Research On The Formation Of Double Emulsion Droplets Based On Vibration Excitation

In recent years,high-quality and high-throughput microdroplets,vesicles and capsules of double emulsion have been widely used in the fields of biology,material chemistry,food safety and medical research.Since the traditional method of preparing double emulsion droplets by mixing and stirring cannot guarantee the uniformity and dispersion of the two emulsion droplets,many researchers began to find that the method of microfluidic chip can be used to prepare double emulsion droplets.It has the advantages of excellent sphericity,high dispersion,high flux and good stability.The method of microfluidic chip is the best way to prepare the double emulsion droplets.In recent years,many researchers have done a lot of research on the preparation method of micro-flow control,which has broadened the new research direction and frontier research focus of engineering thermophysical scale poly-phase flow.In this paper,the mathematical Model of the co-flow microchannel and the theoretical Model of the hydrodynamics of the process of producing double emulsion droplets in the microchannel are established by using the method of phase interface tracking by VOF(Volume of Fluent Model).The process of double emulsion droplet generation in co-flow microchannel was simulated by Fluent.Two typical flow patterns(jet and trickle)are given.There is also a special hybrid flow pattern;The effects of different flow states,different viscosity ratios and different surface tension coefficients on the formation mode and droplet size of double emulsion were analyzed.The law of mutual transformation between two typical flow types,drip flow and jet flow is studied.The critical range of stable droplet and the optimum condition of double emulsion droplet are given.At the same time,the co-flow micro-channel chip was designed and fabricated,and two typical double emulsion droplets were prepared.Contrast no vibration produced by double emulsion drops,At the same time,the test bed and the mechanical vibration platform of the co-flow micro-channel microfluidic emulsifying device are built.The main factors affecting the emulsification process under vibration excitation are analyzed,and the characteristics of uniformity such as size,fracture rate,generation frequency and dispersion degree of the double emulsion droplets under three vibration excitation,X direction vibration and Y direction vibration modes are compared.In summary,the main conclusions of this paper are as follows.(1)to carry out the coordinated flow in micro-channels double emulsion droplet generation theory modeling and numerical simulation research,success find out the jet and drip two typical flow pattern,the three-phase flow ratio is established,which is formed by the viscosity ratio,interfacial tension ratio and the quantitative relationship between the double emulsion droplet size,and systematic analysis of the flow state and the fluid properties on the mechanism of the influence of emulsifying process.The numerical studies show that drip mode the main influencing factors of interfacial tension,and jet impact factor is the most foreign minister viscous force,making break the balance of the Rayleigh-central Plateau instability(jet flow in the capillary instability to break into droplets),so two modes have different characteristics and different shape,size.Double emulsion droplets are more complex than single emulsion droplets,and the two flow patterns can be converted to each other like single emulsion droplets.In the drip mode,the flow rate of the outer phase can be increased,which can be converted into the jet.The change of flow rate of the intermediate fluid will not have too much influence on the formation mode of the droplet,but it can have an effect on the size of the droplet.Changing the flow pattern and droplet size did not play a decisive role.The change of viscosity has a certain effect on the double emulsion droplets,and the two flow patterns can be converted to each other under certain conditions.The change of interfacial tension also plays an important role in the double emulsion droplet.By changing the size of the surface coefficient,the interface can be changed but the size of the double emulsion droplet will not be changed.(2)the effectiveness of numerical calculation of the mathematical model with Based on this,numerical simulation was used to calculate the flow patterns of dispersed phase under different velocity ratios and viscosity ratios of two phases under vibration-free excitation.(3)numerical calculation was carried out for the selected trickle flow and jet flow patterns under the condition of different vibration under the vibration excitation(80Hz,160xm)was analyzed.Then the numerical calculation results of this working condition are obtained from the velocity curve of specific region at different time of the velocity cloud map and the statistics.The above analysis of numerical results under different working conditions from the perspective of quantization provides a reference for understanding the evolution process of different flow patterns under vibration excitation conditions.(4)the area,dispersion,monodispersity and evenness of the fractured droplet under all vibration excitation conditions were statistically analyzed,and the results showed the effectiveness of the formed droplet under different flow patterns under different excitation conditions from a quantitative perspective.(5)numerical study was carried out on the mode transformation of dispersed phase flow and droplet fracture under all excitation conditions.This paper systematically reveals the flow morphology evolution and emulsification mode transformation mechanism of double emulsion formation in the axisymmetric co-flow microchannel,and further discusses the double emulsion droplets generated in the co-flow microchannel under vibration excitation.The related results can provide effective parameters for the design and optimization of the device for the preparation of double emulsion droplets and enrich the additional field vibration to provide some new methods and basic knowledge for the control of double emulsion droplets.