Investigation of effects of auxiliary measures for startup of loop heat pipes

Experiments have been conducted to investigate the feasibility of two active measures, namely, local heating on the evaporator and cooling the compensation chamber, with a thermoelectric cooler. A new passive auxiliary measure, which utilizes the latent heat of phase change material to maintain the compensation chamber temperature at the melting point to help estimate the required superheat, has been presented for the first time. The effects of the three auxiliary measures on startups and the steady-state operation have been investigated. Test results indicate that the three auxiliary measures are helpful in establishing the required liquid superheat and reducing the evaporator temperature overshoot, as well as in lessening the startup time. Local heating on the evaporator near the evaporator outlet will not affect the steady-state operation, whereas local heating on the evaporator near the compensation chamber will lead to either sustaining operating temperature rises or higher operating temperatures. The continued operation of the thermoelectric cooler will decrease the operating temperatures at low heat loads and the typical V operating temperature curve will be changed to a nearly linear one. At too low heat loads, the phase change material can only delay the evaporator temperature rise and gain time for the loop heat pipe to wait for the arrival of a higher heat load, which is more favorable for startups.