Segregation and Spatio-Temporal Dynamics of Granular Shear Flows

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ABSTRACT - 0434279 Particulate processing operations in a wide variety of industries are often poorly understood compared to their fluid processing counterparts. Product quality and consistency is frequently threatened by problems such as non-uniform flow and segregation of constituent components, the latter being especially significant in pharmaceutical manufacture in which maintenance of a homogenous particle mixture is critical. Traditionally, heuristic rules-of-thumb have been used to limit these problems, but these have not reliably predicted flow instabilities and prevented segregation from occurring during scale-up or commissioning. A more desirable approach, from either a quality control, commercial, or regulatory perspective, is the ability to quantitatively predict flow inhomogeneities and segregation rates from fundamental principles, material properties and small-scale laboratory tests, and then to engineer processes accordingly to limit detrimental effects on performance and product uniformity. While there is a growing theoretical basis for granular flow, this has not yet been applied widely to non-uniform or unsteady flows which are typical of industrial situations. Fundamentally, segregation stems from variations in velocity and flow properties, such asgranular temperature, between adjacent regions of a system, preferentially driving particles of a certain type to particular locations. Thus, an initial aim is to numerically and experimentally characterize the flow instabilities and coherent structures occurring spontaneously during Couette and Taylor-Couette flows. Couette and Taylor-Couette flows are perhaps the simplest model geometries encompassing both shear and physical boundary interactions, essential ingredients of practical flows. Particle dynamic simulation techniques will be used to model particle properties and resulting flows will be characterized using Fourier methods and compared to results from kinetic theory. Experimental flows will be examined using Xray tomography, Particle Image Velocimetry (PIV), stream sampling, and image analysis techniques. The subsequent role of instabilities as triggers for segregation will then be investigated, culminating in calculations of segregation flux for a given particle species. Computational and physical experiments will be used to characterize mixing-segregation transitions in terms of relevant dimensionless groups. Underlying instabilities and spontaneous inhomogeneity will be examined in archetypal 2D and 3D Couette and Taylor-Couette flows, utilizing analogies with fluid flows where possible. Mechanisms of particle segregation triggered by the inhomogeneities will be characterized, for high-shear flows typical of mixing or transport operations. A parametric sensitivity analysis will be performed to quantify the role of particle size distribution, density variations, surface properties and particle aspect ratio. Initial work will consider spherical particles with work in latter years allowing for non-spherical particles. Particle shape is rarely considered in fundamental flow and segregation studies, but non-spherical particles predominate in industry and are known to strongly influence flow and segregation. In particular, acicular needle-like morphologies are common in pharmaceutical crystals and these will be studied experimentally and modeled in the simulations. The research initiatives in this proposal will be integrated with educational and outreach initiatives including graduate, undergraduate and high school research training in particle technology. Training in particle technology has been recognized as an area of national need but has traditionally been neglected in the US. A large proportion of the products manufactured within the US are in particulate form or involve significant particle technology. In fact, it has been argued that the handling and manufacture of particulates is at least as important as that of liquids and gases. But the majority of graduating engineers in the U.S. receive little education in this field. As part of this proposal, the PI will continue to advance particle technology into the curriculum at Rutgers. High school students will be given the opportunity for research experience through the Governor's School of Engineering, which attracts New Jersey high school students to Rutgers for a high school-university exchange program. Finally, the PI will continue to target the recruitment of women and minorities.