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Sample records for 3d porous medium

  1. Investigation of foam flow in a 3D printed porous medium in the presence of oil.

    PubMed

    Osei-Bonsu, Kofi; Grassia, Paul; Shokri, Nima

    2017-03-15

    Foams demonstrate great potential for displacing fluids in porous media which is applicable to a variety of subsurface operations such as the enhanced oil recovery and soil remediation. The application of foam in these processes is due to its unique ability to reduce gas mobility by increasing its effective viscosity and to divert gas to un-swept low permeability zones in porous media. The presence of oil in porous media is detrimental to the stability of foams which can influence its success as a displacing fluid. In the present work, we have conducted a systematic series of experiments using a well-characterised porous medium manufactured by 3D printing technique to evaluate the influence of oil on the dynamics of foam displacement under different boundary conditions. The effects of the type of oil, foam quality and foam flow rate were investigated. Our results reveal that generation of stable foam is delayed in the presence of light oil in the porous medium compared to heavy oil. Additionally, it was observed that the dynamics of oil entrapment was dictated by the stability of foam in the presence of oil. Furthermore, foams with high gas fraction appeared to be less stable in the presence of oil lowering its recovery efficiency. Pore-scale inspection of foam-oil dynamics during displacement revealed formation of a less stable front as the foam quality increased, leading to less oil recovery. This study extends the physical understanding of oil displacement by foam in porous media and provides new physical insights regarding the parameters influencing this process.

  2. Experimental study of 3D Rayleigh-Taylor convection between miscible fluids in a porous medium

    NASA Astrophysics Data System (ADS)

    Nakanishi, Yuji; Hyodo, Akimitsu; Wang, Lei; Suekane, Tetsuya

    2016-11-01

    The natural convection of miscible fluids in porous media has applications in several fields, such as geoscience and geoengineering, and can be employed for the geological storage of CO2. In this study, we used X-ray computer tomography to visualize 3D fingering structures associated with the Rayleigh-Taylor instability between miscible fluids in a porous medium. In the early stages of the onset of the Rayleigh-Taylor instability, a fine crinkling pattern gradually appeared at the interface. As the wavelength and amplitude increased, descending fingers formed on the interface and extended vertically downward; in addition, ascending and highly symmetric fingers formed. The adjacent fingers were cylindrical in shape and coalesced to form large fingers. The fingers appearing on the interface tended to become finer with increasing Rayleigh number, which is consistent with linear perturbation theory. When the Péclet number exceeded 10, transverse dispersion increased the finger diameter and enhanced the finger coalescence, strongly impacting the decrease in finger number density. When mechanical dispersion was negligible, the finger-extension velocity and the dimensionless mass-transfer rate scaled with the characteristic velocity and the Rayleigh number with an appropriate length scale. Mechanical dispersion not only reduced the onset time but also enhanced the mass transport.

  3. Highly porous 3D nanofiber scaffold using an electrospinning technique.

    PubMed

    Kim, Geunhyung; Kim, WanDoo

    2007-04-01

    A successful 3D tissue-engineering scaffold must have a highly porous structure and good mechanical stability. High porosity and optimally designed pore size provide structural space for cell accommodation and migration and enable the exchange of nutrients between the scaffold and environment. Poly(epsilon-carprolactone) fibers were electrospun using an auxiliary electrode and chemical blowing agent (BA), and characterized according to porosity, pore size, and their mechanical properties. We also investigated the effect of the BA on the electrospinning processability. The growth characteristic of human dermal fibroblasts cells cultured in the webs showed the good adhesion with the blown web relative to a normal electrospun mat. The blown nanofiber web had good tensile properties and high porosity compared to a typical electrospun nanofiber scaffold.

  4. A Mechanistic Study of Wetting Superhydrophobic Porous 3D Meshes.

    PubMed

    Yohe, Stefan T; Freedman, Jonathan D; Falde, Eric J; Colson, Yolonda L; Grinstaff, Mark W

    2013-08-07

    Superhydrophobic, porous, 3D materials composed of poly( ε -caprolactone) (PCL) and the hydrophobic polymer dopant poly(glycerol monostearate- co- ε -caprolactone) (PGC-C18) are fabricated using the electrospinning technique. These 3D materials are distinct from 2D superhydrophobic surfaces, with maintenance of air at the surface as well as within the bulk of the material. These superhydrophobic materials float in water, and when held underwater and pressed, an air bubble is released and will rise to the surface. By changing the PGC-C18 doping concentration in the meshes and/or the fiber size from the micro- to nanoscale, the long-term stability of the entrapped air layer is controlled. The rate of water infiltration into the meshes, and the resulting displacement of the entrapped air, is quantitatively measured using X-ray computed tomography. The properties of the meshes are further probed using surfactants and solvents of different surface tensions. Finally, the application of hydraulic pressure is used to quantify the breakthrough pressure to wet the meshes. The tools for fabrication and analysis of these superhydrophobic materials as well as the ability to control the robustness of the entrapped air layer are highly desirable for a number of existing and emerging applications.

  5. 3-D Distribution of Retained Colloids in Unsaturated Porous Media

    NASA Astrophysics Data System (ADS)

    Morales, V. L.; Perez-Reche, F. J.; Holzner, M.; Kinzelbach, W. K.; Otten, W.

    2013-12-01

    It is well accepted that colloid transport processes in porous media differ substantially between water saturated and unsaturated conditions. Differences are frequently ascribed to colloid immobilization by association with interfaces with the gas, as well as to restrictions of the liquid medium through which colloids are transported. Such factors depend on interfacial conditions provided by the water saturation of the porous medium. Yet, the current understanding of the importance of colloid retention at gas interfaces is based on observations of single pores or two-dimensional pore network representations, leaving open the question of their statistical significance when all pores in the medium are considered. In order to address this question, column experiments were performed using a model porous medium of glass beads through which colloidal silver particles were transported for conditions of varying water content. X-ray microtomography was subsequently employed as a non-destructive imaging technique to obtain pore-scale information of the entire column regarding: i) the presence and distribution of the four main locations where colloids can become retained (interfaces with the liquid-solid, gas-liquid and gas-solid, and the bulk liquid), ii) deposition profiles of colloids along the column classified by the available retention location, iii) morphological characteristics of the deposited colloidal aggregates, and iv) channel widths of 3-dimensional pore-water network representations. The results presented provide, for the first time, a direct statistical evaluation on the significance of colloid retention by attachment to the liquid-solid, gas-liquid, gas-solid interfaces, and by straining in the bulk liquid. Additionally, an effective-pore structure characteristic is proposed to improve predictions of mass removal by straining under various water saturations. A) Unsaturated conditions. B) Saturated conditions. Left: Tomograph slice illustrating with false

  6. Computing Radiative Transfer in a 3D Medium

    NASA Technical Reports Server (NTRS)

    Von Allmen, Paul; Lee, Seungwon

    2012-01-01

    A package of software computes the time-dependent propagation of a narrow laser beam in an arbitrary three- dimensional (3D) medium with absorption and scattering, using the transient-discrete-ordinates method and a direct integration method. Unlike prior software that utilizes a Monte Carlo method, this software enables simulation at very small signal-to-noise ratios. The ability to simulate propagation of a narrow laser beam in a 3D medium is an improvement over other discrete-ordinate software. Unlike other direct-integration software, this software is not limited to simulation of propagation of thermal radiation with broad angular spread in three dimensions or of a laser pulse with narrow angular spread in two dimensions. Uses for this software include (1) computing scattering of a pulsed laser beam on a material having given elastic scattering and absorption profiles, and (2) evaluating concepts for laser-based instruments for sensing oceanic turbulence and related measurements of oceanic mixed-layer depths. With suitable augmentation, this software could be used to compute radiative transfer in ultrasound imaging in biological tissues, radiative transfer in the upper Earth crust for oil exploration, and propagation of laser pulses in telecommunication applications.

  7. Solute transport through a deforming porous medium

    NASA Astrophysics Data System (ADS)

    Peters, Glen P.; Smith, David W.

    2002-06-01

    Solute transport through a porous medium is typically modelled assuming the porous medium is rigid. However, many applications exist where the porous medium is deforming, including, municipal landfill liners, mine tailings dams, and land subsidence. In this paper, mass balance laws are used to derive the flow and transport equations for a deforming porous medium. The equations are derived in both spatial and material co-ordinate systems. Solute transport through an engineered landfill liner is used as an illustrative example to show the differences between the theory for a rigid porous medium, and small and large deformation analysis of a deforming porous medium. It is found that the large deformation model produces shorter solute breakthrough times, followed by the small deformation model, and then the rigid porous medium model. It is also found that it is important to include spatial and temporal void ratio variations in the large deformation analysis. It is shown that a non-linear large deformation model may greatly reduce the solute breakthrough time, compared to a standard transport analysis typically employed by environmental engineers.

  8. Mathematical Model of Porous Medium Dynamics

    NASA Astrophysics Data System (ADS)

    Gerschuk, Peotr; Sapozhnikov, Anatoly

    1999-06-01

    Semiempirical model describing porous material strains under pulse mechanical and thermal loadings is proposed. Porous medium is considered as continuous one but with special form of pressure dependence upon strain. This model takes into account principal features of porous materials behavior which can be observed when the material is strained in dynamic and static experiments ( non-reversibility of large strains, nonconvexity of loading curve). Elastoplastic properties of porous medium, its damages when it is strained and dynamic fracture are also taken into account. Dispersion of unidirectional motion caused by medium heterogeneity (porousness) is taken into acount by introducing the physical viscosity depending upon pores size. It is supposed that at every moment of time pores are in equilibrium with pressure i.e. kinetic of pores collapse is not taken into account. The model is presented by the system of differential equations connecting pressure and energy of porous medium with its strain. These equations close system of equations of motion and continuity which then is integrated numerically. The proposed model has been tested on carbon materials and porous copper . Results of calculation of these materials shock compressing are in satisfactory agreement with experimental data. Results of calculation of thin plate with porous copper layer collision are given as an illustration.

  9. Macroscopic 3D Porous Graphitic Carbon Nitride Monolith for Enhanced Photocatalytic Hydrogen Evolution.

    PubMed

    Liang, Qinghua; Li, Zhi; Yu, Xiaoliang; Huang, Zheng-Hong; Kang, Feiyu; Yang, Quan-Hong

    2015-08-19

    A macroscopic 3D porous graphitic carbon nitride (g-CN) monolith is prepared by the one-step thermal polymerization of urea inside the framework of a commercial melamine sponge and exhibits improved photocatalytic water-splitting performance for hydrogen evolution compared to g-CN powder due to the 3D porous interconnected network, larger specific surface area, better visible light capture, and superior charge-separation efficiency.

  10. 3D finite element analysis of porous Ti-based alloy prostheses.

    PubMed

    Mircheski, Ile; Gradišar, Marko

    2016-11-01

    In this paper, novel designs of porous acetabular cups are created and tested with 3D finite element analysis (FEA). The aim is to develop a porous acetabular cup with low effective radial stiffness of the structure, which will be near to the architectural and mechanical behavior of the natural bone. For the realization of this research, a 3D-scanner technology was used for obtaining a 3D-CAD model of the pelvis bone, a 3D-CAD software for creating a porous acetabular cup, and a 3D-FEA software for virtual testing of a novel design of the porous acetabular cup. The results obtained from this research reveal that a porous acetabular cup from Ti-based alloys with 60 ± 5% porosity has the mechanical behavior and effective radial stiffness (Young's modulus in radial direction) that meet and exceed the required properties of the natural bone. The virtual testing with 3D-FEA of a novel design with porous structure during the very early stage of the design and the development of orthopedic implants, enables obtaining a new or improved biomedical implant for a relatively short time and reduced price.

  11. A porous 3D cell culture micro device for cell migration study.

    PubMed

    Ma, Liang; Zhou, Changchun; Lin, Biaoyang; Li, Wei

    2010-08-01

    Cell migration under chemoattractant is an important biological step in cancer metastasis that causes the spread of malignant tumor cells. Porous polymeric materials are widely used to mimic the extracellular matrix (ECM) environment for applications such as three dimensional (3D) cell culturing and tissue engineering. In this paper we report a novel 3D cell culture device based on porous polymeric material to study cancer migration. We fabricated a porous channel on a polymeric chip using a selective ultrasonic foaming method. We demonstrate that a chemical concentration gradient could be established through the porous channel due to the slow diffusion process. We show that significant cell migration could be observed through the porous channel within 1-2 weeks of cell culturing when metastatic M4A4-GFP breast cancer cells were induced by 20% fetal bovine serum (FBS).We also developed a mathematical model to evaluate the diffusivity and concentration gradient through the fabricated porous structure.

  12. Method to prepare nanoparticles on porous mediums

    DOEpatents

    Vieth, Gabriel M [Knoxville, TN; Dudney, Nancy J [Oak Ridge, TN; Dai, Sheng [Knoxville, TN

    2010-08-10

    A method to prepare porous medium decorated with nanoparticles involves contacting a suspension of nanoparticles in an ionic liquid with a porous medium such that the particles diffuse into the pores of the medium followed by heating the resulting composition to a temperature equal to or greater than the thermal decomposition temperature of the ionic liquid resulting in the removal of the liquid portion of the suspension. The nanoparticles can be a metal, an alloy, or a metal compound. The resulting compositions can be used as catalysts, sensors, or separators.

  13. Preparation and mechanical property of a novel 3D porous magnesium scaffold for bone tissue engineering.

    PubMed

    Zhang, Xue; Li, Xiao-Wu; Li, Ji-Guang; Sun, Xu-Dong

    2014-09-01

    Porous magnesium has been recently recognized as a biodegradable metal for bone substitute applications. A novel porous Mg scaffold with three-dimensional (3D) interconnected pores and with a porosity of 33-54% was produced by the fiber deposition hot pressing (FDHP) technology. The microstructure and morphologies of the porous Mg scaffold were characterized by scanning electron microscopy (SEM), and the effects of porosities on the microstructure and mechanical properties of the porous Mg were investigated. Experimental results indicate that the measured Young's modulus and compressive strength of the Mg scaffold are ranged in 0.10-0.37 GPa, and 11.1-30.3 MPa, respectively, which are fairly comparable to those of cancellous bone. Such a porous Mg scaffold having a 3D interconnected network structure has the potential to be used in bone tissue engineering.

  14. Application of 3d-ptv To Track Particle Moving Inside Heterogeneous Porous Media

    NASA Astrophysics Data System (ADS)

    Cenedese, A.; Cushman, J. H.; Moroni, M.

    There exist a number of imaging-based measurement techniques for determining 3D velocity fields in an observation volume. Among these are: a) scanning techniques (Guezennec et al. 1994, Moroni and Cushman, 2001); b) holographic techniques (Hin- sch and Hinrichs 1996); c) defocusing techniques (Willert and Gharib 1992); d) stereo- scopic techniques (Maas et al. 1993, Kasagi and Nishino 1990). We have focused our attention on 3D-PTV which is an experimental technique based on reconstructing 3D trajectories of reflecting tracer particles through a stereoscopic recording of image se- quences. Coordinates are determined first and then trajectories are defined. 3D-PTV requires the operator to light a volume of the test section as opposed to 2D techniques that require a light sheet. Stereoscopic methods share the following basic steps (Pa- pantoniou, 1990): a) stereoscopic calibrated imaging and recording of a suitably illu- minated particle flow; b) subsequent photogrammetric analysis of the resulting images to derive the instantaneous 3-D particle positions and c) tracking of the 3-D coordinate sets in time to derive the tracer trajectories. The ideal setup for obtaining highly accu- rate trajectories requires the cameras to be mounted with the distance between them equal to the distance to the center of the measurement volume (with three cameras this requires a hexagonal cell). But the camera arrangement is usually a compromise between ideal geometrical conditions for a homogeneous distribution of accuracies in the measuring volume and practical restrictions associated with the experiment. The position of the cameras in object space (exterior orientation) and the parameters of each camera (interior orientation) are needed to reconstruct the 3D objects. These pa- rameters can be calculated simultaneously in a so-called "bundle adjustment" or by pre-calibration. A matched index (of refraction) porous medium heterogeneous at the bench scale has been constructed by filling

  15. Thermoforming techniques for manufacturing porous scaffolds for application in 3D cell cultivation.

    PubMed

    Borowiec, Justyna; Hampl, Jörg; Gebinoga, Michael; Elsarnagawy, Tarek; Elnakady, Yasser A; Fouad, Hassan; Almajhadi, Fahd; Fernekorn, Uta; Weise, Frank; Singh, Sukhdeep; Elsarnagawy, Dief; Schober, Andreas

    2015-04-01

    Within the scientific community, there is an increasing demand to apply advanced cell cultivation substrates with increased physiological functionalities for studying spatially defined cellular interactions. Porous polymeric scaffolds are utilized for mimicking an organ-like structure or engineering complex tissues and have become a key element for three-dimensional (3D) cell cultivation in the meantime. As a consequence, efficient 3D scaffold fabrication methods play an important role in modern biotechnology. Here, we present a novel thermoforming procedure for manufacturing porous 3D scaffolds from permeable materials. We address the issue of precise thermoforming of porous polymer foils by using multilayer polymer thermoforming technology. This technology offers a new method for structuring porous polymer foils that are otherwise available for non-porous polymers only. We successfully manufactured 3D scaffolds from solvent casted and phase separated polylactic acid (PLA) foils and investigated their biocompatibility and basic cellular performance. The HepG2 cell culture in PLA scaffold has shown enhanced albumin secretion rate in comparison to a previously reported polycarbonate based scaffold with similar geometry.

  16. Barometric pumping of a fractured porous medium

    NASA Astrophysics Data System (ADS)

    Adler, Pierre; Varloteaux, Clément; Mourzenko, Valeri; François Thovert, Jean; Guillon, Sophie; Pili, Eric

    2014-05-01

    Fluctuations in the ambient atmospheric pressure result in motion of air in porous and fractured media. This mechanism, known as barometric (or atmospheric) pumping, efficiently transports gaseous species through the vadose zone to the atmosphere. This is of interest in many environmental and engineering fields, such as transport of trace gases from soil to atmosphere, environmental remediation of contaminated sites, radon in buildings and last but not least detection of nuclear explosions or leakage from carbon sequestration sites. The physical situation has been addressed in the following way. The fractures are modeled as polygonal plane surfaces with a given transmissivity embedded in a porous medium with a given permeability. The fluid is slightly compressible and is assumed to obey Darcy's law in the fractures and the porous medium with exchanges between them. The solute obeys convection-diffusion equations in both media again with exchanges between them. The fractures and the porous medium located in between them are meshed by triangles and tetrahedra. The equations are discretized by the finite volume method. In order to improve numerical precision, a Flux Limiting Scheme is applied to the transport equations ; moreover, special care is devoted to the description of the solute transfer between the fractures and the porous medium. The resulting equations are solved by conjugate gradient algorithms. This model is applied to the Roselend Natural Laboratory. At a 55 m depth, a sealed cavity allows for gas release experiments across fractured porous rocks in the unsaturated zone. The fractures are hexagons with a radius of 5m; their density is larger than 2.4 10-3 m-3; the aperture is of the order of 0.5 mm. The pressure fluctuations are sinusoidal, of amplitude 0.01 bar and period 1 week. The solute concentration is supposed to be equal to 1 at the bottom of the site. Systematic results will be presented. First, the precision of the calculations is assessed

  17. 3-D model of ICME in the interplanetary medium

    NASA Astrophysics Data System (ADS)

    Borgazzi, A.; Lara, A.; Niembro, T.

    2011-12-01

    We developed a method that describes with simply geometry the coordinates of intersection between the leading edge of an ICME and the position of an arbitrary satellite. When a fast CME is ejected from the Sun to the interplanetary space in most of the cases drives a shock. As the CME moves in the corona and later in the interplanetary space more material is stacking in the front and edges of the ejecta. In a first approximation, it is possible to assume the shape of these structures, the CME and the stacked material as a cone of revolution, (the ice-cream model [Schwenn et al., (2005)]). The interface may change due to the interaction of the structure and the non-shocked material in front of the ICME but the original shape of a cone of revolution is preserved. We assume, in a three dimensional geometry, an ice-cream cone shape for the ICME and apply an analytical model for its transport in the interplanetary medium. The goal of the present method is to give the time and the intersection coordinates between the leading edge of the ICME and any satellite that may be in the path of the ICME. With this information we can modelate the travel of the ICME in the interplanetary space using STEREO data.

  18. A 3-D constitutive model for pressure-dependent phase transformation of porous shape memory alloys.

    PubMed

    Ashrafi, M J; Arghavani, J; Naghdabadi, R; Sohrabpour, S

    2015-02-01

    Porous shape memory alloys (SMAs) exhibit the interesting characteristics of porous metals together with shape memory effect and pseudo-elasticity of SMAs that make them appropriate for biomedical applications. In this paper, a 3-D phenomenological constitutive model for the pseudo-elastic behavior and shape memory effect of porous SMAs is developed within the framework of irreversible thermodynamics. Comparing to micromechanical and computational models, the proposed model is computationally cost effective and predicts the behavior of porous SMAs under proportional and non-proportional multiaxial loadings. Considering the pressure dependency of phase transformation in porous SMAs, proper internal variables, free energy and limit functions are introduced. With the aim of numerical implementation, time discretization and solution algorithm for the proposed model are also presented. Due to lack of enough experimental data on multiaxial loadings of porous SMAs, we employ a computational simulation method (CSM) together with available experimental data to validate the proposed constitutive model. The method is based on a 3-D finite element model of a representative volume element (RVE) with random pores pattern. Good agreement between the numerical predictions of the model and CSM results is observed for elastic and phase transformation behaviors in various thermomechanical loadings.

  19. Controlled implant/soft tissue interaction by nanoscale surface modifications of 3D porous titanium implants.

    PubMed

    Rieger, Elisabeth; Dupret-Bories, Agnès; Salou, Laetitia; Metz-Boutigue, Marie-Helene; Layrolle, Pierre; Debry, Christian; Lavalle, Philippe; Vrana, Nihal Engin

    2015-06-07

    Porous titanium implants are widely employed in the orthopaedics field to ensure good bone fixation. Recently, the use of porous titanium implants has also been investigated in artificial larynx development in a clinical setting. Such uses necessitate a better understanding of the interaction of soft tissues with porous titanium structures. Moreover, surface treatments of titanium have been generally evaluated in planar structures, while the porous titanium implants have complex 3 dimensional (3D) architectures. In this study, the determining factors for soft tissue integration of 3D porous titanium implants were investigated as a function of surface treatments via quantification of the interaction of serum proteins and cells with single titanium microbeads (300-500 μm in diameter). Samples were either acid etched or nanostructured by anodization. When the samples are used in 3D configuration (porous titanium discs of 2 mm thickness) in vivo (in subcutis of rats for 2 weeks), a better integration was observed for both anodized and acid etched samples compared to the non-treated implants. If the implants were also pre-treated with rat serum before implantation, the integration was further facilitated. In order to understand the underlying reasons for this effect, human fibroblast cell culture tests under several conditions (directly on beads, beads in suspension, beads encapsulated in gelatin hydrogels) were conducted to mimic the different interactions of cells with Ti implants in vivo. Physical characterization showed that surface treatments increased hydrophilicity, protein adsorption and roughness. Surface treatments also resulted in improved adsorption of serum albumin which in turn facilitated the adsorption of other proteins such as apolipoprotein as quantified by protein sequencing. The cellular response to the beads showed considerable difference with respect to the cell culture configuration. When the titanium microbeads were entrapped in cell

  20. Mechanical properties and shape memory effect of 3D-printed PLA-based porous scaffolds.

    PubMed

    Senatov, F S; Niaza, K V; Zadorozhnyy, M Yu; Maksimkin, A V; Kaloshkin, S D; Estrin, Y Z

    2016-04-01

    In the present work polylactide (PLA)/15wt% hydroxyapatite (HA) porous scaffolds with pre-modeled structure were obtained by 3D-printing by fused filament fabrication. Composite filament was obtained by extrusion. Mechanical properties, structural characteristics and shape memory effect (SME) were studied. Direct heating was used for activation of SME. The average pore size and porosity of the scaffolds were 700μm and 30vol%, respectively. Dispersed particles of HA acted as nucleation centers during the ordering of PLA molecular chains and formed an additional rigid fixed phase that reduced molecular mobility, which led to a shift of the onset of recovery stress growth from 53 to 57°C. A more rapid development of stresses was observed for PLA/HA composites with the maximum recovery stress of 3.0MPa at 70°C. Ceramic particles inhibited the growth of cracks during compression-heating-compression cycles when porous PLA/HA 3D-scaffolds recovered their initial shape. Shape recovery at the last cycle was about 96%. SME during heating may have resulted in "self-healing" of scaffold by narrowing the cracks. PLA/HA 3D-scaffolds were found to withstand up to three compression-heating-compression cycles without delamination. It was shown that PLA/15%HA porous scaffolds obtained by 3D-printing with shape recovery of 98% may be used as self-fitting implant for small bone defect replacement owing to SME.

  1. A 3D porous Ni-Cu alloy film for high-performance hydrazine electrooxidation

    NASA Astrophysics Data System (ADS)

    Sun, Ming; Lu, Zhiyi; Luo, Liang; Chang, Zheng; Sun, Xiaoming

    2016-01-01

    Structural design and catalyst screening are two most important factors for achieving exceptional electrocatalytic performance. Herein we demonstrate that constructing a three-dimensional (3D) porous Ni-Cu alloy film is greatly beneficial for improving the hydrazine oxidation reaction (HzOR) performance. A facile electrodeposition process is employed to synthesize a Ni-Cu alloy film with a 3D hierarchical porous structure. As an integrated electrode for HzOR, the Ni-Cu alloy film exhibits superior catalytic activity and stability to the Ni or Cu counterparts. The synthesis parameters are also systematically tuned for optimizing the HzOR performance. The excellent HzOR performance of the Ni-Cu alloy film is attributed to its high intrinsic activity, large electrochemical specific surface area, and 3D porous architecture which offers a ``superaerophobic'' surface to effectively remove the gas product in a small volume. It is believed that the Ni-Cu alloy film electrode has potential application in direct hydrazine fuel cells as well as other catalytic fields.Structural design and catalyst screening are two most important factors for achieving exceptional electrocatalytic performance. Herein we demonstrate that constructing a three-dimensional (3D) porous Ni-Cu alloy film is greatly beneficial for improving the hydrazine oxidation reaction (HzOR) performance. A facile electrodeposition process is employed to synthesize a Ni-Cu alloy film with a 3D hierarchical porous structure. As an integrated electrode for HzOR, the Ni-Cu alloy film exhibits superior catalytic activity and stability to the Ni or Cu counterparts. The synthesis parameters are also systematically tuned for optimizing the HzOR performance. The excellent HzOR performance of the Ni-Cu alloy film is attributed to its high intrinsic activity, large electrochemical specific surface area, and 3D porous architecture which offers a ``superaerophobic'' surface to effectively remove the gas product in a small

  2. 3D printed porous stainless steel for potential use in medicine

    NASA Astrophysics Data System (ADS)

    Fousová, M.; Kubásek, J.; Vojtěch, D.; Fojt, J.; Čapek, J.

    2017-02-01

    3D printing technologies like Selective Laser Melting (SLM) or Electron Beam Melting (EBM) produce components of very complicated shapes from various kinds of materials. In this work a highly porous (porosity of almost 90 vol. %) stainless steel component was manufactured by SLM. The material was characterized in terms of structure, surface chemistry and mechanical properties. It was observed that mechanical properties of the material were similar to those of trabecular human bone. The tests realized in this work confirmed suitability of the porous material prepared by SLM for the use in medicine, for example, for scaffolds designed to repair bone defects.

  3. Controlled implant/soft tissue interaction by nanoscale surface modifications of 3D porous titanium implants

    NASA Astrophysics Data System (ADS)

    Rieger, Elisabeth; Dupret-Bories, Agnès; Salou, Laetitia; Metz-Boutigue, Marie-Helene; Layrolle, Pierre; Debry, Christian; Lavalle, Philippe; Engin Vrana, Nihal

    2015-05-01

    Porous titanium implants are widely employed in the orthopaedics field to ensure good bone fixation. Recently, the use of porous titanium implants has also been investigated in artificial larynx development in a clinical setting. Such uses necessitate a better understanding of the interaction of soft tissues with porous titanium structures. Moreover, surface treatments of titanium have been generally evaluated in planar structures, while the porous titanium implants have complex 3 dimensional (3D) architectures. In this study, the determining factors for soft tissue integration of 3D porous titanium implants were investigated as a function of surface treatments via quantification of the interaction of serum proteins and cells with single titanium microbeads (300-500 μm in diameter). Samples were either acid etched or nanostructured by anodization. When the samples are used in 3D configuration (porous titanium discs of 2 mm thickness) in vivo (in subcutis of rats for 2 weeks), a better integration was observed for both anodized and acid etched samples compared to the non-treated implants. If the implants were also pre-treated with rat serum before implantation, the integration was further facilitated. In order to understand the underlying reasons for this effect, human fibroblast cell culture tests under several conditions (directly on beads, beads in suspension, beads encapsulated in gelatin hydrogels) were conducted to mimic the different interactions of cells with Ti implants in vivo. Physical characterization showed that surface treatments increased hydrophilicity, protein adsorption and roughness. Surface treatments also resulted in improved adsorption of serum albumin which in turn facilitated the adsorption of other proteins such as apolipoprotein as quantified by protein sequencing. The cellular response to the beads showed considerable difference with respect to the cell culture configuration. When the titanium microbeads were entrapped in cell

  4. Barometric Pumping of a Fractured Porous Medium

    NASA Astrophysics Data System (ADS)

    Adler, P. M.; Mourzenko, V.; Thovert, J. F.; Pili, E.; Guillon, S.

    2014-12-01

    Fluctuations in the ambient atmospheric pressure result in motion of air in porous fractured media. This mechanism, known as barometric pumping, efficiently transports gaseous species through the vadose zone to the atmosphere. This is of interest in fields, such as transport of trace gases from soil to atmosphere, remediation of contaminated sites, radon in buildings, leakage from carbon sequestration sites and detection of nuclear explosions. The fractures are modeled as polygonal plane surfaces with a given transmissivity embedded in a permeable matrix. The slightly compressible fluid obeys Darcy's law in these two media with exchanges between them. The solute obeys convection-diffusion equations in both media again with exchanges. The fractures and the porous medium are meshed by triangles and tetrahedra, respectively. The equations are discretized by the finite volume method. A Flux Limiting Scheme diminishes numerical dispersion ; the solute transfer between the fractures and the porous medium is precisely evaluated. The resulting equations are solved by conjugate gradient algorithms. This model is applied to the Roselend Natural Laboratory. At a 55 m depth, a sealed cavity allows for gas release experiments across fractured porous rocks in the unsaturated zone. The fractures are hexagons with a radius of 5m; their density is larger than 2.4 10-3 m-3; the aperture is about 0.5 mm. The pressure fluctuations are sinusoidal, of amplitude 0.01 bar and period 1 week. The solute concentration is equal to 1 at the bottom. Systematic results will be presented. First, the precision of the calculations is assessed. Second, the pressure and solute concentration fields are displayed and discussed. Third, the influence of the major parameters (fracture density, aperture, porosity, diffusion coefficient,…) is illustrated and discussed. These results are discussed in terms of the amplification of solute transfer to the ground surface by the pressure fluctuations.

  5. Glycerol-mediated nanostructure modification leading to improved transparency of porous polymeric scaffolds for high performance 3D cell imaging.

    PubMed

    Zhao, Shan; Shen, Zhiyuan; Wang, Jingyu; Li, Xiaokang; Zeng, Yang; Wang, Bingjie; He, Yonghong; Du, Yanan

    2014-07-14

    Glycerol is among the most commonly used optical clearing agents for tissues clearance largely due to refractive index (RI) matching between glycerol and the submerged tissues. Here we applied glycerol as structure modifier at both macroscopic (as porogen) and nanoscopic (as nanostructure ameliorant) scales to fabricate transparent porous scaffolds made from poly(ethylene glycol) (PEG) as well as other widely used biomaterials (e.g., PLGA, PA, or gelatin), whose nanostructures, in the scale of light wavelength, dominantly improved the optical transmittance of the scaffolds even when immersed in RI mismatched medium (e.g., culture medium or water). We further exploited the clearing mechanisms based on Mie scattering theory, illustrating that conformational changes of polymer chains induced by solvent effects of glycerol enhanced the anisotropy (i.e., directional alignment) of the nanostructures, leading to reduced crystallinity and scattering of the resulted PEG scaffolds. Our findings represent the first and systematic demonstration with both experimental and theoretical evidence in effectively clearing porous polymeric scaffolds by mechanisms other than RI matching, which could tackle the limitations of current optical imaging of cells cultured within three-dimensional (3D) opaque porous scaffolds, such as poor visibility, low spatial resolution, and small penetration depth.

  6. Reticular synthesis of porous molecular 1D nanotubes and 3D networks

    NASA Astrophysics Data System (ADS)

    Slater, A. G.; Little, M. A.; Pulido, A.; Chong, S. Y.; Holden, D.; Chen, L.; Morgan, C.; Wu, X.; Cheng, G.; Clowes, R.; Briggs, M. E.; Hasell, T.; Jelfs, K. E.; Day, G. M.; Cooper, A. I.

    2017-01-01

    Synthetic control over pore size and pore connectivity is the crowning achievement for porous metal-organic frameworks (MOFs). The same level of control has not been achieved for molecular crystals, which are not defined by strong, directional intermolecular coordination bonds. Hence, molecular crystallization is inherently less controllable than framework crystallization, and there are fewer examples of 'reticular synthesis', in which multiple building blocks can be assembled according to a common assembly motif. Here we apply a chiral recognition strategy to a new family of tubular covalent cages to create both 1D porous nanotubes and 3D diamondoid pillared porous networks. The diamondoid networks are analogous to MOFs prepared from tetrahedral metal nodes and linear ditopic organic linkers. The crystal structures can be rationalized by computational lattice-energy searches, which provide an in silico screening method to evaluate candidate molecular building blocks. These results are a blueprint for applying the 'node and strut' principles of reticular synthesis to molecular crystals.

  7. 3D geometry and hydrodynamic modifications in fractured and porous rock samples through chemical alterations.

    NASA Astrophysics Data System (ADS)

    Noiriel, C. N.

    2011-12-01

    Fractured and porous rocks are the principal path for water flow and potential contamination. Modification of fracture topology and transmissivity by reactive fluids is an important and complex geological process. In carbonate rocks, fractures and porous media properties may change quickly and strongly due to natural processes (e.g. karstification, salt intrusion) or anthropogenic practice (e.g. CO2 geological sequestration). Recent application of X-ray micro-tomography to the Earth Sciences, which allows the visualization of 3D objects with a micrometre resolution, has considerably increased experimental capability by giving access to a 4D spatio-temporal vision (3D geometry + time) of the physical-chemical processes within the rocks. New information is now accessible, which provides a better understanding of the processes and allows the numerical models to be better constrained. I will present the application of X-ray micro-tomography to study changes of petrophysical properties (e.g. porosity, permeability, mineral surface area, etc.) of fractured and porous rocks in response to fluid-rock interactions (dissolution and precipitation). Experimental results will be discussed in regard to numerical modelling of flow and transport. Keywords: X-ray micro-tomography, fracture, porous media, dissolution, precipitation, carbon dioxide sequestration, limestone, reactive surface, geochemical modelling,

  8. Vulnerability mapping of groundwater contamination based on 3D lithostratigraphical models of porous aquifers.

    PubMed

    Ducci, Daniela; Sellerino, Mariangela

    2013-03-01

    The aim of this paper is to apply a methodology in order to reconstruct a lithostratigraphic 3D model of an aquifer so as to define some parameters involved in the evaluation of the aquifer vulnerability to contamination of porous aquifers. The DRASTIC, SINTACS and AVI methods have been applied to an alluvial coastal aquifer of southern Italy. The stratigraphic reconstruction has been obtained by interpolating stratigraphic data from more than one borehole per 2 km. The lithostratigraphic reconstruction of a 3D model has been applied and used for three-dimensional or two-dimensional representations. In the first two methods, the layers of the vadose zone and the aquifer media have been evaluated not only by the interpolation of the single boreholes and piezometers, but also by the 3D model, assigning the scores of the parameters of each layer of the 3D model. The comparison between the maps constructed from the weighted values in each borehole and the maps deriving from the attribution of the values of each layer of the 3D model, highlights that the second representation avoids or minimizes the "bullseye" effect linked to the presence of boreholes with higher or lower values. The study has demonstrated that it is possible to integrate a 3D lithostratigraphic model of an aquifer in the assessment of the parameters involved in the evaluation of the aquifer vulnerability to contamination by Point Count System methods.

  9. Electrochemical fabrication of 2D and 3D nickel nanowires using porous anodic alumina templates

    NASA Astrophysics Data System (ADS)

    Mebed, A. M.; Abd-Elnaiem, Alaa M.; Al-Hosiny, Najm M.

    2016-06-01

    Mechanically stable nickel (Ni) nanowires array and nanowires network were synthesized by pulse electrochemical deposition using 2D and 3D porous anodic alumina (PAA) templates. The structures and morphologies of as-prepared films were characterized by X-ray diffraction and scanning electron microscopy, respectively. The grown Ni nanowire using 3D PAA revealed more strength and larger surface area than has grown Ni use 2D PAA template. The prepared nanowires have a face-centered cubic crystal structure with average grain size 15 nm, and the preferred orientation of the nucleation of the nanowires is (111). The diameter of the nanowires is about 50-70 nm with length 3 µm. The resulting 3D Ni nanowire lattice, which provides enhanced mechanical stability and an increased surface area, benefits energy storage and many other applications which utilize the large surface area.

  10. Representativeness of 2D models to simulate 3D unstable variable density flow in porous media

    NASA Astrophysics Data System (ADS)

    Knorr, Bastian; Xie, Yueqing; Stumpp, Christine; Maloszewski, Piotr; Simmons, Craig T.

    2016-11-01

    Variable density flow in porous media has been studied primarily using numerical models because it is a semi-chaotic and transient process. Most of these studies have been 2D, owing to the computational restrictions on 3D simulations, and the ability to observe variable density flow in 2D experimentation. However, it is recognised that variable density flow is a three-dimensional process. A 3D system may cause weaker variable density flow than a 2D system due to stronger dispersion, but may also result in bigger fingers and hence stronger variable density flow because of more space for fingers to coalesce. This study aimed to determine the representativeness of 2D modelling to simulate 3D variable density flow. 3D homogeneous sand column experiments were conducted at three different water flow velocities with three different bromide tracer solutions mixed with methanol resulting in different density ratios. Both 2D axisymmetric and 3D numerical simulations were performed to reproduce experimental data. Experimental results showed that the magnitude of variable density flow increases with decreasing flow rates and decreasing density ratios. The shapes of the observed breakthrough curves differed significantly from those produced by 2D axisymmetric and 3D simulations. Compared to 2D simulations, the onset of instabilities was delayed but the growth was more pronounced in 3D simulations. Despite this difference, both 2D axisymmetric and 3D models successfully simulated mass recovery with high efficiency (between 77% and 99%). This study indicates that 2D simulations are sufficient to understand integrated features of variable density flow in homogeneous sand column experiments.

  11. High nitrogen-containing cotton derived 3D porous carbon frameworks for high-performance supercapacitors

    NASA Astrophysics Data System (ADS)

    Fan, Li-Zhen; Chen, Tian-Tian; Song, Wei-Li; Li, Xiaogang; Zhang, Shichao

    2015-10-01

    Supercapacitors fabricated by 3D porous carbon frameworks, such as graphene- and carbon nanotube (CNT)-based aerogels, have been highly attractive due to their various advantages. However, their high cost along with insufficient yield has inhibited their large-scale applications. Here we have demonstrated a facile and easily scalable approach for large-scale preparing novel 3D nitrogen-containing porous carbon frameworks using ultralow-cost commercial cotton. Electrochemical performance suggests that the optimal nitrogen-containing cotton-derived carbon frameworks with a high nitrogen content (12.1 mol%) along with low surface area 285 m2 g-1 present high specific capacities of the 308 and 200 F g-1 in KOH electrolyte at current densities of 0.1 and 10 A g-1, respectively, with very limited capacitance loss upon 10,000 cycles in both aqueous and gel electrolytes. Moreover, the electrode exhibits the highest capacitance up to 220 F g-1 at 0.1 A g-1 and excellent flexibility (with negligible capacitance loss under different bending angles) in the polyvinyl alcohol/KOH gel electrolyte. The observed excellent performance competes well with that found in the electrodes of similar 3D frameworks formed by graphene or CNTs. Therefore, the ultralow-cost and simply strategy here demonstrates great potential for scalable producing high-performance carbon-based supercapacitors in the industry.

  12. High nitrogen-containing cotton derived 3D porous carbon frameworks for high-performance supercapacitors

    PubMed Central

    Fan, Li-Zhen; Chen, Tian-Tian; Song, Wei-Li; Li, Xiaogang; Zhang, Shichao

    2015-01-01

    Supercapacitors fabricated by 3D porous carbon frameworks, such as graphene- and carbon nanotube (CNT)-based aerogels, have been highly attractive due to their various advantages. However, their high cost along with insufficient yield has inhibited their large-scale applications. Here we have demonstrated a facile and easily scalable approach for large-scale preparing novel 3D nitrogen-containing porous carbon frameworks using ultralow-cost commercial cotton. Electrochemical performance suggests that the optimal nitrogen-containing cotton-derived carbon frameworks with a high nitrogen content (12.1 mol%) along with low surface area 285 m2 g−1 present high specific capacities of the 308 and 200 F g−1 in KOH electrolyte at current densities of 0.1 and 10 A g−1, respectively, with very limited capacitance loss upon 10,000 cycles in both aqueous and gel electrolytes. Moreover, the electrode exhibits the highest capacitance up to 220 F g−1 at 0.1 A g−1 and excellent flexibility (with negligible capacitance loss under different bending angles) in the polyvinyl alcohol/KOH gel electrolyte. The observed excellent performance competes well with that found in the electrodes of similar 3D frameworks formed by graphene or CNTs. Therefore, the ultralow-cost and simply strategy here demonstrates great potential for scalable producing high-performance carbon-based supercapacitors in the industry. PMID:26472144

  13. Diffuse mass transport in a porous medium

    NASA Astrophysics Data System (ADS)

    Ho, F. G.

    1981-08-01

    Variational methods are used to investigate the problems of diffusive mass transport in a porous medium. Calculations of the effective diffusivities are performed for a model pore structure generated by randomly placed, freely overlapping solid spheres all of the same radius. Effects of the tortuosity of the diffusion paths are considered. Numerical evaluations are used to test some approximate engineering models. For gaseous transition region diffusion the mean free path kinetic theory is used to derive a variational upper bound on the effective transition region diffusivity. For the simultaneous liquid or gas phase Fickian bulk diffusion in the void and Fickian surface diffusion on the pore wall surface, an analytical expression for effective diffusion coefficient is obtained and compared with the usual engineering model of parallel surface and void diffusion. The simultaneous gaseous transition region diffusion in the void and the Fickian surface diffusion on the pore wall surface are examined numerically.

  14. Capillary Condensation in a Fractal Porous Medium

    SciTech Connect

    Broseta, Daniel; Barre, Loic; Vizika, Olga; Shahidzadeh, Noushine; Guilbaud, Jean-Pierre; Lyonnard, Sandrine

    2001-06-04

    Small-angle x-ray and neutron scattering are used to characterize the surface roughness and porosity of a natural rock which are described over three decades in length scales and over nine decades in scattered intensities by a surface fractal dimension D=2.68{+-}0.03 . When this porous medium is exposed to a vapor of a contrast-matched water, neutron scattering reveals that surface roughness disappears at small scales, where a Porod behavior typical of smooth interfaces is observed instead. Water-sorption measurements confirm that such interface smoothing is due predominantly to the water condensing in the most strongly curved asperities rather than covering the surface with a wetting film of uniform thickness.

  15. Construction of 3D hierarchical SnO2 microspheres from porous nanosheets towards NO decomposition

    NASA Astrophysics Data System (ADS)

    Le, Thi Hang; Truong, Quang Duc; Kimura, Takeshi; Li, Huihui; Guo, Chongsen; Yin, Shu; Sato, Tsugio; Ling, Yong-Chien

    2013-01-01

    Three-dimensional (3D) hierarchical architectures are currently attracting worldwide interest owing to their fascinating morphology-dependent properties and potential applications. Herein we constructed SnO2 microspheres with 3D hierarchical flower-like architectures self-assembled with porous SnS2 nanosheets by a facile hydrothermal method with subsequent calcination. The chemical and physical properties as well as photocatalytic application of SnO2 microspheres were investigated. The size and morphology were examined with scanning electron microscopy and transmission electron microscopy. The phase and crystalline structure were determined with powder X-ray diffraction. The UV-Vis absorption property was determined with UV-Vis diffuse reflectance. The photocatalytic activities were evaluated with nitrogen monoxide (NO) decomposition under UV-Vis light irradiation. The effects of calcination temperature on morphology and NO decomposition were also studied.

  16. 3D-printed porous titanium changed femoral head repair growth patterns: osteogenesis and vascularisation in porous titanium.

    PubMed

    Zhu, Wei; Zhao, Yan; Ma, Qi; Wang, Yingjie; Wu, Zhihong; Weng, Xisheng

    2017-04-01

    Osteonecrosis of the femoral head (ONFH) is a major cause of morbidity, and total hip arthroplasty is both traumatic and expensive. Here, we created a gelatine scaffold embedded in uniquely shaped, 3D-printed porous titanium parts, which could attract and promote the proliferation of osteoblasts as well as bone regeneration, as the extracellular matrix (ECM) does in vivo. Interestingly, after hybridisation with platelets, the scaffold exhibited a low yet considerable rate of stable, safe and long-term growth factor release. Additionally, a novel ONFH model was constructed and verified. Scaffolds implanted in this model were found to accelerate bone repair. In conclusion, our scaffold successfully simulates the ECM and considerably accelerates bone regeneration, in which platelets play an indispensable role. We believe that platelets should be emphasised as carriers that may be employed to transport drugs, cytokines and other small molecules to target locations in vivo. In addition, this novel scaffold is a useful material for treating ONFH. An overview of the novel scaffold mimicking the extracellular environment in bone repair. a and b: A gelatine scaffold was cross-linked and freeze-dried within 3D-printed porous titanium. c: Platelets were coated onto the gelatine microscaffold after freeze-drying platelet-rich plasma. d: The microscaffold supported the migration of cells into the titanium pores and their subsequent growth, while the platelets slowly released cell factors, exerting bioactivity.

  17. From micro-scale 3D simulations to macro-scale model of periodic porous media

    NASA Astrophysics Data System (ADS)

    Crevacore, Eleonora; Tosco, Tiziana; Marchisio, Daniele; Sethi, Rajandrea; Messina, Francesca

    2015-04-01

    In environmental engineering, the transport of colloidal suspensions in porous media is studied to understand the fate of potentially harmful nano-particles and to design new remediation technologies. In this perspective, averaging techniques applied to micro-scale numerical simulations are a powerful tool to extrapolate accurate macro-scale models. Choosing two simplified packing configurations of soil grains and starting from a single elementary cell (module), it is possible to take advantage of the periodicity of the structures to reduce the computation costs of full 3D simulations. Steady-state flow simulations for incompressible fluid in laminar regime are implemented. Transport simulations are based on the pore-scale advection-diffusion equation, that can be enriched introducing also the Stokes velocity (to consider the gravity effect) and the interception mechanism. Simulations are carried on a domain composed of several elementary modules, that serve as control volumes in a finite volume method for the macro-scale method. The periodicity of the medium involves the periodicity of the flow field and this will be of great importance during the up-scaling procedure, allowing relevant simplifications. Micro-scale numerical data are treated in order to compute the mean concentration (volume and area averages) and fluxes on each module. The simulation results are used to compare the micro-scale averaged equation to the integral form of the macroscopic one, making a distinction between those terms that could be computed exactly and those for which a closure in needed. Of particular interest it is the investigation of the origin of macro-scale terms such as the dispersion and tortuosity, trying to describe them with micro-scale known quantities. Traditionally, to study the colloidal transport many simplifications are introduced, such those concerning ultra-simplified geometry that usually account for a single collector. Gradual removal of such hypothesis leads to a

  18. A miniature microbial fuel cell with conducting nanofibers-based 3D porous biofilm

    NASA Astrophysics Data System (ADS)

    Jiang, Huawei; Halverson, Larry J.; Dong, Liang

    2015-12-01

    Miniature microbial fuel cell (MFC) technology has received growing interest due to its potential applications in high-throughput screening of bacteria and mutants to elucidate mechanisms of electricity generation. This paper reports a novel miniature MFC with an improved output power density and short startup time, utilizing electrospun conducting poly(3,4-ethylenedioxythiophene) (PEDOT) nanofibers as a 3D porous anode within a 12 μl anolyte chamber. This device results in 423 μW cm-3 power density based on the volume of the anolyte chamber, using Shewanella oneidensis MR-1 as a model biocatalyst without any optimization of bacterial culture. The device also excels in a startup time of only 1hr. The high conductivity of the electrospun nanofibers makes them suitable for efficient electron transfer. The mean pore size of the conducting nanofibers is several micrometers, which is favorable for bacterial penetration and colonization of surfaces of the nanofibers. We demonstrate that S. oneidensis can fully colonize the interior region of this nanofibers-based porous anode. This work represents a new attempt to explore the use of electrospun PEDOT nanofibers as a 3D anode material for MFCs. The presented miniature MFC potentially will provide a high-sensitivity, high-throughput tool to screen suitable bacterial species and mutant strains for use in large-size MFCs.

  19. 3D printing of porous hydroxyapatite scaffolds intended for use in bone tissue engineering applications.

    PubMed

    Cox, Sophie C; Thornby, John A; Gibbons, Gregory J; Williams, Mark A; Mallick, Kajal K

    2015-02-01

    A systematic characterisation of bone tissue scaffolds fabricated via 3D printing from hydroxyapatite (HA) and poly(vinyl)alcohol (PVOH) composite powders is presented. Flowability of HA:PVOH precursor materials was observed to affect mechanical stability, microstructure and porosity of 3D printed scaffolds. Anisotropic behaviour of constructs and part failure at the boundaries of interlayer bonds was highlighted by compressive strength testing. A trade-off between the ability to facilitate removal of PVOH thermal degradation products during sintering and the compressive strength of green parts was revealed. The ultimate compressive strength of 55% porous green scaffolds printed along the Y-axis and dried in a vacuum oven for 6h was 0.88 ± 0.02 MPa. Critically, the pores of 3D printed constructs could be user designed, ensuring bulk interconnectivity, and the imperfect packing of powder particles created an inherent surface roughness and non-designed porosity within the scaffold. These features are considered promising since they are known to facilitate osteoconduction and osteointegration in-vivo. Characterisation techniques utilised in this study include two funnel flow tests, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), compressive strength testing and computed tomography (CT).

  20. Urethral reconstruction with a 3D porous bacterial cellulose scaffold seeded with lingual keratinocytes in a rabbit model.

    PubMed

    Huang, Jian-Wen; Lv, Xiang-Guo; Li, Zhe; Song, Lu-Jie; Feng, Chao; Xie, Min-Kai; Li, Chao; Li, Hong-Bin; Wang, Ji-Hong; Zhu, Wei-Dong; Chen, Shi-Yan; Wang, Hua-Ping; Xu, Yue-Min

    2015-09-11

    The goal of this study was to evaluate the effects of urethral reconstruction with a three-dimensional (3D) porous bacterial cellulose (BC) scaffold seeded with lingual keratinocytes in a rabbit model. A novel 3D porous BC scaffold was prepared by gelatin sponge interfering in the BC fermentation process. Rabbit lingual keratinocytes were isolated, expanded, and seeded onto 3D porous BC. BC alone (group 1, N  =  10), 3D porous BC alone (group 2, N  =  10), and 3D porous BC seeded with lingual keratinocytes (group 3, N  =  10) were used to repair rabbit ventral urethral defects (2.0   ×   0.8 cm). Scanning electron microscopy revealed that BC consisted of a compact laminate while 3D porous BC was composed of a porous sheet buttressed by a dense outer layer. The average pore diameter and porosity of the 3D porous BC were 4.23   ±   1.14 μm and 67.00   ±   6.80%, respectively. At 3 months postoperatively, macroscopic examinations and retrograde urethrograms of urethras revealed that all urethras maintained wide calibers in group 3. Strictures were found in all rabbits in groups 1 and 2. Histologically, at 1 month postoperatively, intact epithelium occurred in group 3, and discontinued epithelium was found in groups 1 and 2. However, groups 2 and 3 exhibited similar epithelial regeneration, which was superior to that of group 1 at 3 months (p  <  0.05). Comparisons of smooth muscle content and endothelia density among the three groups revealed a significant increase at each time point (p  <  0.05). Our results demonstrated that 3D porous BC seeded with lingual keratinocytes enhanced urethral tissue regeneration. 3D porous BC could potentially be used as an optimized scaffold for urethral reconstruction.

  1. Dynamics of osmosis in a porous medium

    PubMed Central

    Cardoso, Silvana S. S.; Cartwright, Julyan H. E.

    2014-01-01

    We derive from kinetic theory, fluid mechanics and thermodynamics the minimal continuum-level equations governing the flow of a binary, non-electrolytic mixture in an isotropic porous medium with osmotic effects. For dilute mixtures, these equations are linear and in this limit provide a theoretical basis for the widely used semi-empirical relations of Kedem & Katchalsky (Kedem & Katchalsky 1958 Biochim. Biophys. Acta 27, 229–246 (doi:10.1016/0006-3002(58)90330-5), which have hitherto been validated experimentally but not theoretically. The above linearity between the fluxes and the driving forces breaks down for concentrated or non-ideal mixtures, for which our equations go beyond the Kedem–Katchalsky formulation. We show that the heretofore empirical solute permeability coefficient reflects the momentum transfer between the solute molecules that are rejected at a pore entrance and the solvent molecules entering the pore space; it can be related to the inefficiency of a Maxwellian demi-demon. PMID:26064566

  2. Structural optimization of 3D porous electrodes for high-rate performance lithium ion batteries.

    PubMed

    Ye, Jianchao; Baumgaertel, Andreas C; Wang, Y Morris; Biener, Juergen; Biener, Monika M

    2015-02-24

    Much progress has recently been made in the development of active materials, electrode morphologies and electrolytes for lithium ion batteries. Well-defined studies on size effects of the three-dimensional (3D) electrode architecture, however, remain to be rare due to the lack of suitable material platforms where the critical length scales (such as pore size and thickness of the active material) can be freely and deterministically adjusted over a wide range without affecting the overall 3D morphology of the electrode. Here, we report on a systematic study on length scale effects on the electrochemical performance of model 3D np-Au/TiO2 core/shell electrodes. Bulk nanoporous gold provides deterministic control over the pore size and is used as a monolithic metallic scaffold and current collector. Extremely uniform and conformal TiO2 films of controlled thickness were deposited on the current collector by employing atomic layer deposition (ALD). Our experiments demonstrate profound performance improvements by matching the Li(+) diffusivity in the electrolyte and the solid state through adjusting pore size and thickness of the active coating which, for 200 μm thick porous electrodes, requires the presence of 100 nm pores. Decreasing the thickness of the TiO2 coating generally improves the power performance of the electrode by reducing the Li(+) diffusion pathway, enhancing the Li(+) solid solubility, and minimizing the voltage drop across the electrode/electrolyte interface. With the use of the optimized electrode morphology, supercapacitor-like power performance with lithium-ion-battery energy densities was realized. Our results provide the much-needed fundamental insight for the rational design of the 3D architecture of lithium ion battery electrodes with improved power performance.

  3. Preparation and Evaluation of Gelatin-Chitosan-Nanobioglass 3D Porous Scaffold for Bone Tissue Engineering

    PubMed Central

    Maji, Kanchan; Dasgupta, Sudip; Pramanik, Krishna; Bissoyi, Akalabya

    2016-01-01

    The aim of the present study was to prepare and characterize bioglass-natural biopolymer based composite scaffold and evaluate its bone regeneration ability. Bioactive glass nanoparticles (58S) in the size range of 20–30 nm were synthesized using sol-gel method. Porous scaffolds with varying bioglass composition from 10 to 30 wt% in chitosan, gelatin matrix were fabricated using the method of freeze drying of its slurry at 40 wt% solids loading. Samples were cross-linked with glutaraldehyde to obtain interconnected porous 3D microstructure with improved mechanical strength. The prepared scaffolds exhibited >80% porosity with a mean pore size range between 100 and 300 microns. Scaffold containing 30 wt% bioglass (GCB 30) showed a maximum compressive strength of 2.2 ± 0.1 MPa. Swelling and degradation studies showed that the scaffold had excellent properties of hydrophilicity and biodegradability. GCB 30 scaffold was shown to be noncytotoxic and supported mesenchymal stem cell attachment, proliferation, and differentiation as indicated by MTT assay and RUNX-2 expression. Higher cellular activity was observed in GCB 30 scaffold as compared to GCB 0 scaffold suggesting the fact that 58S bioglass nanoparticles addition into the scaffold promoted better cell adhesion, proliferation, and differentiation. Thus, the study showed that the developed composite scaffolds are potential candidates for regenerating damaged bone tissue. PMID:26884764

  4. Multi-contrast 3D X-ray imaging of porous and composite materials

    SciTech Connect

    Sarapata, Adrian; Herzen, Julia; Ruiz-Yaniz, Maite; Zanette, Irene; Rack, Alexander; Pfeiffer, Franz

    2015-04-13

    Grating-based X-ray computed tomography allows for simultaneous and nondestructive determination of the full X-ray complex index of refraction and the scattering coefficient distribution inside an object in three dimensions. Its multi-contrast capabilities combined with a high resolution of a few micrometers make it a suitable tool for assessing multiple phases inside porous and composite materials such as concrete. Here, we present quantitative results of a proof-of-principle experiment performed on a concrete sample. Thanks to the complementarity of the contrast channels, more concrete phases could be distinguished than in conventional attenuation-based imaging. The phase-contrast reconstruction shows high contrast between the hardened cement paste and the aggregates and thus allows easy 3D segmentation. Thanks to the dark-field image, micro-cracks inside the coarse aggregates are visible. We believe that these results are extremely interesting in the field of porous and composite materials studies because of unique information provided by grating interferometry in a non-destructive way.

  5. 3-D Numerical Simulation of Hydrostatic Tests of Porous Rocks Using Adapted Constitutive Model

    NASA Astrophysics Data System (ADS)

    Chemenda, A. I.; Daniel, M.

    2014-12-01

    The high complexity and poor knowledge of the constitutive properties of porous rocks are principal obstacles for the modeling of their deformation. Normally, the constitutive lows are to be derived from the experimental data (nominal strains and stresses). They are known, however, to be sensitive to the mechanical instabilities within the rock specimen and the boundary (notably friction) conditions at its ends. To elucidate the impact of these conditions on the measured mechanical response we use 3-D finite-difference simulations of experimental tests. Modeling of hydrostatic tests was chosen because it does not typically involve deformation instabilities. The ends of the cylindrical 'rock sample' are in contact with the 'steel' elastic platens through the frictional interfaces. The whole system is subjected to a normal stress Pc applied to the external model surface. A new constitutive model of porous rocks with the cap-type yield function is used. This function is quadratic in the mean stress σm and depends on the inelastic strain γp in a way to generate strain softening at small σm and strain-hardening at high σm. The corresponding material parameters are defined from the experimental data and have clear interpretation in terms of the geometry of the yield surface. The constitutive model with this yield function and the Drucker-Prager plastic potential has been implemented in 3-D dynamic explicit code Flac3D. The results of an extensive set of numerical simulations at different model parameters will be presented. They show, in particular, that the shape of the 'numerical' hydrostats is very similar to that obtained from the experimental tests and that it is practically insensitive to the interface friction. On the other hand, the stress and strain fields within the specimen dramatically depend on this parameter. The inelastic deformation at the specimen's ends starts well before reaching the grain crushing pressure P* and evolves heterogeneously with Pc

  6. 3D hybrid-porous carbon derived from carbonization of metal organic frameworks for high performance supercapacitors

    NASA Astrophysics Data System (ADS)

    Bao, Weizhai; Mondal, Anjon Kumar; Xu, Jing; Wang, Chengyin; Su, Dawei; Wang, Guoxiu

    2016-09-01

    We report a rational design and synthesis of 3D hybrid-porous carbon with a hierarchical pore architecture for high performance supercapacitors. It contains micropores (<2 nm diameter) and mesopores (2-4 nm), derived from carbonization of unique porous metal organic frameworks (MOFs). Owning to the synergistic effect of micropores and mesopores, the hybrid-porous carbon has exceptionally high ion-accessible surface area and low ion diffusion resistance, which is desired for supercapacitor applications. When applied as electrode materials in supercapacitors, 3D hybrid-porous carbon demonstrates a specific capacitance of 332 F g-1 at a constant charge/discharge current of 500 mA g-1. The supercapacitors can endure more than 10,000 cycles without degradation of capacitance.

  7. Ice-templated Self-assembly of VOPO4-Graphene Nanocomposites for Vertically Porous 3D Supercapacitor Electrodes

    NASA Astrophysics Data System (ADS)

    Lee, Kwang Hoon; Lee, Young-Woo; Lee, Seung Woo; Ha, Jeong Sook; Lee, Sang-Soo; Son, Jeong Gon

    2015-09-01

    A simple ice-templated self-assembly process is used to prepare a three-dimensional (3D) and vertically porous nanocomposite of layered vanadium phosphates (VOPO4) and graphene nanosheets with high surface area and high electrical conductivity. The resulting 3D VOPO4-graphene nanocomposite has a much higher capacitance of 527.9 F g-1 at a current density of 0.5 A g-1, compared with ~247 F g-1 of simple 3D VOPO4, with solid cycling stability. The enhanced pseudocapacitive behavior mainly originates from vertically porous structures from directionally grown ice crystals and simultaneously inducing radial segregation and forming inter-stacked structures of VOPO4-graphene nanosheets. This VOPO4-graphene nanocomposite electrode exhibits high surface area, vertically porous structure to the separator, structural stability from interstacked structure and high electrical conductivity, which would provide the short diffusion paths of electrolyte ions and fast transportation of charges within the conductive frameworks. In addition, an asymmetric supercapacitor (ASC) is fabricated by using vertically porous VOPO4-graphene as the positive electrode and vertically porous 3D graphene as the negative electrode; it exhibits a wide cell voltage of 1.6 V and a largely enhanced energy density of 108 Wh kg-1.

  8. Ice-templated Self-assembly of VOPO4–Graphene Nanocomposites for Vertically Porous 3D Supercapacitor Electrodes

    PubMed Central

    Lee, Kwang Hoon; Lee, Young-Woo; Lee, Seung Woo; Ha, Jeong Sook; Lee, Sang-Soo; Son, Jeong Gon

    2015-01-01

    A simple ice-templated self-assembly process is used to prepare a three-dimensional (3D) and vertically porous nanocomposite of layered vanadium phosphates (VOPO4) and graphene nanosheets with high surface area and high electrical conductivity. The resulting 3D VOPO4–graphene nanocomposite has a much higher capacitance of 527.9 F g−1 at a current density of 0.5 A g−1, compared with ~247 F g−1 of simple 3D VOPO4, with solid cycling stability. The enhanced pseudocapacitive behavior mainly originates from vertically porous structures from directionally grown ice crystals and simultaneously inducing radial segregation and forming inter-stacked structures of VOPO4–graphene nanosheets. This VOPO4–graphene nanocomposite electrode exhibits high surface area, vertically porous structure to the separator, structural stability from interstacked structure and high electrical conductivity, which would provide the short diffusion paths of electrolyte ions and fast transportation of charges within the conductive frameworks. In addition, an asymmetric supercapacitor (ASC) is fabricated by using vertically porous VOPO4–graphene as the positive electrode and vertically porous 3D graphene as the negative electrode; it exhibits a wide cell voltage of 1.6 V and a largely enhanced energy density of 108 Wh kg−1. PMID:26333591

  9. Recent advance in fabricating monolithic 3D porous graphene and their applications in biosensing and biofuel cells.

    PubMed

    Qiu, Hua-Jun; Guan, Yongxin; Luo, Pan; Wang, Yu

    2017-03-15

    Graphene shows great potential in biosensing and bioelectronics. To facilitate graphene's applications and enhance its performance, recently, three-dimensional (3D) graphene-based materials especially free-standing porous graphene with tunable pore size and void space, have attracted increasing attention for bio-related applications owing to their special features. 3D graphene usually shows the following merits such as an interconnected porous network, a high electronic conductivity, a large active surface area, good chemical/thermal stability and can be more easily handled compared with dispersed graphene sheets. With modified surface properties, graphene can also be bio-friendly. These properties make 3D graphene a perfect candidate as high-performance electrode materials in bioelectronics devices. In this review, we discuss recent advance in fabricating monolithic 3D graphene and their applications in biosensing and biofuel cells.

  10. Hierarchical micro-lamella-structured 3D porous copper current collector coated with tin for advanced lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Park, Hyeji; Um, Ji Hyun; Choi, Hyelim; Yoon, Won-Sub; Sung, Yung-Eun; Choe, Heeman

    2017-03-01

    A Novel 3D porous Sn-Cu architecture is prepared as an anode material for use in an advanced lithium-ion battery. Micro-lamellar-structured 3D porous Cu foam, which is electroless-plated with Sn as an active material, is used as anode current collector. Compared to Sn-coated Cu foil, the 3D Sn-Cu foam exhibits superior Li-ion capacity and stable capacity retention, demonstrating the advantage of 3D porous architecture by preserving its structural integrity. In addition, the effect of heat-treatment after Sn plating is investigated. Sn/Sn6Cu5 and SnO2/Cu10Sn3 were formed on and in the 3D Sn-Cu foam under the heat-treatment at 150 °C and 500 °C, respectively. The development of Cu10Sn3 in the 3D Sn-Cu foam heat-treated at 500 °C can be a key factor for the enhanced cyclic stability because the Cu10Sn3 inactively reacts with Li-ion and alleviates the volume expansion of SnO2 as an inactive matrix.

  11. 3D Printing Bioceramic Porous Scaffolds with Good Mechanical Property and Cell Affinity

    PubMed Central

    Chang, Chih-Hao; Lin, Chih-Yang; Liu, Fwu-Hsing; Chen, Mark Hung-Chih; Lin, Chun-Pin; Ho, Hong-Nerng; Liao, Yunn-Shiuan

    2015-01-01

    Artificial bone grafting is widely used in current orthopedic surgery for bone defect problems. Unfortunately, surgeons remain unsatisfied with the current commercially available products. One of the major complaints is that these products cannot provide sufficient mechanical strength to support the human skeletal structure. In this study, we aimed to develop a bone scaffold with better mechanical property and good cell affinity by 3D printing (3DP) techniques. A self-developed 3D printer with laser-aided gelling (LAG) process was used to fabricate bioceramic scaffolds with inter-porous structures. To improve the mechanical property of the bioceramic parts after heating, CaCO3 was added to the silica ceramic slurry. CaCO3 was blended into a homogenous SiO2-sol dispersion at weight ratios varying from 0/100 to 5/95 to 9/91 (w/w). Bi-component CaCO3/SiO2-sol was prepared as a biocomposite for the 3DP scaffold. The well-mixed biocomposite was used to fabricate the bioceramic green part using the LAG method. The varied scaffolds were sintered at different temperatures ranging from 900 to 1500°C, and the mechanical property was subsequently analyzed. The scaffolds showed good property with the composite ratio of 5:95 CaCO3:SiO2 at a sintering temperature of 1300°C. The compressive strength was 47 MPa, and the porosity was 34%. The topography of the sintered 3DP bioceramic scaffold was examined by SEM, EDS and XRD. The silica bioceramic presented no cytotoxicity and good MG-63 osteoblast-like cell affinity, demonstrating good biocompatibility. Therefore, the new silica biocomposite is viable for fabricating 3DP bone bioceramics with improved mechanical property and good cell affinity. PMID:26618362

  12. 3D Printing Bioceramic Porous Scaffolds with Good Mechanical Property and Cell Affinity.

    PubMed

    Chang, Chih-Hao; Lin, Chih-Yang; Liu, Fwu-Hsing; Chen, Mark Hung-Chih; Lin, Chun-Pin; Ho, Hong-Nerng; Liao, Yunn-Shiuan

    2015-01-01

    Artificial bone grafting is widely used in current orthopedic surgery for bone defect problems. Unfortunately, surgeons remain unsatisfied with the current commercially available products. One of the major complaints is that these products cannot provide sufficient mechanical strength to support the human skeletal structure. In this study, we aimed to develop a bone scaffold with better mechanical property and good cell affinity by 3D printing (3DP) techniques. A self-developed 3D printer with laser-aided gelling (LAG) process was used to fabricate bioceramic scaffolds with inter-porous structures. To improve the mechanical property of the bioceramic parts after heating, CaCO3 was added to the silica ceramic slurry. CaCO3 was blended into a homogenous SiO2-sol dispersion at weight ratios varying from 0/100 to 5/95 to 9/91 (w/w). Bi-component CaCO3/SiO2-sol was prepared as a biocomposite for the 3DP scaffold. The well-mixed biocomposite was used to fabricate the bioceramic green part using the LAG method. The varied scaffolds were sintered at different temperatures ranging from 900 to 1500°C, and the mechanical property was subsequently analyzed. The scaffolds showed good property with the composite ratio of 5:95 CaCO3:SiO2 at a sintering temperature of 1300°C. The compressive strength was 47 MPa, and the porosity was 34%. The topography of the sintered 3DP bioceramic scaffold was examined by SEM, EDS and XRD. The silica bioceramic presented no cytotoxicity and good MG-63 osteoblast-like cell affinity, demonstrating good biocompatibility. Therefore, the new silica biocomposite is viable for fabricating 3DP bone bioceramics with improved mechanical property and good cell affinity.

  13. Production and in vitro characterization of 3D porous scaffolds made of magnesium carbonate apatite (MCA)/anionic collagen using a biomimetic approach.

    PubMed

    Sader, Marcia S; Martins, Virginia C A; Gomez, Santiago; LeGeros, Racquel Z; Soares, Gloria A

    2013-10-01

    3D porous scaffolds are relevant biomaterials to bone engineering as they can be used as templates to tissue reconstruction. The aim of the present study was to produce and characterize in vitro 3D magnesium-carbonate apatite/collagen (MCA/col) scaffolds. They were prepared by using biomimetic approach, followed by cross-linking with 0.25% glutaraldehyde solution (GA) and liofilization. Results obtained with Fourier-transform infrared spectroscopy (FT-IR) confirmed the type-B carbonate substitution, while by X-ray diffraction (XRD), a crystallite size of ~10nm was obtained. Optical and electron microscopy showed that the cylindrical samples exhibited an open-porous morphology, with apatite nanocrystals precipitated on collagen fibrils. The cross-linked 3D scaffolds showed integrity when immersed in culture medium up to 14 days. Also, the immersion of such samples into an acid buffer solution, to mimic the osteoclastic resorption environment, promotes the release of important ions for bone repair, such as calcium, phosphorus and magnesium. Bone cells (SaOs2) adhered, and proliferated on the 3D composite scaffolds, showing that synthesis and the cross-linking processes did not induce cytotoxicity.

  14. Carbon Quantum Dots and Their Derivative 3D Porous Carbon Frameworks for Sodium-Ion Batteries with Ultralong Cycle Life.

    PubMed

    Hou, Hongshuai; Banks, Craig E; Jing, Mingjun; Zhang, Yan; Ji, Xiaobo

    2015-12-16

    A new methodology for the synthesis of carbon quantum dots (CQDs) for large production is proposed. The as-obtained CQDs can be transformed into 3D porous carbon frameworks exhibiting superb sodium storage properties with ultralong cycle life and ultrahigh rate capability, comparable to state-of-the-art carbon anode materials for sodium-ion batteries.

  15. Surface functionalization of 3D glass-ceramic porous scaffolds for enhanced mineralization in vitro

    NASA Astrophysics Data System (ADS)

    Ferraris, Sara; Vitale-Brovarone, Chiara; Bretcanu, Oana; Cassinelli, Clara; Vernè, Enrica

    2013-04-01

    Bone reconstruction after tissue loosening due to traumatic, pathological or surgical causes is in increasing demand. 3D scaffolds are a widely studied solution for supporting new bone growth. Bioactive glass-ceramic porous materials can offer a three-dimensional structure that is able to chemically bond to bone. The ability to surface modify these devices by grafting biologically active molecules represents a challenge, with the aim of stimulating physiological bone regeneration with both inorganic and organic signals. In this research work glass ceramic scaffolds with very high mechanical properties and moderate bioactivity have been functionalized with the enzyme alkaline phosphatase (ALP). The material surface was activated in order to expose hydroxyl groups. The activated surface was further grafted with ALP both via silanization and also via direct grafting to the surface active hydroxyl groups. Enzymatic activity of grafted samples were measured by means of UV-vis spectroscopy before and after ultrasonic washing in TRIS-HCl buffer solution. In vitro inorganic bioactivity was investigated by soaking the scaffolds after the different steps of functionalization in a simulated body fluid (SBF). SEM observations allowed the monitoring of the scaffold morphology and surface chemical composition after soaking in SBF. The presence of ALP enhanced the in vitro inorganic bioactivity of the tested material.

  16. Cation Exchange in Dynamic 3D Porous Magnets: Improvement of the Physical Properties.

    PubMed

    Grancha, Thais; Acosta, Alvaro; Cano, Joan; Ferrando-Soria, Jesús; Seoane, Beatriz; Gascon, Jorge; Pasán, Jorge; Armentano, Donatella; Pardo, Emilio

    2015-11-16

    We report two novel three-dimensional porous coordination polymers (PCPs) of formulas Li4{Mn4[Cu2(Me3mpba)2]3}·68H2O (2) and K4{Mn4[Cu2(Me3mpba)2]3}·69H2O (3) obtained-via alkali cation exchange in a single-crystal to single-crystal process-from the earlier reported anionic manganese(II)-copper(II) PCP of formula Na4{Mn4[Cu2(Me3mpba)2]3}·60H2O (1) [Me3mpba(4-) = N,N'-2,4,6-trimethyl-1,3-phenylenebis(oxamate)]. This postsynthetic process succeeds where the direct synthesis in solution from the corresponding building blocks fails and affords significantly more robust PCPs with enhanced magnetic properties [long-range 3D magnetic ordering temperatures for the dehydrated phases (1'-3') of 2.0 (1'), 12.0 (2'), and 20.0 K (3')]. Changes in the adsorptive properties upon postsynthetic exchange suggest that the nature, electrostatic properties, mobility, and location of the cations within the framework are crucial for the enhanced structural stability. Overall, these results further confirm the potential of postsynthetic methods (including cation exchange) to obtain PCPs with novel or enhanced physical properties while maintaining unaltered their open-framework structures.

  17. Highly Porous Gelatin Reinforced 3D Scaffolds for Articular Cartilage Regeneration.

    PubMed

    Amadori, Sofia; Torricelli, Paola; Panzavolta, Silvia; Parrilli, Annapaola; Fini, Milena; Bigi, Adriana

    2015-07-01

    3D highly porous (93% total porosity) gelatin scaffolds were prepared according to a novel, simple method, which implies gelatin foaming, gelification, soaking into ethanol and successive freeze-drying. Reinforcement of the as-prepared scaffolds (GEL) was performed through immersion in aqueous solutions at different gelatin concentrations. Reinforcement solutions with and without genipin addition allowed to prepare two series of samples:cross-linked and uncross-linked samples, respectively. The amount of gelatin adsorbed onto the reinforced samples increases as a function of gelatin concentration in solution and provokes a drastic improvement of the compressive modulus and collapse strength up to values of about 30 and 4 MPa, respectively. The open and interconnected porosity, although slightly reduced, is still of the order of 80% in the samples reinforced with the highest concentration of gelatin. Water uptake ability evaluated after immersion in PBS for 20 s decreases with gelatin reinforcement. The presence of genipin in cross-linked samples reduces gelatin release and stabilizes the scaffolds in solution. Chondrocytes from human articular cartilage adhere, proliferate, and penetrate into the scaffolds. The evaluation of differentiation markers both on the supernatants of cell culture and by means of quantitative polymerase chain reaction (qPCR) indicates a dose-dependent promotion of cell differentiation.

  18. Porous Structures in Stacked, Crumpled and Pillared Graphene-Based 3D Materials

    PubMed Central

    Guo, Fei; Creighton, Megan; Chen, Yantao; Hurt, Robert; Külaots, Indrek

    2015-01-01

    Graphene, an atomically thin material with the theoretical surface area of 2600 m2g−1, has great potential in the fields of catalysis, separation, and gas storage if properly assembled into functional 3D materials at large scale. In ideal non-interacting ensembles of non-porous multilayer graphene plates, the surface area can be adequately estimated using the simple geometric law ~ 2600 m2g−1/N, where N is the number of graphene sheets per plate. Some processing operations, however, lead to secondary plate-plate stacking, folding, crumpling or pillaring, which give rise to more complex structures. Here we show that bulk samples of multilayer graphene plates stack in an irregular fashion that preserves the 2600/N surface area and creates regular slot-like pores with sizes that are multiples of the unit plate thickness. In contrast, graphene oxide deposits into films with massive area loss (2600 to 40 m2g−1) due to nearly perfect alignment and stacking during the drying process. Pillaring graphene oxide sheets by co-deposition of colloidal-phase particle-based spacers has the potential to partially restore the large monolayer surface. Surface areas as high as 1000 m2g−1 are demonstrated here through colloidal-phase deposition of graphene oxide with water-dispersible aryl-sulfonated ultrafine carbon black as a pillaring agent. PMID:26478597

  19. Instant gelation synthesis of 3D porous MoS2@C nanocomposites for lithium ion batteries.

    PubMed

    Fei, Ling; Xu, Yun; Wu, Xiaofei; Chen, Gen; Li, Yuling; Li, Binsong; Deng, Shuguang; Smirnov, Sergei; Fan, Hongyou; Luo, Hongmei

    2014-04-07

    Three-dimensional (3D) nanoporous architectures, possessing high surface area, massive pores, and excellent structural stability, are highly desirable for many applications including catalysts and electrode materials in lithium ion batteries. However, the preparation of such materials remains a major challenge. Here, we introduce a novel method, instant gelation, for the synthesis of such materials. The as-prepared porous 3D MoS2@C nanocomposites, with layered MoS2 clusters or strips ingrained in porous and conductive 3D carbon matrix, indeed showed excellent electrochemical performance when applied as anode materials for lithium ion batteries. Its interconnected carbon network ensures good conductivity and fast electron transport; the micro-, and mesoporous nature effectively shortens the lithium ion diffusion path and provides room necessary for volume expansion. The large specific surface area is beneficial for a better contact between electrode materials and electrolyte.

  20. Simultaneous elastic parameter inversion in 2-D/3-D TTI medium combined later arrival times

    NASA Astrophysics Data System (ADS)

    Bai, Chao-ying; Wang, Tao; Yang, Shang-bei; Li, Xing-wang; Huang, Guo-jiao

    2016-04-01

    Traditional traveltime inversion for anisotropic medium is, in general, based on a "weak" assumption in the anisotropic property, which simplifies both the forward part (ray tracing is performed once only) and the inversion part (a linear inversion solver is possible). But for some real applications, a general (both "weak" and "strong") anisotropic medium should be considered. In such cases, one has to develop a ray tracing algorithm to handle with the general (including "strong") anisotropic medium and also to design a non-linear inversion solver for later tomography. Meanwhile, it is constructive to investigate how much the tomographic resolution can be improved by introducing the later arrivals. For this motivation, we incorporated our newly developed ray tracing algorithm (multistage irregular shortest-path method) for general anisotropic media with a non-linear inversion solver (a damped minimum norm, constrained least squares problem with a conjugate gradient approach) to formulate a non-linear inversion solver for anisotropic medium. This anisotropic traveltime inversion procedure is able to combine the later (reflected) arrival times. Both 2-D/3-D synthetic inversion experiments and comparison tests show that (1) the proposed anisotropic traveltime inversion scheme is able to recover the high contrast anomalies and (2) it is possible to improve the tomographic resolution by introducing the later (reflected) arrivals, but not as expected in the isotropic medium, because the different velocity (qP, qSV and qSH) sensitivities (or derivatives) respective to the different elastic parameters are not the same but are also dependent on the inclination angle.

  1. Intermittent Lagrangian velocities and accelerations in three-dimensional porous medium flow.

    PubMed

    Holzner, M; Morales, V L; Willmann, M; Dentz, M

    2015-07-01

    Intermittency of Lagrangian velocity and acceleration is a key to understanding transport in complex systems ranging from fluid turbulence to flow in porous media. High-resolution optical particle tracking in a three-dimensional (3D) porous medium provides detailed 3D information on Lagrangian velocities and accelerations. We find sharp transitions close to pore throats, and low flow variability in the pore bodies, which gives rise to stretched exponential Lagrangian velocity and acceleration distributions characterized by a sharp peak at low velocity, superlinear evolution of particle dispersion, and double-peak behavior in the propagators. The velocity distribution is quantified in terms of pore geometry and flow connectivity, which forms the basis for a continuous-time random-walk model that sheds light on the observed Lagrangian flow and transport behaviors.

  2. 3D MHD SIMULATION OF FLARE SUPRA-ARCADE DOWNFLOWS IN A TURBULENT CURRENT SHEET MEDIUM

    SciTech Connect

    Cécere, M.; Zurbriggen, E.; Costa, A.; Schneiter, M.

    2015-07-01

    Supra-arcade downflows (SADs) are sunward, generally dark, plasma density depletions originated above posteruption flare arcades. In this paper, using 3D MHD simulations we investigate whether the SAD cavities can be produced by a direct combination of the tearing mode and Kelvin–Helmholtz instabilities leading to a turbulent current sheet (CS) medium or if the current sheet is merely the background where SADs are produced, triggered by an impulsive deposition of energy. We find that to give an account of the observational dark lane structures an addition of local energy, provided by a reconnection event, is required. We suggest that there may be a closed relation between characteristic SAD sizes and CS widths that must be satisfied to obtain an observable SAD.

  3. From ATLASGAL to SEDIGISM: Towards a Complete 3D View of the Dense Galactic Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Schuller, F.; Urquhart, J.; Bronfman, L.; Csengeri, T.; Bontemps, S.; Duarte-Cabral, A.; Giannetti, A.; Ginsburg, A.; Henning, T.; Immer, K.; Leurini, S.; Mattern, M.; Menten, K.; Molinari, S.; Muller, E.; Sánchez-Monge, A.; Schisano, E.; Suri, S.; Testi, L.; Wang, K.; Wyrowski, F.; Zavagno, A.

    2016-09-01

    The ATLASGAL survey has provided the first unbiased view of the inner Galactic Plane at sub-millimetre wavelengths. This is the largest ground-based survey of its kind to date, covering 420 square degrees at a wavelength of 870 µm. The reduced data, consisting of images and a catalogue of > 104 compact sources, are available from the ESO Science Archive Facility through the Phase 3 infrastructure. The extremely rich statistics of this survey initiated several follow-up projects, including spectroscopic observations to explore molecular complexity and high angular resolution imaging with the Atacama Large Millimeter/submillimeter Array (ALMA), aimed at resolving individual protostars. The most extensive follow-up project is SEDIGISM, a 3D mapping of the dense interstellar medium over a large fraction of the inner Galaxy. Some notable results of these surveys are highlighted.

  4. Unimpeded permeation of water through biocidal graphene oxide sheets anchored on to 3D porous polyolefinic membranes

    NASA Astrophysics Data System (ADS)

    Mural, Prasanna Kumar S.; Jain, Shubham; Kumar, Sachin; Madras, Giridhar; Bose, Suryasarathi

    2016-04-01

    3D porous membranes were developed by etching one of the phases (here PEO, polyethylene oxide) from melt-mixed PE/PEO binary blends. Herein, we have systematically discussed the development of these membranes using X-ray micro-computed tomography. The 3D tomograms of the extruded strands and hot-pressed samples revealed a clear picture as to how the morphology develops and coarsens over a function of time during post-processing operations like compression molding. The coarsening of PE/PEO blends was traced using X-ray micro-computed tomography and scanning electron microscopy (SEM) of annealed blends at different times. It is now understood from X-ray micro-computed tomography that by the addition of a compatibilizer (here lightly maleated PE), a stable morphology can be visualized in 3D. In order to anchor biocidal graphene oxide sheets onto these 3D porous membranes, the PE membranes were chemically modified with acid/ethylene diamine treatment to anchor the GO sheets which were further confirmed by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and surface Raman mapping. The transport properties through the membrane clearly reveal unimpeded permeation of water which suggests that anchoring GO on to the membranes does not clog the pores. Antibacterial studies through the direct contact of bacteria with GO anchored PE membranes resulted in 99% of bacterial inactivation. The possible bacterial inactivation through physical disruption of the bacterial cell wall and/or reactive oxygen species (ROS) is discussed herein. Thus this study opens new avenues in designing polyolefin based antibacterial 3D porous membranes for water purification.3D porous membranes were developed by etching one of the phases (here PEO, polyethylene oxide) from melt-mixed PE/PEO binary blends. Herein, we have systematically discussed the development of these membranes using X-ray micro-computed tomography. The 3D tomograms of the extruded strands and

  5. Understanding the effects of dielectric medium, substrate, and depth on electric fields and SERS of quasi-3D plasmonic nanostructures.

    PubMed

    Xu, Jiajie; Kvasnička, Pavel; Idso, Matthew; Jordan, Roger W; Gong, Heng; Homola, Jiří; Yu, Qiuming

    2011-10-10

    The local electric field distribution and the effect of surface-enhanced Raman spectroscopy (SERS) were investigated on the quasi-3D (Q3D) plasmonic nanostructures formed by gold nanohole and nanodisc array layers physically separated by a dielectric medium. The local electric fields at the top gold nanoholes and bottom gold nanodiscs as a function of the dielectric medium, substrate, and depth of Q3D plasmonic nanostructures upon the irradiation of a 785 nm laser were calculated using the three-dimensional finite-difference time-domain (3D-FDTD) method. The intensity of the maximum local electric fields was shown to oscillate with the depth and the stronger local electric fields occurring at the top or bottom gold layer strongly depend on the dielectric medium, substrate, and depth of the nanostructure. This phenomenon was determined to be related to the Fabry-Pérot interference effect and the interaction of localized surface plasmons (LSPs). The enhancement factors (EFs) of SERS obtained from the 3D-FDTD simulations were compared to those calculated from the SERS experiments conducted on the Q3D plasmonic nanostructures fabricated on silicon and ITO coated glass substrates with different depths. The same trend was obtained from both methods. The capabilities of tuning not only the intensity but also the location of the maximum local electric fields by varying the depth, dielectric medium, and substrate make Q3D plasmonic nanostructures well suited for highly sensitive and reproducible SERS detection and analysis.

  6. Design of advanced porous graphene materials: from graphene nanomesh to 3D architectures.

    PubMed

    Jiang, Lili; Fan, Zhuangjun

    2014-02-21

    In order to make full utilization of the high intrinsic surface area of graphene, recently, porous graphene materials including graphene nanomesh, crumpled graphene and graphene foam, have attracted tremendous attention and research interest, owing to their exceptional porous structure (high surface area, and high pore volume) in combination with the inherent properties of graphene, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. Interestingly, porous graphene materials and their derivatives have been explored in a wide range of applications in the fields of electronic and photonic devices, energy storage, gas separation/storage, oil absorption and sensors. This article reviews recent progress in the synthesis, characterization, properties, and applications of porous graphene materials. We aim to highlight the importance of designing different porous structures of graphene to meet future challenges, and the trend on future design of porous graphene materials is analyzed.

  7. Heat pipe effect in porous medium

    SciTech Connect

    Joseph, M.

    1992-12-01

    In this thesis a parametric study of the thermal and hydrologic characteristics of the fractured porous tuffs at Yucca Mountain, Nevada was conducted. The effects of different fracture and matrix properties including permeability, thermal conductivity, specific heat, porosity, and tortuosity on heat pipe performance in the vicinity of the waste package were observed. Computer simulations were carried out using TOUGH code on a Cray YMP-2 supercomputer. None of the fracture parameters affected the heat pipe performance except the mobility of the liquid in the fracture. Matrix permeability and thermal conductivity were found to have significant effect on the heat pipe performance. The effect of mass injection was studied for liquid water and air injected at the fracture boundary. A high rate of mass injection was required to produce any effect on the heat pipe. The fracture-matrix equilibrium is influenced by the matrix permeability and the matrix thermal conductivity.

  8. Fabrication of chitosan-silver nanoparticle hybrid 3D porous structure as a SERS substrate for biomedical applications

    NASA Astrophysics Data System (ADS)

    Jung, Gyeong-Bok; Kim, Ji-Hye; Burm, Jin Sik; Park, Hun-Kuk

    2013-05-01

    We propose a simple, low-cost, large-area, and functional surface enhanced Raman scattering (SERS) substrate for biomedical applications. The SERS substrate with chitosan-silver nanoparticles (chitosan-Ag NPs) hybrid 3D porous structure was fabricated simply by a one-step method. The chitosan was used as a template for the Ag NPs deposition. SERS enhancement by the chitosan-Ag NPs substrate was experimentally verified using rhodamine B as an analyte. Thiolated single stranded DNA was also measured for atopic dermatitis genetic markers (chemokines CCL17) at a low concentration of 5 pM. We successfully designed a novel SERS substrate with silver nanoparticle hybridized 3D porous chitosan that has the potential to become a highly sensitive and selective tool for biomedical applications.

  9. 3D Characterization of the Magnetic Signature of a Medium Sized Impact Crater at Odessa, TX

    NASA Astrophysics Data System (ADS)

    Robinson, A.; Soule, D.; Everett, M.; Rodman, T.; Mangue Ndong, M.; Pereira, A.; Platt, P.; Trahan, A.

    2008-12-01

    Meteorite impacts are a common occurrence throughout Earth's geologic history. Many of the surface expressions of large ancient impacts have been subsequently erased by weathering and erosion processes. The study of preserved meteorite impacts is necessary to better understand this natural hazard which has been increasingly linked to rapid climate change and mass extinctions. The 60 ka Odessa meteorite crater located in Ector Co. Texas, is unique because it is not only well-preserved, but also has been the subject of extensive geologic examination. Geologic mapping and numeric models indicate that the crater was caused by a relatively small oblique impactor. The crater rim is remarkably well exposed. Much of the ejecta blanket is present, although deeply eroded. There has been considerable site disturbance due to drilling, shaft excavation, trenching, construction of a museum, trails, and the oil/gas activity in surrounding fields. Two previous geophysical investigations have shown that our data clearly corresponds to large-scale thrust deformation. With this in mind we have performed 3D high resolution magnetic gradiometer surveys that will allow us to quantify and characterize the magnetic signature of small to medium impacts. We will tie this data set to a 3D photorealistic outcrop image provided by laser scanning with coarser-scale, below-ground geophysical information. Our geophysical imagery provides a useful constraint on numerical simulations of the impact and its immediate regional-scale environmental effects. This information can be used to identify impact sites whose surface expression has been erased by natural erosional processes, allowing for improved frequency estimates and improved geo-hazard assessment.

  10. 3D hierarchical porous graphene aerogel with tunable meso-pores on graphene nanosheets for high-performance energy storage

    PubMed Central

    Ren, Long; Hui, K. N.; Hui, K. S.; Liu, Yundan; Qi, Xiang; Zhong, Jianxin; Du, Yi; Yang, Jianping

    2015-01-01

    New and novel 3D hierarchical porous graphene aerogels (HPGA) with uniform and tunable meso-pores (e.g., 21 and 53 nm) on graphene nanosheets (GNS) were prepared by a hydrothermal self-assembly process and an in-situ carbothermal reaction. The size and distribution of the meso-pores on the individual GNS were uniform and could be tuned by controlling the sizes of the Co3O4 NPs used in the hydrothermal reaction. This unique architecture of HPGA prevents the stacking of GNS and promises more electrochemically active sites that enhance the electrochemical storage level significantly. HPGA, as a lithium-ion battery anode, exhibited superior electrochemical performance, including a high reversible specific capacity of 1100 mAh/g at a current density of 0.1 A/g, outstanding cycling stability and excellent rate performance. Even at a large current density of 20 A/g, the reversible capacity was retained at 300 mAh/g, which is larger than that of most porous carbon-based anodes reported, suggesting it to be a promising candidate for energy storage. The proposed 3D HPGA is expected to provide an important platform that can promote the development of 3D topological porous systems in a range of energy storage and generation fields. PMID:26382852

  11. Multi-thread parallel algorithm for reconstructing 3D large-scale porous structures

    NASA Astrophysics Data System (ADS)

    Ju, Yang; Huang, Yaohui; Zheng, Jiangtao; Qian, Xu; Xie, Heping; Zhao, Xi

    2017-04-01

    Geomaterials inherently contain many discontinuous, multi-scale, geometrically irregular pores, forming a complex porous structure that governs their mechanical and transport properties. The development of an efficient reconstruction method for representing porous structures can significantly contribute toward providing a better understanding of the governing effects of porous structures on the properties of porous materials. In order to improve the efficiency of reconstructing large-scale porous structures, a multi-thread parallel scheme was incorporated into the simulated annealing reconstruction method. In the method, four correlation functions, which include the two-point probability function, the linear-path functions for the pore phase and the solid phase, and the fractal system function for the solid phase, were employed for better reproduction of the complex well-connected porous structures. In addition, a random sphere packing method and a self-developed pre-conditioning method were incorporated to cast the initial reconstructed model and select independent interchanging pairs for parallel multi-thread calculation, respectively. The accuracy of the proposed algorithm was evaluated by examining the similarity between the reconstructed structure and a prototype in terms of their geometrical, topological, and mechanical properties. Comparisons of the reconstruction efficiency of porous models with various scales indicated that the parallel multi-thread scheme significantly shortened the execution time for reconstruction of a large-scale well-connected porous model compared to a sequential single-thread procedure.

  12. Instability of fluid flow over saturated porous medium

    NASA Astrophysics Data System (ADS)

    Lyubimova, Tatyana; Kolchanova, Ekaterina; Lyubimov, Dmitry

    2013-04-01

    We investigate the stability of a fluid flow over a saturated porous medium. The problem is of importance due to the applications to washing out of contaminants from the bottom layer of vegetation, whose properties are similar to the properties of porous medium. In the case of porous medium with the relatively high permeability and porosity the flow involves a part of the fluid saturating the porous medium, with the tangential fluid velocity drop occurring because of the resistance of the solid matrix. The drop leads to the instability analogous to Kelvin-Helmholtz one accompanied by the formation of travelling waves. In the present paper we consider a two-layer system consisting of a pure fluid layer and a porous layer saturated by the fluid located underneath. The system is bounded by a rigid surface at the bottom and a non-deformable free surface at the top. It is under the gravity and inclined at a slight angle to the horizontal axis. The boundary conditions at the interface between the fluid and porous layers are the continuity of fluid velocities and the balance of normal and tangential stresses taking into account the resistance of the solid matrix with respect to the fluid flow near the interface [1-2]. The problem is solved in the framework of the Brinkman model applying the classical shooting algorithm with orthogonalization. The stability boundaries of the stationary fluid flow over the saturated porous medium with respect to the small oscillatory perturbations are obtained for the various values of the Darcy number and the ratio of the porous layer thickness to the full thickness of the system d. It was shown that at the d > 0.5 with increasing the porous layer thickness (or with decreasing of the fluid layer thickness) the stability threshold rises. This is because of the fact that the instability is primarily caused by perturbations located in the fluid layer. At the d < 0.5 the reduction of the porous layer thickness leads to the stability threshold

  13. Efficient triple-grid multiscale finite element method for 3D groundwater flow simulation in heterogeneous porous media

    NASA Astrophysics Data System (ADS)

    Xie, Yifan; Wu, Jichun; Nan, Tongchao; Xue, Yuqun; Xie, Chunhong; Ji, Haifeng

    2017-03-01

    In this paper, an efficient triple-grid multiscale finite element method (ETMSFEM) is proposed for 3D groundwater simulation in heterogeneous porous media. The main idea of this method is to employ new 3D linear base functions and the domain decomposition technique to solve the local reduced elliptical problem, thereby simplifying the base function construction process and improving the efficiency. Furthermore, by using the ETMSFEM base functions, this method can solve Darcy's equation with high efficiency to obtain a continuous velocity field. Therefore, this method can considerably reduce the computational cost of solving for heads and velocities, which is crucial for large-scale 3D groundwater simulations. In the application section, we present numerical examples to compare the ETMSFEM with several classical methods to demonstrate its efficiency and effectiveness.

  14. Fractured porous medium flow analysis using numerical manifold method with independent covers

    NASA Astrophysics Data System (ADS)

    Zhang, Qi-Hua; Lin, Shao-Zhong; Xie, Zhi-Qiang; Su, Hai-Dong

    2016-11-01

    Due to the complexity of geometry and the difficulty of mesh discretization of 3D (three-dimensional) blocks cut by complexly distributed fractures, explicitly considering arbitrary fracture network in fractured porous medium (FPM) flow analysis is very challenging for various numerical methods. In this study, we developed a FPM flow model by taking full advantage of numerical manifold method (NMM) with independent covers. With the independent covers, arbitrarily-shaped 3D blocks identified by block-cutting analysis can be directly used as basic computational elements. Along the boundaries of the divided blocks, fractures elements are generated according to the fractures' apertures. Therefore, it is able to handle very complicated fracture network in 3D flow analysis without need to subdivide 3D blocks into computational meshes. In order to refine the meshes, we introduced artificial fractures with same material properties as surrounding rock into a fracture network, without need to coordinate with the shapes of the blocks. We demonstrated our new model on different 2D examples. At last, we applied our model to 2D and 3D examples with complexly distributed fractures, and achieved reasonable results. The results show that our model is very powerful to analyze fluid flow in arbitrarily and complexly fractured rock mass in 3D.

  15. Asphaltene multilayer growth in porous medium probed by SANS

    NASA Astrophysics Data System (ADS)

    Gummel, J.; Corvis, Y.; Jestin, J.; M'hamdi, J.; Barré, L.

    2009-02-01

    Presence of suspended particles such as asphaltene in crude oils could significantly affect the production by means of deposition in porous media especially near the well bore. We investigate this phenomenon using the ability of Small Angle Neutron Scattering technique to probe directly the asphaltene adsorption process in a porous medium at the nanometer length scale under flow conditions. A device based on a quartz tube filled with SiC particles constitute the porous medium in which an asphaltene solution in a mixture of good (toluene)/bad (heptane) solvent is injected under controlled flow. The contrast matching technique enables to match the porous medium scattering contributions and to measure the signal of the deposit. Such a device can be used for curves surface measurements on a setup originally designed for bulk studies and permit thus the direct comparison with measurements on flat surfaces (neutron reflectivity) and indirect adsorption measurements (adsorption isotherm). We show here that asphaltene in good solvent leads to a monolayer whereas addition of bad solvent results in a multilayer growth which is consistent with the deposition behaviour described in the literature.

  16. The 2D versus 3D imaging trade-off: The impact of over- or under-estimating small throats for simulating permeability in porous media

    NASA Astrophysics Data System (ADS)

    Peters, C. A.; Crandell, L. E.; Um, W.; Jones, K. W.; Lindquist, W. B.

    2011-12-01

    Geochemical reactions in the subsurface can alter the porosity and permeability of a porous medium through mineral precipitation and dissolution. While effects on porosity are relatively well understood, changes in permeability are more difficult to estimate. In this work, pore-network modeling is used to estimate the permeability of a porous medium using pore and throat size distributions. These distributions can be determined from 2D Scanning Electron Microscopy (SEM) images of thin sections or from 3D X-ray Computed Tomography (CT) images of small cores. Each method has unique advantages as well as unique sources of error. 3D CT imaging has the advantage of reconstructing a 3D pore network without the inherent geometry-based biases of 2D images but is limited by resolutions around 1 μm. 2D SEM imaging has the advantage of higher resolution, and the ability to examine sub-grain scale variations in porosity and mineralogy, but is limited by the small size of the sample of pores that are quantified. A pore network model was created to estimate flow permeability in a sand-packed experimental column investigating reaction of sediments with caustic radioactive tank wastes in the context of the Hanford, WA site. Before, periodically during, and after reaction, 3D images of the porous medium in the column were produced using the X2B beam line facility at the National Synchrotron Light Source (NSLS) at Brookhaven National Lab. These images were interpreted using 3DMA-Rock to characterize the pore and throat size distributions. After completion of the experiment, the column was sectioned and imaged using 2D SEM in backscattered electron mode. The 2D images were interpreted using erosion-dilation to estimate the pore and throat size distributions. A bias correction was determined by comparison with the 3D image data. A special image processing method was developed to infer the pore space before reaction by digitally removing the precipitate. The different sets of pore

  17. Homogenization of an incompressible non-Newtonian flow through a thin porous medium

    NASA Astrophysics Data System (ADS)

    Anguiano, María; Suárez-Grau, Francisco Javier

    2017-04-01

    In this paper, we consider a non-Newtonian flow in a thin porous medium Ω _{ɛ} of thickness ɛ which is perforated by periodically solid cylinders of size a_{ɛ}. The flow is described by the 3D incompressible Stokes system with a nonlinear viscosity, being a power of the shear rate (power law) of flow index 1

  18. Transitioning from a single-phase fluid to a porous medium: a boundary layer approach

    NASA Astrophysics Data System (ADS)

    Dalwadi, Mohit P.; Chapman, S. Jon; Oliver, James M.; Waters, Sarah L.

    2014-11-01

    Pressure-driven laminar channel flow is a classic problem in fluid mechanics, and the resultant Poiseuille flow is one of the few exact solutions to the Navier-Stokes equations. If the channel interior is a porous medium (governed by Darcy's law) rather than a single-phase fluid, the resultant behaviour is plug flow. But what happens when these two flow regions are coupled, as is the case for industrial membrane filtration systems or biological tissue engineering problems? How does one flow transition to the other? We use asymptotic methods to investigate pressure-driven flow through a long channel completely blocked by a finite-length porous obstacle. We analytically solve for the flow at both small and large Reynolds number (whilst remaining within the laminar regime). The boundary layer structure is surprisingly intricate for large Reynolds number. In that limit, the structure is markedly different depending on whether there is inflow or outflow through the porous medium, there being six asymptotic regions for inflow and three for outflow. We have extended this result to a wide class of 3D porous obstacles within a Hele-Shaw cell. We obtain general boundary conditions to couple the outer flows, and find that these conditions are far from obvious at higher order.

  19. Oxygen- and Nitrogen-Enriched 3D Porous Carbon for Supercapacitors of High Volumetric Capacity.

    PubMed

    Li, Jia; Liu, Kang; Gao, Xiang; Yao, Bin; Huo, Kaifu; Cheng, Yongliang; Cheng, Xiaofeng; Chen, Dongchang; Wang, Bo; Sun, Wanmei; Ding, Dong; Liu, Meilin; Huang, Liang

    2015-11-11

    Efficient utilization and broader commercialization of alternative energies (e.g., solar, wind, and geothermal) hinges on the performance and cost of energy storage and conversion systems. For now and in the foreseeable future, the combination of rechargeable batteries and electrochemical capacitors remains the most promising option for many energy storage applications. Porous carbonaceous materials have been widely used as an electrode for batteries and supercapacitors. To date, however, the highest specific capacitance of an electrochemical double layer capacitor is only ∼200 F/g, although a wide variety of synthetic approaches have been explored in creating optimized porous structures. Here, we report our findings in the synthesis of porous carbon through a simple, one-step process: direct carbonization of kelp in an NH3 atmosphere at 700 °C. The resulting oxygen- and nitrogen-enriched carbon has a three-dimensional structure with specific surface area greater than 1000 m(2)/g. When evaluated as an electrode for electrochemical double layer capacitors, the porous carbon structure demonstrated excellent volumetric capacitance (>360 F/cm(3)) with excellent cycling stability. This simple approach to low-cost carbonaceous materials with unique architecture and functionality could be a promising alternative to fabrication of porous carbon structures for many practical applications, including batteries and fuel cells.

  20. Oscillatory motion of a viscous fluid in a porous medium

    NASA Astrophysics Data System (ADS)

    Siraev, R. R.

    2015-08-01

    An oscillatory flow of an incompressible fluid in a saturated porous medium in the presence of a solid inclusion has been theoretically studied. Unsteady filtration has been described by the Brinkman-Forchheimer equation, where inertial effects and terms with acceleration characteristic of high filtration rates and the presence of pulsations are taken into account. The convective part of the acceleration is responsible for nonlinear effects near macroinhomogeneities. These effects can play a noticeable role in unsteady flows in the porous medium, as is shown for the problem of a solid ball streamed by an oscillatory flow having a given velocity at infinity. The results indicate that a secondary averaged flow appears in the case of high frequencies and cannot be described by Darcy's or Forchheimer's filtration laws.

  1. Drying of porous materials in a medium with variable potentials

    SciTech Connect

    Liu, J.Y. )

    1991-08-01

    This paper presents an application of the Luikov system of heat and mass transfer equations in dimensionless form to predict the temperature and moisture distributions in a slab of capillary-porous material during drying. The heat and mass potentials of the external medium in the boundary conditions are assumed to vary linearly with time. The method of solution is illustrated by considering the drying of a slab of lumber. Numerical results based on the estimated thermophysical properties of spruce are presented.

  2. Electrospun carbon nanofibers reinforced 3D porous carbon polyhedra network derived from metal-organic frameworks for capacitive deionization

    PubMed Central

    Liu, Yong; Ma, Jiaqi; Lu, Ting; Pan, Likun

    2016-01-01

    Carbon nanofibers reinforced 3D porous carbon polyhedra network (e-CNF-PCP) was prepared through electrospinning and subsequent thermal treatment. The morphology, structure and electrochemical performance of the e-CNF-PCP were characterized using scanning electron microscopy, Raman spectra, nitrogen adsorption-desorption, cyclic voltammetry and electrochemical impedance spectroscopy, and their electrosorption performance in NaCl solution was studied. The results show that the e-CNF-PCP exhibits a high electrosorption capacity of 16.98 mg g−1 at 1.2 V in 500 mg l−1 NaCl solution, which shows great improvement compared with those of electrospun carbon nanofibers and porous carbon polyhedra. The e-CNF-PCP should be a very promising candidate as electrode material for CDI applications. PMID:27608826

  3. Laser 3D printing with sub-microscale resolution of porous elastomeric scaffolds for supporting human bone stem cells.

    PubMed

    Petrochenko, Peter E; Torgersen, Jan; Gruber, Peter; Hicks, Lucas A; Zheng, Jiwen; Kumar, Girish; Narayan, Roger J; Goering, Peter L; Liska, Robert; Stampfl, Jürgen; Ovsianikov, Aleksandr

    2015-04-02

    A reproducible method is needed to fabricate 3D scaffold constructs that results in periodic and uniform structures with precise control at sub-micrometer and micrometer length scales. In this study, fabrication of scaffolds by two-photon polymerization (2PP) of a biodegradable urethane and acrylate-based photoelastomer is demonstrated. This material supports 2PP processing with sub-micrometer spatial resolution. The high photoreactivity of the biophotoelastomer permits 2PP processing at a scanning speed of 1000 mm s(-1), facilitating rapid fabrication of relatively large structures (>5 mm(3)). These structures are custom printed for in vitro assay screening in 96-well plates and are sufficiently flexible to enable facile handling and transplantation. These results indicate that stable scaffolds with porosities of greater than 60% can be produced using 2PP. Human bone marrow stromal cells grown on 3D scaffolds exhibit increased growth and proliferation compared to smooth 2D scaffold controls. 3D scaffolds adsorb larger amounts of protein than smooth 2D scaffolds due to their larger surface area; the scaffolds also allow cells to attach in multiple planes and to completely infiltrate the porous scaffolds. The flexible photoelastomer material is biocompatible in vitro and is associated with facile handling, making it a viable candidate for further study of complex 3D-printed scaffolds.

  4. Microfabrication of complex porous tissue engineering scaffolds using 3D projection stereolithography

    PubMed Central

    Gauvin, Robert; Chen, Ying-Chieh; Lee, Jin Woo; Soman, Pranav; Zorlutuna, Pinar; Nichol, Jason W.; Bae, Hojae; Chen, Shaochen; Khademhosseini, Ali

    2013-01-01

    The success of tissue engineering will rely on the ability to generate complex, cell seeded three-dimensional (3D) structures. Therefore, methods that can be used to precisely engineer the architecture and topography of scaffolding materials will represent a critical aspect of functional tissue engineering. Previous approaches for 3D scaffold fabrication based on top-down and process driven methods are often not adequate to produce complex structures due to the lack of control on scaffold architecture, porosity, and cellular interactions. The proposed projection stereolithography (PSL) platform can be used to design intricate 3D tissue scaffolds that can be engineered to mimic the microarchitecture of tissues, based on computer aided design (CAD). The PSL system was developed, programmed and optimized to fabricate 3D scaffolds using gelatin methacrylate (GelMA). Variation of the structure and prepolymer concentration enabled tailoring the mechanical properties of the scaffolds. A dynamic cell seeding method was utilized to improve the coverage of the scaffold throughout its thickness. The results demonstrated that the interconnectivity of pores allowed for uniform human umbilical vein endothelial cells (HUVECs) distribution and proliferation in the scaffolds, leading to high cell density and confluency at the end of the culture period. Moreover, immunohistochemistry results showed that cells seeded on the scaffold maintained their endothelial phenotype, demonstrating the biological functionality of the microfabricated GelMA scaffolds. PMID:22365811

  5. Real-time 3D imaging of Haines jumps in porous media flow

    PubMed Central

    Berg, Steffen; Ott, Holger; Klapp, Stephan A.; Schwing, Alex; Neiteler, Rob; Brussee, Niels; Makurat, Axel; Leu, Leon; Enzmann, Frieder; Schwarz, Jens-Oliver; Kersten, Michael; Irvine, Sarah; Stampanoni, Marco

    2013-01-01

    Newly developed high-speed, synchrotron-based X-ray computed microtomography enabled us to directly image pore-scale displacement events in porous rock in real time. Common approaches to modeling macroscopic fluid behavior are phenomenological, have many shortcomings, and lack consistent links to elementary pore-scale displacement processes, such as Haines jumps and snap-off. Unlike the common singular pore jump paradigm based on observations of restricted artificial capillaries, we found that Haines jumps typically cascade through 10–20 geometrically defined pores per event, accounting for 64% of the energy dissipation. Real-time imaging provided a more detailed fundamental understanding of the elementary processes in porous media, such as hysteresis, snap-off, and nonwetting phase entrapment, and it opens the way for a rigorous process for upscaling based on thermodynamic models. PMID:23431151

  6. Development and characterization of novel porous 3D alginate-cockle shell powder nanobiocomposite bone scaffold.

    PubMed

    Bharatham, B Hemabarathy; Abu Bakar, Md Zuki; Perimal, Enoch Kumar; Yusof, Loqman Mohamed; Hamid, Muhajir

    2014-01-01

    A novel porous three-dimensional bone scaffold was developed using a natural polymer (alginate/Alg) in combination with a naturally obtained biomineral (nano cockle shell powder/nCP) through lyophilization techniques. The scaffold was developed in varying composition mixture of Alg-nCP and characterized using various evaluation techniques as well as preliminary in vitro studies on MG63 human osteoblast cells. Morphological observations using SEM revealed variations in structures with the use of different Alg-nCP composition ratios. All the developed scaffolds showed a porous structure with pore sizes ideal for facilitating new bone growth; however, not all combination mixtures showed subsequent favorable characteristics to be used for biological applications. Scaffolds produced using the combination mixture of 40% Alg and 60% nCP produced significantly promising results in terms of mechanical strength, degradation rate, and increased cell proliferation rates making it potentially the optimum composition mixture of Alg-nCP with future application prospects.

  7. Fully porous 3D printed titanium femoral stem to reduce stress-shielding following total hip arthroplasty.

    PubMed

    Arabnejad, Sajad; Johnston, Burnett; Tanzer, Michael; Pasini, Damiano

    2016-09-24

    Current hip replacement femoral implants are made of fully solid materials which all have stiffness considerably higher than that of bone. This mechanical mismatch can cause significant bone resorption secondary to stress shielding, which can lead to serious complications such as peri-prosthetic fracture during or after revision surgery. In this work, a high strength fully porous material with tunable mechanical properties is introduced for use in hip replacement design. The implant macro geometry is based off of a short stem taper-wedge implant compatible with minimally invasive hip replacement surgery. The implant micro-architecture is fine-tuned to locally mimic bone tissue properties which results in minimum bone resorption secondary to stress shielding. We present a systematic approach for the design of a 3D printed fully porous hip implant that encompasses the whole activity spectrum of implant development, from concept generation, multiscale mechanics of porous materials, material architecture tailoring, to additive manufacturing, and performance assessment via in vitro experiments in composite femurs. We show that the fully porous implant with an optimized material micro-structure can reduce the amount of bone loss secondary to stress shielding by 75% compared to a fully solid implant. This result also agrees with those of the in vitro quasi-physiological experimental model and the corresponding finite element model for both the optimized fully porous and fully solid implant. These studies demonstrate the merit and the potential of tuning material architecture to achieve a substantial reduction of bone resorption secondary to stress shielding. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

  8. Optimization and Use of 3D sintered porous material in medical field for mixing fibrin glue.

    NASA Astrophysics Data System (ADS)

    Delmotte, Y.; Laroumanie, H.; Brossard, G.

    2012-04-01

    In medical field, Mixing of two or more chemical components (liquids and/or gases) is extremely important as improper mixing can affect the physico-chemical properties of the final product. At Baxter Healthcare Corporation, we are using a sintered porous material (PM) as a micro-mixer in medical device for mixing Fibrinogen and Thrombin in order to obtain a homogeneous polymerized Fibrin glue clot used in surgery. First trials were carried out with an interconnected PM from Porvair® (made of PE - porosity: 40% - permeability: 18Darcy). The injection rate is very low, usually about 10mL/min (Re number about 50) which keeps fluids in a laminar flow. Such a low flow rate does not favour mixing of fluids having gradient of viscosity if a mixer is not used. Promising results that were obtained lead the team to understand this ability to mix fluids which will be presented in the poster. Topology of porous media (PM) which associates a solid phase with interconnected (or not) porous structure is known and used in many commodity products. Researches on PM usually focus on flows inside this structure. By opposition to transport and filtration capacity, as well as mechanic and thermic properties, mixing is rarely associated with PM. However over the past few years, we shown that some type of PM have a real capacity to mix certain fluids. Poster will also describe the problematic of mixing complex biological fluids as fibrinogen and Thrombin. They indeed present a large viscosity difference (ratio about 120) limiting the diffusion and the interaction between the two solutions. As those products are expensive, we used Water (1cPo) and Glycerol 87% (120cPo) which are matching the viscosities of Thrombin and Fibrinogen. A parametric investigation of the "porous micro-mixer" as well as a scale up investigation was carried out to examine the influence of both diffusion and advection to successful mix fluids of different viscosity. Experiments were implemented with Planar Laser

  9. Fabrication of porous 3D flower-like Ag/ZnO heterostructure composites with enhanced photocatalytic performance

    NASA Astrophysics Data System (ADS)

    Liang, Yimai; Guo, Na; Li, Linlin; Li, Ruiqing; Ji, Guijuan; Gan, Shucai

    2015-03-01

    Porous 3D flower-like Ag/ZnO heterostructural composites were fabricated by hydrothermal and photochemical deposition methods, without using any pore-directing reagents and surfactants. The obtained samples were characterized by XRD, SEM, TEM, XPS, BJH, DRS, and PL spectrum. The experiment results show that the silver nanoparticles successfully load on the surface of assembled ZnO flowers. The TEM and SEM morphologies demonstrated unique porous 3D flower-like structure of Ag/ZnO. Such special structure makes larger surface area and more active sites exposed during the reaction, facilitating the transportation of reactants and products and increasing the reaction rate. The photocatalytic degradation experiments under UV irradiation using Rhodamine B (RhB) as a model dye were executed. The relative results demonstrate that the photocatalytic activity of Ag/ZnO is obviously improved compared with the pure ZnO and the commercial TiO2 (Degussa P25), the AZ-15 sample has the highest photocatalytic activity. The Ag/ZnO heterostructure composites promoted the separation of photo-induced electrons and holes, which was proved by photoluminescence spectra (PL).

  10. 3D-printed silicate porous bioceramics using a non-sacrificial preceramic polymer binder.

    PubMed

    Zocca, A; Elsayed, H; Bernardo, E; Gomes, C M; Lopez-Heredia, M A; Knabe, C; Colombo, P; Günster, J

    2015-05-22

    Silicate bioceramics possess an excellent bioactivity; however, shaping them into complex geometries is still challenging. Therefore, this paper aims to present a new strategy for the shaping of a bioglass-ceramic with controlled geometry and properties starting from a glass powder combined with a preceramic polymer, i.e. a silicon resin, and reactive fillers. The powder-based three-dimensional (3D)-printing of wollastonite (CaSiO3)-based silicate bioceramic parts was demonstrated in this work. The resin plays a dual role, as it not only acts as a non-sacrificial binder for the filler powders in the printing process but it also reacts with the fillers to generate the desired bioceramic phases. The mechanical and physical properties, i.e. ball-on-three-balls test, density, porosity and morphology, were evaluated in 3D-printed discs. These samples possessed a total porosity around 64 vol% and a biaxial flexural strength around 6 MPa. The raw materials used in this work also enabled the 3D-printing of scaffolds possessing a designed multi-scale porosity, suitable bioceramic phase assemblage and a compressive strength of 1 MPa (for cylindrical scaffolds with total porosity ~80 vol%). Solubility in TRIS/HCl and in vitro assays, i.e. viability, cytotoxicity and apoptosis assays, were also performed. In vitro tests indicated good cell viability and no cytotoxicity effect on the cells.

  11. PHT3D-UZF: A reactive transport model for variably-saturated porous media

    USGS Publications Warehouse

    Wu, Ming Zhi; Post, Vincent E. A.; Salmon, S. Ursula; Morway, Eric; Prommer, H.

    2016-01-01

    A modified version of the MODFLOW/MT3DMS-based reactive transport model PHT3D was developed to extend current reactive transport capabilities to the variably-saturated component of the subsurface system and incorporate diffusive reactive transport of gaseous species. Referred to as PHT3D-UZF, this code incorporates flux terms calculated by MODFLOW's unsaturated-zone flow (UZF1) package. A volume-averaged approach similar to the method used in UZF-MT3DMS was adopted. The PHREEQC-based computation of chemical processes within PHT3D-UZF in combination with the analytical solution method of UZF1 allows for comprehensive reactive transport investigations (i.e., biogeochemical transformations) that jointly involve saturated and unsaturated zone processes. Intended for regional-scale applications, UZF1 simulates downward-only flux within the unsaturated zone. The model was tested by comparing simulation results with those of existing numerical models. The comparison was performed for several benchmark problems that cover a range of important hydrological and reactive transport processes. A 2D simulation scenario was defined to illustrate the geochemical evolution following dewatering in a sandy acid sulfate soil environment. Other potential applications include the simulation of biogeochemical processes in variably-saturated systems that track the transport and fate of agricultural pollutants, nutrients, natural and xenobiotic organic compounds and micropollutants such as pharmaceuticals, as well as the evolution of isotope patterns.

  12. PHT3D-UZF: A Reactive Transport Model for Variably-Saturated Porous Media.

    PubMed

    Wu, Ming Zhi; Post, Vincent E A; Salmon, S Ursula; Morway, Eric D; Prommer, Henning

    2016-01-01

    A modified version of the MODFLOW/MT3DMS-based reactive transport model PHT3D was developed to extend current reactive transport capabilities to the variably-saturated component of the subsurface system and incorporate diffusive reactive transport of gaseous species. Referred to as PHT3D-UZF, this code incorporates flux terms calculated by MODFLOW's unsaturated-zone flow (UZF1) package. A volume-averaged approach similar to the method used in UZF-MT3DMS was adopted. The PHREEQC-based computation of chemical processes within PHT3D-UZF in combination with the analytical solution method of UZF1 allows for comprehensive reactive transport investigations (i.e., biogeochemical transformations) that jointly involve saturated and unsaturated zone processes. Intended for regional-scale applications, UZF1 simulates downward-only flux within the unsaturated zone. The model was tested by comparing simulation results with those of existing numerical models. The comparison was performed for several benchmark problems that cover a range of important hydrological and reactive transport processes. A 2D simulation scenario was defined to illustrate the geochemical evolution following dewatering in a sandy acid sulfate soil environment. Other potential applications include the simulation of biogeochemical processes in variably-saturated systems that track the transport and fate of agricultural pollutants, nutrients, natural and xenobiotic organic compounds and micropollutants such as pharmaceuticals, as well as the evolution of isotope patterns.

  13. Injection of a reacting fluid into a fractured porous medium

    NASA Astrophysics Data System (ADS)

    Jasinski, L.; Thovert, J.; Mourzenko, V.; Adler, P. M.

    2010-12-01

    The quantitative description of the injection of a reacting fluid from a well into a fractured porous medium is a subject of high interest for CO2 sequestration. Ideally, one wishes to analyze the damages caused by the fluid to the well itself and to its immediate surroundings. In order to attain this goal, one has to solve a coupled system of equations. The first one describes the flow inside two structures, namely the porous medium and the fractures; basically, they are Darcy like equations for one or two phases. The second equations describe the transport of CO2 and the reactions which occur inside the two structures. In addition, one needs constitutive equations in order to predict evolution of these two structures; for instance, one needs an evolution law for permeability as a function of porosity. Three major steps are needed for the numerical solutions. First, an unstructured tetrahedral mesh of the fractures and of the porous matrix located in between is constructed; a particular attention should be paid to the well region since the casing has different properties than the surrounding porous medium. Second, the Darcy equations are discretized and solved, in a finite volume formulation; previous codes have been improved by the systematic use of triple control volumes. Third, the evolution of the solute concentration has to be calculated. This last point is the most difficult one if one wants to avoid numerical diffusion and also inaccurate transfers between the fractures and the media. Various schemes have been tried and the most efficient one is a non linear flux limiting scheme (FLS) of the Superbee type. Because of its importance, the results obtained with the various schemes will be illustrated and discussed. The FLS scheme has been developed for the triple control volume which is a major improvement with respect to the previous codes that were developed in our group. Various physical situations will be illustrated. The theoretical situation of transfer

  14. A novel 3D covalent organic framework membrane grown on a porous α-Al2O3 substrate under solvothermal conditions.

    PubMed

    Lu, Hui; Wang, Chang; Chen, Juanjuan; Ge, Rile; Leng, Wenguang; Dong, Bin; Huang, Jun; Gao, Yanan

    2015-11-04

    A novel approach to grow a 3D COF-320 membrane on a surface-modified porous α-Al2O3 substrate is developed. A compact and uniform COF-320 membrane with a layer thickness of ∼4 μm is obtained. This is the first reported 3D COF functional membrane fabricated successfully on a common porous α-Al2O3 ceramic support. The gas permeation results indicate that the gas transport behavior is mainly governed by the predicted Knudsen diffusion process due to the large nanopores of 3D COF-320.

  15. Numerical methods for a general class of porous medium equations

    SciTech Connect

    Rose, M. E.

    1980-03-01

    The partial differential equation par. deltau/par. deltat + par. delta(f(u))/par. deltax = par. delta(g(u)par. deltau/par. deltax)/par. deltax, where g(u) is a non-negative diffusion coefficient that may vanish for one or more values of u, was used to model fluid flow through a porous medium. Error estimates for a numerical procedure to approximate the solution are derived. A revised version of this report will appear in Computers and Mathematics with Applications.

  16. Filtration of a magnetic fluid in a deformable porous medium

    SciTech Connect

    Taktarov, N.G.

    1985-07-01

    The equations of motion of a magnetizing fluid are obtained in a deformable non-magnetic porous medium. The porosity, magnetic field intensity, and other quantities are in all the equations describing the filtration. Therefore, the whole system of equations must be solved to find these quantities. For instance, just some of the Maxwell equations are now inadequate for finding the magnetic field. The evaluation of the elasticity coefficients for the matrix frame consisting of periodically arranged balls of identical radius is possible, in principle, by using the results of solving the Hertz problem for two contiguous spheres.

  17. Properties and modification of porous 3-D collagen/hydroxyapatite composites.

    PubMed

    Sionkowska, A; Kozłowska, J

    2013-01-01

    A freeze drying technique was used to form porous three-dimensional collagen matrixes modified by the addition of a variable amount of nano-hydroxyapatite. For chemical cross-linking EDC/NHS were used. Physical cross-linking was achieved by dehydrothermal treatment. Mechanical properties, morphology, dissolution, porosity, density, enzymatic degradation and swelling properties of materials have been studied after cross-linking. The density of scaffolds and its compressive modulus increased with an increasing amount of hydroxyapatite and collagen concentration in the composite scaffold, while the swelling ratio and porosity decreased. The studied scaffolds dissolved slowly in PBS solution. DHT cross-linked collagen matrices showed a much faster degradation rate after exposure to collagenase than the EDC cross-linked samples.

  18. Biomimetic interconnected porous keratin-fibrin-gelatin 3D sponge for tissue engineering application.

    PubMed

    Singaravelu, Sivakumar; Ramanathan, Giriprasath; Raja, M D; Nagiah, Naveen; Padmapriya, P; Kaveri, Krishnasamy; Sivagnanam, Uma Tiruchirapalli

    2016-05-01

    The medicated wound dressing material with highly interconnected pores, mimicking the function of the extracellular matrix was fabricated for the promotion of cell growth. In this study, keratin (K), fibrin (F) and gelatin (G) composite scaffold (KFG-SPG) was fabricated by freeze drying technique and the mupirocin (D) drug was successfully incorporated with KFG-SPG (KFG-SPG-D) intended for tissue engineering applications. The fabrication of scaffold was performed without the use of any strong chemical solvents, and the solid sponge scaffold was obtained with well interconnected pores. The porous morphology of the scaffold was confirmed by SEM analysis and exhibited competent mechanical properties. KFG-SPG and KFG-SPG-D possess high level of biocompatibility, cell proliferation and cell adhesion of NIH 3T3 fibroblast and human keratinocytes (HaCaT) cell lines thereby indicating the scaffolds potential as a suitable medicated dressing for wound healing.

  19. One-Pot Synthesis of Fe3O4 Nanoparticle Loaded 3D Porous Graphene Nanocomposites with Enhanced Nanozyme Activity for Glucose Detection.

    PubMed

    Wang, Qingqing; Zhang, Xueping; Huang, Liang; Zhang, Zhiquan; Dong, Shaojun

    2017-03-01

    A novel one-pot strategy is proposed to fabricate 3D porous graphene (3D GN) decorated with Fe3O4 nanoparticles (Fe3O4 NPs) by using hemin as iron source. During the process, graphene oxide was simultaneously reduced and self-assembled to form 3D graphene hydrogel while Fe3O4 NPs synthesized from hemin distributed uniformly on 3D GN. The preparation process is simple, facile, economical, and green. The obtained freeze-dried product (3D GH-5) exhibits outstanding peroxidase-like activity. Compared to the traditional 2D graphene-based nanocomposites, the introduced 3D porous structure dramatically improved the catalytic activity, as well as the catalysis velocity and its affinity for substrate. The high catalytic activity could be ascribed to the formation of Fe3O4 NPs and 3D porous graphene structures. Based on its peroxidase-like activity, 3D GH-5 was used for colorimetric determination of glucose with a low detection limit of 0.8 μM.

  20. Characterization of Silk Fibroin/Chitosan 3D Porous Scaffold and In Vitro Cytology

    PubMed Central

    Zeng, Shuguang; Liu, Lei; Shi, Yong; Qiu, Junqi; Fang, Wei; Rong, Mingdeng; Guo, Zehong; Gao, Wenfeng

    2015-01-01

    Bone tissue engineering is a powerful tool to treat bone defects caused by trauma, infection, tumors and other factors. Both silk fibroin (SF) and chitosan (CS) are non-toxic and have good biocompatibility, but are poor biological scaffolds when used alone. In this study, the microscopic structure and related properties of SF/CS composite scaffolds with different component ratios were examined. The scaffold material most suitable for osteoblast growth was determined, and these results offer an experimental basis for the future reconstruction of bone defects. First, via freeze-drying and chemical crosslinking methods, SF/CS composites with different component ratios were prepared and their structure was characterized. Changes in the internal structure of the SF and CS mixture were observed, confirming that the mutual modification between the two components was complete and stable. The internal structure of the composite material was porous and three-dimensional with a porosity above 90%. We next studied the pore size, swelling ratio, water absorption ratio, degradation and in vitro cell proliferation. For the 40% SF-60% CS group, the pore size of the scaffold was suitable for the growth of osteoblasts, and the rate of degradation was steady. This favors the early adhesion, growth and proliferation of MG-63 cells. In addition to good biocompatibility and satisfactory cell affinity, this material promotes the secretion of extracellular matrix materials by osteoblasts. Thus, 40% SF-60% CS is a good material for bone tissue engineering. PMID:26083846

  1. Physical and mechanical characterisation of 3D-printed porous titanium for biomedical applications.

    PubMed

    El-Hajje, Aouni; Kolos, Elizabeth C; Wang, Jun Kit; Maleksaeedi, Saeed; He, Zeming; Wiria, Florencia Edith; Choong, Cleo; Ruys, Andrew J

    2014-11-01

    The elastic modulus of metallic orthopaedic implants is typically 6-12 times greater than cortical bone, causing stress shielding: over time, bone atrophies through decreased mechanical strain, which can lead to fracture at the implantation site. Introducing pores into an implant will lower the modulus significantly. Three dimensional printing (3DP) is capable of producing parts with dual porosity features: micropores by process (residual pores from binder burnout) and macropores by design via a computer aided design model. Titanium was chosen due to its excellent biocompatibility, superior corrosion resistance, durability, osteointegration capability, relatively low elastic modulus, and high strength to weight ratio. The mechanical and physical properties of 3DP titanium were studied and compared to the properties of bone. The mechanical and physical properties were tailored by varying the binder (polyvinyl alcohol) content and the sintering temperature of the titanium samples. The fabricated titanium samples had a porosity of 32.2-53.4% and a compressive modulus of 0.86-2.48 GPa, within the range of cancellous bone modulus. Other physical and mechanical properties were investigated including fracture strength, density, fracture toughness, hardness and surface roughness. The correlation between the porous 3DP titanium-bulk modulus ratio and porosity was also quantified.

  2. Sustained Reaction Waves Against Flow in Porous Medium: Frozen Fronts

    NASA Astrophysics Data System (ADS)

    Salin, Dominique; Atis, Severine; Auradou, Harold; Saha, Sandeep; Talon, Laurent

    2012-11-01

    Autocatalytic reactions lead to fronts propagating as solitary, self-sustained, waves with a constant velocity and an invariant, flat, concentration profile resulting from a balance between reaction and diffusion. In the presence of a hydrodynamic flow, such fronts, while propagating at a new constant velocity, adapt their shape in order to achieve a balance between reaction diffusion and flow advection all over the front. The issue addressed here is the behaviour of autocatalytic reaction fronts when the forced advection is a heterogeneous flow field. It has been recently observed that in inside a porous medium there exist static, frozen, fronts over a wide range of mean flow rates in the opposite direction of the chemical wave propagation. To account for this dynamical equilibrium where the front is pinned at different points, we use both designed experiments around different configurations of solid obstacles and lattice Boltzmann numerical simulations which allows a control of the flow field heterogeneities. These approach allows us to account for the dependence of the range of observation of frozen states with th control parameters. In the case of the porous medium flow field, the transition to this frozen state is understood in term of percolation like path.

  3. MnO nanoparticles interdispersed in 3D porous carbon framework for high performance lithium-ion batteries.

    PubMed

    Wang, Shengbin; Xing, Yalan; Xu, Huaizhe; Zhang, Shichao

    2014-08-13

    Interdispersed MnO nanoparticles that are anchored and encapsulated in a three-dimensional (3D) porous carbon framework (MnO@CF) have been constructed, which display nanosphere architecture with rich porosity, well-defined carbon framework configuration, and excellent structure stability. When evaluated as an anode material, the MnO@CF exhibits relatively high specific capacity of 939 mA h g(-1) at current rate of 0.2 A g(-1) over 200 cycles and excellent rate capability of 560.2 mA h g(-1) at 4 A g(-1). By virtue of its mechanical stability and desirable ionic/electronic conductivity, the specific design can be a promising approach to fabricate high-performance lithium-ion batteries.

  4. Droplet fragmentation: 3D imaging of a previously unidentified pore-scale process during multiphase flow in porous media

    PubMed Central

    Pak, Tannaz; Butler, Ian B.; Geiger, Sebastian; van Dijke, Marinus I. J.; Sorbie, Ken S.

    2015-01-01

    Using X-ray computed microtomography, we have visualized and quantified the in situ structure of a trapped nonwetting phase (oil) in a highly heterogeneous carbonate rock after injecting a wetting phase (brine) at low and high capillary numbers. We imaged the process of capillary desaturation in 3D and demonstrated its impacts on the trapped nonwetting phase cluster size distribution. We have identified a previously unidentified pore-scale event during capillary desaturation. This pore-scale event, described as droplet fragmentation of the nonwetting phase, occurs in larger pores. It increases volumetric production of the nonwetting phase after capillary trapping and enlarges the fluid−fluid interface, which can enhance mass transfer between the phases. Droplet fragmentation therefore has implications for a range of multiphase flow processes in natural and engineered porous media with complex heterogeneous pore spaces. PMID:25646491

  5. Colloid Transport in Unsaturated Porous Media: 3D Visualization Using Synchrotron X-Ray Microtomography

    NASA Astrophysics Data System (ADS)

    Brueck, C. L.; Meisenheimer, D.; Wildenschild, D.

    2015-12-01

    Understanding the mechanisms controlling colloid transport and deposition in the vadose zone is an important step in protecting our water resources. Not only may these particles themselves be undesirable contaminants, but they can also aid in the transport of smaller, molecular-scale contaminants by chemical attachment. In this research, we examined the influence that air-water interfaces (AWI) and air-water-solid contact lines (AWS) have on colloid deposition and mobilization in three-dimensional systems. We used x-ray microtomography to visualize the transport of hydrophobic colloids as they move through a partially saturated glass bead pack. Drainage and imbibition experiments were conducted using syringe pumps to control the flow of a colloid suspension through the porous media at 0.6 mL/hr. The high ionic strength fluid was adjusted to a pH of 9.5 and a concentration of 1.0 mol/L KI. During the drainage and imbibition, the flow was periodically halted and allowed to equilibrate before collecting the microtomography scans. Dopants were used to enhance the contrast between the four phases (water, air, beads, and colloids), including potassium iodide dissolved in the fluid, and an outer layer of silver coating the colloids. We hypothesized that AWIs and AWSs will scour and mobilize a significant percentage of colloids, and therefore reduce the concentration of colloids along the vertical profile of the column. The concentration of potassium iodide, and thus the ionic strength, necessary for adequate image segmentation was also explored in separate experiments so that the influence of ionic strength on colloid deposition and mobilization can be studied.

  6. 3 D Hierarchical Porous Carbon for Supercapacitors Prepared from Lignin through a Facile Template-Free Method.

    PubMed

    Zhang, Wenli; Lin, Haibo; Lin, Zheqi; Yin, Jian; Lu, Haiyan; Liu, Dechen; Zhao, Mingzhu

    2015-06-22

    Lignin-derived hierarchical porous carbon (LHPC) was prepared through a facile template-free method. Solidification of the lignin-KOH solution resulted in KOH crystalizing within lignin. The crystalized KOH particles in solid lignin acted both as template and activating agent in the heat-treatment process. The obtained LHPC, exhibiting a 3D network, consisted of macroporous cores, mesoporous channels, and micropores. The LHPC comprised 12.27 at % oxygen-containing groups, which resulted in pseudocapacitance. The LHPC displayed a capacitance of 165.0 F g(-1) in 1 M H2 SO4 at 0.05 A g(-1) , and the capacitance was still 123.5 F g(-1) even at 10 A g(-1) . The LHPC also displayed excellent cycling stability with capacitance retention of 97.3 % after 5000 galvanostatic charge-discharge cycles. On account of the facile preparation of LHPC, this paper offers a facile alternative method for the preparation of hierarchical porous carbon for electrochemical energy storage devices.

  7. From Rice Bran to High Energy Density Supercapacitors: A New Route to Control Porous Structure of 3D Carbon

    PubMed Central

    Hou, Jianhua; Cao, Chuanbao; Ma, Xilan; Idrees, Faryal; Xu, Bin; Hao, Xin; Lin, Wei

    2014-01-01

    Controlled micro/mesopores interconnected structures of three-dimensional (3D) carbon with high specific surface areas (SSA) are successfully prepared by carbonization and activation of biomass (raw rice brans) through KOH. The highest SSA of 2475 m2 g−1 with optimized pore volume of 1.21 cm3 g−1 (40% for mesopores) is achieved for KOH/RBC = 4 mass ratio, than others. The as-prepared 3D porous carbon-based electrode materials for supercapacitors exhibit high specific capacitance specifically at large current densities of 10 A g−1 and 100 A g−1 i.e., 265 F g−1 and 182 F g−1 in 6 M KOH electrolyte, respectively. Moreover, a high power density ca. 1223 W kg−1 (550 W L−1) and energy density 70 W h kg−1 (32 W h L−1) are achieved on the base of active material loading (~10 mg cm2) in the ionic liquid. The findings can open a new avenue to use abundant agricultural by-products as ideal materials with promising applications in high-performance energy-storage devices. PMID:25434348

  8. A review on the systematic formulation of 3-D multiparameter full waveform inversion in viscoelastic medium

    NASA Astrophysics Data System (ADS)

    Yang, Pengliang; Brossier, Romain; Métivier, Ludovic; Virieux, Jean

    2016-10-01

    In this paper, we study 3-D multiparameter full waveform inversion (FWI) in viscoelastic media based on the generalized Maxwell/Zener body including arbitrary number of attenuation mechanisms. We present a frequency-domain energy analysis to establish the stability condition of a full anisotropic viscoelastic system, according to zero-valued boundary condition and the elastic-viscoelastic correspondence principle: the real-valued stiffness matrix becomes a complex-valued one in Fourier domain when seismic attenuation is taken into account. We develop a least-squares optimization approach to linearly relate the quality factor with the anelastic coefficients by estimating a set of constants which are independent of the spatial coordinates, which supplies an explicit incorporation of the parameter Q in the general viscoelastic wave equation. By introducing the Lagrangian multipliers into the matrix expression of the wave equation with implicit time integration, we build a systematic formulation of multiparameter FWI for full anisotropic viscoelastic wave equation, while the equivalent form of the state and adjoint equation with explicit time integration is available to be resolved efficiently. In particular, this formulation lays the foundation for the inversion of the parameter Q in the time domain with full anisotropic viscoelastic properties. In the 3-D isotropic viscoelastic settings, the anelastic coefficients and the quality factors using bulk and shear moduli parametrization can be related to the counterparts using P and S velocity. Gradients with respect to any other parameter of interest can be found by chain rule. Pioneering numerical validations as well as the real applications of this most generic framework will be carried out to disclose the potential of viscoelastic FWI when adequate high-performance computing resources and the field data are available.

  9. 3D porous sol-gel matrix incorporated microdevice for effective large volume cell sample pretreatment.

    PubMed

    Lee, Chan Joo; Jung, Jae Hwan; Seo, Tae Seok

    2012-06-05

    In this study, we demonstrated an effective sample pretreatment microdevice that could perform the capture, purification, and release of pathogenic bacteria with a large-volume sample and at a high speed and high-capture yield. We integrated a sol-gel matrix into the microdevice which forms three-dimensional (3D) micropores for the cell solution to pass through and provides a large surface area for the immobilization of antibodies to capture the target Staphylococcus aureus (S. aureus) cells. The antibody was linked to the surface of the sol-gel via a photocleavable linker, allowing the cell-captured antibody moiety to be released by UV irradiation. In addition to the optimization of the antibody immobilization and UV cleavage processes, the cell-capture efficiency was maximized by controlling the sample flow rate with a pumping scheme (3 steps, 5 steps: 3 steps with one flutter step, 7 steps: 3 steps with two flutter steps) and the pumping time (100, 200, and 300 ms). A quantitative capture analysis was performed by targeting a specific gene site of protein A of S. aureus in real-time PCR (RT-PCR). While the 3-step process with an actuation time of 100 ms showed the fastest flow rate (1 mL sample processing time in 10 min), the pumping scheme with the 7-step process and the 300 ms actuation time revealed the highest cell-capture efficiency. A limit of detection study with the 7-step and the 300 ms pumping scheme demonstrated that 100 cells per 100 μL were detected with a 70% yield, and even a single cell could be analyzed via on-chip sample preparation. Thus, our novel sol-gel based microdevice was proven more cost-effective, simple, and efficient in terms of its sample pretreatment ability compared to the use of a conventional 2D flat microdevice. This proposed sample pretreatment device can be further incorporated to an analytical functional unit to realize a micrototal analysis system (μTAS) with sample-in-answer-out capability in the fields of biomedical

  10. Polymer Crosslinked 3-D Assemblies of Nanoparticles: Mechanically Strong Lightweight Porous Materials

    NASA Technical Reports Server (NTRS)

    Leventis, Nicholas

    2005-01-01

    In analogy to supramolecular assemblies, which are pursued because of properties above and beyond those of the individual molecules, self-standing monolithic three-dimensional assemblies of nanoparticles also have unique properties attributed to their structure. For example, ultra low-density 3-D assemblies of silica nanoparticles, known as silica aerogels, are characterized by large internal void space, high surface area and very low thermal conductivity. Aerogels, however, are also extremely fragile materials, limiting their application to a few specialized environments, e.g., in nuclear reactors as Cerenkov radiation detectors, in space (refer to NASA's Stardust Program) and aboard certain planetary vehicles (thermal insulators on Mars Rovers in 1997 and 2004). The fragility problem is traced to well-defined weak points in the aerogel skeletal framework, the interparticle necks. Using the surface functionality of the nanoparticle building blocks as a focal point, we have directed attachment of a conformal polymer coating over the entire framework, rendering all necks wider. Thus, although the bulk density may increase only by 3x, the mesoporosity (pores in the range 2-50 nm) remains unchanged, while the strength of the material increases by up to 300... Having addressed the fragility problem, aerogels are now robust materials, and a variety of applications, ranging from thermal/acoustic insulators to catalyst supports, to platform for sensors, and dielectrics are all within reach. Our approach employs molecular science to manipulate nanoscopic matter for achieving useful macroscopic properties, and in our view it resides at the core of what defines nanotechnology. In that spirit, this technology is expandable in three directions. Thus, we have already crosslinked successfully amine-modified silica, and we anticipate that more rich chemistry will be realized by been creative with the nanoparticle surface modifiers. On the other hand, although we do not expect

  11. Fitting-determined formulation of effective medium approximation for 3D trench structures in model-based infrared reflectrometry.

    PubMed

    Zhang, Chuanwei; Liu, Shiyuan; Shi, Tielin; Tang, Zirong

    2011-02-01

    The success of the model-based infrared reflectrometry (MBIR) technique relies heavily on accurate modeling and fast calculation of the infrared metrology process, which continues to be a challenge, especially for three-dimensional (3D) trench structures. In this paper, we present a simplified formulation for effective medium approximation (EMA), determined by a fitting-based method for the modeling of 3D trench structures. Intensive investigations have been performed with an emphasis on the generality of the fitting-determined (FD)-EMA formulation in terms of trench depth, trench pitch, and incidence angle so that its application is not limited to a particular configuration. Simulations conducted on a taper trench structure have further verified the proposed FD-EMA and demonstrated that the MBIR metrology with the FD-EMA-based model achieves an accuracy one order higher than that of the conventional zeroth-order EMA-based model.

  12. Axisymmetric flows from fluid injection into a confined porous medium

    NASA Astrophysics Data System (ADS)

    Guo, Bo; Zheng, Zhong; Celia, Michael A.; Stone, Howard A.

    2016-02-01

    We study the axisymmetric flows generated from fluid injection into a horizontal confined porous medium that is originally saturated with another fluid of different density and viscosity. Neglecting the effects of surface tension and fluid mixing, we use the lubrication approximation to obtain a nonlinear advection-diffusion equation that describes the time evolution of the sharp fluid-fluid interface. The flow behaviors are controlled by two dimensionless groups: M, the viscosity ratio of displaced fluid relative to injected fluid, and Γ, which measures the relative importance of buoyancy and fluid injection. For this axisymmetric geometry, the similarity solution involving R2/T (where R is the dimensionless radial coordinate and T is the dimensionless time) is an exact solution to the nonlinear governing equation for all times. Four analytical expressions are identified as asymptotic approximations (two of which are new solutions): (i) injection-driven flow with the injected fluid being more viscous than the displaced fluid (Γ ≪ 1 and M < 1) where we identify a self-similar solution that indicates a parabolic interface shape; (ii) injection-driven flow with injected and displaced fluids of equal viscosity (Γ ≪ 1 and M = 1), where we find a self-similar solution that predicts a distinct parabolic interface shape; (iii) injection-driven flow with a less viscous injected fluid (Γ ≪ 1 and M > 1) for which there is a rarefaction wave solution, assuming that the Saffman-Taylor instability does not occur at the reservoir scale; and (iv) buoyancy-driven flow (Γ ≫ 1) for which there is a well-known self-similar solution corresponding to gravity currents in an unconfined porous medium [S. Lyle et al. "Axisymmetric gravity currents in a porous medium," J. Fluid Mech. 543, 293-302 (2005)]. The various axisymmetric flows are summarized in a Γ-M regime diagram with five distinct dynamic behaviors including the four asymptotic regimes and an intermediate regime

  13. Fabrication of 3D porous SF/β-TCP hybrid scaffolds for bone tissue reconstruction.

    PubMed

    Park, Hyun Jung; Min, Kyung Dan; Lee, Min Chae; Kim, Soo Hyeon; Lee, Ok Joo; Ju, Hyung Woo; Moon, Bo Mi; Lee, Jung Min; Park, Ye Ri; Kim, Dong Wook; Jeong, Ju Yeon; Park, Chan Hum

    2016-07-01

    Bio-ceramic is a biomaterial actively studied in the field of bone tissue engineering. But, only certain ceramic materials can resolve the corrosion problem and possess the biological affinity of conventional metal biomaterials. Therefore, the recent development of composites of hybrid composites and polymers has been widely studied. In this study, we aimed to select the best scaffold of silk fibroin and β-TCP hybrid for bone tissue engineering. We fabricated three groups of scaffold such as SF (silk fibroin scaffold), GS (silk fibroin/small granule size of β-TCP scaffold) and GM (silk fibroin/medium granule size of β-TCP scaffold), and we compared the characteristics of each group. During characterization of the scaffold, we used scanning electron microscopy (SEM) and a Fourier transform infrared spectroscopy (FTIR) for structural analysis. We compared the physiological properties of the scaffold regarding the swelling ratio, water uptake and porosity. To evaluate the mechanical properties, we examined the compressive strength of the scaffold. During in vitro testing, we evaluated cell attachment and cell proliferation (CCK-8). Finally, we confirmed in vivo new bone regeneration from the implanted scaffolds using histological staining and micro-CT. From these evaluations, the fabricated scaffold demonstrated high porosity with good inter-pore connectivity, showed good biocompatibility and high compressive strength and modulus. In particular, the present study indicates that the GM scaffold using β-TCP accelerates new bone regeneration of implanted scaffolds. Accordingly, our scaffold is expected to act a useful application in the field of bone tissue engineering. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1779-1787, 2016.

  14. Parametric study of barometric pumping of a fractured porous medium

    NASA Astrophysics Data System (ADS)

    Adler, Pierre; Mourzenko, Valeri; Thovert, Jean Francois; Pili, Eric; Guillon, Sophie

    2015-04-01

    Fluctuations in the ambient atmospheric pressure result in motion of air in porous fractured media. This mechanism, known as barometric pumping, efficiently transports gaseous species through the vadose zone to the atmosphere. This is of interest in fields, such as transport of trace gases from soil to atmosphere, remediation of contaminated sites, radon in buildings, leakage from carbon sequestration sites and detection of nuclear explosions. The fractures are modeled as polygonal plane surfaces with a given transmissivity embedded in a permeable matrix. The slightly compressible fluid obeys Darcy's law in these two media with exchanges between them. The solute obeys convection-diffusion equations in both media again with exchanges. The numerical methodology is briefly described. The fractures and the porous medium are meshed by triangles and tetrahedra, respectively. The equations are discretized by the finite volume method and a Flux Limiting Scheme diminishes numerical dispersion. This model is applied to the Roselend Natural Laboratory. At a 55 m depth, a sealed cavity allows for gas release experiments across fractured porous rocks in the unsaturated zone. The standard case consist of hexagonal fractures with a radius of 5m, of aperture 0.5 mm and of density larger than 2.4 10-3 m-3; the pressure fluctuations are sinusoidal, of amplitude 0.01 bar and period 1 week; the solute concentration is equal to 1 at the bottom. Systematic results will be presented. First, the precision of the calculations is assessed. Second, the pressure and solute concentration fields are displayed and discussed. Within the time limit, the influence of the major parameters (fracture density, aperture, porosity, diffusion coefficient, pressure fluctuations including real recordings, …) is illustrated and discussed relatively to the standard case. Emphasis is put on some paradoxical results which are obtained. These results are discussed in terms of the amplification of solute

  15. Two-phase flow in a chemically active porous medium

    SciTech Connect

    Darmon, Alexandre Dauchot, Olivier; Benzaquen, Michael; Salez, Thomas

    2014-12-28

    We study the problem of the transformation of a given reactant species into an immiscible product species, as they flow through a chemically active porous medium. We derive the equation governing the evolution of the volume fraction of the species, in a one-dimensional macroscopic description, identify the relevant dimensionless numbers, and provide simple models for capillary pressure and relative permeabilities, which are quantities of crucial importance when tackling multiphase flows in porous media. We set the domain of validity of our models and discuss the importance of viscous coupling terms in the extended Darcy’s law. We investigate numerically the steady regime and demonstrate that the spatial transformation rate of the species along the reactor is non-monotonous, as testified by the existence of an inflection point in the volume fraction profiles. We obtain the scaling of the location of this inflection point with the dimensionless lengths of the problem. Eventually, we provide key elements for optimization of the reactor.

  16. Porous-medium convection: new problems from CO2 sequestration

    NASA Astrophysics Data System (ADS)

    Lister, John

    2013-11-01

    Large scale injection and storage of supercritical carbon dioxide (CO2) into deep saline aquifers is proposed to offset anthropogenic emissions and mitigate climate change. Many aspects of the resultant porous flows provoke fundamental fluid-mechanical problems. The rise and spread of the buoyant CO2 plume beneath an overlying impermeable stratum is a classic gravity current, but with the undesirable extra possibility of upward leakage through fractures. Fortunately, long-term trapping mechanisms exist. One such, dissolution of CO2 into the underlying brine, produces a denser solution which thus convects reassuringly downwards. Consideration of the convective flux prompts re-examination of high-Ra convection in a porous medium, which is found to have a strikingly different asymptotic form from that in a pure fluid. The high-Ra regime of Rayleigh-Darcy convection has an ordered interior with a linear mean temperature gradient and a superposed vertical columnar heat-exchanger flow whose wavelength is consistent with the Ra - 5 / 14 scaling predicted by an asymptotic stability analysis. Quantification of the convective dissolution flux allows evolution towards saturation in confined aquifers, or the erosion of a gravity current in open aquifers, to be calculated.

  17. 3D Spatial Distribution of the Intergalactic Medium: The ESO Blues?

    NASA Astrophysics Data System (ADS)

    Rollinde, Emmanuel; Petitjean, Patrick; Pichon, Christophe; Colombi, Stéphane; Aracil, Bastien

    The numerous absorption lines seen in the spectra of distant quasars (the so-called Lyman-α forest) reveal the intergalactic medium (IGM) up to redshifts larger than 5. It is believed that the space distribution of the gas traces the potential wells of the dark matter. Indeed, recent numerical N-body simulations have been successful at reproducing the observed characteristics of the Lyman-α forest (e.g. [1][12][5]). The IGM is therefore seen as a smooth pervasive medium which can be used to study the spatial distribution of the mass on scales larger than the Jeans' length. This idea is reinforced by observations of multiple lines of sight. It is observed that the Lyman-α forest is fairly homogeneous on scale smaller than 100 kpc (e.g. [11]) and highly correlated on scale up to one megaparsec (e.g. [13][3]). The number of suitable multiple lines of sight is small however and the sample need to be significantly enlarged before any firm conclusion can be drawn (see Section 3.3).

  18. 3D model for laser heating of a heterogeneous turbid medium

    NASA Astrophysics Data System (ADS)

    Rossacci, Michael J.; DiMarzio, Charles A.; Lindberg, Scott C.; Pankratov, Michail M.

    1997-05-01

    In order to better understand the interaction of laser light with biological tissue, a light-transport model is integrated with a heat-transport model. The outputs include temperature as a function of position and time, given the illumination conditions and the optical and thermal properties of the tissue. The optical portion of the algorithm is based on the theory of radiative transfer through a turbid medium. Our computer program models multiple scattering in three dimensions using seven discrete irradiances which approximate the radiative transport equation. The distribution of absorbed light in the tissue is calculated and used as the source term in a discrete approximation to the thermal diffusion equation. Recently, we have been using the model to better understand the laser-heating of heterogeneous tissue. Rather than modeling a homogeneous mixture having properties given by weighted averages of those of tissue and blood, we model this medium as an array of blood vessels in a bloodless dermis background. We are currently analyzing temporal and spatial variations of temperature in homogeneous and heterogeneous tissue having identical blood concentrations. A particular application of the model is to the study of laser coagulation tonsillectomy.

  19. Properties of equilibrium carbon dioxide hydrate in porous medium

    NASA Astrophysics Data System (ADS)

    Voronov, V. P.; Gorodetskii, E. E.; Podnek, V. E.; Grigoriev, B. A.

    2016-09-01

    Specific heat capacity, dissociation heat and hydration number of carbon dioxide hydrate in porous medium are determined by adiabatic calorimetry method. The measurements were carried out in the temperature range 250-290 K and in pressure range 1-5 MPa. The measured specific heat of the hydrate is approximately 2.7 J/(g K), which is significantly larger than the specific heat of methane hydrate. In particular, at heating, larger value of the specific heat of carbon dioxide hydrate is a result of gas emission from the hydrate. The hydration number at the hydrate-gas coexistence changes from 6.2 to 6.9. The dissociation heat of carbon dioxide hydrate varies from the 55 kJ/mol near the upper quadruple point to the 57 kJ/mol near the lower quadruple point.

  20. Tear film dynamics: modeling the glycocalyx as a porous medium

    NASA Astrophysics Data System (ADS)

    Siddique, Javed; Mastroberardinob, , Antonio; Braun, Richard; Anderson, Daniel

    2015-11-01

    The human tear film is a complex fluid structure composed of multiple layers: an aqueous layer that comprises most of the film and an outermost thinner lipid layer coat a forest of large transmembrane mucins at the epithelial surface. The glycocalyx helps provide stability to the ocular surface by assisting the tear film to wet it. It is also permeable to water, but less so to ions. We formulate a thin film model based on lubrication theory in order to understand the dynamics between the aqueous layer and the glycocalyx, which we treat as a rigid porous medium. We present numerical solutions for the evolution of the tear film and discuss the roles played by the key parameters of the system. This work was supported by the Simons Foundation Grant No. 281839.

  1. 3D polyaniline porous layer anchored pillared graphene sheets: enhanced interface joined with high conductivity for better charge storage applications.

    PubMed

    Sekar, Pandiaraj; Anothumakkool, Bihag; Kurungot, Sreekumar

    2015-04-15

    Here, we report synthesis of a 3-dimensional (3D) porous polyaniline (PANI) anchored on pillared graphene (G-PANI-PA) as an efficient charge storage material for supercapacitor applications. Benzoic acid (BA) anchored graphene, having spatially separated graphene layers (G-Bz-COOH), was used as a structure controlling support whereas 3D PANI growth has been achieved by a simple chemical oxidation of aniline in the presence of phytic acid (PA). The BA groups on G-Bz-COOH play a critical role in preventing the restacking of graphene to achieve a high surface area of 472 m(2)/g compared to reduced graphene oxide (RGO, 290 m(2)/g). The carboxylic acid (-COOH) group controls the rate of polymerization to achieve a compact polymer structure with micropores whereas the chelating nature of PA plays a crucial role to achieve the 3D growth pattern of PANI. This type of controlled interplay helps G-PANI-PA to achieve a high conductivity of 3.74 S/cm all the while maintaining a high surface area of 330 m(2)/g compared to PANI-PA (0.4 S/cm and 60 m(2)/g). G-PANI-PA thus conceives the characteristics required for facile charge mobility during fast charge-discharge cycles, which results in a high specific capacitance of 652 F/g for the composite. Owing to the high surface area along with high conductivity, G-PANI-PA displays a stable specific capacitance of 547 F/g even with a high mass loading of 3 mg/cm(2), an enhanced areal capacitance of 1.52 F/cm(2), and a volumetric capacitance of 122 F/cm(3). The reduced charge-transfer resistance (RCT) of 0.67 Ω displayed by G-PANI-PA compared to pure PANI (0.79 Ω) stands out as valid evidence of the improved charge mobility achieved by the system by growing the 3D PANI layer along the spatially separated layers of the graphene sheets. The low RCT helps the system to display capacitance retention as high as 65% even under a high current dragging condition of 10 A/g. High charge/discharge rates and good cycling stability are the other

  2. Thermal Dispersion Within a Porous Medium Near a Solid Wall

    NASA Technical Reports Server (NTRS)

    Simon, T.; McFadden, G.; Ibrahim, M.

    2006-01-01

    The regenerator is a key component to Stirling cycle machine efficiency. Typical regenerators are of sintered fine wires or layers of fine-wire screens. Such porous materials are contained within solid-waH casings. Thermal energy exchange between the regenerator and the casing is important to cycle performance for the matrix and casing would not have the same axial temperature profile in an actual machine. Exchange from one to the other may allow shunting of thermal energy, reducing cycle efficiency. In this paper, temperature profiles within the near-wall region of the matrix are measured and thermal energy transport, termed thermal dispersion, is inferred. The data show how the wall affects thermal transport. Transport normal to the mean flow direction is by conduction within the solid and fluid and by advective transport within the matrix. In the near-wall region, both may be interrupted from their normal in-core pattern. Solid conduction paths are broken and scales of advective transport are damped. An equation is presented which describes this change for a wire screen mesh. The near-wall layer typically acts as an insulating layer. This should be considered in design or analysis. Effective thermal conductivity within the core is uniform. In-core transverse thermal effective conductivity values are compared to direct and indirect measurements reported elsewhere and to 3D numerical simulation results, computed previously and reported elsewhere. The 3-D CFD model is composed of six cylinders in cross flow, staggered in arrangement to match the dimensions and porosity of the matrix used in the experiments. The commercial code FLUENT is used to obtain the flow and thermal fields. The thermal dispersion and effective thermal conductivities for the matrix are computed from the results.

  3. A 3D porous zinc MOF constructed from a flexible tripodal ligand: Synthesis, structure, and photoluminescence property

    SciTech Connect

    Wen Lili; Wang Dong'e; Wang Chenggang; Wang Feng; Li Dongfeng Deng Kejian

    2009-03-15

    A new metal-organic framework, [Zn{sub 5}(trencba){sub 2}(OH){sub 2}Cl{sub 2}.4H{sub 2}O] (1) [H{sub 3}trencba=N,N,N',N',N'',N''-tris[(4-carboxylate-2-yl)methyl]-tris (2-aminoethyl)amine], constructed from a flexible tripodal ligand based on C{sub 3} symmetric tris(2-aminoethyl)amine, has been synthesized hydrothermally and characterized by elemental analysis, IR, TG, XRD and single-crystal X-ray diffraction analysis. Compound 1 contains an unprecedented linear penta-nuclear zinc cluster fragment. Each ligand links four penta-nuclear fragments, and every fragment links eight ligands to generate a three-dimensional non-interpenetrated porous framework. The uncoordinated water molecules were observed trapped in the void pores. Compound 1 represents the first example of (6,8)-connected 3D bi-nodal framework based on a single kind of organic ligand. The photoluminescence measurements showed that complex 1 exhibits relatively stronger blue emissions at room temperature than that of the ligand. - Graphical abstract: The MOF [Zn{sub 5}(trencba){sub 2}(OH){sub 2}Cl{sub 2}.4H{sub 2}O] (H{sub 3}trencba=N,N,N',N',N',N'-tris[(4-carboxylate-2-yl)methyl]-tris (2-aminoethyl)amine) reveals a (6,8)-connected bi-nodal three-dimensional porous framework with unprecedented penta-nuclear fragment, which appears to be a good candidate of hybrid inorganic-organic photoactive materials.

  4. Prediction of empirical properties using direct pore-scale simulation of straining through 3D microtomography images of porous media

    NASA Astrophysics Data System (ADS)

    Mirabolghasemi, Maryam; Prodanović, Maša; DiCarlo, David; Ji, Hongyu

    2015-10-01

    Understanding the mechanisms of filtration through porous media is relevant in many engineering applications ranging from waste water treatment and aquifer contamination in environmental engineering to estimating the permeability reduction in near wellbore region during drilling or water re-injection in petroleum engineering. In this paper we present a pore-scale approach that models straining through the pore structures extracted from X-ray tomographic images of rock and grain pack samples from the first principles, enabling the examination of current macroscopic models. While continuum models are widely used for fast prediction of the retention profiles and permeability of the host porous medium, they require a number of phenomenological parameters which are derived from matching experimental results. One of these parameters is the rate of entrapment, which is the sink term in the advection-diffusion equation. Here we find the constitutive relationship for the rate of entrapment as a product of the filtration coefficient, velocity, and concentration and validate it by comparing with core flood experiments. Results show that the pore-scale simulation gives close approximations of filtration coefficient when pore bridging and straining are the main particle capture mechanisms.

  5. 3D Imaging of Porous Media Using Laser Scanning Confocal Microscopy with Application to Microscale Transport Processes

    SciTech Connect

    Fredrich, J.T.

    1999-02-10

    We present advances in the application of laser scanning confocal microscopy (LSCM) to image, reconstruct, and characterize statistically the microgeometry of porous geologic and engineering materials. We discuss technical and practical aspects of this imaging technique, including both its advantages and limitations. Confocal imaging can be used to optically section a material, with sub-micron resolution possible in the lateral and axial planes. The resultant volumetric image data, consisting of fluorescence intensities for typically {approximately}50 million voxels in XYZ space, can be used to reconstruct the three-dimensional structure of the two-phase medium. We present several examples of this application, including studying pore geometry in sandstone, characterizing brittle failure processes in low-porosity rock deformed under triaxial loading conditions in the laboratory, and analyzing the microstructure of porous ceramic insulations. We then describe approaches to extract statistical microgeometric descriptions from volumetric image data, and present results derived from confocal volumetric data sets. Finally, we develop the use of confocal image data to automatically generate a three-dimensional mesh for numerical pore-scale flow simulations.

  6. Structure and visible light luminescence of 3D flower-like Co3O4 hierarchical microstructures assembled by hexagonal porous nanoplates.

    PubMed

    Wang, Wenzhong; Xu, Jie

    2015-01-14

    A two-step strategy has been developed to fabricate 3D flower-like Co3O4 hierarchical microstructures assembled by hexagonal porous nanoplates. The synthetic procedure was described as (1) 3D flower-like α-Co(OH)2 microstructures were prepared by a facile surfactant-free low-temperature hydrothermal process; (2) 3D flower-like Co3O4 hierarchical microstructures were fabricated by annealing the obtained 3D flower-like α-Co(OH)2 microstructures. X-ray diffraction and Raman spectrum analyses demonstrate that the hierarchical microstructures formed from 3D flower-like α-Co(OH)2 microstructures are composed of pure cubic phase Co3O4. Scanning electronic microscopy demonstrates that the as-prepared Co3O4 microstructures exhibit 3D flower-like hierarchical structures assembled by hexagonal porous nanoplates. Photoluminescence demonstrates that these novel 3D flower-like Co3O4 hierarchical microstructures display a broad strong emission in the visible range of 650 to 800 nm with a peak at around 710 nm (1.75 eV), which is very close to the indirect optical band gap of 1.60 eV for Co3O4 thin film. The result indicates that the photoluminescence emission likely originates from the indirect optical band gap emission. The broad photoluminescence emission may be resulted from a wide size distribution of porous nanoplates in 3D hierarchical microstructures. These 3D flower-like Co3O4 hierarchical microstructures with unique optical properties may find new potential applications in visible light emitting materials.

  7. Implicit finite volume and discontinuous Galerkin methods for multicomponent flow in unstructured 3D fractured porous media

    NASA Astrophysics Data System (ADS)

    Moortgat, Joachim; Amooie, Mohammad Amin; Soltanian, Mohamad Reza

    2016-10-01

    We present a new implicit higher-order finite element (FE) approach to efficiently model compressible multicomponent fluid flow on unstructured grids and in fractured porous subsurface formations. The scheme is sequential implicit: pressures and fluxes are updated with an implicit Mixed Hybrid Finite Element (MHFE) method, and the transport of each species is approximated with an implicit second-order Discontinuous Galerkin (DG) FE method. Discrete fractures are incorporated with a cross-flow equilibrium approach. This is the first investigation of all-implicit higher-order MHFE-DG for unstructured triangular, quadrilateral (2D), and hexahedral (3D) grids and discrete fractures. A lowest-order implicit finite volume (FV) transport update is also developed for the same grid types. The implicit methods are compared to an Implicit-Pressure-Explicit-Composition (IMPEC) scheme. For fractured domains, the unconditionally stable implicit transport update is shown to increase computational efficiency by orders of magnitude as compared to IMPEC, which has a time-step constraint proportional to the pore volume of discrete fracture grid cells. However, when lowest-order Euler time-discretizations are used, numerical errors increase linearly with the larger implicit time-steps, resulting in high numerical dispersion. Second-order Crank-Nicolson implicit MHFE-DG and MHFE-FV are therefore presented as well. Convergence analyses show twice the convergence rate for the DG methods as compared to FV, resulting in two to three orders of magnitude higher computational efficiency. Numerical experiments demonstrate the efficiency and robustness in modeling compressible multicomponent flow on irregular and fractured 2D and 3D grids, even in the presence of fingering instabilities.

  8. Decoration of Micro-/Nanoscale Noble Metal Particles on 3D Porous Nickel Using Electrodeposition Technique as Electrocatalyst for Hydrogen Evolution Reaction in Alkaline Electrolyte.

    PubMed

    Qian, Xin; Hang, Tao; Shanmugam, Sangaraju; Li, Ming

    2015-07-29

    Micro-/nanoscale noble metal (Ag, Au, and Pt) particle-decorated 3D porous nickel electrodes for hydrogen evolution reaction (HER) in alkaline electrolyte are fabricated via galvanostatic electrodeposition technique. The developed electrodes are characterized by field emission scanning electron microscopy and electrochemical measurements including Tafel polarization curves, cyclic voltammetry, and electrochemical impedance spectroscopy. It is clearly shown that the enlarged real surface area caused by 3D highly porous dendritic structure has greatly reinforced the electrocatalytic activity toward HER. Comparative analysis of electrodeposited Ag, Au, and Pt particle-decorated porous nickel electrodes for HER indicates that both intrinsic property and size of the noble metal particles can lead to distinct catalytic activities. Both nanoscale Au and Pt particles have further reinforcement effect toward HER, whereas microscale Ag particles exhibit the reverse effect. As an effective 3D hydrogen evolution cathode, the nanoscale Pt-particle-decorated 3D porous nickel electrode demonstrates the highest catalytic activity with an extremely low overpotential of -0.045 V for hydrogen production, a considerable exchange current density of 9.47 mA cm(-2) at 25 °C, and high durability in long-term electrolysis, all of which are attributed to the intrinsic catalytic property and the extremely small size of Pt particles.

  9. Accuracy of the fast multipole boundary element method with quadratic elements in the analysis of 3D porous structures

    NASA Astrophysics Data System (ADS)

    Ptaszny, Jacek

    2015-09-01

    In this work, a fast multipole boundary element method for 3D elasticity problem was developed by the application of the fast multipole algorithm and isoparametric 8-node boundary elements with quadratic shape functions. The problem is described by the boundary integral equation involving the Kelvin solutions. In order to keep the numerical integration error on appropriate level, an adaptive method with subdivision of boundary elements into subelements, described in the literature, was applied. An extension of the neighbour list of boundary element clusters, corresponding to near-field computations, was proposed in order to reduce the truncation error of expansions in problems with high stress concentration. Efficiency of the method is illustrated by numerical examples including a solid with single spherical cavity, solids with two interacting spherical cavities, and numerical homogenization of solids with cubic arrangement of spherical cavities. All results agree with analytical models available in the literature. The examples show that the method can be applied to the analysis of porous structures.

  10. A transferrin variant as the targeting ligand for polymeric nanoparticles incorporated in 3-D PLGA porous scaffolds.

    PubMed

    Lopes, André M; Chen, Kevin Y; Kamei, Daniel T

    2017-04-01

    We have developed doxorubicin (DOX)-loaded poly(lactide-co-glycolide) (PLGA) nanoparticles (DP) conjugated with polyethylene glycol (PEG) and transferrin (Tf) to form Tf-PEG-DPs (TPDPs), and incorporated these TPDPs into three-dimensional (3-D) PLGA porous scaffolds to form a controlled delivery system. To our knowledge, this represents the first use of a Tf variant (oxalate Tf) to improve the targeted delivery of drug-encapsulated nanoparticles (NPs) in PLGA scaffolds to PC3 prostate cancer cells. The PLGA scaffolds with TPDPs incorporated have been shown to release drugs for sustained delivery and provided a continuous release of DOX. The MTS assay was also performed to determine the potency of native and oxalate TPDPs, and a 3.0-fold decrease in IC50 values were observed between the native and oxalate TPDPs. The lower IC50 value for the oxalate version signifies greater potency compared to the native version, since a lower concentration of drug was required to achieve the same therapeutic effect. These results suggest that this technology has potential to become a new implantable polymeric device to improve the controlled and targeted drug delivery of Tf-conjugated NPs for cancer therapy.

  11. Effects of sintering temperature on morphology and mechanical characteristics of 3D printed porous titanium used as dental implant.

    PubMed

    Gagg, Graham; Ghassemieh, Elaheh; Wiria, Florencia Edith

    2013-10-01

    Porous titanium samples were manufactured using the 3D printing and sintering method in order to determine the effects of final sintering temperature on morphology and mechanical properties. Cylindrical samples were printed and split into groups according to a final sintering temperature (FST). Irregular geometry samples were also printed and split into groups according to their FST. The cylindrical samples were used to determine part shrinkage, in compressive tests to provide stress-strain data, in microCT scans to provide internal morphology data and for optical microscopy to determine surface morphology. All of the samples were used in microhardness testing to establish the hardness. Below 1100 °C FST, shrinkage was in the region of 20% but increased to approximately 30% by a FST of 1300 °C. Porosity varied from a maximum of approximately 65% at the surface to the region of 30% internally. Between 97 and 99% of the internal porosity is interconnected. Average pore size varied between 24 μm at the surface and 19 μm internally. Sample hardness increased to in excess of 300 HV0.05 with increasing FST while samples with an FST of below 1250 °C produced an elastic-brittle stress/strain curve and samples above this displayed elastic-plastic behaviour. Yield strength increased significantly through the range of sintering temperatures while the Young's modulus remained fairly consistent.

  12. Flexible 3D porous CuO nanowire arrays for enzymeless glucose sensing: in situ engineered versus ex situ piled.

    PubMed

    Huang, Jianfei; Zhu, Yihua; Yang, Xiaoling; Chen, Wei; Zhou, Ying; Li, Chunzhong

    2015-01-14

    Convenient determination of glucose in a sensitive, reliable and cost-effective way has aroused sustained research passion, bringing along assiduous investigation of high-performance electroactive nanomaterials to build enzymeless sensors. In addition to the intrinsic electrocatalytic capability of the sensing materials, electrode architecture at the microscale is also crucial for fully enhancing the performance. In this work, free-standing porous CuO nanowire (NW) was taken as a model sensing material to illustrate this point, where an in situ formed 3D CuO nanowire array (NWA) and CuO nanowires pile (NWP) immobilized with polymer binder by conventional drop-casting technique were both studied for enzymeless glucose sensing. The NWA electrode exhibited greatly promoted electrochemistry characterized by decreased overpotential for electro-oxidation of glucose and over 5-fold higher sensitivity compared to the NWP counterpart, benefiting from the binder-free nanoarray structure. Besides, its sensing performance was also satisfying in terms of rapidness, selectivity and durability. Further, the CuO NWA was utilized to fabricate a flexible sensor which showed excellent performance stability against mechanical bending. Thanks to its favorable electrode architecture, the CuO NWA is believed to offer opportunities for building high-efficiency flexible electrochemical devices.

  13. Wave propagation in a strongly heterogeneous elastic porous medium: Homogenization of Biot medium with double porosities

    NASA Astrophysics Data System (ADS)

    Rohan, Eduard; Naili, Salah; Nguyen, Vu-Hieu

    2016-08-01

    We study wave propagation in an elastic porous medium saturated with a compressible Newtonian fluid. The porous network is interconnected whereby the pores are characterized by two very different characteristic sizes. At the mesoscopic scale, the medium is described using the Biot model, characterized by a high contrast in the hydraulic permeability and anisotropic elasticity, whereas the contrast in the Biot coupling coefficient is only moderate. Fluid motion is governed by the Darcy flow model extended by inertia terms and by the mass conservation equation. The homogenization method based on the asymptotic analysis is used to obtain a macroscopic model. To respect the high contrast in the material properties, they are scaled by the small parameter, which is involved in the asymptotic analysis and characterized by the size of the heterogeneities. Using the estimates of wavelengths in the double-porosity networks, it is shown that the macroscopic descriptions depend on the contrast in the static permeability associated with pores and micropores and on the frequency. Moreover, the microflow in the double porosity is responsible for fading memory effects via the macroscopic poroviscoelastic constitutive law. xml:lang="fr"

  14. Strategy to Achieve Highly Porous/Biocompatible Macroscale Cell Blocks, Using a Collagen/Genipin-bioink and an Optimal 3D Printing Process.

    PubMed

    Kim, Yong Bok; Lee, Hyeongjin; Kim, Geun Hyung

    2016-11-30

    Recently, a three-dimensional (3D) bioprinting process for obtaining a cell-laden structure has been widely applied because of its ability to fabricate biomimetic complex structures embedded with and without cells. To successfully obtain a cell-laden porous block, the cell-delivering vehicle, bioink, is one of the significant factors. Until now, various biocompatible hydrogels (synthetic and natural biopolymers) have been utilized in the cell-printing process, but a bioink satisfying both biocompatibility and print-ability requirements to achieve a porous structure with reasonable mechanical strength has not been issued. Here, we propose a printing strategy with optimal conditions including a safe cross-linking procedure for obtaining a 3D porous cell block composed of a biocompatible collagen-bioink and genipin, a cross-linking agent. To obtain the optimal processing conditions, we modified the 3D printing machine and selected an optimal cross-linking condition (∼1 mM and 1 h) of genipin solution. To show the feasibility of the process, 3D pore-interconnected cell-laden constructs were manufactured using osteoblast-like cells (MG63) and human adipose stem cells (hASCs). Under these processing conditions, a macroscale 3D collagen-based cell block of 21 × 21 × 12 mm(3) and over 95% cell viability was obtained. In vitro biological testing of the cell-laden 3D porous structure showed that the embedded cells were sufficiently viable, and their proliferation was significantly higher; the cells also exhibited increased osteogenic activities compared to the conventional alginate-based bioink (control). The results indicated the fabrication process using the collagen-bioink would be an innovative platform to design highly biocompatible and mechanically stable cell blocks.

  15. Influence of buoyancy on drainage of a fractal porous medium

    NASA Astrophysics Data System (ADS)

    Huinink, H. P.; Michels, M. A.

    2002-10-01

    The influence of stabilizing hydrostatic pressure gradients on the drainage of a fractal porous medium is studied. The invasion process is treated with invasion percolation (IP) in a gradient. Fractality is mimicked by randomly closing bonds of a network. Two length scales govern the problem: the characteristic length of the pore structure ξs and a length scale ξg above which buoyancy determines the structure of the cluster. When ξs<ξg the local structure of the invading cluster is governed by the interplay of capillarity and the fractal properties of the pore space. Only parts of the backbone of the pore structure can be invaded. Therefore, the obtained fractal dimension for small systems L<ξs is much lower (1.40) than the one for ordinary IP (1.82). On larger length scales, ξsξg, gravity becomes important and ξg scales with the bond number B as ξg~B-0.57, as in ordinary IP, while the fractal dimension becomes equal to the Euclidean one. When ξg<ξs gravity is already important on length scales where the fractality of the medium has to be considered too. On small scales L<ξg, where only capillarity and fractality play a role the cluster structure is again characterized by the fractal dimension of 1.40. On larger length scales, ξgξs the fractal dimension of the invading cluster equals the Euclidean one and ξg~B-0.69.

  16. 3D methodology for modeling and analysis of medium-complexity mechanical assemblies: Application in elevator-car design

    NASA Astrophysics Data System (ADS)

    Karaoglanidis, Georgios A.; Sapidis, Nickolas S.

    2012-12-01

    This paper deals with design methods for medium-complexity mechanical systems, and focuses on two standard steps in such a method: "2D drawing" (included in the early stages of design) and "3D CADmodel simplification & defeaturing" (in the concluding "analysis stages" of a design procedure), whose contribution to mechanical design has always been a controversial subject. On the basis of the state-of-the-art in mechanical design, this "position paper" advocates complete elimination of the above two steps, and details the corresponding modified mechanical-design method. Application of this new design-method on a real-life industrial case (: elevator-car design) is fully analyzed, demonstrating the method's efficacy for mediumcomplexity mechanical assemblies. [Figure not available: see fulltext.

  17. Flow regimes for fluid injection into a confined porous medium

    DOE PAGES

    Zheng, Zhong; Guo, Bo; Christov, Ivan C.; ...

    2015-02-24

    We report theoretical and numerical studies of the flow behaviour when a fluid is injected into a confined porous medium saturated with another fluid of different density and viscosity. For a two-dimensional configuration with point source injection, a nonlinear convection–diffusion equation is derived to describe the time evolution of the fluid–fluid interface. In the early time period, the fluid motion is mainly driven by the buoyancy force and the governing equation is reduced to a nonlinear diffusion equation with a well-known self-similar solution. In the late time period, the fluid flow is mainly driven by the injection, and the governingmore » equation is approximated by a nonlinear hyperbolic equation that determines the global spreading rate; a shock solution is obtained when the injected fluid is more viscous than the displaced fluid, whereas a rarefaction wave solution is found when the injected fluid is less viscous. In the late time period, we also obtain analytical solutions including the diffusive term associated with the buoyancy effects (for an injected fluid with a viscosity higher than or equal to that of the displaced fluid), which provide the structure of the moving front. Numerical simulations of the convection–diffusion equation are performed; the various analytical solutions are verified as appropriate asymptotic limits, and the transition processes between the individual limits are demonstrated.« less

  18. Flow regimes for fluid injection into a confined porous medium

    SciTech Connect

    Zheng, Zhong; Guo, Bo; Christov, Ivan C.; Celia, Michael A.; Stone, Howard A.

    2015-02-24

    We report theoretical and numerical studies of the flow behaviour when a fluid is injected into a confined porous medium saturated with another fluid of different density and viscosity. For a two-dimensional configuration with point source injection, a nonlinear convection–diffusion equation is derived to describe the time evolution of the fluid–fluid interface. In the early time period, the fluid motion is mainly driven by the buoyancy force and the governing equation is reduced to a nonlinear diffusion equation with a well-known self-similar solution. In the late time period, the fluid flow is mainly driven by the injection, and the governing equation is approximated by a nonlinear hyperbolic equation that determines the global spreading rate; a shock solution is obtained when the injected fluid is more viscous than the displaced fluid, whereas a rarefaction wave solution is found when the injected fluid is less viscous. In the late time period, we also obtain analytical solutions including the diffusive term associated with the buoyancy effects (for an injected fluid with a viscosity higher than or equal to that of the displaced fluid), which provide the structure of the moving front. Numerical simulations of the convection–diffusion equation are performed; the various analytical solutions are verified as appropriate asymptotic limits, and the transition processes between the individual limits are demonstrated.

  19. Inclusion-based effective medium models for the field-scale permeability of 3D fractured rock masses

    NASA Astrophysics Data System (ADS)

    Ebigbo, Anozie; Lang, Philipp S.; Paluszny, Adriana; Zimmerman, Robert W.

    2016-04-01

    Fractures that are more permeable than their host rock can act as preferential, or at least additional, pathways for fluid to flow through the rock. The additional transmissivity contributed by these fractures will be of great relevance in several areas of earth science and engineering, such as radioactive waste disposal in crystalline rock, exploitation of fractured hydrocarbon and geothermal reservoirs, or hydraulic fracturing. In describing or predicting flow through fractured rock, the effective permeability of the rock mass, comprising both the rock matrix and a network of fractures, is a crucial parameter, and will depend on several geometric properties of the fractures/networks, such as lateral extent, aperture, orientation, and fracture density. This study investigates the ability of classical inclusion-based effective medium models (following the work of Sævik et al., Transp. Porous Media, 2013) to predict this permeability. In these models, the fractures are represented as thin, spheroidal inclusions, the interiors of which are treated as porous media having a high (but finite) permeability. The predictions of various effective medium models, such as the symmetric and asymmetric self-consistent schemes, the differential scheme, and Maxwell's method, are tested against the results of explicit numerical simulations of mono- and polydisperse isotropic fracture networks embedded in a permeable rock matrix. Comparisons are also made with the Hashin-Shrikman bounds, Snow's model, and Mourzenko's heuristic model (Mourzenko et al., Phys. Rev. E, 2011). This problem is characterised mathematically by two small parameters, the aspect ratio of the spheroidal fractures, α, and the ratio between matrix and fracture permeability, κ. Two different regimes can be identified, corresponding to α/κ < 1 and α/κ > 1. The lower the value of α/κ, the more significant is flow through the matrix. Due to differing flow patterns, the dependence of effective permeability on

  20. 3D numerical simulation of the long range propagation of acoustical shock waves through a heterogeneous and moving medium

    SciTech Connect

    Luquet, David; Marchiano, Régis; Coulouvrat, François

    2015-10-28

    Many situations involve the propagation of acoustical shock waves through flows. Natural sources such as lightning, volcano explosions, or meteoroid atmospheric entries, emit loud, low frequency, and impulsive sound that is influenced by atmospheric wind and turbulence. The sonic boom produced by a supersonic aircraft and explosion noises are examples of intense anthropogenic sources in the atmosphere. The Buzz-Saw-Noise produced by turbo-engine fan blades rotating at supersonic speed also propagates in a fast flow within the engine nacelle. Simulating these situations is challenging, given the 3D nature of the problem, the long range propagation distances relative to the central wavelength, the strongly nonlinear behavior of shocks associated to a wide-band spectrum, and finally the key role of the flow motion. With this in view, the so-called FLHOWARD (acronym for FLow and Heterogeneous One-Way Approximation for Resolution of Diffraction) method is presented with three-dimensional applications. A scalar nonlinear wave equation is established in the framework of atmospheric applications, assuming weak heterogeneities and a slow wind. It takes into account diffraction, absorption and relaxation properties of the atmosphere, quadratic nonlinearities including weak shock waves, heterogeneities of the medium in sound speed and density, and presence of a flow (assuming a mean stratified wind and 3D turbulent ? flow fluctuations of smaller amplitude). This equation is solved in the framework of the one-way method. A split-step technique allows the splitting of the non-linear wave equation into simpler equations, each corresponding to a physical effect. Each sub-equation is solved using an analytical method if possible, and finite-differences otherwise. Nonlinear effects are solved in the time domain, and others in the frequency domain. Homogeneous diffraction is handled by means of the angular spectrum method. Ground is assumed perfectly flat and rigid. Due to the 3D

  1. 3D numerical simulation of the long range propagation of acoustical shock waves through a heterogeneous and moving medium

    NASA Astrophysics Data System (ADS)

    Luquet, David; Marchiano, Régis; Coulouvrat, François

    2015-10-01

    Many situations involve the propagation of acoustical shock waves through flows. Natural sources such as lightning, volcano explosions, or meteoroid atmospheric entries, emit loud, low frequency, and impulsive sound that is influenced by atmospheric wind and turbulence. The sonic boom produced by a supersonic aircraft and explosion noises are examples of intense anthropogenic sources in the atmosphere. The Buzz-Saw-Noise produced by turbo-engine fan blades rotating at supersonic speed also propagates in a fast flow within the engine nacelle. Simulating these situations is challenging, given the 3D nature of the problem, the long range propagation distances relative to the central wavelength, the strongly nonlinear behavior of shocks associated to a wide-band spectrum, and finally the key role of the flow motion. With this in view, the so-called FLHOWARD (acronym for FLow and Heterogeneous One-Way Approximation for Resolution of Diffraction) method is presented with three-dimensional applications. A scalar nonlinear wave equation is established in the framework of atmospheric applications, assuming weak heterogeneities and a slow wind. It takes into account diffraction, absorption and relaxation properties of the atmosphere, quadratic nonlinearities including weak shock waves, heterogeneities of the medium in sound speed and density, and presence of a flow (assuming a mean stratified wind and 3D turbulent ? flow fluctuations of smaller amplitude). This equation is solved in the framework of the one-way method. A split-step technique allows the splitting of the non-linear wave equation into simpler equations, each corresponding to a physical effect. Each sub-equation is solved using an analytical method if possible, and finite-differences otherwise. Nonlinear effects are solved in the time domain, and others in the frequency domain. Homogeneous diffraction is handled by means of the angular spectrum method. Ground is assumed perfectly flat and rigid. Due to the 3D

  2. Investigating the neuroglial differentiation effect of neuroblastoma conditioned medium in human endometrial stem cells cultured on 3D nanofibrous scaffold.

    PubMed

    Ebrahimi-Barough, Somayeh; Hoveizi, Elham; Norouzi Javidan, Abbas; Ai, Jafar

    2015-08-01

    Neural tissue engineering is an important area of research in the field of tissue-engineering especially for neurodegenerative disease such as spinal cord injury. The differentiation capacity of human endometrial stem cells (hEnSCs) into neuronal cells has yet to be elucidated. Here, the major aim of the present study was to investigate the differentiation ability of hEnSCs cultured on polylactic acid/chitosan (PLA/CS) nanofibrous scaffold into neuroglial cells in response to conditioned medium of BE(2)-C human neuroblastoma cells and growth factors. Here we investigated the use PLA/CS scaffold as a three dimensional (3D) system that increased neuro-glial cells differentiation. Human EnSCs after three passages were differentiated in neuro-glial like cells under neuroblastoma conditioned medium with FGF2/PDGF-AA on PLA/CS scaffold. By day 18, differentiated cells were analyzed for expression of neuroglial markers by qRT-PCR and immunofluorescence. The results revealed that hEnSCs attach, grow and differentiation on the nanofibrous PLA/CS scaffold. Additionally, our study showed the expression of neural and glial lineage markers such as Nestin, NF-L, MAP2, PDGFRa, CNP, Olig2, MBP, and GFAP in the level of mRNA and MAP2, Tuj-1, and NF-L in the protein level after 18 days. Our results demonstrate that hEnSCs cultured on PLA/CS nanofibrous scaffold have the potential to differentiate in neuronal and glial cells in presence of neuroblastoma conditioned medium on PLA/CS scaffold. The result of this study may have impact in tissue engineering and cells-base therapy of neurodegenerative diseases and have a great potential for wide application.

  3. Reduced graphene oxide/carbon double-coated 3-D porous ZnO aggregates as high-performance Li-ion anode materials.

    PubMed

    Wi, Sungun; Woo, Hyungsub; Lee, Sangheon; Kang, Joonhyeon; Kim, Jaewon; An, Subin; Kim, Chohui; Nam, Seunghoon; Kim, Chunjoong; Park, Byungwoo

    2015-01-01

    The reduced graphene oxide (RGO)/carbon double-coated 3-D porous ZnO aggregates (RGO/C/ZnO) have been successfully synthesized as anode materials for Li-ion batteries with excellent cyclability and rate capability. The mesoporous ZnO aggregates prepared by a simple solvothermal method are sequentially modified through distinct carbon-based double coating. These novel architectures take unique advantages of mesopores acting as space to accommodate volume expansion during cycling, while the conformal carbon layer on each nanoparticle buffering volume changes, and conductive RGO sheets connect the aggregates to each other. Consequently, the RGO/C/ZnO exhibits superior electrochemical performance, including remarkably prolonged cycle life and excellent rate capability. Such improved performance of RGO/C/ZnO may be attributed to synergistic effects of both the 3-D porous nanostructures and RGO/C double coating.

  4. Reduced graphene oxide/carbon double-coated 3-D porous ZnO aggregates as high-performance Li-ion anode materials

    NASA Astrophysics Data System (ADS)

    Wi, Sungun; Woo, Hyungsub; Lee, Sangheon; Kang, Joonhyeon; Kim, Jaewon; An, Subin; Kim, Chohui; Nam, Seunghoon; Kim, Chunjoong; Park, Byungwoo

    2015-05-01

    The reduced graphene oxide (RGO)/carbon double-coated 3-D porous ZnO aggregates (RGO/C/ZnO) have been successfully synthesized as anode materials for Li-ion batteries with excellent cyclability and rate capability. The mesoporous ZnO aggregates prepared by a simple solvothermal method are sequentially modified through distinct carbon-based double coating. These novel architectures take unique advantages of mesopores acting as space to accommodate volume expansion during cycling, while the conformal carbon layer on each nanoparticle buffering volume changes, and conductive RGO sheets connect the aggregates to each other. Consequently, the RGO/C/ZnO exhibits superior electrochemical performance, including remarkably prolonged cycle life and excellent rate capability. Such improved performance of RGO/C/ZnO may be attributed to synergistic effects of both the 3-D porous nanostructures and RGO/C double coating.

  5. Analysis of Fractional Flow for Transient Two-Phase Flow in Fractal Porous Medium

    NASA Astrophysics Data System (ADS)

    Lu, Ting; Duan, Yonggang; Fang, Quantang; Dai, Xiaolu; Wu, Jinsui

    2016-03-01

    Prediction of fractional flow in fractal porous medium is important for reservoir engineering and chemical engineering as well as hydrology. A physical conceptual fractional flow model of transient two-phase flow is developed in fractal porous medium based on the fractal characteristics of pore-size distribution and on the approximation that porous medium consist of a bundle of tortuous capillaries. The analytical expression for fractional flow for wetting phase is presented, and the proposed expression is the function of structural parameters (such as tortuosity fractal dimension, pore fractal dimension, maximum and minimum diameters of capillaries) and fluid properties (such as contact angle, viscosity and interfacial tension) in fractal porous medium. The sensitive parameters that influence fractional flow and its derivative are formulated, and their impacts on fractional flow are discussed.

  6. Study of flow at the interface of a porous medium using particle image velocimetry

    NASA Astrophysics Data System (ADS)

    Shams Saryazdi, Masoud

    This thesis reports the results of an experimental study of the flow at the interface of a fibrous porous medium and a freely flowing fluid. The model for the porous medium was a square array of parallel rods, and arrays with three different solid volume fractions were tested; namely 2.5%, 5.2%, and 10%. The flow adjacent to the porous medium was a shear flow perpendicular to the interface. It was created by generating circular Couette flow in a narrow channel outside the porous medium. Comprehensive velocity measurements were made inside and outside the various porous media using a PIV system that was developed for the experiment. An adverse pressure gradient in the streamwise direction was found to exist between the rods for the media with solid volume fractions of 5.2% and 10%. However no such pressure gradient was found for the 2.5% medium. The fluid motion corresponding to the adverse pressure gradients inside the medium was circulatory. The slip coefficient proposed by Beavers and Joseph was found directly by measuring the local velocity near the boundary of the porous medium. The slip coefficient for the media tested was found to be approximately 3. Comparisons show that Brinkman's equation in its original form (with the same viscosity inside the porous medium mu* and outside mu) did not produce results that matched the measured velocity field. Furthermore, Brinkman's equation did not produce results that matched the experimental velocity fields using any value of the viscosity ratio, mu*/mu. The measurements show that the slip velocity is small, and that Brinkman's equation with mu*/mu ≈ 9 predicts slip velocities quite well. The shear penetration length decreases as the solid volume fraction increases, and for a porous medium with a solid volume fraction of around 10%, the penetration length is smaller than all length scales of the medium. Therefore, for the higher solid volume fractions tested, shear penetration is practically negligible. Penetration of

  7. Gas anti-solvent precipitation assisted salt leaching for generation of micro- and nano-porous wall in bio-polymeric 3D scaffolds.

    PubMed

    Flaibani, Marina; Elvassore, Nicola

    2012-08-01

    The mass transport through biocompatible and biodegradable polymeric 3D porous scaffolds may be depleted by non-porous impermeable internal walls. As consequence the concentration of metabolites and growth factors within the scaffold may be heterogeneous leading to different cell fate depending on spatial cell location, and in some cases it may compromise cell survival. In this work, we fabricated polymeric scaffolds with micro- and nano-scale porosity by developing a new technique that couples two conventional scaffold production methods: solvent casting-salt leaching and gas antisolvent precipitation. 10-15 w/w solutions of a hyaluronic benzyl esters (HYAFF11) and poly-(lactic acid) (PLA) were used to fill packed beds of 0.177-0.425 mm NaCl crystals. The polymer precipitation in micro and nano-porous structures between the salt crystals was induced by high-pressure gas, then its flushing extracted the residual solvent. The salt was removed by water-wash. Morphological analysis by scanning electron microscopy showed a uniform porosity (~70%) and a high interconnectivity between porous. The polymeric walls were porous themselves counting for 30% of the total porosity. This wall porosity did not lead to a remarkable change in compressive modulus, deformation, and rupture pressure. Scaffold biocompatibility was tested with murine muscle cell line C2C12 for 4 and 7 days. Viability analysis and histology showed that micro- and nano-porous scaffolds are biocompatible and suitable for 3D cell culture promoting cell adhesion on the polymeric wall and allowing their proliferation in layers. Micro- and nano-scale porosities enhance cell migration and growth in the inner part of the scaffold.

  8. Supported 3-D Pt nanostructures: the straightforward synthesis and enhanced electrochemical performance for methanol oxidation in an acidic medium

    NASA Astrophysics Data System (ADS)

    Li, Zesheng; Ji, Shan; Pollet, Bruno G.; Shen, Pei Kang

    2013-10-01

    Noble metal nanostructures with branched morphologies [i.e., 3-D Pt nanoflowers (NFs)] by tri-dimensionally integrating onto conductive carbon materials are proved to be an efficient and durable electrocatalysts for methanol oxidation. The well-supported 3-D Pt NFs are readily achieved by an efficient cobalt-induced/carbon-mediated galvanic reaction approach. Due to the favorable nanostructures (3-D Pt configuration allowing a facile mass transfer) and supporting effects (including framework stabilization, spatially separate feature, and improved charge transport effects), these 3-D Pt NFs manifest much higher electrocatalytic activity and stability toward methanol oxidation than that of the commercial Pt/C and Pt-based electrocatalysts.

  9. Hydromagnetic Flow and Heat Transfer over a Porous Oscillating Stretching Surface in a Viscoelastic Fluid with Porous Medium.

    PubMed

    Khan, Sami Ullah; Ali, Nasir; Abbas, Zaheer

    2015-01-01

    An analysis is carried out to study the heat transfer in unsteady two-dimensional boundary layer flow of a magnetohydrodynamics (MHD) second grade fluid over a porous oscillating stretching surface embedded in porous medium. The flow is induced due to infinite elastic sheet which is stretched periodically. With the help of dimensionless variables, the governing flow equations are reduced to a system of non-linear partial differential equations. This system has been solved numerically using the finite difference scheme, in which a coordinate transformation is used to transform the semi-infinite physical space to a bounded computational domain. The influence of the involved parameters on the flow, the temperature distribution, the skin-friction coefficient and the local Nusselt number is shown and discussed in detail. The study reveals that an oscillatory sheet embedded in a fluid-saturated porous medium generates oscillatory motion in the fluid. The amplitude and phase of oscillations depends on the rheology of the fluid as well as on the other parameters coming through imposed boundary conditions, inclusion of body force term and permeability of the porous medium. It is found that amplitude of flow velocity increases with increasing viscoelastic and mass suction/injection parameters. However, it decreases with increasing the strength of the applied magnetic field. Moreover, the temperature of fluid is a decreasing function of viscoelastic parameter, mass suction/injection parameter and Prandtl number.

  10. Hydromagnetic Flow and Heat Transfer over a Porous Oscillating Stretching Surface in a Viscoelastic Fluid with Porous Medium

    PubMed Central

    Khan, Sami Ullah; Ali, Nasir; Abbas, Zaheer

    2015-01-01

    An analysis is carried out to study the heat transfer in unsteady two-dimensional boundary layer flow of a magnetohydrodynamics (MHD) second grade fluid over a porous oscillating stretching surface embedded in porous medium. The flow is induced due to infinite elastic sheet which is stretched periodically. With the help of dimensionless variables, the governing flow equations are reduced to a system of non-linear partial differential equations. This system has been solved numerically using the finite difference scheme, in which a coordinate transformation is used to transform the semi-infinite physical space to a bounded computational domain. The influence of the involved parameters on the flow, the temperature distribution, the skin-friction coefficient and the local Nusselt number is shown and discussed in detail. The study reveals that an oscillatory sheet embedded in a fluid-saturated porous medium generates oscillatory motion in the fluid. The amplitude and phase of oscillations depends on the rheology of the fluid as well as on the other parameters coming through imposed boundary conditions, inclusion of body force term and permeability of the porous medium. It is found that amplitude of flow velocity increases with increasing viscoelastic and mass suction/injection parameters. However, it decreases with increasing the strength of the applied magnetic field. Moreover, the temperature of fluid is a decreasing function of viscoelastic parameter, mass suction/injection parameter and Prandtl number. PMID:26657931

  11. Hybrid Macro-Porous Titanium Ornamented by Degradable 3D Gel/nHA Micro-Scaffolds for Bone Tissue Regeneration

    PubMed Central

    Yin, Bo; Ma, Pei; Chen, Jun; Wang, Hai; Wu, Gui; Li, Bo; Li, Qiang; Huang, Zhifeng; Qiu, Guixing; Wu, Zhihong

    2016-01-01

    Porous titanium is a kind of promising material for bone substitution, while its bio-inert property results in demand of modifications to improve the osteointegration capacity. In this study, gelatin (Gel) and nano-hydroxyapatite (nHA) were used to construct 3D micro-scaffolds in the pores of porous titanium in the ratios of Gel:nHA = 1:0, Gel:nHA = 1:1, and Gel:nHA = 1:3, respectively. Cell attachment and proliferation, and gene and protein expression levels of osteogenic markers were evaluated in MC3T3-E1 cells, followed by bone regeneration assessment in a rabbit radius defect model. All hybrid scaffolds with different composition ratio were found to have significant promotional effects in cell adhesion, proliferation and differentiation, in which the group with Gel:nHA = 1:1 showed the best performance in vitro, as well as the most bone regeneration volume in vivo. This 3D micro-scaffolds modification may be an innovative method for porous titanium ornamentation and shows potential application values in clinic. PMID:27092492

  12. Synthesis of chitin nanofibers, MWCNTs and MnO2 nanoflakes 3D porous network flexible gel-film for high supercapacitive performance electrodes

    NASA Astrophysics Data System (ADS)

    Liu, Shengnan; Li, Dagang

    2017-03-01

    As the porous structure and conductivity result in improvement of electrochemical properties, the chitin nanofibers (ChNFs), multi-walled carbon nanotubes (MWCNTs) and MnO2 (manganese dioxide) nanoflakes 3D porous network core-shell structure gel-film was fabricated for flexible free-standing supercapacitor electrodes. The electrodes were characterized by various techniques and the results demonstrate that the as-synthesized ChNFs/MWCNTs/MnO2 gel-film electrodes exhibits excellent supercapacitive behaviours. The ChNFs/MWCNTs/MnO2 gel-film electrode shows a high capacitance of 295.2 mF/cm2 at 0.1 mA/cm2 in 1 M Na2SO4 aqueous electrolyte because of its 3D porous structure. Furthermore, the electrodes also showed surprising cycling stability for 5000 cycles with retention rate up to 157.14% at 1 mA/cm2. The data presents great promise in the application of high-performance flexible supercapacitors with the low cost, light-weight and excellent cycling ability.

  13. Binder-Free and Carbon-Free 3D Porous Air Electrode for Li-O2 Batteries with High Efficiency, High Capacity, and Long Life.

    PubMed

    Luo, Wen-Bin; Gao, Xuan-Wen; Shi, Dong-Qi; Chou, Shu-Lei; Wang, Jia-Zhao; Liu, Hua-Kun

    2016-06-01

    Pt-Gd alloy polycrystalline thin film is deposited on 3D nickel foam by pulsed laser deposition method serving as a whole binder/carbon-free air electrode, showing great catalytic activity enhancement as an efficient bifunctional catalyst for the oxygen reduction and evolution reactions in lithium oxygen batteries. The porous structure can facilitate rapid O2 and electrolyte diffusion, as well as forming a continuous conductive network throughout the whole energy conversion process. It shows a favorable cycle performance in the full discharge/charge model, owing to the high catalytic activity of the Pt-Gd alloy composite and 3D porous nickel foam structure. Specially, excellent cycling performance under capacity limited mode is also demonstrated, in which the terminal discharge voltage is higher than 2.5 V and the terminal charge voltage is lower than 3.7 V after 100 cycles at a current density of 0.1 mA cm(-2) . Therefore, this electrocatalyst is a promising bifunctional electrocatalyst for lithium oxygen batteries and this depositing high-efficient electrocatalyst on porous substrate with polycrystalline thin film by pulsed laser deposition is also a promising technique in the future lithium oxygen batteries research.

  14. Selenium encapsulated into 3D interconnected hierarchical porous carbon aerogels for lithium-selenium batteries with high rate performance and cycling stability

    NASA Astrophysics Data System (ADS)

    Jiang, Shaofeng; Zhang, Zhian; Lai, Yanqing; Qu, Yaohui; Wang, XiWen; Li, Jie

    2014-12-01

    Selenium encapsulated into 3D interconnected hierarchical porous carbon aerogels (HPCA) as a carbon/selenium composite material is prepared for lithium-selenium batteries. Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations show the hierarchical porous structures of the carbon aerogels and the homogeneous distribution of selenium in the composite. The performance of the HPCA/Se cathode is evaluated in lithium-selenium batteries using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. It is found that the HPCA/Se cathode shows high rate performance, coulombic efficiency and cycling stability. The HPCA/Se cathode has a highest coulombic efficiency which is kept above 98% after 50th cycle in ionic liquid N-methyl-(n-butyl) pyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) modified electrolyte and retains 309 mAh g-1 after 100 discharge/charge cycles at a high rate of 0.5 C (337.5 mAh g-1) in LiNO3 modified electrolyte, respectively. Even at the current density of 5 C (3375 mAh g-1), it can still maintain at a reversible capacity of 301 mAh g-1. The excellent electrochemical properties benefit from the high electron conductivity and 3D interconnected hierarchical porous structures of the carbon aerogels, which contribute to disperse selenium and absorb polyselenides, and suppress the formation of residual Li2Se layer.

  15. Methyl alcohol used as penetrant inspection medium for porous materials

    NASA Technical Reports Server (NTRS)

    Hendron, J. A.

    1971-01-01

    Porous material thoroughly wetted with alcohol shows persistent wet line or area at locations of cracks or porosity. Inspection is qualitative and repeatable, but is used quantitatively with select samples to grade density variations in graphite blocks. Photography is employed to achieve permanent record of results.

  16. Effect of Layer Thickness and Printing Orientation on Mechanical Properties and Dimensional Accuracy of 3D Printed Porous Samples for Bone Tissue Engineering

    PubMed Central

    Farzadi, Arghavan; Solati-Hashjin, Mehran; Asadi-Eydivand, Mitra; Abu Osman, Noor Azuan

    2014-01-01

    Powder-based inkjet 3D printing method is one of the most attractive solid free form techniques. It involves a sequential layering process through which 3D porous scaffolds can be directly produced from computer-generated models. 3D printed products' quality are controlled by the optimal build parameters. In this study, Calcium Sulfate based powders were used for porous scaffolds fabrication. The printed scaffolds of 0.8 mm pore size, with different layer thickness and printing orientation, were subjected to the depowdering step. The effects of four layer thicknesses and printing orientations, (parallel to X, Y and Z), on the physical and mechanical properties of printed scaffolds were investigated. It was observed that the compressive strength, toughness and Young's modulus of samples with 0.1125 and 0.125 mm layer thickness were more than others. Furthermore, the results of SEM and μCT analyses showed that samples with 0.1125 mm layer thickness printed in X direction have more dimensional accuracy and significantly close to CAD software based designs with predefined pore size, porosity and pore interconnectivity. PMID:25233468

  17. Construction of a 3D porous network of copper film via a template-free deposition method with superior mechanical and electrical properties for micro-energy devices

    NASA Astrophysics Data System (ADS)

    Peng, Yuncheng; Wang, Yao; Deng, Yuan

    2016-08-01

    With the ever increasing level of performance of energy conversion micro-devices, such as thin-film solar cells and thermoelectric micro-generators or coolers, their reliability and stability still remain a challenge. The high electrical and mechanical stability of an electrode is two of the critical factors that affect the long-term life of devices. Here we show that these factors can be achieved by constructing a 3D porous network of nanostructures in copper film using facile magnetron sputtering technology without any templates. The constructed 3D porous network of nanostructures in Cu film provides not only the advantages of light weight, prominently high conductivity, and large elastic deformation, but also the ability to absorb stress, preventing crack propagation, which is crucial for electrodes to maintain stable electrical and mechanical properties under working conditions. The nanopores inside the 3D network are capable of unrestrained deformation under applied stress resulting in strong elastic recovery. This work puts forward a feasible solution for manufacturing electrodes with excellent electrical and mechanical properties for micro-energy devices.

  18. Effect of layer thickness and printing orientation on mechanical properties and dimensional accuracy of 3D printed porous samples for bone tissue engineering.

    PubMed

    Farzadi, Arghavan; Solati-Hashjin, Mehran; Asadi-Eydivand, Mitra; Abu Osman, Noor Azuan

    2014-01-01

    Powder-based inkjet 3D printing method is one of the most attractive solid free form techniques. It involves a sequential layering process through which 3D porous scaffolds can be directly produced from computer-generated models. 3D printed products' quality are controlled by the optimal build parameters. In this study, Calcium Sulfate based powders were used for porous scaffolds fabrication. The printed scaffolds of 0.8 mm pore size, with different layer thickness and printing orientation, were subjected to the depowdering step. The effects of four layer thicknesses and printing orientations, (parallel to X, Y and Z), on the physical and mechanical properties of printed scaffolds were investigated. It was observed that the compressive strength, toughness and Young's modulus of samples with 0.1125 and 0.125 mm layer thickness were more than others. Furthermore, the results of SEM and μCT analyses showed that samples with 0.1125 mm layer thickness printed in X direction have more dimensional accuracy and significantly close to CAD software based designs with predefined pore size, porosity and pore interconnectivity.

  19. Analysis of shape of porous cooled medium for an imposed surface heat flux and temperature

    NASA Technical Reports Server (NTRS)

    Siegel, R.

    1973-01-01

    The surface of a porous cooled medium is to be maintained at a specified design temperature while being subjected to uniform heating by an external source. An analytical method is given for determining the shape of the medium surface that will satisfy these boundary conditions. The analysis accounts for temperature dependent variations of fluid density and viscosity and for temperature dependent matrix thermal conductivity. The energy equation is combined with Darcy's law in such a way that a potential can be defined that satisfies Laplace's equation. All of the heat-transfer and flow quantities are expressed in terms of this potential. The determination of the shape of the porous cooled region is thereby reduced to a free-boundary problem such as in inviscid free jet theory. Two illustrative examples are carried out: a porous leading edge with coolant supplied through a slot and a porous cooled duct with a rectangular outer boundary.

  20. Laser beam melting 3D printing of Ti6Al4V based porous structured dental implants: fabrication, biocompatibility analysis and photoelastic study

    PubMed Central

    Yang, Fei; Chen, Chen; Zhou, QianRong; Gong, YiMing; Li, RuiXue; Li, ChiChi; Klämpfl, Florian; Freund, Sebastian; Wu, XingWen; Sun, Yang; Li, Xiang; Schmidt, Michael; Ma, Duan; Yu, YouCheng

    2017-01-01

    Fabricating Ti alloy based dental implants with defined porous scaffold structure is a promising strategy for improving the osteoinduction of implants. In this study, we use Laser Beam Melting (LBM) 3D printing technique to fabricate porous Ti6Al4V dental implant prototypes with three controlled pore sizes (200, 350 and 500 μm). The mechanical stress distribution in the surrounding bone tissue is characterized by photoelastography and associated finite element simulation. For in-vitro studies, experiments on implants’ biocompatibility and osteogenic capability are conducted to evaluate the cellular response correlated to the porous structure. As the preliminary results, porous structured implants show a lower stress-shielding to the surrounding bone at the implant neck and a more densed distribution at the bottom site compared to the reference implant. From the cell proliferation tests and the immunofluorescence images, 350 and 500 μm pore sized implants demonstrate a better biocompatibility in terms of cell growth, migration and adhesion. Osteogenic genes expression of the 350 μm group is significantly increased alone with the ALP activity test. All these suggest that a pore size of 350 μm provides an optimal provides an optimal potential for improving the mechanical shielding to the surrounding bones and osteoinduction of the implant itself. PMID:28350007

  1. Laser beam melting 3D printing of Ti6Al4V based porous structured dental implants: fabrication, biocompatibility analysis and photoelastic study.

    PubMed

    Yang, Fei; Chen, Chen; Zhou, QianRong; Gong, YiMing; Li, RuiXue; Li, ChiChi; Klämpfl, Florian; Freund, Sebastian; Wu, XingWen; Sun, Yang; Li, Xiang; Schmidt, Michael; Ma, Duan; Yu, YouCheng

    2017-03-28

    Fabricating Ti alloy based dental implants with defined porous scaffold structure is a promising strategy for improving the osteoinduction of implants. In this study, we use Laser Beam Melting (LBM) 3D printing technique to fabricate porous Ti6Al4V dental implant prototypes with three controlled pore sizes (200, 350 and 500 μm). The mechanical stress distribution in the surrounding bone tissue is characterized by photoelastography and associated finite element simulation. For in-vitro studies, experiments on implants' biocompatibility and osteogenic capability are conducted to evaluate the cellular response correlated to the porous structure. As the preliminary results, porous structured implants show a lower stress-shielding to the surrounding bone at the implant neck and a more densed distribution at the bottom site compared to the reference implant. From the cell proliferation tests and the immunofluorescence images, 350 and 500 μm pore sized implants demonstrate a better biocompatibility in terms of cell growth, migration and adhesion. Osteogenic genes expression of the 350 μm group is significantly increased alone with the ALP activity test. All these suggest that a pore size of 350 μm provides an optimal provides an optimal potential for improving the mechanical shielding to the surrounding bones and osteoinduction of the implant itself.

  2. Fabrication of 3D honeycomb-like porous polyurethane-functionalized reduced graphene oxide for detection of dopamine.

    PubMed

    Vilian, A T Ezhil; An, Suyeong; Choe, Sang Rak; Kwak, Cheol Hwan; Huh, Yun Suk; Lee, Jonghwi; Han, Young-Kyu

    2016-12-15

    A three dimensional reduced graphene oxide/polyurethane (RGO-PU) porous material with connected pores was prepared by physical adsorption of RGO onto the surface of porous PU. The porous PU was prepared by directional melt crystallization of a solvent, which produced high pores with controlled orientation. The prepared RGO-PU was characterized by scanning electron microscopy, spectroscopy and electro-chemical methods. The RGO-PU porous material revealed better electrochemical performance, which might be attributed to the robust structure, superior conductivity, large surface area, and good flexibility. Differential pulse voltammetry (DPV) analysis of DA using the RGO-PU exhibited a linear response range over a wide DA concentration of 100-1150pM, with the detection limit of 1pM. This sensor exhibited outstanding anti-interference ability towards co-existing molecules with good stability, sensitivity, and reproducibility. Furthermore, the fabricated sensor was successfully applied for the quantitative analysis of DA in human serum and urine samples with acceptable recovery, which indicates its feasibility for practical application.

  3. Osteogenic potential of human adipose-tissue-derived mesenchymal stromal cells cultured on 3D-printed porous structured titanium.

    PubMed

    Lewallen, Eric A; Jones, Dakota L; Dudakovic, Amel; Thaler, Roman; Paradise, Christopher R; Kremers, Hilal M; Abdel, Matthew P; Kakar, Sanjeev; Dietz, Allan B; Cohen, Robert C; Lewallen, David G; van Wijnen, Andre J

    2016-05-01

    Integration of porous metal prosthetics, which restore form and function of irreversibly damaged joints, into remaining healthy bone is critical for implant success. We investigated the biological properties of adipose-tissue-derived mesenchymal stromal/stem cells (AMSCs) and addressed their potential to alter the in vitro microenvironment of implants. We employed human AMSCs as a practical source for musculoskeletal applications because these cells can be obtained in large quantities, are multipotent, and have trophic paracrine functions. AMSCs were cultured on surgical-grade porous titanium disks as a model for orthopedic implants. We monitored cell/substrate attachment, cell proliferation, multipotency, and differentiation phenotypes of AMSCs upon osteogenic induction. High-resolution scanning electron microscopy and histology revealed that AMSCs adhere to the porous metallic surface. Compared to standard tissue culture plastic, AMSCs grown in the porous titanium microenvironment showed differences in temporal expression for genes involved in cell cycle progression (CCNB2, HIST2H4), extracellular matrix production (COL1A1, COL3A1), mesenchymal lineage identity (ACTA2, CD248, CD44), osteoblastic transcription factors (DLX3, DLX5, ID3), and epigenetic regulators (EZH1, EZH2). We conclude that metal orthopedic implants can be effectively seeded with clinical-grade stem/stromal cells to create a pre-conditioned implant.

  4. Simultaneous heat and mass transfer in a porous medium

    NASA Astrophysics Data System (ADS)

    Siang, H.

    1981-11-01

    Based upon the principle of irreversible thermodynamics, the macroscopic conservation laws of mass, momentum and energy, and equilibrium sorption of the porous concrete system, a set of basic equations for simultaneous mass and heat transfer is developed. An implicit finite difference technique is employed to solve this set of nonlinear partial differential equations. Numerical examples, using the theory developed, are illustrated to deepen the general understanding of the drying, thermal characteristics and related phenomena of hydrated concrete. The developed theoretical model is made nondimensional and an order of magnitude analysis is performed to elucidate the transport phenomenum of heat and mass occurring in a concrete body. In addition to diffusion, both the capillary and evaporation-condensation mechanisms, which are strongly affected by the topology of the porous concrete system, are important in the heat and mass transfer processes.

  5. Non-stationary heat conduction of a porous medium

    NASA Astrophysics Data System (ADS)

    Velinov, T.; Gusev, V.; Bransalov, K.

    1992-01-01

    The thermal diffusion process is examined for a porous sample with idealized arrangement and form of the pores, when its surface is illuminated by a modulated light. A formula for the frequency dependence of the average surface temperature is derived. It is shown that it depends on the porosity, the form of the pores, and the ratio between a characteristic pore size and the thermal wavelength. In the limiting cases of low frequency of modulation and low porosity the results agree well with those quoted in the literature. The frequency dependence of the surface temperature of a microporous rubber sample, glass filtering crucibles, and leather samples have been measured by a PA cell and compared with the analytical results. The influence of various processes on the heat diffusion in porous media is discussed.

  6. Instabilities of a free bilayer flowing on an inclined porous medium.

    PubMed

    Praveen Kumar, A Ananth; Usha, R; Banerjee, Tamal; Bandyopadhyay, Dipankar

    2013-12-01

    The instabilities of a free bilayer flowing on an inclined Darcy-Brinkman porous layer have been explored. The bilayer is composed of a pair of immiscible liquid films with a deformable liquid-liquid interface and a liquid-air free surface. An Orr-Sommerfeld analysis of the governing equations and boundary conditions uncovers that this configuration can be unstable by a pair of long-wave interfacial modes at the free surface and at the interface together with a couple of finite wave-number shear modes originating from the inertial influences at the liquid layers. In particular, one of the shear modes originates beyond a threshold flow rate owing to the slippage at the porous-liquid interface and is found to be the dominant one even when the porous medium is moderately thin, porous, and permeable. The strength of the porous media mediated mode (a) grows with increase in porosity, (b) grows and then remains invariant with increase in thickness, and (c) initially grows and then decays with increase in the permeability of the porous layer. Further, the presence of a lower layer with smaller viscosity and a thicker upper layer is found to facilitate the growth of this newly identified porous media mode. Importantly, beyond a threshold upper to lower thickness and viscosity ratios and the angle of inclination the porous media mode dominates over all the other interfacial or shear modes, highlighting its importance in the bilayer flows down an inclined porous medium. The study showcases the importance of a porous layer in destabilizing a free bilayer flow down an inclined plane, which can be of importance to improve mixing, emulsification, and heat and mass transfer characteristics in the microscale devices.

  7. A comparison of measured and modeled velocity fields for a laminar flow in a porous medium

    NASA Astrophysics Data System (ADS)

    Wood, B. D.; Apte, S. V.; Liburdy, J. A.; Ziazi, R. M.; He, X.; Finn, J. R.; Patil, V. A.

    2015-11-01

    Obtaining highly-resolved velocity data from experimental measurements in porous media is a significant challenge. The goal of this work is to compare the velocity fields measured in a randomly-packed porous medium obtained from particle image velocimetry (PIV) with corresponding fields predicted from direct numerical simulation (DNS). Experimentally, the porous medium was comprised of 15 mm diameter spherical beads made of optical glass placed in a glass flow cell to create the packed bed. A solution of ammonium thiocyanate was refractive-index matched to the glass creating a medium that could be illuminated with a laser sheet without distortion. The bead center locations were quantified using the imaging system so that the geometry of the porous medium was known very accurately. Two-dimensional PIV data were collected and processed to provide high-resolution velocity fields at a single plane within the porous medium. A Cartesian-grid-based fictitious domain approach was adopted for the direct numerical simulation of flow through the same geometry as the experimental measurements and without any adjustable parameters. The uncertainties associated with characterization of the pore geometry, PIV measurements, and DNS predictions were all systematically quantified. Although uncertainties in bead position measurements led to minor discrepancies in the comparison of the velocity fields, the axial and normal velocity deviations exhibited normalized root mean squared deviations (NRMSD) of only 11.32% and 4.74%, respectively. The high fidelity of both the experimental and numerical methods have significant implications for understanding and even for engineering the micro-macro relationship in porous materials. The ability to measure and model sub-pore-scale flow features also has relevance to the development of upscaled models for flow in porous media, where physically reasonable closure models must be developed at the sub-pore scale. These results provide valuable data

  8. Formation of bubbly horizon in liquid-saturated porous medium by surface temperature oscillation.

    PubMed

    Goldobin, Denis S; Krauzin, Pavel V

    2015-12-01

    We study nonisothermal diffusion transport of a weakly soluble substance in a liquid-saturated porous medium in contact with a reservoir of this substance. The surface temperature of the porous medium half-space oscillates in time, which results in a decaying solubility wave propagating deep into the porous medium. In this system, zones of saturated solution and nondissolved phase coexist with ones of undersaturated solution. The effect is first considered for the case of annual oscillation of the surface temperature of water-saturated ground in contact with the atmosphere. We reveal the phenomenon of formation of a near-surface bubbly horizon due to temperature oscillation. An analytical theory of the phenomenon is developed. Further, the treatment is extended to the case of higher frequency oscillations and the case of weakly soluble solids and liquids.

  9. MHD flow through a porous medium adjacent to a stretching sheet: Numerical and an approximate solution

    NASA Astrophysics Data System (ADS)

    Chauhan, D. S.; Agrawal, R.

    2011-05-01

    A viscous incompressible electrically conducting fluid flow through a porous medium over a stretching sheet is considered in the presence of a magnetic field. Such flow problems have relevance in the process of a polymer sheet extrusion from a dye, and the numerical and approximate solutions of these problems are of great interest as these solutions serve practical purposes. By using the technique of stretching variables of the flow concern in porous medium and minimizing the residual of the resulting governing differential equations by the least squares method, we obtained an approximate solution for this problem of flow through porous medium near a stretching sheet. The results are also compared to a numerical solution determined by using the shooting method along with the Runge-Kutta method. The effects of various pertinent parameters on the velocity distribution and the residual function are investigated. The results are depicted graphically and discussed.

  10. Numerical modeling of ground water flow and contaminant transport in a saturated porous medium

    NASA Astrophysics Data System (ADS)

    Valipour, Mohammad S.; Sadeghi, Masoomeh; Mahmoudi, Amir H.; Shahi, Mina; Gandaghi, Hadi

    2012-05-01

    In this paper, numerical modeling and experimental testing of the distribution of pollutants along the water flow in a porous medium is discussed. Governing equations including overall continuity, momentum and species continuity equations are derived for porous medium. The governing equations have been solved numerical using the Finite Volume Method based on collocated grids. The SIMPLE algorithm has been adopted for the pressure _ velocity linked equations. In order to validate the numerical results, experimental data from laboratory apparatus are applied and there is a good agreement among numerical results and experimental test. Finally, the main affecting parameters on the distribution and transport of pollutants porous medium were investigated. Results indicate that, the domain of pollution rises with increasing dispersion coefficient and the dispersion phenomenon overcomes on pollutant transfer. Reduction of porosity has decreased the pollutant transfer and increased velocity has result in the increasing pollutant transport phenomenon but has reduced the domain of the pollution.

  11. Hydrothermal synthesis of 3D hollow porous Fe3O4 microspheres towards catalytic removal of organic pollutants

    PubMed Central

    2014-01-01

    Three-dimensional hollow porous superparamagnetic Fe3O4 microspheres were synthesized via a facile hydrothermal process. A series of characterizations done with X-ray diffraction, Brunauer-Emmett-Teller method, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy indicated that the production of Fe3O4 microspheres possessed good monodispersity, uniform size distribution, hollow and porous structural characters, and strong superparamagnetic behavior. The obtained Fe3O4 microspheres have a diameter of ca. 300 nm, which is composed of many interconnected nanoparticles with a size of ca. 20 nm. The saturation magnetization is 80.6 emu·g-1. The as-prepared products had promising applications as novel catalysts to remove organic pollutants (methylene blue) from wastewater in the presence of H2O2 and ultrasound irradiation. PMID:25520596

  12. Morphologies and wetting properties of copper film with 3D porous micro-nano hierarchical structure prepared by electrochemical deposition

    NASA Astrophysics Data System (ADS)

    Wang, Hongbin; Wang, Ning; Hang, Tao; Li, Ming

    2016-05-01

    Three-dimensional porous micro-nano hierarchical structure Cu films were prepared by electrochemical deposition with the Hydrogen bubble dynamic template. The morphologies of the deposited films characterized by Scanning Electronic Microscopy (SEM) exhibit a porous micro-nano hierarchical structure, which consists of three levels in different size scales, namely the honeycomb-like microstructure, the dendritic substructure and the nano particles. Besides, the factors which influenced the microscopic morphology were studied, including the deposition time and the additive Ethylene diamine. By measuring the water contact angle, the porous copper films were found to be super-hydrophobic. The maximum of the contact angles could reach as high as 162.1°. An empirical correlation between morphologies and wetting properties was revealed for the first time. The pore diameter increased simultaneously with the deposition time while the contact angle decreased. The mechanism was illustrated by two classical models. Such super-hydrophobic three-dimensional hierarchical micro-nano structure is expected to have practical application in industry.

  13. Numerical simulations of impacts involving porous bodies. I. Implementing sub-resolution porosity in a 3D SPH hydrocode

    NASA Astrophysics Data System (ADS)

    Jutzi, Martin; Benz, Willy; Michel, Patrick

    2008-11-01

    In this paper, we extend our Smooth Particle Hydrodynamics (SPH) impact code to include the effect of porosity at a sub-resolution scale by adapting the so-called P-alpha model. Many small bodies in the different populations of asteroids and comets are believed to contain a high degree of porosity and the determination of both their collisional evolution and the outcome of their disruption requires that the effect of porosity is taken into account in the computation of those processes. Here, we present our model and show how porosity interfaces with the elastic-perfectly plastic material description and the brittle fracture model generally used to simulate the fragmentation of non-porous rocky bodies. We investigate various compaction models and discuss their suitability to simulate the compaction of (highly) porous material. Then, we perform simple test cases where we compare results of the simulations to the theoretical solutions. We also present a Deep Impact-like simulation to show the effect of porosity on the outcome of an impact. Detailed validation tests will be presented in a next paper by comparison with high-velocity laboratory experiments on porous materials [Jutzi et al., in preparation]. Once validated at small scales, our new impact code can then be used at larger scales to study impacts and collisions involving brittle solids including porosity, such as the parent bodies of C-type asteroid families or cometary materials, both in the strength- and in the gravity-dominated regime.

  14. Self-Assembled 3D ZnO Porous Structures with Exposed Reactive {0001} Facets and Their Enhanced Gas Sensitivity

    PubMed Central

    Chang, Jin; Ahmad, Muhammad Z.; Wlodarski, Wojtek; Waclawik, Eric R.

    2013-01-01

    Complex three-dimensional structures comprised of porous ZnO plates were synthesized in a controlled fashion by hydrothermal methods. Through subtle changes to reaction conditions, the ZnO structures could be self-assembled from 20 nm thick nanosheets into grass-like and flower-like structures which led to the exposure of high proportions of ZnO {0001} crystal facets for both these materials. The measured surface area of the flower-like and the grass, or platelet-like ZnO samples were 72.8 and 52.4 m2·g−1, respectively. Gas sensing results demonstrated that the porous, flower-like ZnO structures exhibited enhanced sensing performance towards NO2 gas compared with either grass-like ZnO or commercially sourced ZnO nanoparticle samples. The porous, flower-like ZnO structures provided a high surface area which enhanced the ZnO gas sensor response. X-ray photoelectron spectroscopy characterization revealed that flower-like ZnO samples possessed a higher percentage of oxygen vacancies than the other ZnO sample-types, which also contributed to their excellent gas sensing performance. PMID:23820747

  15. Self-assembled 3D ZnO porous structures with exposed reactive {0001} facets and their enhanced gas sensitivity.

    PubMed

    Chang, Jin; Ahmad, Muhammad Z; Wlodarski, Wojtek; Waclawik, Eric R

    2013-07-02

    Complex three-dimensional structures comprised of porous ZnO plates were synthesized in a controlled fashion by hydrothermal methods. Through subtle changes to reaction conditions, the ZnO structures could be self-assembled from 20 nm thick nanosheets into grass-like and flower-like structures which led to the exposure of high proportions of ZnO {0001} crystal facets for both these materials. The measured surface area of the flower-like and the grass, or platelet-like ZnO samples were 72.8 and 52.4 m2∙g-1, respectively. Gas sensing results demonstrated that the porous, flower-like ZnO structures exhibited enhanced sensing performance towards NO2 gas compared with either grass-like ZnO or commercially sourced ZnO nanoparticle samples. The porous, flower-like ZnO structures provided a high surface area which enhanced the ZnO gas sensor response. X-ray photoelectron spectroscopy characterization revealed that flower-like ZnO samples possessed a higher percentage of oxygen vacancies than the other ZnO sample-types, which also contributed to their excellent gas sensing performance.

  16. Numerical investigation of oscillatory multiphase flow in porous medium with chemically active skeleton

    NASA Astrophysics Data System (ADS)

    Konyukhov, A. V.; Zavialov, I. N.

    2016-11-01

    Self-oscillating mode of reaction front propagation in multiphase flow in the porous medium with chemically active skeleton is investigated numerically. The considered flow represents an immiscible displacement process, such that the displacing fluid and the skeleton of the porous medium have chemically active components which react with production of gaseous phase. The calculations have demonstrated strong influence of the reaction kinetics on stability of the reactive flow. The presence of a time delay between the change of concentration of the reactants and the change of the reaction rate is shown to stimulate transition of the reaction front propagation to the oscillatory mode.

  17. 3-D heterogeneous field data versus 2-D simulations. How can it be accomplished in a sedimentary porous formation?

    NASA Astrophysics Data System (ADS)

    Darvini, G.; Salandin, P.

    2009-12-01

    To analyze the impact of the hydraulic conductivity K spatial variability in a real field case (as an example to delimitate a well catchment), numerical simulations can be reasonably developed in a two-dimensional vertical average context. Nevertheless the plume evolution is a consequence of a more complex three-dimensional heterogeneous structure whose vertical variability dominates the dispersion phenomena at local scale. In larger domains, the effect of the vertical heterogeneity combines itself with that one due to the horizontal variability of K, and only when the plume has travelled a large number of (horizontal) integral scales, its evolution can be analyzed in a regional context, under the hypothesis that the transmissivity spatial distribution prevails. Until this limit is reached, the vertical and horizontal variability of K are combined to give a fully 3-D dispersion process. In all these situations, to successfully accomplish the 3-D heterogeneous structure of the aquifer in 2-D simulations, more than the planimetric depth-averaged variability of K must be accounted for. To define the uncertainty related to the use of different planimetric schematizations of the real hydraulic conductivity spatial distribution, we present here the results of some numerical experiments that compare the 3-D plume evolution with 2-D simulations developed by tacking into account different hydraulic conductivity distribution schematization, by considering a hierarchical architecture of media also. This description of a sedimentary formation combined with the finite size of the plume requires theoretical and numerical tools able to take into account the flow field inhomogeneity and the ergodicity lack that characterize the transport phenomena. Following this way it will be possible to quantify / reduce the uncertainty related to a 2-D schematization in a large number of real cases where the domain spans between the local and the regional scale and whose dimension may lead to

  18. Enhanced photovoltaic properties of Nb₂O₅-coated TiO₂ 3D ordered porous electrodes in dye-sensitized solar cells.

    PubMed

    Kim, Hye-Na; Moon, Jun Hyuk

    2012-11-01

    This paper describes the use of Nb₂O₅-coated TiO₂ 3D ordered porous electrodes in dye-sensitized solar cells. We employed bilayer inverse opal structures as a backbone of 3D porous structures, and the number of Nb₂O₅ coatings was controlled, determining the concentration of Nb₂O₅ coating. XPS measurements confirmed the formation of Nb₂O₅. The uniformity of the Nb₂O₅ coating was characterized by elemental mapping using SEM and TEM measurements. Photovoltaic measurement on dye-sensitized solar cells (DSSCs) that incorporated Nb₂O₅/TiO₂ inverse opal electrodes yielded a maximum efficiency of 7.23% for a 3.3 wt % Nb₂O₅ coating on a TiO₂ IO structure. The Nb₂O₅ significantly increased the short-circuit current density (J(SC)). Electrochemical impedance spectroscopy was used to measure the J(SC), revealing an enhanced electron injection upon deposition of the Nb₂O₅ coating.

  19. Synergistic Behavior of Tubes, Junctions, and Sheets Imparts Mechano-Mutable Functionality in 3D Porous Boron Nitride Nanostructures.

    PubMed

    Sakhavand, Navid; Shahsavari, Rouzbeh

    2014-10-02

    One-dimensional (1D) boron nitride nanotube (BNNT) and 2D hexagonal BN (h-BN) are attractive for demonstrating fundamental physics and promising applications in nano-/microscale devices. However, there is a high anisotropy associated with these BN allotropes as their excellent properties are either along the tube axis or in-plane directions, posing an obstacle in their widespread use in technological and industrial applications. Herein, we report a series of 3D BN prototypes, namely, pillared boron nitride (PBN), by fusing single-wall BNNT and monolayer h-BN aimed at filling this gap. We use density functional theory and molecular dynamics simulations to probe the diverse mechano-mutable properties of PBN prototypes. Our results demonstrate that the synergistic effect of the tubes, junctions, and sheets imparts cooperative deformation mechanisms, which overcome the intrinsic limitations of the PBN constituents and provide a number of superior characteristics including 3D balance of strength and toughness, emergence of negative Poisson's ratio, and elimination of strain softening along the armchair orientation. These features, combined with the ultrahigh surface area and lightweight structure, render PBN as a 3D multifunctional template for applications in graphene-based nanoelectronics, optoelectronics, gas storage, and functional composites with fascinating in-plane and out-of-plane tailorable properties.

  20. Synergistic Behavior of Tubes, Junctions, and Sheets Imparts Mechano-Mutable Functionality in 3D Porous Boron Nitride Nanostructures

    PubMed Central

    2015-01-01

    One-dimensional (1D) boron nitride nanotube (BNNT) and 2D hexagonal BN (h-BN) are attractive for demonstrating fundamental physics and promising applications in nano-/microscale devices. However, there is a high anisotropy associated with these BN allotropes as their excellent properties are either along the tube axis or in-plane directions, posing an obstacle in their widespread use in technological and industrial applications. Herein, we report a series of 3D BN prototypes, namely, pillared boron nitride (PBN), by fusing single-wall BNNT and monolayer h-BN aimed at filling this gap. We use density functional theory and molecular dynamics simulations to probe the diverse mechano-mutable properties of PBN prototypes. Our results demonstrate that the synergistic effect of the tubes, junctions, and sheets imparts cooperative deformation mechanisms, which overcome the intrinsic limitations of the PBN constituents and provide a number of superior characteristics including 3D balance of strength and toughness, emergence of negative Poisson’s ratio, and elimination of strain softening along the armchair orientation. These features, combined with the ultrahigh surface area and lightweight structure, render PBN as a 3D multifunctional template for applications in graphene-based nanoelectronics, optoelectronics, gas storage, and functional composites with fascinating in-plane and out-of-plane tailorable properties. PMID:25289114

  1. Template method to controllable synthesis 3D porous NiCo2O4 with enhanced capacitance and stability for supercapacitors.

    PubMed

    Bai, Yang; Wang, Ranran; Lu, Xiaoyu; Sun, Jing; Gao, Lian

    2016-04-15

    We present a facile template method to fabricate NiCo2O4 (NCO) composites with 3D porous structure as electrodes for supercapacitors. SiO2 sol is used as the template to prevent the aggregation of NCO and construct the porous structure with high specific surface area. Meanwhile, the binary metal oxides not only inherit the merits of single nickel oxides or cobalt oxides, but also show superior properties to promote the capacitance. The uniform structure of NCO12 (SiO2/NCO=1:2) is obtained through controlling the mass ratio of SiO2 and NCO. Owing to the dual advantages of porous structure and binary system, NCO12 composites exhibit highly enhanced electrochemical performance compared with those of directly prepared NCO, NCO21 (SiO2/NCO=1:0.5) and NCO14 (SiO2/NCO=1:4). The specific capacitance of NCO12 composite is about 1389 Fg(-1) at 1 Ag(-1). At 4 Ag(-1), the capacitance is still as high as 1090 Fg(-1) together with capacitance retention of 80% over 2500 cycles. The capacitance and stability are higher than those of most previously reported pure NCO composites, which make it a very promising electrode material for energy storage.

  2. Modification of Surface Density of a Porous Medium

    NASA Technical Reports Server (NTRS)

    Stackpoole, Margaret M. (Inventor); Espinoza, Christian (Inventor)

    2016-01-01

    A method for increasing density of a region of a porous, phenolic bonded ("PPB") body adjacent to a selected surface to increase failure tensile strength of the adjacent region and/or to decrease surface recession at elevated temperatures. When the surface-densified PPB body is brought together with a substrate, having a higher failure tensile strength, to form a composite body with a PPB body/substrate interface, the location of tensile failure is moved to a location spaced apart from the interface, the failure tensile strength of the PPB body is increased, and surface recession of the material at elevated temperature is reduced. The method deposits and allows diffusion of a phenolic substance on the selected surface. The PPB body and the substrate may be heated and brought together to form the composite body. The phenolic substance is allowed to diffuse into the PPB body, to volatilize and to cure, to provide a processed body with an increased surface density.

  3. Growth of porous anodized alumina on the sputtered aluminum films with 2D-3D morphology for high specific surface area

    NASA Astrophysics Data System (ADS)

    Liao, M. W.; Chung, C. K.

    2014-08-01

    The porous anodic aluminum oxide (AAO) with high-aspect-ratio pore channels is widely used as a template for fabricating nanowires or other one-dimensional (1D) nanostructures. The high specific surface area of AAO can also be applied to the super capacitor and the supporting substrate for catalysis. The rough surface could be helpful to enhance specific surface area but it generally results in electrical field concentration even to ruin AAO. In this article, the aluminum (Al) films with the varied 2D-3D morphology on Si substrates were prepared using magnetron sputtering at a power of 50 W-185 W for 1 h at a working pressure of 2.5 × 10-1 Pa. Then, AAO was fabricated from the different Al films by means of one-step hybrid pulse anodizing (HPA) between the positive 40 V and the negative -2 V (1 s:1 s) for 3 min in 0.3 M oxalic acid at a room temperature. The microstructure and morphology of Al films were characterized by X-ray diffraction, scanning electron microscope and atomic force microscope, respectively. Some hillocks formed at the high target power could be attributed to the grain texture growth in the normal orientation of Al(1 1 1). The 3D porous AAO structure which is different from the conventional 2D planar one has been successfully demonstrated using HPA on the film with greatly rough hillock-surface formed at the highest power of 185 W. It offers a potential application of the new 3D AAO to high specific surface area devices.

  4. A technique for evaluating bone ingrowth into 3D printed, porous Ti6Al4V implants accurately using X-ray micro-computed tomography and histomorphometry.

    PubMed

    Palmquist, Anders; Shah, Furqan A; Emanuelsson, Lena; Omar, Omar; Suska, Felicia

    2017-03-01

    This paper investigates the application of X-ray micro-computed tomography (micro-CT) to accurately evaluate bone formation within 3D printed, porous Ti6Al4V implants manufactured using Electron Beam Melting (EBM), retrieved after six months of healing in sheep femur and tibia. All samples were scanned twice (i.e., before and after resin embedding), using fast, low-resolution scans (Skyscan 1172; Bruker micro-CT, Kontich, Belgium), and were analysed by 2D and 3D morphometry. The main questions posed were: (i) Can low resolution, fast scans provide morphometric data of bone formed inside (and around) metal implants with a complex, open-pore architecture?, (ii) Can micro-CT be used to accurately quantify both the bone area (BA) and bone-implant contact (BIC)?, (iii) What degree of error is introduced in the quantitative data by varying the threshold values?, and (iv) Does resin embedding influence the accuracy of the analysis? To validate the accuracy of micro-CT measurements, each data set was correlated with a corresponding centrally cut histological section. The results show that quantitative histomorphometry corresponds strongly with 3D measurements made by micro-CT, where a high correlation exists between the two techniques for bone area/volume measurements around and inside the porous network. On the contrary, the direct bone-implant contact is challenging to estimate accurately or reproducibly. Large errors may be introduced in micro-CT measurements when segmentation is performed without calibrating the data set against a corresponding histological section. Generally, the bone area measurement is strongly influenced by the lower threshold limit, while the upper threshold limit has little or no effect. Resin embedding does not compromise the accuracy of micro-CT measurements, although there is a change in the contrast distributions and optimisation of the threshold ranges is required.

  5. Direct growth of carbon nanofibers to generate a 3D porous platform on a metal contact to enable an oxygen reduction reaction.

    PubMed

    Pan, David; Ombaba, Matthew; Zhou, Zhi-You; Liu, Yang; Chen, Shaowei; Lu, Jennifer

    2012-12-21

    For carbon nanotube-based electronics to achieve their full performance potential, it is imperative to minimize the contact resistance between macroscale metal contacts and the carbon nanotube (CNT) nanoelectrodes. We have developed a three-dimensional electrode platform that consists of carbon nanofibers (CNFs) that are directly grown on a metal contact, such as copper (Cu). Carbon nanofiber morphology can be tailored by adjusting the annealing time of a thin electrochemically deposited nickel catalyst layer on copper. We demonstrate that increasing the annealing time increases the amount of copper infused into the nickel catalyst layer. This reduces the carbon deposition rate, and consequently a more well-defined CNF 3D architecture can be fabricated. This direct growth of CNFs on a Cu substrate yields an excellent electron transfer pathway, with contact resistance between CNFs and Cu being comparable to that of a Cu-Cu interface. Furthermore, the excellent bonding strength between CNFs and Cu can be maintained over prolonged periods of ultrasonication. The porous 3D platform affixed with intertwined CNFs allows facile surface functionalization. Using a simple solution soaking procedure, the CNF surface has been successfully functionalized with iron(II) phthalocyanine (FePc). FePc functionalized CNFs exhibit excellent oxygen reduction capability, equivalent to platinum-carbon electrodes. This result demonstrates the technological promise of this new 3D electrode platform that can be exploited in other applications that include sensing, battery, and supercapacitors.

  6. Facile synthesis of 3D porous thermally exfoliated g-C3N4 nanosheet with enhanced photocatalytic degradation of organic dye.

    PubMed

    Yuan, Xiaoya; Zhou, Chou; Jin, Yanrong; Jing, Qiuye; Yang, Yaling; Shen, Xu; Tang, Qi; Mu, Yuanhua; Du, An-Ke

    2016-04-15

    3D porous framework composed of exfoliated ultrathin nanosheets is a hot topic in the field of energy storage and conversion. A facile method to prepare 3D mesoporous C3N4 with few-layered nanosheets interconnected in large quantity via H2SO4 intercalation and subsequent thermal treatment was described herein. The obtained thermally-exfoliated C3N4 (TE-C3N4) was thoroughly characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), UV-Vis diffuse reflectance spectroscopy (DRS) and Brunauer-Emmett-Teller (BET) measurements. The detailed analysis indicated that TE-C3N4 possessed enlarged inter-layer space, enhanced UV-light adsorption and high specific surface area with 3D interconnected structure composed of ultrathin 2D nanosheets. Compared to bulk C3N4, TE-C3N4 showed an enhanced photocatalytic activity for photodegradation of Rhodamine B under UV-light irradiation and exhibited no significant loss of photocatalytic activity after 11 recycled runs. The pseudo-first reaction rate constant for TE-C3N4 was about four times higher than that for pure bulk-C3N4. The better photocatalytic performance could be attributed to more active catalytic sites, prolonged photo-excited carrier lifetime and shorted pathway of the carriers to the reaction sites.

  7. Control of optical transport parameters of 'porous medium – supercritical fluid' systems

    SciTech Connect

    Zimnyakov, D A; Ushakova, O V; Yuvchenko, S A; Bagratashvili, V N

    2015-11-30

    The possibility of controlling optical transport parameters (in particular, transport scattering coefficient) of porous systems based on polymer fibres, saturated with carbon dioxide in different phase states (gaseous, liquid and supercritical) has been experimentally studied. An increase in the pressure of the saturating medium leads to a rise of its refractive index and, correspondingly, the diffuse-transmission coefficient of the system due to the decrease in the transport scattering coefficient. It is shown that, in the case of subcritical saturating carbon dioxide, the small-angle diffuse transmission of probed porous layers at pressures close to the saturated vapour pressure is determined by the effect of capillary condensation in pores. The immersion effect in 'porous medium – supercritical fluid' systems, where the fluid pressure is used as a control parameter, is considered. The results of reconstructing the values of transport scattering coefficient of probed layers for different refractive indices of a saturating fluid are presented. (radiation scattering)

  8. Smoothed Particle Hydrodynamics Modeling of Gravity Currents on a Dry Porous Medium

    NASA Astrophysics Data System (ADS)

    Daly, E.; Grimaldi, S.; Bui, H.

    2014-12-01

    Gravity currents flowing over porous media occur in many environmental processes and industrial applications, such as irrigation, benthic boundary layers, and oil spills. The coupling of the flow over the porous surface and the infiltration of the fluid in the porous media is complex and difficult to model. Of particular interest is the prediction of the position of the runoff front and the depth of the infiltration front. We present here a model for the flow of a finite volume of a highly viscous Newtonian fluid over a dry, homogenous porous medium. The Navier-Stokes equations describing the runoff flow are coupled to the Volume Averaged Navier-Stokes equations for the infiltration flow. The numerical solution of these equations is challenging because of the presence of two free surfaces (runoff and infiltration waves), the lack of fixed boundary conditions at the runoff front, and the difficulties in defining appropriate conditions at the surface of the porous medium. The first two challenges were addressed by using Smoothed Particle Hydrodynamics, which is a Lagrangian, mesh-free particle method particularly suitable for modelling free surface flows. Two different approaches were used to model the flow conditions at the surface of the porous medium. The Two Domain Approach (TDA) assumes that runoff and infiltration flows occur in two separate homogenous domains; here, we assume the continuity of velocity and stresses at the interface of the two domains. The One Domain Approach (ODA) models runoff and infiltration flows as occurring through a medium whose hydraulic properties vary continuously in space. The transition from the hydraulic properties of the atmosphere and the porous medium occur in a layer near the surface of the porous medium. Expressions listed in literature were used to compute the thickness of this transition layer and the spatial variation of porosity and permeability within it. Our results showed that ODA led to slower velocities of the runoff

  9. Single-plane versus three-plane methods for relative range error evaluation of medium-range 3D imaging systems

    NASA Astrophysics Data System (ADS)

    MacKinnon, David K.; Cournoyer, Luc; Beraldin, J.-Angelo

    2015-05-01

    Within the context of the ASTM E57 working group WK12373, we compare the two methods that had been initially proposed for calculating the relative range error of medium-range (2 m to 150 m) optical non-contact 3D imaging systems: the first is based on a single plane (single-plane assembly) and the second on an assembly of three mutually non-orthogonal planes (three-plane assembly). Both methods are evaluated for their utility in generating a metric to quantify the relative range error of medium-range optical non-contact 3D imaging systems. We conclude that the three-plane assembly is comparable to the single-plane assembly with regard to quantification of relative range error while eliminating the requirement to isolate the edges of the target plate face.

  10. Regularity for the porous medium equation with variable exponent: The singular case

    NASA Astrophysics Data System (ADS)

    Henriques, Eurica

    We extend to the singular case the results of [E. Henriques, J.M. Urbano, Intrinsic scaling for PDEs with an exponential nonlinearity, Indiana Univ. Math. J. 55 (5) (2006) 1701-1721] concerning the regularity of weak solutions of the porous medium equation with variable exponent. The method of intrinsic scaling is used to show that local weak solutions are locally continuous.

  11. Fractal continuum model for tracer transport in a porous medium.

    PubMed

    Herrera-Hernández, E C; Coronado, M; Hernández-Coronado, H

    2013-12-01

    A model based on the fractal continuum approach is proposed to describe tracer transport in fractal porous media. The original approach has been extended to treat tracer transport and to include systems with radial and uniform flow, which are cases of interest in geoscience. The models involve advection due to the fluid motion in the fractal continuum and dispersion whose mathematical expression is taken from percolation theory. The resulting advective-dispersive equations are numerically solved for continuous and for pulse tracer injection. The tracer profile and the tracer breakthrough curve are evaluated and analyzed in terms of the fractal parameters. It has been found in this work that anomalous transport frequently appears, and a condition on the fractal parameter values to predict when sub- or superdiffusion might be expected has been obtained. The fingerprints of fractality on the tracer breakthrough curve in the explored parameter window consist of an early tracer breakthrough and long tail curves for the spherical and uniform flow cases, and symmetric short tailed curves for the radial flow case.

  12. The effect of spatial micro-CT image resolution and surface complexity on the morphological 3D analysis of open porous structures

    SciTech Connect

    Pyka, Grzegorz; Kerckhofs, Greet

    2014-01-15

    In material science microfocus X-ray computed tomography (micro-CT) is one of the most popular non-destructive techniques to visualise and quantify the internal structure of materials in 3D. Despite constant system improvements, state-of-the-art micro-CT images can still hold several artefacts typical for X-ray CT imaging that hinder further image-based processing, structural and quantitative analysis. For example spatial resolution is crucial for an appropriate characterisation as the voxel size essentially influences the partial volume effect. However, defining the adequate image resolution is not a trivial aspect and understanding the correlation between scan parameters like voxel size and the structural properties is crucial for comprehensive material characterisation using micro-CT. Therefore, the objective of this study was to evaluate the influence of the spatial image resolution on the micro-CT based morphological analysis of three-dimensional (3D) open porous structures with a high surface complexity. In particular the correlation between the local surface properties and the accuracy of the micro-CT-based macro-morphology of 3D open porous Ti6Al4V structures produced by selective laser melting (SLM) was targeted and revealed for rough surfaces a strong dependence of the resulting structure characteristics on the scan resolution. Reducing the surface complexity by chemical etching decreased the sensitivity of the overall morphological analysis to the spatial image resolution and increased the detection limit. This study showed that scan settings and image processing parameters need to be customized to the material properties, morphological parameters under investigation and the desired final characteristics (in relation to the intended functional use). Customization of the scan resolution can increase the reliability of the micro-CT based analysis and at the same time reduce its operating costs. - Highlights: • We examine influence of the image resolution

  13. 3D dual-confined sulfur encapsulated in porous carbon nanosheets and wrapped with graphene aerogels as a cathode for advanced lithium sulfur batteries

    NASA Astrophysics Data System (ADS)

    Hou, Yang; Li, Jianyang; Gao, Xianfeng; Wen, Zhenhai; Yuan, Chris; Chen, Junhong

    2016-04-01

    Although lithium-sulfur (Li-S) batteries have attracted much attention due to their high theoretical specific energy and low cost, their practical applications have been severely hindered by poor cycle life, inadequate sulfur utilization, and the insulating nature of sulfur. Here, we report a rationally designed Li-S cathode with a dual-confined configuration formed by confining sulfur in 2D carbon nanosheets with an abundant porous structure followed by 3D graphene aerogel wrapping. The porous carbon nanosheets act as the sulfur host and suppress the diffusion of polysulfide, while the graphene conductive networks anchor the sulfur-adsorbed carbon nanosheets, providing pathways for rapid electron/ion transport and preventing polysulfide dissolution. As a result, the hybrid electrode exhibits superior electrochemical performance, including a large reversible capacity of 1328 mA h g-1 in the first cycle, excellent cycling stability (maintaining a reversible capacity of 647 mA h g-1 at 0.2 C after 300 cycles) with nearly 100% Coulombic efficiency, and a high rate capability of 512 mA h g-1 at 8 C for 30 cycles, which is among the best reported rate capabilities.Although lithium-sulfur (Li-S) batteries have attracted much attention due to their high theoretical specific energy and low cost, their practical applications have been severely hindered by poor cycle life, inadequate sulfur utilization, and the insulating nature of sulfur. Here, we report a rationally designed Li-S cathode with a dual-confined configuration formed by confining sulfur in 2D carbon nanosheets with an abundant porous structure followed by 3D graphene aerogel wrapping. The porous carbon nanosheets act as the sulfur host and suppress the diffusion of polysulfide, while the graphene conductive networks anchor the sulfur-adsorbed carbon nanosheets, providing pathways for rapid electron/ion transport and preventing polysulfide dissolution. As a result, the hybrid electrode exhibits superior

  14. Modeling of porous scaffold deformation induced by medium perfusion.

    PubMed

    Podichetty, Jagdeep T; Madihally, Sundararajan V

    2014-05-01

    In this study, we tested the possibility of calculating permeability of porous scaffolds utilized in soft tissue engineering using pore size and shape. We validated the results using experimental measured pressure drop and simulations with the inclusion of structural deformation. We prepared Polycaprolactone (PCL) and Chitosan-Gelatin (CG) scaffolds by salt leaching and freeze drying technique, respectively. Micrographs were assessed for pore characteristics and mechanical properties. Porosity for both scaffolds was nearly same but the permeability varied 10-fold. Elastic moduli were 600 and 9 kPa for PCL and CG scaffolds, respectively, while Poisson's ratio was 0.3 for PCL scaffolds and ∼1.0 for CG scaffolds. A flow-through bioreactor accommodating a 10 cm diameter and 0.2 cm thick scaffold was used to determine the pressure-drop at various flow rates. Additionally, computational fluid dynamic (CFD) simulations were performed by coupling fluid flow, described by Brinkman equation, with structural mechanics using a dynamic mesh. The experimentally obtained pressure drop matched the simulation results of PCL scaffolds. Simulations were extended to a broad range of permeabilities (10(-10) m(2) to 10(-14) m(2) ), elastic moduli (10-100,000 kPa) and Poisson's ratio (0.1-0.49). The results showed significant deviation in pressure drop due to scaffold deformation compared to rigid scaffold at permeabilities near healthy tissues. Also, considering the scaffold as a nonrigid structure altered the shear stress profile. In summary, scaffold permeability can be calculated using scaffold pore characteristics and deformation could be predicted using CFD simulation. These relationships could potentially be used in monitoring tissue regeneration noninvasively via pressure drop.

  15. Motility of Escherichia coli in a quasi-two-dimensional porous medium

    NASA Astrophysics Data System (ADS)

    Sosa-Hernández, Juan Eduardo; Santillán, Moisés; Santana-Solano, Jesús

    2017-03-01

    Bacterial migration through confined spaces is critical for several phenomena, such as biofilm formation, bacterial transport in soils, and bacterial therapy against cancer. In the present work, E. coli (strain K12-MG1655 WT) motility was characterized by recording and analyzing individual bacterium trajectories in a simulated quasi-two-dimensional porous medium. The porous medium was simulated by enclosing, between slide and cover slip, a bacterial-culture sample mixed with uniform 2.98-μ m -diameter spherical latex particles. The porosity of the medium was controlled by changing the latex particle concentration. By statistically analyzing several trajectory parameters (instantaneous velocity, turn angle, mean squared displacement, etc.), and contrasting with the results of a random-walk model developed ad hoc, we were able to quantify the effects that different obstacle concentrations have upon bacterial motility.

  16. Momentum transfer at the interface between a porous medium and a pure fluid

    NASA Astrophysics Data System (ADS)

    Hu, Howard; Zhang, Songpeng

    2015-11-01

    We examine the flow parallel to the interface between a porous medium and a liquid, focusing on the boundary conditions at the interface. When Darcy's law is used to describe the momentum transport in the porous layer, the classic Beavers-Joseph condition relates the shear rate and the slip velocity at the interface with a slip parameter that depends on the structure of the porous surface. When the Brinkman equation is used, the averaged velocity is continuous at the interface, however the fluid shear stress across the interface commonly experiences a jump. This shear stress jump can be expressed in terms of the slip velocity at the interface divided by a length characterized by the square root of the permeability, and a dimensionless stress jump coefficient. In this work, we study the momentum transfer from the clear fluid onto the solid structure at the interface, and proposed a stress partition parameter that characterizes the stress transfer from the clear fluid to the fluid (and solid) phase of the porous medium. Simple models are developed to formulate this stress partition parameter for porous media that are brush-like, long fibers, and random, respectively. Our model predictions are compared with numerical and experimental results in the literature.

  17. Nanohole-Structured and Palladium-Embedded 3D Porous Graphene for Ultrahigh Hydrogen Storage and CO Oxidation Multifunctionalities.

    PubMed

    Kumar, Rajesh; Oh, Jung-Hwan; Kim, Hyun-Jun; Jung, Jung-Hwan; Jung, Chan-Ho; Hong, Won G; Kim, Hae-Jin; Park, Jeong-Young; Oh, Il-Kwon

    2015-07-28

    Atomic-scale defects on carbon nanostructures have been considered as detrimental factors and critical problems to be eliminated in order to fully utilize their intrinsic material properties such as ultrahigh mechanical stiffness and electrical conductivity. However, defects that can be intentionally controlled through chemical and physical treatments are reasonably expected to bring benefits in various practical engineering applications such as desalination thin membranes, photochemical catalysts, and energy storage materials. Herein, we report a defect-engineered self-assembly procedure to produce a three-dimensionally nanohole-structured and palladium-embedded porous graphene hetero-nanostructure having ultrahigh hydrogen storage and CO oxidation multifunctionalities. Under multistep microwave reactions, agglomerated palladium nanoparticles having diameters of ∼10 nm produce physical nanoholes in the basal-plane structure of graphene sheets, while much smaller palladium nanoparticles are readily impregnated inside graphene layers and bonded on graphene surfaces. The present results show that the defect-engineered hetero-nanostructure has a ∼5.4 wt % hydrogen storage capacity under 7.5 MPa and CO oxidation catalytic activity at 190 °C. The defect-laden graphene can be highly functionalized for multipurpose applications such as molecule absorption, electrochemical energy storage, and catalytic activity, resulting in a pathway to nanoengineering based on underlying atomic scale and physical defects.

  18. Analyzing the deformation of a porous medium with account for the collapse of pores

    NASA Astrophysics Data System (ADS)

    Sadovskii, V. M.; Sadovskaya, O. V.

    2016-09-01

    The generalized rheological method is used to construct a mathematical model of small deformations of a porous media with open pores. Changes in the resistance of the material to external mechanical impact at the moment of collapse of the pores is described using the von Mises-Schleicher strength condition. The irreversible deformation is accounted for with the help of the classic versions of the von Mises-Tresca-Saint-Venant yield condition and the condition that simulates the plastic loss of stability of the porous skeleton. Within the framework of the constructed model, this paper describes the analysis of the propagation of plane longitudinal compression waves in a homogeneous medium accompanied with plastic strain of the skeleton and densification of the material. A parallel computational algorithm is developed for the study of the elastoplastic deformation of the porous medium under external dynamics loads. The algorithm and the program are tested by calculating the propagation of plane longitudinal compression shock waves and the extension of the cylindrical cavity in an infinite porous medium. The calculation results are compared with exact solutions, and it is shown that they are in good agreement.

  19. Incompressible fluid flow and heat transfer through a nonsaturated porous medium

    NASA Astrophysics Data System (ADS)

    Saldanha da Gama, R. M.; Martins-Costa, M. L.

    This work studies a nonsaturated flow and the heat transfer associated phenomenon of a newtonian fluid through a rigid porous matrix, using a mixture theory approach in its modelling. The mixture consists of three overlapping continuous constituents: a solid (porous medium), a liquid and an inert gas, included to account for the compressibility of the system as a whole. A set of four nonlinear partial differential equations describe the problem whose hydrodynamical part is approximated by means of a Glimm's scheme combined with an operator splitting technique.

  20. Evaluation of a numerical simulation model for a system coupling atmospheric gas, surface water and unsaturated or saturated porous medium.

    PubMed

    Hibi, Yoshihiko; Tomigashi, Akira; Hirose, Masafumi

    2015-12-01

    Numerical simulations that couple flow in a surface fluid with that in a porous medium are useful for examining problems of pollution that involve interactions among the atmosphere, surface water and groundwater, including, for example, saltwater intrusion along coasts. We previously developed a numerical simulation method for simulating a coupled atmospheric gas, surface water, and groundwater system (called the ASG method) that employs a saturation equation for flow in a porous medium; this equation allows both the void fraction of water in the surface system and water saturation in the porous medium to be solved simultaneously. It remained necessary, however, to evaluate how global pressure, including gas pressure, water pressure, and capillary pressure, should be specified at the boundary between the surface and the porous medium. Therefore, in this study, we derived a new equation for global pressure and integrated it into the ASG method. We then simulated water saturation in a porous medium and the void fraction of water in a surface system by the ASG method and reproduced fairly well the results of two column experiments. Next, we simulated water saturation in a porous medium (sand) with a bank, by using both the ASG method and a modified Picard (MP) method. We found only a slight difference in water saturation between the ASG and MP simulations. This result confirmed that the derived equation for global pressure was valid for a porous medium, and that the global pressure value could thus be used with the saturation equation for porous media. Finally, we used the ASG method to simulate a system coupling atmosphere, surface water, and a porous medium (110m wide and 50m high) with a trapezoidal bank. The ASG method was able to simulate the complex flow of fluids in this system and the interaction between the porous medium and the surface water or the atmosphere.

  1. 3D dual-confined sulfur encapsulated in porous carbon nanosheets and wrapped with graphene aerogels as a cathode for advanced lithium sulfur batteries.

    PubMed

    Hou, Yang; Li, Jianyang; Gao, Xianfeng; Wen, Zhenhai; Yuan, Chris; Chen, Junhong

    2016-04-21

    Although lithium-sulfur (Li-S) batteries have attracted much attention due to their high theoretical specific energy and low cost, their practical applications have been severely hindered by poor cycle life, inadequate sulfur utilization, and the insulating nature of sulfur. Here, we report a rationally designed Li-S cathode with a dual-confined configuration formed by confining sulfur in 2D carbon nanosheets with an abundant porous structure followed by 3D graphene aerogel wrapping. The porous carbon nanosheets act as the sulfur host and suppress the diffusion of polysulfide, while the graphene conductive networks anchor the sulfur-adsorbed carbon nanosheets, providing pathways for rapid electron/ion transport and preventing polysulfide dissolution. As a result, the hybrid electrode exhibits superior electrochemical performance, including a large reversible capacity of 1328 mA h g(-1) in the first cycle, excellent cycling stability (maintaining a reversible capacity of 647 mA h g(-1) at 0.2 C after 300 cycles) with nearly 100% Coulombic efficiency, and a high rate capability of 512 mA h g(-1) at 8 C for 30 cycles, which is among the best reported rate capabilities.

  2. High-performance hybrid supercapacitor with 3D hierarchical porous flower-like layered double hydroxide grown on nickel foam as binder-free electrode

    NASA Astrophysics Data System (ADS)

    Zhang, Luojiang; Hui, Kwun Nam; San Hui, Kwan; Lee, Haiwon

    2016-06-01

    The synthesis of layered double hydroxide (LDH) as electroactive material has been well reported; however, fabricating an LDH electrode with excellent electrochemical performance at high current density remains a challenge. In this paper, we report a 3D hierarchical porous flower-like NiAl-LDH grown on nickel foam (NF) through a liquid-phase deposition method as a high-performance binder-free electrode for energy storage. With large ion-accessible surface area as well as efficient electron and ion transport pathways, the prepared LDH-NF electrode achieves high specific capacity (1250 C g-1 at 2 A g-1 and 401 C g-1 at 50 A g-1) after 5000 cycles of activation at 20 A g-1 and high cycling stability (76.7% retention after another 5000 cycles at 50 A g-1), which is higher than those of most previously reported NiAl-LDH-based materials. Moreover, a hybrid supercapacitor with LDH-NF as the positive electrode and porous graphene nanosheet coated on NF (GNS-NF) as the negative electrode, delivers high energy density (30.2 Wh kg-1 at a power density of 800 W kg-1) and long cycle life, which outperforms the other devices reported in the literature. This study shows that the prepared LDH-NF electrode offers great potential in energy storage device applications.

  3. A new method for evaluation of heat transfer between solid material and fluid in a porous medium

    SciTech Connect

    Ichimiya, K.

    1999-11-01

    Technological applications in which porous materials are utilized include thermal energy storage, geophysical fluid engineering, thermal insulation, heat transfer enhancement, and heat exchangers. The author proposes a new method to estimate the heat transfer between fluid gas and solid material in a porous medium. In the first stage, the local Nusselt numbers on the heated wall of a flow passage with a porous medium are numerically obtained in advance for the parameter H{sub a}, including the volumetric heat transfer coefficient, h{sub {nu}}, between the fluid and the solid material in a porous medium. In the second stage, the experimental Nusselt numbers on the heated wall are obtained by measuring wall temperatures and heat flux. The volumetric heat transfer coefficient, h{sub {nu}}, is evaluated by comparing experimental Nusselt numbers with numerical ones. This method also gives the longitudinal characteristics of the heat transfer in a porous medium.

  4. Bio-Conjugated CNT-Bridged 3D Porous Graphene Oxide Membrane for Highly Efficient Disinfection of Pathogenic Bacteria and Removal of Toxic Metals from Water.

    PubMed

    Nellore, Bhanu Priya Viraka; Kanchanapally, Rajashekhar; Pedraza, Francisco; Sinha, Sudarson Sekhar; Pramanik, Avijit; Hamme, Ashton T; Arslan, Zikri; Sardar, Dhiraj; Ray, Paresh Chandra

    2015-09-02

    More than a billion people lack access to safe drinking water that is free from pathogenic bacteria and toxic metals. The World Health Organization estimates several million people, mostly children, die every year due to the lack of good quality water. Driven by this need, we report the development of PGLa antimicrobial peptide and glutathione conjugated carbon nanotube (CNT) bridged three-dimensional (3D) porous graphene oxide membrane, which can be used for highly efficient disinfection of Escherichia coli O157:H7 bacteria and removal of As(III), As(V), and Pb(II) from water. Reported results demonstrate that versatile membrane has the capability to capture and completely disinfect pathogenic pathogenic E. coli O157:H7 bacteria from water. Experimentally observed disinfection data indicate that the PGLa attached membrane can dramatically enhance the possibility of destroying pathogenic E. coli bacteria via synergistic mechanism. Reported results show that glutathione attached CNT-bridged 3D graphene oxide membrane can be used to remove As(III), As(V), and Pb(II) from water sample at 10 ppm level. Our data demonstrated that PGLa and glutathione attached membrane has the capability for high efficient removal of E. coli O157:H7 bacteria, As(III), As(V), and Pb(II) simultaneously from Mississippi River water.

  5. Molecular tectonics: self-complementary supramolecular Se...N synthons directing assembly of 1D silver chains into 3D porous molecular architectures.

    PubMed

    Zhou, Ai-Ju; Zheng, Shao-Liang; Fang, Yue; Tong, Ming-Liang

    2005-06-27

    Reaction of 2,1,3-benzoselenadiazole (bsd) with AgNO3 results in the formation of a novel model example of a Se...N synthon directed molecular network of different polymorphs at different temperatures. Alpha-[Ag(bsd)2(NO3)] x 0.5bsd formed at ambient temperature, has a 3D porous molecular network constructed with monomeric [Ag(bsd)2(NO3)] motif, and has 1D channels that are encapsulated with 1D arrays of two-fold-disordered dimeric (bsd)2 guests aggregated by the self-complementary nonbonded Se...N interactions. This is the first molecular net directed by supramolecular Se...N synthons. The second polymorph, beta-[Ag(bsd)2(NO3)] x 0.5bsd, formed from an analogous reaction at 50 degrees C, contains a similar 3D molecular network constructed with tetrameric [Ag4(bsd)8(NO3)4] motif and 1D arrays of well-ordered dimeric (bsd)2 guests are encapsulated in the channels. Such ordered (bsd)2 dimers provide an excellent simplified dimeric model for MO calculations of intermolecular nonbonded Se...N interactions.

  6. Fabrication of 3D lawn-shaped N-doped porous carbon matrix/polyaniline nanocomposite as the electrode material for supercapacitors

    NASA Astrophysics Data System (ADS)

    Zhang, Xiuling; Ma, Li; Gan, Mengyu; Fu, Gang; Jin, Meng; Lei, Yao; Yang, Peishu; Yan, Maofa

    2017-02-01

    A facile approach to acquire electrode materials with prominent electrochemical property is pivotal to the progress of supercapacitors. 3D nitrogen-doped porous carbon matrix (PCM), with high specific surface area (SSA) up to 2720 m2 g-1, was obtained from the carbonization and activation of the nitrogen-enriched composite precursor (graphene/polyaniline). Then 3D lawn-shaped PCM/PANI composite was obtained by the simple in-situ polymerization. The morphology and structure of these resulting composites were characterized by combining SEM and TEM measurements, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) spectroscopy analyses and Raman spectroscope. The element content of all samples was evaluated using CHN analysis. The results of electrochemical testing indicated that the PCM/PANI composite displays a higher capacitance value of 527 F g-1 at 1 A g-1 compared to 338 F g-1 for pure PANI, and exhibits appreciable rate capability with a retention of 76% at 20 A g-1 as well as fine long-term cycling performance (with 88% retention of specific capacitance after 1000 cycles at 10 A g-1). Simultaneously, the excellent capacitance performance coupled with the facile synthesis of PCM/PANI indicates it is a promising electrode material for supercapacitors.

  7. Fabrication of 3D interconnected porous TiO2 nanotubes templated by poly(vinyl chloride-g-4-vinyl pyridine) for dye-sensitized solar cells.

    PubMed

    Koh, Joo Hwan; Koh, Jong Kwan; Seo, Jin Ah; Shin, Jong-Shik; Kim, Jong Hak

    2011-09-07

    Porous TiO(2) nanotube arrays with three-dimensional (3D) interconnectivity were prepared using a sol-gel process assisted by poly(vinyl chloride-graft-4-vinyl pyridine), PVC-g-P4VP graft copolymer and a ZnO nanorod template. A 7 µm long ZnO nanorod array was grown from the fluorine-doped tin oxide (FTO) glass via a liquid phase deposition method. The TiO(2) sol-gel solution templated by the PVC-g-P4VP graft copolymer produced a random 3D interconnection between the adjacent ZnO nanorods during spin coating. Upon etching of ZnO, TiO(2) nanotubes consisting of 10-15 nm nanoparticles were generated, as confirmed by wide-angle x-ray scattering (WAXS), energy-filtering transmission electron microscopy (EF-TEM) and field-emission scanning electron microscopy (FE-SEM). The ordered and interconnected nanotube architecture showed an enhanced light scattering effect and increased penetration of polymer electrolytes in dye-sensitized solar cells (DSSC). The energy conversion efficiency reached 1.82% for liquid electrolyte, and 1.46% for low molecular weight (M(w)) and 0.74% for high M(w) polymer electrolytes.

  8. Porous medium coffee ring effect and other factors affecting the first crystallisation time of sodium chloride at the surface of a drying porous medium

    NASA Astrophysics Data System (ADS)

    Hidri, F.; Sghaier, N.; Eloukabi, H.; Prat, M.; Nasrallah, S. Ben

    2013-12-01

    We study the distribution of ions in a drying porous medium up to the formation of first crystals at the surface. The study is based on comparisons between numerical simulations and experiments with packings of glass beads. The experimental configuration, which is representative of many previous drying experiments, is characterized by the formation of an efflorescence fairy ring at the surface of the porous medium. The preferential formation of crystals at the periphery is explained by the combined effect of higher evaporation fluxes at the surface periphery, as in the classical coffee ring problem, and variations in the porosity near the wall bordering the packing. It is shown that both effects have a great impact on the time marking the occurrence of first crystals, which is referred to as the first crystallization time. The experiments indicate that the first crystallization time increases with a decreasing bead size for a given initial ion concentration. This is explained by the variation with bead size of the characteristic size of the near wall region where a preferential desaturation of the sample occurs as a result of the porosity increase near the wall. The study also reveals a significant salt supersaturation effect. This represents a noticeable fact in relation with salt weathering issues.

  9. 3D Porous Architecture of Stacks of β-TCP Granules Compared with That of Trabecular Bone: A microCT, Vector Analysis, and Compression Study

    PubMed Central

    Chappard, Daniel; Terranova, Lisa; Mallet, Romain; Mercier, Philippe

    2015-01-01

    The 3D arrangement of porous granular biomaterials usable to fill bone defects has received little study. Granular biomaterials occupy 3D space when packed together in a manner that creates a porosity suitable for the invasion of vascular and bone cells. Granules of beta-tricalcium phosphate (β-TCP) were prepared with either 12.5 or 25 g of β-TCP powder in the same volume of slurry. When the granules were placed in a test tube, this produced 3D stacks with a high (HP) or low porosity (LP), respectively. Stacks of granules mimic the filling of a bone defect by a surgeon. The aim of this study was to compare the porosity of stacks of β-TCP granules with that of cores of trabecular bone. Biomechanical compression tests were done on the granules stacks. Bone cylinders were prepared from calf tibia plateau, constituted high-density (HD) blocks. Low-density (LD) blocks were harvested from aged cadaver tibias. Microcomputed tomography was used on the β-TCP granule stacks and the trabecular bone cores to determine porosity and specific surface. A vector-projection algorithm was used to image porosity employing a frontal plane image, which was constructed line by line from all images of a microCT stack. Stacks of HP granules had porosity (75.3 ± 0.4%) and fractal lacunarity (0.043 ± 0.007) intermediate between that of HD (respectively 69.1 ± 6.4%, p < 0.05 and 0.087 ± 0.045, p < 0.05) and LD bones (respectively 88.8 ± 1.57% and 0.037 ± 0.014), but exhibited a higher surface density (5.56 ± 0.11 mm2/mm3 vs. 2.06 ± 0.26 for LD, p < 0.05). LP granular arrangements created large pores coexisting with dense areas of material. Frontal plane analysis evidenced a more regular arrangement of β-TCP granules than bone trabecule. Stacks of HP granules represent a scaffold that resembles trabecular bone in its porous microarchitecture. PMID:26528240

  10. 3D Rare earth porous coordination frameworks with formamide generated in situ syntheses: Crystal structure and down- and up-conversion luminescence

    SciTech Connect

    Ma, Xue; Tian, Jing; Yang, Hong-Y.; Zhao, Kai; Li, Xia

    2013-05-01

    The reaction of RE(NO)₃·6H₂O and formamide yielded the coordination polymers, [RE(HCOO)₄]⁻[NH₂CHNH₂]⁺ (RE=Y 1, Eu 2, Gd 3, Tb 4, Dy 5, Er 6, and Yb 7). They possess 3D porous frameworks with the 1D rhombic channels occupied by [NH₂CHNH₂]⁺ cations. Complexes 2 and 4 display the characteristic down-conversion emissions corresponding to ⁵D₀→⁷FJ (J=1–4) transitions of Eu(III) ion and ⁵D₄→⁷FJ (J=6–3) transitions of Tb(III) ion, respectively. Longer lifetime values of 2.128±0.002 ms (⁵D₀) for 2 and 2.132±0.002 ms (⁵D₄) for 4 have been observed. The up-conversion spectra of the Y:Yb,Er and Gd:Yb,Er codoped complexes exhibit three emission bands around 410 (⁴H9/2→⁴I15/2, blue), 518–570 (⁴S3/2, ²H11/2→⁴I15/2, green), and 655 nm (⁴F9/2→⁴I15/2, red). - Graphical Abstract: The complexes [RE(HCOO)₄]⁻[NH₂CHNH₂]⁺ possess 3D porous frameworks. Eu(III) and Tb(III) complexes show characteristic emission of Ln(III) ions. The up-conversion emission of the Y:Yb,Er and Gd:Yb,Er codoped complexes was observed. Highlights: •The reaction of RE(NO)₃·6H₂O and formamide produced complexes [RE(HCOO)₄]⁻[NH₂CHNH₂]⁺. • The complexes possess 3D frameworks with the 1D channels occupied by [NH₂CHNH₂]+ cations. • Eu(III)/Tb(III) complexes display the characteristic down-conversion emission of Ln(III) ions. • The Y:Yb,Er and Gd:Yb,Er doped complexes exhibit the up-conversion emission.

  11. 3D Porous Architecture of Stacks of β-TCP Granules Compared with That of Trabecular Bone: A microCT, Vector Analysis, and Compression Study.

    PubMed

    Chappard, Daniel; Terranova, Lisa; Mallet, Romain; Mercier, Philippe

    2015-01-01

    The 3D arrangement of porous granular biomaterials usable to fill bone defects has received little study. Granular biomaterials occupy 3D space when packed together in a manner that creates a porosity suitable for the invasion of vascular and bone cells. Granules of beta-tricalcium phosphate (β-TCP) were prepared with either 12.5 or 25 g of β-TCP powder in the same volume of slurry. When the granules were placed in a test tube, this produced 3D stacks with a high (HP) or low porosity (LP), respectively. Stacks of granules mimic the filling of a bone defect by a surgeon. The aim of this study was to compare the porosity of stacks of β-TCP granules with that of cores of trabecular bone. Biomechanical compression tests were done on the granules stacks. Bone cylinders were prepared from calf tibia plateau, constituted high-density (HD) blocks. Low-density (LD) blocks were harvested from aged cadaver tibias. Microcomputed tomography was used on the β-TCP granule stacks and the trabecular bone cores to determine porosity and specific surface. A vector-projection algorithm was used to image porosity employing a frontal plane image, which was constructed line by line from all images of a microCT stack. Stacks of HP granules had porosity (75.3 ± 0.4%) and fractal lacunarity (0.043 ± 0.007) intermediate between that of HD (respectively 69.1 ± 6.4%, p < 0.05 and 0.087 ± 0.045, p < 0.05) and LD bones (respectively 88.8 ± 1.57% and 0.037 ± 0.014), but exhibited a higher surface density (5.56 ± 0.11 mm(2)/mm(3) vs. 2.06 ± 0.26 for LD, p < 0.05). LP granular arrangements created large pores coexisting with dense areas of material. Frontal plane analysis evidenced a more regular arrangement of β-TCP granules than bone trabecule. Stacks of HP granules represent a scaffold that resembles trabecular bone in its porous microarchitecture.

  12. Effects of Porous Medium Heterogeneity on Vadose Zone Desiccation: Intermediate-scale Laboratory Experiments and Simulations

    SciTech Connect

    Oostrom, Martinus; Freedman, Vicky L.; Wietsma, Thomas W.; Dane, Jacob H.; Truex, Michael J.

    2012-11-01

    Soil desiccation (drying), involving water evaporation induced by dry gas injection, is a potentially robust vadose zone remediation process to limit contaminant transport through the vadose zone. A series of four intermediate-scale flow cell experiments was conducted in homogeneous and simple layered heterogeneous porous medium systems to investigate the effects of heterogeneity on desiccation of unsaturated porous media. The permeability ratios of porous medium layers ranged from about five to almost two orders of magnitude. The insulated flow cell was equipped with twenty humidity and temperature sensors and a dual-energy gamma system was used to determine water saturations at various times. The multiphase code STOMP was used to simulate the desiccation process. Results show that injected dry gas flowed predominantly in the higher permeability layer and delayed water removal from the lower permeability material. For the configurations tested, water vapor diffusion from the lower to the higher permeability zone was considerable over the duration of the experiments, resulting in much larger relative humidity values of the outgoing air than based on permeability ratios alone. Acceptable numerical matches with the experimental data were obtained when an extension of the saturation-capillary pressure relation below the residual water saturation was used. The agreements between numerical and experimental results suggest that the correct physics are implemented in the simulator and that the thermal and hydraulic properties of the porous media, flow cell wall and insulation materials were properly represented.

  13. New porous medium Poisson-Nernst-Planck equations for strongly oscillating electric potentials

    NASA Astrophysics Data System (ADS)

    Schmuck, M.

    2013-02-01

    We consider the Poisson-Nernst-Planck system which is well-accepted for describing dilute electrolytes as well as transport of charged species in homogeneous environments. Here, we study these equations in porous media whose electric permittivities show a strong contrast compared with the electric permittivity of the electrolyte phase. Our main result is the derivation of convenient low-dimensional equations, that is, of effective macroscopic porous media Poisson-Nernst-Planck equations, which reliably describe ionic transport. The contrast in the electric permittivities between liquid and solid phase and the heterogeneity of the porous medium induce strongly oscillating electric potentials (fields). In order to account for this specific physical scenario, we introduce a modified asymptotic multiple-scale expansion which takes advantage of the nonlinearly coupled structure of the ionic transport equations. This allows for a systematic upscaling resulting in a new effective porous medium formulation which shows a new transport term on the macroscale. Solvability of all arising equations is rigorously verified. The emergence of a new transport term indicates promising physical insights into the influence of the microscale material properties on the macroscale. Hence, systematic upscaling strategies provide a source and a prospective tool to capitalize intrinsic scale effects for scientific, engineering, and industrial applications.

  14. Preferential paths in yield stress fluid flow through a porous medium

    NASA Astrophysics Data System (ADS)

    Guasto, Jeffrey; Waisbord, Nicolas; Stoop, Norbert; Dunkel, Jörn

    2016-11-01

    A broad range of biological, geological, and industrial materials with complex rheological properties are subjected to flow through porous media in applications ranging from oil recovery to food manufacturing. In this experimental study, we examine the flow of a model yield stress fluid (Carbopol micro-gel) through a quasi-2D porous medium, fabricated in a microfluidic channel. The flow is driven by applying a precisely-controlled pressure gradient and measured by particle tracking velocimetry, and our observations are complemented by a pore-network model of the yield stress fluid flow. While remaining unyielded at small applied pressure, the micro-gel begins to yield at a critical pressure gradient, exhibiting a single preferential flow path that percolates through the porous medium. As the applied pressure gradient increases, we observe a subsequent coarsening and invasion of the yielded, fluidized network. An examination of both the yielded network topology and pore-scale flow reveal that two cooperative phenomena are involved in sculpting the preferential flow paths: (1) the geometry of the porous microstructure, and (2) the adhesive surface interactions between the micro-gel and substrate. NSF CBET-1511340.

  15. Liquid film condensation along a vertical surface in a thin porous medium with large anisotropic permeability.

    PubMed

    Sanya, Arthur S O; Akowanou, Christian; Sanya, Emile A; Degan, Gerard

    2014-01-01

    The problems of steady film condensation on a vertical surface embedded in a thin porous medium with anisotropic permeability filled with pure saturated vapour are studied analytically by using the Brinkman-Darcy flow model. The principal axes of anisotropic permeability are oriented in a direction that non-coincident with the gravity force. On the basis of the flow permeability tensor due to the anisotropic properties and the Brinkman-Darcy flow model adopted by considering negligible macroscopic and microscopic inertial terms, boundary-layer approximations in the porous liquid film momentum equation is solved analytically. Scale analysis is applied to predict the order-of-magnitudes involved in the boundary layer regime. The first novel contribution in the mathematics consists in the use of the anisotropic permeability tensor inside the expression of the mathematical formulation of the film condensation problem along a vertical surface embedded in a porous medium. The present analytical study reveals that the anisotropic permeability properties have a strong influence on the liquid film thickness, condensate mass flow rate and surface heat transfer rate. The comparison between thin and thick porous media is also presented.

  16. Porous grain model and equivalent elastic medium approach for predicting effective elastic properties of sedimentary rocks

    NASA Astrophysics Data System (ADS)

    Ruiz, Franklin J.

    This dissertation presents the results of using different inclusion and granular effective medium models and poroelasticity to predict the elastic properties of rocks with complex microstructures. Effective medium models account for the microstructure and texture of rocks, and can be used to predict the type of rock and microstructure from seismic velocities and densities. We introduce the elastic equivalency approach, using the differential effective medium model, to predict the effective elastic moduli of rocks and attenuation. We introduce the porous grain concept and develop rock physics models for rocks with microporosity. We exploit the porous grain concept to describe a variety of arrangements of uncemented and cemented grains with different degrees of hydraulic connectivity in the pore space. We first investigate the accuracy of the differential effective medium and self-consistent estimations of elastic properties of complex rock matrix using composites as analogs. We test whether the differential effective-medium (DEM) and self-consistent (SC) models can accurately estimate the elastic moduli of a complex rock matrix and compare the results with the average of upper and lower Hashin-Shtrikman bounds. We find that when the material microstructure is consistent with DEM, this model is more accurate than both SC and the bound-average method for a variety of inclusion aspect ratios, concentrations, and modulus contrasts. Based on these results, we next pose a question: can a theoretical inclusion model, specifically, the differential effective-medium model (DEM), be used to match experimental velocity data in rocks that are not necessarily made of inclusions (such as elastics)? We first approach this question by using empirical velocity-porosity equations as proxies for data. By finding a DEM inclusion aspect ratio (AR) to match these equations, we find that the required range of AR is remarkably narrow. Moreover, a constant AR of about 0.13 can be used to

  17. Effect of supermolecular structure on oil filtration in a porous medium

    SciTech Connect

    Gal`tsev, V.E.; Ametov, I.M.; Dzyubenko, E.M.

    1995-09-01

    The formation of supermolecular structures during the adsorption of a tar-asphaltene fraction on the surface of grains of rock-forming materials in a porous medium was studied. The effect of these structures on the character of oil filtration in a porous medium is established. The filamentary structures formed have a diameter of 20 to 40 {angstrom}, corresponding to the size of asphaltene associates, and exhibit preferred orientation with a tilt in the direction opposite to the direction of flow. Some residual orientation of filaments is retained upon a change in the direction of flow. On the basis of ENDOR data, a model of a spatially anisotropic asphaltene micelle in oil was developed, which explains the observed character of coagulation and the formation of filamentary structures.

  18. Mixed convection about a cone in a porous medium: The entire regime

    SciTech Connect

    Yih, K.A.

    1999-10-01

    The corresponding problem of convective heat transfer in a porous medium has important application such as design of canisters for nuclear waste disposal, nuclear reactor cooling system, geothermal reservoirs, ceramic processing, and filtration processes. The mixed convective heat transfer about a cone embedded in a saturated porous medium is numerically investigated. The surface of the cone is maintained at variable wall temperature (VWT) or variable heat flux (VHF). The transformed governing equations are solved by Keller box method. Numerical results are presented for the dimensionless temperature profiles and the local Nusselt number. Increasing the exponent {lambda} increases the local Nusselt number. As the cone angle parameter m increases, the local Nusselt number increases (decreases) for the case of VWT (VHF). Moreover, as mixed convection parameter {chi}(or {chi}*) varies from 0 (pure free convection) to 1 (pure forced convection), the local Nusselt number decreases initially, reaches a minimum in the intermediate value of {chi} (or {chi}*) and then increases gradually.

  19. A study on moving mesh finite element solution of the porous medium equation

    NASA Astrophysics Data System (ADS)

    Ngo, Cuong; Huang, Weizhang

    2017-02-01

    An adaptive moving mesh finite element method is studied for the numerical solution of the porous medium equation with and without variable exponents and absorption. The method is based on the moving mesh partial differential equation approach and employs its newly developed implementation. The implementation has several improvements over the traditional one, including its explicit, compact form of the mesh velocities, ease to program, and less likelihood of producing singular meshes. Three types of metric tensor that correspond to uniform and arclength-based and Hessian-based adaptive meshes are considered. The method shows first-order convergence for uniform and arclength-based adaptive meshes, and second-order convergence for Hessian-based adaptive meshes. It is also shown that the method can be used for situations with complex free boundaries, emerging and splitting of free boundaries, and the porous medium equation with variable exponents and absorption. Two-dimensional numerical results are presented.

  20. Methane Gas Hydrate Decomposition in a Porous Medium Upon Injection of a Warm Carbon Dioxide Gas

    NASA Astrophysics Data System (ADS)

    Khasanov, M. K.; Shagapov, V. Sh.

    2016-09-01

    The characteristic features of methane gas hydrate decomposition upon injection of a warm carbon dioxide gas into a porous medium saturated with methane and its hydrate are investigated. A mathematical model is presented for heat and mass transfer in a porous medium accompanied by substitution of methane for carbon dioxide gas in the original gas hydrate. Self-similar solutions of a one-dimensional problem that describe the distribution of basic parameters in a stratum have been constructed. It is shown that there are solutions according to which methane gas hydrate may decompose either with the formation of carbon dioxide gas hydrate alone, or with the formation of both carbon dioxide gas hydrate and a mixture of methane with water. Critical diagrams of the existence of each type of solutions have been drawn.

  1. Unsteady magnetohydrodynamic free convection flow of a second grade fluid in a porous medium with ramped wall temperature.

    PubMed

    Samiulhaq; Ahmad, Sohail; Vieru, Dumitru; Khan, Ilyas; Shafie, Sharidan

    2014-01-01

    Magnetic field influence on unsteady free convection flow of a second grade fluid near an infinite vertical flat plate with ramped wall temperature embedded in a porous medium is studied. It has been observed that magnitude of velocity as well as skin friction in case of ramped temperature is quite less than the isothermal temperature. Some special cases namely: (i) second grade fluid in the absence of magnetic field and porous medium and (ii) Newtonian fluid in the presence of magnetic field and porous medium, performing the same motion are obtained. Finally, the influence of various parameters is graphically shown.

  2. Unsteady Magnetohydrodynamic Free Convection Flow of a Second Grade Fluid in a Porous Medium with Ramped Wall Temperature

    PubMed Central

    Samiulhaq; Ahmad, Sohail; Vieru, Dumitru; Khan, Ilyas; Shafie, Sharidan

    2014-01-01

    Magnetic field influence on unsteady free convection flow of a second grade fluid near an infinite vertical flat plate with ramped wall temperature embedded in a porous medium is studied. It has been observed that magnitude of velocity as well as skin friction in case of ramped temperature is quite less than the isothermal temperature. Some special cases namely: (i) second grade fluid in the absence of magnetic field and porous medium and (ii) Newtonian fluid in the presence of magnetic field and porous medium, performing the same motion are obtained. Finally, the influence of various parameters is graphically shown. PMID:24785147

  3. Thermal instability of a fluid-saturated porous medium bounded by thin fluid layers

    SciTech Connect

    Pillatsis, G.; Taslim, M.E.; Narusawa, U. )

    1987-08-01

    A linear stability analysis is performed for a horizontal Darcy porous layer of depth 2d{sub m} sandwiched between two fluid layers of depth d (each) with the top and bottom boundaries being dynamically free and kept at fixed temperatures. The Beavers-Joseph condition is employed as one of the interfacial boundary conditions between the fluid and the porous layer. The critical Rayleigh number and the horizontal wave number for the onset of convective motion depend on the following four dimensional parameters: {cflx d} (= d{sub m}/d, the depth ratio), {delta} (= {radical}K/d{sub m} with K being the permeability of the porous medium) {alpha} (the proportionality constant in the Beavers-Joseph condition), and k/k{sub m} (the thermal conductivity ratio). In order to analyze the effect of these parameters on the stability condition, a set of numerical solutions is obtained in terms of a convergent series for the respective layers, for the case in which the thickness of the porous layer is much greater than that of the fluid layer. A comparison of this study with the previously obtained exact solution for the case of constant heat flux boundaries is made to illustrate quantitative effects of the interfacial and the top/bottom boundaries on the thermal instability of a combined system of porous and fluid layers.

  4. Thermal conductivity in porous media: Percolation-based effective-medium approximation

    NASA Astrophysics Data System (ADS)

    Ghanbarian, Behzad; Daigle, Hugh

    2016-01-01

    Knowledge of porosity and saturation-dependent thermal conductivities is necessary to investigate heat and water transfer in natural porous media such as rocks and soils. Thermal conductivity in a porous medium is affected by the complicated relationship between the topology and geometry of the pore space and the solid matrix. However, as water content increases from completely dry to fully saturated, the effect of the liquid phase on thermal conductivity may increase substantially. Although various methods have been proposed to model the porosity and saturation dependence of thermal conductivity, most are empirical or quasiphysical. In this study, we present a theoretical upscaling framework from percolation theory and the effective-medium approximation, which is called percolation-based effective-medium approximation (P-EMA). The proposed model predicts the thermal conductivity in porous media from endmember properties (e.g., air, solid matrix, and saturating fluid thermal conductivities), a scaling exponent, and a percolation threshold. In order to evaluate our porosity and saturation-dependent models, we compare our theory with 193 porosity-dependent thermal conductivity measurements and 25 saturation-dependent thermal conductivity data sets and find excellent match. We also find values for the scaling exponent different than the universal value of 2, in insulator-conductor systems, and also different from 0.76, the exponent in conductor-superconductor mixtures, in three dimensions. These results indicate that the thermal conductivity under fully and partially saturated conditions conforms to nonuniversal behavior. This means the value of the scaling exponent changes from medium to medium and depends not only on structural and geometrical properties of the medium but also characteristics (e.g., wetting or nonwetting) of the saturating fluid.

  5. Approximate analytic solutions of stagnation point flow in a porous medium

    NASA Astrophysics Data System (ADS)

    Kumaran, V.; Tamizharasi, R.; Vajravelu, K.

    2009-06-01

    An efficient and new implicit perturbation technique is used to obtain approximate analytical series solution of Brinkmann equation governing the two-dimensional stagnation point flow in a porous medium. Analytical approximate solution of the classical two-dimensional stagnation point flow is obtained as a limiting case. Also, it is shown that the obtained higher order series solutions agree well with the computed numerical solutions.

  6. A numerical inversion of a the Laplace transform solution to radial dispersion in a porous medium.

    USGS Publications Warehouse

    Moench, A.F.; Ogata, A.

    1981-01-01

    A special form of the numerical inversion of the Laplace transform described by Stehfest (1970) is applied to the transformed solution of dispersion in a radial flow system in a porous medium. The inversion is extremely simple to use because the weighting coefficients depend only on the number of terms used in the computation and not upon the transform solution as required by most numerical inversion techniques.-from Authors

  7. Breakage of non-Newtonian character in flow through a porous medium: evidence from numerical simulation.

    PubMed

    Bleyer, J; Coussot, P

    2014-06-01

    We study the flow, through a model two-dimensional porous medium, of Newtonian fluids, power-law fluids, and viscoplastic fluids in the laminar regime and with moderate or dominant effects of the yielding term. A numerical technique able to take properly into account yielding effects in viscoplastic flows without any regularization is used to determine the detailed flow characteristics. We show that as soon as the distance between the disks forming the porous medium is sufficiently small, the velocity field and in particular the distribution function of the velocity of these different fluids in a wide range of flow regimes are similar. Moreover, the volume fraction of fluid at rest is negligible even at low flow rate. Thus the non-Newtonian character of a fluid flowing through such a complex geometry tends to be broken. We suggest that this is due to the fact that in a flow through a channel of rapidly varying cross section, the deformation, and thus the flow field, is imposed on the fluid, a situation that is encountered almost everywhere in a porous medium. These results make it possible to deduce a general expression for Darcy's law of these fluid types and estimate the parameters appearing in this expression.

  8. Oscillation-induced displacement patterns in a two-dimensional porous medium: A lattice Boltzmann study

    NASA Astrophysics Data System (ADS)

    Aursjø, Olav; Knudsen, Henning Arendt; Flekkøy, Eirik G.; Måløy, Knut Jørgen

    2010-08-01

    We present a numerical study of the statistical behavior of a two-phase flow in a two-dimensional porous medium subjected to an oscillatory acceleration transverse to the overall direction of flow. A viscous nonwetting fluid is injected into a porous medium filled with a more viscous wetting fluid. During the whole process sinusoidal oscillations of constant amplitude and frequency accelerates the porous medium sideways, perpendicular to the overall direction of flow. The invasion process displays a transient behavior where the saturation of the defending fluid decreases, before it enters a state of irreducible wetting fluid saturation, where there is no net transport of defending fluid toward the outlet of the system. In this state the distribution of sizes of the remaining clusters are observed to obey a power law with an exponential cutoff. The cutoff cluster size is found to be determined by the flow and oscillatory stimulation parameters. This cutoff size is also shown to be directly related to the extracted amount of defending fluid. Specifically, the results show that the oscillatory acceleration of the system leads to potentially a large increase in extracted wetting fluid.

  9. Coupled consolidation of a porous medium with a cylindrical or a spherical cavity

    NASA Astrophysics Data System (ADS)

    Zhou, Y.; Rajapakse, R. K. N. D.; Graham, J.

    1998-06-01

    This paper presents a theoretical approach to analyse coupled, linear thermoporoelastic fields in a saturated porous medium under radial and spherical symmetry. The governing equations account for compressibility and thermal expansion of constituents, heat sink due to thermal dilatation of water and thermal expansion of the medium, and thermodynamically coupled heat-water flow. It has been reported in the literature that thermodynamically coupled heat-water flows known as thermo-osmosis and thermal filtration have the potential to significantly alter the flow fields in clay-rich barriers in the near field of a underground waste containment scheme. This study presents a mathematical model and examines the effects of thermo-osmosis and thermal-filtration on coupled consolidation fields in a porous medium with a cavity. Analytical solutions of the governing equations are presented in the Laplace transform space. A numerical inversion scheme is used to obtain the time-domain solutions for a cylindrical cavity in a homogeneous or a non-homogeneous medium. A closed form time-domain solution is presented for a spherical cavity in a homogeneous medium. Selected numerical solutions for homogeneous and non-homogeneous media show a significant increase in pore pressure and displacements due to the presence of thermodynamically coupled flows and a negligible influence on temperature.

  10. Boundedness for a 3D chemotaxis-Stokes system with porous medium diffusion and tensor-valued chemotactic sensitivity

    NASA Astrophysics Data System (ADS)

    Wang, Yilong; Li, Xie

    2017-04-01

    This paper deals with the following chemotaxis-Stokes system n_t+u\\cdot nabla n=Δ n^m-nabla \\cdot (nS(x,n,c)\\cdot nabla c), &{}quad xin Ω , t>0, c_t+u\\cdot nabla c=Δ c-nf(c),&{}quad xin Ω , t>0, u_t=Δ u+nabla P+nnabla φ ,&quad xin Ω , t>0,\\ nabla \\cdot u=0,&{}quad xin Ω , t>0. under no-flux boundary conditions in a bounded domain Ω subset R3 with smooth boundary, where m≥ 1, φ in W^{1,∞}(Ω ), f and S are given functions with values in [0, ∞) and R^{3× 3}, respectively. Here S satisfies |S(x,n,c)|7/6, which insures the global existence of bounded weak solution. Our result covers completely and improves the recent result by Wang and Cao (Discrete Contin Dyn Syst Ser B 20:3235-3254, 2015) which asserts, just in the case m=1, the global existence of solutions, but without boundedness, and that by Winkler (Calc Var Partial Differ Equ 54:3789-3828, 2015) which only involves the case of α =0 and requires the convexity of the domain.

  11. Synthesis of functionalized 3D porous graphene using both ionic liquid and SiO2 spheres as "spacers" for high-performance application in supercapacitors.

    PubMed

    Li, Tingting; Li, Na; Liu, Jiawei; Cai, Kai; Foda, Mohamed F; Lei, Xiaomin; Han, Heyou

    2015-01-14

    In this work, a high-capacity supercapacitor material based on functionalized three-dimensional (3D) porous graphene was fabricated by low temperature hydrothermal treatment of graphene oxide (GO) using both ionic liquid (IL) and SiO2 spheres as "spacers". In the synthesis, the introduction of dual "spacers" effectively enlarged the interspace between graphene sheets and suppressed their re-stacking. In addition, the IL also acted as a structure-directing agent playing a crucial role in inducing the formation of unique 3D architectures. Consequently, fast electron/ion transport channels were successfully constructed and numerous oxygen-containing groups on graphene sheets were effectively reserved, which had unique advantages in decreasing ion diffusion resistance and providing additional pseudocapacitance. As expected, the obtained material exhibited superior specific capacitance and rate capability compared to single "spacer" designed electrodes and simultaneously maintained excellent cycling stability. In particular, there was nearly no loss of its initial capacitance after 3000 cycles. In addition, we further assembled a symmetric two-electrode device using the material, which showed outstanding flexibility and low equivalent series resistance (ESR). More importantly, it was capable of yielding a maximum power density of about 13.3 kW kg(-1) with an energy density of about 7.0 W h kg(-1) at a voltage of 1.0 V in 1 M H2SO4 electrolyte. All these impressive results demonstrate that the material obtained by this approach is greatly promising for application in high-performance supercapacitors.

  12. Mathematical modeling of deformation of a porous medium, considering its strengthening due to pore collapse

    SciTech Connect

    Sadovskii, V. M. Sadovskaya, O. V.

    2015-10-28

    Based on the generalized rheological method, the mathematical model describing small deformations of a single-phase porous medium without regard to the effects of a fluid or gas in pores is constructed. The change in resistance of a material to the external mechanical impacts at the moment of pore collapse is taken into account by means of the von Mises–Schleicher strength condition. In order to consider irreversible deformations, alongside with the classical yield conditions by von Mises and Tresca– Saint-Venant, the special condition modeling the plastic loss of stability of a porous skeleton is used. The random nature of the pore size distribution is taken into account. It is shown that the proposed mathematical model satisfies the principles of thermodynamics of irreversible processes. Phenomenological parameters of the model are determined on the basis of the approximate calculation of the problem on quasi-static loading of a cubic periodicity cell with spherical voids. In the framework of the obtained model, the process of propagation of plane longitudinal waves of the compression in a homogenous porous medium, accompanied by the plastic deformation of a skeleton and the collapse of pores, is analyzed.

  13. The estimation of permeability of a porous medium with a generalized pore structure by geometry identification

    NASA Astrophysics Data System (ADS)

    Rezaei Niya, S. M.; Selvadurai, A. P. S.

    2017-03-01

    The paper presents an approach for estimating the permeability of a porous medium that is based on the characteristics of the porous structure. The pressure drop in different fluid flow passages is estimated and these are combined to evaluate the overall reduction. The theory employed is presented and the level of accuracy for different cases is discussed. The successive steps in the solution algorithm are described. The accuracy and computational efficiency of the approach are compared with results obtained from a finite-element-based multiphysics formulation. It is shown that for a comparable accuracy, the computational efficiency of the approach can be two orders of magnitude faster. Finally, the model predictions are examined with conventional relationships that have been reported in the literature and are based on permeability-porosity relationships. It is shown that estimating the permeability of a porous medium using porosity can lead to an order of magnitude error and the expected permeability range in different porosities is presented using 10 000 random structures.

  14. Natural convection heat transfer of nanofluids along a vertical plate embedded in porous medium

    PubMed Central

    2013-01-01

    The unsteady natural convection heat transfer of nanofluid along a vertical plate embedded in porous medium is investigated. The Darcy-Forchheimer model is used to formulate the problem. Thermal conductivity and viscosity models based on a wide range of experimental data of nanofluids and incorporating the velocity-slip effect of the nanoparticle with respect to the base fluid, i.e., Brownian diffusion is used. The effective thermal conductivity of nanofluid in porous media is calculated using copper powder as porous media. The nonlinear governing equations are solved using an unconditionally stable implicit finite difference scheme. In this study, six different types of nanofluids have been compared with respect to the heat transfer enhancement, and the effects of particle concentration, particle size, temperature of the plate, and porosity of the medium on the heat transfer enhancement and skin friction coefficient have been studied in detail. It is found that heat transfer rate increases with the increase in particle concentration up to an optimal level, but on the further increase in particle concentration, the heat transfer rate decreases. For a particular value of particle concentration, small-sized particles enhance the heat transfer rates. On the other hand, skin friction coefficients always increase with the increase in particle concentration and decrease in nanoparticle size. PMID:23391481

  15. Rotationally induced fingering patterns in a two-dimensional heterogeneous porous medium.

    PubMed

    Chen, Ching-Yao; Lin, Ting-Shiang; Miranda, José A

    2016-11-01

    Rotating fluid flows under two-dimensional homogeneous porous media conditions (or in a rotating Hele-Shaw cell) reveal the development of complex interfacial fingering patterns. These pattern-forming structures are characterized by the occurrence of finger competition events, finger pinch-off episodes, as well as by the production of satellite droplets. In this work, we use intensive numerical simulations to investigate how these fully nonlinear pattern growth phenomena are altered by the presence of permeability heterogeneities in the rotating porous medium. This is done by employing a diffuse-interface Darcy-Cahn-Hilliard description of the problem and considering a permeability field presenting a log-Gaussian distribution, characterized by a variance s and a correlation length l. We study how the heterogeneity measures s and l couple to the governing hydrodynamic dimensionless parameters of the problem and introduce important changes on the pattern formation dynamics of the system.

  16. Rotationally induced fingering patterns in a two-dimensional heterogeneous porous medium

    NASA Astrophysics Data System (ADS)

    Chen, Ching-Yao; Lin, Ting-Shiang; Miranda, José A.

    2016-11-01

    Rotating fluid flows under two-dimensional homogeneous porous media conditions (or in a rotating Hele-Shaw cell) reveal the development of complex interfacial fingering patterns. These pattern-forming structures are characterized by the occurrence of finger competition events, finger pinch-off episodes, as well as by the production of satellite droplets. In this work, we use intensive numerical simulations to investigate how these fully nonlinear pattern growth phenomena are altered by the presence of permeability heterogeneities in the rotating porous medium. This is done by employing a diffuse-interface Darcy-Cahn-Hilliard description of the problem and considering a permeability field presenting a log-Gaussian distribution, characterized by a variance s and a correlation length l . We study how the heterogeneity measures s and l couple to the governing hydrodynamic dimensionless parameters of the problem and introduce important changes on the pattern formation dynamics of the system.

  17. Hall effects on peristaltic flow of a Maxwell fluid in a porous medium

    NASA Astrophysics Data System (ADS)

    Hayat, T.; Ali, N.; Asghar, S.

    2007-04-01

    This work is concerned with the peristaltic transport of an incompressible, electrically conducting Maxwell fluid in a planar channel. The flow in the porous space is due to a sinusoidal wave traveling on the channel walls. The Hall effect is taken into account and permeability of porous medium is considered uniform. Modified Darcy's law has been used to model the governing equation. An analytical solution is obtained, which satisfies the momentum equation for the case in which the amplitude ratio is small. The present theoretical model may be considered as mathematical representation to the case of gall bladder and bile duct with stones and dynamics of blood flow in living creatures. Finally, the graphical results are reported and discussed for various values of the physical parameters of interest.

  18. Distribution of flowing fluids in a confined porous medium under microgravity conditions

    NASA Astrophysics Data System (ADS)

    Guo, Boyun; Holder, Donald W.; Carter, Layne

    2004-08-01

    Predicting distribution of flowing fluids in confined porous media under microgravity conditions is vitally important for optimal design of packed bubble column reactors in space stations. Existing correlations have been found inaccurate when applied to microgravity conditions. On the basis of Darcy's law for two-phase flow, a simple mathematical model has been developed in this study. Sensitivity analyses with the model indicate that for a given combination of wetting and nonwetting fluid flow rates, fluid holdups are controlled by relative permeabilities. The effect of gravity on fluid holdup is influenced by the absolute permeability of the porous medium. Fluid distribution is affected by the temperature-dependent fluid properties and wall effect.

  19. Approximate Similarity Solutions to the Boussinesq and the Porous Medium Equations.

    NASA Astrophysics Data System (ADS)

    Telyakovskiy, A. S.

    2003-12-01

    The Boussinesq equation models unconfined groundwater flow under the Dupuit assumpion that the equipotential lines are vertical, making the flowlines horizontal. For certain classes of initial and boundary conditions it is possible to reduce problem to a nonlinear ODE and construct approximate analytical solutions. We extend the approach of Lockington, Parlange, Parlange, and Selker (2000) that constructed quadratic approximate similarity solution for the power-law head boundary condition at the inlet. Our new cubic approximation as the original quadratic approximation preserves the scaling properties of the problem, but it produces much better results. Also, we extend this approach to other types of boundary conditions. Discussed method is rather general and we apply it to the porous medium equation that describes the laminar flow of the polytropic gas through porous media.

  20. Mass transfer and free convection through a porous medium by the presence of a rotating fluid

    NASA Astrophysics Data System (ADS)

    Raptis, A.

    1983-04-01

    An analytical examination of steady, free convective flow and mass transfer through a porous medium bounded by a vertical porous plate in the case of a rotating fluid with a constant angular velocity and a constant temperature at the plate is presented. The fluid is assumed incompressible and viscous, and governing equations are defined for continuity, momentum, energy, and diffusion. Boundary conditions are configured to include the constant heat flux, the species concentration at the plate, and the suction velocity. The primary and secondary velocities were determined for different values of the modified Grashof number, Eckman number, and a permeability parameter. Increases in the Eckman number were accompanied by decreases in the primary velocity, which increased with increases in the permeability parameter or the modified Grashof number. The same was verified for the secondary velocity.

  1. Mathematical Modeling of Magneto Pulsatile Blood Flow Through a Porous Medium with a Heat Source

    NASA Astrophysics Data System (ADS)

    Sharma, B. K.; Sharma, M.; Gaur, R. K.; Mishra, A.

    2015-05-01

    In the present study a mathematical model for the hydro-magnetic non-Newtonian blood flow in the non-Darcy porous medium with a heat source and Joule effect is proposed. A uniform magnetic field acts perpendicular to the porous surface. The governing non-linear partial differential equations have been solved numerically by applying the explicit finite difference Method (FDM). The effects of various parameters such as the Reynolds number, hydro-magnetic parameter, Forchheimer parameter, Darcian parameter, Prandtl number, Eckert number, heat source parameter, Schmidt number on the velocity, temperature and concentration have been examined with the help of graphs. The present study finds its applications in surgical operations, industrial material processing and various heat transfer operations.

  2. Tailored Surface Treatment of 3D Printed Porous Ti6Al4V by Microarc Oxidation for Enhanced Osseointegration via Optimized Bone In-Growth Patterns and Interlocked Bone/Implant Interface.

    PubMed

    Xiu, Peng; Jia, Zhaojun; Lv, Jia; Yin, Chuan; Cheng, Yan; Zhang, Ke; Song, Chunli; Leng, Huijie; Zheng, Yufeng; Cai, Hong; Liu, Zhongjun

    2016-07-20

    3D printed porous titanium (Ti) holds enormous potential for load-bearing orthopedic applications. Although the 3D printing technique has good control over the macro-sturctures of porous Ti, the surface properties that affect tissue response are beyond its control, adding the need for tailored surface treatment to improve its osseointegration capacity. Here, the one step microarc oxidation (MAO) process was applied to a 3D printed porous Ti6Al4V (Ti64) scaffold to endow the scaffold with a homogeneous layer of microporous TiO2 and significant amounts of amorphous calcium-phosphate. Following the treatment, the porous Ti64 scaffolds exhibited a drastically improved apatite forming ability, cyto-compatibility, and alkaline phosphatase activity. In vivo test in a rabbit model showed that the bone in-growth at the untreated scaffold was in a pattern of distance osteogenesis by which bone formed only at the periphery of the scaffold. In contrast, the bone in-growth at the MAO-treated scaffold exhibited a pattern of contact osteogenesis by which bone formed in situ on the entire surface of the scaffold. This pattern of bone in-growth significantly increased bone formation both in and around the scaffold possibly through enhancement of bone formation and disruption of bone remodeling. Moreover, the implant surface of the MAO-treated scaffold interlocked with the bone tissues through the fabricated microporous topographies to generate a stronger bone/implant interface. The increased osteoinetegration strength was further proven by a push out test. MAO exhibits a high efficiency in the enhancement of osteointegration of porous Ti64 via optimizing the patterns of bone in-growth and bone/implant interlocking. Therefore, post-treatment of 3D printed porous Ti64 with MAO technology might open up several possibilities for the development of bioactive customized implants in orthopedic applications.

  3. A model for ion transport during drying of a porous medium

    NASA Astrophysics Data System (ADS)

    Guglielmini, Laura; Gontcharov, Alexandre; Aldykiewicz, Antonio; Stone, Howard

    2007-11-01

    Salt crystallization at the surface or in the body of a porous medium has been recognized as a major mechanism in the deterioration of construction materials and historical monuments. Crystal formations on the surface of bricks, concrete, stones, called efflorescences, lead to fast obsolescence of building and monuments finishing, while crystal growth inside the material, called subflorescences, causes crack formation, which may lead to major structural damages. A number of studies have been devoted to the analysis of crystal growth in an elementary pore and aim at explaining the stress generated by crystallization. From a fluid mechanical point of view the physics of water transport and salt distribution in the porous medium turns out to be quite complex, since it is a function of the pore structure and wettability characteristics, of granule size and of the thermal properties of the material. It also depends on the transient environmental conditions the surface is exposed to and on the effective diffusivity of salt at different saturation conditions. We present here a simple theoretical model of the first phase of the drying process, during which water is uniformly distributed throughout the medium and often efflorescences occurs, which aims at characterizing the physics involved in the process.

  4. An endothelial cultured condition medium embedded porous PLGA scaffold for the enhancement of mouse embryonic stem cell differentiation.

    PubMed

    Li, Ching-Wen; Pan, Wei-Ting; Ju, Jyh-Cherng; Wang, Gou-Jen

    2016-04-12

    In this study, we have developed a microporous poly(lactic-co-glycolic acid) (PLGA) scaffold that combines a continuous release property and a three-dimensional (3D) scaffolding technique for the precise and efficient formation of endothelial cell lineage from embryonic stem cells (ESCs). Eight PLGA scaffolds (14.29%, 16.67%, 20% and 25% concentrations of PLGA solutions) mixed with two crystal sizes of sodium chloride (NaCl) were fabricated by leaching. Then, vascular endothelial cell conditioned medium (ECCM) mixed with gelatin was embedded into the scaffold for culturing of mouse embryonic stem cells (mESCs). The 14.29% PLGA scaffolds fabricated using non-ground NaCl particles (NG-PLGA) and the 25% PLGA containing scaffolds fabricated using ground NaCl particles (G-PLGA) possessed minimum and maximum moisture content and bovine serum albumin (BSA) content properties, respectively. These two groups of scaffolds were used for future experiments in this study. Cell culture results demonstrated that the proposed porous scaffolds without growth factors were sufficient to induce mouse ESCs to differentiate into endothelial-like cells in the early culture stages, and combined with embedded ECCM could provide a long-term inducing system for ESC differentiation.

  5. Improving the -3 dB bandwidth of medium power GaN-based LEDs through periodic micro via-holes for visible light communications

    NASA Astrophysics Data System (ADS)

    Zhou, Zheng; Yan, Bing; Teng, Dongdong; Liu, Lilin; Wang, Gang

    2017-06-01

    Medium power GaN-based light emitting diode (LED) chips with periodic micro via-holes are designed and fabricated. The active area of each chip is 200 μm×800 μm and the diameter of each micro via-hole is 50 μm. For comparison, an LED chip with only one big via-hole (Diameter=86.6 μm) is also fabricated under the same conditions as the control partner. Both kinds of LED chips have an equal effective PN junction area. Experimentally, the LED with periodic via-holes exhibits higher output optical power and the -3 dB modulation bandwidth by about 33% and 48%, respectively, than the LED with only one bigger via-hole. The method of concurrently improving modulation and optical performances of power-type LED chips through periodic micro via-holes take the advantages of easy fabrication, suitable for mass-production.

  6. Dislocation mechanisms and 3D twin architectures generate exceptional strength-ductility-toughness combination in CrCoNi medium-entropy alloy.

    PubMed

    Zhang, Zijiao; Sheng, Hongwei; Wang, Zhangjie; Gludovatz, Bernd; Zhang, Ze; George, Easo P; Yu, Qian; Mao, Scott X; Ritchie, Robert O

    2017-02-20

    Combinations of high strength and ductility are hard to attain in metals. Exceptions include materials exhibiting twinning-induced plasticity. To understand how the strength-ductility trade-off can be defeated, we apply in situ, and aberration-corrected scanning, transmission electron microscopy to examine deformation mechanisms in the medium-entropy alloy CrCoNi that exhibits one of the highest combinations of strength, ductility and toughness on record. Ab initio modelling suggests that it has negative stacking-fault energy at 0K and high propensity for twinning. With deformation we find that a three-dimensional (3D) hierarchical twin network forms from the activation of three twinning systems. This serves a dual function: conventional twin-boundary (TB) strengthening from blockage of dislocations impinging on TBs, coupled with the 3D twin network which offers pathways for dislocation glide along, and cross-slip between, intersecting TB-matrix interfaces. The stable twin architecture is not disrupted by interfacial dislocation glide, serving as a continuous source of strength, ductility and toughness.

  7. Dislocation mechanisms and 3D twin architectures generate exceptional strength-ductility-toughness combination in CrCoNi medium-entropy alloy

    NASA Astrophysics Data System (ADS)

    Zhang, Zijiao; Sheng, Hongwei; Wang, Zhangjie; Gludovatz, Bernd; Zhang, Ze; George, Easo P.; Yu, Qian; Mao, Scott X.; Ritchie, Robert O.

    2017-02-01

    Combinations of high strength and ductility are hard to attain in metals. Exceptions include materials exhibiting twinning-induced plasticity. To understand how the strength-ductility trade-off can be defeated, we apply in situ, and aberration-corrected scanning, transmission electron microscopy to examine deformation mechanisms in the medium-entropy alloy CrCoNi that exhibits one of the highest combinations of strength, ductility and toughness on record. Ab initio modelling suggests that it has negative stacking-fault energy at 0K and high propensity for twinning. With deformation we find that a three-dimensional (3D) hierarchical twin network forms from the activation of three twinning systems. This serves a dual function: conventional twin-boundary (TB) strengthening from blockage of dislocations impinging on TBs, coupled with the 3D twin network which offers pathways for dislocation glide along, and cross-slip between, intersecting TB-matrix interfaces. The stable twin architecture is not disrupted by interfacial dislocation glide, serving as a continuous source of strength, ductility and toughness.

  8. Dislocation mechanisms and 3D twin architectures generate exceptional strength-ductility-toughness combination in CrCoNi medium-entropy alloy

    PubMed Central

    Zhang, Zijiao; Sheng, Hongwei; Wang, Zhangjie; Gludovatz, Bernd; Zhang, Ze; George, Easo P.; Yu, Qian; Mao, Scott X.; Ritchie, Robert O.

    2017-01-01

    Combinations of high strength and ductility are hard to attain in metals. Exceptions include materials exhibiting twinning-induced plasticity. To understand how the strength-ductility trade-off can be defeated, we apply in situ, and aberration-corrected scanning, transmission electron microscopy to examine deformation mechanisms in the medium-entropy alloy CrCoNi that exhibits one of the highest combinations of strength, ductility and toughness on record. Ab initio modelling suggests that it has negative stacking-fault energy at 0K and high propensity for twinning. With deformation we find that a three-dimensional (3D) hierarchical twin network forms from the activation of three twinning systems. This serves a dual function: conventional twin-boundary (TB) strengthening from blockage of dislocations impinging on TBs, coupled with the 3D twin network which offers pathways for dislocation glide along, and cross-slip between, intersecting TB-matrix interfaces. The stable twin architecture is not disrupted by interfacial dislocation glide, serving as a continuous source of strength, ductility and toughness. PMID:28218267

  9. Mathematical model for the peristaltic flow of nanofluid through eccentric tubes comprising porous medium

    NASA Astrophysics Data System (ADS)

    Nadeem, S.; Riaz, Arshad; Ellahi, R.; Akbar, Noreen Sher

    2014-08-01

    Mathematical model for peristaltic flow of nanofluid between eccentric tubes is investigated through a porous medium. Assumptions of long wavelength and low Reynolds number are carried out to observe the intestinal flow. The flow is considered to be unsteady and incompressible. Analytical solutions are evaluated through homotopy perturbation method. The expression of pressure rise is obtained through numerical integration whose data is presented in table. The problems under consideration are made dimensionless to reduce the complication of the analysis and to merge the extra parameters. All the emerging parameters affecting the flow phenomenon are discussed graphically. Trapping bolus scheme is also presented through streamlines for various pertinent quantities.

  10. Numerical solutions for steady thermal convection from a concentrated source in a porous medium

    SciTech Connect

    Hickox, C.E.; Watts, H.A.

    1980-06-01

    Solutions for the steady, axisymmetric velocity and temperature fields associated with a point source of thermal energy in a fluid-saturated porous medium are obtained numerically through use of similarity transformations. The two cases considered are those of a point source located on the lower, insulated boundary of a semi-infinite region and a point source embedded in an infinite region. Numerical results are presented from which complete descriptions of the velocity and temperature fields can be constructed for Rayleigh numbers ranging from 10/sup -3/ to 10/sup 2/.

  11. Ultimate regime of high Rayleigh number convection in a porous medium.

    PubMed

    Hewitt, Duncan R; Neufeld, Jerome A; Lister, John R

    2012-06-01

    Well-resolved direct numerical simulations of 2D Rayleigh-Bénard convection in a porous medium are presented for Rayleigh numbers Ra≤4×10(4) which reveal that, contrary to previous indications, the linear classical scaling for the Nusselt number, Nu~Ra, is attained asymptotically. The flow dynamics are analyzed, and the interior of the vigorously convecting system is shown to be increasingly well described as Ra→∞ by a simple columnar "heat-exchanger" model with a single horizontal wave number k and a linear background temperature field. The numerical results are approximately fitted by k~Ra(0.4).

  12. Magnetohydrodynamic flow of water/ethylene glycol based nanofluids with natural convection through a porous medium

    NASA Astrophysics Data System (ADS)

    Zeeshan, A.; Ellahi, R.; Hassan, M.

    2014-12-01

    In this study, the natural convection boundary layer flow along with inverted cone, magnetic and heat generation on water and ethylene glycol based nanofluids is considered by means of variable wall temperature. Porous medium is also taken into account. The physical problem is first modeled and then the governing equations are transformed into nonlinear ordinary differential equations under the assumptions of the Boussinesq approximation. Analytical solutions of nonlinear coupled equations are obtained by the homotopy analysis method. Correlation of skin friction and heat transfer rate corresponding to active parameters is also presented. Obtained results are illustrated by graphs and tables in order to see the effects of physical parameters.

  13. Prostate cancer xenografts engineered from 3D precision-porous poly(2-hydroxyethyl methacrylate) hydrogels as models for tumorigenesis and dormancy escape

    PubMed Central

    Long, Thomas J.; Sprenger, Cynthia C.; Plymate, Stephen R.; Ratner, Buddy D.

    2014-01-01

    Synthetic biomaterial scaffolds show promise for in vitro and in vivo 3D cancer models. Tumors engineered in biomaterial scaffolds have shown evidence of being more physiologically relevant than some traditional preclinical model systems, and synthetic biomaterials provide the added benefit of defined and consistent microenvironmental control. Here, we examine sphere-templated poly(2-hydroxyethyl methacrylate) (pHEMA) scaffolds as the basis for engineering xenografts from multiple human prostate cancer cell lines. pHEMA scaffolds seeded and pre-cultured with tumorigenic M12 cells prior to implantation generated tumors in athymic nude mice, demonstrating the ability of the scaffolds to be used as a synthetic vehicle for xenograft generation. pHEMA scaffolds seeded with LNCaP C4-2 cells, which require Matrigel or stromal cell support for tumor formation, were poorly tumorigenic up to twelve weeks after implantation even when Matrigel was infused into the scaffold, demonstrating a lack of necessary pro-tumorigenic signaling within the scaffolds. Finally, M12mac25 cells, which are ordinarily rendered non-tumorigenic through the expression of the tumor suppressor insulin-like growth factor binding protein 7 (IGFBP7), displayed a tumorigenic response when implanted within porous pHEMA scaffolds. These M12mac25 tumors showed a significantly higher macrophage infiltration within the scaffolds driven by the foreign body response to the materials. These findings show the potential for this biomaterials-based model system to be used in the study of prostate cancer tumorigenesis and dormancy escape. PMID:24942815

  14. Integrated compartmental model for describing the transport of solute in a fractured porous medium. [FRACPORT

    SciTech Connect

    DeAngelis, D.L.; Yeh, G.T.; Huff, D.D.

    1984-10-01

    This report documents a model, FRACPORT, that simulates the transport of a solute through a fractured porous matrix. The model should be useful in analyzing the possible transport of radionuclides from shallow-land burial sites in humid environments. The use of the model is restricted to transport through saturated zones. The report first discusses the general modeling approach used, which is based on the Integrated Compartmental Method. The basic equations of solute transport are then presented. The model, which assumes a known water velocity field, solves these equations on two different time scales; one related to rapid transport of solute along fractures and the other related to slower transport through the porous matrix. FRACPORT is validated by application to a simple example of fractured porous medium transport that has previously been analyzed by other methods. Then its utility is demonstrated in analyzing more complex cases of pulses of solute into a fractured matrix. The report serves as a user's guide to FRACPORT. A detailed description of data input, along with a listing of input for a sample problem, is provided. 16 references, 18 figures, 3 tables.

  15. Hall Effect on Thermal Instability of Viscoelastic Dusty Fluid in Porous Medium

    NASA Astrophysics Data System (ADS)

    Singh, M.; Gupta, R. K.

    2013-08-01

    The effect of Hall currents and suspended dusty particles on the hydromagnetic stability of a compressible, electrically conducting Rivlin-Ericksen elastico viscous fluid in a porous medium is considered. Following the linearized stability theory and normal mode analysis the dispersion relation is obtained. For the case of stationary convection, Hall currents and suspended particles are found to have destabilizing effects whereas compressibility and magnetic field have stabilizing effects on the system. The medium permeability, however, has stabilizing and destabilizing effects on thermal instability in contrast to its destabilizing effect in the absence of the magnetic field. The critical Rayleigh numbers and the wave numbers of the associated disturbances for the onset of instability as stationary convection are obtained and the behavior of various parameters on critical thermal Rayleigh numbers are depicted graphically. The magnetic field, Hall currents and viscoelasticity parameter are found to introduce oscillatory modes in the systems, which did not exist in the absence of these parameters

  16. Theoretical and experimental investigation of thermohydrologic processes in a partially saturated, fractured porous medium

    SciTech Connect

    Green, R.T.; Manteufel, R.D.; Dodge, F.T.; Svedeman, S.J.

    1993-07-01

    The performance of a geologic repository for high-level nuclear waste will be influenced to a large degree by thermohydrologic phenomena created by the emplacement of heat-generating radioactive waste. The importance of these phenomena is manifest in that they can greatly affect the movement of moisture and the resulting transport of radionuclides from the repository. Thus, these phenomena must be well understood prior to a definitive assessment of a potential repository site. An investigation has been undertaken along three separate avenues of analysis: (i) laboratory experiments, (ii) mathematical models, and (iii) similitude analysis. A summary of accomplishments to date is as follows. (1) A review of the literature on the theory of heat and mass transfer in partially saturated porous medium. (2) A development of the governing conservation and constitutive equations. (3) A development of a dimensionless form of the governing equations. (4) A numerical study of the importance and sensitivity of flow to a set of dimensionless groups. (5) A survey and evaluation of experimental measurement techniques. (6) Execution of laboratory experiments of nonisothermal flow in a porous medium with a simulated fracture.

  17. Approaching Equilibrium: The Evolution of CO2 in a Porous Medium

    NASA Astrophysics Data System (ADS)

    Cohen, Y.; Rothman, D.

    2012-12-01

    Understanding the microscopic mechanisms of mineral weathering rates has motivated studies of dissolution and precipitation for decades. Many applications, including the global carbon cycle and sub- surface carbon dioxide sequestration justify the importance of a full comprehension of the mechanism. The injection of carbon dioxide into a porous medium drives the system into far-from-equilibrium conditions where forces, surface phenomena, and other processes become crucial for the long-term stability of the system. A complete physical picture able to predict the pattern formation and the structure developing within the porous medium is lacking and cannot be associated only with empirical kinetic laws. Here we propose a theoretical model that couples transport, reaction, and the intricate geometry of the rock. The model concerns the different time scales when the system is far from equilibrium and when approaching a steady state. We use analytical theory and numerical simulations to study the short and the long term behavior of the carbon dioxide as it dissolves and precipitates in a fluid-rock system.

  18. Probing ganglia dissolution and mobilization in a water-saturated porous medium using MRI

    SciTech Connect

    Johns, M.L.; Gladden, L.F.

    2000-05-01

    Magnetic resonance imaging (MRI) is used to probe the evolution of geometric characteristics such as the volume, shape, surface area, and cluster size of octanol ganglia trapped in a model porous medium, in this case a packing of spheres, as they dissolve into a mobile aqueous phase. The resulting pore-scale information is used to assess various assumptions used in existing models of the dissolution process. Dissolution of the ganglia was characterized by a reduction in the overall number of ganglia with little effect on the shape and mean of the volume distribution of the ganglia. This apparently anomalous result is explained by dissolution of the ganglia until they reach a critical size, which is dependent on the structure of the pore space, at which point they are mobilized and subsequently removed from the porous medium. The shape of the entrapped ganglia is characterized by a fractal dimension in the range 2.2--2.3, suggesting that models which assume a Euclidean geometry for the entrapped ganglia are appropriate. No significant change in the shape of entrapped ganglia is observed during dissolution. In agreement with the results of earlier workers, most hydrocarbon ganglia exist as singlets within the pore structure.

  19. Physical Properties and Behavior of a Dense, Viscous Brine in Porous Medium Systems

    NASA Astrophysics Data System (ADS)

    Murphy, L. M.; Johnson, D. N.; Pedit, J. A.; Farthing, M. W.; Miller, C. T.

    2006-12-01

    Dense nonaqueous phase liquids (DNAPLs) are both a long-term source of groundwater contamination and a health risk to humans at low concentrations. The challenges of DNAPL remediation have led to the study of a novel mobilization-based strategy known as Brine-Based Remediation Technology (BBRT), which utilizes a dense brine to control the mobilized contaminant phase. Due to the unique application of such brines in the subsurface, there are many open issues addressing the behavior and properties of these brines in porous medium systems. To begin to address some of the open issues, a three-dimensional laboratory experiment was performed to monitor in situ density during brine barrier establishment and removal. Using a calcium bromide solution, this experiment demonstrated that a brine barrier density could be effectively established, sufficiently maintained to support common DNAPLs, and substantially recovered through active flushing. This experiment also demonstrated that highly viscous brines mound around injection wells, suggesting that an understanding of the effects of viscosity is required in flow and transport modeling. Since many flow and transport models fail to account for the physical properties of these brines, constitutive relations describing density and viscosity as a function of solute concentration were defined and incorporated into SUTRA, a model for saturated-unsaturated, variable-density groundwater flow with solute transport, to predict flow and transport of calcium bromide in a porous medium system.

  20. An improved method for measuring the compactness factor in a porous medium

    SciTech Connect

    Murphy, T.J.; Bowman, W.J.

    1996-12-31

    The motivation for the current research was to determine if reducing the thickness of the wire screens in a stacked-screen regenerator, thereby reducing the dead volume, could be accomplished without adversely affecting the compactness factor (j{sub H}/f). During the course of this research an improved method for determining the heat transfer and pressure drop characteristics of a porous medium regenerator was developed. The focus of this paper is to describe this improved approach. The approach integrates experimental data/data reduction with a numerical model to study the flow of helium through a series of stacked, wire-screen regenerators of different geometries and a range of Reynolds numbers typically found in the operation of Stirling cycle cryocoolers. The experimental component is based on the classical transient, step-change temperature technique. The data reduction employs MATLAB to filter, parameterize, and assemble a data file for use with a FORTRAN program. The numerical model is an explicit, finite-difference scheme for incompressible flow in a one-dimensional porous medium. The model includes: (1) the measured inlet temperature trace rather than an idealized one, (2) the important effect of energy exchange between the gas and the tube surrounding the regenerator matrix, and (3) an algorithm for choosing the heat transfer coefficient based on the sponge effect delay time.

  1. Laboratory investigations of the physics of steam flow in a porous medium

    USGS Publications Warehouse

    Herkelrath, W.N.; Moench, A.F.

    1982-01-01

    Experiments were carried out in the laboratory to test a theory of transient flow of pure steam in a uniform porous medium. This theory is used extensively in modeling pressure-transient behavior in vapor-dominated geothermal systems. Transient, superheated steam-flow experiments were run by bringing a cylinder of porous material to a uniform initial pressure, and then making a step increase in pressure at one end of the sample, while monitoring the pressure-transient breakthrough at the other end. It was found in experiments run at 100?, 125?, and 146?C that the time required for steam-pressure transients to propagate through an unconsolidated material containing sand, silt, and clay was 10 to 25 times longer than predicted by theory. It is hypothesized that the delay in the steam-pressure transient was caused by adsorption of steam in the porous sample. In order to account for steam adsorption, a sink term was included in the conservation of mass equation. In addition, energy transfer in the system has to be considered because latent heat is released when steam adsorption occurs, increasing the sample temperature by as much as 10?C. Finally, it was recognized that the steam pressure was a function of both the temperature and the amount of adsorption in the sample. For simplicity, this function was assumed to be in equilibrium adsorption isotherm, which was determined by experiment. By solving the modified mass and energy equations numerically, subject to the empirical adsorption isotherm relationship, excellent theoretical simulation of the experiments was achieved. The experiments support the hypothesis that adsorption of steam can strongly influence steam pressure-transient behavior in porous media; the results suggest that the modified steam-flow theory, which includes steam adsorption terms, should be used in modeling steam flow in vapor-dominated geothermal systems.

  2. Two-dimensional network simulation of diffusion driven coarsening of foam inside a porous medium

    SciTech Connect

    Cohen, D.; Patzek, T.W.; Radke, C.J.

    1996-04-01

    In order to use foams in subsurface applications, it is necessary to understand their stability in porous media. Diffusion driven coarsening of a stationary or nonflowing foam in a porous medium results in changing gas pressures and a coarsening of the foam texture. A two-dimensional network simulation has been created that predicts the behavior of foam in a porous medium by physically specifying the locations of all the lamellae in the system and by solving the complete set of Young-Laplace and diffusion equations. An hourglass approximates the shape of the pores, and the pore walls are considered to be highly water wet. A singularity arises in the system of differential algebraic equations due to the curvature of the pore walls. This singularity is a signal that the system must undergo oscillations or sudden lamellar rearrangements before the diffusion process can continue. Newton-Raphson iteration is used along with Keller`s method of arc-length continuation and a new jump resolution technique to locate and resolve bifurcations in the system of coupled lamellae. Gas bubbles in pore throats are regions of encapsulated pressure. As gas is released from these bubbles during diffusion, the pressure of the bubbles in the pore bodies increases. When the pressure increase is scaled by the characteristic Young-Laplace pressure, the equilibrium time for the diffusion process is scaled by the ratio of the square of the characteristic length to the gas diffusivity and two dimensionless groups. One describes the ease with which gas can diffuse through a lamella, the second represents the amount of gas encapsulated within the pore throats initially. Given this scaling, the resulting plots of pressure versus time and normalized lamellae positions versus time are universal for all system sizes and characteristics. This is true as long as the initial lamella distribution is the same in each case.

  3. Instability of uniform gas flow within liquid-saturated porous medium

    NASA Astrophysics Data System (ADS)

    Tsiberkin, Kirill

    2014-05-01

    Problem of flow instability in porous media are important for applied fields like mining, water supply, etc. There is a fundamental interest to mechanisms are influence on flow too. E.g., a viscous fingering is typical phenomenon of displacement processes in porous medium [1,2]. The instability of gas flow in liquid-saturated domain have no wide studies but it can make significant influence on heat and mass transport. If the one phase have a high saturation, the other phase will form the droplets are break and captured within pores due to the capillary forces [2-4]. It is possible to neglect the capillarity if the saturation of both fluids exceed a percolation thresholds [5,6]. We consider an infinite flat layer of uniform porous medium is saturated with gas and liquid have close saturation. Its upper boundary is impermeable for liquid phase and gas can pass freely through the border, and the down boundary is permeable for both phases. The temperature and pressure are fixed at the top while their gradients are fixed at the bottom side. Neglecting the capillarity, gas solubility, liquid evaporation and any phase transitions, we obtain a steady solution and study its' stability. The governing parameter of the flow is α = αgAPe, αg = (ρwCg )/(ρsCs), A = ρstatvstat (1) where Pe is the thermal Peclet number determines a ratio between convective and conductive heat transfer, αg is ratio of thermal capacities of fluid and matrix, and A is determined by gas density and velocity in the steady state. Analyzing the perturbations, we found that a long-wave instability realizes in the system. The critical value of parameter is: αc = a1 + k2a2 + O(ρg/ρw), (2) where a1,a2 are positive coefficients are calculated using thermal perturbations combinations and k is wave number along horizontal direction. The minimal αc equals 2.47, and it correspond the critical Peclet number near 200 in the methane-water system. An error of the dependence is of order of gas to water

  4. Gas and solute diffusion in partially saturated porous media: Percolation theory and Effective Medium Approximation compared with lattice Boltzmann simulations

    NASA Astrophysics Data System (ADS)

    Ghanbarian, Behzad; Daigle, Hugh; Hunt, Allen G.; Ewing, Robert P.; Sahimi, Muhammad

    2015-01-01

    Understanding and accurate prediction of gas or liquid phase (solute) diffusion are essential to accurate prediction of contaminant transport in partially saturated porous media. In this study, we propose analytical equations, using concepts from percolation theory and the Effective Medium Approximation (EMA) to model the saturation dependence of both gas and solute diffusion in porous media. The predictions of our theoretical approach agree well with the results of nine lattice Boltzmann simulations. We find that the universal quadratic scaling predicted by percolation theory, combined with the universal linear scaling predicted by the EMA, describes diffusion in porous media with both relatively broad and extremely narrow pore size distributions.

  5. The flow of a foam in a two-dimensional porous medium

    NASA Astrophysics Data System (ADS)

    Géraud, Baudouin; Jones, Siân. A.; Cantat, Isabelle; Dollet, Benjamin; Méheust, Yves

    2016-02-01

    Foams have been used for decades as displacing fluids for enhanced oil recovery and aquifer remediation, and more recently, for remediation of the vadose zone, in which case foams carry chemical amendments. Foams are better injection fluids than aqueous solutions due to their low sensitivity to gravity and because they are less sensitive to permeability heterogeneities, thus allowing a more uniform sweep. The latter aspect results from their peculiar rheology, whose understanding motivates the present study. We investigate foam flow through a two-dimensional porous medium consisting of circular obstacles positioned randomly in a horizontal transparent Hele-Shaw cell. The local foam structure is recorded in situ, which provides a measure of the spatial distribution of bubble velocities and sizes at regular time intervals. The flow exhibits a rich phenomenology including preferential flow paths and local flow nonstationarity (intermittency) despite the imposed permanent global flow rate. Moreover, the medium selects the bubble size distribution through lamella division-triggered bubble fragmentation. Varying the mean bubble size of the injected foam, its water content, and mean velocity, we characterize those processes systematically. In particular, we measure the spatial evolution of the distribution of bubble areas, and infer the efficiency of bubble fragmentation depending on the various control parameters. We furthermore show that the distributions of bubble sizes and velocities are correlated. This study sheds new light on the local rheology of foams in porous media and opens the way toward quantitative characterization of the relationship between medium geometry and foam flow properties. It also suggests that large-scale models of foam flows in the subsurface should account for the correlation between bubble sizes and velocities.

  6. Velocity and stress jump conditions between a porous medium and a fluid

    NASA Astrophysics Data System (ADS)

    Valdés-Parada, Francisco J.; Aguilar-Madera, Carlos G.; Ochoa-Tapia, J. Alberto; Goyeau, Benoît

    2013-12-01

    Modeling transport phenomena in hierarchical systems can be carried out by either a one domain approach or a two domain approach. The first one involves assuming the system as a pseudo-continuum and is expressed in terms of position-dependent effective medium coefficients. In the two domain approach, the differential equations have position-independent coefficients but require accounting for the corresponding boundary conditions that couple the equations between each homogeneous region. For momentum transport between a porous medium and a fluid, stress boundary conditions have been derived in terms of a jump coefficient that needs to be predicted within a two-domain approach formulation. However, continuity of the velocity is postulated at the dividing surface. In this work, we propose a methodology for the derivation of boundary conditions for both the velocity and the stress. These conditions are expressed in terms of jump coefficients that are computed from the solution of an ancillary macroscopic closure problem. This problem accounts for the deviations from the one and two domain approaches. From the closure problem solution we were also able to determine the position at which the jump conditions should be applied, i.e., the dividing surface position. In addition, we used this methodology adopting the assumptions proposed by Ochoa-Tapia and Whitaker as well as those by Beavers and Joseph. We found that any version of the two domain approach was in agreement with the one domain approach in the bulk of the porous medium and the fluid. However, the same is not true for the process of capturing the essential information of the inter-region.

  7. Boundary Layer Flow Past a Stretching Surface in a Porous Medium Saturated by a Nanofluid: Brinkman-Forchheimer Model

    PubMed Central

    Khan, Waqar A.; Pop, Ioan M.

    2012-01-01

    In this study, the steady forced convection flow and heat transfer due to an impermeable stretching surface in a porous medium saturated with a nanofluid are investigated numerically. The Brinkman-Forchheimer model is used for the momentum equations (porous medium), whereas, Bongiorno’s model is used for the nanofluid. Uniform temperature and nanofluid volume fraction are assumed at the surface. The boundary layer equations are transformed to ordinary differential equations in terms of the governing parameters including Prandtl and Lewis numbers, viscosity ratio, porous medium, Brownian motion and thermophoresis parameters. Numerical results for the velocity, temperature and concentration profiles, as well as for the reduced Nusselt and Sherwood numbers are obtained and presented graphically. PMID:23077541

  8. Oxygen Transfer in a Fluctuating Capillary Fringe: Impact of Porous Medium Heterogeneity

    NASA Astrophysics Data System (ADS)

    Haberer, C.; Rolle, M.; Cirpka, O. A.; Grathwohl, P.

    2013-12-01

    Mass transfer of oxygen from the atmosphere, across the capillary fringe, to anoxic groundwater is of primary importance for many biogeochemical processes affecting groundwater quality. The controlling mechanisms for oxygen transfer across the capillary fringe are the diffusive/dispersive transport as well as mass exchange between entrapped air and groundwater. In addition, the presence of physical heterogeneity in the porous medium may strongly affect the oxygen fluxes. We performed quasi two-dimensional flow-through experiments at the laboratory bench-scale to study the effect of a coarse-material inclusion, located in proximity of the water table, on flow and oxygen transfer in the capillary fringe. Flow and transport were monitored under both steady-state and transient flow conditions, the latter obtained by fluctuating the water table. We visually inspected the complex flow field using a dye tracer solution, measured vertical oxygen profiles across the capillary fringe at high spatial resolution, and determined oxygen fluxes in the effluent of the flow-through chamber. Our results show that the coarse-material inclusion significantly affected oxygen transfer during the different phases of the experiments. At steady state, the oxygen flux across the unsaturated/saturated interface was considerably enhanced due to flow focusing in the fully water-saturated coarse lens. During drainage, the capillary barrier effect prevented water to drain from the fine material overlying the coarse lens. The entrapped oxygen-rich aqueous phase contributed to the total amount of oxygen supplied to the system when the water table was raised back to its initial level. In case of imbibition, also pronounced entrapment of air occurred in the coarse lens, causing oxygen to partition between the aqueous and gaseous phases. Thus, we found that oxygen transfer across the capillary fringe was significantly enhanced by the coarse-material inclusion due to flow focusing, the capillary

  9. Laminar film condensation along a vertical plate embedded in an anisotropic porous medium with oblique principal axes

    NASA Astrophysics Data System (ADS)

    Degan, Gérard; Sanya, Arthur; Akowanou, Christian

    2016-10-01

    This work analytically investigates the problem of steady film condensation along a vertical surface embedded in an anisotropic porous medium filled with a dry saturated vapor. The porous medium is anisotropic in permeability whose principal axes are oriented in a direction which is oblique to the gravity vector. On the basis of the generalized Darcy's law and within the boundary layer approximations, similar solutions have been obtained for the temperature and flow patterns in the condensate. Moreover, closed form solutions for the boundary layer thickness and heat transfer rate have been obtained in terms of the governing parameters of the problem.

  10. Modeling tree water flow as an unsaturated flow through a porous medium.

    PubMed

    Aumann, Craig A; Ford, E David

    2002-12-21

    The electric circuit analogy has had a profound influence on how tree physiologists measure, model and think about tree water flow. For example, previous models that attempt to account for changes in saturation use the electric circuit analogy to define capacitance as the change in saturation per change in pressure. Given that capacitance is constant, this relationship implies that subjecting a block of wood to a pressure of -2.5 MPa for 2 min results in the same change in saturation as subjecting the same block to the same pressure for 2 days. Given the definition of capacitance, it is unclear how the electric circuit analogy could be used to predict changes in saturation separately from changes in pressure. The inadequacies in the electric circuit analogy discussed in this paper necessitate a new theory of tree water flow that recognizes the sapwood as being a porous medium and explicitly deals with the full implications of the unsaturated flow occurring in the sapwood. The theory proposed in this paper combines the Cohesion theory with a mathematical theory of multiphase flow through porous media. Based on this theory, both saturated and unsaturated tree water flow models are presented. Previous partial differential equation models of tree water flow based on the electric circuit analogy are shown to be mathematically equivalent to the model of saturated porous flow. The unsaturated model of tree water flow explicitly models the pressure profile and the rates of change in saturation and specific interfacial area (a measure of how the water in the unsaturated sapwood is partitioned between mobile and immobile components). The unsaturated model highlights the differences between saturated and unsaturated flow and the need to measure the variables governing tree water flow at higher spatial and temporal resolutions.

  11. Can mineral precipitation reduce the breakthrough time in dissolving porous medium?

    NASA Astrophysics Data System (ADS)

    Budek, Agnieszka; Szymczak, Piotr

    2015-04-01

    We investigate the chemical erosion of porous media using a 2D network model in which the system is represented as a series of interconnected pipes. We consider a system with two coupled reactions involving dissolution of a solid component and precipitation of dissolution products, which results in the overall change of pore diameters. Importantly, the topology of the network is allowed to change dynamically during the simulation: as the diameters of the eroding pores become comparable with the interpore distances, the pores are joined together, thus changing the interconnections within the network. With this model, we investigate different growth regimes in an evolving porous medium, identifying the mechanisms responsible for the emergence of specific patterns. We study the change of permeability of the system in time. The crucial parameter here is the ratio of dissolution to precipitation reaction rates. Depending on its value, the permeability either increases, decreases or oscillates in time. Finally, we consider practically important problem of finding an optimum reactions rates that give a maximum increase in permeability for a given amount of dissolving reactant. Somewhat paradoxically, we find that precipitation can, for a particular range of parameters, make the dissolution more efficient by focusing it in localized regions.

  12. Micromorphic homogenization of a porous medium: elastic behavior and quasi-brittle damage

    NASA Astrophysics Data System (ADS)

    Hütter, Geralf; Mühlich, Uwe; Kuna, Meinhard

    2015-11-01

    Today it is well known that the classical Cauchy continuum theory is insufficient to describe the deformation behavior of solids if gradients occur over distances which are comparable to the microstructure of the material. This becomes crucial e.g., for small specimens or during localization of deformation induced by material degradation (damage). Higher-order continuum approaches like micromorphic theories are established to address such problems. However, such theories require the formulation of respective constitutive laws, which account for the microstructural interactions. Especially in damage mechanics such laws are mostly formulated in a purely heuristic way, which leads to physical and numerical problems. In the present contribution, the fully micromorphic constitutive law for a porous medium is obtained in closed form by homogenization based on the minimal boundary conditions concept. It is shown that this model describes size effects of porous media like foams adequately. The model is extended toward quasi-brittle damage overcoming the physical and numerical limitations of purely heuristic approaches.

  13. A one-domain approach for modeling and simulation of free fluid over a porous medium

    NASA Astrophysics Data System (ADS)

    Chen, Huangxin; Wang, Xiao-Ping

    2014-02-01

    We propose a one-domain approach based on the Brinkman model for the modeling and simulation of the transport phenomenon between free fluid and a porous medium. A thin transition layer is introduced between the free fluid region and the porous media region, across which the porosity and permeability undergo a rapid but continuous change. We study the behavior of the solution to the one-domain model analytically and numerically. Using the method of matched asymptotic expansion, we recover the Beavers-Joseph-Saffman (BJS) interface condition as the thickness of the transition layer goes to zero. We also calculate the error estimates between the leading order solution of the one-domain model and the standard Darcy-Stokes model of two-domain model with BJS condition. Numerical methods are developed for both the one-domain model and the two-domain model. Numerical results are presented to support the analytical results, thereby justifying the one-domain model as a good approximation to the two domain Stokes-Darcy model.

  14. Identification of the Permeability Field of Porous Medium from the Injection of Passive Tracer

    SciTech Connect

    Zhan, Lang; Yortsos, Y.C.

    1999-10-18

    In this paper, a method was proposed which focused on the question, namely on how to invert data on arrival times at various (and numerous) points in the porous medium to map the permeability field. The method, elements of which were briefly described in (9), is based on a direct inversion of the data, as will be described below , rather than on the optimization of initial random (or partly constrained) guesses of the permeability field, to match the available data, as typically done in the analogous problem of pressure transients. The direct inversion is based on two conditions, that Darcy's law for single-phase flow in porous media is valid, and that dispersion of the concentration of the injected tracer is negligible. While the former is a well-accepted premise, the latter depends on injection and field conditions, and may not necessarily apply in all cases. Based on these conditions, we formulate a nonlinear boundary value problem, the coefficients of which depend on the experimental arrival time data.

  15. A Newton-Krylov solution to the porous medium equations in the agree code

    SciTech Connect

    Ward, A. M.; Seker, V.; Xu, Y.; Downar, T. J.

    2012-07-01

    In order to improve the convergence of the AGREE code for porous medium, a Newton-Krylov solver was developed for steady state problems. The current three-equation system was expanded and then coupled using Newton's Method. Theoretical behavior predicts second order convergence, while actual behavior was highly nonlinear. The discontinuous derivatives found in both closure and empirical relationships prevented true second order convergence. Agreement between the current solution and new Exact Newton solution was well below the convergence criteria. While convergence time did not dramatically decrease, the required number of outer iterations was reduced by approximately an order of magnitude. GMRES was also used to solve problem, where ILU without fill-in was used to precondition the iterative solver, and the performance was slightly slower than the direct solution. (authors)

  16. A numerical model of controlled bioinduced mineralization in a porous medium to prevent corrosion

    NASA Astrophysics Data System (ADS)

    Afanasyev, Michael; van Paassen, Leon; Heimovaara, Timo

    2013-04-01

    This paper presents a numerical model of controlled bioinduced mineralization in a porous medium as a possible corrosion protection mechanism. Corrosion is a significant economic problem - recent reports evaluate the annual cost of metal corrosion as 3-4% of the gross domestic product (GDP), in both developed and developing countries. Corrosion control methods currently used are costly and unsustainable as they require the use of larger volumes of materials, hazardous chemicals and regular inspections. As an alternative corrosion control method, bioinduced deposition of protective mineral layers has been proposed. Bioinduced precipitation of calcite has already been investigated for CO2 geological sequestration and soil improvement. To our knowledge, though, no numerical study of biomineralization for corrosion protection has been described yet. Our model includes three phases - solid, biofilm and mobile water. In the latter the reactive elements are dissolved, which are involved in the precipitation and the biofilm growth. The equations that describe the pore water flow, chemical reactions in the mobile water, consumption of substrate and expulsion of metabolic products by the biofilm are briefly presented. Also, the changes in porosity and permeability of the porous medium through biofilm growth and solids precipitation are included. Our main assumptions are that the biofilm is uniform, has a constant density and composition, that all chemical reactions except for substrate consumption occur in the mobile water, and that the precipitates are uniformly distributed on the surface of the solids. We validate the model with simple analytical solutions and against experimental data. The metabolism of the micro-organisms introduces changes in the physical and chemical characteristics of the environment, such as concentrations of chemicals and pH levels. As an extension to the model, we couple these changes to the rates of biofilm growth and precipitation rates. The

  17. Breaking of non-Newtonian character in flows through a porous medium.

    PubMed

    Chevalier, T; Rodts, S; Chateau, X; Chevalier, C; Coussot, P

    2014-02-01

    From NMR measurements we show that the velocity field of a yield stress fluid flowing through a disordered well-connected porous medium is very close to that for a Newtonian fluid. In particular, it is shown that no arrested regions exist even at very low velocities, for which the solid regime is expected to be dominant. This suggests that these results obtained for strongly nonlinear fluid can be extrapolated to any nonlinear fluid. We deduce a generalized form of Darcy's law for such materials and provide insight into the physical origin of the coefficients involved in this expression, which are shown to be moments of the second invariant of the strain rate tensor.

  18. Darcy Flow in a Wavy Channel Filled with a Porous Medium

    SciTech Connect

    Gray, Donald D; Ogretim, Egemen; Bromhal, Grant S

    2013-05-17

    Flow in channels bounded by wavy or corrugated walls is of interest in both technological and geological contexts. This paper presents an analytical solution for the steady Darcy flow of an incompressible fluid through a homogeneous, isotropic porous medium filling a channel bounded by symmetric wavy walls. This packed channel may represent an idealized packed fracture, a situation which is of interest as a potential pathway for the leakage of carbon dioxide from a geological sequestration site. The channel walls change from parallel planes, to small amplitude sine waves, to large amplitude nonsinusoidal waves as certain parameters are increased. The direction of gravity is arbitrary. A plot of piezometric head against distance in the direction of mean flow changes from a straight line for parallel planes to a series of steeply sloping sections in the reaches of small aperture alternating with nearly constant sections in the large aperture bulges. Expressions are given for the stream function, specific discharge, piezometric head, and pressure.

  19. Transient, radial temperature distribution in a porous medium during fluid injection

    SciTech Connect

    Dunn, J.C.; Nilson, R.H.

    1982-01-01

    Analytical and numerical solutions are presented for the transient, radial temperature distribution in a porous medium which is subjected to a constant-rate injection of an incompressible fluid from a wellbore. The formulation includes energy transfer by conduction and convection, and the Danckwerts boundary condition is applied at the finite-radius wellbore. At late times, the numerical solutions approach a self-similar form which can be described in terms of the incomplete Gamma function. In typical petroleum and geothermal applications, convergence to the asymptotic similarity solutions occurs on a time scale of roughly one hour. The results are generally applicable to a broad range of convection-diffusion phenomena which are best described in radial coordinates.

  20. Natural convection on a vertical plate in a saturated porous medium with internal heat generation

    NASA Astrophysics Data System (ADS)

    Guedda, M.; Sriti, M.; Achemlal, D.

    2014-08-01

    The main goal of this paper is to re-exam a class of exact solutions for the two-dimensional free convection boundary layers induced by a heated vertical plate embedded in a saturated porous medium with an exponential decaying heat generation. The temperature distribution of the plate has been assumed to vary as a power of the axial coordinate measured from the leading edge of the plate and subjected to an applied lateral mass flux. The boundary layer equations are solved analytically and numerically using a fifth-order Runge-Kutta scheme coupled with the shooting iteration method. As for the classical problem without internal heat generation, it is proved that multiple (unbounded) solutions arise for any and for any suction/injection parameter. For such solutions, the asymptotic behavior as the similarity variable approaches infinity is determined.

  1. Effects of a random porosity model on double diffusive natural convection in a porous medium enclosure

    SciTech Connect

    Fu, W.S.; Ke, W.W.

    2000-01-01

    A double diffusive natural convection in a rectangular enclosure filled with porous medium is investigated numerically. The distribution of porosity is based upon the random porosity model. The Darcy-Brinkman-Forchheimer model is used and the factors of heat flux, mean porosity and standard deviation are taken into consideration. The SIMPLEC method with iterative processes is adopted to solve the governing equations. The effects of the random porosity model on the distributions of local Nusselt number are remarkable and the variations of the local Nusselt number become disordered. The contribution of latent heat transfer to the total heat transfer of the high Rayleigh number is larger than that of the low Rayleigh number and the variations of the latent heat transfer are not in order.

  2. Thermosolutal instability of a radiating partially-ionized plasma in a porous medium

    NASA Astrophysics Data System (ADS)

    Opara, F. E.

    1994-03-01

    The thermosolutal instability of a radiating two-component plasma, in a porous medium in the presence of a uniform vertical magnetic field, is examined with respect to the effects of collision frequency and radiative transfer. A combination of the Bestman and Chandrasekar methods is used to solve the eigenvalue problem with two-dimensional disturbances for the case of stationary convection. Radiation present on the onset of instability is found to have a destabilizing effect for even a very small radiation parameter, of the order alpha (0.1); concentration gradient on the other hand has a stabilizing effect on the system. The effect of collision on the onset of stationary cells diminished for the optical thin non-grey plasma-near equilibrium. This is of paramount importance in cosmic ray physics, as the interaction between the ionized and neutral gas components represents a state which often exists in the universe.

  3. Modeling and Analysis of Unsteady Axisymmetric Squeezing Fluid Flow through Porous Medium Channel with Slip Boundary

    PubMed Central

    Qayyum, Mubashir; Khan, Hamid; Rahim, M. Tariq; Ullah, Inayat

    2015-01-01

    The aim of this article is to model and analyze an unsteady axisymmetric flow of non-conducting, Newtonian fluid squeezed between two circular plates passing through porous medium channel with slip boundary condition. A single fourth order nonlinear ordinary differential equation is obtained using similarity transformation. The resulting boundary value problem is solved using Homotopy Perturbation Method (HPM) and fourth order Explicit Runge Kutta Method (RK4). Convergence of HPM solution is verified by obtaining various order approximate solutions along with absolute residuals. Validity of HPM solution is confirmed by comparing analytical and numerical solutions. Furthermore, the effects of various dimensionless parameters on the longitudinal and normal velocity profiles are studied graphically. PMID:25738864

  4. Application of MSOR iteration with Newton scheme for solutions of 1D nonlinear porous medium equations

    NASA Astrophysics Data System (ADS)

    Chew, J. V. L.; Sulaiman, J.

    2016-06-01

    This paper considers Newton-MSOR iterative method for solving 1D nonlinear porous medium equation (PME). The basic concept of proposed iterative method is derived from a combination of one step nonlinear iterative method which known as Newton method with Modified Successive Over Relaxation (MSOR) method. The reliability of Newton-MSOR to obtain approximate solution for several PME problems is compared with Newton-Gauss-Seidel (Newton-GS) and Newton-Successive Over Relaxation (Newton-SOR). In this paper, the formulation and implementation of these three iterative methods have also been presented. From four examples of PME problems, numerical results showed that Newton-MSOR method requires lesser number of iterations and computational time as compared with Newton-GS and Newton-SOR methods.

  5. Experimental and Numerical Analysis of Air Trapping in a Porous Medium with Coarse Textured Inclusions

    NASA Astrophysics Data System (ADS)

    Szymańska, Paulina; Tisler, Witold; Schütz, Cindi; Szymkiewicz, Adam; Neuweiler, Insa; Helmig, Rainer

    2016-12-01

    The paper presents a 2D upward infiltration experiment performed on a model porous medium consisting of fine sand background with two inclusions made of coarser sands. The purpose of the experiment was to investigate the effects of structural air trapping, which occurs during infiltration as a result of heterogeneous material structure. The experiment shows that a significant amount of air becomes trapped in each of the inclusions. Numerical simulations were carried out using the two-phase water-air flow model and the Richards equation. The experimental results can be reproduced with good accuracy only using a two-phase flow model, which accounts for both structural and pore-scale trapping. On the other hand, the Richards equation was not able to represent the structural trapping caused by material heterogeneity.

  6. Modeling of seismic field in porous medium:Simulation study of single pore and pore ensemble effects

    NASA Astrophysics Data System (ADS)

    Shatskaya, A. A.; Nemirovich-Danchenko, M. M.; Terre, D. A.

    2015-11-01

    The article considers the effect of porous media on elastic wave field. Based on numerical modeling, diffraction pattern of the wave propagating through a single pore in carbonates has been produced. Matrix properties (calcite and dolomite) and fluid (water) are modeled based on thin core section image. The qualitative comparison with the available computational data has been performed. Provided that ensemble of pores is involved, the effect of porous medium on seismic field has been studied. For comparison with experimental data the model of porous sintered aluminum Al-6061 has been considered. The processing of numerical modeling results made it possible to estimate average velocities in the model of porous aluminum and compare them with physical modeling data. The provided estimates have indicated qualitative (single pore) and quantitative (ensemble of pores) correlation of simulation and experiment results.

  7. Porous medium convection at large Rayleigh number: Studies of coherent structure, transport, and reduced dynamics

    NASA Astrophysics Data System (ADS)

    Wen, Baole

    Buoyancy-driven convection in fluid-saturated porous media is a key environmental and technological process, with applications ranging from carbon dioxide storage in terrestrial aquifers to the design of compact heat exchangers. Porous medium convection is also a paradigm for forced-dissipative infinite-dimensional dynamical systems, exhibiting spatiotemporally chaotic dynamics if not "true" turbulence. The objective of this dissertation research is to quantitatively characterize the dynamics and heat transport in two-dimensional horizontal and inclined porous medium convection between isothermal plane parallel boundaries at asymptotically large values of the Rayleigh number Ra by investigating the emergent, quasi-coherent flow. This investigation employs a complement of direct numerical simulations (DNS), secondary stability and dynamical systems theory, and variational analysis. The DNS confirm the remarkable tendency for the interior flow to self-organize into closely-spaced columnar plumes at sufficiently large Ra (up to Ra ≃ 105), with more complex spatiotemporal features being confined to boundary layers near the heated and cooled walls. The relatively simple form of the interior flow motivates investigation of unstable steady and time-periodic convective states at large Ra as a function of the domain aspect ratio L. To gain insight into the development of spatiotemporally chaotic convection, the (secondary) stability of these fully nonlinear states to small-amplitude disturbances is investigated using a spatial Floquet analysis. The results indicate that there exist two distinct modes of instability at large Ra: a bulk instability mode and a wall instability mode. The former usually is excited by long-wavelength disturbances and is generally much weaker than the latter. DNS, strategically initialized to investigate the fully nonlinear evolution of the most dangerous secondary instability modes, suggest that the (long time) mean inter-plume spacing in

  8. On the role of the pore filling medium in photoluminescence from photochemically etched porous silicon

    NASA Astrophysics Data System (ADS)

    Kolasinski, Kurt W.; Barnard, John C.; Ganguly, Santanu; Koker, Lynne; Wellner, Anja; Aindow, Mark; Palmer, Richard E.; Field, Christian N.; Hamley, Paul A.; Poliakoff, Martyn

    2000-09-01

    Porous silicon thin films created under laser illumination in fluoride solutions without biasing have been studied by a variety of techniques to investigate the film structure and photoluminescence (PL). The use of ultrathin silicon wafers allows us to perform plan view transmission electron microscopy studies without recourse to thinning procedures that might adversely affect the film structure. Supercritically dried samples are compared to air dried samples and clearly demonstrate the deleterious effects of air drying on film structure. PL studies were performed (a) while the sample is submerged in aqueous HF, (b) in Ar after rinsing in ethanol, and (c) in air after rinsing in ethanol. The wavelength of light used to fabricate the film is found to correlate strongly with the peak PL wavelength when measured in solution. Little correlation is found in Ar or in air. Exposure to air can change the PL spectrum dramatically on a time scale of just seconds. We demonstrate that samples can exhibit essentially identical PL spectra in one medium but have spectra that differ from one another when the samples are placed in a different medium. The PL results indicate that band-to-band recombination cannot explain photon emission under all circumstances, and that surface states must also be involved in radiative processes under those conditions in which the bands are sufficiently separated to allow for the appearance of gap states.

  9. Full waveform inversion of seismic waves reflected in a stratified porous medium

    NASA Astrophysics Data System (ADS)

    De Barros, Louis; Dietrich, Michel; Valette, Bernard

    2010-09-01

    In reservoir geophysics applications, seismic imaging techniques are expected to provide as much information as possible on fluid-filled reservoir rocks. Since seismograms are, to some degree, sensitive to the mechanical parameters and fluid properties of porous media, inversion methods can be devised to directly estimate these quantities from the waveforms obtained in seismic reflection experiments. An inversion algorithm that uses a generalized least-squares, quasi-Newton approach is described to determine the porosity, permeability, interstitial fluid properties and mechanical parameters of porous media. The proposed algorithm proceeds by iteratively minimizing a misfit function between observed data and synthetic wavefields computed with the Biot theory. Simple models consisting of plane-layered, fluid-saturated and poro-elastic media are considered to demonstrate the concept and evaluate the performance of such a full waveform inversion scheme. Numerical experiments show that, when applied to synthetic data, the inversion procedure can accurately reconstruct the vertical distribution of a single model parameter, if all other parameters are perfectly known. However, the coupling between some of the model parameters does not permit the reconstruction of several model parameters at the same time. To get around this problem, we consider composite parameters defined from the original model properties and from a priori information, such as the fluid saturation rate or the lithology, to reduce the number of unknowns. Another possibility is to apply this inversion algorithm to time-lapse surveys carried out for fluid substitution problems, such as CO2 injection, since in this case only a few parameters may vary as a function of time. We define a two-step differential inversion approach which allows us to reconstruct the fluid saturation rate in reservoir layers, even though the medium properties are poorly known.

  10. Studying the flow dynamics of a karst aquifer system with an equivalent porous medium model.

    PubMed

    Abusaada, Muath; Sauter, Martin

    2013-01-01

    The modeling of groundwater flow in karst aquifers is a challenge due to the extreme heterogeneity of its hydraulic parameters and the duality in their discharge behavior, that is, rapid response of highly conductive karst conduits and delayed drainage of the low-permeability fractured matrix after recharge events. There are a number of different modeling approaches for the simulation of the karst groundwater dynamics, applicable to different aquifer as well as modeling problem types, ranging from continuum models to double continuum models to discrete and hybrid models. This study presents the application of an equivalent porous model approach (EPM, single continuum model) to construct a steady-state numerical flow model for an important karst aquifer, that is, the Western Mountain Aquifer Basin (WMAB), shared by Israel and the West-Bank, using MODFLOW2000. The WMAB was used as a catchment since it is a well-constrained catchment with well-defined recharge and discharge components and therefore allows a control on the modeling approach, a very rare opportunity for karst aquifer modeling. The model demonstrates the applicability of equivalent porous medium models for the simulation of karst systems, despite their large contrast in hydraulic conductivities. As long as the simulated saturated volume is large enough to average out the local influence of karst conduits and as long as transport velocities are not an issue, EPM models excellently simulate the observed head distribution. The model serves as a starting basis that will be used as a reference for developing a long-term dynamic model for the WMAB, starting from the pre-development period (i.e., 1940s) up to date.

  11. A coupling concept for two-phase compositional porous-medium and single-phase compositional free flow

    NASA Astrophysics Data System (ADS)

    Mosthaf, K.; Baber, K.; Flemisch, B.; Helmig, R.; Leijnse, A.; Rybak, I.; Wohlmuth, B.

    2011-10-01

    Domains composed of a porous part and an adjacent free-flow region are of special interest in many fields of application. So far, the coupling of free flow with porous-media flow has been considered only for single-phase systems. Here we extend this classical concept to two-component nonisothermal flow with two phases inside the porous medium and one phase in the free-flow region. The mathematical modeling of flow and transport phenomena in porous media is often based on Darcy's law, whereas in free-flow regions the (Navier-) -Stokes equations are used. In this paper, we give a detailed description of the employed subdomain models. The main contribution is the developed coupling concept, which is able to deal with compositional (miscible) flow and a two-phase system in the porous medium. It is based on the continuity of fluxes and the assumption of thermodynamic equilibrium, and uses the Beavers-Joseph-Saffman condition. The phenomenological explanations leading to a simple, solvable model, which accounts for the physics at the interface, are laid out in detail. Our model can account for evaporation and condensation processes at the interface and is used to model evaporation from soil influenced by a wind field in a first numerical example.

  12. Mass transport at the interface between a highly permeable porous medium and an open channel flow

    NASA Astrophysics Data System (ADS)

    Moretto, C.; Pokrajac, D.

    2012-04-01

    Hyporheic exchange has been extensively studied in the literature. The majority of papers present the results of field studies and the associated engineering simulation models. The number of laboratory studies is smaller. Most of them are focused on the bulk scale effects, since the measurements within the bed at the grain scale are difficult and therefore rare. Measurement within the pores of a permeable bed becomes possible for some idealized pore configurations. Pokrajac and Manes (2009) and Manes et al. (2009) use constant diameter spheres packed in a cubic pattern, which form straight pores (with variable cross-sectional area) in three orthogonal directions. Their results include detailed velocity measurements and the characteristics of turbulence at the fluid/porous interface, but not the mass transport. The experimental study reported here uses the same porous medium and extends this work by including grain-scale mass transport measurements. The results presented involve the hydrodynamics and the mass transport at the fluid/pore interface and within the first pore under the surface of the medium. The experiments are carried out in a 11m long and 40cm wide tilting flume. The porous medium, placed on the flume bed, is composed of 5 layers of 12mm diameter plastic spheres packed in a cubic pattern. This arrangement was chosen in order to have a regular matrix, thereby allowing measurements of the velocities and solute concentration within a pore. The measurement window covers a central section of a longitudinal pore which is visible through a lateral pore. The velocity field is measured by means of the Particle Image Velocimetry (PIV), and the concentration field is measured using the Laser Induced Fluorescence (LIF). These two techniques allow simultaneous non-intrusive measurements within a single pore. The experiments involved uniform, fully developed turbulent flow. The experimental conditions were: bed slope = 0.01, water depth = 45mm, depth

  13. Guar gum solutions for improved delivery of iron particles in porous media (part 1): porous medium rheology and guar gum-induced clogging.

    PubMed

    Gastone, Francesca; Tosco, Tiziana; Sethi, Rajandrea

    2014-10-01

    The present work is the first part of a comprehensive study on the use of guar gum to improve delivery of microscale zero-valent iron particles in contaminated aquifers. Guar gum solutions exhibit peculiar shear thinning properties, with high viscosity in static conditions and lower viscosity in dynamic conditions: this is beneficial both for the storage of MZVI dispersions, and also for the injection in porous media. In the present paper, the processes associated with guar gum injection in porous media are studied performing single-step and multi-step filtration tests in sand-packed columns. The experimental results of single-step tests performed by injecting guar gum solutions prepared at several concentrations and applying different dissolution procedures evidenced that the presence of residual undissolved polymeric particles in the guar gum solution may have a relevant negative impact on the permeability of the porous medium, resulting in evident clogging. The most effective preparation procedure which minimizes the presence of residual particles is dissolution in warm water (60°C) followed by centrifugation (procedure T60C). The multi-step tests (i.e. injection of guar gum at constant concentration with a step increase of flow velocity), performed at three polymer concentrations (1.5, 3 and 4g/l) provided information on the rheological properties of guar gum solutions when flowing through a porous medium at variable discharge rates, which mimic the injection in radial geometry. An experimental protocol was defined for the rheological characterization of the fluids in porous media, and empirical relationships were derived for the quantification of rheological properties and clogging with variable injection rate. These relationships will be implemented in the second companion paper (Part II) in a radial transport model for the simulation of large-scale injection of MZVI-guar gum slurries.

  14. Guar gum solutions for improved delivery of iron particles in porous media (Part 1): Porous medium rheology and guar gum-induced clogging

    NASA Astrophysics Data System (ADS)

    Gastone, Francesca; Tosco, Tiziana; Sethi, Rajandrea

    2014-10-01

    The present work is the first part of a comprehensive study on the use of guar gum to improve delivery of microscale zero-valent iron particles in contaminated aquifers. Guar gum solutions exhibit peculiar shear thinning properties, with high viscosity in static conditions and lower viscosity in dynamic conditions: this is beneficial both for the storage of MZVI dispersions, and also for the injection in porous media. In the present paper, the processes associated with guar gum injection in porous media are studied performing single-step and multi-step filtration tests in sand-packed columns. The experimental results of single-step tests performed by injecting guar gum solutions prepared at several concentrations and applying different dissolution procedures evidenced that the presence of residual undissolved polymeric particles in the guar gum solution may have a relevant negative impact on the permeability of the porous medium, resulting in evident clogging. The most effective preparation procedure which minimizes the presence of residual particles is dissolution in warm water (60 °C) followed by centrifugation (procedure T60C). The multi-step tests (i.e. injection of guar gum at constant concentration with a step increase of flow velocity), performed at three polymer concentrations (1.5, 3 and 4 g/l) provided information on the rheological properties of guar gum solutions when flowing through a porous medium at variable discharge rates, which mimic the injection in radial geometry. An experimental protocol was defined for the rheological characterization of the fluids in porous media, and empirical relationships were derived for the quantification of rheological properties and clogging with variable injection rate. These relationships will be implemented in the second companion paper (Part II) in a radial transport model for the simulation of large-scale injection of MZVI-guar gum slurries.

  15. A 3-dimensional micro- and nanoparticle transport and filtration model (MNM3D) applied to the migration of carbon-based nanomaterials in porous media

    NASA Astrophysics Data System (ADS)

    Bianco, Carlo; Tosco, Tiziana; Sethi, Rajandrea

    2016-10-01

    Engineered nanoparticles (NPs) in the environment can act both as contaminants, when they are unintentionally released, and as remediation agents when injected on purpose at contaminated sites. In this work two carbon-based NPs are considered, namely CARBO-IRON®, a new material developed for contaminated site remediation, and single layer graphene oxide (SLGO), a potential contaminant of the next future. Understanding and modeling the transport and deposition of such NPs in aquifer systems is a key aspect in both cases, and numerical models capable to simulate NP transport in groundwater in complex 3D scenarios are necessary. To this aim, this work proposes a modeling approach based on modified advection-dispersion-deposition equations accounting for the coupled influence of flow velocity and ionic strength on particle transport. A new modeling tool (MNM3D - Micro and Nanoparticle transport Model in 3D geometries) is presented for the simulation of NPs injection and transport in 3D scenarios. MNM3D is the result of the integration of the numerical code MNMs (Micro and Nanoparticle transport, filtration and clogging Model - Suite) in the well-known transport model RT3D (Clement et al., 1998). The injection in field-like conditions of CARBO-IRON® (20 g/l) amended by CMC (4 g/l) in a 2D vertical tank (0.7 × 1.0 × 0.12 m) was simulated using MNM3D, and compared to experimental results under the same conditions. Column transport tests of SLGO at a concentration (10 mg/l) representative of a possible spill of SLGO-containing waste water were performed at different values of ionic strength (0.1 to 35 mM), evidencing a strong dependence of SLGO transport on IS, and a reversible blocking deposition. The experimental data were fitted using the numerical code MNMs and the ionic strength-dependent transport was up-scaled for a full scale 3D simulation of SLGO release and long-term transport in a heterogeneous aquifer. MNM3D showed to potentially represent a valid tool for

  16. Soret and Dufour Effects on MHD Peristaltic Flow of Jeffrey Fluid in a Rotating System with Porous Medium

    PubMed Central

    Hayat, Tasawar; Rafiq, Maimona; Ahmad, Bashir

    2016-01-01

    The objective of present paper is to examine the peristaltic flow of magnetohydrodynamic (MHD) Jeffrey fluid saturating porous space in a channel through rotating frame. Unlike the previous attempts, the flow formulation is based upon modified Darcy's law porous medium effect in Jeffrey fluid situation. In addition the impacts due to Soret and Dufour effects in the radiative peristaltic flow are accounted. Rosseland’s approximation has been utilized for the thermal radiative heat flux. Lubrication approach is implemented for the simplification. Resulting problems are solved for the stream function, temperature and concentration. Graphical results are prepared and analyzed for different parameters of interest entering into the problems. PMID:26808387

  17. Heat and mass transfer in magneto-biofluid flow through a non-Darcian porous medium with Joule effect

    NASA Astrophysics Data System (ADS)

    Sharma, B. K.; Mishra, A.; Gupta, S.

    2013-07-01

    In the present study, a mathematical model for the hydromagnetic non-Newtonian biofluid flow in the non-Darcy porous medium with Joule effect is proposed. A uniform magnetic field acts perpendicularly to the porous surface. The governing nonlinear partial differential equations are transformed into linear ones which are solved numerically by applying the explicit finite difference method. The effects of various parameters, like Reynolds number and hydro-magnetic, Forchheimer, and Darcian parameters, Prandtl, Eckert, and Schmidt numbers, on the velocity, temperature, and concentration are presented graphically. The results of the study can find applications in surgical operations, industrial material processing, and various heat transfer processes.

  18. The flow of an aqueous foam through a two-dimensional porous medium

    NASA Astrophysics Data System (ADS)

    Dollet, B.; Jones, S. A.; Géraud, B.; Meheust, Y.; Cox, S. J.; Cantat, I.

    2013-12-01

    Flowing foams are used in many engineering and technical applications. A well-known application is oil recovery. Another one is the remediation of polluted soils: the foam is injected into the ground in order to mobilize chemical species present in the medium. Apart from potential interesting physico-chemical and biochemical properties, foams have peculiar flow properties that applications might benefit of. In particular, viscous dissipation arises mostly from the contact zones between the soap films and the walls, which results in peculiar friction laws allowing the foam to invade narrow pores more efficiently than Newtonian fluids would. We investigate the flow of a two-dimensional foam in three geometrical configurations. The flow velocity field and pressure field can both be reconstructed from the kinematics of the foam bubbles. We first consider a medium consisting of two parallel channels with different widths, at fixed medium porosity, that is, at fixed total combined width of the two channels. The flow behavior is highly dependent on the foam structure within the narrowest of the two channels [1]; consequently, the flux ratio between the two channels exhibits a non-monotonic dependence on the ratio of their widths. We then consider two parallel channels that are respectively convergent and divergent. The resulting flow kinematics imposes asymmetric bubble deformations in the two channels; these deformations strongly impact the foam/wall friction, and consequently the flux distribution between the two channels, causing flow irreversibility. We quantitatively predict the flux ratio as a function of the channel widths by modeling pressure drops of both viscous and capillary origins. This study reveals the crucial importance of boundary-induced bubble deformation on the mobility of a flowing foam. We then study how film-wall friction, capillary pressures and bubble deformation impact the flow of a foam in a two-dimensional porous medium consisting of randomly

  19. Maintenance of a bone collagen phenotype by osteoblast-like cells in 3D periodic porous titanium (Ti-6Al-4 V) structures fabricated by selective electron beam melting.

    PubMed

    Hrabe, Nikolas W; Heinl, Peter; Bordia, Rajendra K; Körner, Carolin; Fernandes, Russell J

    2013-01-01

    Regular 3D periodic porous Ti-6Al-4 V structures were fabricated by the selective electron beam melting method (EBM) over a range of relative densities (0.17-0.40) and pore sizes (500-1500 µm). Structures were seeded with human osteoblast-like cells (SAOS-2) and cultured for four weeks. Cells multiplied within these structures and extracellular matrix collagen content increased. Type I and type V collagens typically synthesized by osteoblasts were deposited in the newly formed matrix with time in culture. High magnification scanning electron microscopy revealed cells attached to surfaces on the interior of the structures with an increasingly fibrous matrix. The in-vitro results demonstrate that the novel EBM-processed porous structures, designed to address the effect of stress-shielding, are conducive to osteoblast attachment, proliferation and deposition of a collagenous matrix characteristic of bone.

  20. Bridging aero-fracture evolution with the characteristics of the acoustic emissions in a porous medium

    NASA Astrophysics Data System (ADS)

    Turkaya, Semih; Toussaint, Renaud; Eriksen, Fredrik; Zecevic, Megan; Daniel, Guillaume; Flekkøy, Eirik; Måløy, Knut Jørgen

    2015-09-01

    The characterization and understanding of rock deformation processes due to fluid flow is a challenging problem with numerous applications. The signature of this problem can be found in Earth Science and Physics, notably with applications in natural hazard understanding, mitigation or forecast (e.g. earthquakes, landslides with hydrological control, volcanic eruptions), or in industrial applications such as hydraulic-fracturing, steam-assisted gravity drainage, CO sequestration operations or soil remediation. Here we investigate the link between the visual deformation and the mechanical wave signals generated due to fluid injection into porous media. In a rectangular Hele-Shaw Cell, side air injection causes burst movement and compaction of grains along with channeling (creation of high permeability channels empty of grains). During the initial compaction and emergence of the main channel, the hydraulic fracturing in the medium generates a large non-impulsive low frequency signal in the frequency range 100 Hz - 10 kHz. When the channel network is established, the relaxation of the surrounding medium causes impulsive aftershock-like events, with high frequency (above 10 kHz) acoustic emissions, the rate of which follows an Omori Law. These signals and observations are comparable to seismicity induced by fluid injection. Compared to the data obtained during hydraulic fracturing operations, low frequency seismicity with evolving spectral characteristics have also been observed. An Omori-like decay of microearthquake rates is also often observed after injection shut-in, with a similar exponent p≃0.5 as observed here, where the decay rate of aftershock follows a scaling law dN/dt ∝(t-t₀ )-p . The physical basis for this modified Omori law is explained by pore pressure diffusion affecting the stress relaxation.

  1. Thermal convection of magneto compressible couple-stress fluid saturated in a porous medium with Hall current

    NASA Astrophysics Data System (ADS)

    Mehta, C. B.; Singh, M.; Kumar, S.

    2016-02-01

    An investigation is made on the effect of Hall currents on thermal instability of a compressible couple-stress fluid in the presence of a horizontal magnetic field saturated in a porous medium. The analysis is carried out within the framework of the linear stability theory and normal mode technique. A dispersion relation governing the effects of viscoelasticity, Hall currents, compressibility, magnetic field and porous medium is derived. For the stationary convection a couple-stress fluid behaves like an ordinary Newtonian fluid due to the vanishing of the viscoelastic parameter. Compressibility, the magnetic filed and couple-stress parameter have stabilizing effects on the system whereas Hall currents and medium permeability have a destabilizing effect on the system, but in the absence of Hall current couple-stress has a destabilizing effect on the system. It has been observed that oscillatory modes are introduced due to the presence of viscoelasticity, magnetic field porous medium and Hall currents which were non-existent in their absence.

  2. Steady boundary layer slip flow along with heat and mass transfer over a flat porous plate embedded in a porous medium.

    PubMed

    Aziz, Asim; Siddique, J I; Aziz, Taha

    2014-01-01

    In this paper, a simplified model of an incompressible fluid flow along with heat and mass transfer past a porous flat plate embedded in a Darcy type porous medium is investigated. The velocity, thermal and mass slip conditions are utilized that has not been discussed in the literature before. The similarity transformations are used to transform the governing partial differential equations (PDEs) into a nonlinear ordinary differential equations (ODEs). The resulting system of ODEs is then reduced to a system of first order differential equations which was solved numerically by using Matlab bvp4c code. The effects of permeability, suction/injection parameter, velocity parameter and slip parameter on the structure of velocity, temperature and mass transfer rates are examined with the aid of several graphs. Moreover, observations based on Schmidt number and Soret number are also presented. The result shows, the increase in permeability of the porous medium increase the velocity and decrease the temperature profile. This happens due to a decrease in drag of the fluid flow. In the case of heat transfer, the increase in permeability and slip parameter causes an increase in heat transfer. However for the case of increase in thermal slip parameter there is a decrease in heat transfer. An increase in the mass slip parameter causes a decrease in the concentration field. The suction and injection parameter has similar effect on concentration profile as for the case of velocity profile.

  3. Steady Boundary Layer Slip Flow along with Heat and Mass Transfer over a Flat Porous Plate Embedded in a Porous Medium

    PubMed Central

    Aziz, Asim; Siddique, J. I.; Aziz, Taha

    2014-01-01

    In this paper, a simplified model of an incompressible fluid flow along with heat and mass transfer past a porous flat plate embedded in a Darcy type porous medium is investigated. The velocity, thermal and mass slip conditions are utilized that has not been discussed in the literature before. The similarity transformations are used to transform the governing partial differential equations (PDEs) into a nonlinear ordinary differential equations (ODEs). The resulting system of ODEs is then reduced to a system of first order differential equations which was solved numerically by using Matlab bvp4c code. The effects of permeability, suction/injection parameter, velocity parameter and slip parameter on the structure of velocity, temperature and mass transfer rates are examined with the aid of several graphs. Moreover, observations based on Schmidt number and Soret number are also presented. The result shows, the increase in permeability of the porous medium increase the velocity and decrease the temperature profile. This happens due to a decrease in drag of the fluid flow. In the case of heat transfer, the increase in permeability and slip parameter causes an increase in heat transfer. However for the case of increase in thermal slip parameter there is a decrease in heat transfer. An increase in the mass slip parameter causes a decrease in the concentration field. The suction and injection parameter has similar effect on concentration profile as for the case of velocity profile. PMID:25531301

  4. Reactive-convective dissolution in a porous medium: the storage of carbon dioxide in saline aquifers.

    PubMed

    Ghoshal, Parama; Kim, Min Chan; Cardoso, Silvana S S

    2016-12-21

    We quantify the destabilising effect of a first-order chemical reaction on the fingering instability of a diffusive boundary layer in a porous medium. Using scaling, we show that the dynamics of such a reactive boundary layer is fully determined by two dimensionless groups: Da/Ra(2), which measures the timescale for convection compared to those for reaction and diffusion; and βC/βA, which reflects the density change induced by the product relative to that of the diffusing solute. Linear stability and numerical results for βC/βA in the range 0-10 and Da/Ra(2) in the range 0-0.01 are presented. It is shown that the chemical reaction increases the growth rate of a transverse perturbation and favours large wavenumbers compared to the inert system. Higher βC/βA and Da/Ra(2) not only accelerate the onset of convection, but crucially also double the transport of the solute compared to the inert system. Application of our findings to the storage of carbon dioxide in carbonate saline aquifers reveals that chemical equilibrium curtails this increase of CO2 flux to 50%.

  5. Parameters analysis of a porous medium model for treatment with hyperthermia using OpenMP

    NASA Astrophysics Data System (ADS)

    Freitas Reis, Ruy; dos Santos Loureiro, Felipe; Lobosco, Marcelo

    2015-09-01

    Cancer is the second cause of death in the world so treatments have been developed trying to work around this world health problem. Hyperthermia is not a new technique, but its use in cancer treatment is still at early stage of development. This treatment is based on overheat the target area to a threshold temperature that causes cancerous cell necrosis and apoptosis. To simulate this phenomenon using magnetic nanoparticles in an under skin cancer treatment, a three-dimensional porous medium model was adopted. This study presents a sensibility analysis of the model parameters such as the porosity and blood velocity. To ensure a second-order solution approach, a 7-points centered finite difference method was used for space discretization while a predictor-corrector method was used to time evolution. Due to the massive computations required to find the solution of a three-dimensional model, this paper also presents a first attempt to improve performance using OpenMP, a parallel programming API.

  6. Updating an equivalent porous medium karst aquifer model using the coupled continuum pipe-flow method

    NASA Astrophysics Data System (ADS)

    Saller, S. P.; Ronayne, M. J.; Long, A. J.

    2013-12-01

    Karst conduits are commonly treated as high-conductivity zones in equivalent porous medium (EPM) models. In this study, an EPM model for a Paleozoic age carbonate aquifer was updated to include discrete conduits, and flow was simulated using the coupled continuum pipe-flow method. The modeled area, encompassing 2000 square km of the Madison aquifer in western South Dakota (USA), includes four karst springs with contributing conduit networks. The updated model considered the same observation data that were used to calibrate the EPM model: measured hydraulic heads at matrix observation wells and estimated springflow. Adjusted parameters included the conduit locations and hydraulic properties, as well as the matrix hydraulic conductivity distribution. Inferred karst pathways from environmental tracer analysis were used to guide the placement of conduits. The new coupled continuum pipe-flow model is characterized by a simpler conductivity distribution; extreme high-K values used in the EPM model are not necessary when conduit flow is explicitly simulated. Results are presented to illustrate the influence of conduits on simulated flow behavior.

  7. Double diffusive convection in a porous medium layer saturated with an Oldroyd nanofluid

    NASA Astrophysics Data System (ADS)

    Umavathi, J. C.; Sasso, Maurizio

    2017-01-01

    The onset of double diffusive convection in a horizontal layer of a porous medium saturated with an Oldroyd nanofluid is studied using linear and non-linear stability analysis. The modified Darcy-Oldroyd model is used for the momentum equation. The model used for the Oldroyd nanofluid incorporates the effects of Brownian motion and thermophoresis. The thermal energy equations include the diffusion and cross diffusion terms. The linear theory depends on normal mode technique and the onset criterion for stationary and oscillatory convection is derived analytically. The effects of various governing parameters viz., concentration Rayleigh number, nanofluid Lewis number, modified diffusivity ratio, Soret and Dufour parameters, Solutal Rayleigh number, Vadasz number, Lewis number, relaxation, and retardation parameters, viscosity ratio and conductivity ratio on the stationary and oscillatory convections are presented graphically. The non-linear theory based on the representation of Fourier series method is used to find the heat and mass transport. The effect of various parameters on transient heat and mass transfer is also brought out and nonlinear analysis depends on a minimal representation of double Fourier series. We also study the effect of time on transient Nusselt numbers which is found to be oscillatory when time is small. However, when time becomes very large all the three transient Nusselt values approaches to their steady state values.

  8. Supercritical Hadley circulation within a layer of fluid saturated porous medium: Bifurcation to traveling wave

    SciTech Connect

    Manole, D.M.; Lage, J.L.; Antohe, B.V.

    1995-12-31

    Hadley circulation induced by horizontal and vertical temperature gradients imposed on a fluid saturated porous medium layer is simulated numerically. The flow is assumed to be longitudinal, that is the secondary flow is composed of cells with axes transverse to the direction of the Hadley circulation. Critical (bifurcation) states predicted theoretically via linear stability analysis are verified by the numerical results giving confidence on the accuracy of the method. Several values of horizontal Rayleigh number, Ra{sub h}, and vertical Rayleigh number, Ra{sub v}, are studied. Results indicate that beyond a threshold horizontal Rayleigh number value the flow and temperature fields evolve from subcritical Hadley circulation to a supercritical time periodic flow. The secondary flow emerges in the form of a traveling wave aligned with the main (Hadley) flow direction. This traveling wave is characterized, at supercritical low vertical Rayleigh numbers, by the continuous drifting of two horizontal layers of flow cells that move in opposite directions. As the vertical Rayleigh number increases, the traveling wave becomes characterized by a unique layer of cells drifting in the direction opposite to the applied horizontal temperature gradient. Numerical animation unravels the main features of the transport process. This simplified model is of fundamental and practical importance, for instance, to the study of geothermal activities, underground transport of pollutants, paper processing, crystal growth, building insulation, and gas reservoirs.

  9. Kinematics in a slowly drying porous medium: Reconciliation of pore network simulations and continuum modeling

    NASA Astrophysics Data System (ADS)

    Attari Moghaddam, Alireza; Kharaghani, Abdolreza; Tsotsas, Evangelos; Prat, Marc

    2017-02-01

    We study the velocity field in the liquid phase during the drying of a porous medium in the capillarity-dominated regime with evaporation from the top surface. A simple mass balance in the continuum framework leads to a linear variation of the filtration velocity across the sample. By contrast, the instantaneous slice-averaged velocity field determined from pore network simulations leads to step velocity profiles. The vertical velocity profile is almost constant near the evaporative top surface and zero close to the bottom of the sample. The relative extent of the two regions with constant velocity is dictated by the position of the most unstable meniscus. It is shown that the continuum and pore network results can be reconciled by averaging the velocity field obtained from the pore network simulations over time. This opens up interesting prospects regarding the transport of dissolved species during drying. Also, the study reveals the existence of an edge effect, which is not taken into account in the classical continuum models of drying.

  10. Adaptation of Delftia acidovorans for degradation of 2,4-dichlorophenoxyacetate in a microfluidic porous medium.

    PubMed

    Yoon, Hongkyu; Leibeling, Sabine; Zhang, Changyong; Müller, Roland H; Werth, Charles J; Zilles, Julie L

    2014-07-01

    Delftia acidovorans MC1071 can productively degrade R-2-(2,4-dichlorophenoxy)propionate (R-2,4-DP) but not 2,4-dichlorophenoxyacetate (2,4-D) herbicides. This work demonstrates adaptation of MC1071 to degrade 2,4-D in a model two-dimensional porous medium (referred to here as a micromodel). Adaptation for 2,4-D degradation in the 2 cm-long micromodel occurred within 35 days of exposure to 2,4-D, as documented by substrate removal. The amount of 2,4-D degradation in the adapted cultures in two replicate micromodels (~10 and 20 % over 142 days) was higher than a theoretical maximum (4 %) predicted using published numerical simulation methods, assuming instantaneous biodegradation and a transverse dispersion coefficient obtained for the same pore structure without biomass present. This suggests that the presence of biomass enhances substrate mixing. Additional evidence for adaptation was provided by operation without R-2,4-DP, where degradation of 2,4-D slowly decreased over 20 days, but was restored almost immediately when R-2,4-DP was again provided. Compared to suspended growth systems, the micromodel system retained the ability to degrade 2,4-D longer in the absence of R-2,4-DP, suggesting slower responses and greater resilience to fluctuations in substrates might be expected in the soil environment than in a chemostat.

  11. Mean and variance of DNAPL ringer development in a saturated, randomly heterogeneous porous medium.

    SciTech Connect

    Tartakovsky, A. M.; Neuman, S. P.; Tartakovsky, D. M.

    2001-01-01

    Chlorinated organic solvents such as TCE and PCE are among the most ubiquitous and problematic groundwater contaminants at many sites. They usually enter the subsurface in the form of organic liquids which exhibit low miscibility with water and thus form a separate dense non-aqueous phase liquid (DNAPL). Here we analyze the movement of DNAPL in a three-dimensional randomly heterogeneous porous medium saturated with water. We consider the fluid interface between DNAPL and water to form a sharp boundary at which the capillary pressure head, assumed equal to the entry pressure head of DNAPL, is prescribed either deterministically or randomly. We treat log hydraulic conductivity as a statistically homogeneous random field with given mean, variance and covariance, This allows us to cast the corresponding boundary-value problem in the form of an integro-differential equation, in which the parameters and domain of integration are random. Expanding this equation in a Taylor series about the mean position of the front, and averaging in probability space, yields leading-order ensemble I moment equations for the mean and variance of front evolution with time. Previously we solved these moment equations analytically in one-dimension with gravity, to first order in the variance of log conductivity, and compared our solution with the results of Monte Carlo sjmulations. Here we solve the same moment equations numerically in two-spatial dimensions without gravity.

  12. Interface scaling in a two-dimensional porous medium under combined viscous, gravity, and capillary effects.

    PubMed

    Méheust, Yves; Løvoll, Grunde; Måløy, Knut Jørgen; Schmittbuhl, Jean

    2002-11-01

    We have investigated experimentally the competition between viscous, capillary, and gravity forces during drainage in a two-dimensional synthetic porous medium. The displacement of a mixture of glycerol and water by air at constant withdrawal rate has been studied. The setup can be tilted to tune gravity, and pressure is recorded at the outlet of the model. Viscous forces tend to destabilize the displacement front into narrow fingers against the stabilizing effect of gravity. Subsequently, a viscous instability is observed for sufficiently large withdrawal speeds or sufficiently low gravity components on the model. We predict the scaling of the front width for stable situations and characterize it experimentally through analyses of the invasion front geometry and pressure recordings. The front width under stable displacement and the threshold for the instability are shown, both experimentally and theoretically, to be controlled by a dimensionless number F which is defined as the ratio of the effective fluid pressure drop (i.e., average hydrostatic pressure drop minus viscous pressure drop) at pore scale to the width of the fluctuations in the threshold capillary pressures.

  13. Thermal gravitational separation of ternary mixture n-dodecane/isobutylbenzene/tetralin components in a porous medium

    NASA Astrophysics Data System (ADS)

    Larabi, Mohamed Aziz; Mutschler, Dimitri; Mojtabi, Abdelkader

    2016-06-01

    Our present work focuses on the coupling between thermal diffusion and convection in order to improve the thermal gravitational separation of mixture components. The separation phenomenon was studied in a porous medium contained in vertical columns. We performed analytical and numerical simulations to corroborate the experimental measurements of the thermal diffusion coefficients of ternary mixture n-dodecane, isobutylbenzene, and tetralin obtained in microgravity in the international space station. Our approach corroborates the existing data published in the literature. The authors show that it is possible to quantify and to optimize the species separation for ternary mixtures. The authors checked, for ternary mixtures, the validity of the "forgotten effect hypothesis" established for binary mixtures by Furry, Jones, and Onsager. Two complete and different analytical resolution methods were used in order to describe the separation in terms of Lewis numbers, the separation ratios, the cross-diffusion coefficients, and the Rayleigh number. The analytical model is based on the parallel flow approximation. In order to validate this model, a numerical simulation was performed using the finite element method. From our new approach to vertical separation columns, new relations for mass fraction gradients and the optimal Rayleigh number for each component of the ternary mixture were obtained.

  14. A transformation approach for the derivation of boundary conditions between a curved porous medium and a free fluid

    NASA Astrophysics Data System (ADS)

    Dobberschütz, Sören; Böhm, Michael

    2010-02-01

    The behaviour of a free fluid flow above a porous medium, both separated by a curved interface, is investigated. By carrying out a coordinate transformation, we obtain the description of the flow in a domain with a straight interface. Using periodic homogenisation, the effective behaviour of the transformed partial differential equations in the porous part is given by a Darcy law with non-constant permeability matrix. Then the fluid behaviour at the porous-liquid interface is obtained with the help of generalised boundary-layer functions: Whereas the velocity in normal direction is continuous across the interface, a jump appears in tangential direction. Its magnitude seems to be related to the slope of the interface. Therefore the results indicate a generalised law of Beavers and Joseph.

  15. A morphological-approach for two-phase porous medium-transport and optimum design applications in energy engineering

    SciTech Connect

    Travkin, V.S.; Gratton, L.; Catton, I.

    1994-12-31

    Design optimization procedures for transport in porous structures that can be used in different engineering fields are developed for applications ranging from heat and mass exchangers and reactors in mechanical engineering design to environmental engineering usage. Using second order turbulent models, equation sets are obtained for turbulent filtration and two-temperature or two-concentration diffusion in non-isotropic porous media and interphase exchange and micro-roughness. The basis for transforming the integral-differential transport equations into differential equations with probability density functions governing their coefficients and source terms is accomplished by prescribing the statistical structure of the capillary or globular porous medium morphology. Though several different closure models for the source terms for uniform, non-uniform, non-isotropic and specifically random non-isotropic highly porous layers have been successfully developed, quite different situations arise when attempting to describe processes occurring in irregular or random morphologies. Results, obtained with the help of exact closure modeling for canonical morphologies, open a new field of possibilities for searching for optimal designs of spatial heterogeneous transport structures. A way to find and govern momentum transport through a capillary nonintersecting medium by altering its morphometric characteristics is given as validation of the process.

  16. Porous gravity currents: A survey to determine the joint influence of fluid rheology and variations of medium properties

    NASA Astrophysics Data System (ADS)

    Ciriello, Valentina; Longo, Sandro; Chiapponi, Luca; Di Federico, Vittorio

    2016-06-01

    We develop a model to grasp the combined effect of rheology and spatial stratifications on two-dimensional non-Newtonian gravity-driven flow in porous media. We consider a power-law constitutive equation for the fluid, and a monomial variation of permeability and porosity along the vertical direction (transverse to the flow) or horizontal direction (parallel to the flow). Under these assumptions, similarity solutions are derived in semi-analytical form for thin gravity currents injected into a two-dimensional porous medium and having constant or time-varying volume. The extent and shape of the porous domain affected by the injection is significantly influenced by the interplay of model parameters. These describe the fluid (flow behaviour index n), the spatial heterogeneity (coefficients β, γ, δ, ω for variations of permeability and porosity in the horizontal or vertical direction), and the type of release (volume exponent α). Theoretical results are validated against two sets of experiments with α = 1 (constant inflow) conducted with a stratified porous medium (simulated by superimposing layers of glass beads of different diameter) and a Hele-Shaw analogue for power-law fluid flow, respectively. In the latter case, a recently established Hele-Shaw analogy is extended to the variation of properties parallel to the flow direction. Comparison with experimental results shows that the proposed model is able to capture the propagation of the current front and the current profile.

  17. Continued development of a semianalytical solution for two-phase fluid and heat flow in a porous medium

    SciTech Connect

    Doughty, C.; Pruess, K.

    1991-06-01

    Over the past few years the authors have developed a semianalytical solution for transient two-phase water, air, and heat flow in a porous medium surrounding a constant-strength linear heat source, using a similarity variable {eta} = r/{radical}t. Although the similarity transformation approach requires a simplified geometry, all the complex physical mechanisms involved in coupled two-phase fluid and heat flow can be taken into account in a rigorous way, so that the solution may be applied to a variety of problems of current interest. The work was motivated by adverse to predict the thermohydrological response to the proposed geologic repository for heat-generating high-level nuclear wastes at Yucca Mountain, Nevada, in a partially saturated, highly fractured volcanic formation. The paper describes thermal and hydrologic conditions near the heat source; new features of the model; vapor pressure lowering; and the effective-continuum representation of a fractured/porous medium.

  18. Numerical heat transfer study in a scattering, absorbing and emitting semi-transparent porous medium in a cylindrical enclosure

    NASA Astrophysics Data System (ADS)

    Timoumi, M.; Chérif, B.; Sifaoui, M. S.

    2005-12-01

    In this paper, heat transfer problem through a semi-transparent porous medium in a cylindrical enclosure is investigated. The governing equations for this problem and the boundary conditions are non-linear differential equations depending on the dimensionless radial coordinate, Planck number N, scattering albedo ω, walls emissivity and thermal conductivity ratio kr. The set of differential equations are solved by a numerical technique taken from the IMSL MATH/LIBRARY. Various results are obtained for the dimensionless temperature profiles in the solid and fluid phases and the radiative heat flux. The effects of some radiative properties of the medium on the heat transfer rate are examined.

  19. Analytical solution to the diffusion, sorption and decay chain equation in a saturated porous medium between two reservoirs.

    PubMed

    Guzman, Juan; Maximov, Serguei; Escarela-Perez, Rafael; López-García, Irvin; Moranchel, Mario

    2015-01-01

    The diffusion and distribution coefficients are important parameters in the design of barrier systems used in radioactive repositories. These coefficients can be determined using a two-reservoir configuration, where a saturated porous medium is allocated between two reservoirs filled by stagnant water. One of the reservoirs contains a high concentration of radioisotopes. The goal of this work is to obtain an analytical solution for the concentration of all radioisotopes in the decay chain of a two-reservoir configuration. The analytical solution must be obtained by taking into account the diffusion and sorption processes. Concepts such as overvalued concentration, diffusion and decay factors are employed to this end. It is analytically proven that a factor of the solution is identical for all chains (considering a time scaling factor), if certain parameters do not change. In addition, it is proven that the concentration sensitivity, due to the distribution coefficient variation, depends of the porous medium thickness, which is practically insensitive for small porous medium thicknesses. The analytical solution for the radioisotope concentration is compared with experimental and numerical results available in literature.

  20. Nonlinear instability of an Oldroyd elastico–viscous magnetic nanofluid saturated in a porous medium

    SciTech Connect

    Moatimid, Galal M.; Alali, Elham M. M. Ali, Hoda S. M.

    2014-09-15

    Through viscoelastic potential theory, a Kelvin-Helmholtz instability of two semi-infinite fluid layers, of Oldroydian viscoelastic magnetic nanofluids (MNF), is investigated. The system is saturated by porous medium through two semi-infinite fluid layers. The Oldroyd B model is utilized to describe the rheological behavior of viscoelastic MNF. The system is influenced by uniform oblique magnetic field that acts at the surface of separation. The model is used for the MNF incorporated the effects of uniform basic streaming and viscoelasticity. Therefore, a mathematical simplification must be considered. A linear stability analysis, based upon the normal modes analysis, is utilized to find out the solutions of the equations of motion. The onset criterion of stability is derived; analytically and graphs have been plotted by giving numerical values to the various parameters. These graphs depict the stability characteristics. Regions of stability and instability are identified and discussed in some depth. Some previous studies are recovered upon appropriate data choices. The stability criterion in case of ignoring the relaxation stress times is also derived. To relax the mathematical manipulation of the nonlinear approach, the linearity of the equations of motion is taken into account in correspondence with the nonlinear boundary conditions. Taylor's theory is adopted to expand the governing nonlinear characteristic equation according to of the multiple time scales technique. This analysis leads to the well-known Ginzburg–Landau equation, which governs the stability criteria. The stability criteria are achieved theoretically. To simplify the mathematical manipulation, a special case is considered to achieve the numerical estimations. The influence of orientation of the magnetic fields on the stability configuration, in linear as well as nonlinear approaches, makes a dual role for the magnetic field strength in the stability graphs. Stability diagram is plotted for

  1. Experimental and numerical simulations of heat transfers between flowing water and a horizontal frozen porous medium

    NASA Astrophysics Data System (ADS)

    Roux, N.; Costard, F.; Grenier, C. F.

    2013-12-01

    In permafrost-affected regions, hydrological changes due to global warming are still under investigation. But yet, we can already foresee from recent studies that for example, the variability and intensity of surface/subsurface flow are likely to be affected by permafrost degradation. And the feedback induced by such changes on permafrost degradation is still not clearly assessed. Of particular interest are lake and river-taliks. A talik is a permanently unfrozen zone that lies below rivers or lake. They should play a key role in these interactions given that they are the only paths for groundwater flow in permafrost regions. Thus heat transfers on a regional scale are potentially influenced by groundwater circulation. The aim of our study is therefore to investigate the evolution of river taliks. We developed a multidisciplinary approach coupling field investigation, experimental studies in a cold room and numerical modeling. In Central Yakutia, Siberia, where permafrost is continuous, we recently installed instruments to monitor ground temperature and water pressure in a river talik between two thermokarst lakes. We present here the coupling of numerical modeling and laboratory experiments in order to look after the main parameters controlling river-talik installation. In a cold room at IDES, where a metric scale channel is filled with sand as a porous medium, we are able to control air, water and permafrost temperature, but also water flow, so that we can test various parameter sets for a miniaturized river. These results are confronted with a numerical model developed at the LSCE with Cast3m (www-cast3m.cea.fr), that couples heat and water transfer. In particular, expressions for river-talik heat exchange terms are investigated. A further step will come in the near future with results from field investigation providing the full complexity of a natural system. Keywords: Talik, River, Numerical Modeling, Cold Room, Permafrost.

  2. A comparison of physicochemical methods for the remediation of porous medium systems contaminated with tar

    NASA Astrophysics Data System (ADS)

    Hauswirth, Scott C.; Miller, Cass T.

    2014-10-01

    The remediation of former manufactured gas plant (FMGP) sites contaminated with tar DNAPLs (dense non-aqueous phase liquids) presents a significant challenge. The tars are viscous mixtures of thousands of individual compounds, including known and suspected carcinogens. This work investigates the use of combinations of mobilization, solubilization, and chemical oxidation approaches to remove and degrade tars and tar components in porous medium systems. Column experiments were conducted using several flushing solutions, including an alkaline-polymer (AP) solution containing NaOH and xanthan gum (XG), a surfactant-polymer (SP) solution containing Triton X-100 surfactant (TX100) and XG, an alkaline-surfactant-polymer (ASP) solution containing NaOH, TX100, and XG, and base-activated sodium persulfate both with and without added TX100. The effectiveness of the flushing solutions was assessed based on both removal of polycyclic aromatic hydrocarbon (PAH) mass and on the reduction of dissolved-phase PAH concentrations. SP flushes of 6.6 to 20.9 PV removed over 99% of residual PAH mass and reduced dissolved-phase concentrations by up to two orders of magnitude. ASP flushing efficiently removed 95-96% of residual PAH mass within about 2 PV, and significantly reduced dissolved-phase concentrations of several low molar mass compounds, including naphthalene, acenaphthene, fluorene, and phenanthrene. AP flushing removed a large portion of the residual tar (77%), but was considerably less effective than SP and ASP in terms of the effect on dissolved PAH concentrations. Persulfate was shown to oxidize tar components, primarily those with low molar mass, however, the overall degradation was relatively low (30-50% in columns with low initial tar saturations), and the impact on dissolved-phase concentrations was minimal.

  3. 3D Porous Graphene Aerogel Cathode with High Sulfur Loading and Embedded TiO2 Nanoparticles for Advanced Lithium-Sulfur Batteries.

    PubMed

    Huang, Jian-Qiu; Wang, Zhenyu; Xu, Zheng-Long; Chong, Woon Gie; Qin, Xianying; Wang, Xiangyu; Kim, Jang-Kyo

    2016-10-07

    Three-dimensional graphene aerogel/TiO2/sulfur (GA/TiO2/S) composites are synthesized through a facile, one-pot hydrothermal route as the cathode for lithium-sulfur batteries. With a high sulfur content of 75.1 wt%, the conductive, highly porous composite electrode delivers a high discharge capacity of 512 mAh/g after 250 cycles at a current rate of 1 C with a low capacity decay of 0.128% per cycle. The excellent capacities and cyclic stability arise from several unique functional features of the cathode. (i) The conductive graphene aerogel framework ameliorates ion/electron transfer while accommodating the volume expansion induced during discharge; and (ii) TiO2 nanoparticles play an important role in restricting the dissolution of polysulfides by chemical bonds with sulfur.

  4. Three-Dimensional (3D) Bicontinuous Hierarchically Porous Mn2O3 Single Crystals for High Performance Lithium-Ion Batteries.

    PubMed

    Huang, Shao-Zhuan; Jin, Jun; Cai, Yi; Li, Yu; Deng, Zhao; Zeng, Jun-Yang; Liu, Jing; Wang, Chao; Hasan, Tawfique; Su, Bao-Lian

    2015-10-06

    Bicontinuous hierarchically porous Mn2O3 single crystals (BHP-Mn2O3-SCs) with uniform parallelepiped geometry and tunable sizes have been synthesized and used as anode materials for lithium-ion batteries (LIBs). The monodispersed BHP-Mn2O3-SCs exhibit high specific surface area and three dimensional interconnected bimodal mesoporosity throughout the entire crystal. Such hierarchical interpenetrating porous framework can not only provide a large number of active sites for Li ion insertion, but also good conductivity and short diffusion length for Li ions, leading to a high lithium storage capacity and enhanced rate capability. Furthermore, owing to their specific porosity, these BHP-Mn2O3-SCs as anode materials can accommodate the volume expansion/contraction that occurs with lithium insertion/extraction during discharge/charge processes, resulting in their good cycling performance. Our synthesized BHP-Mn2O3-SCs with a size of ~700 nm display the best electrochemical performance, with a large reversible capacity (845 mA h g(-1) at 100 mA g(-1) after 50 cycles), high coulombic efficiency (>95%), excellent cycling stability and superior rate capability (410 mA h g(-1) at 1 Ag(-1)). These values are among the highest reported for Mn2O3-based bulk solids and nanostructures. Also, electrochemical impedance spectroscopy study demonstrates that the BHP-Mn2O3-SCs are suitable for charge transfer at the electrode/electrolyte interface.

  5. Three-Dimensional (3D) Bicontinuous Hierarchically Porous Mn2O3 Single Crystals for High Performance Lithium-Ion Batteries

    NASA Astrophysics Data System (ADS)

    Huang, Shao-Zhuan; Jin, Jun; Cai, Yi; Li, Yu; Deng, Zhao; Zeng, Jun-Yang; Liu, Jing; Wang, Chao; Hasan, Tawfique; Su, Bao-Lian

    2015-10-01

    Bicontinuous hierarchically porous Mn2O3 single crystals (BHP-Mn2O3-SCs) with uniform parallelepiped geometry and tunable sizes have been synthesized and used as anode materials for lithium-ion batteries (LIBs). The monodispersed BHP-Mn2O3-SCs exhibit high specific surface area and three dimensional interconnected bimodal mesoporosity throughout the entire crystal. Such hierarchical interpenetrating porous framework can not only provide a large number of active sites for Li ion insertion, but also good conductivity and short diffusion length for Li ions, leading to a high lithium storage capacity and enhanced rate capability. Furthermore, owing to their specific porosity, these BHP-Mn2O3-SCs as anode materials can accommodate the volume expansion/contraction that occurs with lithium insertion/extraction during discharge/charge processes, resulting in their good cycling performance. Our synthesized BHP-Mn2O3-SCs with a size of ~700 nm display the best electrochemical performance, with a large reversible capacity (845 mA h g-1 at 100 mA g-1 after 50 cycles), high coulombic efficiency (>95%), excellent cycling stability and superior rate capability (410 mA h g-1 at 1 Ag-1). These values are among the highest reported for Mn2O3-based bulk solids and nanostructures. Also, electrochemical impedance spectroscopy study demonstrates that the BHP-Mn2O3-SCs are suitable for charge transfer at the electrode/electrolyte interface.

  6. Synthesis, characterisation and adsorption properties of a porous copper(II) 3D coordination polymer exhibiting strong binding enthalpy and adsorption capacity for carbon dioxide.

    PubMed

    Eckold, Pierre; Gee, William J; Hill, Matthew R; Batten, Stuart R

    2012-11-21

    The synthesis and characterisation of microporous coordination polymers containing copper(II) or cobalt(II) and 2-(pyridin-4-yl)malonaldehyde (Hpma) is described and the gas adsorption properties evaluated. Single-crystal X-ray structure determinations identified the structures as [M(pma)(2)]·2X (M = Cu, 1; Co, 2; X = MeOH, MeCN), which contain 3D networks with rutile topology and continuous 1D rectangular channels with diameters ranging from 3 to 4 Å. The materials exhibit low BET surface areas of 143 m(2) g(-1), but possess large capacities for carbon dioxide capture of 14.1 wt%. The small pore channels are shown to account for this, delivering a particularly strong binding enthalpy to adsorbed CO(2) of 38 kJ mol(-1), and a very large adsorption capacity relative to the low surface area.

  7. Instability of plane-parallel flow of incompressible liquid over a saturated porous medium

    NASA Astrophysics Data System (ADS)

    Lyubimova, T. P.; Lyubimov, D. V.; Baydina, D. T.; Kolchanova, E. A.; Tsiberkin, K. B.

    2016-07-01

    The linear stability of plane-parallel flow of an incompressible viscous fluid over a saturated porous layer is studied to model the instability of water flow in a river over aquatic plants. The saturated porous layer is bounded from below by a rigid plate and the pure fluid layer has a free, undeformable upper boundary. A small inclination of the layers is imposed to simulate the riverbed slope. The layers are inclined at a small angle to the horizon. The problem is studied within two models: the Brinkman model with the boundary conditions by Ochoa-Tapia and Whitaker at the interface, and the Darcy-Forchheimer model with the conditions by Beavers and Joseph. The neutral curves and critical Reynolds numbers are calculated for various porous layer permeabilities and relative thicknesses of the porous layer. The results obtained within the two models are compared and analyzed.

  8. Instability of plane-parallel flow of incompressible liquid over a saturated porous medium.

    PubMed

    Lyubimova, T P; Lyubimov, D V; Baydina, D T; Kolchanova, E A; Tsiberkin, K B

    2016-07-01

    The linear stability of plane-parallel flow of an incompressible viscous fluid over a saturated porous layer is studied to model the instability of water flow in a river over aquatic plants. The saturated porous layer is bounded from below by a rigid plate and the pure fluid layer has a free, undeformable upper boundary. A small inclination of the layers is imposed to simulate the riverbed slope. The layers are inclined at a small angle to the horizon. The problem is studied within two models: the Brinkman model with the boundary conditions by Ochoa-Tapia and Whitaker at the interface, and the Darcy-Forchheimer model with the conditions by Beavers and Joseph. The neutral curves and critical Reynolds numbers are calculated for various porous layer permeabilities and relative thicknesses of the porous layer. The results obtained within the two models are compared and analyzed.

  9. Experimental and numerical simulations of heat transfers between flowing water and a frozen porous medium

    NASA Astrophysics Data System (ADS)

    Roux, Nicolas; Grenier, Christophe; Costard, François

    2015-04-01

    In permafrost-affected regions, hydrological changes due to global warming are still under investigation. But yet, we can already foresee from recent studies that for example, the variability and intensity of surface/subsurface flow are likely to be affected by permafrost degradation. The feedback induced by such changes on permafrost degradation is still not clearly assessed. Of particular interest are lake and river's taliks. A talik is a permanently unfrozen zone that lies below rivers or lakes. They are likely to play a key role in the formerly presented interactions, given that they are the only paths for groundwater flow in permafrost regions. Thus heat transfers on a regional scale are influenced by groundwater circulation. The aim of our study is therefore to investigate the evolution of river's taliks. In addition, they are the only perennial liquid water resources in continuous permafrost environments. The issue associated is to what extent can taliks develop into the future because of climate change and how likely are they to become open taliks, connecting sub-permafrost water with surface water with potentially strong geochemical changes? We developed a multidisciplinary approach coupling field investigation, experimental studies in a cold room and numerical modeling. The field investigation concerns Central Yakutia, Siberia, where we have installed instruments to monitor ground temperatures and water pressure in a small river's talik between two thermokarst lakes. We present here the results corresponding to the cold room experimental work, associating numerical modeling and laboratory experiments in order to look after the main parameters controlling river's talik installation and validate our numerical simulation approach. In a cold room at GEOPS, where a metric scale channel is filled with a porous medium (sand or silty-clay), we are able to control air, water and permafrost initial temperature, but also water flow. At initial time, the "river

  10. Approach of Computational Fluid Dynamics of VOF Model in Two Phase flow through Porous Medium under Microgravity Condition

    NASA Astrophysics Data System (ADS)

    Hasan, Raisul

    2016-07-01

    In this research paper firstly theoretical analysis and design of the porous matrix for filtration and selection of associated liquid (highly viscous and low viscous liquid) is carried out. Hence, porosity of the bed has been found out followed by a detailed CFD analysis of the flow to identify displacement structure (fingering: due to the nonlinear interactions among viscous, capillary and gravitational forces). Moreover, an experiment will be with synthetic porous medium consists of a single layer of glass beads which are then positioned homogeneously or non-homogeneously between two Perspex sheets and then fluid displacement structure/fingering will be photographed. Then the effort will be made to validate results with the experiment based photograph and then the CFD model will be extended to microgravity condition KEYWORDS: CFD, Fingering, microgravity, Non-homogeneously, Capillary .

  11. Heterobimetallic MOFs containing tetrathiocyanometallate building blocks: pressure-induced spin crossover in the porous {Fe(II)(pz)[Pd(II)(SCN)4]} 3D coordination polymer.

    PubMed

    Muñoz-Lara, Francisco J; Arcís-Castillo, Zulema; Muñoz, M Carmen; Rodríguez-Velamazán, J Alberto; Gaspar, Ana B; Real, José A

    2012-10-15

    Here we describe the synthesis, structure, and magnetic properties of two related coordination polymers made up of self-assembling Fe(II) ions, pyrazine (pz), and the tetrathiocyanopalladate anion. Compound {Fe(MeOH)(2)[Pd(SCN)(4)]}·pz (1a) is a two-dimensional coordination polymer where the Fe(II) ions are equatorially coordinated by the nitrogen atoms of four [Pd(SCN)(4)](2-) anions, each of which connects four Fe(II) ions, forming corrugated layers {Fe[Pd(SCN)(4)]}(∞). The coordination sphere of Fe(II) is completed by the oxygen atoms of two CH(3)OH molecules. The layers stack one on top of each other in such a way that the included pz molecule establishes strong hydrogen bonds with the coordinated methanol molecules of adjacent layers. Compound {Fe(pz)[Pd(SCN)(4)]} (2) is a three-dimensional porous coordination polymer formed by flat {Fe[Pd(SCN)(4)]}(∞) layers pillared by the pz ligand. Thermal analysis of 1a shows a clear desorption of the two coordinated CH(3)OH molecules giving a rather stable phase (1b), which presumably is a polymorphic form of 2. The magnetic properties of the three derivatives are typical of the high-spin Fe(II) compounds. However, compounds 1b and 2, with coordination sphere [FeN(6)], show thermal spin crossover behavior at pressures higher than ambient pressure (10(5) MPa).

  12. Bacterial inhibition potential of 3D rapid-prototyped magnesium-based porous composite scaffolds–an in vitro efficacy study

    PubMed Central

    Ma, Rui; Lai, Yu-xiao; Li, Long; Tan, Hong-lue; Wang, Jia-li; Li, Ye; Tang, Ting-ting; Qin, Ling

    2015-01-01

    Bone infections are common in trauma-induced open fractures with bone defects. Therefore, developing anti-infection scaffolds for repairing bone defects is desirable. This study develoepd novel Mg-based porous composite scaffolds with a basal matrix composed of poly(lactic-co-glycolicacid) (PLGA) and tricalcium phosphate (TCP). A unique low-temperature rapid prototyping technology was used to fabricate the scaffolds, including PLGA/TCP (PT), PLGA/TCP/5%Mg (PT5M), PLGA/TCP/10%Mg (PT10M), and PLGA/TCP/15%Mg (PT15M). The bacterial adhesion and biofilm formation of Staphylococcus aureus were evaluated. The results indicated that the Mg-based scaffolds significantly inhibited bacterial adhesion and biofilm formation compared to PT, and the PT10M and PT15M exhibited significantly stronger anti-biofilm ability than PT5M. In vitro degratation tests revealed that the degradation of the Mg-based scaffolds caused an increase of pH, Mg2+ concentration and osmolality, and the increased pH may be one of the major contributing factors to the antibacterial function of the Mg-based scaffolds. Additionally, the PT15M exhibited an inhibitory effect on cell adhesion and proliferation of MC3T3-E1 cells. In conclusion, the PLGA/TCP/Mg scaffolds could inhibit bacterial adhesion and biofilm formation, and the PT10M scaffold was considered to be an effective composition with considerable antibacterial ability and good cytocompatibility. PMID:26346217

  13. Evaluation of a coupled model for numerical simulation of a multiphase flow system in a porous medium and a surface fluid.

    PubMed

    Hibi, Yoshihiko; Tomigashi, Akira

    2015-09-01

    Numerical simulations that couple flow in a surface fluid with that in a porous medium are useful for examining problems of pollution that involve interactions among atmosphere, water, and groundwater, including saltwater intrusion along coasts. Coupled numerical simulations of such problems must consider both vertical flow between the surface fluid and the porous medium and complicated boundary conditions at their interface. In this study, a numerical simulation method coupling Navier-Stokes equations for surface fluid flow and Darcy equations for flow in a porous medium was developed. Then, the basic ability of the coupled model to reproduce (1) the drawdown of a surface fluid observed in square-pillar experiments, using pillars filled with only fluid or with fluid and a porous medium and (2) the migration of saltwater (salt concentration 0.5%) in the porous medium using the pillar filled with fluid and a porous medium was evaluated. Simulations that assumed slippery walls reproduced well the results with drawdowns of 10-30 cm when the pillars were filled with packed sand, gas, and water. Moreover, in the simulation of saltwater infiltration by the method developed in this study, velocity was precisely reproduced because the experimental salt concentration in the porous medium after saltwater infiltration was similar to that obtained in the simulation. Furthermore, conditions across the boundary between the porous medium and the surface fluid were satisfied in these numerical simulations of square-pillar experiments in which vertical flow predominated. Similarly, the velocity obtained by the simulation for a system coupling flow in surface fluid with that in a porous medium when horizontal flow predominated satisfied the conditions across the boundary. Finally, it was confirmed that the present simulation method was able to simulate a practical-scale surface fluid and porous medium system. All of these numerical simulations, however, required a great deal of

  14. RhBMP-2 loaded 3D-printed mesoporous silica/calcium phosphate cement porous scaffolds with enhanced vascularization and osteogenesis properties

    NASA Astrophysics Data System (ADS)

    Li, Cuidi; Jiang, Chuan; Deng, Yuan; Li, Tao; Li, Ning; Peng, Mingzheng; Wang, Jinwu

    2017-01-01

    A major limitation in the development of effective scaffolds for bone regeneration has been the limited vascularization of the regenerating tissue. Here, we propose the development of a novel calcium phosphate cement (CPC)-based scaffold combining the properties of mesoporous silica (MS) with recombinant human bone morphogenic protein-2 (rhBMP-2) to facilitate vascularization and osteogenesis. Specifically, the development of a custom MS/CPC paste allowed the three-dimensional (3D) printing of scaffolds with a defined macroporous structure and optimized silicon (Si) ions release profile to promote the ingrowth of vascular tissue at an early stage after implantation in support of tissue viability and osteogenesis. In addition, the scaffold microstructure allowed the prolonged release of rhBMP-2, which in turn significantly stimulated the osteogenesis of human bone marrow stromal cells in vitro and of bone regeneration in vivo as shown in a rabbit femur defect repair model. Thus, the combination MS/CPC/rhBMP-2 scaffolds might provide a solution to issues of tissue necrosis during the regeneration process and therefore might be able to be readily developed into a useful tool for bone repair in the clinic.

  15. RhBMP-2 loaded 3D-printed mesoporous silica/calcium phosphate cement porous scaffolds with enhanced vascularization and osteogenesis properties

    PubMed Central

    Li, Cuidi; Jiang, Chuan; Deng, Yuan; Li, Tao; Li, Ning; Peng, Mingzheng; Wang, Jinwu

    2017-01-01

    A major limitation in the development of effective scaffolds for bone regeneration has been the limited vascularization of the regenerating tissue. Here, we propose the development of a novel calcium phosphate cement (CPC)-based scaffold combining the properties of mesoporous silica (MS) with recombinant human bone morphogenic protein-2 (rhBMP-2) to facilitate vascularization and osteogenesis. Specifically, the development of a custom MS/CPC paste allowed the three-dimensional (3D) printing of scaffolds with a defined macroporous structure and optimized silicon (Si) ions release profile to promote the ingrowth of vascular tissue at an early stage after implantation in support of tissue viability and osteogenesis. In addition, the scaffold microstructure allowed the prolonged release of rhBMP-2, which in turn significantly stimulated the osteogenesis of human bone marrow stromal cells in vitro and of bone regeneration in vivo as shown in a rabbit femur defect repair model. Thus, the combination MS/CPC/rhBMP-2 scaffolds might provide a solution to issues of tissue necrosis during the regeneration process and therefore might be able to be readily developed into a useful tool for bone repair in the clinic. PMID:28128363

  16. New insights in the velocity dependency of the external mass transfer coefficient in 2D and 3D porous media for liquid chromatography.

    PubMed

    Deridder, Sander; Desmet, Gert

    2012-03-02

    Numerical calculations of the mobile zone mass transfer rate in a variety of ordered 2D and 3D structures are presented. These calculations are in line with earlier theoretical and experimental findings made in the field of chemical engineering and suggest that the Sherwood-number (Sh(m)) appearing in the mobile phase mass transfer term of the general plate height expression of liquid chromatography is not correctly predicted by the Wilson-Geankoplis--or the Kataoka--or the penetration model expression that have been used up to now to in the field of LC, and that at least more research is needed before these expressions can be continued to be used with confidence. The aforementioned expressions were obtained by neglecting the effect of axial dispersion on the mass transfer process, and it seems that they therefore underestimate the true Sh(m)-number by a factor of 2-5 around the minimum of the van Deemter-curve. New correlations describing the variation of the Sh(m)-coefficient as a function of the reduced velocity for a number of other packing geometries (tetrahedral monolith, 2D pillar array) are proposed. These correlations are in agreement with earlier theoretical and experimental studies showing that at low velocities the local-driving force-based Sh(m)-value is of the order of 10-20 in a packed bed column with an external porosity on the order of 35-40%.

  17. A multi-scale Lattice Boltzmann model for simulating solute transport in 3D X-ray micro-tomography images of aggregated porous materials

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoxian; Crawford, John W.; Flavel, Richard J.; Young, Iain M.

    2016-10-01

    The Lattice Boltzmann (LB) model and X-ray computed tomography (CT) have been increasingly used in combination over the past decade to simulate water flow and chemical transport at pore scale in porous materials. Because of its limitation in resolution and the hierarchical structure of most natural soils, the X-ray CT tomography can only identify pores that are greater than its resolution and treats other pores as solid. As a result, the so-called solid phase in X-ray images may in reality be a grey phase, containing substantial connected pores capable of conducing fluids and solute. Although modified LB models have been developed to simulate fluid flow in such media, models for solute transport are relatively limited. In this paper, we propose a LB model for simulating solute transport in binary soil images containing permeable solid phase. The model is based on the single-relaxation time approach and uses a modified partial bounce-back method to describe the resistance caused by the permeable solid phase to chemical transport. We derive the relationship between the diffusion coefficient and the parameter introduced in the partial bounce-back method, and test the model against analytical solution for movement of a pulse of tracer. We also validate it against classical finite volume method for solute diffusion in a simple 2D image, and then apply the model to a soil image acquired using X-ray tomography at resolution of 30 μm in attempts to analyse how the ability of the solid phase to diffuse solute at micron-scale affects the behaviour of the solute at macro-scale after a volumetric average. Based on the simulated results, we discuss briefly the danger in interpreting experimental results using the continuum model without fully understanding the pore-scale processes, as well as the potential of using pore-scale modelling and tomography to help improve the continuum models.

  18. Higher-order compositional modeling of three-phase flow in 3D fractured porous media based on cross-flow equilibrium

    NASA Astrophysics Data System (ADS)

    Moortgat, Joachim; Firoozabadi, Abbas

    2013-10-01

    Numerical simulation of multiphase compositional flow in fractured porous media, when all the species can transfer between the phases, is a real challenge. Despite the broad applications in hydrocarbon reservoir engineering and hydrology, a compositional numerical simulator for three-phase flow in fractured media has not appeared in the literature, to the best of our knowledge. In this work, we present a three-phase fully compositional simulator for fractured media, based on higher-order finite element methods. To achieve computational efficiency, we invoke the cross-flow equilibrium (CFE) concept between discrete fractures and a small neighborhood in the matrix blocks. We adopt the mixed hybrid finite element (MHFE) method to approximate convective Darcy fluxes and the pressure equation. This approach is the most natural choice for flow in fractured media. The mass balance equations are discretized by the discontinuous Galerkin (DG) method, which is perhaps the most efficient approach to capture physical discontinuities in phase properties at the matrix-fracture interfaces and at phase boundaries. In this work, we account for gravity and Fickian diffusion. The modeling of capillary effects is discussed in a separate paper. We present the mathematical framework, using the implicit-pressure-explicit-composition (IMPEC) scheme, which facilitates rigorous thermodynamic stability analyses and the computation of phase behavior effects to account for transfer of species between the phases. A deceptively simple CFL condition is implemented to improve numerical stability and accuracy. We provide six numerical examples at both small and larger scales and in two and three dimensions, to demonstrate powerful features of the formulation.

  19. 3D quantification of dynamic fluid-fluid interfaces in porous media with fast x-ray microtomography: A comparison with quasi-equilibrium methods

    NASA Astrophysics Data System (ADS)

    Meisenheimer, D.; Brueck, C. L.; Wildenschild, D.

    2015-12-01

    X-ray microtomography imaging of fluid-fluid interfaces in three-dimensional porous media allows for the testing of thermodynamically derived predictions that seek a unique relationship between capillary pressure, fluid saturation, and specific interfacial area (Pc-Sw-Anw). Previous experimental studies sought to test this functional dependence under quasi-equilibrium conditions (assumed static on the imaging time-scale); however, applying predictive models developed under static conditions for dynamic scenarios can lead to substantial flaws in predicted outcomes. Theory and models developed using dynamic data can be verified using fast x-ray microtomography which allows for the unprecedented measurement of developing interfacial areas, curvatures, and trapping behaviors of fluid phases in three-dimensional systems. We will present results of drainage and imbibition experiments of air and water within a mixture of glass beads. The experiments were performed under both quasi-equilibrium and dynamic conditions at the Advanced Photon Source (APS) at Argonne National Laboratory. Fast x-ray microtomography was achieved by utilizing the high brilliance of the x-ray beam at the APS under pink-beam conditions where the white beam is modified with a 4 mm Al absorber and a 0.8 mrad Pt-coated mirror to eliminate low and high-energy photons, respectively. We present a comparison of the results from the quasi-equilibrium and dynamic experiments in an effort to determine if the Pc-Sw-Anw relationship is comparable under either experimental condition and to add to the discussion on whether the Pc-Sw-Anw relationship is unique as hypothesized by existing theory.

  20. The effects of magnetohydrodynamic and radiation on flow of second grade fluid past an infinite inclined plate in porous medium

    SciTech Connect

    Ismail, Zulkhibri; Khan, Ilyas; Nasir, Nadirah Mohd; Awang, Rahimah Jusoh; Salleh, Mohd Zuki; Shafie, Sharidan

    2015-02-03

    An analysis of the exact solutions of second grade fluid problem for unsteady magnetohydrodynamic (MHD) flows past an infinite inclined plate in a porous medium is presented. It is assumed that the bounding infinite inclined plate has a constant temperature with radiation effects. Based on Boussinesq approximation the expressions for dimensionless velocity, temperature and concentration are obtained by using Laplace transform method. The derived solutions satisfying the involved differential equations, and all the boundary and initial conditions. The influence of various parameters on the velocity has been illustrated graphically and analyzed.

  1. Heat Source/Sink in a Magneto-Hydrodynamic Non-Newtonian Fluid Flow in a Porous Medium: Dual Solutions.

    PubMed

    Hayat, Tasawar; Awais, Muhammad; Imtiaz, Amna

    2016-01-01

    This communication deals with the properties of heat source/sink in a magneto-hydrodynamic flow of a non-Newtonian fluid immersed in a porous medium. Shrinking phenomenon along with the permeability of the wall is considered. Mathematical modelling is performed to convert the considered physical process into set of coupled nonlinear mathematical equations. Suitable transformations are invoked to convert the set of partial differential equations into nonlinear ordinary differential equations which are tackled numerically for the solution computations. It is noted that dual solutions for various physical parameters exist which are analyzed in detail.

  2. Irreversibility analysis of hydromagnetic flow of couple stress fluid with radiative heat in a channel filled with a porous medium

    NASA Astrophysics Data System (ADS)

    Eegunjobi, A. S.; Makinde, O. D.

    Numerical analysis of the intrinsic irreversibility of a mixed convection hydromagnetic flow of an electrically conducting couple stress fluid through upright channel filled with a saturated porous medium and radiative heat transfer was carried out. The thermodynamics first and second laws were employed to examine the problem. We obtained the dimensionless nonlinear differential equations and solves numerically with shooting procedure joined with a fourth order Runge-Kutta-Fehlberg integration scheme. The temperature and velocity obtained, used to analyse the entropy generation rate together with some various physical parameters of the flow. Our results are presented graphically and talk over.

  3. MHD flow of a micropolar fluid over a stretchable disk in a porous medium with heat and mass transfer

    SciTech Connect

    Rauf, A. Meraj, M. A.; Ashraf, M.; Batool, K.; Hussain, M.

    2015-07-15

    This article studies the simultaneous impacts of heat and mass transfer of an incompressible electrically conducting micropolar fluid generated by the stretchable disk in presence of porous medium. The thermal radiation effect is accounted via Rosseland’s approximation. The governing boundary layer equations are reduced into dimensionless form by employing the suitable similarity transformations. A finite difference base algorithm is utilized to obtain the solution expressions. The impacts of physical parameters on dimensionless axial velocity, radial velocity, micro-rotation, temperature and concentrations profiles are presented and examined carefully. Numerical computation is performed to compute shear stress, couple stress, heat and mass rate at the disk.

  4. Heat Source/Sink in a Magneto-Hydrodynamic Non-Newtonian Fluid Flow in a Porous Medium: Dual Solutions

    PubMed Central

    Hayat, Tasawar; Awais, Muhammad; Imtiaz, Amna

    2016-01-01

    This communication deals with the properties of heat source/sink in a magneto-hydrodynamic flow of a non-Newtonian fluid immersed in a porous medium. Shrinking phenomenon along with the permeability of the wall is considered. Mathematical modelling is performed to convert the considered physical process into set of coupled nonlinear mathematical equations. Suitable transformations are invoked to convert the set of partial differential equations into nonlinear ordinary differential equations which are tackled numerically for the solution computations. It is noted that dual solutions for various physical parameters exist which are analyzed in detail. PMID:27598314

  5. On the stability and uniqueness of the flow of a fluid through a porous medium

    NASA Astrophysics Data System (ADS)

    Hill, A. A.; Rajagopal, K. R.; Vergori, L.

    2016-06-01

    In this short note, we study the stability of flows of a fluid through porous media that satisfies a generalization of Brinkman's equation to include inertial effects. Such flows could have relevance to enhanced oil recovery and also to the flow of dense liquids through porous media. In any event, one cannot ignore the fact that flows through porous media are inherently unsteady, and thus, at least a part of the inertial term needs to be retained in many situations. We study the stability of the rest state and find it to be asymptotically stable. Next, we study the stability of a base flow and find that the flow is asymptotically stable, provided the base flow is sufficiently slow. Finally, we establish results concerning the uniqueness of the flow under appropriate conditions, and present some corresponding numerical results.

  6. Additively Manufactured 3D Porous Ti-6Al-4V Constructs Mimic Trabecular Bone Structure and Regulate Osteoblast Proliferation, Differentiation and Local Factor Production in a Porosity and Surface Roughness Dependent Manner

    PubMed Central

    Cheng, Alice; Humayun, Aiza; Cohen, David J.; Boyan, Barbara D.; Schwartz, Zvi

    2014-01-01

    Additive manufacturing by laser sintering is able to produce high resolution metal constructs for orthopaedic and dental implants. In this study, we used a human trabecular bone template to design and manufacture Ti-6Al-4V constructs with varying porosity via laser sintering. Characterization of constructs revealed interconnected porosities ranging from 15–70% with compressive moduli of 2063–2954 MPa. These constructs with macro porosity were further surface-treated to create a desirable multi-scale micro-/nano-roughness, which has been shown to enhance the osseointegration process. Osteoblasts (MG63 cells) exhibited high viability when grown on the constructs. Proliferation (DNA) and alkaline phosphatase specific activity (ALP), an early differentiation marker, decreased as porosity increased, while osteocalcin (OCN), a late differentiation marker, as well as osteoprotegerin (OPG), vascular endothelial growth factor (VEGF) and bone morphogenetic proteins 2 and 4 (BMP2, BMP4) increased with increasing porosity. 3D constructs with the highest porosity and surface modification supported the greatest osteoblast differentiation and local factor production. These results indicate that additively manufactured 3D porous constructs mimicking human trabecular bone and produced with additional surface treatment can be customized for increased osteoblast response. Increased factors for osteoblast maturation and differentiation on high porosity constructs suggest the enhanced performance of these surfaces for increasing osseointegration in vivo. PMID:25287305

  7. Numerical Study of Non-Newtonian Boundary Layer Flow of Jeffreys Fluid Past a Vertical Porous Plate in a Non-Darcy Porous Medium

    NASA Astrophysics Data System (ADS)

    Ramachandra Prasad, V.; Gaffar, S. Abdul; Keshava Reddy, E.; Bég, O. Anwar

    2014-07-01

    Polymeric enrobing flows are important in industrial manufacturing technology and process systems. Such flows are non-Newtonian. Motivated by such applications, in this article we investigate the nonlinear steady state boundary layer flow, heat, and mass transfer of an incompressible Jefferys non-Newtonian fluid past a vertical porous plate in a non-Darcy porous medium. The transformed conservation equations are solved numerically subject to physically appropriate boundary conditions using a versatile, implicit, Keller-box finite-difference technique. The numerical code is validated with previous studies. The influence of a number of emerging non-dimensional parameters, namely Deborah number (De), Darcy number (Da), Prandtl number (Pr), ratio of relaxation to retardation times (λ), Schmidt number (Sc), Forchheimer parameter (Λ), and dimensionless tangential coordinate (ξ) on velocity, temperature, and concentration evolution in the boundary layer regime are examined in detail. Furthermore, the effects of these parameters on surface heat transfer rate, mass transfer rate, and local skin friction are also investigated. It is found that the boundary layer flow is decelerated with increasing De and Forchheimer parameter, whereas temperature and concentration are elevated. Increasing λ and Da enhances the velocity but reduces the temperature and concentration. The heat transfer rate and mass transfer rates are found to be depressed with increasing De and enhanced with increasing λ. Local skin friction is found to be decreased with a rise in De, whereas it is elevated with increasing λ. An increasing Sc decreases the velocity and concentration but increases temperature.

  8. Similarity Solution for Combined Free-Forced Convection Past a Vertical Porous Plate in a Porous Medium with a Convective Surface Boundary Condition

    NASA Astrophysics Data System (ADS)

    Garg, P.; Purohit, G. N.; Chaudhary, R. C.

    2016-12-01

    This paper studies the mathematical implications of the two dimensional viscous steady laminar combined free-forced convective flow of an incompressible fluid over a semi infinite fixed vertical porous plate embedded in a porous medium. It is assumed that the left surface of the plate is heated by convection from a hot fluid which is at a temperature higher than the temperature of the fluid on the right surface of the vertical plate. To achieve numerical consistency for the problem under consideration, the governing non linear partial differential equations are first transformed into a system of ordinary differential equations using a similarity variable and then solved numerically under conditions admitting similarity solutions. The effects of the physical parameters of both the incompressible fluid and the vertical plate on the dimensionless velocity and temperature profiles are studied and analysed and the results are depicted both graphically and in a tabular form. Finally, algebraic expressions and the numerical values are obtained for the local skin-friction coefficient and the local Nusselt number.

  9. Determining Pore Pressures Along a Slip Surface Within a Saturated Elastic-Plastic Porous Medium

    NASA Astrophysics Data System (ADS)

    Viesca, R. C.; Rice, J. R.; Dunham, E. M.

    2008-12-01

    Here we consider shear rupture along a slip surface in a fluid-saturated elastic-plastic porous medium, like in landslide and earthquake modeling, and assume that there are different poro-elasto-plastic response properties on the two sides of the slip surface. This different response may be because the fault bordering materials are dissimilar, or just because one side is actively yielding and the other is not, or is yielding but in a different mode. In effect, we are representing a core about a slip surface that divides two similar or contrasting materials. This representation is especially relevant in earthquake rupture dynamics. Studies of mature fault zones have noted a trend of fractured host rock extending 10--100m from the fault, with an ultracataclastic core ~100mm about or to one side of the principal slip surface (e.g., Chester and Chester, Tectonophys, 1998; Chester et al., Columbia Univ Pr, 2004). Furthermore, there is likely to exist a material contrast that may come from accumulating km of slip and a bias in accumulated damage. The local pore pressure at the slip surface influences the rupture dynamics because, through the effective stress concept, it controls the local shear strength along the fault, a feature neglected as a simplification in our preliminary poro-elasto-plastic modeling of dynamic rupture (Viesca et al., JGR, 2008). To determine pore pressures at the slip surface under locally elastic-plastic response, we must consider pore pressure discontinuities about that surface that arise in an undrained treatment of off-fault material and their amelioration within resulting thin diffusive boundary layers, such that pore pressure and fluid mass flux in the normal direction are continuous at the slip surface. Our approach builds on previous work considering the effect of contrasts in poroelastic properties on rupture propagation (Rudnicki and Rice, JGR, 2006; Dunham and Rice, JGR, 2008). Here we find expressions for the undrained pore pressure

  10. Study of the fluid flow characteristics in a porous medium for CO2 geological storage using MRI.

    PubMed

    Song, Yongchen; Jiang, Lanlan; Liu, Yu; Yang, Mingjun; Zhou, Xinhuan; Zhao, Yuechao; Dou, Binlin; Abudula, Abuliti; Xue, Ziqiu

    2014-06-01

    The objective of this study was to understand fluid flow in porous media. Understanding of fluid flow process in porous media is important for the geological storage of CO2. The high-resolution magnetic resonance imaging (MRI) technique was used to measure fluid flow in a porous medium (glass beads BZ-02). First, the permeability was obtained from velocity images. Next, CO2-water immiscible displacement experiments using different flow rates were investigated. Three stages were obtained from the MR intensity plot. With increasing CO2 flow rate, a relatively uniform CO2 distribution and a uniform CO2 front were observed. Subsequently, the final water saturation decreased. Using core analysis methods, the CO2 velocities were obtained during the CO2-water immiscible displacement process, which were applied to evaluate the capillary dispersion rate, viscous dominated fractional flow, and gravity flow function. The capillary dispersion rate dominated the effects of capillary, which was largest at water saturations of 0.5 and 0.6. The viscous-dominant fractional flow function varied with the saturation of water. The gravity fractional flow reached peak values at the saturation of 0.6. The gravity forces played a positive role in the downward displacements because they thus tended to stabilize the displacement process, thereby producing increased breakthrough times and correspondingly high recoveries. Finally, the relative permeability was also reconstructed. The study provides useful data regarding the transport processes in the geological storage of CO2.

  11. Rayleigh-Benard convection subject to time dependent wall temperature/gravity in a fluid-saturated anisotropic porous medium

    NASA Astrophysics Data System (ADS)

    Malashetty, M. S.; Basavaraja, D.

    The effect of time-periodic temperature/gravity modulation at the onset of convection in a Boussinesq fluid-saturated anisotropic porous medium is investigated by making a linear stability analysis. Brinkman flow model with effective viscosity larger than the viscosity of the fluid is considered to give a more general theoretical result. The perturbation method is applied for computing the critical Rayleigh and wave numbers for small amplitude temperature/gravity modulation. The shift in the critical Rayleigh number is calculated as a function of frequency of the modulation, viscosity ratio, anisotropy parameter and porous parameter. We have shown that it is possible to advance or delay the onset of convection by time-periodic modulation of the wall temperature and to advance convection by gravity modulation. It is also shown that the small anisotropy parameter has a strong influence on the stability of the system. The effect of viscosity ratio, anisotropy parameter, the porous parameter and the Prandtl number is discussed.

  12. Nonlinear Stress/Strain Behavior of a Synthetic Porous Medium at Seismic Frequencies

    NASA Astrophysics Data System (ADS)

    Roberts, P. M.; Ibrahim, R. H.

    2008-12-01

    Laboratory experiments on porous core samples have shown that seismic-band (100 Hz or less) mechanical, axial stress/strain cycling of the porous matrix can influence the transport behavior of fluids and suspended particles during steady-state fluid flow through the cores. In conjunction with these stimulated transport experiments, measurements of the applied dynamic axial stress/strain were made to investigate the nonlinear mechanical response of porous media for a poorly explored range of frequencies from 1 to 40 Hz. A unique core-holder apparatus that applies low-frequency mechanical stress/strain to 2.54-cm-diameter porous samples during constant-rate fluid flow was used for these experiments. Applied stress was measured with a load cell in series with the source and porous sample, and the resulting strain was measured with an LVDT attached to the core face. A synthetic porous system consisting of packed 1-mm-diameter glass beads was used to investigate both stress/strain and stimulated mass-transport behavior under idealized conditions. The bead pack was placed in a rubber sleeve and static confining stresses of 2.4 MPa radial and 1.7 MPa axial were applied to the sample. Sinusoidal stress oscillations were applied to the sample at 1 to 40 Hz over a range of RMS stress amplitude from 37 to 275 kPa. Dynamic stress/strain was measured before and after the core was saturated with deionized water. The slope of the linear portion of each stress/strain hysteresis loop was used to estimate Young's modulus as a function of frequency and amplitude for both the dry and wet sample. The modulus was observed to increase after the dry sample was saturated. For both dry and wet cases, the modulus decreased with increasing dynamic RMS stress amplitude at a constant frequency of 23 Hz. At constant RMS stress amplitude, the modulus increased with increasing frequency for the wet sample but remained constant for the dry sample. The observed nonlinear behavior of Young's modulus

  13. Interaction of reactive fronts during transport in a homogeneous porous medium with initial small non-uniformity.

    PubMed

    Chen, Jui-Sheng; Liu, Chen-Wuing

    2004-08-01

    A reactive fluid circulating within a porous medium can dissolve minerals with which it is out of equilibrium and modify the porosity and permeability. The positive feedback between fluid transport and mineral dissolution causes complex reaction front morphologies such as fingers or wormholes. This study presents a numerical model to investigate reaction front instability, temporal aquifer porosity, and species concentration evolution during reactive transport in a homogeneous porous medium with two small, initially local non-uniformities. Simulation results indicate that a stable planar front develops for a small upstream pressure gradient while the growth of two non-uniformities becomes unstable for a large upstream pressure gradient. Moreover, the unstable reaction front may be either double- or single-finger in shape. Reaction front shape selection depends on the spacing of the two local non-uniformities and the upstream pressure gradients. A behavior diagram is constructed to identify a planar, single- or double-front morphology. The critical non-uniformities spacing at which a reaction front begins to merge into a single-finger decreases with increasing upstream pressure gradient.

  14. On the movement of a liquid front in an unsaturated, fractured porous medium, Part 2, Mathematical theory

    SciTech Connect

    Nitao, J.J.

    1989-06-01

    A simplified equation of motion is derived for the flow of liquid through an idealized one-dimensional fracture situated in an unsaturated imbibing porous medium. The equation is valid for the case where the matrix material has a much lower saturated conductivity than that of the fracture and the capillary tension in the matrix is sufficiently stronger than gravity. Asymptotic solutions are given for the motion of the liquid front in a parallel fracture system. With the introduction of natural time constants and dimensionless parameters, the flow behavior can be shown to possess various temporal flow regimes. This work is part of the Nevada Nuclear Waste Storage Project and is applicable to understanding some of the various physical parameters affecting liquid flow through a fracture in an unsaturated porous medium, and is particularly useful as a step in understanding the hydrological processes around a nuclear waste repository in an unsaturated environment as well as in other applications where unsaturated fracture flow conditions exist. The solutions are also relevant to numerical model verification. 10 refs., 2 tabs.

  15. Multicomponent effective medium-correlated random walk theory for the diffusion of fluid mixtures through porous media.

    PubMed

    Bonilla, Mauricio R; Bhatia, Suresh K

    2012-01-10

    Molecular transport in nanoconfined spaces plays a key role in many emerging technologies for gas separation and storage, as well as in nanofluidics. The infiltration of fluid mixtures into the voids of porous frameworks having complex topologies is common place to these technologies, and optimizing their performance entails developing a deeper understanding of how the flow of these mixtures is affected by the morphology of the pore space, particularly its pore size distribution and pore connectivity. Although several techniques have been developed for the estimation of the effective diffusivity characterizing the transport of single fluids through porous materials, this is not the case for fluid mixtures, where the only alternatives rely on a time-consuming solution of the pore network equations or adaptations of the single fluid theories which are useful for a limited type of systems. In this paper, a hybrid multicomponent effective medium-correlated random walk theory for the calculation of the effective transport coefficients matrix of fluid mixtures diffusing through porous materials is developed. The theory is suitable for those systems in which component fluxes at the single pore level can be related to the potential gradients of the different species through linear flux laws and corresponds to a generalization of the classical single fluid effective medium theory for the analysis of random resistor networks. Comparison with simulation of the diffusion of binary CO(2)/H(2)S and ternary CO(2)/H(2)S/C(3)H(8) gas mixtures in membranes modeled as large networks of randomly oriented pores with both continuous and discrete pore size distributions demonstrates the power of the theory, which was tested using the well-known generalized Maxwell-Stefan model for surface diffusion at the single pore level.

  16. Study of acoustic radiation during air stream filtration through a porous medium

    NASA Astrophysics Data System (ADS)

    Zaslavskii, Yu. M.; Zaslavskii, V. Yu.

    2012-11-01

    The paper presents results of laboratory experiments on studying the characteristics of acoustic emission generated by a flow of compressed air, which is filtered by porous pumice samples with and without partial fluid saturation. The construction features of the laboratory setup and details of the experiments are described. Porous samples with dry and partially fluid-filled pores are used. The visual patterns of the acoustic emission spectrum, which occurs under stationary filtration of the compressed air, are presented, and its amplitude-frequency distribution characteristic for different sample porosities and different degrees of their fluid saturation is shown. It is demonstrated that the relaxation times of the emission noise level differ. This is revealed during the sharp elimination of the drop in pressure from such samples, i.e., in the nonstationary filtration mode.

  17. Numerical investigation on laminar round-jet impinging on a surface at uniform heat flux in a channel partially filled with a porous medium

    NASA Astrophysics Data System (ADS)

    Buonomo, B.; Diana, A.; Manca, O.; Nardini, S.

    2017-01-01

    Horizontal channel partially filled with porous media and a single round jet impinging on the porous medium are numerically investigated. The wall facing the round jet is partially heated at uniform heat flux. A two-dimensional axial symmetric flow in the channel is assumed to evaluate the thermal behavior within the channel. The analysis in the porous medium is accomplished in local thermal equilibrium conditions and under the Brinkman–Forchheimer-extended Darcy law assumption. The problem is solved employing the Ansys-Fluent code. Results are given in terms of stream function and temperature fields of fluid and solid matrix, wall temperature profiles, air velocity and temperature profiles along the transversal section of channel. The Peclet number ranges from 1 to 1000 and Rayleigh number values are 10, 50, 100 and 1000. Reynolds jet number, solid wall distance and wall heat flux effects on thermal and fluid dynamic behaviors are investigated. Results indicate that Nusselt number has the highest value for the channel with a porous medium of thickness equal to the channel gap, whereas it presents very small changes increasing the porous medium length on the heated wall. Correlations among average Nusselt, Peclet and Rayleigh numbers are proposed.

  18. Europeana and 3D

    NASA Astrophysics Data System (ADS)

    Pletinckx, D.

    2011-09-01

    The current 3D hype creates a lot of interest in 3D. People go to 3D movies, but are we ready to use 3D in our homes, in our offices, in our communication? Are we ready to deliver real 3D to a general public and use interactive 3D in a meaningful way to enjoy, learn, communicate? The CARARE project is realising this for the moment in the domain of monuments and archaeology, so that real 3D of archaeological sites and European monuments will be available to the general public by 2012. There are several aspects to this endeavour. First of all is the technical aspect of flawlessly delivering 3D content over all platforms and operating systems, without installing software. We have currently a working solution in PDF, but HTML5 will probably be the future. Secondly, there is still little knowledge on how to create 3D learning objects, 3D tourist information or 3D scholarly communication. We are still in a prototype phase when it comes to integrate 3D objects in physical or virtual museums. Nevertheless, Europeana has a tremendous potential as a multi-facetted virtual museum. Finally, 3D has a large potential to act as a hub of information, linking to related 2D imagery, texts, video, sound. We describe how to create such rich, explorable 3D objects that can be used intuitively by the generic Europeana user and what metadata is needed to support the semantic linking.

  19. Active targeting in a random porous medium by chemical swarm robots with secondary chemical signaling

    NASA Astrophysics Data System (ADS)

    Grančič, Peter; Štěpánek, František

    2011-08-01

    The multibody dynamics of a system of chemical swarm robots in a porous environment is investigated. The chemical swarm robots are modeled as Brownian particles capable of delivering an encapsulated chemical payload toward a given target location and releasing it in response to an external stimulus. The presence of chemical signals (chemo-attractant) in the system plays a crucial role in coordinating the collective movement of the particles via chemotaxis. For a number of applications, such as distributed chemical processing and targeted drug delivery, the understanding of factors that govern the collective behavior of the particles, especially their ability to localize a given target, is of immense importance. A hybrid modeling methodology based on the combination of the Brownian dynamics method and diffusion problem coupled through the chemotaxis phenomena is used to analyze the impact of a varying signaling threshold and the strength of chemotaxis on the ability of the chemical robots to fulfill their target localization mission. The results demonstrate that the selected performance criteria (the localization half time and the success rate) can be improved when an appropriate signaling process is chosen. Furthermore, for an optimum target localization strategy, the topological complexity of the porous environment needs to be reflected.

  20. Vapour-liquid phase diagram for an ionic fluid in a random porous medium.

    PubMed

    Holovko, M F; Patsahan, O; Patsahan, T

    2016-10-19

    We study the vapour-liquid phase behaviour of an ionic fluid confined in a random porous matrix formed by uncharged hard sphere particles. The ionic fluid is modelled as an equimolar binary mixture of oppositely charged equisized hard spheres, the so-called restricted primitive model (RPM). Considering the matrix-fluid system as a partly-quenched model, we develop a theoretical approach which combines the method of collective variables with the extension of the scaled-particle theory (SPT) for a hard-sphere fluid confined in a disordered hard-sphere matrix. The approach allows us to formulate the perturbation theory using the SPT for the description of the thermodynamics of the reference system. The phase diagrams of the RPM in matrices of different porosities and for different size ratios of matrix and fluid particles are calculated in the random-phase approximation and also when the effects of higher-order correlations between ions are taken into account. Both approximations correctly reproduce the basic effects of porous media on the vapour-liquid phase diagram, i.e. with a decrease of porosity the critical point shifts towards lower fluid densities and lower temperatures and the coexistence region gets narrower. For the fixed matrix porosity, both the critical temperature and the critical density increase with an increase of size of matrix particles and tend to the critical values of the bulk RPM.

  1. Vapour-liquid phase diagram for an ionic fluid in a random porous medium

    NASA Astrophysics Data System (ADS)

    Holovko, M. F.; Patsahan, O.; Patsahan, T.

    2016-10-01

    We study the vapour-liquid phase behaviour of an ionic fluid confined in a random porous matrix formed by uncharged hard sphere particles. The ionic fluid is modelled as an equimolar binary mixture of oppositely charged equisized hard spheres, the so-called restricted primitive model (RPM). Considering the matrix-fluid system as a partly-quenched model, we develop a theoretical approach which combines the method of collective variables with the extension of the scaled-particle theory (SPT) for a hard-sphere fluid confined in a disordered hard-sphere matrix. The approach allows us to formulate the perturbation theory using the SPT for the description of the thermodynamics of the reference system. The phase diagrams of the RPM in matrices of different porosities and for different size ratios of matrix and fluid particles are calculated in the random-phase approximation and also when the effects of higher-order correlations between ions are taken into account. Both approximations correctly reproduce the basic effects of porous media on the vapour-liquid phase diagram, i.e. with a decrease of porosity the critical point shifts towards lower fluid densities and lower temperatures and the coexistence region gets narrower. For the fixed matrix porosity, both the critical temperature and the critical density increase with an increase of size of matrix particles and tend to the critical values of the bulk RPM.

  2. Coupled heat and mass transfer by natural convection adjacent to a permeable horizontal cylinder in a saturated porous medium

    SciTech Connect

    Yih, K.A.

    1999-04-01

    Coupled heat and mass transfer (or double-diffusion) driven by buoyancy, due to temperature and concentration variations in a saturated porous medium, has several important applications in geothermal and geophysical engineering such as the migration of moisture through the air contained in fibrous insulation, the extraction of geothermal energy, underground disposal of nuclear wastes, and the spreading of chemical contaminants through water-saturated soil. Here, the heat and mass transfer characteristics of free convection about a permeable horizontal cylinder embedded in porous media under the coupled effects of thermal and mass diffusion are numerically analyzed. The surface of the horizontal cylinder is maintained at a uniform wall temperature and uniform wall concentration. The transformed governing equations are obtained and solved by Keller box method. Numerical results for the dimensionless temperature profiles, the dimensionless concentration profiles, the Nusselt number and the Sherwood number are presented. Increasing the buoyancy ratio N and the transpiration parameter f{sub w} increases the Nusselt number and the Sherwood number. For thermally assisting flow, when Lewis number Le increases, the Nusselt (Sherwood) number decreases (increases). Whereas, for thermally opposing flow, both the Nusselt number and the Sherwood number increase with increasing the Lewis number.

  3. Magnetohydrodynamic peristaltic transport of couple stress fluid through porous medium in an inclined asymmetric channel with heat transfer

    NASA Astrophysics Data System (ADS)

    Ramesh, K.; Devakar, M.

    2015-11-01

    In the present paper, the effects of magnetic field and heat transfer on the peristaltic flow of an incompressible couple stress fluid through porous medium in an inclined asymmetric channel have been studied under the long wavelength approximation. The exact solutions of the resultant governing equations have been obtained for the stream function, pressure gradient, temperature and heat transfer coefficients. The pressure difference and frictional forces have been computed numerically. The effects of Hartmann number, Darcy number, Grashof number, couple stress parameter, heat generation parameter and inclination angle on the heat characteristics, velocity characteristics, pumping characteristics and trapping phenomena are discussed in detail. It is found that the pressure gradient increases from horizontal channel to vertical channel. The best pumping can be seen at higher Hartmann number. The size of trapped bolus decreases with the increase of couple stress parameter and the strength of the magnetic flied. Increase of heat generation parameter increases the pressure gradient, temperature and the size of the bolus.

  4. Analytic Approximate Solutions of Mixed Convection about an Inclined Flat Plate Embedded in a Porous Medium Filled with Nanofluids

    NASA Astrophysics Data System (ADS)

    Rasekh, A.; Ganji, D. D.

    2013-08-01

    This work is focused on the study of the mixed convection heat transfer over an inclined flat plate in a porous medium saturated with nanofluids. The governed partial differential equations are transformed into ordinary differential equations, which are obtained by similarity solution. A Padé technique is introduced and combined with differential transform method (DTM) with the aim of extending the convergence area of the series solutions. Comparisons are made between the results of the proposed method and the numerical method (fourth-order Rung-Kutta), as well as available results from the literature in solving this problem, and excellent agreement has been observed. The effects of the pertinent parameters, namely wall suction/injection parameter, mixed convection parameter, prescribed constant, nanoparticles volume fraction factor, and different nanoparticles, on the temperature distribution along with local Nusselt number are presented graphically and the physical aspects of the problem are highlighted and discussed.

  5. Stability Analysis and Internal Heating Effect on Oscillatory Convection in a Viscoelastic Fluid Saturated Porous Medium Under Gravity Modulation

    NASA Astrophysics Data System (ADS)

    Bhadauria, B. S.; Singh, M. K.; Singh, A.; Singh, B. K.; Kiran, P.

    2016-12-01

    In this paper, we investigate the combined effect of internal heating and time periodic gravity modulation in a viscoelastic fluid saturated porous medium by reducing the problem into a complex non-autonomous Ginzgburg-Landau equation. Weak nonlinear stability analysis has been performed by using power series expansion in terms of the amplitude of gravity modulation, which is assumed to be small. The Nusselt number is obtained in terms of the amplitude for oscillatory mode of convection. The influence of viscoelastic parameters on heat transfer has been discussed. Gravity modulation is found to have a destabilizing effect at low frequencies and a stabilizing effect at high frequencies. Finally, it is found that overstability advances the onset of convection, more with internal heating. The conditions for which the complex Ginzgburg-Landau equation undergoes Hopf bifurcation and the amplitude equation undergoes supercritical pitchfork bifurcation are studied.

  6. Numerical Simulation of MHD Hiemenz Flow of a Micropolar Fluid towards a Nonlinear Stretching Surface through a Porous Medium

    NASA Astrophysics Data System (ADS)

    Sharma, Rajesh; Bhargava, Rama

    2015-07-01

    In this article, the two-dimensional boundary layer problem of Hiemenz flow (two-dimensional flow of a fluid near a stagnation point) of an incompressible micropolar fluid towards a nonlinear stretching surface placed in a porous medium in the presence of transverse magnetic field is examined. The resulting nonlinear differential equations governing the problem have been transformed by a similarity transformation into a system of nonlinear ordinary differential equations which are solved numerically by the Element Free Galerkin method. The influence of various parameters on the velocity, microrotation, temperature, and concentration is shown. Some of the results are compared with the Finite Element Method. Finally, validation of the numerical results is demonstrated for local skin friction ? for hydrodynamic micropolar fluid flow on a linearly stretching surface.

  7. Multiple Solutions of an Unsteady Stagnation-Point Flow with Melting Heat Transfer in a Darcy-Brinkman Porous Medium

    NASA Astrophysics Data System (ADS)

    Khalid Aurangzaib, M.; Bhattacharyya, Krishnendu; Shafie, Sharidan

    2016-06-01

    The characteristics of the unsteady boundary layer flow with melting heat transfer near a stagnation-point towards a flat plate embedded in a DarcyBrinkman porous medium with thermal radiation are investigated. The governing partial differential equations are transformed into self-similar ordinary differential equations by similarity transformations. The transformed self-similar equations are solved numerically using bvp4c from Matlab for several values of the flow parameters. The study reveals that the multiple solutions exist for the decelerating (A < 0) flow, whereas for the accelerating (A ≥ 0) flow, the solution is unique. The results also indicate that the melting phenomenon increases the rate of heat transfer and delays the boundary layer separation. To validate the current numerical results, comparison with available results is made and found to be in a good agreement.

  8. Effects of mechanical dispersion on the morphological evolution of a chemical dissolution front in a fluid-saturated porous medium

    NASA Astrophysics Data System (ADS)

    Chen, Jui-Sheng; Liu, Chen-Wuing; Lai, Geng-Xin; Ni, Chuen-Fa

    2009-06-01

    SummaryThe dissolution-induced finger or wormhole patterns in porous medium or fracture rock play a crucial role in a variety of scientific, industrial, and engineering practices. Although previous studies have extensively presented a number of numerical models which couples a system of nonlinear governing equations of porosity change due to mineral dissolution, the conservations of groundwater flow and transport of chemical species to investigate the morphological pattern of a chemical dissolution front within a fluid-saturated porous medium, whereas the mechanical dispersion effect has generally been neglected in the model development. This study addresses the effects of mechanical dispersion on the morphological evolution of a chemical dissolution front for a variety of cases. Mechanical dispersion processes is incorporated with the coupled nonlinear governing equation system so as to rebuild a newly numerical model. The results of numerical simulations demonstrate that mechanical dispersion has pronounced impacts on the morphological pattern of the chemical dissolution front. For single local non-uniformity case, mechanical dispersion reduces the finger length of an unstable single-fingering front or retains the shape of a stable planar front while speeding up the front advancement. In the case of two local non-uniformities, adding mechanical dispersion with different flow conditions can yield one of the following results: (1) the shape of the stable planar front is maintained but its advancement is accelerated; (2) the shape of the unstable single-fingering front is maintained but its length is reduced; (3) the unstable double-fingering front is merged into an unstable single-fingering front; and (4) the shape of the unstable double-fingering front is preserved but its fingering length is reduced. A comparison between the behavior diagrams of dissolution front morphology (with and without considering mechanical dispersion) shows that the double-fingering front

  9. The effects of buoyancy on shear-induced melt bands in a compacting porous medium

    NASA Astrophysics Data System (ADS)

    Butler, S. L.

    2009-03-01

    It has recently been shown [Holtzman, B., Groebner, N., Zimmerman, M., Ginsberg, S., Kohlstedt, D., 2003. Stress-driven melt segregation in partially molten rocks. Geochem. Geophys. Geosyst. 4, Art. No. 8607; Holtzman, B.K., Kohlstedt, D.L., 2007. Stress-driven melt segregation and strain partitioning in partially molten rocks: effects of stress and strain. J. Petrol. 48, 2379-2406] that when partially molten rock is subjected to simple shear, bands of high and low porosity are formed at a particular angle to the direction of instantaneous maximum extension. These have been modeled numerically and it has been speculated that high porosity bands may form an interconnected network with a bulk, effective permeability that is enhanced in a direction parallel to the bands. As a result, the bands may act to focus mantle melt towards the axis of mid-ocean ridges [Katz, R.F., Spiegelman, M., Holtzman, B., 2006. The dynamics of melt and shear localization in partially molten aggregates. Nature 442, 676-679]. In this contribution, we examine the combined effects of buoyancy and matrix shear on a deforming porous layer. The linear theory of Spiegelman [Spiegelman, M., 1993. Flow in deformable porous media. Part 1. Simple analysis. J. Fluid Mech. 247, 17-38; Spiegelman, M., 2003. Linear analysis of melt band formation by simple shear. Geochem. Geophys. Geosyst. 4, doi:10.1029/2002GC000499, Article 8615] and Katz et al. [Katz, R.F., Spiegelman, M., Holtzman, B., 2006. The dynamics of melt and shear localization in partially molten aggregates. Nature 442, 676-679] is generalized to include both the effects of buoyancy and matrix shear on a deformable porous layer with strain-rate dependent rheology. The predictions of linear theory are compared with the early time evolution of our 2D numerical model and they are found to be in excellent agreement. For conditions similar to the upper mantle, buoyancy forces can be similar to or much greater than matrix shear-induced forces. The

  10. Experiment and theory for heterogeneous nucleation of protein crystals in a porous medium.

    PubMed

    Chayen, Naomi E; Saridakis, Emmanuel; Sear, Richard P

    2006-01-17

    The determination of high-resolution structures of proteins requires crystals of suitable quality. Because of the new impetus given to structural biology by structural genomics/proteomics, the problem of crystallizing proteins is becoming increasingly acute. There is therefore an urgent requirement for the development of new efficient methods to aid crystal growth. Nucleation is the crucial step that determines the entire crystallization process. Hence, the holy grail is to design a "universal nucleant," a substrate that induces the nucleation of crystals of any protein. We report a theory for nucleation on disordered porous media and its experimental testing and validation using a mesoporous bioactive gel-glass. This material induced the crystallization of the largest number of proteins ever crystallized using a single nucleant. The combination of the model and the experimental results opens up the scope for the rational design of nucleants, leading to alternative means of controlling crystallization.

  11. Onset of centrifugal convection in a magnetic-fluid-saturated porous medium

    NASA Astrophysics Data System (ADS)

    Saravanan, S.; Yamaguchi, H.

    2005-08-01

    This paper concerns the influence of magnetic field on the onset of centrifugal convection in a magnetic-fluid-filled differentially heated porous layer placed in zero-gravity environment by linear stability theory. The axis of rotation of the layer is placed anywhere within its boundaries, which leads to an alternating direction of the centrifugal body force. The critical centrifugal Rayleigh number, the critical wave number, and the eigenfunctions corresponding to two-dimensional flow pattern at the threshold are calculated using a combination of analytical and numerical methods. Results show significant effects even for low magnetic-field strength when the axis location is located near the cold boundary. It is found that the magnetic field has a destabilizing effect and can be suitably adjusted depending on the axis location and particle magnetization to induce more developed convection currents.

  12. Numerical and experimental analysis of the porous medium reservoir at Pittsfield, Illinois

    SciTech Connect

    Wiles, L.E.; Erikson, R.L.; Allen, R.D.; Doherty, T.J.

    1981-08-01

    Numerical and experimental predictions of the St. Peter sandstone reservoir behavior at Pittsfield, Illinois, are being conducted. These analyses are based upon field and laboratory determinations of structural dimensions and physical properties and upon operating CAES design conditions. Numerical modeling addresses bubble development, water coning, thermal development and reservoir dehydration. Air injection rate is calculated as a function of time. The advance of the 50% saturation front during bubble development is depicted in depth versus radius curves for time periods up to 60 days. Experimental analysis embraces ground water chemistry, permeability and dehydration. Permeability of the St. Peter is highly variable due to vertical changes in lithology and variable friability. The new CAES porous media flow facility simulates field conditions of air flow rate, confining pressure, desaturation profile and dynamic stress.

  13. Conditional stability for thermal convection in a rotating couple-stress fluid saturating a porous medium with temperature and pressure dependent viscosity

    NASA Astrophysics Data System (ADS)

    Sunil; Choudhary, Shalu; Mahajan, Amit

    2013-08-01

    A nonlinear stability threshold for rotation in a couple-stress fluid heated from below saturating a porous medium with temperature and pressure dependent viscosity is exactly the same as the linear instability boundary. This optimal result is important because it shows that linearized instability theory has captured completely the physics of the onset of convection. The effects of couple-stress parameter, variable dependent viscosity, medium permeability, Taylor number and Darcy-Brinkman number on the onset of convection are also analysed.

  14. Natural thermal convection in fractured porous media

    NASA Astrophysics Data System (ADS)

    Adler, P. M.; Mezon, C.; Mourzenko, V.; Thovert, J. F.; Antoine, R.; Finizola, A.

    2015-12-01

    In the crust, fractures/faults can provide preferential pathways for fluid flow or act as barriers preventing the flow across these structures. In hydrothermal systems (usually found in fractured rock masses), these discontinuities may play a critical role at various scales, controlling fluid flows and heat transfer. The thermal convection is numerically computed in 3D fluid satured fractured porous media. Fractures are inserted as discrete objects, randomly distributed over a damaged volume, which is a fraction of the total volume. The fluid is assumed to satisfy Darcy's law in the fractures and in the porous medium with exchanges between them. All simulations were made for Rayleigh numbers (Ra) < 150 (hence, the fluid is in thermal equilibrium with the medium), cubic boxes and closed-top conditions. Checks were performed on an unfractured porous medium and the convection cells do start for the theoretical value of Ra, namely 4p². 2D convection was verified up to Ra=800. The influence of parameters such as fracture aperture (or fracture transmissivity), fracture density and fracture length is studied. Moreover, these models are compared to porous media with the same macroscopic permeability. Preliminary results show that the non-uniqueness associated with initial conditions which makes possible either 2D or 3D convection in porous media (Schubert & Straus 1979) is no longer true for fractured porous media (at least for 50porous medium is in good agreement with an unfractured porous medium of the same bulk permeability.

  15. 3d-3d correspondence revisited

    DOE PAGES

    Chung, Hee -Joong; Dimofte, Tudor; Gukov, Sergei; ...

    2016-04-21

    In fivebrane compactifications on 3-manifolds, we point out the importance of all flat connections in the proper definition of the effective 3d N = 2 theory. The Lagrangians of some theories with the desired properties can be constructed with the help of homological knot invariants that categorify colored Jones polynomials. Higgsing the full 3d theories constructed this way recovers theories found previously by Dimofte-Gaiotto-Gukov. As a result, we also consider the cutting and gluing of 3-manifolds along smooth boundaries and the role played by all flat connections in this operation.

  16. Dual-function growth medium and structural soil for use as porous pavement.

    PubMed

    Sloan, John J; Hegemann, Mary Ann; George, Steve A

    2008-01-01

    Permeable grass-covered surfaces can reduce the quantity of storm water runoff and filter out potentially harmful chemicals. The objective of this study was to develop permeable structural soils that sustained healthy turf growth and filtered heavy metals from contaminated pavement runoff. The basic soil medium was a 50:50 mixture (v/v) of expanded shale (ExSh) and quartz sand (QS). The ExSh component consisted of (i) large-diameter particles (3-6 mm), (ii) small-diameter particles (1-3 mm), or (iii) a 50:50 mixture (v/v) of the two. The basic blends were mixed with 0, 10, and 20% sphagnum peat moss (v/v) and 0, 10, and 20% natural zeolites (v/v) and placed in 15-cm-diameter pots in a greenhouse. Bermudagrass plugs were planted in each pot. The addition of sphagnum peat moss to the basic ExSh/QS blend increased bermudagrass growth and improved plant response to added fertilizer. Zeolites had no significant effect on plant growth in the absence of sphagnum peat moss. Growing mediums that contained 10 to 20% sphagnum peat moss and 10 to 20% zeolites consistently produced more bermudagrass biomass than the unamended ExSh/QS mixture. Changing the ratio of small- to large-diameter ExSh in the basic medium did not affect bermudagrass yield. Very low amounts of Cd, Cu, Pb, and Zn were recovered in leachate after the addition of 10 mg metal per pot, suggesting that most heavy metals (>99%) were retained in the growing mediums. Zeolites reduced the amount of Cd and Pb in leachate water, but not Cu or Zn.

  17. The effect of spatially varying velocity field on the transport of radioactivity in a porous medium.

    PubMed

    Sen, Soubhadra; Srinivas, C V; Baskaran, R; Venkatraman, B

    2016-10-01

    In the event of an accidental leak of the immobilized nuclear waste from an underground repository, it may come in contact of the flow of underground water and start migrating. Depending on the nature of the geological medium, the flow velocity of water may vary spatially. Here, we report a numerical study on the migration of radioactivity due to a space dependent flow field. For a detailed analysis, seven different types of velocity profiles are considered and the corresponding concentrations are compared.

  18. A numerical study of convection in a layered porous medium heated from below

    SciTech Connect

    Hickox, C.E.; Chu, Tze Yao.

    1990-01-01

    As part of the Magma Energy Project being pursued at Sandia National Laboratories, a drilling program has been initiated within the Long Valley caldera near Mammoth Lakes, California. Seismological evidence obtained in this region suggests the presence of a relatively shallow magma body. We have performed a numerical simulation for a simplified model of the Long Valley geothermal system in order to elucidate the nature of the large-scale thermal structure within the system and to assess implications for the drilling program. The two-dimensional model consists of three horizontal layers, the upper two of which are porous and saturated with a single phase fluid. The system is limited in horizontal extent and heated uniformly from below. An associated planar, natural convective flow is thus produced. The results of our simulation indicate the possibility of wide variations in vertical temperature profiles for the model system, depending on the location of the drilling operation. Thus it can be inferred that, during the early stages of drilling, the vertical temperature distribution is not a reliable indicator of the presence or absence of a magma body at depth. 14 refs., 5 figs., 4 tabs.

  19. Model of fluid flow and internal erosion of a porous fragile medium

    NASA Astrophysics Data System (ADS)

    Kudrolli, Arshad; Clotet, Xavier

    2016-11-01

    We discuss the internal erosion and transport of particles leading to heterogeneity and channelization of a porous granular bed driven by fluid flow by introducing a model experimental system which enables direct visualization of the evolution of porosity from the single particle up to the system scale. Further, we develop a hybrid hydrodynamic-statistical model to understand the main ingredients needed to simulate our observations. A uniqueness of our study is the close coupling of the experiments and simulations with control parameters used in the simulations derived from the experiments. Understanding this system is of fundamental importance to a number of geophysical processes, and in the extraction of hydrocarbons in the subsurface including the deposition of proppants used in hydraulic fracturing. We provide clear evidence for the importance of curvature of the interface between high and low porosity regions in determining the flux rate needed for erosion and the spatial locations where channels grow. This material is based upon work supported by the U.S. Department of Energy Office of Science, Office of Basic Energy Sciences program under DE-SC0010274.

  20. Natural convection experiments in a liquid-saturated porous medium bounded by vertical coaxial cylinders

    SciTech Connect

    Reda, D.C.

    1983-01-01

    An experimental effort is presently underway to investigate natural convection phenomena in liquid-saturated porous media utilizing a geometry, and hydrodynamic/thermal boundary conditions, relevant to the problem of nuclear-waste isolation in geologic repositories. During the first phase of this research program, detailed measurements were made of the steady-state thermal field throughout an annular test region bounded by a vertical, constant-heat-flux, inner cylinder and a concentrically-placed, constant-temperature, outer cylinder. An overlying, constant-pressure, fluid layer was utilized to supply a permeable upper surface boundary condition. Results showed the heater surface temperature to increase with increasing vertical distance due to the presence of a buoyantly-driven upflow. The measured temperature difference (..delta..T) between the average heater surface temperature and the constant, outer-surface, temperature was found to be progressively below the straight-line/conduction-only solution for ..delta..T vs power input as the latter was systematically increased. Comparisons between measured results and numerical predictions generated with the finite-element code MARIAH showed very good agreement, thereby contributing to the qualification of this code for repository-design applications.

  1. 3D and Education

    NASA Astrophysics Data System (ADS)

    Meulien Ohlmann, Odile

    2013-02-01

    Today the industry offers a chain of 3D products. Learning to "read" and to "create in 3D" becomes an issue of education of primary importance. 25 years professional experience in France, the United States and Germany, Odile Meulien set up a personal method of initiation to 3D creation that entails the spatial/temporal experience of the holographic visual. She will present some different tools and techniques used for this learning, their advantages and disadvantages, programs and issues of educational policies, constraints and expectations related to the development of new techniques for 3D imaging. Although the creation of display holograms is very much reduced compared to the creation of the 90ies, the holographic concept is spreading in all scientific, social, and artistic activities of our present time. She will also raise many questions: What means 3D? Is it communication? Is it perception? How the seeing and none seeing is interferes? What else has to be taken in consideration to communicate in 3D? How to handle the non visible relations of moving objects with subjects? Does this transform our model of exchange with others? What kind of interaction this has with our everyday life? Then come more practical questions: How to learn creating 3D visualization, to learn 3D grammar, 3D language, 3D thinking? What for? At what level? In which matter? for whom?

  2. Impact of kinetic mass transfer on free convection in a porous medium

    NASA Astrophysics Data System (ADS)

    Lu, Chunhui; Shi, Liangsheng; Chen, Yiming; Xie, Yueqing; Simmons, Craig T.

    2016-05-01

    We investigate kinetic mass transfer effects on unstable density-driven flow and transport processes by numerical simulations of a modified Elder problem. The first-order dual-domain mass transfer model coupled with a variable-density-flow model is employed to describe transport behavior in porous media. Results show that in comparison to the no-mass-transfer case, a higher degree of instability and more unstable system is developed in the mass transfer case due to the reduced effective porosity and correspondingly a larger Rayleigh number (assuming permeability is independent on the mobile porosity). Given a constant total porosity, the magnitude of capacity ratio (i.e., immobile porosity/mobile porosity) controls the macroscopic plume profile in the mobile domain, while the magnitude of mass transfer timescale (i.e., the reciprocal of the mass transfer rate coefficient) dominates its evolution rate. The magnitude of capacity ratio plays an important role on the mechanism driving the mass flux into the aquifer system. Specifically, for a small capacity ratio, solute loading is dominated by the density-driven transport, while with increasing capacity ratio local mass transfer dominated solute loading may occur at later times. At significantly large times, however, both mechanisms contribute comparably to solute loading. Sherwood Number could be a nonmonotonic function of mass transfer timescale due to complicated interactions of solute between source zone, mobile zone and immobile zone in the top boundary layer, resulting in accordingly a similar behavior of the total mass. The initial assessment provides important insights into unstable density-driven flow and transport in the presence of kinetic mass transfer.

  3. Effect of nonionic surfactant partitioning on the dissolution kinetics of residual perchloroethylene in a model porous medium

    NASA Astrophysics Data System (ADS)

    Sharmin, Rumana; Ioannidis, Marios A.; Legge, Raymond L.

    2006-01-01

    At concentrations above the critical micelle concentration, surfactants can significantly enhance the solubilization of residual nonaqueous phase liquids (NAPL) and, for this reason, are the focus of research on surfactant-enhanced aquifer remediation (SEAR). As a consequence of their amphiphilic nature, surfactants may also partition to various extents between the organic and aqueous phases, thereby affecting SEAR performance. We report here on the observation and analysis of the effect of surfactant partitioning on the dissolution kinetics of residual perchloroethylene (PCE) by aqueous solutions (1000 mg/L) of the non-ionic surfactant Triton X-100 in a model porous medium. For this fluid system, batch equilibration experiments showed that the surfactant partitions strongly into the NAPL (NAPL-water partition coefficient equal to 12.5). Dynamic interfacial tension (IFT) measurements were employed to study surfactant diffusion and interfacial adsorption. The dynamic IFT measurements were consistent with partitioning of the surfactant between the two liquid phases. PCE dissolution experiments, conducted in a transparent glass micromodel using an aqueous surfactant solution, were contrasted to experiments using clean water. Surfactant partitioning was observed to delay significantly the onset of micellar solubilization of PCE, an observation reproduced by a numerical model. This effect is attributed to the reduction of surfactant concentration in the immediate vicinity of the NAPL-water interface, which accompanies transport of the surfactant into the NAPL. Accordingly, it is suggested that both the rate and the extent of diffusion of the surfactant into the NAPL affect the onset of and the driving force for micellar solubilization. While many surfactants do not readily partition in NAPL, this possibility must be considered when selecting non-ionic surfactants for the enhanced solubilization of residual chlorinated solvents in porous media.

  4. Numerical simulation of heat transfer and fluid flow of Water-CuO Nanofluid in a sinusoidal channel with a porous medium

    NASA Astrophysics Data System (ADS)

    Nazari, Saman; Toghraie, Davood

    2017-03-01

    This study has compared the convection heat transfer of Water-based fluid flow with that of Water-Copper oxide (CuO) nanofluid in a sinusoidal channel with a porous medium. The heat flux in the lower and upper walls has been assumed constant, and the flow has been assumed to be two-dimensional, steady, laminar, and incompressible. The governing equations include equations of continuity, momentum, and energy. The assumption of thermal equilibrium has been considered between the porous medium and the fluid. The effects of the parameters, Reynolds number and Darcy number on the thermal performance of the channel, have been investigated. The results of this study show that the presence of a porous medium in a channel, as well as adding nanoparticles to the base fluid, increases the Nusselt number and the convection heat transfer coefficient. Also the results show that As the Reynolds number increases, the temperature gradient increases. In addition, changes in this parameter are greater in the throat of the flow than in convex regions due to changes in the channel geometry. In addition, porous regions reduce the temperature difference, which in turn increases the convective heat transfer coefficient.

  5. RT3D tutorials for GMS users

    SciTech Connect

    Clement, T.P.; Jones, N.L.

    1998-02-01

    RT3D (Reactive Transport in 3-Dimensions) is a computer code that solves coupled partial differential equations that describe reactive-flow and transport of multiple mobile and/or immobile species in a three dimensional saturated porous media. RT3D was developed from the single-species transport code, MT3D (DoD-1.5, 1997 version). As with MT3D, RT3D also uses the USGS groundwater flow model MODFLOW for computing spatial and temporal variations in groundwater head distribution. This report presents a set of tutorial problems that are designed to illustrate how RT3D simulations can be performed within the Department of Defense Groundwater Modeling System (GMS). GMS serves as a pre- and post-processing interface for RT3D. GMS can be used to define all the input files needed by RT3D code, and later the code can be launched from within GMS and run as a separate application. Once the RT3D simulation is completed, the solution can be imported to GMS for graphical post-processing. RT3D v1.0 supports several reaction packages that can be used for simulating different types of reactive contaminants. Each of the tutorials, described below, provides training on a different RT3D reaction package. Each reaction package has different input requirements, and the tutorials are designed to describe these differences. Furthermore, the tutorials illustrate the various options available in GMS for graphical post-processing of RT3D results. Users are strongly encouraged to complete the tutorials before attempting to use RT3D and GMS on a routine basis.

  6. 3D Imaging.

    ERIC Educational Resources Information Center

    Hastings, S. K.

    2002-01-01

    Discusses 3 D imaging as it relates to digital representations in virtual library collections. Highlights include X-ray computed tomography (X-ray CT); the National Science Foundation (NSF) Digital Library Initiatives; output peripherals; image retrieval systems, including metadata; and applications of 3 D imaging for libraries and museums. (LRW)

  7. 3D velocity distribution of P- and S-waves in a biotite gneiss, measured in oil as the pressure medium: Comparison with velocity measurements in a multi-anvil pressure apparatus and with texture-based calculated data

    NASA Astrophysics Data System (ADS)

    Lokajíček, T.; Kern, H.; Svitek, T.; Ivankina, T.

    2014-06-01

    Ultrasonic measurements of the 3D velocity distribution of P- and S-waves were performed on a spherical sample of a biotite gneiss from the Outokumpu scientific drill hole. Measurements were done at room temperature and pressures up to 400 and 70 MPa, respectively, in a pressure vessel with oil as a pressure medium. A modified transducer/sample assembly and the installation of a new mechanical system allowed simultaneous measurements of P- and S-wave velocities in 132 independent directions of the sphere on a net in steps of 15°. Proper signals for P- and S-waves could be recorded by coating the sample surface with a high-viscosity shear wave gel and by temporal point contacting of the transmitter and receiver transducers with the sample surface during the measurements. The 3D seismic measurements revealed a strong foliation-related directional dependence (anisotropy) of P- and S-wave velocities, which is confirmed by measurements in a multi-anvil apparatus on a cube-shaped specimen of the same rock. Both experimental approaches show a marked pressure sensitivity of P- and S-wave velocities and velocity anisotropies. With increasing pressure, P- and S-wave velocities increase non-linearly due to progressive closure of micro-cracks. The reverse is true for velocity anisotropy. 3D velocity calculations based on neutron diffraction measurements of crystallographic preferred orientation (CPO) of major minerals show that the intrinsic bulk anisotropy is basically caused by the CPO of biotite constituting about 23 vol.% of the rock. Including the shape of biotite grains and oriented low-aspect ratio microcracks into the modelling increases bulk anisotropy. An important finding from this study is that the measurements on the sample sphere and on the sample cube displayed distinct differences, particularly in shear wave velocities. It is assumed that the differences are due to the different geometries of the samples and the configuration of the transducer-sample assembly

  8. MHD Natural Convection Flow of Casson Nanofluid over Nonlinearly Stretching Sheet Through Porous Medium with Chemical Reaction and Thermal Radiation.

    PubMed

    Ullah, Imran; Khan, Ilyas; Shafie, Sharidan

    2016-12-01

    In the present work, the effects of chemical reaction on hydromagnetic natural convection flow of Casson nanofluid induced due to nonlinearly stretching sheet immersed in a porous medium under the influence of thermal radiation and convective boundary condition are performed numerically. Moreover, the effects of velocity slip at stretching sheet wall are also examined in this study. The highly nonlinear-coupled governing equations are converted to nonlinear ordinary differential equations via similarity transformations. The transformed governing equations are then solved numerically using the Keller box method and graphical results for velocity, temperature, and nanoparticle concentration as well as wall shear stress, heat, and mass transfer rate are achieved through MATLAB software. Numerical results for the wall shear stress and heat transfer rate are presented in tabular form and compared with previously published work. Comparison reveals that the results are in good agreement. Findings of this work demonstrate that Casson fluids are better to control the temperature and nanoparticle concentration as compared to Newtonian fluid when the sheet is stretched in a nonlinear way. Also, the presence of suspended nanoparticles effectively promotes the heat transfer mechanism in the base fluid.

  9. Aligned magnetic field and cross-diffusion effects of a nanofluid over an exponentially stretching surface in porous medium

    NASA Astrophysics Data System (ADS)

    Sulochana, C.; Sandeep, N.; Sugunamma, V.; Rushi Kumar, B.

    2016-06-01

    In this paper, we investigated the effects of aligned magnetic field, thermal radiation, heat generation/absorption, cross-diffusion, viscous dissipation, heat source and chemical reaction on the flow of a nanofluid past an exponentially stretching sheet in porous medium. The governing partial differential equations are transformed to set of ordinary differential equations using self-similarity transformation, which are then solved numerically using bvp4c Matlab package. Finally the effects of various non-dimensional parameters on velocity, temperature, concentration, skin friction, local Nusselt and Sherwood numbers are thoroughly investigated and presented through graphs and tables. We observed that an increase in the aligned angle strengthens the applied magnetic field and decreases the velocity profiles of the flow. Soret and Dufour numbers are helpful to enhance the heat transfer rate. An increase in the heat source parameter, radiation parameter and Eckert number increases the mass transfer rate. Mixed convection parameter has tendency to enhance the friction factor along with the heat and mass transfer rate.

  10. Analysis of heat transfer for unsteady MHD free convection flow of rotating Jeffrey nanofluid saturated in a porous medium

    NASA Astrophysics Data System (ADS)

    Mohd Zin, Nor Athirah; Khan, Ilyas; Shafie, Sharidan; Alshomrani, Ali Saleh

    In this article, the influence of thermal radiation on unsteady magnetohydrodynamics (MHD) free convection flow of rotating Jeffrey nanofluid passing through a porous medium is studied. The silver nanoparticles (AgNPs) are dispersed in the Kerosene Oil (KO) which is chosen as conventional base fluid. Appropriate dimensionless variables are used and the system of equations is transformed into dimensionless form. The resulting problem is solved using the Laplace transform technique. The impact of pertinent parameters including volume fraction φ , material parameters of Jeffrey fluid λ1 , λ , rotation parameter r , Hartmann number Ha , permeability parameter K , Grashof number Gr , Prandtl number Pr , radiation parameter Rd and dimensionless time t on velocity and temperature profiles are presented graphically with comprehensive discussions. It is observed that, the rotation parameter, due to the Coriolis force, tends to decrease the primary velocity but reverse effect is observed in the secondary velocity. It is also observed that, the Lorentz force retards the fluid flow for both primary and secondary velocities. The expressions for skin friction and Nusselt number are also evaluated for different values of emerging parameters. A comparative study with the existing published work is provided in order to verify the present results. An excellent agreement is found.

  11. Flow and heat transfer in a Maxwell liquid film over an unsteady stretching sheet in a porous medium with radiation.

    PubMed

    Waheed, Shimaa E

    2016-01-01

    A problem of flow and heat transfer in a non-Newtonian Maxwell liquid film over an unsteady stretching sheet embedded in a porous medium in the presence of a thermal radiation is investigated. The unsteady boundary layer equations describing the problem are transformed to a system of non-linear ordinary differential equations which is solved numerically using the shooting method. The effects of various parameters like the Darcy parameter, the radiation parameter, the Deborah number and the Prandtl number on the flow and temperature profiles as well as on the local skin-friction coefficient and the local Nusselt number are presented and discussed. It is observed that increasing values of the Darcy parameter and the Deborah number cause an increase of the local skin-friction coefficient values and decrease in the values of the local Nusselt number. Also, it is noticed that the local Nusselt number increases as the Prandtl number increases and it decreases with increasing the radiation parameter. However, it is found that the free surface temperature increases by increasing the Darcy parameter, the radiation parameter and the Deborah number whereas it decreases by increasing the Prandtl number.

  12. MHD Natural Convection Flow of Casson Nanofluid over Nonlinearly Stretching Sheet Through Porous Medium with Chemical Reaction and Thermal Radiation

    NASA Astrophysics Data System (ADS)

    Ullah, Imran; Khan, Ilyas; Shafie, Sharidan

    2016-11-01

    In the present work, the effects of chemical reaction on hydromagnetic natural convection flow of Casson nanofluid induced due to nonlinearly stretching sheet immersed in a porous medium under the influence of thermal radiation and convective boundary condition are performed numerically. Moreover, the effects of velocity slip at stretching sheet wall are also examined in this study. The highly nonlinear-coupled governing equations are converted to nonlinear ordinary differential equations via similarity transformations. The transformed governing equations are then solved numerically using the Keller box method and graphical results for velocity, temperature, and nanoparticle concentration as well as wall shear stress, heat, and mass transfer rate are achieved through MATLAB software. Numerical results for the wall shear stress and heat transfer rate are presented in tabular form and compared with previously published work. Comparison reveals that the results are in good agreement. Findings of this work demonstrate that Casson fluids are better to control the temperature and nanoparticle concentration as compared to Newtonian fluid when the sheet is stretched in a nonlinear way. Also, the presence of suspended nanoparticles effectively promotes the heat transfer mechanism in the base fluid.

  13. Natural convection in square cavity filled with ferrofluid saturated porous medium in the presence of uniform magnetic field

    NASA Astrophysics Data System (ADS)

    Javed, Tariq; Mehmood, Z.; Abbas, Z.

    2017-02-01

    This article contains numerical results for free convection through square enclosure enclosing ferrofluid saturated porous medium when uniform magnetic field is applied upon the flow along x-axis. Heat is provided through bottom wall and a square blockage placed near left or right bottom corner of enclosure as a heat source. Left and right vertical boundaries of the cavity are considered insulated while upper wall is taken cold. The problem is modelled in terms of system of nonlinear partial differential equations. Finite element method has been adopted to compute numerical simulations of mathematical problem for wide range of pertinent flow parameters including Rayleigh number, Hartman number, Darcy number and Prandtl number. Analysis of results reveals that the strength of streamline circulation is an increasing function of Darcy and Prandtl number where convection heat transfer is dominant for large values of these parameters whereas increase in Hartman number has opposite effects on isotherms and streamline circulations. Thermal conductivity and hence local heat transfer rate of fluid gets increased when ferroparticles are introduced in the fluid. Average Nusselt number increases with increase in Darcy and Rayleigh numbers while it is decreases when Hartman number is increased.

  14. Miscible gravitational instability of initially stable horizontal interface in a porous medium: Non-monotonic density profiles

    NASA Astrophysics Data System (ADS)

    Kim, Min Chan

    2014-11-01

    To simulate a CO2 sequestration process, some researchers employed a water/propylene glycol (PPG) system which shows a non-monotonic density profile. Motivated by this fact, the stability of the diffusion layer of two miscible fluids saturated in a porous medium is analyzed. For a non-monotonic density profile system, linear stability equations are derived in a global domain, and then transformed into a system of ordinary differential equations in an infinite domain. Initial growth rate analysis is conducted without the quasi-steady state approximation (QSSA) and shows that initially the system is unconditionally stable for the least stable disturbance. For the time evolving case, the ordinary differential equations are solved applying the eigen-analysis and numerical shooting scheme with and without the QSSA. To support these theoretical results, direct numerical simulations are conducted using the Fourier spectral method. The results of theoretical linear stability analyses and numerical simulations validate one another. The present linear and nonlinear analyses show that the water/PPG system is more unstable than the CO2/brine one, and the flow characteristics of these two systems are quite different from each other.

  15. Mathematical Analysis of Hall Effect on Transient Hartman Flow about a Rotating Horizontal Permeable Surface in a Porous Medium under Inclined Magnetic Field.

    PubMed

    Suresh, M; Manglik, A

    2014-01-01

    This paper proposes the exact solution for unsteady flow of a viscous incompressible electrically conducting fluid past a impulsively started infinite horizontal surface which is rotating with an angular velocity embedded in a saturated porous medium under the influence of strong magnetic field with hall effect. Our study focuses on the change of direction of the external magnetic field on the flow system which leads to change in the flow behavior and skin frictional forces at the boundary. Systems of flow equations are solved using Laplace transform technique. The impacts of control parameters Hartman number, rotation of the system, hall effect, inclination of the magnetic field, and Darcy number on primary and secondary velocities are shown graphically, skin friction at horizontal boundary in tabular form. For validating our results, in the absence of permeability of the porous medium and inclination of the magnetic field the results are in good agreement with the published results.

  16. Mathematical Analysis of Hall Effect on Transient Hartman Flow about a Rotating Horizontal Permeable Surface in a Porous Medium under Inclined Magnetic Field

    PubMed Central

    Suresh, M.; Manglik, A.

    2014-01-01

    This paper proposes the exact solution for unsteady flow of a viscous incompressible electrically conducting fluid past a impulsively started infinite horizontal surface which is rotating with an angular velocity embedded in a saturated porous medium under the influence of strong magnetic field with hall effect. Our study focuses on the change of direction of the external magnetic field on the flow system which leads to change in the flow behavior and skin frictional forces at the boundary. Systems of flow equations are solved using Laplace transform technique. The impacts of control parameters Hartman number, rotation of the system, hall effect, inclination of the magnetic field, and Darcy number on primary and secondary velocities are shown graphically, skin friction at horizontal boundary in tabular form. For validating our results, in the absence of permeability of the porous medium and inclination of the magnetic field the results are in good agreement with the published results. PMID:27433540

  17. Ferrocyanide Safety Program: Waste tank sludge rheology within a hot spot or during draining. Homogeneous flow versus flow through a porous medium

    SciTech Connect

    Fauske, H.K.; Cash, R.J.

    1993-11-01

    The conditions under which ferrocyanide waste sludge flows as a homogeneous non-Newtonian two-phase (solid precipitate-liquid) mixture rather than as a liquid through a porous medium (of stationary precipitate) are examined theoretically, based on the notion that the preferred rheological behavior of the sludge is the one which imposes the least resistance to the sludge flow. The homogeneous two-phase mixture is modeled as a power-law fluid and simple criteria are derived that show that the homogeneous power-law sludge-flow is a much more likely flow situation than the porous medium model of sludge flow. The implication of this finding is that the formation of a hot spot or the drainage of sludge from a waste tank are not likely to result in the uncovering (drying) and subsequent potential overheating of the reactive-solid component of the sludge.

  18. AE3D

    SciTech Connect

    Spong, Donald A

    2016-06-20

    AE3D solves for the shear Alfven eigenmodes and eigenfrequencies in a torodal magnetic fusion confinement device. The configuration can be either 2D (e.g. tokamak, reversed field pinch) or 3D (e.g. stellarator, helical reversed field pinch, tokamak with ripple). The equations solved are based on a reduced MHD model and sound wave coupling effects are not currently included.

  19. Slip Analysis at Fluid-Solid Interface in MHD Squeezing Flow of Casson Fluid through Porous Medium

    NASA Astrophysics Data System (ADS)

    Qayyum, Mubashir; Khan, Hamid; Khan, Omar

    An unsteady squeezing flow of Casson fluid having Magneto Hydro Dynamic effect and passing through porous medium channel with slip at the boundaries has been modelled and analyzed. Similarity transformations are applied to the governing partial differential equations of the Casson model to get a highly non-linear fourth order ordinary differential equation. The obtained equation is then solved analytically using the Homotopy Perturbation Method (HPM) for uniform and non-uniform slip at the boundaries. Five cases of boundary conditions, representing slip at upper wall only, uniform slip at both walls, non-uniform slip where slip at upper wall is greater than that of lower wall, non-uniform slip where slip at lower wall is greater than that of upper wall, and slip at lower wall only are considered and thoroughly investigated. Validation is performed by solving the equation numerically using fourth order explicit Runge Kutta method (ERK4). Both analytical and numerical results show good agreement. Lastly, the effects of various fluid parameters on the velocity profile are investigated for each case graphically. Analysis of these plots show that the positive and negative squeeze numbers have opposite effect on the velocity profile throughout all the cases. It is also observed that various fluid parameters like Casson, MHD, and Permeability have similar effects on the velocity profile in the cases when slip is occurring at the upper wall only, and non-uniform slip at both the boundaries with slip at lower wall is greater than upper wall. Furthermore, similar effects have been observed when slip is uniform at both the boundaries, and in case of non-uniform slip with slip at lower wall is less than the upper wall.

  20. Porous wall hollow glass microspheres as a medium or substrate for storage and formation of novel materials

    DOEpatents

    Wicks, George G; Serkiz, Steven M.; Zidan, Ragaiy; Heung, Leung K.

    2014-06-24

    Porous wall hollow glass microspheres are provided as a template for formation of nanostructures such as carbon nanotubes, In addition, the carbon nanotubes in combination with the porous wall hollow glass microsphere provides an additional reaction template with respect to carbon nanotubes.

  1. 3-D Seismic Interpretation

    NASA Astrophysics Data System (ADS)

    Moore, Gregory F.

    2009-05-01

    This volume is a brief introduction aimed at those who wish to gain a basic and relatively quick understanding of the interpretation of three-dimensional (3-D) seismic reflection data. The book is well written, clearly illustrated, and easy to follow. Enough elementary mathematics are presented for a basic understanding of seismic methods, but more complex mathematical derivations are avoided. References are listed for readers interested in more advanced explanations. After a brief introduction, the book logically begins with a succinct chapter on modern 3-D seismic data acquisition and processing. Standard 3-D acquisition methods are presented, and an appendix expands on more recent acquisition techniques, such as multiple-azimuth and wide-azimuth acquisition. Although this chapter covers the basics of standard time processing quite well, there is only a single sentence about prestack depth imaging, and anisotropic processing is not mentioned at all, even though both techniques are now becoming standard.

  2. Radiochromic 3D Detectors

    NASA Astrophysics Data System (ADS)

    Oldham, Mark

    2015-01-01

    Radiochromic materials exhibit a colour change when exposed to ionising radiation. Radiochromic film has been used for clinical dosimetry for many years and increasingly so recently, as films of higher sensitivities have become available. The two principle advantages of radiochromic dosimetry include greater tissue equivalence (radiologically) and the lack of requirement for development of the colour change. In a radiochromic material, the colour change arises direct from ionising interactions affecting dye molecules, without requiring any latent chemical, optical or thermal development, with important implications for increased accuracy and convenience. It is only relatively recently however, that 3D radiochromic dosimetry has become possible. In this article we review recent developments and the current state-of-the-art of 3D radiochromic dosimetry, and the potential for a more comprehensive solution for the verification of complex radiation therapy treatments, and 3D dose measurement in general.

  3. Bootstrapping 3D fermions

    DOE PAGES

    Iliesiu, Luca; Kos, Filip; Poland, David; ...

    2016-03-17

    We study the conformal bootstrap for a 4-point function of fermions <ψψψψ> in 3D. We first introduce an embedding formalism for 3D spinors and compute the conformal blocks appearing in fermion 4-point functions. Using these results, we find general bounds on the dimensions of operators appearing in the ψ × ψ OPE, and also on the central charge CT. We observe features in our bounds that coincide with scaling dimensions in the GrossNeveu models at large N. Finally, we also speculate that other features could coincide with a fermionic CFT containing no relevant scalar operators.

  4. Bootstrapping 3D fermions

    SciTech Connect

    Iliesiu, Luca; Kos, Filip; Poland, David; Pufu, Silviu S.; Simmons-Duffin, David; Yacoby, Ran

    2016-03-17

    We study the conformal bootstrap for a 4-point function of fermions <ψψψψ> in 3D. We first introduce an embedding formalism for 3D spinors and compute the conformal blocks appearing in fermion 4-point functions. Using these results, we find general bounds on the dimensions of operators appearing in the ψ × ψ OPE, and also on the central charge CT. We observe features in our bounds that coincide with scaling dimensions in the GrossNeveu models at large N. Finally, we also speculate that other features could coincide with a fermionic CFT containing no relevant scalar operators.

  5. Venus in 3D

    NASA Technical Reports Server (NTRS)

    Plaut, Jeffrey J.

    1993-01-01

    Stereographic images of the surface of Venus which enable geologists to reconstruct the details of the planet's evolution are discussed. The 120-meter resolution of these 3D images make it possible to construct digital topographic maps from which precise measurements can be made of the heights, depths, slopes, and volumes of geologic structures.

  6. 3D photoacoustic imaging

    NASA Astrophysics Data System (ADS)

    Carson, Jeffrey J. L.; Roumeliotis, Michael; Chaudhary, Govind; Stodilka, Robert Z.; Anastasio, Mark A.

    2010-06-01

    Our group has concentrated on development of a 3D photoacoustic imaging system for biomedical imaging research. The technology employs a sparse parallel detection scheme and specialized reconstruction software to obtain 3D optical images using a single laser pulse. With the technology we have been able to capture 3D movies of translating point targets and rotating line targets. The current limitation of our 3D photoacoustic imaging approach is its inability ability to reconstruct complex objects in the field of view. This is primarily due to the relatively small number of projections used to reconstruct objects. However, in many photoacoustic imaging situations, only a few objects may be present in the field of view and these objects may have very high contrast compared to background. That is, the objects have sparse properties. Therefore, our work had two objectives: (i) to utilize mathematical tools to evaluate 3D photoacoustic imaging performance, and (ii) to test image reconstruction algorithms that prefer sparseness in the reconstructed images. Our approach was to utilize singular value decomposition techniques to study the imaging operator of the system and evaluate the complexity of objects that could potentially be reconstructed. We also compared the performance of two image reconstruction algorithms (algebraic reconstruction and l1-norm techniques) at reconstructing objects of increasing sparseness. We observed that for a 15-element detection scheme, the number of measureable singular vectors representative of the imaging operator was consistent with the demonstrated ability to reconstruct point and line targets in the field of view. We also observed that the l1-norm reconstruction technique, which is known to prefer sparseness in reconstructed images, was superior to the algebraic reconstruction technique. Based on these findings, we concluded (i) that singular value decomposition of the imaging operator provides valuable insight into the capabilities of

  7. Influence of phase connectivity on the relationship among capillary pressure, fluid saturation, and interfacial area in two-fluid-phase porous medium systems

    DOE PAGES

    McClure, James E.; Berrill, Mark A.; Gray, William G.; ...

    2016-09-02

    Here, multiphase flow in porous medium systems is typically modeled using continuum mechanical representations at the macroscale in terms of averaged quantities. These models require closure relations to produce solvable forms. One of these required closure relations is an expression relating fluid pressures, fluid saturations, and, in some cases, the interfacial area between the fluid phases, and the Euler characteristic. An unresolved question is whether the inclusion of these additional morphological and topological measures can lead to a non-hysteretic closure relation compared to the hysteretic forms that are used in traditional models, which typically do not include interfacial areas, ormore » the Euler characteristic. We develop a lattice-Boltzmann (LB) simulation approach to investigate the equilibrium states of a two-fluid-phase porous medium system, which include disconnected now- wetting phase features. The proposed approach is applied to a synthetic medium consisting of 1,964 spheres arranged in a random, non-overlapping, close-packed manner, yielding a total of 42,908 different equilibrium points. This information is evaluated using a generalized additive modeling approach to determine if a unique function from this family exists, which can explain the data. The variance of various model estimates is computed, and we conclude that, except for the limiting behavior close to a single fluid regime, capillary pressure can be expressed as a deterministic and non-hysteretic function of fluid saturation, interfacial area between the fluid phases, and the Euler characteristic. This work is unique in the methods employed, the size of the data set, the resolution in space and time, the true equilibrium nature of the data, the parameterizations investigated, and the broad set of functions examined. The conclusion of essentially non-hysteretic behavior provides support for an evolving class of two-fluid-phase flow in porous medium systems models.« less

  8. Influence of phase connectivity on the relationship among capillary pressure, fluid saturation, and interfacial area in two-fluid-phase porous medium systems

    SciTech Connect

    McClure, James E.; Berrill, Mark A.; Gray, William G.; Miller, Cass T.

    2016-09-02

    Here, multiphase flow in porous medium systems is typically modeled using continuum mechanical representations at the macroscale in terms of averaged quantities. These models require closure relations to produce solvable forms. One of these required closure relations is an expression relating fluid pressures, fluid saturations, and, in some cases, the interfacial area between the fluid phases, and the Euler characteristic. An unresolved question is whether the inclusion of these additional morphological and topological measures can lead to a non-hysteretic closure relation compared to the hysteretic forms that are used in traditional models, which typically do not include interfacial areas, or the Euler characteristic. We develop a lattice-Boltzmann (LB) simulation approach to investigate the equilibrium states of a two-fluid-phase porous medium system, which include disconnected now- wetting phase features. The proposed approach is applied to a synthetic medium consisting of 1,964 spheres arranged in a random, non-overlapping, close-packed manner, yielding a total of 42,908 different equilibrium points. This information is evaluated using a generalized additive modeling approach to determine if a unique function from this family exists, which can explain the data. The variance of various model estimates is computed, and we conclude that, except for the limiting behavior close to a single fluid regime, capillary pressure can be expressed as a deterministic and non-hysteretic function of fluid saturation, interfacial area between the fluid phases, and the Euler characteristic. This work is unique in the methods employed, the size of the data set, the resolution in space and time, the true equilibrium nature of the data, the parameterizations investigated, and the broad set of functions examined. The conclusion of essentially non-hysteretic behavior provides support for an evolving class of two-fluid-phase flow in porous medium systems models.

  9. On the propagation of a quasi-static disturbance in a heterogeneous, deformable, and porous medium with pressure-dependent properties

    SciTech Connect

    Vasco, D.W.

    2011-10-01

    Using an asymptotic technique, valid when the medium properties are smoothly-varying, I derive a semi-analytic expression for the propagation velocity of a quasi-static disturbance traveling within a nonlinear-elastic porous medium. The phase, a function related to the propagation time, depends upon the properties of the medium, including the pressure-sensitivities of the medium parameters, and on pressure and displacement amplitude changes. Thus, the propagation velocity of a disturbance depends upon its amplitude, as might be expected for a nonlinear process. As a check, the expression for the phase function is evaluated for a poroelastic medium, when the material properties do not depend upon the fluid pressure. In that case, the travel time estimates agree with conventional analytic estimates, and with values calculated using a numerical simulator. For a medium with pressure-dependent permeability I find general agreement between the semi-analytic estimates and estimates from a numerical simulation. In this case the pressure amplitude changes are obtained from the numerical simulator.

  10. Simulation of contaminant flow ina laboratory-scale porous system

    SciTech Connect

    Rashidi, M.

    1995-12-01

    The microscopic movement of contaminants in a porous medium has been simulated in an experiment. The approach has been to study the microscale transport processes using a novel nonintrusive fluorescence imaging technique developed in our laboratories. The system studied consists of a packed porous column with a refractive index-matched fluid seeded with fluorescent tracer particles (for flow measurements) or an organic dye (for contaminant concentration measurements). Microscopic measurements of contaminant concentration, contaminant velocity, and pore geometry were obtained in a full three-dimensional volume of the test section at a good accuracy and a high resolution. 3D plots of these measurements show the complex geometry of the porous medium. It is also seen that near the contaminant front there is a significant correlation between the flow and the contaminant concentration. The goal is to use these and future results toward better understanding of contaminant flow and report thorough natural porous media.

  11. Double-diffusive mixed convection boundary layer flow from a vertical flat plate embedded in a porous medium filled by a nanofluid

    NASA Astrophysics Data System (ADS)

    Yasin, Mohd Hafizi Mat; Ishak, Anuar

    2016-11-01

    The objective of this study is to investigate the effects of mass suction on double diffusive mixed convection boundary layer flow from a vertical flat plate embedded in a porous medium filled by a nanofluid using Buongiorno's model. The appropriate similarity transformation is used to reduce the partial differential equations into a system of ordinary differential equation, which is then solved numerically using a shooting method. The effects of mass suction parameter on the flow field and heat transfer characteristics are presented and discussed.

  12. Lie symmetry analysis of a double-diffusive free convective slip flow with a convective boundary condition past a radiating vertical surface embedded in a porous medium

    NASA Astrophysics Data System (ADS)

    Afify, A. A.; Uddin, Md. J.

    2016-09-01

    A numerical study of a steady two-dimensional double-diffusive free convection boundary layer flow over a vertical surface embedded in a porous medium with slip flow and convective boundary conditions, heat generation/absorption, and solar radiation effects is performed. A scaling group of transformations is used to obtain the governing boundary layer equations and the boundary conditions. The transformed equations are then solved by the fourth- and fifth-order Runge-Kutta-Fehlberg numerical method with Maple 13. The results for the velocity, temperature, and concentration profiles, as well as the skin friction coefficient, the Nusselt number, and the Sherwood number are presented and discussed.

  13. An Effective Continuum Model for the Liquid-to-Gas Phase Change in a Porous Medium Driven by Solute Diffusion: II. Constant Liquid Withdrawal Rates

    SciTech Connect

    Tsimpanogiannis, Ioannis N.; Yortsos, Yanis C.

    2001-08-15

    This report describes the development of an effective continuum model to describe the nucleation and subsequent growth of a gas phase from a supersaturated, slightly compressible binary liquid in a porous medium, driven by solute diffusion.This report also focuses on the processes resulting from the withdrawal of the liquid at a constant rate. As before, the model addresses two stages before the onset of bulk gas flow, nucleation and gas phase growth. Because of negligible gradients due to gravity or viscous forces, the critical gas saturation, is only a function of the nucleation fraction.

  14. Exact analysis of MHD flow of a Walters'-B fluid over an isothermal oscillating plate embedded in a porous medium

    NASA Astrophysics Data System (ADS)

    Ali, Farhad; Saqib, Muhammad; Khan, Ilyas; Sheikh, Nadeem Ahmad; Jan, Syed Aftab Alam

    2017-02-01

    This paper carries out an exact analysis of the MHD free convection flow of a Walters'-B fluid over an oscillating isothermal vertical plate embedded in a porous medium. Exact solutions are produced for velocity, temperature and concentration with the aid of the Laplace transform technique. Similarly, at the wall, the corresponding shear stress is also calculated from the velocity expression. The obtained results confirm an excellent agreement with previously published work. The influence of various pertinent parameters is plotted and illustrated graphically. Finally, the numerical results for the skin friction are exhibited in tabular form.

  15. Visualizing 3D Fracture Morphology in Granular Media

    NASA Astrophysics Data System (ADS)

    Dalbe, M. J.; Juanes, R.

    2015-12-01

    Multiphase flow in porous media plays a fundamental role in many natural and engineered subsurface processes. The interplay between fluid flow, medium deformation and fracture is essential in geoscience problems as disparate as fracking for unconventional hydrocarbon production, conduit formation and methane venting from lake and ocean sediments, and desiccation cracks in soil. Recent work has pointed to the importance of capillary forces in some relevant regimes of fracturing of granular materials (Sandnes et al., Nat. Comm. 2011), leading to the term hydro-capillary fracturing (Holtzman et al., PRL 2012). Most of these experimental and computational investigations have focused, however, on 2D or quasi-2D systems. Here, we develop an experimental set-up that allows us to observe two-phase flow in a 3D granular bed, and control the level of confining stress. We use an index matching technique to directly visualize the injection of a liquid in a granular media saturated with another, immiscible liquid. We determine the key dimensionless groups that control the behavior of the system, and elucidate different regimes of the invasion pattern. We present result for the 3D morphology of the invasion, with particular emphasis on the fracturing regime.

  16. Visualizing 3D fracture morphology in granular media

    NASA Astrophysics Data System (ADS)

    Dalbe, Marie-Julie; Juanes, Ruben

    2015-11-01

    Multiphase flow in porous media plays a fundamental role in many natural and engineered subsurface processes. The interplay between fluid flow, medium deformation and fracture is essential in geoscience problems as disparate as fracking for unconventional hydrocarbon production, conduit formation and methane venting from lake and ocean sediments, and desiccation cracks in soil. Recent work has pointed to the importance of capillary forces in some relevant regimes of fracturing of granular materials (Sandnes et al., Nat. Comm. 2011), leading to the term hydro-capillary fracturing (Holtzman et al., PRL 2012). Most of these experimental and computational investigations have focused, however, on 2D or quasi-2D systems. Here, we develop an experimental set-up that allows us to observe two-phase flow in a 3D granular bed, and control the level of confining stress. We use an index matching technique to directly visualize the injection of a liquid in a granular media saturated with another, immiscible liquid. We determine the key dimensionless groups that control the behavior of the system, and elucidate different regimes of the invasion pattern. We present result for the 3D morphology of the invasion, with particular emphasis on the fracturing regime.

  17. Twin Peaks - 3D

    NASA Technical Reports Server (NTRS)

    1997-01-01

    The two hills in the distance, approximately one to two kilometers away, have been dubbed the 'Twin Peaks' and are of great interest to Pathfinder scientists as objects of future study. 3D glasses are necessary to identify surface detail. The white areas on the left hill, called the 'Ski Run' by scientists, may have been formed by hydrologic processes.

    The IMP is a stereo imaging system with color capability provided by 24 selectable filters -- twelve filters per 'eye.

    Click below to see the left and right views individually. [figure removed for brevity, see original site] Left [figure removed for brevity, see original site] Right

  18. 3D and beyond

    NASA Astrophysics Data System (ADS)

    Fung, Y. C.

    1995-05-01

    This conference on physiology and function covers a wide range of subjects, including the vasculature and blood flow, the flow of gas, water, and blood in the lung, the neurological structure and function, the modeling, and the motion and mechanics of organs. Many technologies are discussed. I believe that the list would include a robotic photographer, to hold the optical equipment in a precisely controlled way to obtain the images for the user. Why are 3D images needed? They are to achieve certain objectives through measurements of some objects. For example, in order to improve performance in sports or beauty of a person, we measure the form, dimensions, appearance, and movements.

  19. 3D Audio System

    NASA Technical Reports Server (NTRS)

    1992-01-01

    Ames Research Center research into virtual reality led to the development of the Convolvotron, a high speed digital audio processing system that delivers three-dimensional sound over headphones. It consists of a two-card set designed for use with a personal computer. The Convolvotron's primary application is presentation of 3D audio signals over headphones. Four independent sound sources are filtered with large time-varying filters that compensate for motion. The perceived location of the sound remains constant. Possible applications are in air traffic control towers or airplane cockpits, hearing and perception research and virtual reality development.

  20. A Diffuse Interface Model for solid-liquid-air dissolution problems based on a porous medium theory

    NASA Astrophysics Data System (ADS)

    Luo, H.; Quintard, M.; Debenest, G.; Laouafa, F.

    2011-12-01

    The underground cavities may be dissolved by the flows of groundwater where the dissolution mainly happens at the liquid-solid interface. In many real cases, the cavities are not occupied only by the water, but also the gas phase, e.g., air, or other gases. In this case, there are solid-liquid-gas three phases. Normally, the air does not participate the dissolution. However, it may influence the dissolution as the position of the solid-liquid interface may gradually lower down with the dissolution process. Simulating the dissolution problems with multi- moving interfaces is a difficult task but rather interesting to study the evolution of the underground cavities. In this paper, we propose a diffuse interface model (DIM) to simulate the three-phase dissolution problem, based on a porous medium theory and a volume averaging theory te{Whitaker1999,Golfier2002,Quintard1994}. The interface is regarded as a continuous layer where the phase indicator (mainly for solid-liquid interface) and phase saturation (mainly for liquid-gas interface) vary rapidly but smoothly. The DIM equations enable us to simulate the moving interface under a fixed mesh system, instead of a deformed or moving mesh. Suppose we have three phases, solid, liquid and gas. The solid phase contains only species A. The gas phase contains only the air. The volume averaging theory is used to upscale the balance equations. The final DIM equations are presented below. The balance equation of solid phase can be written as {partialrho_{s}(1-\\varepsilon_{f})}/{partial t}=-K_{sl} where \\varepsilonf represents the volume fraction of the fluids (liquid+gas) and Ksl refers to the mass exchange between the solid phase and the liquid phase. Ksl cam be expressed as K_{sl}=rho_{l}alpha(omega_{eq}-Omega_{Al}). The balance equations of liquid phase can be written as {partialrho_{l}\\varepsilon_{f}S_{l}}/{partial t}+nabla\\cdot(rho_{l}{V}_{l})= K_{sl}. The balance equation of liquid phase can be written as {partialrho

  1. Preferential water and solute fluxes in a model macropored porous medium as a function of flow rate

    NASA Astrophysics Data System (ADS)

    batany, stephane; Peyneau, Pierre-Emmanuel; Lassabatere, Laurent; Bechet, Beatrice; Faure, Pamela; Dangla, Patrick

    2016-04-01

    Macropores in soils can induce preferential flow and increase solute transport. Close to water saturation, most of the water flows through macropores at a much higher rate than it would in the same soil without any macropore. Preferential flow and water infiltration in soils with macropores have been investigated with different modeling approaches. Most of these are based on dual porosity or dual permeability approaches. These approaches consider that macropored soils are constituted by the association of two regions exchanging water, a matrix and a macropore domain, both of them obeying Darcy's law. Nevertheless, these approaches restrict preferential flow to the macropore domain and cannot simulate any enhancement of flow in the matrix surrounding the macropores. However, this hypothesis has been strongly questioned by several studies that had investigated solute transfer in macropored soils for which solute breakthrough curves (BTCs) were in complete disagreement with the flow restriction to the macropore domain. Thus, the understanding of water infiltration in soils requires more investigations regarding the effect of macropore and cracks in soils. The proposed paper aims at investigating water flow and tracer transport in a water saturated model macropored system as a function of the flow rate. Various solutes were injected in a 5 cm diameter, 14.5 cm high column filled with 425-800 μm diameter glass beads glued together. A 3 mm diameter Teflon rod inserted along the axis of the column during the preparation of the system was removed after the consolidation of the porous medium to create a macropore. Several flow rates - always ensuring a laminar flow - were tested, from values for which the diffusion transport rate is similar to the advective transport rate to values several orders of magnitude higher for which advection dominates. For all flow rates, solute BTCs were analyzed using the moment method and MIM model to quantify the volume of water visited by

  2. Hydrodispersive characterization of a sandy porous medium by tracer tests carried out in laboratory on undisturbed soil samples

    NASA Astrophysics Data System (ADS)

    Ferrante, Aldo Pedro; Fallico, Carmine; Rios, Ana C.; Fernanda Rivera, Maria; Santillan, Patricio; Salazar, Mario

    2013-04-01

    The contamination of large areas and correspondent aquifers often imposes to implement some recovery operations which are generally complex and very expensive. Anyway, these interventions necessarily require the preventive characterization of the aquifers to be reclaimed and in particular the knowledge of the relevant hydrodispersive parameters. The determination of these parameters requires the implementation tracer tests for the specific site (Sauty JP, 1978). To reduce cost and time that such test requires tracer tests on undisturbed soil samples, representative of the whole aquifer, can be performed. These laboratory tests are much less expensive and require less time, but the results are certainly less reliable than those obtained by field tests for several reasons, including the particular scale of investigation. In any case the hydrodispersive parameters values, obtained by tests carried out in laboratory, can provide useful information on the considered aquifer, allowing to carry out initial verifications on the transmission and propagation of the pollutants in the aquifer considered. For this purpose, tracer tests with inlet of short time were carried out in the Soil Physics Laboratory of the Department of Soil Protection (University of Calabria), on a series of sandy soil samples with six different lengths, repeating each test with three different water flow velocities (5 m/d; 10 m/s and 15 m/d) (J. Feyen et al., 1998). The lengths of the samples taken into account are respectively 15 cm, 24 cm, 30 cm, 45 cm, 60 cm and 75 cm, while the solution used for each test was made of 100 ml of water and NaCl with a concentration of this substance corresponding to 10 g/L. For the porous medium taken into consideration a particle size analysis was carried out, resulting primarily made of sand, with total porosity equal to 0.33. Each soil sample was placed in a flow cell in which was inlet the tracer from the bottom upwards, measuring by a conductivimeter the

  3. Oscillatory MHD Convective Flow of Second Order Fluid Through Porous Medium in a Vertical Rotating Channel in Slip-Flow Regime with Heat Radiation

    NASA Astrophysics Data System (ADS)

    Garg, B. P.; Singh, K. D.; Bansal, A. K.

    2015-02-01

    An analysis of an oscillatory magnetohydrodynamic (MHD) convective flow of a second order (viscoelastic), incompressible, and electrically conducting fluid through a porous medium bounded by two infinite vertical parallel porous plates is presented. The two porous plates with slip-flow condition and the no-slip condition are subjected respectively to a constant injection and suction velocity. The pressure gradient in the channel varies periodically with time. A magnetic field of uniform strength is applied in the direction perpendicular to the planes of the plates. The induced magnetic field is neglected due to the assumption of a small magnetic Reynolds number. The temperature of the plate with no-slip condition is non-uniform and oscillates periodically with time and the temperature difference of the two plates is assumed high enough to induce heat radiation. The entire system rotates in unison about the axis perpendicular to the planes of the plates. Adopting complex variable notations, a closed form solution of the problem is obtained. The analytical results are evaluated numerically and then presented graphically to discuss in detail the effects of different parameters of the problem. The velocity, temperature and the skin-friction in terms of its amplitude and phase angle have been shown graphically to observe the effects of the viscoelastic parameter γ, rotation parameter Ω, suction parameter λ , Grashof number Gr, Hartmann number M, the pressure A, Prandtl number Pr, radiation parameter N and the frequency of oscillation ω .

  4. 3D Surgical Simulation

    PubMed Central

    Cevidanes, Lucia; Tucker, Scott; Styner, Martin; Kim, Hyungmin; Chapuis, Jonas; Reyes, Mauricio; Proffit, William; Turvey, Timothy; Jaskolka, Michael

    2009-01-01

    This paper discusses the development of methods for computer-aided jaw surgery. Computer-aided jaw surgery allows us to incorporate the high level of precision necessary for transferring virtual plans into the operating room. We also present a complete computer-aided surgery (CAS) system developed in close collaboration with surgeons. Surgery planning and simulation include construction of 3D surface models from Cone-beam CT (CBCT), dynamic cephalometry, semi-automatic mirroring, interactive cutting of bone and bony segment repositioning. A virtual setup can be used to manufacture positioning splints for intra-operative guidance. The system provides further intra-operative assistance with the help of a computer display showing jaw positions and 3D positioning guides updated in real-time during the surgical procedure. The CAS system aids in dealing with complex cases with benefits for the patient, with surgical practice, and for orthodontic finishing. Advanced software tools for diagnosis and treatment planning allow preparation of detailed operative plans, osteotomy repositioning, bone reconstructions, surgical resident training and assessing the difficulties of the surgical procedures prior to the surgery. CAS has the potential to make the elaboration of the surgical plan a more flexible process, increase the level of detail and accuracy of the plan, yield higher operative precision and control, and enhance documentation of cases. Supported by NIDCR DE017727, and DE018962 PMID:20816308

  5. Martian terrain - 3D

    NASA Technical Reports Server (NTRS)

    1997-01-01

    An area of rocky terrain near the landing site of the Sagan Memorial Station can be seen in this image, taken in stereo by the Imager for Mars Pathfinder (IMP) on Sol 3. 3D glasses are necessary to identify surface detail. This image is part of a 3D 'monster' panorama of the area surrounding the landing site.

    Mars Pathfinder is the second in NASA's Discovery program of low-cost spacecraft with highly focused science goals. The Jet Propulsion Laboratory, Pasadena, CA, developed and manages the Mars Pathfinder mission for NASA's Office of Space Science, Washington, D.C. JPL is an operating division of the California Institute of Technology (Caltech). The Imager for Mars Pathfinder (IMP) was developed by the University of Arizona Lunar and Planetary Laboratory under contract to JPL. Peter Smith is the Principal Investigator.

    Click below to see the left and right views individually. [figure removed for brevity, see original site] Left [figure removed for brevity, see original site] Right

  6. Towards a rigorous mesoscale modeling of reactive flow and transport in an evolving porous medium and its applications to soil science

    NASA Astrophysics Data System (ADS)

    Ray, Nadja; Rupp, Andreas; Knabner, Peter

    2016-04-01

    Soil is arguably the most prominent example of a natural porous medium that is composed of a porous matrix and a pore space. Within this framework and in terms of soil's heterogeneity, we first consider transport and fluid flow at the pore scale. From there, we develop a mechanistic model and upscale it mathematically to transfer our model from the small scale to that of the mesoscale (laboratory scale). The mathematical framework of (periodic) homogenization (in principal) rigorously facilitates such processes by exactly computing the effective coefficients/parameters by means of the pore geometry and processes. In our model, various small-scale soil processes may be taken into account: molecular diffusion, convection, drift emerging from electric forces, and homogeneous reactions of chemical species in a solvent. Additionally, our model may consider heterogeneous reactions at the porous matrix, thus altering both the porosity and the matrix. Moreover, our model may additionally address biophysical processes, such as the growth of biofilms and how this affects the shape of the pore space. Both of the latter processes result in an intrinsically variable soil structure in space and time. Upscaling such models under the assumption of a locally periodic setting must be performed meticulously to preserve information regarding the complex coupling of processes in the evolving heterogeneous medium. Generally, a micro-macro model emerges that is then comprised of several levels of couplings: Macroscopic equations that describe the transport and fluid flow at the scale of the porous medium (mesoscale) include averaged time- and space-dependent coefficient functions. These functions may be explicitly computed by means of auxiliary cell problems (microscale). Finally, the pore space in which the cell problems are defined is time- and space dependent and its geometry inherits information from the transport equation's solutions. Numerical computations using mixed finite

  7. Thermodynamically Constrained Averaging Theory Approach for Modeling Flow and Transport Phenomena in Porous Medium Systems: 8. Interface and Common Curve Dynamics

    PubMed Central

    Gray, William G.; Miller, Cass T.

    2010-01-01

    This work is the eighth in a series that develops the fundamental aspects of the thermodynamically constrained averaging theory (TCAT) that allows for a systematic increase in the scale at which multiphase transport phenomena is modeled in porous medium systems. In these systems, the explicit locations of interfaces between phases and common curves, where three or more interfaces meet, are not considered at scales above the microscale. Rather, the densities of these quantities arise as areas per volume or length per volume. Modeling of the dynamics of these measures is an important challenge for robust models of flow and transport phenomena in porous medium systems, as the extent of these regions can have important implications for mass, momentum, and energy transport between and among phases, and formulation of a capillary pressure relation with minimal hysteresis. These densities do not exist at the microscale, where the interfaces and common curves correspond to particular locations. Therefore, it is necessary for a well-developed macroscale theory to provide evolution equations that describe the dynamics of interface and common curve densities. Here we point out the challenges and pitfalls in producing such evolution equations, develop a set of such equations based on averaging theorems, and identify the terms that require particular attention in experimental and computational efforts to parameterize the equations. We use the evolution equations developed to specify a closed two-fluid-phase flow model. PMID:21197134

  8. Thermodynamically Constrained Averaging Theory Approach for Modeling Flow and Transport Phenomena in Porous Medium Systems: 8. Interface and Common Curve Dynamics.

    PubMed

    Gray, William G; Miller, Cass T

    2010-12-01

    This work is the eighth in a series that develops the fundamental aspects of the thermodynamically constrained averaging theory (TCAT) that allows for a systematic increase in the scale at which multiphase transport phenomena is modeled in porous medium systems. In these systems, the explicit locations of interfaces between phases and common curves, where three or more interfaces meet, are not considered at scales above the microscale. Rather, the densities of these quantities arise as areas per volume or length per volume. Modeling of the dynamics of these measures is an important challenge for robust models of flow and transport phenomena in porous medium systems, as the extent of these regions can have important implications for mass, momentum, and energy transport between and among phases, and formulation of a capillary pressure relation with minimal hysteresis. These densities do not exist at the microscale, where the interfaces and common curves correspond to particular locations. Therefore, it is necessary for a well-developed macroscale theory to provide evolution equations that describe the dynamics of interface and common curve densities. Here we point out the challenges and pitfalls in producing such evolution equations, develop a set of such equations based on averaging theorems, and identify the terms that require particular attention in experimental and computational efforts to parameterize the equations. We use the evolution equations developed to specify a closed two-fluid-phase flow model.

  9. Education System Using Interactive 3D Computer Graphics (3D-CG) Animation and Scenario Language for Teaching Materials

    ERIC Educational Resources Information Center

    Matsuda, Hiroshi; Shindo, Yoshiaki

    2006-01-01

    The 3D computer graphics (3D-CG) animation using a virtual actor's speaking is very effective as an educational medium. But it takes a long time to produce a 3D-CG animation. To reduce the cost of producing 3D-CG educational contents and improve the capability of the education system, we have developed a new education system using Virtual Actor.…

  10. 3D field harmonics

    SciTech Connect

    Caspi, S.; Helm, M.; Laslett, L.J.

    1991-03-30

    We have developed an harmonic representation for the three dimensional field components within the windings of accelerator magnets. The form by which the field is presented is suitable for interfacing with other codes that make use of the 3D field components (particle tracking and stability). The field components can be calculated with high precision and reduced cup time at any location (r,{theta},z) inside the magnet bore. The same conductor geometry which is used to simulate line currents is also used in CAD with modifications more readily available. It is our hope that the format used here for magnetic fields can be used not only as a means of delivering fields but also as a way by which beam dynamics can suggest correction to the conductor geometry. 5 refs., 70 figs.

  11. Silk-based anisotropical 3D biotextiles for bone regeneration.

    PubMed

    Ribeiro, Viviana P; Silva-Correia, Joana; Nascimento, Ana I; da Silva Morais, Alain; Marques, Alexandra P; Ribeiro, Ana S; Silva, Carla J; Bonifácio, Graça; Sousa, Rui A; Oliveira, Joaquim M; Oliveira, Ana L; Reis, Rui L

    2017-04-01

    Bone loss in the craniofacial complex can been treated using several conventional therapeutic strategies that face many obstacles and limitations. In this work, novel three-dimensional (3D) biotextile architectures were developed as a possible strategy for flat bone regeneration applications. As a fully automated processing route, this strategy as potential to be easily industrialized. Silk fibroin (SF) yarns were processed into weft-knitted fabrics spaced by a monofilament of polyethylene terephthalate (PET). A comparative study with a similar 3D structure made entirely of PET was established. Highly porous scaffolds with homogeneous pore distribution were observed using micro-computed tomography analysis. The wet state dynamic mechanical analysis revealed a storage modulus In the frequency range tested, the storage modulus values obtained for SF-PET scaffolds were higher than for the PET scaffolds. Human adipose-derived stem cells (hASCs) cultured on the SF-PET spacer structures showed the typical pattern for ALP activity under osteogenic culture conditions. Osteogenic differentiation of hASCs on SF-PET and PET constructs was also observed by extracellular matrix mineralization and expression of osteogenic-related markers (osteocalcin, osteopontin and collagen type I) after 28 days of osteogenic culture, in comparison to the control basal medium. The quantification of convergent macroscopic blood vessels toward the scaffolds by a chick chorioallantoic membrane assay, showed higher angiogenic response induced by the SF-PET textile scaffolds than PET structures and gelatin sponge controls. Subcutaneous implantation in CD-1 mice revealed tissue ingrowth's accompanied by blood vessels infiltration in both spacer constructs. The structural adaptability of textile structures combined to the structural similarities of the 3D knitted spacer fabrics to craniofacial bone tissue and achieved biological performance, make these scaffolds a possible solution for tissue

  12. Bioinspired gas bubble spontaneous and directional transportation effects in an aqueous medium.

    PubMed

    Ma, Rui; Wang, Jingming; Yang, Zhongjia; Liu, Meng; Zhang, Jingjing; Jiang, Lei

    2015-04-08

    A series of well-ordered, 3D gradient porous interconnected network surfaces composed of micro-nano hierarchical geometries is constructed on a copper wire. A continuous gas film can be trapped around its interface in an aqueous medium acting as an effective channel for gas transportation. Driving by the difference of the Laplace pressure, gas bubbles can be transported spontaneously and directionally.

  13. Intraoral 3D scanner

    NASA Astrophysics Data System (ADS)

    Kühmstedt, Peter; Bräuer-Burchardt, Christian; Munkelt, Christoph; Heinze, Matthias; Palme, Martin; Schmidt, Ingo; Hintersehr, Josef; Notni, Gunther

    2007-09-01

    Here a new set-up of a 3D-scanning system for CAD/CAM in dental industry is proposed. The system is designed for direct scanning of the dental preparations within the mouth. The measuring process is based on phase correlation technique in combination with fast fringe projection in a stereo arrangement. The novelty in the approach is characterized by the following features: A phase correlation between the phase values of the images of two cameras is used for the co-ordinate calculation. This works contrary to the usage of only phase values (phasogrammetry) or classical triangulation (phase values and camera image co-ordinate values) for the determination of the co-ordinates. The main advantage of the method is that the absolute value of the phase at each point does not directly determine the coordinate. Thus errors in the determination of the co-ordinates are prevented. Furthermore, using the epipolar geometry of the stereo-like arrangement the phase unwrapping problem of fringe analysis can be solved. The endoscope like measurement system contains one projection and two camera channels for illumination and observation of the object, respectively. The new system has a measurement field of nearly 25mm × 15mm. The user can measure two or three teeth at one time. So the system can by used for scanning of single tooth up to bridges preparations. In the paper the first realization of the intraoral scanner is described.

  14. 'Diamond' in 3-D

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This 3-D, microscopic imager mosaic of a target area on a rock called 'Diamond Jenness' was taken after NASA's Mars Exploration Rover Opportunity ground into the surface with its rock abrasion tool for a second time.

    Opportunity has bored nearly a dozen holes into the inner walls of 'Endurance Crater.' On sols 177 and 178 (July 23 and July 24, 2004), the rover worked double-duty on Diamond Jenness. Surface debris and the bumpy shape of the rock resulted in a shallow and irregular hole, only about 2 millimeters (0.08 inch) deep. The final depth was not enough to remove all the bumps and leave a neat hole with a smooth floor. This extremely shallow depression was then examined by the rover's alpha particle X-ray spectrometer.

    On Sol 178, Opportunity's 'robotic rodent' dined on Diamond Jenness once again, grinding almost an additional 5 millimeters (about 0.2 inch). The rover then applied its Moessbauer spectrometer to the deepened hole. This double dose of Diamond Jenness enabled the science team to examine the rock at varying layers. Results from those grindings are currently being analyzed.

    The image mosaic is about 6 centimeters (2.4 inches) across.

  15. Prominent rocks - 3D

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Many prominent rocks near the Sagan Memorial Station are featured in this image, taken in stereo by the Imager for Mars Pathfinder (IMP) on Sol 3. 3D glasses are necessary to identify surface detail. Wedge is at lower left; Shark, Half-Dome, and Pumpkin are at center. Flat Top, about four inches high, is at lower right. The horizon in the distance is one to two kilometers away.

    Mars Pathfinder is the second in NASA's Discovery program of low-cost spacecraft with highly focused science goals. The Jet Propulsion Laboratory, Pasadena, CA, developed and manages the Mars Pathfinder mission for NASA's Office of Space Science, Washington, D.C. JPL is an operating division of the California Institute of Technology (Caltech). The Imager for Mars Pathfinder (IMP) was developed by the University of Arizona Lunar and Planetary Laboratory under contract to JPL. Peter Smith is the Principal Investigator.

    Click below to see the left and right views individually. [figure removed for brevity, see original site] Left [figure removed for brevity, see original site] Right

  16. Saffman-Taylor fingering: why it is not a proper upscaled model of viscous fingering in a (even two-dimensional) random porous medium

    NASA Astrophysics Data System (ADS)

    Meheust, Y.; Toussaint, R.; Lovoll, G.; Maloy, K. J.

    2015-12-01

    P.G. Saffman & G. Taylor (1958) studied the stability of the interface between two immiscible fluids of different densities and viscosities when one displaces the other inside a Hele-Shaw (HS) cell. They showed that with a horizontal cell and if the displaced fluid is the more viscous, the interface is unstable and leads to a viscous fingering which they nearly fully modeled [1]. The HS geometry was introduced as a geometry imposing the same flow behavior as the Darcy-scale flow in a two-dimensional (2D) porous medium, and therefore allowing an analogy between the two configurations. This is however not obvious, since capillary forces act at very different scales in the two. Later, researchers performing unstable displacement experiments in HS cells containing random 2D porous media also observed viscous fingering at large viscosity ratios, but with invasion patterns very different from those of Saffman and Taylor (ST) [2-3]. It was however considered that the two processes were both Laplacian growth processes, i.e., processes in which the invasion probability density is proportional to the pressure gradient. Ten years ago, we investigated viscously-unstable drainage in 2D porous media experimentally and measured the growth activity as well as occupation probability maps for the invasion process [4-5]. We concluded that in viscous fingering in 2D porous media, the activity was rather proportional to the square of the pressure gradient magnitude (a so-called DBM model of exponent 2), so that the universality class of the growth/invasion process was different from that of ST viscous fingering. We now strengthen our claim with new results based on the comparison of (i) pressure measurements with the pressure field around a finger such as described by the ST analytical model, and (ii) branching angles in the invasion patterns with those expected for DBMs of various exponents. [1] Saffman, P. G. and Taylor, G. Proc. Soc. London 1958(Ser A 245), 312-329. [2] Lenormand, R

  17. A comparison of numerical and semi-analytical methods for the case of heat transfer equations arising in porous medium

    NASA Astrophysics Data System (ADS)

    Parand, K.; Rad, J. A.; Ahmadi, M.

    2016-09-01

    Natural convective heat transfer in porous media which is of importance in the design of canisters for nuclear waste disposal has received considerable attention during the past few decades. This paper presents a comparison between two different analytical and numerical methods, i.e. pseudospectral and Adomian decomposition methods. The pseudospectral approach makes use of the orthogonal rational Jacobi functions; this method reduces the solution of the problem to a solution of a system of algebraic equations. Numerical results are compared with each other, showing that the pseudospectral method leads to more accurate results and is applicable on similar problems.

  18. Hierarchically Porous Electrocatalyst with Vertically Aligned Defect-Rich CoMoS Nanosheets for the Hydrogen Evolution Reaction in an Alkaline Medium.

    PubMed

    Wu, Zexing; Guo, Junpo; Wang, Jie; Liu, Rong; Xiao, Weiping; Xuan, Cuijuan; Xia, Kedong; Wang, Deli

    2017-02-15

    Effective electrocatalysts for the hydrogen evolution reaction (HER) in alkaline electrolytes can be developed via a simple solvothermal process. In this work, first, the prepared CoMoS nanomaterials through solvothermal treatment have a porous, defect-rich, and vertically aligned nanostructure, which is beneficial for the HER in an alkaline medium. Second, electron transfer from cobalt to MoS2 that reduces the unoccupied d orbitals of molybdenum can also enhance the HER kinetics in an alkaline medium. This has been demonstrated via a comparison of the catalytic performances of CoMoS, CoS, and MoS2. Third, the solvothermal treatment time evidently impacts the electrocatalytic activity. As a result, after 24 h of solvothermal treatment, the prepared CoMoS nanomaterials exhibit the lowest onset potential (42 mV) and overpotential (98 mV) for delivering a current density of 10 mA cm(-2) in a 1 M KOH solution. Thus, this study provides a simple method to prepare efficient electrocatalysts for the HER in an alkaline medium.

  19. Three-dimensional (3D) printing of mouse primary hepatocytes to generate 3D hepatic structure

    PubMed Central

    Kim, Yohan; Kang, Kyojin; Jeong, Jaemin; Paik, Seung Sam; Kim, Ji Sook; Park, Su A; Kim, Wan Doo; Park, Jisun

    2017-01-01

    Purpose The major problem in producing artificial livers is that primary hepatocytes cannot be cultured for many days. Recently, 3-dimensional (3D) printing technology draws attention and this technology regarded as a useful tool for current cell biology. By using the 3D bio-printing, these problems can be resolved. Methods To generate 3D bio-printed structures (25 mm × 25 mm), cells-alginate constructs were fabricated by 3D bio-printing system. Mouse primary hepatocytes were isolated from the livers of 6–8 weeks old mice by a 2-step collagenase method. Samples of 4 × 107 hepatocytes with 80%–90% viability were printed with 3% alginate solution, and cultured with well-defined culture medium for primary hepatocytes. To confirm functional ability of hepatocytes cultured on 3D alginate scaffold, we conducted quantitative real-time polymerase chain reaction and immunofluorescence with hepatic marker genes. Results Isolated primary hepatocytes were printed with alginate. The 3D printed hepatocytes remained alive for 14 days. Gene expression levels of Albumin, HNF-4α and Foxa3 were gradually increased in the 3D structures. Immunofluorescence analysis showed that the primary hepatocytes produced hepatic-specific proteins over the same period of time. Conclusion Our research indicates that 3D bio-printing technique can be used for long-term culture of primary hepatocytes. It can therefore be used for drug screening and as a potential method of producing artificial livers. PMID:28203553

  20. Influences of Flow Transients and Porous Medium Heterogeneity on Colloid-Associated Contaminant Transport in the Vadose Zone

    SciTech Connect

    James Saiers; Joseph Ryan

    2006-07-02

    Radionuclides, metals, and dense non-aqueous phase liquids have contaminated about six billion cubic meters of soil at Department of Energy (DOE) sites. The subsurface transport of many of these contaminants is facilitated by colloids (i.e., microscopic, waterborne particles). The first step in the transport of contaminants from their sources to off-site surface water and groundwater is migration through the vadose zone. Developing our understanding of the migration of colloids and colloid-associated contaminants through the vadose zone is critical to assessing and controlling the release of contaminants from DOE sites. In this study, we examined the mobilization, transport, and filtration (retention) of mineral colloids and colloidassociated radionuclides within unsaturated porous media. This investigation involved laboratory column experiments designed to identify properties that affect colloid mobilization and retention and pore-scale visualization experiments designed to elucidate mechanisms that govern these colloid-mass transfer processes. The experiments on colloid mobilization and retention were supplemented with experiments on radionuclide transport through porous media and on radionuclide adsorption to mineral colloids. Observations from all of these experiments – the column and visualization experiments with colloids and the experiments with radionuclides – were used to guide the development of mathematical models appropriate for describing colloids and colloid-facilitated radionuclide transport through the vadose zone.

  1. A time-asymptotic one equation non-equilibrium model for reactive transport in a two phase porous medium

    NASA Astrophysics Data System (ADS)

    Yohan, D.; Gerald, D.; Magali, G.; Michel, Q.

    2008-12-01

    The general problem of transport and reaction in multiphase porous media has been a subject of extensive studies during the last decades. For example, biologically mediated porous media have seen a long history of research from the environmental engineering point of view. Biofilms (aggregate of microorganisms coated in a polymer matrix generated by bacteria) have been particularly examined within the context of bioremediation in the subsurface zone. Five types of models may be used to describe these kinds of physical system: 1) one-equation local mass equilibrium models when the assumption of local mass equilibrium is valid 2) two equations models when the assumption of local mass equilibrium is not valid 3) one equation non-equilibrium models 4) mixed models coupling equations solved at two different scales 5) one equation time-asymptotic models. In this presentation, we use the method of volume averaging with closure to extend the time- asymptotic model at the Darcy scale to the reactive case. Closure problems are solved for simple unit cells, and the macro-scale model is validated against pore-scale simulations.

  2. Effect of low-concentration rhamnolipid on transport of Pseudomonas aeruginosa ATCC 9027 in an ideal porous medium with hydrophilic or hydrophobic surfaces.

    PubMed

    Zhong, Hua; Liu, Guansheng; Jiang, Yongbing; Brusseau, Mark L; Liu, Zhifeng; Liu, Yang; Zeng, Guangming

    2016-03-01

    The success of effective bioaugmentation processes for remediation of soil and groundwater contamination requires effective transport of the injected microorganisms in the subsurface environment. In this study, the effect of low concentrations of monorhamnolipid biosurfactant solutions on transport of Pseudomonas aeruginosa in an ideal porous medium (glass beads) with hydrophilic or hydrophobic surfaces was investigated by conducting miscible-displacement experiments. Transport behavior was examined for both glucose-grown and hexadecane-grown cells, with low and high surface hydrophobicity, respectively. A clean-bed colloid deposition model was used for determination of deposition rate coefficients. Results show that cells with high surface hydrophobicity exhibit greater retention than cells with low surface hydrophobicity. Rhamnolipid affects cell transport primarily by changing cell surface hydrophobicity, with an additional minor effect by increasing solution ionic strength. There is a good linear relation between k and rhamnolipid-regulated cell surface hydrophobicity presented as bacterial-adhesion-to-hydrocarbon (BATH) rate of cells (R(2)=0.71). The results of this study show the importance of hydrophobic interaction for transport of bacterial cells in silica-based porous media, and the potential of using low-concentration rhamnolipid solutions for facilitating bacterial transport in bioaugmentation efforts.

  3. Effect of low-concentration rhamnolipid on transport of Pseudomonas aeruginosa ATCC 9027 in ideal porous medium with hydrophilic or hydrophobic surfaces

    PubMed Central

    Zhong, Hua; Liu, Guansheng; Jiang, Yongbing; Brusseau, Mark L.; Liu, Zhifeng; Liu, Yang; Zeng, Guangming

    2016-01-01

    The success of effective bioaugmentation processes for remediation of soil and groundwater contamination requires effective transport of the injected microorganisms in the subsurface environment. In this study, the effect of low concentrations of monorhamnolipid biosurfactant solutions on transport of Pseudomonas aeruginosa in an ideal porous medium (glass beads) with hydrophilic or hydrophobic surfaces was investigated by conducting miscible-displacement experiments. Transport behavior was examined for both glucose-grown and hexadecane-grown cells, with low or high surface hydrophobicity, respectively. A clean-bed colloid deposition model was used for determination of deposition rate coefficients. Results show that cells with high surface hydrophobicity exhibit greater retention than cells with low surface hydrophobicity. Rhamnolipid affects cell transport primarily by changing cell surface hydrophobicity, with an additional minor effect by increasing solution ionic strength. There is a good linear relation between k rhamnolipid-regulated cell surface hydrophobicity presented as bacterial-adhesion-to-hydrocarbon (BATH) rate of cells (R2 = 0.71). The results of this study show the importance of hydrophobic interaction for transport of bacterial cells in silica-based porous media, and the potential of using low-concentration rhamnolipid solutions for facilitating bacterial transport in bioaugmentation efforts. PMID:26722821

  4. Conjugate effects of heat and mass transfer on MHD free convection flow over an inclined plate embedded in a porous medium.

    PubMed

    Ali, Farhad; Khan, Ilyas; Samiulhaq; Shafie, Sharidan

    2013-01-01

    The aim of this study is to present an exact analysis of combined effects of radiation and chemical reaction on the magnetohydrodynamic (MHD) free convection flow of an electrically conducting incompressible viscous fluid over an inclined plate embedded in a porous medium. The impulsively started plate with variable temperature and mass diffusion is considered. The dimensionless momentum equation coupled with the energy and mass diffusion equations are analytically solved using the Laplace transform method. Expressions for velocity, temperature and concentration fields are obtained. They satisfy all imposed initial and boundary conditions and can be reduced, as special cases, to some known solutions from the literature. Expressions for skin friction, Nusselt number and Sherwood number are also obtained. Finally, the effects of pertinent parameters on velocity, temperature and concentration profiles are graphically displayed whereas the variations in skin friction, Nusselt number and Sherwood number are shown through tables.

  5. Conjugate Effects of Heat and Mass Transfer on MHD Free Convection Flow over an Inclined Plate Embedded in a Porous Medium

    PubMed Central

    Ali, Farhad; Khan, Ilyas; Samiulhaq; Shafie, Sharidan

    2013-01-01

    The aim of this study is to present an exact analysis of combined effects of radiation and chemical reaction on the magnetohydrodynamic (MHD) free convection flow of an electrically conducting incompressible viscous fluid over an inclined plate embedded in a porous medium. The impulsively started plate with variable temperature and mass diffusion is considered. The dimensionless momentum equation coupled with the energy and mass diffusion equations are analytically solved using the Laplace transform method. Expressions for velocity, temperature and concentration fields are obtained. They satisfy all imposed initial and boundary conditions and can be reduced, as special cases, to some known solutions from the literature. Expressions for skin friction, Nusselt number and Sherwood number are also obtained. Finally, the effects of pertinent parameters on velocity, temperature and concentration profiles are graphically displayed whereas the variations in skin friction, Nusselt number and Sherwood number are shown through tables. PMID:23840321

  6. MHD Marangoni boundary layer flow and heat transfer of pseudo-plastic nanofluids over a porous medium with a modified model

    NASA Astrophysics Data System (ADS)

    Lin, Yanhai; Zheng, Liancun; Zhang, Xinxin

    2015-11-01

    We present a research for the MHD Marangoni boundary layer flow and heat transfer in pseudo-plastic power law nanofluids over a porous medium driven by temperature gradient. A variable magnetic field is considered. Four different types of nanoparticles, copper, aluminum oxide, copper oxide, and titanium oxide are considered with pseudo-plastic power-law carboxy methyl cellulose (CMC)-water used as base fluids. A generalized Fourier law proposed by Zheng for varying thermal conductivity of nanofluids is taken into account, and the surface tension is assumed a quadratic function of the temperature. The governing partial differential equations (PDEs) are formulated, and similarity solutions are obtained numerically using shooting technique combined with Runge-Kutta iteration program and Newton's scheme. The effects of various physical parameters on horizontal velocity component and temperature curves are discussed and graphically illustrated in details.

  7. Analysis of the Laminar Newtonian Fluid Flow Through a Thin Fracture Modelled as a Fluid-Saturated Sparsely Packed Porous Medium

    NASA Astrophysics Data System (ADS)

    Pažanin, Igor; Siddheshwar, Pradeep G.

    2017-03-01

    In this article we investigate the fluid flow through a thin fracture modelled as a fluid-saturated porous medium. We assume that the fracture has constrictions and that the flow is governed by the prescribed pressure drop between the edges of the fracture. The problem is described by the Darcy-Lapwood-Brinkman model acknowledging the Brinkman extension of the Darcy law as well as the flow inertia. Using asymptotic analysis with respect to the thickness of the fracture, we derive the explicit higher-order approximation for the velocity distribution. We make an error analysis to comment on the order of accuracy of the method used and also to provide rigorous justification for the model.

  8. Thermal-diffusion and MHD for Soret and Dufour’s effects on Hiemenz flow and mass transfer of fluid flow through porous medium onto a stretching surface

    NASA Astrophysics Data System (ADS)

    Abdel-Rahman, Gamal M.

    2010-06-01

    In this paper, the thermal-diffusion and magnetic field effects on a stagnation point flowing over a flat stretching surface have been obtained and studied numerically with the variation of the viscosity under the Soret and Dufour's effects. The governing continuity, momentum, energy and concentration equations are converted into a system of non-linear ordinary differential equations by means of similarity transformation. The resulting system of coupled non-linear ordinary differential equations is solved numerically. Numerical results were presented for velocity, temperature and concentration profiles for different parameters of the problem as radiation parameter, magnetic field parameter, porous medium parameter, endothermic chemical reaction, heat source parameter, stretching parameter, the Soret and Dufour number and other. Also the effects of the pertinent parameters on the skin friction, the rate of heat and mass transfer are obtained and discussed numerically and illustrated graphically.

  9. Mixed convective boundary layer flow over a vertical wedge embedded in a porous medium saturated with a nanofluid: Natural Convection Dominated Regime

    PubMed Central

    2011-01-01

    A boundary layer analysis is presented for the mixed convection past a vertical wedge in a porous medium saturated with a nano fluid. The governing partial differential equations are transformed into a set of non-similar equations and solved numerically by an efficient, implicit, iterative, finite-difference method. A parametric study illustrating the influence of various physical parameters is performed. Numerical results for the velocity, temperature, and nanoparticles volume fraction profiles, as well as the friction factor, surface heat and mass transfer rates have been presented for parametric variations of the buoyancy ratio parameter Nr, Brownian motion parameter Nb, thermophoresis parameter Nt, and Lewis number Le. The dependency of the friction factor, surface heat transfer rate (Nusselt number), and mass transfer rate (Sherwood number) on these parameters has been discussed. PMID:21711715

  10. The effect of transpiration on coupled heat and mass transfer in mixed convection over a vertical plate embedded in a saturated porous medium

    SciTech Connect

    Yih, K.A.

    1997-03-01

    Effect of transpiration velocity on the heat and mass transfer characteristics of mixed convection about a permeable vertical plate embedded in a saturated porous medium under the coupled effects of thermal and mass diffusion is numerically analyzed. The plate is maintained at a uniform temperature and species concentration with constant transpiration velocity. The transformed governing equations are solved by Keller box method. Numerical results for the local Nusselt number and local Sherwood number are presented. In general, it has been found for thermally assisted flow that the local surface heat and mass transfer rates increase owing to suction of fluid. This trend reversed for blowing of fluid. It is apparent that the Lewis number has a pronounced effect on the local Sherwood number than it does on the local Nusselt number. Increasing the Lewis number decreases (increases) the local heat (mass) transfer rate.

  11. Unsteady magnetohydrodynamic flow of a fourth grade fluid caused by an impulsively moving plate in a Darcy porous medium ߞ A group-theoretical analysis

    NASA Astrophysics Data System (ADS)

    Carrim, A. H.; Aziz, Taha; Mahomed, F. M.; Khalique, Chaudry Masood

    2016-06-01

    The effects of non-Newtonian fluids are investigated by means of an appropriate model studying the flow of a fourth grade fluid. The geometry of this model is described by the unsteady unidirectional flow of an incompressible fluid over an infinite flat plate within a porous medium. The fluid is electrically conducting in the presence of a uniform applied magnetic field. The classical Lie symmetry approach is utilized in order to construct group invariant solutions to the governing higher-order nonlinear partial differential equation (PDE). The conditional symmetry approach has also been utilized to solve the governing model. Some new classes of conditional symmetry solutions have been obtained for the model equation in the form of closed-form exponential functions. The invariant solution corresponding to the nontraveling wave type is considered to be the most significant solution for the fluid flow model under investigation since it directly incorporates the physical behavior of the flow model.

  12. Simple buffers for 3D STORM microscopy.

    PubMed

    Olivier, Nicolas; Keller, Debora; Rajan, Vinoth Sundar; Gönczy, Pierre; Manley, Suliana

    2013-06-01

    3D STORM is one of the leading methods for super-resolution imaging, with resolution down to 10 nm in the lateral direction, and 30-50 nm in the axial direction. However, there is one important requirement to perform this type of imaging: making dye molecules blink. This usually relies on the utilization of complex buffers, containing different chemicals and sensitive enzymatic systems, limiting the reproducibility of the method. We report here that the commercial mounting medium Vectashield can be used for STORM of Alexa-647, and yields images comparable or superior to those obtained with more complex buffers, especially for 3D imaging. We expect that this advance will promote the versatile utilization of 3D STORM by removing one of its entry barriers, as well as provide a more reproducible way to compare optical setups and data processing algorithms.

  13. Upscaling of CO 2 vertical migration through a periodic layered porous medium: The capillary-free and capillary-dominant cases

    NASA Astrophysics Data System (ADS)

    Mouche, Emmanuel; Hayek, Mohamed; Mügler, Claude

    2010-09-01

    We present an upscaled model for the vertical migration of a CO 2 plume through a vertical column filled with a periodic layered porous medium. This model may describe the vertical migration of a CO 2 plume in a perfectly layered horizontal aquifer. Capillarity and buoyancy are taken into account and semi-explicit upscaled flux functions are proposed in the two following cases: (i) capillarity is the main driving force and (ii) buoyancy is the only driving force. In both cases, we show that the upscaled buoyant flux is a bell-shaped function of the saturation, as in the case of a homogeneous porous medium. In the capillary-dominant case, we show that the upscaled buoyant flux is the harmonic mean of the buoyant fluxes in each layer. The upscaled saturation is governed by the continuity of the capillary pressure at the interface between layers. In the capillary-free case, the upscaled buoyant flux and upscaled saturation are determined by the flux continuity condition at the interface. As the flux is not continuous over the entire range of saturation, the upscaled saturation is only defined where continuity is verified, i.e. in two saturation domains. As a consequence, the upscaled buoyant flux is described by a piecewise continuous function. Two analytical approximations of this flux are proposed and this capillary-free upscaled model is validated for two cases of heterogeneity. Upscaled and cell averaged saturations are in good agreement. Furthermore, the proposed analytical upscaled fluxes provide satisfactory approximations as long as the saturation set at the inlet of the column is in a range where analytical and numerical upscaled fluxes are close.

  14. Role of Desorption Kinetics and Porous Medium Heterogeneity in Colloid-Facilitated Transport of Cesium and Strontium: Preliminary Results

    NASA Astrophysics Data System (ADS)

    Dittrich, T. M.; Ryan, J. N.

    2008-12-01

    The presence of mobile colloids (particles between 1 nm and 1 μm in size) in natural soil and groundwater systems has been well established. Colloids generally have a high sorptive capacity resulting from their high surface area to mass ratio, which makes them effective sorbents of low solubility, strongly sorbing contaminants. Mobile colloids that sorb contaminants can increase the apparent solubility and rate of transport of the contaminants when desorption from the colloids is slow relative to the rate of flow. This process is known as colloid-facilitated transport (CFT). The additional transport of contaminants associated with mobile colloids should be accounted for to accurately predict transport rates of strongly-sorbing contaminants in the environment. Some examples of contaminants that have the potential for CFT are hydrophobic pesticides, polycyclic aromatic hydrocarbons (PAHs), actinide cations (e.g., Th, U, Pu, Am), and many metals (e.g, Pb, Cu, Hg). Many low solubility contaminants that have the potential for CFT are also harmful or toxic to humans, underscoring the importance of accurate modeling techniques to protect water sources from contamination. Contaminated Department of Energy (DOE) sites have been particularly valuable research opportunities for studying the transport of radionuclides in the natural environment. The DOE has conducted energy and weapons research and development in thirty-one states and Puerto Rico and has introduced many toxic and radioactive chemicals into surface waters, soils, and groundwater. Field experiments on DOE sites including the Nevada Test Site, the Hanford 200 Area tank farm, Rocky Flats CO, and Oak Ridge TN, have confirmed that metals and radionuclides have moved further than expected due to colloid-facilitated transport. The major goal of this research project is to identify and quantify the effects of sorption kinetics on colloid- facilitated transport in unsaturated porous media. This information will be used

  15. Evolution and persistence of cross-directional statistical dependence during finite-Péclet transport through a real porous medium

    NASA Astrophysics Data System (ADS)

    Most, Sebastian; Bijeljic, Branko; Nowak, Wolfgang

    2016-11-01

    Transport of passive, dissolved compounds in fully-saturated complex porous media frequently exhibits non-Fickian characteristics. One of the most interesting questions is to ascertain the time scales at which it is possible to describe transport as a statistically independent process. Therefore, we study the mechanisms for evolution and then the decrease of non-Fickianity as a function of increasing time. Adopting the Lagrangian perspective, we provide a nonlinear copula analysis of advective-diffusive processes by analyzing particle trajectories in a real porous media, as provided by direct numerical simulations on the three-dimensional image of Doddington sandstone. First, we analyze the memory effects between time-consecutive particle position increments and cross dependence between longitudinal and transversal particle position increments as a function of given time increments and time lags between consecutive time increments. Second, we investigate the influence of the Péclet regime on the temporal evolution of dependence. Our main findings are: (a) Cross dependence between longitudinal and transversal particle position increments is persistent over the investigated range of time increments, even though this aspect has been neglected up to date. (b) Lower Péclet numbers lead to a weaker dependence that is, however, more persistent over time than in higher-Péclet transport regimes. We confirm that non-Fickianity comes from spatial coherence associated with heterogeneities of the velocity field that introduce cross dependence and memory into the transport process. Overall, we show that memory and cross dependence are persistent in and among all directions, that the dependence is highly-nonlinear, occurs at different temporal scales, and is dependent on the Péclet number.

  16. Full-color holographic 3D printer

    NASA Astrophysics Data System (ADS)

    Takano, Masami; Shigeta, Hiroaki; Nishihara, Takashi; Yamaguchi, Masahiro; Takahashi, Susumu; Ohyama, Nagaaki; Kobayashi, Akihiko; Iwata, Fujio

    2003-05-01

    A holographic 3D printer is a system that produces a direct hologram with full-parallax information using the 3-dimensional data of a subject from a computer. In this paper, we present a proposal for the reproduction of full-color images with the holographic 3D printer. In order to realize the 3-dimensional color image, we selected the 3 laser wavelength colors of red (λ=633nm), green (λ=533nm), and blue (λ=442nm), and we built a one-step optical system using a projection system and a liquid crystal display. The 3-dimensional color image is obtained by synthesizing in a 2D array the multiple exposure with these 3 wavelengths made on each 250mm elementary hologram, and moving recording medium on a x-y stage. For the natural color reproduction in the holographic 3D printer, we take the approach of the digital processing technique based on the color management technology. The matching between the input and output colors is performed by investigating first, the relation between the gray level transmittance of the LCD and the diffraction efficiency of the hologram and second, by measuring the color displayed by the hologram to establish a correlation. In our first experimental results a non-linear functional relation for single and multiple exposure of the three components were found. These results are the first step in the realization of a natural color 3D image produced by the holographic color 3D printer.

  17. Embedding objects during 3D printing to add new functionalities.

    PubMed

    Yuen, Po Ki

    2016-07-01

    A novel method for integrating and embedding objects to add new functionalities during 3D printing based on fused deposition modeling (FDM) (also known as fused filament fabrication or molten polymer deposition) is presented. Unlike typical 3D printing, FDM-based 3D printing could allow objects to be integrated and embedded during 3D printing and the FDM-based 3D printed devices do not typically require any post-processing and finishing. Thus, various fluidic devices with integrated glass cover slips or polystyrene films with and without an embedded porous membrane, and optical devices with embedded Corning(®) Fibrance™ Light-Diffusing Fiber were 3D printed to demonstrate the versatility of the FDM-based 3D printing and embedding method. Fluid perfusion flow experiments with a blue colored food dye solution were used to visually confirm fluid flow and/or fluid perfusion through the embedded porous membrane in the 3D printed fluidic devices. Similar to typical 3D printed devices, FDM-based 3D printed devices are translucent at best unless post-polishing is performed and optical transparency is highly desirable in any fluidic devices; integrated glass cover slips or polystyrene films would provide a perfect optical transparent window for observation and visualization. In addition, they also provide a compatible flat smooth surface for biological or biomolecular applications. The 3D printed fluidic devices with an embedded porous membrane are applicable to biological or chemical applications such as continuous perfusion cell culture or biocatalytic synthesis but without the need for any post-device assembly and finishing. The 3D printed devices with embedded Corning(®) Fibrance™ Light-Diffusing Fiber would have applications in display, illumination, or optical applications. Furthermore, the FDM-based 3D printing and embedding method could also be utilized to print casting molds with an integrated glass bottom for polydimethylsiloxane (PDMS) device replication

  18. Single-layer graphene-assembled 3D porous carbon composites with PVA and Fe₃O₄ nano-fillers: an interface-mediated superior dielectric and EMI shielding performance.

    PubMed

    Rao, B V Bhaskara; Yadav, Prasad; Aepuru, Radhamanohar; Panda, H S; Ogale, Satishchandra; Kale, S N

    2015-07-28

    In this study, a novel composite of Fe3O4 nanofiller-decorated single-layer graphene-assembled porous carbon (SLGAPC) with polyvinyl alcohol (PVA) having flexibility and a density of 0.75 g cm(-3) is explored for its dielectric and electromagnetic interference (EMI) response properties. The composite is prepared by the solution casting method and its constituents are optimized as 15 wt% SLGAPC and 20 wt% Fe3O4 through a novel solvent relaxation nuclear magnetic resonance experiment. The PVA-SLGAPC-Fe3O4 composite shows high dielectric permittivity in the range of 1 Hz-10 MHz, enhanced by a factor of 4 as compared to that of the PVA-SLGAPC composite, with a reduced loss by a factor of 2. The temperature dependent dielectric properties reveal the activation energy behaviour with reference to the glass transition temperature (80 °C) of PVA. The dielectric hysteresis with the temperature cycle reveals a remnant polarization. The enhanced dielectric properties are suggested to be the result of improvement in the localized polarization of the integrated interface system (Maxwell-Wagner-Sillars (MWS) polarization) formed by the uniform adsorption of Fe3O4 on the surface of SLGAPC conjugated with PVA. The EMI shielding property of the composite with a low thickness of 0.3 mm in the X-band (8.2-12.4 GHz) shows a very impressive shielding efficiency of ∼15 dB and a specific shielding effectiveness of 20 dB (g cm(-3))(-1), indicating the promising character of this material for flexible EMI shielding applications.

  19. 3D Spectroscopy in Astronomy

    NASA Astrophysics Data System (ADS)

    Mediavilla, Evencio; Arribas, Santiago; Roth, Martin; Cepa-Nogué, Jordi; Sánchez, Francisco

    2011-09-01

    Preface; Acknowledgements; 1. Introductory review and technical approaches Martin M. Roth; 2. Observational procedures and data reduction James E. H. Turner; 3. 3D Spectroscopy instrumentation M. A. Bershady; 4. Analysis of 3D data Pierre Ferruit; 5. Science motivation for IFS and galactic studies F. Eisenhauer; 6. Extragalactic studies and future IFS science Luis Colina; 7. Tutorials: how to handle 3D spectroscopy data Sebastian F. Sánchez, Begona García-Lorenzo and Arlette Pécontal-Rousset.

  20. Spherical 3D isotropic wavelets

    NASA Astrophysics Data System (ADS)

    Lanusse, F.; Rassat, A.; Starck, J.-L.

    2012-04-01

    Context. Future cosmological surveys will provide 3D large scale structure maps with large sky coverage, for which a 3D spherical Fourier-Bessel (SFB) analysis in spherical coordinates is natural. Wavelets are particularly well-suited to the analysis and denoising of cosmological data, but a spherical 3D isotropic wavelet transform does not currently exist to analyse spherical 3D data. Aims: The aim of this paper is to present a new formalism for a spherical 3D isotropic wavelet, i.e. one based on the SFB decomposition of a 3D field and accompany the formalism with a public code to perform wavelet transforms. Methods: We describe a new 3D isotropic spherical wavelet decomposition based on the undecimated wavelet transform (UWT) described in Starck et al. (2006). We also present a new fast discrete spherical Fourier-Bessel transform (DSFBT) based on both a discrete Bessel transform and the HEALPIX angular pixelisation scheme. We test the 3D wavelet transform and as a toy-application, apply a denoising algorithm in wavelet space to the Virgo large box cosmological simulations and find we can successfully remove noise without much loss to the large scale structure. Results: We have described a new spherical 3D isotropic wavelet transform, ideally suited to analyse and denoise future 3D spherical cosmological surveys, which uses a novel DSFBT. We illustrate its potential use for denoising using a toy model. All the algorithms presented in this paper are available for download as a public code called MRS3D at http://jstarck.free.fr/mrs3d.html

  1. 3D Elevation Program—Virtual USA in 3D

    USGS Publications Warehouse

    Lukas, Vicki; Stoker, J.M.

    2016-04-14

    The U.S. Geological Survey (USGS) 3D Elevation Program (3DEP) uses a laser system called ‘lidar’ (light detection and ranging) to create a virtual reality map of the Nation that is very accurate. 3D maps have many uses with new uses being discovered all the time.  

  2. Highly compressible 3D periodic graphene aerogel microlattices

    SciTech Connect

    Zhu, Cheng; Han, T. Yong-Jin; Duoss, Eric B.; Golobic, Alexandra M.; Kuntz, Joshua D.; Spadaccini, Christopher M.; Worsley, Marcus A.

    2015-04-22

    Graphene is a two-dimensional material that offers a unique combination of low density, exceptional mechanical properties, large surface area and excellent electrical conductivity. Recent progress has produced bulk 3D assemblies of graphene, such as graphene aerogels, but they possess purely stochastic porous networks, which limit their performance compared with the potential of an engineered architecture. Here we report the fabrication of periodic graphene aerogel microlattices, possessing an engineered architecture via a 3D printing technique known as direct ink writing. The 3D printed graphene aerogels are lightweight, highly conductive and exhibit supercompressibility (up to 90% compressive strain). Moreover, the Young’s moduli of the 3D printed graphene aerogels show an order of magnitude improvement over bulk graphene materials with comparable geometric density and possess large surface areas. Ultimately, adapting the 3D printing technique to graphene aerogels realizes the possibility of fabricating a myriad of complex aerogel architectures for a broad range of applications.

  3. Highly compressible 3D periodic graphene aerogel microlattices

    NASA Astrophysics Data System (ADS)

    Zhu, Cheng; Han, T. Yong-Jin; Duoss, Eric B.; Golobic, Alexandra M.; Kuntz, Joshua D.; Spadaccini, Christopher M.; Worsley, Marcus A.

    2015-04-01

    Graphene is a two-dimensional material that offers a unique combination of low density, exceptional mechanical properties, large surface area and excellent electrical conductivity. Recent progress has produced bulk 3D assemblies of graphene, such as graphene aerogels, but they possess purely stochastic porous networks, which limit their performance compared with the potential of an engineered architecture. Here we report the fabrication of periodic graphene aerogel microlattices, possessing an engineered architecture via a 3D printing technique known as direct ink writing. The 3D printed graphene aerogels are lightweight, highly conductive and exhibit supercompressibility (up to 90% compressive strain). Moreover, the Young's moduli of the 3D printed graphene aerogels show an order of magnitude improvement over bulk graphene materials with comparable geometric density and possess large surface areas. Adapting the 3D printing technique to graphene aerogels realizes the possibility of fabricating a myriad of complex aerogel architectures for a broad range of applications.

  4. Highly compressible 3D periodic graphene aerogel microlattices

    PubMed Central

    Zhu, Cheng; Han, T. Yong-Jin; Duoss, Eric B.; Golobic, Alexandra M.; Kuntz, Joshua D.; Spadaccini, Christopher M.; Worsley, Marcus A.

    2015-01-01

    Graphene is a two-dimensional material that offers a unique combination of low density, exceptional mechanical properties, large surface area and excellent electrical conductivity. Recent progress has produced bulk 3D assemblies of graphene, such as graphene aerogels, but they possess purely stochastic porous networks, which limit their performance compared with the potential of an engineered architecture. Here we report the fabrication of periodic graphene aerogel microlattices, possessing an engineered architecture via a 3D printing technique known as direct ink writing. The 3D printed graphene aerogels are lightweight, highly conductive and exhibit supercompressibility (up to 90% compressive strain). Moreover, the Young's moduli of the 3D printed graphene aerogels show an order of magnitude improvement over bulk graphene materials with comparable geometric density and possess large surface areas. Adapting the 3D printing technique to graphene aerogels realizes the possibility of fabricating a myriad of complex aerogel architectures for a broad range of applications. PMID:25902277

  5. Pore-scale modeling of Capillary Penetration of Wetting Liquid into 3D Fibrous Media: A Critical Examination of Equivalent Capillary Concept

    NASA Astrophysics Data System (ADS)

    Palakurthi, Nikhil Kumar; Ghia, Urmila; Comer, Ken

    2013-11-01

    Capillary penetration of liquid through fibrous porous media is important in many applications such as printing, drug delivery patches, sanitary wipes, and performance fabrics. Historically, capillary transport (with a distinct liquid propagating front) in porous media is modeled using capillary-bundle theory. However, it is not clear if the capillary model (Washburn equation) describes the fluid transport in porous media accurately, as it assumes uniformity of pore sizes in the porous medium. The present work investigates the limitations of the applicability of the capillary model by studying liquid penetration through virtual fibrous media with uniform and non-uniform pore-sizes. For the non-uniform-pore fibrous medium, the effective capillary radius of the fibrous medium was estimated from the pore-size distribution curve. Liquid penetration into the 3D virtual fibrous medium at micro-scale was simulated using OpenFOAM, and the numerical results were compared with the Washburn-equation capillary-model predictions. Preliminary results show that the Washburn equation over-predicts the height rise in the early stages (purely inertial and visco-inertial stages) of capillary transport.

  6. The influence of buoyancy contrasts on miscible source sink flows in a porous medium with thermal inertia

    NASA Astrophysics Data System (ADS)

    Nigam, Mats S.; Woods, Andrew W.

    We investigate the displacement of one fluid through an inclined porous sheet by the injection of a second fluid of different density. Using numerical simulation we explore the role of the density contrast between the injected and the reservoir fluid on the displacement process, in the cases where the density contrast originates from either compositional contrasts and/or temperature contrasts between the fluids. In the case where the density contrast originates from compositional differences between the fluids, the density front moves with the fluid fluid front, and gravity may accelerate or decelerate the time for the injected liquid to reach the sink. In the case where the density contrast originates from a temperature contrast between the injected fluid and the reservoir fluid, then the density front follows the thermal front. Therefore, owing to thermal inertia, it lags behind the fluid fluid front. This has a quantitative impact on the time required for the injected liquid to reach the sink. If there are both thermal and compositional contrasts between the injected and reservoir fluid, then the thermal and compositional fronts become decoupled in space. The two fronts may lead to complementary or opposing density changes; the different cases lead to vastly different patterns of displacement and time at which the injected liquid reaches the sink, even if the net change in density between reservoir and the injected fluid is the same. We discuss the implications of these phenomena for water injection in sub-surface hydrocarbon and geothermal reservoirs. In an Appendix, we note how a viscosity across both the thermal front and the fluid fluid front can also lead to a rich spectrum of flow patterns, especially if one front is stable and the other unstable to viscous instability.

  7. 3D World Building System

    ScienceCinema

    None

    2016-07-12

    This video provides an overview of the Sandia National Laboratories developed 3-D World Model Building capability that provides users with an immersive, texture rich 3-D model of their environment in minutes using a laptop and color and depth camera.

  8. 3D Buckligami: Digital Matter

    NASA Astrophysics Data System (ADS)

    van Hecke, Martin; de Reus, Koen; Florijn, Bastiaan; Coulais, Corentin

    2014-03-01

    We present a class of elastic structures which exhibit collective buckling in 3D, and create these by a 3D printing/moulding technique. Our structures consist of cubic lattice of anisotropic unit cells, and we show that their mechanical properties are programmable via the orientation of these unit cells.

  9. 3D World Building System

    SciTech Connect

    2013-10-30

    This video provides an overview of the Sandia National Laboratories developed 3-D World Model Building capability that provides users with an immersive, texture rich 3-D model of their environment in minutes using a laptop and color and depth camera.

  10. LLNL-Earth3D

    SciTech Connect

    2013-10-01

    Earth3D is a computer code designed to allow fast calculation of seismic rays and travel times through a 3D model of the Earth. LLNL is using this for earthquake location and global tomography efforts and such codes are of great interest to the Earth Science community.

  11. Market study: 3-D eyetracker

    NASA Technical Reports Server (NTRS)

    1977-01-01

    A market study of a proposed version of a 3-D eyetracker for initial use at NASA's Ames Research Center was made. The commercialization potential of a simplified, less expensive 3-D eyetracker was ascertained. Primary focus on present and potential users of eyetrackers, as well as present and potential manufacturers has provided an effective means of analyzing the prospects for commercialization.

  12. Euro3D Science Conference

    NASA Astrophysics Data System (ADS)

    Walsh, J. R.

    2004-02-01

    The Euro3D RTN is an EU funded Research Training Network to foster the exploitation of 3D spectroscopy in Europe. 3D spectroscopy is a general term for spectroscopy of an area of the sky and derives its name from its two spatial + one spectral dimensions. There are an increasing number of instruments which use integral field devices to achieve spectroscopy of an area of the sky, either using lens arrays, optical fibres