Experimental Study of Thermal Performance of a Flat Loop Heat Pipe

Abstract

Thermal management is an important issue for electronic cooling application. Choosing an efficient cooling technique depends on thermal performance, reliability, manufacturing cost, and prospects for minimization of packaging cost. Based on these grounds, Loop heat pipe (LHP) is a highly efficient two-phase cooling system used for passive cooling of critical components especially in satellite technology. Loop Heat Pipe uses capillary action to circulate cooling fluid. The capillary pressure developed in the pores of the wick material provides the driving force to pump the fluid. A loop heat pipe with flat evaporator has been designed and fabricated. An experimental study was performed to investigate the loop performance at different heat loads. LHP was instrumented with thermocouples to measure the temperature history at various locations of loop. Also the LHP was designed to be transparent to visualize the two phase flow phenomena. Temperature oscillations have been observed in the evaporator, vapor line and condenser during the startup of operation of the LHP. Performance of LHP has been evaluated at a certain range of evaporator heat loads. The minimum thermal resistance of LHP was 0.78 °C/W for a heat load of 100 W while the maximum was 3.1 °C/W for a heat load of 20 W. The maximum heat transfer coefficient in the evaporator was 14114 W/m 2 ℃ for a heat load of 100 W. In addition, it was found that the determination of startup and/or unstart is necessary for control and operation of LHP.