Mid Sweden University

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.

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.

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.