An effective droplet sieving method by a trapezoidal stepped microchannel

The droplet sieving process in a trapezoidal stepped microchannel was visually investigated. The sieving mechanism of the small droplet and the moving trajectory of the main droplet were studied. Three flow patterns were found in the experiment: incomplete sieving, complete sieving and main droplet loss regimes. The results show that with the increase of continuous phase superficial velocity Ut, the flow pattern evolves from incomplete sieving to complete sieving and finally to the main droplet loss regimes. The continuous phase flow rate range for the complete sieving regime increases with the growth of main droplet size. Meanwhile, the influences of droplet size and flow rate of continuous phase on the sieving process were investigated. The sieving efficiency decreases with the increase of droplet size of small droplets, whereas it is almost unaffected by the main droplet size. Under the same continuous phase flow rate of regulating channel, the higher continuous phase flow rate of the main channel would lead to lower sieving efficiency.