不同流道型式之蒸發熱交換器的熱傳性能研究

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题名:	不同流道型式之蒸發熱交換器的熱傳性能研究
作者:	李至誠;Lee, Chih-Cheng
贡献者:	機械工程學系
关键词:	兩相蒸發器;直線流道;漸擴型;山型紋;可視畫觀察
日期:	2017-08-21
上传时间:	2017-10-27 16:20:17 (UTC+8)
出版者:	國立中央大學
摘要:	本研究設計直線流道型、漸擴型以及山型紋之兩相蒸發熱交換器，比較各型式之熱傳性能，並透過可視化觀察分析流動及熱傳之關係。直線流道型尺寸共三種: 1. 鰭片高度及間距分別為2、1 mm，2. 鰭片高度及間距分別為2、2 mm，3. 鰭片高度及間距分別為5、1 mm。漸擴型之流道設計為鰭片間距1 mm，鰭片高度2 mm 沿流動方向縮減至1 mm 形成傾斜鰭片。山型紋型式之鰭片間距及高度分別為1、2 mm，傾斜角度為 30度。鰭片高度為5 mm 之直線流道型熱交換器具有最高之熱傳量，且飽和溫差最低，熱傳性能最好。其原因為流道內之流動情形以波浪流為主，流道表面仍有液體補充，使表面溫度較低。而鰭片高度為2 mm 之直線型、漸擴型流道，流道內以柱狀流為主，汽體佔據流道亦發生局部乾涸現象使飽和溫差較大。傾斜鰭片之設計使汽泡團聚於流道上方，並無法有效排除汽泡，流道內以汽體為主熱傳性能低。山型紋之流道於實驗中未發生燒乾之現象，但無法從可視化觀察到液體團聚於流道之間，且飽和溫差大。鰭片高度5 mm 之直線流道具有最低熱阻為0.067 °C/W，相較於其他型式熱傳量高，且不易乾涸，為本研究設計之最佳型式。;In this study, we designed two-phase evaporative heat exchangers with: straight fin type, expansion type and chevron, and compared the heat transfer performance of each type. There are three geometry of straight fin type: 1. Fin height 2 mm with fin spacing 1 mm, 2. Fin height2 mm with fin spacing 2 mm, 3. Fin height 5 mm with fin spacing 1 mm. The fin space of the expansion type is 1 mm, and fin height reduced from 2 mm to 1 mm. The space and height of the chevron are 1, 2 mm and the inclination angle is 30 °. The straight fin type with the fin height of 5 mm has the highest heat transfer rate, and the wall superheat temperature is the lowest, which means that the heat transfer performance is the best. The flow pattern inside the channel are wavy flow, which keep the channel surface wetted. So that the surface temperature become low. When fin height is 2 mm, the flow pattern become slug flow by small hydraulic diameter. Which cause the channel surface become partial dry out easier. The expansion designed allows the bubble to cover the channel, which let vapor stock in the channel. The chevron does not cause dry out in the experiment, but it can’t be observed the liquid between the flow channel from the visualization. The straight fin type with a fin height of 5 mm has a minimum thermal resistance of 0.067 °C W. Heat transfer rate is higher than other types and the flow pattern inside the channel is not easy to dry out, so that it is the best type in this study.
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