高性能鐵氟龍毛細結構應用於迴路式熱管之研究

The Study of the High Performance PTFE Wick structure Applied to Loop Heat Pipe

吳政芳(Cheng-Fang Wu)

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(2015年)

https://doi.org/10.6342/NTU.2015.02015

摘要

迴路式熱管(Loop Heat Pipe)為一被動之二相熱傳元件，相較於傳統之散熱元件其具有下列優點：高熱傳量、長距離傳輸以及低熱阻等，對於未來之電子元件散熱需求有相當大的發展潛力。迴路式熱管內最重要之原件為蒸發器內部的毛細結構，其主要用來吸收液態工質並提供迴路式熱管足夠之毛細力，在傳統迴路式熱管中常見的毛細結構材質多屬於金屬，如：銅、鎳等。高分子毛細結構較少為被研究，但近年來持續有國外研究團隊不斷對聚四氟乙烯(鐵氟龍)毛細結構做研究，不過其熱傳性能皆有所限制。因此本研究擬採用不同於文獻毛細結構之製作方式來突破其熱傳限制，並透過電子式掃描顯微鏡(SEM)與水銀測孔儀分析其內部孔徑結構。
本研究透過燒結法製作鐵氟龍毛細結構，於水銀測孔量測結果中發現到，燒結之毛細結構內部存在類似於雙孔徑之孔徑分佈，有別於單孔徑之鐵氟龍孔洞材毛細結構，並且其內部大孔徑之孔洞分佈對於迴路式熱管熱傳性能擁有正相關之影響。在熱傳性能測試結果上較文獻而言，最大熱傳量較文獻的 40~70 W 約有 3~5倍左右的提升，最大熱通量上則較文獻的 4 W/cm2 增加約 2.5 倍，在系統總熱阻上也較文獻之 0.9 ℃/W 來得低。
在實驗結果上，同樣以燒結法製作之金屬鎳毛細結構於同一迴路式熱管測試系統中進行熱傳性能測試，以氨做為工作流體時，鐵氟龍毛細結構之熱傳測試結果與金屬鎳毛結構不相上下，兩者之最大熱傳量皆可達 600 W；系統總熱阻上鐵氟龍約 0.141 ℃/W 較金屬鎳毛細結構 0.171 ℃/W 約少了 20 %。在孔徑分析上，由電子式掃描顯微鏡及孔徑曲線上可以看到兩者孔洞結構之差異，金屬鎳毛細結構上屬於單一孔徑之孔洞結構，有別於鐵氟龍類似雙孔徑之分佈結果。
總結本研究之成果，透過燒結法所製作之鐵氟龍毛細結構由於其內部特殊之孔徑分佈情形，使得高分子毛細結構之迴路式熱管性顯著提升，並且與金屬鎳毛細結構不相上下；另一方面由於鐵氟龍於製程上較安全且有良好之加工性及保存穩定性等優點，因此對於高性能迴路式熱管之研究具有相當之優勢。

關鍵字

高分子毛細結構 ； 迴路式熱管 ； 鐵氟龍 ； 孔徑分佈

並列摘要

Loop heat pipe(LHP),which is a passive two phase thermal transport device, it has lots of advantages as following: high heat capacity, long transport distance and low thermal resistance, comparing to traditional thermal transport devices. It has great development potential for electronic cooling in the future. However, in the LHPs, there is an important unit in the evaporator, wick structure, which must supply enough capillary force and absorb liquid working fluid. Currently, most wick structures of LHPs are manufactured by metal material, such as nickel or copper. On the other hand, the polymer wicks have been kept researching by some group recently but there heat performances still have limitations. Therefore, this study uses other manufacture differ from papers to make polytetrafluoroethene (PTFE) wick and try to break this performance limitations. Further to analyze the wick’s porous structure by using scanning electron microscope (SEM) and mercury porosimeter.
In this study, the main objective is to use PTFE as wick material and to manufacture the polymer wick by sintering. From the porous distribution results by mercury porosimeter, the porous distribution of sintering PTFE wick is similar to bi-porous distribution that is different from the mono-porous PTFE wick which made by porous PTFE material. However, the larger porous distribution has positive correction with LHP’s heat transfer performance. On LHP performance test, comparing with paper’s results, the critical heat load is 3~5 times larger than 40~70 W, the maximum heat flux also increase 2.5 times than 4 W/cm2, and the total thermal resistance is less than 0.9℃/W from references presented.
On the other hand, the LHP system install with PTFE and nickel wick which both manufactured by sintering and use ammonia as working fluid. Comparing with the test result, it shows that the critical heat load about PTFE and nickel wick both can reach 600 W and the total thermal resistance with PTFE wick is about 0.141 ℃/W that is less 20 % about nickel wick’s 0.171 ℃/W. Otherwise, the wick’s micro-structures are different from PTFE and nickel wick. From SEM and porous distribution, even using the same mono-porous sintering manufacture process, nickel and PTFE wick have different porous distribution. The porous distribution of nickel wick is mono-porous but PTFE is similar to bi-porous.
In all, the PTFE wick which manufactured by sintering has particular porous distribution that differ from mono-porous wick. However, the similar bi-porous distribution is benefit to improve the performance of the LHP with PTFE wick and that is as good as nickel wick. Compared with nickel wick, the PTFE wick has more advantages including safely manufacture process, excellent machinability and persistence. So that, the PTFE wick has great development potential on high performance’s LHP.

並列關鍵字

Polymer wick structure ； Loop heat pipe ； Polytetrafluoroethene (PTFE) ； Porous distribution

參考文獻

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