Droplet Formation In Different Structutes Microchannels

Microfluidic droplet generation is an important branch of microfluidics,which has the advantages of close and stable system,high efficiency of mass transfer and less reagent consumption.Its application covers drug delivery and controlled release,encapsulation of active material,biochemical separation and other fields.The size and the dispersibility of droplet are critical for the applications.The droplet formation is determined by the geometric parameters of the incompatible fluid junction,the flow rate of the each phase and the physical parameters likes viscosity,density of the fluid and the interfacial tension.In this paper,experimental and numerical simulation methods were used to study the droplet formation process of T-junction with a constriction microchannel and microchannels induced by interfacial tension.The influence of the constriction width,two phase flow rate,physical parameters and other factors on droplet formation size are studied.Meanwhile,the prediction formula of the droplet formation size in the two microchannels have been derived.The specific research contents include:Generation of droplets in the T-junction with a constriction microchannel.T-junction with a constriction microchannel is designed for the controlled production of monodisperse microdroplets,which could produce droplets with the same size under a lower flow resistance.The influence of the microchannel structure,operating conditions,and physical properties on the dispersion rules is systematically investigated by combinations of micro-particle image velocimetry(Micro-PIV),high-speed camera and numerical simulation.Compared to the traditional T-junction channel,the T-junction with a constriction microchannel can generate smaller droplets whose size conforms to the size prediction formula of the traditional T-junction channel.It is found that the velocity vector of the T-junction with a constriction microchannel is faster than that in the T-junction channel at each stage of droplet generation.The droplet size is mainly based on the Ca number,the flow rate ratio and viscosity ratio of the continuous phases in our channel,and the range of the index of Ca with the droplet size is found.The constriction width has a significant influence on the dispersion rule,as there is a decreasing tendency for the droplet size with reducing constriction width.The influence of geometric size on droplet formation in microchannels induced by interfacial tension.This paper uses interfacial tension-induced microchannel,focusing on the effect of the droplet generating cavity angle,generating cavity length,generating cavity width and the expansion angle of curved wall on the droplet sizes,determine the optimal structure with less speed dependence.The generation process is visualized by high-speed camera system,and the flow patterns are resolved by micro-PIV system.Sunflower oil and deionized water are used as the oil phase and the water phase,respectively.To obtain the suitable size drops,the flow rates of the continuous phase and dispersed phase are set in the range of 30~50?L/min and1~20?L/min separately.In order to reduce the number of experiments,Taguchi method to design experimental channel.The results show that the influence of the droplet size under each parameter in different speeds is:generating cavity angle>generating cavity length>generating cavity width.The optimal cavity size is generating cavity angle is 30°,generating cavity length is 0.5mm,generating cavity width is 2.6mm.In addition,the critical size of the droplet of two phase interfacial rupture is derived.?=0°,the dispersed phase can't fracture to droplets,and?>0°,the droplet formation.?=8°,the influence of the fluid rate on the droplet size is smaller.The influence of junction structure on droplet formation in microchannels induced by interfacial tension.The junction structure,interfacial tension and two-phase viscosity on droplet formation in microchannels induced by interfacial tension is studied.Under the same conditions,the droplet size increases with the increase of?,and the droplet size is less dependent on the flow rate in the F-microchannel.In the flow rate of the dispersed phase is 5-6?L/min,there is a critical value,so that when the droplet is at Q_d=0-5?L/min,the droplet size decreases with the decrease of interfacial tension,at Q_d=6-10?L/min,the droplet size increases as the interfacial tension decreases.At the same time,as the viscosity ratio increases,the droplet size also increases,and the generation time of the droplet increases.