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Particle-level simulation of forming of the fiber network in papermaking
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
Responsible organisation
2008 (English)In: International Journal of Engineering Science, ISSN 0020-7225, Vol. 46, no 9, 858-876 p.Article in journal (Refereed) Published
Abstract [en]

A model for particle-level simulation of fiber suspensions has been used to simulate paper sheet forming on a roll-blade former. The fibers were modeled as chains of fiber segment, flowing and interacting with the medium and with each other. The incompressible three-dimensional Navier-Stokes equations were used to describe the fluid motion. Real pulps were analyzed to provide raw material data for the simulations. Dewatering was simulated by moving two model forming fabrics toward each other through a fiber suspension. Close examination of the dewatering process revealed that no large concentration gradients develop through the thickness of the pulp suspension. In this sense, twin-wire dewatering does not resemble a filtration process. The effects of the jet-to-wire speed difference on the network structure of the paper were investigated. The structural features of interest were fiber orientation anisotropy, mass density distribution and three-dimensionality of the fiber network. It was demonstrated that these simulated structural features were in qualitative agreement with experimental data found in the literature.

Place, publisher, year, edition, pages
2008. Vol. 46, no 9, 858-876 p.
Keyword [en]
fiber suspension, forming, dewatering, fiber, paper, fiber network, simulation
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-4582DOI: 10.1016/j.ijengsci.2008.03.008ISI: 000258021900002Scopus ID: 2-s2.0-44949106201Local ID: 5733OAI: oai:DiVA.org:miun-4582DiVA: diva2:29614
Projects
Stochastic Modelling of Paper Structures
Available from: 2008-11-20 Created: 2008-11-14 Last updated: 2009-03-19Bibliographically approved
In thesis
1. Modelling and simulation of paper structure development
Open this publication in new window or tab >>Modelling and simulation of paper structure development
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

 

 

 

 

 

A numerical tool has been developed for particle-level simulations of fibre suspension flows, particularly forming of the fibre network structure of paper sheets in the paper machine. The model considers inert fibres of various equilibrium shapes, and finite stiffness, interacting with each other through normal, frictional, and lubrication forces, and with the surrounding fluid medium through hydrodynamic forces. Fibre–fluid interactions in the non-creeping flow regime are taken into account, and the two-way coupling between the solids and the fluid phases is included by enforcing momentum conservation between phases. The incompressible three-dimensional Navier–Stokes equations are employed tomodel themotion of the fluid medium.

The validity of the model has been tested by comparing simulation results with experimental data from the literature. It was demonstrated that the model predicts well the motion of isolated fibres in shear flow over a wide range of fibre flexibilities. It was also shown that the model predicts details of the orientation distribution of

 

multiple, straight, rigid fibres in a sheared suspension. Furthermore, model predictions of the shear viscosity and first normal stress difference were in fair agreement with experimental data found in the literature. Since the model is based solely on first principles physics, quantitative predictions could be made without any parameter fitting.

 

Based on these validations, a series of simulations have been performed to investigate the basic mechanisms responsible for the development of the stress tensor components for monodispersed, non-Brownian fibres suspended in a Newtonian fluid in shear flow. The effects of fibre aspect ratio, concentration, and inter-particle friction, as well as the tendency of fibre agglomeration, were examined in the nonconcentrated regimes. For the case of well dispersed suspensions, semi-empirical relationships were found between the aforementioned fibre suspension properties, and the steady state apparent shear viscosity, and the first/second normal stress differences.

 

Finally, simulations have been conducted for the development of paper structures in the forming section of the paper machine. The conditions used for the simulations were retrieved from pilot-scale forming trial data in the literature, and from real pulp fibre analyses. Dewatering was simulated by moving two forming fabrics toward each other through a fibre suspension. Effects of the jet-to-wire speed difference on the fibre orientation anisotropy, the mass density distribution, and three-dimensionality of the fibre network, were investigated. Simulation results showed that the model captures well the essential features of the forming effects on these paper structure parameters, and also posed newquestions on the conventional wisdom of the forming mechanics.

 

 

Place, publisher, year, edition, pages
Sundsvall: Department of Natural Sciences, Engineering and Mathematics, Mid Sweden University, 2008. 64 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 60
Keyword
Forming, Fibre, Paper, Fibre suspension, Paper structure, Simulation, Rheology
National Category
Chemical Engineering Other Engineering and Technologies
Identifiers
urn:nbn:se:miun:diva-7003 (URN)978-91-86073-10-7 (ISBN)
Public defence
2008-10-28, O102, Mid Sweden University, Holmgatan 10, Sundsvall, 09:30 (English)
Opponent
Supervisors
Available from: 2008-11-12 Created: 2008-11-12 Last updated: 2009-03-19Bibliographically approved

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