Three-Dimensional Numerical Simulation of Particle Focusing and Separation in Viscoelastic Fluids.

Chen Ni,Di Jiang

doi:10.3390/mi11100908

Abstract

Particle focusing and separation using viscoelastic microfluidic technology have attracted lots of attention in many applications. In this paper, a three-dimensional lattice Boltzmann method (LBM) coupled with the immersed boundary method (IBM) is employed to study the focusing and separation of particles in viscoelastic fluid. In this method, the viscoelastic fluid is simulated by the LBM with two sets of distribution functions and the fluid–particle interaction is calculated by the IBM. The performance of particle focusing under different microchannel aspect ratios (AR) is explored and the focusing equilibrium positions of the particles with various elasticity numbers and particle diameters are compared to illustrate the mechanism of particle focusing and separation in viscoelastic fluids. The results indicate that, for particle focusing in the square channel (AR = 1), the centerline single focusing becomes a bistable focusing at the centerline and corners as El increases. In the rectangular channels (AR < 1), particles with different diameters have different equilibrium positions. The equilibrium position of large particles is closer to the wall, and large particles have a faster lateral migration speed and few large particles migrate towards the channel center. Compared with the square channel, the rectangular channel is a better design for particle separation.

Highlights

Particle focusing is essential for particle counting and detection [1]
The viscoelastic microfluidics using viscoelastic fluids can achieve a single equilibrium position focusing of particles in a simple straight channel, and particles in viscoelastic fluids can migrate to the walls or corners by overcoming the repulsion between the wall and the particles due to inertia
The concept of elasto-inertial particle focusing was first proposed by Yang et al [7], who realized the single-line focusing of particles in the center of the square channel by combining the elastic force and inertial lift

Summary

Introduction

Particle focusing is essential for particle counting and detection [1]. In addition, particle separation from mixed samples is a key step in applications such as medical diagnosis and chemical analysis [2]. Raffiee et al [19] used 3D numerical simulation to study the lift force distribution acting on particles in the viscoelastic fluid They predicted the equilibrium positions under different parameters and analyzed the stability of the different equilibrium points. Yu et al [20] used a fictitious domain method to study the focusing equilibrium positions of the particles in the square channel under different Re and Wi. In their study, as the fluid elasticity increases, the equilibrium positions occur successively at the cross-section midline, diagonal, corner, and the center of the channel. The interaction between particles and viscoelastic fluid is calculated by the IBM [23,24,25] Through this method, particle focusing under different elastic numbers El is studied and the influence of cross-section AR on particle focusing is discussed. We explored the size-based separation of particles in different cross-section AR channels, by studying the migration phenomenon of particles with different diameters

Numerical Methods

IBM for the Interaction between Particles and Fluid

Channel Model and Validation

Particle Focusing

Particle Separation