A loop heat pipe with flat evaporator (FLHP) is manufactured from copper, and filled with ultrapure water as the working fluid. The heat transfer characteristics have been studied experimentally. The gravity impacts the heat transfer characteristics of the FLHP in different orientations. Operation of the FLHP at orientations against the gravity which is the evaporator above the condenser leads to the higher temperature of the evaporator and the lower loop heat transfer performance. At horizontal orientation with the evaporator above the compensation chamber (CC), the working fluid is difficult to reach the wick and has the highest temperature. With the increasing of the heat load up to more than 300 W, the loop thermal resistance decreases and approaches a minimum value of about 0.2 K/W at the vertical orientation helped by gravity. Experimental results show that the start-up with low power needs a temperature overshoot. Oscillations with high frequency (with periods on the order of seconds to minutes) and high amplitude (with temperature changes on the order of tens degree Kelvin) are observed. A model is developed, which shows the working fluid distributing in the evaporator wick may result such oscillations. In most cases, the highest amplitude in the loop is observed in the liquid line near CC, and the lowest amplitude is in the CC.
Gravity effects on the performance of a flat loop heat pipe
Gravitationsauswirkungen auf die Leistung eines Plattenverdampfer-Wärmerohrs
International Topical Team Workshop on Two-Phase Systems for Ground and Space Applications, 4 ; S95-S102
Microgravity Science and Technology ; 21 , Supplementary Issue 1
2009
8 Seiten, 9 Bilder, 1 Tabelle, 7 Quellen
Conference paper
English
Thermal Characteristics of a Flat Evaporator Miniature Loop Heat Pipe
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