Instability And Segregation In Bounded Gas Particle Fluidized Beds And Granular Flows
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Instability And Segregation In Bounded Gas Particle Fluidized Beds And Granular Flows
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Author : Xue Liu
language : en
Publisher:
Release Date : 2006
Instability And Segregation In Bounded Gas Particle Fluidized Beds And Granular Flows written by Xue Liu and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with Gas flow categories.
Finally, we extend our work to investigate the steady state solutions of boundary-driven and body-force-driven granular flows and gas-particle fluidized beds with a bi-disperse particle mixture. Granular energy equipartition breaks down with an increase in the system inelasticity and the mass ratio, whereas the effect of the size ratio is very small if the two particle species have the same mass. The segregation of total particles and each individual particle species is enhanced when the effect of non-equipartition of granular energy is considered. The species segregation is enhanced with a decrease in the system elasticity, an increase in the average solids fraction or an increase in the size ratio, due to the competition of three diffusion forces: the thermal diffusion force, the ordinary diffusion force and the pressure diffusion force. For gas-particle fluidized beds and granular flows in a channel, we find that for the kinetic theory models used in the present study, the solids fraction and the granular temperature profiles are quite similar.
Instability And Segregation In Bounded Gas Particle And Granular Flows
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Author : Xue Liu
language : de
Publisher: VDM Publishing
Release Date : 2008
Instability And Segregation In Bounded Gas Particle And Granular Flows written by Xue Liu and has been published by VDM Publishing this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008 with Science categories.
Fluid-particle and granular flows exhibit rather complex behavior, for example, the occurrence of bubbles and clusters in gas-particle flows, and clogging and size segregation in granular flows. This work is to advance our understanding of granular and gas particle flows using computational simulations. In gas-particle fluidized beds, confined between parallel solid walls, non-uniform solids distribution is observed and the flow profiles are strongly related to the physical and operating parameters, such as particle inelasticity, gravity, bed width and mean solids fraction. A stability analysis has been carried out to investigate the instabilities in gas-particle flows and the generation of cluster, bubbles or streamers in gas-fluidized beds. For boundary driven and body-force-driven granular flows and gas-particle fluidized beds with polydisperse particle mixtures, the particle species segregation is enhanced with a decrease in the system elasticity, an increase in the average solids fraction or an increase in the size ratio, due to the competition of diffusion forces. The distribution of granular energy and its effect on the segregation is also considered in this work.
Mutiscale Modeling Of Segregation In Granular Flows
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Author :
language : en
Publisher:
Release Date : 2007
Mutiscale Modeling Of Segregation In Granular Flows written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2007 with categories.
Modeling and simulation of segregation phenomena in granular flows are investigated. Computational models at different scales ranging from particle level (microscale) to continuum level (macroscale) are employed in order to determine the important microscale physics relevant to macroscale modeling. The capability of a multi-fluid model to capture segregation caused by density difference is demonstrated by simulating grain-chaff biomass flows in a laboratory-scale air column and in a combine harvester. The multi-fluid model treats gas and solid phases as interpenetrating continua in an Eulerian frame. This model is further improved by incorporating particle rotation using kinetic theory for rapid granular flow of slightly frictional spheres. A simplified model is implemented without changing the current kinetic theory framework by introducing an effective coefficient of restitution to account for additional energy dissipation due to frictional collisions. The accuracy of predicting segregation rate in a gas-fluidized bed is improved by the implementation. This result indicates that particle rotation is important microscopic physics to be incorporated into the hydrodynamic model. Segregation of a large particle in a dense granular bed of small particles under vertical. vibration is studied using molecular dynamics simulations. Wall friction is identified as a necessary condition for the segregation. Large-scale force networks bearing larger-than-average forces are found with the presence of wall friction. The role of force networks in assisting rising of the large particle is analyzed. Single-point force distribution and two-point spatial force correlation are computed. The results show the heterogeneity of forces and a short-range correlation. The short correlation length implies that even dense granular flows may admit local constitutive relations. A modified minimum spanning tree (MST) algorithm is developed to asymptotically recover the force statistics in the force networks. This algorithm provides a possible route to constructing a continuum model with microstructural information supplied from it. Microstructures in gas fluidized beds are also analyzed using a hybrid method, which couples the discrete element method (DEM) for particle dynamics with the averaged two-fluid (TF) equations for the gas phase. Multi-particle contacts are found in defluidized regions away from bubbles in fluidized beds. The multi-particle contacts invalidate the binary-collision assumption made in the kinetic theory of granular flows for the defluidized regions. Large ratios of contact forces to drag forces are found in the same regions, which confirms the relative importance of contact forces in determining particle dynamics in the defluidized regions.
Iutam Symposium On Segregation In Granular Flows
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Author : Anthony D. Rosato
language : en
Publisher: Springer Science & Business Media
Release Date : 2013-04-17
Iutam Symposium On Segregation In Granular Flows written by Anthony D. Rosato and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013-04-17 with Technology & Engineering categories.
Segregation is a pervasive phenomenon whereby a flowing granular mass consisting of particles with diverse physical properties becomes spatially inhomogeneous. In the industrial sector that deals with the handling and processing of bulk solids, this non-uniformity is highly undesirable since blend homogeneity is generally a stringent requirement of most products. In the arena of geophysical flows, segregation can enhance the destructive capabilities of natural events such as avalanches and landslides. During the last 15 years, these issues have provided motivation and fostered collaborations between the communities of mathematicians, engineers, industrial researchers, and physicists to develop predictive models of segregation by integrating the perspectives and approaches of each. The collection of unique papers brings to light many of the perplexing scientific and technical issues in our current understanding of this complex phenomenon. It addresses advances in experiment, computational modeling and theory. This volume is one of the very few books devoted entirely to problems of segregation of particulate solids.
Dissertation Abstracts International
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Author :
language : en
Publisher:
Release Date : 2007
Dissertation Abstracts International written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2007 with Dissertations, Academic categories.
Solids Segregation In Gas Fluidized Beds Of Large Particles
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Author : Charles Stuart Daw
language : en
Publisher:
Release Date : 1985
Solids Segregation In Gas Fluidized Beds Of Large Particles written by Charles Stuart Daw and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1985 with Fluidization categories.
Segregation Of Granular Particles In Suspension Flow
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Author : Jessica Tsay
language : en
Publisher:
Release Date : 2004
Segregation Of Granular Particles In Suspension Flow written by Jessica Tsay and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2004 with categories.
An experiment was conducted to investigate the development of longitudinal stripes of granular particles due to instabilities in particle suspension flow. Research was conducted to characterize environmental phenomena related to granular flows, namely avalanches, mudslides, and the movement of glaciers. Results show the stripes were found to appear with a particle concentration of 10% by volume at angles of 20 degrees, at a particle concentration of 20% and 30% by volume at 20, 30, and 40 degrees, and at a particle concentration for 40% by volume at 20 degrees. The application of a shear stress intensified the development of the instabilities, and in experimental trials where stripes were not initially seen, the application of a shear stress was able to induce the fluid to develop the instability.
Directory Of Graduate Research
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Author : American Chemical Society. Committee on Professional Training
language : en
Publisher:
Release Date : 2005
Directory Of Graduate Research written by American Chemical Society. Committee on Professional Training and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2005 with Biochemistry categories.
Faculties, publications and doctoral theses in departments or divisions of chemistry, chemical engineering, biochemistry and pharmaceutical and/or medicinal chemistry at universities in the United States and Canada.
Closures For Course Grid Simulation Of Fluidized Gas Particle Flows
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Author :
language : en
Publisher:
Release Date : 2010
Closures For Course Grid Simulation Of Fluidized Gas Particle Flows written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
Gas-particle flows in fluidized beds and riser reactors are inherently unstable, and they manifest fluctuations over a wide range of length and time scales. Two-fluid models for such flows reveal unstable modes whose length scale is as small as ten particle diameters. Yet, because of limited computational resources, gas-particle flows in large fluidized beds are invariably simulated by solving discretized versions of the two-fluid model equations over a coarse spatial grid. Such coarse-grid simulations do not resolve the small-scale spatial structures which are known to affect the macroscale flow structures both qualitatively and quantitatively. Thus there is a need to develop filtered two-fluid models which are suitable for coarse-grid simulations and capturing the effect of the small-scale structures through closures in terms of the filtered variables. The overall objective of the project is to develop validated closures for filtered two-fluid models for gas-particle flows, with the transport gasifier as a primary, motivating example. In this project, highly resolved three-dimensional simulations of a kinetic theory based two-fluid model for gas-particle flows have been performed and the statistical information on structures in the 100-1000 particle diameters length scale has been extracted. Based on these results, closures for filtered two-fluid models have been constructed. The filtered model equations and closures have been validated against experimental data and the results obtained in highly resolved simulations of gas-particle flows. The proposed project enables more accurate simulations of not only the transport gasifier, but also many other non-reacting and reacting gas-particle flows in a variety of chemical reactors. The results of this study are in the form of closures which can readily be incorporated into existing multi-phase flow codes such as MFIX (www.mfix.org). Therefore, the benefits of this study can be realized quickly. The training provided by this project has prepared a PhD student to enter research and development careers in DOE laboratories or chemicals/energy-related industries.
Cfd Simulation Of Mixing And Segregation In A Tapered Fluidized Bed
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Author :
language : en
Publisher:
Release Date :
Cfd Simulation Of Mixing And Segregation In A Tapered Fluidized Bed written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on with categories.
Fluidization of different materials results either in a well-mixed or a segregated bed. Depending upon the operating conditions, smaller particles (floatsam) tend to rise to the bed, and larger particles (jetsam) tend to sink to the bottom of the bed. The tapered fluidized bed can be used to overcome certain draw backs of the gas-solid system because of the fact that a velocity gradient exists along the axial direction of the bed with increase in cross-sectional area. To study the dynamic characteristics of the homogenous mixture of regular and irregular particles several experiments have been carried out with varying compositions. The particle flow pattern and granule segregation in tapered fluidized bed have been studied by first fluidizing the beds of varying total mass and granule fractions and then defluidize them suddenly to freeze the composition, section the bed in layers, and determine the composition in each layer by sieving. A series of unsteady, three-fluid CFD simulations were performed using FLUENTTM 6.2. Simulation parameters viz. solution technique, grid, maximum packing fraction and operating conditions like gas velocity were each investigated for the relative effects on particle mixing and segregation. Good agreement of solid volume fraction profile was obtained between the experimental results and simulation results for regular particles.