Rocking and Rolling, Slipping and Sticking: Wet and Dry Granular Flow
Series: CBE Departmental Seminars
Location: Elgin Room (E-Quad A224)
Date/Time: Wednesday, October 16, 2013, 4:00 p.m. - 5:00 p.m.
Granular materials are encountered throughout nature and across almost all industries, ranging from mineral processing to pharmaceutical manufacturing. Unit operations handling granular materials are notoriously inefficient and plagued by problems rarely encountered in their fluid counterparts. One of the dominant issues affecting particulate processes is size segregation, or the tendency of particles differing in size to separate from one another during processing. Such behavior can be extremely troublesome in the pharmaceutical industry, for example, where segregation of a drug substance from the inactive excipients can result in the production of out-of-spec tablets. This situation can potentially lead to millions of dollars lost to waste, increased down time and start-up delays in an industry where 80% of all products are tablets and capsules and drug compounds can be worth millions of dollars per kilogram. Despite the severity of the problem, our ability to predict whether a given granular mixture will segregate is limited, and even more lacking are approaches to minimize the occurrence of such segregation. In this talk we will discuss work we have done on developing an understanding of granular flow and segregation in vertically vibrated cylinders and bladed mixers. The segregation of binary, ternary and polydisperse mixtures is studied experimentally and computationally. We find that the presence of the other species besides the smallest and largest size is responsible for dramatic reductions in the final degree of segregation compared to a binary mixture. In addition, we quantify orders of magnitude reduction in the segregation rate of a mixture of polydisperse spheres compared to a binary mixture. This reduction in segregation coincides with an increase in diffusive and convective mixing and correlates with a lower average system density. In this talk we will also discuss scale-up of granular flow in bladed mixers and contrast wet and dry flows. Finally, we will discuss the application of these results to improving the operation of pharmaceutical processes.