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Fibre orientation control related to papermaking
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0003-3737-0091
2007 (English)In: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, Vol. 129, no 4, 457-465 p.Article in journal (Refereed) Published
Abstract [en]

The orientation of fibers suspended in a shear flow flowing over a solid wall has been studied experimentally. The possibility to control this orientation with physical surface modifications, ridges, has also been studied. The fiber suspension was driven by gravity down a slightly inclined glass plate and a CCD-camera was used to capture images of the fibers in the flow. Image analysis based on the concept of steerable filters extracted the position and orientation of the fibers in the plane of the image. From these data, the velocity of the fibers was determined. When viewing the flow from the side, the velocity of the fibers at different heights was measured and found to agree with the theoretical solution for Newtonian flow down an inclined plate. Moving the camera so that the flow was filmed from below, the orientation and velocity of fibers in the plane parallel to the solid surface was determined. The known relationship between the velocity and the wall normal position of the fibers made it possible to determine the height above the plate for each identified fiber. Far away from the wall, the fibers were aligned with the flow direction in both cases. In a region close to the smooth plate surface the fibers oriented themselves perpendicular to the flow direction. This change in orientation did not occur when the surface structure was modified with ridges.

Place, publisher, year, edition, pages
2007. Vol. 129, no 4, 457-465 p.
Keyword [en]
simple shear-flow, ellipsoidal particles, viscous-fluid, motion, suspensions
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-6781DOI: 10.1115/1.2436583ISI: 000245692000011Scopus ID: 2-s2.0-34248184588OAI: oai:DiVA.org:kth-6781DiVA: diva2:11588
Available from: 2007-02-15 Created: 2007-02-15 Last updated: 2011-11-07Bibliographically approved
In thesis
1. Orientation of fibres in suspensions flowing over a solid surface
Open this publication in new window or tab >>Orientation of fibres in suspensions flowing over a solid surface
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

The orientation of fibres suspended in a viscous fluid, flowing over a solid surface, has been studied experimentally. A shear layer was generated, by letting the suspension flow down an inclined plate. Far upstream from the measuring section the suspension was accelerated to obtain an initial orientation of the fibres aligned with the flow direction. A CCD-camera was used to visualise the fibres. The velocity profile of the fibres coincided with the theoretical expression for fully developed flow of Newtonian liquid down an inclined wall.

The orientation of the fibres was analysed in planes parallel to the solid surface. At distances from the wall larger than one fibre length the fibres performed a tumbling motion in the flow-gradient plane in what appeared to be Jeffery-like orbits. Closer to the wall a difference was found between fibres of aspect ratio rp = 10 and 40. The longer fibres of rp = 40 kept their orientation, aligned with the flow, also in the near wall region. For the shorter fibres the orientation shifted gradually, to orientations closer to the vorticity axis, when the distance from the wall was decreased. In the very proximity to the wall the fibres were aligned with the vorticity, perpendicular to the direction of the flow. Another distinction, most likely related to the fibre orientation, was seen in the wall normal concentration profile. Due to sedimentation effects fibres accumulated in the near wall region. For fibres of rp = 10 a peak in concentration was found at the wall, while for r=40 the maximum concentration was found approximately half a fibre length from the wall. It is previously known that a fibre can interact with the wall in what is referred to as a "pole vaulting" motion away from the wall. It is suggested, as a likely explanation to the location of the maximum concentration, that fibres of rp = 40 perform this motion, while fibres of rp=10 do not.

In another experiment the surface of the wall was modified with ridges. For fibres of rp = 10 there were no longer any fibres oriented perpendicular to the flow direction in the near wall region.

The main application in mind throughout this work is papermaking. The study is considered to be of fundamental character and is not applicable in a direct sense. The difference between the flow situation in the experiments and the paper machine is discussed further.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. vi, 32 p.
Series
Trita-MEK, ISSN 0348-467X ; 2007:01
Keyword
fluid mechanics, fibre orientation, shear flow, fibre suspension, papermaking
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-4278 (URN)978-91-7178-555-8 (ISBN)
Presentation
2007-02-23, Sundbladssalen, STFI-Packforsk, Drottning Kristinas väg 61, Stockholm, 09:00
Opponent
Supervisors
Note
QC 20101103Available from: 2007-02-15 Created: 2007-02-15 Last updated: 2010-11-03Bibliographically approved
2. Near wall fibre orientation in flowing suspensions
Open this publication in new window or tab >>Near wall fibre orientation in flowing suspensions
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with fibre orientation in wall-bounded shear flows. The primary application in mind is papermaking. The study is mainly experimental,but is complemented with theoretical considerations.The main part of the thesis concerns the orientation of slowly settlingfibres in a wall-bounded viscous shear flow. This is a flow case not dealt withpreviously even at small Reynolds numbers. Experiments were conducted usingdilute suspensions with fibres having aspect ratios of rp ≈ 7 and 30. It is foundthat the wall effect on the orientation is small for distances from the wall wherethe fibre centre is located farther than half a fibre length from the wall. Farfrom the wall most fibres were oriented close to the flow direction. Closer tothe wall than half a fibre length the orientation distribution first shifted to bemore isotropic and in the very proximity of the wall the fibres were orientedclose to perpendicular to the flow direction, nearly aligned with the vorticityaxis. This was most evident for the shorter fibres with rp ≈ 7.Due to the density difference between the fibres and the fluid there is anincreased concentration near the wall. Still, a physical mechanism is requiredin order for a fibre initially oriented close to the flow direction at about half afibre length from the wall to change its orientation to aligned with the vorticityaxis once it has settled down to the wall. A slender body approach is usedin order to estimate the effect of wall reflection and repeated wall contacts onthe fibre rotation. It is found that the both a wall reflection, due to settlingtowards the wall, and contact between the fibre end and the wall are expectedto rotate the fibre closer to the vorticity axis. A qualitative agreement withthe experimental results is found in a numerical study based on the theoreticalestimation.In addition an experimental study on fibre orientation in the boundarylayers of a headbox is reported. The orientation distribution in planes parallelto the wall is studied. The distribution is found to be more anisotropic closerto the wall, i.e. the fibres tend to be oriented closer to the flow direction nearthe wall. This trend is observed sufficiently far upstream in the headbox.Farther downstream no significant change in the orientation distribution couldbe detected for different distances from the wall.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. vi, 49 p.
Series
Trita-MEK, ISSN 0348-467X ; 2009:03
Keyword
fluid mechanics, fibre orientation, shear flow, wall effect, fibre suspension, papermaking
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-9995 (URN)978-91-7415-240-1 (ISBN)
Public defence
2009-03-27, E2, Lindstedsvägen 3, Stockholm, 10:15 (English)
Opponent
Supervisors
Note
QC 20100706Available from: 2009-03-02 Created: 2009-02-26 Last updated: 2010-07-21Bibliographically approved

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