Numerical and experimental determination of effective in-plane permeability of the porous transport layer in a polymer electrolyte membrane fuel cell

A methodology is presented here to determine the in-plane permeability of the porous transport layer (PTL) in a polymer electrolyte membrane fuel cell (PEMFC). The method makes use of a novel combination of computational fluid dynamics (CFD) and experimental characterization to arrive at this important transport property. The CFD model was developed using commercial software by Fluent Inc. The experimental work consisted of measuring pressure drop between transits of a single serpentine flow field geometry that was geometrically equivalent to the CFD model. The in-plane permeability was adjusted in the model until the pressure drop measured in the experimental work was obtained. This in-plane permeability was then said to be the effective in-plane permeability of the PTL sample tested. It is an effective value and not the true value because the PTL was homogenized in the model and a uniform PTL thickness was used. This is the convention is the vast majority of CFD models of PEMFCs in the literature, therefore, the values presented here can be easily applied. The methodology was applied to three different types of PTL with two different gasket thicknesses. The effective in-plane permeability values obtained were on the order of 10-10m2 when a 370mum gasket was used and 10-11m2 when a 250/mum gasket was used. These numbers are in general agreement with values published in the literature. The impact of PTL thickness and PTL permeability on the velocity field and pressure gradient in a PEMFC were investigated with the three-dimensional CFD model. An analysis of the impact of flow field plate geometry and clamping pressure on the homogeneity and uniformity of the PTL was initiated through finite element method (FEM) structural analysis and microindentation. The objective was to develop a technique whereby the thickness profile of an "as-loaded" PTL could be determined. With this knowledge, a PEMFC modeller could use measurements of permeability as a function of thickness to accurately determine the permeability as a function of position.