Gas distribution and droplet removal of metal foam flow field for proton exchange membrane fuel cells

Abstract

Recently, porous metal foam has gained much attention as an alternative gas distributor of proton exchange membrane fuel cells. However, the gas distribution in the intricate porous flow field is different from the conventional flow channels and the liquid droplet behavior remains unclear. Thus, this study numerically investigated the two-phase mass transport capacities of the metal foam flow field. The metal foam morphology is reconstructed based on X-ray computational tomography technique and the two-phase interface is capture by volume of fluid method. A divergent gas transport mode is observed, which promotes the uniformity and convection of gas reactant flow with a much lower permeability than conventional flow channels. The heterogeneity of metal foam pore distribution should be minimized to reduce the pore-scale weak flow area. In addition, the air drag force on liquid droplet grows with droplet diameter in a similar way to that of a flow channel, but the resistance for liquid removal is no longer the shear force by wall surface but the adhesion by ligament surface. The hydrophobicity of ligaments is found necessary to reduce liquid retention phenomenon. In addition, the variation of gas velocity exhibits a stronger influence than droplet diameter on liquid removal, indicating that the metal foam flow field is applicable to high-current-density operation conditions for proton exchange membrane fuel cells.