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Abstract
This thesis presents studies of boundarydriven acoustic streaming in microfluidic channels,
which is a steady flow of the fluid initiated by the interactions of an oscillating acoustic
standing wave and the rigid walls of the microchannel. The studies present analysis of the
acoustic resonance, the acoustic streaming flow, and the forces on suspended microparticles.
The work is motivated by the application of particle focusing by acoustic radiation forces in
medical, environmental and food sciences. Here acoustic streaming is most often unwanted,
because it limits the focusability of particles smaller than a given critical size. One of the
main goals of this thesis work has been to overcome this limitation.
The main text of this thesis serves to give an introduction to the theory and numerical models applied in the five journal papers supplied in the Appendixes, which constitute this thesis work.
Based on first and secondorder perturbation theory, assuming small acoustic amplitudes, we derived the timedependent governing equations under adiabatic conditions. The adiabatic first and secondorder equations are solved analytically for the acoustic field between two orthogonally oscillating plates. Furthermore, under general thermodynamic conditions, we derive the timedependent first and secondorder equations for the conservation of mass, momentum, and energy. The coupling from fluid equations to particle motion is achieved through the expressions for the streaminginduced drag force and the acoustic radiation force acting on particles suspended in the fluid. Lastly, the numerical method is discussed, with emphasis on how proper numerical convergence is ensured.
Three numerical studies are presented, in which the acoustic resonance and the acoustic streaming flow are investigated, both in the transient regime and in the purely periodic state. The solutions for the periodic acoustic resonance and the steady streaming flow are used to simulate the motion of suspended particle in a Lagrangian description, which mimics experimental particle tracking velocimetry.
In the forth study, the numerical model is used to engineer a single roll streaming flow, which does not counteract the focusing by the acoustic radiation force, contrary to the usual quadrupolar streaming flow. The single roll streaming flow is observed experimentally in a nearlysquare channel, and acoustophoretic focusing of E. coli bacteria and 0.6 µm particles is achieved. These particles are considerably smaller than the critical particle size of approximately 2 µm for the usual halfwavelength resonance in a rectangular channel.
The fifth study presents a quantitative comparison of analytical, numerical, and experimental results for the streaminginduced drag force dominated motion of particles suspended in a waterfilled microchannel supporting a transverse halfwavelength resonance. The experimental and theoretical results agree within a mean relative dierence of approximately 20%, a low deviation given stateoftheart in the field. Furthermore, the analytical solution for the acoustic streaming in rectangular channels with arbitrary large heighttowidth ratios is derived. This accommodates the analytical theory of acoustic streaming to applications within acoustofluidics.
The main text of this thesis serves to give an introduction to the theory and numerical models applied in the five journal papers supplied in the Appendixes, which constitute this thesis work.
Based on first and secondorder perturbation theory, assuming small acoustic amplitudes, we derived the timedependent governing equations under adiabatic conditions. The adiabatic first and secondorder equations are solved analytically for the acoustic field between two orthogonally oscillating plates. Furthermore, under general thermodynamic conditions, we derive the timedependent first and secondorder equations for the conservation of mass, momentum, and energy. The coupling from fluid equations to particle motion is achieved through the expressions for the streaminginduced drag force and the acoustic radiation force acting on particles suspended in the fluid. Lastly, the numerical method is discussed, with emphasis on how proper numerical convergence is ensured.
Three numerical studies are presented, in which the acoustic resonance and the acoustic streaming flow are investigated, both in the transient regime and in the purely periodic state. The solutions for the periodic acoustic resonance and the steady streaming flow are used to simulate the motion of suspended particle in a Lagrangian description, which mimics experimental particle tracking velocimetry.
In the forth study, the numerical model is used to engineer a single roll streaming flow, which does not counteract the focusing by the acoustic radiation force, contrary to the usual quadrupolar streaming flow. The single roll streaming flow is observed experimentally in a nearlysquare channel, and acoustophoretic focusing of E. coli bacteria and 0.6 µm particles is achieved. These particles are considerably smaller than the critical particle size of approximately 2 µm for the usual halfwavelength resonance in a rectangular channel.
The fifth study presents a quantitative comparison of analytical, numerical, and experimental results for the streaminginduced drag force dominated motion of particles suspended in a waterfilled microchannel supporting a transverse halfwavelength resonance. The experimental and theoretical results agree within a mean relative dierence of approximately 20%, a low deviation given stateoftheart in the field. Furthermore, the analytical solution for the acoustic streaming in rectangular channels with arbitrary large heighttowidth ratios is derived. This accommodates the analytical theory of acoustic streaming to applications within acoustofluidics.
Original language  English 

Place of Publication  Kongens Lyngby 

Publisher  Technical University of Denmark 
Number of pages  148 
Publication status  Published  2015 
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Dive into the research topics of 'Acoustic streaming in microchannels: The trinity of analytics, numerics and experiments'. Together they form a unique fingerprint.Projects
 1 Finished

Theory and design of microsystems for clinical acoustoactivated cell sorting
Tribler, P. M. (PhD Student), Bruus, H. (Main Supervisor), Sørensen, J. N. (Examiner), Dual, J. (Examiner) & GlynneJones, P. (Examiner)
15/04/2012 → 19/11/2015
Project: PhD