Liquid water leaving the porous diffusion layer enters the flow channels as a thin liquid film in PEMFC. A multiphase model is used to describe the flow of liquid water as a thin film along the flow passage walls. As liquid water reaches the surface of the diffusion layer, it is introduced into the gas flow passage as a thin liquid film of drops, where shear between the gas flow and film surface can move the film. Gravitational and surface tension forces are taken into account. Reentry of liquid water from the thin film back into the diffusion layer is permitted.

Water vapor mole fraction contours in the oxidizer channel