Modelling and experimental investigation of the shape change of a sessile water droplet during freezing

Water droplet freezing process is studied theoretically and experimentally. A theoretical model is developed to simulate the freezing of water droplet on a cold surface, it considers the effects of both supercooling and gravity and assumes that the freezing front (ice-water interface) has a shape of spherical crown. Experiments are conducted on a 20μL water droplet deposited on a cold aluminum plate, and the droplet freezing behaviors including the triple-phase contact line (freezing front at tri-junction) movement and droplet profile evolution are observed and analyzed using the image recognition technology. Two correlations that describe the evolution of the height of three-phase line and that of the contact angle of ice-water mixture on ice are developed by combining the theory and experiment and are added to the model to make it close. The water droplet freezing process is simulated and the freezing characteristics including the droplet profile and the contact angle of ice-water mixture on ice are obtained. The final droplet freezing profile as well as the freezing time calculated by the model are compared with the experimental results and a reasonable agreement is achieved.