Mathematical model of heat and mass transfer in a wick structure of a loop heat pipe

A mathematical steady-state model of a loop heat pipe (LHP) system was developed in this study. The model was based on the energy conservation and the phase-change heat transfer in porous media. The evaporator temperature was predicted including using a monoporous wick structure and using a biporous wick structure, which has two characteristic pore sizes. Experiments were also executed in this study. The model indicated that the monoporous wick with narrow pore size distribution accumulated gradually the vapor blanket; it brought the higher thermal resistance at increasing heat load. The biporous wick with the lager pores providing the passages for vapor and thus improved the heat transfer capacity of a LHP´s evaporator. The calculation results showed that, at 10°C of sink temperature, 25°C of ambient temperature, and 350W of heat load, the evaporator temperature of monoporous wick was 88°C and the thermal resistance of the vapor blanket was 0.13°C/W, 60% of the total thermal resistance of the system (0.22°C/W). At the same modeling condition, the evaporator temperature of biporous wick was 50°C and the thermal resistance of the vapor blanket was 0.003°C/W, about 3% of the total thermal resistance (0.1°C/W). It indicated the biporous wick effectively enhanced the heat transfer performance of a LHP. To summarize, the development of this model could be a useful tool for predicting the performance of a LHP using the monoporous and biporous wicks.