毛細結構潤濕性於迴路式熱管熱傳影響研究

Abstract

迴路式熱管為一種具相變化的被動熱傳裝置，相較於傳統熱管，其優點有：遠距熱傳輸、低熱阻與高熱傳量等。於熱傳過程中，迴路式熱管蒸發器中毛細結構之潤濕性將影響毛細力、脫離壓力及蒸發薄膜，進而影響迴路式熱管熱傳性能，但其相關討論文獻至今仍然缺乏，故本研究擬探討毛細結構潤濕性對於迴路式熱管熱傳性能之影響。 本研究以銅為毛細結構材質，以水為迴路式熱管工質，並以氧化法及靜電疊層改變銅毛細結構潤濕性。研究結果顯示，於單孔徑毛細結構(monoporous wick)熱傳實驗中，潤濕性增加將造成臨界熱通量下降，而接觸角一旦大於90˚，將導致工質無法進入毛細結構時，造成迴路式熱管將無法啟動。 學者認為潤濕性對於毛細蒸發的影響將隨孔徑大小不同有所改變，故本研究以粒徑105~125μm之碳酸鈉顆粒為孔洞成型劑製造具相對大孔之雙孔徑毛細結構，並探討潤濕性對其熱傳性能之影響，發現潤濕性對雙孔徑毛細結構(biporous wick)影響與單孔徑毛細結構有所不同。研究結果顯示，雙孔徑毛細結構熱傳實驗中，潤濕性較佳之毛細結構有較低之壁面溫度及系統總熱阻。

Loop heat pipe (LHP) is a passive two phase heat transfer device, which has ability to transport heat in long-distance, low thermal resistance, and high heat transfer capacity compared with a traditional heat pipe. During thermal transfer process, the wettability of the wick in the evaporator of LHP has impacts on capillary force, disjoining pressure and evaporative thin film. Then, it could affect the heat transfer performance of LHP significantly. However, the related research about the effect of wettability on LHP’s evaporation still lacks. Therefore, the purpose of this article is to discuss the impact of wick wettability on heat transfer performance of loop heat pipe. In this study, the material of wick was copper, and the working fluid was water. The methods to change wick’s wettability were the oxidation and the layer-by-layer thin film coating. In the experiment results of monoporous wick, as the wick’s wettability increased, the critical heat load reduced. While the wick’s contact angle was more than 90°the working fluid did not penetrate into the wick. That caused that loop heat pipe could not start. The impact of wick wettability on film evaporation also varies with pore size. Therefore, in this study, the biporous wick was manufactured by using Na2CO3 powder as pore former which has 105~125μm in diameter. The impact of wettability in biporous wick on the heat transfer performance in LHP was discussed. The biporous experiment result indicated that the wick had a good wettability which leaded a lower evaporator wall temperature as well as a lower total thermal resistance.