Impact dynamics and solidification behaviour of a molten droplet on a flat surface at different Weber numbers

Molten metal droplet impingement and subsequent solidification phenomena in both inert and non-inert gas environment exist widely in various industrial applications. Exposing a molten droplet to air allows to form an oxide layer on the droplet surface which greatly influences the thermophysical properties of the droplet. While previous studies demonstrated the influence of oxide layer on the spreading dynamics, understanding of the impact dynamics is still missing when solidification is involved. To address this issue, in the present study, high-speed imaging was used to determine the interaction dynamics and solidification behaviour of a molten droplet of three different compositions onto a solid surface over a range of Weber numbers (We<150) in an open atmosphere. Two distinct outcomes were noted – (1) rebound and (2) disintegration demarcated by a critical Weber number. Upon impingement, each droplet exhibited periodic spreading and recoiling behaviour which was subsequently dampened by the simultaneous solidification process. The maximum droplet spread area and droplet spreading time were shown to increase and decrease with Weber number, respectively following a power law form. It was shown that in all cases, oscillation and solidification time decreased with Weber number. Finally, a recovery type exponential profile was utilised to describe the droplet spreading kinetics.