Loop heat pipes (LHPs) are attractive two-phase thermal control devices for satellites, electronics and many other applications. They are capable of transporting heat efficiently for long distances up to several meters at any orientation. This paper investigated the heat transfer characteristics of loop heat pipes with long distances and small diameter transport lines. Small stainless steel tubes of 2 mm and 3 mm in inner diameters were chosen as liquid lines and vapor lines of the LHPs. The local thermal resistances in the evaporator of the 6 m-LHP were researched and analyzed, which indicated that the thermal resistance between the aluminum block and the vapor in the vapor channel accounted for a major proportion of the total thermal resistance. The effect of heat sink temperatures on the performance of the 6 m-LHP were compared with 10°C, 15°C, 20°C and 25°C cooling water temperatures. Moreover, the thermal characteristics of LHPs with transport distances of 2 m and 16 m were also experimentally investigated. The 16 m-LHP could achieve a heat transfer capacity of 100 W and the 2 m-LHP could reach more than 339 W, on the premise of the evaporator temperature below 100°C. The thermal resistance of the 2 m-LHP could achieve 0.125°C/W.
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