Analytical modelling of water droplet behavior at the gas channel corner for proton exchange membrane fuel cells

Abstract

Water management is of significant importance to achieving high performance of proton exchange membrane fuel cells. In recent years, droplets emerged from the rib surface and accumulated at the channel corner have been found to be a crucial part of water flooding. In this study, an analytical model is first proposed to quantitatively estimate the variation in the morphology and dynamic behavior of growing droplets with consideration of the channel sidewall interaction. In order to predict the water geometry, the flow channel with compressed gas diffusion layer (GDL) is described mathematically, and water behavior at steady state and dynamic state are both evaluated through the geometric and force analysis. The model results indicate that the droplet profile transforms from concave to convex when its size grows, in which process contact angles and channel shape play an important role. Compared with the graphite channel, the droplet in the metallic channel is more inclined to be adsorbed on the sidewall and GDL, resulting in a higher adhesion force and a lower gas shear force. The critical gas velocities for the detachment of various droplets are quantitatively predicted to avoid water flooding. The model is helpful to understand the droplet behavior in the presence of channel sidewall interaction.