Micro-Level and Macro-Level Flow Mechanics of Wet Granular Media

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

ABSTRACT - 0411634 Intellectual Merit. Processes involving the flow of solid particles are ubiquitous in both nature (landslides, planetary rings, etc.) and industry (pharmaceuticals, food products, chemical process industries), though a predictive understanding of their behavior remains an elusive goal. Of particular interest in the proposed effort are systems involving particles coated with a thin layer of viscous fluid - i.e., wet solids. Such particulate systems are found in a wide range of applications, including fluidized-bed granulation, mixing of pharmaceuticals, pollen transport, filtration, etc. Such systems are known to display characteristics that are typically not exhibited by their dry counterparts, namely the presence of particle agglomerates. A predictive knowledge of agglomeration formation, rearrangement, growth, and break-up is a key element in the rational design of wet-solid processes, though such a predictive tool is not currently available. The current effort aims to address the aforementioned need, with a particular focus on viscous (dynamic) effects occurring between wetted particles, which are relatively unexplored as compared to the capillary (static) effects of wetted systems and viscous effects of fully-immersed systems. A combination of theory, experiments, and discrete-particle simulations will be used to answer the following critical questions associated with wet solids: (i) Will an agglomerate form when two "free" particles collide? (ii) If an agglomerate is not formed, what is the impact of the liquid layer on the post-collisional particle motion? (iii) If an agglomerate does form, what is the result of a collision with a third particle? (iv) How do these micro-level physics impact the macro-level (continuum) behavior of both granular and gas-solid systems? More specifically, a combination of experiments and fundamental theory based on lubrication, capillary forces, and solid mechanics will be used to develop stick/bounce and breakup criteria for small agglomerates. The theory will require only measurable solid and liquid properties for solution. To bridge this micro-level physics with macro-level behavior, the microphysical theory will be incorporated into discrete-particle simulations. The effect of the liquid layer on continuum quantities like stress will be assessed via an examination of simple shear flow of a granular material. Furthermore, discrete-particle simulations will also be carried out for a specific gassolid operation, namely fluidized-bed granulation (or enlargement), in an effort to describe some non-intuitive behavior observed in such systems. This work will be a collaboration between the PI (Prof. Christine Hrenya) and the co-PI (Prof. Rob Davis), who have extensive background in the theoretical, experimental, and simulation aspects associated with particulate flows. Broader Impacts. The broader impacts of the work include the following: (i) a more fundamental understanding of wetted particulate system, (ii) training of graduate students in the area of particle technology, which has been identified as a national need [1-3], and (iii) sharing of learned information with both the technical community (via presentations and peer-reveiwed publications) and the student community (via incorporation into coursework, training programs, and outreach).