具偏斜曲線毛細結構之迴路式熱管

Abstract

具有高熱傳量、傳輸距離長、自動啟發與主動調節等優點的迴路式熱管，應用於航空科技與電子熱傳方面有極大潛力；本文旨在研究小型化迴路式熱管的性能提升，根據迴路式熱管文獻指出：迴路式熱管小型化後蒸發器內的二相熱傳元件毛細結構對迴路式熱管性能之表現更加敏感，傳統迴路式熱管之毛細結構製作均採用單粉燒結，但其單孔徑曲線分佈易造成蒸氣阻塞，導致毛細結構乾涸，造成性能上限制。因此本實驗將不同粒徑的粉末混合來製作出具偏斜形式孔徑曲線分佈的毛細結構，使得毛細結構內孔徑曲線既能保有小孔徑的毛細力，也能同時擁有大孔徑的滲透度；實驗過程中首先利用粉末比例與燒結溫度來控制毛細結構內孔徑曲線的偏移程度，之後實際地進行熱傳測試，最後對具偏斜曲線孔徑分佈之毛細結構與單孔徑曲線毛細結構，做其熱傳能力比較與分析。 實驗結果顯示：利用混粉製作之毛細結構，確實提昇迴路式熱管性能，主要的原因在高瓦數時較佳的孔徑曲線分佈能使蒸氣順暢地排出；而在混粉比例為75%、燒結溫度在700℃，並在蒸發器溫度為85℃下，有其最大熱傳量為：200W、熱阻為：0.367℃/W，相較同樣條件下之單孔徑曲線毛細結構100W熱傳性能增強100%。具偏斜曲線孔徑分佈之毛細結構不僅增強熱傳性能同時也降低熱阻，在未來高熱傳量的應用領域方面有其應用價值。

Loop heat pipes（LHPs）,which possess the advantages including high transfer capacity, long transport distance, self-priming and active control, have great potential for spacecrafts and electronic cooling. The main purpose of this study is to enhance the performance of miniature LHPs. According to the literatures, when a LHP is miniaturized for electronic cooling, its performance would become more sensitive to the structure of the capillary wick in the evaporator. Traditionally, mono-porous sintered wicks were used in LHPs; however, the pore size distribution of mono-porous wick is intolerant of boiling inside the capillary structure, which leads to dry-out in capillary structure. In order to improve this drawback, this study manufactures the wick structure with skewed pore size distribution by using two particle sizes of the same material. Such a wick structure incorporates the higher capillarity of small-size pores and the better permeability of big-size pores. In the experiments, different mixing ratio and sintered temperature were used to control skewed level of pore size distribution. The thermal performances of wicks with skewed pore size distribution were then tested and a comparison was made between mono-porous wicks and the wicks with skewed pore size distribution for the heat transport capability of the LHP. The present experimental results show that the wick with skewed pore size distribution can make the vapor generated at high heat flux vents smoothly, and hence enhance the performance of LHPs. With the mixing ratio of 75% and the sintering temperature of 700℃, the manufactured LHP achieves the heat capacity of 200W at the allowable evaporator temperature of 85℃ and thermal resistance is 0.367℃/W. In comparison with a mono-porous wick, the performance is enhanced about 100%. The wick structures with skewed pore size distribution have not only increased the heat transfer performance but also reduced the thermal resistance. With this kind of wicks, LHPs would have more attractive applications to high heat flux in the future.