Energy conservation during single droplet impact on deep liquid pool and jet formation

This paper investigates the impact of single droplets impinged into a deep liquid pool at atmospheric pressure. The single-droplet dynamics of three impinging liquid samples with different surface tensions, viscosities, and densities were experimentally investigated. The time evolution from droplet impingement on the pool surface to jet formation was recorded by a high-speed video camera. The impact velocity and droplet diameter were varied as 1.0–3.2 m/s and 1.8–3.0 mm respectively, and the liquid-pool depth was fixed at 30 mm. The cavity volume was affected by the impact parameters, indicating a clear correlation between drop diameter and impact velocity. For the water droplets, the jet volume was decreased and increased under lower and higher impact velocity conditions, respectively. For ethanol droplets, the jet volume increased at higher impact velocity and larger droplet diameter. To gain deeper physical insight into the jet formation, the energy balance of droplet impingement onto the liquid pool surface was estimated. Approximately 28% of the impact energy was invested in cavity formation, regardless of the liquid properties. The remaining energy was most likely dissipated or consumed at the surface. All of the cavity energy in all samples was consumed in jet formation.