| Summary: | 博士 === 元智大學 === 機械工程學系 === 98 === When a proton exchange membrane fuel cell (PEMFC) is in operation, the transport/distributions of fuel, water and reactants are not uniform due to the effects of the channel/rib of the flow field structures. The cell performance and life are greatly influenced by these non-uniform distributions.
In this study, a novel multi-functional micro sensor is developed to diagnose the in-situ local area cell performance. The micro sensor is fabricated by MEMS technology. It can measure voltage, temperature and resistance. The substrate of the micro sensor is SS 304 stainless steel of 40 μm thick. The micro sensor is flexible, low cost, with excellent mechanical properties. The manufacturing procedures and the optimal parameters for the micro sensor fabrication have been demonstrated. Through these results, multi-functional, variety of scales, and custom-made micro sensors were fabricated.
The results of in-situ performance variations show that significant local voltage variations take place at the under-the-rib area due to a more serious water flooding and fuel starvation as compared with that at the under-the-channel area. However, when the cell is operated at lower gas relative humidity, liquid water stored at the under-the-rib area will hydrate the membrane and further increases the local voltage.
For the water removal analysis, results show that liquid water removal rate is also non-uniform in the MEA. At the under-the-channel area, liquid water removal is governed by both convective and diffusive flux of the through-plane drying. Thus, liquid water is almost completely removed of the 30 seconds of gas purge. On the other hand, liquid water stored at the under-the-rib area is not easy to remove during the 1 minute gas purge process. Thus, the membrane re-hydration through the internal diffusive flux is faster than that at the under-the-channel area. Consequently, it may result in lower performance of the fuel cell cold start, local fuel starvation, and membrane degradation.
Through these studies, in-depth fundamental understanding of fuel cell local transport phenomena has been demonstrated. The design and fabrication of novel micro sensor has been realized. The functions of novel sensors have been proven. The micro sensor may also be applied to other applications and research areas to diagnose in-situ detailed local data to study fundamental phenomena.
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