The Experts below are selected from a list of 46698 Experts worldwide ranked by ideXlab platform
Charnjung Kim - One of the best experts on this subject based on the ideXlab platform.
-
steady liquid water Saturation Distribution in hydrophobic gas diffusion layers with engineered pore paths an invasion percolation pore network analysis
Journal of Power Sources, 2010Co-Authors: Kyujin Lee, Jin Hyun Nam, Jung Ho Kang, Charnjung KimAbstract:The modification of pore structures in gas-diffusion layers (GDLs) has long been studied in the context of efforts to facilitate liquid water transport and to reduce flooding. Such improvements can theoretically improve the performance of polymer electrolyte membrane fuel cells (PEMFCs). Recent experimental studies have demonstrated that engineered pore paths in hydrophobic GDLs, in the form of either large vertical slits or holes, can be advantageous for water management in PEMFCs. In this study, a pore-network model is employed to obtain the steady Saturation Distribution of liquid water in hydrophobic GDLs with several engineered pore paths. The pore-network results clearly indicate the merits of engineered pore paths in reducing liquid water Saturation levels in hydrophobic GDLs. The mechanism by which these engineered pore paths reduce liquid water flooding is discussed in reference to the invasion-percolation process in porous media.
-
steady Saturation Distribution in hydrophobic gas diffusion layers of polymer electrolyte membrane fuel cells a pore network study
Journal of Power Sources, 2010Co-Authors: Kyujin Lee, Jin Hyun Nam, Charnjung KimAbstract:A pore-network model is developed to simulate liquid water transport in a hydrophobic gas-diffusion layer (GDL) during the operation of polymer electrolyte membrane fuel cells (PEMFCs). The steady Saturation Distribution in GDLs is determined through a numerical procedure using a pore-network model combined with invasion-percolation path-finding and subsequent viscous two-phase flow calculation. The simulation results indicate that liquid water transport in hydrophobic GDLs is a strongly capillary-driven process that almost reaches the pure invasion-percolation limit with zero capillary number. A uniform flux condition is found to better reflect the actual phenomenon occurring at the inlet boundary for liquid water entering a GDL than a uniform pressure condition. The simulation further clarifies the effect of the invaded pore fraction at a uniform-flux inlet boundary in modifying water transport in GDLs. Finally, the effect of the GDL thickness on the steady Saturation Distribution is investigated.
-
pore network analysis of two phase water transport in gas diffusion layers of polymer electrolyte membrane fuel cells
Electrochimica Acta, 2009Co-Authors: Kyujin Lee, Jin Hyun Nam, Charnjung KimAbstract:Abstract A pore-network model was developed to study the water transport in hydrophobic gas diffusion layers (GDLs) of polymer electrolyte membrane fuel cells (PEMFCs). The pore structure of GDL materials was modeled as a regular cubic network of pores connected by throats. The governing equations for the two-phase flow in the pore-network were obtained by considering the capillary pressure in the pores, and the entry pressure and viscous pressure drop through the throats. Numerical results showed that the Saturation Distribution in GDLs maintained a concave shape, indicating the water transport in GDLs was strongly influenced by capillary processes. Parametric studies were also conducted to examine the effects of several geometrical and capillary properties of GDLs on the water transport behavior and the Saturation Distribution. The proper inlet boundary condition for the liquid water entering GDLs was discussed along with its effects on the Saturation Distribution.
Kyujin Lee - One of the best experts on this subject based on the ideXlab platform.
-
steady liquid water Saturation Distribution in hydrophobic gas diffusion layers with engineered pore paths an invasion percolation pore network analysis
Journal of Power Sources, 2010Co-Authors: Kyujin Lee, Jin Hyun Nam, Jung Ho Kang, Charnjung KimAbstract:The modification of pore structures in gas-diffusion layers (GDLs) has long been studied in the context of efforts to facilitate liquid water transport and to reduce flooding. Such improvements can theoretically improve the performance of polymer electrolyte membrane fuel cells (PEMFCs). Recent experimental studies have demonstrated that engineered pore paths in hydrophobic GDLs, in the form of either large vertical slits or holes, can be advantageous for water management in PEMFCs. In this study, a pore-network model is employed to obtain the steady Saturation Distribution of liquid water in hydrophobic GDLs with several engineered pore paths. The pore-network results clearly indicate the merits of engineered pore paths in reducing liquid water Saturation levels in hydrophobic GDLs. The mechanism by which these engineered pore paths reduce liquid water flooding is discussed in reference to the invasion-percolation process in porous media.
-
steady Saturation Distribution in hydrophobic gas diffusion layers of polymer electrolyte membrane fuel cells a pore network study
Journal of Power Sources, 2010Co-Authors: Kyujin Lee, Jin Hyun Nam, Charnjung KimAbstract:A pore-network model is developed to simulate liquid water transport in a hydrophobic gas-diffusion layer (GDL) during the operation of polymer electrolyte membrane fuel cells (PEMFCs). The steady Saturation Distribution in GDLs is determined through a numerical procedure using a pore-network model combined with invasion-percolation path-finding and subsequent viscous two-phase flow calculation. The simulation results indicate that liquid water transport in hydrophobic GDLs is a strongly capillary-driven process that almost reaches the pure invasion-percolation limit with zero capillary number. A uniform flux condition is found to better reflect the actual phenomenon occurring at the inlet boundary for liquid water entering a GDL than a uniform pressure condition. The simulation further clarifies the effect of the invaded pore fraction at a uniform-flux inlet boundary in modifying water transport in GDLs. Finally, the effect of the GDL thickness on the steady Saturation Distribution is investigated.
-
pore network analysis of two phase water transport in gas diffusion layers of polymer electrolyte membrane fuel cells
Electrochimica Acta, 2009Co-Authors: Kyujin Lee, Jin Hyun Nam, Charnjung KimAbstract:Abstract A pore-network model was developed to study the water transport in hydrophobic gas diffusion layers (GDLs) of polymer electrolyte membrane fuel cells (PEMFCs). The pore structure of GDL materials was modeled as a regular cubic network of pores connected by throats. The governing equations for the two-phase flow in the pore-network were obtained by considering the capillary pressure in the pores, and the entry pressure and viscous pressure drop through the throats. Numerical results showed that the Saturation Distribution in GDLs maintained a concave shape, indicating the water transport in GDLs was strongly influenced by capillary processes. Parametric studies were also conducted to examine the effects of several geometrical and capillary properties of GDLs on the water transport behavior and the Saturation Distribution. The proper inlet boundary condition for the liquid water entering GDLs was discussed along with its effects on the Saturation Distribution.
Jerome A Neufeld - One of the best experts on this subject based on the ideXlab platform.
-
upscaling multiphase viscous to capillary transitions in heterogeneous porous media
Journal of Fluid Mechanics, 2021Co-Authors: G P Benham, M J Bickle, Jerome A NeufeldAbstract:Upscaling the effect of heterogeneities in porous media is crucial for macroscopic flow predictions, with numerous applications in energy and environmental settings. In this study, we derive simple semi-analytical expressions for the upscaling of multiphase flow in a porous medium with a range of vertical heterogeneities. We use this upscaling to give insight into how the flow transitions between a viscous flow regime, in which macroscopic pressure gradients dominate over heterogeneity-driven capillary forces, and a capillary flow regime, in which these capillary forces dominate and set the Saturation Distribution of the flow. In particular, by studying the dynamics of flow in an aquifer, we demonstrate that different regions lie within the viscous and capillary flow regimes whilst other regions lie in between these regimes. By modifying the classic Buckley–Leverett problem for fluid displacement we demonstrate where and when the flow transitions between these regimes and how this affects flooding speeds. Then, we discuss the implications of these results in the case of carbon dioxide sequestration, making comparisons with field data.
-
the effects of capillary forces on the axisymmetric propagation of two phase constant flux gravity currents in porous media
Physics of Fluids, 2013Co-Authors: Madeleine J Golding, Herbert E Huppert, Jerome A NeufeldAbstract:The effects of capillary forces on the propagation of two-phase, constant-flux gravity currents in a porous medium are studied analytically and numerically in an axisymmetric geometry. The fluid within a two-phase current generally only partially saturates the pore space it invades. For long, thin currents, the Saturation Distribution is set by the vertical balance between gravitational and capillary forces. The capillary pressure and relative permeability of the fluid in the current depend on this Saturation. The action of capillary forces reduces the average Saturation, thereby decreasing the relative permeability throughout the current. This results in a thicker current, which provides a steeper gradient to drive flow, and a more blunt-nose profile. The relative strength of gravity and capillary forces remains constant within a two-phase gravity current fed by a constant flux and spreading radially, due to mass conservation. For this reason, we use an axisymmetric representation of the framework develo...
-
the effects of capillary forces on the axisymmetric propagation of two phase constant flux gravity currents in porous media
Physics of Fluids, 2013Co-Authors: Madeleine J Golding, Herbert E Huppert, Jerome A NeufeldAbstract:The effects of capillary forces on the propagation of two-phase, constant-flux gravity currents in a porous medium are studied analytically and numerically in an axisymmetric geometry. The fluid within a two-phase current generally only partially saturates the pore space it invades. For long, thin currents, the Saturation Distribution is set by the vertical balance between gravitational and capillary forces. The capillary pressure and relative permeability of the fluid in the current depend on this Saturation. The action of capillary forces reduces the average Saturation, thereby decreasing the relative permeability throughout the current. This results in a thicker current, which provides a steeper gradient to drive flow, and a more blunt-nose profile. The relative strength of gravity and capillary forces remains constant within a two-phase gravity current fed by a constant flux and spreading radially, due to mass conservation. For this reason, we use an axisymmetric representation of the framework developed by Golding et al. [“Two-phase gravity currents in porous media,” J. Fluid Mech. 678, 248–270 (2011)]10.1017/jfm.2011.110, to investigate the effect on propagation of varying the magnitude of capillary forces and the pore-size Distribution. Scaling analysis indicates that axisymmetric two-phase gravity currents fed by a constant flux propagate like t1/2, similar to their single-phase counterparts [S. Lyle, H. E. Huppert, M. Hallworth, M. Bickle, and A. Chadwick, “Axisymmetric gravity currents in a porous medium,” J. Fluid Mech. 543, 293–302 (2005)]10.1017/S0022112005006713, with the effects of capillary forces encapsulated in the constant of proportionality. As a practical application of our new concepts and quantitative evaluations, we discuss the implications of our results for the process of carbon dioxide (CO2) sequestration, during which gravity currents consisting of supercritical CO2 propagate in rock saturated with aqueous brine. We apply our two-phase model including capillary forces to quantitatively assess seismic images of CO2 spreading at Sleipner underneath the North Sea.
Jin Hyun Nam - One of the best experts on this subject based on the ideXlab platform.
-
steady liquid water Saturation Distribution in hydrophobic gas diffusion layers with engineered pore paths an invasion percolation pore network analysis
Journal of Power Sources, 2010Co-Authors: Kyujin Lee, Jin Hyun Nam, Jung Ho Kang, Charnjung KimAbstract:The modification of pore structures in gas-diffusion layers (GDLs) has long been studied in the context of efforts to facilitate liquid water transport and to reduce flooding. Such improvements can theoretically improve the performance of polymer electrolyte membrane fuel cells (PEMFCs). Recent experimental studies have demonstrated that engineered pore paths in hydrophobic GDLs, in the form of either large vertical slits or holes, can be advantageous for water management in PEMFCs. In this study, a pore-network model is employed to obtain the steady Saturation Distribution of liquid water in hydrophobic GDLs with several engineered pore paths. The pore-network results clearly indicate the merits of engineered pore paths in reducing liquid water Saturation levels in hydrophobic GDLs. The mechanism by which these engineered pore paths reduce liquid water flooding is discussed in reference to the invasion-percolation process in porous media.
-
steady Saturation Distribution in hydrophobic gas diffusion layers of polymer electrolyte membrane fuel cells a pore network study
Journal of Power Sources, 2010Co-Authors: Kyujin Lee, Jin Hyun Nam, Charnjung KimAbstract:A pore-network model is developed to simulate liquid water transport in a hydrophobic gas-diffusion layer (GDL) during the operation of polymer electrolyte membrane fuel cells (PEMFCs). The steady Saturation Distribution in GDLs is determined through a numerical procedure using a pore-network model combined with invasion-percolation path-finding and subsequent viscous two-phase flow calculation. The simulation results indicate that liquid water transport in hydrophobic GDLs is a strongly capillary-driven process that almost reaches the pure invasion-percolation limit with zero capillary number. A uniform flux condition is found to better reflect the actual phenomenon occurring at the inlet boundary for liquid water entering a GDL than a uniform pressure condition. The simulation further clarifies the effect of the invaded pore fraction at a uniform-flux inlet boundary in modifying water transport in GDLs. Finally, the effect of the GDL thickness on the steady Saturation Distribution is investigated.
-
pore network analysis of two phase water transport in gas diffusion layers of polymer electrolyte membrane fuel cells
Electrochimica Acta, 2009Co-Authors: Kyujin Lee, Jin Hyun Nam, Charnjung KimAbstract:Abstract A pore-network model was developed to study the water transport in hydrophobic gas diffusion layers (GDLs) of polymer electrolyte membrane fuel cells (PEMFCs). The pore structure of GDL materials was modeled as a regular cubic network of pores connected by throats. The governing equations for the two-phase flow in the pore-network were obtained by considering the capillary pressure in the pores, and the entry pressure and viscous pressure drop through the throats. Numerical results showed that the Saturation Distribution in GDLs maintained a concave shape, indicating the water transport in GDLs was strongly influenced by capillary processes. Parametric studies were also conducted to examine the effects of several geometrical and capillary properties of GDLs on the water transport behavior and the Saturation Distribution. The proper inlet boundary condition for the liquid water entering GDLs was discussed along with its effects on the Saturation Distribution.
Matthew M Mench - One of the best experts on this subject based on the ideXlab platform.
-
quantification of temperature driven flow in a polymer electrolyte fuel cell using high resolution neutron radiography
Journal of The Electrochemical Society, 2011Co-Authors: Marta C Hatzell, A Turhan, Soowhan Kim, Daniel S Hussey, David L Jacobson, Matthew M MenchAbstract:In this study, the effect of a controlled temperature gradient on water transport across a single fuel cell was quantitatively investigated using high-resolution neutron imaging. The direction of liquid water transport under isothermal and non-isothermal conditions was observed in both hydrophilic and hydrophobic diffusion media (DM). The change in Distribution of liquid Saturation with time revealed two different mechanisms of water transport; capillary driven flow and phase-change induced (PCI) flow, in which a water vapor concentration gradient is created by condensation at a colder location. This concentration gradient drives diffusion flow toward the colder location. A maximum liquid Saturation plateau of ca. 30% was shown for all conditions tested, indicating a critical transition between pendular and funicular modes of liquid water storage was captured. Based on this, it is suggested that PCI-flow may be the main mode of liquid transport below this critical transition threshold, above which, capillary flow dominates. As expected, both average cell temperature and the magnitude of temperature gradient were shown to significantly affect the rate of condensation within the DM. Experimental results were compared with water Saturation Distribution model predictions from literature and show reasonable qualitative agreement. Finally, it was concluded that current available models significantly over predict vapor phase diffusive transport in saturated fuel cell media using a Bruggeman type model.
-
quantification of temperature driven flow in a polymer electrolyte fuel cell using high resolution neutron radiography
Journal of The Electrochemical Society, 2011Co-Authors: Marta C Hatzell, A Turhan, Daniel S Hussey, David L Jacobson, Matthew M MenchAbstract:In this study, the effect of a controlled temperature gradient on water transport across a single fuel cell was quantitatively investigated using high-resolution neutron imaging. The direction of liquid water transport under isothermal and non-isothermal conditions was observed in both hydrophilic and hydrophobic diffusion media (DM). The change in Distribution of liquid Saturation with time revealed two different mechanisms of water transport; capillary driven flow and phase-change induced (PCI) flow, in which a water vapor concentration gradient is created by condensation at a colder location. This concentration gradient drives diffusion flow toward the colder location. A maximum liquid Saturation plateau of ca. 30% was shown for all conditions tested, indicating a critical transition between pendular and funicular modes of liquid water storage was captured. Based on this, it is suggested that PCI-flow may be the main mode of liquid transport below this critical transition threshold, above which, capillary flow dominates. As expected, both average cell temperature and the magnitude of temperature gradient were shown to significantly affect the rate of condensation within the DM. Experimental results were compared with water Saturation Distribution model predictions from literature and show reasonable qualitative agreement. Finally, it was concluded that current available models significantly over predict vapor phase diffusive transport in saturated fuel cell media using a Bruggeman type model.
