Molecular dynamics study of the initial frosting phenomenon on cold surfaces from ordinary-low to cryogenic temperatures.

Frost formation is a prevalent phase transition phenomenon in both natural environments and industrial processes. Current research on frost formation mechanisms and processes has primarily focused on macroscopic scales. This macroscopic focus limits the ability to investigate thoroughly the nanoscale dynamic processes and underlying mechanisms, particularly the systematic evolution characteristics during initial frost formation under ordinary-low and cryogenic conditions. In this study, a physical model for the initial stage of frost formation on cryogenic surfaces was developed using molecular dynamics simulations, enabling nanoscale investigation of early-stage frost formation at low temperatures. The simulation results demonstrate that the frost morphology on copper surfaces varies with substrate temperature, consistent with experimental observations. By employing MATLAB for phase identification of water molecules, we found that the frost crystal structure transitions from dendritic to clustered morphology as the cold surface temperature decreases. This transition results in a nonmonotonic variation in frost coverage area: it decreases first, then increases, and subsequently decreases again. Furthermore, the frost formation completion time does not vary monotonically with decreasing cold surface temperature. Within the temperature range of -90 ◦C to -30 ◦C, the completion time decreases with temperature reduction; whereas between -130 ◦C and -90 ◦C, the formation time increases with further cooling. All these variations are significantly influenced by the evolving frost morphology patterns.