Operational characteristics of a miniature loop heat pipe with flat evaporator

This paper specifically addresses the thermal characteristics of the miniature Loop Heat Pipe (mLHP) with the flat disk shaped evaporator, 10 mm thick and 30 mm in diameter, for the thermal control of the compact electronic equipments. The loop was made of copper with nickel wick and water as the working fluid. Detailed study was conducted on the start-up reliability of the mLHP at high as well as low heat loads. It was found that the device was able to start-up at input power as low as 5 W, however the start-up time was very high at such heat loads. During the testing of mLHP under step and random power cycles, the thermal response presented by the loop to achieve steady state was very short. At low heat loads, thermal and hydraulic oscillations were observed throughout the loop. The amplitudes of these fluctuations were very high at condenser inlet and liquid line exit. It is expected that the extent and nature of the oscillations occurrence is dependent on the thermal and hydrodynamic conditions inside the compensation chamber. Overall, the effect of these oscillations on the thermal performance of the mLHP was not very significant. In the horizontal orientation, the device was able to transfer maximum heat load of 70 W with evaporator temperature below limit. The thermal resistance (RmLHP) of the mLHP lies between 0.17 to 5.66 °C/W.