鐵氟龍毛細結構應用於迴路式熱管之研究

The Study of the PTFE Wick Structure Applied to Loop Heat Pipe

辜子維(Tzu-Wei Gu)

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.2014.03171

摘要

迴路式熱管(Loop Heat Pipe, LHP)是一種高傳熱量、低熱阻、長傳輸距離的被動二相熱傳裝置，具有相當大的潛力應用在航太科技及電子元件散熱。目前迴路式熱管中之毛細結構大多為高熱傳導係數的金屬毛細結構，像是鎳、鈦和銅等等，但應用於迴路式熱管時，因金屬材料熱導係數高易有熱洩漏問題而降低性能；因此，需要有更低熱傳導係數的毛細結構來解決熱洩漏的問題，且為因應當今迴路式熱管高性能、輕薄短小、價格低廉之需求，高分子毛細結構被高度的討論。故本研究擬探討使用低熱導係數的高分子毛細結構改善熱洩漏問題，提高迴路式熱管之熱通量。
本研究首次嘗試使用燒結法製造可應用於迴路式熱管之高分子毛細結構─聚四氟乙烯(鐵氟龍)，藉由改變鐵氟龍粉末之粒徑大小來調整有效孔徑、孔隙度以及滲透度，並且改變毛細結構之厚度，藉由熱傳性能測試探討鐵氟龍毛細結構之最佳參數及其孔洞結構。
在實驗方面，將參數組合(厚度1.75 mm、有效孔徑1.7 μm、孔隙度50%、滲透度6.2×10-12 m2)之鐵氟龍毛細結構於迴路式熱管中進行熱傳性能測試，在電子元件容許操作溫度85 ℃下，熱傳量可達450W，系統最低熱阻為0.145 ℃/W，而最大熱傳量可達600W。與金屬鎳毛細結構(厚度1.75 mm、有效孔徑3.6 μm、孔隙度70%、滲透度7×10-13 m2)比較，鐵氟龍毛細結構之補償室溫度明顯比金屬鎳之補償室溫度低，顯示其可有效改善熱洩漏之問題，且在熱傳性能方面，最大熱傳量約為金屬鎳毛細結構的120% (500W)，最低系統熱阻方面亦較金屬毛細結構的0.156 ℃/W來得低。
總結本研究之成果，鐵氟龍毛細結構可略為提升迴路式熱管之性能並且有效地改善迴路式熱管熱洩漏之問題，提高熱傳量並降低操作溫度，且與金屬毛細結構相比，有製程較為安全、製造成本較低、較好加工等優點，對於未來高功率元件的冷卻而言，鐵氟龍毛細結構有高度應用之潛力。

關鍵字

高分子毛細結構 ； 迴路式熱管 ； 熱洩漏 ； 鐵氟龍

並列摘要

Loop heat pipe (LHP), which is a passive two-phase thermal transport device with high heat capacity and long transport distance, has a great potential for applications to spacecrafts and electronic cooling. Currently, most wick structures of LHPs are manufactured by sintering metal powder, such as nickel, titanium, or copper powder; however, the use of metal wicks, with metal’s high thermal conductivity, may allow heat to transfer into the evaporator core too easily, causing the “heat leakage” problem. To solve this problem, and to meet the requirements of recent LHPs, such as high performance, low cost, small size, and light weight, the use of polymer wick structures has been discussed recently as a solution.
Therefore, the main objectives of this study are to use polytetrafluoroethene (PTFE), which has low thermal conductivity, as wick material and to manufacture the polymer wick structure by sintering. When sintering, the effective pore radius, permeability, and porosity of the wick can be controlled by adjusting the particle size of PTFE. This study also varies the wick’s thickness to find the optimal parameters for the PTFE wick.
A PTFE wick structure with thickness of 1.75 mm, effective pore radius of 1.7 μm, permeability of 6.2×10-12 m2, and porosity of 50% is installed into a LHP system to carry out heat transfer performance testing. Under operating temperature of 85°C, the LHP with PTFE wick structure has highest heat load of 450W and lowest thermal resistance of 0.145°C/W; its critical heat load approaches 600W. Compared with a metal wick structure with thickness of 1.75 mm, effective pore radius of 3.6 μm, permeability of 7×10-13 m2, and porosity of 70%, a PTFE wick structure, with its low thermal conductivity, can reduce the compensation chamber’s temperature. This shows that the low thermal conductivity wick can effectively reduce the heat leakage problem. The performance of the LHP with a PTFE wick structure is also better than that of the LHP with a metal wick structure, increasing the critical heat load by about 120% (from 500W to 600W).The lowest thermal resistance is lower than that of the LHP with a metal wick structure (0.156 ℃/W).
In all, PTFE wick structure can significantly improve the heat leakage problem of a metal-wick LHP as well as effectively increase the LHP’s heat load and decrease the lowest thermal resistance. Compared with a metal wick structure, a PTFE wick has many advantages in its manufacturing process, including lower cost, more controllability, and higher safety, demonstrating high potential for application to LHPs and similar high heat capacity cooling devices.

並列關鍵字

Polymer Wick Structure ； Loop Heat Pipe ； Heat Leakage ； Polytetrafluoroethene (PTFE)

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