Numerical Study on the Liquid-Liquid Interface Evolution during Droplet Coalescence

The liquid-liquid interface evolution characteristic during droplets coalescence in the surrounding liquid is numerically studied taking no account of the influence of the gravity. The influences of viscosity ratio of internal and external fluids as well as the relative size and Oh number of the droplets on the coalescence process are analyzed. The results show that, three coalescence types are indicated in this numerical study. With the decrease of viscosity ratio and Oh, the droplet coalescence type transforms from coalescence with no pinch-off to coalescence with pinch-off. As the radius radio of the larger and smaller droplets decreases, the coalescence type transforms from “coalescence with single pinch-off” to “coalescence with double pinch-offs” or “coalescence with no pinch-off”. The liquid bridge radius increases slower under the less viscosity ratio and larger Oh due to the greater viscous resistance during coalescence process. The dimensionless pinch-off time of the neck decreases with the increase of the viscosity ratio and radius radio, and the decrease of Oh. And when viscosity ratio is greater than 10 and Oh is less than 0.01, the dimensionless pinch-off time changes little.