Operational characteristics of the miniature loop heat pipe with non-condensable gases

The present paper experimentally investigates the effect of non-condensable gases (NCGs) on the thermal performance of the miniature loop heat pipe (mLHP). Copper mLHP with the flat disk shaped evaporator, 30 mm diameter and 10 mm thick, and fin-and-tube type condenser, 50 mm length and 10 mm height, located at a distance of 150 mm was used in the study. The device which was designed for the thermal control of computer microprocessor was capable of transferring maximum heat load of 70 W while maintaining evaporator temperature below 100 °C limit for electronic equipments. Water was used as the heat transfer fluid inside the mLHP. All the tests were conducted with the evaporator and condenser at the same horizontal level. Simple methods were devised to detect and purge the generated NCG out of the loop heat pipe without disassembling the system. Experiments conducted to classify the trends in the NCG production and storage revealed that majority of the gas is generated in the first few thermal runs and is accumulated in the compensation chamber. Sensitivity tests show that overall effect of the NCG is to elevate the steady-state operating temperature of the loop and increase the start-up time required by the evaporator to achieve stable conditions for the given heat load. As an outcomes of the research work, it can be concluded that mLHPs are more tolerable to the NCGs than conventional heat pipes due to the presence of compensation chamber that can accumulate most of the released gas without major performance degradation.