Analogue tuning of particle focusing in elasto-inertial flow

Abstract

We report a unique tuneable analogue trend in particle focusing in the laminar and weak viscoelastic regime of elasto-inertial flows. We observe experimentally that particles in circular cross-section microchannels can be tuned to any focusing bandwidths that lie between the “Segre-Silberberg annulus” and the centre of a circular microcapillary. We use direct numerical simulations to investigate this phenomenon and to understand how minute amounts of elasticity affect the focussing of particles at increasing flow rates. An Immersed Boundary Method is used to account for the presence of the particles and a FENE-P model is used to simulate the presence of polymers in a Non-Newtonian fluid. The numerical simulations study the dynamics and stability of finite size particles and are further used to analyse the particle behaviour at Reynolds numbers higher than what is allowed by the experimental setup. In particular, we are able to report the entire migration trajectories of the particles as they reach their final focussing positions and extend our predictions to other geometries such as the square cross section. We believe complex effects originate due to a combination of inertia and elasticity in the weakly viscoelastic regime, where neither inertia nor elasticity are able to mask each other’s effect completely, leading to a number of intermediate focusing positions. The present study provides a fundamental new understanding of particle focusing in weakly elastic and strongly inertial flows, whose findings can be exploited for potentially multiple microfluidics-based biological sorting applications.

Lab-in-a-fiber-based integrated particle separation and counting

“…A possible explanation for this is the distorted first normal stress difference that builds up around the particle, leading to an oscillatory stretching around its surface. The interested reader is referred to the work by Indradumna 43 for further analysis of the different migration dynamics leading to the oscillatory behavior of particles in circular channels in weak fluid elastic flows. While more work is needed to fully elucidate the observation of weak oscillatory behavior, there is a huge potential to exploit the strict sizedependent migration of particles for high-resolution separation applications, which has been the focus of the current work.…”

“…33 Furthermore, it was shown that the fibers can be co-drawn with compatible materials so that conductive domains can be integrated at arbitrary locations along channel walls. 43 In this work, we present elasto-inertial particle separation with high efficiency followed by particle counting in an integrated all-fiber microfluidic component. The overall configuration of the component is shown in Fig.…”

“…33 Furthermore, it was shown that the fibers can be co-drawn with compatible materials so that conductive domains can be integrated at arbitrary locations along channel walls. 43…”