A. Jäsberg

Lattice-Boltzmann Simulation of Capillary Rise Dynamics

We report results of extensive two-phase lattice-Boltzmann simulations of capillary rise dynamics. We demonstrate that the method can be used to model the hydrodynamic behaviour inside a capillary tube provided that the diameter of the tube is large enough, typically at least 30 lattice units. We also present results for the dependence of the cosine of the dynamic contact angle on the capillary number Ca. Its deviation from the static advancing contact angle has a power-law form, with the value of the exponent very close to 3/2 for capillary rise at zero gravity, while behaviour is more complex in the presence of gravity.

Evaluation of a lattice-Boltzmann method for mercury intrusion porosimetry simulations

We have simulated intrusion of a non-wetting liquid into pores of varying shape and size. Simulations were based on the lattice-Boltzmann method and the Shan-Chen multiphase model. The liquid-solid contact angle for pores with circular cross-section was found to be equal to that for pores with square cross-section, and constant even for small pore sizes if the discretised shape of the circular cross-section was taken into account. For comparison, contact angle was also determined for a liquid column descending in a capillary tube, and the results were found to be consistent. Application of the method to mercury intrusion porosimetry is discussed.

Simulations of non-spherical particles suspended in a shear flow

The lattice-Boltzmann method was used to investigate the effects of the shape and concentration of the particles on the rheological properties of non-Brownian suspensions for non-zero Reynolds numbers. Several case studies were analyzed and the methods used were found to give accurate predictions for these systems. The viscosity of suspensions of both spherical and non-spherical particles was determined as functions of shear rate and concentration of particles. It was shown that, for high shear rates, shear thickening appears. This phenomenon is particularly pronounced for particles of irregular shape.

Hydrodynamical forces acting on particles in a two-dimensional flow near a solid wall

The hydrodynamical forces acting on a single particle and on a random rigid array of particles suspended in a two-dimensional shear flow of Newtonian fluid near a rigid wall were studied numerically in the flow regime where the relevant Reynolds numbers are of the order of unity. The simulations were done with conventional finite volume method for single-particle cases and with lattice-Boltzmann method for many-particle cases. A set of comparison cases was solved with both methods in order to check the accuracy of the lattice-Boltzmann method. For the single-particle case analytic formulae for the longitudinal drag force and for the transverse lift force were found. A modification to Darcys law is proposed which takes into account the increase of the drag force near a moving wall. In the flow conditions studied here, the lift force acting on the particle array was found to be repulsive close to the wall, but becomes weakly attractive as the distance from the wall is increased.

The effect of in-line foam generation on foam quality and sheet formation in foam forming

Abstract Foam forming has recently attracted increasing interest due to the paper industry’s continual efforts to find new possibilities to minimize raw material consumption, and to improve energy and water efficiency. Foam forming is also thought to be a possible solution to the industry’s need to widen its product portfolio with novel and more valuable products. In foam forming, foam properties (air content, bubble size and half-life) are obviously key process variables, but there are only a few studies in which their effect on the sheet properties have been studied in pilot conditions. Moreover, all previous studies have used foam generated in stirring tanks, and there are hitherto no studies in which in-line foam generation has been considered. In this paper both these gaps are filled with experiments performed in VTT’s pilot foam forming environment. The combination of tank and in-line generation was found to work well in foam forming, providing extra flexibility for foam generation and decreasing surfactant needs. The results show that foam forming generally improves formation, but the foam quality can have a significant effect on sheet properties.