In order to optimize the coupling between the heat pipe and the cold source, and to study the influence of different condenser lengths on the performance of heat pipes, a nitrogen charged Ω-shaped axially grooved heat pipe with a gas reservoir working at ambient temperature was designed based on the heat transport demand for space cryogenic applications. The supercritical startup performance of the heat pipe in the liquid nitrogen temperature zone and the heat transfer performance under different condenser heat fluxes are tested. The experimental results reveal that the heat pipe with gas reservoir starts up rapidly, and the length of the condenser has no effect on the start-up rate. When the filling rate of the heat pipe is 100%, for a given operating temperature under the same heat load, with the decrease in the condenser length, the heat pipe requires a greater degree of subcooling at the condenser to dissipate heat, so the thermal resistance of the heat pipe increases. Meanwhile, the heat transfer capacity will decrease. It is because the decrease of capillary pressure due to the increase of the contact angle of the working fluid on the wick surface. At a given operating temperature and the same length of the condenser, when the heat load increases, the heat transfer coefficient of evaporator and condenser will increase, so the thermal resistance of the heat pipe will decrease accordingly.

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