Study on a loop heat pipe for a long-distance heat transport under anti-gravity condition

This paper reports the test results and evaluation of gravity effects on long-distance loop heat pipe (LLHP) with 10 m distances for heat transport. First, the LLHP was designed based on the one-dimensional steady-state model, fabricated and tested. Test results showed the LLHP could transport heat up to 340 W for 10 m and the thermal resistance between the evaporator and the condenser was 0.12 K/W under horizontal condition. Next, the LLHP was tested in top-heat mode. The maximum heat transports were 310, 270, 220 W and the thermal resistances were 0.15, 0.17, 0.22 K/W under 30, 60, 100 cm anti-gravity condition respectively. The heat transfer efficiency of the LLHP was discussed in detail. The evaluation results showed 71.4% of the 340 W heat load was dissipated at the condenser under the horizontal condition. On the other hand, 62.8, 61.8, 57.1% of the maximum heat load was dissipated at the condenser under 30, 60, 100 cm anti-gravity condition respectively. The calculation model was in good agreement with the experimental results by considering the existence of a vapor pocket between the evaporator case and the vapor-liquid interface. This analysis indicated the vapor blanket generates easily and becomes thicker as anti-gravity effect increases.