Effect of dielectrophoresis on the coalescence of binary droplets under a non-uniform electric field.

• In previous works, the dielectrophoresis is thought to be advantage because it can pull the droplets towards the place of strongest electric field intensity. In this work, it has been shown that different types of dielectrophoresis have different effects on coalescence of binary droplets. • This work reveals that there exists a critical distance of coalescence for binary droplets under non-uniform electric field. Even, a stronger electric field intensity makes the coalescence of binary droplets more difficult. Electric field assisted coalescence has been widely applied to separate water from water/oil (W/O) emulsions in the petroleum industry because of its high efficiency and large throughput. Under a non-uniform electric field, the coalescence results from the combination of the dieilectrophoresis force and dipole–dipole attraction. In previous works, the non-uniform electric field was thought to be advantageous because the dielectrophoresis force pulls droplets to a certain place. However, it was shown in this work that different types of dielectrophoresis have different effects on coalescence. Positive dielectrophoresis had adverse effects on causing binary droplets to separate. However, negative dielectrophoresis had an advantageous effect. For positive dielectrophoresis, there is a critical distance of coalescence. The results showed that the critical distance decreases with an increase of the electric field intensity and continuous phase viscosity and also decreases with an increase of the diameter of the droplet in the lower position. Thus, a stronger electric field intensity and lower viscosity might be a disadvantage if the electric field is non-uniform. These conclusions are important supplements for the mechanism of non-uniform electric field assisted coalescence, which has significant guidance for the design of an electrocoalescer. [ABSTRACT FROM AUTHOR]