Numerical Investigation of the Phase-Change Heat Transfer Mechanism in Sodium Heat Pipes

Alkali metal working fluids are extensively studied for their efficiency in high-temperature heat pipes, widely used in high-heat flux dissipation. This study used numerical simulations to analyze the phase-change heat transfer performance of high-temperature heat pipes with sodium. The variations in the phase-change heat transfer process and overall performance were investigated under different heating powers, filling ratios, inclination angles, and contact angles. Key aspects, such as the distribution of gas-liquid phases, wall temperature fluctuations, and overall thermal resistance, were also studied. Comparing the simulation results with published experimental data revealed a maximum relative error of 2.7% for heat resistance, indicating the high accuracy of the method. The computational results of this study indicated that the overall thermal resistance decreased with increasing heating power. Concerning the filling ratio, both excessively low and high values hinder optimal heat transfer. The minimum heat resistance was achieved with a filling ratio of 30% and an inclination angle of 90°. A hydrophilic evaporator surface promoted easier bubble detachment, enhancing heat transfer efficiency. This study provides detailed thermal characteristics of high-temperature alkali metal heat pipes, providing theoretical support for future high-temperature thermal engineering applications.