The impact of sample size on transport properties of carbon-paper and carbon-cloth GDLs: Direct simulation using the lattice Boltzmann model.

The transport properties of gas diffusion layer (GDL) in proton exchange membrane fuel cell are important parameters in fuel cell modelling, and one method to measure them is to simulate the transport of each species at spatial resolutions of a few microns in a microstructure of the GDL. One issue in this method is the size of the microstructure as using an unnecessarily big sample could substantially increase the computational cost. Both carbon-paper and carbon-cloth GDLs are investigated and their microstructures are obtained using numerical generation and X-ray micro-tomography respectively at a resolution of 1.733 µm. For each reconstructed GDL, we use the orthorhombic lattice Boltzmann model to simulate fluid flow through some subsamples taken from it in both the in-plane and the through-plane directions; the results show that the permeability of all subsamples is anisotropic in that their permeability in the in-plane direction is higher than in the through-plane direction. For each GDL, we compare its permeability calculated using samples of different sizes and find its representative elementary volume (REV) – a volume above which the calculated permeability represents the average ability of the GDL to conduct fluids. [ABSTRACT FROM AUTHOR]