Impact and freezing characteristics of deionized water droplets on cold curved surfaces

Abstract

Processes involving droplet impact and subsequent freezing occur widely in practical engineering applications. In the present study, a visualization experimental setup is utilized to investigate the effects of the impact of single millimeter-scale droplets on curved surfaces at room and low temperatures. The influences of the Weber number We, wall temperature, and wall wettability on the dynamics of droplet impact and the characteristics of ice formation are examined. The morphological evolution of droplet impact and the variations of the dimensionless spreading coefficient are analyzed. The results indicate that at high We (We = 277), droplets reach their maximum spread on cold walls in a shorter time than on room-temperature walls, and their peak spreading coefficient is smaller. Upon impact with a cold wall, droplets exhibit a spread–splatter behavior. Low temperatures suppress the oscillatory behavior of droplets on a curved wall. In the case of a hydrophilic wall surface, as the impact We increases from 42 to 277, the impact mode gradually transitions from spread–retract–freeze to spread–splatter–freeze. The maximum spreading coefficient first increases and then decreases with increasing impact We. At high We (We = 277), the wall wettability has a minimal effect on the dynamics of droplet impact and freezing, with a spread–splatter–freeze mode being exhibited for both hydrophobic and hydrophilic walls, and the final freezing morphology is similar.