Research On Flow Characteristics And Mixing Performance Of Passive Micro-mixer

The micro-mixer is an important pretreatment device that makes full contact between two or more micro-volume fluids and completes rapid and efficient mixing by using microchannel structure.With the characteristics of less reagent consumption,high stability,easy integration and high safety,it is widely used in biochemical detection,chromatographic analysis and other fields.Ultra Performance Liquid Chromatography(UPLC)is an important equipment for biochemical chromatography analysis.Among them,the high-performance micro-mixer can achieve sufficient mixing of detection reagents and improve detection accuracy.This paper aims at the passive micro-mixer with two different structures of square wave and embedded obstacle.Through the combination of experiments and numerical simulations,the effect of structure size on the fluid flow characteristics and mixing performance in the micro-mixer is investigated.The mixing mechanism of the UPLC micro-mixer was investigated,and its mixing performance was optimized.(1)Study on the influence of flow characteristics and mixing performance of channel structure square wave micro-mixer.Aiming at the square wave micro-mixer,the flow characteristics and mixing performance of fluid under different channel Re conditions were studied through experiment and numerical simulation methods,and the relationship between channel width and height on fluid flow characteristics and mixing performance was analyzed.The mixing process is divided into two phases,molecular diffusion domination and convection diffusion domination,based on the size of Re.The factor that affects the mixing index in the molecular diffusion dominant phase is the characteristic diffusion length,and the factor that affects the mixing index in the convection diffusion dominant phase is the size and intensity of the vortex induced by the centrifugal force.In the dominant phase of molecular diffusion,the reduction of the channel width can significantly increase the mixing index,which is more significant than the reduction of the channel height.In the dominant phase of convection diffusion,the secondary flow vortex develops most full and the mixing index is the largest when the channel aspect ratio is 1: 1.On this basis,reducing the cross-sectional size of the channel can increase the vortex intensity and increase the mixing index.(2)Study on the influence of geometric configuration on the mixing performance of the embedded obstacle micro-mixer.For the embedded obstacle micro-mixer with a mixing chamber,the effects of the shape of the mixing chamber on the mixing performance were studied,and the flow characteristics of the fluid in the mixing chamber were analyzed.The effects of chaos and jet effects on the mixing performance of the embedded obstacle micro-mixer were explored by changing the geometry size of obstacles and slits.In the range of Re ≤ 1 and Re ≥ 20,the hexagonal mixing chamber micro-mixer has better mixing performance than the other two types of micro-mixers,and has the characteristics of high mixing index and small pressure drop.The vortex in front of the obstacle causes a phenomenon of cross-concentration flow in the process of fluid mixing,which enlarges the interface area between the fluids and promotes the full mixing of the fluids.Increasing the height of the obstacle can enlarge the size of the vortex behind the obstacle and promote mixing.Narrowing the width of the slit can promote the jet effect and be more conducive to the phenomenon of fluid flow across concentration,which can significantly increase the mixing index,but it will also cause a greater increase in pressure drop.(3)Study on the influence of structure size of UPLC micro-mixer on mixing performance.For UPLC micro-mixer,the flow state and mixing characteristics of the fluid in the mixing chamber were analyzed.The influence of the presence and size of the microbead structure,the spacing and inclination angle of inlet channel on the mixing index and pressure drop were studied.The structure size of the micro-mixer was optimized.The existence of microbeads in the mixing chamber enhances the disturbance of the fluid and makes full use of the chaos effect and jet effect to promote the fluid mixing.The increase of microbead diameter enhances the chaos effect of the fluid and increases the mixing index while the pressure drop decreases.The shortening of the inlet channel space and the increase of the inclination angle can enhance the collision between the two fluids and promote mixing without affecting the pressure drop.Within the research range,the mixing performance of the micro-mixer with 480μm diameter microbeads filled in the mixing chamber,inlet channel spacing 0mm,and inlet channel inclination angle 45° is optimal.When the total flow at the inlet was 5 ml/min,the mixing index of the optimized micro-mixer increased 27.31%.