Capillary interactions, aggregate formation and the rheology of particle-laden flows: a lattice Boltzmann study

TL;DR

This study uses a lattice Boltzmann and discrete element method to explore how capillary bridges influence particle aggregation and rheology in suspensions, revealing complex effects of microstructure and fluid properties on viscosity.

Contribution

It introduces a coupled simulation approach to analyze the microstructure-rheology relationship in particle-laden flows with capillary interactions.

Findings

Capillary interactions lead to filament or globular cluster formation.

Filaments decrease suspension viscosity at high capillary strengths.

Fluid viscosity non-trivially affects suspension viscosity.

Abstract

The agglomeration of particles caused by the formation of capillary bridges has a decisive impact on the transport properties of a variety of at a first sight very different systems such as capillary suspensions, fluidized beds in chemical reactors, or even sand castles. Here, we study the connection between the microstructure of the agglomerates and the rheology of fluidized suspensions using a coupled lattice Boltzmann and discrete element method approach. We address the influence of the shear rate, the secondary fluid surface tension, and the suspending liquid viscosity. The presence of capillary interactions promotes the formation of either filaments or globular clusters, leading to an increased suspension viscosity. Unexpectedly, filaments have the opposite effect on the viscosity as compared to globular clusters, decreasing the suspension viscosity at larger capillary interaction strengths. In addition, we show that the suspending fluid viscosity also has a non-trivial influence on the effective viscosity of the suspension, a fact usually not taken into account by empirical models.