具雙孔徑毛細結構迴路式熱管之熱傳分析

Heat Transfer Analysis of a Loop Heat Pipe with Biporous Wicks

陳俊男(Chun-Nan Chen)

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(2008年)

https://doi.org/10.6342/NTU.2008.00567

摘要

近年來隨著高功率電子元件等產品對散熱器之熱傳需求不斷提升，如何藉由高性能毛細結構來提升迴路式熱管熱傳能力，是一個重要的課題。本研究旨在添加孔洞成型劑於鎳粉中進行燒結，製造出具雙孔徑分布之毛細結構
，並探討在迴路式熱管內，雙孔徑毛細結構不同孔洞變化下的熱傳性能與行為。研究方法藉由改變孔洞成型劑粒徑(32~88μm)、含量(20~25vol%)以及燒結溫度(650~750℃)，搭配使用二水準因子設計的統計方法，分析出各參數對迴路式熱管的熱傳能力之影響程度與趨勢，並建立統計經驗模型，以找出最佳的雙孔徑毛細結構參數。最後，再與單孔徑毛細結構做熱傳性能的比較。
研究結果顯示孔洞成型劑的含量對迴路式熱管熱傳能力的影響程度最大，貢獻百分比為76.8%，其次是孔洞成型劑粒徑貢獻百分比為15.6%，而燒結溫度影響不明顯，貢獻度僅0.2%。並且在孔洞成型劑粒徑縮小、含量增多的情況下，可獲得性能較佳的雙孔徑毛細結構。透過經驗模型之建議，最佳的雙孔徑毛細結構參數為：孔洞成型劑粒徑範圍在20~32μm，孔洞成型劑含量25vol%，燒結溫度750℃。
實際測試結果在熱沉10℃與容許溫度85℃下，結果顯示最佳之雙孔徑毛細結構其總熱傳量可達570W、熱阻為0.08℃/W，比起單孔徑毛細結構的熱傳性能350W、熱阻為0.22℃/W，整體性能具有相當的提升。此外，雙孔徑毛細結構最高熱傳傳係數可達68 KW/m2.℃，與單孔徑毛細結構熱傳係數10 KW/m2.℃相比約提升6.8倍。針對最佳雙孔徑毛細結構明顯先升後降的趨勢，於不同熱通量下可將之分為三個階段，較低熱通量時(約130KW/m2以下)熱傳係數變化平緩，相似於單孔徑毛細結構性能變化。而隨著熱通量之增加(約130~210KW/m2)薄膜蒸發面積得以延伸，導致熱傳係數急速增高。在高熱通情況下(約210KW/m2以上)推測液體薄膜經蒸發已部分乾涸，造成性能逐漸衰退。

關鍵字

迴路式熱管 ； 雙孔徑毛細結構 ； 單孔徑毛細結構 ； 熱傳係數

並列摘要

In recent years, the high-power electronic devices cause the increasing demand of heat dissipation. Thus, how to improve the heat transfer capacity of a loop heat pipe (LHP) by the wick structure will be an important topic. The purpose of this article is to discuss the heat transfer performance and behavior of biporous wick which made by the mixture of nickel powders and pore former. The study was conducted following a statistical method using a two-level factorial plan involving three variables: the particle of pore former (32~88μm), the pore former content(20~25vol%),and sintering temperature (650~750℃). Moreover, the empirical model was built to determine the optimized parameter combination of the biporous wick. Finally, the heat transport capability of the LHP between monoporous wicks and biporous wicks has been investigated.
The results showed that the pore former content is a primary effect (percent contribution is 76.8%) for performance of LHP. Particle size of pore formers is minor effect (percent contribution is 15.6%), and sintering temperature is a little effect. The better parameters of biporous wick is tend to have smaller particle size of pore former, more pore former contents. The best parameters of the biporous wick is obtained with the empirical model: The range of particle size of pore former is 20~32μm, pore former content is 25vol%, and sintering temperature is 750℃.
Experimental results showed that, at the sink temperature of 10℃ and the allowable evaporator temperature of 85℃, the maximum heat transfer capacity of the best biporous wick achieved 570W and the minimum total thermal resistance was 0.08℃/W. Comparing to a monoporous wick for 350W and 0.22℃/W. In addition, the heat transfer coefficient in the evaporator of the best biporous wick reached to a maximum value of 68KW/m2•℃, which was approximately 6.8 times higher than that of the monoporous wick. With the increase of the imposed heat flux, the heat transfer coefficient of the best biporous wick increases to a maximum value and then decreases afterwards. The special heat transfer curve can be divided into three different regions. In lower heat flux(below 130KW/m2), the heat transfer performance of biporous wick is almost like that of a monoporous wick. The biporous wick had an increased surface area available for thin film evaporation at higher heat flux(130~210KW/m2). Therefore, the heat transfer coefficient reaches rapidly a maximum value. In high heat flux (above 210KW/m2), the performance of biporous wick decay gradually because the dryout starts to occur in the wick.

並列關鍵字

biporous wick, monoporous wick ； Loop heat pipe ； heat transfer coefficient

參考文獻

[1] Maydanik, Y. F., Fershtater, Y. G., and Pastukhov, V.,“Thermoregulation of Loops with Capillary Pumping for Space Use,” SAE Paper 921169, 1992.

[2] Goncharov, K. A., Loop Heat Pipes in Thermal Control Systems for ‘‘Obzor’’ Spacecraft, Proceedings of the 25th International Conference on Environmental Systems, San Diego, CA, Paper 951555, 1995.

[4] Liao, Q., and Zhao, T. S., “Evaporative Heat Transfer in a Capillary Transfer,” Vol. 13, No. 1, pp.126-133, 1999.

[8] Rosenfeld, J. H. and North, M. T.," Porous Media Heat Exchangers for Cooling of High-power Optical Components", Optical Engineering, Vo1.34, No.2, pp.335-341, 1995.

[10] Chen, Z. Q., Cheng, P., and Zhao, T. S.,“An Experimental Study of Two Phase Flow and Boiling Heat Transfer in Bi-dispersed Porous Channels,”Int. Commun. Heat Mass Transfer, Vol. 27, No.3, pp. 293–302, 2000.