Fluid dynamics in a two dimensional fluidized bed of large particles

Observation shows that bubbles in large particle fluidized beds behave quite differently from beds of fine particles. They expand and can grow faster than they rise. Bubbles in fine particle beds seem to grow primarily by coalescence, while in large particle beds they are observed to grow mainly without coalescence. The aim of this study was to gain a better insight into bubble behavior in fluidized beds of intermediate and large particles (particle diameter greater than 0.4 mm), and understand the cause of the observed bubble growth. In the theoretical part of this work it is shown that emulsion voidage invariability, incompressible viscous gas flow and potential solids flow assumed by existing theoretical two-phase models cannot account for the observed gas accumulation within bubbles. A simplified theoretical form for the gas accumulation rate in a cylindrical bubble is developed. It is based on different areas of gas inflow and outflow at the bubble boundary, and on the fact that the emulsion voidages above and below the bubble are different. It was shown that voidage variations in the emulsion phase around a bubble are important to bubble growth considerations. The experimental cases analyzed for single growing two dimensional bubbles indicate a higher voidage at the wake region, than the voidage at the nose of the bubble. It was found that a relatively small difference in emulsion voidage above and below the bubble can cause significant gas accumulation within the bubble reaching values comparable to the gas throughflow. Finally the movement of bubbles in the vicinity of an immersed tube and pressure-time curves representing the slow bubble and rapid bubble growth regime, and the transition range are analyzed in order to identify important bubble behavior characteristics. An experimental set up was developed making possible simultaneous permanent recording of the two-dimensional bubble behavior and instantaneous pressure data acquisition at multiple locations in an area under study. Lapsed cinematography and a special circuit activating the data acquisition system was used. The experimental set up enabled the collection of a large amount of data which gave valuable information about fluid dynamic behavior in the vicinity of an immersed tube. Experiments were performed at atmospheric pressure and room temperature in a two-dimensional fluidized bed with an immersed 50.8.mm (2 in) in diameter internal located at a height 0.35 m above the distributor plate. Glass, sand and dolomite particles with mean surface particle diameters of 0.65 to 2.6 mm were used. Superficial air velocities used spanned a region from well below minimum fluidization conditions to 2.82 m/s

Excavations at Azoria, 2003-2004, Part 1: The Archaic Civic Complex

This article constitutes the first of two reports on fieldwork conducted at Azoria in eastern Crete during the 2003 and 2004 excavation seasons. The focus of excavation was on the South Acropolis, where buildings of Archaic date (7th-early 5th century b.c.) suggesting public or civic functions have come to light. The complex includes a possible andreion on the west slope, a cult building on the terrace south of the peak, and storerooms and kitchens associated with a monumental public building on the southwest terrace. A 3rd-century b.c. dump on the southeast slope provides important information about the limited reoccupation of the site in the Hellenistic period

Etude des milieux stratifiés : Reconnaissance des coefficients de réflexion par les techniques de traitement du signal

Une analyse de la réponse d'un milieu stratifié à une sollicitation ultrasonore en incidence normale est proposée dans cette étude. Ce milieu, assimilable à un filtre, est essentiellement caractérisé par les paramètres suivants: nombre, nature et épaisseur des couches insonifiées. L'étude de la propagation dans le milieu, moyennant certaines hypothèses, conduit à la détermination de la réponse impulsionnelle permettant la reconnaissance des coefficients de réflexion. Il est effectivement possible de mesurer sur un tel enregistrement les retards introduits par les strates successives et les amplitudes des échos réfléchis par les dioptres correspondants. On montre que l'application du modèle de Robinson modifié permet de ramener un milieu stratifié hétérochrone à un milieu stratifié isochrone. L'équation caractérisant le milieu permet, par un algorithme programmé, de déduire à partir du paramètre d'ordre k, les paramètres k-1, k-2, etc... représentant les coefficients de réflexion des dioptres k-1, k-2 .... Une synthétisation de la réponse impulsionnelle a également été réalisée par ordinateur en intercorrélant le signal émis avec le signal réfléchi par le milieu. En outre on a effectué, sur le plan expérimental, une simulation du milieu en utilisant un réseau de capteurs décalés. Les applications possibles de ce travail s'étendent au domaine biomédical, à la sismologie, ainsi qu'au contrôle non destructif des matériaux

Scalable Object Encoding Using Multiplicative Multilinear Inter-camera Prediction in the Context of Free View 3D Video

Part 10: Image-Video Classification and ProcessingInternational audienceRecent advancements in 3D television allow for the capture of scene depth from multiple cameras and the interactive selection of view point and direction within a certain range, the so-called Free Viewpoint Video (FVV). State-of-the-art video codecs such as H.264/AVC exploit the large amount of inter-view statistical dependencies by combined temporal and inter-view prediction, i.e. prediction from temporally neighboring images as well as from images in adjacent views. This is known as Multi-view Video Coding (MVC). We propose herein an alternative object oriented video coding scheme for multi-view video with associated multiple depth data (N-video plus N-depth). A structure that we call a Multi-view Video Plane (MVP) is introduced. Object planes associated with a certain view are approximated as multilinear components of an image that are projected onto other views in a tensor-like fashion. The order of the tensor equals the number of multiple views. The coefficients of the tensor subspace projections as well as the updates of the multi-linear components (object-planes) are quantized and transmitted in the MPEG stream. Motion-compensated prediction is carried out in order to transmit the residual object planes (P-frames) using conventional MPEG algorithms