Mixed Wettability Influence on Water Droplet Behaviour in a PEM Fuel Cell Channel

The utilization of hydrogen in low-temperature Proton Exchange Membrane Fuel Cells (PEMFCs) stands out as a compelling prospect for driving a widespread shift towards green industry practices. Despite significant advancements, a comprehensive understanding of water behaviour and dynamics within PEMFCs remains crucial for their extensive integration in propulsion applications. Striking a delicate balance between flooding and drying conditions poses a challenge for achieving stable and efficient PEMFC operation. In this study, a preliminary experimental investigation was conducted focusing on carbon-paper Gas Diffusion Layer (GDL) and gas channel walls. The static, advancing and receding contact angles were measured and utilized as boundary conditions for simulations. The influence of membrane humidity was also examined during the experimental campaign. 3D CFD simulations were performed on a straight portion of a PEMFC channel with a selected domain length of 5 mm and a section of 1x1 mm. Two classes of droplets (0.05 mm³ and 0.075 mm³) were deposited in the middle of the channel and in double contact conditions between the GDL and the wall. To account for the significant difference in contact angles, the relative boundary condition for the GDL was set equal to the experimental static angle (128°), while a User Defined Function (UDF) for dynamic contact angle was implemented based on observed contact angle hysteresis (45° / 55°) and literature correlations. The droplet behaviour was studied under constant 10 m/s inlet velocity and atmospheric pressure outlet. The research results contribute valuable insights into water management within gas channels. The mixing contact angle condition highlighted the differences in motion behaviour on the two surfaces: droplets tend to roll on the GDL, while the high wettability of the walls leads to slug/film formation.