Impact Dynamics of Water Droplets on Suspended Ultrathin Layers of Oil

The findings on droplet impact dynamics can help in determining careful applications of droplets such as spray cooling, oil spill control, emulsion formation, etc. The current study investigates water droplet impingement on a deep pool of water covered with a suspended ultrathin layer of silicone oil. Changing the size and velocity of the impacting droplets as well as the viscosity of the suspended oil layers affect the characteristics of the formed craters and follow-up jets. It was observed that when the viscosity of the oil layers decreased to a minimum of 1 cSt, the jet height and crater dimensions (width and depth) reached to their extreme values. The characteristic dimensions of craters and jets were the highest for droplet sizes of around 4.2 mm and release heights of 750 mm, which translates to We number of nearly 710. The impact dynamics were also characterized qualitatively through specifying the type of crown/crater formation, jet pinch-off modes, and the number of secondary droplets. It was seen that top pinch-off modes were likely to occur when large (4.2 mm in diameter) droplets impact 1 cSt oil layers released from a height of 750 mm (We ≈ 710, Re ≈ 15500). The impact dynamics of immiscible fluids could be used as a basis for understanding droplet interactions in applications such as water in oil emulsion formation.