Thesis (M.A.)--University of Wisconsin--Madison, 1946. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 24).

Heat transfer tubes and other surfaces fixed inside fluidized beds are subjected to buffetting forces due to solids and gas motion. Coupled with erosion and corrosion, these forces can lead to tube failure. The objective of the present work was to investigate the nature and origin of the forces acting on tubes immersed horizontally in gas fluidized beds, and to provide information to be used in structural design of heat exchanger tube bundles. Experiments were carried out in a column of cross-section 215 x 200 mm and height 1.5 m. The fluidizing gas was air and the bed was operating at ambient temperature. The parameters varied in the experiments were superficial gas velocity (from U[sub=mf] to U[sub=mf] + 1.4 m/s), static bed height (from 0.30 m to 0.45 m), mean particle size (from 185 to 430 μm), particle density (from 920 to 4100 kg/m³), tube diameter (from 15 to 32 mm) and tube shape (finned vs. unfinned). All tubes were mounted horizontally at a height of 0.30 m above the orifice plate distributor. Both vertical and horizontal forces were measured on tubes in isolation and on tubes within arrays of different configurations. For some runs, local pressure variations at the surface of the test tubes were also measured simultaneously with the forces. The relation between force characteristics and bubble properties was examined by separate experiments involving injection of single bubbles. Statistical parameters of the measured forces have been calculated. Instantaneous forces on each tube within a freely bubbling bed consisted of a series of pulses whose magnitudes, durations and rate of occurrence depend on the operating parameters. The magnitude of the forces is strongly influenced by superficial gas velocity, slightly dependent on particle size, and moderately affected by bed depth and particle density. Horizontal forces are generally of significantly lower magnitude than vertical components and oscillate from side to side with a zero mean. Forces can be characterized as containing both periodic and random components and are statistically stationary. The primary frequency content of the forces is in the range 0-20 HZ, with the major frequencies being almost independent of the operating conditions and always below 10 HZ at the height of measurement, 300 mm above the distributor. The trends are consistent with the hydrodynamics of bubbling fluidized beds. Force pulses have been found to be related to bubble motion, and pulse maxima correspond to arrival of bubbles at the tube surface. The intensity of forces on individual tubes within an array have been found to depend on the position of the tube in the array. The intensity of forces can be reduced significantly by using reasonably tight inter-tube spacings and by reducing the level of the tube-bundle above the gas distributor. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

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A thesis submitted to the Faculty of Engineering, University of the Witwatersrand, Johanneaburg, in fulfilment of the requirerments for the degree of Doctor of Philosophy. / In this work a new high speed metal forming process is experimentally and theoretically investigated and discussed. The high speed metal forming is carried out in a liquid shock tube. The pressure energy of a liquid shock wave, which is generated non-explosively is used to form the metal workpiece.(abbreviation abstract) / Andrew Chakane 2019

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La thèse porte sur le développement d'un couplage entre un code de mécanique des fluides et un de code mécanique des structures afin de modéliser le départ en instabilité d'une structure soumise à un chargement fluide-élastique. Dans un premier temps, la méthodologie de couplage est présentée. Celle-ci englobe les modèles de couplage permettant de résoudre le décalage lié à une résolution partitionnée des équations fluide et structure, les méthodes de déformation de maillage afin de permettre aux deux milieux de rester en contact et les méthodes de projections afin de transférer les données d'un domaine à l'autre Dans un second temps, une étude semi-analytique est menée sur les schémas de couplage partitionnés. Le cas de deux cylindres vibrant dans un fluide parfait au repos est étudié pour lequel une solution analytique en termes de conservation de l'énergie est connue. Ce cas permet de tester un ensemble de schémas et de vérifier leur bon comportement quant à la conservation de l'énergie du domaine étudié. Il permet également de quantifier l'erreur liée au code de calcul. Dans un troisième temps, une étude sur l'instabilité d'une structure flexible soumise à un écoulement interne est menée. Elle démontre que la structure part en instabilité à partir d'une certaine vitesse d'écoulement. Ce cas est repris afin d'introduire une méthode d'incertitude. Le but est de montrer la possibilité d'utiliser la méthode du chaos polynomial afin d'étudier une probabilité de dépassement de seuil (le départ en instabilité de la structure) lorsqu'une variable en entrée est incertaine. Dans un dernier temps, une étude sur les faisceaux de tubes est menée. Des études sont menées avec un unique tube mobile ou un ensemble de tubes mobiles. Des simulations sont réalisées avec un fluide au repos afin de comparer les résultats à des données analytiques et numériques. Puis des simulations sous écoulements sont réalisées afin de montrer afin de mettre en évidence le départ en instabilité des structures qui varie selon le nombre de tubes mobiles. / The PhD deals with coupling between a fluid mechanics and a structure mechanism code in order to simulate the instabilities departure of flow induced vibrations. Firstly, methodology is presented: coupling scheme which allows staggered procedure, mesh deformation in order to aIIow interface tracking and exchange of information for non-matching interface. Secondly, a study on staggered procedure is performed with the case of two moving cylinders in a quiescent fluid. Results are compared to an analytical solution in order to check the coupling scheme behaviour and in order to quantify the energy conservation of the code. Thirdly, the stability of a pipe conveying tluid is performed. Results show the instability departure of the structure for a critical velocity. The uncertainty management is applied on this case in order to study the over threshold probability (instability departure) when an input variable is uncertain. Finally, the coupling is applied to tube bundles. Cases with one and several moving tubes are performed. Cases with quiescent fluid are compared results to analytical and numerical results. Flow simulations show instability departure which differ when one or several moving tubes are used.