Shape Variation of Sessile Water Droplet during Freezing

When a water droplet is deposited on a cold surface, it may freeze into a singular shape, which is studied theoretically and experimentally. A new dynamic curved interface model is developed to simulate the shape evolution of water droplet during freezing. The model considers the effects of supercooling and gravity, and assumes the freezing front as a spherical surface, it adopts the dynamic growth angle and perpendicular relationship at the triple-phase point. Experiments are conducted on 20 µL water droplets on a cold surface and the evolution of triple-phase point height is recorded to get a fitting correlation which relates such a height with time. Based on the correlation, the model is solved to obtain the water droplet shape evolution during freezing. The initial profile, recalescence profile, final freezing profile of the droplet as well as the total freezing time calculated by the model all agree well with the experimental results. The calculation results show that the freezing rates at different places of the freezing front interface are different, and the freezing rate decreases with increasing interface height.