This award supports a unified research program of modeling, analysis and computation to better characterize and understand granular flows, in particular, granular flows in the presence of interstitial fluid. Dry granular materials may be characterized as a fourth state of matter. Granular media can support stresses like a solid, but also can flow like a liquid, or, under some conditions, like a gas. While deforming, a granular sample may dilate or consolidate, depending on packing conditions. These features lead to a dynamics of granular materials whose richness and scope rivals that of fluid dynamics. At the same time, particle materials used in technological applications are becoming smaller, and, consequently, the presence of interstitial fluid is becoming increasingly important. This is particularly true in the use of toner powders in xerography, where the small size of the power particles means higher quality copies. As they move, these small light particles (about 10 micron diameter) are strongly influenced by the surrounding gas, and particle motion is intimately coupled to fluid motion. Furthermore, owing to van der Waals attraction, these toner powders are cohesive, often tending to clump. The introduction of controlled fluid flow, through fluidization and vibration, is a common mechanism for breaking the cohesive attractions and controlling particle motion. In a very different application, new ideas for drying and coating larger particles (about 500 micron diameter) use rapid vertical vibration of a flat plate to accelerate a granular mass. Because of the large acceleration, interstitial fluid again plays an important role in the motion of particles. Theoretical and numerical techniques will be used to characterize state diagrams, study the stability of layers of fluidized powder under tilting, and study the onset of bubbling and clumping.
The combined flow of particles and fluid has many other industrial applications, such as particle flow in pressurized vessels, cat-cracking, transport by lubrication, and heat transfer. In these applications, transport and handling of powders presents a significant difficulty. Without a better understanding of particle-fluid flows, products that exploit new particle technologies may not come on-line as quickly, nor with sufficient reliability. In this regard, it is useful to note a study by the Rand Corporation showing that, because of an inability to accurately predict powder behavior, solids-producing manufacturing plants performed on average at 63% of design capacity, compared to 84% for liquids-producing plants. The analysis and computations performed during this project, together with experiments by other academic and industrial researchers, will help to provide the needed characterization of these flows.
