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Orientation of elongated particles in shear and extensional flow
KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Elongated particles in fluid flows are a big part of the world we are living in. Gaining knowledge on how particles behave in different fluid flows can potentially increase the efficiency of industrial processes and decrease the world's energy consumption as well as improve the properties of future materials.

In this thesis, the orientation of elongated particles in two different flows are studied. The first case is a dilute fibre suspension in a turbulent flow and the second case is a semi-dilute fibril dispersion in a laminar flow. The fibres (cellulose acetate) are at least three orders of magnitude larger than the fibrils (nano-fibrillated cellulose).

The turbulent flow case is half of a full channel flow, characterised by the friction Reynolds number, and is experimentally examined. This experiment is closely related to the papermaking process. Laser Doppler velocimetry measurements are preformed without fibres in order to make sure that the flow is turbulent and fully developed. Images of the fibres in the flow are acquired using a CCD-camera, from which it is possible to detect the fibres in an image processing step and extract both the positions and orientations of the fibres. A large parameter study is carried out, where the aspect ratio of the fibres, concentration and Reynolds number are changed. Short fibres are observed to align perpendicular to the flow, while the longer fibres are found to align in the flow direction. The fibres are also seen to accumulate in streamwise streaks, believed to be caused by velocity structures in the turbulent flow.

The second flow case studied focusses on a semi-dilute dispersion in a laminar flow. It includes both experiments and numerical calculations of the fibril orientation. The aim of this study is to demonstrate that it is possible to control the fibril orientation with a fluid. In a semi-dilute dispersion, fibrils are interacting. However, no flocs or networks are formed. A flow focusing apparatus is used in order to hydrodynamically accelerate the dispersion with an outer fluid (sheath) flow. The mean orientation in the flow direction is experimentally studied by detecting the birefringence of the flowing dispersion. The orientation distribution is calculated by solving the Smoluchowski equation. The fibrils are seen to align in the flow direction both in the experiments and the calculations. Moreover, the alignment is found to increase with increasing acceleration.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , viii, 25 p.
Series
Trita-MEK, ISSN 0348-467X ; 2012:11
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-95282ISBN: 978-91-7501-404-3 (print)OAI: oai:DiVA.org:kth-95282DiVA: diva2:527398
Presentation
2012-06-15, Seminarierummet, Brinellvägen 32, KTH, Stockholm, 14:00 (English)
Opponent
Supervisors
Note
QC 20120607Available from: 2012-06-07 Created: 2012-05-21 Last updated: 2012-06-07Bibliographically approved
List of papers
1. Measurement of width and streakiness of particle streaks in turbulent flows
Open this publication in new window or tab >>Measurement of width and streakiness of particle streaks in turbulent flows
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(English)Article in journal (Other academic) Submitted
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-96613 (URN)
Note
QS 2012Available from: 2012-06-07 Created: 2012-06-07 Last updated: 2014-09-08Bibliographically approved
2. Fibre orientation and fibre streaks in turbulent wall bounded flow
Open this publication in new window or tab >>Fibre orientation and fibre streaks in turbulent wall bounded flow
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(English)Manuscript (preprint) (Other academic)
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-96616 (URN)
Note

QS 2012

Available from: 2012-06-07 Created: 2012-06-07 Last updated: 2014-10-03Bibliographically approved
3. Orientation of nano-fibrillated cellulose in accelerated flow
Open this publication in new window or tab >>Orientation of nano-fibrillated cellulose in accelerated flow
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(English)Manuscript (preprint) (Other academic)
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-96618 (URN)
Note
QS 2012Available from: 2012-06-07 Created: 2012-06-07 Last updated: 2012-06-07Bibliographically approved

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