Experiment study on heat transfer capability of an innovative gravity assisted ultra-thin looped heat pipe

This paper introduced a kind of gravity assisted ultra-thin looped heat pipe (ULHP) with 1.5 mm thick wickless flat evaporator that can be applied for power battery thermal management system, and investigated the heat transfer capability of the ULHP. Air cooling was used as the condensation method considering its advantage of low price and wide application in all walks of life. A series of experiments were conducted under different condensation powers during the same heating load range which started from 20 W to 80 W, to find out the best condensation condition of the ULHP. Further experiments were conducted under the best condensation condition to clarify the heat transfer capability of the ULHP, during which the start -up temperature, the minimum start-up heat load and the thermal resistance were discussed. The experiment results indicated that the ULHP can work most effectively as the fan voltage was 9 V, under which the ULHP can start up at minimum heat flux of 0.22 W/cm2, with the start-up temperature of 47 °C, and the minimum thermal resistance was just 0.097 W/K during the heat load range from 20 W to 120 W. Compared with vertical placed miniature looped heat pipe with wick structure flat evaporator (MFLHP) in literature, the ULHP can start under lower heat flux with lower temperature and lower thermal resistance, which showed an improved performance of ULHP than traditional MFLHP.