LAUSR

Collision of a droplet and a hydrophobic particle in mid-air was investigated. To study the impact outcomes, specifically the lamella formation, a numerical simulation tool was developed and verified with impact experiments (water droplets and glass particles, ρrel = 0.41). The velocity field within the lamella showed that the flow inside the liquid film moves in two opposite directions along the lamella axis of symmetry: one is generated through the momentum transfer from the particle, and the other is due to the droplet initial velocity. This causes the lamella to be stretched in the same direction as the particle moves and forms a rim at the end of the lamella. Although a larger droplet-to-particle diameter ratio (Dr) increased the impact duration, it did not change the collision outcomes and two opposite flows still exist inside a thicker liquid film. However, the liquid viscosity affects impact outcomes; as viscosity increased, a thicker film remained on the particle, the liquid film became shorter, and the lamella formation was hindered accordingly. The pressure of the ambient gas also affects the liquid film formation. Unlike the literature of the drop impact on a flat surface, our results indicate that by increasing the ambient pressure, the lamella formation will be suppressed (hence chance of splashing). The pressure gradient around the liquid film creates a downward force that hinders the stretching of the liquid film. The effect of the ambient pressure on lamella formation is only significant for relatively higher gas pressures (i.e., Pamb > 2 Patm).