A water-oil emulsion dynamics in an inhomogeneous high-frequency electric field

Abstract

The article presents the results of an experimental and numerical study of the behavior of a water-oil emulsion in an inhomogeneous electric field conducted to investigate the prospects of using the dielectrophoretic effect for the separation of liquid dispersed media. The problem is considered under conditions of neutral buoyancy of the dispersed phase, when the dynamics of droplet inclusions is determined solely by the action of the dielectrophoretic force. The inhomogeneous electric field was created by a system of coaxial cylindrical electrodes. The experiments were carried out in an alternating electric field with a frequency of 10 kHz, which made it possible to avoid the manifestation of electrophoretic and electrokinetic phenomena. We studied both the dynamics of individual droplets in an electric field and the change in the content of the dispersed phase at different moments of time. It was found that water droplets always move in the direction of the intensity gradient, eventually accumulating on the internal electrode. The time it takes a single drop to reach the inner electrode significantly depends on its size and the initial distance to the inner electrode, the magnitude of the effective voltage, and the permittivity of the dispersion medium. It is shown that when choosing the initial distance from the drop to the inner electrode and the total time of the drop movement as measurement units for the current distance and time, respectively, the results of all experiments form a single dependence in these dimensionless variables. It was found that the emulsion separation rate increases with an increase in the average droplet size, the effective voltage, the dielectric constant of the dispersion medium and the initial concentration of droplets. It is shown that in the latter case, the dependence is due to the presence of cases of droplet coalescence, the frequency of which increases with increasing concentration. The results obtained during numerical simulation are in good quantitative agreement with the experiment. In conclusion, the results of the laboratory and numerical experiments are compared, the advantages of the proposed method of electrodehydration in comparison with existing approaches are discussed.