Inertial focusing of finite-size particles in microchannels

Abstract

At finite Reynolds numbers, Re, particles migrate across laminar flow streamlines to their equilibrium positions in microchannels. This migration is attributed to a lift force, and the balance between this lift and gravity determines the location of particles in channels. Here we demonstrate that velocity of finite-size particles located near a channel wall differs significantly from that of an undisturbed flow, and that their equilibrium position depends on this, referred to as slip velocity, difference. We then present theoretical arguments, which allow us to generalize expressions for a lift force, originally suggested for some limiting cases and Re ≪ 1, to finite-size particles in a channel flow at Re ≤ 20. Our theoretical model, validated by lattice Boltzmann simulations, provides considerable insight into inertial migration of finite-size particles in microchannel and suggests some novel microfluidic approaches to separate them by size or density at a moderate Re. † Email address for correspondence: aes50@yandex.ru ‡

Inertial migration of neutrally buoyant particles in superhydrophobic channels

“…In the no-slip channel ( Fig. 7(a)), the migration velocity curve is similar to reported earlier for smaller particles [23]. The flow in the channel is symmetric, leading to focusing of particles at two symmetric equilibrium positions.…”

“…However, the particle velocity in the channel can differ significantly from that of a fluid due to hydrodynamic interactions with the walls. It has recently been suggested that in a symmetric no-slip hydrophilic channel this difference can be characterized by the correction functions h ξ and h η [23]:…”

Inertial focusing of non-neutrally buoyant spherical particles in curved microfluidic ducts

“…Observe that the inertial lift force on the particle gets stronger as the particle nears the bottom wall and this acts as a re-suspension mechanism to elevate the particle a little from the bottom wall. This is also observed in much simpler studies of the combined effects of gravity and inertial lift force on a spherical particle suspended in flow between two plane parallel walls (Asmolov et al 2018). Further, although to a lesser extent, the secondary component of the background flows acts to pull the particle up from the bottom wall in the half of the duct adjacent to the inside wall (relative to the centre of the duct bend).…”

Inertial Microfluidics for Single-Cell Manipulation and Analysis

“…This interesting lateral particle migration was also known as the "tubular pinch effect." After the first discovery of this phenomenon in the 1960s, a number of theoretical studies (Saffman 1965;Cox and Brenner 1968;Ho and Leal 1974;Schonberg and Hinch 1989;Asmolov 1999;Matas et al 2004;Asmolov et al 2018) have been carried out to uncover its underlying physics. Up until now, the most well-accepted explanation is that this lateral particle migration is caused by the inertial lift force (F L ) which is actually the resultant of the shear-gradient-induced inertial lift force (F LS ) and the wall-induced inertial lift force (F LW ) (Di Carlo et al 2007).…”