Capillary-bridge Forces Between Solid Particles: Insights from Lattice Boltzmann Simulations

TL;DR

This study uses lattice Boltzmann simulations to analyze capillary-bridge forces between solid particles, revealing limitations of existing models especially at large contact angles, and providing insights into non-axisymmetric bridge effects.

Contribution

It introduces detailed numerical simulations of capillary bridges with a focus on non-axisymmetric effects and assesses the accuracy of various analytical models.

Findings

Some analytical models outperform others in predicting capillary forces.

All models fail for contact angles larger than π/2, showing limitations in current theories.

Capillary forces can be repulsive at certain contact angles and separations.

Abstract

Liquid capillary-bridge formation between solid particles has a critical influence on the rheological properties of granular materials and, in particular, on the efficiency of fluidized bed reactors. The available analytical and semi-analytical methods have inherent limitations, and often do not cover important aspects, like the presence of non-axisymmetric bridges. Here, we conduct numerical simulations of the capillary bridge formation between equally and unequally-sized solid particles using the lattice Boltzmann method, and provide an assessment of the accuracy of different families of analytical models. We find that some of the models taken into account are shown to perform better than others. However, all of them fail to predict the capillary force for contact angles larger than $\pi/2$, where a repulsive capillary force attempts to push the solid particle outwards to minimize the surface energy, especially at a small separation distance.