A study on the mechanism of water vapour condensation inhibition by nanostructures on the copper surface

Frost on the evaporator surface of an air source heat pump can seriously reduce the heat pump coefficient of the unit, and the surface nanostructure is the key to effectively inhibiting water vapour condensation in the early stages of frosting. In this paper, the wetting process of nanodroplets on square column type, prismatic cone type and prismatic platform nanostructures was studied by molecular dynamics, and the nucleation and growth process of water vapour on three nanostructures were analysed. It was found that the droplets in the prismatic cone structure were less likely to reach a stable wetting state than in the other two structures. For the condensation process of water vapour on the surface of the three nanostructures, water molecules are more distributed on the surface of the prismatic cone matrix with a smaller size, and less distributed on the surface of the square column matrix with a larger size. The order of the clusters starting to merge is square column matrix, prismatic platform matrix and prismatic cone matrix. The results showed that the stable coagulation rates are, in descending order, a square columnar matrix, a prismatic platform matrix and a prismatic cone matrix. With the increase in the height of the prismatic cone matrix surface structure, the condensation rate of water vapour accelerates, the droplet size increases, and the condensation nucleus decreases. These findings can provide microscopic and fundamental suggestions for surface structure design to inhibit the early frosting of water vapour in the air.