Molecular dynamics simulation of droplet nucleation and growth on a rough surface: revealing the microscopic mechanism of the flooding mode.

Droplet nucleation and growth have a significant influence on dropwise condensation heat transfer. Controlling the droplet nucleation and growth with a high-precision surface to realize the dropwise condensation heat transfer enhancement is a promising method. Molecular dynamics simulation is employed to investigate the effects of heat flux, surface wettability and adjacent droplet size on the new droplet's nucleation and growth. Simulation results indicate that the high heat flux can lead to droplet nucleation and growth inside the rough structure and finally a Wenzel droplet will form due to the coalescence between the inside droplet and the initial existing droplet. However, for a surface with a larger contact angle, the droplet in the Wenzel state will transfer to the Cassie state due to droplet coalescence. In addition, it is also related to the size of the existing droplet whether or not the nucleation process occurs. For the first time, the droplet nucleation radius is introduced to quantitatively determine the droplet nucleation state (inside or outside the nanostructures) and whether the droplet could achieve the state transition from Wenzel to Cassie or not in the growth process.