Impingement and freezing of two water droplets on an ice surface

In the present study, we report the detailed impact and freezing processes of two water droplets on an ice surface. The effects of the ice surface temperature, Weber number, and droplet time lag on the impact and freezing processes were experimentally investigated. The results showed that the time lag between the two water droplets played an important role on the formation and evolution of the central uprising sheet. As the increase of the droplet time lag, the increase rate of the spreading factor at the early stage of the droplet spreading process decreased. In addition, the droplet time lag was found to have apparent influence on the final ice bead morphology. Under the same Weber number and ice surface temperature conditions, the increase of the time lag could lead to the increase of the number of the fingering-like structures. Moreover, both droplet Weber number and ice surface temperature had apparent effects on the maximum radial distance of the primary ice beads. As the decrease of the ice surface temperature, the primary ice bead height increased apparently.