Dynamic behavior and driving force model of droplet formation in a T-junction microchannel

The formation mechanism and breakup process of droplets in a T-junction microchannel are illustrated by analyzing the dynamic behavior and driving forces. The changes in the pressure in the microchannel during the four stages of droplet breakup and the effects of the capillary number are obtained. The driving force model of the droplet breakup is obtained by analyzing the magnitude and position of the forces acting on the emerging droplets. Furthermore, the governing equations of the droplet breakup and predictive equations for the equivalent length and generation frequency of the droplet are obtained. The influences of the capillary numbers of the continuous phase, the viscosity ratio, the flow ratio, and the channel size on the droplet generation parameters are analyzed. To verify the predictive formula of the equivalent length of a droplet, the effects of the capillary number and viscosity ratio on the droplet length and frequency are determined. The theoretical analysis and experimental results indicate that the droplet length is inversely proportional to the capillary number and directly proportional to the flow rate ratio and the viscosity ratio. The influence of the flow rate ratio is greater than that of the viscosity ratio. The wall affects the droplet formation and the shape of the droplets but does not affect the size of the droplets.