Simulation research on the boiling heat transfer characteristics of liquid sodium under microgravity

With the advancement of space nuclear power technology, sodium-cooled fast reactors have become a promising energy solution for space systems. However, the heat transfer mechanism of liquid metal sodium boiling in microgravity is unclear, and there is a lack of effective methods to prevent heat transfer degradation. This study conducts a numerical investigation on liquid sodium flow boiling in space sodium-cooled fast reactors under microgravity using a two-fluid model. A comparative analysis of heat transfer performance between microgravity and normal gravity conditions is performed, and the effects of inlet velocity and subcooling degree on boiling behavior in vertical channels under microgravity are systematically examined. The results demonstrate that, compared to normal gravity, microgravity degrades the boiling heat transfer performance of liquid sodium, advances the boiling onset time, and increases susceptibility to heat transfer deterioration. Enhancing inlet velocity or subcooling significantly improves heat transfer under microgravity. Notably, no heat transfer deterioration occurs when the inlet velocity reaches 2.0 m·s^-1combined with an inlet subcooling of 300 K. This work elucidates the unique heat transfer characteristics of liquid sodium flow boiling under microgravity and provides critical theoretical insights for the safety design of the primary loop in space sodium-cooled fast reactors under microgravity environments.