Dynamics Of Bubble Breakup In Microchannels

Micro-chemical engineering and technology is one of the frontiers in modern chemical engineering.The breakup dynamics of droplets and bubbles in microchannels are the basis of the multiphase process in parallelized microchannels during the numbering-up.The progress in dynamics of bubble and droplet breakup in microchannels will be summarized from the aspects of flow transition conditions for breakup,interfacial dynamics and size manipulation.The rupture behavior and influencing factors of bubbles and droplets in symmetrical microchannels,asymmetrical microchannels,microfluidic device with multi-level branching channels,bypass microchannels and microchannel with obstructed structure are discussed.The shortcomings of the related researches on bubble and droplet breakup behavior at microscale are pointed out.The dynamics of bubble rupture in Y type microchannels,T type microchannels and multistage T type microchannels are explored.The dynamics of partially obstructed breakup of bubbles in microfluidic Y-junctions were observed and investigated by a high-speed camera.The combination of dimensionless power-law and geometric model was applied to study the effects of capillary number,bubble length and channel angle on the bubble rupture process.In the squeezing process,the gas-liquid interface curve follows the parabolic model.For the evolution of the bubble neck during breakup,the increase of the bubble length,the channel angle and the capillary number leads to the decrease of the focus distanceα.The chord m increases with the increase of the capillary number and the decrease of the bubble length,and it would reach the maximum value when the channel angle is 90degree.In the fast pinch-off stage during bubble breakup,the bubble’s neck curve no longer conforms to the parabolic model,so the focus and chord no longer exist.For the evolution of the bubble head during breakup,the value ofγis approaching to 1 with the increase of the capillary number and the bubble length,and with the close of the channel angle to 90 degree.It is found that the quadrilateral model can be applied for the partially obstructed rupture of bubbles in the symmetrical microfluidic Y-junction.The dynamics of bubble rupture in a T type microchannels were observed and investigated by a high-speed camera.The dynamics of bubble neck includes squeezing process and the fast pinch-off stage.In the squeezing process,it was found that the values ofα₁ andα₂ in the power law were influenced by viscous force.The values of m₁ and m₂ are only related to the capillary number.They are negatively correlated with the capillary number.In the fast pinch-off stage,the change of the neck width of bubbles is affected by the surface tension.When the width of the bubble neck gradually decreases,the bubble will breakup and generate two daughter bubbles.The bubble breakup and distribution in a multistage T type microchannels were observed and investigated by a high-speed camera.When the operating conditions are changed,the initial bubble length will be changed.But the minimum daughter bubble length will not change.The resistance caused by the disturbance at the junction will cause a slight decrease in the length of bubbles in motion.The resistance due to disturbance is related to the configuration of microchannels.When microchannels have the convergence structure at the outlet,the disturbance caused by bubble coalescence and collision is greater.When the microchannel only has a cavity structure,fewer bubbles will collide and coalesce,and the disturbance will be smaller.