Gouttelettes d'eau et champ électrique

Electrocoalescence is the phenomenon of merging droplets of conducting liquid, suspended in an insulating liquid (or in a gas), under the action of an electric field. This phenomenon is important for the petroleum industry as it is used to increase the size of water droplets suspended in crude oils and, therefore, to drastically reduce the time required to separate water and oil phases under the gravity effect. However, due to the chemical complexity of crude oils and to the numerous processes involved, the electrocoalescence phenomenon is far from being fully understood and the control and the increase of the electrocoalescers' efficiency has been a challenge over the past century. To overcome the complexity of a study on electrocoalescence, which requires multidisciplinary knowledge (chemistry, electrostatics and fluid mechanics), an ongoing collaboration between Norway and France has been launched in 2000. Our goal is to establish a criterion for coalescence of two water droplets in crude oil as a function of the different parameters involved: densities, viscosities, interfacial tension, flow velocity and shear, presence of particles and chemical species, etc. We focus particularly on the understanding of the interface disruption mechanism of two close droplets subjected to an electric field. The strength of our approach lies in the combined use of asymptotic analytical approaches, numerical simulations and experiments to perform quasi-steady and dynamic electrocoalescence.