Scale invariant hydrodynamic focusing and sorting of inertial particles by size in spiral micro channels

Abstract

The hydrodynamic separation of spherical particles in flows at low Reynolds numbers is a very active area of research in microfluidic engineering due to the many important biomedical applications. In particular, curved channels such as spiral channels are of growing interest because the lift and drag force exerted on inertial particles can be used to hydrodynamically separate the particles. In this paper we present a scale invariant classification of the lateral focusing of particles in highly curved spiral micro channels with a square cross section. We then use this scale invariant classification to demonstrate the separation of particles in two-particle mixtures across a large range of sizes. We thus show that our results can be used to systematically design the geometry of devices and select flow parameters to separate particles by size in a mixture.