(39c) Fluid-Like Properties of Powders: Rheology in the Intermediate Flow Regime

Manufacture
of solid dosage forms is a microcosm of powder technology, involving synthesis and
processing of fine powders through a variety of particle formation, communition, blending, compaction, and coating
processes.  Common to these
operations is the bulk flow of powders in a regime in which particles
experience a range of interactions from collisions to more enduring frictional
contacts with neighboring particles. 
This is termed the "intermediate" flow regime, and it has only
recently begun to be studied with rigor. 
Quantitative models for industrially-relevant powder flows do not exist,
and for this reason the design and scaling of these unit operations is largely
empirical.  To begin to address
this gap, NSF funded a powder flow collaboratory,
lead by the International Fine Particle Research Institute (IFPRI), to bring
together a small group of experimentalists and modelers in order to explore the
state of development of powder flow models.  In the collaboratory, the results
of two IFPRI-funded flow experiments, a particle-level study of two-dimensional
hopper flows and a continuum-level study of Couette
flows were provided to the modelers in order to test the fidelity of their
models. The results of this effort revealed key gaps, both experimental and
theoretical, in our understanding of and ability to model dense, active powder
flows. I will present in this talk the key findings and a set of industrially
relevant results achieved during the NSF funded program.