Design optimization and experimental demonstration of a gravity-assisted cryogenic loop heat pipe

Cryogenic loop heat pipe (CLHP) is an efficient two-phase heat transfer device utilized for cooling electronic components within a cryogenic operating temperature range (3-220 K), such as an infrared detector and superconductive magnet. Compared with the prevalent cryogenic loop heat pipe which uses a capillary starter pump to achieve the startup, this research studied a gravity-assisted CLHP that uses gravity to achieve the startup. In this way, the configuration of gravity-assisted CLHP became simple, and the preconditioning could be achieved without consuming the extra heat load on the capillary starter pump. This proposed CLHP is intended for use in ground and space (in the gravitational environment such as the Moon and Mars). A comprehensive design method including the design optimization of the gas reservoir and compensation chamber (CC) volumes was newly established by considering the variation of vapor-liquid distribution in CC during the operating temperature range, resulting in a significant reduction of at least 40 % in the gas reservoir volume compared to conventional CLHP designs. Then the fabrication and the experimental investigation were implemented. Nitrogen was selected as the working fluid. The CLHP was designed to transport heat exceeding 20 W over a distance of 2 m within the operating temperature range of 80-110 K. Based on the experimental result, the startup was achieved, and the heat transfer performance satisfied the design requirement. Additionally, the detailed operating characteristics of the CLHP, including the gravity effect, the startup behavior, and the hysteresis phenomena that occurred in the temperature of the evaporator, pressure, and thermal resistance, were also first reported and thoroughly investigated.