Drop coalescence through planar surfaces

A high-speed digital camera is used to investigate the important parameters of drop coalescence at a planar interface. A series of experiments have been performed to observe coalescing drops at the interface between two immiscible fluids. A variety of fluids have been used to fully investigate the effects of physical properties of fluids involved in this phenomenon. It has been shown that the important dimensionless parameter in this process is the Ohnesorge number, Oh=μ∕ρRσ, which dictates the regime of coalescence. We have also shown that for Oh>1, drops fully coalesce but when Oh<1, drops partially coalesce and a secondary drop is created. We show the dependence of the ratio of secondary drop radius to the primary drop on the regime of coalescence (inertia or viscous). Using the scaling arguments, we developed a relationship between the drop ratio and the Ohnesorge number that shows good agreement with our experimental results.