Deformation and break-up of aqueous drops in dielectric liquids in high electric fields

In the petroleum industries, high electric fields are used in the separatio n of aqueous drops from an oil phase. However, high electric fields can als o deform and break up the drops. Under a high uniform electric field, a dro p is usuary a prolate spheroid, but it can also be of different forms such as a lamella penetrating into the continuous phase, or a drop with a flat s urface on one side and a cone on the other side. The deformed drop shape de pends greatly on the electrical conductivity, viscosity, surface tension an d density of both liquid phases. Droplets can be produced from a prolate dr op head, while the tail has a lamella penetrating into the continuous phase . The onset of drop break-up occurs at an electric field strength of betwee n 300 and 350 kV/m, corresponding to an electric Weber number of between 0. 06 and 0.13. The current Weber number needs some modifications before it ca n be fully applied to characterise the onset of drop break-up. However, the form of the applied electric field is important. With pulsed de fields, dr op deformation and detachment rates are influenced by the field strength an d the pulsing frequency. (C) 2001 Elsevier Science B.V. Ail rights reserved .