Predicting Transport Properties of Porous Layers Based on Pore-Scale Models


Jürgen Becker, Andreas Wiegmann
Fraunhofer ITWM, Kaiserslautern, Germany


Abstract 

This talk consists of two parts. In the first part, we will present the tools and methods
we use to determine transport properties of porous media. In the second part of the
talk we will apply these methods to simulate and analyze porous layers of a PEM fuel
cell.
Central in our approach is the 3D structure model of the pore structure, represented
as a 3D voxel image. Such a model can originate from a CT image of the media,
segmented into solid and void parts by choice of a threshold. Or, a 3D model can be
constructed virtually.
Next, various properties of the structure can be determined numerically. Some, like
surface area and pore size distribution, can be determined purely geometrically.
Transport properties like diffusivity, permeability or conductivity require to solve a
partial differential equation. For example, the permeability can be obtained from the
solution of the Stokes equation. Even more involved is the determination of twophase
flow properties. Here, we use the pore morphology method to obtain the
capillary pressure - saturation relationship. A combination of this method with singlephase
flow computations allows us to determine relative permeabilitiies.
As exemplary application we will consider a PEM fuel cell. In fact, the membrane
electrode assembly (MEA) of a PEM fuel cell consists of several porous layers on
both the cathode and the anode side: the gas diffusion layer (GDL), the catalyst layer
(CL) and sometimes a micro-porous layer (MPL) in between. We will present both CT
based and virtually created GDL models and show the numerically determined
properties. Where available, the results will be compared with experimental data.


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Last modified: Fri Oct 15 10:15:15 W. Europe Standard 2010