Research On Flow Pattern Evolution And Droplet Formation In Cross Flow Focusing Under Vibration Excitation

Single or compound microdroplets,bubbles,particles and capsules prepared under flow focusing structure have important application background in medicine,materials,chemistry,food science,biological science and other fields.Flow focusing is a typical capillary flow phenomenon.One of its principles is that the fluid flowing from the capillary tube passes through the orifice to form a stable conical jet structure.The second principle is that the incoming fluid in the microchannel is crushed by the incoming fluid in the other microchannel into droplets due to fracture or interface instability.Researchers on inflow phase capillary vibration excitation can not only ensure droplet property,but also can improve for the lack of additional field,such as: the frequency of the droplet size,shape,and the geometric structure of compound droplets are difficult to be precise control,but the former applying vibration excitation method can guarantee the dispersed phase in the process of forming mix,based on this,the global vibration on microchannel internal incentives to conduct research also has its practical application value.(1)This paper verify the effectiveness of numerical calculation of mathematical models under conditions without vibration excitation and with vibration excitation through experiments.Based on this,the dispersive phase flow patterns of two phases with different velocity ratios and viscosity ratios under non-vibration excitation were statistically analyzed by numerical simulation,and seven typical flow patterns under different working conditions were selected: drip,jet,pulsating,plunger,satellite drip,bubble drip and chaotic flow.(2)Numerical calculations were carried out for seven selected flow patterns under different vibration frequencies and amplitudes in the excitation direction of X and Y,and the evolution process of flow patterns under low frequency vibration excitation(30Hz,160?m)was analyzed.Then the velocity changes of droplet fracture forming and unfractured dispersed phase flow pattern were obtained from the velocity cloud diagram and velocity curve of specific region at different time points.Further study of the high frequency vibration excitation conditions(480 Hz,160?m)under cross flow is focused on the forming process of droplet fracture,from the angle of inertia force and viscous force relative to the size of the forming process of the droplet under the condition of vibration are analyzed,and the above to the numerical results under different working conditions from the Angle of quantitative analysis,to understand the different flow pattern in the evolution process of vibration excitation conditions,provide a reference.(3)The area of the forming droplet,the dispersion of the forming droplet and the forming frequency of the mondisperse droplet were analyzed statistically under all the vibration excitation conditions.The statistical analysis provides a practical reference for choosing the size of forming droplets and working conditions in engineering applications.(4)For all the incentive condition of the dispersed phase flow pattern transition and the numerical research in the form of droplets fracture in two phase than the same viscosity,two phase flow pattern turns the weber number(We)in size at the same time,the specific flow pattern will because quantitative inertial force/viscous force size We will change the way the dispersed phase flow state and fracture exists difference;when the two-phase viscosity ratio changes(the viscosity of the dispersed phase increases),the capillary number(Ca)of the flow state and the droplet fracture forming mode in the jet flow pattern will change due to the change of the viscosity of the dispersed phase,and the change of the Y-excited direction is more than that in the X-excited direction.