Experimental and numerical study on the frozen deposition and startup of a sodium heat pipe

• The frozen front position is not fixed and appears as multi frozen areas. • The mass migration patten is influenced by the output and input power conditions. • The frozen deposition shows a fingering-like distribution and blocked the wick. • Temperature difference can go up to a few hundred degrees. • The shortened effective working length deteriorates the heat transfer ability. Sodium heat pipes are important heat transfer components for space craft, especially in the thermal management like waste heat dissipation. However, they would experience the mass migration phenomenon when the equipment is dormant, the sodium will freeze and deposit in the condenser section. Few studies focused on this issue, however, the phase transition process inside the heat pipe and the recovery of heat transfer performance were not clarified. In this paper, the mass migration is studied experimentally and numerically. It is found that the frozen front position is not fixed, but related to the experimental condition. The temperature difference can reach 430 °C when sodium is freezing, and the heat pipe completely loses the isothermal property. The simulations refer to the experimental conditions. It is also shown that the ratio of output power to input power influence the freezing patterns. The freezing happens at multiple areas, and they finally merge into a complete frozen area. As it fully blocks the wick and diffuses into the vapor chamber, the deposition presents a fingering-like distribution. The blockage in wick reduces the effective condenser working length, leading to the deterioration of heat transfer performance. This work lays a foundation for the prediction of liquid metal migration and the development of corresponding elimination strategies for heat pipe.