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  • 1.
    Uesaka, Tetsu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Wiklund, Hanna
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Holmvall, Martin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Fluid-Structure Interactions in Random Fibre Networks2012Conference paper (Refereed)
  • 2.
    Wiklund, Hanna
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Lattice Boltzmann simulations of two-phased flow in fibre network systems2012Doctoral 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.

  • 3.
    Wiklund, Hanna
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Lindström, S. B.
    Department of Fibre and Polymer Technology, Royal Institute of Technology, SE-100 44 Stockholm.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Boundary condition considerations in lattice Boltzmann formulations of wetting binary fluids2011In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 182, no 10, p. 2192-2200Article in journal (Refereed)
    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.

  • 4.
    Wiklund, Hanna S.
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Microfluidics of imbibition in random porous media2013In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 87, no 2, p. 023006-Article in journal (Refereed)
    Abstract [en]

    A free-energy lattice Boltzmann approach has been used to perform simulations of liquid penetration into random porous media. We focus our study on the effects of microstructures, particularly microtopography, on liquid penetration driven by capillary force and external pressure. For this purpose we set up a model structure that consists of a network of interconnected capillaries with varying pore geometries. The results showed that the discontinuities in the solid-surface curvature, as are present as corners on the capillary surfaces, have strong influences on liquid penetration through their pinning effects and interactions with local geometry. DOI: 10.1103/PhysRevE.87.023006

  • 5.
    Wiklund, Hanna
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Edge-wicking: Micro-fluidics of two-dimensional liquid penetrationinto porous structures2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 2, p. 403-408Article in journal (Refereed)
    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.

  • 6.
    Wiklund, Hanna
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Micro-fluidics of "water bond"2011In: Progress in Paper Physics Seminar, Graz, Austria: Verlag der Technischen Universität Graz , 2011Conference paper (Other academic)
  • 7.
    Wiklund, Hanna
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Microfluidics of wicking in random porous mediaManuscript (preprint) (Other academic)
  • 8.
    Wiklund, Hanna
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Simulations of shearing of capillary bridges2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 136, no 9, p. Art. no. 094703-Article in journal (Refereed)
    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.

1 - 8 of 8
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