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1、英语科技论文实用写作方法作业课程班级号：2学院：能动学院系别： 班级： ()Mail： 键入文字 键入文字 英语科技论文实用写作方法作业 键入文字 键入文字An Experimental study on Evaporation/Boiling HeatTransfer in Sintered Porous WickSUN Zhen HONG Fang-Jun ZHENG Ping(School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China)Abstract We has des
2、igned and established an experimental apparatus to study the evaporation/boiling heat transfer in particle sintered porous wick under the working condition of heat pipe. The effects of particle size as well as the thickness and volumetric porosity of porous wick on evaporation/boiling heat transfer
3、were investigated by using distilled water as working fluid. It was found that for the fixed particle size and porosity, there exists an optimal wick thickness corresponding to the maximum heat transfer coefficient. For the fixed thickness of porous wick, there is an optimal porosity when the heat f
4、lux is relatively low, however, the smaller the porosity is, and the higher the heat transfer coefficient is when heat flux is relatively high. An evaporation/boiling heat transfer model was also summarized to give plausible explanations of experimental results.Key words particle sintered; porous wi
5、ck; evaporation/boiling; heat pipe0 IntroductionThe flat heat pipe is a high-performance thermal diffusion technology which connects the electronic chip (heat sauce) and the heat sink. It can be considered as a twodimension heat pipe from the direction of steam flow. The particle sintered porous wic
6、k is an important internal structure of the flat heat pipe. When the flat heat pipe is on the stable running period and the liquid level is lower than the upper surface of the porous wick, the phase transition occurs. To distinguish it from the pool boiling, this phase transition is called evaporati
7、on/boiling heat transfer. The evaporation and boiling heat transfer of refrigerant in and at the surface of porous wick is one of the important factors influencing heat pipes property. Although much literature about porous wick boiling heat transfer has been published (see paper 1, 2 and their refer
8、ences), much of the research was about pool boiling or one-dimension heat pipe, and little research was aimed at evaporation/boiling heat transfer in sintered 3-5 porous wick in flat heat pipe.Hanlon and Mal 3 examined the evaporation/boiling heat transfer of thick cooper (1.9mm) particle sintered p
9、orous wick, and they found that boiling would occur and bubbles appeared in wick which led to a decline of heat transfer when the heat flux was between 5-20w/cm2. The performance of heat transfer would decline with the increase of wicks thickness. Li, Peterson et al. 4, 5 studied the 0.37-1 mm (bubb
10、les departure diameter) cooper wicks evaporation/boiling heat transfer. They found that the critical heat flux increased with the increase of wicks thickness, while the heat transfer coefficient changed little. They considered that the evaporation of liquid film on porous wicks surface was the main
11、way of heat transfer, and also there existed an optimal porosity corresponding to the maximal critical heat flux. The optimal porosity was related to the thickness of porous wick and the size of the mesh: when the diameter of meshs cooper wire was fixed, the heat transfer coefficient decreased with
12、the increase of porosity.键入文字 键入文字 英语科技论文实用写作方法作业 键入文字 键入文字From the research 3-5 above, the liquid level evened the surface of porous wick according to the overflow principle; meanwhile those experiments were conducted at the atmosphere pressure which didnt correspond to the heat pipe working condit
13、ion. In this study, an experiment investigation in heat pipe (vacuum decompression) condition was done to characterize the effects from wicks diameter, type and porous wicks thickness (PM8PM2, PM6PM9PM3 at the condition of same heat flux. We can conclude that for the spray powder, when the porosity
14、is fixed, there is an optimal thickness of wick which corresponds to the maximum heat transfer coefficient. The reason can be explained as below: the ways of porous wick evaporation/boiling heat transfer include the conduction between solids in wick, convection between liquids in liquid region and t
15、he film evaporation of liquid-vapor interface in and on the wick; the thick wick has a better diffusion effect and larger convection transfer area, then the liquid-vapor interface will increase after the formation of gas province; meanwhile thickening the wick will increase the thermal resistance in
16、 gas province and the vapors overflow resistance which causes an increase in liquids superheat. The interaction of the factors above makes the existence of optimal thickness of wick. It can be seen from Fig. 5 that when the thickness of wick increases, the maximum heat transfer coefficients heat flux decreases. That is the reason why the heat conduction in liquid region and the formation of gas province lead to a declin
