Insights into the breaking and dynamic mixing of microemulsion (W/O) in the T-junction microchannel

Abstract

In this paper we conduct a numerical simulation study of droplet generation and dynamic mixing in T-junction microchannels to investigate the effects of two-phase flow rate, viscosity of the dispersed phase and wall wettability on the mixing quality of droplets. It is found that both droplet size and contact length of droplets with the wall are key factors affecting mixing. The larger the droplet size, the worse the mixing effect, and the larger the contact length of droplets with the wall, the better the mixing effect. At the same time, the size of the droplet also constrains the contact length of droplets with the wall. The larger the size of the droplet, the greater the contact length of droplets with the wall, so that an equilibrium is reached, and when the size of the droplet is large enough, this equilibrium will be broken. As the viscosity of the dispersed phase increases, the internal circulation of the droplets becomes difficult and the droplets break up later, which reduces the mixing efficiency. As the contact angle increases, the inner wall of the channel becomes more hydrophobic and the viscous shear of the continuous phase dominates the mixing, changing the direction of the droplet's internal circulation. The precondition for the continuous phase viscous shear to dominate the mixing is that, there exists the velocity difference between the continuous phase fluid and the droplet, and there will be no good mixing effect otherwise. The droplets with good mixing quality should meet the following conditions: reduce the viscosity of the dispersed phase, prepare droplets with smaller size, make the droplets contact with the wall as much as possible, and let the viscous shear of the wall dominate the mixing.