavazzini, Alberto; Giovannini, Pier Paolo; Greco, Roberto; Marchetti, Nicola; Massi, Alessandro; Pasti, Luisa
2013-06-10
The heterogeneous proline-catalyzed aldol reaction was investigated under continuous-flow conditions by means of a packed-bed microreactor. Reaction-progress kinetic analysis (RPKA) was used in combination with nonlinear chromatography for the interpretation, under synthetically relevant conditions, of important mechanistic aspects of the heterogeneous catalytic process at a molecular level. The information gathered by RPKA and nonlinear chromatography proved to be highly complementary and allowed for the assessment of optimal operating variables. In particular, the determination of the rate-determining step was pivotal for optimizing the feed composition. On the other hand, the competitive product inhibition was responsible for the unexpected decrease in the reaction yield following an apparently obvious variation in the feed composition. The study was facilitated by a suitable 2D instrumental arrangement for simultaneous flow reaction and online flow-injection analysis. PMID:23589216
Continuous flow Sonogashira C-C coupling using a heterogeneous palladium-copper dual reactor.
Tan, Li-Min; Sem, Zhi-Yu; Chong, Wei-Yuan; Liu, Xiaoqian; Hendra; Kwan, Wei Lek; Lee, Chi-Lik Ken
2013-01-01
We report the development of a heterogeneous catalyst system on continuous flow chemistry. A palladium (Pd) coated tubular reactor was placed in line with copper (Cu) tubing using a continuous flow platform, and a Sonogashira C-C coupling reaction was used to evaluate the performance. The reactions were favorably carried out in the Cu reactor, catalyzed by the traces of leached Pd from the Pd reactor. The leached Pd and Cu were trapped with a metal scavaging resin at the back-end of the continuous flow system, affording a genuine approach toward green chemistry. PMID:23248977
Effective parameters for two-phase flow in a porous medium with periodic heterogeneities
Ataie-Ashtiani, B; Hassanizadeh, S M.; Oostrom, Martinus ); Celia, M A.; White, Mark D. )
2000-12-01
The study of non-aqueous phase liquid (NAPL) transport in groundwater requires a correct description of multiphase flow in porous media. For the simulation of multiphase flow a number of material-dependent parameters have to be known. These include relationships between capillary pressure, relative permeability, and saturation. One of the major difficulties in characterizing a porous medium is the presence of small-scale heterogeneities, which have distinctly different multiphase flow properties than the main medium. Such heterogeneities can considerably affect the spreading behavior of non-aqueous liquids. They are often sources of localized pools of pollutants. For most practical purposes, the details of fluid distribution in such a medium are not of interest. It is also computationally not feasible to discretise a compositional multiphase model at such small scales. Even if a detailed numerical model is constructed, it is virtually impossible to obtain data for these heterogeneities. Thus, instead of modeling the subsurface at the scale of micro-heterogeneities, it is desirable to model it at a higher scale, as a homogenized medium, with effective properties.
The Null Space Monte Carlo Uncertainty Analysis of Heterogeneity for Preferential Flow Simulation
NASA Astrophysics Data System (ADS)
Ghasemizade, M.; Radny, D.; Schirmer, M.
2014-12-01
Preferential flow paths can have a huge impact on the amount and time of runoff generation, particularly in areas where subsurface flow dominates this process. In order to simulate preferential flow mechanisms, many different approaches have been suggested. However, the efficiency of such approaches are rarely investigated in a predictive sense. The main reason is that the models which are used to simulate preferential flows require many parameters. This can lead to a dramatic increase of model run times, especially in the context of highly nonlinear models which themselves are demanding. We attempted in this research to simulate the daily recharge values of a weighing lysimeter, including preferential flows, with the 3-D physically based model HydroGeoSphere. To accomplish that, we used the matrix pore concept with varying hydraulic conductivities within the lysimeter to represent heterogeneity. It was assumed that spatially correlated heterogeneity is the main driver of triggering preferential flow paths. In order to capture the spatial distribution of hydraulic conductivity values we used pilot points and geostatistical model structures. Since hydraulic conductivity values at each pilot point are functioning as parameters, the model is a highly parameterized one. Due to this fact, we used the robust and newly developed method of null space Monte Carlo for analyzing the uncertainty of the model outputs. Results of the uncertainty analysis show that the method of pilot points is reliable in order to represent preferential flow paths.
Hydrodynamics of semifluidization in gas-solid systems
Ho, T.C.; Yau, S.J.; Hopper, J.R.
1985-01-01
Semifluidized bed hydrodynamics, including minimum semifluidization velocity, packed bed formation and pressure drop across the bed, were studied in gas-solid fluidized beds. Experiments were carried out in beds of 0.203, 0.129 and 0.105 m I.D. Experimental parameters examined included gas velocity, semifluidized particles, static bed height and expansion ratio. Empirical and semi-empirical models were derived. The results were compared with those available in the literature.
NASA Astrophysics Data System (ADS)
Ghysels, Gert; Huysmans, Marijke
2015-04-01
Characterization of groundwater-surface water exchange fluxes is important for assessing riparian ecology, determining quantity and quality of pumped groundwater close to rivers, modeling groundwater flow, predicting flood peaks and low flows, and river water quality. The exchange fluxes between river and aquifer are strongly influenced by the hydraulic conductivity of the riverbed which can vary several orders of magnitude and shows a strong spatial variation. Direct measurement of riverbed hydraulic conductivity is cumbersome and therefore often indirect data such as temperature data or calibration of groundwater models are used to constrain riverbed hydraulic conductivity. In these approaches, the riverbed is usually represented as a homogeneous geological structure and the spatial variation of riverbed hydraulic conductivity is thus neglected. However, neglecting this spatial variation can lead to systematic underestimation of net river-aquifer exchange fluxes and may have important implications for the estimation of peak mass flows, for the hydrochemistry of streambed sediments, nutrient cycling and biogeochemical gradients. The MODFLOW software is the most wide-spread package used for groundwater modelling. In MODFLOW rivers are usually modelled using the River-package. However, in this package no distinction can be made between horizontal and vertical riverbed hydraulic conductivity and the riverbed cannot be subdivided into layers with different hydraulic characteristics. Riverbed sediments are strongly layered and thus another approach is advised. Different ways of introducing heterogeneous riverbeds in MODFLOW groundwater flow models are explored and compared. The influence of heterogeneous riverbeds on groundwater-surface water exchange fluxes is analyzed for two case studies: the Aa River in the Nete catchment and a stretch of the Dijle River near the nature reserve 'de Doode Bemde' (Belgium). For both cases fine-scale distributed local groundwater flow
Flow channeling and analysis of tracer tests in heterogeneous porous media
Moreno, Luis; Tsang, Chin-Fu
2001-11-03
Flow and solute transport through porous medium with strongly varying hydraulic conductivity are studied by numerical simulations. The heterogeneity of the porous medium is defined by {sigma} and {lambda}{prime}, which are, respectively, the standard deviation of natural log of permeability values and its correlation range {lambda} divided by transport distance L. The development of flow channeling as a function of these two parameters is demonstrated. The results show that for large heterogeneities, the flow is highly channelized and solute is transported through a few fast paths, and the corresponding breakthrough curves show a high peak at very early times, much shorter than the mean residence time. This effect was studied for a converging radial flow, to simulate tracer tests in a fracture zone or contact-thickness aquifer. It is shown that {sigma}{sup 2}{lambda}{prime} is an appropriate parameter to characterize the tracer dispersion and breakthrough curves. These results are used to study tracer breakthrough data from field experiments performed with nonsorbing tracers. A new procedure is proposed to analyze the results. From the moments of the residence-time distribution represented by the breakthrough curves, the heterogeneity of the porous medium, as characterized by {sigma}{sup 2}{lambda}{prime} and the mean residence time t{sub o}, may be determined.
NASA Astrophysics Data System (ADS)
Caballero-Miranda, C. I.; Alva-Valdivia, L. M.; González-Rangel, J. A.; Gogitchaishvili, A.; Urrutia-Fucugauchi, J.; Kontny, A.
2016-02-01
The within-flow vertical variation of anisotropy of the magnetic susceptibility (AMS) of three basaltic flow profiles from the Xitle volcano were investigated in relation to the lava flow-induced shear strain. Rock magnetic properties and opaque microscopy studies have shown that the magnetic mineralogy is dominated by Ti-poor magnetite with subtle vertical variations in grain size distribution: PSD grains dominate in a thin bottommost zone, and from base to top from PSD-MD to PSD-SD grains are found. The vertical variation of AMS principal direction patterns permitted identification of two to three main lava zones, some subdivided into subzones. The lower zone is very similar in all profiles with the magnetic foliation dipping toward the flow source, whereas the upper zone has magnetic foliation dipping toward the flow direction or alternates between dipping against and toward the flow direction. The K1 (maximum AMS axis) directions tend to be mostly parallel to the flow direction in both zones. The middle zone shows AMS axes diverging among profiles. We present heterogeneous strain ellipse distribution models for different flow velocities assuming similar viscosity to explain the AMS directions and related parameters of each zone. Irregular vertical foliations and transverse to flow lineation of a few samples at the bottommost and topmost part of profiles suggest SD inverse fabric, levels of intense friction, or degassing effects in AMS orientations.
Gas-solid reaction-rate enhancement by pressure cycling
NASA Astrophysics Data System (ADS)
Sohn, H. Y.; Aboukheshem, M. B.
1992-06-01
An experimental study and mathematical modeling of the effects of external pressure cycling on gas-solid reactions have been conducted using the reduction of nickel oxide pellets by hy-drogen. Experiments were carried out in two phases: In the first phase, the intrinsic kinetic parameters were measured, and in the second phase, the gas-solid reaction was carried out under a constant or cycling external pressure. The effects of the frequency and amplitude of pressure cycling were studied at various reaction conditions. Pressure cycling substantially increases the overall rate of the reaction. A mathematical model was developed from the first principles to establish the extent of the overall reaction-rate enhancement and subsequently to analyze the experimental observations. The calculated values from the mathematical model are in good agreement with the experimental results. The effects are most pronounced when the overall rate under a constant pressure is controlled by diffusion. Depending on the reaction condition, a very large degree of rate enhancement could be achieved. Furthermore, low-amplitude pressure waves, like acoustic waves, could significantly increase the rates of gas-solid reactions.
Field testing the role of heterogeneity at the inter-well scale during two phase flow
NASA Astrophysics Data System (ADS)
Hovorka, S. D.; Gulf Coast Carbon Center; Geoseq
2011-12-01
Connectivity of rocks with different fluid flow properties (reservoir architecture) is a major source of uncertainty in predicting multi-phase fluid flow. Multi-institution research teams have completed three major DOE-funded test programs in which movement of supercritical CO2 through brine-saturated fluvial sandstones was observed with multiple tools. In each test, closely spaced wells (30 to 100 m) were drilled to reservoir depth so that the amount of reservoir complexity sampled between the wells would be reduced and higher resolution measurements of change could be obtained during time-lapse monitoring. During one test (Frio 1), an exceptionally homogeneous injection zone produced by marine reworking of a fine-grained fluvial sandstone of the Upper Frio Formation produced a classic-wedge-shaped CO2 plume. The maximum area occupied by CO2 was the result of radial expansion of the plume near the injection well; this produced plume down-building. Away from the injection well , the importance of gravity-override increased. A second test at the same well array in a deeper sandstone (Frio 2) was sited in heterogeneous (gravel to muddy sandstone) high permeability (>3 Darcy), weakly cemented fluvial sandstone. A slow injection rate over a small interval at the flow unit base was used to accentuate buoyancy effects. Measurements of plume migration through time using tracers and cross-well seismic documented interaction between near-well radial flow and vertical rise. However, because of discontinuous fast paths in gravel zones and CO2 ponding against muddy sandstone baffles, reservoir heterogeneity was a dominant influence in short-term plume evolution. The third test interval in the SECARB "Early" test documented response of amalgamated gravel and sandstone point bars in which heterogeneity was reduced by cementation. CO2 injection rate was increased incrementally and flow-rate dependent reservoir responses observed. These suggest that capillary-entry pressure and
Quantitative prediction of clustering instabilities in gas-solid homogeneous cooling systems
NASA Astrophysics Data System (ADS)
Hrenya, Christine; Mitrano, Peter; Li, Xiaoqi; Yin, Xiaolong
2014-11-01
Dynamic particle clusters are widely documented in gas-solid flow systems, including gasification units for coal or biomass, gravity-driven flow over an array of tubes, pneumatic transport lines, etc. Continuum descriptions based on kinetic theory have been known for over a decade to qualitatively predict the presence of such clustering instabilities. The quantitative ability of such continuum descriptions is relatively unexplored, however, and remains unclear given the low-Knudsen assumption upon which the descriptions are based. In particular, the concentration gradient is relatively large across the boundary between the cluster and the surrounding dilute region, which is counter to the small-gradient assumption inherent in the low-Knudsen-number expansion. In this work, we use direct numerical simulations (DNS) of a gas-solid homogeneous cooling system to determine the critical system size needed for the clustering instability to develop. We then compare the results to the same quantity predicted by a continuum description based on kinetic theory. The agreement is quite good over a wide range of parameters. This finding is reminiscent of molecular fluids, namely the ability of the Navier-Stokes equations to predict well outside the expected range of Knudsen numbers.
Zhou, Quanlin; Liu, Hui-Hai; Bodvarsson, Gudmundur S; Oldenburg, Curtis M
2003-01-01
The heterogeneity of hydrogeologic properties at different scales may have different effects on flow and transport processes in a subsurface system. A model for the unsaturated zone of Yucca Mountain, Nevada, is developed to represent complex heterogeneity at two different scales: (1) layer scale corresponding to geologic layering and (2) local scale. The layer-scale hydrogeologic properties are obtained using inverse modeling, based on the available measurements collected from the Yucca Mountain site. Calibration results show a significant lateral and vertical variability in matrix and fracture properties. Hydrogeologic property distributions in a two-dimensional, vertical cross-section of the site are generated by combining the average layer-scale matrix and fracture properties with local-scale perturbations generated using a stochastic simulation method. The unsaturated water flow and conservative (nonsorbing) tracer transport through the cross-section are simulated for different sets of matrix and fracture property fields. Comparison of simulation results indicates that the local-scale heterogeneity of matrix and fracture properties has a considerable effect on unsaturated flow processes, leading to fast flow paths in fractures and the matrix. These paths shorten the travel time of a conservative tracer from the source (repository) horizon in the unsaturated zone to the water table for small fractions of total released tracer mass. As a result, the local-scale heterogeneity also has a noticeable effect on global tracer transport processes, characterized by an average breakthrough curve at the water table, especially at the early arrival time of tracer mass. However, the effect is not significant at the later time after 20% tracer mass reaches the water table. The simulation results also verify that matrix diffusion plays an important role in overall solute transport processes in the unsaturated zone at Yucca Mountain. PMID:12498572
Davey, H M; Kell, D B
1996-01-01
The most fundamental questions such as whether a cell is alive, in the sense of being able to divide or to form a colony, may sometimes be very hard to answer, since even axenic microbial cultures are extremely heterogeneous. Analyses that seek to correlate such things as viability, which is a property of an individual cell, with macroscopic measurements of culture variables such as ATP content, respiratory activity, and so on, must inevitably fail. It is therefore necessary to make physiological measurements on individual cells. Flow cytometry is such a technique, which allows one to analyze cells rapidly and individually and permits the quantitative analysis of microbial heterogeneity. It therefore offers many advantages over conventional measurements for both routine and more exploratory analyses of microbial properties. While the technique has been widely applied to the study of mammalian cells, is use in microbiology has until recently been much more limited, largely because of the smaller size of microbes and the consequently smaller optical signals obtainable from them. Since these technical barriers no longer hold, flow cytometry with appropriate stains has been used for the rapid discrimination and identification of microbial cells, for the rapid assessment of viability and of the heterogeneous distributions of a wealth of other more detailed physiological properties, for the analysis of antimicrobial drug-cell interactions, and for the isolation of high-yielding strains of biotechnological interest. Flow cytometric analyses provide an abundance of multivariate data, and special methods have been devised to exploit these. Ongoing advances mean that modern flow cytometers may now be used by nonspecialists to effect a renaissance in our understanding of microbial heterogeneity. PMID:8987359
NASA Astrophysics Data System (ADS)
Ben Slimene, Erij; Lassabatere, Laurent; Winiarski, Thierry; Gourdon, Remy
2015-04-01
Large cities are mostly situated in areas close to water resources in order to meet the water needs of their populations. Alluvial soils harbor large aquifers that are used to supply water, the Rhone-Alpes region being a good illustration. However, the increase of soil sealing has led to the development of best management practices such as infiltration basins which are aimed at infiltrating stormwater in order to reduce the amount of water collected and treated in usual systems. Yet, these infiltration basins are mainly settled over highly permeable geologic formations so as to ensure water infiltration and a proper functioning of these infiltration basins. Most of these formations are strongly heterogeneous, since they are made of different materials with contrasting sedimentological properties (e.g. particle size distribution) and transfer properties. This paper addresses flow modeling during the infiltration phase in the vadose zone underneath infiltration basins settled over a strongly heterogeneous glaciofluvial deposit. In particular, we want to pinpoint numerically the worst conditions with regards to preferential flow, in terms of initial hydric conditions (initial water contents) and imposed flow rates. For this purpose, a numerical study is proposed on the basis of previous studies offering a sedimentological description of the subsoil with the detail of its architecture and a precise description of the different lithofacies and their hydraulic properties. Considering this, we worked on a section (13.5m long and 2.5m high) for which a complete sedimentological and hydraulic description had already been performed. Water infiltration was modeled for different initial and boundary conditions (mostly the values of the flux imposed at surface). At first, different numerical tests and adjustments have been made including mesh optimization with regards to both accuracy and computation time. Following these tests, the "tight" mesh has been validated since it
Ishitani, Haruro; Saito, Yuki; Tsubogo, Tetsu; Kobayashi, Shū
2016-03-18
Synthesis of β-nitrostyrene derivatives and their following reactions through two-step continuous-flow protocols with heterogeneous catalysts are described. In the first step to provide β-nitrostyrenes from aromatic aldehydes and nitromethane, readily available amino-functionalized silica gel was employed as a catalyst and gave the products continuously for at least 100 h with high selectivity. In the second step, reactions of β-nitrostyrenes, solid bases, immobilized bases, solid acids, and chiral supported metals and nonmetals were used as catalysts, and seven kinds of nitro-containing organic compounds could be effectively synthesized through the two-step continuous-flow systems. PMID:26926210
Stability of haline density-driven flows in saturated heterogeneous media
NASA Astrophysics Data System (ADS)
Musuuza, Jude; Attinger, Sabine; Radu, Florin
2010-05-01
Density-driven flows occur in deep aquifers due to temperature differences and in coastal aquifers and refuse dumps due to solute concentration differences. Its relevance cuts across many practical applications like (normal and nuclear) waste repository management, exploitation of geothermal energy resources, enhanced oil recovery from aquifers and remediation of contaminated sites. A typical feature of density dependent flow problems is that they can become unstable (physically or numerically). A big challenge has been the absence of a general criterion that states whether flow is physically stable or unstable and the optimum computational grid resolution needed to solve the problem without creating numerical (artificial) instabilities. The homogenization theory ideas from [1] were extended in [2] to derive a stability criterion for density-driven flows in saturated homogeneous porous media. The criterion included the effects of density, viscosity and velocity but could not adequately predict the onset of fingering when velocity was varied. That study is extended here to include dispersive and medium heterogeneity effects. The specific objective is to answer the question: under what conditions do heterogeneities stabilise or destabilise flow? The homogenization theory ideas from [1] are again used to derive expressions for the elements of the macrodispersion tensor for flow aligned parallel to gravity. The dependency of the temporal evolution of the coefficients on the density contrast, heterogeneity variance, transverse dispersivity, anisotropy and correlation length are then investigated and the results checked against numerical simulations performed with the software toolbox d3 f. The work will be extended to include temperature effects and it is hoped that the ideas can be extended to flow in unsaturated soils. REFERENCES [1]Held, R., S. Attinger, and W. Kinzelbach (2005), Homogenization and effective parameters for the Henry problem in heterogeneous
NASA Astrophysics Data System (ADS)
Lewis, A. J.; Druhan, J. L.; Maher, K.
2013-12-01
A comprehensive understanding of how fluids flow through physically heterogeneous porous media is essential to the prediction of contaminant mobility and resource sustainability in groundwater systems. Although many analytical and numerical methods exist to quantify the effects of physical heterogeneity on permeability and reactivity, to date, very few studies have attempted to physically design a known type of heterogeneity within a system, observe the effects on reactive transport, and compare those results to numerical models. We have designed and implemented an experimental procedure to address the effects of physical heterogeneity on tracer propagation by building several cylindrical columns with different known geometries of variable permeability. In these fabricated systems we observe the effects of each permeability distribution on solute transport and reactivity. The experimental data are compared against simulated tracer breakthroughs from the reactive transport code Crunchflow, using analytical solutions for effective permeability based on the geometry of the column pack. We employ chemically homogeneous sand of two distinct grain size distributions to construct 10 cm diameter x 30 cm length cylindrical columns. The sand we use is ultra-high purity, nonreactive crystalline silica (SiO2). The coarse grain sand has a particle size distribution between 0.149-0.297 mm diameter and the fine grain between 0.074-0.149 mm diameter. A reference column consisting of a homogeneous pack of the coarse grain sand is contrasted with two columns utilizing both grain sizes. One column is constructed of an inner core of fine grain sand surrounded by an outer annulus of coarse grain sand, and a second is built with one hemisphere of fine grain and one hemisphere of coarse grand sand. The volumes of coarse and fine grain sand used in both heterogeneous columns are equal, and the porosity of the sands are 44% for the coarse grain and 42% for the fine grain. When packed into
Rockhold, M L
1993-02-01
A field-scale, unsaturated flow and solute transport experiment at the Las Cruces trench site in New Mexico was simulated as part of a blind'' modeling exercise to demonstrate the ability or inability of uncalibrated models to predict unsaturated flow and solute transport in spatially variable porous media. Simulations were conducted using a recently developed multiphase flow and transport simulator. Uniform and heterogeneous soil models were tested, and data from a previous experiment at the site were used with an inverse procedure to estimate water retention parameters. A spatial moment analysis was used to provide a quantitative basis for comparing the mean observed and simulated flow and transport behavior. The results of this study suggest that defensible predictions of waste migration and fate at low-level waste sites will ultimately require site-specific data for model calibration.
Paillet, Frederick L.
1998-01-01
A numerical model of flow in the vicinity of a borehole is used to analyze flowmeter data obtained with high-resolution flowmeters. The model is designed to (1) precisely compute flow in a borehole, (2) approximate the effects of flow in surrounding aquifers on the measured borehole flow, (3) allow for an arbitrary number (N) of entry/exit points connected to M < N far-field aquifers, and (4) be consistent with the practical limitations of flowmeter measurements such as limits of resolution, typical measurement error, and finite measurement periods. The model is used in three modes: (1) a quasi-steady pumping mode where there is no ambient flow, (2) a steady flow mode where ambient differences in far-field water levels drive flow between fracture zones in the borehole, and (3) a cross-borehole test mode where pumping in an adjacent borehole drives flow in the observation borehole. The model gives estimates of transmissivity for any number of fractures in steady or quasi-steady flow experiments that agree with straddle-packer test data. Field examples show how these cross-borehole-type curves can be used to estimate the storage coefficient of fractures and bedding planes and to determine whether fractures intersecting a borehole at different locations are hydraulically connected in the surrounding rock mass.
Revisiting low-fidelity two-fluid models for gas-solids transport
NASA Astrophysics Data System (ADS)
Adeleke, Najeem; Adewumi, Michael; Ityokumbul, Thaddeus
2016-08-01
Two-phase gas-solids transport models are widely utilized for process design and automation in a broad range of industrial applications. Some of these applications include proppant transport in gaseous fracking fluids, air/gas drilling hydraulics, coal-gasification reactors and food processing units. Systems automation and real time process optimization stand to benefit a great deal from availability of efficient and accurate theoretical models for operations data processing. However, modeling two-phase pneumatic transport systems accurately requires a comprehensive understanding of gas-solids flow behavior. In this study we discuss the prevailing flow conditions and present a low-fidelity two-fluid model equation for particulate transport. The model equations are formulated in a manner that ensures the physical flux term remains conservative despite the inclusion of solids normal stress through the empirical formula for modulus of elasticity. A new set of Roe-Pike averages are presented for the resulting strictly hyperbolic flux term in the system of equations, which was used to develop a Roe-type approximate Riemann solver. The resulting scheme is stable regardless of the choice of flux-limiter. The model is evaluated by the prediction of experimental results from both pneumatic riser and air-drilling hydraulics systems. We demonstrate the effect and impact of numerical formulation and choice of numerical scheme on model predictions. We illustrate the capability of a low-fidelity one-dimensional two-fluid model in predicting relevant flow parameters in two-phase particulate systems accurately even under flow regimes involving counter-current flow.
Keska, Jerry K.; Hincapie, Juan; Jones, Richard
2011-02-15
In the steady-state flow of a heterogeneous mixture such as an air-liquid mixture, the velocity and void fraction are space- and time-dependent parameters. These parameters are the most fundamental in the analysis and description of a multiphase flow. The determination of flow patterns in an objective way is extremely critical, since this is directly related to sudden changes in spatial and temporal changes of the random like characteristic of concentration. Flow patterns can be described by concentration signals in time, amplitude, and frequency domains. Despite the vital importance and countless attempts to solve or incorporate the flow pattern phenomena into multiphase models, it has still been a very challenging topic in the scientific community since the 1940's and has not yet reached a satisfactory solution. This paper reports the experimental results of the impact of fluid viscosity on flow patterns for two-phase flow. Two-phase flow was created in laboratory equipment using air and liquid as phase medium. The liquid properties were changed by using variable concentrations of glycerol in water mixture which generated a wide-range of dynamic viscosities ranging from 1 to 1060 MPa s. The in situ spatial concentration vs. liquid viscosity and airflow velocity of two-phase flow in a vertical ID=50.8 mm pipe were measured using two concomitant computer-aided measurement systems. After acquiring data, the in situ special concentration signals were analyzed in time (spatial concentration and RMS of spatial concentration vs. time), amplitude (PDF and CPDF), and frequency (PSD and CPSD) domains that documented broad flow pattern changes caused by the fluid viscosity and air velocity changes. (author)
NASA Astrophysics Data System (ADS)
Hamed, Ali M.; Ranjan, Prateek; Sadowski, Matthew J.; Nepf, Heidi M.; Chamorro, Leonardo P.
2015-11-01
An experimental investigation of the flow within and above model canopies was carried out to determine the effect of canopy height heterogeneity on the structure and spatial distribution of the turbulence. Two 800 mm long models with 20% blockage were placed in a 2.5 m long refractive-index-matching channel. The first model (base case) is constituted of equal height (h) square bar elements arranged in a staggered configuration. The other model bars had two heights (h +1/3h and h-1/3h) alternated every two rows. Particle image velocimetry was used to map the flow field at three locations spanning the length of the canopy under three confinement ratios H/h =2, 3, and 4, where H is the free surface height. The experiments were performed at Reynolds number ReH = 6800 , 10200, and 13600. Refractive index matching renders the canopy invisible and grants full optical access allowing the flow field within the canopy to be measured by PIV. Turbulence statistics complemented with POD, quadrant analysis, and LES decomposition reveal the distinctive effect of the height heterogeneity on the shear layer that forms on top of the canopy, and on the free flow over the canopies.
Fluidization onset and expansion of gas-solid fluidized beds
Jones, O.C.; Shin, T.S.
1984-08-01
A simple, mass conservation-based, kinematic model is presented for accurately predicting both the onset of fluidization and the degree of (limit of) bed expansion in bubbling gas-solid fluidized beds. The model is consistant with inception correlations exisiting in the literature. Since the method has a sound physical basis, it might be expected to provide scaling between laboratory-scale fluidized beds and large-scale systems. This scaling ability, however, remains to be demonstrated as does the application to pressurized systems and where the terminal Reynolds numbers exceed 1000, (Archimedes numbers over about 3.2 x 10/sup 5/).
Process of preparing nitrogen trifluoride by gas-solid reaction
Aramaki, M.; Kobayashi, Y.; Nakamura, T.; Nakano, H.; Suenaga, T.
1985-09-24
NF3 is prepared with good yields by reaction between fluorine gas and an ammonium complex of a metal fluoride, such as (NH4)3AIF6, in solid phase. The metal flouride ammonium complex may be one additionally containing an alkali metal, such as (NH4)2NaAIF6. The gas-solid reaction is carried out preferably at temperatures above 80 C. and at relatively low partial pressures of fluorine in the gas phase of the reaction system, so that the reaction is easy to control.
NASA Astrophysics Data System (ADS)
Zech, Alraune; Zehner, Björn; Kolditz, Olaf; Attinger, Sabine
2016-01-01
Ground water flow systems of shallow sedimentary basins are studied in general by analyzing the fluid dynamics at the real world example of the Thuringian Basin. The impact of the permeability distribution and density differences on the flow velocity pattern, the salt concentration, and the temperature distribution is quantified by means of transient coupled simulations of fluid flow, heat, and mass transport processes. Simulations are performed with different permeabilities in the sedimentary layering and heterogeneous permeability distributions as well as with a non-constant fluid density. Three characteristic numbers are useful to describe the effects of permeability on the development of flow systems and subsurface transport: the relation of permeability between aquiclude and aquifer, the variance, and the correlation length of the log-normal permeability distribution. Density dependent flow due to temperature or concentration gradients is of minor importance for the distribution of the flow systems, but can lead to increased mixing dissolution of salt. Thermal convection is in general not present. The dominant driver of groundwater flow is the topography in combination with the permeability distribution. The results obtained for the Thuringian Basin give general insights into the dynamics of a small sedimentary basin due to the representative character of the basin structure as well as the transferability of the settings to other small sedimentary basins.
Relationship of core-scale heterogeneity with non-Darcy flow coefficients
Al-Rumhy, M.H.; Kalam, M.Z.
1996-06-01
An experimental research program to investigate the effects of liquid saturations upon non-Darcy flow coefficients is presented. the presence of a wetting phase fluid plays an important role in high velocity flow of a gas well, producing condensate or water, and in propped fractures containing liquid saturations. This study initially examines the errors commonly encountered but ignored in evaluating the permeabilities and the coefficient of inertial resistance during the flow of gases through porous media. Experimental techniques, such as constant overburden pressure, changing overburden pressure, forward flow, and backpressure flow, are applied to optimize and obtain accurate evaluations of Klinkenberg parameters and inertial resistance coefficients for a selection of Omani reservoir cores. Gas-slippage factor significantly influences the derived viscous and inertial coefficients from high-velocity gas flow data. An increasing wetting phase saturation increases the non-Darcy coefficient up to thirty-fold. Analysis of the experimental data revealed that unique relationships exist between the non-Darcy flow coefficients and the equivalent liquid permeability, porosity, and liquid saturation. Heterogeneity of the core as mapped by pore-scale measurements provide an insight into the mechanism for such a large increase in the non-Darcy coefficients.
Stuglik, Michał T; Babik, Wiesław
2016-07-01
The role of gene flow in species formation is a major unresolved issue in speciation biology. Progress in this area requires information on the long-term patterns of gene flow between diverging species. Here, we used thousands of single-nucleotide polymorphisms derived from transcriptome resequencing and a method modeling the joint frequency spectrum of these polymorphisms to reconstruct patterns of historical gene flow between two Lissotriton newts: L. vulgaris (Lv) and L. montandoni (Lm). We tested several models of divergence including complete isolation and various scenarios of historical gene flow. The model of secondary contact received the highest support. According to this model, the species split from their common ancestor ca. 5.5 million years (MY) ago, evolved in isolation for ca. 2 MY, and have been exchanging genes for the last 3.5 MY Demographic changes have been inferred in both species, with the current effective population size of ca. 0.7 million in Lv and 0.2 million in Lm. The postdivergence gene flow resulted in two-directional introgression which affected the genomes of both species, but was more pronounced from Lv to Lm. Interestingly, we found evidence for genomic heterogeneity of interspecific gene flow. This study demonstrates the complexity of long-term gene flow between distinct but incompletely reproductively isolated taxa which divergence was initiated millions of years ago. PMID:27386093
Willans, S.M.; McCarthy, I.D. )
1991-03-01
The distribution of tibial blood flow was measured by injecting approximately (600-1000) x 10(3) 15 mu microspheres, labelled with either tin-113 (113Sn) or cobalt-57 (57Co) into femoral arteries of five mature greyhounds. The diaphyseal cortex, stripped of periosteum and devoid of marrow, was sawn into 40 pieces (10 transverse sections x 4 anatomical quarters/section). Relative deposition densities of the 113Sn microspheres in 40 pieces of cortex were found. These values, together with their associated masses, proved, from a statistical point of view, that flow rate heterogeneity was substantial in the diaphysis. In particular, for the diaphyseal cortex, distribution of relative deposition densities (flow rates) in six bones was found to be positively-skewed with a relative dispersion ((SD/mean) x 100) of approximately 40%.
Numerical solution of the three-dimensional fluid flow in a rotating heterogeneous porous channel
NASA Astrophysics Data System (ADS)
Havstad, Mark A.; Vadasz, Peter
1999-09-01
A numerical solution to the problem of the three-dimensional fluid flow in a long rotating heterogeneous porous channel is presented. A co-ordinate transformation technique is employed to obtain accurate solutions over a wide range of porous media Ekman number values and consequent boundary layer thicknesses. Comparisons with an approximate asymptotic solution (for large values of Ekman number) and with theoretical predictions on the validity of Taylor-Proudman theorem in porous media for small values of Ekman number show good qualitative agreement. An evaluation of the boundary layer thickness is presented and a power-law correlation to Ekman number is shown to well-represent the results for small values of Ekman number. The different three-dimensional fluid flow regimes are presented graphically, demonstrating the distinct variation of the flow field over the wide range of Ekman numbers used. Copyright
NASA Astrophysics Data System (ADS)
Ague, J. J.
2004-12-01
Fluids are generally expected to be driven upward in the deep parts of orogens, but permeability heterogeneity and anisotropy must also be considered to properly interpret fluid infiltration and kinetic reaction histories preserved in the rock record. This paper focuses on new 2-D models of Darcian fluid flow incorporating permeability contrasts between rock units, the permeability tensor, and reactive fluid sources (e.g., dehydration). Factor of ten contrasts between the minimum and maximum permeability values in anisotropic rocks can strongly divert flow, but contrasts of as little as a factor of two still influence flow behavior. The first example considers fluid flow in subduction zone mélange, Syros, Greece. Geochemical evidence suggests that the interiors of meta-mafic blocks of oceanic crust in the mélange underwent limited fluid-rock reaction, despite extensive dehydration and decarbonation of the subduction complex. Modeling shows that if the blocks have lower permeability than the surrounding serpentine-rich matrix, then flow is diverted around the blocks resulting in little infiltration except at block margins, consistent with field relations. In this way, the subducted oceanic crust could preserve little evidence of fluid infiltration, even though considerable flow occurred through the mélange. The largest fluid fluxes are concentrated in matrix where blocks are in close proximity, and this effect increases as the anisotropy of the matrix increases. The lack of fluid infiltration into blocks could account for the observed limited metamorphism and strong kinetic overstepping of reactions that in some cases allowed preservation of ocean-floor mineral assemblages even at blueschist-eclogite facies conditions. The second example examines fluid flow through a folded sequence in which the direction of maximum permeability is parallel to the folded layering, and is based on field relations of Barrovian metamorphic sequences in CT, USA, and Scotland. As the
Hayat, Tasawar; Qayyum, Sumaira; Imtiaz, Maria; Alsaedi, Ahmed
2016-01-01
Two-dimensional stretched flow of Jeffrey fluid in view of Cattaneo-Christov heat flux is addressed. Effects of homogeneous-heterogeneous reactions are also considered. Suitable transformations are used to form ordinary differential equations. Convergent series solutions are computed. Impact of significant parameters on the velocity, temperature, concentration and skin friction coefficient is addressed. Analysis of thermal relaxation is made. The obtained results show that ratio of relaxation to retardation times and Deborah number have inverse relation for velocity profile. Temperature distribution has decreasing behavior for Prandtl number and thermal relaxation time. Also concentration decreases for larger values of strength of homogeneous reaction parameter while it increases for strength of heterogeneous reaction parameter. PMID:26859675
Impact of Cattaneo-Christov Heat Flux in Jeffrey Fluid Flow with Homogeneous-Heterogeneous Reactions
Hayat, Tasawar; Qayyum, Sumaira; Imtiaz, Maria; Alsaedi, Ahmed
2016-01-01
Two-dimensional stretched flow of Jeffrey fluid in view of Cattaneo-Christov heat flux is addressed. Effects of homogeneous-heterogeneous reactions are also considered. Suitable transformations are used to form ordinary differential equations. Convergent series solutions are computed. Impact of significant parameters on the velocity, temperature, concentration and skin friction coefficient is addressed. Analysis of thermal relaxation is made. The obtained results show that ratio of relaxation to retardation times and Deborah number have inverse relation for velocity profile. Temperature distribution has decreasing behavior for Prandtl number and thermal relaxation time. Also concentration decreases for larger values of strength of homogeneous reaction parameter while it increases for strength of heterogeneous reaction parameter. PMID:26859675
Geodynamo Models With a Thick Stable Layer and Heterogeneous CMB Heat Flow
NASA Astrophysics Data System (ADS)
Christensen, U. R.
2015-12-01
The upward revision of the thermal conductivity in the Earth's core makes it plausible that the mean heat flow at the core-mantle boundary (CMB) could be only afraction of what can be conducted down the core adiabat (perhaps one half). The upper part of the fluid core would be stably stratified to substantial depth. This is inconsistent with evidence for upwelling flow near the CMB from observations ofof magnetic flux expulsion. Heat flow at the CMB is likely very heterogeneous and would still be superadiabatic in some regions of the CMB. The dynamics of such a system is unclear. Gubbins et al. (Phys. Earth Planet. Int., in press, 2015)suggest that the locally unstable gradient would mix up the stable layer as a wholeand replace it by a weakly convecting one. We study dynamo models driven by a codensity flux from the inner core. On the outer boundary an inverse (on average) gradient is imposed, leading to stable stratification of the top 40% of the fluid shell. In addition to control cases with homogeneous CMB flux, we run models with two unstableregions centered on the equator. In the latter cases a predominantly horizontal circulation in a thin layer immediately below the outer boundary redistributes the heat that is conducted radially upward in the stable layer and transports ittowards the high heat-flow spots. Radial flow below these spots does not penetrate deeply into the stable layer, nor does the layer become mixed up to a significant degree. A dynamo operates in the convecting deep interior, however, its dipole moment is low in comparison to the Earth value. Heat flow heterogeneity at the CMB does not sem to solve the problems that exist for the geodynamo when the average heat flux is substantially subadiabatic.
Unravelling textural heterogeneity in obsidian: Shear-induced outgassing in the Rocche Rosse flow
NASA Astrophysics Data System (ADS)
Shields, J. K.; Mader, H. M.; Caricchi, L.; Tuffen, H.; Mueller, S.; Pistone, M.; Baumgartner, L.
2016-01-01
Obsidian flow emplacement is a complex and understudied aspect of silicic volcanism. Of particular importance is the question of how highly viscous magma can lose sufficient gas in order to erupt effusively as a lava flow. Using an array of methods we study the extreme textural heterogeneity of the Rocche Rosse obsidian flow in Lipari, a 2 km long, 100 m thick, ~ 800 year old lava flow, with respect to outgassing and emplacement mechanisms. 2D and 3D vesicle analyses and density measurements are used to classify the lava into four textural types: 'glassy' obsidian (< 15% vesicles), 'pumiceous' lava (> 40% vesicles), high aspect ratio, 'shear banded' lava (20-40% vesicles) and low aspect ratio, 'frothy' obsidian with 30-60% vesicles. Textural heterogeneity is observed on all scales (m to μm) and occurs as the result of strongly localised strain. Magnetic fabric, described by oblate and prolate susceptibility ellipsoids, records high and variable degrees of shearing throughout the flow. Total water contents are derived using both thermogravimetry and infrared spectroscopy to quantify primary (magmatic) and secondary (meteoric) water. Glass water contents are between 0.08-0.25 wt.%. Water analysis also reveals an increase in water content from glassy obsidian bands towards 'frothy' bands of 0.06-0.08 wt.%, reflecting preferential vesiculation of higher water bands and an extreme sensitivity of obsidian degassing to water content. We present an outgassing model that reconciles textural, volatile and magnetic data to indicate that obsidian is generated from multiple shear-induced outgassing cycles, whereby vesicular magma outgasses and densifies through bubble collapse and fracture healing to form obsidian, which then re-vesiculates to produce 'dry' vesicular magma. Repetition of this cycle throughout magma ascent results in the low water contents of the Rocche Rosse lavas and the final stage in the degassing cycle determines final lava porosity. Heterogeneities in
Abril, Meritxell; Muñoz, Isabel; Menéndez, Margarita
2016-05-15
In temporary Mediterranean streams, flow fragmentation during summer droughts originates an ephemeral mosaic of terrestrial and aquatic habitat types. The heterogeneity of habitat types implies a particular ecosystem functioning in temporary streams that is still poorly understood. We assessed the initial phases of leaf litter decomposition in selected habitat types: running waters, isolated pools and moist and dry streambed sediments. We used coarse-mesh litter bags containing Populus nigra leaves to examine decomposition rates, microbial biomass, macroinvertebrate abundance and dissolved organic carbon (DOC) release rates in each habitat type over an 11-day period in late summer. We detected faster decomposition rates in aquatic (running waters and isolated pools) than in terrestrial habitats (moist and dry streambed sediments). Under aquatic conditions, decomposition was characterized by intense leaching and early microbial colonization, which swiftly started to decompose litter. Microbial colonization in isolated pools was primarily dominated by bacteria, whereas in running waters fungal biomass predominated. Under terrestrial conditions, leaves were most often affected by abiotic processes that resulted in small mass losses. We found a substantial decrease in DOC release rates in both aquatic habitats within the first days of the study, whereas DOC release rates remained relatively stable in the moist and dry sediments. This suggests that leaves play different roles as a DOC source during and after flow fragmentation. Overall, our results revealed that leaf decomposition is heterogeneous during flow fragmentation, which has implications related to DOC utilization that should be considered in future regional carbon budgets. PMID:26930306
NASA Astrophysics Data System (ADS)
Arora, B.; Wainwright, H. M.; Spycher, N.
2013-12-01
This study aims at understanding key hydrogeochemical processes dictating pH behavior and U transport at the Savannah River Site (SRS) F-Area, South Carolina, with particular focus on the impact of chemical and physical heterogeneities. Acidic waste solutions containing low level radioactivity from numerous isotopes were discharged to a series of unlined seepage basins at the F-Area, from 1955 through 1989, which resulted in a nearly 1 km long acidic uranium plume. Reactive facies is a new approach that spatially characterizes linked flow and geochemical properties over large domains, where it is typically challenging to obtain parameters with sufficient resolution for reactive transport modeling. This approach - based on the hypothesis that we can identify geological units that have unique distributions of reactive transport properties - allows us to integrate various types of datasets (e.g., historical data, laboratory analysis, crosshole and surface geophysics) for estimating heterogeneous reactive transport parameters. At the SRS F-Area, data mining and iteration with laboratory analysis identified two reactive facies coincident with the depositional facies, which have distinct distributions of reactive transport properties: %fines, permeability, and Al:Fe ratio (proxy for kaolinite:geothite ratio). The reactive facies over the plume-scale domain was estimated based on measured data (foot-by-foot core analysis, cone penetrometer, crosshole seismic and surface seismic data) and integrated using the Bayesian framework. In parallel, a numerical reactive transport model was developed including saturated and unsaturated flow, and complex geochemical processes such as U(VI) and H+ adsorption (surface complexation) onto sediments and dissolution and precipitation of Al and Fe minerals. By combining the developed reactive transport model with the estimated spatial distribution of reactive transport parameters, we perform stochastic simulations of U and pH plume
NASA Astrophysics Data System (ADS)
Baloch, A.; Grant, P. W.; Webster, M. F.
2002-12-01
A finite-element study of two- and three-dimensional incompressible viscoelastic flows in a planar lid-driven cavity and concentric rotating cylinders is presented. The hardware platforms consist of both homogeneous and heterogeneous clusters of workstations. A semi-implicit time-stepping Taylor-Galerkin scheme is employed using the message passing mechanism provided by the Parallel Virtual Machine libraries. DEC-alpha, Intel Solaris and AMD-K7(Athlon) Linux clusters are utilized. Parallel results are compared against single processor (sequentially) solutions, using the parallelism paradigm of domain decomposition. Communication is effectively masked and practically ideal, linear speed-up with the number of processors is realized.
NASA Astrophysics Data System (ADS)
Kleissl, J.; Dziobak, M. P.; Honrath, R. E.
2004-12-01
A combination of standard meteorological equipment (3d sonic anemometer, energy balance sensors) and Crossbow MPR400 (Mica2) wireless motes and sensorboards were deployed along the slope of Pico mountain in the Azores, Portugal, between z = 1200 m and z = 2300 m MSL. The isolated location and uniform, conic shape make Pico mountain an ideal location to study orographic effects. This experiment focuses on upslope and downslope flow. Cost effective wireless sensor technology allows for high density of observations in time and space as necessary for characterization of flows over heterogeneous surfaces. Thus the features of upslope and downslope flows (speed, location and duration) and their effect on atmospheric physics and chemistry (temperature, relative humidity) can be studied in great detail. Synchronous measurements of O3, CO, NOx, NOy and NMHC at the PICO-NARE observatory (Honrath et al. 2004) situated at the mountaintop give further clues on airmass origin and dispersion. Findings regarding the occurrence and impacts of upslope and downslope flow and the advantages and disadvantages of wireless sensors relative to standard meteorological instruments will be presented. In particular, practical issues of wireless sensor deployment, such as durability in harsh conditions, power management, accuracy, and cost will be discussed.
NASA Astrophysics Data System (ADS)
Schmalzl, J.
2003-04-01
Convective flows govern much of the dynamics of the Earth. Examples of such flows are convection in the Earth's mantle, convection in magma chambers and much of the dynamics of the world oceans. Nowadays these time-dependent flows are often studied by means of three dimensional (3D) numerical models which solve the equations for the transport of heat and momentum alternatingly. These flows are often driven by a temperature difference. But for many flows there is also an active or passive chemical component that has to be considered. One characteristics of these flows is that the chemical diffusivity is very small. Implementing such a chemical field with a very low diffusivity into a numerical model using a field approach is difficult due to numerical diffusion introduced by the Eulerian schemes. Using Lagrangian tracers is also difficult in 3D flow since a massive amount of tracers is needed. We therefore have implemented a tracer-mesh method which tracks only the position of the interface between the two different components. Compared to a 2D tracer-line the insertion of new 3D surface-elements in highly deformed regions is however more complex. This is due to the topology of the mesh which changes because of the adaptive refinement. Luckily the refinement of polygonal meshes is a very active field of research in computer graphics and has been termed "Subdivision Surfaces". There is a wealth of different subdivision schemes with different properties. We applied the Butterfly scheme and the Loop scheme for the refinement of tracer meshes. When a density difference is connected to a chemical component it often acts as a restoring force. In many cases, the governing flow is spatially heterogenous and the spatial location of the heterogeneities is varying in time (e.g. the location of an upwelling plume). The restoring force of the density contrast may result in a situation where a highly deformed, and therefore highly refined region, returns to a simple geometry. In
NASA Astrophysics Data System (ADS)
Schmalzl, J.; Loddoch, A.
2003-12-01
Convective flows govern much of the dynamics of the Earth. Examples of such flows are convection in the Earth's mantle, convection in magma chambers and much of the dynamics of the world oceans. Nowadays these time-dependent flows are often studied by means of three dimensional (3D) numerical models which solve the equations for the transport of heat and momentum alternatingly. These flows are often driven by a temperature difference. But for many flows there is also an active or passive chemical component that has to be considered. One characteristics of these flows is that the chemical diffusivity is very small. Implementing such a chemical field with a very low diffusivity into a numerical model using a field approach is difficult due to numerical diffusion introduced by the Eulerian schemes. Using Lagrangian tracers is also difficult in 3D flow since a massive amount of tracers is needed. We therefore have implemented a tracer-mesh method which tracks only the position of the interface between the two different components. Compared to a 2D tracer-line the insertion of new 3D surface-elements in highly deformed regions is however more complex. This is due to the topology of the mesh which changes because of the adaptive refinement. Luckily the refinement of polygonal meshes is a very active field of research in computer graphics and has been termed "Subdivision Surfaces". There is a wealth of different subdivision schemes with different properties. We applied the Butterfly scheme and the Loop scheme for the refinement of tracer meshes. When a density difference is connected to a chemical component it often acts as a restoring force. In many cases, the governing flow is spatially heterogenous and the spatial location of the heterogeneities is varying in time (e.g. the location of an upwelling plume). The restoring force of the density contrast may result in a situation where a highly deformed, and therefore highly refined region, returns to a simple geometry. In
Bulk-density distributions of solids in the freeboard of a gas-solid fluidized bed
Shen, B.C.; Fan, L.T.; Walawender, W.P.
1995-05-01
The freeboard region above the bubbling zone of a gas-solid fluidized bed provides the space not only for the disengagement of particles but also for additional contact and reaction between the particles and gas. The flow pattern and behavior of particles as well as their bulk-density distribution in the freeboard have a significant impact on the efficiency of fluidization. The results of numerous previous experimental studies indicate that the bulk density of solids essentially decreases exponentially as a function of the height of the freeboard. In the present work, this distribution has been obtained by first derived the Fokker-Planck equation from the linearized equation of motion of a single particle and then transforming this Fokker-Planck equation into that for the bulk-density distribution of solids. Its simplification to the one-dimensional case readily gives rise to an exponential distribution and agrees well with the available experimental data.
Weak Galerkin finite element methods for Darcy flow: Anisotropy and heterogeneity
Lin, Guang; Liu, Jiangguo; Mu, Lin; Ye, Xiu
2014-10-11
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.
NASA Astrophysics Data System (ADS)
Nagao, Junji; Matsuo, Shigeru; Setoguchi, Toshiaki; Kim, Heuy Dong
2010-08-01
Shock tubes are devices in which the state of a gas is changed suddenly from one uniform state to another by the passage of shock and expansion waves. In the theory of ideal shock tube flow, it is customarily assumed that the unsteady expansion and shock waves generated by diaphragm rupture are a perfectly centered plane wave. However, such waves are generally not centered, or may not even by plane in practice. In the present research, the time-dependent behavior of homogeneous and heterogeneous condensation of moist air in the shock tube is investigated by using a computational fluid dynamics work. Further, the numerical and experimental studies were carried out in order to investigate the effect of the diaphragm rupture process on the flow characteristics of expansion and shock waves generated near the diaphragm.
Compositional heterogeneity of the Sugarloaf melilite nephelinite flow, Honolulu Volcanics, Hawai'i
NASA Astrophysics Data System (ADS)
Clague, David A.; Frey, Frederick A.; Garcia, Michael O.; Huang, Shichun; McWilliams, Michael; Beeson, Melvin H.
2016-07-01
The Sugarloaf flow is a melilite nephelinite erupted from the Tantalus rift during rejuvenated-stage volcanism on O'ahu, the Honolulu Volcanics. The flow ponded in Mānoa Valley forming a ∼15 m thick flow which was cored and sampled in a quarry. Nepheline from a pegmatoid segregation in the flow yielded a 40Ar-39Ar age of 76 ka. This age, combined with others, indicates that the Tantalus rift eruptions are some of the youngest on O'ahu. Honolulu Volcanics erupt on average about every 35-40 ka indicating that future eruptions are possible. We evaluated the compositional variability of 19 samples from the flow, including 14 from the core. Twelve samples are representative of the bulk flow, four are dark- or light-colored variants, one is a heavy rare earth element (REE)-enriched pegmatoid, and two visually resemble the bulk flow, but have chemical characteristics of the dark and light variants. Our objective was to determine intraflow heterogeneity in mineralogy and composition. Variable abundances of Na2O, K2O, Sr, Ba, Rb, Pb and U in the flow were caused by post-eruptive mobility in a vapor phase, most likely during or soon after flow emplacement, and heterogeneous deposition of secondary calcite and zeolites. Relative to fine-grained samples, a pegmatoid vein that crosscuts the flow is enriched in incompatible trace elements except Sr and TiO2. Element mobility after eruption introduced scatter in trace element ratios including light-REE/heavy-REE, and all ratios involving mobile elements K, Rb, Ba, Sr, Pb, and U. Lavas from some of the 37 Honolulu Volcanics vents have crosscutting REE patterns in a primitive mantle-normalized plot. Such patterns have been interpreted to reflect variable amounts of residual garnet during partial melting. Previous studies of lavas from different vents concluded that garnet, phlogopite, amphibole, and Fe-Ti oxides were residual phases of the partial melting processes that created the Honolulu Volcanics (Clague and Frey, 1982; Yang
Hayat, T; Hussain, Zakir; Alsaedi, A; Farooq, M
2016-01-01
This article examines the effects of homogeneous-heterogeneous reactions and Newtonian heating in magnetohydrodynamic (MHD) flow of Powell-Eyring fluid by a stretching cylinder. The nonlinear partial differential equations of momentum, energy and concentration are reduced to the nonlinear ordinary differential equations. Convergent solutions of momentum, energy and reaction equations are developed by using homotopy analysis method (HAM). This method is very efficient for development of series solutions of highly nonlinear differential equations. It does not depend on any small or large parameter like the other methods i. e., perturbation method, δ-perturbation expansion method etc. We get more accurate result as we increase the order of approximations. Effects of different parameters on the velocity, temperature and concentration distributions are sketched and discussed. Comparison of present study with the previous published work is also made in the limiting sense. Numerical values of skin friction coefficient and Nusselt number are also computed and analyzed. It is noticed that the flow accelerates for large values of Powell-Eyring fluid parameter. Further temperature profile decreases and concentration profile increases when Powell-Eyring fluid parameter enhances. Concentration distribution is decreasing function of homogeneous reaction parameter while opposite influence of heterogeneous reaction parameter appears. PMID:27280883
NASA Astrophysics Data System (ADS)
Nakamura, Masato R.; Castaldi, Marco J.; Themelis, Nickolas J.
2008-11-01
Flow, mixing, and size segregation of heterogeneous granular particles are intriguing phenomena. In order to characterize the behavior of heterogeneous particle, a two-dimensional stochastic model of particle flow and mixing within the packed bed on a traveling grate was developed. The model was calibrated and validated by means of a physical model of the reverse acting grate, using tracer particles ranging from 6 -- 22 cm in diameter. It was found that the motion of the traveling grate, whose speed ranged from 15 to 90 reciprocations/hr, increases the mean residence time of small and medium particles by 69% and 8%, respectively, while decreasing the mean residence time of large particles by 19%. This is because of size segregation known as the Brazil Nut Effect. When the ratio of particle diameter to the height of moving bar, d/h, increases from 0.46 to 1.69, the mixing diffusion coefficient, De at 60/hr., decreases from 96 to 38.4. This indicates that the height of the moving bars should be greater than the diameter of targeted particles.
Hayat, T.; Hussain, Zakir; Alsaedi, A.; Farooq, M.
2016-01-01
This article examines the effects of homogeneous-heterogeneous reactions and Newtonian heating in magnetohydrodynamic (MHD) flow of Powell-Eyring fluid by a stretching cylinder. The nonlinear partial differential equations of momentum, energy and concentration are reduced to the nonlinear ordinary differential equations. Convergent solutions of momentum, energy and reaction equations are developed by using homotopy analysis method (HAM). This method is very efficient for development of series solutions of highly nonlinear differential equations. It does not depend on any small or large parameter like the other methods i. e., perturbation method, δ—perturbation expansion method etc. We get more accurate result as we increase the order of approximations. Effects of different parameters on the velocity, temperature and concentration distributions are sketched and discussed. Comparison of present study with the previous published work is also made in the limiting sense. Numerical values of skin friction coefficient and Nusselt number are also computed and analyzed. It is noticed that the flow accelerates for large values of Powell-Eyring fluid parameter. Further temperature profile decreases and concentration profile increases when Powell-Eyring fluid parameter enhances. Concentration distribution is decreasing function of homogeneous reaction parameter while opposite influence of heterogeneous reaction parameter appears. PMID:27280883
NASA Astrophysics Data System (ADS)
Severino, Gerardo; de Bartolo, Samuele; Toraldo, Gerardo; Srinivasan, Gowri; Viswanathan, Hari
2012-12-01
Diverging radial flow takes place in a heterogeneous porous medium where the log conductivity Y = ln K is modeled as a stationary random space function (RSF). The flow is steady, and is generated by a fully penetrating well. A linearly sorbing solute is injected through the well envelope, and we aim at computing the average flux concentration (breakthrough curve). A relatively simple solution for this difficult problem is achieved by adopting, similar to Indelman and Dagan (1999), a few simplifying assumptions: (i) a thick aquifer of large horizontal extent, (ii) mildly heterogeneous medium, (iii) strongly anisotropic formation, and (iv) large Peclet number. By introducing an appropriate Lagrangian framework, three-dimensional transport is mapped onto a one-dimensional domain (τ, t) where τ and t represent the fluid travel and current time, respectively. Central for this approach is the probability density function of the RSF τthat is derived consistently with the adopted assumptions stated above. Based on this, it is shown that the travel time can be regarded as a Gaussian random variable only in the far field. The breakthrough curves are analyzed to assess the impact of the hydraulic as well as reactive parameters. Finally, the travel time approach is tested against a forced-gradient transport experiment and shows good agreement.
Inference of permeability heterogeneity from joint inversion of transient flow and temperature data
NASA Astrophysics Data System (ADS)
Zhang, Zhishuai; Jafarpour, Behnam; Li, Lianlin
2014-06-01
Characterization of the rock permeability distribution in compartmentalized deep aquifers, enhanced geothermal systems, and hydrocarbon reservoirs is important for predicting the flow and transport behavior in these formations. Reliable prediction of the fluid flow and transport processes can, in turn, lead to effective development of the subsurface energy and environmental resources. In deep formations where thermal gradients are significant, the transient temperature data can provide valuable information about the permeability distribution with depth and about the vertical fluid displacement. This paper examines the importance of temperature data in resolving the distribution of permeability with depth by jointly, and individually, integrating the transient temperature and flow data. We demonstrate that when estimating permeability distributions in deep geothermal reservoirs, incorporating temperature data can increase the resolution of the permeability distribution profile with depth. To illustrate the importance of temperature measurements, we adopt a coupled transient heat and fluid flow as a forward model to predict the heat and fluid transport in a geothermal reservoir and develop an adjoint model for efficient computation of the gradient information for model calibration. We perform a series of numerical experiments for integration of flow and pressure data alone, temperature data alone, and flow and pressure jointly with temperature data. In each case, we apply the maximum A-posteriori (MAP) method and the randomized maximum likelihood (RML) method for inversion and uncertainty quantification. Analysis of the sensitivity of temperature and production data to heterogeneous permeability distributions reveals that the temperature of fluid, even when measured at the surface, is sensitive to the permeability distribution in the vertical extent of the reservoir. Hence, temperature measurements can be augmented with flow-related data to enhance the resolution of
Spatial connectivity in a highly heterogeneous aquifer: From cores to preferential flow paths
Bianchi, M.; Zheng, C.; Wilson, C.; Tick, G.R.; Liu, Gaisheng; Gorelick, S.M.
2011-01-01
This study investigates connectivity in a small portion of the extremely heterogeneous aquifer at the Macrodispersion Experiment (MADE) site in Columbus, Mississippi. A total of 19 fully penetrating soil cores were collected from a rectangular grid of 4 m by 4 m. Detailed grain size analysis was performed on 5 cm segments of each core, yielding 1740 hydraulic conductivity (K) estimates. Three different geostatistical simulation methods were used to generate 3-D conditional realizations of the K field for the sampled block. Particle tracking calculations showed that the fastest particles, as represented by the first 5% to arrive, converge along preferential flow paths and exit the model domain within preferred areas. These 5% fastest flow paths accounted for about 40% of the flow. The distribution of preferential flow paths and particle exit locations is clearly influenced by the occurrence of clusters formed by interconnected cells with K equal to or greater than the 0.9 decile of the data distribution (10% of the volume). The fraction of particle paths within the high-K clusters ranges from 43% to 69%. In variogram-based K fields, some of the fastest paths are through media with lower K values, suggesting that transport connectivity may not require fully connected zones of relatively homogenous K. The high degree of flow and transport connectivity was confirmed by the values of two groups of connectivity indicators. In particular, the ratio between effective and geometric mean K (on average, about 2) and the ratio between the average arrival time and the arrival time of the fastest particles (on average, about 9) are consistent with flow and advective transport behavior characterized by channeling along preferential flow paths. ?? 2011 by the American Geophysical Union.
NASA Astrophysics Data System (ADS)
Grathwohl, P.; Piepenbrink, M.; Eberhardt, C.; Kasper, M.; Gauglitz, G.
2005-12-01
Natural attenuation (mainly biodegradation) of organic pollutants in groundwater often depends on mixing of electron donors and acceptors in the plume fringes, the spatial distribution of these highly reactive zones, compared to the volume of the whole plume, is quite small and characterized by steep concentration gradients. Mixing in the field is the result of transverse dispersion, which is a function of groundwater flow velocity, the typical length scale in the aquifer (e.g. grain size) as well as the aquifer heterogeneities, and the dynamics of the natural flow system. The objectives of this work are to investigate dispersion-limited reactions in well-controlled bench-scale experiments i.e. to elaborate how heterogeneities and transient conditions at the field scale (in time and space) influence the overall natural attenuation rates of organic pollutants in groundwater. Experiments in which (a) the spreading of a conservative tracer cloud or (b) the reaction of two reaction partners at the plume fringe is limited by transverse dispersion are currently investigated in the lab. As the quantification of transverse dispersivities in heterogeneous media under transient flow conditions requires monitoring with high resolution in space and time new optical tools (CCD camera) are employed for the quantitative mapping of the plumes.The first experiments were conducted at bench scale using a continuous injection of a conservative colour tracers (fluorescine), which show absorption only at a specific range of wavelengths in the visible spectrum, a quantification of this tracers is thus possible by its colour depth. Quality control of the quantification obtained by the CCD set-up is done via conventional sampling and analysis at the outlet ports during steady state flow conditions. Currently, well controlled acid-base reactions, are monitored by the colour changes of pH-indicators.This efficient spatially and time-resolved monitoring of concentration gradient changes by
High-performance Integrated numerical methods for Two-phase Flow in Heterogeneous Porous Media
NASA Astrophysics Data System (ADS)
Chueh, Chih-Che; Djilali, Ned; Bangerth, Wolfgang
2010-11-01
Modelling of two-phase flow in heterogeneous porous media has been playing a decisive role in a variety of areas. However, how to efficiently and accurately solve the governing equation in the flow in porous media remains a challenge. In order to ensure the accurate representative flow field and simultaneously increase the computational efficiency, we incorporate a number of state-of-the-art techniques into a numerical framework on which more complicated models in the field of multi-phase flow in porous media will be based. Such a numerical framework consists of a h-adaptive refinement method, an entropy-based artificial diffusive term, a new adaptive operator splitting method and efficient preconditioners. In particular, it is emphasized that we propose a new efficient adaptive operator splitting to avoid solving a time-consuming pressure-velocity part every saturation time step and, most importantly, we also provide a theoretically numerical analysis as well as proof. A few benchmarks will be demonstrated in the presentation.
Naff, R.L.; Haley, D.F.; Sudicky, E.A.
1998-01-01
In this, the first of two papers concerned with the use of numerical simulation to examine flow and transport parameters in heterogeneous porous media via Monte Carlo methods, Various aspects of the modelling effort are examined. In particular, the need to save on core memory causes one to use only specific realizations that have certain initial characteristics; in effect, these transport simulations are conditioned by these characteristics. Also, the need to independently estimate length Scales for the generated fields is discussed. The statistical uniformity of the flow field is investigated by plotting the variance of the seepage velocity for vector components in the x, y, and z directions. Finally, specific features of the velocity field itself are illuminated in this first paper. In particular, these data give one the opportunity to investigate the effective hydraulic conductivity in a flow field which is approximately statistically uniform; comparisons are made with first- and second-order perturbation analyses. The mean cloud velocity is examined to ascertain whether it is identical to the mean seepage velocity of the model. Finally, the variance in the cloud centroid velocity is examined for the effect of source size and differing strengths of local transverse dispersion.
The Effect of Preferential Flow on Colloidal Transport in Unsaturated Heterogeneous Sand
NASA Astrophysics Data System (ADS)
Mishurov, M.; Yakirevich, A.; Weisbrod, N.; Kuznetsov, M.
2006-12-01
Transport of colloids may be greatly enhanced by the presence of preferential flow pathways (PF). The impact of PF on the overall colloid transport was investigated in unsaturated heterogeneous sand under steady-state flow conditions. The experiments were conducted in a 30 cm column, with 11.5 cm internal diameter. Two types of acid-cleaned sand were used to pack the column: coarse (d50 = 1.2 mm) and fine (d50 = 0.36 mm). Heterogeneity created by three continuous bodies of fine sand (within a column of coarse sand) comprised 3.7% of the total sand volume. Water content and pressure head in the coarse sand were monitored with three pairs of TDR probes and tensiometers, respectively, evenly spaced along the column length. Experiments were performed under three different flow rates applied at the top of the column using a rain simulator. Negative pressure (-8, -6, and -5.5 cm corresponding to flow rates of 0.1, 0.2 and 0.4 cm/min, respectively) was maintained at the bottom of the column to produce a constant water content profile (11, 12 and 14% by volume, respectively) in coarse sand. Numerical simulations that were carried out using a double porosity, double permeability model and the Hydrus-2D model, showed higher water content, hydraulic conductivity and, as a result, greater flux in fine sand compared with the bulk of coarse sand. Three sizes of fluorescent latex microspheres were used: 1, 0.2 and 0.02 μm in a mixture with conservative tracers (LiBr). A pulse injection of one water column volume (corresponding to a prescribed water content) of solution was followed by flushing with artificial rainwater. The main features of the breakthrough curves (BTCs) obtained from the heterogeneously packed column were earlier arrival of tracer concentration front (as early as 0.25 water column volume) and tailing. Colloid arrival occurred at effectively the same time as that of conservative tracers, with the exception of the smallest colloids (0.02 μm), which arrived with
Evaluation of a Heterogeneity Preserving Inversion Method for Subsurface Unsaturated Flow
NASA Astrophysics Data System (ADS)
Zhang, Y.; Schaap, M. G.; Neuman, S. P.; Guadagnini, A.; Riva, M.
2013-12-01
Natural recharge to groundwater in semi-arid regions is driven by unsaturated flow through an often deep vadose zone. Understanding and modeling such flow requires knowledge of the subsurface heterogeneity of hydraulic properties. It is expensive and labor intensive to measure such properties, making it necessary to rely on other sources of information. Pedotransfer functions (PTFs) constitute cheap and viable tools to estimate hydraulic properties from soil or sediment texture. Due to the predominantly empirical nature of PTFs and the fact that PTFs are often based on data derived from small laboratory samples, biased estimates of hydraulic parameters may be produced that would likely bias modeled field scale deep vadose zone flow. In this work, an inversion framework that treats the subsurface as a composite medium formed by different zones, each associated with spatially heterogeneous hydraulic parameters, is developed to allow (a) preserving the details of the subsurface heterogeneous nature and (b) assuring consistency among hydraulic parameters associated with different regions of the domain. The approach is demonstrated through a field application, which considers the Maricopa site near Phoenix, Arizona. The study site is a 50x50 meter and 15 meter deep vadose zone at which a 28-day constant-rate infiltration experiment was conducted in 2001. Moisture content at the site was measured daily with neutron thermalization at 400 locations during the infiltration period, and at irregular intervals 100 and 200 days prior and after infiltration, respectively. A PTF based on the Rosetta model is applied on the basis of measured spatial distributions of textural and bulk density data to provide initial estimates of the three-dimensional structure of hydraulic properties. Simple linear functions are defined that transform the PTF estimates of soil hydraulic properties values into hydraulic parameters that minimize the objective functions for the domain, while zonation
Study on Two-Phase Flow in Heterogeneous Porous Media by Light Transmission Method
NASA Astrophysics Data System (ADS)
Qiao, W.
2015-12-01
The non-aqueous phase liquid (NAPL) released to the subsurface can form residual ganglia and globules occupying pores and also accumulate and form pools, in which multiphase system forms. Determining transient fluid saturations in a multiphase system is essential to understand the flow characteristics of systems and to perform effective remediation strategies. As a non-destructive and non-invasive laboratory technique utilized for the measurement of liquid saturation in porous media, light transmission is of the lowest cost and safe. Utilization of Coupled Charge Device camera in light transmission systems provides a nearly instantaneous high-density array of spatial measurements over a very large dynamic range. The migration of NAPL and air spariging technique applied to remove NAPL in aquifer systems are typically two-phase flow problem. Because of the natural aquifer normally being heterogeneous, two 2-D sandboxes (Length55cm×width1.3cm×hight45cm) are set up to study the migration of gas and DNAPL in heterogeneous porous media based on light transmission method and its application in two-phase flow. Model D for water/gas system developed by Niemet and Selker (2001) and Model NW-A for water/NAPL system developed by Zhang et al. (2014) are applied for the calculation of fluid saturation in the two experiments, respectively. The gas injection experiments show that the gas moves upward in the irregular channels, piling up beneath the low permeability lenses and starting lateral movement. Bypassing the lenses, the gas moves upward and forms continuous distribution in the top of the sandbox. The faster of gas injects, the wider of gas migration will be. The DNAPL infiltration experiment shows that TCE mainly moves downward as the influence of gravity, stopping vertical infiltration when reaching the low permeability lenses because of its failure to overcome the capillary pressure. Then, TCE accumulates on the surface and starts transverse movement. Bypassing the
An Inverse Model of Three-Dimensional Flow and Transport in Heterogeneous Porous Media
NASA Astrophysics Data System (ADS)
Robinson, B. A.; Vrugt, J. A.; Yoon, H.; Zhang, C.; Werth, C. J.; Kitanidis, P. K.; Lichtner, P. C.; Lu, C.
2007-12-01
A three-dimensional flow and transport model was developed to simulate the results of a laboratory-scale experiment in which snapshots of concentration were obtained using magnetic resonance imaging (MRI) during the displacement of tracer through a 14 by 8 by 8 cm flow cell. The medium was deliberately constructed to be heterogeneous with a known spatial correlation structure using sand of five different grain-size distributions. The extremely well characterized flow cell and large, high-precision data set of concentrations during displacement make this a unique experiment for examining the validity of flow and transport models, and for exploring new methods for interpreting large data sets using advanced optimization algorithms. A transport model was constructed by solving the steady state flow equations using the Finite Element Heat and Mass (FEHM) code, using FEHM's particle tracking transport model for simulating tracer migration. The particle tracking model was selected so that precise estimates of the transport parameters could be obtained that are not corrupted by numerical dispersion; a large number of particles (typically one million) were required to provide accuracy. The inverse model included nine uncertain parameters, the five permeability values of the individual sand units, and four dispersion/diffusion parameters. The inverse problem was solved with AMALGAM and DREAM, two recently developed self-adaptive multimethod optimization algorithms. The computations were enabled by performing both the transport model and the optimization loop on a high-performance computing cluster. Computational results indicate that parameter estimates and increased understanding of the behavior of the system can be obtained, and significant improvements in the fit to the data over hand calibration can be achieved, using this inverse modeling approach. The study also illustrates that numerical methods that make effective use of high- performance computing resources and
Capillary transit time heterogeneity and flow-metabolism coupling after traumatic brain injury
Østergaard, Leif; Engedal, Thorbjørn S; Aamand, Rasmus; Mikkelsen, Ronni; Iversen, Nina K; Anzabi, Maryam; Næss-Schmidt, Erhard T; Drasbek, Kim R; Bay, Vibeke; Blicher, Jakob U; Tietze, Anna; Mikkelsen, Irene K; Hansen, Brian; Jespersen, Sune N; Juul, Niels; Sørensen, Jens CH; Rasmussen, Mads
2014-01-01
Most patients who die after traumatic brain injury (TBI) show evidence of ischemic brain damage. Nevertheless, it has proven difficult to demonstrate cerebral ischemia in TBI patients. After TBI, both global and localized changes in cerebral blood flow (CBF) are observed, depending on the extent of diffuse brain swelling and the size and location of contusions and hematoma. These changes vary considerably over time, with most TBI patients showing reduced CBF during the first 12 hours after injury, then hyperperfusion, and in some patients vasospasms before CBF eventually normalizes. This apparent neurovascular uncoupling has been ascribed to mitochondrial dysfunction, hindered oxygen diffusion into tissue, or microthrombosis. Capillary compression by astrocytic endfeet swelling is observed in biopsies acquired from TBI patients. In animal models, elevated intracranial pressure compresses capillaries, causing redistribution of capillary flows into patterns argued to cause functional shunting of oxygenated blood through the capillary bed. We used a biophysical model of oxygen transport in tissue to examine how capillary flow disturbances may contribute to the profound changes in CBF after TBI. The analysis suggests that elevated capillary transit time heterogeneity can cause critical reductions in oxygen availability in the absence of ‘classic' ischemia. We discuss diagnostic and therapeutic consequences of these predictions. PMID:25052556
NASA Astrophysics Data System (ADS)
Chang, Ching-Min; Yeh, Hund-Der
2016-09-01
This work describes an investigation of the spatial statistical structure of specific discharge field and solute transport process of a nonreactive solute at the field scale through a heterogeneous deformable porous medium. The flow field is driven by a vertical gradient in the excess pore water pressure induced by a step increase in load applied on the upper part of a finite-thickness aquifer. The non-stationary spectral representation is adopted to characterize the spatial covariance of the specific discharge field necessary for the development of the solute particle trajectory statistics using the Lagrangian formalism. We show that the statistics of the specific discharge and particle trajectory derived herein are non-stationary and functions of the coefficient of soil compressibility, μ. The effect of μ on the relative variation of specific discharge and the solute particle trajectory statistics are analyzed upon evaluating our expressions.
An improved multi-value cellular automata model for heterogeneous bicycle traffic flow
NASA Astrophysics Data System (ADS)
Jin, Sheng; Qu, Xiaobo; Xu, Cheng; Ma, Dongfang; Wang, Dianhai
2015-10-01
This letter develops an improved multi-value cellular automata model for heterogeneous bicycle traffic flow taking the higher maximum speed of electric bicycles into consideration. The update rules of both regular and electric bicycles are improved, with maximum speeds of two and three cells per second respectively. Numerical simulation results for deterministic and stochastic cases are obtained. The fundamental diagrams and multiple states effects under different model parameters are analyzed and discussed. Field observations were made to calibrate the slowdown probabilities. The results imply that the improved extended Burgers cellular automata (IEBCA) model is more consistent with the field observations than previous models and greatly enhances the realism of the bicycle traffic model.
NASA Astrophysics Data System (ADS)
Nicolaides, C.; Cueto-Felgueroso, L.; Juanes, R.
2013-12-01
Fluid mixing plays a fundamental role in many natural and engineered processes, including groundwater flows in heterogeneous media [1], enhanced oil recovery, and microfluidic lab-on-a-chip systems. Recent work has explored the effect of viscosity contrast on mixing, suggesting that the unstable displacement of fluids with different viscosities, or viscous fingering, provides a powerful mechanism to increase fluid-fluid interfacial area and enhance mixing [2]. However, existing studies have not incorporated the effect of medium heterogeneity on the mixing rate. Here, we characterize the evolution of mixing between two fluids of different viscosity on heterogeneous porous media. We focus on a practical scenario of divergent-convergent flow--a quarter five spot geometry--prototypical of well-driven groundwater flows [3]. We discuss the effect of permeability heterogeneity and viscosity contrast on mixing efficiency and breakthrough curves, and we rationalize the nontrivial mixing behavior that emerges from the competition between the creation of fluid-fluid interfacial area and channeling. [1] M. Dentz, T. Le Borgne, A. Englert, and B. Bijeljic, Mixing, spreading and reaction in heterogeneous media: A brief review, J. Contam. Hydrol. 120, 1-17 (2011). [2] B. Jha, L. Cueto-Felgueroso, and R. Juanes, Fluid mixing from viscous fingering. Phys. Rev. Lett. 106, 194502 (2011) [3] J. Luo, M. Dentz, O. A. Cirpka, and P. K. Kitanidis, Breakthrough curve tailing in a dipole flow field, Water Resour. Res. 43(9), W09403 (2007).
Generalized gas-solid adsorption modeling: Single-component equilibria
Ladshaw, Austin; Yiacoumi, Sotira; Tsouris, Costas; DePaoli, David W.
2015-01-07
Over the last several decades, modeling of gas–solid adsorption at equilibrium has generally been accomplished through the use of isotherms such as the Freundlich, Langmuir, Tóth, and other similar models. While these models are relatively easy to adapt for describing experimental data, their simplicity limits their generality to be used with many different sets of data. This limitation forces engineers and scientists to test each different model in order to evaluate which one can best describe their data. Additionally, the parameters of these models all have a different physical interpretation, which may have an effect on how they can bemore » further extended into kinetic, thermodynamic, and/or mass transfer models for engineering applications. Therefore, it is paramount to adopt not only a more general isotherm model, but also a concise methodology to reliably optimize for and obtain the parameters of that model. A model of particular interest is the Generalized Statistical Thermodynamic Adsorption (GSTA) isotherm. The GSTA isotherm has enormous flexibility, which could potentially be used to describe a variety of different adsorption systems, but utilizing this model can be fairly difficult due to that flexibility. To circumvent this complication, a comprehensive methodology and computer code has been developed that can perform a full equilibrium analysis of adsorption data for any gas-solid system using the GSTA model. The code has been developed in C/C++ and utilizes a Levenberg–Marquardt’s algorithm to handle the non-linear optimization of the model parameters. Since the GSTA model has an adjustable number of parameters, the code iteratively goes through all number of plausible parameters for each data set and then returns the best solution based on a set of scrutiny criteria. Data sets at different temperatures are analyzed serially and then linear correlations with temperature are made for the parameters of the model. The end result is a full set
Generalized gas-solid adsorption modeling: Single-component equilibria
Ladshaw, Austin; Yiacoumi, Sotira; Tsouris, Costas; DePaoli, David W.
2015-01-07
Over the last several decades, modeling of gas–solid adsorption at equilibrium has generally been accomplished through the use of isotherms such as the Freundlich, Langmuir, Tóth, and other similar models. While these models are relatively easy to adapt for describing experimental data, their simplicity limits their generality to be used with many different sets of data. This limitation forces engineers and scientists to test each different model in order to evaluate which one can best describe their data. Additionally, the parameters of these models all have a different physical interpretation, which may have an effect on how they can be further extended into kinetic, thermodynamic, and/or mass transfer models for engineering applications. Therefore, it is paramount to adopt not only a more general isotherm model, but also a concise methodology to reliably optimize for and obtain the parameters of that model. A model of particular interest is the Generalized Statistical Thermodynamic Adsorption (GSTA) isotherm. The GSTA isotherm has enormous flexibility, which could potentially be used to describe a variety of different adsorption systems, but utilizing this model can be fairly difficult due to that flexibility. To circumvent this complication, a comprehensive methodology and computer code has been developed that can perform a full equilibrium analysis of adsorption data for any gas-solid system using the GSTA model. The code has been developed in C/C++ and utilizes a Levenberg–Marquardt’s algorithm to handle the non-linear optimization of the model parameters. Since the GSTA model has an adjustable number of parameters, the code iteratively goes through all number of plausible parameters for each data set and then returns the best solution based on a set of scrutiny criteria. Data sets at different temperatures are analyzed serially and then linear correlations with temperature are made for the parameters of the model. The end result is a full set of
The recovering of the contaminant release history in heterogeneous and partially known flow field
NASA Astrophysics Data System (ADS)
Zanini, A.; Cupola, F.; Tanda, M. G.
2015-12-01
The recovering of the release history of a pollutant in an aquifer is a subject that obtains the researchers attention since 1990 because the knowledge of the pollutant discharge history can be a useful tool to share, among the responsible parties, the costs of the remediation actions. The methods developed are based on the perfect knowledge of the flow field where the pollutant event has occurred. But very often this perfect knowledge is only an unattainable hope: few boreholes and pumping tests are usually available and realizing new ones can lead to unacceptable costs. An evaluation of the reliability of the results obtained with the procedures for the recovering of the release history in heterogeneous and partially known flow field can be a very useful subject under the point of view of researchers and the practitioners. In fact the different methods can be more or less sensitive to the problem or give information that includes or not an uncertainty evaluation; moreover it can be possible to quantify the adequate amount of the site characterization actions. In this work we deal with a geostatistically based approach that in the past we have successfully applied on a perfect-known transmissivity field. The objective of the actual study is to investigate the importance of the knowledge of the hydraulic conductivity field and to identifying the minimum information required for recovering an acceptable release history. At this aim we built a numerical model of a 2-D confined aquifer with rectangular shape characterized by a heterogeneous hydraulic conductivity field. We estimate the conductivity field through a kriging interpolation starting from values sampled on a regular grids of different density and on that partially known field we estimate the pollutant release history. The results show that the reliability of the recovered release history, of course, increases with the density of the grid but meaningful indications can be obtained also with not very detailed
NASA Astrophysics Data System (ADS)
Kuhlmann, A.; Neuweiler, I.; van der Zee, S. E. A. T. M.; Helmig, R.
2012-02-01
We analyze the combined effects of the spatial variability of soil hydraulic properties and the water uptake by plant roots on unsaturated water flow. For this analysis, we use a simplified macroscopic root water uptake model which is usually applied only for homogeneous or layered soil and therefore we also determine whether it is applicable for multidimensional heterogeneous media. Analytical solutions for mean and variance of pressure head (first-order second-moment approximations) in layered media and numerical solutions of two-dimensional (2-D) autocorrelated multi-Gaussian and non multi-Gaussian parameter fields are analyzed for steady state and transient flow conditions. For non-Gaussian topological features, that have little influence on the mean and the variance of the pressure field if root water uptake is ignored, we test whether the influence is significant if root water uptake is accounted for. The results reveal that, in field structures with large patches of coarse material, local regions with pressure head values at the wilting point develop; these are surrounded by wet material. Without a compensation mechanism for local stress, the global transpiration demand is not met if local wilting occurs. Various compensation mechanisms are tested that depend, respectively, on the saturation, the relative conductivity or a strategy where the deficit in the global uptake rate is equally distributed to unstressed locations. The strategies lead to a global actual transpiration rate at the potential value and attenuate the formation of locally wilted areas. Wilted regions can, however, still occur, and may be an artifact of the simplified model concept as root-soil interactions are neglected. Therefore simplified macroscopic models for root water uptake should be used with caution in heterogeneous media.
NASA Astrophysics Data System (ADS)
De Schepper, G.; Therrien, R.; Refsgaard, J.
2012-12-01
Subsurface drainage is a common agricultural practice in poorly drained production fields to guarantee the productivity of crops and to reduce flooding risks. The impact of shallow tile-drainage networks on groundwater flow patterns and associated nitrate transport from the surface needs to be quantified for adequate agricultural management. A challenge is to represent tile-drain networks in numerical models, at the field scale, while accounting for the influence of subsurface heterogeneities on flow and transport. A numerical model of a tile-drainage system has been developed with the fully integrated HydroGeoSphere model for the Lillebaek agricultural catchment, Denmark. The Lillebaek catchment is an experimental study area where hydraulic heads, stream and drain discharges, as well as groundwater and surface water nitrate concentrations are regularly measured. This catchment includes various tile-drainage networks that are monitored on a daily basis; the one we have been focusing on is about 5 ha within a 34 ha model domain. The Lillebaek catchment subsurface is made of about 30 m thick Quaternary deposits which consist of a local sandy aquifer with upper and lower clayey till units, confining the aquifer in the upper part. The main modelling objective is to assess the influence of tile drains on the water flow pattern within the confining clayey till unit with and on the nitrate reduction zone depth, also known as the redox-interface, while accounting for local geological heterogeneities. Using the national-scale geological model for Denmark combined with available local data, a hydrogeological model at field scale has been generated. A proper representation of the tile-drains geometry is essential to calibrate and validate the water flow model associated with nitrate transport. HydroGeoSphere can represent drains directly into a model as one-dimensional features, which however requires a very fine mesh discretization that limits the size of the simulation
Ultrasonic levitation for the examination of gas/solid reactions
NASA Astrophysics Data System (ADS)
Kavouras, A.; Krammer, G.
2003-10-01
An experimental setup based on acoustic levitation for the examination of gas/solid reactions is presented. In this setup single particles in the diameter range 1 mm-30 μm can be held against gravity for any wanted time in a defined gas atmosphere at elevated temperatures. The change of particle size, shape, and position can be measured and recorded using an optical device, consisting of a camera and a long range microscope. Basic experiments with inert particles of different shape and solid density have shown that the axial position of a reacting particle can be employed to derive its weight change. A method to evaluate this change of the recorded position for the according weight change is proposed. Exemplary results in the context of dry flue gas cleaning using Ca(OH)2 powder are presented. Single Ca(OH)2 particles are exposed to a well defined gas atmosphere and after some time these particles are retrieved from the ultrasonic field for further analyses. Only an in situ measurement of the particle weight change (i.e., without removing the particle from the well defined reactive atmosphere) brings information regarding the uptake of water by the sorbent, which accompanies SO2 and HCl absorption.
Real time mass flux measurements of gas-solid suspensions at low velocities
Saunders, J H; Chao, B T; Soo, S L
1981-01-01
In previous work, measurement of the particulate mass flux was made based upon a novel electrostatic technique. A small conducting wire sensor was inserted in the flow and as each particle hit the sensor an individual pulse of current was identified. Through suitable electronic circuitry, the number of pulses in a given time were counted. This was a direct measure of the number of particle-probe collisions which was related to local particle mass flow. The technique is currently limited to monodisperse suspensions. A primary advantage of the impact counter system is that the output does not depend upon the magnitude of the actual charge transfer. As long as the pulses are sufficiently above the noise level, variations in charge transfer will not affect the measurement. For the current work, the technique was applied to vertical gas-solid flow where the fluid velocity was slightly above the particle terminal velocity. Under these conditions a sufficient signal to noise ratio was not found. The Cheng-Soo charge transfer theory indicated that the low particle-sensor impact velocity was responsible. The probe system was then modified by extracting a particulate sample isokinetically and accelerating the particles to a sufficient velocity by an area reduction in the sampling tube. With this technique the signal to noise ratio was about 12 to 1. Mass flux results are shown to compare favorably with filter collection and weighing.
A stochastic multiscale framework for modeling flow through random heterogeneous porous media
Ganapathysubramanian, B.; Zabaras, N.
2009-02-01
Flow through porous media is ubiquitous, occurring from large geological scales down to the microscopic scales. Several critical engineering phenomena like contaminant spread, nuclear waste disposal and oil recovery rely on accurate analysis and prediction of these multiscale phenomena. Such analysis is complicated by inherent uncertainties as well as the limited information available to characterize the system. Any realistic modeling of these transport phenomena has to resolve two key issues: (i) the multi-length scale variations in permeability that these systems exhibit, and (ii) the inherently limited information available to quantify these property variations that necessitates posing these phenomena as stochastic processes. A stochastic variational multiscale formulation is developed to incorporate uncertain multiscale features. A stochastic analogue to a mixed multiscale finite element framework is used to formulate the physical stochastic multiscale process. Recent developments in linear and non-linear model reduction techniques are used to convert the limited information available about the permeability variation into a viable stochastic input model. An adaptive sparse grid collocation strategy is used to efficiently solve the resulting stochastic partial differential equations (SPDEs). The framework is applied to analyze flow through random heterogeneous media when only limited statistics about the permeability variation are given.
An Improved Discrete-Time Model for Heterogeneous High-Speed Train Traffic Flow
NASA Astrophysics Data System (ADS)
Xu, Yan; Jia, Bin; Li, Ming-Hua; Li, Xin-Gang
2016-03-01
This paper aims to present a simulation model for heterogeneous high-speed train traffic flow based on an improved discrete-time model (IDTM). In the proposed simulation model, four train control strategies, including departing strategy, traveling strategy, braking strategy, overtaking strategy, are well defined to optimize train movements. Based on the proposed simulation model, some characteristics of train traffic flow are investigated. Numerical results indicate that the departure time intervals, the station dwell time, the section length, and the ratio of fast trains have different influence on traffic capacity and train average velocity. The results can provide some theoretical support for the strategy making of railway departments. Supported by the National Basic Research Program of China under Grant No. 2012CB725400, the National Natural Science Foundation of China under Grant No. 71222101, the Research Foundation of State Key Laboratory of Rail Traffic Control and Safety under Grant No. RCS2014ZT16, and the Fundamental Research Funds for the Central Universities No. 2015YJS088, Beijing Jiaotong University
STRUCTURAL HETEROGENEITIES AND PALEO FLUID FLOW IN AN ANALOG SANDSTONE RESERVOIR 2001-2004
Pollard, David; Aydin, Atilla
2005-02-22
Fractures and faults are brittle structural heterogeneities that can act both as conduits and barriers with respect to fluid flow in rock. This range in the hydraulic effects of fractures and faults greatly complicates the challenges faced by geoscientists working on important problems: from groundwater aquifer and hydrocarbon reservoir management, to subsurface contaminant fate and transport, to underground nuclear waste isolation, to the subsurface sequestration of CO2 produced during fossil-fuel combustion. The research performed under DOE grant DE-FG03-94ER14462 aimed to address these challenges by laying a solid foundation, based on detailed geological mapping, laboratory experiments, and physical process modeling, on which to build our interpretive and predictive capabilities regarding the structure, patterns, and fluid flow properties of fractures and faults in sandstone reservoirs. The material in this final technical report focuses on the period of the investigation from July 1, 2001 to October 31, 2004. The Aztec Sandstone at the Valley of Fire, Nevada, provides an unusually rich natural laboratory in which exposures of joints, shear deformation bands, compaction bands and faults at scales ranging from centimeters to kilometers can be studied in an analog for sandstone aquifers and reservoirs. The suite of structures there has been documented and studied in detail using a combination of low-altitude aerial photography, outcrop-scale mapping and advanced computational analysis. In addition, chemical alteration patterns indicative of multiple paleo fluid flow events have been mapped at outcrop, local and regional scales. The Valley of Fire region has experienced multiple episodes of fluid flow and this is readily evident in the vibrant patterns of chemical alteration from which the Valley of Fire derives its name. We have successfully integrated detailed field and petrographic observation and analysis, process-based mechanical modeling, and numerical
NASA Astrophysics Data System (ADS)
Samanta, Susanta Kumar; Mandal, Nibir; Chakraborty, Chandan
2002-07-01
Rocks that are mechanically heterogeneous due to the presence of stiff or rigid inclusions floating in a ductile matrix, commonly show a variety of micro- to macro-scale structures developing under the influence of heterogeneous flow field in the neighbourhood of the inclusions. It is of fundamental importance to apprehend the nature of strain heterogeneity around inclusions to understand progressive development of structures associated with rigid inclusions such as strain shadow, foliation drag, porphyroclast mantle, porphyroblast inclusion trails, intragranular fractures, etc. The development of these diverse types of structures can be analyzed with the help of a suitable hydrodynamic theory. In this paper, we review different continuum models that have been proposed to characterize the heterogeneous flow field around rigid inclusions, focusing on recent developments. Recent studies reveal that Jeffery's [Proc. R. Soc. Lond. A 120 (1922) 161.] theory dealing with the motion of ellipsoidal rigid bodies in an infinitely extended viscous medium is more general in nature, and applicable for modeling the heterogeneous flow around both equant and inequant shapes of inclusions and ideal or non-ideal shear deformation of the matrix. The application of this theory, therefore, has advantages over other models, based on Lamb's [Lamb, H., 1932. Hydrodynamics. Cambridge University Press, Cambridge.] theory dealing with spherical inclusions. The review finally illustrates numerical simulations based on hydrodynamic theories, highlighting the controls of physical and kinematic factors on the progressive development of the structures mentioned above.
NASA Astrophysics Data System (ADS)
Angulo-Jaramillo, R.; Bien, L.; Hehn, V.; Winiarski, T.
2011-12-01
Colloidal particles transport through vadose zone can contribute to fast transport of contaminants into groundwater. The objective is to study the preferential flow and transport of colloids in heterogeneous unsaturated soil subjected to high organic matter entry. A physically based model is developed based on a large laboratory lysimeter than usual laboratory column experiments. LUGH-Lysimeter for Unsaturated Groundwater Hydrodynamics- is used to embed a soil monolith (1.6 m3) made of different cross-bedded lithological types with contrasting hydraulic properties. The filling material is a carbonated graded sand and gravel from the fluvioglacial vadose zone of the east of Lyon (France). Materials are 3D arranged on contrasting textured lithofacies analogous to the sedimentary lithology of a fluvioglacial cross-bedded deposit. Tracer (Br 1E-2M) and colloid solutions were injected in a pulse mode using a rainfall simulator. Colloid solution is Chlamydomonas reinhardtii at 3.2E+6 units/mL concentration. These unicellular algae can be considered as spherical particles from 6 to 10 μm in diam. Their resistance and doubling time of cell growth are greater than the transfer time in the lysimeter. Algae moving into the porous medium do not immediately reproduce, and then the population size remains constant. During this period, called the lag phase (1 to 2 days), the cells are metabolically active and increase only in cell size. Tensiometers, TDR and electric resistivity enable measurements of the parameters related to flow, solute and colloid transfer. Eluted solutions are sampled by 15 separated fraction collectors, leading to independent breakthrough curves. Eluted colloid concentration is measured by spectrofluorometry. The model approach combines Richards equation, coupled to a convective-dispersive equation with a source/sink term for particle transport and mobilization. Macroscopic particle attachment/detachment from pores is assumed to follow first-order kinetics
NASA Astrophysics Data System (ADS)
Jin, G.
2012-12-01
Multiphase flow modeling is an important numerical tool for a better understanding of transport processes in the fields including, but not limited to, petroleum reservoir engineering, remedy of ground water contamination, and risk evaluation of greenhouse gases such as CO2 injected into deep saline reservoirs. However, accurate numerical modeling for multiphase flow remains many challenges that arise from the inherent tight coupling and strong non-linear nature of the governing equations and the highly heterogeneous media. The existence of counter current flow which is caused by the effect of adverse relative mobility contrast and gravitational and capillary forces will introduce additional numerical instability. Recently multipoint flux approximation (MPFA) has become a subject of extensive research and has been demonstrated with great success in reducing considerable grid orientation effects compared to the conventional single point upstream (SPU) weighting scheme, especially in higher dimensions. However, the present available MPFA schemes are mathematically targeted to certain types of grids in two dimensions, a more general form of MPFA scheme is needed for both 2-D and 3-D problems. In this work a new upstream weighting scheme based on multipoint directional incoming fluxes is proposed which incorporates full permeability tensor to account for the heterogeneity of the porous media. First, the multiphase governing equations are decoupled into an elliptic pressure equation and a hyperbolic or parabolic saturation depends on whether the gravitational and capillary pressures are presented or not. Next, a dual secondary grid (called finite volume grid) is formulated from a primary grid (called finite element grid) to create interaction regions for each grid cell over the entire simulation domain. Such a discretization must ensure the conservation of mass and maintain the continuity of the Darcy velocity across the boundaries between neighboring interaction regions
NASA Astrophysics Data System (ADS)
Ţene, Matei; Al Kobaisi, Mohammed Saad; Hajibeygi, Hadi
2016-09-01
This paper introduces an Algebraic MultiScale method for simulation of flow in heterogeneous porous media with embedded discrete Fractures (F-AMS). First, multiscale coarse grids are independently constructed for both porous matrix and fracture networks. Then, a map between coarse- and fine-scale is obtained by algebraically computing basis functions with local support. In order to extend the localization assumption to the fractured media, four types of basis functions are investigated: (1) Decoupled-AMS, in which the two media are completely decoupled, (2) Frac-AMS and (3) Rock-AMS, which take into account only one-way transmissibilities, and (4) Coupled-AMS, in which the matrix and fracture interpolators are fully coupled. In order to ensure scalability, the F-AMS framework permits full flexibility in terms of the resolution of the fracture coarse grids. Numerical results are presented for two- and three-dimensional heterogeneous test cases. During these experiments, the performance of F-AMS, paired with ILU(0) as second-stage smoother in a convergent iterative procedure, is studied by monitoring CPU times and convergence rates. Finally, in order to investigate the scalability of the method, an extensive benchmark study is conducted, where a commercial algebraic multigrid solver is used as reference. The results show that, given an appropriate coarsening strategy, F-AMS is insensitive to severe fracture and matrix conductivity contrasts, as well as the length of the fracture networks. Its unique feature is that a fine-scale mass conservative flux field can be reconstructed after any iteration, providing efficient approximate solutions in time-dependent simulations.
Barth, G.R.; Hill, M.C.; Illangasekare, T.H.; Rajaram, H.
2001-01-01
As a first step toward understanding the role of sedimentary structures in flow and transport through porous media, this work deterministically examines how small-scale laboratory-measured values of hydraulic conductivity relate to in situ values of simple, artificial structures in an intermediate-scale (10 m long), two-dimensional, heterogeneous, laboratory experiment. Results were judged based on how well simulations using measured values of hydraulic conductivities matched measured hydraulic heads, net flow, and transport through the tank. Discrepancies were investigated using sensitivity analysis and nonlinear regression estimates of the in situ hydraulic conductivity that produce the best fit to measured hydraulic heads and net flow. Permeameter and column experiments produced laboratory measurements of hydraulic conductivity for each of the sands used in the intermediate-scale experiments. Despite explicit numerical representation of the heterogeneity the laboratory-measured values underestimated net flow by 12-14% and were distinctly smaller than the regression-estimated values. The significance of differences in measured hydraulic conductivity values was investigated by comparing variability of transport predictions using the different measurement methods to that produced by different realizations of the heterogeneous distribution. Results indicate that the variations in measured hydraulic conductivity were more important to transport than variations between realizations of the heterogeneous distribution of hydraulic conductivity.
Analysis of the Impact of Soil Heterogeneity on the Spatial Variation of Unsaturated Flow
NASA Astrophysics Data System (ADS)
Patterson, Matthew; Gimenez, Daniel; Kerry, Ruth; Goovaerts, Pierre
2016-04-01
Modelling infiltration into soils with deterministic models requires knowledge of the hydraulic properties of that soil. Informing a model with these properties is complex because of the spatial heterogeneity of hydraulic properties that naturally occurs in all soils . The objective of this work was to analyze the effects that contrasting synthetic heterogeneities have on spatial outflows using a three-dimensional numerical model. An undisturbed soil column of 32 cm diameter and 50 cm height was used in an outflow experiment in the laboratory, where outflow was collected from the bottom of the column in 145 spatially-varied outflow cells and the column was subjected to multiple inflow rates. After the completion of the experiment, 30 sub-cores of 8 cm diameter and 5 cm height were extracted from the column and used to measure hydraulic properties and texture through a combination of pressure plate extractor, automated evaporation method, and a dewpoint potentiometer. The spatial heterogeneity of the soil in the column was represented by a Local Indicator of Spatial Autocorrelation (LISA - Local Moran's I) clustering algorithm, which used both texture and Electrical Resistivity Tomography data to identify significant clusters of points with high (HH) and low (LL) values and values that were not part of a significant cluster (NS). Each cluster was also assigned a numerical index based on LISA. Effective hydraulic properties were assigned to the HH and LL clusters and NS points based on the location of the 30 sub-cores and their average hydraulic properties. Resistivity data were used with omni-directional variograms with ranges of 5 and 15 cm and a nugget of 0.25 to conditionally simulate 50 realizations of 3-D data based on each variogram. The LISA algorithm was then used to detect significant clusters in these data and classify them as HH, LL or NS. Importing the resulting 100 sets of synthetic clusters and their corresponding effective hydraulic properties into
NASA Astrophysics Data System (ADS)
Li, Y.; Kazemifar, F.; Blois, G.; Christensen, K. T.
2015-12-01
Multiphase flow of water and supercritical carbon dioxide (CO2) in porous media is central to geological sequestration of CO2 into saline aquifers. However, our fundamental understanding of the coupled flow dynamics of CO2 and water in complex geologic media still remains limited, especially at the pore scale. Recently, studies have been carried out in 2D homogeneous models with the micro-PIV technique, yielding very interesting observations of pore-scale flow transport. The primary aim of this work is to leverage this experimental protocol to quantify the pore-scale flow of water and liquid/supercritical CO2 in 2D heterogeneous porous micromodels under reservoir-relevant conditions. The goal is to capture the dynamics of this multi-phase flow in a porous matrix that mimics the heterogeneity of natural rock. Fluorescent microscopy and the micro-PIV technique are employed to simultaneously measure the spatially-resolved instantaneous velocity field in the water and quantify the instantaneous spatial configuration of both phases. The results for heterogeneous micromodels will be presented and compared with those for homogeneous micromodels, yielding valuable insight into flow processes at the pore scale in natural rock.
NASA Astrophysics Data System (ADS)
Jankovic, I.
2002-05-01
can be used to infer the effective conductivity of the medium. As many as 100,000 inhomogeneities are placed inside the domain for 2D simulations. Simulations in 3D were limited to 50,000 inclusions. A large number of simulations was conducted on a massively parallel supercomputer cluster at the Center for Computational Research, University at Buffalo. Simulations range from mildly heterogeneous formations to highly heterogeneous formations (variance of the logarithm of conductivity equal to 10) and from sparsely populated systems to systems where inhomogeneities cover 95% of the volume. Particles are released and tracked inside the core of constant mean velocity. Following the particle tracking, various medium, flow, and transport statistics are computed. These include: spatial moments of particle positions, probability density function of hydraulic conductivity and each component of velocity, their two-point covariance function in the direction of flow and normal to it, covariance of Lagrangean velocities, and probability density function of travel times to various break-through locations. Following the analytic nature of the flow solution, all the results are presented in dimensionless forms. For example, the dispersion coefficients are made dimensionless with respect to the mean velocity and size of inhomogeneities. Detailed results will be presented and compared to well known first-order results and the results that are based on simple approximate transport solutions of Aldo Fiori.
NASA Astrophysics Data System (ADS)
Buczko, U.; Gerke, H. H.; Hangen, E.; Hüttl, R. F.
2003-04-01
Water balances of forest sites are often estimated using 1-dimensional numerical models and tensiometer data from different depths. The magnitude of groundwater recharge calculated in such a way in most cases cannot be verified experimentally. In heterogeneous soils, water flows are spatially highly variable. The objective of this contribution is to compare the flow and deep percolation within a reclaimed mine soil which was calculated with a 1D numerical model, with seepage water collected, spatially-resolved, in-situ. Further, it is aimed at improving the methodology for calculating water balances and element budgets on heterogeneous mine soils, using 2D models with spatial variability. At the study site “Bärenbrück” near Cottbus, a lignitic mine soil afforested in 1982 with Pinus nigra, the components of the water balance were simulated with a 1D numerical model (SOIL/COUP) for a period from May 1995 to September 2001, using meteorological data and measured water tensions in soil depths 15, 60, and 100 cm. At the same site, soil water percolates were extracted continually in-situ at a soil depth of 110 cm from June 2000 until September 2001 within the framework of a cell-lysimeter study. 2D simulations were performed with the numerical model HYDRUS-2D, using evapotranspiration data obtained with the 1D-model. In the balance period between 4/96 and 3/99, the simulated deep percolation ranges between 30.4 and 35.2 mm per year, whereas during the dryer years 6/1999 5/2000 and 6/2000 5/2001 it amounts to 6.6 mm and 1.5 mm, respectively. The average deep percolation based on the in-situ suction plate data during the same period was 11 mm for the period 6/1999 5/2000 and 24.3 mm for 6/2000 5/2001, although spatially highly variable. Consequently, for the period 6/2000 5/2001, groundwater recharge based on measured in-situ data is by one order of magnitude higher than those simulated with the 1D model. The 2D numerical simulations are used to explain this
Investigation of Gas Solid Fluidized Bed Dynamics with Non-Spherical Particles
Choudhuri, Ahsan
2013-06-30
One of the largest challenges for 21st century is to fulfill global energy demand while also reducing detrimental impacts of energy generation and use on the environment. Gasification is a promising technology to meet the requirement of reduced emissions without compromising performance. Coal gasification is not an incinerating process; rather than burning coal completely a partial combustion takes place in the presence of steam and limited amounts of oxygen. In this controlled environment, a chemical reaction takes place to produce a mixture of clean synthetic gas. Gas-solid fluidized bed is one such type of gasification technology. During gasification, the mixing behavior of solid (coal) and gas and their flow patterns can be very complicated to understand. Many attempts have taken place in laboratory scale to understand bed hydrodynamics with spherical particles though in actual applications with coal, the particles are non-spherical. This issue drove the documented attempt presented here to investigate fluidized bed behavior using different ranges of non-spherical particles, as well as spherical. For this investigation, various parameters are controlled that included particle size, bed height, bed diameter and particle shape. Particles ranged from 355 µm to 1180 µm, bed diameter varied from 2 cm to 7 cm, two fluidized beds with diameters of 3.4 cm and 12.4 cm, for the spherical and non-spherical shaped particles that were taken into consideration. Pressure drop was measured with increasing superficial gas velocity. The velocity required in order to start to fluidize the particle is called the minimum fluidization velocity, which is one of the most important parameters to design and optimize within a gas-solid fluidized bed. This minimum fluidization velocity was monitored during investigation while observing variables factors and their effect on this velocity. From our investigation, it has been found that minimum fluidization velocity is independent of bed
NASA Astrophysics Data System (ADS)
Yadav, B. K.; Tomar, J.; Harter, T.
2014-12-01
We investigate nitrate movement from non-point sources in deep, heterogeneous vadose zones, using multi-dimensional variably saturated flow and transport simulations. We hypothesize that porous media heterogeneity causes saturation variability that leads to preferential flow systems such that a significant portion of the vadose zone does not significantly contribute to flow. We solve Richards' equation and the advection-dispersion equation to simulate soil moisture and nitrate transport regimes in plot-scale experiments conducted in the San Joaquin Valley, California. We compare equilibrium against non-equilibrium (dual-porosity) approaches. In the equilibrium approach we consider each soil layer to have unique hydraulic properties as a whole, while in the dual-porosity approach we assume that large fractions of the porous flow domain are immobile. However we consider exchange of water and solute between mobile and immobile zone using the appropriate mass transfer terms. The results indicate that flow and transport in a nearly 16 m deep stratified vadose zone comprised of eight layers of unconsolidated alluvium experiences highly non-uniform, localized preferential flow and transport patterns leading to accelerated nitrate transfer. The equilibrium approach largely under-predicted the leaching of nitrate to groundwater while the dual-porosity approach showed higher rates of nitrate leaching, consistent with field observations. The dual-porosity approach slightly over-predicted nitrogen storage in the vadose zone, which may be the result of limited matrix flow or denitrification not accounted for in the model. Results of this study may be helpful to better predict fertilizer and pesticide retention times in deep vadose zone, prior to recharge into the groundwater flow system. Keywords: Nitrate, Preferential flow, Heterogeneous vadose zone, Dual-porosity approach
Heterogeneities of in- and out-flows in the Mediterranean Sea
NASA Astrophysics Data System (ADS)
Millot, Claude
2014-01-01
mix; thus, accurately predicting the outflow characteristics in the Atlantic Ocean appears almost impossible. Herein, we first propose a fully objective description of the AWs and MWs during two GIBEX campaigns. Where the AWs and the MWs do not markedly mix, they are defined in terms of density and temperature ranges. Where a MW mixes with one of the AWs down to the bottom, the mixing line characteristics allow for that MW to be followed from one section to one downstream and for the validation of our concept: while superimposed east of the Strait, the MWs come to be juxtaposed within the Strait before becoming superimposed again. We also analysed additional CTD time series collected by the University of Malaga on the south and north sides of the southern sill of Espartel. We demonstrate the following: (a) even though the MWs at the sill (E) and on the south side (ES) were roughly the same, the densest ones out-flowed at ES, i.e., at depths shallower than at E, (b) the MWs on the north side (EN) were very different from those at E and each mixed with different AWs, and (c) using the mixing lines computed from each time series, the data recorded at E and ES allow for the retrieval, with good accuracy, of those recorded at Camarinal (C), which is not the case for the data recorded at EN. Finally we emphasise how different the AWs' heterogeneities are from the MWs' heterogeneities. The inflow is sucked into the Mediterranean Sea, due to the water budget (E-P) deficit there, and it can be composed of any type of AW present west of the Strait at any time and any specific location. The outflow is a product of the Mediterranean Sea, which is like a machine producing a series of MWs that first circulate as alongslope density currents before entering the Strait in a specific order and at specific locations. Consequently, we attempt to schematise the AWs-MWs mixing processes and our understanding of the outflow dynamics. Notwithstanding the difficulty of the working conditions
NASA Astrophysics Data System (ADS)
Hayat, Tasawar; Imtiaz, Maria; Alsaedi, Ahmed
2015-12-01
This paper addresses the steady three-dimensional boundary layer flow of viscous nanofluid. The flow is caused by a permeable stretching surface with second order velocity slip and homogeneous-heterogeneous reactions. Water is treated as base fluid and copper as nanoparticle. An incompressible fluid fills the porous space. The fluid is electrically conducting in the presence of an applied magnetic field. A system of ordinary differential equations is obtained by using suitable transformations. Convergent series solutions are derived. Impact of various pertinent parameters on the velocity, concentration and skin friction coefficient is discussed. Analysis of the obtained results shows that the flow field is influenced appreciably by the presence of velocity slip parameters. Also concentration distribution decreases for larger values of strength of homogeneous reaction parameter while it increases for strength of heterogeneous reaction parameter.
A theory for modeling ground-water flow in heterogeneous media
Cooley, Richard L.
2004-01-01
Construction of a ground-water model for a field area is not a straightforward process. Data are virtually never complete or detailed enough to allow substitution into the model equations and direct computation of the results of interest. Formal model calibration through optimization, statistical, and geostatistical methods is being applied to an increasing extent to deal with this problem and provide for quantitative evaluation and uncertainty analysis of the model. However, these approaches are hampered by two pervasive problems: 1) nonlinearity of the solution of the model equations with respect to some of the model (or hydrogeologic) input variables (termed in this report system characteristics) and 2) detailed and generally unknown spatial variability (heterogeneity) of some of the system characteristics such as log hydraulic conductivity, specific storage, recharge and discharge, and boundary conditions. A theory is developed in this report to address these problems. The theory allows construction and analysis of a ground-water model of flow (and, by extension, transport) in heterogeneous media using a small number of lumped or smoothed system characteristics (termed parameters). The theory fully addresses both nonlinearity and heterogeneity in such a way that the parameters are not assumed to be effective values. The ground-water flow system is assumed to be adequately characterized by a set of spatially and temporally distributed discrete values, ?, of the system characteristics. This set contains both small-scale variability that cannot be described in a model and large-scale variability that can. The spatial and temporal variability in ? are accounted for by imagining ? to be generated by a stochastic process wherein ? is normally distributed, although normality is not essential. Because ? has too large a dimension to be estimated using the data normally available, for modeling purposes ? is replaced by a smoothed or lumped approximation y?. (where y is a
Heterogeneous atmospheric chemistry
NASA Technical Reports Server (NTRS)
Schryer, D. R.
1982-01-01
The present conference on heterogeneous atmospheric chemistry considers such topics concerning clusters, particles and microparticles as common problems in nucleation and growth, chemical kinetics, and catalysis, chemical reactions with aerosols, electron beam studies of natural and anthropogenic microparticles, and structural studies employing molecular beam techniques, as well as such gas-solid interaction topics as photoassisted reactions, catalyzed photolysis, and heterogeneous catalysis. Also discussed are sulfur dioxide absorption, oxidation, and oxidation inhibition in falling drops, sulfur dioxide/water equilibria, the evidence for heterogeneous catalysis in the atmosphere, the importance of heterogeneous processes to tropospheric chemistry, soot-catalyzed atmospheric reactions, and the concentrations and mechanisms of formation of sulfate in the atmospheric boundary layer.
Parallel Computation of Flow in Heterogeneous Media Modelled by Mixed Finite Elements
NASA Astrophysics Data System (ADS)
Cliffe, K. A.; Graham, I. G.; Scheichl, R.; Stals, L.
2000-11-01
In this paper we describe a fast parallel method for solving highly ill-conditioned saddle-point systems arising from mixed finite element simulations of stochastic partial differential equations (PDEs) modelling flow in heterogeneous media. Each realisation of these stochastic PDEs requires the solution of the linear first-order velocity-pressure system comprising Darcy's law coupled with an incompressibility constraint. The chief difficulty is that the permeability may be highly variable, especially when the statistical model has a large variance and a small correlation length. For reasonable accuracy, the discretisation has to be extremely fine. We solve these problems by first reducing the saddle-point formulation to a symmetric positive definite (SPD) problem using a suitable basis for the space of divergence-free velocities. The reduced problem is solved using parallel conjugate gradients preconditioned with an algebraically determined additive Schwarz domain decomposition preconditioner. The result is a solver which exhibits a good degree of robustness with respect to the mesh size as well as to the variance and to physically relevant values of the correlation length of the underlying permeability field. Numerical experiments exhibit almost optimal levels of parallel efficiency. The domain decomposition solver (DOUG, http://www.maths.bath.ac.uk/~parsoft) used here not only is applicable to this problem but can be used to solve general unstructured finite element systems on a wide range of parallel architectures.
Criaud, Annie, Fouassier, Philippe; Fouillac, Christian; Brach, Michel
1988-01-01
Three geothermal wells tapping the Dogger aquifer were studied in detail for their variations in chemical composition with time or conditions of exploitation. Analytical improvements for the determination of Cl, SO{sub 4}, Ca, Mg, Na and K make it possible to detect variations respectively of 0.15, 0.8, 0.6, 1.8, 1.8 and 1.4 %. Despite the fact that the natural flow may be important in some parts of the basin aquifer, we conclude that this factor is not responsible for the small variations noticed in mineralization within the one year survey period. The results concerning reactive and nonreactive species are best explained if a vertical heterogeneity of the chemistry of the fluid is assumed. A number of calcareous sub-layers, already demonstrated by geological studies, contribute to varying degrees to the production of the hot water. The changes in pumping rates, which are fixed according to external requirements, play a major role in the hydrodynamic and chemical disequilibrium of the wells. The consequences for the geothermal exploitations are emphasized.
NASA Astrophysics Data System (ADS)
Lachhab, A.
2015-12-01
The study site is located at the Center for Environmental Education and Research (CEER) at Susquehanna University. Electrical Resistivity and Seismic Refraction Tomography (ERT and SRT), as well as several pumping tests were performed to identify zones of heterogeneities and hydrogeophysical characteristics of a shallow unconfined aquifer. The combination of these methods was selected to study the local geology and the subsurface preferential pathways of groundwater flow. 22 Dipole-Dipole ERT transects with 56 electrodes each and 11 SRT transects with 24 geophones each were performed. Drilling logs of 5 observation wells located within the site were also used. All drilling logs showed clearly the heterogeneity of the aquifer when compared to each other. The combination of ERT and SRT indicated that a potential zone of preferential flow is present within the aquifer and can be accurately identified based on the approach adopted in this study. The drilling logs served to specifically identify the soil and the geological formations making the heterogeneity of the aquifer. 3D ERT and SRT block diagrams were generated to connect all formations shown in the 2D tomography profiles to visualize the pathways of preferential flow and non-conductive formations. While ERT has proven to show saturated areas of the subsurface, SRT was more effective in identifying the bedrock-soil discontinuity and other near surface formations contributing to the local heterogeneity.
Formation of ordered gas-solid structures via solidification in metal-hydrogen systems
Shapovalov, V.I. |
1998-12-31
This work contains theoretical discussions concerning the large amount of previously published experimental data related to gas eutectic transformations in metal-hydrogen systems. Theories of pore nucleation and growth in these gas-solid materials will be presented and related to observed morphologies and structures. This work is intended to be helpful to theorists that work with metal-hydrogen systems, and experimentalists engaged in manufacturing technology development of these ordered gas-solid structures.
Study of a novel rotary cyclone gas-solid separator
NASA Astrophysics Data System (ADS)
Ling, Zhiguang; Deng, Xingyong
2003-08-01
Based on the analytical study of the characteristics of fine particle motion in swirling flow, a new design idea on flow organization and construction aimed at increasing the positive radial flow in the separation chamber of the rotary cyclone separator (PRV type) was proposed. Experimental verification including the test of variation of separation efficiency and pressure loss with the first and secondary flow ratio show that this new type separator has higher and more stable separation efficiency in broad flow ratio range while the pressure loss is far below the conventional rotary cyclone separator and even comparable with that of simple cyclone separator
NASA Astrophysics Data System (ADS)
Le Borgne, T.; Dentz, M.; Ginn, T. R.; Villermaux, E.
2015-12-01
Reactive mixing processes play a central role in a range of porous media systems, including CO2 sequestration operations, reactive geothermal dipoles, biofilms, or flow-through reactors. Many of these reactions are limited by fluid mixing processes that bring the reactants into contact. Hence, the temporal dynamics of effective global reactivity is determined by the creation of concentration gradients by fluid stretching and their dissipation by diffusion [1,2]. From the analysis of the elongation and aggregation of lamellar structures formed in the transported scalar fields, we derive analytical predictions for the probability density functions of concentration gradients in heterogeneous Darcy flows over a large range of Péclet numbers and permeability field variances. In this framework, we show that heterogeneous Darcy fields generate highly intermittent concentration fields, as manifested by the spatial scaling of structure functions. The resulting effective reaction rates display a range of temporal behaviors that depend on the degree of heterogeneity. In the large Damköhler limit, we derive analytical expressions for these temporal scalings in the different regimes that arise when exploring the Péclet number space. We generalize these results for different random flows, including turbulent flows. References:[1] Le Borgne, T., M. Dentz, E. Villermaux, The lamellar description of mixing in porous media, J. of Fluid Mech., vol. 770, pp. 458-498 [2] Le Borgne, T., M. Dentz, E. Villermaux, Stretching, coalescence and mixing in porous media, Phys. Rev. Lett., 110, 204501 (2013)
NASA Astrophysics Data System (ADS)
McClure, J. E.; Prins, J. F.; Miller, C. T.
2014-07-01
Multiphase flow implementations of the lattice Boltzmann method (LBM) are widely applied to the study of porous medium systems. In this work, we construct a new variant of the popular “color” LBM for two-phase flow in which a three-dimensional, 19-velocity (D3Q19) lattice is used to compute the momentum transport solution while a three-dimensional, seven velocity (D3Q7) lattice is used to compute the mass transport solution. Based on this formulation, we implement a novel heterogeneous GPU-accelerated algorithm in which the mass transport solution is computed by multiple shared memory CPU cores programmed using OpenMP while a concurrent solution of the momentum transport is performed using a GPU. The heterogeneous solution is demonstrated to provide speedup of 2.6× as compared to multi-core CPU solution and 1.8× compared to GPU solution due to concurrent utilization of both CPU and GPU bandwidths. Furthermore, we verify that the proposed formulation provides an accurate physical representation of multiphase flow processes and demonstrate that the approach can be applied to perform heterogeneous simulations of two-phase flow in porous media using a typical GPU-accelerated workstation.
Zhou, L; Qu, Z G; Ding, T; Miao, J Y
2016-04-01
The gas-solid adsorption process in reconstructed random porous media is numerically studied with the lattice Boltzmann (LB) method at the pore scale with consideration of interparticle, interfacial, and intraparticle mass transfer performances. Adsorbent structures are reconstructed in two dimensions by employing the quartet structure generation set approach. To implement boundary conditions accurately, all the porous interfacial nodes are recognized and classified into 14 types using a proposed universal program called the boundary recognition and classification program. The multiple-relaxation-time LB model and single-relaxation-time LB model are adopted to simulate flow and mass transport, respectively. The interparticle, interfacial, and intraparticle mass transfer capacities are evaluated with the permeability factor and interparticle transfer coefficient, Langmuir adsorption kinetics, and the solid diffusion model, respectively. Adsorption processes are performed in two groups of adsorbent media with different porosities and particle sizes. External and internal mass transfer resistances govern the adsorption system. A large porosity leads to an early time for adsorption equilibrium because of the controlling factor of external resistance. External and internal resistances are dominant at small and large particle sizes, respectively. Particle size, under which the total resistance is minimum, ranges from 3 to 7 μm with the preset parameters. Pore-scale simulation clearly explains the effect of both external and internal mass transfer resistances. The present paper provides both theoretical and practical guidance for the design and optimization of adsorption systems. PMID:27176384
NASA Astrophysics Data System (ADS)
Zhou, L.; Qu, Z. G.; Ding, T.; Miao, J. Y.
2016-04-01
The gas-solid adsorption process in reconstructed random porous media is numerically studied with the lattice Boltzmann (LB) method at the pore scale with consideration of interparticle, interfacial, and intraparticle mass transfer performances. Adsorbent structures are reconstructed in two dimensions by employing the quartet structure generation set approach. To implement boundary conditions accurately, all the porous interfacial nodes are recognized and classified into 14 types using a proposed universal program called the boundary recognition and classification program. The multiple-relaxation-time LB model and single-relaxation-time LB model are adopted to simulate flow and mass transport, respectively. The interparticle, interfacial, and intraparticle mass transfer capacities are evaluated with the permeability factor and interparticle transfer coefficient, Langmuir adsorption kinetics, and the solid diffusion model, respectively. Adsorption processes are performed in two groups of adsorbent media with different porosities and particle sizes. External and internal mass transfer resistances govern the adsorption system. A large porosity leads to an early time for adsorption equilibrium because of the controlling factor of external resistance. External and internal resistances are dominant at small and large particle sizes, respectively. Particle size, under which the total resistance is minimum, ranges from 3 to 7 μm with the preset parameters. Pore-scale simulation clearly explains the effect of both external and internal mass transfer resistances. The present paper provides both theoretical and practical guidance for the design and optimization of adsorption systems.
Laser studies of chemical dynamics at the gas-solid interface
NASA Astrophysics Data System (ADS)
Cavanagh, Richard R.; King, David S.
The DOE funded research program Laser Studies of Chemical Dynamics at the Gas-Solid Interface has taken a detailed, microscopic view of molecules desorbed from surfaces in order to gain an understanding of energy flow and interaction potentials and how these control chemical reactivity at interfaces. Successful completion of these experiments required technical expertise both in surface science and laser-based molecular dynamics, a collaborative situation that exists in the NIST center for Atomic, Molecular and Optical Physics. During the three year period covered by this progress report, our goal was to use state-resolved techniques to examine a single chemisorption system in detail, and to observe how changes in the interaction potential or method of surface excitation are manifest in the desorption dynamics. The system chosen was NO/Pt(111). Studies were undertaken in which the effects on the NO-Pt interaction potential of coadsorbates--both weakly (CO) and strongly (NH(sub 3)) interacting-- could be examined. In addition, attempts were to be made to study non- equilibrium dynamics by using pulsed laser heating.
Lattice Boltzmann simulation of gas-solid adsorption processes at pore scale level
NASA Astrophysics Data System (ADS)
Zhou, L.; Qu, Z. G.; Chen, L.; Tao, W. Q.
2015-11-01
A two-dimensional lattice Boltzmann (LB) approach was established to implement kinetic concentration boundary conditions in interfacial mass-transfer processes and to simulate the adsorption process in porous media at pore scale and mesoscopic levels. A general treatment was applied to conduct three types of concentration boundary conditions effectively and accurately. Applicability for adsorption was verified by two benchmark examples, which were representative of the interparticle mass transport and intraparticle mass transport in the adsorption system, respectively. The gas-solid adsorption process in reconstructed porous media at the pore scale level was numerically investigated. Mass-transfer processes of the adsorption reaction were simulated by executing Langmuir adsorption kinetics on surfaces of adsorbent particles. Meanwhile, the homogeneous solid diffusion model (HSDM) was used for mass transport in interior particles. The transient adsorbed amount was obtained in detail, and the impact of flow condition, porosity, and adsorbent particle size on the entire dynamic adsorption performance was investigated. The time needed to approach steady state decreased with increased fluid velocity. Transient adsorption capability and time consumption to equilibrium were nearly independent of porosity, whereas increasing pore size led to a moderating adsorption rate and more time was consumed to approach the saturation adsorption. Benefiting from the advantages of the LB method, both bulk and intraparticle mass transfer performances during adsorption can be obtained using the present pore scale approach. Thus, interparticle mass transfer and intraparticle mass transfer are the two primary segments, and intraparticle diffusion has the dominant role.
Heterogeneities of in- and out-flows in the Mediterranean Sea
NASA Astrophysics Data System (ADS)
Millot, Claude
2014-01-01
mix; thus, accurately predicting the outflow characteristics in the Atlantic Ocean appears almost impossible. Herein, we first propose a fully objective description of the AWs and MWs during two GIBEX campaigns. Where the AWs and the MWs do not markedly mix, they are defined in terms of density and temperature ranges. Where a MW mixes with one of the AWs down to the bottom, the mixing line characteristics allow for that MW to be followed from one section to one downstream and for the validation of our concept: while superimposed east of the Strait, the MWs come to be juxtaposed within the Strait before becoming superimposed again. We also analysed additional CTD time series collected by the University of Malaga on the south and north sides of the southern sill of Espartel. We demonstrate the following: (a) even though the MWs at the sill (E) and on the south side (ES) were roughly the same, the densest ones out-flowed at ES, i.e., at depths shallower than at E, (b) the MWs on the north side (EN) were very different from those at E and each mixed with different AWs, and (c) using the mixing lines computed from each time series, the data recorded at E and ES allow for the retrieval, with good accuracy, of those recorded at Camarinal (C), which is not the case for the data recorded at EN. Finally we emphasise how different the AWs' heterogeneities are from the MWs' heterogeneities. The inflow is sucked into the Mediterranean Sea, due to the water budget (E-P) deficit there, and it can be composed of any type of AW present west of the Strait at any time and any specific location. The outflow is a product of the Mediterranean Sea, which is like a machine producing a series of MWs that first circulate as alongslope density currents before entering the Strait in a specific order and at specific locations. Consequently, we attempt to schematise the AWs-MWs mixing processes and our understanding of the outflow dynamics. Notwithstanding the difficulty of the working conditions
Peng, You; Bardeesi, Adham Sameer A.; Bardisi, Ekhlas Samir A.; Liao, Xinxue
2016-01-01
Background The vessel heterogeneity of thrombolysis in myocardial infarction (TIMI) frame count (TFC) in patients with coronary slow flow (CSF) remains to be further evaluated, and the correlation between TFC heterogeneity and P-wave dispersion (PWD) has not been elucidated. We aim to investigate the vessel heterogeneity of TFC in coronary arteries, and its relation to PWD in patients with CSF and otherwise normal coronary arteries. Methods We studied 72 patients with angiographically documented CSF and 66 age- and gender-matched control subjects. The coefficient of variation (CV) and mean TFC of the three vessels were calculated. P-wave duration and PWD were measured on the standard electrocardiograms (ECGs). Results The mean TFC and CV were both significantly higher in CSF patients than in controls (P<0.001 for both comparisons). The maximum P-wave duration (Pmax) and PWD were found to be significantly higher in CSF patients than in controls (P<0.001 for both comparisons). In patients with CSF, both Pmax and PWD were mildly correlated to mean TFC (r=0.318, P=0.009; and r=0.307, P=0.010), and were more significantly correlated to CV (r=0.506, P<0.001; and r=0.579, P<0.001). Conclusions These data demonstrate that variability of TFC in three coronary arteries is increased in CSF patients, and that the vessel heterogeneity in coronary flow might be intimately associated with PWD. PMID:27076943
Moschetta, Eric G; Negretti, Solymar; Chepiga, Kathryn M; Brunelli, Nicholas A; Labreche, Ying; Feng, Yan; Rezaei, Fateme; Lively, Ryan P; Koros, William J; Davies, Huw M L; Jones, Christopher W
2015-05-26
Flexible composite polymer/oxide hollow fibers are used as flow reactors for heterogeneously catalyzed reactions in organic synthesis. The fiber synthesis allows for a variety of supported catalysts to be embedded in the walls of the fibers, thus leading to a diverse set of reactions that can be catalyzed in flow. Additionally, the fiber synthesis is scalable (e.g. several reactor beds containing many fibers in a module may be used) and thus they could potentially be used for the large-scale production of organic compounds. Incorporating heterogeneous catalysts in the walls of the fibers presents an alternative to a traditional packed-bed reactor and avoids large pressure drops, which is a crucial challenge when employing microreactors. PMID:25865826
NASA Astrophysics Data System (ADS)
Pedretti, Daniele; Fiori, Aldo
2013-10-01
We analyze conservative solute transport under convergent flow to a well in perfectly stratified porous media, in which the hydraulic conductivity is treated as a random spatial function along the vertical direction (K(z)). The stratified model provides a rare exception of an exact analytical solution of travel time distributions in the proximity of pumping wells, and it is used here to obtain insights about ergodic and nonergodic transport conditions under nonuniform flow conditions. In addition, it provides a benchmark for numerical models aiming to correctly reproduce convergent flow transport in heterogeneous media, such as indicating the minimum number of layers required to obtain ergodic travel time distributions using only one model realization. The model provides important insights about the shape of the depth-integrated concentrations over time measured at the well (breakthrough curves, BTCs), which are usually applied to obtain transport parameters of the subsurface. It can be applied to any degree of system's heterogeneity and using either resident or flux-weighted injection modes. It can be built using different probabilistic distributions of K. In our analysis, we consider a log-normal K distribution, and the results indicate that, especially for highly heterogeneous systems, described by the log-K variance (σY2), the minimum number of layers required for from one model simulation to reproduce ergodic travel time distributions can be prohibitively high, e.g., above 106 for σY2=8 considering flux-weighted injections. This issue poses serious concerns for numerical applications aiming to simulate transport in the proximity of pumping wells. In addition, this simple solution confirms that stratification can lead BTCs to display strong preferential flow and persistent, power-law-like late-time tailing. Since the latter are common phenomenological macroscale evidences of other microscale hydrodynamic processes than pure advection (e.g., mass
Benkert, A; Blum, M; Meyer, F; Wilks, R G; Yang, W; Bär, M; Reinert, F; Heske, C; Weinhardt, L
2014-01-01
We present a novel gas cell designed to study the electronic structure of gases and gas/solid interfaces using soft x-ray emission and absorption spectroscopies. In this cell, the sample gas is separated from the vacuum of the analysis chamber by a thin window membrane, allowing in situ measurements under atmospheric pressure. The temperature of the gas can be regulated from room temperature up to approximately 600 °C. To avoid beam damage, a constant mass flow can be maintained to continuously refresh the gaseous sample. Furthermore, the gas cell provides space for solid-state samples, allowing to study the gas/solid interface for surface catalytic reactions at elevated temperatures. To demonstrate the capabilities of the cell, we have investigated a TiO2 sample behind a mixture of N2 and He gas at atmospheric pressure. PMID:24517824
Benkert, A. E-mail: l.weinhardt@kit.edu; Blum, M.; Meyer, F.; Wilks, R. G.; Yang, W.; Bär, M.; and others
2014-01-15
We present a novel gas cell designed to study the electronic structure of gases and gas/solid interfaces using soft x-ray emission and absorption spectroscopies. In this cell, the sample gas is separated from the vacuum of the analysis chamber by a thin window membrane, allowing in situ measurements under atmospheric pressure. The temperature of the gas can be regulated from room temperature up to approximately 600 °C. To avoid beam damage, a constant mass flow can be maintained to continuously refresh the gaseous sample. Furthermore, the gas cell provides space for solid-state samples, allowing to study the gas/solid interface for surface catalytic reactions at elevated temperatures. To demonstrate the capabilities of the cell, we have investigated a TiO{sub 2} sample behind a mixture of N{sub 2} and He gas at atmospheric pressure.
NASA Astrophysics Data System (ADS)
Benson, S. M.; Hingerl, F.; Pini, R.
2013-12-01
New imaging techniques and approaches are providing unparalleled insight into the influence of sub-core scale heterogeneities on single and multiphase flows. Quantification of sub core-scale porosity, permeability, and even capillary pressure curves at a spatial scale of about 1-10 cubic millimeters is now possible. This scale provides a critical link in the continuum of spatial scales needed to link pore-scale processes to core-scale and field scale flow and transport. Data from such studies can be used to directly test the veracity of models for flow and transport in heterogeneous rocks, provide data for multi-stage upscaling, and reveal insights about physical/chemical processes heretofore neglected. Here we present data from three emerging techniques capable of imaging and quantifying transport properties and phenomena at the sub-core scale: magnetic resonance imaging (MRI); positron emission tomography (PET); and X-Ray CT scanning. Direct imaging of spatially resolved fluid velocities and porosity is possible with MRI (Romanenko et al., 2012). These data can be inverted to provide permeability and porosity maps at a spatial scale of ~10 cubic millimeter. PET imaging can be used to track movement of a radioactive tracer through a rock and simultaneously measure effluent tracer concentrations at a similar resolution (Boutchko et al., 2012). X-ray CT scanning of multiphase flow experiments can be used to measure capillary pressure curves and through scaling relationships, to calculate permeability at a scale of about 1 cubic millimeters(Krause et al., 2011; Pini et al., 2013). Strengths and shortcomings of these techniques are discussed--along with the benefits of combining them. Together these techniques provide a new platform from which to probe more deeply the ubiquitous influence of heterogeneity on subsurface flow and transport processes, and ultimately improve predictions of subsurface transport. Boutchk et al., 2012. Imaging and modeling of flow in porous
NASA Astrophysics Data System (ADS)
Bulicek, M. C.; Metge, D. W.; Mohanty, S. K.; Harvey, R. W.; Ryan, J. N.
2013-12-01
Intermittent flows of rainwater frequently mobilize pathogenic microbes attached to subsurface soils, thereby causing groundwater contamination. The potential of intermittent rainfall to mobilize diverse pathogens (e.g., size, shape, taxa) remains understudied for heterogeneous soil systems. This study investigates the combined effects of microbe size and shape, intermittent flow, and soil physical heterogeneity on the transport, retention and mobilization of microbes through an intact, fractured shale saprolite core. Microbes, including MS-2 bacteriophage (~26 nm), Pseudomonas stutzeri bacteria (~1 μm), and Cryptosporidium parvum oocysts (3.6 μm), and 0.5 μm fluorescent microspheres (FMS), preceded by a bromide tracer, were applied to the core to obtain breakthrough. After breakthrough, the core was subjected to intermittent rainfalls to mobilize the attached microbes and FMS. Water samples were collected using 19 spatially-arranged outlet ports at the core base to resolve the effect of soil physical heterogeneity. Water infiltrated through only eight of 19 total sampling ports, which indicated water partially bypassed soil matrices and infiltrated through macropores. Bromide recovery was less than 100%, which indicated diffusion of bromide into the soil matrix. Macropores and the soil matrix dominated flow were characterized based on the cumulative bromide recovery within individual sampling ports. Thus, lower recovery was attributed to increased matrix diffusion and higher recovery indicated the presence of macropores. Intermittent flow mobilized previously sequestered microbes and FMS; however, mobilization varied with the size of microbes/FMS and sampling ports. Greater mobilization occurred through macropores compared to soil matrices. Mobilization of larger, spherical C. parvum oocysts was greater than that of the smaller, spherical MS-2 bacteriophage and the rod-shaped P. stutzeri bacteria during intermittent flow. This suggested shear forces mobilize
NASA Astrophysics Data System (ADS)
Tecklenburg, Jan; Neuweiler, Insa; Carrera, Jesus; Dentz, Marco
2016-05-01
We study modeling of two-phase flow in highly heterogeneous fractured and porous media. The flow behaviour is strongly influenced by mass transfer between a highly permeable (mobile) fracture domain and less permeable (immobile) matrix blocks. We quantify the effective two-phase flow behavior using a multirate rate mass transfer (MRMT) approach. We discuss the range of applicability of the MRMT approach in terms of the pertinent viscous and capillary diffusion time scales. We scrutinize the linearization of capillary diffusion in the immobile regions, which allows for the formulation of MRMT in the form of a non-local single equation model. The global memory function, which encodes mass transfer between the mobile and the immobile regions, is at the center of this method. We propose two methods to estimate the global memory function for a fracture network with given fracture and matrix geometry. Both employ a scaling approach based on the known local memory function for a given immobile region. With the first method, the local memory function is calculated numerically, while the second one employs a parametric memory function in form of truncated power-law. The developed concepts are applied and tested for fracture networks of different complexity. We find that both physically based parameter estimation methods for the global memory function provide predictive MRMT approaches for the description of multiphase flow in highly heterogeneous porous media.
Gas sampling system for reactive gas-solid mixtures
Daum, Edward D.; Downs, William; Jankura, Bryan J.; McCoury, Jr., John M.
1990-01-01
An apparatus and method for sampling gas containing a reactive particulate solid phase flowing through a duct and for communicating a representative sample to a gas analyzer. A sample probe sheath 32 with an angular opening 34 extends vertically into a sample gas duct 30. The angular opening 34 is opposite the gas flow. A gas sampling probe 36 concentrically located within sheath 32 along with calibration probe 40 partly extends in the sheath 32. Calibration probe 40 extends further in the sheath 32 than gas sampling probe 36 for purging the probe sheath area with a calibration gas during calibration.
Gas sampling system for reactive gas-solid mixtures
Daum, Edward D.; Downs, William; Jankura, Bryan J.; McCoury, Jr., John M.
1989-01-01
An apparatus and method for sampling a gas containing a reactive particulate solid phase flowing through a duct and for communicating a representative sample to a gas analyzer. A sample probe sheath 32 with an angular opening 34 extends vertically into a sample gas duct 30. The angular opening 34 is opposite the gas flow. A gas sampling probe 36 concentrically located within sheath 32 along with calibration probe 40 partly extend in the sheath 32. Calibration probe 40 extends further in the sheath 32 than gas sampling probe 36 for purging the probe sheath area with a calibration gas during calibration.
NASA Astrophysics Data System (ADS)
Zech, Alraune; Zehner, Björn; Kolditz, Olaf; Attinger, Sabine
2016-04-01
Ground water flow systems of the Thuringian Basin are studied by analyzing the fluid dynamics at this real world example of a shallow sedimentary basin. The impact of the permeability distribution and density differences on the flow velocity pattern, the salt concentration, and the temperature distribution is quantified by means of transient coupled simulations of fluid flow, heat, and mass transport processes. Simulations are performed with different permeabilities in the sedimentary layering and heterogeneous permeability distributions as well as with a non-constant fluid density. Three characteristic numbers are useful to describe the effects of permeability on the development of flow systems and subsurface transport: the relation of permeability between aquiclude and aquifer, the variance, and the correlation length of the log-normal permeability distribution. Density dependent flow due to concentration gradients is of minor importance for the distribution of the flow systems, but can lead to increased mixing dissolution of salt. Thermal convection is in general not present. The dominant driver of groundwater flow is the topography in combination with the permeability distribution. The results obtained for the Thuringian Basin give general insights into the dynamics of a small sedimentary basin due to the representative character of the basin structure as well as the transferability of the settings to other small sedimentary basins.
NASA Astrophysics Data System (ADS)
Parker, L. B.; Yarwood, R. R.; Kraft, E. L.; Selker, J. S.
2003-12-01
Gaseous flow dynamics in unsaturated media were examined with respect to microbial colonization, liquid flow rates, and textural heterogeneities. A light transmission chamber consisting of two glass sheets mounted in an aluminum frame in front of a light bank was packed with translucent quartz sand and brought to unsaturated conditions. To visualize gas transport, carbon dioxide was introduced to the chamber at varying rates in combination with different liquid flow rates and textural inclusions. A methyl red pH indicator solution was used in conjunction with a liquid-cooled camera to monitor carbon dioxide concentrations and infer transport dynamics throughout the system. To explore whether gas-phase nutrients would stimulate microbial growth, acetate and ammonia vapors were pumped through a chamber inoculated with Pseudomonas fluorescens HK44. Naphthalene vapor pulses were used to induce bioluminescence, allowing imaging of responsive colonies.
Rudroff, Thorsten; Weissman, Jessica A; Bucci, Marco; Seppänen, Marko; Kaskinoro, Kimmo; Heinonen, Ilkka; Kalliokoski, Kari K
2014-01-01
The purpose of this study was to investigate blood flow and its heterogeneity within and among the knee muscles in five young (26 ± 6 years) and five old (77 ± 6 years) healthy men with similar levels of physical activity while they performed two types of submaximal fatiguing isometric contraction that required either force or position control. Positron emission tomography (PET) and [15O]-H2O were used to determine blood flow at 2 min (beginning) and 12 min (end) after the start of the tasks. Young and old men had similar maximal forces and endurance times for the fatiguing tasks. Although muscle volumes were lower in the older subjects, total muscle blood flow was similar in both groups (young men: 25.8 ± 12.6 ml min−1; old men: 25.1 ± 15.4 ml min−1; age main effect, P = 0.77) as blood flow per unit mass of muscle in the exercising knee extensors was greater in the older (12.5 ± 6.2 ml min−1 (100 g)−1) than the younger (8.6 ± 3.6 ml min−1 (100 g)−1) men (age main effect, P = 0.001). Further, blood flow heterogeneity in the exercising knee extensors was significantly lower in the older (56 ± 27%) than the younger (67 ± 34%) men. Together, these data show that although skeletal muscles are smaller in older subjects, based on the intact neural drive to the muscle and the greater, less heterogeneous blood flow per gram of muscle, old fit muscle achieves adequate exercise hyperaemia. Key points The results of previous studies that attempted to demonstrate the effects of ageing on skeletal muscle blood flow are controversial because these studies used indirect assessments of skeletal muscle blood flow obtained via whole limb blood flow measurements that provide no information on the distribution of blood flow within particular muscles. We used positron emission tomography to measure blood flow per gram of muscle in old and young men with similar levels of physical activity
Vimalchand, Pannalal; Liu, Guohai; Peng, WanWang
2010-08-10
The system of the present invention includes a centripetal cyclone for separating particulate material from a particulate laden gas solids stream. The cyclone includes a housing defining a conduit extending between an upstream inlet and a downstream outlet. In operation, when a particulate laden gas-solids stream passes through the upstream housing inlet, the particulate laden gas-solids stream is directed through the conduit and at least a portion of the solids in the particulate laden gas-solids stream are subjected to a centripetal force within the conduit.
Engdahl, N.B.; Vogler, E.T.; Weissmann, G.S.
2010-01-01
River-aquifer exchange is considered within a transition probability framework along the Rio Grande in Albuquerque, New Mexico, to provide a stochastic estimate of aquifer heterogeneity and river loss. Six plausible hydrofacies configurations were determined using categorized drill core and wetland survey data processed through the TPROGS geostatistical package. A base case homogeneous model was also constructed for comparison. River loss was simulated for low, moderate, and high Rio Grande stages and several different riverside drain stage configurations. Heterogeneity effects were quantified by determining the mean and variance of the K field for each realization compared to the root-mean-square (RMS) error of the observed groundwater head data. Simulation results showed that the heterogeneous models produced smaller estimates of loss than the homogeneous approximation. Differences between heterogeneous and homogeneous model results indicate that the use of a homogeneous K in a regional-scale model may result in an overestimation of loss but comparable RMS error. We find that the simulated river loss is dependent on the aquifer structure and is most sensitive to the volumetric proportion of fines within the river channel. Copyright 2010 by the American Geophysical Union.
NASA Astrophysics Data System (ADS)
Russo, David
2016-04-01
Detailed numerical analyses of flow and transport were used to investigate the effect of spatially connected features on the transport in three-dimensional (3-D), spatially heterogeneous, combined vadose zone-groundwater flow systems. Formations with spatially connected fine- and coarse-textured features (SCFT- and SCCT-formations, respectively), representing the10th and the 90th percentiles of the distributions of the formation's hydraulic parameters, respectively, were considered here. Results of the analyses suggest that in steady-state flow, when the unsaturated zone of the combined flow domains is relatively wet, as compared with a Multivariate-Gaussian (MG) formation, spatially connected features may reduce the solute first arrival time, particularly in the SCCT-formation, and may enhance the spreading of the solute breakthrough, particularly in the SCFT-formation. The effect of the spatially connected features on the hydrological response, however, decreases as the unsaturated zone becomes drier. The latter result stems from the decrease in the fraction of the water-filled, pore-space occupied by the connected structures, with decreasing water content. The latter finding also explains the result that the response of more realistic, combined flow systems, whose unsaturated zone is associated with transient flow and relatively low, intermittent water contents, is essentially independent of the spatially connected features of the formations, regardless of their soil texture.
Simmons, C T; Fenstemaker, T R; Sharp, J M
2001-11-01
In certain hydrogeological situations, fluid density variations occur because of changes in the solute or colloidal concentration, temperature, and pressure of the groundwater. These include seawater intrusion, high-level radioactive waste disposal, groundwater contamination, and geothermal energy production. When the density of the invading fluid is greater than that of the ambient one, density-driven free convection can lead to transport of heat and solutes over larger spatial scales and significantly shorter time scales than compared with diffusion alone. Beginning with the work of Lord Rayleigh in 1916, thermal and solute instabilities in homogeneous media have been studied in detail for almost a century. Recently, these theoretical and experimental studies have been applied in the study of groundwater phenomena, where the assumptions of homogeneity and isotropy rarely, if ever, apply. The critical role that heterogeneity plays in the onset as well as the growth and/or decay of convective motion is discussed by way of a review of pertinent literature and numerical simulations performed using a variable-density flow and solute transport numerical code. Different styles of heterogeneity are considered and range from continuously "trending" heterogeneity (sinusoidal and stochastic permeability distributions) to discretely fractured geologic media. Results indicate that both the onset of instabilities and their subsequent growth and decay are intimately related to the structure and variance of the permeability field. While disordered heterogeneity tends to dissipate convection through dispersive mixing, an ordered heterogeneity (e.g., sets of vertical fractures) allows instabilities to propagate at modest combinations of fracture aperture and separation distances. Despite a clearer understanding of the processes that control the onset and propagation of instabilities, resultant plume patterns and their migration rates and pathways do not appear amenable to
NASA Astrophysics Data System (ADS)
Gjetvaj, Filip; Russian, Anna; Gouze, Philippe; Dentz, Marco
2015-10-01
Both flow field heterogeneity and mass transfer between mobile and immobile domains have been studied separately for explaining observed anomalous transport. Here we investigate non-Fickian transport using high-resolution 3-D X-ray microtomographic images of Berea sandstone containing microporous cement with pore size below the setup resolution. Transport is computed for a set of representative elementary volumes and results from advection and diffusion in the resolved macroporosity (mobile domain) and diffusion in the microporous phase (immobile domain) where the effective diffusion coefficient is calculated from the measured local porosity using a phenomenological model that includes a porosity threshold (ϕθ) below which diffusion is null and the exponent n that characterizes tortuosity-porosity power-law relationship. We show that both flow field heterogeneity and microporosity trigger anomalous transport. Breakthrough curve (BTC) tailing is positively correlated to microporosity volume and mobile-immobile interface area. The sensitivity analysis showed that the BTC tailing increases with the value of ϕθ, due to the increase of the diffusion path tortuosity until the volume of the microporosity becomes negligible. Furthermore, increasing the value of n leads to an increase in the standard deviation of the distribution of effective diffusion coefficients, which in turn results in an increase of the BTC tailing. Finally, we propose a continuous time random walk upscaled model where the transition time is the sum of independently distributed random variables characterized by specific distributions. It allows modeling a 1-D equivalent macroscopic transport honoring both the control of the flow field heterogeneity and the multirate mass transfer between mobile and immobile domains.
Shang, Yu; Yu, Guoqiang
2014-09-29
Conventional semi-infinite analytical solutions of correlation diffusion equation may lead to errors when calculating blood flow index (BFI) from diffuse correlation spectroscopy (DCS) measurements in tissues with irregular geometries. Very recently, we created an algorithm integrating a Nth-order linear model of autocorrelation function with the Monte Carlo simulation of photon migrations in homogenous tissues with arbitrary geometries for extraction of BFI (i.e., αD{sub B}). The purpose of this study is to extend the capability of the Nth-order linear algorithm for extracting BFI in heterogeneous tissues with arbitrary geometries. The previous linear algorithm was modified to extract BFIs in different types of tissues simultaneously through utilizing DCS data at multiple source-detector separations. We compared the proposed linear algorithm with the semi-infinite homogenous solution in a computer model of adult head with heterogeneous tissue layers of scalp, skull, cerebrospinal fluid, and brain. To test the capability of the linear algorithm for extracting relative changes of cerebral blood flow (rCBF) in deep brain, we assigned ten levels of αD{sub B} in the brain layer with a step decrement of 10% while maintaining αD{sub B} values constant in other layers. Simulation results demonstrate the accuracy (errors < 3%) of high-order (N ≥ 5) linear algorithm in extracting BFIs in different tissue layers and rCBF in deep brain. By contrast, the semi-infinite homogenous solution resulted in substantial errors in rCBF (34.5% ≤ errors ≤ 60.2%) and BFIs in different layers. The Nth-order linear model simplifies data analysis, thus allowing for online data processing and displaying. Future study will test this linear algorithm in heterogeneous tissues with different levels of blood flow variations and noises.
NASA Astrophysics Data System (ADS)
Shang, Yu; Yu, Guoqiang
2014-09-01
Conventional semi-infinite analytical solutions of correlation diffusion equation may lead to errors when calculating blood flow index (BFI) from diffuse correlation spectroscopy (DCS) measurements in tissues with irregular geometries. Very recently, we created an algorithm integrating a Nth-order linear model of autocorrelation function with the Monte Carlo simulation of photon migrations in homogenous tissues with arbitrary geometries for extraction of BFI (i.e., αDB). The purpose of this study is to extend the capability of the Nth-order linear algorithm for extracting BFI in heterogeneous tissues with arbitrary geometries. The previous linear algorithm was modified to extract BFIs in different types of tissues simultaneously through utilizing DCS data at multiple source-detector separations. We compared the proposed linear algorithm with the semi-infinite homogenous solution in a computer model of adult head with heterogeneous tissue layers of scalp, skull, cerebrospinal fluid, and brain. To test the capability of the linear algorithm for extracting relative changes of cerebral blood flow (rCBF) in deep brain, we assigned ten levels of αDB in the brain layer with a step decrement of 10% while maintaining αDB values constant in other layers. Simulation results demonstrate the accuracy (errors < 3%) of high-order (N ≥ 5) linear algorithm in extracting BFIs in different tissue layers and rCBF in deep brain. By contrast, the semi-infinite homogenous solution resulted in substantial errors in rCBF (34.5% ≤ errors ≤ 60.2%) and BFIs in different layers. The Nth-order linear model simplifies data analysis, thus allowing for online data processing and displaying. Future study will test this linear algorithm in heterogeneous tissues with different levels of blood flow variations and noises.
Large-Eddy Simulation Study of the Effects on Flow of a Heterogeneous Forest at Sub-Tree Resolution
NASA Astrophysics Data System (ADS)
Schlegel, Fabian; Stiller, Jörg; Bienert, Anne; Maas, Hans-Gerd; Queck, Ronald; Bernhofer, Christian
2015-01-01
The effect of three-dimensional plant heterogeneity on flow past a clearing is investigated by means of large-eddy simulation. A detailed representation of the canopy has been acquired by terrestrial laser scanning for a patch of approximately length and width at the field site "Tharandter Wald", near the city of Dresden, Germany. The scanning data are used to produce a highly resolved, three-dimensional plant area distribution representing the actual canopy. Hence, the vegetation maintains a rich horizontal and vertical structure including the three-dimensional clearing. The scanned plant area density is embedded in a larger domain, which is filled with a heterogeneous forest generated by the virtual canopy generator of Bohrer et al. (Tellus B 59:566-576, 2007). Based on forest inventory maps and airborne laser scanning, the characteristics of the actual canopy are preserved. Furthermore, the topography is extracted from a digital terrain model with some modifications to accommodate for periodic boundary conditions. A large-eddy simulation is performed for neutral atmospheric conditions and compared to simulations of a two-dimensional plant area density and an one-year-long field experiment conducted at the corresponding field site. The results reveal a considerable influence of the plant heterogeneity on the mean velocity field as well as on the turbulent quantities. The three-dimensional environment, e.g., the oblique edges combined with horizontal and vertical variations in plant area density and the topography create a sustained vertical and cross-flow velocity. Downstream of the windward forest edge an enhanced gust zone develops, whose intensity and relative position are influenced by the local canopy density and, therefore, is not constant along the edge. These results lead us to the conclusion that the usage of a three-dimensional plant area distribution is essential for capturing the flow features inside the canopy and within the mixing layer above.
A Renormalization-Group Approach of the Up-Scaling Problem of Flow in Heterogeneous Porous Media
NASA Astrophysics Data System (ADS)
noetinger, B.
2001-12-01
Powerful methods coming from statistical physics are becoming increasingly popular to get a faithful theoretical description of flow and transport in heterogeneous aquifers that are described by mean of geostatistics. However,in current practice people still use Monte Carlo simulations that are well suited to account for complex boundaries and flow patterns. Here, we present an approach intending to up-scale directly the geostatistical description rather than realization by realization as usual. It is based upon a renormalization group analysis close in spirit with previous works and P King and Jaekel and Vereecken. Using a so called "weak approximation"(Neuman and Orr) , we obtain differential equations driving the permeability variogram parameters as a function of the wave-vector cut-off smoothing the permeability maps. At the end of the process, in the isotropic case, the Landau Lifshitz Matheron conjecture is recovered. This conjecture appears thus as being a consequence of both renormalization approach and the weak approximation. The approach is currently being generalized to anisotropic media. These results can be used to perform cheaper Monte Carlo simulations at a coarser scale. P. King, The Use of Field Theoretic Methods for the Study of Flow in Heterogeneous Porous Medium", J. Phys. A.: Math. Gen. 20, pp3935-3947,1987 U. Jaekel and H. Vereecken, Renormalization Group Analysis of Macrodispersion in a Directed Random Flow, Water Resources Research,33,10,pp 2287-2299, 1997 Neuman, S.P. and Orr, S. "Prediction of Steady State Flow in Nonuniform Geologic Media by Conditional Moments: Exact non local Formalism, Effective Conductivities and Weak Approximation", Water Resources Research 29 (2)341-364 (1993) Noetinger, B. Computing the Effective Permeability of log-normal permeability fields using renormalization methods. C.R . Acad. Des Sciences,Sciences de la Terre et des Planètes, 331 353-357 (2000)
A combined PIV/LIF-system for the measurement of heterogeneous drag reduction effects in a pipe-flow
NASA Astrophysics Data System (ADS)
Saadeh, M.; Strauss, K.; Schneider, T.
Particle Image Velocimetry (PIV) technique combined with flow visualization was applied in heterogeneous drag reduction to examine the motion of the polymer thread and the mixing process of polymer and water simultaneously at Reynolds numbers of 15000. The instantaneous velocity profiles for water/polymer motion showed in some cross-sections differences in the velocities of the two phases which indicates an interaction between the polymer thread and the water phase. The results of this interaction have not a significant effect on the drag reduction compared with the influence of the mixing process.
NASA Astrophysics Data System (ADS)
Hayat, Tasawar; Imtiaz, Maria; Alsaedi, Ahmed; Almezal, Saleh
2016-03-01
This paper investigates the steady two-dimensional magnetohydrodynamic (MHD) flow of an Oldroyd-B fluid over a stretching surface with homogeneous-heterogeneous reactions. Characteristics of relaxation time for heat flux are captured by employing new heat flux model proposed by Christov. A system of ordinary differential equations is obtained by using suitable transformations. Convergent series solutions are derived. Impacts of various pertinent parameters on the velocity, temperature and concentration are discussed. Analysis of the obtained results shows that fluid relaxation and retardation time constants have reverse behavior on the velocity and concentration fields. Also temperature distribution decreases for larger values of thermal relaxation time.
NASA Astrophysics Data System (ADS)
Di Federico, V.; Longo, S.; Ciriello, V.; Chiapponi, L.
2015-12-01
A theoretical and experimental analysis of non-Newtonian gravity-driven flow in porous media with spatially variable properties is presented. The motivation for our study is the rheological complexity exhibited by several environmental contaminants (wastewater sludge, oil pollutants, waste produced by the minerals and coal industries) and remediation agents (suspensions employed to enhance the efficiency of in-situ remediation). Natural porous media are inherently heterogeneous, and this heterogeneity influences the extent and shape of the porous domain invaded by the contaminant or remediation agent. To grasp the combined effect of rheology and spatial heterogeneity, we consider: a) the release of a thin current of non-Newtonian power-law fluid into a 2-D, semi-infinite and saturated porous medium above a horizontal bed; b) perfectly stratified media, with permeability and porosity varying along the direction transverse (vertical) or parallel (horizontal) to the flow direction. This continuous variation of spatial properties is described by two additional parameters. In order to represent several possible spreading scenarios, we consider: i) instantaneous injection with constant mass; ii) continuous injection with time-variable mass; iii) instantaneous release of a mound of fluid, which can drain freely out of the formation at the origin (dipole flow). Under these assumptions, scalings for current length and thickness are derived in self similar form. An analysis of the conditions on model parameters required to avoid an unphysical or asymptotically invalid result is presented. Theoretical results are validated against multiple sets of experiments, conducted for different combinations of spreading scenarios and types of stratification. Two basic setups are employed for the experiments: I) direct flow simulation in an artificial porous medium constructed superimposing layers of glass beads of different diameter; II) a Hele-Shaw (HS) analogue made of two parallel
Naff, R.L.; Haley, D.F.; Sudicky, E.A.
1998-01-01
In this, the second of two papers concerned with the use of numerical simulation to examine flow and transport parameters in heterogeneous porous media via Monte Carlo methods, results from the transport aspect of these simulations are reported on. Transport simulations contained herein assume a finite pulse input of conservative tracer, and the numerical technique endeavors to realistically simulate tracer spreading as the cloud moves through a heterogeneous medium. Medium heterogeneity is limited to the hydraulic conductivity field, and generation of this field assumes that the hydraulic- conductivity process is second-order stationary. Methods of estimating cloud moments, and the interpretation of these moments, are discussed. Techniques for estimation of large-time macrodispersivities from cloud second-moment data, and for the approximation of the standard errors associated with these macrodispersivities, are also presented. These moment and macrodispersivity estimation techniques were applied to tracer clouds resulting from transport scenarios generated by specific Monte Carlo simulations. Where feasible, moments and macrodispersivities resulting from the Monte Carlo simulations are compared with first- and second-order perturbation analyses. Some limited results concerning the possible ergodic nature of these simulations, and the presence of non- Gaussian behavior of the mean cloud, are reported on as well.
Schindler, Thomas H.; Zhang, Xiao-Li; Vincenti, Gabriella; Mhiri, Leila; Nkoulou, Rene; Just, Hanjoerg; Ratib, Osman; Mach, Francois; Dahlbom, Magnus; Schelbert, Heinrich R
2009-01-01
Background To evaluate the diagnostic value of a PET-measured heterogeneity in longitudinal myocardial blood flow (MBF) during cold pressor testing (CPT) and global MBF response to CPT from rest (ΔMBF) for identification of coronary vasomotor dysfunction. Methods and Results In 35 patients, CPT-induced alterations in epicardial luminal area were determined with quantitative angiography as reference. MBF was assessed over the whole left ventricle as global MBF, and regionally in the mid and mid-distal myocardium as MBF difference or MBF heterogeneity with 13N-ammonia and PET. The sensitivity and specifity of a longitudinal MBF difference in the identification of epicardial vasomotor dysfunction was significantly higher than the global ΔMBF to CPT, respectively (88% vs. 79% and 82% vs. 64%, p<0.05). Combining both parameters resulted in an optimal sensitivity of 100% at the expense of an intermediate specifity of 73%. The diagnostic accuracy was highest for the combined analysis, than those for the MBF difference or global ΔMBF alone (91 vs. 86% and 74%, respectively, p<0.05). Conclusions The combined evaluation of a CPT-induced heterogeneity in longitudinal MBF and the change in global MBF from rest may emerge as a new promising analytic approach to further optimize the identification and characterization of coronary vasomotor dysfunction. PMID:17826322
Luxmoore, R.J.; Tharp, M.L.
1993-03-01
Compacted soil barriers constructed at landfill sites have some degree of heterogeneity in hydraulic properties that may lead to a decline in barrier integrity and performance. A computer modeling study of the water dynamics of compacted soil barriers for a mesic site in eastem Tennessee was undertaken to identify possible situations that could lead to barrier failure. A water dynamics model for soil-plant systems (UTM) was applied to three landful construction scenarios, and varying degrees of heterogeneity of hydraulic properties for the cap and liner were introduced with a scaling procedure. Simulations were conducted for three annual contrasting rainfall conditions, and sensitivity analysis and Monte Carlo methods were used in the investigation.
NASA Astrophysics Data System (ADS)
Russo, David
2015-05-01
Detailed numerical analyses of flow and transport were used to investigate the effect of spatially connected features on transport in three-dimensional (3-D), spatially heterogeneous, combined vadose zone-groundwater flow systems. Formations with spatially connected fine-textured and coarse-textured features (F-formation and C-formation, respectively), representing the10th and the 90th percentiles of the distributions of the formation's hydraulic parameters, respectively, were considered here. Results of the analyses suggest that in steady state flow, when the unsaturated zone of the combined flow domains is relatively wet, as compared with a Multivariate-Gaussian (MG) formation, spatially connected features may reduce the solute first arrival time, particularly in the C-formation, and may enhance the spreading of the solute breakthrough, particularly in the F-formation. The effect of the spatially connected features on the hydrological response, however, decreases as the unsaturated zone becomes drier. The latter result stems from the decrease in the fraction of the water-filled, pore-space occupied by the connected structures, with decreasing water content. The latter finding also explains the result that the response of more realistic, combined flow systems, whose unsaturated zone is associated with relatively low, intermittent water contents, is essentially independent of the spatially connected features of the formations, regardless of their soil texture.
Heterogeneous physical and chemical processes in a rarefied-gas flow in channels
NASA Astrophysics Data System (ADS)
Rebrov, A. K.; Yudin, I. B.
2016-05-01
A flow with physical and chemical reactions on hot surfaces is investigated. On the basis of physical experiments, determining the hydrogen-dissociation degree in rarefied gas and calculation of the flow by the method of direct simulation Monte Carlo (DSMC), it is possible to specify certain unknown constants of interaction of molecules and atoms with a tungsten surface. By the example of the hydrogen flow in a hightemperature tungsten cylindrical channel, the role of dissociation, sorption, and recombination processes is shown in a wide range of flow regimes from free-molecular to continuum.
METHOD FOR VARIATION OF GRAIN SIZE IN STUDIES OF GAS-SOLID REACTIONS INVOLVING CAO
The paper describes a method for varying grain size in studies of gas-solid reactions involving CaO. (Note: Introducing grain size as an independent experimental variable should contribute to improved understanding of reactions in porous solids.) Calcining 1 micrometer CaCO3 part...
Utilization of the Recycle Reactor in Determining Kinetics of Gas-Solid Catalytic Reactions.
ERIC Educational Resources Information Center
Paspek, Stephen C.; And Others
1980-01-01
Describes a laboratory scale reactor that determines the kinetics of a gas-solid catalytic reaction. The external recycle reactor construction is detailed with accompanying diagrams. Experimental details, application of the reactor to CO oxidation kinetics, interphase gradients, and intraphase gradients are discussed. (CS)
Müller, Florian Jenny, Patrick Meyer, Daniel W.
2013-10-01
Monte Carlo (MC) is a well known method for quantifying uncertainty arising for example in subsurface flow problems. Although robust and easy to implement, MC suffers from slow convergence. Extending MC by means of multigrid techniques yields the multilevel Monte Carlo (MLMC) method. MLMC has proven to greatly accelerate MC for several applications including stochastic ordinary differential equations in finance, elliptic stochastic partial differential equations and also hyperbolic problems. In this study, MLMC is combined with a streamline-based solver to assess uncertain two phase flow and Buckley–Leverett transport in random heterogeneous porous media. The performance of MLMC is compared to MC for a two dimensional reservoir with a multi-point Gaussian logarithmic permeability field. The influence of the variance and the correlation length of the logarithmic permeability on the MLMC performance is studied.
Ferchaud, Anne-Laure; Hansen, Michael M
2016-01-01
Heterogeneous genomic divergence between populations may reflect selection, but should also be seen in conjunction with gene flow and drift, particularly population bottlenecks. Marine and freshwater three-spine stickleback (Gasterosteus aculeatus) populations often exhibit different lateral armour plate morphs. Moreover, strikingly parallel genomic footprints across different marine-freshwater population pairs are interpreted as parallel evolution and gene reuse. Nevertheless, in some geographic regions like the North Sea and Baltic Sea, different patterns are observed. Freshwater populations in coastal regions are often dominated by marine morphs, suggesting that gene flow overwhelms selection, and genomic parallelism may also be less pronounced. We used RAD sequencing for analysing 28 888 SNPs in two marine and seven freshwater populations in Denmark, Europe. Freshwater populations represented a variety of environments: river populations accessible to gene flow from marine sticklebacks and large and small isolated lakes with and without fish predators. Sticklebacks in an accessible river environment showed minimal morphological and genomewide divergence from marine populations, supporting the hypothesis of gene flow overriding selection. Allele frequency spectra suggested bottlenecks in all freshwater populations, and particularly two small lake populations. However, genomic footprints ascribed to selection could nevertheless be identified. No genomic regions were consistent freshwater-marine outliers, and parallelism was much lower than in other comparable studies. Two genomic regions previously described to be under divergent selection in freshwater and marine populations were outliers between different freshwater populations. We ascribe these patterns to stronger environmental heterogeneity among freshwater populations in our study as compared to most other studies, although the demographic history involving bottlenecks should also be considered in the
NASA Astrophysics Data System (ADS)
Nick, H. M.; Matthai, S. K.
2009-05-01
In heterogeneous porous media material discontinuities affect single phase flow as well as multiphase flow. The finite-element method allows to represent such boundaries using piecewise constant or linear material property variations from finite element to element. However, when a node-centered complementary finite volume method is used to model transport across these material interfaces, this discretization can not represent jump discontinuities in concentration or saturation. To overcome this dilemma there are two options, one can either enrich the nodes at the interfaces by additional degrees of freedom or explode the model along the interfaces. This technique, is another way of resolving this problem. Interface nodes are multiplicated so that they match in number the material domains which they join. Here, we use this latter approach, developing an IMPES transport model that can evolve discontinuities at material interfaces in a heterogeneous porous medium. To achieve pressure continuity across the exploded material interfaces, we implement a new implicit algorithm. For the transport equation, we develop a higher-order-accurate scheme which captures jump discontinuity of the transport variable. We use operator-splitting to solve the transport equation after the pressure equation, with the finite volume method, modeling diffusion implicitly employing the finite element method. We verify the new method by a comparison between its results and those of the continuous one. The main advantage of the discontinuous scheme is the resolution of the effects of the material discontinuities. The first order discretization dependency is removed.
NASA Astrophysics Data System (ADS)
Carranza-Diaz, O.; Brovelli, A.; Rossi, L.; Barry, D. A.
2009-04-01
Horizontal, subsurface flow constructed wetlands are wastewater treatment devices. The influent polluted water flows through a porous substrate where the contaminants are removed, for example by microbial oxidation, surface adsorption and mineral precipitation. These systems are widely used with varying degrees of success to treat municipal and agricultural contaminated waters and remove the organic carbon and nutrient load. Constructed wetlands are an appealing and promising technology, because they (i) are potentially very efficient in removing the pollutants, (ii) require only a small external energy input and (iii) require low maintenance. However, practical experience has shown that the observed purification rate is highly variable and is often much smaller than expected. One of the numerous reasons proposed to explain the variable efficiency of constructed wetlands is the existence of highly conductive zones within the porous substrate, which produce a dramatic reduction of the hydraulic residence time and therefore directly decreases the overall water purification rate. This work aims to understand quantitatively the relationship between the spatial variability in the hydraulic properties of the substrate and the effective residence time in constructed wetlands. We conducted two suites of stochastic numerical simulations, modelling the transport of a conservative tracer in a three-dimensional simulated constructed wetland in one case, and the microbial oxidation of a carbon source in the other. Within each group of simulations, different hydraulic conductivity fields were tested. These were based on a log-normal, spatially correlated random field (with exponential spatial correlation). The amount of heterogeneity was varied by changing the variance correlation length in the three directions. For each set of parameters, different realizations are considered to deduce both the expected residence time for a certain amount of heterogeneity, and its range of
Ben Ghacham, Alia; Cecchi, Emmanuelle; Pasquier, Louis-César; Blais, Jean-François; Mercier, Guy
2015-11-01
Mineral carbonation (MC) represents a promising alternative for sequestering CO2. In this work, the CO2 sequestration capacity of the available calcium-bearing materials waste concrete and anorthosite tailings is assessed in gas-solid-liquid and gas-solid routes using 18.2% flue CO2 gas. The objective is to screen for a better potential residue and phase route and as the ultimate purpose to develop a cost-effective process. The results indicate the possibility of removing 66% from inlet CO2 using waste concrete for the aqueous route. However, the results that were obtained with the carbonation of anorthosite were less significant, with 34% as the maximal percentage of CO2 removal. The difference in terms of reactivity could be explained by the accessibility to calcium. In fact, anorthosite presents a framework structure wherein the calcium is trapped, which could slow the calcium dissolution into the aqueous phase compared to the concrete sample, where calcium can more easily leach. In the other part of the study concerning gas-solid carbonation, the results of CO2 removal did not exceed 15%, which is not economically interesting for scaling up the process. The results obtained with waste concrete samples in aqueous phase are interesting. In fact, 34.6% of the introduced CO2 is converted into carbonate after 15 min of contact with the gas without chemical additives and at a relatively low gas pressure. Research on the optimization of the aqueous process using waste concrete should be performed to enhance the reaction rate and to develop a cost-effective process. PMID:26292776
A priori models for predicting drag reduction for flow over heterogeneous slip boundaries
NASA Astrophysics Data System (ADS)
Heck, Margaret; Papavassiliou, Dimitrios
2015-11-01
Slip at fluid-fluid/fluid-solid interfaces is a subject of interest for many engineering applications, ranging from porous materials to biomedical devices to separation processes. Despite remarkable effort to include the effects of surface topology and various flow and physical properties in models describing fluid slip, the mathematical description of flow over mixed slip boundaries is still under investigation. Using similarity theory, which is based on the generalized homogeneity of physical laws governing most systems and takes advantage of similarity in the spatial distribution of characteristics of motion, the equivalent slip velocity is shown to be a function of the geometry of a microfluidic system. The results are used to predict the slip velocity for flow over surfaces with periodically repeating no-slip/free-shear boundaries in the shape of rectangles for 16%-50% solid fractions. The equivalent slip velocity for flow over rectangular boundaries can then be related to the those for flow over surfaces with square and circular no-slip boundaries using characteristic length ratios. The models developed using this apporach can be directly used to estimate the slip velocity for flow over various free-shear/no-slip boundaries for Couette, laminar flow conditions.
NASA Astrophysics Data System (ADS)
Fachri, Muhammad; Tveranger, Jan; Braathen, Alvar; Schueller, Sylvie
2013-07-01
We demonstrate that truncated Gaussian simulation (TGS), which is typically used for modeling of sedimentary rocks, can be employed to reproduce detailed damage zone structure as observed in outcrops. The basic modeled units employed are fault facies classified according to deformation density. Published damage zone field maps are re-drawn as fault facies maps and used for deriving geostatistical descriptions of model input parameters. We apply the modeling method for damage zones related to three scenarios: an isolated fault, branching faults and double-tip interacting faults. Constrained by the resulting TGS models, a series of damage zone permeability models are generated by systematically modulating five modeling factors related to different heterogeneity scales. Single-phase flow simulations reveal that fault facies proportion and damage zone width are the most influential factors, followed by deformation band frequency. Deformation band permeability and fault facies extent are the least important factors. Modifying fault facies proportion and damage zone width mainly change the flow retardation/enhancement in the models, whereas modifying deformation band frequency, deformation band permeability and fault facies extent mainly change the flow tortuosity in the models. Finally, we examine hierarchical modeling and upscaling procedures to incorporate our fine-scale models into flow simulation models.
NASA Astrophysics Data System (ADS)
Juez, C.; Ferrer-Boix, C.; Murillo, J.; Hassan, M. A.; García-Navarro, P.
2016-01-01
In order to study the morphological evolution of river beds composed of heterogeneous material, the interaction among the different grain sizes must be taken into account. In this paper, these equations are combined with the two-dimensional shallow water equations to describe the flow field. The resulting system of equations can be solved in two ways: (i) in a coupled way, solving flow and sediment equations simultaneously at a given time-step or (ii) in an uncoupled manner by first solving the flow field and using the magnitudes obtained at each time-step to update the channel morphology (bed and surface composition). The coupled strategy is preferable when dealing with strong and quick interactions between the flow field, the bed evolution and the different particle sizes present on the bed surface. A number of numerical difficulties arise from solving the fully coupled system of equations. These problems are reduced by means of a weakly-coupled strategy to numerically estimate the wave celerities containing the information of the bed and the grain sizes present on the bed. Hence, a two-dimensional numerical scheme able to simulate in a self-stable way the unsteady morphological evolution of channels formed by cohesionless grain size mixtures is presented. The coupling technique is simplified without decreasing the number of waves involved in the numerical scheme but by simplifying their definitions. The numerical results are satisfactorily tested with synthetic cases and against experimental data.
Discontinuous approximation of viscous two-phase flow in heterogeneous porous media
NASA Astrophysics Data System (ADS)
Bürger, Raimund; Kumar, Sarvesh; Sudarshan Kumar, Kenettinkara; Ruiz-Baier, Ricardo
2016-09-01
Runge-Kutta Discontinuous Galerkin (RKDG) and Discontinuous Finite Volume Element (DFVE) methods are applied to a coupled flow-transport problem describing the immiscible displacement of a viscous incompressible fluid in a non-homogeneous porous medium. The model problem consists of nonlinear pressure-velocity equations (assuming Brinkman flow) coupled to a nonlinear hyperbolic equation governing the mass balance (saturation equation). The mass conservation properties inherent to finite volume-based methods motivate a DFVE scheme for the approximation of the Brinkman flow in combination with a RKDG method for the spatio-temporal discretization of the saturation equation. The stability of the uncoupled schemes for the flow and for the saturation equations is analyzed, and several numerical experiments illustrate the robustness of the numerical method.
A stochastic mixed finite element heterogeneous multiscale method for flow in porous media
Ma Xiang; Zabaras, Nicholas
2011-06-01
A computational methodology is developed to efficiently perform uncertainty quantification for fluid transport in porous media in the presence of both stochastic permeability and multiple scales. In order to capture the small scale heterogeneity, a new mixed multiscale finite element method is developed within the framework of the heterogeneous multiscale method (HMM) in the spatial domain. This new method ensures both local and global mass conservation. Starting from a specified covariance function, the stochastic log-permeability is discretized in the stochastic space using a truncated Karhunen-Loeve expansion with several random variables. Due to the small correlation length of the covariance function, this often results in a high stochastic dimensionality. Therefore, a newly developed adaptive high dimensional stochastic model representation technique (HDMR) is used in the stochastic space. This results in a set of low stochastic dimensional subproblems which are efficiently solved using the adaptive sparse grid collocation method (ASGC). Numerical examples are presented for both deterministic and stochastic permeability to show the accuracy and efficiency of the developed stochastic multiscale method.
NASA Astrophysics Data System (ADS)
Zanini, A.; Butera, I.; Tanda, M.
2006-12-01
The interest in environmental issues has led great attention to the quality of groundwater. Since '90 increasing attention has been paid to the problem of recovering the release history of a pollutant because the knowledge of the pollution injection function gives information about the future pollution spread, allows a better planning of remediation actions and it can be a useful tool for sharing the costs of remediation among the actors. The present work contains the last results obtained through an inverse procedure (Snodgrass and Kitanidis, 1997) which allows the recovering of the pollutant release history from a few concentration measurements; it is applied to very severe cases of non-uniform flow conditions. The application of the inverse procedure is possible if one knows the transfer function, which describes the transport process. This function can be analytically determined if the problem has a simple geometry and regular boundary conditions. The inverse procedure in hand, initially developed for a 1-D homogeneous isotropic aquifer, has been extended by the writers (see Butera et al., 2004) to multidimensional aquifers using the numerical modeling. In complex cases, such as non-uniform flow field, reactive transport and unsaturated aquifers, the transfer function can be numerically inferred using the methodology. The applications showed in this meeting concern with very complicate flow conditions that allow to evaluate the power of the methodology. Three cases are presented: - The first analyzed case consists in a fully saturated aquifer with highly heterogeneity conductivity field and a pumping well. - The second case describes a fully saturated aquifer, highly heterogeneous, contaminated by a reactive pollutant. - The last and most tricky case studies the diffusion of a pollutant, due to the leakage from a tank, through an unsaturated aquifer. The pollutant release history is satisfactory recovered in all of the studied cases.
NASA Astrophysics Data System (ADS)
Davies, Geoffrey F.
2009-10-01
Geophysical evidence and numerical models of mantle stirring imply the source of mid-ocean ridge basalts (MORBs) comprises most of the mantle, excepting only the D″ region and the "superpile" anomalies deep under Africa and the Pacific. Geophysical evidence is also strong that the mantle is heated substantially from within. Geochemical inferences of a strongly depleted MORB source are inconsistent with this picture because they would require the MORB source to be heated mainly from below and because they cannot accommodate all of the Earth's incompatible elements. Lacking any other large mantle reservoir, the MORB source is required to balance the global uranium budget, which implies a U concentration of about 10 ng/g, more than double recent estimates. The MORB source would then have been depleted only by a factor of two in highly incompatible elements, rather than four or more, relative to is primitive composition. Both geophysical and geochemical evidence support a heterogeneous, multicomponent MORB source. Surprisingly, former plume material may comprise 25% of the MORB source, and this alone could add 50-100% to previous inventories of incompatible elements. Previous geochemical estimates may also be less secure because of a continuing focus on the more common, more depleted MORBs, because of long chains of geochemical inference, and because of a reliance on peridotites that may not have equilibrated with the mean composition of the heterogeneous source. Mean compositions are of most geophysical relevance, rather than putative end-member compositions, but mean compositions will be difficult to estimate accurately because more enriched components are less common and more variable. Nevertheless, a reconciliation of geochemical and geophysical inferences seems possible.
Bias and uncertainty in regression-calibrated models of groundwater flow in heterogeneous media
Cooley, R.L.; Christensen, S.
2006-01-01
Groundwater models need to account for detailed but generally unknown spatial variability (heterogeneity) of the hydrogeologic model inputs. To address this problem we replace the large, m-dimensional stochastic vector ?? that reflects both small and large scales of heterogeneity in the inputs by a lumped or smoothed m-dimensional approximation ????*, where ?? is an interpolation matrix and ??* is a stochastic vector of parameters. Vector ??* has small enough dimension to allow its estimation with the available data. The consequence of the replacement is that model function f(????*) written in terms of the approximate inputs is in error with respect to the same model function written in terms of ??, ??,f(??), which is assumed to be nearly exact. The difference f(??) - f(????*), termed model error, is spatially correlated, generates prediction biases, and causes standard confidence and prediction intervals to be too small. Model error is accounted for in the weighted nonlinear regression methodology developed to estimate ??* and assess model uncertainties by incorporating the second-moment matrix of the model errors into the weight matrix. Techniques developed by statisticians to analyze classical nonlinear regression methods are extended to analyze the revised method. The analysis develops analytical expressions for bias terms reflecting the interaction of model nonlinearity and model error, for correction factors needed to adjust the sizes of confidence and prediction intervals for this interaction, and for correction factors needed to adjust the sizes of confidence and prediction intervals for possible use of a diagonal weight matrix in place of the correct one. If terms expressing the degree of intrinsic nonlinearity for f(??) and f(????*) are small, then most of the biases are small and the correction factors are reduced in magnitude. Biases, correction factors, and confidence and prediction intervals were obtained for a test problem for which model error is
Kinetics study of heterogeneous reactions of ozone with erucic acid using an ATR-IR flow reactor.
Leng, Chunbo; Hiltner, Joseph; Pham, Hai; Kelley, Judas; Mach, Mindy; Zhang, Yunhong; Liu, Yong
2014-03-01
The ozone initiated heterogeneous oxidation of erucic acid (EA) thin film was investigated using a flow system combined with attenuated total reflection infrared spectroscopy (ATR-IR) over wide ranges of ozone concentrations (0.25-60 ppm), thin film thickness (0.1-1.0 μm), temperatures (263-298 K), and relative humidities (0-80% RH) for the first time. Pseudo-first-order rate constants, kapp, and overall reactive uptake coefficients, γ, were obtained through changes in the absorbance of C[double bond, length as m-dash]O stretching bands at 1695 cm(-1), which is assigned to the carbonyl group in carboxylic acid. Results showed that the reaction followed the Langmuir-Hinshelwood mechanism and kapp was largely dominated by surface reaction over bulk phase reaction. In addition, both the kapp and the γ values showed very strong temperature dependences (∼two orders of magnitude) over the temperature range; in contrast, they only slightly increased with increasing RH values from 0-80%. According to the kapp values as a function of temperature, the activation energy for the heterogeneous reaction was estimated to be 80.6 kJ mol(-1). Our results have suggested that heterogeneous reactions between ozone and unsaturated solid surfaces likely have a substantially greater temperature dependence than liquid ones. Moreover, the hygroscopic properties of EA thin films before and after exposure to ozone were also studied by measurement of water uptake. Based on the hygroscopicity data, the insignificant RH effect on reaction kinetics was probably due to the relatively weak water uptake by the unreacted and reacted EA thin films. PMID:24457621
NASA Astrophysics Data System (ADS)
Hangen, E.; Gerke, H. H.; Schaaf, W.; Hüttl, R. F.
2003-04-01
Flow and transport processes in forest-reclaimed lignitic mine soils are required to quantify water and element budgets, which are important for long-term predictions of restored ecosystem stability and development of mining area water quality. Soil water pressure head and solute concentration measurements using tensiometers and suction cups showed strong spatial heterogeneity possibly indicating preferential flow effects. Properties and spatial structures of the mostly sandy mine soils and transport processes, however, have not sufficiently been known for detailed assessments. The objective of this study was to quantitatively analyse flow paths and measure amount and spatial distribtion of leaching. Water and element fluxes were studied at a reclaimed mine spoil site, which was afforested in 1982 with Pinus nigra. At a 3.3 m2 plot, the total percolating water was collected in 110 cm soil depth by 45 squared suction cells of 27 cm edge length each. A multi-tracer solution containing deuterium, bromide, and terbuthylazine was applied evenly at the plot surface and imposed to natural infiltration. Leaching was measured for a period of about 2 years. One third of the cells never delivered any drainage water while few cells had large drainage rates which in one case even exceeded local infiltration rates. About 71 % of the drainage was through 9 % of the area. The spatial distribution of the leached bromide tracer did not always correspond with that of drainage. Relative concentrations of bromide and deuterium were similar. Terbuthylazine was observed only sporadically during the first drainage period and at relatively small concentrations just above the analytical detection limit. Leaching patterns of the sorptive herbicide indicate only relatively small nonequilibrium-type preferential flow. Sediment structures, water repellent regions, and tree root distributions seem to be important for funneling and flow path formation.
Technology Transfer Automated Retrieval System (TEKTRAN)
Bombus bifarius is a widespread bumble bee that occurs in montane regions of western North America. This species has several major color polymorphisms, and shows evidence of genetic structuring among regional populations. We test whether this structure is evidence for discrete gene flow barriers tha...
NASA Astrophysics Data System (ADS)
Meheust, Y.; De Dreuzy, J.; Pichot, G.
2011-12-01
Flow channeling and permeability scaling in fractured media have been classically addressed either at the fracture- or at the network- scales. In the latter case they are linked to the topological structure of the network, while at the fracture scale they are controlled by the variability of the local aperture distribution inside individual fractures. In this study we analyze these two combined effects, investigating how flow localization below the scale of individual fractures influences that at the network scale and the resulting medium permeability. This is done by use of a new highly-resolved 3D discrete fracture network model (DFN). The local apertures of individual fractures are distributed according to a truncated Gaussian law, and exhibit self-affine spatial correlations that are bounded by an upper cutoff scale Lc; Lc and the fracture closure, defined as the ratio of the aperture fluctuations at scale Lc to the mean aperture, are considered homogeneous over the DFN. The network topology is controlled by a homogeneous scalar fracture density and a power law fracture length distribution. We have varied these features to investigate a large variety of DFN topologies, from sparse networks with varying degrees of fracture interconnections, flow bottlenecks and dead-ends (Fig. 1a), to dense well-connected networks (Fig. 1b). We have also investigated a large range of fracture closures, performing extensive simulations of about 105 different DFN realizations. At the fracture scale, accounting for local aperture fluctuations leads to a monotical deviation (which can exceed 50%) of the equivalent fracture transmissivity from the parallel plate behavior. At the network scale we observe a complex interaction between flow channeling within fracture planes and flow localization in the network. This interaction is controlled by the location of fracture interactions with respect to that of low local transmissivity zones (particularly the closed zones), in the fracture
NASA Astrophysics Data System (ADS)
Abushaikha, Ahmad S.; Blunt, Martin J.; Gosselin, Olivier R.; Pain, Christopher C.; Jackson, Matthew D.
2015-10-01
We present a new control volume finite element method that improves the modelling of multi-phase fluid flow in highly heterogeneous and fractured reservoirs, called the Interface Control Volume Finite Element (ICVFE) method. The method drastically decreases the smearing effects in other CVFE methods, while being mass conservative and numerically consistent. The pressure is computed at the interfaces of elements, and the control volumes are constructed around them, instead of at the elements' vertices. This assures that a control volume straddles, at most, two elements, which decreases the fluid smearing between neighbouring elements when large variations in their material properties are present. Lowest order Raviart-Thomas vectorial basis functions are used for the pressure calculation and first-order Courant basis functions are used to compute fluxes. The method is a combination of Mixed Hybrid Finite Element (MHFE) and CVFE methods. Its accuracy and convergence are tested using three dimensional tetrahedron elements to represent heterogeneous reservoirs. Our new approach is shown to be more accurate than current CVFE methods.
Study of Parameters Effect on Hydrodynamics of a Gas-Solid Chamber Experimentally and Numerically
NASA Astrophysics Data System (ADS)
Hamzehei, Mahdi; Rahimzadeh, Hassan
2012-04-01
In this research, gas velocity, initial static bed height and particle size effect on hydrodynamics of a non-reactive gas-solid fluidized bed chamber were studied experimentally and computationally. A multi fluid Eulerian model incorporating the kinetic theory for solid particles was applied to simulate the unsteady state behavior of this chamber and momentum exchange coefficients were calculated by using the Syamlal- O'Brien drag functions. Simulation results were compared with the experimental data in order to validate the CFD model. Pressure drops predicted by the simulations at different particle sizes and initial static bed height were in good agreement with experimental measurements at superficial gas velocity higher than the minimum fluidization velocity. Simulation results also indicated that small bubbles were produced at the bottom of the bed. These bubbles collided with each other as they moved upwards forming larger bubbles. Furthermore, this comparison showed that the model can predict hydrodynamic behavior of gas solid fluidized bed chambers reasonably well.
Imtiaz, Maria; Hayat, Tasawar; Alsaedi, Ahmed
2016-01-01
This paper looks at the flow of Jeffrey fluid due to a curved stretching sheet. Effect of homogeneous-heterogeneous reactions is considered. An electrically conducting fluid in the presence of applied magnetic field is considered. Convective boundary conditions model the heat transfer analysis. Transformation method reduces the governing nonlinear partial differential equations into the ordinary differential equations. Convergence of the obtained series solutions is explicitly discussed. Characteristics of sundry parameters on the velocity, temperature and concentration profiles are analyzed by plotting graphs. Computations for pressure, skin friction coefficient and surface heat transfer rate are presented and examined. It is noted that fluid velocity and temperature through curvature parameter are enhanced. Increasing values of Biot number correspond to the enhancement in temperature and Nusselt number. PMID:27583457
NASA Astrophysics Data System (ADS)
Antoine, Germain; Cazilhac, Marine; Monnoyer, Quentin; Jodeau, Magali; Gratiot, Nicolas; Besnier, Anne-Laure; Henault, Fabien; Le Brun, Matthieu
2015-04-01
The dynamic of suspended sediments in highly turbulent and concentrated flow is an important issue to better predict the sediment propagation along mountain rivers. In such extreme environments, the spatial and temporal variability of hydraulic and sediment parameters are difficult to measure: the flow velocity and the suspended sediment concentration (SSC) could be high (respectively several m/s and g/l) and rapidly variable. Simple methods are commonly used to estimate water discharge and mean or punctual SSC. But no method has been used successfully in a mountain river to estimate during a whole event the spatial distribution of flow velocity and SSC, as well as sediment parameters like grain size or settling velocity into a river cross section. This leads to these two questions: in such conditions, can we calculate sediment fluxes with one sediment concentration measurement? How can we explain the spatial heterogeneity of sediment characteristics? In this study, we analyze sampled data from a very well instrumented river reach in the Northern French Alps: the Arc-Isère River system. This gravel-bed river system is characterized by large concentrations of fines sediments, coming from the highly erodible mountains around. To control the hydraulic, sedimentary and chemical parameters from the catchment head, several gauging stations have been established since 2006. Especially, several measurements are usually done during the flushing of the dams located on the upper part of the river. During the flushing event of June 2014, we instrumented the gauging station located just upstream the confluence between the Isere and the Arc River, at the outlet of the Arc River watershed. ADCP measurements have been performed to estimate the spatial distribution of the flow velocity (up to 3 m/s), and turbidimeters and automatic samplers have been used to estimate the spatial distribution of the SSC into the cross section (up to 6 g/l). These samples have been directly analyzed
NASA Astrophysics Data System (ADS)
Gerhard, J. I.; Grant, G. P.; Kueper, B. H.
2005-12-01
Following a dense, nonaqueous phase liquid (DNAPL) release to the subsurface, little is known about the rate of DNAPL migration and the time required for its eventual immobilization. Numerical simulations can fill this knowledge gap on the condition that the employed models are sufficiently validated; however, to date, validation for transient DNAPL migration has been limited to one-dimensional homogenous systems (Gerhard and Kueper, 2003). This research focuses on spatially and temporally validating the multiphase numerical model DNAPL-3D (and its associated constitutive relationships) for the infiltration, redistribution, and immobilization of a transient, fixed-volume DNAPL release in two-dimensional heterogeneous porous media. For this purpose, a two-dimensional bench scale experiment was conducted involving the release of 1,2-dichloroethane into an initially water saturated, spatially correlated, randomly heterogeneous sand pack. An image capture and analysis system permitted digital tracking of the evolving DNAPL body until migration ceased. The porous media employed in the bench scale experiment consisted of six, single mesh size sand types for which hysteretic nonwetting phase (NWP) relative permeability-saturation (krN-S) relationships were independently measured at the local scale. The local scale experiments revealed a correlation between porous media mean grain diameter and the maximum value of NWP relative permeability. Predictions of the bench scale experiment with DNAPL-3D were successful in reproducing the observed, complex DNAPL release in both space and time without any model calibration. The simulations revealed that model validation is only possible when the correlation of krN-S relationships to porous media type is accounted for in the formulation of the numerical model. Field scale simulations indicate that both the volume of porous media invaded by NWP, and the time required for NWP migration to cease, will be under predicted if correlation
Pressure dependence of the melting temperature of solids - Rare-gas solids
NASA Technical Reports Server (NTRS)
Schlosser, Herbert; Ferrante, John
1991-01-01
A method presented by Schlosser et al. (1989) for analyzing the pressure dependence of experimental melting-temperature data is applied to rare-gas solids. The plots of the logarithm of the reduced melting temperature vs that of the reduced pressure are straight lines in the absence of phase transitions. The plots of the reduced melting temperatures for Ar, Kr, and Xe are shown to be approximately straight lines.
Ababou, R.
1991-08-01
This report develops a broad review and assessment of quantitative modeling approaches and data requirements for large-scale subsurface flow in radioactive waste geologic repository. The data review includes discussions of controlled field experiments, existing contamination sites, and site-specific hydrogeologic conditions at Yucca Mountain. Local-scale constitutive models for the unsaturated hydrodynamic properties of geologic media are analyzed, with particular emphasis on the effect of structural characteristics of the medium. The report further reviews and analyzes large-scale hydrogeologic spatial variability from aquifer data, unsaturated soil data, and fracture network data gathered from the literature. Finally, various modeling strategies toward large-scale flow simulations are assessed, including direct high-resolution simulation, and coarse-scale simulation based on auxiliary hydrodynamic models such as single equivalent continuum and dual-porosity continuum. The roles of anisotropy, fracturing, and broad-band spatial variability are emphasized. 252 refs.
NASA Astrophysics Data System (ADS)
Shapiro, A.; Fedorovich, E.; Gibbs, J. A.
2015-06-01
An analytical solution of the Boussinesq equations for the motion of a viscous stably stratified fluid driven by a surface thermal forcing with large horizontal gradients (step changes) is obtained. This analytical solution is one of the few available for wall-bounded buoyancy-driven flows. The solution can be used to verify that computer codes for Boussinesq fluid system simulations are free of errors in formulation of wall boundary conditions and to evaluate the relative performances of competing numerical algorithms. Because the solution pertains to flows driven by a surface thermal forcing, one of its main applications may be for testing the no-slip, impermeable wall boundary conditions for the pressure Poisson equation. Examples of such tests are presented.
Effect of the Entrapped air on Water Flow in Heterogeneous Soil: Experimental Set- up
NASA Astrophysics Data System (ADS)
Snehota, M.; Sobotkova, M.; Cislerova, M.
2008-12-01
Temporal variations of steady state water flow rates were observed in laboratory infiltration experiments done on a sample of compacted sand and on an undisturbed soil sample (Eutric Cambisol). These variations are found to be in relation with entrapped air content. Infiltration-outflow experiments consisted of a series of ponded infiltration runs with seepage face boundary condition at the lower end of columns. The amount of the entrapped was derived from continuous weighing of the sample. The initial water contents were different for each run, which led to different amount of the air trapped in the soil during the first stages of infiltrations. The results of the experiments done on undisturbed soil showed that the flux rates and water contents varied during quasi-steady state. This finding contradicts the standard theory. The fluctuations of the water content during the steady state flow can be ascribed to the variations in volume of the entrapped air. Similarly, shape of the bromide breakthrough curve, which were performed simultaneously during the quasi-steady state varied for undisturbed soil. The same behaviour was not observed in the sample of homogeneous sand. Computer tomography was used to characterize the structure of the undisturbed soil sample with focus on potential preferential flow pathways, which are likely to host the entrapped air. To formulate more general conclusions, an extended series of infiltration outflow and bromide breakthrough experiments is in progress. This research has been supported by research project GACR 103/08/1552 and MSMT CEZ MSM 6840770002.
Local velocity measurements in heterogeneous and time-dependent flows of a micellar solution.
Decruppe, J P; Greffier, O; Manneville, S; Lerouge, S
2006-06-01
We present and discuss the results of pointwise velocity measurements performed on a viscoelastic micellar solution made of cetyltrimethylammonium bromide and sodium salicylate in water, respectively, at the concentrations of 50 and 100 mmol. The sample is contained in a Couette device and subjected to flow in the strain controlled mode. This particular solution shows shear banding and, in a narrow range of shear rates at the right end of the stress plateau, apparent shear thickening occurs. Time-dependent recordings of the shear stress in this range reveal that the flow has become unstable and that large sustained oscillations of the shear stress and of the first normal stresses difference emerge and grow in the flow. Local pointwise velocity measurements clearly reveal a velocity profile typical of shear banding when the imposed shear rate belongs to the plateau, but also important wall slip in the entire range of velocity gradients investigated. In the oscillations regime, the velocity is recorded as a function of time at a fixed point close to the rotor of the Couette device. The time-dependent velocity profile reveals random fluctuations but, from time to time, sharp decreases much larger than the standard deviation are observed. An attempt is made to correlate these strong variations with the stress oscillations and a correlation coefficient r is computed. However, the small value found for the coefficient r does not allow us to draw a final conclusion as concerns the correlation between stress oscillations and velocity fast decreases. PMID:16906838
NASA Astrophysics Data System (ADS)
RamReddy, Chetteti; Pradeepa, Teegala
2016-05-01
Based on the nonlinear variation of density with temperature (NDT) in the buoyancy term, the mixed convection flow along a vertical plate of a micropolar fluid saturated porous medium is considered. In addition, the effect of homogeneous-heterogeneous reaction and convective boundary condition has been taken into account. Using lie scaling group transformations, the similarity representation is attained for the system of partial differential equations, prior to being solved by a spectral quasilinearization method. The results show that in the presence of aiding and opposing flow situations, both the species concentration and mass transfer rate decreases when the strength of homogeneous and heterogeneous reaction parameters are enhanced.
NASA Astrophysics Data System (ADS)
Sanan, Patrick; May, Dave; Schenk, Olaf; Rupp, Karl
2016-04-01
Scalable solvers for mantle convection and lithospheric dynamics with highly heterogeneous viscosity structure typically require the use of a multigrid method. To leverage new hybrid CPU-accelerator architectures on leadership compute clusters, multigrid hierarchies which can reduce communication and use high available arithmetic intensity are at a premium, motivating more aggressive coarsening schemes and smoothers. We present results of a comparative study of two competitive GPU-enabled subdomain smoothers within an additive Schwarz method. Chebyshev-Jacobi smoothing has been shown to be an effective smoother, and its nature as a low-communication method built from basic linear algebra routines allows its use on a wide range of devices with current libraries. ILU smoothing is also of interest and is known to provide robust smoothing in some cases, but has traditionally been difficult to use in a fine-grained parallel environment. However, a recently-introduced variant by Chow and Patel allows for incomplete factorizations to be computed and applied in these environments, hence allowing us to study them as well. We use and extend the pTatin3D, PETSc, and ViennaCL libraries to integrate promising methods into a realistic application framework.
Persistent questions of heterogeneity, uncertainty, and scale in subsurface flow and transport
NASA Astrophysics Data System (ADS)
Kitanidis, Peter K.
2015-08-01
When Water Resources Research was launched in 1965, heterogeneity, uncertainty, and scale issues in subsurface hydrology were in the backburner. Only about 10 years later, under the stimulus of dealing with solute transport problems, these problems received attention. The stochastic approach brought tools to deal both with problems of upscaling, also known as homogenization and coarse-graining, and uncertainty quantification. Effective conductivity and effective dispersion, also known as macrodispersion, coefficients in statistically homogeneous formations were extensively studied. Mixing, in its role of affecting reaction rates, started receiving attention. While in the dispersion problem emphasis was on Fickian representations, more sophisticated models have also been studied. Uncertainty quantification in the inverse problem has also made progress and geostatistical ideas, as well as ideas originating in signal processing, influenced how we approach problems of inference like interpolation and inverse modeling. My view is that we should emphasize information aspects, i.e., the collection of more and better data, their correct assimilation, the quantification of uncertainty associated with predictions, and the selection of designs or policies that accurately reflect what we actually know and thus manage risk. Progress in this department has been hampered by ingrained ideas, inadequate training, and inadequate resources. Research in problems of upscaling will continue to shed new light and provide better tools to deal with onerous problems. At the same time, no cure is more universally potent than using a more refined grid. Finally, although research is active, the diffusion of research results to education and practice has been slow.
NASA Astrophysics Data System (ADS)
Büsing, Henrik
2014-05-01
The geological sequestration of CO2 is considered as one option to mitigate anthropogenic effects on climate change. To describe the behavior of CO2 underground we consider mass balance equations for the two phases, CO2 and brine, which include the dissolution of CO2 into the brine phase and of H2O into the gas phase (c.f. [1]). After discretization in time with the implicit Euler method and in space with the Box method (c.f. [2]), we end up with a nonlinear system of equations. Newton's method is used to solve these systems, where the required Jacobians are obtained by automatic differentiation (AD) (c.f. [3]). In contrast to approximate Jacobians via finite differences, AD gives exact Jacobians through a source code transformation. These exact Jacobians have the advantage that no additional errors are introduced by the derivative computation. In consequence, fewer Newton iterations are needed and a performance increase during derivative computation can be observed (c.f. [4]). During the initial stage of a CO2 sequestration scenario the movement of the CO2 plume is driven by advective and buoyancy forces. After injection is finished solubility and density driven flow become dominant. We examine the performance of different iterative solvers and preconditioners for these two stages. To this end, we consider standard ILU preconditioning with BiCGStab as iterative solver, as well as GMRES, and algebraic and geometric multigrid methods. Our test example considers, on the one hand, a homogeneous permeability distribution and, on the other hand, a heterogeneous one. In the latter case we sample a heterogeneous porosity field from a Gaussian distribution and, subsequently, derive the corresponding permeabilities after [5]. Finally, we examine to which extent the amount of dissolved CO2 depends on the heterogeneities in the reservoir. References [1] Spycher, N., Pruess, K., & Ennis-King, J., 2003. CO2-H2O mixtures in the geological sequestration of CO2. I. Assessment and
Analysis of hydrodynamic fluctuations in heterogeneous adjacent multidomains in shear flow.
Bian, Xin; Deng, Mingge; Tang, Yu-Hang; Karniadakis, George Em
2016-03-01
We analyze hydrodynamic fluctuations of a hybrid simulation under shear flow. The hybrid simulation is based on the Navier-Stokes (NS) equations on one domain and dissipative particle dynamics (DPD) on the other. The two domains overlap, and there is an artificial boundary for each one within the overlapping region. To impose the artificial boundary of the NS solver, a simple spatial-temporal averaging is performed on the DPD simulation. In the artificial boundary of the particle simulation, four popular strategies of constraint dynamics are implemented, namely the Maxwell buffer [Hadjiconstantinou and Patera, Int. J. Mod. Phys. C 08, 967 (1997)], the relaxation dynamics [O’Connell and Thompson, Phys. Rev. E 52, R5792 (1995)], the least constraint dynamics [Nie et al.,J. Fluid Mech. 500, 55 (2004); Werder et al., J. Comput. Phys. 205, 373 (2005)], and the flux imposition [Flekkøy et al., Europhys. Lett. 52, 271 (2000)], to achieve a target mean value given by the NS solver. Going beyond the mean flow field of the hybrid simulations, we investigate the hydrodynamic fluctuations in the DPD domain. Toward that end, we calculate the transversal autocorrelation functions of the fluctuating variables in k space to evaluate the generation, transport, and dissipation of fluctuations in the presence of a hybrid interface. We quantify the unavoidable errors in the fluctuations, due to both the truncation of the domain and the constraint dynamics performed in the artificial boundary. Furthermore, we compare the four methods of constraint dynamics and demonstrate how to reduce the errors in fluctuations. The analysis and findings of this work are directly applicable to other hybrid simulations of fluid flow with thermal fluctuations. PMID:27078489
Analysis of hydrodynamic fluctuations in heterogeneous adjacent multidomains in shear flow
NASA Astrophysics Data System (ADS)
Bian, Xin; Deng, Mingge; Tang, Yu-Hang; Karniadakis, George Em
2016-03-01
We analyze hydrodynamic fluctuations of a hybrid simulation under shear flow. The hybrid simulation is based on the Navier-Stokes (NS) equations on one domain and dissipative particle dynamics (DPD) on the other. The two domains overlap, and there is an artificial boundary for each one within the overlapping region. To impose the artificial boundary of the NS solver, a simple spatial-temporal averaging is performed on the DPD simulation. In the artificial boundary of the particle simulation, four popular strategies of constraint dynamics are implemented, namely the Maxwell buffer [Hadjiconstantinou and Patera, Int. J. Mod. Phys. C 08, 967 (1997), 10.1142/S0129183197000837], the relaxation dynamics [O'Connell and Thompson, Phys. Rev. E 52, R5792 (1995), 10.1103/PhysRevE.52.R5792], the least constraint dynamics [Nie et al., J. Fluid Mech. 500, 55 (2004), 10.1017/S0022112003007225; Werder et al., J. Comput. Phys. 205, 373 (2005), 10.1016/j.jcp.2004.11.019], and the flux imposition [Flekkøy et al., Europhys. Lett. 52, 271 (2000), 10.1209/epl/i2000-00434-8], to achieve a target mean value given by the NS solver. Going beyond the mean flow field of the hybrid simulations, we investigate the hydrodynamic fluctuations in the DPD domain. Toward that end, we calculate the transversal autocorrelation functions of the fluctuating variables in k space to evaluate the generation, transport, and dissipation of fluctuations in the presence of a hybrid interface. We quantify the unavoidable errors in the fluctuations, due to both the truncation of the domain and the constraint dynamics performed in the artificial boundary. Furthermore, we compare the four methods of constraint dynamics and demonstrate how to reduce the errors in fluctuations. The analysis and findings of this work are directly applicable to other hybrid simulations of fluid flow with thermal fluctuations.
NASA Astrophysics Data System (ADS)
Shapiro, A.; Fedorovich, E.; Gibbs, J. A.
2015-03-01
An analytical solution of the Boussinesq equations for the motion of a viscous stably stratified fluid driven by a surface thermal forcing with large horizontal gradients (step changes) is obtained. The solution can be used to verify that computer codes for Boussinesq fluid system simulations are free of errors in formulation of wall boundary conditions, and to evaluate the relative performances of competing numerical algorithms. Because the solution pertains to flows driven by a surface thermal forcing, one of its main applications may be for testing the no-slip, impermeable wall boundary conditions for the pressure Poisson equation. Examples of such tests are presented.
NASA Astrophysics Data System (ADS)
Aricò, Costanza; Sinagra, Marco; Tucciarelli, Tullio
2012-02-01
A novel methodology is proposed for the solution of the flow equation in a variably saturated heterogeneous porous medium. The computational domain is descretized using triangular meshes and the governing PDEs are discretized using a lumped in the edge centres numerical technique. The dependent unknown variable of the problem is the piezometric head. A fractional time step methodology is applied for the solution of the original system, solving consecutively a prediction and a correction problem. A scalar potential of the flow field exists and in the prediction step a MArching in Space and Time (MAST) formulation is applied for the sequential solution of the Ordinary Differential Equation of the cells, ordered according to their potential value computed at the beginning of the time step. In the correction step, the solution of a large linear system with order equal to the number of edges is required. A semi-analytical procedure is also proposed for the solution of the prediction step. The computational performance, the order of convergence and the mass balance error have been estimated in several tests and compared with the results of other literature models.
NASA Astrophysics Data System (ADS)
Jones, T.; Detwiler, R. L.
2015-12-01
Mineral precipitation significantly alters the transport properties of fractured rock. In an idealized parallel-plate fracture with uniform surface reactivity, the injection of a supersaturated fluid leads to faster precipitation near the inlet and rapid sealing of the fracture. However, it is likely that physical and chemical heterogeneities will perturb local reaction rates. Predicting the evolution of transport properties in heterogeneous fractures requires an improved understanding of the feedback between mineral precipitation and fluid flow. We present results from three experiments in transparent analog fractures: i) uniform aperture with uniform surface reactivity, ii) uniform aperture with heterogeneous surface reactivity, and iii) variable aperture with heterogeneous reactivity. We controlled surface reactivity by exposing one fracture surface to a solution supersaturated with calcium carbonate for different durations. We then injected a metastable mixture with log-saturation-index of 1.44 at a constant rate of 0.5 ml/min. Transmitted light techniques provided quantitative measurements of fracture aperture and fluid transport over the flow field. In the homogeneous fracture (i), as expected, aperture decreased most rapidly along the inlet. In the variable aperture fracture (iii), we observed enhanced reduction rates in small aperture regions; these local reactions organized flow into thin pathways that connected regions of low surface reactivity and grew to span the length of the fracture over the six-month duration of the experiment. An ongoing experiment (ii) will clarify the relative importance of chemical heterogeneity versus aperture variability on the formation of these preferential pathways.
Brine heterogeneity and dispersed interstitial advective flow underneath the sea of galilee, Israel
NASA Astrophysics Data System (ADS)
Weinstein, Y.; Katz, A.; Kastner, M.; Nishri, A.; Jannasch, H.
2003-04-01
Saline groundwater from submerged sources is today the main source of salts to the Sea of Galilee, supplying annually 72,000 tons chloride to the lake. MOSQUITO flux-meters were deployed during April to September 2001 at seven shallow Kinneret sites in order to study the dispersed interstitial flow. Each instrument carried 3-5 Osmo-Samplers that continuously sampled pore fluids at various depths in the sediment (0-45 cm). Samples were analyzed for their chemistry and for concentration of Na-fluorescein that was previously injected into the sediment. In general, oncentrations of conservative elements (e.g. Cl, Na, B) increase with depth into the sediment at all sites. However, concentrations vary significantly from one site to another. For instance, in sub-lacustrine brines next to the Tiberias Hot Springs Cl concentration reaches more than 14,500 mg/l at 35 cm below lake floor (not much less than the 18,000 mg/l in the nearby on-shore springs), while at other stations, brines are diluted by meteoric water to less than 1,500 mg/l Cl. Ion ratios in pore water indicate that the shallow parts of Lake Kinneret are underlain by several, separate, brine pockets, that are sometimes located very close to each other and discharge to the same area. Pore water at the east and northwest of the lake have Na/Cl ionic ratios between 0.7 and 0.8, similar to that of the overlying lake water, while at the west and south, ratios are significantly lower (<0.6 and <0.5, respectively), indicating larger degree of evaporation of the original brine end-member. Brines next to Tiberias Hot Springs have significantly higher Br/Cl and lower Mg/Cl ratios than pore water from other sites. Eastern shore sub-lacusrine brines (next to Gofra) are distinguished by their very high Sr/Cl and B/Cl ratios. Advective flow rates were derived from temporal patterns of Na-fluorescein concentration in pore water. Flow rates were between 0 and 80 cm/yr. Annual fluxes through the shallow part of the lake are
Analysis of unit mobility ratio well-to-well tracer flow to determine reservoir heterogeneity
Abbaszadeh-Dehghani, M.
1983-02-01
This study has been performed in 2 related sections. In the first section, exact analytic equations have been derived to define breakthrough curves for different developed flooding patterns for unit mobility ratio. The breakthrough curves have been correlated into a single curve. Because of this correlation, it is concluded that the breakthrough curve for any other repeating pattern should also lie near this same correlating curve. An analytic definition of breakthrough curves for a developed 5-spot at various mobility ratios also is included. Flow of a tracer slug in various developed patterns is discussed. In each system, an expression was derived to define the concentration of tracer in a streamtube. A computer program based on a nonlinear optimization technique was developed which analyzes a tracer breakthrough profile from a stratified reservoir. A 5-spot field example which has been decomposed into several layers is shown to illustrate the use of the research.
Stability analysis of non-inertial thin film flow over a heterogeneously heated porous substrate
NASA Astrophysics Data System (ADS)
Kumawat, Tara Chand; Tiwari, Naveen
2016-02-01
The dynamics and linear stability of a gravity drive thin film flowing over non-uniformly heated porous substrate are studied. A governing equation for the evolution of film-thickness is derived within the lubrication approximation. Darcy-Brinkman equation is used to model flow in the porous medium along with a tangential stress-jump condition at the interface of the porous layer and the fluid film. A temperature profile is imposed at the solid wall to model an embedded heater beneath the porous layer. At the upstream edge of the heater, an opposing thermocapillary stress at the liquid-air interface leads to the formation of a thermocapillary ridge. The ridge becomes unstable beyond a critical Marangoni number leading to the formation of rivulets that are periodic in the spanwise direction. Increase in the values of parameters such as Darcy number, stress jump coefficient, and porosity is shown to have stabilizing effect on the film dynamics. The critical Marangoni number is shown to increase monotonically with Darcy number for various values of porosity. At large values of stress-jump coefficient, a non-monotonic variation in critical Marangoni number versus Darcy number is shown. A correlation is developed numerically for the ratio of critical Marangoni number at large Darcy number to that for a non-porous substrate as a function of porosity and thickness of the porous substrate. A transient growth analysis is carried out followed by non-linear stability analysis. The non-modal growth is found to be negligible thus indicating that the eigenvalues are physically determinant.
Petascale direct numerical simulation of blood flow on 200K cores and heterogeneous architectures
Sampath, Rahul S; Veerapaneni, Shravan; Biros, George; Zorin, Denis; Vuduc, Richard; Vetter, Jeffrey S; Moon, Logan; Malhotra, Dhairya; Shringarpure, Aashay; Rahimian, Abtin; Lashuk, Ilya; Chandramowlishwaran, Aparna
2010-01-01
We present a fast, petaflop-scalable algorithm for Stokesian particulate flows. Our goal is the direct simulation of blood, which we model as a mixture of a Stokesian fluid (plasma) and red blood cells (RBCs). Directly simulating blood is a challenging multiscale, multiphysics problem. We report simulations with up to 260 million deformable RBCs. The largest simulation amounts to 90 billion unknowns in space. In terms of the number of cells, we improve the state-of-the art by several orders of magnitude: the previous largest simulation, at the same physical fidelity as ours, resolved the flow of O(1,000-10,000) RBCs. Our approach has three distinct characteristics: (1) we faithfully represent the physics of RBCs by using nonlinear solid mechanics to capture the deformations of each cell; (2) we accurately resolve the long-range, N-body, hydrodynamic interactions between RBCs (which are caused by the surrounding plasma); and (3) we allow for highly non-uniform spatial distributions of RBCs. The new method has been implemented in the software library MOBO (for 'Moving Boundaries'). We designed MOBO to support parallelism at all levels, including inter-node distributed memory parallelism, intra-node shared memory parallelism, data parallelism (vectorization), and fine-grained multithreading for GPUs. We have implemented and optimized the majority of the computation kernels on both Intel/AMD x86 and NVidia's Tesla/Fermi platforms for single and double floating point precision. Overall, the code has scaled on 256 CPU-GPUs on the Teragrid's Lincoln cluster and on 200,000 AMD cores of the Oak Ridge National Laboratory's Jaguar PF system. In our largest simulation, we have achieved 0.7 Petaflops/s of sustained performance on Jaguar.
Gedye, Craig A.; Hussain, Ali; Paterson, Joshua; Smrke, Alannah; Saini, Harleen; Sirskyj, Danylo; Pereira, Keira; Lobo, Nazleen; Stewart, Jocelyn; Go, Christopher; Ho, Jenny; Medrano, Mauricio; Hyatt, Elzbieta; Yuan, Julie; Lauriault, Stevan; Kondratyev, Maria; van den Beucken, Twan; Jewett, Michael; Dirks, Peter; Guidos, Cynthia J.; Danska, Jayne; Wang, Jean; Wouters, Bradly; Neel, Benjamin; Rottapel, Robert; Ailles, Laurie E.
2014-01-01
Cell surface proteins have a wide range of biological functions, and are often used as lineage-specific markers. Antibodies that recognize cell surface antigens are widely used as research tools, diagnostic markers, and even therapeutic agents. The ability to obtain broad cell surface protein profiles would thus be of great value in a wide range of fields. There are however currently few available methods for high-throughput analysis of large numbers of cell surface proteins. We describe here a high-throughput flow cytometry (HT-FC) platform for rapid analysis of 363 cell surface antigens. Here we demonstrate that HT-FC provides reproducible results, and use the platform to identify cell surface antigens that are influenced by common cell preparation methods. We show that multiple populations within complex samples such as primary tumors can be simultaneously analyzed by co-staining of cells with lineage-specific antibodies, allowing unprecedented depth of analysis of heterogeneous cell populations. Furthermore, standard informatics methods can be used to visualize, cluster and downsample HT-FC data to reveal novel signatures and biomarkers. We show that the cell surface profile provides sufficient molecular information to classify samples from different cancers and tissue types into biologically relevant clusters using unsupervised hierarchical clustering. Finally, we describe the identification of a candidate lineage marker and its subsequent validation. In summary, HT-FC combines the advantages of a high-throughput screen with a detection method that is sensitive, quantitative, highly reproducible, and allows in-depth analysis of heterogeneous samples. The use of commercially available antibodies means that high quality reagents are immediately available for follow-up studies. HT-FC has a wide range of applications, including biomarker discovery, molecular classification of cancers, or identification of novel lineage specific or stem cell markers. PMID:25170899
Pohlmeier, A.; Ruetzel, H.
1996-07-15
Rapid kinetics and equilibrium of the ion exchange of Na{sup +} by Cd{sup 2+} at illite are studied by the stopped-flow technique and DPASV, respectively, as an example for reactions at heterogeneous surfaces. For the first time both kinetics and equilibrium are analyzed for the same system by kinetic- and affinity-spectra, taking into consideration the heterogeneity of binding sites. It is possible to calculate model independent kinetic spectra by means of the CONTIN program; the isotherm is evaluated by Sips` distribution function. Monomodal distribution functions are found, characterized by mean values and half widths at half height in the range between 0.2 and 0.3 log (k/s{sup {minus}1}) for the kinetics and 0.16 log (K/L/mol) for the affinity. From both analyses the mean ion exchange coefficient is determined as 2.2 {+-} 0.4 mol/liter and 1.5 {+-} 0.4 mol/liter, respectively. The kinetics are rapid; only one process is observed that is assigned to the binding of Cd{sup 2+} at the outer surface. The high activation-enthalpy of 35 kJ/mol proves that the exchange reaction of 2 Na{sup +} by cd{sup 2+} at the binding site is the rate-determining step and not the diffusion to the surface. The large negative activation-entropy of {minus}105 J/mol K indicates that this rate-determining step is of associative nature.
Srinivasan, Vivek J; Yu, Esther; Radhakrishnan, Harsha; Can, Anil; Climov, Mihail; Leahy, Conor; Ayata, Cenk; Eikermann-Haerter, Katharina
2015-10-01
Although microvascular dysfunction accompanies cognitive decline in aging, vascular dementia, and Alzheimer's disease, tools to study microvasculature longitudinally in vivo are lacking. Here, we use Doppler optical coherence tomography (OCT) and angiography for noninvasive, longitudinal imaging of mice with chronic cerebral hypoperfusion for up to 1 month. In particular, we optimized the OCT angiography method to selectively image red blood cell (RBC)-perfused capillaries, leading to a novel way of assessing capillary supply heterogeneity in vivo. After bilateral common carotid artery stenosis (BCAS), cortical blood flow measured by Doppler OCT dropped to half of baseline throughout the imaged tissue acutely. Microscopic imaging of the capillary bed with OCT angiography further revealed local heterogeneities in cortical flow supply during hypoperfusion. The number of RBC-perfused capillaries decreased, leading to increased oxygen diffusion distances in the days immediately after BCAS. Linear regression showed that RBC-perfused capillary density declined by 0.3% for a drop in flow of 1 mL/100 g per minute, and decreases in RBC-perfused capillary density as high as 25% were observed. Taken together, these results demonstrate the existence of local supply heterogeneity at the capillary level even at nonischemic global flow levels, and demonstrate a novel imaging method to assess this heterogeneity. PMID:26243708
Prediction of horizontal gas-solid flows under different gravitational fields
NASA Astrophysics Data System (ADS)
Laín, Santiago; Sommerfeld, Martin
2014-11-01
In this paper the performance of horizontal pneumatic conveying under different gravity environments is evaluated. An Euler-Lagrange approach validated versus ground experiments is employed to predict the relevant particle variables such as particle mass flux, mean conveying and fluctuating velocities in terrestrial, lunar and micro-gravity conditions. Gravity reduced computations predict a reduction in the global particle-wall collision frequency. Also, in the case of low wall roughness and small particle mass loading, reduction of gravity acceleration implies an increase of particle-wall collision frequency with the upper wall of the channel affecting greatly the particle mass flux profile. In the case of high wall roughness and/or high particle-to-fluid mass loading (i.e., around 1.0) particle conveying characteristics are similar in the three gravity conditions evaluated. This is due to the fact that both, wall roughness and inter-particle collisions reduce gravitational settling. However, the influence of gravity on the additional pressure loss along the channel due to the conveying of the particles is much reduced.
Non-catalytic heterogeneous biodiesel production via a continuous flow system.
Kwon, Eilhann E; Yi, Haakrho; Park, Jongseok; Seo, Jaegun
2012-06-01
This study provides a novel methodology for biodiesel (FAME) production under ambient pressure, which resolves most drawbacks of current commercialized biodiesel conversion via the transesterification reaction. This has been achieved by means of a thermo-chemical process and a true continuous flow system. This also enables combination of esterification of free fatty acids (FFAs) and transesterification of triglycerides into a single process without utilizing a catalyst, and leads to a 98-99±0.5 % conversion efficiency of FAME within 1 min in the temperature range of 350-500 °C. High FFA content in oil feedstock is not a matter of the new process, which enables the use of a broader variety of feedstocks, including all edible and inedible fats. Another feature of this novel method is that it does not produce wastewater. Thus, the new process has potential to spur a breakthrough in the lowest cost of biodiesel production. Moreover, this method also requires utilization of carbon dioxide during biodiesel production, an additional environmental benefit. PMID:22520224
Beaubien, A; Keita, L; Jolicoeur, C
1987-01-01
The influence of various surfactants on the biological activity of a mixed aerobic culture has been investigated by using flow microcalorimetry. The response of the culture to the addition of homologous n-alkylcarboxylates (C2 to C16) and n-alkylpyridinium bromides (C11 to C14) has been examined under endogenous and substrate saturation conditions, and inhibitory concentrations (MIC or the concentration which decreased the initial activity (heat flux) of the culture by 50%) were determined for each state. Under both conditions, the n-alkylpyridinium bromides were found to be more toxic than the n-alkylcarboxylates of identical chain length, thus confirming that the head group of the amphiphiles plays an important role in the microbial toxicity of surfactants. The relationship observed between the concentration at which 50% of the activity is lost and the chain length of the surfactant further confirms that cellular toxicity is also dependent on surfactant hydrophobicity. In relation to the biodegradability of surfactants in mixed aerobic cultures, the low concentration effects of n-alkylcarboxylates on endogenous culture were investigated in some detail. There appear to be compounded indications that these surfactants are rapidly metabolized by the microorganisms of the mixed culture, at least for homologs lower than C10. PMID:3426221
Analysis of unit mobility ratio well-to-well tracer flow to determine reservoir heterogeneity
Abbaszadeh-Dehghani, M.
1982-01-01
This study was carried out in two related sections. In the first section, exact analytic equations were derived to define breakthrough curves (displacing fluid cut versus pore volumes injected, or area swept versus pore volume injected) for different developed flooding patterns for unit mobility ratio. The breakthrough curves were correlated into a single curve. Because of this correlation, it was concluded that the breakthrough curve for any other repeating pattern should also lie near this same correlating curve. The first section also includes an analytical definition of breakthrough curves for a developed five-spot at various mobility ratios. In the derivations, it was assumed that the streamlines were independent of mobility ratio. The results of the analysis showed that the breakthrough areal sweep efficiencies at various mobility ratios were nearly independent of mobility ratios, while the post-breakthrough performance differed for each mobility ratio. The second part discusses flow of a tracer slug in various developed patterns. In each system, an expression was derived to define the concentration of tracer in a streamtube. These expressions integrated over all the streamlines produced a set of equations describing tracer production curves from homogeneous patterns. The study shows that the effluent tracer concentration depends upon the pattern geometry and size, and the dispersion constant of the formation. A computer program based on a non-linear optimization technique was developed which analyzes a tracer breakthrough profile from a stratified reservoir. The program computes porosity-thickness and fractional permeability-thickness for each layer. The algorithm utilizes the equations of a developed five-spot pattern and the parameters obtained in correlating the tracer production curves.
Analysis of unit mobility ratio well-to-well tracer flow to determine reservoir heterogeneity
Abbaszadeh-Dehghani, M.; Brigham, W.E.
1983-02-01
This study has been carried out in two related sections. In the first section, exact analytic equations have been derived to define breakthrough curves for different developed flooding well patterns for unit mobility ratio. The first section also includes an extension of an analytical definition of pattern breakthrough curves for mobility ratio other than one. The second part discusses flow of a tracer slug in various patterns. In each system, the longitudinal mixing of the tracer slug in a general streamtube of the pattern has been formulated mathematically. A line integral along a streamtube was derived which represents the length of the mixed zone. When this line integral was substituted into the mixing equation, an expression for the concentration of tracer at any location within a streamtube resulted. The study shows that the effluent tracer concentration depends upon the pattern geometry and size, and the dispersion constant of the formation. Tracer production curves for the different patterns considered have also been correlated into a set of curves depending on a/..cap alpha.., (a = distance between like wells, ..cap alpha.. = dispersion constant). The correlation was achieved by deriving two sets of correction factors, one for tracer peak concentration, and another for a/..cap alpha.. ratio. As a result of this correlation, a tracer response from any repeated homogeneous pattern can be estimated from the response of an equivalent five-spot system by utilizing the correction factors. A computer program based on a non-linear optimization technique was developed which decomposes a detected tracer breakthrough profile from a multilayered system into responses from individual layers. The algorithm utilizes the equations of the five-spot pattern in conjunction with the developed correction factors. A five-spot field example which has been successfully decomposed into several layers is shown to illustrate the use of this research. 42 figures, 15 tables.
McKenna, Sean Andrew; Yoon, Hongkyu; Hart, David Blaine
2010-12-01
Heterogeneity plays an important role in groundwater flow and contaminant transport in natural systems. Since it is impossible to directly measure spatial variability of hydraulic conductivity, predictions of solute transport based on mathematical models are always uncertain. While in most cases groundwater flow and tracer transport problems are investigated in two-dimensional (2D) systems, it is important to study more realistic and well-controlled 3D systems to fully evaluate inverse parameter estimation techniques and evaluate uncertainty in the resulting estimates. We used tracer concentration breakthrough curves (BTCs) obtained from a magnetic resonance imaging (MRI) technique in a small flow cell (14 x 8 x 8 cm) that was packed with a known pattern of five different sands (i.e., zones) having cm-scale variability. In contrast to typical inversion systems with head, conductivity and concentration measurements at limited points, the MRI data included BTCs measured at a voxel scale ({approx}0.2 cm in each dimension) over 13 x 8 x 8 cm with a well controlled boundary condition, but did not have direct measurements of head and conductivity. Hydraulic conductivity and porosity were conceptualized as spatial random fields and estimated using pilot points along layers of the 3D medium. The steady state water flow and solute transport were solved using MODFLOW and MODPATH. The inversion problem was solved with a nonlinear parameter estimation package - PEST. Two approaches to parameterization of the spatial fields are evaluated: (1) The detailed zone information was used as prior information to constrain the spatial impact of the pilot points and reduce the number of parameters; and (2) highly parameterized inversion at cm scale (e.g., 1664 parameters) using singular value decomposition (SVD) methodology to significantly reduce the run-time demands. Both results will be compared to measured BTCs. With MRI, it is easy to change the averaging scale of the observed
Ababou, R.; Bagtzoglou, A.C.
1993-06-01
This report documents BIGFLOW 1.1, a numerical code for simulating flow in variably saturated heterogeneous geologic media. It contains the underlying mathematical and numerical models, test problems, benchmarks, and applications of the BIGFLOW code. The BIGFLOW software package is composed of a simulation and an interactive data processing code (DATAFLOW). The simulation code solves linear and nonlinear porous media flow equations based on Darcy`s law, appropriately generalized to account for 3D, deterministic, or random heterogeneity. A modified Picard Scheme is used for linearizing unsaturated flow equations, and preconditioned iterative methods are used for solving the resulting matrix systems. The data processor (DATAFLOW) allows interactive data entry, manipulation, and analysis of 3D datasets. The report contains analyses of computational performance carried out using Cray-2 and Cray-Y/MP8 supercomputers. Benchmark tests include comparisons with other independently developed codes, such as PORFLOW and CMVSFS, and with analytical or semi-analytical solutions.
NASA Astrophysics Data System (ADS)
Pflieger, M.; Goriaux, M.; Temime-Roussel, B.; Gligorovski, S.; Monod, A.; Wortham, H.
2009-03-01
There is currently a need for reliable experimental procedures to follow the heterogeneous processing simulating the atmospheric conditions. This work offers an alternative experimental device to study the behaviour of semi-volatile organic compounds (SVOC) that presumably exhibit extremely slow reactivity (e.g. pesticides) towards the atmospheric oxidants such as ozone and OH. Naphthalene was chosen as a test compound since it was widely studied in the past and hence represents a good reference. Prior to ozone exposure, the gaseous naphthalene was adsorbed via gas-solid equilibrium on silica and XAD-4 particles. Then, the heterogeneous reaction of ozone with adsorbed naphthalene was investigated in specially designed flow tube reactors. After the reaction, the remaining naphthalene (adsorbed on particles surface) was extracted, filtered and analyzed by Gas Chromatography-Flame Ionization Detector (GC-FID). Thus, the kinetics results were obtained following the consumption of naphthalene. Using this procedure, the rate constants of heterogeneous ozonolysis of naphthalene (kO3 silica=2.26 (±0.09)×10-17 cm3 molec-1 s-1 and kO3 XAD-4=4.29 (±1.06)×10-19 cm3 molec-1 s-1) were determined for silica and XAD-4 particles, at 25°C and relative humidity <0.7%. The results show that the nature of the particles significantly affects the kinetics and that heterogeneous ozonolysis of naphthalene is faster than its homogeneous ozonolysis in the gas phase.
NASA Astrophysics Data System (ADS)
Singh, Jaideep; Bailey, Kevin G.; Lu, Zheng-Tian; Mueller, Peter; O'Connor, Thomas P.; Xu, Chen-Yu; Tang, Xiaodong
2013-04-01
Optical detection of single atoms captured in solid noble gas matrices provides an alternative technique to study rare nuclear reactions relevant to nuclear astrophysics. I will describe the prospects of applying this approach for cross section measurements of the ^22Ne,,),25Mg reaction, which is the crucial neutron source for the weak s process inside of massive stars. Noble gas solids are a promising medium for the capture, detection, and manipulation of atoms and nuclear spins. They provide stable and chemically inert confinement for a wide variety of guest species. Because noble gas solids are transparent at optical wavelengths, the guest atoms can be probed using lasers. We have observed that ytterbium in solid neon exhibits intersystem crossing (ISC) which results in a strong green fluorescence (546 nm) under excitation with blue light (389 nm). Several groups have observed ISC in many other guest-host pairs, notably magnesium in krypton. Because of the large wavelength separation of the excitation light and fluorescence light, optical detection of individual embedded guest atoms is feasible. This work is supported by DOE, Office of Nuclear Physics, under contract DE-AC02-06CH11357.
Role of fluctuations in instability generation in gas-solid suspensions
NASA Astrophysics Data System (ADS)
Subramaniam, Shankar; Mehrabadi, Mohammad; Kolakaluri, Ravi; Tenneti, Sudheer
2013-11-01
Stability analysis of gas-solid suspensions using kinetic theory (Koch, Phys. Fluids, 1990) relies on a number density function (NDF) that is based on the canonical (constant number) ensemble. Euler-Lagrange simulations of a model problem are used to show that this approach does not accurately represent the scale-dependent interphase coupling between different realizations of the gas velocity field and fluctuations in the number of particles naturally occurring in fluidized beds. The grand-canonical (or variable number) ensemble is better suited to representing this coupling, and it is shown how the NDF can be related to this ensemble. The evolution of the grand-canonical NDF then leads to instabilities and growth of spatial fluctuations in the number density of a homogeneous suspension. This analysis leads to a different explanation for the growth of instabilities in homogeneous gas-solid suspensions that does not require perturbations in the average number density. Rather it is shown that the interaction of different realizations of the gas velocity field with individual realizations of the particle field leads to the growth of instabilities due to the dependence of drag on local volume fraction in each realization, that is extracted from particle-resolved DNS data. This work is partially supported by NSF CBET 1134500.
NASA Astrophysics Data System (ADS)
Kroeger, Karsten F.; Bland, Kyle J.; Fohrmann, Miko; Funnell, Rob H.
2010-05-01
in heat generation due to crustal heterogeneity, and changes in heat advection and effects of tectono-sedimentary processes related to the formation of a subduction zone. The results of the model indicate that surface heat flow in the Taranaki Basin varies by as much as 20 mW/m2 due to the variability in crustal heat generation. Other individual factors such as change in mantle heat advection, tectonic subsidence, uplift and crustal thickening, and related sedimentary processes, only result in a variability of up to 10 mW/m2. The model further suggests that increased heating of the upper crust due to additional mantle heat advection related to the onset of subduction is still an ongoing process. Combined with low heat generation potential of parts of the crust and a cooling effect of crustal thickening, the lag in the additional heat transfer from the mantle explains why the surface heat-flow in the Taranaki Basin is 10-20 mW/m2 lower than in more typical back-arc areas around other Pacific plate margins.
NASA Astrophysics Data System (ADS)
Yoon, H.; McKenna, S. A.; Hart, D. B.
2010-12-01
Heterogeneity plays an important role in groundwater flow and contaminant transport in natural systems. Since it is impossible to directly measure spatial variability of hydraulic conductivity, predictions of solute transport based on mathematical models are always uncertain. While in most cases groundwater flow and tracer transport problems are investigated in two-dimensional (2D) systems, it is important to study more realistic and well-controlled 3D systems to fully evaluate inverse parameter estimation techniques and evaluate uncertainty in the resulting estimates. We used tracer concentration breakthrough curves (BTCs) obtained from a magnetic resonance imaging (MRI) technique in a small flow cell (14 x 8 x 8 cm) that was packed with a known pattern of five different sands (i.e., zones) having cm-scale variability. In contrast to typical inversion systems with head, conductivity and concentration measurements at limited points, the MRI data included BTCs measured at a voxel scale (~0.2 cm in each dimension) over 13 x 8 x 8 cm with a well controlled boundary condition, but did not have direct measurements of head and conductivity. Hydraulic conductivity and porosity were conceptualized as spatial random fields and estimated using pilot points along layers of the 3D medium. The steady state water flow and solute transport were solved using MODFLOW and MODPATH. The inversion problem was solved with a nonlinear parameter estimation package - PEST. Two approaches to parameterization of the spatial fields are evaluated: 1) The detailed zone information was used as prior information to constrain the spatial impact of the pilot points and reduce the number of parameters; and 2) highly parameterized inversion at cm scale (e.g., 1664 parameters) using singular value decomposition (SVD) methodology to significantly reduce the run-time demands. Both results will be compared to measured BTCs. With MRI, it is easy to change the averaging scale of the observed concentration
Role of distortion in the hcp vs fcc competition in rare-gas solids
NASA Astrophysics Data System (ADS)
Krainyukova, N. V.
2011-05-01
As a prototype of an initial or intermediate structure between hcp and fcc lattices we consider a distorted bcc crystal. We calculate the temperature and pressure dependences of the lattice parameters for the heavier rare gas solids Ar, Kr, Xe in a quasiharmonic approximation with Aziz potentials, and confirm earlier predictions that the hcp structure predominates over fcc in the bulk within wide ranges of P and T. The situation is different for confined clusters with up to 105 atoms, where, owing to the specific surface energetics and terminations, structures with five-fold symmetry made up of fcc fragments are dominant. As a next step we consider the free relaxation of differently distorted bcc clusters, and show that two types (monoclinic and orthorhombic) of initial distortion are a driving force for the final hcp vs fcc configurations. Possible energy relationships between the initial and final structures are obtained and analyzed.
Abnormal heat liberation triggered by current in a D/Pd gas-solid system
NASA Astrophysics Data System (ADS)
Lu, Xin; Tian, Jian
2015-08-01
A relationship was studied among D/Pd gas-solid system current, pressure and producing excess heating in this paper. The results indicated that when the pressure of deuterium is at 9 × 104 Pa, electric current is 8 A and lasting heat is 40 days, the superheating energy is 280 MJ, the maximum superheating power is 80 W and averaging to each palladium atom energy for the superheating energy is 1.7 × 104 eV. Analysis of the sample by SEM (scanning electron microscopy) and EDS (energy dispersive spectrometry) found that after the current triggering the surface of sample was changed and new elements such as Pb, Sn, Ca, and Ag appeared. The results suggested that the superheating appeared come from a nuclear transmutation.
Zhou, Quanlin; Gelhar, Lynn W.; Jacobs, Bruce
2002-05-31
The effects of subsurface heterogeneity on two-phase flow can be observed from the characterization functions of field-scale effective relative permeability and capillary pressure with respect to mean saturation. Numerical experiments were used to evaluate such effective properties of two-phase flow in a heterogeneous medium with properties representing the Borden Aquifer, and compared with the results of stochastic analysis developed using a spectral perturbation technique that employs a stationary, stochastic representation of the spatial variability of soil properties. Arbitrary forms of the relative permeability and capillary pressure characteristic functions with respect to saturation can be used in the theoretical analysis and numerical code. A statistical scaling procedure, which is a generalization of Leverett scaling, was developed for the relationship between intrinsic permeability and two capillary parameters. The procedure for estimating the effective properties of two-phase flow using numerical simulation consists of three-steps. Firstly, a local-scale heterogeneous system with random fields of intrinsic permeability and two capillary parameters was generated. Secondly, numerical simulation of single-phase flow in the system, with different sets of flow boundary conditions for different directions, was performed; the field-scale effective saturated hydraulic conductivity tensor was calculated on the basis of the mean Darcy law. The tensor obtained numerically is very close to that determined using the generalized spectral-perturbation approximation. Finally, a number of numerical experiments on two-phase flow in the system were conducted with different infiltration rates of DNAPL; the field-scale effective relative permeability and capillary pressure functions were obtained. In each experiment, a highly heterogeneous saturation field was obtained, leading to large variations of actual nonwetting phase permeability (combination of intrinsic permeability
NASA Astrophysics Data System (ADS)
Merino-Martín, L.; Moreno-de las Heras, M.; Pérez-Domingo, S.; Espigares, T.; Nicolau, J. M.
2012-05-01
Hydrological heterogeneity is recognized as a fundamental ecosystem attribute in drylands controlling the flux of water and energy through landscapes. Therefore, mosaics of runoff and sediment source patches and sinks are frequently identified in these dry environments. There is a remarkable scarcity of studies about hydrological spatial heterogeneity in restored slopes, where ecological succession and overland flow are interacting. We conducted field research to study the hydrological role of patches and slopes along an "overland flow gradient" (gradient of overland flow routing through the slopes caused by different amounts of run-on coming from upslope) in three reclaimed mining slopes of Mediterranean-continental climate. We found that runoff generation and routing in non-rilled slopes showed a pattern of source and sink areas of runoff. Such hydrological microenvironments were associated with seven vegetation patches (characterized by plant community types and cover). Two types of sink patches were identified: shrub Genista scorpius patches could be considered as "deep sinks", while patches where the graminoids Brachypodium retusum and Lolium perenne dominate were classified as "surface sinks" or "runoff splays". A variety of source patches were also identified spanning from "extreme sources" (Medicago sativa patches; equivalent to bare soil) to "poor sources" (areas scattered by dwarf-shrubs of Thymus vulgaris or herbaceous tussocks of Dactylis glomerata). Finally, we identified the volume of overland flow routing along the slope as a major controlling factor of "hydrological diversity" (heterogeneity of hydrological behaviours quantified as Shannon diversity index): when overland flow increases at the slope scale hydrological diversity diminishes.
Schindler, Thomas H.; Facta, Alvaro D.; Prior, John O.; Cadenas, Jerson; Zhang, Xiao-Li; Li, Yanjie; Sayre, James; Goldin, Jonathan
2016-01-01
Purpose To determine the relationship between carotid intima–media thickness (IMT), coronary artery calcification (CAC), and myocardial blood flow (MBF) at rest and during vasomotor stress in type 2 diabetes mellitus (DM). Methods In 68 individuals, carotid IMT was measured using high-resolution vascular ultrasound, while the presence of CAC was determined with electron beam tomography (EBT). Global and regional MBF was determined in milliliters per gram per minute with 13N-ammonia and positron emission tomography (PET) at rest, during cold pressor testing (CPT), and during adenosine (ADO) stimulation. Results There was neither a relationship between carotid IMT and CAC (r=0.10, p=0.32) nor between carotid IMT and coronary circulatory function in response to CPT and during ADO (r=−0.18, p=0.25 and r=0.10, p=0.54, respectively). In 33 individuals, EBT detected CAC with a mean Agatston-derived calcium score of 44±18. There was a significant difference in regional MBFs between territories with and without CAC at rest and during ADO-stimulated hyperemia (0.69±0.24 vs. 0.74±0.23 and 1.82±0.50 vs. 1.95±0.51 ml/g/min; p≤0.05, respectively) and also during CPT in DM but less pronounced (0.81±0.24 vs. 0.83±0.23 ml/g/min; p=ns). The increase in CAC was paralleled with a progressive regional decrease in resting as well as in CPT- and ADO-related MBFs (r=−0.36, p≤0.014; r=−0.46, p≤0.007; and r=−0.33, p≤0.041, respectively). Conclusions The absence of any correlation between carotid IMT and coronary circulatory function in type 2 DM suggests different features and stages of early atherosclerosis in the peripheral and coronary circulation. PET-measured MBF heterogeneity at rest and during vasomotor stress may reflect downstream fluid dynamic effects of coronary artery disease (CAD)-related early structural alterations of the arterial wall. PMID:18704406
NASA Astrophysics Data System (ADS)
Merino-Martín, L.; Moreno-de Las Heras, M.; Pérez-Domingo, S.; Espigares, T.; Nicolau, J. M.
2011-11-01
Hydrological heterogeneity is recognized as a fundamental ecosystem attribute in drylands controlling the flux of water and energy through landscapes. Therefore, mosaics of runoff and sediment sinks and source patches are frequently identified in these dry environments. There is a remarkable scarcity of studies about hydrological spatial heterogeneity in restored slopes, where ecological succession and overland flow are interacting. We conducted a field research to study the hydrological role of patches and slopes along an overland flow gradient in three reclaimed slopes coming from mining reclamation in a Mediterranean-continental climate. We found that runoff generation and routing in non-rilled slopes showed a pattern of source and sink areas of runoff. Such hydrological microenvironments were associated to seven vegetation patches (characterized by plant community types and cover). Two types of sink patches were identified: shrub Genista scorpius patches could be considered as a "deep sink", while patches where the graminoids Brachypodium retusum and Lolium perenne dominate were classified as "surface sinks" or "runoff splays". A variety of source patches were also identified spanning from "extreme sources" (Medicago sativa patches; equivalent to bare soil) to "poor sources" (areas scattered by dwarf-shrubs of Thymus vulgaris or herbaceous tussocks of Dactylis glomerata). Finally, we identified the volume of overland flow routing along the slope as a controlling major factor of hydrological diversity: when overland flow increases at the slope scale hydrological diversity diminishes.
NASA Astrophysics Data System (ADS)
Pflieger, Maryline; Monod, Anne; Wortham, Henri
To better understand the atmospheric behaviour of pesticides, heterogeneous ozonolysis of three herbicides (alachlor, terbuthylazine and trifluralin) adsorbed on silica particles were performed in a flow reactor. The experimental setup used in this study and previously validated ( Pflieger et al., 2009) has been specially developed to investigate extremely slow reactivity. The pesticides were adsorbed on particles using a gas/solid adsorption equilibrium, in order to simulate atmospheric conditions. After exposure to ozone concentrations ranging from 5 to 41 ppm during 90 min to 6 h, the kinetics were calculated by comparing the initial and the remaining amounts of pesticides adsorbed on silica particles. This work offers the first results of heterogeneous ozonolysis of alachlor and trifluralin adsorbed on mineral particles. Although alachlor and terbuthylazine were expected to react with ozone, no degradation was observed which leads to a lifetime higher than 8 months towards ozonolysis (for 40 ppb of O 3). A significant degradation of trifluralin adsorbed on silica particles by heterogeneous ozonolysis was observed. The experimental data could be fit by both the Langmuir-Rideal and the Langmuir-Hinshelwood models resulting in atmospheric lifetimes (towards heterogeneous ozonolysis) of 40 and 32 days respectively (for 40 ppb of O 3). These results are discussed and compared to other studies.
Rybolt, T.R.; Epperson, M.T.; Weaver, H.W.; Thomas, H.E.; Clare, S.E.; Manning, B.M.; McClung, J.T.
1995-07-01
Gas-solid chromatography was used to determine the Henry`s law second gas-solid virial coefficients within the temperature range of 314--615 K for ethane, propane, butane, isobutane, pentane, hexane, heptane, chloromethane, dichloromethane, trichloromethane, tetrachloromethane, trichlorofluoromethane (Freon 11), chlorodifluoromethane (Freon 22), dichlorodifluoromethane (Freon 12), methyl ether, ethyl ether, and sulfur hexafluoride with Carbopack B, a microporous carbon adsorbent. The temperature dependence of the second gas-solid virial coefficients of these adsorbates was used in conjunction with analyses based on a graphical method, a single-surface numeric integration method, a single-surface analytic expression method, and a two-surface analytic expression method to determine the gas-solid interaction energies and other parameters. The interaction energies were correlated with a ratio of the critical temperature divided by the square root of the critical pressure. The four methods were compared in their abilities to successfully calculate second gas-solid virial coefficient values.
NASA Astrophysics Data System (ADS)
Prasad, Awadhesh; Simmons, Craig T.
2003-01-01
The situation of a dense fluid overlying a lighter one is potentially unstable and under certain conditions may result in fingers of dense contaminant freely convecting downward. Free convection causes increased contaminant transport over larger distances and over shorter timescales than is possible by diffusion alone. Unlike free convection in homogenous porous media, free convection in heterogeneous porous media has received relatively little attention. In this study, a well-understood problem of transient free convection in homogeneous porous media, theElder [1967b] "short heater" problem has been modified to study the effects of heterogeneity in permeability distributions on solute transport processes using a stochastic framework. A set of measurable indicator characteristics including solute fluxes, solute present, center of gravity and finger penetration depth are used in the quantitative analysis of output. Heterogeneity in the permeability distribution provides both the triggering mechanism for the onset of instabilities and also controls their subsequent growth and/or decay. Results show that (1) an increase in the standard deviation of the log permeability field results in a greater degree of instability at earlier times but promotes stability at later times, (2) an increase in the horizontal correlation length of the log permeability field creates laterally extensive low-permeability zones that dissipate upward and downward motion needed to maintain convection and therefore causes a reduction in the degree of instability, (3) a greater degree of heterogeneity causes greater uncertainty in predictions, and (4) traditional predictive methods such as the Rayleigh number (based upon an average permeability) do not generally work in their application to heterogeneous systems. Probability of exceedence analysis also demonstrates that analyses based upon homogeneous assumptions will typically underestimate, often quite significantly, the value of key measurable
Kinetics of thermochemical gas-solid reactions important in the Venus sulfur cycle
NASA Technical Reports Server (NTRS)
Fegley, Bruce, Jr.
1988-01-01
The thermochemical net reaction CaCO3 + SO2 yields CaSO4 + CO is predicted to be an important sink for incorporation of SO2 into the Venus crust. The reaction rate law was established to understand the dependence of rate on experimental variables such as temperature and partial pressure of SO2, CO2, and O2. The experimental approach was a variant of the thermogravimetric method often employed to study the kinetics of thermochemical gas-solid reactions. Clear calcite crystals were heated at constant temperature in SO2-bearing gas streams for varying time periods. Reaction rate was determined by three independent methods. A weighted linear least squares fit to all rate data yielded a rate equation. Based on the Venera 13, 14 and Vega 2 observations of CaO content of the Venus atmosphere, SO2 at the calculated rate would be removed from the Venus atmosphere in about 1,900,00 years. The most plausible endogenic source of the sulfur needed to replenish atmospheric SO2 is volcanism. The annual amount of erupted material needed for the replenishment depends on sulfur content; three ratios are used to calculate rates ranging from 0.4 to 11 cu km/year. This geochemically derived volcanism rate can be used to test if geophysically derived rates are correct. The work also suggests that Venus is less volcanically active than the Earth.
Origin of melting point depression for rare gas solids confined in carbon pores
NASA Astrophysics Data System (ADS)
Morishige, Kunimitsu; Kataoka, Takaaki
2015-07-01
To obtain insights into the mechanism of the melting-point depression of rare gas solids confined in crystalline carbon pores, we examined the freezing and melting behavior of Xe and Ar confined to the crystalline pores of ordered mesoporous carbons as well as compressed exfoliated graphite compared to the amorphous pores of ordered mesoporous silicas, by means of X-ray diffraction. For the Xe and Ar confined to the crystalline carbon pores, there was no appreciable thermal hysteresis between freezing and melting. Furthermore, the position of the main diffraction peak did not change appreciably on freezing and melting. This strongly suggests that the liquids confined in the carbon pores form a multilayered structure parallel to the smooth walls. For the Xe and Ar confined to the amorphous silica pores, on the other hand, the position of the main diffraction peak shifted into higher scattering angle on freezing suggested that the density of the confined solid is distinctly larger than for the confined liquid. Using compressed exfoliated graphite with carbon walls of higher crystallinity, we observed that three-dimensional (3D) microcrystals of Xe confined in the slit-shaped pores melted to leave the unmelted bilayers on the pore walls below the bulk triple point. The lattice spacing of the 3D microcrystals confined is larger by ˜0.7% than that of the bilayer next to the pore walls in the vicinity of the melting point.
Origin of melting point depression for rare gas solids confined in carbon pores
Morishige, Kunimitsu Kataoka, Takaaki
2015-07-21
To obtain insights into the mechanism of the melting-point depression of rare gas solids confined in crystalline carbon pores, we examined the freezing and melting behavior of Xe and Ar confined to the crystalline pores of ordered mesoporous carbons as well as compressed exfoliated graphite compared to the amorphous pores of ordered mesoporous silicas, by means of X-ray diffraction. For the Xe and Ar confined to the crystalline carbon pores, there was no appreciable thermal hysteresis between freezing and melting. Furthermore, the position of the main diffraction peak did not change appreciably on freezing and melting. This strongly suggests that the liquids confined in the carbon pores form a multilayered structure parallel to the smooth walls. For the Xe and Ar confined to the amorphous silica pores, on the other hand, the position of the main diffraction peak shifted into higher scattering angle on freezing suggested that the density of the confined solid is distinctly larger than for the confined liquid. Using compressed exfoliated graphite with carbon walls of higher crystallinity, we observed that three-dimensional (3D) microcrystals of Xe confined in the slit-shaped pores melted to leave the unmelted bilayers on the pore walls below the bulk triple point. The lattice spacing of the 3D microcrystals confined is larger by ∼0.7% than that of the bilayer next to the pore walls in the vicinity of the melting point.
Venus volcanism: Rate estimates from laboratory studies of sulfur gas-solid reactions
NASA Technical Reports Server (NTRS)
Ehlers, K.; Fegley, B., Jr.; Prinn, R. G.
1989-01-01
Thermochemical reactions between sulfur-bearing gases in the atmosphere of Venus and calcium-, iron-, magnesium-, and sulfur-bearing minerals on the surface of Venus are an integral part of a hypothesized cycle of thermochemical and photochemical reactions responsible for the maintenance of the global sulfuric acid cloud cover on Venus. SO2 is continually removed from the Venus atmosphere by reaction with calcium bearing minerals on the planet's surface. The rate of volcanism required to balance SO2 depletion by reactions with calcium bearing minerals on the Venus surface can therefore be deduced from a knowledge of the relevant gas-solid reaction rates combined with reasonable assumptions about the sulfur content of the erupted material (gas + magma). A laboratory program was carried out to measure the rates of reaction between SO2 and possible crustal minerals on Venus. The reaction of CaCO3(calcite) + SO2 yields CaSO4 (anhydrite) + CO was studied. Brief results are given.
Origin of melting point depression for rare gas solids confined in carbon pores.
Morishige, Kunimitsu; Kataoka, Takaaki
2015-07-21
To obtain insights into the mechanism of the melting-point depression of rare gas solids confined in crystalline carbon pores, we examined the freezing and melting behavior of Xe and Ar confined to the crystalline pores of ordered mesoporous carbons as well as compressed exfoliated graphite compared to the amorphous pores of ordered mesoporous silicas, by means of X-ray diffraction. For the Xe and Ar confined to the crystalline carbon pores, there was no appreciable thermal hysteresis between freezing and melting. Furthermore, the position of the main diffraction peak did not change appreciably on freezing and melting. This strongly suggests that the liquids confined in the carbon pores form a multilayered structure parallel to the smooth walls. For the Xe and Ar confined to the amorphous silica pores, on the other hand, the position of the main diffraction peak shifted into higher scattering angle on freezing suggested that the density of the confined solid is distinctly larger than for the confined liquid. Using compressed exfoliated graphite with carbon walls of higher crystallinity, we observed that three-dimensional (3D) microcrystals of Xe confined in the slit-shaped pores melted to leave the unmelted bilayers on the pore walls below the bulk triple point. The lattice spacing of the 3D microcrystals confined is larger by ∼0.7% than that of the bilayer next to the pore walls in the vicinity of the melting point. PMID:26203042
Rehmat, A.; Saxena, S.C.; Land, R.H.
1980-09-01
A mechanistic model is developed for coal char combustion, with sulfur retention by limestone or dolomite sorbent, in a gas fluidized bed employing noncatalytic single pellet gas-solid reactions. The shrinking core model is employed to describe the kinetics of chemical reactions taking place on a single pellet; changes in pellet size as the reaction proceeds are considered. The solids are assumed to be in back-mix condition whereas the gas flow is regarded to be in plug flow. Most char combustion occurs near the gas distributor plate (at the bottom of the bed), where the bubbles are small and consequently the mass transfer rate is high. For such a case, the analysis is considerably simplified by ignoring the bubble phase since it plays an insignificant role in the overall rate of carbon conversion. Bubble-free operation is also encounterd in the turbulent regime, where the gas flow is quite high and classical bubbles do not exist. Formulation of the model includes setting up heat and mass balance equations pertaining to a single particle (1) exposed to a varying reactant concentration along the height of the bed and (2) whose size changes during reaction. These equations are then solved numerically to account for particles of all sizes in the bed in obtaining the overall carbon conversion efficiency and resultant sulfur retention. In particular, the influence on sorbent requirement of several fluid-bed variables such as oxygen concentration profile, particle size, reaction rate for sulfation reaction, and suflur adsorption efficiency are examined.
Dodd, Ian C.; Egea, Gregorio; Davies, William J.
2008-01-01
When soil moisture is heterogeneous, sap flow from, and ABA status of, different parts of the root system impact on leaf xylem ABA concentration ([X-ABA]leaf). The robustness of a model for predicting [X-ABA]leaf was assessed. ‘Two root-one shoot’ grafted sunflower (Helianthus annuus L.) plants received either deficit irrigation (DI, each root system received the same irrigation volumes) or partial rootzone drying (PRD, only one root system was watered and the other dried the soil). Irrespective of whether relative sap flow was assessed using sap flow sensors in vivo or by pressurization of de-topped roots, each root system contributed similarly to total sap flow during DI, while sap flow from roots in drying soil declined linearly with soil water potential (Ψsoil) during PRD. Although Ψsoil of the irrigated pot determined the threshold Ψsoil at which sap flow from roots in drying soil decreased, the slope of this decrease was independent of the wet pot Ψsoil. Irrespective of whether sap was collected from the wet or dry root system of PRD plants, or a DI plant, root xylem ABA concentration increased as Ψsoil declined. The model, which weighted ABA contributions of each root system according to the sap flow from each, almost perfectly explained [X-ABA] immediately above the graft union. That the model overestimated measured [X-ABA]leaf may result from changes in [X-ABA] along the transport pathway or an artefact of collecting xylem sap from detached leaves. The implications of declining sap flow through partially dry roots during PRD for the control of stomatal behaviour and irrigation scheduling are discussed. PMID:18940933
NASA Astrophysics Data System (ADS)
Kihm, J.; Kim, J.
2006-12-01
A series of numerical simulations using a fully coupled hydrogeomechanical numerical model, which is named COWADE123D, is performed to analyze groundwater flow and land deformation in an unsaturated heterogeneous slope and its stability under various rainfall rates. The slope is located along a dam lake in Republic of Korea. The slope consists of the Cretaceous granodiorite and can be subdivided into the four layers such as weathered soil, weathered rock, intermediate rock, and hard rock from its ground surface due to weathering process. The numerical simulation results show that both rainfall rate and heterogeneity play important roles in controlling groundwater flow and land deformation in the unsaturated slope. The slope becomes more saturated, and thus its overall hydrogeomechanical stability deteriorates, especially in the weathered rock and weathered soil layers, as the rainfall increases up to the maximum daily rainfall rate in the return period of one year. However, the slope becomes fully saturated, and thus its hydrogeomechanical responses are almost identical under more than such a critical rainfall rate. From the viewpoint of hydrogeology, the pressure head, and hence the hydraulic head increase as the rainfall rate increases. As a result, the groundwater table rises, the unsaturated zone reduces, the seepage face expands from the slope toe toward the slope crest, and the groundwater flow velocity increases along the seepage face. Particularly, the groundwater flow velocity increases significantly in the weathered soil and weathered rock layers as the rainfall rate increases. This is because their hydraulic conductivity is relatively higher than that of the intermediate rock and hard rock layers. From the viewpoint of geomechanics, the horizontal displacement increases, while the vertical displacement decreases toward the slope toe as the rainfall rate increases. This may result from the buoyancy effect associated with the groundwater table rise as the
Seaman, S.; Dyar, D; Marinkovic, N
2009-01-01
This study focuses on the origin of flow-banded rhyolites that consist of compositionally similar darker and lighter flow bands of contrasting texture and color. Infrared radiation was used to obtain Fourier transform infrared (FTIR) spectra from which water concentrations were calculated, and to map variations in water concentrations across zones of spherulites and glass from the 23 million year old Sycamore Canyon lava flow of southern Arizona. Lighter-colored, thicker flow bands consist of gray glass, fine-grained quartz, and large (1.0 to 1.5 mm) spherulites. Darker-colored, thinner flow bands consist of orange glass and smaller (0.1 to 0.2 mm) spherulites. The centers of both large and small spherulites are occupied by either (1) a quartz or sanidine crystal, (2) a granophyric intergrowth, or (3) a vesicle. Mapping of water concentration (dominantly OH- in glass and OH- and H2O in sanidine crystals) illustrates fluctuating water availability during quenching of the host melt. Textures of large spherulites in the lighter (gray) bands in some cases indicate complex quenching histories that suggest that local water concentration controlled the generation of glass versus crystals. Small spherulites in darker (orange) bands have only one generation of radiating crystal growth. Both the glass surrounding spherulites, and the crystals in the spherulites contain more water in the gray flow bands than in the orange flow bands. Flow banding in the Sycamore Canyon lava flow may have originated by the stretching of a magma that contained pre-existing zones (vesicles or proto-vesicles) of contrasting water concentration, as the magma flowed in the conduit and on the surface. Variation in the original water concentration in the alternating layers is interpreted to have resulted in differences in undercooling textures in spherulites in the lighter compared to the darker flow bands.
NASA Astrophysics Data System (ADS)
Seaman, Sheila J.; Dyar, M. Darby; Marinkovic, Nebojsa
2009-06-01
This study focuses on the origin of flow-banded rhyolites that consist of compositionally similar darker and lighter flow bands of contrasting texture and color. Infrared radiation was used to obtain Fourier transform infrared (FTIR) spectra from which water concentrations were calculated, and to map variations in water concentrations across zones of spherulites and glass from the ~ 23 million year old Sycamore Canyon lava flow of southern Arizona. Lighter-colored, thicker flow bands consist of gray glass, fine-grained quartz, and large (1.0 to 1.5 mm) spherulites. Darker-colored, thinner flow bands consist of orange glass and smaller (0.1 to 0.2 mm) spherulites. The centers of both large and small spherulites are occupied by either (1) a quartz or sanidine crystal, (2) a granophyric intergrowth, or (3) a vesicle. Mapping of water concentration (dominantly OH - in glass and OH - and H 2O in sanidine crystals) illustrates fluctuating water availability during quenching of the host melt. Textures of large spherulites in the lighter (gray) bands in some cases indicate complex quenching histories that suggest that local water concentration controlled the generation of glass versus crystals. Small spherulites in darker (orange) bands have only one generation of radiating crystal growth. Both the glass surrounding spherulites, and the crystals in the spherulites contain more water in the gray flow bands than in the orange flow bands. Flow banding in the Sycamore Canyon lava flow may have originated by the stretching of a magma that contained pre-existing zones (vesicles or proto-vesicles) of contrasting water concentration, as the magma flowed in the conduit and on the surface. Variation in the original water concentration in the alternating layers is interpreted to have resulted in differences in undercooling textures in spherulites in the lighter compared to the darker flow bands.
NASA Astrophysics Data System (ADS)
Irvine, Dylan J.; Cartwright, Ian; Post, Vincent E. A.; Simmons, Craig T.; Banks, Eddie W.
2016-02-01
Steady state 1-D analytical solutions to estimate groundwater fluxes from temperature profiles are an attractive option because they are simple to apply, with no complex boundary or initial conditions. Steady state solutions have been applied to estimate both aquifer scale fluxes as well as to estimate groundwater discharge to streams. This study explores the sources of uncertainty in flux estimates from regional scale aquifers caused by sensor precision, aquifer heterogeneity, multidimensional flow and variations in surface temperature due to climate change. Synthetic temperature profiles were generated using 2-D groundwater flow and heat transport models with homogeneous and heterogeneous hydraulic and thermal properties. Temperature profiles were analyzed assuming temperature can be determined with a precision between 0.1°C and 0.001°C. Analysis of synthetic temperature profiles show that the Bredehoeft and Papadopulos (1965) method can provide good estimates of the mean vertical Darcy flux over the length of the temperature profile. Reliable flux estimates were obtained when the ratio of vertical to horizontal flux was as low as 0.1, and in heterogeneous media, providing that temperature at the upper boundary was constant in time. However, temporal increases in surface temperature led to over-estimation of fluxes. Overestimates increased with time since the onset of, and with the rate of surface warming. Overall, the Bredehoeft and Papadopulos (1965) method may be more robust for the conditions with constant temperature distributions than previously thought, but that transient methods that account for surface warming should be used to determine fluxes in shallow aquifers.
NASA Astrophysics Data System (ADS)
Nimmo, J. R.
2014-12-01
A condition that initiates macropore flow at the land surface is the application of water faster than it can infiltrate into the soil matrix material. Sometimes this is taken to require ponding, but accumulated evidence shows preferential flow to be commonplace when wetness is less than saturation and when macropores are not completely filled. Examples include water flowing into shrinkage cracks or funneled into macropores by hydrophobic surface material. A more inclusive criterion is that macropore flow is generated when the water application rate exceeds the infiltrability of a small area associated with a macropore. A new model based on this criterion considers the representative elementary area (REA), as would be appropriate for measurement of field-scale infiltrability, to be divided into a mosaic of functional sub-areas (FSA). A single value of matrix infiltrability characterizes each FSA. The REA as a mosaic of FSAs is hydraulically represented by a characteristic distribution of infiltrabilities. During rainfall or irrigation, each FSA absorbs water into its soil matrix material up to the rate of its matrix infiltrability. Water applied in excess of this infiltrability is assumed to flow into a macropore within or adjacent to the FSA, becoming preferential flow. Especially if crusted or hydrophobic, an FSA can generate preferential flow even during low-intensity rainfall when other FSAs are absorbing all incident water into the matrix. The total flux of preferential flow at given depth is the sum of contributions from all FSAs. In this way the characteristic distribution of FSA infiltrabilities controls the field-scale partitioning of matrix and macropore flow as an emergent phenomenon. Illustrative case studies use field-measured data concerning water application rate and preferential flux. Results show this model can quantitatively represent observations of preferential flow occurring in relatively dry soils or at modest rainfall intensities.
A new model for two-dimensional numerical simulation of pseudo-2D gas-solids fluidized beds
Li, Tingwen; Zhang, Yongmin
2013-10-11
Pseudo-two dimensional (pseudo-2D) fluidized beds, for which the thickness of the system is much smaller than the other two dimensions, is widely used to perform fundamental studies on bubble behavior, solids mixing, or clustering phenomenon in different gas-solids fluidization systems. The abundant data from such experimental systems are very useful for numerical model development and validation. However, it has been reported that two-dimensional (2D) computational fluid dynamic (CFD) simulations of pseudo-2D gas-solids fluidized beds usually predict poor quantitative agreement with the experimental data, especially for the solids velocity field. In this paper, a new model is proposed to improve the 2D numerical simulations of pseudo-2D gas-solids fluidized beds by properly accounting for the frictional effect of the front and back walls. Two previously reported pseudo-2D experimental systems were simulated with this model. Compared to the traditional 2D simulations, significant improvements in the numerical predictions have been observed and the predicted results are in better agreement with the available experimental data.
NASA Astrophysics Data System (ADS)
Nunes, J. P. P.; Bijeljic, B.; Blunt, M. J.
2015-12-01
Carbonate rocks are notoriously difficult to characterize. Their abrupt facies variations give rise to drastic changes in the petrophysical properties of the reservoir. Such heterogeneity, when further associated with variations in rock mineralogy due to diagenetic processes, result in a challenging scenario to model from the pore to the field scale. Micro-CT imaging is one of the most promising technologies to characterize porous rocks. The understanding at the pore scale of reactive and non-reactive transport is being pushed forward by recent developments in both imaging capability - 3D images with resolution of a few microns - and in modeling techniques - flow simulations in giga-cell models. We will present a particle-based method capable of predicting the evolution of petrophysical properties of carbonate cores subjected to CO2 injection at reservoir conditions (i.e. high pressures and temperatures). Reactive flow is simulated directly on the voxels of high resolution micro-CT images of rocks. Reactants are tracked using a semi-analytical streamline tracing algorithm and rock-fluid interaction is controlled by the diffusive flux of particles from the pores to the grains. We study the impact of the flow field heterogeneity and of the injection rate on the sample-averaged (i.e. effective) reaction rate of calcite dissolution in three rocks of increasing complexity: a beadpack, an oolitic limestone and a bioclastic limestone. We show how decreases in the overall dissolution rate depend on both the complexity of the pore space and also on the flow rate. This occurs even in chemically homogenous rocks. Our results suggest that the large differences observed between laboratory and field scale rates could, in part, be explained by the inhomogeneity in the flow field at the pore scale and the consequent transport-limited flux of reactants at the solid surface. Our results give valuable insight into the processes governing carbonate dissolution and provide a starting
Tang, M J; Camp, J C J; Rkiouak, L; McGregor, J; Watson, I M; Cox, R A; Kalberer, M; Ward, A D; Pope, F D
2014-09-25
Silica (SiO2) is an important mineral present in atmospheric mineral dust particles, and the heterogeneous reaction of N2O5 on atmospheric aerosol is one of the major pathways to remove nitrogen oxides from the atmosphere. The heterogeneous reaction of N2O5 with SiO2 has only been investigated by two studies previously, and the reported uptake coefficients differ by a factor of >10. In this work two complementary laboratory techniques were used to study the heterogeneous reaction of SiO2 particles with N2O5 at room temperature and at different relative humidities (RHs). The uptake coefficients of N2O5, γ(N2O5), were determined to be (7.2 ± 0.6) × 10(-3) (1σ) at 7% RH and (5.3 ± 0.8) × 10(-3) (1σ) at 40% RH for SiO2 particles, using the aerosol flow tube technique. We show that γ(N2O5) determined in this work can be reconciled with the two previous studies by accounting for the difference in geometric and BET derived aerosol surface areas. To probe the particle phase chemistry, individual micrometer sized SiO2 particles were optically levitated and exposed to a continuous flow of N2O5 at different RHs, and the composition of levitated particles was monitored online using Raman spectroscopy. This study represents the first investigation into the heterogeneous reactions of levitated individual SiO2 particles as a surrogate for mineral dust. Relative humidity was found to play a critical role: while no significant change of particle composition was observed by Raman spectroscopy during exposure to N2O5 at RH of <2%, increasing the RH led to the formation of nitrate species on the particle surface which could be completely removed after decreasing the RH back to <2%. This can be explained by the partitioning of HNO3 between the gas and adsorbed phases. The atmospheric implications of this work are discussed. PMID:25188692
Plener, Laure; Lorenz, Nicola; Reiger, Matthias; Ramalho, Tiago; Gerland, Ulrich
2015-01-01
ABSTRACT Quorum sensing (QS) is a communication process that enables a bacterial population to coordinate and synchronize specific behaviors. The bioluminescent marine bacterium Vibrio harveyi integrates three autoinducer (AI) signals into one quorum-sensing cascade comprising a phosphorelay involving three hybrid sensor kinases: LuxU; LuxO, an Hfq/small RNA (sRNA) switch; and the transcriptional regulator LuxR. Using a new set of V. harveyi mutants lacking genes for the AI synthases and/or sensors, we assayed the activity of the quorum-sensing cascade at the population and single-cell levels, with a specific focus on signal integration and noise levels. We found that the ratios of kinase activities to phosphatase activities of the three sensors and, hence, the extent of phosphorylation of LuxU/LuxO are important not only for the signaling output but also for the degree of noise in the system. The pools of phosphorylated LuxU/LuxO per cell directly determine the amounts of sRNAs produced and, consequently, the copy number of LuxR, generating heterogeneous quorum-sensing activation at the single-cell level. We conclude that the ability to drive the heterogeneous expression of QS-regulated genes in V. harveyi is an inherent feature of the architecture of the QS cascade. IMPORTANCE V. harveyi possesses one of the most complex quorum-sensing (QS) cascades known, using three different autoinducers (AIs) to control the induction of, e.g., bioluminescence, virulence factors, and biofilm and exoprotease production. We constructed various V. harveyi mutants to study the impact of each component and subsystem of the QS signaling cascade on QS activation at the population and single-cell levels. We found that the output was homogeneous only in the presence of all AIs. In the absence of any one AI, QS activation varied from cell to cell, resulting in phenotypic heterogeneity. This study elucidates a molecular design principle which enables a tightly integrated signaling
NASA Astrophysics Data System (ADS)
Leslie, S. R.; Mahan, K. H.; Regan, S.; Williams, M. L.
2011-12-01
Deep crustal strike-slip shear zones play a fundamental role in lower crustal flow. Although commonly modeled in two-dimensions, regional considerations suggest that large-scale crustal flow is a heterogeneous, three-dimensional process. The Athabasca granulite terrane, western Canadian Shield, exposes a large region of high-pressure tectonite (>20,000 km2) that provides a natural example of ancient lower crustal flow and an analog for similar processes active today in other regions. Regional heterogeneous deformation permits preservation of Neoarchean deformation fabrics and metamorphic textures. The Cora Lake shear zone (CLsz) is a NW-dipping km-scale mylonite to ultramylonite zone that forms a discrete tectonic discontinuity between two rheologically distinct Neoarchean lower-crustal domains. Northwest of the CLsz, the domain is primarily underlain by ~2.6 Ga felsic to mafic metaplutonic gneisses and interlayered ~2.55 Ga felsic granulite. Lithologies here preserve Neoarchean granulite-facies metamorphism coupled with partial melting and synkinematic melt-enhanced ESE-directed subhorizontal flow at ~0.9 GPa (~30 km paleodepths). Southeast of the CLsz, the Chipman domain is underlain by ~3.2 Ga metatonalite gneiss, an extensive ~1.9 Ga mafic dike swarm, and generally minor ~2.55 Ga mafic and felsic granulite. In contrast to the northwest, lithologies of the western Chipman domain document higher pressures at ~1.3 GPa (~40 km paleodepths) synchronous with development of a gently dipping Neoarchean gneissic fabric. Strong, anhydrous Chipman domain lithologies and melt-weakened lithologies to the northwest are juxtaposed by sinistral to sinistral-normal oblique shear along the CLsz, consistent with higher pressures (deeper paleodepths) documented in the footwall Chipman domain. A notable and pervasive feature along strike of the CLsz in the western Chipman domain is the marked increase in abundance of m-scale layers of mafic and felsic granulite westward with
NASA Astrophysics Data System (ADS)
Ishibashi, Takuya; Watanabe, Noriaki; Hirano, Nobuo; Okamoto, Atsushi; Tsuchiya, Noriyoshi
2015-01-01
The present study evaluates aperture distributions and fluid flow characteristics for variously sized laboratory-scale granite fractures under confining stress. As a significant result of the laboratory investigation, the contact area in fracture plane was found to be virtually independent of scale. By combining this characteristic with the self-affine fractal nature of fracture surfaces, a novel method for predicting fracture aperture distributions beyond laboratory scale is developed. Validity of this method is revealed through reproduction of the results of laboratory investigation and the maximum aperture-fracture length relations, which are reported in the literature, for natural fractures. The present study finally predicts conceivable scale dependencies of fluid flows through joints (fractures without shear displacement) and faults (fractures with shear displacement). Both joint and fault aperture distributions are characterized by a scale-independent contact area, a scale-dependent geometric mean, and a scale-independent geometric standard deviation of aperture. The contact areas for joints and faults are approximately 60% and 40%. Changes in the geometric means of joint and fault apertures (µm), em, joint and em, fault, with fracture length (m), l, are approximated by em, joint = 1 × 102 l0.1 and em, fault = 1 × 103 l0.7, whereas the geometric standard deviations of both joint and fault apertures are approximately 3. Fluid flows through both joints and faults are characterized by formations of preferential flow paths (i.e., channeling flows) with scale-independent flow areas of approximately 10%, whereas the joint and fault permeabilities (m2), kjoint and kfault, are scale dependent and are approximated as kjoint = 1 × 10-12 l0.2 and kfault = 1 × 10-8 l1.1.
NASA Astrophysics Data System (ADS)
Corona, Roberto; Curreli, Matteo; Montaldo, Nicola; Oren, Ram
2013-04-01
Mediterranean ecosystems are commonly heterogeneous savanna-like ecosystems, with contrasting plant functional types (PFT) competing for the water use. Mediterranean regions suffer water scarcity due to the dry climate conditions. In semi-arid regions evapotranspiration (ET) is the leading loss term of the root-zone water budget with a yearly magnitude that may be roughly equal to the precipitation. Despite the attention these ecosystems are receiving, a general lack of knowledge persists about the estimate of ET and the relationship between ET and the plant survival strategies for the different PFTs under water stress. During the dry summers these water-limited heterogeneous ecosystems are mainly characterized by a simple dual PFT-landscapes with strong-resistant woody vegetation and bare soil since grass died. In these conditions due to the low signal of the land surface fluxes captured by the sonic anemometer and gas analyzer the widely used eddy covariance may fail and its ET estimate is not robust enough. In these conditions the use of the sap flow technique may have a key role, because theoretically it provides a direct estimate of the woody vegetation transpiration. Through the coupled use of the sap flow sensor observations, a 2D foot print model of the eddy covariance tower and high resolution satellite images for the estimate of the foot print land cover map, the eddy covariance measurements can be correctly interpreted, and ET components (bare soil evaporation and woody vegetation transpiration) can be separated. The case study is at the Orroli site in Sardinia (Italy). The site landscape is a mixture of Mediterranean patchy vegetation types: trees, including wild olives and cork oaks, different shrubs and herbaceous species. An extensive field campaign started in 2004. Land-surface fluxes and CO2 fluxes are estimated by an eddy covariance technique based micrometeorological tower. Soil moisture profiles were also continuously estimated using water
Fox, Don T.; Guo, Luanjing; Fujita, Yoshiko; Huang, Hai; Redden, George
2015-12-17
Formation of mineral precipitates in the mixing interface between two reactant solutions flowing in parallel in porous media is governed by reactant mixing by diffusion and dispersion and is coupled to changes in porosity/permeability due to precipitation. The spatial and temporal distribution of mixing-dependent precipitation of barium sulfate in porous media was investigated with side-by-side injection of barium chloride and sodium sulfate solutions in thin rectangular flow cells packed with quartz sand. The results for homogeneous sand beds were compared to beds with higher or lower permeability inclusions positioned in the path of the mixing zone. In the homogeneous and high permeability inclusion experiments, BaSO_{4} precipitate (barite) formed in a narrow deposit along the length and in the center of the solution–solution mixing zone even though dispersion was enhanced within, and downstream of, the high permeability inclusion. In the low permeability inclusion experiment, the deflected BaSO_{4} precipitation zone broadened around one side and downstream of the inclusion and was observed to migrate laterally toward the sulfate solution. A continuum-scale fully coupled reactive transport model that simultaneously solves the nonlinear governing equations for fluid flow, transport of reactants and geochemical reactions was used to simulate the experiments and provide insight into mechanisms underlying the experimental observations. Lastly, migration of the precipitation zone in the low permeability inclusion experiment could be explained by the coupling effects among fluid flow, reactant transport and localized mineral precipitation reaction.
Cardenas, M.B.; Harvey, J.W.; Packman, A.I.; Scott, D.T.
2008-01-01
Temperature is a primary physical and biogeochemical variable in aquatic systems. Field-based measurement of temperature at discrete sampling points has revealed temperature variability in fluvial systems, but traditional techniques do not readily allow for synoptic sampling schemes that can address temperature-related questions with broad, yet detailed, coverage. We present results of thermal infrared imaging at different stream discharge (base flow and peak flood) conditions using a handheld IR camera. Remotely sensed temperatures compare well with those measured with a digital thermometer. The thermal images show that periphyton, wood, and sandbars induce significant thermal heterogeneity during low stages. Moreover, the images indicate temperature variability within the periphyton community and within the partially submerged bars. The thermal heterogeneity was diminished during flood inundation, when the areas of more slowly moving water to the side of the stream differed in their temperature. The results have consequences for thermally sensitive hydroelogical processes and implications for models of those processes, especially those that assume an effective stream temperature. Copyright ?? 2008 John Wiley & Sons, Ltd.
Lin, Guang; Tartakovsky, Alexandre M.
2009-05-01
In this study, a probabilistic collocation method (PCM) on sparse grids was used to solve stochastic equations describing flow and transport in three-dimensional in saturated, randomly heterogeneous porous media. Karhunen-Lo\\`{e}ve (KL) decomposition was used to represent the three-dimensional log hydraulic conductivity $Y=\\ln K_s$. The hydraulic head $h$ and average pore-velocity $\\bf v$ were obtained by solving the three-dimensional continuity equation coupled with Darcy's law with random hydraulic conductivity field. The concentration was computed by solving a three-dimensional stochastic advection-dispersion equation with stochastic average pore-velocity $\\bf v$ computed from Darcy's law. PCM is an extension of the generalized polynomial chaos (gPC) that couples gPC with probabilistic collocation. By using the sparse grid points, PCM can handle a random process with large number of random dimensions, with relatively lower computational cost, compared to full tensor products. Monte Carlo (MC) simulations have also been conducted to verify accuracy of the PCM. By comparing the MC and PCM results for mean and standard deviation of concentration, it is evident that the PCM approach is computational more efficient than Monte Carlo simulations. Unlike the conventional moment-equation approach, there is no limitation on the amplitude of random perturbation in PCM. Furthermore, PCM on sparse grids can efficiently simulate solute transport in randomly heterogeneous porous media with large variances.
Continuous Flow Aerobic Alcohol Oxidation Reactions Using a Heterogeneous Ru(OH)x/Al2O3 Catalyst
2015-01-01
Ru(OH)x/Al2O3 is among the more versatile catalysts for aerobic alcohol oxidation and dehydrogenation of nitrogen heterocycles. Here, we describe the translation of batch reactions to a continuous-flow method that enables high steady-state conversion and single-pass yields in the oxidation of benzylic alcohols and dehydrogenation of indoline. A dilute source of O2 (8% in N2) was used to ensure that the reaction mixture, which employs toluene as the solvent, is nonflammable throughout the process. A packed bed reactor was operated isothermally in an up-flow orientation, allowing good liquid–solid contact. Deactivation of the catalyst during the reaction was modeled empirically, and this model was used to achieve high conversion and yield during extended operation in the aerobic oxidation of 2-thiophene methanol (99+% continuous yield over 72 h). PMID:25620869
d'Alessio, M. A.; Williams, C.F.; Burgmann, R.
2006-01-01
Heat flow measurements along much of the San Andreas fault (SAF) constrain the apparent coefficient of friction (??app) of the fault to 0.2 should be detectable even with the sparse existing observations, implying that ??app for the creeping section is as low as the surrounding SAF. Because the creeping section does not slip in large earthquakes, the mechanism controlling its weakness is not related to dynamic processes resulting from high slip rate earthquake ruptures. Copyright 2006 by the American Geophysical Union.
Fox, Don T.; Guo, Luanjing; Fujita, Yoshiko; Huang, Hai; Redden, George
2015-12-17
Formation of mineral precipitates in the mixing interface between two reactant solutions flowing in parallel in porous media is governed by reactant mixing by diffusion and dispersion and is coupled to changes in porosity/permeability due to precipitation. The spatial and temporal distribution of mixing-dependent precipitation of barium sulfate in porous media was investigated with side-by-side injection of barium chloride and sodium sulfate solutions in thin rectangular flow cells packed with quartz sand. The results for homogeneous sand beds were compared to beds with higher or lower permeability inclusions positioned in the path of the mixing zone. In the homogeneous andmore » high permeability inclusion experiments, BaSO4 precipitate (barite) formed in a narrow deposit along the length and in the center of the solution–solution mixing zone even though dispersion was enhanced within, and downstream of, the high permeability inclusion. In the low permeability inclusion experiment, the deflected BaSO4 precipitation zone broadened around one side and downstream of the inclusion and was observed to migrate laterally toward the sulfate solution. A continuum-scale fully coupled reactive transport model that simultaneously solves the nonlinear governing equations for fluid flow, transport of reactants and geochemical reactions was used to simulate the experiments and provide insight into mechanisms underlying the experimental observations. Lastly, migration of the precipitation zone in the low permeability inclusion experiment could be explained by the coupling effects among fluid flow, reactant transport and localized mineral precipitation reaction.« less
NASA Astrophysics Data System (ADS)
Camporese, M.; Salandin, P.; Darvini, G.; Durigon, R.; Pizzaia, P.
2009-12-01
The uncertainty characterizing the description of hydraulic properties of aquifers, together with those implied in the process modeling and measurement errors, can be successfully dealt with by stochastic approaches, which allow the interpretation and the prediction of flow and transport processes in natural heterogeneous formations. The practical application of these approaches still encounters many difficulties, mainly due to the need for a detailed hydrogeological characterization of the site and to the unsuitability of the models, sometimes related to simplistic schematizations when describing in random terms the aquifer and its processes. The need to describe the spatial joint probability distribution of the hydraulic properties at different scales demands a large amount of data, to be obtained by several in situ and laboratory measurements. Moreover, modeling of these processes is often limited by the hypotheses of statistical homogeneity of the flow field and ergodicity of the dispersive process. These approaches are not suitable for the cases of practical interest, where the finite domain is characterized by irregular shapes and the flow field can be highly non-homogeneous, due to the influence of the boundary conditions, the presence of localized pumpings or inflows, or the lack of spatial stationarity of the hydraulic conductivity. Such circumstances emerge clearly in the real case of Settolo, an alluvial phreatic aquifer in a piedmont area of Northeastern Italy, where the effects related to the variability of the geological structures crossed by paleo-riverbeds and characterized by different facies, to the interactions between watercourses and the aquifer, to the recharge linked to the precipitation, and to the correct interpretation of concentration measurements of solutes must be challenged for an effective protection and/or a sustainable exploitation of the water resources. For these reasons, a careful site characterization is in progress, with a
NASA Astrophysics Data System (ADS)
Phillips, S. P.; Green, C. T.; Zamora, C.
2006-05-01
Multi-scale models of ground-water flow were developed as part of a study of the transport and fate of agricultural chemicals by the National Water-Quality Assessment (NAWQA) Program of the US Geological Survey. Agricultural chemicals of interest included forms of nitrogen and selected pesticides A three- dimensional local-scale model (17 square km) surrounds a well-instrumented, 1-km transect near the Merced River within a principally agricultural land-use setting. This model is nested within a regional-scale model (2,700 square km) of northeastern San Joaquin Valley, California, which provides hydrologically reasonable boundary conditions for the local model. Boundary fluxes were passed from the regional to local model using a hydraulic-conductivity-weighted distribution. The heterogeneity of aquifer materials was incorporated explicitly into the regional and local models. Three-dimensional kriging was used to interpolate sediment texture data from about 3,500 drillers' logs in the regional model area. The resulting distribution of sediment texture was used to estimate hydraulic parameters for each cell in the 16-layer regional model. A subset of these data was used to generate multiple transition-probability-based realizations of hydrofacies distributions for the 110-layer local model. Explicit depiction of heterogeneity in hydraulic conductivity and porosity in the local model incorporates macro-scale hydrodynamic dispersion into the flow model, allowing more direct comparison of particle-tracking results to tracer-derived estimates of ground-water age. Water levels measured in multi-depth wells along the 1-km transect were used to calibrate the local model (median error 0.12 m). Two-dimensional heat-flow models calibrated using continuous multi-depth temperature data from below the bed of the Merced River suggest an annual range of ground-water inflow of about 0-2.4 cm/d for water year 2005. This estimate compares reasonably well to the 4 cm/d simulated in the
Saiers, James; Ryan, Joseph
2005-06-01
Our research is guided by an EMSP objective to improve conceptual and predictive models of contaminant movement in vadose-zone environments. As described in the report National Roadmap for Vadose-Zone Science and Technology [DOE, 2001], soil-water colloids are capable of adsorbing contaminants, such as radionuclides and metals, and facilitating their migration through the vadose zone and towards groundwater reservoirs. Our research centers on advancing understanding of this phenomenon. In particular, we are combining mathematical modeling with laboratory experimentation at pore and column scales to (1) elucidate the effects of porewater-flow transients on colloid mobilization in unsaturated porous media; (2) explore the sensitivity of colloid deposition rates to changes in porewater chemistry and colloid mineralogy; (3) develop mathematical models appropriate for simulating colloid mobilization, transport, and deposition under both steady-flow and transient-flow conditions; (4) identify mechanisms that govern mineral-colloid mobilization and deposition in unsaturated porous media; (5) quantify the effects of mineral-grain geometry and surface roughness on colloid-filtration rates; and (6) evaluate the influences of colloids on the transport of strontium and cesium (i.e., DOE-contaminants-of-concern) through soils and sediments.
Pruess, K.
1992-06-01
Contamination of soils and groundwater from volatile organic compounds (VOCs), such as organic solvents and hydrocarbon fuels, is a problem at many industrial facilities. Key to successfully characterizing, containing, and eventually remediating the contamination is a thorough understanding, based on sound scientific principles, of the complex interplay of physical, chemical, and biological processes in geologic media, which affect the migration and distribution of the contaminants, and their response to remediation operations. This report focusses on physical mechanisms that affect contaminant behavior under the conditions encountered at the Savannah River site (SRS). Although other contaminants are present at the site, for the purpose of this discussion we will restrict ourselves to the processes following a spill and infiltration of trichloroethylene (TCE), which is the main contaminant at the location of the Integrated Demonstration Project. We begin by briefly describing the main physical processes following release of TCE into the subsurface. Subsequently we will present simple engineering models that can help to evaluate contaminant migration processes in a semi-quantitative way. Finally, we will discuss results of detailed numerical simulations of TCE infiltration into a heterogeneous medium consisting of sands and clays. These simulations attempt to shed light on the initial distribution of contaminants at the site prior to the start of remediation operations. We also point out limitations of present numerical modeling capabilities, and identify issues that require further research in order that a realistic description of contaminant behavior in the subsurface may be achieved.
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
Tian, Sicong; Jiang, Jianguo
2012-12-18
Direct gas-solid carbonation reactions of residues from an air pollution control system (APCr) were conducted using different combinations of simulated flue gas to study the impact on CO₂ sequestration. X-ray diffraction analysis of APCr determined the existence of CaClOH, whose maximum theoretical CO₂ sequestration potential of 58.13 g CO₂/kg APCr was calculated by the reference intensity ratio method. The reaction mechanism obeyed a model of a fast kinetics-controlled process followed by a slow product layer diffusion-controlled process. Temperature is the key factor in direct gas-solid carbonation and had a notable influence on both the carbonation conversion and the CO₂ sequestration rate. The optimal CO₂ sequestrating temperature of 395 °C was easily obtained for APCr using a continuous heating experiment. CO₂ content in the flue gas had a definite influence on the CO₂ sequestration rate of the kinetics-controlled process, but almost no influence on the final carbonation conversion. Typical concentrations of SO₂ in the flue gas could not only accelerate the carbonation reaction rate of the product layer diffusion-controlled process, but also could improve the final carbonation conversion. Maximum carbonation conversions of between 68.6% and 77.1% were achieved in a typical flue gas. Features of rapid CO₂ sequestration rate, strong impurities resistance, and high capture conversion for direct gas-solid carbonation were proved in this study, which presents a theoretical foundation for the applied use of this encouraging technology on carbon capture and storage. PMID:23181908
Saiers, James E.; Ryan, Joseph
2003-06-15
During the past year (June 2003 to June 2004), work at Yale has centered on investigating the influences of porewater pH, flow transients, and the presence of natural organic matter (NOM) on the deposition and mobilization of clay colloids (kaolinite and illite) within columns packed with unsaturated porous media. The experiments on pH and flow-transient effects were described in our First-Term Progress Report (which covered the initial 18 months of the study) and will not be repeated here. More recent experiments on the role of NOM in colloid transport proved equally as interesting. Even at porewater concentrations as low as 0.2 mg/L, soil-humic acid substantially lowered clay-colloid deposition rates compared to the case in which soil-humic acid was absent from the porewater. We attribute this to adsorption of the humic acid to the positively charged edge sites of the clay colloids, which effectively reduced the colloid affinity for negatively charged air- and solid-water interfaces. Comparison of the results of the column experiments to calculations of a new mathematical model has sharpened our inferences regarding mechanisms that govern the rate-limited deposition and mobilization of colloids. We are testing these inferences by carrying out flow-and-transport visualization experiments. We have constructed a semi-transparent representation of a porous medium, consisting of a rectangular parallel-plate chamber that encloses 3-5 layers of uniformly sized sand grains. Ceramic plates fused to the ends of the chamber maintain the capillary tension and syringe pumps (located at the inlet and outlet ends) regulate the flow of water and colloids through the partially saturated sand. By placing the chamber beneath a microscope, we can examine the distribution of colloids between air-water and solid-water interfaces, directly measure the kinetics of deposition onto these interfaces, and observe the mechanisms that contribute to the release of immobile colloids. To date
NASA Technical Reports Server (NTRS)
Lauretta, Dante S.
2004-01-01
Recent studies of opaque minerals in primitive ordinary chondrites suggest that metal grains exposed at chondrule boundaries were corroded when volatile elements recondensed after the transient heating event responsible for chondrule formation. Metal grains at chondrule boundaries in the Bishunpur (LL3.1) chondrite are rimmed by troilite and fayalite. If these layers formed by gas solid reaction, then the composition of the corrosion products can provide information on the chondrule formation environment. Given the broad similarities among chondrules from different chondrite groups, similar scale layers should occur on chondrules in other primitive meteorite groups. Here I report on metal grains at chondrule boundaries in Vigarano (CV3).
NASA Astrophysics Data System (ADS)
Bickerton, Simon
Liquid Composite Molding (LCM) encompasses a growing list of composite material manufacturing techniques. These processes have provided the promise for complex fiber reinforced plastics parts, manufactured from a single molding step. In recent years a significant research effort has been invested in development of process simulations, providing tools that have advanced current LCM technology and broadened the range of applications. The requirement for manufacture of larger, more complex parts has motivated investigation of active control of LCM processes. Due to the unlimited variety of part geometries that can be produced, finite element based process simulations will be used to some extent in design of actively controlled processes. Ongoing efforts are being made to improve material parameter specification for process simulations, increasing their value as design tools. Several phenomena occurring during mold filling have been addressed through flow visualization experimentation and analysis of manufactured composite parts. The influence of well defined air channels within a mold cavity is investigated, incorporating their effects within existing filling simulations. Three different flow configurations have been addressed, testing the application of 'equivalent permeabilities', effectively approximating air channels as representative porous media. LCM parts having doubly curved regions require preform fabrics to undergo significant, and varying deformation throughout a mold cavity. Existing methods for predicting preform deformation, and the resulting permeability distribution have been applied to a conical mold geometry. Comparisons between experiment and simulation are promising, while the geometry studied has required large deformation over much of the part, shearing the preform fabric beyond the scope of the models applied. An investigational study was performed to determine the magnitude of effect, if any, on mold filling caused by corners within LCM mold
NASA Astrophysics Data System (ADS)
Morgan, D. S.; Hinkle, S. R.; Weick, R. J.
2002-12-01
Flow and transport simulation models were developed at two scales to assess the long-term effects of on-site waste disposal systems on groundwater quality in a shallow alluvial aquifer system near La Pine, Oregon. First, a sub-aquifer scale (6 km2 area, 30-m thickness) model was used to test concepts and estimate flow and transport parameters along a flowpath where detailed hydrogeologic and geochemical data were available from nested wells and a high-density array of direct-push samples. Then, an aquifer scale (640 km2 area, 37-m thickness) model was calibrated assuming steady flow with transient historical nitrate loading and observed nitrate concentration data from 1960 to 2000. Groundwater age-dates and observations of hydraulic head and flux to streams were used to constrain and calibrate the models. Boundary flux conditions for the aquifer scale model were extracted using telescoping mesh refinement techniques from a regional scale flow model (11,700 km2 area, 550-m thickness) developed in a previous investigation of the upper Deschutes basin (see Gannett and Lite, this session). The hydrogeologic framework for the models was developed using transitional probability geostatistics. Lithologic descriptions from 390 geologic logs were categorized into three hydrofacies: gravel and coarse sand, fine-to-medium sand, and silt-clay. The three-dimensional hydrofacies model (realization) was constructed using information on volumetric proportions, mean lengths, and juxtapositional tendencies. The upper surface of an extensive low-permeability layer was mapped from well logs and merged with the geostatistical realization to complete the hydrogeologic model. Geochemical and hydrogeologic data were collected at multiple scales to advance the understanding of NO3- sources and the physical and chemical processes affecting its transport and fate. Relations between NO3-, Cl-, and geochemical indicators of redox conditions, and N2 isotope and concentration data, indicate that
Bolton, E.W.; Lasaga, A.C.; Rye, D.M.
1999-01-01
The kinetics of dissolution and precipitation is of central importance to understanding the long-term evolution of fluid flows in crustal environments, with implications for problems as diverse as nuclear waste disposal and crustal evolution. The authors examine the dynamics of such evolution for several geologically relevant permeability distributions (models for en-echelon cracks, an isolated sloping fractured zone, and two sloping high-permeability zones that are close enough together to interact). Although the focus is on a simple quartz matrix system, generic features emerge from this study that can aid in the broader goal of understanding the long-term feedback between flow and chemistry, where dissolution and precipitation is under kinetic control. Examples of thermal convection in a porous medium with spatially variable permeability reveal features of central importance to water-rock interaction. After a transient phase, an accelerated rate of change of porosity may be used with care to decrease computational time, as an alternative to the quasi-stationary state approximation (Lichtner, 1988). Kinetic effects produce features not expected by traditional assumptions made on the basis of equilibrium, for example, that cooling fluids are oversaturated and heating fluids are undersaturated with respect to silicic acid equilibrium. Indeed, the authors observe regions of downwelling oversaturated fluid experiencing heating and regions of upwelling, yet cooling, undersaturated fluid. When oscillatory convection is present, the amplitudes of oscillation generally increase with time in near-surface environments, whereas amplitudes tend to decrease over long times near the heated lower boundary. The authors examine the scaling behavior of characteristic length scales, of terms in the solute equation, and of the typical deviation from equilibrium, each as a function of the kinetic rate parameters.
Xu, Guiling; Liang, Cai; Chen, Xiaoping; Liu, Daoyin; Xu, Pan; Shen, Liu; Zhao, Changsui
2013-01-01
This paper presents a review and analysis of the research that has been carried out on dynamic calibration for optical-fiber solids concentration probes. An introduction to the optical-fiber solids concentration probe was given. Different calibration methods of optical-fiber solids concentration probes reported in the literature were reviewed. In addition, a reflection-type optical-fiber solids concentration probe was uniquely calibrated at nearly full range of the solids concentration from 0 to packed bed concentration. The effects of particle properties (particle size, sphericity and color) on the calibration results were comprehensively investigated. The results show that the output voltage has a tendency to increase with the decreasing particle size, and the effect of particle color on calibration result is more predominant than that of sphericity. PMID:23867745
Massara, S.; Schmitt, D.; Bretault, A.; Lemasson, D.; Darmet, G.; Verwaerde, D.; Struwe, D.; Pfrang, W.; Ponomarev, A.
2012-07-01
In the framework of a substantial improvement on FBR core safety connected to the development of a new Gen IV reactor type, heterogeneous core with innovative features are being carefully analyzed in France since 2009. At EDF R and D, the main goal is to understand whether a strong reduction of the Na-void worth - possibly attempting a negative value - allows a significant improvement of the core behavior during an unprotected loss of flow accident. Also, the physical behavior of such a core is of interest, before and beyond the (possible) onset of Na boiling. Hence, a cutting-edge heterogeneous design, featuring an annular shape, a Na-plena with a B{sub 4}C plate and a stepwise modulation of fissile core heights, was developed at EDF by means of the SDDS methodology, with a total Na-void worth of -1 $. The behavior of such a core during the primary phase of a severe accident, initiated by an unprotected loss of flow, is analyzed by means of the SAS-SFR code. This study is carried-out at KIT and EDF, in the framework of a scientific collaboration on innovative FBR severe accident analyses. The results show that the reduction of the Na-void worth is very effective, but is not sufficient alone to avoid Na-boiling and, hence, to prevent the core from entering into the primary phase of a severe accident. Nevertheless, the grace time up to boiling onset is greatly enhanced in comparison to a more traditional homogeneous core design, and only an extremely low fraction of the fuel (<0.1%) enters into melting at the end of this phase. A sensitivity analysis shows that, due to the inherent neutronic characteristics of such a core, the gagging scheme plays a major role on the core behavior: indeed, an improved 4-zones gagging scheme, associated with an enhanced control rod drive line expansion feed-back effect, finally prevents the core from entering into sodium boiling. This major conclusion highlights both the progress already accomplished and the need for more detailed
NASA Astrophysics Data System (ADS)
Dages, Cecile; Samouelian, Anatja; Lanoix, Marthe; Dollinger, Jeanne; Chakkour, Sara; Chovelon, Gabrielle; Trabelsi, Khouloud; Voltz, Marc
2015-04-01
Ditches are involved in the transfer of pesticide to surface and groundwaters (e.g. Louchart et al., 2001). Soil horizons underlying ditch beds may present specific soil characteristics compared to neighbouring field soils due to erosion/deposition processes, to the specific biological activities (rooting dynamic and animal habitat) in the ditches (e.g. Vaughan et al., 2008) and to management practices (burning, dredging, mowing,...). Moreover, in contrast to percolation processes in field soils that can be assumed to be mainly 1D vertical, those occurring in the ditch beds are by essence 2D or even 3D. Nevertheless, due to a lake of knowledge, these specific aspects of transfer within ditch beds are generally omitted for hydrological simulation at the catchment scale (Mottes et al., 2014). Accordingly, the aims of this study were i) to characterize subsurface solute transfer through ditch beds and ii) to determine equivalent hydraulic parameters of the ditch beds for use in catchment scale hydrological simulations. A complementary aim was to evaluate the error in predictions performed when percolation in ditches is assumed to be similar to that in the neighbouring field soil. First, bromide transfer experiments were performed on undisturbed soil column (15 cm long with a 15 cm inner-diameter), horizontally and vertically sampled within each soil horizon underlying a ditch bed and within the neighboring field. Columns were sampled at the Roujan catchment (Hérault, France), which belongs to the long term Mediterranean hydrological observatory OMERE (Voltz and Albergel, 2002). Second, for each column, a set of parameters was determined by inverse optimization with mobile-immobile or dual permeability models, with CXTFIT (Toride et al., 1999) or with HYDRUS (Simunek et al., 1998). Third, infiltration and percolation in the ditch was simulated by a 2D flow domain approach considering the 2D variation in hydraulic properties of the cross section of a ditch bed. Last
NASA Astrophysics Data System (ADS)
Kempka, Thomas; Class, Holger; Görke, Uwe-Jens; Norden, Ben; Kolditz, Olaf; Kühn, Michael; Walter, Lena; Wang, Wenqing; Zehner, Björn
2013-04-01
CO2 injection at the Ketzin pilot site located in Eastern Germany (Brandenburg) about 25 km west of Berlin is undertaken since June 2008 with a scheduled total amount of about 70,000 t CO2 to be injected into the saline aquifer represented by the Stuttgart Formation at a depth of 630 m to 650 m until the end of August 2013. The Stuttgart Formation is of fluvial origin determined by high-permeablity sandstone channels embedded in a floodplain facies of low permeability indicating a highly heterogeneous distribution of reservoir properties as facies distribution, porosity and permeability relevant for dynamic flow simulations. Following the dynamic modelling activities discussed by Kempka et al. (2010), a revised geological model allowed us to history match CO2 arrival times in the observation wells and reservoir pressure with a good agreement (Martens et al., 2012). Consequently, the validated reservoir model of the Stuttgart Formation at the Ketzin pilot site enabled us to predict the development of reservoir pressure and the CO2 plume migration in the storage formation by dynamic flow simulations. A benchmark study of industrial (ECLIPSE 100 as well as ECLIPSE 300 CO2STORE and GASWAT) and scientific dynamic flow simulations codes (TOUGH2-MP/ECO2N, OpenGeoSys and DuMuX) was initiated to address and compare the simulator capabilities considering a highly complex reservoir model. Hence, our dynamic flow simulations take into account different properties of the geological model such as significant variation of porosity and permeability in the Stuttgart Formation as well as structural geological features implemented in the geological model such as seven major faults located at the top of the Ketzin anticline. Integration of the geological model into reservoir models suitable for the different dynamic flow simulators applied demonstrated that a direct conversion of reservoir model discretization between Finite Volume and Finite Element flow simulators is not feasible
Stotler, R.L.; Frape, S.K.; El Mugammar, H.T.; Johnston, C.; Judd-Henrey, I.; Harvey, F.E.; Drimmie, R.; Jones, J.P.
2011-01-01
The Waterloo Moraine is a stratigraphically complex system and is the major water supply to the cities of Kitchener and Waterloo in Ontario, Canada. Despite over 30 years of investigation, no attempt has been made to unify existing geochemical data into a single database. A composite view of the moraine geochemistry has been created using the available geochemical information, and a framework created for geochemical data synthesis of other similar flow systems. Regionally, fluid chemistry is highly heterogeneous, with large variations in both water type and total dissolved solids content. Locally, upper aquifer units are affected by nitrate and chloride from fertilizer and road salt. Typical upper-aquifer fluid chemistry is dominated by calcium, magnesium, and bicarbonate, a result of calcite and dolomite dissolution. Evidence also suggests that ion exchange and diffusion from tills and bedrock units accounts for some elevated sodium concentrations. Locally, hydraulic "windows" cross connect upper and lower aquifer units, which are typically separated by a clay till. Lower aquifer units are also affected by dedolomitization, mixing with bedrock water, and locally, upward diffusion of solutes from the bedrock aquifers. A map of areas where aquifer units are geochemically similar was constructed to highlight areas with potential hydraulic windows. ?? 2010 Springer-Verlag.
V. Yucel; D. G. Levitt
2001-11-01
Two low-level Radioactive Waste Management Sites (RWMSs), consisting of shallow land burial disposal units at the Nevada Test Site (NTS), are managed by Bechtel Nevada for the U.S. Department of Energy, National Nuclear Security Administration. The NTS has an arid climate with annual average precipitation of about 17 cm at the Area 3 RWMS and about 13 cm at the Area 5 RWMS. The vadose zone is about 490 m thick at the Area 3 RWMS, and about 235 m thick at the Area 5 RWMS. Numerous studies indicate that under current climatic conditions, there is generally no groundwater recharge at these sites. Groundwater recharge may occur at isolated locations surrounding the RWMSs, such as in large drainage washes. However, groundwater recharge scenarios (and radionuclide transport) at the RWMSs are modeled in support of Performance Assessment (PA) documents required for operation of each RWMS. Recharge scenarios include conditions of massive subsidence and flooding, and recharge resulting from deep infiltration through bare-soil waste covers. This paper summarizes the groundwater recharge scenarios and travel time estimates that have been conducted in support of the PAs, and examines the effects of soil hydraulic property heterogeneity on flow.
ERIC Educational Resources Information Center
Miranda, R.
1989-01-01
Described is a heterogeneous catalysis course which has elements of materials processing embedded in the classical format of catalytic mechanisms and surface chemistry. A course outline and list of examples of recent review papers written by students are provided. (MVL)
Knochenmus, Lari A.; Robinson, James L.
1996-01-01
MODFLOW and MODPATH numerical models were used to generate areas of contribution to public supply wells for simulated hypothetical anisotropy and heterogeneous carbonate aquifer systems. The simulations incorporated, to varying degrees, the anisotropy and heterogeneity observed in a karst carbonate aquifer system. These include: isotropic and homogeneous single-layer system, doubly-porous single-layer system, and interconnected vertically and horizontally heterogeneous system. The study indicated that the distribution and nature of aquifer anisotropy and heterogeneity will affect the simulated size, shape, and orientation of areas of contribution in karst carbonate aquifer systems.
Explorations into thermodynamics analogies and critical points in reference to gas-solid transport
Mathur, M.P.; Wildman, D.; Tuba, S.T.; Klinzing, G.E.
1984-01-01
The use of analogies to explain transport processes is not new. The idea of borrowing concepts from thermodynamics and applying them to transport cases are also known. Experimental data from several investigators where the solid voidage has been determined experimentally have been analyzed to test the ability of a cubic van der Waals equation to represent the solid flow, gas flow and voidage. Using the van der Waals format phase diagrams have been constructed for a number of particulate systems which have been scrutinized. From this information the critical properties of the solids can be found. A generalized reduced properties plot has been constructed and has been shown to be unique in representing all the data. Exploration into the pressure drop domain has shown a relationship between the phase diagrams by an analytical approach. 9 references, 8 figures, 1 table.
Explorations into thermodynamic analogies and critical points in reference to gas-solid transport
Mathur, M.P.; Klinzing, G.E.; Tuba, S.T.; Wildman, D.J.
1984-01-01
The use of analogies to explain transport processes is not new, nor is the idea of borrowing concepts from thermodynamics and applying them to transport phenomena. Experimental data from several investigations, where the solid voidage has been determined experimentally, have been analyzed to test the ability of a cubi van der Waals equation to represent the solid flow, gas flow, and voidage. Using the van der Waals format, phase diagrams have been constructed for a number of particulate systems. From this information, the critical properties of the solids can be found. A generalized reduced-properties plot seems to correlate the existing data satisfactorily. The same approach is pursued to interpret the pressure drop data.
Explorations into thermodynamic analogies and critical points in reference to gas-solid transport
Mathur, M.P.; Wildman, D.J.; Tuba, S.T.; Klinzing, G.E.
1984-11-01
The use of analogies to explain transport processes is not new, nor is the idea of borrowing concepts from thermodynamics and applying them to transport phenomena. Experimental data from several investigations, where the solid voidage has been determined experimentally, have been analyzed to test the ability of a cubic van der Waals equation to represent the solid flow, gas flow, and voidage. Using the van der Waals format, phase diagrams have been constructed for a number of particulate systems. From this information, the critical properties of the solids can be found. A generalized reduced-properties plot seems to correlate the existing data satisfactorily. The same approach is pursued to interpret the pressure drop data. 10 refs., 8 figs.
A one-dimensional model for gas-solid heat transfer in pneumatic conveying
NASA Astrophysics Data System (ADS)
Smajstrla, Kody Wayne
A one-dimensional ODE model reduced from a two-fluid model of a higher dimensional order is developed to study dilute, two-phase (air and solid particles) flows with heat transfer in a horizontal pneumatic conveying pipe. Instead of using constant air properties (e.g., density, viscosity, thermal conductivity) evaluated at the initial flow temperature and pressure, this model uses an iteration approach to couple the air properties with flow pressure and temperature. Multiple studies comparing the use of constant or variable air density, viscosity, and thermal conductivity are conducted to study the impact of the changing properties to system performance. The results show that the fully constant property calculation will overestimate the results of the fully variable calculation by 11.4%, while the constant density with variable viscosity and thermal conductivity calculation resulted in an 8.7% overestimation, the constant viscosity with variable density and thermal conductivity overestimated by 2.7%, and the constant thermal conductivity with variable density and viscosity calculation resulted in a 1.2% underestimation. These results demonstrate that gas properties varying with gas temperature can have a significant impact on a conveying system and that the varying density accounts for the majority of that impact. The accuracy of the model is also validated by comparing the simulation results to the experimental values found in the literature.
On the Superficial Gas Velocity in Deep Gas-Solid Fluidized Beds
Li, Tingwen; Grace, John; Shadle, Lawrence; Guenther, Chris
2011-11-15
The superficial gas velocity is one of the key parameters used to determine the flow hydrodynamics in gas–solids fluidized beds. However, the superficial velocity varies with height in practice, and there is no consistent basis for its specification. Different approaches to determine the superficial gas velocity in a deep gas–solids system are shown to cause difficulties in developing models and in comparing predictions with experimental results. In addition, the reference conditions for superficial gas velocity are important in modeling of deep gas–solids systems where there is a considerable pressure drop.
Efendiev, Yalchin; Datta-Gupta, Akhil; Jafarpour, Behnam; Mallick, Bani; Vassilevski, Panayot
2015-11-09
In this proposal, we have worked on Bayesian uncertainty quantification for predictions of fows in highly heterogeneous media. The research in this proposal is broad and includes: prior modeling for heterogeneous permeability fields; effective parametrization of heterogeneous spatial priors; efficient ensemble- level solution techniques; efficient multiscale approximation techniques; study of the regularity of complex posterior distribution and the error estimates due to parameter reduction; efficient sampling techniques; applications to multi-phase ow and transport. We list our publications below and describe some of our main research activities. Our multi-disciplinary team includes experts from the areas of multiscale modeling, multilevel solvers, Bayesian statistics, spatial permeability modeling, and the application domain.
NASA Astrophysics Data System (ADS)
Ali, Neven Y.
The work focuses on implementing for the first time advanced non-invasive measurement techniques to evaluate the scale-up methodology of gas-solid spouted beds for hydrodynamics similarity that has been reported in the literature based on matching dimensionless groups and the new mechanistic scale up methodology that has been developed in our laboratory based on matching the radial profile of gas holdup since the gas dynamics dictate the hydrodynamics of the gas-solid spouted beds. These techniques are gamma-ray computed tomography (CT) to measure the cross-sectional distribution of the phases' holdups and their radial profiles along the bed height and radioactive particle tracking (RPT) to measure in three-dimension (3D) solids velocity and their turbulent parameters. The measured local parameters and the analysis of the results obtained in this work validate our new methodology of scale up of gas-solid spouted beds by comparing for the similarity the phases' holdups and the dimensionless solids velocities and their turbulent parameters that are non-dimensionalized using the minimum spouting superficial gas velocity. However, the scale-up methodology of gas-solid spouted beds that is based on matching dimensionless groups has not been validated for hydrodynamics similarity with respect to the local parameters such as phases' holdups and dimensionless solids velocities and their turbulent parameters. Unfortunately, this method was validated in the literature by only measuring the global parameters. Thus, this work confirms that validation of the scale-up methods of gas-solid spouted beds for hydrodynamics similarity should reside on measuring and analyzing the local hydrodynamics parameters.
Torsional rheometer for granular materials slurries and gas-solid mixtures and related methods
Rajagopal, Chandrika; Rajagopal, Kumbakonam R.; Yalamanchili, Rattaya C.
1997-01-01
A torsional rheometer apparatus for determining rheological properties of a specimen is provided. A stationary plate and a rotatable plate are in generally coaxial position and structured to receive a specimen therebetween. In one embodiment, at least one of the plates and preferably both have roughened specimen engaging surfaces to serve to reduce undesired slippage between the plate and the specimen. A motor is provided to rotate the rotatable plate and a transducer for monitoring forces applied to the stationary plate and generating output signals to a computer which determines the desired rheological properties are provided. In one embodiment, the roughened surfaces consist of projections extending toward the specimen. Where granular material is being evaluated, it is preferred that the roughness of the plate is generally equal to the average size of the granular material being processed. In another embodiment, an air-solid mixture is processed and the roughened portions are pore openings in the plates. Air flows through the region between the two pore containing plates to maintain the solid materials in suspension. In yet another embodiment, the base of the stationary plate is provided with a deformable capacitance sensor and associated electronic means.
Torsional rheometer for granular materials slurries and gas-solid mixtures and related methods
Rajagopal, C.; Rajagopal, K.R.; Yalamanchili, R.C.
1997-03-11
A torsional rheometer apparatus for determining rheological properties of a specimen is provided. A stationary plate and a rotatable plate are in generally coaxial position and structured to receive a specimen there between. In one embodiment, at least one of the plates and preferably both have roughened specimen engaging surfaces to serve to reduce undesired slippage between the plate and the specimen. A motor is provided to rotate the rotatable plate and a transducer for monitoring forces applied to the stationary plate and generating output signals to a computer which determines the desired rheological properties are provided. In one embodiment, the roughened surfaces consist of projections extending toward the specimen. Where granular material is being evaluated, it is preferred that the roughness of the plate is generally equal to the average size of the granular material being processed. In another embodiment, an air-solid mixture is processed and the roughened portions are pore openings in the plates. Air flows through the region between the two pore containing plates to maintain the solid materials in suspension. In yet another embodiment, the base of the stationary plate is provided with a deformable capacitance sensor and associated electronic means. 17 figs.
El-Naas, Muftah H; El Gamal, Maisa; Hameedi, Suhaib; Mohamed, Abdel-Mohsen O
2015-06-01
Mineral CO2 sequestration is a promising process for the reduction of carbon dioxide emissions to the atmosphere. In this paper, alkaline calcium-rich dust particles collected from bag filters of electric arc furnaces (EAF) for steel making were utilized as a viable raw material for mineral CO2 sequestration. The dust particles were pre-treated through hydration, drying and screening. The pre-treated particles were then subjected to direct gas-solid carbonation reaction in a fluidized-bed reactor. The carbonated products were characterized to determine the overall sequestration capacity and the mineralogical structures. Leaching tests were also performed to measure the extracted minerals from the carbonated dust and evaluate the carbonation process on dust stabilization. The experimental results indicated that CO2 could be sequestered using the pre-treated bag house dust. The maximum sequestration of CO2 was 0.657 kg/kg of dust, based on the total calcium content. The highest degree of carbonation achieved was 42.5% and the carbonation efficiency was 69% at room temperature. PMID:25846002
NASA Astrophysics Data System (ADS)
Qiu, Bao; Zhang, Minghao; Wu, Lijun; Wang, Jun; Xia, Yonggao; Qian, Danna; Liu, Haodong; Hy, Sunny; Chen, Yan; An, Ke; Zhu, Yimei; Liu, Zhaoping; Meng, Ying Shirley
2016-07-01
Lattice oxygen can play an intriguing role in electrochemical processes, not only maintaining structural stability, but also influencing electron and ion transport properties in high-capacity oxide cathode materials for Li-ion batteries. Here, we report the design of a gas-solid interface reaction to achieve delicate control of oxygen activity through uniformly creating oxygen vacancies without affecting structural integrity of Li-rich layered oxides. Theoretical calculations and experimental characterizations demonstrate that oxygen vacancies provide a favourable ionic diffusion environment in the bulk and significantly suppress gas release from the surface. The target material is achievable in delivering a discharge capacity as high as 301 mAh g-1 with initial Coulombic efficiency of 93.2%. After 100 cycles, a reversible capacity of 300 mAh g-1 still remains without any obvious decay in voltage. This study sheds light on the comprehensive design and control of oxygen activity in transition-metal-oxide systems for next-generation Li-ion batteries.
NASA Astrophysics Data System (ADS)
Nuth, Joseph A.; Johnson, Natasha M.; Ferguson, Frank T.; Carayon, Alicia
2016-06-01
We report the ratio of the initial carbon available as CO that forms gas-phase compounds compared to the fraction that deposits as a carbonaceous solid (the gas/solid branching ratio) as a function of time and temperature for iron, magnetite, and amorphous iron silicate smoke catalysts during surface-mediated reactions in an excess of hydrogen and in the presence of N2. This fraction varies from more than 99% for an amorphous iron silicate smoke at 673 K to less than 40% for a magnetite catalyst at 873 K. The CO not converted into solids primarily forms methane, ethane, water, and CO2, as well as a very wide range of organic molecules at very low concentration. Carbon deposits do not form continuous coatings on the catalytic surfaces, but instead form extremely high surface area per unit volume "filamentous" structures. While these structures will likely form more slowly but over much longer times in protostellar nebulae than in our experiments due to the much lower partial pressure of CO, such fluffy coatings on the surfaces of chondrules or calcium aluminum inclusions could promote grain-grain sticking during low-velocity collisions.
Xu, Hui; Fei, Qiang; Shan, Hongyan; Huan, Yanfu; Mi, Hongyu; Zhang, Hanqi; Li, Guanghua; Feng, Guodong
2016-01-01
The pneumatic nebulization gas-solid microextraction device fascinating us is because it directly atomized organic samples to cross a solid-phase microextraction (SPME) cartridge without any pretreatment. In this work, both the spray chamber and SPME column of the extraction device were heated. We found that this would significantly improve the extraction efficiency of this method. Then, this method was used to detect seven triazine herbicides (atraton, desmetryn, atrazine, terbumeton, terbuthylazine, terbutryn, and dipropetryn) in drinking alcohol samples. The experimental results indicated that this extraction procedure could conveniently, efficiently and accurately concentrate any triazine herbicides from drinking alcohol samples. The limits of detection (LODs) were from 0.08 to 0.23 μg L(-1), the limits of quantification (LOQs) were from 0.27 to 0.78 μg L(-1). We used this method to detect triazine herbicides in five white spirit samples. Four concentrations were chosen (5, 25, 50 and 100 μg L(-1)) as the amounts of spikes to investigate the recovery and precision of the present PN-GSME method. The recoveries ranged from 95.91 to 106.67%. The relative standard deviations were not more than 6.51%. Also this method matches the requirement of the maximum residue limits of the European Union. PMID:26860563
NASA Astrophysics Data System (ADS)
Nuth, Joseph A.; Johnson, Natasha M.; Ferguson, Frank T.; Carayon, Alicia
2016-07-01
We report the ratio of the initial carbon available as CO that forms gas-phase compounds compared to the fraction that deposits as a carbonaceous solid (the gas/solid branching ratio) as a function of time and temperature for iron, magnetite, and amorphous iron silicate smoke catalysts during surface-mediated reactions in an excess of hydrogen and in the presence of N2. This fraction varies from more than 99% for an amorphous iron silicate smoke at 673 K to less than 40% for a magnetite catalyst at 873 K. The CO not converted into solids primarily forms methane, ethane, water, and CO2, as well as a very wide range of organic molecules at very low concentration. Carbon deposits do not form continuous coatings on the catalytic surfaces, but instead form extremely high surface area per unit volume "filamentous" structures. While these structures will likely form more slowly but over much longer times in protostellar nebulae than in our experiments due to the much lower partial pressure of CO, such fluffy coatings on the surfaces of chondrules or calcium aluminum inclusions could promote grain-grain sticking during low-velocity collisions.
Qiu, Bao; Zhang, Minghao; Wu, Lijun; Wang, Jun; Xia, Yonggao; Qian, Danna; Liu, Haodong; Hy, Sunny; Chen, Yan; An, Ke; Zhu, Yimei; Liu, Zhaoping; Meng, Ying Shirley
2016-01-01
Lattice oxygen can play an intriguing role in electrochemical processes, not only maintaining structural stability, but also influencing electron and ion transport properties in high-capacity oxide cathode materials for Li-ion batteries. Here, we report the design of a gas-solid interface reaction to achieve delicate control of oxygen activity through uniformly creating oxygen vacancies without affecting structural integrity of Li-rich layered oxides. Theoretical calculations and experimental characterizations demonstrate that oxygen vacancies provide a favourable ionic diffusion environment in the bulk and significantly suppress gas release from the surface. The target material is achievable in delivering a discharge capacity as high as 301 mAh g(-1) with initial Coulombic efficiency of 93.2%. After 100 cycles, a reversible capacity of 300 mAh g(-1) still remains without any obvious decay in voltage. This study sheds light on the comprehensive design and control of oxygen activity in transition-metal-oxide systems for next-generation Li-ion batteries. PMID:27363944
Computational analysis for dry-ice sublimation assisted CO2 jet impingement flow
NASA Astrophysics Data System (ADS)
Kwak, Songmi; Lee, Jaeseon
2015-11-01
The flow and heat transfer characteristics of the novel gas-solid two-phase jet impingement are investigated computationally. When the high pressure carbon dioxide (CO2) flow passes through a nozzle or orifice, it experiences the sudden expansion and the rapid temperature drop occurred by Joule-Thomson effect. This temperature drop causes the lower bulk jet fluid temperature than the CO2 sublimation line, so dry-ice becomes formed. By using CO2 gas-solid mixture as a working fluid of jet impingement, it is expected the heat transfer enhancement can be achieved due to the low bulk temperature and the additional phase change latent heat. In this study, 2D CFD model is created to predict the cooling effect of gas-solid CO2 jet. The gas-solid CO2 flow is considered by Euler-Lagrangian approach of mixed phase and the additional heat transfer module is embedded to account for the sublimation phenomena of the solid state CO2. The jet flow and heat transfer performance of gas-solid CO2 jet is investigated by the variance of flow parameter like Reynolds number, solid phase concentration and jet geometries.
Tian, Sicong; Jiang, Jianguo; Chen, Xuejing; Yan, Feng; Li, Kaimin
2013-12-01
Direct gas-solid carbonation of steel slag under various operational conditions was investigated to determine the sequestration of the flue gas CO2 . X-ray diffraction analysis of steel slag revealed the existence of portlandite, which provided a maximum theoretical CO2 sequestration potential of 159.4 kg CO 2 tslag (-1) as calculated by the reference intensity ratio method. The carbonation reaction occurred through a fast kinetically controlled stage with an activation energy of 21.29 kJ mol(-1) , followed by 10(3) orders of magnitude slower diffusion-controlled stage with an activation energy of 49.54 kJ mol(-1) , which could be represented by a first-order reaction kinetic equation and the Ginstling equation, respectively. Temperature, CO2 concentration, and the presence of SO2 impacted on the carbonation conversion of steel slag through their direct and definite influence on the rate constants. Temperature was the most important factor influencing the direct gas-solid carbonation of steel slag in terms of both the carbonation conversion and reaction rate. CO2 concentration had a definite influence on the carbonation rate during the kinetically controlled stage, and the presence of SO2 at typical flue gas concentrations enhanced the direct gas-solid carbonation of steel slag. Carbonation conversions between 49.5 % and 55.5 % were achieved in a typical flue gas at 600 °C, with the maximum CO2 sequestration amount generating 88.5 kg CO 2 tslag (-1) . Direct gas-solid carbonation of steel slag showed a rapid CO2 sequestration rate, high CO2 sequestration amounts, low raw-material costs, and a large potential for waste heat utilization, which is promising for in situ carbon capture and sequestration in the steel industry. PMID:23913597
Veetil, Sanoopkumar Puthiya; Pasquier, Louis-César; Blais, Jean-François; Cecchi, Emmanuelle; Kentish, Sandra; Mercier, Guy
2015-09-01
Mineral carbonation of serpentinite mining residue offers an environmentally secure and permanent storage of carbon dioxide. The strategy of using readily available mining residue for the direct treatment of flue gas could improve the energy demand and economics of CO2 sequestration by avoiding the mineral extraction and separate CO2 capture steps. The present is a laboratory scale study to assess the possibility of CO2 fixation in serpentinite mining residues via direct gas-solid reaction. The degree of carbonation is measured both in the absence and presence of water vapor in a batch reactor. The gas used is a simulated gas mixture reproducing an average cement flue gas CO2 composition of 18 vol.% CO2. The reaction parameters considered are temperature, total gas pressure, time, and concentration of water vapor. In the absence of water vapor, the gas-solid carbonation of serpentinite mining residues is negligible, but the residues removed CO2 from the feed gas possibly due to reversible adsorption. The presence of small amount of water vapor enhances the gas-solid carbonation, but the measured rates are too low for practical application. The maximum CO2 fixation obtained is 0.07 g CO2 when reacting 1 g of residue at 200 °C and 25 barg (pCO2 ≈ 4.7) in a gas mixture containing 18 vol.% CO2 and 10 vol.% water vapor in 1 h. The fixation is likely surface limited and restricted due to poor gas-solid interaction. It was identified that both the relative humidity and carbon dioxide-water vapor ratio have a role in CO2 fixation regardless of the percentage of water vapor. PMID:25940479
Zimmermann, Matthias; Escrig, Stéphane; Hübschmann, Thomas; Kirf, Mathias K.; Brand, Andreas; Inglis, R. Fredrik; Musat, Niculina; Müller, Susann; Meibom, Anders; Ackermann, Martin; Schreiber, Frank
2015-01-01
Populations of genetically identical microorganisms residing in the same environment can display marked variability in their phenotypic traits; this phenomenon is termed phenotypic heterogeneity. The relevance of such heterogeneity in natural habitats is unknown, because phenotypic characterization of a sufficient number of single cells of the same species in complex microbial communities is technically difficult. We report a procedure that allows to measure phenotypic heterogeneity in bacterial populations from natural environments, and use it to analyze N2 and CO2 fixation of single cells of the green sulfur bacterium Chlorobium phaeobacteroides from the meromictic lake Lago di Cadagno. We incubated lake water with 15N2 and 13CO2 under in situ conditions with and without NH4+. Subsequently, we used flow cell sorting with auto-fluorescence gating based on a pure culture isolate to concentrate C. phaeobacteroides from its natural abundance of 0.2% to now 26.5% of total bacteria. C. phaeobacteroides cells were identified using catalyzed-reporter deposition fluorescence in situ hybridization (CARD-FISH) targeting the 16S rRNA in the sorted population with a species-specific probe. In a last step, we used nanometer-scale secondary ion mass spectrometry to measure the incorporation 15N and 13C stable isotopes in more than 252 cells. We found that C. phaeobacteroides fixes N2 in the absence of NH4+, but not in the presence of NH4+ as has previously been suggested. N2 and CO2 fixation were heterogeneous among cells and positively correlated indicating that N2 and CO2 fixation activity interact and positively facilitate each other in individual cells. However, because CARD-FISH identification cannot detect genetic variability among cells of the same species, we cannot exclude genetic variability as a source for phenotypic heterogeneity in this natural population. Our study demonstrates the technical feasibility of measuring phenotypic heterogeneity in a rare bacterial
Production of amylases from rice by solid-state fermentation in a gas-solid spouted-Bed bioreactor
Silva; Yang
1998-07-01
A gas-solid spouted-bed bioreactor was developed to produce amylases from rice in solid-state fermentation by Aspergillus oryzae. The spouted-bed bioreactor was developed to overcome many of the problems inherent to large-scale solid-state fermentation, including mass- and heat-transfer limitations in the conventional tray reactors and solids-handling difficulties seen in packed-bed bioreactors. The solid-state fermentation results from the tray-type reactor with surface aeration were poor because of mass- and heat-transfer problems. A packed-bed bioreactor with continuous aeration through the rice bed produced high protein and enzymes, but the fermented rice was difficult to remove and process due to the formation of large chunks of rice aggregates knitted together with fungal mycelia. Also, the fermentation was not uniform in the packed bed. The spouted-bed bioreactor with intermittent spouting with air achieved high production levels in both total protein and enzymes (alpha-amylase, beta-amylase, and glucoamylase) that were comparable to those found in the packed-bed bioreactor, but without the nonuniformity and solids-handling problems. However, continual spouting was found to be detrimental to this solid-state fermentation, possibly because of shear or impact damage to fungal mycelia during spouting. Increasing spouting frequency from 4-h intervals to 1-h intervals decreased protein and enzyme production. Other operating conditions critical to the fermentation include proper humidification to prevent drying of the substrate and control of reactor wall temperature to prevent excessive condensation, which would interfere with proper spouting. PMID:9694679
NASA Astrophysics Data System (ADS)
Suliman, F.; Futsaether, C.; Oxaal, U.; Haugen, L. E.; Jenssen, P.
2006-09-01
Effects of the inlet and outlet position on flow patterns of saturated fluids in a horizontal subsurface-flow constructed wetland were investigated experimentally using a quasi two-dimensional flow cell representing a vertical cross-section in the longitudinal direction of the wetland. The filter medium consisted of glass beads that were either uniformly sized or a mixture of sizes with a distribution corresponding to wetland filter media. Flow through the filter bed was visualized by injecting dyed fluid into the water-saturated model. Next, breakthrough curves were obtained using chloride tracer. Flow through the homogeneous filter formed by uniformly sized beads displayed a clear density-driven component. Using mixed sizes, finer and coarser beads tended to separate into alternating and incomplete layers. Flow occurred preferentially along roughly horizontal high-conductivity paths of coarser filter material. Density-driven vertical flow was much slower than the horizontal flow. Nevertheless, appropriate positioning of the inlet and less importantly the outlet could to some extent mitigate the dominant effect of the medium stratification on the flow patterns. Using inlet-outlet configurations that forced the flow through larger portions of the filter bed by injecting into low-conductivity layers and opposing the gravity-driven flow increased the treatment efficiency.
NASA Astrophysics Data System (ADS)
Pini, R.; Benson, S. M.
2012-12-01
Capillary pressure and relative permeability functions are characteristic curves that, when coupled to the continuum-scale equations of motion, allow for a description of multiphase displacement processes in porous media. Traditionally, these properties are measured in the laboratory and are implemented into reservoir simulations to predict the behavior at the field-scale. There is an increasing awareness that detailed investigations are required to understand the role of the inherent heterogeneity of the rock samples used in the experiments on the measured multiphase properties. In fact, although a significant amount of simulation work has explored the effect of heterogeneities on Pc-kr-S relationships, very few experimental studies report on displacements with well-characterized, naturally heterogeneous media. To extend the current data set and to support these numerical findings, more laboratory data are therefore required that have been obtained under a variety of conditions and on cores from different geological settings. A direct practical implication of these studies would be the definition of a minimum scale at which heterogeneities have to be resolved, so that mathematical models would adequately capture the observed displacement patterns. Moreover, the coupling of experiments and theory will serve as a firm starting point for testing scale-up methods. In this study, results from core-flooding experiments are presented that have been carried out at representative conditions on a variety of naturally heterogeneous core samples. Results are presented from a newly developed technique that allows measuring drainage capillary pressure curves during core-flooding experiments; data have been collected at different temperature (25 and 50C), at different pressures (2 and 9MPa) and with different fluid pairs (CO2/water, N2/water and CO2/brine), thus showing the applicability of the novel technique in a wide range of interfacial tension levels. Additionally, Pc
Carbon-14 immobilization via the CO/sub 2/-Ba(OH)/sub 2/ hydrate gas-solid reaction
Haag, G.L.
1980-01-01
Although no restrictions have been placed on the release of carbon-14, it has been identified as a potential health hazard due to the ease in which it may be assimilated into the biosphere. The intent of the Carbon-14 Immobilization Program, funded through the Airborne Waste Program Management Office, is to develop and demonstrate a novel process for restricting off-gas releases of carbon-14 from various nuclear facilities. The process utilizes the CO/sub 2/-Ba(OH)/sub 2/ hydrate gas-solid reaction to directly remove and immobilize carbon-14. The reaction product, BaCO/sub 3/, possesses both the thermal and chemical stability desired for long-term waste disposal. The process is capable of providing decontamination factors in excess of 1000 and reactant utilization of greater than 99% in the treatment of high volumetric, airlike (330 ppM CO/sub 2/) gas streams. For the treatment of an air-based off-gas stream, the use of packed beds of Ba(OH)/sub 2/.8H/sub 2/O flakes to remove CO/sub 2/ has been demonstrated. However, the operating conditions must be maintained between certain upper and lower limits with respect to the partial pressure of water. If the water vapor pressure in the gas is less than the dissociation vapor pressure of Ba(OH)/sub 2/.8H/sub 2/O, the bed will deactivate. If the vapor pressure is considerably greater, pressure drop problems will increase with increasing humidity as the particles curl and degrade. Results have indicated that when operated in the proper regime, the bulk of the increase in pressure drop results from the conversion of Ba(OH)/sub 2/.8H/sub 2/O to BaCO/sub 3/ and not from the hydration of the commercial Ba(OH)/sub 2/.8H/sub 2/O (i.e. Ba(OH)/sub 2/.7.50H/sub 2/O) to Ba(OH)/sub 2/.8H/sub 2/O.
Wilburn, Kaley M; Mwandumba, Henry C; Jambo, Kondwani C; Boliar, Saikat; Solouki, Sabrina; Russell, David G; Gludish, David W
2016-01-01
8E5/LAV cells harbor a single HIV provirus, and are used frequently to generate standards for HIV genome quantification. Using flow cytometry-based in situ mRNA hybridization validated by qPCR, we find that different batches of 8E5 cells contain varying numbers of cells lacking viral mRNA and/or viral genomes. These findings raise concerns for studies employing 8E5 cells for quantitation, and highlight the value of mRNA FISH and flow cytometry in the detection and enumeration of HIV-positive cells. PMID:27515378
Multiphase flow in wells and pipelines
Sharma, M.P. ); Rohatgi, U.S. )
1992-01-01
This conference focuses primarily on multi-phase flow modeling and calculation methods for oil and gas although two papers focus more on the fluid mechanics of fluidized beds. Papers include theoretical, numerical modeling, experimental investigation, and state-of-the-art review aspects of multiphase flow. The theme of the symposium being general, the papers reflect generality of gas-liquid, liquid-solid, and gas solid flows. One paper deals with nuclear reactor safety as it relates to fluid flow through the reactor.
NASA Astrophysics Data System (ADS)
Park, Sung Sil; Dyussekenov, Nurzhan; Sohn, H. Y.
2010-02-01
The top-blow injection technique of a gas-solid mixture through a circular lance is used in the Mitsubishi Continuous Smelting Process. One of the inherent problems associated with this injection is the severe erosion of the hearth refractory below the lances. A new configuration of the lance to form an annular gas-solid jet rather than a circular jet was designed in the laboratory scale. With this new configuration, solid particles leave the lance at a much lower velocity than the gas, and the penetration behavior of the jet is significantly different than with the circular lance in which the solid particles leave the lance at the same high velocity as the gas. The results of cold model tests using an air-sand jet issuing from a circular lance and an annular lance into a water bath showed that the penetration of the annular jet is much less sensitive to the variations in particle feed rate as well as gas velocity than that of the circular jet. Correlation equations for the penetration depth for both circular and annular jets show agreement among the experimentally obtained values.
Pao-Chung Lin; Cheng-Wei Huang; Ching-Ta Hsiao; Hsisheng Teng
2008-04-15
Magnesium hydroxide extracted from magnesium-bearing minerals is considered a promising agent for binding CO{sub 2} as a carbonate mineral in a gas-solid reaction. An efficient extraction route consisting of hydrothermal treatment on serpentine in HCl followed by NaOH titration for Mg(OH){sub 2} precipitation was demonstrated. The extracted Mg(OH){sub 2} powder had a mean crystal domain size as small as 12 nm and an apparent surface area of 54 m{sup 2}/g. Under one atmosphere of 10 vol% CO{sub 2}/N{sub 2}, carbonation of the serpentine-derived Mg(OH){sub 2} to 26% of the stoichiometric limit was achieved at 325{sup o}C in 2 h; while carbonation of a commercially available Mg(OH){sub 2}, with a mean crystal domain size of 33 nm and an apparent surface area of 3.5 m{sup 2}/g, reached only 9% of the stoichiometric limit. The amount of CO{sub 2} fixation was found to be inversely proportional to the crystal domain size of the Mg(OH){sub 2} specimens. The experimental data strongly suggested that only a monolayer of carbonates was formed on the crystal domain boundary in the gas-solid reaction, with little penetration of the carbonates into the crystal domain. 24 refs., 6 figs., 2 tabs.
Ferrer, Pilar; da Silva, Iván; Rubio-Zuazo, Juan; Alfonso, Belén F; Trobajo, Camino; Khainakov, Sergei; Garcia, Jose R; Garcia-Granda, Santiago; Castro, Germán R
2012-01-01
A portable powder-liquid high-corrosion-resistant reaction cell has been designed to follow in situ reactions by X-ray powder diffraction (XRD) and X-ray absorption spectroscopy (XAS) techniques. The cell has been conceived to be mounted on the experimental stations for diffraction and absorption of the Spanish CRG SpLine-BM25 beamline at the European Synchrotron Radiation Facility. Powder reactants and/or products are kept at a fixed position in a vertical geometry in the X-ray pathway by a porous membrane, under forced liquid reflux circulation. Owing to the short pathway of the X-ray beam through the cell, XRD and XAS measurements can be carried out in transmission configuration/mode. In the case of the diffraction technique, data can be collected with either a point detector or a two-dimensional CCD detector, depending on specific experimental requirements in terms of space or time resolution. Crystallization processes, heterogeneous catalytic processes and several varieties of experiments can be followed by these techniques with this cell. Two experiments were carried out to demonstrate the cell feasibility: the phase transformations of layered titanium phosphates in boiling aqueous solutions of phosphoric acid, and the reaction of copper carbonate and L-isoleucine amino acid powders in boiling aqueous solution. In this last case the shrinking of the solid reactants and the formation of Cu(isoleucine)(2) is observed. The crystallization processes and several phase transitions have been observed during the experiments, as well as an unexpected reaction pathway. PMID:22186649
David Roelant; Seckin Gokaltun
2009-06-30
A circulating fluidized bed (CFB) built at FIU was used to study particle motion in the riser in order to simulate flow regimes in a cold gasifier. High speed imaging was used in order to capture the dynamics of the particles flowing in the riser. The imaging method used here is called the shadow sizing technique which allowed the determination of particle areas and trajectories at various flow rates in the riser. The solid volume fraction and particle velocities calculated using the images acquired during the experiments can be related to granular temperature in order to detect formations of clusters in the riser section of the CFB. The shadow sizing technique was observed to be an effective method in detecting dynamics of particles in motion and formation of clusters when supported with high-speed imaging.
NASA Astrophysics Data System (ADS)
Geiger, S.; Driesner, T.; Coumou, D.
2005-12-01
We compare temperature-based and enthalpy-based numerical schemes for compressible non-isothermal subsurface fluid flow. We formulate a diffusion equation for the fluid pressure, a diffusion equation for heat conduction, and an equation for the advective transport of temperature or enthalpy in the fluid. These equations can readily be solved by a combination of finite element and higher-order finite volume methods, which are capable of preserving steep temperature gradients in advection dominated flows and handling complex two- and three-dimensional geologic structures with orders of magnitude variation in permeability. Since the time-scale of pressure diffusion is slower than the time-scale for advective fluid flow, it is possible to decouple the equations and use implicit finite element methods for the parabolic (diffusion) equations and explicit finite volume methods for the hyperbolic (advection) equations. For single-phase flow, we use the thermal wave speed to compute the advection of the temperature field on the finite volumes. Since the thermal front is advected at a slower rate than the actual fluid flow, a significant (i.e., a factor 10 at liquid and a factor 1000 at vapor conditions) computational speedup can be achieved in comparison to the formulation where enthalpy is advected. The results for temperature-based and enthalpy-based formulations at vapor or liquid conditions, however, are identical and compare extremely well with results obtained from other codes that use fully coupled solution techniques. Our results do not improve if we use Picard iteration to couple the pressure, conduction, and advection equations. For the enthalpy-based transport schemes, we use a Newton iteration to equilibrate the energy in the fluid and rock. This also allows us to use more modern equation of states for complex multi-component systems, that are formulated in terms of pressure p, temperature T, and composition X, and hence cannot use the specific enthalpy h to
NASA Astrophysics Data System (ADS)
Chang, J. S.; Sohn, H. Y.
2012-08-01
Top-blow injection of a gas-solid jet through a circular lance is used in the Mitsubishi Continuous Smelting Process. One problem associated with this injection is the severe erosion of the hearth refractory below the lances. A new configuration of the lance to form an annular gas-solid jet rather than the circular jet was designed in this laboratory. With this new configuration, the solid particles fed through the center tube leave the lance at a much lower velocity than the gas, and the penetration behavior of the jet is significantly different from that with a circular lance where the solid particles leave the lance at the same high velocity as the gas. In previous cold-model investigations in this laboratory, the effects of the gas velocity, particle feed rate, lance height of the annular lance, and the cross-sectional area of the gas jet were studied and compared with the circular lance. This study examined the effect of the density and size of the solid particles on the penetration behavior of the annular gas-solid jet, which yielded some unexpected results. The variation in the penetration depth with the density of the solid particles at the same mass feed rate was opposite for the circular lance and the annular lance. In the case of the circular lance, the penetration depth became shallower as the density of the solid particles increased; on the contrary, for the annular lance, the penetration depth became deeper with the increasing density of particles. However, at the same volumetric feed rate of the particles, the density effect was small for the circular lance, but for the annular lance, the jets with higher density particles penetrated more deeply. The variation in the penetration depth with the particle diameter was also different for the circular and the annular lances. With the circular lance, the penetration depth became deeper as the particle size decreased for all the feed rates, but with the annular lance, the effect of the particle size was
Characterizing hydrogeologic heterogeneity using lithologic data
Flach, G.; Hamm, LL.L.; Harris, M.K.; Thayer, P.A.; Haselow, J.S.; Smits, A.D.
1997-06-13
Large-scale (>1 m) variability in hydraulic conductivity is usually the main influence on field-scale groundwater flow patterns and dispersive transport. Incorporating realistic hydraulic conductivity heterogeneity into flow and transport models is paramount to accurate simulations, particularly for contaminant migration. Sediment lithologic descriptions and geophysical logs typically offer finer spatial resolution, and therefore more potential information about site-scale heterogeneity, than other site characterization data. In this study, a technique for generating a heterogeneous, three- dimensional hydraulic conductivity field from sediment lithologic descriptions is presented. The approach involves creating a three-dimensional, fine-scale representation of mud (silt and clay) percentage using a stratified interpolation algorithm. Mud percentage is then translated into horizontal and vertical conductivity using direct correlations derived from measured data and inverse groundwater flow modeling. Lastly, the fine-scale conductivity fields are averaged to create a coarser grid for use in groundwater flow and transport modeling.
Symonds, R.B.; Reed, M.H.
1993-01-01
This paper documents the numerical formulations, thermochemical data base, and possible applications of computer programs, SOLVGAS and GASWORKS, for calculating multicomponent chemical equilibria in gas-solid-liquid systems. SOLVGAS and GASWORKS compute simultaneous equilibria by solving simultaneously a set of mass balance and mass action equations written for all gas species and for all gas-solid or gas-liquid equilibria. Examples of gas-evaporation-from-magma and precipitation-with-cooling calculations for volcanic gases collected from Mount St. Helens are shown. -from Authors
Gas-solid difference in charge-changing cross sections for bare and H-like nickel ions at 200 MeV/u
Ogawa, H.; Sakamoto, N.; Tsuchida, H.; Geissel, H.; Fettouhi, A.; Knoebel, R. K.; Litvinov, Yu. A.; Fritzsche, S.; Portillo, M.; Scheidenberger, C.; Weick, H.; Becker, F.; Boutin, D.; Kindler, B.; Lommel, B.; Muenzenberg, G.; Stadlmann, J.; Winkler, M.; Yao, N.; Shevelko, V. P.
2007-02-15
It is well known that the density of the target can have a crucial impact on charge-changing collisions of partially ionized heavy ions. However, the basic understanding of this experimental observation is hampered by the difficulty in knowing the charge-state evolution of projectiles inside solids. Therefore, the present experiments with 200 MeV/u bare and H-like nickel ions were performed to study charge-changing cross sections in different monatomic and compound gases and solids. The experimental results clearly demonstrate that the electron-loss cross sections in solids increase by about 40% compared to gases. The results support the Bohr-Lindhard model which predicts this gas-solid difference originating from enhanced ionization of excited ions. The experimental results are compared with recent theoretical estimates.
Meichtry, Jorge M; Levy, Ivana K; Mohamed, Hanan H; Dillert, Ralf; Bahnemann, Detlef W; Litter, Marta I
2016-03-16
The dynamics of the transfer of electrons stored in TiO2 nanoparticles to As(III) , As(V) , and uranyl nitrate in water was investigated by using the stopped-flow technique. Suspensions of TiO2 nanoparticles with stored trapped electrons (etrap (-) ) were mixed with solutions of acceptor species to evaluate the reactivity by following the temporal evolution of etrap (-) by the decrease in the absorbance at λ=600 nm. The results indicate that As(V) and As(III) cannot be reduced by etrap (-) under the reaction conditions. In addition, it was observed that the presence of As(V) and As(III) strongly modified the reaction rate between O2 and etrap (-) : an increase in the rate was observed if As(V) was present and a decrease in the rate was observed in the presence of As(III) . In contrast with the As system, U(VI) was observed to react easily with etrap (-) and U(IV) formation was observed spectroscopically at λ=650 nm. The possible competence of U(VI) and NO3 (-) for their reduction by etrap (-) was analyzed. The inhibition of the U(VI) photocatalytic reduction by O2 could be attributed to the fast oxidation of U(V) and/or U(IV) . PMID:26710930
Changing Emulsion Dynamics with Heterogeneous Surface Wettability
NASA Astrophysics Data System (ADS)
Tsai, Peichun Amy; Meng, Qiang; Zhang, Yali; Li, Jiang; Lammertink, Rob; Chen, Haosheng
2015-11-01
We elucidate the effect of heterogeneous surface wettability on the morphology and dynamics of microfluidic emulsions, generated by a co-flowing device. We first design a useful methodology of modifying a micro-capillary with desired heterogeneous wettability, such as alternating hydrophilic and hydrophobic regions. Subsequently, the effects of flow rates and heterogeneous wettability on the emulsion morphology and motion in the micro-capillary are investigated. Our experimental data reveal a universal critical time scale of advective emulsions, above which the microfluidic emulsions remain intact, whereas below this time-scale emulsions become adhesive or inverse. A simple model based on a force balance can be used to explain this critical transition. These results show a control of emulsion dynamics by tuning the droplet size and the Capillary number, the ratio of viscous to surface effects, with heterogeneous surface wettability.
Surface Structure of Kio (3) Grown By Heterogeneous Reaction of Ozone With Ki (001)
Brown, M.A.; Liu, Z.; Ashby, P.D.; Mehta, A.; Grimm, R.L.; Hemminger, J.C.
2009-05-12
The crystal structure of KIO{sub 3} grown by heterogeneous surface oxidation of KI (001) with ozone is reported. Under ambient reaction conditions (RH {approx}35%, room temperature) a thick layer of KIO{sub 3} grows at the gas-solid interface. Two doublets are present in the I(4d) X-ray photoelectron spectroscopy structure measurements, characteristic of unreacted KI (I{sup -}) from the substrate and the oxidized KIO{sub 3} (I{sup 5+}) reaction product. X-ray diffraction measurements confirm the presence at the interface of randomly oriented polycrystalline-triclinic KIO{sub 3} with an average particle diameter of 15 nm. KIO{sub 3} particle diameters determined from the X-ray diffraction peak widths are consistent with the results of atomic force microscopy. There is no X-ray powder diffraction evidence to suggest that the underlying KI substrate is altered in any manner during this heterogeneous interfacial reaction.
Heterogeneous fuel for hybrid rocket
NASA Technical Reports Server (NTRS)
Stickler, David B. (Inventor)
1996-01-01
Heterogeneous fuel compositions suitable for use in hybrid rocket engines and solid-fuel ramjet engines, The compositions include mixtures of a continuous phase, which forms a solid matrix, and a dispersed phase permanently distributed therein. The dispersed phase or the matrix vaporizes (or melts) and disperses into the gas flow much more rapidly than the other, creating depressions, voids and bumps within and on the surface of the remaining bulk material that continuously roughen its surface, This effect substantially enhances heat transfer from the combusting gas flow to the fuel surface, producing a correspondingly high burning rate, The dispersed phase may include solid particles, entrained liquid droplets, or gas-phase voids having dimensions roughly similar to the displacement scale height of the gas-flow boundary layer generated during combustion.
Sulfur Dioxide Capture by Heterogeneous Oxidation on Hydroxylated Manganese Dioxide.
Wu, Haodong; Cai, Weimin; Long, Mingce; Wang, Hairui; Wang, Zhiping; Chen, Chen; Hu, Xiaofang; Yu, Xiaojuan
2016-06-01
Here we demonstrate that sulfur dioxide (SO2) is efficiently captured via heterogeneous oxidation into sulfate on the surface of hydroxylated manganese dioxide (MnO2). Lab-scale activity tests in a fluidized bed reactor showed that the removal efficiency for a simulated flue gas containing 5000 mg·Nm(-3) SO2 could reach nearly 100% with a GHSV (gas hourly space velocity) of 10000 h(-1). The mechanism was investigated using a combination of experimental characterizations and theoretical calculations. It was found that formation of surface bound sulfate proceeds via association of SO2 with terminal hydroxyls. Both H2O and O2 are essential for the generation of reactive terminal hydroxyls, and the indirect role of O2 in heterogeneous SO2 oxidation at low temperature was also revealed. We propose that the high reactivity of terminal hydroxyls is attributed to the proper surface configuration of MnO2 to adsorb water with degenerate energies for associative and dissociative states, and maintain rapid proton dynamics. Viability analyses suggest that the desulfurization method that is based on such a direct oxidation reaction at the gas/solid interface represents a promising approach for SO2 capture. PMID:27123922
NASA Astrophysics Data System (ADS)
El-Geassy, A. A.; Seetheraman, S.
2016-03-01
Ammonium molybdate and ferrous oxalate were used for the synthesis of nano-structured Mo-Fe intermetallics. Co-precipitation technique was applied to produce Mo/Fe precursors containing 58/42, 72/28 and 30/70 mass% respectively. The different phases formed were identified by XRD. The macro- and microstructures were microscopically examined by Reflected Light Microscope (RLM) and Scanning Electron Microscope (SEM) coupled with Electron Dispersion Spectroscopy (EDS). TG-DTA-DSC technique was applied to follow up the behavior of precursors up to 900oC (10K/min.). Endothermic peaks were detected at 97.8, 196.9 and 392.7oC due to the decomposition reactions to produce MoO3 and Fe2O3. The exothermic peak resulted at 427.8oC is due to the solid state reaction between these oxides to form Fe2(MoO4)3. Precursors were isothermally reduced at 600-850oC in a flow of purified H2 and the O2-weight loss from the reduction reactions was continuously recorded as a function of time. The isothermal reduction behavior of precursors was investigated. The structures of reduced products and the different phases formed were investigated and correlated with the reduction conditions. At >60% reduction extents, Fe2(MoO4)3] phase was first reduced to Fe2MoO3O8 before the formation of FeMo, while FeMoO4 and MoO2 were reduced to FeMo and Mo. In precursors containing higher content of Fe2O3, FeMo, Fe3Mo and Fe phases were produced. The visual observation of reduced samples showed that the volume was gradually shrinking with rise in temperature up to 800oC and beyond which a measurable swelling was observed reaching about 170% at 900oC.
Phenotypically heterogeneous populations in spatially heterogeneous environments
NASA Astrophysics Data System (ADS)
Patra, Pintu; Klumpp, Stefan
2014-03-01
The spatial expansion of a population in a nonuniform environment may benefit from phenotypic heterogeneity with interconverting subpopulations using different survival strategies. We analyze the crossing of an antibiotic-containing environment by a bacterial population consisting of rapidly growing normal cells and slow-growing, but antibiotic-tolerant persister cells. The dynamics of crossing is characterized by mean first arrival times and is found to be surprisingly complex. It displays three distinct regimes with different scaling behavior that can be understood based on an analytical approximation. Our results suggest that a phenotypically heterogeneous population has a fitness advantage in nonuniform environments and can spread more rapidly than a homogeneous population.
Gritti, Fabrice; Guiochon, Georges A
2006-03-01
The extension of the {Psi} function developed by Toth from equilibria taking place at gas-solid interfaces to those taking place at liquid-solid interfaces was investigated. The results were applied to conventional liquid-solid systems used in reversed-phase liquid chromatography (RPLC). The adsorbents in these systems are made of porous silica having a hydrophobic solid surface obtained by chemically bonding C{sub 18} alkyl chains to a porous silica gel then endcapping the surface with trimethylsilyl groups. The liquid is an aqueous solution of an organic solvent, most often methanol or acetonitrile. The probe compound used here is phenol. Adsorption data of phenol were measured using the dynamic frontal analysis (FA) method. The excess adsorption of the organic solvent was measured using the minor disturbance (MD) method. Activity coefficients in the bulk were estimated through the UNIFAC group contributions. The results show that the {Psi} function predicts 90% of the total free energy of immersion, {Delta}F, of the solid when the concentration of phenol is moderate (typically less than 10 g/L). At higher concentrations, the nonideal behavior of the bulk liquid phase becomes significant and it may contribute up to about 30% of {Delta}F. The high concentration of adsorbed molecules of phenol at the interface decreases the interfacial tension, {sigma}, by about 18 mN/m, independently of the structure of the adsorbed phase and of the nature of the organic solvent.
Jones, L.H.; Swanson, B.I.
1983-08-01
From polarization studies of high resolution IR spectra of SF/sub 6/ and SeF/sub 6/ trapped in noble gas solids we show that much of the structure observed for the stretching mode represents site symmetry split components for low symmetry trapping sites, the triply-degenerate ..nu../sub 3/ mode being split into a doubly- and singly-degenerate mode. Most of the sites showing polarization are orientationally ordered with the singly-degenerate component perpendicular to the substrate. We attribute the driving force for ordering to guest--host interaction potentials which result in registry between the molecules and the (111) growth plane during deposition. The observed orientational ordering combined with high temperature annealing studies has allowed the identification of the symmetry of certain trapping sites and further analysis of vibrational dephasing dynamics. Several sites with the same nominal symmetry and structure can be tracked through the matrices discussed herein. The implications of the ordering of impurity structure in a host lattice formed by vapor deposition are discussed.
Patterns of Emphysema Heterogeneity
Valipour, Arschang; Shah, Pallav L.; Gesierich, Wolfgang; Eberhardt, Ralf; Snell, Greg; Strange, Charlie; Barry, Robert; Gupta, Avina; Henne, Erik; Bandyopadhyay, Sourish; Raffy, Philippe; Yin, Youbing; Tschirren, Juerg; Herth, Felix J.F.
2016-01-01
Background Although lobar patterns of emphysema heterogeneity are indicative of optimal target sites for lung volume reduction (LVR) strategies, the presence of segmental, or sublobar, heterogeneity is often underappreciated. Objective The aim of this study was to understand lobar and segmental patterns of emphysema heterogeneity, which may more precisely indicate optimal target sites for LVR procedures. Methods Patterns of emphysema heterogeneity were evaluated in a representative cohort of 150 severe (GOLD stage III/IV) chronic obstructive pulmonary disease (COPD) patients from the COPDGene study. High-resolution computerized tomography analysis software was used to measure tissue destruction throughout the lungs to compute heterogeneity (≥ 15% difference in tissue destruction) between (inter-) and within (intra-) lobes for each patient. Emphysema tissue destruction was characterized segmentally to define patterns of heterogeneity. Results Segmental tissue destruction revealed interlobar heterogeneity in the left lung (57%) and right lung (52%). Intralobar heterogeneity was observed in at least one lobe of all patients. No patient presented true homogeneity at a segmental level. There was true homogeneity across both lungs in 3% of the cohort when defining heterogeneity as ≥ 30% difference in tissue destruction. Conclusion Many LVR technologies for treatment of emphysema have focused on interlobar heterogeneity and target an entire lobe per procedure. Our observations suggest that a high proportion of patients with emphysema are affected by interlobar as well as intralobar heterogeneity. These findings prompt the need for a segmental approach to LVR in the majority of patients to treat only the most diseased segments and preserve healthier ones. PMID:26430783
Seismoelectric effects due to mesoscopic heterogeneities
NASA Astrophysics Data System (ADS)
Jougnot, Damien; Rubino, J. GermáN.; Carbajal, Marina Rosas; Linde, Niklas; Holliger, Klaus
2013-05-01
While the seismic effects of wave-induced fluid flow due to mesoscopic heterogeneities have been studied for several decades, the role played by these types of heterogeneities on seismoelectric phenomena is largely unexplored. To address this issue, we have developed a novel methodological framework which allows for the coupling of wave-induced fluid flow, as inferred through numerical oscillatory compressibility tests, with the pertinent seismoelectric conversion mechanisms. Simulating the corresponding response of a water-saturated sandstone sample containing mesoscopic fractures, we demonstrate for the first time that these kinds of heterogeneities can produce measurable seismoelectric signals under typical laboratory conditions. Given that this phenomenon is sensitive to key hydraulic and mechanical properties, we expect that the results of this pilot study will stimulate further exploration on this topic in several domains of the Earth, environmental, and engineering sciences.
Tihansky, A.B.
2005-01-01
Chloride concentrations have been increasing over time in water from wells within and near the Eldridge-Wilde well field, near the coast in west-central Florida. Variable increases in chloride concentrations from well to well over time are the combined result of aquifer heterogeneity and ground-water pumping within the Upper Floridan aquifer. Deep mineralized water and saline water associated with the saltwater interface appear to move preferentially along flow zones of high transmissivity in response to ground-water withdrawals. The calcium-bicarbonate-type freshwater of the Upper Floridan aquifer within the study area is variably enriched with ions by mixing with introduced deep and saline ground water. The amount and variability of increases in chloride and sulfate concentrations at each well are related to well location, depth interval, and permeable intervals intercepted by the borehole. Zones of high transmissivity characterize the multilayered carbonate rocks of the Upper Floridan aquifer. Well-developed secondary porosity within the Tampa/Suwannee Limestones and the Avon Park Formation has created producing zones within the Upper Floridan aquifer. The highly transmissive sections of the Avon Park Formation generally are several orders of magnitude more permeable than the Tampa/Suwannee Limestones, but both are associated with increased ground-water flow. The Ocala Limestone is less permeable and is dominated by primary, intergranular porosity. Acoustic televiewer logging, caliper logs, and borehole flow logs (both electromagnetic and heat pulse) indicate that the Tampa/Suwannee Limestone units are dominated by porosity owing to dissolution between 200 and 300 feet below land surface, whereas the porosity of the Avon Park Formation is dominated by fractures that occur primarily from 600 to 750 feet below land surface and range in angle from horizontal to near vertical. Although the Ocala Limestone can act as a semiconfining unit between the Avon Park
Gay, Laura; Baker, Ann-Marie; Graham, Trevor A.
2016-01-01
The population of cells that make up a cancer are manifestly heterogeneous at the genetic, epigenetic, and phenotypic levels. In this mini-review, we summarise the extent of intra-tumour heterogeneity (ITH) across human malignancies, review the mechanisms that are responsible for generating and maintaining ITH, and discuss the ramifications and opportunities that ITH presents for cancer prognostication and treatment. PMID:26973786
Dispersivity in heterogeneous permeable media
Chesnut, D.A.
1994-01-01
When one fluid displaces another through a one-dimensional porous medium, the composition changes from pure displacing fluid at the inlet to pure displaced fluid some distance downstream. The distance over which an arbitrary percentage of this change occurs is defined as the mixing zone length, which increases with increasing average distance traveled by the displacement front. For continuous injection, the mixing zone size can be determined from a breakthrough curve as the time required for the effluent displacing fluid concentration to change from, say, 10% to 90%. In classical dispersion theory, the mixing zone grows in proportion to the square root of the mean distance traveled, or, equivalently, to the square root of the mean breakthrough time. In a multi-dimensional heterogeneous medium, especially at field scales, the size of the mixing zone grows almost linearly with mean distance or travel time. If an observed breakthrough curve is forced to fit the, clinical theory, the resulting effective dispersivity, instead of being constant, also increases almost linearly with the spatial or temporal scale of the problem. This occurs because the heterogeneity in flow properties creates a corresponding velocity distribution along the different flow pathways from the inlet to the outlet of the system. Mixing occurs mostly at the outlet, or wherever the fluid is sampled, rather than within the medium. In this paper, we consider the effects. of this behavior on radionuclide or other contaminant migration.
Heterogeneous Reaction gaseous chlorine nitrate and solid sodium chloride
NASA Technical Reports Server (NTRS)
Timonen, Raimo S.; Chu, Liang T.; Leu, Ming-Taun
1994-01-01
The heterogeneous reaction of gaseous chlorine nitrate and solid sodium chloride was investigated over a temperature range of 220 - 300 K in a flow-tube reactor interfaced with a differentially pumped quadrupole mass spectrometer.
Heterogeneous Atmospheric Chemistry
NASA Astrophysics Data System (ADS)
Schryer, David R.
In the past few years it has become increasingly clear that heterogeneous, or multiphase, processes play an important role in the atmosphere. Unfortunately the literature on the subject, although now fairly extensive, is still rather dispersed. Furthermore, much of the expertise regarding heterogeneous processes lies in fields not directly related to atmospheric science. Therefore, it seemed desirable to bring together for an exchange of ideas, information, and methodologies the various atmospheric scientists who are actively studying heterogeneous processes as well as other researchers studying similar processes in the context of other fields.
Asymmetric reactions in continuous flow
Mak, Xiao Yin; Laurino, Paola
2009-01-01
Summary An overview of asymmetric synthesis in continuous flow and microreactors is presented in this review. Applications of homogeneous and heterogeneous asymmetric catalysis as well as biocatalysis in flow are discussed. PMID:19478913
Haag, G.L.
1983-09-01
The removal of trace components from gas streams via irreversible gas-solid reactions in an area of interest to the chemical engineering profession. This research effort addresses the use of fixed beds of Ba(OH)/sub 2/ hydrate flakes for the removal of an acid gas, CO/sub 2/, from air that contains approx. 330 ppM/sub v/ CO/sub 2/. Areas of investigation encompassed: (1) an extensive literature review of Ba(OH)/sub 2/ hydrate chemistry, (2) microscale studies on 0.150-g samples to develop a better understanding of the reaction, (3) process studies at the macroscale level with 10.2-cm-ID fixed-bed reactors, and (4) the development of a model for predicting fixed-bed performance. Experimental studies indicated fixed beds of commercial Ba(OH)/sub 2/.8H/sub 2/O flakes at ambient temperatures to be capable of high CO/sub 2/-removal efficiencies (effluent concentrations <100 ppB), high reactant utilization (>99%), and an acceptable pressure drop (1.8 kPa/m at a superficial gas velocity of 13 cm/s). Ba(OH)/sub 2/.8H/sub 2/O was determined to be more reactive toward CO/sub 2/ than either Ba(OH)/sub 2/.3H/sub 2/O or Ba(OH)/sub 2/.1H/sub 2/O. A key variable in the development of this fixed-bed process was relative humidity. Operation at conditions with effluent relative humidities >60% resulted in significant recrystallization and restructuring of the flake and subsequent pressure-drop problems.
Overview of medium heterogeneity and transport processes
Tsang, Y.; Tsang, C.F.
1993-11-01
Medium heterogeneity can have significant impact on the behavior of solute transport. Tracer breakthrough curves from transport in a heterogeneous medium are distinctly different from that in a homogeneous porous medium. Usually the shape of the breakthrough curves are highly non-symmetrical with a fast rise at early times and very long tail at late times, and often, they consist of multiple peaks. Moreover, unlike transport in a homogeneous medium where the same transport parameters describe the entire medium, transport through heterogeneous media gives rise to breakthrough curves which have strong spatial dependence. These inherent characteristics of transport in heterogeneous medium present special challenge to the performance assessment of a potential high level nuclear waste repository with respect to the possible release of radio nuclides to the accessible environment. Since an inherently desirable site characteristic for a waste repository is that flow and transport should be slow, then transport measurements in site characterization efforts will necessarily be spatially small and temporally short compare to the scales which are of relevance to performance assessment predictions. In this paper we discuss the role of medium heterogeneity in site characterization and performance assessment. Our discussion will be based on a specific example of a 3D heterogeneous stochastic model of a site generally similar to, the Aespoe Island, the site of the Hard Rock Laboratory in Southern Sweden. For our study, alternative 3D stochastic fields of hydraulic conductivities conditioned on ``point`` measurements shall be generated. Results of stochastic flow and transport simulations would be used to address the issues of (1) the relationship of tracer breakthrough with the structure of heterogeneity, and (2) the inference from small scale testing results to large scale and long term predictions.
Heterogeneous reactions in aircraft gas turbine engines
NASA Astrophysics Data System (ADS)
Brown, R. C.; Miake-Lye, R. C.; Lukachko, S. P.; Waitz, I. A.
2002-05-01
One-dimensional flow models and unity probability heterogeneous rate parameters are used to estimate the maximum effect of heterogeneous reactions on trace species evolution in aircraft gas turbines. The analysis includes reactions on soot particulates and turbine/nozzle material surfaces. Results for a representative advanced subsonic engine indicate the net change in reactant mixing ratios due to heterogeneous reactions is <10-6 for O2, CO2, and H2O, and <10-10 for minor combustion products such as SO2 and NO2. The change in the mixing ratios relative to the initial values is <0.01%. Since these estimates are based on heterogeneous reaction probabilities of unity, the actual changes will be even lower. Thus, heterogeneous chemistry within the engine cannot explain the high conversion of SO2 to SO3 which some wake models require to explain the observed levels of volatile aerosols. Furthermore, turbine heterogeneous processes will not effect exhaust NOx or NOy levels.
Teaching Heterogeneous Classes.
ERIC Educational Resources Information Center
Millrood, Radislav
2002-01-01
Discusses an approach to teaching heterogeneous English-as-a-Second/Foreign-Language classes. Draws on classroom research data to describe the features of a success-building lesson context. (Author/VWL)
Towards heterogeneous distributed debugging
Damodaran-Kamal, S.K.
1995-04-01
Several years of research and development in parallel debugger design have given up several techniques, though implemented in a wide range of tools for an equally wide range of systems. This paper is an evaluation of these myriad techniques as applied to the design of a heterogeneous distributed debugger. The evaluation is based on what features users perceive as useful, as well as the ease of implementation of the features using the available technology. A preliminary architecture for such a heterogeneous tool is proposed. Our effort in this paper is significantly different from the other efforts at creating portable and heterogeneous distributed debuggers in that we concentrate on support for all the important issues in parallel debugging, instead of simply concentrating on portability and heterogeneity.
Heterogeneity and Scaling in Geologic Media
Gregory N. Boitnott; Gilles Y. Bussod; Paul N. Hagin; Stephen R. Brown
2005-04-18
The accurate characterization and remediation of contaminated subsurface environments requires the detailed knowledge of subsurface structures and flow paths. Enormous resources are invested in scoping and characterizing sites using core sampling, 3-D geophysical surveys, well tests, etc.... Unfortunately, much of the information acquired is lost to compromises and simplifications made in constructing numerical grids for the simulators used to predict flow and transport from the contaminated area to the accessible environment. In rocks and soils, the bulk geophysical and transport properties of the matrix and of fracture systems are determined by the juxtaposition of geometric features at many length scales. In the interest of computational efficiency, recognized heterogeneities are simplified, averaged out, or entirely ignored in spite of recent studies that recognize that: (1) Structural and lithologic heterogeneities exist on all scales in rocks. (2) Small heterogeneities influence, and can control the physical and chemical properties of rocks. In this work we propose a physically based approach for the description and treatment of heterogeneities, that highlights the use of laboratory equipment designed to measure the effect on physical properties of fine scale heterogeneities observed in rocks and soils. We then discuss the development of an integration methodology that uses these measurements to develop and upscale flow and transport models. Predictive simulations are 'calibrated' to the measured heterogeneity data, and subsequently upscaled in a way that is consistent with the transport physics and the efficient use of environmental geophysics. This methodology provides a more accurate interpretation and representation of the subsurface for both environmental engineering and remediation. We show through examples, (i) the important influence of even subtle heterogeneity in the interpreting of geophysical data, and (ii) how physically based upscaling can lead
Fluid dynamics of active heterogeneities in a mantle plume conduit
NASA Astrophysics Data System (ADS)
Farnetani, C. G.; Limare, A.; Hofmann, A. W.
2015-12-01
Laboratory experiments and numerical simulations indicate that the flow of a purely thermal plume preserves the azimuthal zonation of the source region, thus providing a framework to attribute a deep origin to the isotopic zonation of Hawaiian lavas. However, previous studies were limited to passive heterogeneities not affecting the flow. We go beyond this simplification by considering active heterogeneities which are compositionally denser, or more viscous, and we address the following questions: (1) How do active heterogeneities modify the axially symmetric velocity field of the plume conduit? (2) Under which conditions is the azimuthal zonation of the source region no longer preserved in the plume stem? (3) How do active heterogeneities deform during upwelling and what is their shape once at sublithospheric depths? We conducted both laboratory experiments, using a Particle Image Velocimetry (PIV) to calculate the velocity field, and high resolution three-dimensional simulations where millions of tracers keep track of the heterogeneous fluid. For compositionally denser heterogeneities we cover a range of buoyancy ratios 0heterogeneities, the range of viscosity ratios is 0<λ<20, where λ=ηheterogeneity/ηfluid and η is viscosity. The initial heterogeneity has the arbitrary shape of a sphere and we vary its volume and its distance from the plume axis. We find that by increasing λ, the shape of the heterogeneity changes from filament-like to blob-like characterized by internal rotation and little stretching. By increasing B the heterogeneity tends to spread at the base of the plume stem and to rise as a tendril close to the axis, so that the initial zonation may be poorly preserved. We also find that the plume velocity field can be profoundly modified by active heterogeneities, and we explore the relation between strain rates and the evolving shape of the upwelling heterogeneity.
Characterization of Paper Heterogeneity
NASA Astrophysics Data System (ADS)
Considine, John M.
Paper and paperboard are the most widely-used green materials in the world because they are renewable, recyclable, reusable, and compostable. Continued and expanded use of these materials and their potential use in new products requires a comprehensive understanding of the variability of their mechanical properties. This work develops new methods to characterize the mechanical properties of heterogeneous materials through a combination of techniques in experimental mechanics, materials science and numerical analysis. Current methods to analyze heterogeneous materials focus on crystalline materials or polymer-crystalline composites, where material boundaries are usually distinct. This work creates a methodology to analyze small, continuously-varying stiffness gradients in 100% polymer systems and is especially relevant to paper materials where factors influencing heterogeneity include local mass, fiber orientation, individual pulp fiber properties, local density, and drying restraint. A unique approach was used to understand the effect of heterogeneity on paper tensile strength. Additional variation was intentionally introduced, in the form of different size holes, and their effect on strength was measured. By modifying two strength criteria, an estimate of strength in the absence of heterogeneity was determined. In order to characterize stiffness heterogeneity, a novel load fixture was developed to excite full-field normal and shear strains for anisotropic stiffness determination. Surface strains were measured with digital image correlation and were analyzed with the VFM (Virtual Fields Method). This approach led to VFM-identified stiffnesses that were similar to values determined by conventional tests. The load fixture and VFM analyses were used to measure local stiffness and local stiffness variation on heterogeneous anisotropic materials. The approach was validated on simulated heterogeneous materials and was applied experimentally to three different paperboards
Impact of Aquifer Heterogeneities on Autotrophic Denitrification.
NASA Astrophysics Data System (ADS)
McCarthy, A.; Roques, C.; Selker, J. S.; Istok, J. D.; Pett-Ridge, J. C.
2015-12-01
Nitrate contamination in groundwater is a big challenge that will need to be addressed by hydrogeologists throughout the world. With a drinking water standard of 10mg/L of NO3-, innovative techniques will need to be pursued to ensure a decrease in drinking water nitrate concentration. At the pumping site scale, the influence and relationship between heterogeneous flow, mixing, and reactivity is not well understood. The purpose of this project is to incorporate both physical and chemical modeling techniques to better understand the effect of aquifer heterogeneities on autotrophic denitrification. We will investigate the link between heterogeneous hydraulic properties, transport, and the rate of autotrophic denitrification. Data collected in previous studies in laboratory experiments and pumping site scale experiments will be used to validate the models. The ultimate objective of this project is to develop a model in which such coupled processes are better understood resulting in best management practices of groundwater.
Distributional Scaling in Heterogeneous Aquifers
NASA Astrophysics Data System (ADS)
Polsinelli, J. F.
2015-12-01
An investigation is undertaken into the fractal scaling properties of the piezometric head in a heterogeneous unconfined aquifer. The governing equations for the unconfined flow are derived from conservation of mass and the Darcy law. The Dupuit approximation will be used to model the dynamics. The spatially varying nature of the tendency to conduct flow (e.g. the hydraulic conductivity) is represented as a stochastic process. Experimental studies in the literature have indicated that the conductivity belongs to a class of non-stationary stochastic fields, called H-ss fields. The uncertainty in the soil parameters is imparted onto the flow variables; in groundwater investigations the potentiometric head will be a random function. The structure of the head field will be analyzed with an emphasis on the scaling properties. The scaling scheme for the modeling equations and the simulation procedure for the saturated hydraulic conductivity process will be explained, then the method will be validated through numerical experimentation using the USGS Modflow-2005 software. The results of the numerical simulations demonstrate that the head will exhibit multi-fractal scaling if the hydraulic conductivity exhibits multi-fractal scaling and the differential equations for the groundwater equation satisfy a particular set of scale invariance conditions.
Shock Initiation of Heterogeneous Explosives
Reaugh, J E
2004-05-10
The fundamental picture that shock initiation in heterogeneous explosives is caused by the linking of hot spots formed at inhomogeneities was put forward by several researchers in the 1950's and 1960's, and more recently. Our work uses the computer hardware and software developed in the Advanced Simulation and Computing (ASC) program of the U.S. Department of Energy to explicitly include heterogeneities at the scale of the explosive grains and to calculate the consequences of realistic although approximate models of explosive behavior. Our simulations are performed with ALE-3D, a three-dimensional, elastic-plastic-hydrodynamic Arbitrary Lagrange-Euler finite-difference program, which includes chemical kinetics and heat transfer, and which is under development at this laboratory. We developed the parameter values for a reactive-flow model to describe the non-ideal detonation behavior of an HMX-based explosive from the results of grain-scale simulations. In doing so, we reduced the number of free parameters that are inferred from comparison with experiment to a single one - the characteristic defect dimension. We also performed simulations of the run to detonation in small volumes of explosive. These simulations illustrate the development of the reaction zone and the acceleration of the shock front as the flame fronts start from hot spots, grow, and interact behind the shock front. In this way, our grain-scale simulations can also connect to continuum experiments directly.
NASA Astrophysics Data System (ADS)
Pruhs, Kirk
A particularly important emergent technology is heterogeneous processors (or cores), which many computer architects believe will be the dominant architectural design in the future. The main advantage of a heterogeneous architecture, relative to an architecture of identical processors, is that it allows for the inclusion of processors whose design is specialized for particular types of jobs, and for jobs to be assigned to a processor best suited for that job. Most notably, it is envisioned that these heterogeneous architectures will consist of a small number of high-power high-performance processors for critical jobs, and a larger number of lower-power lower-performance processors for less critical jobs. Naturally, the lower-power processors would be more energy efficient in terms of the computation performed per unit of energy expended, and would generate less heat per unit of computation. For a given area and power budget, heterogeneous designs can give significantly better performance for standard workloads. Moreover, even processors that were designed to be homogeneous, are increasingly likely to be heterogeneous at run time: the dominant underlying cause is the increasing variability in the fabrication process as the feature size is scaled down (although run time faults will also play a role). Since manufacturing yields would be unacceptably low if every processor/core was required to be perfect, and since there would be significant performance loss from derating the entire chip to the functioning of the least functional processor (which is what would be required in order to attain processor homogeneity), some processor heterogeneity seems inevitable in chips with many processors/cores.
NASA Astrophysics Data System (ADS)
Ganjeh-Ghazvini, Mostafa; Masihi, Mohsen; Baghalha, Morteza
2015-10-01
The prediction of flow behavior in porous media can provide useful insights into the mechanisms involved in CO2 sequestration, petroleum engineering and hydrology. The multi-phase flow is usually simulated by solving the governing equations over an efficient model. The geostatistical (or fine grid) models are rarely used for simulation purposes because they have too many cells. A common approach is to coarsen a fine gird realization by an upscaling method. Although upscaling can speed up the flow simulation, it neglects the fine scale heterogeneity. The heterogeneity loss reduces the accuracy of simulation results. In this paper, the relation between heterogeneity loss during upscaling and accuracy of flow simulation is studied. A realization is divided into some clusters. Every cluster consists of a number of neighboring cells whose permeability values belong to a pre-known interval. The concept of coefficient of variation is applied to define the intra-cluster and inter-cluster heterogeneity numbers. These numbers are then calculated for some fine grid and corresponding upscaled models. The heterogeneous fine grid models are generated by the process of fractional Brownian motion. After simulating water-oil displacement in both fine and coarse models, the relation between flow performance error and heterogeneity loss is investigated. An upper limit for the degree of coarsening is also suggested according to this relation.
Multiscale hyporheic exchange through strongly heterogeneous sediments
NASA Astrophysics Data System (ADS)
Pryshlak, Timothy T.; Sawyer, Audrey H.; Stonedahl, Susa H.; Soltanian, Mohamad Reza
2015-11-01
Heterogeneity in hydraulic conductivity (K) and channel morphology both control surface water-groundwater exchange (hyporheic exchange), which influences stream ecosystem processes and biogeochemical cycles. Here we show that heterogeneity in K is the dominant control on exchange rates, residence times, and patterns in hyporheic zones with abrupt lithologic contrasts. We simulated hyporheic exchange in a representative low-gradient stream with 300 different bimodal K fields composed of sand and silt. Simulations span five sets of sand-silt ratios and two sets of low and high K contrasts (1 and 3 orders of magnitude). Heterogeneity increases interfacial flux by an order of magnitude relative to homogeneous cases, drastically changes the shape of residence time distributions, and decreases median residence times. The positioning of highly permeable sand bodies controls patterns of interfacial flux and flow paths. These results are remarkably different from previous studies of smooth, continuous K fields that indicate only moderate effects on hyporheic exchange. Our results also show that hyporheic residence times are least predictable when sand body connectivity is low. As sand body connectivity increases, the expected residence time distribution (ensemble average for a given sand-silt ratio) remains approximately constant, but the uncertainty around the expectation decreases. Including strong heterogeneity in hyporheic models is imperative for understanding hyporheic fluxes and solute transport. In streams with strongly heterogeneous sediments, characterizing lithologic structure is more critical for predicting hyporheic exchange metrics than characterizing channel morphology.
NASA Technical Reports Server (NTRS)
Liou, D. W.; Lee, W. M.
1972-01-01
New analytical tool is available to calculate the degree of foam heterogeneity based on the measurement of gas diffusivity values. Diffusion characteristics of plastic foam are described by a system of differential equations based on conventional diffusion theory. This approach saves research and computation time in studying mass or heat diffusion problems.
Heterogeneous waste processing
Vanderberg, Laura A.; Sauer, Nancy N.; Brainard, James R.; Foreman, Trudi M.; Hanners, John L.
2000-01-01
A combination of treatment methods are provided for treatment of heterogeneous waste including: (1) treatment for any organic compounds present; (2) removal of metals from the waste; and, (3) bulk volume reduction, with at least two of the three treatment methods employed and all three treatment methods emplyed where suitable.
Comparing Assayed Surface Heterogeneity Under Low Versus Maximum Attachment Conditions
NASA Astrophysics Data System (ADS)
Rasmuson, J. A.
2014-12-01
It has long been suspected that nanoscale heterogeneity is responsible for colloid attachment to surfaces under conditions unfavorable to attachment. Recently, mechanistic colloid force and torque simulations have been applied to arrays of experimental data to back out nanoscale heterogeneity that is representative of the collector surface. These recent experiments were performed under flowing conditions with limited colloid attachment. This presentation explores whether surface heterogeneity backed out from experiments performed under conditions designed to maximize attachment (e.g., non-flowing followed by elution) yields a characteristic heterogeneity that can be reproduced on surfaces backed out under other conditions. The nature of attachment under flowing vs. non-flowing conditions differed for large (2.0 μm) relative to small (0.25 μm) colloids. For example, the maximum loading of small colloids was the same under flowing conditions versus non-flowing conditions followed by elution. The maximum loading of large colloids however was much lower under flowing conditions relative to non-flowing conditions followed by elution. This difference indicates a mechanism contributing to the attachment of large colloids that is not included in mechanistic force and torque balances. These possible mechanisms are reviewed and strategies to incorporate them are discussed. The reproducibility of attachments and their spatial distribution will also be examined.
Altering Emulsion Stability with Heterogeneous Surface Wettability
Meng, Qiang; Zhang, Yali; Li, Jiang; Lammertink, Rob G. H.; Chen, Haosheng; Tsai, Peichun Amy
2016-01-01
Emulsions–liquid droplets dispersed in another immiscible liquid–are widely used in a broad spectrum of applications, including food, personal care, agrochemical, and pharmaceutical products. Emulsions are also commonly present in natural crude oil, hampering the production and quality of petroleum fuels. The stability of emulsions plays a crucial role in their applications, but controlling the stability without external driving forces has been proven to be difficult. Here we show how heterogeneous surface wettability can alter the stability and dynamics of oil-in-water emulsions, generated by a co-flow microfluidic device. We designed a useful methodology that can modify a micro-capillary of desired heterogeneous wettability (e.g., alternating hydrophilic and hydrophobic regions) without changing the hydraulic diameter. We subsequently investigated the effects of flow rates and heterogeneous wettability on the emulsion morphology and motion. The experimental data revealed a universal critical timescale of advective emulsions, above which the microfluidic emulsions remain stable and intact, whereas below they become adhesive or inverse. A simple theoretical model based on a force balance can be used to explain this critical transition of emulsion dynamics, depending on the droplet size and the Capillary number–the ratio of viscous to surface effects. These results give insight into how to control the stability and dynamics of emulsions in microfluidics with flow velocity and different wettability. PMID:27256703
Altering Emulsion Stability with Heterogeneous Surface Wettability
NASA Astrophysics Data System (ADS)
Meng, Qiang; Zhang, Yali; Li, Jiang; Lammertink, Rob G. H.; Chen, Haosheng; Tsai, Peichun Amy
2016-06-01
Emulsions–liquid droplets dispersed in another immiscible liquid–are widely used in a broad spectrum of applications, including food, personal care, agrochemical, and pharmaceutical products. Emulsions are also commonly present in natural crude oil, hampering the production and quality of petroleum fuels. The stability of emulsions plays a crucial role in their applications, but controlling the stability without external driving forces has been proven to be difficult. Here we show how heterogeneous surface wettability can alter the stability and dynamics of oil-in-water emulsions, generated by a co-flow microfluidic device. We designed a useful methodology that can modify a micro-capillary of desired heterogeneous wettability (e.g., alternating hydrophilic and hydrophobic regions) without changing the hydraulic diameter. We subsequently investigated the effects of flow rates and heterogeneous wettability on the emulsion morphology and motion. The experimental data revealed a universal critical timescale of advective emulsions, above which the microfluidic emulsions remain stable and intact, whereas below they become adhesive or inverse. A simple theoretical model based on a force balance can be used to explain this critical transition of emulsion dynamics, depending on the droplet size and the Capillary number–the ratio of viscous to surface effects. These results give insight into how to control the stability and dynamics of emulsions in microfluidics with flow velocity and different wettability.
Altering Emulsion Stability with Heterogeneous Surface Wettability.
Meng, Qiang; Zhang, Yali; Li, Jiang; Lammertink, Rob G H; Chen, Haosheng; Tsai, Peichun Amy
2016-01-01
Emulsions-liquid droplets dispersed in another immiscible liquid-are widely used in a broad spectrum of applications, including food, personal care, agrochemical, and pharmaceutical products. Emulsions are also commonly present in natural crude oil, hampering the production and quality of petroleum fuels. The stability of emulsions plays a crucial role in their applications, but controlling the stability without external driving forces has been proven to be difficult. Here we show how heterogeneous surface wettability can alter the stability and dynamics of oil-in-water emulsions, generated by a co-flow microfluidic device. We designed a useful methodology that can modify a micro-capillary of desired heterogeneous wettability (e.g., alternating hydrophilic and hydrophobic regions) without changing the hydraulic diameter. We subsequently investigated the effects of flow rates and heterogeneous wettability on the emulsion morphology and motion. The experimental data revealed a universal critical timescale of advective emulsions, above which the microfluidic emulsions remain stable and intact, whereas below they become adhesive or inverse. A simple theoretical model based on a force balance can be used to explain this critical transition of emulsion dynamics, depending on the droplet size and the Capillary number-the ratio of viscous to surface effects. These results give insight into how to control the stability and dynamics of emulsions in microfluidics with flow velocity and different wettability. PMID:27256703
Simulation of water flow in terrestrial systems
Energy Science and Technology Software Center (ESTSC)
2008-12-18
ParFlow is a parallel, variabley saturated groundwater flow code that is especially suitable for large scale problem. ParFlow simulates the three-dimensional saturated and variably saturated subsurface flow in heterogeneous porous media in three spatial dimensions. ParFlow's developemt and appkication has been on-ging for more than 10 uear. ParFlow has recently been extended to coupled surface-subsurface flow to enabel the simulation of hillslope runoff and channel routing in a truly integrated fashion. ParFlow simulates the three-dimensionalmore » varably saturated subsurface flow in strongly heterogeneous porous media in three spatial dimension.« less
NASA Astrophysics Data System (ADS)
Steinkamp, John A.
1984-09-01
Flow cytometry instrumentation developed from early efforts to count cells and particles in liquid suspension as they passed through a sensing device. Since the mid-1960's sophisticated instruments have been designed for analyzing cells based on various cytological, biochemical, and functional properties. These instruments have revolutionized automated cell analysis methods in that measurements are made at high speed, multiparameter data is correlated on each cell, statistical precision is high, and cells are separated in high purity from heterogeneous mixtures for identification and functional analysis. Advanced instruments capable of measuring cell volume, surface area, multicolor fluorescence, fluorescence polarization, light scatter within various angular regions, and axial light loss (extinction) at different wavelengths are being used in biomedical research for analyzing and sorting normal and abnormal cell populations. This article reviews the development of flow cytometers, the conceptual basis of flow measurements, and discusses some of the numerous applications of the technology in biology and medicine.
Heterogeneities in granular dynamics.
Mehta, A; Barker, G C; Luck, J M
2008-06-17
The absence of Brownian motion in granular media is a source of much complexity, including the prevalence of heterogeneity, whether static or dynamic, within a given system. Such strong heterogeneities can exist as a function of depth in a box of grains; this is the system we study here. First, we present results from three-dimensional, cooperative and stochastic Monte Carlo shaking simulations of spheres on heterogeneous density fluctuations. Next, we juxtapose these with results obtained from a theoretical model of a column of grains under gravity; frustration via competing local fields is included in our model, whereas the effect of gravity is to slow down the dynamics of successively deeper layers. The combined conclusions suggest that the dynamics of a real granular column can be divided into different phases-ballistic, logarithmic, activated, and glassy-as a function of depth. The nature of the ground states and their retrieval (under zero-temperature dynamics) is analyzed; the glassy phase shows clear evidence of its intrinsic ("crystalline") states, which lie below a band of approximately degenerate ground states. In the other three phases, by contrast, the system jams into a state chosen randomly from this upper band of metastable states. PMID:18541918
Atmospheric Heterogeneous Stereochemistry
NASA Astrophysics Data System (ADS)
Stokes, G. Y.; Buchbinder, A. M.; Geiger, F. M.
2009-12-01
This paper addresses the timescale and mechanism of heterogeneous interactions of laboratory models of organic-coated mineral dust and ozone. We are particularly interested in investigating the role of stereochemistry in heterogeneous oxidation reactions involving chiral biogenic VOCs. Using the surface-specific nonlinear optical spectroscopy, sum frequency generation, we tracked terpene diastereomers during exposure to 10^11 to 10^13 molecules of ozone per cm^3 in 1 atm helium to model ozone-limited and ozone-rich tropospheric conditions. Our kinetic data indicate that the diastereomers which orient their reactive C=C double bonds towards the gas phase exhibit heterogeneous ozonolysis rate constants that are two times faster than diastereomers that orient their C=C double bonds away from the gas phase. Insofar as our laboratory model studies are representative of real world environments, our studies suggest that the propensity of aerosol particles coated with chiral semivolatile organic compounds to react with ozone may depend on stereochemistry. Implications of these results for chiral markers that would allow for source appointment of anthropogenic versus biogenic carbon emissions will be discussed.
Shannan, Batool; Perego, Michela; Somasundaram, Rajasekharan; Herlyn, Meenhard
2016-01-01
Melanoma is among the most aggressive and therapy-resistant human cancers. While great strides in therapy have generated enthusiasm, many challenges remain. Heterogeneity is the most pressing issue for all types of therapy. This chapter summarizes the clinical classification of melanoma, of which the research community now adds additional layers of classifications for better diagnosis and prediction of therapy response. As the search for new biomarkers increases, we expect that biomarker analyses will be essential for all clinical trials to better select patient populations for optimal therapy. While individualized therapy that is based on extensive biomarker analyses is an option, we expect in the future genetic and biologic biomarkers will allow grouping of melanomas in such a way that we can predict therapy outcome. At this time, tumor heterogeneity continues to be the major challenge leading inevitably to relapse. To address heterogeneity therapeutically, we need to develop complex therapies that eliminate the bulk of the tumor and, at the same time, the critical subpopulations. PMID:26601857
Characterizing hydrogeologic heterogeneity using lithologic data
Flach, G.P.; Hamm, L.L.; Harris, M.K.; Thayer, P.A.; Haselow, J.S.; Smits, A.D.
1995-12-31
Large-scale (> 1 m) variability in hydraulic conductivity is usually the main influence on field-scale groundwater flow patterns and dispersive transport. Sediment lithologic descriptions and geophysical logs typically offer finer spatial resolution, and therefore more potential information about site-scale heterogeneity, than other site characterization data. In this study, a technique for generating a heterogeneous, three-dimensional hydraulic conductivity field from sediment lithologic descriptions is presented. The approach involves creating a three-dimensional, fine-scale representation of mud (silt + clay) percentage using a stratified interpolation algorithm. Mud percentage is then translated into horizontal and vertical conductivity using direct correlations derived from measured data and inverse groundwater flow modeling. Lastly, the fine-scale conductivity fields are averaged to create a coarser grid for use in groundwater flow and transport modeling. The approach is demonstrated using a finite-element groundwater flow model of a Savannah River Site solid radioactive and hazardous waste burial ground. Hydrostratigraphic units in the area consist of fluvial, deltaic, and shallow marine sand, mud and calcareous sediment that exhibit abrupt facies changes over short distances.
MULTIGRID HOMOGENIZATION OF HETEROGENEOUS POROUS MEDIA
Dendy, J.E.; Moulton, J.D.
2000-10-01
This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL); this report, however, reports on only two years research, since this project was terminated at the end of two years in response to the reduction in funding for the LDRD Program at LANL. The numerical simulation of flow through heterogeneous porous media has become a vital tool in forecasting reservoir performance, analyzing groundwater supply and predicting the subsurface flow of contaminants. Consequently, the computational efficiency and accuracy of these simulations is paramount. However, the parameters of the underlying mathematical models (e.g., permeability, conductivity) typically exhibit severe variations over a range of significantly different length scales. Thus the numerical treatment of these problems relies on a homogenization or upscaling procedure to define an approximate coarse-scale problem that adequately captures the influence of the fine-scale structure, with a resultant compromise between the competing objectives of computational efficiency and numerical accuracy. For homogenization in models of flow through heterogeneous porous media, We have developed new, efficient, numerical, multilevel methods, that offer a significant improvement in the compromise between accuracy and efficiency. We recently combined this approach with the work of Dvorak to compute bounded estimates of the homogenized permeability for such flows and demonstrated the effectiveness of this new algorithm with numerical examples.
Dealing with spatial heterogeneity
NASA Astrophysics Data System (ADS)
Marsily, Gh.; Delay, F.; Gonçalvès, J.; Renard, Ph.; Teles, V.; Violette, S.
2005-03-01
Heterogeneity can be dealt with by defining homogeneous equivalent properties, known as averaging, or by trying to describe the spatial variability of the rock properties from geologic observations and local measurements. The techniques available for these descriptions are mostly continuous Geostatistical models, or discontinuous facies models such as the Boolean, Indicator or Gaussian-Threshold models and the Markov chain model. These facies models are better suited to treating issues of rock strata connectivity, e.g. buried high permeability channels or low permeability barriers, which greatly affect flow and, above all, transport in aquifers. Genetic models provide new ways to incorporate more geology into the facies description, an approach that has been well developed in the oil industry, but not enough in hydrogeology. The conclusion is that future work should be focused on improving the facies models, comparing them, and designing new in situ testing procedures (including geophysics) that would help identify the facies geometry and properties. A world-wide catalog of aquifer facies geometry and properties, which could combine site genesis and description with methods used to assess the system, would be of great value for practical applications. On peut aborder le problème de l'hétérogénéité en s'efforçant de définir une perméabilité équivalente homogène, par prise de moyenne, ou au contraire en décrivant la variation dans l'espace des propriétés des roches à partir des observations géologiques et des mesures locales. Les techniques disponibles pour une telle description sont soit continues, comme l'approche Géostatistique, soit discontinues, comme les modèles de faciès, Booléens, ou bien par Indicatrices ou Gaussiennes Seuillées, ou enfin Markoviens. Ces modèles de faciès sont mieux capables de prendre en compte la connectivité des strates géologiques, telles que les chenaux enfouis à forte perméabilité, ou au contraire les faci
Dealing with spatial heterogeneity
NASA Astrophysics Data System (ADS)
Marsily, Gh.; Delay, F.; Gonçalvès, J.; Renard, Ph.; Teles, V.; Violette, S.
2005-03-01
Heterogeneity can be dealt with by defining homogeneous equivalent properties, known as averaging, or by trying to describe the spatial variability of the rock properties from geologic observations and local measurements. The techniques available for these descriptions are mostly continuous Geostatistical models, or discontinuous facies models such as the Boolean, Indicator or Gaussian-Threshold models and the Markov chain model. These facies models are better suited to treating issues of rock strata connectivity, e.g. buried high permeability channels or low permeability barriers, which greatly affect flow and, above all, transport in aquifers. Genetic models provide new ways to incorporate more geology into the facies description, an approach that has been well developed in the oil industry, but not enough in hydrogeology. The conclusion is that future work should be focused on improving the facies models, comparing them, and designing new in situ testing procedures (including geophysics) that would help identify the facies geometry and properties. A world-wide catalog of aquifer facies geometry and properties, which could combine site genesis and description with methods used to assess the system, would be of great value for practical applications. On peut aborder le problème de l'hétérogénéité en s'efforçant de définir une perméabilité équivalente homogène, par prise de moyenne, ou au contraire en décrivant la variation dans l'espace des propriétés des roches à partir des observations géologiques et des mesures locales. Les techniques disponibles pour une telle description sont soit continues, comme l'approche Géostatistique, soit discontinues, comme les modèles de faciès, Booléens, ou bien par Indicatrices ou Gaussiennes Seuillées, ou enfin Markoviens. Ces modèles de faciès sont mieux capables de prendre en compte la connectivité des strates géologiques, telles que les chenaux enfouis à forte perméabilité, ou au contraire les faci
Genetic Heterogeneity in Algerian Human Populations
Deba, Tahria; Calafell, Francesc; Benhamamouch, Soraya; Comas, David
2015-01-01
The demographic history of human populations in North Africa has been characterized by complex processes of admixture and isolation that have modeled its current gene pool. Diverse genetic ancestral components with different origins (autochthonous, European, Middle Eastern, and sub-Saharan) and genetic heterogeneity in the region have been described. In this complex genetic landscape, Algeria, the largest country in Africa, has been poorly covered, with most of the studies using a single Algerian sample. In order to evaluate the genetic heterogeneity of Algeria, Y-chromosome, mtDNA and autosomal genome-wide makers have been analyzed in several Berber- and Arab-speaking groups. Our results show that the genetic heterogeneity found in Algeria is not correlated with geography or linguistics, challenging the idea of Berber groups being genetically isolated and Arab groups open to gene flow. In addition, we have found that external sources of gene flow into North Africa have been carried more often by females than males, while the North African autochthonous component is more frequent in paternally transmitted genome regions. Our results highlight the different demographic history revealed by different markers and urge to be cautious when deriving general conclusions from partial genomic information or from single samples as representatives of the total population of a region. PMID:26402429
Heterogeneous Dynamics During Creep of Rod Containing Polymer Nanocomposites
NASA Astrophysics Data System (ADS)
Toepperwein, Gregory; Riggleman, Robert; de Pablo, Juan
2012-02-01
Polymer glasses exhibit regions of locally higher or lower mobility leading to heterogeneous dynamics. While heterogeneous dynamics have been examined in some detail in pure polymers, less is known about polymer nanocomposites (PNCs). We have previously studied PNCs, providing descriptions of how particles alter the network of entanglements, measuring local mechanical heterogeneity, demonstrating strain response under uniaxial deformation, and examining crazing and failure under multiaxial deformation. In the present work, we examine dynamic heterogeneity in rod-containing PNCs by performing creep deformation simulations and monitoring several measures of mobility. We are able to directly probe how dynamic heterogeneity evolves during deformation, and explore the origins of molecular mobility in polymer glasses. Examination of the segmental motion of a PNC undergoing creep reveals that the glassy heterogeneity of these systems decreases significantly following the onset of flow. It is found that the more heterogeneous distribution of relaxation times characteristic of PNCs in the bulk remains unaltered regardless of deformation state. It is found that the mobility and heterogeneity of PNCs are less susceptible to change upon deformation than those for the pure polymer.
Micromechanical modeling of heterogeneous energetic materials
Baer, M.R.; Kipp, M.E.; Swol, F. van
1998-09-01
In this work, the mesoscale processes of consolidation, deformation and reaction of shocked porous energetic materials are studied using shock physics analysis of impact on a collection of discrete HMX crystals. High resolution three-dimensional CTH simulations indicate that rapid deformation occurs at material contact points causing large amplitude fluctuations of stress states having wavelengths of the order of several particle diameters. Localization of energy produces hot-spots due to shock focusing and plastic work near grain boundaries as material flows to interstitial regions. These numerical experiments demonstrate that hot-spots are strongly influenced by multiple crystal interactions. Chemical reaction processes also produce multiple wave structures associated with particle distribution effects. This study provides new insights into the micromechanical behavior of heterogeneous energetic materials strongly suggesting that initiation and reaction of shocked heterogeneous materials involves states distinctly different than single jump state descriptions.
Scroll waves pinned to moving heterogeneities
NASA Astrophysics Data System (ADS)
Ke, Hua; Zhang, Zhihui; Steinbock, Oliver
2015-03-01
Three-dimensional excitable systems can self-organize vortex patterns that rotate around one-dimensional phase singularities called filaments. In experiments with the Belousov-Zhabotinsky reaction and numerical simulations, we pin these scroll waves to translating inert cylinders and demonstrate the controlled repositioning of their rotation centers. If the pinning site extends only along a portion of the filament, the phase singularity is stretched out along the trajectory of the heterogeneity, which effectively writes the singularity into the system. Its trailing end point follows the heterogeneity with a lower velocity. This velocity, its dependence on the placement of the anchor, and the shape of the filament are explained by a curvature flow model.
Heterogeneity in expected longevities.
Pijoan-Mas, Josep; Ríos-Rull, José-Víctor
2014-12-01
We develop a new methodology to compute differences in the expected longevity of individuals of a given cohort who are in different socioeconomic groups at a certain age. We address the two main problems associated with the standard use of life expectancy: (1) that people's socioeconomic characteristics change, and (2) that mortality has decreased over time. Our methodology uncovers substantial heterogeneity in expected longevities, yet much less heterogeneity than what arises from the naive application of life expectancy formulae. We decompose the longevity differences into differences in health at age 50, differences in the evolution of health with age, and differences in mortality conditional on health. Remarkably, education, wealth, and income are health-protecting but have very little impact on two-year mortality rates conditional on health. Married people and nonsmokers, however, benefit directly in their immediate mortality. Finally, we document an increasing time trend of the socioeconomic gradient of longevity in the period 1992-2008, and we predict an increase in the socioeconomic gradient of mortality rates for the coming years. PMID:25391225
Biclustering with heterogeneous variance.
Chen, Guanhua; Sullivan, Patrick F; Kosorok, Michael R
2013-07-23
In cancer research, as in all of medicine, it is important to classify patients into etiologically and therapeutically relevant subtypes to improve diagnosis and treatment. One way to do this is to use clustering methods to find subgroups of homogeneous individuals based on genetic profiles together with heuristic clinical analysis. A notable drawback of existing clustering methods is that they ignore the possibility that the variance of gene expression profile measurements can be heterogeneous across subgroups, and methods that do not consider heterogeneity of variance can lead to inaccurate subgroup prediction. Research has shown that hypervariability is a common feature among cancer subtypes. In this paper, we present a statistical approach that can capture both mean and variance structure in genetic data. We demonstrate the strength of our method in both synthetic data and in two cancer data sets. In particular, our method confirms the hypervariability of methylation level in cancer patients, and it detects clearer subgroup patterns in lung cancer data. PMID:23836637
Heterogeneous broadband network
NASA Astrophysics Data System (ADS)
Dittmann, Lars
1995-11-01
Although the vision for the future Integrated Broadband Communication Network (IBCN) is an all optical network, it is certain that for a long period to come, the network will remain very heterogeneous, with a mixture of different physical media (fiber, coax and twisted pair), transmission systems (PDH, SDH, ADSL) and transport protocols (TCP/IP, AAL/ATM, frame relay). In the current work towards the IBCN, the ATM concept is considered the generic network protocol for both public and private network, with the ability to use different underlying transmission protocols and, through adaptation protocols, provide the appropriate services (old as well as new) to the customer. One of the major difficulties of heterogeneous network is the restriction that is usually given by the lowest common denominator, e.g. in terms of single channel capacity. A possible way to overcome these limitations is by extending the ATM concept with a multilink capability, that allows us to use separate resources as one common. The improved flexibility obtained by this protocol extension further allows a real time optimization of network and call configuration, without any impact on the quality of service seen from the user. This paper describes an example of an ATM based multilink protocol that has been experimentally implemented within the RACE project 'STRATOSPHERIC'. The paper outlines the complexity of introducing an extra network functionality compared with the added value, such as an improved ability to recover an error due to a malfunctioning network component.
Seismoelectric effects caused by mesoscopic heterogeneities
NASA Astrophysics Data System (ADS)
Germán Rubino, J.; Jougnot, Damien; Rosas Carbajal, Marina; Linde, Niklas; Holliger, Klaus
2013-04-01
When a seismic wave propagates through a fluid saturated porous medium, it produces a relative motion between the fluid phase and the rock matrix. In the presence of an electric double layer at the fluid-solid interface, this movement introduces a separation of electrical charges which in turn generates a time-varying electrical source current and a resulting distribution of electrical potential. The presence of mesoscopic heterogeneities, that is, heterogeneities having sizes larger than the typical pore size but smaller than the prevailing wavelength, can induce a significant oscillatory fluid flow in response to the propagation of seismic waves. Indeed, the energy dissipation related to this phenomenon is considered to be one of the most common and important seismic attenuation mechanisms operating in the shallow part of the crust. Given that the amount of fluid flow produced by this phenomenon can be significant, a potentially important seismoelectric signal is also expected in such media. However, to the best of the authors' knowledge, the role played by mesoscopic wave-induced fluid flow on seismoelectric phenomenon is so far largely unexplored. In this work, we propose a numerical approach for computing seismoelectric signals related to the presence of mesoscopic heterogeneities. To this end, we consider a two-dimensional representative rock sample containing mesoscopic heterogeneities and apply an oscillatory compression on its top boundary. The solid phase is neither allowed to move on the bottom boundary nor to have horizontal displacements on the lateral boundaries and the fluid is not allowed to flow into or out of the sample. The fluid velocity field is determined by solving the quasi-static poroelastic equations in the space-frequency domain under the governing boundary conditions. Next, the seismoelectric conversion is calculated using the so-called effective electrical excess charge approach, which has been recently developed in streaming potential
Large epidemic thresholds emerge in heterogeneous networks of heterogeneous nodes
NASA Astrophysics Data System (ADS)
Yang, Hui; Tang, Ming; Gross, Thilo
2015-08-01
One of the famous results of network science states that networks with heterogeneous connectivity are more susceptible to epidemic spreading than their more homogeneous counterparts. In particular, in networks of identical nodes it has been shown that network heterogeneity, i.e. a broad degree distribution, can lower the epidemic threshold at which epidemics can invade the system. Network heterogeneity can thus allow diseases with lower transmission probabilities to persist and spread. However, it has been pointed out that networks in which the properties of nodes are intrinsically heterogeneous can be very resilient to disease spreading. Heterogeneity in structure can enhance or diminish the resilience of networks with heterogeneous nodes, depending on the correlations between the topological and intrinsic properties. Here, we consider a plausible scenario where people have intrinsic differences in susceptibility and adapt their social network structure to the presence of the disease. We show that the resilience of networks with heterogeneous connectivity can surpass those of networks with homogeneous connectivity. For epidemiology, this implies that network heterogeneity should not be studied in isolation, it is instead the heterogeneity of infection risk that determines the likelihood of outbreaks.
NASA Astrophysics Data System (ADS)
Zheng, Y.; Liu, Q.; Li, Y.
2012-03-01
Solids moving with a gas stream in a pipeline can be found in many industrial processes, such as power generation, chemical, pharmaceutical, food and commodity transfer processes. A mass flow rate of the solids is important characteristic that is often required to be measured (and controlled) to achieve efficient utilization of energy and raw materials in pneumatic conveying systems. The methods of measuring the mass flow rate of solids in a pneumatic pipeline can be divided into direct and indirect (inferential) measurements. A thermal solids' mass flow-meter, in principle, should ideally provide a direct measurement of solids flow rate, regardless of inhomogeneities in solids' distribution and environmental impacts. One key issue in developing a thermal solids' mass flow-meter is to characterize the heat transfer between the hot pipe wall and the gas-solids dense phase flow. The Eulerian continuum modeling with gas-solid two phases is the most common method for pneumatic transport. To model a gas-solid dense phase flow passing through a heated region, the gas phase is described as a continuous phase and the particles as the second phase. This study aims to describe the heat transfer characteristics between the hot wall and the gas-solids dense phase flow in pneumatic pipelines by modeling a turbulence gas-solid plug passing through the heated region which involves several actual and crucial issues: selections of interphase exchange coefficient, near-wall region functions and different wall surface temperatures. A sensitivity analysis was discussed to identify the influence on the heat transfer characteristics by selecting different interphase exchange coefficient models and different boundary conditions. Simulation results suggest that sensitivity analysis in the choice of models is very significant. The simulation results appear to show that a combination of choosing the Syamlal-O'Brien interphase exchange coefficient model and the standard k-ɛ model along with
Disordered hyperuniform heterogeneous materials.
Torquato, Salvatore
2016-10-19
Disordered hyperuniform many-body systems are distinguishable states of matter that lie between a crystal and liquid: they are like perfect crystals in the way they suppress large-scale density fluctuations and yet are like liquids or glasses in that they are statistically isotropic with no Bragg peaks. These systems play a vital role in a number of fundamental and applied problems: glass formation, jamming, rigidity, photonic and electronic band structure, localization of waves and excitations, self-organization, fluid dynamics, quantum systems, and pure mathematics. Much of what we know theoretically about disordered hyperuniform states of matter involves many-particle systems. In this paper, we derive new rigorous criteria that disordered hyperuniform two-phase heterogeneous materials must obey and explore their consequences. Two-phase heterogeneous media are ubiquitous; examples include composites and porous media, biological media, foams, polymer blends, granular media, cellular solids, and colloids. We begin by obtaining some results that apply to hyperuniform two-phase media in which one phase is a sphere packing in d-dimensional Euclidean space [Formula: see text]. Among other results, we rigorously establish the requirements for packings of spheres of different sizes to be 'multihyperuniform'. We then consider hyperuniformity for general two-phase media in [Formula: see text]. Here we apply realizability conditions for an autocovariance function and its associated spectral density of a two-phase medium, and then incorporate hyperuniformity as a constraint in order to derive new conditions. We show that some functional forms can immediately be eliminated from consideration and identify other forms that are allowable. Specific examples and counterexamples are described. Contact is made with well-known microstructural models (e.g. overlapping spheres and checkerboards) as well as irregular phase-separation and Turing-type patterns. We also ascertain a family
J. Helble; Clara Smith; David Miller
2009-08-31
The overall goal of this project was to produce a working dynamic model to predict the transformation and partitioning of trace metals resulting from combustion of a broad range of fuels. The information provided from this model will be instrumental in efforts to identify fuels and conditions that can be varied to reduce metal emissions. Through the course of this project, it was determined that mercury (Hg) and arsenic (As) would be the focus of the experimental investigation. Experiments were therefore conducted to examine homogeneous and heterogeneous mercury oxidation pathways, and to assess potential interactions between arsenic and calcium. As described in this report, results indicated that the role of SO{sub 2} on Hg oxidation was complex and depended upon overall gas phase chemistry, that iron oxide (hematite) particles contributed directly to heterogeneous Hg oxidation, and that As-Ca interactions occurred through both gas-solid and within-char reaction pathways. Modeling based on this study indicated that, depending upon coal type and fly ash particle size, vaporization-condensation, vaporization-surface reaction, and As-CaO in-char reaction all play a role in arsenic transformations under combustion conditions.
[Neutrophilic functional heterogeneity].
2006-02-01
Blood neutrophilic functional heterogeneity is under discussion. The neutrophils of one subpopulation, namely killer neutrophils (Nk), potential phagocytes, constitute a marginal pool and a part of the circulating pool, intensively produce active oxygen forms (AOF) and they are adherent to the substrate. The neutrophils of another subpopulation, cager neutrophils (Nc), seem to perform a transport function of delivering foreign particles to the competent organs, to form about half of the circulating pool, to produce APC to a lesser extent, exclusively for self-defense and, probably, in usual conditions, to fail to interact with substrate. Analysis of the experimental findings suggests that the phylogenetic age of Nk is older than that of Nc and Nk has predominantly a tendency to spontaneous apoptosis under physiological conditions. PMID:16610631
Multipartite entanglement in heterogeneous systems
NASA Astrophysics Data System (ADS)
Goyeneche, Dardo; Bielawski, Jakub; Życzkowski, Karol
2016-07-01
Heterogeneous bipartite quantum pure states, composed of two subsystems with a different number of levels, cannot have both reductions maximally mixed. In this work, we demonstrate the existence of a wide range of highly entangled states of heterogeneous multipartite systems consisting of N >2 parties such that every reduction to one and two parties is maximally mixed. Two constructions of generating genuinely multipartite maximally entangled states of heterogeneous systems for an arbitrary number of subsystems are presented. Such states are related to quantum error correction codes over mixed alphabets and mixed orthogonal arrays. Additionally, we show the advantages of considering heterogeneous systems in practical implementations of multipartite steering.
Interconnecting heterogeneous database management systems
NASA Technical Reports Server (NTRS)
Gligor, V. D.; Luckenbaugh, G. L.
1984-01-01
It is pointed out that there is still a great need for the development of improved communication between remote, heterogeneous database management systems (DBMS). Problems regarding the effective communication between distributed DBMSs are primarily related to significant differences between local data managers, local data models and representations, and local transaction managers. A system of interconnected DBMSs which exhibit such differences is called a network of distributed, heterogeneous DBMSs. In order to achieve effective interconnection of remote, heterogeneous DBMSs, the users must have uniform, integrated access to the different DBMs. The present investigation is mainly concerned with an analysis of the existing approaches to interconnecting heterogeneous DBMSs, taking into account four experimental DBMS projects.
A heterogeneous multiscale method for poroelasticity
NASA Astrophysics Data System (ADS)
Delgado, Paul M.
In this thesis, we develop and analyze a heterogeneous multiscale model for coupled fluid flow and solid deformation in porous media based on operator splitting and finite volume method. The splitting method results in two elliptic multiscale PDE's in the form of a reaction diffusion equation and a linear elasticity equation. We extend our previous multiscale method from 1D to higher dimensions and develop new approaches for the inclusion of mixed boundary conditions and source terms. We derive an error estimate for our multiscale method and analyze the stability of our splitting method. We also test the effectiveness of our method in the case of steady state linear poroelasticity.
Methods for Characterizing the Co-development of Biofilm and Habitat Heterogeneity
Li, Xiaobao; Song, Jisun L.; Culotti, Alessandro; Zhang, Wei; Chopp, David L.; Lu, Nanxi; Packman, Aaron I.
2016-01-01
Biofilms are surface-attached microbial communities that have complex structures and produce significant spatial heterogeneities. Biofilm development is strongly regulated by the surrounding flow and nutritional environment. Biofilm growth also increases the heterogeneity of the local microenvironment by generating complex flow fields and solute transport patterns. To investigate the development of heterogeneity in biofilms and interactions between biofilms and their local micro-habitat, we grew mono-species biofilms of Pseudomonas aeruginosa and dual-species biofilms of P. aeruginosa and Escherichia coli under nutritional gradients in a microfluidic flow cell. We provide detailed protocols for creating nutrient gradients within the flow cell and for growing and visualizing biofilm development under these conditions. We also present protocols for a series of optical methods to quantify spatial patterns in biofilm structure, flow distributions over biofilms, and mass transport around and within biofilm colonies. These methods support comprehensive investigations of the co-development of biofilm and habitat heterogeneity. PMID:25866914
Methods for characterizing the co-development of biofilm and habitat heterogeneity.
Li, Xiaobao; Song, Jisun L; Culotti, Alessandro; Zhang, Wei; Chopp, David L; Lu, Nanxi; Packman, Aaron I
2015-01-01
Biofilms are surface-attached microbial communities that have complex structures and produce significant spatial heterogeneities. Biofilm development is strongly regulated by the surrounding flow and nutritional environment. Biofilm growth also increases the heterogeneity of the local microenvironment by generating complex flow fields and solute transport patterns. To investigate the development of heterogeneity in biofilms and interactions between biofilms and their local micro-habitat, we grew mono-species biofilms of Pseudomonas aeruginosa and dual-species biofilms of P. aeruginosa and Escherichia coli under nutritional gradients in a microfluidic flow cell. We provide detailed protocols for creating nutrient gradients within the flow cell and for growing and visualizing biofilm development under these conditions. We also present protocols for a series of optical methods to quantify spatial patterns in biofilm structure, flow distributions over biofilms, and mass transport around and within biofilm colonies. These methods support comprehensive investigations of the co-development of biofilm and habitat heterogeneity. PMID:25866914
Symonds, R.B. ); Reed, M.H. )
1993-10-01
This paper documents the numerical formulations, thermochemical data base, and possible applications of computer programs, SOLVGAS and GASWORKS, for calculating multicomponent chemical equilibria in gas-solid-liquid systems. SOLVGAS and GASWORKS compute simultaneous equilibria by solving simultaneously a set of mass balance and mass action equations written for all gas species and for all gas-solid or gas-liquid equilibria. The programs interface with a thermo-chemical data base, GASTHERM, which contains coefficients for retrieval of the equilibrium constants from 25[degrees] to 1200[degrees]C. The programs and data base model dynamic chemical processes in 30- to 40-component volcanic-gas systems. The authors can model gas evaporation from magma, mixing of magmatic and hydrothermal gases, precipitation of minerals during pressure and temperature decrease, mixing of volcanic gas with air, and reaction of gases with wall rock. Examples are given of the gas-evaporation-from-magma and precipitation-with-cooling calculations for volcanic gases collected from Mt. St. Helens in September 1981. The authors predict: (1) the amounts of trace elements volatilized from shallow magma, deep magma, and wall rock, and (2) the solids that precipitate from the gas upon cooling. The predictions are tested by comparing them with the measured trace-element concentrations in gases and the observed sublimate sequence. This leads to the following conclusions: (1) most of the trace elements in the Mt. St. Helens gases are volatilized from shallow magma as simple chlorides; (2) some elements (for example, Al, Ca) exist dominantly in rock aerosols, not gases, in the gas stream; (3) near-surface cooling of the gases triggers precipitation of oxides, sulfides, halides, tungstates, and native elements; and (4) equilibrium cooling of the gases to 100[degrees]C causes most trace elements, except for Hg, Sb, and Se, to precipitate from the gas. 94 refs., 30 figs., 7 tabs.
Bias of apparent tracer ages in heterogeneous environments.
McCallum, James L; Cook, Peter G; Simmons, Craig T; Werner, Adrian D
2014-01-01
The interpretation of apparent ages often assumes that a water sample is composed of a single age. In heterogeneous aquifers, apparent ages estimated with environmental tracer methods do not reflect mean water ages because of the mixing of waters from many flow paths with different ages. This is due to nonlinear variations in atmospheric concentrations of the tracer with time resulting in biases of mixed concentrations used to determine apparent ages. The bias of these methods is rarely reported and has not been systematically evaluated in heterogeneous settings. We simulate residence time distributions (RTDs) and environmental tracers CFCs, SF6 , (85) Kr, and (39) Ar in synthetic heterogeneous confined aquifers and compare apparent ages to mean ages. Heterogeneity was simulated as both K-field variance (σ(2) ) and structure. We demonstrate that an increase in heterogeneity (increase in σ(2) or structure) results in an increase in the width of the RTD. In low heterogeneity cases, widths were generally on the order of 10 years and biases generally less than 10%. In high heterogeneity cases, widths can reach 100 s of years and biases can reach up to 100%. In cases where the temporal variations of atmospheric concentration of individual tracers vary, different patterns of bias are observed for the same mean age. We show that CFC-12 and CFC-113 ages may be used to correct for the mean age if analytical errors are small. PMID:23550995
SIMULATING VENTILATION DISTRIBUTION IN HETEROGENOUS LUNG INJURY USING A BINARY TREE DATA STRUCTURE
Colletti, Ashley A.; Amini, Reza; Kaczka, David W.
2011-01-01
To determine the impact of mechanical heterogeneity on the distribution of regional flows and pressures in the injured lung, we developed an anatomic model of the canine lung comprised of an asymmetric branching airway network which can be stored as binary tree data structure. The entire tree can be traversed using a recursive flow divider algorithm, allowing for efficient computation of acinar flow and pressure distributions in a mechanically heterogeneous lung. These distributions were found to be highly dependent on ventilation frequency and the heterogeneity of tissue elastances, reflecting the preferential distribution of ventilation to areas of lower regional impedance. PMID:21872852
Heterogeneous nanofluids: natural convection heat transfer enhancement
2011-01-01
Convective heat transfer using different nanofluid types is investigated. The domain is differentially heated and nanofluids are treated as heterogeneous mixtures with weak solutal diffusivity and possible Soret separation. Owing to the pronounced Soret effect of these materials in combination with a considerable solutal expansion, the resulting solutal buoyancy forces could be significant and interact with the initial thermal convection. A modified formulation taking into account the thermal conductivity, viscosity versus nanofluids type and concentration and the spatial heterogeneous concentration induced by the Soret effect is presented. The obtained results, by solving numerically the full governing equations, are found to be in good agreement with the developed solution based on the scale analysis approach. The resulting convective flows are found to be dependent on the local particle concentration φ and the corresponding solutal to thermal buoyancy ratio N. The induced nanofluid heterogeneity showed a significant heat transfer modification. The heat transfer in natural convection increases with nanoparticle concentration but remains less than the enhancement previously underlined in forced convection case. PMID:21711755
Heterogeneous nanofluids: natural convection heat transfer enhancement.
Oueslati, Fakhreddine Segni; Bennacer, Rachid
2011-01-01
Convective heat transfer using different nanofluid types is investigated. The domain is differentially heated and nanofluids are treated as heterogeneous mixtures with weak solutal diffusivity and possible Soret separation. Owing to the pronounced Soret effect of these materials in combination with a considerable solutal expansion, the resulting solutal buoyancy forces could be significant and interact with the initial thermal convection. A modified formulation taking into account the thermal conductivity, viscosity versus nanofluids type and concentration and the spatial heterogeneous concentration induced by the Soret effect is presented. The obtained results, by solving numerically the full governing equations, are found to be in good agreement with the developed solution based on the scale analysis approach. The resulting convective flows are found to be dependent on the local particle concentration φ and the corresponding solutal to thermal buoyancy ratio N. The induced nanofluid heterogeneity showed a significant heat transfer modification. The heat transfer in natural convection increases with nanoparticle concentration but remains less than the enhancement previously underlined in forced convection case. PMID:21711755
Heterogeneous nanofluids: natural convection heat transfer enhancement
NASA Astrophysics Data System (ADS)
Oueslati, Fakhreddine Segni; Bennacer, Rachid
2011-12-01
Convective heat transfer using different nanofluid types is investigated. The domain is differentially heated and nanofluids are treated as heterogeneous mixtures with weak solutal diffusivity and possible Soret separation. Owing to the pronounced Soret effect of these materials in combination with a considerable solutal expansion, the resulting solutal buoyancy forces could be significant and interact with the initial thermal convection. A modified formulation taking into account the thermal conductivity, viscosity versus nanofluids type and concentration and the spatial heterogeneous concentration induced by the Soret effect is presented. The obtained results, by solving numerically the full governing equations, are found to be in good agreement with the developed solution based on the scale analysis approach. The resulting convective flows are found to be dependent on the local particle concentration φ and the corresponding solutal to thermal buoyancy ratio N. The induced nanofluid heterogeneity showed a significant heat transfer modification. The heat transfer in natural convection increases with nanoparticle concentration but remains less than the enhancement previously underlined in forced convection case.
Energetics of hydrothermal convection in heterogeneous ocean crust
NASA Astrophysics Data System (ADS)
Ruepke, Lars; Hasenclever, Joerg; Andersen, Christine
2015-04-01
Recent advances in hydrothermal flow modeling have revealed the key thermodynamic and fluid-dynamic controls on hydrothermal convection and vent temperatures at oceanic spreading centers. The observed upper limit to black smoker vent temperatures of approx. 400°C can be explained by the thermodynamic properties of water (Jupp and Schultz, 2000). Likewise, 3D models of hydrothermal flow at fast-spreading ridges show cylindrical upwellings with closely interwoven recharge flow (Coumou et al., 2008, Hasenclever et al., 2014). While these studies provide a robust theoretical basis for hydrothermal flow observations at fast-spreading ridges, the situation at slow-spreading ridges is different. The slow-spreading Mid-Atlantic Ridge produces highly heterogeneous crust along its tectonic and magmatic segments with significant permeability contrasts across structural and lithological interfaces. The sub-seafloor permeability structure has a strong control on vent field location such that off-axis hydrothermal systems are apparently consistently located at outcropping fault zones. We have recently shown that preferential flow along high-permeability conduits inevitably leads to the entrainment of cold ambient seawater (Andersen et al., 2014), which causes a temperature drop that is difficult to reconcile with fault-related high-temperature venting. A fundamental question is therefore how hydrothermal fluids can maintain their high temperature while flowing kilometers from a driving heat source through highly heterogeneous crust to a vent site at the seafloor? We address this question by exploring the energetics of hydrothermal convection in heterogeneous ocean crust using 2D and 3D flow simulations. In our analysis we focus on the energy balance of rising hydrothermal plumes and on mixing processes at permeability boundaries, with the aim to establish a more robust theoretical framework for hydrothermal flow through highly heterogeneous seafloor.
Physical mechanisms of flow resistance in textured microchannels
NASA Astrophysics Data System (ADS)
Game, Simon; Papageorgiou, Demetrios; Keaveny, Eric; Hodes, Marc
2015-11-01
Transport in microchannels can be enhanced by replacing flat, no-slip boundaries with boundaries etched with longitudinal grooves containing an inert gas, resulting in an effective slip flow. Various physical considerations which are often omitted from mathematical models play a significant role in the behaviour of this flow. Such considerations include: gas viscosity, meniscus curvature, finite channel cross-sections, molecular slip on the gas/liquid or gas/solid interfaces. Using a computationally efficient, multi-element, Chebyshev collocation method, we are able to quantify and combine each of these physical effects. We have shown that for physically realistic parameter values, including each of these effects significantly alters the volumetric flow rate, and hence these effects should not be ignored. Using this framework, we hope to manipulate these effects in order to minimise the flow resistance of the channel.
Political Jurisdictions in Heterogeneous Communities.
ERIC Educational Resources Information Center
Alesina, Alberto; Baqir, Reza; Hoxby, Caroline
2004-01-01
We investigate whether political jurisdictions form in response to the trade-off between economies of scale and the costs of a heterogeneous population. We consider heterogeneity in income, race, ethnicity, and religion, and we test the model using American school districts, school attendance areas, municipalities, and special districts. We find…
Biomarker Discovery for Heterogeneous Diseases
Wallstrom, Garrick; Anderson, Karen S.; LaBaer, Joshua
2013-01-01
Background Modern genomic and proteomic studies reveal that many diseases are heterogeneous, comprising multiple different subtypes. The common notion that one biomarker can be predictive for all patients may need to be replaced by an understanding that each subtype has its own set of unique biomarkers, affecting how discovery studies are designed and analyzed. Methods We used Monte Carlo simulation to measure and compare the performance of eight selection methods with homogeneous and heterogeneous diseases using both single-stage and two-stage designs. We also applied the selection methods in an actual proteomic biomarker screening study of heterogeneous breast cancer cases. Results Different selection methods were optimal and more than 2-fold larger sample sizes were needed for heterogeneous diseases compared with homogeneous diseases. We also found that for larger studies, two-stage designs can achieve nearly the same statistical power as single-stage designs at significantly reduced cost. Conclusions We found that disease heterogeneity profoundly affected biomarker performance. We report sample size requirements and provide guidance on the design and analysis of biomarker discovery studies for both homogeneous and heterogeneous diseases. Impact We have shown that studies to identify biomarkers for the early detection of heterogeneous disease require different statistical selection methods and larger sample sizes than if the disease were homogeneous. These findings provide a methodological platform for biomarker discovery of heterogeneous diseases. PMID:23462916
NASA Astrophysics Data System (ADS)
Litvinova, T.; Petrova, A.
2009-04-01
The study of magnetic anomaly field structure of the Barents Sea water area along seismic and extended profiles intersecting known fields is carried out. Geomagnetic and density sections down to 40 km depth are constructed. This allowed the estimation of heterogeneities of the Barents Sea water area deep structure. The analysis of geomagnetic and density sections along extended profiles showed the confinedness of oil-and-gas bearing provinces to deep permeable zones characterized by reduced magnetic and density features. Based on the analysis of permeable zones, regional diagnostic features similar to those obtained earlier in oil-and-gas bearing provinces in other regions, for example, in Timan-Pechora, Volga-Urals and Siberian, as well as in the Northern and Norwegian seas water areas, are revealed. The analysis of magnetic and gravity fields over the region area allowed the delineation of weakened zones as intersection areas of weakly magnetic areals with reduced density. Within the Barents Sea water area, permeable areas with lenticular-laminated structure of the upper and lower Earth's crust containing weakly magnetic areals with reduced rock density within the depth range of 8-12 and 15-20 km are revealed. Such ratio of magnetic and density heterogeneities in the Earth's crust is characteristic for zones with proved oil-and-gas content in the European part of the Atlantic Ocean water area. North Kildin field on 1 AR profile is confined to a trough with thick weakly magnetic stratum discontinuously traced to a depth of 6-10 km. At a depth of approximately 15 km, a lens of weakly magnetic and porous formations is observed. Ludlov field in the North Barents trough is confined to a zone of weakly magnetic rocks with reduced density traced to a depth of 8-9 km. Deeper, at Н=15 km, a lenticular areal of weakly magnetic formations with reduced density is observed. The profile transecting the Stockman field shows that it is located in the central part of a permeable
Two-Phase Flow Simulations through Experimentally Studied Porous Media Analogies
Crandall, D.M.; Ahmadi, G.; Smith, D.H.
2007-07-01
of the fluids were shown to affect the percent of displaced fluid, with lower capillary number and higher viscosity ratio displacing a greater amount of the wetting fluid. Displacement of a non-wetting, in-place fluid by a less viscous, wetting fluid (the case of imbibition; contact angle > 90°) is then studied with the numerical model. The invading fluid is shown to preferentially move into small throats and displace a larger percent of the in-place fluid than observed in the drainage case. The interface was also observed to have a higher fractal dimension, closer to 2. These results highlight the potential for greater fundamental understanding of liquid-gas-solid interactions in heterogeneous, porous media that can be obtained from computational fluid dynamics (CFD). Situations, which are difficult to experimentally study, can be examined with CFD in a manner that more accurately accounts for the geological conditions relevant to CO2 sequestration. This allows for greater accuracy in the prediction of storage capacity within known geological structures. This study shows that as the contact angle between the invading fluid and the defending fluid increase, a greater portion of the porous medium is invaded. Thus, a greater portion of CO2 can be sequestered in reservoirs that are not strongly water wet. Low flow rates are shown to increase the final percent saturation of the invading fluid as well, regardless of wetting conditions.
Spatial heterogeneity in the heart: recent insights and open questions.
Decking, Ulrich K M
2002-12-01
Within the left ventricular myocardium and despite its rather homogeneous structure, local myocardial perfusion varies substantially. Areas of low and high local flow differ with regard to substrate uptake, energy turnover, and demand. This spatial heterogeneity is related to distinct differences in local protein expression, forming the basis of a novel homeostatic mechanism. PMID:12433979
Meichtry, Jorge M; Dillert, Ralf; Bahnemann, Detlef W; Litter, Marta I
2015-06-01
The dynamics of the transfer of electrons stored in TiO2 nanoparticles to Cr(VI) in aqueous solution have been investigated using the stopped flow technique. TiO2 nanoparticles were previously irradiated under UV light in the presence of formic acid, and trapped electrons (e(trap)(-)) were made to react with Cr(VI) as acceptor species; other common acceptor species such as O2 and H2O2 were also tested. The temporal evolution of the number of trapped electrons was followed by the decrease in the absorbance at 600 nm, and the kinetics of the electron-transfer reaction was modeled. Additionally, the rate of formation of the surface complex between Cr(VI) and TiO2 was determined with the stopped flow technique by following the evolution of the absorbance at 400 nm of suspensions of nonirradiated TiO2 nanoparticles and Cr(VI) at different concentrations. An approximately quadratic relationship was observed between the maximum absorbance of the surface complex and the concentration of Cr(VI), suggesting that Cr(VI) adsorbs onto the TiO2 surface as dichromate. The kinetic analyses indicate that the electron transfer from TiO2 to Cr(VI) does not require the previous formation of the Cr(VI)-TiO2 surface complex, at least the complex detected here through the stopped flow experiments. When previously irradiated TiO2 was used to follow the evolution of the Cr(VI)-TiO2 complex, an inhibition of the formation of the complex was observed, which can be related to the TiO2 deactivation caused by Cr(III) deposition. PMID:25974749
Angiotensin II receptor heterogeneity
Herblin, W.F.; Chiu, A.T.; McCall, D.E.; Ardecky, R.J.; Carini, D.J.; Duncia, J.V.; Pease, L.J.; Wong, P.C.; Wexler, R.R.; Johnson, A.L. )
1991-04-01
The possibility of receptor heterogeneity in the angiotensin II (AII) system has been suggested previously, based on differences in Kd values or sensitivity to thiol reagents. One of the authors earliest indications was the frequent observation of incomplete inhibition of the binding of AII to adrenal cortical membranes. Autoradiographic studies demonstrated that all of the labeling of the rat adrenal was blocked by unlabeled AII or saralasin, but not by DuP 753. The predominant receptor in the rat adrenal cortex (80%) is sensitive to dithiothreitol (DTT) and DuP 753, and is designated AII-1. The residual sites in the adrenal cortex and almost all of the sites in the rat adrenal medulla are insensitive to both DTT and DuP 753, but were blocked by EXP655. These sites have been confirmed by ligand binding studies and are designated AII-2. The rabbit adrenal cortex is unique in yielding a nonuniform distribution of AII-2 sites around the outer layer of glomerulosa cells. In the rabbit kidney, the sites on the glomeruli are AII-1, but the sites on the kidney capsule are AII-2. Angiotensin III appears to have a higher affinity for AII-2 sites since it inhibits the binding to the rabbit kidney capsule but not the glomeruli. Elucidation of the distribution and function of these diverse sites should permit the development of more selective and specific therapeutic strategies.
NASA Astrophysics Data System (ADS)
Sukhanov, Vitaly I.
1991-02-01
The paper summarizes the results of investigations performed to obtain deep 3-D holograms with 102 i0 mkm physical thickness allowing the postexposure amplification and the a posteriori changing of the grating parameters. This aim has been achieved by developing heterogeneous systems on the basis of porous glass with light-sensitive compositions introduced into it. 1. INTRODUCTION. LIGHT-SENSITIVE MEDIA FOR 3-D HOLOGRAMS RECORDING. The 3-D holograms have many useful properties: very high diffraction efficiency angular and spectral selectivity but low level of noise. It shoud be noted that in this case deep 3-D holograms are dealt with whose physical thickness is as high as 102 -i mkm. Such hologram recording is usually done using homogeneous light-sensitive media for example dyed acid-halide and electrooptical crystals photochrome glass photostructurized polimer compositions and so on. The nature of photophisical and photochemical processes responsible for the light sensitivity of these materials exclude the possibility of post-exposure treatment. This does not allow to enhance the recorded holograms and considerably hampers their fixing or makes it practically impossible. The object of our work is to create the media which are quite suitable for two-stage processes of the deep hologram formation with post-exposure processing. Such material must satisfy the following requirements: a)they must have high permeability for the developing substances in order to make the development duration suitable for practical applications b)they must be shrinkproof to prevent deformation of the
Ultrasonic detection of solid phase mass flow ratio of pneumatic conveying fly ash
NASA Astrophysics Data System (ADS)
Duan, Guang Bin; Pan, Hong Li; Wang, Yong; Liu, Zong Ming
2014-04-01
In this paper, ultrasonic attenuation detection and weight balance are adopted to evaluate the solid mass ratio in this paper. Fly ash is transported on the up extraction fluidization pneumatic conveying workbench. In the ultrasonic test. McClements model and Bouguer-Lambert-Beer law model were applied to formulate the ultrasonic attenuation properties of gas-solid flow, which can give the solid mass ratio. While in the method of weigh balance, the averaged mass addition per second can reveal the solids mass flow ratio. By contrast these two solid phase mass ratio detection methods, we can know, the relative error is less.
A 3D CFD simulation of liquid flow in an ironmaking blast furnace
NASA Astrophysics Data System (ADS)
Shen, Yansong; Guo, Baoyu; Chew, Sheng; Austin, Peter; Yu, Aibing
2013-07-01
A three-dimensional CFX-based mathematical model is developed to describe the flow-heat transfer-chemical reactions behaviours of gas-solid-liquid phases in an ironmaking blast furnace (BF), where the raceway cavity is considered explicitly. The typical in-furnace phenomena of an operating blast furnace, in particular, the liquid flow in the lower part of a blast furnace is simulated in aspects of velocity and volume fraction. This model offers a cost-effective tool to understand and optimize blast furnace operation.
Modeling of confined turbulent fluid-particle flows using Eulerian and Lagrangian schemes
NASA Technical Reports Server (NTRS)
Adeniji-Fashola, A.; Chen, C. P.
1990-01-01
Two important aspects of fluid-particulate interaction in dilute gas-particle turbulent flows (the turbulent particle dispersion and the turbulence modulation effects) are addressed, using the Eulerian and Lagrangian modeling approaches to describe the particulate phase. Gradient-diffusion approximations are employed in the Eulerian formulation, while a stochastic procedure is utilized to simulate turbulent dispersion in the Lagrangina formulation. The k-epsilon turbulence model is used to characterize the time and length scales of the continuous phase turbulence. Models proposed for both schemes are used to predict turbulent fully-developed gas-solid vertical pipe flow with reasonable accuracy.
Percolation and permeability of heterogeneous fracture networks
NASA Astrophysics Data System (ADS)
Adler, Pierre; Mourzenko, Valeri; Thovert, Jean-François
2013-04-01
Natural fracture fields are almost necessarily heterogeneous with a fracture density varying with space. Two classes of variations are quite frequent. In the first one, the fracture density is decreasing from a given surface; the fracture density is usually (but not always see [1]) an exponential function of depth as it has been shown by many measurements. Another important example of such an exponential decrease consists of the Excavated Damaged Zone (EDZ) which is created by the excavation process of a gallery [2,3]. In the second one, the fracture density undergoes some local random variations around an average value. This presentation is mostly focused on the first class and numerical samples are generated with an exponentially decreasing density from a given plane surface. Their percolation status and hydraulic transmissivity can be calculated by the numerical codes which are detailed in [4]. Percolation is determined by a pseudo diffusion algorithm. Flow determination necessitates the meshing of the fracture networks and the discretisation of the Darcy equation by a finite volume technique; the resulting linear system is solved by a conjugate gradient algorithm. Only the flow properties of the EDZ along the directions which are parallel to the wall are of interest when a pressure gradient parallel to the wall is applied. The transmissivity T which relates the total flow rate per unit width Q along the wall through the whole fractured medium to the pressure gradient grad p, is defined by Q = - T grad p/mu where mu is the fluid viscosity. The percolation status and hydraulic transmissivity are systematically determined for a wide range of decay lengths and anisotropy parameters. They can be modeled by comparison with anisotropic fracture networks with a constant density. A heuristic power-law model is proposed which accurately describes the results for the percolation threshold over the whole investigated range of heterogeneity and anisotropy. Then, the data
Node assignment in heterogeneous computing
NASA Technical Reports Server (NTRS)
Som, Sukhamoy
1993-01-01
A number of node assignment schemes, both static and dynamic, are explored for the Algorithm to Architecture Mapping Model (ATAMM). The architecture under consideration consists of heterogeneous processors and implements dataflow models of real-time applications. Terminology is developed for heterogeneous computing. New definitions are added to the ATAMM for token and assignment classifications. It is proved that a periodic execution is possible for dataflow graphs. Assignment algorithms are developed and proved. A design procedure is described for satisfying an objective function in an heterogeneous architecture. Several examples are provided for illustration.
High performance simulation of environmental tracers in heterogeneous domains.
Gardner, William P; Hammond, Glenn; Lichtner, Peter
2015-04-01
In this study, we use PFLOTRAN, a highly scalable, parallel, flow, and reactive transport code to simulate the concentrations of 3H, 3He, CFC-11, CFC-12, CFC-113, SF6, 39Ar, and the mean groundwater age in heterogeneous fields on grids with an excess of 10 million nodes. We utilize this computational platform to simulate the concentration of multiple tracers in high-resolution, heterogeneous 2D and 3D domains, and calculate tracer-derived ages. Tracer-derived ages show systematic biases toward younger ages when the groundwater age distribution contains water older than the maximum tracer age. The deviation of the tracer-derived age distribution from the true groundwater age distribution increases with increasing heterogeneity of the system. However, the effect of heterogeneity is diminished as the mean travel time gets closer to the tracer age limit. Age distributions in 3D domains differ significantly from 2D domains. 3D simulations show decreased mean age, and less variance in age distribution for identical heterogeneity statistics. High-performance computing allows for investigation of tracer and groundwater age systematics in high-resolution domains, providing a platform for understanding and utilizing environmental tracer and groundwater age information in heterogeneous 3D systems. PMID:24372403
NASA Astrophysics Data System (ADS)
Li, Y. Z.; Zhao, L. Z.; Wang, C.; Lu, Z.; Bai, H. Y.; Wang, W. H.
2015-07-01
The relaxation dynamics in unfreezing process of metallic glasses is investigated by the activation-relaxation technique. A non-monotonic dynamical microstructural heterogeneities evolution with temperature is discovered, which confirms and supplies more features to flow units concept of glasses. A flow unit perspective is proposed to microscopically describe this non-monotonic evolution of the dynamical heterogeneities as well as its relationship with the deformation mode development of metallic glasses.
Heterogeneous Reactions in Atmospheric Aerosols Observed Using ATOFMS
NASA Astrophysics Data System (ADS)
Ryan, Sullivan
2005-03-01
The heterogeneous aging of natural atmospheric particles by reactive gases in the troposphere has been investigated in a flow-tube reactor using Aerosol Time-of-Flight Mass Spectrometry (ATOFMS) to monitor changes in the particle composition in real-time. Sea- salt and mineral dust aerosols were introduced into the flow tube simultaneously and reacted with nitric acid in a relative rate experiment. ATOFMS is a single-particle technique and thus enables us to distinguish which particle type accumulates more nitric acid. This allows us to determine if the differing surface area or kinetics is driving the partitioning of nitric acid between the sea salt and dust. The results of these and other aerosol flow-tube kinetics experiments will be presented. The atmospheric implications will be emphasized, particularly in relation to observations made by ATOFMS of heterogeneous reactions occurring in particles over the Pacific Ocean during ACE-Asia.
Heterogeneous Oxidation of Catechol.
Pillar, Elizabeth A; Zhou, Ruixin; Guzman, Marcelo I
2015-10-15
Natural and anthropogenic emissions of aromatic hydrocarbons from biomass burning, agro-industrial settings, and fossil fuel combustion contribute precursors to secondary aerosol formation (SOA). How these compounds are processed under humid tropospheric conditions is the focus of current attention to understand their environmental fate. This work shows how catechol thin films, a model for oxygenated aromatic hydrocarbons present in biomass burning and combustion aerosols, undergo heterogeneous oxidation at the air-solid interface under variable relative humidity (RH = 0-90%). The maximum reactive uptake coefficient of O3(g) by catechol γO3 = (7.49 ± 0.35) × 10(-6) occurs for 90% RH. Upon exposure of ca. 104-μm thick catechol films to O3(g) mixing ratios between 230 ppbv and 25 ppmv, three main reaction pathways are observed. (1) The cleavage of the 1,2 carbon-carbon bond at the air-solid interface resulting in the formation of cis,cis-muconic acid via primary ozonide and hydroperoxide intermediates. Further direct ozonolysis of cis,cis-muconic yields glyoxylic, oxalic, crotonic, and maleic acids. (2) A second pathway is evidenced by the presence of Baeyer-Villiger oxidation products including glutaconic 4-hydroxy-2-butenoic and 5-oxo-2-pentenoic acids during electrospray ionization mass spectrometry (MS) and ion chromatography MS analyses. (3) Finally, indirect oxidation by in situ produced hydroxyl radical (HO(•)) results in the generation of semiquinone radical intermediates toward the synthesis of polyhydoxylated aromatic rings such as tri-, tetra-, and penta-hydroxybenzene. Remarkably, heavier polyhydroxylated biphenyl and terphenyl products present in the extracted oxidized films result from coupling reactions of semiquinones of catechol and its polyhydroxylated rings. The direct ozonolysis of 1,2,3- and 1,2,4-trihydroxybenezene yields 2- and 3-hydroxy-cis,cis-muconic acid, respectively. The production of 2,4- or 3,4-dihdroxyhex-2-enedioic acid is
Homogeneous, Heterogeneous, and Enzymatic Catalysis.
ERIC Educational Resources Information Center
Oyama, S. Ted; Somorjai, Gabor A.
1988-01-01
Discusses three areas of catalysis: homegeneous, heterogeneous, and enzymatic. Explains fundamentals and economic impact of catalysis. Lists and discusses common industrial catalysts. Provides a list of 107 references. (MVL)
Heterogeneity in motor driven transport
NASA Astrophysics Data System (ADS)
Tabei, Ali
2015-03-01
I will discuss quantitative analysis of particle tracking data for motor driven vesicles inside an insulin secreting cell. We use this method to study the dynamical and structural heterogeneity inside the cell. I will discuss our effort to explain the origin of observed heterogeneity in intracellular transport. Finally, I will explain how analyzing directional correlations in transport trajectories reveals self-similarity in the diffusion media.
Laboratory Studies of Heterogeneous Chemical Processes of Atmospheric Importance
NASA Technical Reports Server (NTRS)
Molina, Mario J.
2004-01-01
The objective of this study is to conduct measurements of chemical kinetics parameters for heterogeneous reactions of importance in the stratosphere and the troposphere. It involves the elucidation of the mechanism of the interaction of HCl vapor with ice surfaces, which is the first step in the heterogeneous chlorine activation processes, as well as the investigation of the atmospheric oxidation mechanism of soot particles emitted by biomass and fossil fuels. The techniques being employed include turbulent flow-chemical ionization mass spectrometry and optical ellipsometry, among others.
Analysis of active renin heterogeneity.
Katz, S A; Malvin, R L; Lee, J; Kim, S H; Murray, R D; Opsahl, J A; Abraham, P A
1991-09-01
Active renin is a heterogeneous enzyme that can be separated into multiple forms with high-resolution isoelectric focusing. The isoelectric heterogeneity may result from differences in glycosylation between the different forms. In order to determine the relationship between active renin heterogeneity and differences in composition or attachment of oligosaccharides, two separate experiments were performed: (i) Tunicamycin, which interferes with normal glycosylation processing, increased the proportion of relatively basic renin forms secreted into the incubation media by rat renal cortical slices. (ii) Endoglycosidase F, which enzymatically removes carbohydrate from some classes of glycoprotein, similarly increased the proportion of relatively basic forms when incubated with active human recombinant renin. In addition, further studies with inhibitors of human renin activity revealed that the heterogeneous renin forms were similarly inhibited by two separate renin inhibitors. These results are consistent with the hypothesis that renin isoelectric heterogeneity is due in part to differences in carbohydrate moiety attachment and that the heterogeneity of renin does not influence access of direct renin inhibitors to the active site of renin. PMID:1908097
Predictive modeling of particle-laden turbulent flows. Final report
Shaffer, F.; Bolio, E.J.; Hrenya, C.M.
1993-12-31
Earlier work of Sinclair and Jackson which treats the laminar flow of gas-solid suspensions is extended to model dilute turbulent flow. The random particle motion, often exceeding the turbulent fluctuations in the gas, is obtained using a model based on kinetic theory of granular materials. A two-equation low Reynolds number turbulence model is, modified to account for the presence of the dilute particle phase. Comparisons of the model predictions with available experimental data for the mean and fluctuating velocity profiles for both phases indicate that the resulting theory captures many of the flow features observed in the pneumatic transport of large particles. The model predictions did not manifest an extreme sensitivity to the degree of inelasticity in the particle-particle collisions for the range of solid loading ratios investigated.
The effect of soil heterogeneity on ATES performance
NASA Astrophysics Data System (ADS)
Sommer, W.; Rijnaarts, H.; Grotenhuis, T.; van Gaans, P.
2012-04-01
Due to an increasing demand for sustainable energy, application of Aquifer Thermal Energy Storage (ATES) is growing rapidly. Large-scale application of ATES is limited by the space that is available in the subsurface. Especially in urban areas, suboptimal performance is expected due to thermal interference between individual wells of a single system, or interference with other ATES systems or groundwater abstractions. To avoid thermal interference there are guidelines on well spacing. However, these guidelines, and also design calculations, are based on the assumption of a homogeneous subsurface, while studies report a standard deviation in logpermeability of 1 to 2 for unconsolidated aquifers (Gelhar, 1993). Such heterogeneity may create preferential pathways, reducing ATES performance due to increased advective heat loss or interference between ATES wells. The role of hydraulic heterogeneity of the subsurface related to ATES performance has received little attention in literature. Previous research shows that even small amounts of heterogeneity can result in considerable uncertainty in the distribution of thermal energy in the subsurface and an increased radius of influence (Ferguson, 2007). This is supported by subsurface temperature measurements around ATES wells, which suggest heterogeneity gives rise to preferential pathways and short-circuiting between ATES wells (Bridger and Allen, 2010). Using 3-dimensional stochastic heat transport modeling, we quantified the influence of heterogeneity on the performance of a doublet well energy storage system. The following key parameters are varied to study their influence on thermal recovery and thermal balance: 1) regional flow velocity, 2) distance between wells and 3) characteristics of the heterogeneity. Results show that heterogeneity at the scale of a doublet ATES system introduces an uncertainty up to 18% in expected thermal recovery. The uncertainty increases with decreasing distance between ATES wells. The
Yokoyama, Takamichi; Cao, Duyen H; Stoumpos, Constantinos C; Song, Tze-Bin; Sato, Yoshiharu; Aramaki, Shinji; Kanatzidis, Mercouri G
2016-03-01
The development of Sn-based perovskite solar cells has been challenging because devices often show short-circuit behavior due to poor morphologies and undesired electrical properties of the thin films. A low-temperature vapor-assisted solution process (LT-VASP) has been employed as a novel kinetically controlled gas-solid reaction film fabrication method to prepare lead-free CH3NH3SnI3 thin films. We show that the solid SnI2 substrate temperature is the key parameter in achieving perovskite films with high surface coverage and excellent uniformity. The resulting high-quality CH3NH3SnI3 films allow the successful fabrication of solar cells with drastically improved reproducibility, reaching an efficiency of 1.86%. Furthermore, our Kelvin probe studies show the VASP films have a doping level lower than that of films prepared from the conventional one-step method, effectively lowering the film conductivity. Above all, with (LT)-VASP, the short-circuit behavior often obtained from the conventional one-step-fabricated Sn-based perovskite devices has been overcome. This study facilitates the path to more successful Sn-perovskite photovoltaic research. PMID:26877089
Jenkins, Samantha L; Almond, Matthew J; Hollins, Peter
2005-05-01
Single crystals of trans-cinnamic acid and of a range of derivatives of this compound containing halogen substituents on the aromatic ring have been reacted with 165 Torr pressure of bromine vapour in a sealed desiccator at 20 degrees C for 1 week. Infrared and Raman microspectroscopic examination of the crystals shows that bromination of the aliphatic double bond, but not of the aromatic ring, has occurred. It is demonstrated also that the reaction is truly gas solid in nature. A time-dependent study of these reactions shows that they do not follow a smooth diffusion-controlled pathway. Rather the reactions appear to be inhomogeneous and to occur at defects within the crystal. The reaction products are seen to flake from the surface of the crystal. It is shown, therefore, that these are not single crystal to single crystal transitions, as have been observed previously for the photodimerisation of trans-cinnamic acid and several of its derivatives. It is shown that there are no by-products of the reaction and that finely ground samples react to form the same products as single crystals. PMID:19787900
NASA Astrophysics Data System (ADS)
Krasokha, Nikolaj; Weber, Sebastian; Huth, Stephan; Zumsande, Kathrin; Theisen, Werner
2012-11-01
This work deals with gas-solid interactions between a high-alloyed steel powder and the surrounding atmosphere during continuous heating. It is motivated by the recently developed corrosion-resistant CrMnCN austenitic cast steels. Here, powder metallurgical processing would be desirable to manufacture highly homogeneous parts and/or novel corrosion-resistant metal-matrix composites. However, the successful use of this new production route calls for a comprehensive investigation of interactions between the sintering atmosphere and the metallic powder to prevent undesirable changes to the chemical composition, e.g., degassing of nitrogen or evaporation of manganese. In this study, dilatometric measurements combined with residual gas analysis, high-temperature X-ray diffraction (XRD) measurements, and thermodynamic equilibrium calculations provided detailed information about the influence of different atmospheric conditions on the microstructure, constitution, and densification behavior of a gas-atomized CrMnCN steel powder during continuous heating. Intensive desorption of nitrogen led to the conclusion that a vacuum atmosphere is not suitable for powder metallurgical (PM) processing. Exposure to an N2-containing atmosphere resulted in the formation of nitrides and lattice expansion. Experimental findings have shown that the N content can be controlled by the nitrogen partial pressure. Furthermore, the reduction of surface oxides because of a carbothermal reaction at elevated temperatures and the resulting enhancement of the powder's densification behavior are discussed in this work.
Cell heterogeneity during the cell cycle
Darzynkiewicz, Z.; Crissman, H.; Traganos, F.; Steinkamp, J.
1982-12-01
Using flow cytometry, populations of Chinese hamster ovary cells, asynchronous and synchronized in the cycle, were measured with respect to cellular RNA- and protein-content, as well as cell light scatter properties. Heterogeneities of cell populations were expressed as coefficients of variation (c.v.) in percent of the respective mean values. Populations of cells immediately after mitosis have about 15% higher c.v. than mitotic cell populations, regardless of whether RNA, proteins, or light scatter are measured. These data indicate that cytoplasmic constituents are unequally distributed into the daughter cells during cytokinesis and that unequal cytokinesis generates intercellular metabolic variability during the cycle. An additional increase in heterogeneity, although of smaller degree, occurs during G/sub 2/ phase. Populations of S-phase cells are the most uniform, having 20-30% lower c.v. than the postmitotic cells. Cell progression through S does not involve any significant increase in intercellular variability with respect to RNA or protein content. In unperturbed exponentially growing cultures a critical RNA content is required for G/sub 1/ cells prior to their entrance into S. The cell residence times in the equalization compartments are exponentially distributed, which may reflect the randomness generated by the uneven division of metabolic constituents to daughter cells during cytokinesis. The cell heterogeneities were presently estimated at two metabolic levels, transcription (RNA content) and translation (proteins). The most uniform were populations stained for RNA and the highest variability was observed after staining of proteins. This suggests that the regulatory mechanisms equalizing cells in the cell cycle may operate primarily at the level of DNA transcription.
Heterogeneous ageing of skeletal muscle microvascular function.
Muller-Delp, Judy M
2016-04-15
The distribution of blood flow to skeletal muscle during exercise is altered with advancing age. Changes in arteriolar function that are muscle specific underlie age-induced changes in blood flow distribution. With advancing age, functional adaptations that occur in resistance arterioles from oxidative muscles differ from those that occur in glycolytic muscles. Age-related adaptations of morphology, as well as changes in both endothelial and vascular smooth muscle signalling, differ in muscle of diverse fibre type. Age-induced endothelial dysfunction has been reported in most skeletal muscle arterioles; however, unique alterations in signalling contribute to the dysfunction in arterioles from oxidative muscles as compared with those from glycolytic muscles. In resistance arterioles from oxidative muscle, loss of nitric oxide signalling contributes significantly to endothelial dysfunction, whereas in resistance arterioles from glycolytic muscle, alterations in both nitric oxide and prostanoid signalling underlie endothelial dysfunction. Similarly, adaptations of the vascular smooth muscle that occur with advancing age are heterogeneous between arterioles from oxidative and glycolytic muscles. In both oxidative and glycolytic muscle, late-life exercise training reverses age-related microvascular dysfunction, and exercise training appears to be particularly effective in reversing endothelial dysfunction. Patterns of microvascular ageing that develop among muscles of diverse fibre type and function may be attributable to changing patterns of physical activity with ageing. Importantly, aerobic exercise training, initiated even at an advanced age, restores muscle blood flow distribution patterns and vascular function in old animals to those seen in their young counterparts. PMID:26575597
Estimating Parameters of Aquifer Heterogeneity from Transient Pumping Test
NASA Astrophysics Data System (ADS)
Zech, Alraune; Müller, Sebastian; Attinger, Sabine
2015-04-01
We present a new method for interpreting drawdowns of transient pumping tests in heterogeneous porous media. The vast majority of natural aquifers are characterized by heterogeneity, which can be statistically represented by parameters such as geometric mean bar K, variance σ^2, and correlation length ℓ of hydraulic conductivity. Our method can be understood as extension of the effective well flow method [Zech et al., 2012] from steady state to transient pumping tests. It allows a direct parameter estimation of bar K, σ^2, ℓ from head measurements under well flow conditions. The method is based on a representative description of hydraulic conductivity for radial flow regimes K_CG. It was derived previously using the upscaling procedure Radial Coarse Graining in combination with log-normal hydraulic conductivity. A semi-analytical solution for the mean drawdown of transient pumping tests was derived by combining the upscaled solution for the radially adapted hydraulic conductivity K_CG and the groundwater flow equation under well flow conditions. The dependency of the drawdown solution on the statistical quantities of the porous medium allows us to inversely estimate bar K, σ^2, ℓ from pumping test data. We used an ensemble of transient pumping test simulations to verify the drawdown solution. We generated pumping tests in heterogeneous media for various values of the statistical parameters bar K, σ^2, ℓ and evaluated their impact on the drawdown behavior as well as on the temporal evolution. We further examined the impact of several aspects like the location of an observation well or the local conductivity at the pumping well on the drawdown behavior. Zech, A., C. L. Schneider, and S. Attinger, 2012, The Extended Thiem's solution: Including the impact of heterogeneity, Water Resour. Res., 48, W10535, doi:10.1029/2012WR011852.
Reaction Selectivity in Heterogeneous Catalysis
Somorjai, Gabor A.; Kliewer, Christopher J.
2009-02-02
The understanding of selectivity in heterogeneous catalysis is of paramount importance to our society today. In this review we outline the current state of the art in research on selectivity in heterogeneous catalysis. Current in-situ surface science techniques have revealed several important features of catalytic selectivity. Sum frequency generation vibrational spectroscopy has shown us the importance of understanding the reaction intermediates and mechanism of a heterogeneous reaction, and can readily yield information as to the effect of temperature, pressure, catalyst geometry, surface promoters, and catalyst composition on the reaction mechanism. DFT calculations are quickly approaching the ability to assist in the interpretation of observed surface spectra, thereby making surface spectroscopy an even more powerful tool. HP-STM has revealed three vitally important parameters in heterogeneous selectivity: adsorbate mobility, catalyst mobility, and selective site-blocking. The development of size controlled nanoparticles from 0.8 to 10 nm, of controlled shape, and of controlled bimetallic composition has revealed several important variables for catalytic selectivity. Lastly, DFT calculations may be paving the way to guiding the composition choice for multi-metallic heterogeneous catalysis for the intelligent design of catalysts incorporating the many factors of selectivity we have learned.
Tiedeman, C.R.; Hsieh, P.A.
2002-01-01
Converging radial-flow and two-well tracer tests are simulated in two-dimensional aquifers to investigate the effects of heterogeneity and forced-gradient test configuration on longitudinal dispersivity (??L) estimates, and to compare ??L estimates from forced-gradient tests with ??L values that characterize solute spreading under natural-gradient flow. Results indicate that in both mildly and highly heterogeneous aquifers, ??L estimates from two-well tests are generally larger than those from radial-flow tests. In mildly heterogeneous aquifers, ??L estimates from two-well tests with relatively large tracer transport distances are similar to ??L values from natural-gradient simulations. In highly heterogeneous aquifers, ??L estimates from two-well tests at all tracer transport distances are typically smaller than ??L values from natural-gradient simulations.
Analyzing the Tumor Microenvironment by Flow Cytometry.
Young, Yoon Kow; Bolt, Alicia M; Ahn, Ryuhjin; Mann, Koren K
2016-01-01
Flow cytometry is an essential tool for studying the tumor microenvironment. It allows us to quickly quantify and identify multiple cell types in a heterogeneous sample. A brief overview of flow cytometry instrumentation and the appropriate considerations and steps in building a good flow cytometry staining panel are discussed. In addition, a lymphoid tissue and solid tumor leukocyte infiltrate flow cytometry staining protocol and an example of flow cytometry data analysis are presented. PMID:27581017
Heterogenous catalysis mediated by plasmon heating.
Adleman, James R; Boyd, David A; Goodwin, David G; Psaltis, Demetri
2009-12-01
We introduce a new method for performing and miniaturizing many types of heterogeneous catalysis involving nanoparticles. The method makes use of the plasmon resonance present in nanoscale metal catalysts to provide the necessary heat of reaction when illuminated with a low-power laser. We demonstrate our approach by reforming a flowing, liquid mixture of ethanol and water over gold nanoparticle catalysts in a microfluidic channel. Plasmon heating of the nanoparticles provides not only the heat of reaction but the means to generate both water and ethanol vapor locally over the catalysts, which in turn allows the chip and the fluid lines to remain at room temperature. The measured products of the reaction, CO(2), CO, and H(2), are consistent with catalytic steam reforming of ethanol. The approach, which we refer to as plasmon-assisted catalysis, is general and can be used with a variety of endothermic catalytic processes involving nanoparticles. PMID:19908825
Solute transport in heterogeneous porous formations
NASA Astrophysics Data System (ADS)
Demmy, George Gary, Jr.
1999-10-01
This work quantifies relationships between the spatial, or Eulerian, distribution of the properties of a chemically and physically heterogeneous porous medium and those as observed along the natural, or Lagrangian, trajectories that a fluid particle traces in a steady and irrotational flow. From these relationships, expressions that relate the transport of solutes through the porous medium along the natural trajectories to the aforementioned Eulerian distributions are developed. The effects of injection mode upon global measures of transport as reflected by the temporal moments of breakthrough curves and spatial moments of a solute plume are developed. The coupled effects of correlation of a linear equilibrium sorption to the underlying log hydraulic conductivity field and injection mode on the evolving temporal moments of mass breakthrough curve and the coupled effects of correlation of a first-order decay coefficient and injection mode upon the spatial moments of a solute plume are examined.
Shock wave structure in heterogeneous reactive media
Baer, M.R.
1997-06-01
Continuum mixture theory and mesoscale modeling are applied to describe the behavior of shock-loaded heterogeneous media. One-dimensional simulations of gas-gun experiments demonstrate that the wave features are well described by mixture theory, including reflected wave behavior and conditions where significant reaction is initiated. Detailed wave fields are resolved in numerical simulations of impact on a lattice of discrete explosive {open_quotes}crystals{close_quotes}. It is shown that rapid distortion first occurs at material contact points; the nature of the dispersive fields includes large amplitude fluctuations of stress over several particle pathlengths. Localization of energy causes {open_quotes}hot-spots{close_quotes} due to shock focusing and plastic work as material flows into interstitial regions.
Quantifying tumour heterogeneity with CT
Miles, Kenneth A.
2013-01-01
Abstract Heterogeneity is a key feature of malignancy associated with adverse tumour biology. Quantifying heterogeneity could provide a useful non-invasive imaging biomarker. Heterogeneity on computed tomography (CT) can be quantified using texture analysis which extracts spatial information from CT images (unenhanced, contrast-enhanced and derived images such as CT perfusion) that may not be perceptible to the naked eye. The main components of texture analysis can be categorized into image transformation and quantification. Image transformation filters the conventional image into its basic components (spatial, frequency, etc.) to produce derived subimages. Texture quantification techniques include structural-, model- (fractal dimensions), statistical- and frequency-based methods. The underlying tumour biology that CT texture analysis may reflect includes (but is not limited to) tumour hypoxia and angiogenesis. Emerging studies show that CT texture analysis has the potential to be a useful adjunct in clinical oncologic imaging, providing important information about tumour characterization, prognosis and treatment prediction and response. PMID:23545171
Heterogeneous surfaces to repel proteins.
Shen, Lei; Zhu, Jintao
2016-02-01
The nonspecific adsorption of proteins is usually undesirable on solid surfaces as it induces adverse responses, such as platelet adhesion on medical devices, negative signals of biosensors and contamination blockage of filtration membranes. Thus, an important scheme in material science is to design and fabricate protein-repulsive surfaces. Early approaches in this field focused on homogeneous surfaces comprised of single type functionality. Yet, recent researches have demonstrated that surfaces with heterogeneities (chemistry and topography) show promising performance against protein adsorption. In this review, we will summarize the recent achievements and discuss the new perspectives in the research of developing and characterizing heterogeneous surfaces to repel proteins. The protein repulsion mechanisms of different heterogeneous surfaces will also be discussed in details, followed by the perspective and challenge of this emerging field. PMID:26691416
Resource heterogeneity can facilitate cooperation
Kun, Ádám; Dieckmann, Ulf
2013-01-01
Although social structure is known to promote cooperation, by locally exposing selfish agents to their own deeds, studies to date assumed that all agents have access to the same level of resources. This is clearly unrealistic. Here we find that cooperation can be maintained when some agents have access to more resources than others. Cooperation can then emerge even in populations in which the temptation to defect is so strong that players would act fully selfishly if their resources were distributed uniformly. Resource heterogeneity can thus be crucial for the emergence and maintenance of cooperation. We also show that resource heterogeneity can hinder cooperation once the temptation to defect is significantly lowered. In all cases, the level of cooperation can be maximized by managing resource heterogeneity. PMID:24088665
Simulator for heterogeneous dataflow architectures
NASA Technical Reports Server (NTRS)
Malekpour, Mahyar R.
1993-01-01
A new simulator is developed to simulate the execution of an algorithm graph in accordance with the Algorithm to Architecture Mapping Model (ATAMM) rules. ATAMM is a Petri Net model which describes the periodic execution of large-grained, data-independent dataflow graphs and which provides predictable steady state time-optimized performance. This simulator extends the ATAMM simulation capability from a heterogenous set of resources, or functional units, to a more general heterogenous architecture. Simulation test cases show that the simulator accurately executes the ATAMM rules for both a heterogenous architecture and a homogenous architecture, which is the special case for only one processor type. The simulator forms one tool in an ATAMM Integrated Environment which contains other tools for graph entry, graph modification for performance optimization, and playback of simulations for analysis.
Static heterogeneities in liquid water
NASA Astrophysics Data System (ADS)
Stanley, H. Eugene; Buldyrev, Sergey V.; Giovambattista, Nicolas
2004-10-01
The thermodynamic behavior of water seems to be closely related to static heterogeneities. These static heterogeneities are related to the local structure of water molecules, and when properly characterized, may offer an economical explanation of thermodynamic data. The key feature of liquid water is not so much that the existence of hydrogen bonds, first pointed out by Linus Pauling, but rather the local geometry of the liquid molecules is not spherical or oblong but tetrahedral. In the consideration of static heterogeneities, this local geometry is critical. Recent experiments suggested more than one phase of amorphous solid water, while simulations suggest that one of these phases is metastable with respect to another, so that in fact there are only two stable phases.