雙孔徑毛細結構於銅水迴路式熱管性能增強研究

Abstract

迴路式熱管是一種兩相被動熱傳裝置，相較於傳統熱管，有傳輸距離更長，低熱阻與高熱傳量等優點。但是，單孔徑毛細結構在高熱負載時，內部孔洞容易受蒸氣佔據，導致熱傳性能受到限制。本研究擬採用雙孔徑毛細結構改善此缺點，提升熱傳性能。 另一方面，自再潤濕流體擁有表面張力隨溫度呈非線性變化的特性，學者認為，作為工作流體運用在改善以毛細壓力為驅動力之散熱元件的熱傳性能上，極具潛力。若僅是改變工作流體就能讓熱傳性能顯著提升，跟其他系統元件製程繁複的設計比較下，更容易被產業所接受。目前已經有應用在傳統熱管的相關文獻，但並未發現應用於迴路式熱管上。 本研究以銅為毛細結構材質製作雙孔徑毛細結構改善熱傳性能，再研究自再潤濕流體對迴路式熱管的性能影響。測試結果為，雙孔徑毛細結構能有效提升銅水迴路式熱管能有效提升臨界熱負載以及將低系統總熱阻，分別由150W提升至450W以及0.72降至0.27此外，自再潤濕流體搭配單孔徑毛細結構於迴路式熱管測試結果，相較於工作流體為水，亦能有效提高臨界熱負載以及降低系統總熱阻，分別由150W提升至350W以及0.72降至0.32然而搭配雙孔徑毛細結構僅在低熱負載下些微降低系統總熱阻，臨界熱負載以及高熱負載下的系統總熱阻跟水比起來，表現較差。吾人建議，若要自再潤濕流體應用在迴路式熱管達到性能提升之效果，需評估適合的操作條件 關鍵字：迴路式熱管、自再潤濕流體、蒸氣層、馬蘭哥尼效應、表面張力

Comparing with the traditional heat pipe, the loop heat pipe(LHP) is a passive heat transfer device which has high heat removal and low thermal resistance even at long transporting distances. However, under high heat load condition, pores in the monoporous wick are occupied by vapor, and the heat transfer performance is thus restricted. Therefore, in this study, we intend to use biporous wick structure to improve this weakness. Since the surface tension of a self-rewetting fluid displays a non-linear variation as temperature changes, researchers regard it as a potential working fluid to improve the performance of capillary-pumping heat transfer device. Such method is easier and much simpler to accomplish compared with other more complicated systems; thus, if it is possible to improve the heat transfer performance through such an easy method, self-rewetting fluid will be more acceptable to the industry. Currently, there are already papers that apply this kind of working fluid to heat pipe systems, but applications to loop heat pipe have not been found. In this study, we use copper to manufacture the biporous wick to enhance the heat transfer performance. We then observe the influence of applying self-rewetting fluid in the loop heat pipe system. Experimental results show that using biporous wick efficiently increases the critical heat load and reduces the total thermal resistance. More specifically, the heat load increased from 150W to 350W and the total thermal resistance from 0.72to 0.32. Also, using self-rewetting fluid as the working fluid in a monoporous wick loop heat pipe system also increases the critical heat load and reduces total thermal resistance; that is, the heat load increased from 150W to 350W and the total thermal resistance decreased from 0.72 from 0.72to 0.32. On the other hand, under low heat load condition, applying self-rewetting fluid to the biporous wick loop heat pipe system only reduced the total thermal resistance very little. Furthermore, the critical heat flux is lower and total thermal resistance is also higher than using water as working fluid. We suggest that detailed assessment is definitely required in order to effectively use self-rewetting fluid to enhance the heat transfer performance of loop heat pipe. Key words: Loop heat pipe, biporous wick, vapor blanket, self-rewetting fluid, Marangoni effect