The Experts below are selected from a list of 20934 Experts worldwide ranked by ideXlab platform
Tianshou Zhao - One of the best experts on this subject based on the ideXlab platform.
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numerical investigations of effect of membrane electrode assembly structure on water crossover in a liquid feed direct methanol fuel cell
Journal of Power Sources, 2009Co-Authors: Weiwei Yang, Tianshou ZhaoAbstract:Abstract A two-phase mass-transport model is employed to investigate the water transport behaviour through the membrane electrode assembly (MEA) of a liquid-feed direct methanol fuel cell (DMFC). Emphasis is placed on examining the effects of each constituent component design of the MEA, including catalyst layers, microPorous layers and membranes, on each of the three water crossover mechanisms: electro-osmotic drag, diffusion, and convection. The results show that lowering the diffusion flux of water or enhancing the convection flux of water (termed as the back-flow flux) through the membrane are both feasible to suppress water crossover in DMFCs. It is found that the reduction in the diffusion flux of water can be mainly achieved through optimum design of the anode Porous layers, as the effect of the cathode Porous Region on water crossover by diffusion is relatively smaller. On the other hand, the design of the cathode Porous layers plays a more important role in increasing the back-flow flux of water from the cathode to anode.
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numerical investigations of effect of membrane electrode assembly structure on water crossover in a liquid feed direct methanol fuel cell
Journal of Power Sources, 2009Co-Authors: Weiwei Yang, Tianshou ZhaoAbstract:Abstract A two-phase mass-transport model is employed to investigate the water transport behaviour through the membrane electrode assembly (MEA) of a liquid-feed direct methanol fuel cell (DMFC). Emphasis is placed on examining the effects of each constituent component design of the MEA, including catalyst layers, microPorous layers and membranes, on each of the three water crossover mechanisms: electro-osmotic drag, diffusion, and convection. The results show that lowering the diffusion flux of water or enhancing the convection flux of water (termed as the back-flow flux) through the membrane are both feasible to suppress water crossover in DMFCs. It is found that the reduction in the diffusion flux of water can be mainly achieved through optimum design of the anode Porous layers, as the effect of the cathode Porous Region on water crossover by diffusion is relatively smaller. On the other hand, the design of the cathode Porous layers plays a more important role in increasing the back-flow flux of water from the cathode to anode.
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two phase mass transport model for direct methanol fuel cells with effect of non equilibrium evaporation and condensation
Journal of Power Sources, 2007Co-Authors: Weiwei Yang, Tianshou ZhaoAbstract:Abstract A two-phase, mass-transport model for liquid-feed direct methanol fuel cells (DMFCs) is developed by taking into account the effect of non-equilibrium evaporation and condensation of methanol and water. The comparison between the present model and other models indicates that the present model yields more reasonable predictions of cell performance. Particularly, it is shown that the models that invoke a thermodynamic-equilibrium assumption between phases will overestimate mass-transport rates of methanol and water, thereby resulting in an inaccurate prediction of cell performance. The parametric study using the present model reveals that the gas coverage at the flow channel–diffusion-layer interface is directly related to the gas-void fraction inside the anode Porous Region; increasing the gas-void fraction will increase the mass-transfer resistance of methanol and thus lower cell performance. The effects of the geometric dimensions of the cell structure, such as channel width and rib width, on cell performance are also investigated with the model developed in this work.
Weiwei Yang - One of the best experts on this subject based on the ideXlab platform.
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numerical investigations of effect of membrane electrode assembly structure on water crossover in a liquid feed direct methanol fuel cell
Journal of Power Sources, 2009Co-Authors: Weiwei Yang, Tianshou ZhaoAbstract:Abstract A two-phase mass-transport model is employed to investigate the water transport behaviour through the membrane electrode assembly (MEA) of a liquid-feed direct methanol fuel cell (DMFC). Emphasis is placed on examining the effects of each constituent component design of the MEA, including catalyst layers, microPorous layers and membranes, on each of the three water crossover mechanisms: electro-osmotic drag, diffusion, and convection. The results show that lowering the diffusion flux of water or enhancing the convection flux of water (termed as the back-flow flux) through the membrane are both feasible to suppress water crossover in DMFCs. It is found that the reduction in the diffusion flux of water can be mainly achieved through optimum design of the anode Porous layers, as the effect of the cathode Porous Region on water crossover by diffusion is relatively smaller. On the other hand, the design of the cathode Porous layers plays a more important role in increasing the back-flow flux of water from the cathode to anode.
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numerical investigations of effect of membrane electrode assembly structure on water crossover in a liquid feed direct methanol fuel cell
Journal of Power Sources, 2009Co-Authors: Weiwei Yang, Tianshou ZhaoAbstract:Abstract A two-phase mass-transport model is employed to investigate the water transport behaviour through the membrane electrode assembly (MEA) of a liquid-feed direct methanol fuel cell (DMFC). Emphasis is placed on examining the effects of each constituent component design of the MEA, including catalyst layers, microPorous layers and membranes, on each of the three water crossover mechanisms: electro-osmotic drag, diffusion, and convection. The results show that lowering the diffusion flux of water or enhancing the convection flux of water (termed as the back-flow flux) through the membrane are both feasible to suppress water crossover in DMFCs. It is found that the reduction in the diffusion flux of water can be mainly achieved through optimum design of the anode Porous layers, as the effect of the cathode Porous Region on water crossover by diffusion is relatively smaller. On the other hand, the design of the cathode Porous layers plays a more important role in increasing the back-flow flux of water from the cathode to anode.
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two phase mass transport model for direct methanol fuel cells with effect of non equilibrium evaporation and condensation
Journal of Power Sources, 2007Co-Authors: Weiwei Yang, Tianshou ZhaoAbstract:Abstract A two-phase, mass-transport model for liquid-feed direct methanol fuel cells (DMFCs) is developed by taking into account the effect of non-equilibrium evaporation and condensation of methanol and water. The comparison between the present model and other models indicates that the present model yields more reasonable predictions of cell performance. Particularly, it is shown that the models that invoke a thermodynamic-equilibrium assumption between phases will overestimate mass-transport rates of methanol and water, thereby resulting in an inaccurate prediction of cell performance. The parametric study using the present model reveals that the gas coverage at the flow channel–diffusion-layer interface is directly related to the gas-void fraction inside the anode Porous Region; increasing the gas-void fraction will increase the mass-transfer resistance of methanol and thus lower cell performance. The effects of the geometric dimensions of the cell structure, such as channel width and rib width, on cell performance are also investigated with the model developed in this work.
K D P Nigam - One of the best experts on this subject based on the ideXlab platform.
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a two phase eulerian approach using relative permeability concept for modeling of hydrodynamics in trickle bed reactors at elevated pressure
Chemical Engineering Research & Design, 2010Co-Authors: Arnab Atta, Shantanu Roy, K D P NigamAbstract:Most commercial trickle-bed reactors (TBRs) employed in hydroprocessing and other industrially relevant operations normally operate at elevated pressures. Two-phase pressure drop and liquid holdup are two foremost important hydrodynamic parameters to consider for analysis and design of a TBR, including those operating at higher pressures. Even after several decades of research efforts directed towards the development of TBR technology, know-how about the hydrodynamics of two-phase flow in a TBR especially operating at high-pressure conditions has been inadequate. In this study, an effort has been made to assess the complex hydrodynamics of high-pressure TBR through the development of a Computational Fluid Dynamics (CFD) based model to predict pressure drop and liquid saturation. A two-phase Eulerian CFD model envisaging the flow field as Porous Region has been utilized for evaluating these hydrodynamic parameters. Different combinations of relative permeability correlations in the closure terms have been exercised to realize the best fit. The comparisons between model predictions and numerous experimental data, collected from different independent sources under a varied set of operating conditions, lead to the favourable implementation of this less computationally intensive, yet first-principle based CFD model to forecast the two-phase hydrodynamics for high-pressure TBRs.
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investigation of liquid maldistribution in trickle bed reactors using Porous media concept in cfd
Chemical Engineering Science, 2007Co-Authors: Arnab Atta, Shantanu Roy, K D P NigamAbstract:A three-dimensional CFD model for simulating two-phase flow in trickle-bed reactors (TBRs) is presented. Based on Porous media concept, a two-phase Eulerian model (rather than computationally demanding traditional three-phase Eulerian model) describing the flow domain as Porous Region is presented to understand and forecast the liquid maldistribution in TBRs under cold-flow conditions. The drag forces between phases have been accounted by employing the relative permeability concept [Saez, A. E., Carbonell, R. G., 1985. Hydrodynamic parameters for gas–liquid cocurrent flow in packed beds. A.I.Ch.E. Journal 31, 52–62]. The model predictions are validated against experimental data reported in literature, notably using the liquid distribution studies of Marcendelli [1999. Hydrodynamique, Transfert de Chaleur Particule-Fluide et Distribution des phases dans les Reacteurs a lit Fixe a Ecoulement a Co-courant Descendant de Gaz et de Liquide. Doctoral Thesis. INPL, Nancy, France]. Various distributor configurations reported therein have been recreated in the CFD model and sensitivity studies have been performed. Good agreement is obtained between the reported experimental results and this proposed first-principle based CFD model. Finally, the concept of distribution uniformity is discussed and applied to the CFD model predictions. The CFD model is subjected to a systematic sensitivity study in order to explore better liquid distribution alternatives.
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prediction of pressure drop and liquid holdup in trickle bed reactor using relative permeability concept in cfd
Chemical Engineering Science, 2007Co-Authors: Arnab Atta, Shantanu Roy, K D P NigamAbstract:Abstract A Computational Fluid Dynamics (CFD) model based on Porous media concept is presented to model the hydrodynamics of two-phase flow in trickle-bed reactors (TBRs). The aim of this study is to develop a comprehensive CFD based model for predicting hydrodynamic parameters in trickle-bed reactors under cold-flow conditions. The two-phase Eulerian model describing the flow domain as a Porous Region has been used to simulate the macroscale multiphase flow in trickle beds operating under trickle flow regime using FLUENT 6.2 software. The closure terms for phase interactions have been addressed by adopting the relative permeability concept [Saez, A.E., Carbonell, R.G., 1985. Hydrodynamic parameters for gas–liquid cocurrent flow in packed beds. A.I.Ch.E. Journal 31, 52–62]. The model has been evaluated by comparing predictions with the data (collected under a varied set of laboratory conditions) available in the open literature. It is shown that while being relatively simple in structure, this CFD model is flexible and predictive for a large body of experimental data presented in the open literature.
E I Saad - One of the best experts on this subject based on the ideXlab platform.
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axisymmetric motion of a Porous sphere through a spherical envelope subject to a stress jump condition
Meccanica, 2016Co-Authors: E I SaadAbstract:The flow problem of an incompressible axisymmetrical quasisteady translation and steady rotation of a Porous sphere in an eccentric spherical container is discussed using a combined analytical–numerical technique. A continuity of velocity components and normal stress together with the stress jump condition for the tangential stress are used at the interface between Porous and clear-fluid Regions. The fluid flow outside the particle is governed by the classical Stokes equations while the fluid flow inside the Porous Region is treated by Brinkman model. In order to solve the Stokes equations for the flow field, a general solution is constructed from the superposition of the basic solutions in the two spherical coordinate systems based on both the Porous sphere and spherical envelope. Solutions for translational and rotational motion of Porous eccentric spherical particle in a spherical envelope are obtained using the boundary collocation technique. The hydrodynamic drag force and couple exerted by the surrounding fluid on the Porous particle which is proportional to the translational and angular velocities, respectively, are calculated with good convergence for various values of the ratio of Porous-to-container radii, the relative distance between the centers of the Porous and container, the stress jump coefficient, and a coefficient that is proportional to the permeability. In the limits of the motions of a Porous sphere in a concentric container and near a container surface with a small curvature, the numerical values of the normalized drag force and the normalized coupling coefficient are in good agreement with the available values in the literature.
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slow motion of a Porous sphere translating along the axis of a circular cylindrical pore subject to a stress jump condition
Transport in Porous Media, 2014Co-Authors: E I Saad, M S FaltasAbstract:The coupled flow problem of an incompressible axisymmetrical quasisteady motion of a Porous sphere translating in a viscous fluid along the axis of a circular cylindrical pore is discussed using a combined analytical–numerical technique. At the fluid–Porous interface, the stress jump boundary condition for the tangential stress along with continuity of normal stress and velocity components are employed. The flow through the Porous particle is governed by the Brinkman model and the flow in the outside Porous Region is governed by Stokes equations. A general solution for the field equations in the clear Region is constructed from the superposition of the fundamental solutions in both cylindrical and spherical coordinate systems. The boundary conditions are satisfied first at the cylindrical pore wall by the Fourier transforms and then on the surface of the Porous particle by a collocation method. The collocation solutions for the normalized hydrodynamic drag force exerted by the clear fluid on the Porous particle is calculated with good convergence for various values of the ratio of radii of the Porous sphere and pore, the stress jump coefficient, and a coefficient that is proportional to the permeability. The shape effect of the cylindrical pore on the axial translation of the Porous sphere is compared with that of the particle in a spherical cavity; it found that the Porous particle in a circular cylindrical pore in general attains a lower hydrodynamic drag than in a spherical envelope.
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stokes flow past an assemblage of axisymmetric Porous spherical shell in cell models effect of stress jump condition
Meccanica, 2013Co-Authors: E I SaadAbstract:The quasisteady axisymmetrical flow of an incompressible viscous fluid past an assemblage of Porous concentric spherical shell-in-cell model is studied. Boundary conditions on the cell surface that correspond to the Happel, Kuwabara, Kvashnin and Cunningham/Mehta-Morse models are considered. At the fluid-Porous interfaces, the stress jump boundary condition for the tangential stresses along with continuity of normal stress and velocity components are employed. The Brinkman’s equation in the Porous Region and the Stokes equation for clear fluid are used. The hydrodynamic drag force acting on the Porous shell by the external fluid in each of the four boundary conditions on the cell surface is evaluated. It is found that the normalized mobility of the particles (the hydrodynamic interaction among the Porous shell particles) depends not only on the permeability of the Porous shells and volume fraction of the Porous shell particles, but also on the stress jump coefficient. As a limiting case, the drag force or mobility for a suspension of Porous spherical shells reduces to those for suspensions of impermeable solid spheres and of Porous spheres with jump.
Arnab Atta - One of the best experts on this subject based on the ideXlab platform.
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a two phase eulerian approach using relative permeability concept for modeling of hydrodynamics in trickle bed reactors at elevated pressure
Chemical Engineering Research & Design, 2010Co-Authors: Arnab Atta, Shantanu Roy, K D P NigamAbstract:Most commercial trickle-bed reactors (TBRs) employed in hydroprocessing and other industrially relevant operations normally operate at elevated pressures. Two-phase pressure drop and liquid holdup are two foremost important hydrodynamic parameters to consider for analysis and design of a TBR, including those operating at higher pressures. Even after several decades of research efforts directed towards the development of TBR technology, know-how about the hydrodynamics of two-phase flow in a TBR especially operating at high-pressure conditions has been inadequate. In this study, an effort has been made to assess the complex hydrodynamics of high-pressure TBR through the development of a Computational Fluid Dynamics (CFD) based model to predict pressure drop and liquid saturation. A two-phase Eulerian CFD model envisaging the flow field as Porous Region has been utilized for evaluating these hydrodynamic parameters. Different combinations of relative permeability correlations in the closure terms have been exercised to realize the best fit. The comparisons between model predictions and numerous experimental data, collected from different independent sources under a varied set of operating conditions, lead to the favourable implementation of this less computationally intensive, yet first-principle based CFD model to forecast the two-phase hydrodynamics for high-pressure TBRs.
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investigation of liquid maldistribution in trickle bed reactors using Porous media concept in cfd
Chemical Engineering Science, 2007Co-Authors: Arnab Atta, Shantanu Roy, K D P NigamAbstract:A three-dimensional CFD model for simulating two-phase flow in trickle-bed reactors (TBRs) is presented. Based on Porous media concept, a two-phase Eulerian model (rather than computationally demanding traditional three-phase Eulerian model) describing the flow domain as Porous Region is presented to understand and forecast the liquid maldistribution in TBRs under cold-flow conditions. The drag forces between phases have been accounted by employing the relative permeability concept [Saez, A. E., Carbonell, R. G., 1985. Hydrodynamic parameters for gas–liquid cocurrent flow in packed beds. A.I.Ch.E. Journal 31, 52–62]. The model predictions are validated against experimental data reported in literature, notably using the liquid distribution studies of Marcendelli [1999. Hydrodynamique, Transfert de Chaleur Particule-Fluide et Distribution des phases dans les Reacteurs a lit Fixe a Ecoulement a Co-courant Descendant de Gaz et de Liquide. Doctoral Thesis. INPL, Nancy, France]. Various distributor configurations reported therein have been recreated in the CFD model and sensitivity studies have been performed. Good agreement is obtained between the reported experimental results and this proposed first-principle based CFD model. Finally, the concept of distribution uniformity is discussed and applied to the CFD model predictions. The CFD model is subjected to a systematic sensitivity study in order to explore better liquid distribution alternatives.
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prediction of pressure drop and liquid holdup in trickle bed reactor using relative permeability concept in cfd
Chemical Engineering Science, 2007Co-Authors: Arnab Atta, Shantanu Roy, K D P NigamAbstract:Abstract A Computational Fluid Dynamics (CFD) model based on Porous media concept is presented to model the hydrodynamics of two-phase flow in trickle-bed reactors (TBRs). The aim of this study is to develop a comprehensive CFD based model for predicting hydrodynamic parameters in trickle-bed reactors under cold-flow conditions. The two-phase Eulerian model describing the flow domain as a Porous Region has been used to simulate the macroscale multiphase flow in trickle beds operating under trickle flow regime using FLUENT 6.2 software. The closure terms for phase interactions have been addressed by adopting the relative permeability concept [Saez, A.E., Carbonell, R.G., 1985. Hydrodynamic parameters for gas–liquid cocurrent flow in packed beds. A.I.Ch.E. Journal 31, 52–62]. The model has been evaluated by comparing predictions with the data (collected under a varied set of laboratory conditions) available in the open literature. It is shown that while being relatively simple in structure, this CFD model is flexible and predictive for a large body of experimental data presented in the open literature.