Water management is a critical factor in the performance and durability of a proton exchange membrane (PEM) fuel cell. In situ experiments are needed to gain a better understanding of water transport within the channels of the cell during operation. In this work a 50 cm2 fuel cell with optical access is designed and tested in an in situ experimental facility. Two-phase flow in the cathode channels of the cell is observed, and flow patterns are characterized. Three primary two-phase structures are identified — slug flow, film flow, and mist flow — and a flow pattern map is developed. A comparison between in situ and ex-situ flow pattern maps shows that ex-situ experimentation can be used to predict some in situ flow characteristics, but cannot capture the effects of reaction kinetics or relative humidity. The total pressure drop signature is seen to be a useful parameter for predicting two-phase flow dynamics in the gas channels. In addition, channel to channel flow variation caused by the presence of liquid water in the cathode channels is investigated using entrance region pressure drop measurements.

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