The formation of micro droplets involved a complex mechanism deriving from the competition between the interfacial tension, viscous shearing and other counterparts. In the present study, a volume-of-fluid (VOF) method within FLUENT software was used to study the droplet formation in a T-junction microchannel. By varying the velocity of continuous phase, we got droplet formation in “squeezing” process, and the shifting to “dripping” regime at a critical Capillary number. The pressure and velocity changing in both regimes were investigated in detail, supporting the result that the squeezing was dominated by the upstream pressure rising and the dripping was driven by shearing force. The numerical results hold a good agreement with the previously experimental measurements using confocal micro-PIV system. Furthermore, the motion inside an emerging droplet was also studied, showing intricate circulation flow.

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