液滴撞击过冷壁面的结冰特性实验研究

To enrich the understanding of droplet spreading dynamics and the mechanism of freezing behavior, the role of surface temperature in influencing the droplet freezing process is investigated experimentally by a high-speed camera. The evolution of spreading diameter and the physical mechanism of different freezing patterns are analyzed. A hydrophilic silicon wafer and a relatively high impact velocity are chosen to enlarge the contact area between the droplet and substrate. Along with a high surface subcooling, the heat transfer rate through the droplet is enhanced. Upon increasing the surface subcooling, the maximum spreading diameter slightly decreases due to a relatively larger viscous dissipation. The effect of surface temperature on the spreading process is relatively smaller compared with the freezing process. The final freezing morphology is a central cap at a relatively high surface temperature, while a unique single-ring pattern is formed at a relatively low surface temperature. The formation of the single-ring icing is attributed to the ice nucleation at the central region induced by the enhanced heat transfer rate, resulting in an additional freezing front advancing both outwards and upwards during the freezing process. A freezing regime map described by the dimensionless heat conduction rate and Weber number indicating the conditions for the emergence of different ice profiles are proposed. This approach provides new insights for controlling ice profiles in droplet-based applications.