Investigating the effect of double-layer wick thickness ratio on heat transfer, performance of loop heat pipe

This study investigated the effect of double-layer wick thickness ratio on the heat transfer performance of loop heat pipe (LHP). With the outer layer of the wick being biporous to allow vapor to travel and the inner layer being monoporous to provide capillary force, the wick used in this study eliminated the problems with wick's structural strength and difficulty in vapor release encountered when using a monoporous wick. By changing the double-layer wick thickness ratio, the LHP heat transfer performance was enhanced. Under a fixed total wick thickness, the double-layer wick thickness ratio was varied by adjusting the biporous and monoporous layers' thicknesses; higher thickness ratio corresponds to the wick having more biporous wick characteristics, and lower thickness ratio corresponds to the wick being more like a monoporous wick. In this study, the ratios investigated were 0.28, 0.42, 0.57, 0.71, 0.86, and 1. Results showed that at 0.57, the highest heat load under 85 degrees C was 1060 W, the total thermal resistance was 0.065 degrees C/W, the heat flux was 50 W/cm(2), the heat transfer coefficient was 188 kW/m(2) degrees C, and the porosity was 82%. Compared with the double-layer wick performance reported thus far, performance was increased by about 50%, and compared with that of the monoporous wick, the performance increase was about 200%. The best thickness ratio was successfully determined, and the critical heat load reached, for the first time, the order of kW. A trend line and empirical equation for LHP performance results for monoporous (thickness ratio 0) [1], double-layer (thickness ratio 0.28 similar to 0.86), and biporous (thickness ratio 1) wicks were fitted and established, providing a reference for future designs. (C) 2014 Elsevier Masson SAS. All rights reserved.