Cette étude est consacrée à la compréhension des phénomènes mis en jeu dans les écoulements fluidisés denses verticaux ascendant et descendant, ainsi que dans leur couplage avec un écoulement fluidisé dense horizontal dans une enceinte à pression contrôlée. Tout d'abord une étude hydrodynamique, réalisée dans une colonne de fluidisation classique sans circulation de solide, a permis de déterminer les différentes grandeurs caractéristiques de la suspension lors de sa fluidisation et de sa désaération, indispensables à la compréhension et à la modélisation des écoulements : Vitesses minimales de fluidisation et de bullage. Porosités au minimum de fluidisation et de bullage. Porosité de la phase dense. Vitesse de désaération et de sédimentation. Puis, l'influence des paramètres tant géométriques (diamètre de la colonne d'expédition, longueur de la partie horizontale, …) qu'opératoires (vitesses de fluidisation de la partie horizontale et d'aération de la colonne d'expédition, politique de dégazage, …) sur le comportement global de deux unités pilotes a mis en évidence les paramètres clés du procédé : Vitesse de fluidisation de la partie horizontale. Politique de dégazage. Aération de la colonne d'expédition. Les transferts de gaz entre les différentes zones du procédé ont également été mis en évidence grâce à l'utilisation d'un traceur gazeux. Enfin, une modélisation de type monodirectionnelle est entreprise dans le but de simuler le comportement des suspensions fluidisées denses en écoulement verticaux ascendant et descendant. Les résultats obtenus concordent de manière très satisfaisante avec les mesures expérimentales. Ils permettent de mettre en évidence les mécanismes de transport ascendant de solide. De plus, le logiciel de calcul ainsi créé permet d'optimiser les dimensions d'une conduite verticale accueillant une suspension fluidisée dense en écoulement descendant afin d'en garantir le bon fonctionnement. / This study is dedicated to the understanding of the phenomena involved in dense fluidized upward and downward flows, and their coupling with a dense fluidized horizontal flow in a pressure controlled chamber. First of all, a hydrodynamic study, conducted in a solid particles flow-free cylindrical fluidization column, is initiated to determine the fluidization and de-aeration characteristics parameters, required to the flows understanding and modeling: Minimum fluidization and minimum bubbling rates. Minimum fluidization and minimum bubbling voidages. Dense phase voidage. De-aeration and sedimentation rates. Then, the geometric (upward-flow zone diameter, horizontal chamber length, …) and operating (horizontal chamber fluidization rate, degassing policy, …) parameters influences on two pilot-scaled unities behavior highlights the process key parameters: Horizontal chamber fluidization rate. Degassing policy. Upward-flow additional aeration. The use of helium tracking also highlights the gas transfer phenomena between horizontal, vertical upward, and vertical downward flow zones. Finally, a monodirectional model is created in order to simulate dense gas/solid suspensions behavior in vertical upward and downward flows. The computed results are concordant with the experimental data and highlight the upward solid conveyance mechanisms. The computation software can also optimize the downward pipe dimensions with the aim of maintaining a good flow.

Der vorliegende Beitrag befasst sich mit dem Verhalten von Vibrationsförderern. Speziell für Förderer, welche nach dem Gleitprinzip arbeiten, werden Zusammenhänge zwischen der Antriebslage, dem Fördergut sowie der Ausrichtung des Förderorgans beschrieben. Durch Anwendung der vorgestellten Prinzipien wird eine Berechnungsmethode für die Fördergeschwindigkeit abgeleitet und anschließend mit Versuchswerten verglichen. / This paper deals with the behavior of vibrating conveyors. Especially for conveyors, using a sliding principle of movement, relations between the drive position, the conveyed goods and the orientation of the means of transport are described. By applying the principles presented, a method for calculating the conveying velocity is derived and compared with experimental values.

In order to mitigate the risk of global warming by reducing CO2 emissions, the co-firing technique, burning pulverized coal and granular biomass together in conventional pulverised fuel power station boilers, has been advocated to generate “greener” electricity to satisfy energy demand while continuing to utilize existing rich coal resources. A major problem is controllably distributing fuel mixtures of pulverized coal and granular biomass in a common pipeline, thus saving much investment. This is still under development in many co-firing studies. This research into particle dynamics in pipe flow was undertaken in order to address the problem of controllable distribution in co-firing techniques and gain an improved understanding of pneumatic conveying mechanisms. The objectives of this research were, firstly, to numerically evaluate the influence of various factors on the behaviour of particles of the different materials in a horizontal pipe gas-solid flow, secondly, to develop an extended technique of Laser Doppler Anemometry in order to determine cross-sectional characteristics of the solid phase flow in the horizontal and vertical legs of a pneumatic conveying system, and, thirdly, to develop a novel imaging system for visualizing particle trajectories by using a high definition camcorder on a cross-section illuminated by a white halogen light sheet. Finally, a comparison was made of cross-sectional flow characteristics established by experiments and those simulated by using a commercial Computational Fluid Dynamics code (Fluent) and the coupling calculations of Fluent & EDEM (a commercial code of Discrete Element Method) respectively. Particle dynamic behaviour of the solid phase in a dilute horizontal pipe flow was investigated numerically by using the Discrete Phase Model (DPM) in Fluent 6.2.16. The numerical results indicate that the Saffman force plays an important role in re-suspending particles at the lower pipe boundary and that three critical parameters of the critical air: conveying velocity, the critical particle size and the critical pipe roughness, exist in pneumatic conveying systems. The Stokes number can be used as a similarity criterion to classify the dimensionless mean particle velocity of the different materials in the fully developed region. An extended Laser Doppler Anemometry (LDA) technique has been developed to measure the distributions of particle velocities and particle number over a whole pipe cross section in a dilute pneumatic conveying system. The first extension concentrates on a transform matrix for predicting the refracted laser beams’ crossing point in a pipe according to the shift coordinate of the 3D computer-controlled traverse system on which the probes of the LDA system were mounted. Another part focussed on the proper sampling rate of LDA for measurements on the gas-solid pipe flow with polydispersing particles. A suitable LDA sampling rate should ensure that enough data is recorded in the measurement interval to precisely calculate the particle mean velocity or other statistical values at every sample point. The present study explores the methodology as well as fundamentals of measurements of the local instantaneous density of particles as a primary standard using a laser facility. The extended LDA technique has also been applied to quantitatively investigate particle dynamic behaviour in the horizontal and vertical pipes of a dilute pneumatic conveying system. Three kinds of glass beads were selected to simulate the pulverized coal and biomass pellets transported in a dilute pneumatic conveying system. Detailed information on the cross-sectional spatial distributions of the axial particle velocity and particle number rate is reported. In the horizontal pipe section, experimental data on a series of cross-sections clearly illustrate two uniform fluid patterns of solid phase: an annular structure describing the cross-sectional distribution of the axial particle velocity and a stratified configuration describing particle number rate. In the vertical pipe downstream of an elbow R/D=1.3, a horseshoe-shaped feature, which shows that the axial particle velocity is highest in wall regions of the pipe on the outside of the bend for all three types of glass beads on the section 0D close to the elbow outlet. The developments of cross-sectional distributions of particle number rate indicate that the horseshoe-shaped feature of particle flow pattern is rapidly dispersed for particles with high inertia. A video & image processing system has been built using a high definition camcorder and a light sheet from a source consisting of a halogen lamp. A set of video and image processing algorithms has been developed to extract particle information from each frame in a video. The experimental results suggest that the gas-solid flow in a dilute pneumatic conveying system is always heterogeneous and unsteady. The parameter of particle mass mean size is superior to particle number mean size for statistically describing the unsteady properties of gas-solid pipe flow. It is also demonstrated that the local data of particle number rate or concentration are represented by a stratified structure of the flow pattern over a horizontal pipe cross-section. Finally, comparisons of numerically predicated flow patterns and experimental ones show that there is reasonable agreement at pipe cross-sections located at horizontal positions less than half the product of particle mean velocity and mean free fall time in the pipe from the particle inlet. Further away from the inlet, the numerical results show flow patterns which are increasingly divergent from the experimental results along the pipe in the direction of flow. This discrepancy indicates that particles’ spatial distribution in the pipe is not accurately predicted by the Discrete Phase Model or Fluent coupled with EDEM.

In this work the electrostatics of the pneumatic conveying of granular materials in a non-conducting (PVC) vertical pipe is studied using Electrical Capacitance Tomography (ECT) system. The non-conducting wall in general attains static charges arising from particle-wall collisions in the initial periods of conveying process and then reaches equilibrium with the surroundings. The polarity of particles and conveying pipe inner wall agrees reasonably well with the contact potential difference measurements. The perturbations in the capacitance signal due to charge accumulation are larger with smaller air superficial velocity. The denser flow regimes give larger wall residual charge. Wall charging process shows similar trend by surface potential and ECT measurements. The addition of small amount (0.5% by weight) of anti-static agent (Larostat-519) in the powder form decreases the electrostatic charge generation by altering the patterns for particle-particle and particle-wall collisions. / Singapore-MIT Alliance (SMA)

Research Doctorate - Doctor of Philosophy (PhD) / Slug flow dense phase pneumatic conveying can be a most reliable, efficient method for handling a remarkably wide range of dry bulk solids. Models for pressure drop over slugs in the low-velocity slug-flow pneumatic conveying by many researchers only took the force balance into account with the pressure drop. However, the nature of the slug flow pneumatic conveying is discontinuous and seldom becomes steady during the conveying period which requires further investigation. The fundamental understanding to gas/slug interaction in this thesis is that, by being a dynamic system, the faster a slug moves at a speed, the larger the space is left behind the slug. The gas feeding into the conveying system has to fill the increased space first then permeates through the slug and provides a push force on the slug. With gas permeation rate defined by the permeability factor, the derivative of the upstream pressure based on the air mass conservation law has been developed. For a given conveying system, the pressure in the pneumatic conveying system can be solved for steady conditions or numerically simulated for unsteady conditions. Parametric analysis have been conducted for pressure drop factors and found that slug velocity is the major reason causing the pressure fluctuation in the pneumatic conveying system. To verify the pressure drop model, this model has been applied to single slug cases and compared with experimental results for five different bulk materials, showing good results. Three distinct zones, i.e. Fixed Bed Zone, Initial Slug Zone and Reliable Slug Zone, have been found to exist in the relationship between slip velocity and pressure gradient. Lastly this model has also been applied to a multiple slug system under uniform conditions. In all, the fundamental gas pressure/pressure drop model developed in this thesis approaches slug flow conveying from a different viewpoint from the traditional momentum and material stress models developed by previous researchers, and provides a way of assessing the non-steady flow behaviour in granular dense phase pneumatic conveying. This model not only attains a better understanding of slug flow behaviour but also increases the accuracy of predicting the parameters.

Research Doctorate - Doctor of Philosophy (PhD) / Slug flow dense phase pneumatic conveying can be a most reliable, efficient method for handling a remarkably wide range of dry bulk solids. Models for pressure drop over slugs in the low-velocity slug-flow pneumatic conveying by many researchers only took the force balance into account with the pressure drop. However, the nature of the slug flow pneumatic conveying is discontinuous and seldom becomes steady during the conveying period which requires further investigation. The fundamental understanding to gas/slug interaction in this thesis is that, by being a dynamic system, the faster a slug moves at a speed, the larger the space is left behind the slug. The gas feeding into the conveying system has to fill the increased space first then permeates through the slug and provides a push force on the slug. With gas permeation rate defined by the permeability factor, the derivative of the upstream pressure based on the air mass conservation law has been developed. For a given conveying system, the pressure in the pneumatic conveying system can be solved for steady conditions or numerically simulated for unsteady conditions. Parametric analysis have been conducted for pressure drop factors and found that slug velocity is the major reason causing the pressure fluctuation in the pneumatic conveying system. To verify the pressure drop model, this model has been applied to single slug cases and compared with experimental results for five different bulk materials, showing good results. Three distinct zones, i.e. Fixed Bed Zone, Initial Slug Zone and Reliable Slug Zone, have been found to exist in the relationship between slip velocity and pressure gradient. Lastly this model has also been applied to a multiple slug system under uniform conditions. In all, the fundamental gas pressure/pressure drop model developed in this thesis approaches slug flow conveying from a different viewpoint from the traditional momentum and material stress models developed by previous researchers, and provides a way of assessing the non-steady flow behaviour in granular dense phase pneumatic conveying. This model not only attains a better understanding of slug flow behaviour but also increases the accuracy of predicting the parameters.

Thesis (Professional Degree)--University of Missouri, School of Mines and Metallurgy, 1938. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed April 20, 2010)

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Kok-Meng Lee; Committee Member: Bruce Webster; Committee Member: Shreyes Melkote.

Thesis (Ph.D.)--University of Wollongong, 2001. / Typescript. Bibliographical references: leaf 218-232.

Thesis (M.Eng.Sc.)--University of Queensland, 2003. / Includes bibliography.