Numerical Simulations of Gaseous Mixture Flow in Porous Electrodes for PEM Fuel Cells by the Lattice Boltzmann Method

Throughout the last decade, a considerable amount of work has been carried out in order to obtain ever more refined models of proton exchange membrane (PEM) fuel cells. While many of the phenomena occurring in a fuel cell have been described with ever more complex models, the flow of gaseous mixtures in the porous electrodes has continued to be modeled with Darcy’s law in order to take into account interactions with the solid structure and with Fick’s law in order to take into account interactions among species. Both of these laws derive from the macroscopic continuum approach, which essentially consists of applying some sort of homogenization technique which properly averages the underlying microscopic phenomena for producing measurable quantities. Unfortunately, these quantities in the porous electrodes of fuel cells are sometimes measurable only in principle. For this reason, this type of approach introduces uncertain macroscopic parameters which can significantly affect the numerical results. This paper is part of an ongoing effort to address the problem following an alternative approach. The key idea is to numerically simulate the underlying microscopic phenomena in an effort to bring the mathematical description nearer to actual reality. In order to reach this goal, some recently developed mesoscopic tools appear to be very promising since the microscopic approach is in this particularly case partially included in the numerical method itself. In particular, the lattice Boltzmann models treat the problem by reproducing the collisions among particles of the same type, among particles belonging to different species, and finally among the species and the solid obstructions. Recently, a procedure based on a lattice Boltzmann model for calculating the hydraulic constant as a function of material structure and applied pressure gradient was defined and applied. This model has since been extended in order to include gaseous mixtures with different methods being considered in order to simulate the coupling strength among the species. The present paper reports the results of this extended model for PEM fuel cell applications and in particular for the analysis of the fluid flow of gaseous mixtures through porous electrodes. Because of the increasing computational needs due to both three–dimensional descriptions and multi-physics models, the need for large parallel computing is indicated and some features of this improvement are reported.