Inertial focusing of spherical particles in rectangular microchannels over a wide range of Reynolds numbers

Abstract

Inertial microfluidics has emerged as an important tool for manipulating particles and cells. For a better design of inertial microfluidic devices, we conduct 3D direct numerical simulations (DNS) and experiments to determine the complicated dependence of focusing behaviour on the particle size, channel aspect ratio, and channel Reynolds number. We find that the well-known focusing of the particles at the two centers of the long channel walls occurs at a relatively low Reynolds number, whereas additional stable equilibrium positions emerge close to the short walls with increasing Reynolds number. Based on the numerically calculated trajectories of particles, we propose a two-stage particle migration which is consistent with experimental observations. We further present a general criterion to secure good focusing of particles for high flow rates. This work thus provides physical insight into the multiplex focusing of particles in rectangular microchannels with different geometries and Reynolds numbers, and paves the way for efficiently designing inertial microfluidic devices.

Size-Based Separation of Particles and Cells Utilizing Viscoelastic Effects in Straight Microchannels

“…Moreover, inertial focusing pattern becomes more complex at higher Reynolds number Re, often resulting in unfavorable multiple lateral equilibrium positions. 37 41 There are two approaches to achieve viscoelastic separation, either by employing sheath flow (kinetic separation) or by engineering channel geometry (equilibrium separation). Nam et al successfully separated platelets from diluted whole blood with high efficiency of 99% using a sheath flow microdevice where RBCs were focused along the centerline whereas platelets remained near the side walls.…”

“…Moreover, inertial focusing pattern becomes more complex at higher Reynolds number Re, often resulting in unfavorable multiple lateral equilibrium positions. 37 Considering the condition of 0.07 h a D > for successful inertial focusing of particles, 38 the channel cross-section has to be scaled down with decreasing particle sizes [ h D , the hydraulic diameter, is defined as…”

Direct measurement of particle inertial migration in rectangular microchannels

“…Though there are many theories for the magnitudes of inertial focusing forces, direct experimental measurement of these forces remains an unmet challenge. Indeed existing theory [2][3][4][5], numerical simulations [6][7][8], and indirect experimental measurements [9] have produced contradictory scalings for the dependence of forces on particle size and velocity. In this paper, we directly measure inertial migration velocities by tracking the motion of particles in a rectangular channel over Reynolds numbers ranging from 30 to 180, and find that their measured migration velocities agree well with existing asymptotic theory [5].…”

Lateral migration of dual droplet trains in a double spiral microchannel

“…The last decade has seen extensive development of microfluidic approaches for particle/cell manipulation by either active methods using external force fields [10][11][12][13][14] or passive methods depending on hydrodynamic forces [15][16][17]. More recently, inertial migration has been increasingly involved for manipulation of rigid particles by hydrodynamic forces [18][19][20]. The inertial lift on a rigid particle stems from the asymmetry of pressure and viscous stresses on the particle surface in a Poiseuille flow at infinite Reynolds numbers (Re > 1, and Re U L = / m , where ρ and η are the density and viscosity of the carrier fluid, respectively, U m the mean channel velocity, and L the channel characteristic length) [16,20,21].…”