Atomistic Description of Interdroplet Ice-Bridge Formation during Condensation Frosting

The propagation of frost in an assembly of supercooled dew droplets takes place by the formation of ice protrusions that bridge ice particles and still-liquid droplets. In this work, we develop a Kinetic Monte Carlo (KMC) model to study the formation kinetics of the ice protrusions. The KMC simulations reproduce well the experimental results reported in the literature. The elongation speed of the ice protrusions does not depend on the droplet size but increases when the interdroplet distance decreases, the temperature increases, or the substrate wettability increases. While 2D diffusion of the water molecules on the substrate surface is sufficient to explain the process kinetics, high 3D (vapor) water-molecule concentration can lead to the development of 3D lateral branches on the ice protrusions. A 1D analytical model based on the water-molecule concentration gradient between a droplet and a nearby ice particle reproduces well the simulation results and highlights the relation between the protrusion elongation kinetics and parameters like the interdroplet distance, the water diffusivity, and the concentration gradient. The bridge-formation time has a quadratic dependence on the droplet-ice distance. Comparing the simulations, the analytical model, and the experimental results of the literature, we conclude that the propagation of frost on a flat substrate in an assembly of supercooled dew droplets with interdroplet spacing larger than about 1 mu m is limited by water-molecule diffusivity.

Automated summary

The propagation of frost in supercooled dew droplets occurs through the formation of ice protrusions that bridge ice particles and still-liquid droplets. A Kinetic Monte Carlo (KMC) model is developed to study the formation kinetics of these ice protrusions. The KMC simulations accurately reproduce the experimental results reported in the literature. The elongation speed of the ice protrusions is not affected by the droplet size but increases with a decrease in interdroplet distance, an increase in temperature, or an increase in substrate wettability.