Experimental study on loop heat pipe with two-wick flat evaporator

A flat-type loop heat pipe (FLHP) is considered promising for applications in the field of thermal control and electronic cooling owing to its many advantages such as high heat transfer capability with small temperature difference, easy installation, and lack of moving parts. However, it suffers from drawbacks such as high back-conduction in the evaporator. Many studies have aimed to improve the performance of FLHPs by changing the working fluid or porous materials. In a loop heat pipe (LHP) with a flat evaporator, the compensation chamber (CC) is usually in the vapor-liquid two-phase state owing to backward conduction of the wick and side-wall conduction of the evaporator. When the heat load is in a certain range, bubbles are generated and then annihilated in the compensation chamber, and the temperature and pressure fluctuate, causing unstable LHP operation. To eliminate or reduce back-conduction in the flat evaporator, this study develops a loop heat pipe with two primary sintered nickel powder wicks arranged in an evaporator made of brass and using methanol and acetone as the working fluids. The startup and operation are studied under variable conditions with different heat loads. The experimental results show that our novel LHP can start up successfully and operate in a wide heat load range of 10-170 W. When the temperature of the contact surface between the simulated heat source and the evaporator does not exceed 90 °C, the maximum heat load can reach 170 W, which corresponds to a heat flux of 17.7 W/cm2.