Investigating Evaporation in Gas Diffusion Layers for Fuel Cells with X-ray Computed Tomography

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• 作者：Iryna V. ZenyukAdrien Lamibrac ; Jens Eller ; Dilworth Y. Parkinson ; Federica MaroneFelix N. Büchi ; Adam Z. Weber
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：December 22, 2016
• 年：2016
• 卷：120
• 期：50
• 页码：28701-28711
• 全文大小：730K
• ISSN：1932-7455

文摘

Understanding evaporation in porous media and the associated water distribution for a given saturation is critical for optimizing many different technologies including polymer–electrolyte fuel cells. In these devices, heat and mass-transport are coupled due to the two-phase transport of water and operating temperatures from subzero to 80 °C. Especially critical is understanding phase change in the mixed wettability, carbon gas-diffusion layers (GDLs). While previous works have measured evaporation rates empirically for a given saturation, there remains a need to explore the mechanisms governing evaporation, which are tied directly to the internal water distribution. In this article, liquid-water evaporation rates in GDLs are measured in situ using synchrotron X-ray computed tomography (CT). X-ray CT allows visualizing the evaporating water-front location and interfacial water/air surface area, thereby enabling true surface-area based evaporation rates. It is found that the overall specific evaporation rate is essentially constant as a function of saturation and that the water/air interfacial area scales almost linearly with saturation. To isolate transport and kinetic contributions to the overall evaporation rate, we systematically varied gas flow rate and composition. A three-dimensional mathematical model with direct meshes of liquid-water evaporation fronts from the X-ray CT studies allowed for the determination that the evaporation is transport limited. The overall results provide insight into evaporation phenomena in porous media.