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Modelling and simulation of paper structure development
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
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 [en]
Forming, Fibre, Paper, Fibre suspension, Paper structure, Simulation, Rheology
National Category
Chemical Engineering Other Engineering and Technologies
Identifiers
URN: urn:nbn:se:miun:diva-7003ISBN: 978-91-86073-10-7 (print)OAI: oai:DiVA.org:miun-7003DiVA: diva2:117360
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
List of papers
1.
The record could not be found. The reason may be that the record is no longer available or you may have typed in a wrong id in the address field.
2. Particle-level simulation of forming of the fiber network in papermaking
Open this publication in new window or tab >>Particle-level simulation of forming of the fiber network in papermaking
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.

Keyword
fiber suspension, forming, dewatering, fiber, paper, fiber network, simulation
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-4582 (URN)10.1016/j.ijengsci.2008.03.008 (DOI)000258021900002 ()2-s2.0-44949106201 (Scopus ID)5733 (Local ID)5733 (Archive number)5733 (OAI)
Projects
Stochastic Modelling of Paper Structures
Available from: 2008-11-20 Created: 2008-11-14 Last updated: 2009-03-19Bibliographically approved
3. Simulation of semidilute suspensions of non-Brownian fibres in shear flow
Open this publication in new window or tab >>Simulation of semidilute suspensions of non-Brownian fibres in shear flow
2008 (English)In: Journal of Chemical Physics, ISSN 0021-9606, Vol. 128, no 2, 024901- p.Article in journal (Refereed) Published
Abstract [en]

Particle-level simulations are performed to study semidilute suspensions of monodispersed non-Brownian fibers in shear flow, with a Newtonian fluid medium. The incompressible three-dimensional Navier-Stokes equations are used to describe the motion of the medium, while fibers are modeled as chains of fiber segments, interacting with the fluid through viscous drag forces. The two-way coupling between the solids and the fluid phase is taken into account by enforcing momentum conservation. The model includes long-range and short-range hydrodynamic fiber-fiber interactions, as well as mechanical interactions. The simulations rendered the time-dependent fiber orientation distribution, whose time average was found to agree with experimental data in the literature. The viscosity and first normal stress difference was calculated from the orientation distribution using the slender body theory of Batchelor [J. Fluid Mech. 46, 813--829 (1971)], with corrections for the finite fiber aspect ratios. The viscosity was also obtained from direct computation of the shear stresses of the suspension for comparison. These two types of predictions compared well in the semidilute regime. At higher concentrations, however, a discrepancy was seen, most likely due to mechanical interactions, which are only accounted for in the direct computation method. The simulated viscosity determined directly from shear stresses was in good agreement with experimental data found in the literature. The first normal stress difference was found to be proportional to the square of the volume concentration of fibers in the semidilute regime. As concentrations approached the concentrated regime, the first normal stress difference became proportional to volume concentration.

Keyword
fiber suspension, fiber orientation distribution, suspension microstructure, Jeffery orbit, hydrodynamic fiber interactions, suspension viscosity, first normal stress difference, shear flow, simulation
National Category
Chemical Engineering Other Engineering and Technologies
Identifiers
urn:nbn:se:miun:diva-413 (URN)10.1063/1.2815766 (DOI)000252450100036 ()18205469 (PubMedID)2-s2.0-38349164723 (Scopus ID)5052 (Local ID)5052 (Archive number)5052 (OAI)
Projects
Stochastic Modelling of Paper Structures
Available from: 2008-11-29 Created: 2008-11-13 Last updated: 2009-03-19Bibliographically approved
4. Simulation of the motion of flexible fibres in viscous fluid flow
Open this publication in new window or tab >>Simulation of the motion of flexible fibres in viscous fluid flow
2007 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 19, no 11, 113307Article in journal (Refereed) Published
Abstract [en]

A model for flexible fibers in viscous fluid flow is proposed, and its predictions compared with experiments found in the literature. The incompressible three-dimensional Navier-Stokes equations are employed to describe the fluid motion, while fibers are modeled as chains of fiber segments, interacting with the fluid through viscous and dynamic drag forces. Fiber segments, from the same or from different fibers, interact with each other through normal, frictional and lubrication forces. Momentum conservation is enforced on the system to capture the two-way coupling between phases. Quantitative predictions could be made, and showed good agreement with experimental data, for the period time of Jeffery orbits in shear flow, as well as for the amount of bending of flexible fibers in shear flow. Simulations, using the proposed model, also successfully reproduced the different regimes of motion for threadlike particles, ranging from rigid fiber motion to complicated orbiting behavior, including coiling and self-entanglement.

Keyword
fiber, fluid flow, fiber suspension, fiber flexibility, simulation
National Category
Other Engineering and Technologies Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-412 (URN)10.1063/1.2778937 (DOI)000251325700018 ()2-s2.0-36849039349 (Scopus ID)5051 (Local ID)5051 (Archive number)5051 (OAI)
Projects
Stochastic Modelling of Paper Structures
Available from: 2008-11-20 Created: 2008-11-13 Last updated: 2016-09-26Bibliographically approved

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