Numerical Determination of Two-Phase Material Parameters of a Gas Diffusion Layer Using Tomography Images

2008 ◽  
Vol 5 (2) ◽  
Author(s):  
Jürgen Becker ◽  
Volker Schulz ◽  
Andreas Wiegmann
Keyword(s):  
Diffusion Layer ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
Pore Morphology ◽  
Two Phase ◽  
Material Parameters ◽  
3D Tomography ◽  
Tomography Image ◽  
Parameter Values

In this paper, we give a complete description of the process of determining two-phase material parameters for a gas diffusion layer: Starting from a 3D tomography image of the gas diffusion layer the distribution of gas and water phases is determined using the pore morphology method. Using these 3D phase distributions, we are able to determine permeability, diffusivity, and heat conductivity as a function of the saturation of the porous medium with comparatively low numerical costs. Using a reduced model for the compression of the gas diffusion layer, the influence of the compression on the parameter values is studied.

Predicting Phase-Change Rate in PEFC Gas Diffusion Layer

2008 ◽  
Author(s):  
Suman Basu ◽  
Chao-Yang Wang ◽  
Ken S. Chen
Keyword(s):  
Phase Change ◽  
Diffusion Layer ◽  
Practical Interest ◽  
Catalyst Layer ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
Reduction Reaction ◽  
Polymer Electrolyte Fuel Cell ◽  
Two Phase ◽  
Change Rate

Water and heat are produced in the cathode catalyst layer of a polymer electrolyte fuel cell (PEFC) due to the oxygen-reduction reaction. Efficient water removal from the gas diffusion layer (GDL) to the flow channel is critical to achieve high and stable PEFC performance. Water transport and removal strongly depend on local temperature because the saturation concentration of water vapor rises rapidly with temperature, particularly in the temperature range of practical interest to PEFC applications. Detailed investigations of two-phase flow in the GDL have been reported in the literature, but not on the rate of phase change – either from liquid to vapor as in the case of evaporation or from vapor to liquid as in the case of condensation. In the present work, a two-phase, non-isothermal numerical model is used to elucidate the phase-change rate inside the cathode GDL of a PEFC. Results computed from our model enable a basic understanding of the phase-change processes occurring in a PEFC.

Impact of Microchannel Boundary Conditions on Gas Diffusion Layer Saturation and Transport in Fuel Cells

2008 ◽  
Author(s):  
Kenneth M. Armijo ◽  
Van P. Carey
Keyword(s):  
Boundary Condition ◽  
Fuel Cell ◽  
Boundary Conditions ◽  
Diffusion Layer ◽  
Oxygen Transport ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
Two Phase ◽  
Fuel Cell Performance ◽  
Phase Transport

Flooding within a Polymer Electrolyte Membrane (PEM) fuel cell occurs during operation as a result of product water vapor condensing near the surface of the cathode; this can be detrimental to fuel cell performance due to its role in reducing oxygen transport throughout the GDL. Previous Gas Diffusion Layer (GDL) transport models have made use of a zero-saturation boundary condition at the GDL/Oxygen (O2) gas channel (GC) interface. However, the physical correctness of this saturation boundary condition is still unclear. Further investigation of the saturation boundary condition could lead to a more robust model of the GDL saturation distribution and cathodic flooding. This exploration provides a one-dimensional two-phase transport model for saturation as well as liquid water and gaseous oxygen pressure distributions throughout the cathode-side gas diffusion layer (GDL) within a PEM fuel cell. The focus of this investigation is on the impact of non-zero saturation boundary conditions at the GDL / GC interface, and its impact on two-phase transport within the porous medium, with regard to fuel cell performance. Saturation boundary conditions at this location are determined based on GDL interfacial liquid coverage of water droplets that diffuse through the porous medium during operation and block oxygen transport paths. The results of this investigation suggest that non-zero saturation boundary conditions at the GDL/GC interface are evident when analyzing two-phase phenomena, which affect the overall saturation distribution throughout the GDL, and consequent performance of the fuel cell. In addition, GDL membranes with large porosities were found to improve gas and liquid transport by lowering the saturation at the GDL / Cathode interface that would otherwise impede oxygen transport.

scholarly journals On the hydrophobicity and hydrophilicity of the cathode gas diffusion layer in a polymer electrolyte fuel cell

2013 ◽  
Vol 469 (2154) ◽  
pp. 20120695 ◽  
Author(s):  
M. Vynnycky ◽  
A. Gordon
Keyword(s):  
Fuel Cell ◽  
Polymer Electrolyte ◽  
Diffusion Layer ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
Cell Performance ◽  
Polymer Electrolyte Fuel Cell ◽  
Liquid Region ◽  
Catalytic Layer ◽  
Two Phase

An anomaly in the modelling of two-phase flow in the porous cathode gas diffusion layer (GDL) of a polymer electrolyte fuel cell is investigated asymptotically and numerically. Although not commented on previously in literature, the generalized Darcy model used most commonly leads to the surprising prediction that a hydrophilic GDL can lead to better cell performance, in terms of current density, than a hydrophobic one. By analysing a reduced one-dimensional steady-state model and identifying the capillary number as a small dimensionless parameter, we find a potential flaw in the original model, associated with the constitutive relation linking the capillary pressure and the pressures of the wetting and non-wetting phases. Correcting this, we find that, whereas a hydrophilic GDL can sustain a two-phase (gas/liquid) region near the water-producing catalytic layer and gas phase only region further away, a hydrophobic GDL cannot; furthermore, hydrophobic GDLs are found to lead to better cell performance than hydrophilic GDLs, as is indeed experimentally the case.

Analytical Solution for Two-Phase Flow in PEMFC Gas Diffusion Layer

2006 ◽  
Author(s):  
Mingfei Gan ◽  
Lea-Der Chen
Keyword(s):  
Water Management ◽  
Analytical Solution ◽  
Oxygen Concentration ◽  
Active Layer ◽  
Diffusion Layer ◽  
Liquid Water ◽  
Flow Model ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
Two Phase

Thermal and water management is critical to fuel cell performance. It has been shown that gas diffusion layer (GDL) can impose the mass transport limit; for example, it can block the reactant transport to active layer when flooding occurs at high current density conditions. Micro porous layer (MPL) in conjunction with backing layer (BL) has been used as a GDL material and was shown to be effective for water management. To study the transport processes in GDL and MPL modified GDL, an analytical solution is derived current study for calculation of two-phase, multicomponent transport in GDL. Two models were considered, the unsaturated flow model (UFM) and the separate flow model (SFM). Comparison of the calculated saturation level and oxygen mass fraction shows that UFM calculation can underestimate, as well as overestimate the saturation and oxygen concentration. The SFM was used to study the effects due to GDL property variations. The calculation shows that increase in liquid water transport in an MPL modified GDL is due to the abrupt change of liquid water flow rate when a step change in porosity or permeability is imposed. The calculation further shows that particle size of around 1 μm would be a good choice for MPL as it results in higher oxygen concentration at active layer and lower saturation in GDL.

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