Generation Mechanism And Transport Characteristics Of Slug Flow In Microscale Rectangular Channel

Micro-droplet manipulation is an important content of microfluidic technology,and also one of the most widely studied microfluidic technology.It is a technology to using two or more immiscible liquids' interaction to generate a single microscale dispersed droplet and to their precise manipulation.Microdroplets include slug flow,monodispersed droplets flow,and droplets populations flow.Wherein,slug flow refers to the large droplets flow which fully fill in the intersection of micro channels,which directly contact the channel walls or spaced by a thin liquid film of continuous phase.Generation and transport of slug flow perform different characteristics comparing with other flow patterns,which has attracted many attentions of the researchers.Slug flow has a wide range of applications in research areas as the micro dosing,micro separation,micro concentration and etc.This paper mainly researches on the formation mechanism and transport properties of slug flow in microchannel with rectangular section.Base on microscale fluid mechanics theory,this paper analyzes the role of micro fluid gravity,inertial force,shear force,interfacial tension force,and characterizes the relative size by using the dimensionless parameter,finds dominant factor in microscale flow.This paper fully consider the interfacial tension and the influence of surface wettability,and establish the mathematical model which suit for microscale of slug flow.The slug flow is simulated based on the flow field analysis software,setting the initial and boundary conditions,meshing and finite element calculation,generation and transport processes.The variation of the slug flow length,shape and other acts are studied by the change of the main control parameters.According to the advantage of the numerical simulation results,the generated pressure of the channel triggered by the slug flow is computed and discussed.Using numerical method,the transport properties of slug flow is studied.The dynamic contact Angle and corners rounded appearance characteristics are investigated and the influence of various parameters is analyzed.Internal circulation in micro-droplet of slug flow has a great influence on mass transfer.In this paper,the influence of flow rate to the intensity of internal circulation is studied.Through constructing experiment platform for slug flow and combining with microscale particle image velocimetry system(Micro-PIV),slug flow generation process is observed.By changing the parameters,the generation law of slug flow is summarized.Through the analysis of experimental results,the change curves of the length of the droplet along with the two phase flow,the flow ratio,of viscosity are established.The research shows that:viscous shear force,interfacial tension,pressure difference dynamic change in the generated process of slug flow.Among them,the pressure difference is the main driving force to the micro droplet.The generation of slug flow is affected by the flow ratio,flow,continuous phase viscosity,interfacial tension and surface wettability.Slug liquid droplets generated decreases with the increase of the flow rate,viscosity of continuous phase,the increasing of contact angle,and increases with the increase of the interfacial tension.Through data analysis,the characteristic length of the droplet with the fitting formula of capillary number Ca is obtained,which can predict the size of the droplets.The shape of slug flow in the process of transport is affected by the channel geometry,fluid physical parameters,surface wettability,and the curvature before and after is not in asymmetry.Contact Angle is in conformity with the laws of Tanner.If the micro droplet as a frame of reference,except two big circulation inside the droplets,there are also two pairs of small circulations on the front and back side.The influences of flow rate to strength of circulation is studied,which find that the strength of circulation increases with the increase of flow rate and.