Coalescence of charged droplets in outer fluids.

A controlled technique to produce a precise volume of fluid species, such as water droplets, has critical importance in a variety of industrial applications. Electric field provided a well-established method to produce charged water droplets with a controlled volume. The coalescence of produced charged water droplets, however, impedes the efficiency of electric field-assisted methods. Whereas the coalescence of stationary single droplets, often charged, is overwhelmingly studied in air or vacuum, the effects of surrounding medium and approaching velocity are neglected. Systematic series of experiments and simulations were designed to address the effect of viscosity as well as approaching velocity on the coalescence of charged water droplets in viscous surrounding mediums (μ = 100 & 1000 cSt). Results suggested that increasing the electrical conductivity of water droplets with lower approaching velocity diminishes the chance of coalescence between water droplets. The higher viscosity of surrounding medium resulted in a lower chance of coalescence between water droplets while droplets with stronger electrical conductivities underwent a lower deformation inside the dielectric medium. Finally, results suggested that water chain formation, which is reportedly a main retarding factor in electrocoalescers, took place for droplets with intermediate sizes in higher viscosities of surrounding medium.