Research On The Thermophoresis And Magnetophoresis Coupled Inertial Sorting Of Microparticles

Microparticle refers to the particle with a diameter of 0.1-5 ?m,such as aerosol,biological cell,and so on.Microparticle sorting according to the physical properties is very common manipulation in bioengineering,environmental engineering and material engineering.Microparticles sorting is an important technology for microparticle manipulation in line with the density,magnetic permeability,electrification and size of the microparticle.Sorting means that,the different particles being suspended in liquid fully dispersed will be focused at different balance position.Focusing process can be controlled by the forces on the microparticles.The most common and accepted approach is inertial sorting.However,it is necessary for the sorting of microparticle with a diameter of 0.1-5 ?m to impose external forces,such as thermaophoretic and magnetophoretic force,to induce additional lateral migration,because of the lack of larger enough inertia force on microparticles.The main works in present dissertation involve:1)Analysis of the forces on a microparticle suspended in fluid: They are weight and buoyancy,viscous drag,all kinds of lifts,thermophoretic force,pressure gradient force,added mass force,Brownian force,Basset force,except sonophoretic force,electrophoretic and dielectrophoretic force,magnetophoretic force,photophoretic force,and so on.On the basis of analysis of the forces on the microparticles,it can be concluded that,the viscous drag and thermophoretic force are two most important forces for sorting microparticles with a diameter of 0.5-5 ?m.The Brownian force will influence the particle sorting efficiency for the microparticles smaller the 0.5 ?m.Contrarily,the inertial force will dominate in the sorting process for microparticles larger than 5 ?m.It can't be easily sorted only by inertial force for microparticles of0.5-5 ?m,hence,electrophoresis,magnetophoresis,thermophoresis coupled inertial sorting should be available.2)Investigation on the sorting regularities inertial sorting: For sorting three kinds of particles in blood,known as platelet(2 ?m),red blood cell(7 ?m)and white blood cell(15 ?m),the influences of three important factors,named flow rate,width depth radio and expansion-contraction ratio of rectangle microchannel,on the efficiency of inertial sorting were analyzed.It is concluded,the sorting efficiency is highest at unit particle Reynolds number.3)Research on the magnetophoresis coupled inertial sorting:Magnetophoresis coupled inertial sorting is a good approaches to sort the particles with a closed diameter.The non-magnetic particles with a closed diameter(for instance,3 ?m and 4?m particle),which suspended in magnetic fluid,can be sorted by the assistance of an external magnetic field.Based on the establishment of numerical model being consistent of magnetic model,flow model and particle model,numerical simulations for various inlet velocities,various inlet-velocity ratios,magnetic intensities and expansion ratios are carried out to calculate the sorting efficiency.Numerical results show us that,lower inlet velocity,smaller inlet-velocity ratio,greater magnetic intensity and mediate expansion ratio are beneficial to higher sorting efficiency.The numerical results are partially verified by micro-PIV experiments.4)Research on the thermophoresis coupled inertial sorting: In allusion to the submicroparticles with a diameter of 0.1 ?m?0.5 ?m and 1.0 ?m,thermophoretic migrations induced by temperature gradient across the microchannel width must be applied to drive the submicroparticle for high temperature zone to lower temperature one when a temperature difference between two channel walls are imposed.The reason may be no enough inertia force for such a small particle.Numerical results show us,the balance positions of microparticles are mainly relative to thermophoretic force and viscous drag on them.Furthermore,thermophoresis coupled inertial sorting is utilized to separate microparticles with diameter of 0.5 ?m and1.0 ?m.Numerical simulations for various inlet velocities,various inlet-velocity ratios,constraction-expansion ratios and temperature differences between two channel walls are carried out to calculate the sorting efficiency.Numerical results indicate that,a smaller inlet velocity(2 mm/s),a mediate inlet-velocity ratio,a larger constractionexpansion ratio,and a 10 K temperature difference is beneficial to enhance sorting efficiency.Partial numerical results are verified by the microPIV experiments.This paper consist of five chapters.The first chapter is the introduction of the history and current status of research on microfluidic chips.The second chapter analyzes the knowledge of microparticle sorting.The third chapter is research on the inertial trapping of microparticles in an expansion-contraction microfluidic device and a negative magnetophoresis coupled inertial sorter for non-magnetic micro-particles.The fourth chapter is investigation on the thermophoresis-coupled inertial sorting of submicroparticles in a micro-channel.The last chapter is the conclusion and prospect,some conclusions about the thermophoresis,magnetophoresis coupled inertial sorting of microparticles are given,which can guide us to design a microsorter.Furthermore,a perspective in our work is presented.