Numerical simulation of high inertial liquid-in-gas droplet in a T-junction microchannel

Abstract

Aqueous microdroplet generation involving high inertial air flow inside a T-junction microchannel was studied numerically. The volume of fluid method was employed to track the interface between two immiscible fluids: water and air. The effects of high inertial air flow on the water droplet generation were investigated. At various Re and Ca numbers, unique flow regime mapping including squeezing, dripping, jetting, unstable dripping, and unstable jetting and their transitions were determined. Unstable dripping and unstable jetting flow regimes are new regimes which have not been previously reported in the liquid–liquid system. The flow structure in these two flow regimes is affected by the high inertial nature of the continuous phase which is negligible in the conventional liquid–liquid system. It was found that the stable aqueous droplets are generated in the squeezing and dripping flow regimes. On the other hand, the unstable dripping flow regime is unable to sustain spherical droplets as they travel downstream. In the unstable jetting flow regime, a stream of water is fragmented into multi-satellite droplets and threads of different sizes as it moves downstream. The behavior of the unstable jetting flow regime cannot be characterized due to the effect of high inertial air flow on the water stream. The results show that droplet size increases as Ca and Re numbers increase and decrease, respectively. As both Ca and Re numbers increase, droplet generation frequency increases, reaching its maximum at 223 Hz. Finally, the effect of different contact angles at 120–180° on droplet size, detachment time, and droplet generation frequency was investigated. The results of this research provide valuable insight into the understanding of high throughput oil-free aqueous droplet generation within a gas flow.