Frequency effect on streaming phenomenon induced by Rayleigh surface acoustic wave in microdroplets

Mansour Alghane, Yong Qing Fu, Baixin Chen, Yan Li, Marc Phillipe Yves Desmulliez, A Walton

Research output: Contribution to journalArticle

Abstract

Acoustic streaming of ink particles inside a water microdroplet generated by a surface acoustic wave (SAW) has been studied numerically using a finite volume numerical method and these results have been verified using experimental measurements. Effects of SAW excitation frequency, droplet volume, and radio-frequency (RF) power are investigated, and it has been shown that SAW excitation frequency influences the SAW attenuation length, lSAW, and hence the acoustic energy absorbed by liquid. It has also been observed that an increase of excitation frequency generally enhances the SAW streaming behavior. However, when the frequency exceeds a critical value that depends on the RF power applied to the SAW device, weaker acoustic streaming is observed resulting in less effective acoustic mixing inside the droplet. This critical value is characterised by a dimensionless ratio of droplet radius to SAW attenuation length, i.e., Rd/lSAW. With a mean value of Rd/lSAW?˜?1, a fast and efficient mixing can be induced, even at the lowest RF power of 0.05 mW studied in this paper. On the other hand, for the Rd/lSAW ratios much larger than ~1, significant decreases in streaming velocities were observed, resulting in a transition from regular (strong) to irregular (weak) mixing/flow. This is attributed to an increased absorption rate of acoustic wave energy that leaks into the liquid, resulting in a reduction of the acoustic energy radiated away from the SAW interaction region towards the droplet free surface. It has been demonstrated in this study that a fast and efficient mixing process with a smaller RF power could be achieved if the ratio of Rd/lSAW?=?1 in the SAW-droplet based microfluidics
Original languageEnglish
Article number084902
Number of pages12
JournalJournal of Applied Physics
Volume112
Issue number8
DOIs
Publication statusPublished - 2012

Fingerprint

acoustics
radio frequencies
acoustic streaming
acoustic excitation
acoustic attenuation
wave attenuation
wave excitation
surface acoustic wave devices
inks
wave interaction
liquids
energy
low frequencies
radii
water
excitation

Keywords

  • Droplet
  • CFD
  • SAW
  • Mixing
  • Frequency

Cite this

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title = "Frequency effect on streaming phenomenon induced by Rayleigh surface acoustic wave in microdroplets",
abstract = "Acoustic streaming of ink particles inside a water microdroplet generated by a surface acoustic wave (SAW) has been studied numerically using a finite volume numerical method and these results have been verified using experimental measurements. Effects of SAW excitation frequency, droplet volume, and radio-frequency (RF) power are investigated, and it has been shown that SAW excitation frequency influences the SAW attenuation length, lSAW, and hence the acoustic energy absorbed by liquid. It has also been observed that an increase of excitation frequency generally enhances the SAW streaming behavior. However, when the frequency exceeds a critical value that depends on the RF power applied to the SAW device, weaker acoustic streaming is observed resulting in less effective acoustic mixing inside the droplet. This critical value is characterised by a dimensionless ratio of droplet radius to SAW attenuation length, i.e., Rd/lSAW. With a mean value of Rd/lSAW?˜?1, a fast and efficient mixing can be induced, even at the lowest RF power of 0.05 mW studied in this paper. On the other hand, for the Rd/lSAW ratios much larger than ~1, significant decreases in streaming velocities were observed, resulting in a transition from regular (strong) to irregular (weak) mixing/flow. This is attributed to an increased absorption rate of acoustic wave energy that leaks into the liquid, resulting in a reduction of the acoustic energy radiated away from the SAW interaction region towards the droplet free surface. It has been demonstrated in this study that a fast and efficient mixing process with a smaller RF power could be achieved if the ratio of Rd/lSAW?=?1 in the SAW-droplet based microfluidics",
keywords = "Droplet, CFD, SAW, Mixing, Frequency",
author = "Mansour Alghane and Fu, {Yong Qing} and Baixin Chen and Yan Li and Desmulliez, {Marc Phillipe Yves} and A Walton",
year = "2012",
doi = "10.1063/1.4758282",
language = "English",
volume = "112",
journal = "Journal of Applied Physics",
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Frequency effect on streaming phenomenon induced by Rayleigh surface acoustic wave in microdroplets. / Alghane, Mansour; Fu, Yong Qing; Chen, Baixin; Li, Yan; Desmulliez, Marc Phillipe Yves; Walton, A.

In: Journal of Applied Physics, Vol. 112, No. 8, 084902, 2012.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Frequency effect on streaming phenomenon induced by Rayleigh surface acoustic wave in microdroplets

AU - Alghane, Mansour

AU - Fu, Yong Qing

AU - Chen, Baixin

AU - Li, Yan

AU - Desmulliez, Marc Phillipe Yves

AU - Walton, A

PY - 2012

Y1 - 2012

N2 - Acoustic streaming of ink particles inside a water microdroplet generated by a surface acoustic wave (SAW) has been studied numerically using a finite volume numerical method and these results have been verified using experimental measurements. Effects of SAW excitation frequency, droplet volume, and radio-frequency (RF) power are investigated, and it has been shown that SAW excitation frequency influences the SAW attenuation length, lSAW, and hence the acoustic energy absorbed by liquid. It has also been observed that an increase of excitation frequency generally enhances the SAW streaming behavior. However, when the frequency exceeds a critical value that depends on the RF power applied to the SAW device, weaker acoustic streaming is observed resulting in less effective acoustic mixing inside the droplet. This critical value is characterised by a dimensionless ratio of droplet radius to SAW attenuation length, i.e., Rd/lSAW. With a mean value of Rd/lSAW?˜?1, a fast and efficient mixing can be induced, even at the lowest RF power of 0.05 mW studied in this paper. On the other hand, for the Rd/lSAW ratios much larger than ~1, significant decreases in streaming velocities were observed, resulting in a transition from regular (strong) to irregular (weak) mixing/flow. This is attributed to an increased absorption rate of acoustic wave energy that leaks into the liquid, resulting in a reduction of the acoustic energy radiated away from the SAW interaction region towards the droplet free surface. It has been demonstrated in this study that a fast and efficient mixing process with a smaller RF power could be achieved if the ratio of Rd/lSAW?=?1 in the SAW-droplet based microfluidics

AB - Acoustic streaming of ink particles inside a water microdroplet generated by a surface acoustic wave (SAW) has been studied numerically using a finite volume numerical method and these results have been verified using experimental measurements. Effects of SAW excitation frequency, droplet volume, and radio-frequency (RF) power are investigated, and it has been shown that SAW excitation frequency influences the SAW attenuation length, lSAW, and hence the acoustic energy absorbed by liquid. It has also been observed that an increase of excitation frequency generally enhances the SAW streaming behavior. However, when the frequency exceeds a critical value that depends on the RF power applied to the SAW device, weaker acoustic streaming is observed resulting in less effective acoustic mixing inside the droplet. This critical value is characterised by a dimensionless ratio of droplet radius to SAW attenuation length, i.e., Rd/lSAW. With a mean value of Rd/lSAW?˜?1, a fast and efficient mixing can be induced, even at the lowest RF power of 0.05 mW studied in this paper. On the other hand, for the Rd/lSAW ratios much larger than ~1, significant decreases in streaming velocities were observed, resulting in a transition from regular (strong) to irregular (weak) mixing/flow. This is attributed to an increased absorption rate of acoustic wave energy that leaks into the liquid, resulting in a reduction of the acoustic energy radiated away from the SAW interaction region towards the droplet free surface. It has been demonstrated in this study that a fast and efficient mixing process with a smaller RF power could be achieved if the ratio of Rd/lSAW?=?1 in the SAW-droplet based microfluidics

KW - Droplet

KW - CFD

KW - SAW

KW - Mixing

KW - Frequency

U2 - 10.1063/1.4758282

DO - 10.1063/1.4758282

M3 - Article

VL - 112

JO - Journal of Applied Physics

JF - Journal of Applied Physics

SN - 0021-8979

IS - 8

M1 - 084902

ER -