Research on mass and heat transfer phenomena in micro-channels under freezing condition in PEM fuel cells

研究了在包括冻结温度在内的各种条件下，在薄微通道中产生水的现象。开发了实验装置，以允许目视观察燃料电池内部的现象。实验结果表明，在较大的电流密度下，电池电压在较短的时间内下降，并确定了温度条件下不允许电压下降的极限电流密度。增加操作压力促进水的产生，并且这对于干气操作是优选的，但是其在冻结温度下劣化性能。目视观察显示了分离器通道中液态水的产生和流动，发现槽电压变化与通道中未被水堵塞的开口面积之间存在良好的相关性。实验还表明了均匀的细胞结合压力对于细胞区域上均匀反应的重要性。在冷冻条件下电池电压下降之前和之后，在电池中视觉观察中没有识别出差异，但是通过热照相机检测到一些变化。这一变化的意义将在今后的研究中进一步探讨。

Research was made to identify the phenomena of water production in thin micro-channels under variety of conditions including freezing temperatures Experimental apparatus was developed to allow visual observation of the phenomena inside in the fuel cell. The result of the experiment showed that cell voltage dropped in shorter time with larger current density and the limiting current densities allowing no voltage drop were identified for temperature conditions. Increasing operating pressure promotes water production, and this works preferable for the dry gas operation hut it deteriorates performance under freezing temperatures. Visual observation showed production and flows of liquid water in separator channels, sod good correlation was found between cell voltage change and open areas free from water plugging in channels. The experiment also showed the importance of uniform binding pressure of the cell for the uniform reactions over the cell area. No difference in the visual observation was recognized in the cell before and after the cell voltage drop under freezing conditions, but some change was detected by thermal camera. The meaning of this change will he further investigated in the next research.