Flows and mixing in channels with misaligned superhydrophobic walls

TL;DR

This paper introduces a theoretical framework and simulations to analyze how misaligned superhydrophobic channel surfaces generate transverse shear flows, leading to complex mixing patterns that depend on flow conditions.

Contribution

It proposes a novel effective shear tensor approach to quantify transverse flows in misaligned superhydrophobic channels, supported by theoretical and simulation results.

Findings

Transverse shear induces complex flow patterns and vertical mixing.

Flow behavior varies with Reynolds number, showing vortices at low Reynolds and isolated vortices at high Reynolds.

The approach enables passive control of flow and mixing in microfluidic channels.

Abstract

Aligned superhydrophobic surfaces with the same texture orientation reduce drag in the channel and generate secondary flows transverse to the direction of the applied pressure gradient. Here we show that a transverse shear can be easily generated by using superhydrophobic channels with misaligned textured surfaces. We propose a general theoretical approach to quantify this transverse flow by introducing the concept of an effective shear tensor. To illustrate its use, we present approximate theoretical solutions and Dissipative Particle Dynamics simulations for striped superhydrophobic channels. Our results demonstrate that the transverse shear leads to complex flow patterns, which provide a new mechanism of a passive vertical mixing at the scale of a texture period. Depending on the value of Reynolds number two different scenarios occur. At relatively low Reynolds number the flow represents a transverse shear superimposed with two co-rotating vortices. For larger Reynolds number these vortices become isolated, by suppressing fluid transport in the transverse direction.