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Acoustic Separation of Submicron Solid Particles in air
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0002-4171-5091
KTH, School of Engineering Sciences (SCI), Mechanics. Polytechnique Montréal, Canada.
2015 (English)In: Ultrasonics, ISSN 0041-624X, E-ISSN 1874-9968, Vol. 63Article in journal (Refereed) Published
Abstract [en]

The use of ultrasound to continuously separate submicron particles suspended in air is investigated in a rectangular channel with adjustable height. An electrostatic transducer is used to generate a standing wave in the 50-80 kHz frequency range and the particles experience forces within the acoustic field causing them to concentrate at the pressure nodes. To assess the effect of several key design parameters on the separation efficiency, a simple method based on light scattering is implemented to provide information on the particle concentrations as a function of position in the channel. The images acquired are processed to yield a separation efficiency metric that is used to evaluate the effect of acoustic, flow and geometrical parameters. The results show that, in qualitative agreement with theoretical models, the maximum separation efficiency increases with the pressure amplitude of the sound wave. The separation efficiency is also linearly proportional to the standing wave frequency, when it is varied between 50-80 kHz. On the other hand, the effect of the average fluid velocity is less pronounced than expected, suggesting that in our channel separation is not limited by the interaction length between the acoustic field and the suspended particles. The effect of the parallelism of the reflector relative to the transducer is also investigated.

Place, publisher, year, edition, pages
2015. Vol. 63
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
URN: urn:nbn:se:kth:diva-167638DOI: 10.1016/j.ultras.2015.06.021ISI: 000359603000017Scopus ID: 2-s2.0-84945200466OAI: oai:DiVA.org:kth-167638DiVA: diva2:813384
Note

Updated from manuscript to article.

QC 20150909

Available from: 2015-05-22 Created: 2015-05-22 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Acoustic separation of submicron particles in gaseous flows
Open this publication in new window or tab >>Acoustic separation of submicron particles in gaseous flows
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The separation of submicron particles suspended in gaseous flows is a problem of great importance and is the subject of sustained research efforts. This is motivated by several challenges presented by modern science and technology requiring high separation efficiencies for submicron particles.Continuous acoustic particles separation is a novel technique based on the acoustophoresis phenomenon, in which a particle within an acoustic field is manipulated using acoustic forces on its surface. This technique has the potential to overcome some of the limitations of common techniques for the separation of submicron particles, as well as performing advanced tasks such as sorting particles according to their size or density.In this thesis, the separation of submicron solid particles suspended in air is investigated experimentally, with a focus on the effect of key design parameters (acoustic, flow, geometry) on the efficiency of the process. A simple method based on laser light scattering was also used to provide qualitative information on the particle number density as a function of position in the channel. This technique allowed to quickly investigate the effect of a wide range of parameters on the acoustic separation efficiency including the pressure amplitude, the frequency of the standing wave, the average flow velocity and the parallelism of the channel walls.   The results demonstrate conclusively that acoustic manipulation is possible for submicron particles and that the acoustic force scales following the trends expected from theoretical models developed in the continuum regime. From the size of the particles used it however follows that the observed separation is the result of transition regime acoustophoresis, with a Knudsen number on the order of 0.2.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. viii, 47 p.
Series
TRITA-MEK, ISSN 0348-467X ; 2015:06
Keyword
Acoustic, submicron particles, gaseous flows, separation
National Category
Engineering and Technology
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-167629 (URN)978-91-7595-604-6 (ISBN)
Presentation
2015-05-27, E2, Lindstedtsvägen 3, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20150522

Available from: 2015-05-22 Created: 2015-05-22 Last updated: 2016-05-27Bibliographically approved
2. Acoustic separation and electrostatic sampling of submicron particles suspended in air
Open this publication in new window or tab >>Acoustic separation and electrostatic sampling of submicron particles suspended in air
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

We investigate experimentally the effects of acoustic forces on submicron aerosol in a channel flow. This technique can potentially overcome some of the limitations of conventional separation systems and provide advanced manipulation capabilities such as sorting according to size or density. The theoretical framework for acoustophoresis at such small length scales where molecular effects are expected to be significant is still incomplete and in need of experimental validation. The main objectives of this thesis are to identify the physical limitations and capabilities of acoustophoretic manipulation for submicron aerosol particles.

Two sets of experiments were carried out: first, qualitative results revealed that acoustic manipulation is possible for submicron particles in air and that the acoustic force follows the trend expected by theoretical models developed for particles in inviscid fluids. The acoustic force on submicron particles was estimated in a second set of measurements performed with quantitative diagnostic tools. Comparison of these results with available theoretical models for the acoustic radiation forces demonstrates that for such small particles additional forces have to be considered. At submicron length scales, the magnitude of the forces observed is orders of magnitude higher than the predictions from the inviscid theory.

One potential application for acoustophoresis is specifically investigated in this thesis: assist electrostatic precipitation (ESP) samplers to target very small aerosols, such as those carrying airborne viruses. To identify the shortcomings of ESP samplers that acoustophoresis should overcome, two ESP designs have been investigated to quantify capture efficiency as a function of the particle size and of the air velocity in a wind tunnel. The results reveal that both designs have limitations when it comes to sampling submicron aerosol particles. When exposed to polydispersed suspensions they behave as low-pass filters.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 77 p.
Series
TRITA-MEK, ISSN 0348-467X
Keyword
Acoustic, separation, acoustophoresis
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-196857 (URN)978-91-7729-221-0 (ISBN)
Public defence
2016-12-16, D3, Lindstedsvägen 5, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20161125

Available from: 2016-11-25 Created: 2016-11-24 Last updated: 2016-11-25Bibliographically approved

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