Simulation Analysis And Experimental Research On Droplet Generation Mechanism In Cross Focusing Microchannels

In recent years,the micro-droplet has been widely used in biochemical analysis,medical detection,material synthesis,food processing,environmental monitoring and other fields.The key of micro-droplet is the control of microscale multiphase flow.The cross focusing microchannel is advantageous in controlling the size range and stability of droplet generation.Therefore,it has important research significance and application value.Considering the application of micro-droplet digital PCR as the background,the main research contents is to study the influence factors of droplet generation size and generation frequency in the cross focusing microchannels,and the basic law of droplet generation is researched by numerical simulation and experimental methods.For the generation process of droplet in cross focusing microchannels,the effects of continuous phase flow rate,continuous phase viscosity,dispersed phase viscosity,interfacial tension coefficient and wall contact angle on droplet generated diameter and frequency are researched by numerical simulation.Simulation results show that:(1)with the increase of continuous phase flow rate,the droplet diameter would decrease,while the generation frequency would increase;(2)the droplet diameter decreases as the continuous phase viscosity increases,and the generation frequency increases;(3)when the dispersed phase viscosity exceeds the continuous phase viscosity,jet flow will appear and the droplet cannot be generated for the water-in-oil system;(4)the droplet diameter decreases with the increasing interfacial tension coefficient,while the frequency would increase;(5)increasing the wall contact Angle is contributing for the generation of droplet.For the influence of microchannel structure parameters on droplet generation,the structure parameters that affect the droplet generated diameter and frequency are studied by numerical simulation.Simulation results show that:(1)droplet diameter decreases with the increase of continuous phase entrance width and generation frequency increases;(2)when the dispersed phase entrance width increases,droplet diameter would increase,and generation frequency would increase at high flow rate;(3)droplet diameter increases as the cross focusing outlet width increases,while generation frequency decreases.(4)droplet diameter increases with the increasing depth of the channel,and generation frequency is basically stable.(5)The multiple factors structural parameters affecting droplet generation is studied by orthogonal test method,and the generation diameter and frequency is predicted,thus obtaining the optimal cross focused microchannel structural parameters for the droplet diameter of 70 μm and the frequency of 1000 Hz.By using the comprehensive evaluation method and the range method,the primary and secondary relationship of the structural parameters affecting droplet generation is obtained: cross-focused outlet width,channel depth,continuous phase entrance width,dispersed phase entrance width;and the optimal combination of structural parameters is gained: the continuous phase entrance width is 65 μm,the dispersed phase entrance width is 55 μm,the cross-focused outlet width is 65 μm,and the channel depth is 50 μm.Finally,the droplet generation experiment is carried out,and the experiment research show that:(1)the design of cross focusing microchannel according to the optimal structural parameters is verified;(2)the influence of inlet pressure of dispersed phase: with the increase of inlet pressure of dispersed phase,the droplet diameter increases and the generation frequency decreases.