Numerical Simulation Of Particle Elasto-inertial Migration In Microchannels

The design and manufacture of microfluidic chips are highly integrated with biological particle manipulation and micro-nano advanced manufacturing technology,and have broad medical application prospects in the research and development of rapid detection medical equipment.In recent years,microfluidic technology has become an important means of particle focusing and separation,because of the advantages of small sample volume,high throughput,and simple control.Among them,viscoelastic focusing technology makes it easier to achieve three-dimensional focusing of particles,and can manipulate particles with a large-scale span and a wide range of fluid flow.It has become a new trend of particle/cell processing,and has attracted more and more attention.To learn more details about mechanisms of particle elasto-inertial migration mechanism in viscoelastic flows,the lattice Boltzmann method(LBM)coupled with the immersed boundary method(IBM)is employed to simulate the migration process of particles in viscoelastic flow,and the migration laws of particles with different sizes and shapes in microchannels with different aspect ratios are studied.The research results of this paper are summarized as follows(1)The viscoelastic focusing mechanism of particles in the straight microchannel is studied.Firstly,the focusing phenomena of particles in Newtonian fluid and viscoelastic fluid with the same flow intensity are compared,and the effects of inertial lift and elastic force acting on particles are analyzed.The results show that under the action of elastic force,the particles are focused toward the channel center,and the particle speed are reduced by the viscoelastic force.Secondly,the migration behavior of particles in the microchannel is calculated under the conditions of Reynolds number Re=1.0 and Weissenberg number Wi=0.1?1.5.The results show that when Wi is small,the elastic force is not enough to resist the original inertial lift to push the particles to the center of the channel.High Wi will attenuate the particle rotation and the flow stretching,which also weaken the lateral viscoelastic effects on the particle.The best focusing parameters are obtained by comparison.In addition,the separatrix for particle focusing toward the channel centerline or the channel walls is observed in the simulation.Finally,the effects of flow velocity and particle size on particle migration are explored.(2)The migration characteristics of particles in microchannels with different aspect ratios are studied.Firstly,the particles with diameters of 6 ?m and 12 ?m have been released in straight microchannels with aspect ratios of 1,1/2,1/3,and 1/4 to simulate and calculate their migration behavior in the viscoelastic fluids,and the influence of different elasticity numbers El on particle migration in different aspect ratio microchannels has been investigated.The results show that large particles have faster lateral migration speed and smaller separatrix region.When El is larger,more small particles can be focused toward the channel center.Secondly,the focusing equilibrium positions of 6 ?m and 12 ?m particles in microchannels with different aspect ratios are compared to explore the particle size-based sorting.The calculation results show that in the rectangular cross-section straight microchannel with an aspect ratio less than 1,particles with different diameters have different focusing equilibrium positions,and the focusing equilibrium position of large particles is closer to the channel wall,which proves that the rectangular cross-section microchannel is a better particle sorting design structure than the square cross-section microchannel.(3)The migration characteristics of elliptical particles with different aspect ratios are studied.Elliptical particles with the same area(two-dimensional)and volume(three-dimensional)but with aspect ratio of 1 ? 5 are constructed respectively,and their migration motion in viscoelastic solution was calculated.The influence of Weissenberg number Wi on the focusing and rotation of particles with different aspect ratios and the possibility of particle sorting based on particle shape are explored.The results show that elliptical particles with different aspect ratios have different rotation periods and migration velocities in viscoelastic fluid.The particles with large aspect ratios have slower rotational speeds and migration velocities to the channel centerline.The distribution of viscoelastic force on the upper and lower sides of the particle with larger aspect ratio is smoother,which reduces the elastic force that pushes the particles to the channel centerline and makes the lateral migration speed of the particle slower.As the results,the difference of particle focusing efficiency can help us to separate the various aspect ratio particle successfully.What is more,particles with different aspect ratios have different focusing equilibrium positions in the rectangular cross-section microchannel with an aspect ratio of 1/2.By adjusting the values of Wi and Re,the shape-based sorting of particles with different aspect ratios can be realized in turn.By numerical simulation method,the migration mechanism of particles in viscoelastic fluid is systematically studied and the effect of the channel interface aspect ratio,particle size and shape,etc.on the sorting are explored.It provides a theoretical basis for the analysis of viscoelastic microfluidic focusing and sorting mechanism,and has important reference value for the design and development of particle sorting devices.