The Study of the High Performance PTFE Wick structure Applied to Loop Heat Pipe
Date Issued
2015
Date
2015
Author(s)
Wu, Cheng-Fang
Abstract
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.
Subjects
Polymer wick structure
Loop heat pipe
Polytetrafluoroethene (PTFE)
Porous distribution
Type
thesis
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