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Lattice Boltzmann simulations of two-phased flow in fibre network systems
Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Two-phase flow in microfluidic systems is of great interest for many scientificand engineering problems. Especially in the pulp and paper area, the problems spanfrom fibre-fibre interactions in the consolidation process of papermaking to edgewickingin paper board during the aseptic treatment of liquid packaging.The objective of this thesis is to gain a fundamental understanding of the microfluidicmechanisms that play a significant role in various problems of two-phaseflow in fibre networks. To achieve this objective a new method for the treatment ofwetting boundary conditions in the lattice Boltzmann model has been developed.The model was validated and compared with the previous treatments of wettingboundary conditions, by using two test cases: droplet spreading and capillary intrusion.The new wetting boundary condition was shown to give more accurate resultsfor a wider range of contact angles than previous methods, and capillary intrusioncould be simulated with higher accuracy even at a relatively low resolution.As an application of the developed method, two examples of two-phase flowproblems in fibre networks are taken: the shear resistance of liquid bridges, as relatedto the wet web strength, and liquid penetration into porous structures, as related toedge-wicking in paper board. The shear resistance force was shown to depend verylittle on surface tension and contact angle. Instead, the shear resistance is a dynamicforce and a major contributing factor is the distortion of the flow field caused bythe presence of interfaces. This distortion of the flow field is size-dependent: thesmaller the bridge, the larger the proportion of the distorted flow field and thus alarger shear resistance force per unit width. In other words, multiple small bridgeshave an enhancement effect on shear resistance. The results from the simulations ofliquid penetration into porous structures showed that the discontinuities in the solidsurfacecurvature, as are present in the formof corners on the capillary surfaces, havestrong influences on liquid penetration through their pinning effects and also theirinteractions with local geometry. The microtopography can therefore, accelerate,decelerate and, in some cases, even stop the liquid penetration into random porousmedia.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University , 2012. , 43 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 130
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:miun:diva-16475ISBN: 978-91-87103-23-0 (print)OAI: oai:DiVA.org:miun-16475DiVA: diva2:534255
Supervisors
Available from: 2012-06-15 Created: 2012-06-15 Last updated: 2012-11-21Bibliographically approved
List of papers
1. Boundary condition considerations in lattice Boltzmann formulations of wetting binary fluids
Open this publication in new window or tab >>Boundary condition considerations in lattice Boltzmann formulations of wetting binary fluids
2011 (English)In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 182, no 10, 2192-2200 p.Article in journal (Refereed) Published
Abstract [en]

We propose a new lattice Boltzmann numerical scheme for binary-fluid surface interactions. The new scheme combines the existing binary free energy lattice Boltzmann method [Swift et al., Phys. Rev. E 54 (1996)] and a new wetting boundary condition for diffuse interface methods in order to eliminate spurious variations in the order parameter at solid surfaces. We use a cubic form for the surface free energy density and also take into account the contribution from free energy in the volume when discretizing the wetting boundary condition. This allows us to eliminate the spurious variation in the order parameter seen in previous implementations. With the new scheme a larger range of equilibrium contact angles are possible to reproduce and capillary intrusion can be simulated at higher accuracy at lower resolution. © 2011 Elsevier B.V. All rights reserved.

Keyword
Binary fluid, Boundary condition, Lattice Boltzmann, Wetting surface
National Category
Computer and Information Science
Identifiers
urn:nbn:se:miun:diva-14196 (URN)10.1016/j.cpc.2011.05.019 (DOI)000293486000012 ()2-s2.0-79960070654 (Scopus ID)
Available from: 2011-07-19 Created: 2011-07-19 Last updated: 2017-05-04Bibliographically approved
2. Simulations of shearing of capillary bridges
Open this publication in new window or tab >>Simulations of shearing of capillary bridges
2012 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 136, no 9, Art. no. 094703- p.Article in journal (Refereed) Published
Abstract [en]

Capillary bridges are considered as the major source of interaction forces acting in wet particulate systems. We study the dynamic shear resistance by using a lattice Boltzmann numerical scheme for a binary fluid. The shear resistance force showed very little dependence on surface tension and contact angle. Instead, the shear resistance is a dynamic phenomenon and a major contributing factor is the distortion of the flow field caused by the presence of interfaces. This distortion of the flow field is geometry-dependent: in smaller diameter bridges the proportion of this distorted flow field becomes larger and it makes a major contribution to the shear resistance force. In other words multiple bridges have an enhancement effect on shear resistance.

Keyword
Binary fluids; Contributing factor; Dynamic phenomena; Enhancement effects; Interaction forces; Lattice boltzmann; Numerical scheme; Particulate systems; Shear resistance forces; Shear resistances
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:miun:diva-16469 (URN)10.1063/1.3689293 (DOI)000301664200043 ()22401464 (PubMedID)2-s2.0-84858212377 (Scopus ID)
Available from: 2012-06-15 Created: 2012-06-15 Last updated: 2013-01-15Bibliographically approved
3. Edge-wicking: Micro-fluidics of two-dimensional liquid penetrationinto porous structures
Open this publication in new window or tab >>Edge-wicking: Micro-fluidics of two-dimensional liquid penetrationinto porous structures
2012 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 27, no 2, 403-408 p.Article in journal (Refereed) Published
Abstract [en]

We have performed free-energy-based two-dimensional lattice Boltzmann simulations of the penetration of liquid into the edge of a porous material. The purpose was to gain further insight into possible mechanisms involved in the penetration of liquid into the unsealed edges of paper and paper board. In order to identify the fundamental mechanisms we have focused on a model structure that consists of a network of interconnected capillaries. Two different mechanisms were identified: pinning at corners of solid surfaces and increased pressure in dead-end pores. These mechanisms significantly decelerate or even stop the liquid penetration into the porous structures.

Keyword
Edge-wicking; Lattice Boltzmann; Micro-fluidics; Porous structure
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:miun:diva-16472 (URN)10.3183/NPPRJ-2012-27-02-p403-408 (DOI)000315696000032 ()2-s2.0-84865204016 (Scopus ID)
Available from: 2013-04-04 Created: 2012-06-15 Last updated: 2013-04-04Bibliographically approved
4. Microfluidics of wicking in random porous media
Open this publication in new window or tab >>Microfluidics of wicking in random porous media
(English)Manuscript (preprint) (Other academic)
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:miun:diva-16473 (URN)
Available from: 2012-06-15 Created: 2012-06-15 Last updated: 2016-12-09Bibliographically approved

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