Experimental study of heat transfer capacity for loop heat pipe with flat disk evaporator

Abstract

Loop heat pipes are passive heat transfer devices which can meet the heat dissipation requirement of high-power electronic devices in aerospace and terrestrial applications. This paper investigates the operating characteristic of a stainless steel-ammonia loop heat pipe with a flat disk evaporator. A biporous wick made from sintered nickel powders was used to produce the capillary force. The heat transfer distance was 1.6 m and the allowable heater surface temperature was below 70 °C. Tests demonstrated that the loop could operate under a heat load ranging from 2.5 W to 180 W (heat flux 0.15–10.8 W/cm2) at heat sink temperature of −10 °C. In addition, variable conductance mode and constant conductance mode existed, and no obvious temperature overshoot or pulsation was observed. The evaporator inlet temperature went through a staged decline due to the effect of initial driving force of vapor expansion during the start-up process. Meanwhile, under the synergy of heat leaks from heater surface and long transport line, whether the vapor phase would form inside the compensation chamber could result in a large discrepancy in temperature trends. The minimum evaporator thermal resistance was 0.096 °C/W at heat sink temperature of −10 °C and the minimum LHP thermal resistance was 0.252 °C/W at heat sink temperature of 10 °C.