The Study of the PTFE Wick Structure Applied to Loop Heat Pipe
Date Issued
2014
Date
2014
Author(s)
Gu, Tzu-Wei
Abstract
Loop heat pipe (LHP), which is a passive two-phase thermal transport device with high heat capacity and long transport distance, has a great potential for applications to spacecrafts and electronic cooling. Currently, most wick structures of LHPs are manufactured by sintering metal powder, such as nickel, titanium, or copper powder; however, the use of metal wicks, with metal’s high thermal conductivity, may allow heat to transfer into the evaporator core too easily, causing the “heat leakage” problem. To solve this problem, and to meet the requirements of recent LHPs, such as high performance, low cost, small size, and light weight, the use of polymer wick structures has been discussed recently as a solution.
Therefore, the main objectives of this study are to use polytetrafluoroethene (PTFE), which has low thermal conductivity, as wick material and to manufacture the polymer wick structure by sintering. When sintering, the effective pore radius, permeability, and porosity of the wick can be controlled by adjusting the particle size of PTFE. This study also varies the wick’s thickness to find the optimal parameters for the PTFE wick.
A PTFE wick structure with thickness of 1.75 mm, effective pore radius of 1.7 μm, permeability of 6.2×10-12 m2, and porosity of 50% is installed into a LHP system to carry out heat transfer performance testing. Under operating temperature of 85°C, the LHP with PTFE wick structure has highest heat load of 450W and lowest thermal resistance of 0.145°C/W; its critical heat load approaches 600W. Compared with a metal wick structure with thickness of 1.75 mm, effective pore radius of 3.6 μm, permeability of 7×10-13 m2, and porosity of 70%, a PTFE wick structure, with its low thermal conductivity, can reduce the compensation chamber’s temperature. This shows that the low thermal conductivity wick can effectively reduce the heat leakage problem. The performance of the LHP with a PTFE wick structure is also better than that of the LHP with a metal wick structure, increasing the critical heat load by about 120% (from 500W to 600W).The lowest thermal resistance is lower than that of the LHP with a metal wick structure (0.156 ℃/W).
In all, PTFE wick structure can significantly improve the heat leakage problem of a metal-wick LHP as well as effectively increase the LHP’s heat load and decrease the lowest thermal resistance. Compared with a metal wick structure, a PTFE wick has many advantages in its manufacturing process, including lower cost, more controllability, and higher safety, demonstrating high potential for application to LHPs and similar high heat capacity cooling devices.
Subjects
高分子毛細結構
迴路式熱管
熱洩漏
鐵氟龍
Type
thesis
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