Two-Phase Flow Pressure Drop Hysteresis under Typical Operating Conditions for a Proton Exchange Membrane Fuel Cell

Two-phase flow pressure drop hysteresis was studied under conditions typical of an operating PEM fuel cell. Two-phase flow hysteresis occurs when the gas and liquid flow rates are increased and decreased along the same path but exhibit different pressure drops. Variables studied include temperature (30-90 degrees C), air stoichiometry (1-4), and gas diffusion layer. The results were analyzed relative to a baseline of fully humidified air at 75 degrees C and a stoichiometry of 2 with a SGL Carbon 25 BC GDL. The percentage change between ascending and descending pressure drop is used to quantify the relative magnitude of the hysteresis. It was found that a sufficient air stoichiometry (>= 4) can reduce the hysteresis, the GDL properties affect the water breakthrough mechanism and shift the onset of the hysteresis zone, and higher temperatures reduce the relative magnitude of the hysteresis effect. These results correlate well with photographs of the cathode channel two-phase flow.