Molecular Dynamics Study on Boiling Heat Transfer Characteristics of Liquid Sodium on Cross-groove Surfaces

Liquid sodium is widely used as a high-temperature heat transfer medium because of its high thermal conductivity, low viscosity, and wide liquid temperature range. Boiling heat transfer of liquid sodium plays an important role in ensuring efficient heat removal and operational safety in advanced energy systems. However, experimental investigation of microscopic boiling behavior is extremely difficult due to the chemical reactivity of liquid sodium and the harsh operating environment. Molecular dynamics simulation provides an effective approach for exploring boiling phenomena at the atomic scale. In this study, molecular dynamics simulations were conducted to investigate the effects of cross-groove nanostructures on the boiling heat transfer behavior of liquid sodium. Three types of solid surfaces were considered, including a smooth surface (T0) and two cross-groove surfaces (T1 and T2) with identical solid-liquid contact areas but different groove geometries. The simulations were performed using the LAMMPS software package. A gold substrate was employed as the heating wall, and liquid sodium was initially equilibrated before being heated to induce boiling. Periodic boundary conditions were applied in the lateral directions, while a reflective boundary condition was imposed in the normal direction. The boiling process was analyzed in terms of bubble nucleation behavior, boiling morphology evolution, system energy variation, heat flow rate response, and atomic potential energy distribution near the solid-liquid interface. The results show that, compared with the smooth surface, cross-groove surfaces exhibit an earlier onset of bubble nucleation. During the subsequent boiling development stage, the formation process of a continuous vapor film on cross-groove surfaces is relatively prolonged, whereas the smooth surface transitions more rapidly into film boiling. Quantitative analysis indicates that the T1 cross-groove structure maintains the highest average heat flow rate during the boiling process, reaching 3.78×10⁻⁷ W, which is higher than that of the smooth surface T0 (3.43×10⁻⁷ W). The T2 surface also shows improved heat transfer performance compared with T0, although its enhancement effect is less pronounced than that of T1. Analysis of atomic potential energy distributions reveals distinct differences in interfacial phase characteristics under different surface structures. For deeper cross-groove structures, the groove interior regions are predominantly occupied by the liquid phase during boiling, which is beneficial for maintaining energy exchange near the solid-liquid interface. At the molecular dynamics scale, this study elucidates the evolution characteristics of liquid sodium boiling heat transfer influenced by cross-groove nanostructures and provides theoretical support for the structural optimization of high-temperature liquid-metal heat transfer interfaces.