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Fibre orientation near a wall of a headbox.
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. (Linné Flow Centre)
KTH, School of Engineering Sciences (SCI), Mechanics. (Linné Flow Centre)
2010 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 25, 204-212 p.Article in journal (Refereed) Published
Abstract [en]

Experimental results on the fibre orientation in a laboratory scale headbox are reported. A steerable filter was used to determine the orientation of bleached unbeaten birch fibres at different distances from one of the inclined walls of the headbox contraction. Due to optical limitations only dilute suspensions were studied. It is shown that the fibre orientation distribution varies with the distance from the wall. Sufficiently far upstream in the headbox a more anisotropic distribution is found closer to the wall as compared to farther away from the wall.

Place, publisher, year, edition, pages
2010. Vol. 25, 204-212 p.
Keyword [en]
Fibre suspension; Orientation; Anisotropy; Shear flow; Boundary layer; Headbox
National Category
Mechanical Engineering
URN: urn:nbn:se:kth:diva-10001ISI: 000279341100009OAI: diva2:200921
Uppdaterad från konferensbidrag till artikel 20100706 QC 20100706Available from: 2009-03-02 Created: 2009-03-02 Last updated: 2010-12-17Bibliographically approved
In thesis
1. 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.
Trita-MEK, ISSN 0348-467X ; 2009:03
fluid mechanics, fibre orientation, shear flow, wall effect, fibre suspension, papermaking
National Category
Fluid Mechanics and Acoustics
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)
QC 20100706Available from: 2009-03-02 Created: 2009-02-26 Last updated: 2010-07-21Bibliographically approved

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