Effect of Weber number and impact angle on solidification behaviour of a molten droplet on an inclined surface

• Oxidised molten droplet-solid surface interactions studied for Weber numbers < 150 and impact angle 45° ≤ φ ≤ 90°. • Maximum droplet spread increased with Weber number but decreased with impact angle. • A power law correlation obtained to quantify droplet spreading time with Weber number. • A kinetic model derived to determine the transient droplet spreading rate accounting for the effect of impact angle. • Two regime maps developed showing unsolidified mass and the dominant mode of spreading. Molten droplet impingement on an inclined surface and subsequent solidification occurs widely in various industrial applications. While the interaction behaviour of a molten droplet on a solid flat surface is well understood, understanding the interaction and subsequent solidification behaviour on an inclined surface is very limited. In the present study, high-speed imaging was used to determine interaction dynamics and solidification behaviour of a molten droplet of three different compositions onto an inclined solid surface over a range of normal Weber number ( We n < 135) and impact angle (ϕ ≥ 45°). Five major interaction outcomes − (1) rebound, (2) disintegration, (3) partial rebound, (4) rivulet, and (5) combined effect of spreading and detachment were observed. Upon impingement, each droplet deforms asymmetrically on an inclined surface. The maximum spread ratio was shown to increase with the increase in normal Weber number and decrease with the decrease in impact angle. The spreading time was found to follow a power law form. It was found that at higher impact angles, the entire mass of the initial droplet solidified on the surface, whereas at lower impact angles only a portion of the droplet mass solidified. The solidification time of the impinged droplet was highly dependent on the amount of droplet mass that remained on the surface. A recovery type exponential profile was used to describe the droplet spreading kinetics. Finally, two regime maps were developed based on the Weber number and impact angle.