Molecular dynamics simulation of the evaporation of liquid sodium film in the presence of non-condensable gas

•The evaporation of thin liquid sodium film inside high-temperature sodium heat pipe is first investigated by the molecular dynamics method. The Ar is added into the system to study the NCG’s (Non-Condensable Gas) evaporation.•Equilibrium simulation and the non-equilibrium simulation are achieved. The MAC (Mass Accommodation Coefficient), the net mass flux, the heat transfer coefficient at the liquid–gas interface are acquired. The NCG’s effects on evaporation are discussed.•This work can provide a reference for the optimal design and numerical simulation of high-temperature the sodium heat pipe. Understanding the evaporation of the thin liquid sodium film is important for deeply studying the heat transfer inside sodium heat pipe. In the present work, molecular dynamics is employed to investigate the evaporation of the thin liquid sodium film. The simulation system is a cuboid and consists of an upper gold wall and a bottom one. The sodium fluid exists between the walls. For studying the Non-Condensable Gas’s (NCG) effect on the evaporation, the Ar is added into the evaporation system. Based on the startup and normal operation of the sodium heat pipe, eight different cases are studied. The equilibrium simulation is achieved by setting the same temperature of the solid walls. The Mass Accommodation Coefficients (MACs) of eight cases are acquired. By setting the walls at different temperatures, the non-equilibrium is built. The evolution of the evaporating liquid film is observed. The net evaporation flux (Jnet), the heat transfer coefficient (h) at the liquid–gas interface are obtained. It is found that the NCG’s effects on the Jnet are achieved through its influence on the MAC. When the variation of the MAC is above 27%, NCG’s effects on the Jnet are more obvious. In 600–700 K, 840–1020 K, the NCG suppresses the evaporation heat transfer and the maximum decrement is 150–200 kW∙m−2∙K−1. Whereas in 690–810 K, the NCG has an enhancement effect and the growing magnitude is 15–40 kW∙m−2∙K−1. This study could provide the mechanism supplement and extension for the macroscopic investigation of the sodium heat pipe.