Fluid viscoelasticity controls acoustic streaming via shear waves

TL;DR

This paper demonstrates how fluid viscoelasticity influences acoustic streaming in microchannels, revealing control mechanisms via shear waves and stress interplay, with potential applications in microfluidic particle manipulation.

Contribution

It introduces a novel framework linking viscoelastic properties and acoustic streaming regimes through the Streaming Coefficient and shear wave dynamics.

Findings

Streaming is enhanced when $C_s>1$

Streaming is suppressed when $0 extless C_s extless 1$

Streaming is reversed when $C_s<0$

Abstract

Control of acoustic streaming can significantly impact fluid and particle transport in microfluidics. We report enhancement, suppression, and reversal of acoustic streaming inside a rectangular microchannel by controlling the fluid viscoelastic properties. Our study reveals that the streaming regimes depend on Deborah number ($De$) and viscous diffusion number ($Dv$), expressed in terms of a Streaming Coefficient ($C_s$). We find streaming is enhanced when $C_s>1$, suppressed for $0\leq C_s\leq1$, and reversed when $C_s<0$. We explain the regimes in terms of the interplay between the Reynolds and viscoelastic stresses that collectively drive fluid motion. Remarkably, we discover the role of viscoelastic shear waves in acoustic streaming transition characterized by the ratio of acoustic attenuation length and shear wavelength. We gain deeper insight into the streaming transition by examining energy dynamics in terms of the loss and storage moduli. Our study may find applications in acousto-microfluidics systems for particle handling and fluid pumping/mixing.