自再潤濕流體於迴路式熱管之熱傳增強研究

Heat Transfer Enhancement of Loop Heat Pipe with Self-Rewetting fluid

朱茂榕(Mao-Long Chu)

指導教授 ： 陳瑤明

國立臺灣大學/工學院/機械工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.02625

摘要

本文運用自再潤濕流體（Self-Rewetting Fuild），應用於迴路式熱管，探討其對熱傳性能影響效應。自再潤濕流體具有改變表面張力之線性關係之能力，可將較冷液體主動推送到加熱面，有與一般流體不同之特性，可延緩乾涸現象發生。其中，自再潤濕流體添加物之成份與濃度為十分重要參數，因此，本文將對自再潤濕流體進行不同濃度和不同成分的實驗，探討其熱傳增強效應。
實驗結果顯示，添加自再潤濕流體能顯著提升迴路式熱管的性能，包括臨界熱通量與熱阻值。在不同成分的實驗中，我們選用了丁、戊、己三種醇類，並發現在添加醇類水溶液後，己醇的表面張力下降幅度最小，轉折點最早，其熱阻值達到0.32℃/W，在200W以前具有最低的操作溫度及熱阻值。在濃度的實驗中發現，最佳濃度為醇類溶於水中之標準狀態下的最大溶解度。添加戊醇2.2%水溶液，臨界熱負載可達到400W，系統總熱阻為0.33℃/W。其中，以添加丁醇6%水溶液為佳，臨界熱負載可達到500W，系統總熱阻最低達到0.26℃/W。相較於純水之工作流體的迴路式熱管之性能，熱通量提升了100%，熱阻降低了30%，顯見，自再潤濕流體具有提升迴路式熱管熱傳性能的潛力。

關鍵字

迴路式熱管 ； 自再潤濕流體 ； 熱傳增強

並列摘要

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 contents and concentrations of self-rewetting fluid on heat transfer performances of LHP as well as compares the results with those from using water as working fluid. Previous studies have shown that using self-rewetting fluid as working fluid can enhance the heat transfer mechanisms of pool boiling, traditional heat pipes, and wickless heat pipes. Compared to 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 dry out and thus increasing the critical heat load.
Concerning the effect of varying the concentration of butanol and petanol aqueous solutions on heat transfer performance of LHP, butanol concentrations ranging from 2% to 8% is investigated, and pentanol concentrations ranging from 1% to 3% is investigated. Experimental results show that 6% butanol aqueous solution results in the best heat transfer performance of LHP; compared with that of water, the critical heat load is increased by 100% and the total thermal resistance is decreased on average by 30%.
Concerning the effect of changing the components of self-rewetting working fluid, the fluids considered are butanol, pentanol, hexanol, with the concentration of each being the maximum solubility concentration in water under standard conditions. Experimental results show that, compared with those from 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 200W 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 500W and minimum total thermal resistance of 0.26°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 aqueous solution is the most effective in enhancing the heat transfer performance of LHP.

並列關鍵字

Loop heat pipe ； Self-rewetting fluid ； Heat transfer enhancement

參考文獻

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