Freezing dynamics of supercooled micro-sized water droplets

Abstract

The freezing of mini-sized supercooled water droplet includes two successive stages, rapid porous dendritic ice formation in recalescence stage and gradual ice growth in solidification stage. However, the freezing of supercooled micro-sized water droplet is significantly different and remains ambiguous. By implementing crystallization kinetics into heat and mass transfer analysis in the present study, a 3-dimensional numerical model is built to depict the fast freezing dynamics of micro-sized water droplets with diameters of 10 and 1 μm. The temporal evolutions of temperature and solid mass fraction during freezing process are elaborated, revealing two specific freezing patterns of the micro-sized droplets. For the water droplet with d = 10 μm, the propagation of porous ice decelerates due to strong heat conduction within the droplet. While for the water droplet with d = 1 μm, the cold energy is abundant for ice freezing due to strong heat exchange with external cold air stream, leading to the consecutive propagation of compact ice with solid mass fraction of 1.0. Furthermore, the influences of the location and number of the nucleation site on the freezing process are discussed. Limited by the external heat transfer, the freezing time is independent of the number of nucleation site for the water droplet with d = 10 μm. For the water droplet with d = 1 μm with abundant cold energy, multiple nucleation sites can accelerate the freezing of the droplet.