Electrocoalescence Criterion of Conducting Droplets Suspended in a Viscous Fluid

Abstract

Coalescence of conducting droplets dispersed in an immiscible medium can be facilitated by an electric field. However, droplets recoil promptly after contact in sufficiently high electric fields if the cone angle between droplets exceeds a critical value. To elucidate the critical condition for droplet coalescence, the behavior of two suspended droplets after contact with a direct current electric field is studied. It is shown that the critical angle is determined not only by the droplet geometry but also conductivity, surfactant concentration, and size. As the droplet conductivity increases, more identical ions accumulate on the adjacent interfaces of two droplets due to the faster ionic migration, which results in Coulombic repulsion between droplets and a reduced critical angle. For surfactant-laden droplets, film drainage induces a surfactant concentration gradient on the leading edges of droplets, and then Marangoni stress is formed to reduce the critical angle. In the case of large droplets, the bridge transiently expands under the action of directional flow caused by further droplet deformation, but eventually breaks due to opposite electrostatic forces. Based on this finding, the electrocoalescence criterion can be determined and employed to facilitate droplet coalescence in various applications.

Charge-Transfer-Induced Noncoalescence and Chain Formation of Free Droplets under a Pulsed DC Electric Field

“…The radii of droplets gradually increase with time after experiencing continual coalescence. The critical electric field strength for droplet coalescence gradually decreases as the droplet radius increases . Therefore, when exceeding the critical electric field strength, large droplets no longer coalesce but form short droplet chains from the right electrode plate.…”

“…The critical electric field strength for droplet coalescence gradually decreases as the droplet radius increases. 39 Therefore, when exceeding the critical electric field strength, large droplets no longer coalesce but form short droplet chains from the right electrode plate. However, the short droplet chain is unstable and disintegrates after a while.…”

Electrocoagulation with AC Electrical Current at Low Voltage for Separation of Crude Glycerol from Biodiesel Product Mixture

“…After that glycerol molecules had moved closer and linked together. Finally, they had precipitated to the bottom [14][15][16]. Additionally, AC was applied to reduce corrosion of electrodes that can impact to efficiency loss of current transfer [17].…”

Non‐coalescence and chain formation of droplets under an alternating current electric field

“…Lu et al 16 found that the critical cone angle gradually increases and then remains at 27° as the viscosity of droplet increases. Luo et al 17 experimentally showed that the critical cone angle reduces with the increase in conductivity of droplets or concentration of surfactant. Nevertheless, a few scholars considered that the charge transfer is the fundamental mechanism of droplet non‐coalescence.…”