Visualization of two-phase flow phenomena in polymer electrolyte membrane fuel cells by neutron radiography

Water behavior in an operating polymer electrolyte fuel cell (PEFC) was visualized by using neutron radiography, and the cell voltage and the pressure drop between the inlet and outlet of air were simultaneously measured. The PEFC is compliant with Japan Automobile Research Institute (JARI) standard PEFCs. An electrode area of 50×50 mm2 was visualized, and the cell temperature was kept at 80°C. The effects of channel geometry, i.e., single- and triple-serpentine, relative humidity of air, and current density, were investigated. From the experiments, it can be confirmed that fluctuation of area-average water thickness in a triple-serpentine channel is larger than that in a single-serpentine channel, and water in the channel is likely to accumulate at corners of the channel in the single- serpentine channel. Furthermore, movement of condensed water is strongly related to cell voltage and pressure drop. For a few minutes after the operation, the average thickness of water at the rib is thicker than that at the channel. Furthermore, a network modeling to predict the gas-velocity distributions was proposed. Based on the water depth in the channel and the gas diffusion layer, gas-velocity distributions were obtained. The pressure drops in single-phase flow were in good agreement with the experimental results under low gas-flow rate. The model could predict the pressure drop based on the water thickness in the PEFC. © 2010 by Begell House, Inc.