Study On The Breakup Behavior Of Bubble/droplet In Microchannels With Different Configurations

Since the 21 st century,microfluidic technology has attracted increasing attention from academia and industry because of its advantages of good heat and mass transfer performance,high efficiency and controllability,and small sample volume.In this paper,a high-speed camera was used to investigate the bubble and droplet breakup behaviors in microchannels with different configurations.The breakup behaviors,dynamics and interfacial evolution for bubble breakup in shear-thinning non-Newtonian fluids in a symmetrical T-junction were investigated.The effects of liquid phase rheological property and two phases flow rates on the bubble breakup process were analyzed.According to the bubble breakup dynamics and interfacial phenomena,it could be found that the rheological property of the liquid affected significantly the breakup process of bubble.In terms of the evolution of the minimum width of the bubble neck with time,the bubble breakup process could be divided into three stages: squeezing,transition,and rapid pinch-off stage.For the transition and rapid pinch-off stage,the power-law exponent remains unchanged with the liquid phase flow rate,but rises with the increase of the concentrations of carboxymethyl cellulose sodium(CMC)solutions.The rapid pinch-off stage is jointly controlled by the viscous shear force and the interfacial tension.Shear-thinning nonNewtonian fluid mainly affects bubble breakup process by changing the viscous shear force.The breakup behaviors of droplets in the three-dimensional(3-D)pore-throat microchannel were investigated experimentally.The effects of the dispersed phase viscosity,two phases flow rates on the droplet breakup process were studied.Three flow patterns were observed when the droplets flowed out the pore-throat structure:spherical breakup,non-spherical breakup and non-breakup.The results showed that,when the flow rate of one phase was fixed,the size of the first daughter droplet decreased with the increase of the flow rate of the other phase.Except extremely low capillary number of the continuous phase,the increases of the viscosity of the dispersed phase or the flow rates of two phases were not conducive to the breakup of droplet.The breakup behavior of droplet in a multi-branch microchannel was studied.The effects of the initial length of the mother droplet and the capillary number on the breakup process and size of droplet were analyzed.The experimental results showed that the length of the daughter droplets in each branch channel increased with the length of the mother droplet.From first branch to fifth branch,the influencing degree of the mother droplet on the daughter droplet declined in sequence,and the length of the daughter droplets in fifth maintained nearly unchanged.Under the same length of the mother droplet,the length of the daughter droplets decreased with the increase of the capillary number,regardless of the uniform breakup or the non-uniform breakup.Furthermore,a prediction model of the daughter droplet size for each branch channel was proposed.The predicted values of the daughter droplets length are in good agreement with the experimental data.