Discrete particle simulation of particulate systems: A review of major applications and findings

Review of discrete particle modeling of fluidized beds

Pyoclastic density currents are awesome volcanic phenomena that can wreak destruction on a regional scale and can impact global climate. They deposit ignimbrites, which include vast impact lansdscape-modifying sheets with volumes exceeding 1000 km3.This book takes stock of our understanding of pyroclastic density currents and presents a new conceptual framework for investigating how ignimbrites are deposited. It integrates the results of field-based studies, laboratory experiments and numerical modelling, including work on clastic sedimentologym and industrial particle transport. Topics covered include the behaviour or particulate currents, mechanisms of clast support and segregation, interpreting ignimbrite lithofacies and architectures, and future research directions. The new approach focuses on processes and conditions within the lower flow-boundary zone of currents. Superb diagrams explain many new concepts, while the 95 photographs make an explanatiry atlas of deposit types. This is essential reading for workers investigating volcanic hazards, and for anyone wishing to interpret modern or ancient ignimbrites, as well as other catastrophically emplaced sediments.

“Given the depth of scholarship that they have brought to the subject, the power of their arguments, and the degree of synthesis with other fields, this would seemto qualify as a seminal work… I think that this will be the paper on the topic that others will have to contend with for many years to come.” Marcus Bursik, State University of New York

Pyroclastic density currents and the sedimentation of ignimbrites

Process Modeling in the Pharmaceutical Industry using the Discrete Element Method

This report presents a numerical study of segregation and mixing of binary mixtures of particles in a gas-fluidized bed by means of discrete particle simulation, where the motion of individual particles is 3-D and the flow of continuous gas is 2-D. Periodic boundary conditions are applied to the front and rear walls to represent a bed of large thickness with a relatively small number of particles. Two initial packing conditions are used in this simulation: completely separated, with the flotsam (1 × 10−3 m in diameter) on the top of the jetsam (2 × 10−3 m in diameter), and well mixed. The flotsam and jetsam are of the same density, with each counting 50% in weight. Gas is injected uniformly at the bottom. Two superficial gas velocities, 1.0 and 1.4 m/s, are used in the simulation, producing significant segregation and good mixing, respectively. The results show that the degree and rate of segregation or mixing are significantly affected by gas velocity and the final equilibrium states are not affected by the initial packing states for a given gas velocity. Significant segregation occurs at a gas velocity of 1.0 m/s, with the top fluidized layer rich in flotsam and the bottom defluidized layer rich in jetsam, whereas there was less segregation at 1.4 m/s with most of the bed fluidized. The simulated results are qualitatively comparable with those observed in the physical experiments conducted under similar conditions. On this basis, the mixing kinetics obtained from the numerical simulation is quantified with a weighted Lacey mixing index and explained in terms of microdynamic results in relation to particle–particle and particle–fluid interactions. It is proposed that an appropriate sampling size should be able to describe properly the two extremes: well mixed and fully segregated. The results also demonstrate that size segregation occurs as a result of the strong fluid drag force lifting the flotsam before a dynamical equilibrium is reached, and the particle–particle interaction, like the particle–fluid interaction, plays an important role in achieving uniform fluidization. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1713–1728, 2004

Discrete particle simulation of gas fluidization of particle mixtures

Experimental validation of granular dynamics simulations of gas-fluidised beds with homogeneous inflow conditions using Positron Emission Particle Tracking

Attrition of porous glass particles in a fluidised bed

Publisher Summary This chapter discusses the positron emission particle tracking (PEPT). PEPT is a technique for tracking a single radioactive tracer particle by detecting the distribution of emitted γ-rays. Like other radioactive particle tracking techniques, it allows non-invasive observation of the motion of a single particle within a dense optically-opaque system, which may contain many other similar particles. It differs from other tracking techniques in that it uses positron emitting radioisotopes, which have the unique attribute that their decay leads to simultaneous emission of a pair of back-to-back γ-rays. The PEPT technique employs an iterative algorithm to discard the corrupt annihilation vectors. Starting with a set of vectors, it finds the point in space that minimises the total perpendicular distance from all the vectors to the point. Those vectors with a perpendicular distance greater than some multiple of the mean distance are rejected, and the process is repeated using just the remaining vectors; this continues till a specified fraction of the original set remains. The chapter discusses various applications of PEPT and the examples presented here—fluidization, mixing in rotating drums and in rotating shaft devices and gravity flow—each demonstrate different advantages of the PEPT technique. In each case, particle tracking reveals details of the physical basis for the phenomena under observation. This more detailed observation will enable more physically realistic models for particulate processes to be derived,

Positron emission particle tracking: Particle velocities in gas fluidised beds, mixers and other applications

The dynamics of large particles in a four-compartment interconnected fluidized bed

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Experimental validation of granular dynamics simulations of gas-fluidised beds with homogeneous inflow conditions using Positron Emission Particle Tracking

Attrition of porous glass particles in a fluidised bed

Positron emission particle tracking: Particle velocities in gas fluidised beds, mixers and other applications

The dynamics of large particles in a four-compartment interconnected fluidized bed