Breakup Of Bubbles/Drops In Microfluidic Y-junctions

In recent years, with the rapid development of the micro-chemical technology,much attention has been devoted to the bubbles (drops)-based microfluidics, bubbles(drops) breakup has been a hot area of research. A high-speed camera was utilized toinvestigate experimentally flow patterns, breakup dynamics and distributions ofbubbles (drops) in microfluidic Y-junctions. The effects of two-phase flow rates, fluidproperties, and bifurcation angles on the bubbles (drops) breakup were alsoresearched.Three regimes of the bubble (drops) flow at the bifurcations were observed: thebreakup with permanent obstruction (B1); the breakup with gaps (B2) and thenon-breakup (NB). The transitions between different regimes were studied, and acorrelation to predict the transitions of bubbles (drops) breakup flow pattern wasdeveloped. The experimental results showed that: the breakup of bubbles (drops)depended on the initial length of bubbles (drops) and the capillary number. And thehigher were the viscosity of the continuous phase and the degree of asymmetry of thebifurcation angles, the higher was the capillary number of the bubbles (drops)breakup.Dynamics of bubbles (drops) breakup were investigated under different regimes.The breakup with permanent obstruction (B1) contained two stages: squeezing stageand rapid breakup stage. In squeezing stage, the breakup process was only controlledby the augmented pressure. The breakup time decreased with the increase of the flowrate of continous phase. In rapid breakup stage, the duration time was very short. Thestage was controlled by the neck shape of bubbles (drops), and was not affected by theflow rate and viscosity of continous phase. The breakup with gaps (B2) consisted ofthree stages: squeezing stage, squeezing-stretching stage and rapid breakup stage. Thesqueezing stage and the rapid breakup stage were similar to the stages of B1. Thesqueezing-stretching stage was controlled by the viscous force and inertia force,except for the augment pressure. The results showed that, with the increase ofcontinuous phase flow rate, continuous viscosity and the degree of asymmetry of thebifurcation angles, the breakup time decreased. The distribution laws of the bubbles (drops) breakup in Y-bifurcatingmicrochannels (30°,60°and30°,90°) were studied. The effects of flow rates of bothphases and physical properties of continuous fluids on distributions of breakingbubbles (drops) were investigated. The results showed that both breakup lengths ofdaughter bubbles (drops) increased with the flow rates of the dispersed phases, anddecreased with the increase of the continuous viscosities and flow rates. The degree ofasymmetrical breakup increased with the increase of the dispersed phases flow rate,and decreased with the increase of the flow rates and viscosities of the continuousphase.