A two-dimensional (2-D), mathematical model is adopted to investigate the development of circulation patterns for compressible, laminar, and shear driven flow inside a rectangular cavity. The bottom of the cavity is free to move at a specified speed and the aspect ratio of the cavity is changed from 1.0 to 1.5. The vertical sides and the bottom of the cavity are assumed insulated. The cavity is filled with a compressible fluid with Prandtl number, Pr =1. The governing equations are solved numerically using the commercial Computational Fluid Dynamics (CFD) package ANSYS FLUENT 2015 and compared with the results for the primitive variables of the problem obtained using in house CFD code based on Coupled Modified Strongly Implicit Procedure (CMSIP). The simulations are carried out for the unsteady, lid driven cavity flow problem with moving boundary (bottom) for different Reynolds number, Mach numbers, bottom velocities and high initial pressure and temperature.

Abstract: The thesis work is part of a project that aims to develop a reliable CFD model to investigate the fluid-dynamics of a fluidized bubbling bed during gasification of refuse derived fuel (RDF) from sorted municipal solid waste (MSW). Gasification is a thermochemical process that converts carbon-containing materials into syngas. In this specific context scaling up is challenging because it implies dealing with a complex chemistry combined to heat and mass transfer phenomena in a multi-phase fluid environment. CFD modeling could represent a potential tool to predict the impact of the reactor configuration and operating conditions on gas yield, composition and potential contaminants. Validation of CFD simulations for such systems has been so far possible using different sophisticated experimental tools, allowing to link the model with experimental data. However, such high tech equipment may not always be available, especially at industrial scale. Hence, this work focuses on investigating the accuracy and numerical sensitivity of two different CFD models employed in the characterization of dense solid-particle flows in bubbling fluidized beds. The key parameter adopted to describe and quantify the dynamic behavior of this multiphase system is the power spectral density (PSD) distribution of pressure fluctuations. This PSD function was used to assess the accuracy of CFD models using one set of operating condition. The same type of analysis, extended to a wider range of operating conditions, may lead to a robust validation of the numerical models presented in this work. In spite of his measurement simplicity, pressure drop data present a strong connection with the bed fluid-dynamics and its interpretation could help to improve the fluidized bed technologies very fast, pushing CFD models closer to applications. / Résumé : Le but de ce projet est de développer un modèle CFD fiable pour étudier la dynamique des fluides d'un lit fluidisé en régime bullant pendant la gazéification de combustibles solides de récupération (CSR) triés à partir de déchets solides municipaux (DSM). La gazéification est un processus thermochimique qui convertit les matériaux contenant du carbone en gaz de synthèse. La mise à l'échelle est difficile dans ce cas car elle implique une chimie complexe combinée aux phénomènes de transfert de chaleur et de masse dans un environnement fluide multiphasique. La modélisation CFD représente un outil potentiel pour prédire l'impact de la configuration du réacteur et des conditions de fonctionnement sur le rendement, la composition et les contaminants potentiels du gaz. La validation des simulations CFD pour de tels systèmes a été jusqu'à présent possible grâce à l’utilisation de différents outils expérimentaux sophistiqués, permettant de lier le modèle aux données expérimentales. Toutefois, un tel équipement de pointe n’est pas toujours disponible, en particulier à l'échelle industrielle. Par conséquent, ce travail se concentre sur l'étude de la précision et de la sensibilité numérique de deux modèles CFD différents, utilisés dans la caractérisation des flux de particules solides denses dans les lits fluidisés bouillonnants. Le paramètre clé adopté pour décrire et quantifier le comportement dynamique de ce système multiphase est la distribution de la densité spectrale de puissance (DSP) des fluctuations de pression. La fonction DSP a été utilisée pour évaluer la précision des modèles CFD en utilisant un ensemble de conditions de fonctionnement. Le même type d'analyse, étendu à une plus large gamme de conditions de fonctionnement, peut conduire à une validation robuste des modèles numériques présentés dans ce travail. En dépit de sa simplicité de mesure, les données de chute de pression présentent une importante corrélation avec les lits fluidisés, de plus, leur interprétation pourrait aider à améliorer ces technologies très rapidement, poussant les modèles CFD plus près des applications.

Rotating bed reactors are used throughout the process industry. They are usedboth in the chemical industry and other industrial sectors, such as pharmaceuticals and the textile industry in decolorization due to by-products or contaminants.SpinChem AB manufactures rotary bed reactors (RBRs) to perform chemical reactions between liquids and solids. The solid material consists of spherical particles0.1 mm - 1 mm in diameter that are packed between two cylindrical spaces in theRBR. The goal of this project work is to determine the power number, the axial force thatthe RBRn experiences, the torque requirement on the motor and power consumptionof the the RBR when a fully developed turbulent flow is achieved. The purpose ofthe work is to optimize the technology from the energy usage point of view, makethe product simple and easily accessible for chemical and industrial processes as acontribution to the development of sustainable society. In order to achieve the purpose and goal of the projects, Computational Fluid Dynamics (CFD) combined withexperimental models were used. Computation were made in COMSOL Multiphysicsfor two turbulence models. In it, the rotating machinery was used with moving meshtechnique for both the standard k−ε model and the SST k−ω turbulence models.The result is then compared with the empirical models. Investigation were done for two models of the rotating bed reactors (RBRs). Onemodel is called RBR S2 with relatively small size and RBR S14 which is a muchlarger version. For RBR S2 the experimental results turned out to be, an output ofpower number which is 3.4, torque requirement of 0.03 Nm, power consumption of3 W and a thrust force of 0.11 N. While the simulation results turned out to bean output of power number which is about 1.2, torque requirement of 0.013 Nm, apower consumption of 2 W and thrust force of 0.8 N. Similarly, the experimentalresult for RBR S14 was as follows. A power number of 0.53, torque requirement of0.41 Nm, power consumption of 6 W and a thrust force of 4.16 N. The simulationresults turned out to be, a power number of 0.34, torque requirement of 0,40 Nm,a power consumption of 4.14 W and thrust force of 3.61 N. With the help of the calculated power numbers, the power required to rotate theRBR can then be determined. Power number is determined when a fully developedturbulent flow is achieved. For RBRS2, a fully developed turbulent flow is achievedat Re = 2.8·104 and the angular velocity at that Reynolds number is about 830RPM. At that speed, the power is shown to be about 4 W for RBRS2. For RBRS14,a fully developed turbulent flow is achieved at Re = 1.5 · 105 and then the speed atthat Reynols number is about 83 RPM. The power need at that stage is shown tobe about 20 W. / Roterande bäddreaktorer används inom hela processindustrin. De används bådeinom den kemiska industrin och andra industriella sektor såsom, läkemedel och textilindustrin vid avfärgning på grund av biprodukter eller föroreningar. SpinChemAB tillverkar roterande bed reaktorer (RBR) för att utföra kemiska reaktioner mellan vätska och fasta material. Det fasta materialet består av sfäriska partiklar på0,1 mm - 1 mm i diameter som packas mellan två cylindrar i RBRn. Målet med detta projektarbete var att bestämma effekt nummer, effekt som krävsvid det effekt nummer, kravet på vridmoment från motorn samt den axiella kraftensom den roterande bäddreaktorn upplever när ett fullt utvecklat turbulent flöde uppnåtts. Syftet med arbetet var optimera teknologin ur energianvändningssynpunkt, göra den enkel och lättillgänglig för kemiska och industriella processer som ett bidragför hållbar samhällsutveckling. För att kunna uppnå syftet och målet med projekten användes, avancerade beräkningsmetoder i födes mekanik (CFD) i kombinationmed experimentella modeller. Beräkningar gjordes i COMSOL Multiphysics för tvåturbulenta modeller. I de användes roterande maskineriet med en medföljande mesh (moving mesh) för både standard k-ε modellen och SST k-ω modellen. Resultatet jämfördes sedan med de empiriska modellerna. Undersökningarna gjordes för två modeller av RBR. Ena modellen heter RBR S2med relativt små tillstorlek och RBR S14 som är mycket större version. För RBR S2visar den experimentella resultaten ett effekt nummer på 3,4, vridmoment på 0,03Nm, effekt förbrukning på 3 W och en axiellkraft ("thrust force") på 0,11 N. Simuleringsresultatet visar ett effekt nummer på 1,2, vridmoment på 0,013 Nm, effektförbrukning på 2 W och en axiellkraft på 0,8 N. För RBR S14 visade det experimentella resultatet ett effekt nummer på 0,53, vridmoment på 0,41 Nm, effektförbrukning på 6 W och en axiellkraft ("thrust force") på 4,16 N. Simuleringsresultatetvisade att effekt nummer var 0,34, vridmoment på 0,40 Nm, effektförbrukning på4,14 W och en axiellkraft på 3,61 N. Med hjälp av de framräknade effektnummer kan effekten som behövs rotera RBRnbestämmas. Effektnummer bestäms när ett fullt utvecklat turbulent flöde uppnåtts. För RBRS2 uppnås ett fullt utvecklat turbulent flöde vid Re = 2,8·04 och vinkelhastigheten är 830 RPM vid det Reynolds nummer. Effekten som krävs för att drivaRBRn vid det läge är ca 4 W för RBRS2. För RBRS14 uppnås ett fullt utvecklatturbulent flöde vid Re = 1,5·105 och då har vi en hastighet på 83 RPM. Vid denhastighet visas effekten vara ca 20 W.