Initial rates of aggregation for dilute, granular flows of wet particles

Abstract

Molecular dynamics (MD) simulations are used to determine the agglomeration rates of wet grains (particles coated with a viscous, liquid layer) engaged in simple shear flow under dilute conditions. In this work, a closed-form model derived from the elastohydrodynamic theory describes the normal restitution coefficient for binary collisions. Unlike previous MD studies, the particle deformation is not assumed to depend on a particle “overlap” (penetration), but instead depends on the formal coupling of Hertzian deformation theory with lubrication theory. The initial rate of doublet formation is studied as a function of system properties and the energy input to the system. In addition to the system properties, the distribution of relative velocities in the system is found to be a key factor influencing the initial rates of clustering. A theory based on estimating the collision frequency and the critical velocity below which no rebound is observed—due to viscous dissipation—is found to provide a good approximation of the initial aggregation rate. The rate of aggregation is found to increase with increasing number of particles in the system, increasing solid fraction, decreasing overall Stokes number, and decreasing compliance parameter.

Wet granular flows in a bladed mixer: Experiments and simulations of monodisperse spheres

“…Figure 9b shows that stresses are higher near the cylinder wall leading to the formation of smaller agglomerates in this region. This is consistent with the agglomeration behavior observed in wet shear flows, where the extent of agglomeration is reduced when the amount of shearing is increased 25, 26. Similar agglomerate sizes are observed near the cylinder wall at the different moisture contents since similar τ θ r * values are obtained in this region.…”

“…However, the case of granular flow in bladed mixers in the presence of cohesion has received less attention despite the fact that cohesion is present in many industrial scenarios where bladed mixers are used (i.e., wet granulation, agitated drying). Most of the research on wet granular flows has been performed for prototypical geometries such as simple shear flows,25, 26 discharging hoppers,27 or rotating drums 28, 29. It remains unclear whether the results obtained in these simple geometries could be extended to more complex systems such as bladed mixers.…”

A model to predict liquid bridge formation between wet particles based on direct numerical simulations

“…However, their data is only in fair agreement with the proposed model, and they have not provided a model for the prediction of the liquid bridge volume. In summary, a large number of researchers have focused on particle collision dynamics without a detailed analysis of liquid bridge formation …”

Agglomeration and de-agglomeration of rotating wet doublets

“…One common method to further understand the experimental observations is through discrete element method (DEM) simulations (Mikami, Kamiya & Horio 1998;Talu, Tardos & Khan 2000;Li & McCarthy 2005;Chaudhuri et al 2006;Weber & Hrenya 2006;Kantak, Hrenya & Davis 2009). The DEM contains microscopic (particle-level) descriptions of the inter-particle forces due to the liquid bridge between particles, though more have focused on the capillary (static) forces than on the viscous (dynamic) forces.…”