126 Experimental Investigation of Miniature Loop Heat Pipe with Flat Evaporator

Loop heat pipes (LHPs) are heat transfer devices whose operating principle is based on the evaporation and condensation of a working fluid, and which use the capillary pumping forces to ensure the fluid circulation. A series of tests have been carried out with a miniature loop heat pipe (mLHP) with flat evaporator and fin-and-tube type condenser. The loop is made of pure copper with stainless mesh wick and acetone as working fluid. Detailed study is conducted on the start-up reliability of the mLHP at high as well as low heat loads. During the testing of mLHP under step power cycles, the thermal response presented by the loop to achieve steady state is very short. At some heat loads, temperature oscillations are observed throughout the loop. It is observed that the extent and nature of the oscillations occurrence is dependent on the thermal and hydrodynamic conditions inside the compensation chamber. The effects of different liquid charging ratios and tilt angles to the start-up and the temperature oscillation are studied in detail.