Numerical Analysis And Experimental Research Of Microfluidic Mixing Behavior Under Magnetic Field

Microfluidics is an emerging technology that effectively controls substances in microchannel.It has a wide range of applications in materials,biology,and chemistry.However,the fluid is in a low Reynolds environment under microscale,and the fluid movement is dominated by molecular diffusion,which causes the mixing process slowly and the analysis efficiency decreased.The external field excitation micromixing method based on permanent magnets has received extensive attention due to its advantages of no heat generation,compact structure,and no complicated control strategy.However,the research of the magnetic field source system is mainly based on the single magnet system up to now,and there are problems such as a small flow rate range and poor controllability.Therefore,the dynamic mixing characteristics of the fluid in the microchannel under different magnet structures is compared,and the mechanism of the magnetic field on the micromixing system is analyzed with numerical simulation and experimental research.On this basis,a new multimagnet combination scheme with high efficiency and rapid mixing is proposed and realized,which is of great importance for designing microfluidic chip parameters and improving mixing performance.In terms of numerical simulation,based on the basic theory of microfluidic mixing under magnetic field,this paper constructs a magnetic field simulation model and multiphysics coupling simulation model on the finite element simulation software COMSOL.Considering the influence of particle migration on the microfluid mixing behavior,the characteristics of mixed morphology and terminal concentration distribution in microchannels under magnetic field are simulated.The research shows that the magnetic forces under different magnetic field configurations have different effects on the magnetohydrodynamic behavior,and the introduction of the particle migration characteristics plays a significant role in improving the mixing effect of the micromixing behavior.It lays a foundation for the study of fluid flow behavior and the mechanism of magnetic mixing in subsequent experiments.In terms of experimental research,a microfluidics research platform which consists of a series of corresponding devices is set up,including a syringe pump,a microscope,a highspeed camera,and a visualization software.The experiment for researching the microfluidic mixing behavior under different magnetic fields are implemented on the Y-type microfluidic chip with the research platform.The variation of ferrofluid mixing behavior,the fluid mixing morphology and the terminal concentration distribution characteristics in microchannels are obtained under different magnet structures.The reasearch shows that the axial force is dominant under the single permanent magnet,which can achieve the mixing of large flow rate range,but the mixing efficiency is low.The radial force is dominant under the double permanent magnets,which can achieve uniform mixing at lower flow rates.Furthermore,combined with numerical analysis,the mechanism and effect of magnetic field distribution,particle agglomeration and particle migration on fluid mixing behavior are clarified.Finally,aiming at the requirements of microfluidic mixing technology of high efficiency,high speed and wide application range,a new type of microfluidic magnetic mixing scheme with three magnets for axial force radial force combination is proposed by combining the advantages of single permanent magnet and double permanent magnets system on the basis of the above research.The experimental research is carried out on the microfluidic research platform.The results show that the scheme can adapt to a wider flow range while maintaining efficient mixing.The feasibility and effectiveness of the scheme are verified,and the optimization of the hybrid characteristics of the scheme is further clarified.It provides a new design strategy for widening the flow rate range of high efficiency mixing.