Experimental study on thermal performance of a long-distance helium two-phase closed thermosyphon

Abstract

Long-distance helium two-phase closed thermosyphons (TPCT) have significant potential for cooling superconducting magnets due to their simple structure and low thermal resistance. In this work, a helium TPCT is designed and fabricated with a vertical heat transfer distance of 860 mm. Experiments on helium TPCT are conducted with variations in heat power (0 – 1.3 W) and filling ratios (9.1% – 72.8%). Results demonstrate that the filling of helium can accelerate the cooling rate of thermosyphon. The heat transfer limit of the helium TPCT initially increases and then decreases as the filling ratio is increased. Two different heat transfer limit modes can be recognized: the dry-out limit, which emerges in the low to medium filling ratio (9.1% – 41.1%), and the boiling limit, which emerges in the high filling ratio (50.4% – 72.8%). The temperature and pressure characteristics exhibit significant differences between these two heat transfer limit modes. As the heat power increases, the total thermal resistance of the helium TPCT shows a downward trend. However, once the heat power exceeds the heat transfer limit, the thermal resistance increases sharply. The designed helium TPCT exhibits optimal thermal performance at a filling ratio of 50.4%, with a heat transfer limit of 1.15 W, a thermal resistance is approximately 0.18 K∙W⁻¹, and an effective thermal conductivity is approximately 23,800 W∙m⁻¹∙K⁻¹, demonstrating the superiority of TPCT for cooling superconducting magnets. The heat transport mechanisms revealed in the present study are expected to contribute to the design of high-efficiency helium heat pipes and facilitate their engineering applications.