Chaotic mixing in a planar, curved channel using periodic slip

TL;DR

This paper introduces a new method for chaotic micromixing in curved channels by using alternating slip at the walls to induce streamline crossing and chaos, with optimal slip conditions enhancing mixing efficiency.

Contribution

It presents a novel physical approach to induce chaos in micromixers through wall slip, supported by analytical velocity solutions and chaos analysis, improving mixing in curved channels.

Findings

Wide channels exhibit better mixing than tall channels.

An optimal slip length maximizes mixing efficiency.

Counter-rotating Dean vortices enhance mixing at low slip and Reynolds numbers.

Abstract

We propose a novel strategy for designing chaotic micromixers using curved channels confined between two flat planes. The location of the separatrix between the Dean vortices, induced by centrifugal force, is dependent on the location of the maxima of axial velocity. An asymmetry in the axial velocity profile can change the location of the separatrix. This is achieved physically by introducing slip alternatingly at the top and bottom walls. This leads to streamline crossing and Lagrangian chaos. An approximate analytical solution of the velocity field is obtained using perturbation theory. This is used to find the Lagrangian trajectories of fluid particles. Poincare sections taken at periodic locations in the axial direction are used to study the extent of chaos. The extent of mixing, for low slip and low Reynolds numbers, is shown to be greater when Dean vortices in adjacent half cells are counter-rotating. Wide channels are observed to have much better mixing than tall channels; an important observation not made for separatrix flows till now. Eulerian indicators are used to gauge the extent of mixing with varying slip length and it is shown that an optimum slip length exists which maximizes the mixing in a particular geometry.