Modelling of a microfluid ultrasonic particle separator
Modelling of a microfluid ultrasonic particle separator
Particles within an ultrasonic standing wave experience an acoustic force causing the particles to
move to certain positions within the acoustic field. This phenomenon can be used to manipulate
particles and so provides a means to separate, concentrate or trap particles, cells or spores. The
work described is applied to a micro-engineered flow-through device for processing small samples
and incorporates a fluid filled chamber of depth typically between 100 and 200?m, and therefore
approaches microfluidic dimensions. The successful design and subsequent performance of such
devices rely on the predictability of particle trajectories which are influenced predominantly by
acoustic and fluid flow fields. Therefore, the majority of this research seeks an understanding of
the nature of these fields and, in turn, reliable simulation of particle trajectories.
Computational fluid dynamics (CFD) modelling is used to develop a robust 2-dimensional
model of the device’s microchannels and is used to predict the presence of eddy regions, associated
with the etch fabrication techniques, which are likely to disrupt the separation process. Based on
a geometric study, simulations and subsequent test results on a fabricated device have revealed
geometric modifications which minimise these eddy flows and promote the existence of laminar
flow within the main channel of the device.
Finite element analysis (FEA) provides a method to investigate the 2-dimensional characteristics
of the acoustic field and reveals variations in acoustic pressure across the width of the device,
giving rise to lateral radiation forces frequently reported in similar ultrasonic devices. This work
investigates acoustic enclosure modes in 2 or 3-dimensions as a possible cause of these lateral
variations, with modelled results matching well with experiment.
A particle force model has also been developed which predicts the motion of particles through
the device, and by which concentration and separation performance may be calculated. This tool is
used to investigate acoustic design, operating conditions and separation performance for both the
micro-engineered device and a device based on a quarter-wavelength, providing valuable insight
into various trends observed.
The novelty in this work is the application of macro-scale numerical techniques to microengineered
ultrasonic particle manipulators and the execution of an extensive analysis of the design
and operation of such devices. These analyses have demonstrated, and therefore have explained,
various phenomena associated with the fluid and acoustic fields, and how they influence particle
separation performance. The development of similar devices can be aided by the use of the
numerical simulation methods featured throughout this thesis.
Townsend, Rosemary Jane
0452b21c-a758-4d4a-925b-1511d9296d62
February 2006
Townsend, Rosemary Jane
0452b21c-a758-4d4a-925b-1511d9296d62
Townsend, Rosemary Jane
(2006)
Modelling of a microfluid ultrasonic particle separator.
University of Southampton, School of Engineering Sciences, Doctoral Thesis, 261pp.
Record type:
Thesis
(Doctoral)
Abstract
Particles within an ultrasonic standing wave experience an acoustic force causing the particles to
move to certain positions within the acoustic field. This phenomenon can be used to manipulate
particles and so provides a means to separate, concentrate or trap particles, cells or spores. The
work described is applied to a micro-engineered flow-through device for processing small samples
and incorporates a fluid filled chamber of depth typically between 100 and 200?m, and therefore
approaches microfluidic dimensions. The successful design and subsequent performance of such
devices rely on the predictability of particle trajectories which are influenced predominantly by
acoustic and fluid flow fields. Therefore, the majority of this research seeks an understanding of
the nature of these fields and, in turn, reliable simulation of particle trajectories.
Computational fluid dynamics (CFD) modelling is used to develop a robust 2-dimensional
model of the device’s microchannels and is used to predict the presence of eddy regions, associated
with the etch fabrication techniques, which are likely to disrupt the separation process. Based on
a geometric study, simulations and subsequent test results on a fabricated device have revealed
geometric modifications which minimise these eddy flows and promote the existence of laminar
flow within the main channel of the device.
Finite element analysis (FEA) provides a method to investigate the 2-dimensional characteristics
of the acoustic field and reveals variations in acoustic pressure across the width of the device,
giving rise to lateral radiation forces frequently reported in similar ultrasonic devices. This work
investigates acoustic enclosure modes in 2 or 3-dimensions as a possible cause of these lateral
variations, with modelled results matching well with experiment.
A particle force model has also been developed which predicts the motion of particles through
the device, and by which concentration and separation performance may be calculated. This tool is
used to investigate acoustic design, operating conditions and separation performance for both the
micro-engineered device and a device based on a quarter-wavelength, providing valuable insight
into various trends observed.
The novelty in this work is the application of macro-scale numerical techniques to microengineered
ultrasonic particle manipulators and the execution of an extensive analysis of the design
and operation of such devices. These analyses have demonstrated, and therefore have explained,
various phenomena associated with the fluid and acoustic fields, and how they influence particle
separation performance. The development of similar devices can be aided by the use of the
numerical simulation methods featured throughout this thesis.
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thesis_Townsend.pdf
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More information
Published date: February 2006
Organisations:
University of Southampton
Identifiers
Local EPrints ID: 46695
URI: http://eprints.soton.ac.uk/id/eprint/46695
PURE UUID: c7079f50-b93f-4821-a6d7-5e484e551d75
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Date deposited: 13 Jul 2007
Last modified: 13 Mar 2019 21:02
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Author:
Rosemary Jane Townsend
University divisions
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