  Pore structures and gas transport properties in porous separators for polymer
electrolyte fuel cells are evaluated both experimentally and through
simulations. In the experiments, the gas permeabilities of two porous samples,
a conventional sample and one with low electrical resistivity, are measured by
a capillary flow porometer, and the pore size distributions are evaluated with
mercury porosimetry. Local pore structures are directly observed with micro
X-ray computed tomography (CT). In the simulations, the effective diffusion
coefficients of oxygen and the air permeability in porous samples are
calculated using random walk Monte Carlo simulations and computational fluid
dynamics (CFD) simulations, respectively, based on the X-ray CT images. The
calculated porosities and air permeabilities of the porous samples are in good
agreement with the experimental values. The simulation results also show that
the in-plane permeability is twice the through-plane permeability in the
conventional sample, whereas it is slightly higher in the low-resistivity
sample. The results of this study show that CFD simulation based on micro X-ray
CT images makes it possible to evaluate anisotropic gas permeabilities in
anisotropic porous media.
