Study On Gas-Liquid Two-Phase Flow And Bubble Generation And Breakup Behavior In Microchannel

The dynamic characteristics of bubbles are the most basic content in the study of gas-liquid two-phase flow.With the increasing application of microfluidic technology in various fields,the value and significance of research on bubble behavior in microchannel is also becoming more and more important.In this paper,the VOF method is used to simulate the formation process and breakup behavior of bubbles in the non-equal Y-type bifurcation microchannel,while the FTM method is used to study the interaction between bubbles during the process of ascent.Firstly,a physical model of a two-dimensional non-equal Y-shaped bifurcation microchannel is established.The generation process of bubbles and the breakup behavior at the bifurcation under two-dimensional simulation conditions were studied,the simulation results are compared with the existing experimental results to verify the correctness of the model and the effectiveness of the method.The characteristics of each stage in the bubble generation process,the pressure changes in the channel,and the influence of wall wettability under the two bubble generation mechanisms of Squeezing mechanism and Shearing mechanism are compared and analyzed.It is found that the bubble formation process under the Squeezing mechanism is dominated by the extrusion action of the continuous phase,while the bubble formation under the Shearing mechanism is derived from the shearing action of the continuous phase.Under the Shearing mechanism,the pressure drop at the centerline of the channel is larger during bubble generation,but the bubble generation process under this mechanism is less affected by wall wettability,while the wall wettability has a more pronounced effect on bubble formation under the Squeezing mechanism.As the contact angle increases,the length of the bubble generation shows a change in the concave function.When studying the breakup behavior of bubbles at the bifurcation,the focus is on the variation of the minimum neck width.The linear fit of the minimum neck width with time in the slow extrusion process is highly correlated.Secondly,the physical model of three-dimensional non-equal Y-type bifurcation microchannel is established.Based on the two-dimensional simulation,the effects of different computational dimensions on the same simulation process are compared and analyzed.The study found that the bubble generation and the breakup time in the twodimensional simulation lag behind the equivalent situation in the three-dimensional simulation,which is consistent with the conclusions reached by other scholars.And make full use of the advantages of the 3D model in visualizing the physical process,making up for the lack of the 2D simulation study that can't deal with the spatial dimension problem,the variation law of gas phase ratio on the cross section under different influencing factors is summarized,it is found that when the velocity of the liquid phase is greater than the velocity of the gas phase,as the ratio of the velocity of the gas phase fluid to the liquid phase decreases,the proportion of the gas phase in the cross section gradually decreases.The gas phase distribution in the cross section is octagonal,there is a flow of liquid phase in the corner around the channel,forming a liquid film between the gas phase fluid and the channel wall.The presence of the liquid film allows the bubble to move in the channel at a speed greater than the velocity of the liquid phase,which made the phenomenon of speed slip appear.As the velocity of the bubble increases,the velocity slip increases,and the proportion of the gas phase in the cross section decreases.Finally,the rising process of two bubbles under four different initial shapes was simulated by using the FTM method.And the difference in velocity and pressure distribution was compared,It is found that the initial shape of the two bubbles has an effect on the speed and the degree of deformation that occur during the ascending motion,the circular bubble is slower than the oval bubble during the ascent,the deformation of the upper bubble is larger than that of the lower bubble,but the lower bubble has a greater speed due to the wake of the upper bubble.The upper bubble gradually becomes a hat shape while the lower bubble gradually becomes a bullet.Due to the presence of low-pressure zone between the two bubbles,the upper and lower bubbles will polymerize to form a new bubble under the pressure difference.