The gas diffusion layers (GDLs) are key components in proton exchange membrane fuel cells and understanding fluid flow through them plays a significant role in improving fuel cell performance. We used a combination of multiple-relaxation time (MRT) lattice Boltzmann method (LBM) and X-ray micro tomography imaging technology to compare results on dependence of the permeability calculation on the different system size of the computational gas diffusion layer sample. The micro-structures of the carbon paper (HP_1.76) and carbon cloth (HP_1.733) GDL were all digitizing 3D images acquired by X-ray computed micro-tomography at a resolution of 1.76 and 1.733 microns meter respectively, and the fluid flow was simulated by applying pressure gradient in both the through-plane and in-plane direction respectively. The lattice Boltzmann method for permeability calculation has already been tested in our previous work. In this work, we will focus on the permeability calculation of the realistic gas diffusion layer samples depend on the different size samples. The results show the permeability increases with fluctuations as the porosity rises. All the permeability and porosity converge to the value of large size sample that can be regarding a representative volume element. As the porosity and permeability of these Porous samples differs significantly for each other, the anisotropic permeability is nearly same for each one. We can choose part of the sample to calculate the characters if the sample is too big to calculate. We systematically study the effect of system size and periodic boundary condition and validate Darcy’s law from the linear dependence of the flux on the body force exerted.

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