Droplet flow characteristics on experimentally measured gas diffusion layer surfaces of polymer electrolyte membrane fuel cells

Abstract

Understanding water droplet flow characteristics on realistic gas diffusion layer (GDL) surfaces is crucial for designing high-performance fuel cells. In this paper, droplet flow characteristics on experimentally measured GDL surfaces with different roughnesses are investigated by a volume of fluid (VOF) method in a gas channel (GC). GDL surface morphologies with different roughnesses are obtained by changing the Polytetrafluoroethylene (PTFE) content in the GDL and measured by a 3-dimensional surface metrology microscope. Results show that a low PTFE content reduces the GDL surface contact angle and increases the surface roughness, thus increasing the water droplet discharge time, spreading area and deformation. As the PTFE content increasing, the GDL surface contact angle increases and the surface roughness decreases, thereby yielding a relatively smooth flow process and short water droplet discharge time. Additionally, the water droplet flow characteristics on smooth GDL surfaces are comparatively examined. We find that even when flowing on a surface with the same contact angle, water droplet flow on rough GDL surfaces tends to yield a longer discharge time, larger spreading area, stronger fluctuations and larger pressure drop than on smooth GDL surfaces, further indicating that the GDL surface roughness exhibits a noteworthy influence on water droplet flow.