Role of shear airflow in the icing of sessile water droplets

Icing of sessile water droplets under shear airflow on low-temperature surfaces is widespread in nature and engineering fields, and understanding its characteristics holds scientific and engineering importances. In this work, visual experiments on droplet icing under shear airflow are conducted to systematically investigate the effects of airflow velocity, surface temperature, and droplet volume. The results show that the room-temperature shear airflow generally slows down the freezing stage with the movement rate of the ice-water interface on the windward side lower than that on the leeward side. The distinct movement rate results in an inclined ice-water interface and a deflected freezing tip. An increase in the airflow velocity prolongs the freezing time of droplets and enlarges the deflection angle of the freezing tip, and these trends become more pronounced at a higher surface temperature and with a larger droplet volume. Based on the heat transfer analysis, a theoretical model is proposed to predict the freezing time and the deflection angle of the freezing tip. The inverse of the freezing time, normalized by the thermal diffusion time, is scaled as the product of the Stefan number and the 0.6 power of Reynolds number. Additionally, the sine of the freezing tip's deflection angle is directly proportional to the Nusselt number. The findings provide insights into the physical mechanisms of droplet icing under shear airflow and may improve the prediction accuracy of frosting and icing.