In the present work, the phenomenon of droplet formation by dripping at a micro T-junction in liquid-liquid mixing was studied experimentally. The drop formation process consisted of three stages: the X-Y growth, X growth, and the detachment stages. In the X-Y growth stage, the bulged part of the disperse phase grows both in X (parallel to the main channel) and Y (lateral to the main channel) directions. The X-Y growth stage is followed by the X growth stage where the bulged part grows only in the main channel direction. Subsequently, in the detachment stage, the drag force exerted by the continuous phase becomes larger than the surface tension force between the two phases and the bulged part is finally separated into a droplet with regular intervals through a rapid necking process. Droplet sizes were estimated from the drop generation frequency and the flow rate of the disperse phase, and were also confirmed by direct measurements through photography. The sizes of the micro droplets generally decrease with the larger flow rate of the continuous phase or with a smaller flow rate of the disperse phase. This is due to the increase of the interfacial shear force between the two phases through the increase in the relative velocity. The droplet size also decreases with increase of the viscosity of the either phase. This again is due to the increase of the interfacial shear force (and hence the drag force) between the phases when the viscosity of either phase becomes large. The measured drop sizes will serve as a set of the benchmarking data for the development of a droplet detachment model in the dripping mode at micro T-junctions.

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