The emulsion flow in a parallel microchannel with converging-diverging branches, various channel constriction ratios, and variable throat lengths leads to a passive droplet sorting perspective, which is what we highlight here. Larger size droplets are shown to flow through the path of less resistance while smaller droplets travel in the other branch, depending on the difference in flow resistances that are caused by the geometric constrictions in the parallel branches. Our findings show that, when all other geometric and physical characteristics of the system are held constant, the constriction ratio, as opposed to the throat length variation, can be used to more efficiently modify droplet sorting performance. Additionally, it is discovered that lowering the emulsion flow rate and raising the dispersion phase viscosity enhances droplet separation.
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