Electrostatic Coalescer uses electrical fields to induce droplet coalescence in water-in-crude-oil emulsions to increasing the droplet size.
The droplet diameter increase the settling speed and destabilizes the emulsion. The effects on the water droplet arise from the very different dielectric properties of the conductive water droplets dispersed in the insulating oil.
Water droplets have a permittivity that is much higher than the surrounding oil. Furthermore, water with dissolved salt is also a very good conductor.
When an uncharged droplet is subjected to an AC electric field the field will polarize the droplet creating an electric field around the droplet to counteract the external field.
As the water droplet is very conductive the induced charges will reside on the surface. The droplet has no net charge but one positive and one negative side.
Inside the droplet the electric field is zero. When two droplets with induced dipoles gets close to each other, they will experience a force pulling the droplets closer until they coalesce.