Heat Transfer Analysis of a Loop Heat Pipe with Biporous Wicks

• Main Authors: Chun-Nan Chen, 陳俊男
• Other Authors: Yau-Ming Chen
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/40969420730557999181

碩士 === 國立臺灣大學 === 機械工程學研究所 === 96 === 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.