Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session E30: Granular Flows: Mixing, Segregation and Separation |
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Chair: Richard Lueptow, Northwestern University Room: F151 |
Sunday, November 20, 2016 5:37PM - 5:50PM |
E30.00001: Mixing dynamics of cutting and shuffling for granular materials Richard M. Lueptow, Zafir Zaman, Mengqi Yu, Paul P. Park, Julio M. Ottino, Paul B. Umbanhowar Chaotic dynamics has been shown to play a major role in fluid mixing, but the study of its relevance to granular flows has only recently begun. We utilize a simple 3D geometry, a half-filled spherical tumbler rotated alternately by $\le \pi $/2 about two perpendicular horizontal axes, to develop a dynamical systems framework for granular mixing and non-mixing. In these systems, mixing can only occur during flow (from stretching due to shear and from collisional diffusion in the flowing layer) or by material separation intrinsic to the rotation protocol resulting from cutting and shuffling. In X-ray subsurface visualization experiments, surprisingly persistent (O(100) iterations) non-mixing elliptical regions and larger non-mixing barriers occur as predicted by both a continuum model and an idealized theoretical model (with an infinitely thin flowing layer) based on the mathematics of piece-wise isometries. In these models, the stretching in the flowing layer vanishes as the flowing layer thickness decreases to reveal the underlying skeleton of the mixing. This dynamical systems perspective provides insight into mixing and non-mixing phenomena unique to granular materials. [Preview Abstract] |
Sunday, November 20, 2016 5:50PM - 6:03PM |
E30.00002: Stratification of size-bidisperse granular mixtures in a quasi-2D bounded heap with periodic flow modulation Hongyi Xiao, Zhekai Deng, Paul Umbanhowar, Julio Ottino, Richard Lueptow Segregation of disperse granular materials in unsteady flows is ubiquitous in nature and industry, yet remains largely unexplored. In this study, unsteady flows are generated by feeding size-bidisperse granular mixtures onto a quasi-2D bounded heap using alternating feed rates, which results in stratified layers of large and small particles. The mechanism of stratification is investigated in detail using Discrete Element Method (DEM) simulations of the flow. During the transition from the slow to the fast feed rate, a segregating wedge propagates downstream and forms a large particle layer extending upstream. During the opposite transition, upstream segregated small particles relax downstream and form a small particle layer extending downstream. The transient kinematics from DEM simulations are quantified and used to inform a time-dependent continuum model that captures the interplay of advection, diffusion, and segregation in the flowing layer. The continuum model reproduces the principle characteristics of the stratification patterns observed in experiments and simulations. [Preview Abstract] |
Sunday, November 20, 2016 6:03PM - 6:16PM |
E30.00003: Streamwise transport in multi-component granular flows Chris Johnson, Andrew Hogg, Jeremy Phillips Thin free-surface avalanches of granular material occur widely in nature and industry. In these contexts the flows often contain particles of a wide range of sizes, which separate from one another due to particle size segregation. This segregation is troublesome in industry (where a well-mixed state is usually desired) and is an important mechanism for determining the runout and morphology of natural avalanches and debris flows. In this talk we develop a model for the spatial and temporal evolution of the particle size distribution in a granular flow, due to particle segregation, diffusion and advection processes. We use asymptotic solutions of this model to formulate equations governing the depth-integrated particle size distribution. These equations naturally extend the shallow-water models often used to predict the dynamics of monodisperse avalanches. Our modelling shows that particles in granular avalanches may strongly segregate in the direction of flow, even when the segregation is relatively weak compared to diffusive mixing and the avalanche is nearly homogeneous throughout its depth. We demonstrate this surprising phenomenon through comparison with discrete particle simulations. [Preview Abstract] |
Sunday, November 20, 2016 6:16PM - 6:29PM |
E30.00004: Application of methods for quantifying maximum potential segregation and actual segregation risk to design of powder blends David Goldfarb, Stephen Conway, Michael Gentzler As described in a recent publication (Gentzler, Tardos, Michaels, \textit{Powder Technology}, 2015), the tendency of pharmaceutical powders to demix due to segregation can threaten the content uniformity of solid dosage forms. Using the methodology established in this publication, examples of analysis and optimization of pharmaceutical formulations to evaluate the potential for segregation during formulation and reduce the risk of content uniformity issues upon scale-up are provided. Modification to active components and excipient properties are considered and a systematic risk assessment approach for multi-component blends emerges. Use of the measurements to understand excipient and raw material sensitivities in lieu of pilot and commercial-scale production tests is described. This approach has the potential for being readily applied to the study of the segregation risk potential outside the pharmaceutical industry. [Preview Abstract] |
Sunday, November 20, 2016 6:29PM - 6:42PM |
E30.00005: Segregating photoelastic particles in free-surface granular flows. Amalia L. Thomas, Nathalie M. Vriend We experimentally investigate bimodal avalanches of photoelastic discs between two narrow side-walls. We visualize the physical phenomena that occur during segregation and quantify the dynamic appearance of force chains within the bulk of the flow from fringe patterns using photoelastic theory. The photoelastic technique has been used in granular research for almost half a century and has been applied in a variety of quasi-steady systems. We have now adapted the technique to perform well within dynamic granular flows where collisions are short-lived and force chains are formed and broken continuously. Our photoelastic urethane discs are cast in-house to provide high-resolution fringe patterns and a high stress-optic coefficient. In addition we carried out stress relaxation tests to study the viscoelastic properties of the photoelastic material, and measured the speed of force transmission and dampening from a moving particle onto a static chain of particles. In our avalanche experiments, we also employ particle tracking and particle velocimetry techniques to measure the general flow field within the avalanche. The overall goal of our work is to investigate and quantify the influence of the distribution of forces on the fundamental processes that drive segregation. [Preview Abstract] |
Sunday, November 20, 2016 6:42PM - 6:55PM |
E30.00006: Hydrodynamics and Segregation in Poiseuille Flow of a Binary Granular Mixture Ronak Gupta, Meheboob Alam Steady State profiles of hydrodynamic fields have been computed for the Poiseulle flow of a dilute bi-disperse granular mixture using DSMC (direct simulation Monte Carlo) method. The effects of mass bidispersity and inelasticity are studied and it is found that species segregation follows a non-monotonic trend with increasing mass-ratio if the particles are inelastic. Mixture velocity shows a similar trend. Nonequipartition of granular temperature is expectedly enhanced with increasing mass-ratio and inelasticity, but is additionally a strong function of Knudsen number. Effort is made to compare simulation results with a continuum theory for dilute binary granular mixtures, with the aim being to check if theory is able to predict the novel segregation tendencies uncovered in DSMC simulations. [Preview Abstract] |
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