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首页> 外文期刊>International Journal of Heat and Mass Transfer >A pore-level direct numerical investigation of water evaporation characteristics under air and hydrogen in the gas diffusion layers of polymer electrolyte fuel cells
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A pore-level direct numerical investigation of water evaporation characteristics under air and hydrogen in the gas diffusion layers of polymer electrolyte fuel cells

机译：聚合物电解质燃料电池气体扩散层中空气和氢气下水蒸发特性的孔级直接数值研究

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摘要

During the operation of polymer electrolyte fuel cells (PEFC) liquid water clusters generated due to electrochemical reactions in the gas diffusion layers (GDL) create a resistance against gas transport towards the catalyst layers (CL), and hence must be efficiently removed to maintain the cell performance, a process often realized by means of forced evaporation. Water accumulation is of interest not only for the cathode GDL but also for the anode GDL, particularly under thermoneutral cell operation whereby liquid water can be added to either anode or cathode channel flows. Although many works studied water evaporation in air and especially at moderate temperatures, less effort has been devoted in investigating evaporation at elevated temperatures and at the anode side, where hydrogen flows in the gas channels. In this work, direct numerical simulation is used to characterize evaporation at pore level for both anode and cathode sides and at different temperatures (up to 80 degrees C), for which experimental data are rare and micro-scale transport is often difficult to assess in the laboratory. Realistic water distribution and porous GDL geometry, acquired from X-ray tomography, have been used while regularized distributions of liquid water are further considered in order to investigate evaporation at various saturation levels. Key results indicate that (a) the water evaporation rate in hydrogen flows can be up to 4 times larger than the corresponding one in air flows at the same gas stream velocity and temperature, (b) the predicted vertical evaporation-induced velocities under hydrogen are an order of magnitude bigger than the corresponding ones under air and they can grow large enough at elevated temperatures to potentially hamper hydrogen transport towards the CLs. (C) 2018 Elsevier Ltd. All rights reserved.
机译：在聚合物电解质燃料电池（PEFC）的运行过程中，由于气体扩散层（GDL）中的电化学反应而产生的液态水团簇会产生抵抗气体向催化剂层（CL）传输的阻力，因此必须有效地除去以保持电池性能，通常通过强制蒸发来实现的过程。水的积聚不仅对阴极GDL感兴趣，而且对阳极GDL也很重要，特别是在热中性电池操作下，由此可以将液态水添加到阳极或阴极通道流中。尽管许多工作研究了空气中（尤其是在中等温度下）的水蒸发，但是在研究高温和阳极侧（其中氢气在气体通道中流动）的蒸发方面，人们花费了更少的精力。在这项工作中，直接数值模拟被用来表征阳极和阴极侧以及不同温度（最高80摄氏度）在孔隙水平的蒸发，其实验数据很少，并且通常难以评估微观尺度的传输。实验室。已经使用了从X射线断层扫描获得的真实水分布和多孔GDL几何形状，同时还考虑了液态水的规则分布，以便研究各种饱和度水平下的蒸发。关键结果表明：（a）在相同的气流速度和温度下，氢流中的水蒸发速率可以是空气中水蒸发速率的4倍，（b）在氢下预测的垂直蒸发诱发速度为比空气中的相应碳氢化合物大一个数量级，并且它们在高温下会增长到足够大，从而有可能阻碍氢向碳纳米管的传输。 （C）2018 Elsevier Ltd.保留所有权利。

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