Acoustic streaming and thermal instability of flow generated by ultrasound in a cylindrical container

Adam Green,Junru Wu,Dong Ma,Jeffrey S Marshall

doi:10.1063/1.4965899

Abstract

A vertically orientated ultrasonic transducer contained within a closed cylindrical Pyrex tube was used to study the acoustic streaming flow within a cylindrical container. A particle-image velocimetry (PIV) system incorporating fluorescent 1.5 μm seeding particles suspended in a mixture of diethyl-phthalate and ethanol, whose optical index was matched to that of Pyrex, was used to allow for undistorted PIV imaging within the Pyrex tube. Temperature on the end-wall surface and acoustic pressure within the cylinder were measured for different end-wall materials. Variables considered included acoustic absorption and reflection coefficients, ultrasound intensity, container height, and thermal properties of the end-wall material. It was observed that a quasi-steady flow field driven by acoustic streaming is rapidly established within the container, which is typically dominated by a stationary vortex ring with downward flow along the ring axis. After sufficient time this quasi-stationary flow exhibits a thermal instability causing it to transform into a secondary flow state. Different types of secondary flow states were observed, including cases where the flow along the cylinder axis is oriented upward toward the ultrasound transducer and cases where the axial flow changes directions along the cylinder axis.

Highlights

Liposomes from a suspension onto a substrate, either to deliver drugs to a tissue that is cancerous or otherwise diseased (Huang, 2008 and Schroeder et al, 2009) or to deliver antibiotic chemicals to a biofilm (Ma et al, 2015)
A particle-image velocimetry (PIV) system incorporating fluorescent 1.5 μm seeding particles suspended in a mixture of diethyl-phthalate and ethanol, whose optical index was matched to that of Pyrex, was used to allow for undistorted PIV imaging within the Pyrex tube
The analysis and experimental results of Moudjed et al (2015) showed that the acoustic streaming flow generated by an acoustic transducer is closely approximated by that generated by a simple parallel wave approximation, even in the transducer near field, so we do not expect the acoustic streaming flow to be sensitive to the small variation of acoustic pressure within the ultrasound beam

Summary

Introduction

Liposomes from a suspension onto a substrate, either to deliver drugs to a tissue that is cancerous or otherwise diseased (Huang, 2008 and Schroeder et al, 2009) or to deliver antibiotic chemicals to a biofilm (Ma et al, 2015). The effect of acoustic streaming on the Rayleigh-Bénard thermal instability problem, in which the applied temperature gradient is normal to the dominant flow and sound propagation direction, was examined numerically by Hadid et al (2012). While the flow along the cylinder axis was always directed downward toward the impingement surface in the Marshall and Wu (2015) computations, the simulations were performed for a relatively short time period for which the end-wall surface temperature remains below the critical value required for thermal over-turning.

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Results

Conclusion