Experimental investigation of droplet impact on dry surface in a variable ambient pressure environment.

In this study, the effects of the ambient pressure on the dynamics of the impact of a Newtonian droplet on a dry surface are investigated using high-speed photography. Video acquisition of droplet impact was performed at 20,000 frames per second in a transparent chamber pressurized up to 4 atm using water droplets with a 3 mm diameter at an impact velocity of approx. 3 m/s.

Previous studies demonstrate that reducing the ambient pressure can suppress splash on a dry surface due to the lack of entrapment of the ambient gas between the droplet and the surface. These studies implemented sub-atmospheric ambient pressures to reduce the trapped gas bubble and suppress the formation of the secondary droplet formation. The present study further examines the effect of changes in pressure on bubble entrapment on droplet impact by analyzing droplet impact on a dry surface in a super-atmospheric pressure environment.

The results show that, under the ambient pressure of 4 atm, small secondary droplets (~50 µm in diameter) were ejected during impact, while no secondary droplets were observed under the atmospheric ambient pressure. In the pressurized condition, the secondary droplets were ejected at approximately 0.25 µs after the droplet impact, well before the formation of the droplet corona.