Particle slip velocity influences inertial focusing of particles in curved microchannels

Saurabh Deshpande,Phanindra Tallapragada

doi:10.1038/s41598-018-30171-9

Abstract

Size based separation and identification of particles in microfluidics through purely hydrodynamic means has gained significant interest due to a number of possible biomedical applications. Curved micro-channels, particularly spiral micro-channels with rectangular cross-section and the dynamics of particles in such channels have been extensively researched to achieve size based separation of particles. In this paper we present evidence that sheds new light on the dynamics of particles in such curved channels; that a unique particle slip velocity is associated with the focusing positions in the cross sections, which leads to a balance of forces. Our experiments therefore imply that the forces acting on the particle lead to convergence to an attractor in both the physical space (the cross section of the channel) and the slip velocity space.

Highlights

Background on Particle Slip Velocity andFocusingTaking a dynamical systems point of view, several papers[12,13,14,15,16], have predicted the clustering and size based segregation of particles in some canonical two and three dimensional fluid flows
We show that distinct particle axial slip velocities are associated with particle spatial focusing positions in a spiral channel’s cross section, i.e. particle focusing phenomenon is due to a convergence of particle dynamics spatially as well as in slip velocity
We show through our experiments that a necessary condition for such an equilibrium position could be that the particle slip velocity be nonzero

Summary

Introduction

Taking a dynamical systems point of view, several papers[12,13,14,15,16], have predicted the clustering and size based segregation of particles in some canonical two and three dimensional fluid flows. The calculations in these papers are based on a simplification of the Maxey-Riley equation[17], that governs the motion of a small spherical neutrally buoyant particle, d (v − u) = −[(v − u) ⋅ ∇]u − 2 St−1(v − u) dt (1). The length scale relevant to particle focusing in a microchannel is the hydraulic d29iaRmedLe2p2te, rw, dhhe,roefLthies a length channel.

Methods

Discussion

Conclusion