Inertial Migration Behavior Of Complex Characteristic Particles In A Serpentine Microchannel

The advent of the microfluidic chips helps the point-of-care testing technique to develop vigorously,and the inertial microfluidic chip,which frees the particle manipulation from sheath flow controls and external force generators,has attracted increasing attention.The purpose of this article is to study the migration behavior of various size,stiffness and shape particles in inertial microfluidic channel based on Lattice Boltzmann method(LBM)coupled with Immersed boundary method(IBM),which calculates the distribution of the fluid flied and the interaction between flow and particles.The simulation model is parallelized through CUDA toolkit which multiplies the calculation effectiveness.Detailed works of this article are elucidated as follows.(1)Migration behavior of particles with different sizes.Diameter 5 μm and 10 μm particles have been released in a symmetrical serpentine microchannel to study the particle migration behaviors.The calculation results show that when the flow intensity is low,the balance of inertial lift force and the Dean flow drag force at lower flow intensities leads the particles to flow along the sidewalls.As the flow intensity becomes stronger,the alternation of Dean flow direction takes the dominant role and has special hydrodynamic effects to focus the particles at channel center and separate the particles into double trajectories which agree well with the Dean flow direction when the flow intensity is higher.It is found that because of the volume effects,large particles flow away from walls and are more prone to rotate with the Dean vortex and have better focusing performance closer to the channel center,which makes large particles can be separated from the small particles at specific flow intensities.The experimental validation has been performed to show that simulation results of particle trajectory agree well with the real situation.It is reliable to calculate particle migration through Lattice Boltzmann method coupled with Immersed boundary method.(2)Migration behavior and shape transformation of deformable particles.Migration behavior and shape transformation of deformable particles in both inertial straight channel and symmetrical serpentine channel have been studied,and the deformation-induced lift forces have also been calculated.In an aspect ratio(AR)=0.5 straight channel,particles focus at the horizontal midline of the channel and the softer particles focus closer to the vertical center than the less soft ones.Then particles are released in the symmetrical serpentine channel with the same AR=0.5 cross-section.Because of the different focusing positions in vertical direction of various deformable particles,particles are under various intensities of Dean flows.More deformable particles focus closer to the channel vertical center and are under stronger influence of Dean flow.The trajectories of more deformable particles agree better with the Dean flow direction and thus the particles with different deformability can be separated through serpentine channel.(3)Migration behavior and direction transformation of ellipsoid particles.Sphere and ellipsoid particles with aspect ratio of 3:1 and 5:1 have been released in a straight microchannel first to study their focusing pattern.Three kinds of particles have same volumes but they have different shapes.The ellipsoid particles with larger aspect ratios focus closer to the channel center and have longer periods of rotation.However,the distances between focusing trajectories of the different shape ellipsoid particles are very small,which has bad influence on the ellipsoid particle separation.In order to improve the separation performance,the structure of the microchannel is rearranged.Through the migration behavior of a 5:1 ellipsoid particle in a narrow straight microchannel,it is can be found that the wall effect disturbs the rotation of the ellipsoid particle whose longest axis is comparable to the channel width.An AR=0.25 serpentine channel is applied to separate the different shape ellipsoid particles.The extra low channel height disturbs the particle rotation in vertical direction and strengthens the particle focusing in the horizontal plane,which expands the distance between focusing trajectories of different shape particles and optimizes the separation performance of them.In addition,this article systematically analyzes the direction of ellipsoid particles in the serpentine microchannel.Manipulation method of particle direction is found and provides a new solution for particle ordered alignment and self-assembly.