Liquid metal heat pipes serve as critical thermal conductivity components in spacecraft, exhibiting excellent heat transfer and isothermal performance. However, during actual space exploration missions, sodium heat pipes may operate under conditions significantly lower than the design specifications. Such conditions can lead to liquid freezing and deposition in the condenser section, causing the working fluid to migrate toward this region.

This study aims to investigate the impact of mass migration on the operational characteristics of sodium heat pipes through experimental analysis and numerical simulations.

The sodium heat pipe with wire mesh liquid absorbing core was taken as the research object, and computational fluid dynamics (CFD) method was applied to numerical simulation of the flow field and phase change flow process inside a sodium heat pipe. Meanwhile, experiments were conducted on a full-scale (1:1) sodium heat pipe test bench, and electromagnetic coils were employed for heating whilst a water-cooled casing facilitated heat dissipation was enabling power balance adjustment. Then, the volume of fluid (VOF)-Lee-solidification-melting model was utilized to simulate the vapor-liquid-solid phase transition flow process by incorporating the capillary force of the wick via User-Defined Functions (UDF).

The experiment and simulation results indicate a heat transfer hysteresis effect during the re-start process following mass migration, leading to delayed heat dissipation and compromising the stability and reliability of system operation. The wick at the site of frozen deposition becomes obstructed by solidified material, rendering it incapable of participating in the condensation and heat dissipation processes. Consequently, the effective heat dissipation length is substantially reduced, ultimately resulting in complete failure.

Results of this study demonstrate that mass migration adversely affects the thermal conductivity and isothermal properties of the heat pipe, thereby influencing the thermal stability of the overall system.