Performance of a High-power Loop Heat pipe in Variable Temperature Environments

This paper presents test results of an experimental study of a large-sized loop heat pipe (LHP). The main objective was to investigate the start-up and operation characteristics and the heat transfer capability in the long-term testing process (A total of 160.5 operating hours of the LHP were accumulated for the test). The evaporator casing of the experimental LHP was made of aluminum alloy and housed a polytetrafluoroethylene (PTFE) wick with an average pore diameter of 40.6 nm and a porosity of 32.37%. The vapor line and liquid line, each has an inner diameter of 6 mm, were made of aluminum tubes with a length of 4090 mm and 3320 mm, respectively. Ammonia was employed as the working fluid. Testing consisted of numerous start-ups, stepwise heating and shut-downs was carried out in a horizontal position under non-vacuum closed atmosphere provided by a high and low temperature thermo humid environment simulation room. The results showed that the LHP could start up and work normally between 100 W and 400 W. When the heat load was 400 W, the temperature difference between the evaporator and condenser were less than 10 ℃, 20 ℃ at the environment temperatures of -30 ℃ and -60 ℃, respectively. In the test of repeated cycles of loop start-up and shut-down at 400 W, start-up failures occurred at 60 mins and 120 mins when the ambient temperatures were controlled at -30 ℃ and -60 ℃ respectively, and successful start-ups were realized prior to these time. However, when applying a 100 W stepwise heating power to the evaporator, the LHP could operate normally again. When the environment was controlled at 0 ℃, such incidence didn't occur even over 300 mins.