Numerical simulation of water droplet dynamics in a right angle gas channel of a polymer electrolyte membrane fuel cell

Abstract

The dynamics of liquid water emerging from a micro pore on a gas diffusion layer (GDL) surface into a right angle gas channel of a polymer electrolyte membrane (PEM) fuel cell is investigated numerically with the volume of fluid method. As the GDL surface contact angle decreases, droplets from the outer and inner pores tend to move along the side walls or the lower edges and droplets from the center pore show complex patterns of behavior. As the hydrophobicity of the side and top walls increases, the GDL surface water coverage ratio increases, while the water volume fraction decreases. While the higher GDL surface water coverage ratio hinders the diffusion of reactants to reaction sites, the lower water volume fraction is advantageous in preventing water flooding in the gas channel. Therefore, in general gas channel geometry, the GDL surface water coverage ratio and the water volume fraction may compete with each other to determine the performance of PEM fuel cells, while changing the hydrophobicity of the side and top walls. As the air inlet velocity increases, liquid water moves faster and the water volume fraction decreases. As the water injection velocity increases, the moving speed of the water and the water volume fraction increase.