Abstract
During the operation of proton exchange membrane (PEM) fuel cells, water is produced in the cathode side. The produced water passes through the porous structure of the electrode and emerges from the surface of the gas diffusion layer (GDL) within the flow channel. The emerged droplet is constantly fed through liquid columns which are formed underneath the droplet within the GDL. This study focuses on dynamics of growing droplets on the surface of the GDL which are exposed to shear gas flow. High-speed imaging was implemented to visualize droplet dynamics from emergence to detachment as the pressure drop across the droplet was measured simultaneously. Images were processed with MATLAB code which was developed in-house to obtain droplet lateral area and the location of the droplet centroid. Results clearly demonstrated that droplets underwent an oscillatory mode for both superficial gas velocities tested in this study. While the oscillatory motion was observed both in horizontal (i.e. stream-wise direction) and vertical directions, the amplitude of the oscillation was greater in the horizontal direction. In addition, the oscillation amplitude was observed to increase with droplet size and reached the maximum value upon droplet detachment. For a superficial gas velocity of 10.76 m/s, the oscillation amplitude upon detachment was as high as around 0.16 mm in x direction while the corresponding oscillation in y direction was around 0.06 mm. Study of contact angles revealed that while the advancing and receding contact angles for the superficial gas velocity of 4.17 m/s are higher than angles for the superficial gas velocity of 10.76 m/s, the contact angle hysteresis for both velocities were almost identical upon detachment.
