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.
The current work attempts to explore the role of DC electric fields on neutrally charged coalescing conductive droplets. The droplet is isolated inside of silicone oil and allowed to coalesce into a planar bulk of its own fluid under the influence of the electric field. The effect of this additional field in conjunction with the effects of other physical properties of the liquids including viscosity and interfacial tension are studied with the use of a digital high-speed camera. By scaling the electric field appropriately, distinct regions of behavior are defined in which electrically induced partial coalescence occurs within a viscous environment. Furthermore, it is shown that droplet size and field strength will determine if the processes of coalescence leads to either jet formation or Taylor cone formation on the planar interface for sufficiently strong electric fields.
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