Executive Summary
The primary aim of this project is to provide fundamental information regarding the manner in which agglomerates of fine particles disperse in response to the application of hydrodynamic shear. A major emphasis of the research supported under this IFPRI grant involves investigation of the role of certain time-dependent (dynamic) phenomena in governing dispersion associated with non-steady shear flows or fluid wetting phenomena. In addition, we are interested in assessing the role of binders in governing dispersion behavior. We also developed predictive analytical models for the various modes and kinetics of the dispersion process Three principal experimental tools have been used throughout this work. One allows the observation of dispersion in steady simple-shear flows of controllable intensity. A second other enables the application of a time-varying shear stress with controlled frequency and amplitude. The third technique enables sensing of the micromechanical behavior of particle clusters and/or the forces associated with the deformation of liquid bridges between individual pairs of particles. This report details progress in five parallel and related thrust areas:
(1) The relationships between agglomerate characteristics, flow conditions, and dispersion phenomena (mode and kinetics) for “dry” agglomerates. This topic includes the development and validation of a new model for predicting dispersion kinetics.
(2) The identification of a new mode of dispersion (adhesive failure) and an analysis of the conditions under which it occurs.
(3) The importance of flow dynamics (time-varying flows) on the dispersion process. This topic also includes the development of a mathematical analytical approach for analyzing the influence of flow dynamics on dispersion tendencies.
(4) Characterization and analysis of the micromechanics of particle clusters, including those with interstitial fluids and/or liquid bridges. This topic also leads to a modeling approach useful for the understanding and prediction of dispersion mode.
(5) Development of a detailed, fundamental model that provides precise information on the dispersion of clusters ranging in size down to the nanometer scale.