Coalescence characteristics of droplets dispersed in oil subjected to electric and centrifugal fields

The demulsification and dewatering process is an important link in the resource utilization of waste oil. Compared with a single method, a coupling device based on high-voltage electric and swirl centrifugal fields can better realize emulsion demulsification and dewatering. As the main factor affecting the separation performance of a coupling device, the droplet size distribution changes dynamically owing to droplet coalescence. However, the coalescence characteristics of droplets under double-field coupling are unclear. Therefore, a numerical model is established in this study by coupling the electric and flow fields governing equations, and the droplet population balance equation to imitate droplet coalescence and breakup. With the finite element method, the dynamic variation and coalescence characteristics of droplets under different double-field coupling conditions are analyzed. Results show that droplet size decreases as vorticity increases, and vorticity disturbance will cause droplet size distribution instability. Droplet size is inversely proportional to oil volume fraction under the same inlet conditions. When the inlet Reynolds numbers (Re) is less than 12940, the coalescence effect is the dominant factor, but when Re is 12940, the breakage effect is the dominant factor. The regions where the droplet coalescence effect are dominant mainly include the near-wall region of the coupling and small cone and underflow pipe sections. Furthermore, the degree of coalescence does not directly determine the grade efficiency.