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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.

A proton exchange membrane fuel cell (PEMFC) must maintain a balance between the hydration level required for efficient proton transfer and excess liquid water that can impede the flow of gases to the electrodes where the reactions take place. Therefore, it is critically important to understand the two-phase flow of liquid water combined with either the co-flowing hydrogen (anode) or air (cathode) streams. In this paper, we describe the design of an in-situ test apparatus that enables investigation of two-phase channel flow within PEMFCs, including the flow of water from the porous gas diffusion layer (GDL) into the channel gas flows; the flow of water within the bipolar plate channels themselves; and the dynamics of flow through multiple channels connected to common manifolds which maintain a uniform pressure differential across all possible flow paths. These two-phase flow effects have been studied at relatively low operating temperatures under steady-state conditions and during transient air purging sequences.