Numerical Simulation And Experimental Study Of Slug Flow In Microchannel

Microfluidics technology is widely used in many fields such as chemical engineering and biological engineering due to its easy to control,high efficiency and safety.The size of microbubbles generated in microfluidics device is uniform with two phase fluid.The flow in microchannel is accompanied by a complex mechanical process.The study of the formation of slug flow helps to understand the bubble generation mechanism.At present,the study of the generation of slug flow,especially for the interface of gas and liquid,needs further improve.Through numerical simulation and experiment,the generation mechanism of slug flow is investigated,focusing on the change of phase interface and the information of physical fields.Finally we discuss the generation characteristics of slug and its main influencing factors.Based on the above contents,the main work is as follows:(1)To study the generation of slug flow,the two phase flow numerical model of T-junction microchannel was adopted.By studying the changes of phase interface,the generation cycle of slug flow was divided into two stages and one moment.The first stage was retraction process,during which the ends of gas were rapidly retracted under the effect of surface tension.The second stage was bubbling process.In the case of continuous feeding,the slug was constantly growing.Under the shear of the liquid phase,the gas on the below wall was continuously getting thinner.When the surface tension could not maintain the shape,the gas broke into a slug,which was the"breaking moment".(2)The flow process was accompanied by constant changes of pressure field and velocity field.The results showed that the pressure field near the fracture position changed dramatically at breaking moment.Viscosity had the greatest influence on the overall pressure variation of the center line.The surface tension help slug maintain sphere and the curvature of phase interface downstream was less than that of upstream.According to the velocity field,the phase interface was the position with the maximum velocity and most complex forces.There were vortexes at two ends of the slug which pushed the slug to move downstream.(3)Through constructing microscopy-high speed camera system,shoot the speed generation of slug flow,then analyzed to get the generation characteristics(characteristic length and generation cycle).The results showed that the flow rates of gas and liquid had the most influence on generation characteristics of slug and the surface tension least.By increase of viscosity,smaller bubbles were generated with short generation cycle.The characteristic length was about 400?m and generation cycle 4.5 ms.(4)Through dimensionless analysis,there was a functional relationship between the characteristic length of slug,the flow rate ratio_*Q,Reynolds number Re and weber number We.The experience formula was obtained by linear regression analysis.The formula showed that under the condition of invariable channel size,the characteristic length of slug increased with the increase of gas flow rate and the decrease of liquid flow rate.Besides,the characteristic length was affected by inertial force and viscous force,while the influence of surface tension could be ignored.