Taylor bubble splitting, flow and coalescence in branching microchannels: An experimental and numerical simulation study

Two novel branching microchannels were proposed for achieving efficient bubble splitting and precise control of their size. A combined numerical simulation and experimental approach was adopted to study the splitting behavior of mother bubbles and the hydrodynamic and coalescence properties of daughter bubbles in two branching microchannels. The research results indicate that the bubble-splitting process in channels BMC-2 and BMC-3 is the same, undergoing three stages: squeezing, neck break and pinching-off. The neck break stage in the BMC-3 channel significantly slows down due to changes in the stress point of the bubbles and the enhanced interfacial tension at the bubble tail. In the symmetrically splitting channel, the daughter bubbles exhibit a notable uniformity, characterized by a length deviation of less than 2.82%. A calculation method for predicting the volume of daughter bubbles in the BMC-3 channel has been developed based on the ideal bubble shape characteristics. The method's accuracy has been validated through experiments and numerical simulations with an error of less than 8.3%. Controlled non-uniform splitting of bubbles was achieved through the BMC-3 channel, and the correlation between the volume fraction of daughter bubbles (φd) in the BMC-3 channel and the Re number was determined. It was observed that φd-subII gradually decreases with increasing Re number and converges to 40%, whereas both φd-subI and φd-subII exhibit gradual increments and tend to approximate 30%. Void fraction significantly influences the velocity of daughter bubbles in the BMC-3 channel, but the bubble velocity in the subⅡ channel is always notably higher than the other two subchannels. The necessary conditions for preventing the coalescence of daughter bubbles in the branching channels were elucidated.