Computational Fluid Dynamics of Water Droplet Formation and Detachment from Gas Diffusion Layer

Liquid water removal from a polymer electrolyte membrane fuel cell bipolar plate channel is critical for optimal performance and durability. A two-dimensional, two-phase computational fluid dynamics (CFD) model was created to simulate water droplet formation and removal. The numerical domain consist of a gas diffusion layer (GDL) and channel. The polytetrafluoroethylene (PTFE) loading in the GDL was varied by changing the surface tension and contact angle. The effect of 10%, 15%, and 20% PTFE loading on the droplet detachment velocity and penetration pressure was studied. It was found that increasing the PTFE loading decreased the detachment velocity due to lower wetting at the GDL surface. However, increasing the PTFE loading had the consequence of raising the required capillary pressure to penetrate the GDL. This was due to initial spreading of the water below the GDL and the formation of local water paths, which was observed for the higher PTFE loadings.