自再潤濕流體於迴路式熱管之應用研究

Abstract

本研究目的在於使用自再潤濕流體做為工作流體，毛細結構材質為燒結銅毛細結構，首次應用於迴路式熱管，並探討改變自再潤濕流體的濃度與成分，與工作流體為水作熱傳性能分析比較。過去學者發現將自再潤濕流體做為工作流體，可增強池沸騰、傳統熱管與無芯熱管的熱傳性能，因為自再潤濕流體其表面張力隨溫度變化呈現非線性關係，不同於純物質流體，表面張力只會隨著溫度遞增而遞減，當溫度增加到某特定溫度時，該水溶液的表面張力反而會隨著溫度增加而遞增，產生馬蘭哥尼流，可將冷態液體推送至加熱面，延緩乾涸的發生，提升臨界熱通量。 在探討改變丁醇水溶液的濃度，範圍2%~8%，對於迴路式熱管熱傳性能影響實驗中，研究結果顯示，6%的丁醇水溶液有最好之迴路式熱管性能，較工作流體為水，臨界熱負載增強了130%，系統總熱阻平均約降低了50%。 在探討改變自再潤濕流體的成份，其工作流體為水中添加丁醇、戊醇、己醇、 庚醇，濃度選用各醇類於水中在標準狀態下的最大溶解度，對於迴路式熱管熱傳性能影響實驗中，研究結果顯示，各醇類水溶液相較工作流體為水，皆可使迴路式熱管的系統總熱阻下降及操作溫度下降，提升臨界熱負載。而在各醇類水溶液的熱傳性能分析上，在操作溫度在90℃以前，其己醇水溶液相較於其他醇類水溶液，熱負載較大達到250W且系統總熱阻最低達到0.33℃/W；操作溫度超過90℃後，己醇水溶液已達到臨界熱負載，系統不能達穩態，而丁醇水溶液性能表現最好，臨界熱負載可達到350W，系統總熱阻最低達到0.32℃/W。因此，各醇類水溶液熱傳分析結果，丁醇水溶液有較大的操作溫度範圍、臨界熱負載最大且系統總熱阻最低，對於迴路式熱管有最佳的熱傳性能表現。

The objective of this study is the application of self-rewetting fluid as the working fluid on loop heat pipe (LHP), with sintered copper as the chosen capillary structure material; this study also investigates the effect of using different components and concentrations of self-rewetting fluid as well as compares their heat transfer performances with that of water. Previous studies have show that using self-rewetting fluid as working fluid can enhance the heat transfer mechanisms of pool boiling,traditional heat pipe, and wickless heat pipe. Compared with using pure substance as working fluid, where the surface tension decreases linearly with increasing temperature, self-rewetting fluid’s surface tension has a non-linear relationship with temperature changes; therefore, at a certain temperature, the self-rewetting fluid’s surface tension increases with increasing temperature, resulting in the Marangoni effect, and the condensed liquid can be transported to the heating surface, delaying the occurrence of dryout and thus increasing the critical heat load. Concerning the effect of varying the concentration of butanol aqueous solution on heat transfer performance of LHP, concentrations ranging from 2% to 8% is investigated. Experimental results show that 6% butanol aqueous solution results in the the best heat transfer performance of LHP; compared with that of water, the critical heat load is increased by 130% and the total thermal resistance is decreased on average by 50%. Concerning the effect of changing the components of self-rewetting working fluid, the fluids considered are butanol, pentanol, hexanol, and heptanol, with the concentration of each as the maximum solubility concentration in water under standard conditions. Experimental results show that, compared with using water as working fluid, using self-rewetting fluid can allow the total thermal resistance of LHP system to decrease, increasing the critical heat load. Concerning the heat transfer performance of different self-rewetting fluids, under operating temperature of 90°C or lower, hexanol aqueous solution achieves the largest heat load of 250W and lowest total thermal resistance of 0.33°C/W; at operating temperatures higher than 90°C, hexanol aqueous solution has already reach the critical heat load, causing the system to be unstable, but butanol aqueous solution achieves the best results, with maximum critical heat load of 350W and minimum total thermal resistance of 0.32°C/W. Therefore, after analysis of the heat transfer performance of various self-rewetting fluids, butanol water solution has the largest operating temperature range, highest critical heat load, and lowest total thermal resistance, indicating that butanol water solution is most effective on heat transfer performance of LHP.