Non‐coalescence behavior of neutral droplets suspended in oil under a direct current electric field

Abstract

The excessive electric field gives rise to droplet non-coalescence and droplet chains in the electric dehydrator, which severely deteriorates oil-water separation efficiency and even leads to short circuit. To reveal the underlying mechanism of droplet noncoalescence, dynamic behavior of two neutral droplets in silicone oil under a direct current electric field is investigated by using high-speed photography. The experimental results show that there exists a critical electric field strength above which two droplets will bounce off after the contact. The critical electric field strength of droplet non-coalescence is affected by the initial separation distance between droplets, the radius of droplet, and the surfactant concentration. Whether the non-coalescence behavior occurs in the electric field is determined by the competition of electric force and capillary force, which dominates the evolution of tiny connection channel.

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

“…The field of view in Figure 9h is darker than that in Figure 9g, which is caused by lowering the light intensity of LED light. The critical electric field strength for complete coalescence gradually reduces as the droplet radius increases 30 . As time goes by, the droplet radius gradually increases due to the droplet coalescence.…”

Behavior Evolution of Droplets Suspended in Castor Oil under Alternating Current Electric Field

“…Moreover, according to the dipole-induced-dipole theory, 11 the enhancement of electric field strength can increase the electrostatic force, which is conducive to the improvement of demulsification efficiency. However, Huang et al 12 discovered that when E reaches a particular value, the droplets could not coalesce after contact. Obviously, this behavior evolution of droplets after contact does not work for demulsification.…”

“…Therefore, it is necessary to reveal the mechanisms of droplet behavior evolution for the optimization of the electric demulsification process, and many researchers have conducted experimental and theoretical studies. 16−18 Huang et al 12 studied the effects of initial separation distance between droplets, droplet radius, and surfactant concentration on the critical coalescence electric field strength E c . It was shown that E c first declines and then maintains as the initial separation distance increases.…”

Deformation and breakup of water droplets containing polymer under a DC electric field

“…6,7 Especially for petrochemical industry, the high voltage electric field is widely used to demulsify the water-in-oil emulsion in the oil field and refinery. [8][9][10][11] Nevertheless, with the extensive application of polymer flooding technology, the emulsion contains a large number of polymer molecules, easily leading to a significant rise in the electric current and the collapse of electric field. 12,13 This will stop the electric dehydrator from working and deteriorate the oil-water separation efficiency, seriously restricting the development and application of electrostatic demulsification technology.…”

“…Examples of these include the droplet deformation and breakup in the thunderstorm, 1 electrostatic atomization, 2,3 electrospinning, 4 electrohydrodynamic inkjet printing, 5 and droplet manipulation in microfluidic and MEMS devices 6,7 . Especially for petrochemical industry, the high voltage electric field is widely used to demulsify the water‐in‐oil emulsion in the oil field and refinery 8–11 . Nevertheless, with the extensive application of polymer flooding technology, the emulsion contains a large number of polymer molecules, easily leading to a significant rise in the electric current and the collapse of electric field 12,13 .…”