Variation of focusing patterns of laterally migrating particles in a square-tube flow due to non-Newtonian elastic force

TL;DR

This study investigates how non-Newtonian elastic forces influence the focusing patterns of particles in square-tube flows, revealing concentration-dependent transitions and underlying elastic force mechanisms through experiments and simulations.

Contribution

It provides new insights into particle focusing behavior in viscoelastic fluids, combining experimental and numerical approaches to elucidate elastic force effects.

Findings

Particles focus on midline or diagonal depending on polymer concentration

Numerical simulations replicate experimental focusing patterns

Elastic forces due to normal stress difference drive pattern transitions

Abstract

The elasto-inertial effects on particle focusing in a square-tube flow were investigated experimentally and numerically. Microscale experiments using spherical particles in dilute polymer solutions demonstrated that the particles are focused on the midline and/or the diagonal in a downstream cross-section, depending on the polymer concentration. Numerical computations based on the FENE-P model for the viscoelastic flow reproduced these focusing patterns. It was revealed that the transitions among the patterns are accounted for by the elastic forces due to the first normal stress difference and the polymer elongation, which are the essentials of the viscoelastic fluid.