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Water management is critical to the successful implementation of proton exchange membrane (PEM) fuel cells in the automotive transportation sector. Liquid water appears in the fuel cells not only from the water generated at the cathode catalyst layer but also as a result of condensation of water vapor within the humidified gases. Topics of intense current interest include the microscopic flow of liquid water through the membrane, catalyst layers, and gas diffusion layers; the macroscopic interaction between water and the gas flow at the gas diffusion layer interface; and the two-phase, multicomponent flow through the gas channels. Recent work published in this area is reviewed and recommendations for future work are outlined. [ABSTRACT FROM AUTHOR]

Flow boiling in mini- and microchannels offer very high heat transfer capabilities and find applications in many emerging technologies, such as electronics cooling and fuel cells. The low flow rate employed in such geometries, coupled with the small flow channels, often results in a laminar flow with all flow as liquid. Since the single-phase flow with all liquid is in the laminar range, the flow boiling correlations developed for conventional tubes with an inner diameter larger than 3 mm and turbulent flow need to be carefully reviewed. In the present work, flow boiling correlation for large diameter tubes developed by Kandlikar [1, 2] is modified for flow boiling in minichannels by using the laminar single-phase heat transfer coefficient for all liquid flow. The correlation is also extended for flow boiling in microchannels using the nucleate boiling as the dominant part of the original correlation. The trends in heat transfer coefficient versus quality are compared in the laminar and deep laminar regions in minichannels and microchannels. Excellent agreement is obtained between predicted values and experimental data. [ABSTRACT FROM AUTHOR]