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Modelling the effect of shear flow on fibre orientation anisotropy in a planar contraction
Metso Paper Karlstad AB.
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0002-2906-9306
University of British Columbia, Vancouver.
University of British Columbia, Vancouver.
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2007 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 22, no 3, 376-382 p.Article in journal (Refereed) Published
Abstract [en]

The effect of turbulence generating vanes and its location in a planar contraction on fibre orientation anisotropy was studied by mathematical modelling. We use single phase CFD (Computational Fluid Dynamic) modelling as an input for the fibre orientation dispersion model to study the effect of shear flow and turbulence in an accelerated fluid flow on fibre orientation anisotropy. For different streamlines in the contracting channel, the fibre orientation distribution model is solved, and the fibre orientation anisotropy could be studied along streamlines near the vane wall and vane tip and further away downstream. The boundary layer did decrease the fibre orientation anisotropy both in the plane of paper and in the plane of contraction, i.e the fibres were less oriented. For the outlet profile of the contraction the fibre orientation anisotropy was more effected by the blunt vane tip than the tapered one. Experimental results in the literature were used to validate this modelling approach and a good qualitative agreement was achieved.

Place, publisher, year, edition, pages
2007. Vol. 22, no 3, 376-382 p.
Keyword [en]
fibre; orientation; anisotropy; turbulence; dispersion; modelling
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-8482ISI: 000250025000014Scopus ID: 2-s2.0-34948865620OAI: oai:DiVA.org:kth-8482DiVA: diva2:13818
Note
QC 20100812 Uppdaterad från konferensbidrag till artikel(20101202). Tidigare titel: Modelling a turbulent dilute fibre suspension in a planar contraction: Effect of vane types, vane position and wall boundary layer on fibre orientation distribution.Available from: 2008-05-16 Created: 2008-05-16 Last updated: 2010-12-02Bibliographically approved
In thesis
1. Fibre Orientation Modelling Applied to Contracting Flows Related to Papermaking
Open this publication in new window or tab >>Fibre Orientation Modelling Applied to Contracting Flows Related to Papermaking
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The main goal of this work was to develop numerical models for studying the behaviour of fibres in an accelerated flow. This is of special interest for e.g. papermaking. The early stage of the paper manufacturing process determines most of the final properties of a paper sheet. The complexity of studying the flow of fibre suspensions both experimentally and numerically emphasises a need for new ideas and developments.

By means of solving the evolution of a convective-dispersion equation, i.e. the Fokker-Planck equation, a fully 3D approach with respect to the position and the two fibre angles, polar and azimuthal angles, following a streamline is presented. As an input to the fibre orientation model the turbulent flow field is solved by Computational Fluid Dynamics (CFD) with second-order closure in the turbulence model. In this work two new hypotheses have been presented for the variation of the non-dimensional rotational diffusivity with non-dimensional fibre length, Lf /η and the Reynolds number based on the Taylor micro-scale of the turbulence, Reλ Parameters for the two new hy- potheses and earlier models are determined with the aim of achieving a general relation and a value of the rotational dispersion coeffcient of stiff fibres in an anisotropic turbulent fluid flow. Earlier modelling work has been focused on solving the planar approach, i.e. assuming all fibres to be in one plane. This planar approach is discussed and compared with the fully 3D approach and its validity is evaluated.

The optimization of parameters for the different hypotheses correlated on a central streamline, showed a good agreement with an independent experimental result in the undisturbed region. Moreover, it is particularly interesting that the boundary layer region and the wake region are predicted fairly well and the phenomena are well described, which has not been the case earlier. It seems that the new hypothesis based on the variation of the non-dimensional fibre length, Lf /η gives the best correlation in these shear-layer regions. Further- more it was established that the planar approach fails to predict shear layers, i.e. the boundary layer and the wake regions. As emphasized in the theory section, the planar formulation is strictly valid only if all fibres are oriented in one plane, which is not the case in the shear layers. In the undisturbed region, the 3D and the planar approaches, agree in their results. This leads to the conclusion that both approaches are suitable when shear layers are not studied.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. x, 36 p.
Series
Trita-MEK, ISSN 0348-467X ; 2008:03
Keyword
Fokker-Planck, fibre orientation, shear flow, fibre suspension, planar contraction, headbox, turbulent flow
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-4762 (URN)
Public defence
2008-06-05, Sal L1, KTH, Drottning Kristinas väg 30, Stockholm, 10:00
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Supervisors
Note
QC 20100812Available from: 2008-05-16 Created: 2008-05-16 Last updated: 2010-08-12Bibliographically approved

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