Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session M13: Granular Flows IV: Mixing, Segregation and Separation |
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Chair: Kimberly Hill, University of Minnesota Room: 301 |
Tuesday, November 26, 2013 8:00AM - 8:13AM |
M13.00001: Diffusion in linearly sheared granular packing Joshua Dijksman, Jie Ren, Robert Behringer We study shear-induced diffusion in a linearly sheared, dense disordered packing of frictional photoelastic disks. We can track both displacements and rotational motion, and measure interparticle forces obtained from the photoelastic response of the disks. In these experiments, volume fraction and shear amplitude are the control parameters. We probe the non-affine displacements, both in the transient of a single shear deformation, and during cyclic shear. We observe fine structure in the nonffine displacement fields and find that the diffusion anisotropy shows nontrivial dynamics. Additionally, we find that both rotational and translational diffusion increases with density for all but the highest densities. [Preview Abstract] |
Tuesday, November 26, 2013 8:13AM - 8:26AM |
M13.00002: Rate-Based Particle Separation: A Granular ``Chromatograph" Diana Lievano, Joseph McCarthy The effective separation of particles is key to numerous processes and industries handling solid materials. By making an analogy to fluids separations, here we describe a ``granular chromatograph'' where particle-wall cohesion leads to ``adsorption'' rates that dictate a particle's traversal down a channel. This adsorption bias leads to differential flow rates of particles that vary in properties, such as size, density, and wetting characteristics. A rate-based separation technique, based on this observation, will be explored. [Preview Abstract] |
Tuesday, November 26, 2013 8:26AM - 8:39AM |
M13.00003: Modeling segregation of bidisperse granular materials: A parametric study Conor Schlick, Yi Fan, Paul Umbanhowar, Julio Ottino, Richard Lueptow Predicting segregation and mixing of size bidisperse granular material is a challenging problem with many industrial applications. Using an accurate segregation model based on kinematic properties of the flow that we recently developed, we present a parametric study of segregation of bidisperse granular material in quasi-two-dimensional bounded heaps. The model depends on the P\'{e}clet number, Pe, which is the ratio of the advection rate to the diffusion rate, and $\Lambda $, which is the ratio of the segregation rate to the advection rate. Both dimensionless parameters depend on the feed rate, the particle size ratio, and the system size. Systematic variation of $\Lambda $ and Pe demonstrates how the spatial particle configuration depends on the interplay of advection, segregation, and diffusion. At large values of Pe and $\Lambda $, segregation dominates and the heap consists of distinct regions of small (upstream) and large (downstream) particles, whereas at low values of Pe and $\Lambda $, diffusion dominates which results in a well-mixed heap. Advection plays an important role for large Pe and small $\Lambda $ and preserves the initial configuration of particles in the feed zone. [Preview Abstract] |
Tuesday, November 26, 2013 8:39AM - 8:52AM |
M13.00004: Segregation of Particles by Size and Density in Dense Sheared Flows: Gravity, Temperature Gradients, and Stress Partitioning Danielle Tan, Kimberly Hill In sheared mixtures of different-sized (same density) particles modestly larger particles tend to go up (toward the free surface), and the smaller particles, down, commonly referred to as the ``Brazil-nut problem'' or ``kinetic sieving.'' If the larger particles are sufficiently denser than the smaller particles, the segregation reverses. Using theory and simulations, we have recently shown that the segregation fluxes among particles differing \textit{in size only} are driven by two effects: (1) the difference between the partitioning of kinetic and contact stresses among the species in the mixture and (2) a kinetic stress gradient. Specifically, the higher granular temperature of the smaller particles segregates them downward along a kinetic stress gradient toward lower temperatures, and larger particles upward. We adapt the theory to mixtures differing in both size and density and use simulations to show that when the larger particles are sufficiently dense, the theory captures the observed segregation reversal through a reversal in the relative granular temperature born by the two species. In other words, with increasing material density, the larger particles bear increasing fractions of the local kinetic stresses, and the segregation reverses as the larger particles bear a higher fraction than their local concentration in the mixture. [Preview Abstract] |
Tuesday, November 26, 2013 8:52AM - 9:05AM |
M13.00005: Modeling segregation of bidisperse granular materials: Model development Yi Fan, Conor Schlick, Paul Umbanhowar, Julio Ottino, Richard Lueptow Predicting segregation of size bidisperse granular materials is a challenging problem. In this talk, we present a theoretical model that captures the interplay between advection, segregation, and diffusion. The fluxes associated with these three driving factors depend on the underlying kinematics, whose characteristics play key roles in determining final particle segregation configurations. Unlike previous models of segregation, our model uses parameters based on kinematic measures instead of arbitrarily adjustable fitting parameters. This permits the theoretical prediction of species concentration within the entire flowing layer as particles segregate in the depth direction while they flow downhill. The model achieves quantitative agreement with both experimental and DEM simulation results when applied to quasi-two-dimensional bounded heaps, and can be readily adapted to other flow geometries. [Preview Abstract] |
Tuesday, November 26, 2013 9:05AM - 9:18AM |
M13.00006: Flow modulation based control of granular stratification in heaps Paul B. Umbanhowar, Yi Fan, David McDonald, Julio M. Ottino, Richard M. Lueptow Gravity driven flows of initially mixed granular media composed of non-monodisperse particles spontaneously segregate for a wide range of particle and flow parameters. For heaps of size-bidisperse particles formed in the quasi-two-dimensional geometry of a vertical Hele-Shaw cell, segregation is in the form of stratified layers of large and small particle-rich bands that are nominally parallel to the free surface of the heap. Stratification occurs at low fill rates where flow down the heap manifests as a series of intermittent and irregularly sized avalanches. This non-steady flow causes variation in stratum thickness and streamwise extent. In this talk we describe how temporal modulation of the fill rate can generate ordered strata at high fill rates. In particular, we show how, for a duty cycle variation of the flow rate, the modulation parameters determine the wavelength and streamwise extent of the layers. We explain our results in terms of the dependence of the dynamic repose angle on flow rate. Finally we describe how the upstream extent of the strata increases with decreasing gap width and is related to the jamming probability of the large particles. [Preview Abstract] |
Tuesday, November 26, 2013 9:18AM - 9:31AM |
M13.00007: Passive Separation of Granular Materials Joseph McCarthy, Diana Lievano Despite its industrial importance, particle separation techniques remain typically quite ``low tech'' and often are energy-intensive (e.g., sieving) or environmentally unfriendly (e.g., froth floatation) or both. Rate-based separation processes, on the other hand, represent a unique approach to particle separation that has the potential to be more flexible, more efficient, and more environmentally friendly than existing ``low tech'' techniques. In the present paper, we highlight a passive granular separation technique, where particles of differing properties flow through a device often called a Galton board. In this type of device, the gravity-driven flow of particles down an inclined plane causes collisions between the particles and distributed pegs along the board. Collisions between particles as well as between particles and pegs results in a diffusion-like motion of particles perpendicular to the flow. The extent of separation (i.e., how far one type of particle is removed from another) depends on the different distances traversed by the two types of particles and, ultimately, on the collision rate and energy dissipation for particle-peg events. A simple theory, based on statistics and single-collision mechanics, will be set forth for comparison with our results. [Preview Abstract] |
Tuesday, November 26, 2013 9:31AM - 9:44AM |
M13.00008: Exotic patterns and convection control in a vibrated bed of binary granular mixtures Meheboob Alam, Istafaul Ansari Experiments have been carried out in a harmonically shaken quasi-2D bed of glass and steel particles for a wide range of shaking strengths and relative number fractions of two species. The goal is to understand the role of bidispersity and other control parameters on the resulting pattern formation dynamics and segregation. We report novel patterns displaying the coexistence of sub-harmonic/harmonic and disordered states, and a partial analog of granular Rayleigh-Benard convection. The former patterns bear striking similarities with Chimera-states in the sense that they represent a coexisting state of synchronous and asynchronous patterns. The horizontal segregation of glass and steel particles is responsible for the genesis of such phase-coexisting patterns. We demonstrate a simple recipe to control ``buoyancy-driven'' granular convection. [Preview Abstract] |
Tuesday, November 26, 2013 9:44AM - 9:57AM |
M13.00009: Suppression and emergence of granular segregation under cyclic shear Matt Harrington, Joost H. Weijs, Wolfgang Losert Heterogeneous mixtures of granular materials have a tendency to segregate under various dynamics disturbances, including shear. While several models have been proposed for segregation in various contexts, there is still much to learn about the mechanisms of shear-induced segregation, particularly at the particle-scale. We have performed experiments on a three dimensional (3D) bidisperse mixture in a split-bottom geometry, under both steady and oscillatory shear. The Refractive Index Matched Scanning technique captures dynamics within the full 3D system. While the pile continuously segregates under steady shear, we find that the cyclically driven system either remains mixed or segregates slowly, depending on shear amplitude. We also characterize the segregating and non-segregating regimes by determining local reversibility with respect to space and structure, as well as observing the emergence of a convective flow field. [Preview Abstract] |
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