Introduction
Agglomerates of fine particles are pervasive in industry. In many particle processing applications, the agglomerates are carried within a suspending fluid, and hydrodynamic shear is applied to break the agglomerate into fragments and to distribute the fragments throughout the suspending media. The underlying purpose of this research it to obtain a fundamental understanding of the various factors that influence this dispersion process. Such information can lead to the development of interfacial engineering strategies aimed at improving the outcome of dispersion processes, or to better design of dispersion equipment.
Our general 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 focus of the work supported under the IFPRI grant involves investigation of how certain time-dependent (dynamic) behaviors can influence the outcome of dispersion processes. Dynamic effects can arise in several facets of the dispersion process. For instance, in practical processing equipment, complex shear histories are inherent. Also, the wetting and spreading of fluids associated with contacting particles and agglomerates with processing fluids are dynamic effects. Finally, for some materials, dissolution of the solids plays a significant role.
For 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.