Experimental investigation of the operating characteristics of a hybrid loop heat pipe using pump assistance

A loop heat pipe (LHP) is one of the two-phase cooling technologies used in passive cooling systems. The LHP is an efficient heat transfer device, but its extreme power density can cause dry-out at the evaporator. Many researchers have predicted that passive devices will not be able to meet future cooling challenges because of this limitation. The objective of this research is to design a modified LHP that overcomes the dry-out problem by adding a diaphragm pump to accelerate fluid transportation (called a hybrid loop heat pipe, HLHP). The pump installed on the liquid line is coupled with a reservoir. The developed HLHP works passively using wick capillary pressure when there is no sign of dry-out. When dry-out occurs, the pump is activated via diaphragm pumping and has a temperature controller. Thus, the working fluid is circulated by both the capillary force and driving force of the diaphragm pump during the heat-transfer process. The operating characteristics of the HLHP under a variety of heat load supply and low-power start-up conditions have been investigated. The experimental results indicate that the installation of a diaphragm pump in a modified LHP system can prevent the occurrence of dry-out in the evaporator and significantly reduce the evaporator temperature.