Recalescence characteristics of supercooled sessile water droplets under shear airflow

Icing phenomenon of supercooled sessile water droplets under shear airflow is common, with the recalescence stage playing a significant role in the overall icing process. However, existing studies have mainly focused on the recalescence characteristics of supercooled sessile droplets under natural convection, while the recalescence stage under airflow conditions has received limited attention. In this study, experiments are conducted to investigate the recalescence behavior of supercooled sessile water droplets under shear airflow. The effects of airflow parameters and droplet characteristics on the recalescence stage are systematically analyzed. Experimental results show that, after the onset of recalescence, the primary dendrite grows preferentially and stops when reaching the droplet edge, while the secondary dendrites continue extending. Using the moment when the primary dendrite reaches the droplet edge as a boundary, the recalescence process can be divided into two stages. Stage I is mainly influenced by the degree of supercooling; the greater the supercooling, the faster the dendritic growth and the shorter the duration. Stage II is primarily influenced by dendritic growth spacing, which increases with higher airflow velocity, elevated airflow and surface temperatures, and larger droplet volume, thereby prolonging the duration of stage II. Based on these findings, a theoretical prediction model for dendritic growth velocity and a correlation for recalescence duration are developed using crystallization kinetics, exhibiting prediction deviations of below 20% for dendritic growth velocity and below 25% for recalescence duration. Additionally, the influences of various factors on dendritic growth spacing are qualitatively revealed.