Measurement and Evaluation of Dynamic Kinetics for Dispersion or Consolidation of Powder Agglomerates

Publication Reference: 
Author Last Name: 
Donald L. Feke
Report Type: 
ARR - Annual Report
Research Area: 
Particle Formation
Publication Year: 
United States

The co-processing of fine-particle agglomerates and liquids is common in industrial practice. In many applications, the processing goal is the reduction of the agglomerate size (or possibly complete breakage of the agglomerate into its constituent particles) and distribution of the fragments throughout the liquid medium. To accomplish this, hydrodynamic shear can bc applied to the suspension by various mechanical means. The underlying motivation for this research is to obtain a fundamental understanding of the various factors that influence the dispersion behavior of agglomerates. Attainment of such an understanding may facilitate the development of interfacial engineering strategies aimed at improving the outcome of dispersion processes or to the design of more efficient dispersion equipment.

Our basic approach is to study the dispersion behavior of well-characterized single agglomerates in controlled flow fields. This allows us to establish the links between the fundamental properties of an agglomerate and dispersion characteristics such as critical shear stress for dispersion, mode and kinetics of fragmentation, and the evolution of the fragment size distribution.

The specific emphasis of the work supported under this IFPRl grant involves investigation of how certain time-dependent (dynamic) phenomena affect the outcome of dispersion processes. Such time-dependent effects are inherent in several aspects of the dispersion process. For instance, in practical processing equipment, the agglomerates are subject to complex shear histories. The contacting of particles and agglomerates with processing liquids leads to wetting and spreading phenomena that change over the course of time. Also, for soluble materials, dissolution is a time-dependent effect.

In the first year of this IFPRI grant, the bulk of the research effort was devoted to the development of a new experimental approach for the investigation of the influence of dynamic effects on dispersion behavior. This entailed the design (and redesign) of a dynamic dispersion chamber, and construction of it and the ancillary equipment. Preliminary experiments were done to validate the experimental techniques and to refine the analytical procedures. In the second year, we performed additional modifications to the experimental device and refined our experimental procedures, This allowed us to complete additional experimental studies that highlight the dramatic influence of time-dependent effects on the outcome of dispersion.  In addition, we performed a thorough modeling study of the flow and shear fields present within our experimental device. This modeling enables us to analyze the results of our experiments, and to understand the limitations of our dispersion chamber.