Experimental and simulation study of flow patterns in the combined flow focusing and T-junction device

This paper presents a study of droplets generation, particularly examining different regimes or patterns of the flow by a novel device that combines two principles for droplets generation (flow focusing and T-junction (FF-TJ)) under different flow conditions, named combined FF-TJ. The study involves both experiment and simulation. From the experiment mineral oil and distilled water, three regimes (namely continuous regime, jetting regime, and squeezing regime) were found. This finding was subsequently confirmed by the simulation, which thus also gave a validation of the simulation system. The simulation was further employed to study the relationship among various parameters, including the velocities of the flows (i.e. sheath flow, middle flow, and crossflow) in the context the three regimes. We observed that the three regimes were determined by two critical values of the velocity of the middle flow, and . Interestingly, it was further found that the two critical values remained the same, independent of the velocity of the sheath flow. We further investigated the effects of the velocity ratio (the middle flow to the sheath flow, ) and the capillary number of the crossflow on the microsphere diameter. Overall, this paper presents a comprehensive study of the FF-TJ device and the associated implications for microsphere or droplet generation.