Dynamics of Frost Propagation on Breath Figures

We investigate the process of condensation frosting on flat surfaces using thermal imaging microscopy. This method is particularly well-suited to characterize the frosting of polydisperse assemblies of dew droplets, also called breath figures, that transform into ice droplets by the propagation of frost fronts. The front propagation speed is found to be a nonmonotonous function of the characteristic droplet size of the breath figure. In our experimental conditions, the propagation speed is maximum around 70 mu m s(-1) for a characteristic droplet radius of around 300 mu m. We mainly show that the frost propagation speed is governed by the competition between two characteristic time scales. The first one is the freezing time of individual droplets, and the other one is the formation time of interdroplet ice bridges that grow from frozen to liquid droplets. In addition, the experiments reveal that the mean ice bridge speed is constant regardless of the characteristic radius of the liquid droplets in the breath figure. A theoretical mean-field analysis without any adjustable parameters recovers all of the features of the front propagation observed in experiments.

Automated summary

In this study, the process of condensation frosting on flat surfaces was investigated using thermal imaging microscopy. The results showed that the propagation speed of frost fronts is affected by the characteristic droplet size of the breath figure and is governed by the competition between the freezing time of individual droplets and the formation time of interdroplet ice bridges. Additionally, it was found that the mean ice bridge speed remains constant regardless of the characteristic radius of the liquid droplets in the breath figure.