Within a proton exchange membrane fuel cell (PEMFC), the transport route of liquid water begins at the cathode catalyst layer, and then progresses into the gas diffusion layer (GDL) where it then goes into the flow channel. At times, significant accumulation of liquid droplets can be seen on either side of the membrane on the surface of the flow channel. In this work, liquid water and the flow dynamics within the transport channel were examined experimentally, with the channel acting as an optical window. Ex situ interpretations of the liquid water and flow patterns inside the channel were established. Liquid water droplet movements were analyzed by considering the change of the contact angle with different flow rates. Also, various surface roughness of stainless steel was used to determine the relationships between flow rate and the contact angles. When liquid water is found within the gas channels of PEMFCs, the channels' characteristic changes become more dominant and it becomes more of a necessity to monitor the effects. Physical motion of water droplets in the flow channels of PEMFCs is important. The surface roughness properties were used to describe the contact angle and the droplet removal force on the stainless steel flow channel.

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