Micro-droplet Formation Mechanism And Two-phase Flow Characteristics At Microfluidic Y-junctions

Micro-droplet generated by the Microfluidic system has unique characteristics offluid mechanics and scale effect, which is more widely used in biomedical, aerospacethermal control, energy and chemical fields, and becomes an international researchhotspot in various related disciplines. The flow fields of the two-phase junction arechanged with the differed geometry structure and size of microchannel, so that thesize and uniformity of the micro-droplets are controlled. Therefore variousapplications of microfluidic system can be achieved according to the changedmicrochannel geometry. The superiority making use of this geometric configurationsof microchannel in microfluidic applications is gradually shown owing to themicro-droplets produced by Y-junctions microchannel are smaller and more stable.Currently the factors which influence the two-phase flow within Y-junctionsmicrochannel still need to be further researched to have an extensive applicationvalue.The formation mechanisms of micro-droplets and the two phase interfacemorphology characteristics in Y-junctions microchannel are studied by experimentand numerical simulation.(1) Numerical simulation and experimental study on droplet breakupcharacteristics in Y-junctions microchannel. Differed flow patterns characteristicswithin the droplets rupture process in Y-junctions microchannel are studied bychanging the Y-angle of Y-junctions microchannel, two-phase liquid properties andother parameters. It is shown that droplets start to generate at the junction of the twophases liquid in Y-junctions microchannel with the increasing capillary number of thecontinuous phase. The formation of the droplets will undergo the squeezing, transientand dripping mechanism. Various flow patterns can be obtained corresponding to thediffered droplet formation mechanism. However, the position of droplets breakup willvary with the Y-angle changes, and the position is further away from the intersectionof the two phases with the decreasing of the Y-angle and the flow flux of continuousphase. The droplets will more stable and lead to produce accompanying dropletsdifficultly when Y-angle is maintained between90~135.(2) Numerical simulation and experimental study on two-phase flowcharacteristics in Y-junctions microchannel. Different droplets generate mechanisms and two-phase flow characteristics are studied in various Y-angle of Y-junctionsmicrochannel by using of high-speed digital microscope system and Micro-PIV. It isobtained that the shearing action on dispersed phase will increase with the decreasesof Y-angle under the squeezing mechanism. The velocities profiles for continuousphase in main channel present asymmetric parabolic distribution with dropletsgeneration process, and droplets rupture process accompanied by cyclical internalpressure changes in the two-phase liquid. Droplets generation cycle is influenced bytwo-phase liquid capillary number, Y-angle and wettability between dispersed liquidand channel wall. The droplet size associates with two-phase capillary number, andget its largest value when Y-angle being180.(3) Numerical simulation and experimental study on droplets generation indiffered geometry of Y-junctions microchannel. Effects of geometrical factors ondroplet size and formation cycle are studied by changing Y-angle and aspect ratio ofY-junctions and anti-Y-junctions microchannel. It is given that smaller size andshorter generation cycle of droplets can be generated by anti-Y-junctionsmicrochannel. But as long as the absolute value of the angle of intersection oftwo-phase liquid is decreased, the droplets size and generating cycle can also reducedno matter in Y-junctions or anti-Y-junctions microchannel. However, the influence ofY-angle on droplet size and generating cycle will vary with the channel depthchanges.