Molecular dynamics simulation of water vapor condensation on nanostructured surfaces

The frosting of the air source heat pump evaporator reduces the system heating efficiency. Compared to active defrosting, utilizing passive methods such as superhydrophobic surfaces to inhibit defrosting can effectively reduce power consumption. In this paper, the condensation nucleation of water vapor on the copper surface with nanostructures was simulated by molecular dynamics. The effect of solid-liquid interaction strength on the nucleation characteristics at the early stage of frost formation was analyzed. The results show that as solid-liquid interaction strength increases, the condensate droplets evolve from Cassie to Wenzel state, which promotes the frosting process of the droplets. The process of Wenzel state droplets merging to form the Cassie state was found due to the combination of surface free energy and nanostructure. The transition mechanism of the droplet wetting state is revealed through the distribution of potential energy on the nanostructure surface. The area and value of the low potential energy region near the nanostructure surface increases with the solid-liquid interaction strength, which enhances the attraction of the surface to water molecules.