Formation of droplets of yield stress non-Newtonian fluids at T-junctions within parallelized microchannels

The effects of yield stress on the flow pattern, and the breakup mechanism, formation frequency and size of droplets at T-junctions within symmetrical parallelized microchannels are investigated experimen-tally. Carbopol gel and cyclohexane with 5 wt% span 20 are used as dispersed and continuous phases, respectively. Three flow patterns are observed, including parallel flow, jetting flow-elongated droplets, and dripping flow-slug/cloud droplets. Based on the yield stress characteristics, the breakup dynamics of the liquid-liquid interface during droplet formation under different flow patterns, flow rates and Carbopol concentrations are studied. The results reveal that the yield stress would enlarge the thickness of liquid film, weaken the squeezing force of the continuous phase and enhance the resistance of the dis-persed phase, which greatly slow down the droplet formation. Finally, the stable and uniform operating ranges of liquid-liquid two-phase flow in yield stress non-Newtonian fluids are obtained, and the semi -empirical formulas for droplet size prediction are established. (c) 2023 Elsevier Ltd. All rights reserved.