Study On Liquid-Liquid Two-phase Flow Characteristics And Breakup Behavior Of Y-shaped Microchannels

Since the introduction of microelectromechanical systems,natural science and engineering technology have begun to develop towards miniaturization,and the field of microfluidics has become a research hotspot.There is growing interest in both academic research and practical applications of microfluidics.Microfluidic systems are widely used in multiphase flow processes due to their many advantages,such as miniaturization,high mass and heat transfer performance,enhanced mixing,fast response,energy and raw material savings,greater stability and safety,and repeatability.Different microchemical fields have different requirements for droplet size,so the research on liquid-liquid two-phase flow focuses on the precise control and prediction of droplet size.The research on the characteristics of liquid-liquid two-phase flow and the influencing factors of droplet breaking behavior provides a basis for the design of microchannel reactors and the precise control of slug flow.In this paper,the characteristics of liquid-liquid two-phase flow in Y-shaped microchannels with different inlet angles are firstly studied by combining numerical simulation and experiment,and the effects of two-phase flow rate and inlet angle on droplet length are analyzed in detail.Then,the breakup characteristics of immiscible liquid-liquid two-phase fluids in symmetrical Y-shaped microchannels are studied by experimental methods.Both experiments used distilled water with a mass fraction of 0.5%SDS as the continuous phase and silicone oil as the dispersed phase.The physical parameters of the fluid in the simulation were the same as those of the experimental working fluid.In the experimental study of the liquid-liquid two-phase flow characteristics in the Yshaped microchannel,it is found that the main flow patterns observed are long slug flow and slug flow at the operating flow rate of this paper.The long slug flow and the slug flow have similar generation stages,namely the filling stage,the block stage and the shear stage successively.The change trend of droplet length at different inlet angles is firstly decreased slightly,then increased significantly,and finally decreased slightly.The generation time of droplets in the microchannels with different inlet angles is different.The droplets with inlet angles of 30° and 120° have similar and longer generation times,and the droplets with inlet angles of 60° have the shortest generation time,followed by those with 90°.The droplet length Ld decreases with the increase of the continuous phase volume flow qc,and increases with the increase of the dispersed phase volume flow qd.The droplet dimensionless length(Ld/W)decreases with the increase of the continuous phase capillary number(Cac),and with the increase of the two-phase flow ratio q.The relationship between the droplet length and the inlet angle is taken as the dividing line at 60°.When the inlet angle is less than 60°,it is negative correlation,and when it is greater than 60°,it is positive correlation.The inlet angle has a significant effect on the droplet size,with 60° favoring the formation of smaller droplets.Based on the influence of the above factors on the droplet length,a multivariate regression analysis was used,and the ratio of the volume flow rate of the discrete phase to the continuous phase,the capillary number of the continuous phase and the inlet angle were used as parameters,and a dimensionless prediction correlation formula for the length of the droplet was proposed.The correlation prediction works well.The characteristics of liquid-liquid two-phase flow in Y-shaped microchannel were simulated and studied.Using the VOF model,the droplet formation process in Y-shaped microchannels with different inlet angles(30°,60°,90° and 120°)was studied.It mainly includes the study of continuous phase velocity vector and two-phase pressure change.The formation of droplets was found to be accompanied by periodic changes in the two-phase pressure and the continuous-phase velocity vector.The mechanism of the droplet formation process was further studied from the microscopic point of view,and the reason for the change of the droplet length with the two-phase inlet angle was explained.The experimental method is used to study the droplet breaking characteristics of immiscible liquid-liquid two-phase fluid in symmetric Y-junction microchannels.Three breakup behaviors were observed:breakup with permanent tunnel,breakup with temporary tunnel,and no breakup.Two stages of the change of the neck width of the sub-droplet during the breakup process were discovered:rapid breakup stage and thread breakup stage.The effect of the breakup behavior on the flow pattern was investigated,and it was found that the breakup behavior of the droplets made the slug flow area smaller,and a new flow pattern was observed:droplet flow.The length of the sub-droplet increases with the increase of the volume flow rate of the dispersed phase and the ratio of the volume flow rate of the dispersed phase to the continuous phase,and decreases with the increase of the volume flow rate and the capillary number of the continuous phase.Based on the influence of the two-phase flow parameters on the length of the sub-droplet,a correlation formula for the length of the sub-droplet with good predictive performance is proposed.