The Study of PTFE Wick Structure Applied to Flat Plate Loop Heat Pipe

Loop heat pipe, compared to a conventional heat pipe, is a passive phase change, heat transfer device having the advantages of long-distance heat transfer, low thermal resistance and high heat transfer capacity etc. The key point of it is the wick structure. Because of its wide-range compatibility of working fluid and low thermal conductivity coefficient, as a wick material, nickel can replace copper using in loop heat pipe nowadays. In recent years, the power density of electronic components rises with thermal processing required per unit density gradually increased, causing metal wick structures hard to resist heat leakage, which becomes a new researching issue. Non-metallic wick structure- Teflon (PTFE), has a low thermal conductivity coefficient and good plasticity, so Japanese scholars in recent years [20] attempts to apply PTFE to the loop-type heat pipe. This study attempts to design and build air-cooling flat-plate loop heat pipe used in thermoelectric wafer with the target thermoelectric cooling wattage of 85W, operating temperature below 100℃ and the thermal resistance less than 0.5K/W. By the thermal performance test, this this study not only improve the condenser length and fin design, but also change the material of wick structure and the amount of working fluid filled in that, in order to find the proper air-cooling flat-plate loop heat pipe and achieve low operating temperature with low thermal resistance target. Based on the result of experiments, after calculating and testing, it goes that it is the best cooling length of 250mm; the working fluid is filled 60% of the total volume of the loop heat pipe. Under these parameters, this study uses Teflon wick structure as heat-transfer-performance tests on air-cooling flat-plate loop heat pipe. With target wattage 85W, its operating temperature is of 58℃, the system thermal resistance of 0.38 K/W, the compensation chamber temperature of 28℃. Compared with the metal wick structure like nickel and copper at 85W, they have the operating temperatures of 75℃ and 79℃ separately, thermal resistance 0.58K/W and 0.63K/W, the compensation chamber temperature of 39℃ and 45℃.The Teflon wick structure has better heat transfer performance from above. Summarize the results; this study successfully established air-cooling flat-plate loop heat pipe, and using Teflon as wick structures, which effectively reduce the operating temperature and the thermal resistance without heat leakage. Compared to metal wick structures, Teflon wick structures have lower manufacturing costs, better processing, etc. Moreover, the Teflon wick structures have high potential of high-power cooling element in the future.