| Summary: | Compact power generation systems which consist of methanol reformer and Polymer Electrolyte Fuel Cell (PEFC) are greatly required as emergency power source. In this system, PEFC exhaust heat can be utilized for evaporating methanol solution before reforming. To use PEFC exhaust heat (80 - 90 °C), a microchannel (MC) heat exchanger is suggested as an evaporator because of supplying heat more efficiently. However, phase change phenomena of methanol solution in a MC are not clarified. In this study, the transparent double-pipe heat exchanger including the MC (channel diameter: 0.5 mm) was employed. Then, phase change phenomena in the MC were visualized with varying concentration. As a result, cyclic flow pattern was observed by using a high-speed camera. A small liquid column was generated periodically in the MC and the liquid phase gradually evaporated. Visualized images also indicated existence of thin liquid film on the inner wall of MC. By using an X-ray observation system, thickness of thin liquid film was able to be measured. The distribution of liquid film thickness was affected by the difference of solution and flow rate.
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