Magnetohydrodynamic (MHD) flows in annular channels are of great current interest due to experimental search for the so-called magnetorotational instability (MRI) which is important for astrophysical applications (accretion disk physics, magnetic dynamo effect). <p>The main point of MRI experiments is to study the stability of liquid metal rotating in an external magnetic field. Two different types of fluid rotation are proposed: Taylor-Couette flow between rotating coaxial cylinders and electrically driven flow in transverse magnetic field. The implementation of MRI experiments and explanation of experimental results requires a theoretical study of the equilibrium and the stability of MHD flow in an annular channel. This is one of the main tasks of present thesis.<p>For study of equilibrium Taylor-Couette and electrically driven flows, a numerical code is developed which is based on the finite difference scheme with Jacobi iterations. The structure of flows is calculated for different parameters of the experiment. Effect of the inertia on the rotation profiles is investigated in detail. The approximate analytical expressions are obtained for radial profiles of rotation that can be used for optimization of the experimental device for MRI investigation. Equilibrium Taylor-Couette and electrically driven flows are compared from the perspective of experimental studies of MRI.<p>The spectral stability of electrically driven flow is studied by solving the eigen-value problem. This study is performed in the frames of both ideal and dissipative MHD models. It is shown that electrically driven flow can be destabilized through the mechanism of MRI if fluid velocity exceeds some instability threshold, which is determined by non-axisymmetric modes. The obtained results are compared with available experimental data.<p>A general variational method is developed for the stability study of MHD flows of ideal compressible fluids. It is shown that the linearized dynamics of such fluids has an infinite set of invariants. A necessary and sufficient stability criterion can be obtained after inclusion of one or several such invariants in analysis. An analytical example is presented to confirm the fruitfulness of the developed method.

Magnetohydrodynamic (MHD) flows in annular channels are of great current interest due to experimental search for the so-called magnetorotational instability (MRI) which is important for astrophysical applications (accretion disk physics, magnetic dynamo effect). <p>The main point of MRI experiments is to study the stability of liquid metal rotating in an external magnetic field. Two different types of fluid rotation are proposed: Taylor-Couette flow between rotating coaxial cylinders and electrically driven flow in transverse magnetic field. The implementation of MRI experiments and explanation of experimental results requires a theoretical study of the equilibrium and the stability of MHD flow in an annular channel. This is one of the main tasks of present thesis.<p>For study of equilibrium Taylor-Couette and electrically driven flows, a numerical code is developed which is based on the finite difference scheme with Jacobi iterations. The structure of flows is calculated for different parameters of the experiment. Effect of the inertia on the rotation profiles is investigated in detail. The approximate analytical expressions are obtained for radial profiles of rotation that can be used for optimization of the experimental device for MRI investigation. Equilibrium Taylor-Couette and electrically driven flows are compared from the perspective of experimental studies of MRI.<p>The spectral stability of electrically driven flow is studied by solving the eigen-value problem. This study is performed in the frames of both ideal and dissipative MHD models. It is shown that electrically driven flow can be destabilized through the mechanism of MRI if fluid velocity exceeds some instability threshold, which is determined by non-axisymmetric modes. The obtained results are compared with available experimental data.<p>A general variational method is developed for the stability study of MHD flows of ideal compressible fluids. It is shown that the linearized dynamics of such fluids has an infinite set of invariants. A necessary and sufficient stability criterion can be obtained after inclusion of one or several such invariants in analysis. An analytical example is presented to confirm the fruitfulness of the developed method.

Extraction processes employing emulsion liquid membranes (ELMs), water-in-oil emulsions dispersed in aqueous phase, have been shown to be highly efficient in removing a variety of organic and inorganic contaminants from industrial wastewaters. As a result, they have been considered as alternative technologies to other more common separation processes such as pressure-driven membrane processes. Unfortunately, a widespread use of the ELM process has been limited due to the instability of emulsion globules against fluid shear. Breakup of emulsions and subsequent release of the internal receptor phase to the external donor phase would nullify the extraction process. Numerous studies have been, therefore, made in the past to enhance the stability of ELMs. Examples include adding more surfactants into the membrane phase and increasing the membrane viscosity. However, increased stability has been unfortunately accompanied by loss in extraction efficiency and rate in most reported attempts. The primary objective of this research is to apply the ELMs in a unique contacting device, a Taylor-Couette column, which provides a relatively low and uniform fluid shear that helps maintaining the stability of emulsion without compromising the extraction efficiency of a target compound. The ELM used in this study is made of membrane phase converted into non-Newtonian fluid by polymer addition, which provides additional uncommon remedy for the problem. This innovative ELM process was optimized to treat various types of simulated industrial wastewaters containing selected phenolic compounds and heavy metals. Experiments performed in this study suggested that the newly developed ELM process achieved exceptionally high overall removal efficiencies for the removal of these target compounds in relatively short contact time. Mechanistic predictive models were further developed and verified with the experimental data. Combined with the experimental data and novel mathematical predictive models, this study is expected to have a high impact on immediate practices of emulsion liquid membrane technologies in relevant industries.

The main focus of this work is to investigate thermal performance of self-contained drum motor drive systems (SCDMDS). All components of a SCDMDS are contained inside a rotating drum including the electric motor, gearbox, and an air/oil multiphase flow. A considerable amount of heat is generated within the SCDMDS from various sources, namely, the electric motor losses, the oil viscous dissipation and the gearbox losses. In meantime, a limited amount of heat is dissipated through the surface of the rotating drum and the side flanges. Therefore, a SCDMDS sometimes encounters a serious overheating problem, which often results in electric motor failure. The different heat generation and dissipation mechanisms as well as the two-phase flow within the SCDMDS have been studied experimentally and numerically under different operating parameters, namely, the oil level (OV), the drum rotational speed (N), the torque (ζ), the number of motor poles (n) and the electric motor dimensions. The effects of rubber lagging material and thickness as well as the use of rubber belts have been investigated as well. The numerical part of the present study has been carried out using Ansys-CFX and was validated using experimental data. Results showed that the optimum oil level (OV) for the best thermal performance is about 65%. The increase in the rotational speed (N) enhanced the heat transfer within the SCDMDS due to the improved oil splashing. Viscous dissipation (VD) between the motor stator and the rotating drive drum was found to be almost negligible. However, oil viscous dissipation within the gap between the motor rotor and stator was found to have an important effect on the thermal performance. An analytical model has been developed and implemented using MATLAB to estimate VD within the motor. The losses from the gearbox were studied experimentally and numerically considering planetary and co-axial gear trains. The numerical work was carried out using the KISSsoft and KISSsys software. Results showed that the increase in the drum rotational speed (N) or the drum torque (ζ) increased the gearbox losses. In the planetary gearbox, any increase in the OV increases the churning losses, however, the increase in OV increased the losses in the co-axial gearbox up to OV = 31% beyond which the losses remained constant. After understanding the complex interplay between all the heat generating and dissipating mechanisms within the SCDMDS, a number of possible modifications have been proposed in order to resolve the overheating problem. The effect of cooling the electric motor by using an axial air flow has been investigated. The effect of adding fins along the inner surface of the outer rotating drum has also been studied. Correlations of the various contributing mechanisms have been developed. Based on a thermal resistance network, a SCDMDS sizing and performance assessment computer software tool in the form of a digital twin (DT) has been developed. A user-friendly interface has been developed using Visual Basics and Excel. The DT estimates temperature distribution and the amount of heat generated and dissipated from each component within the SCDMDS and hence it identifies whether the case is considered safe to operate or overheating is expected. In overheated cases, the DT also suggests several possible modifications the user could consider to resolve the overheating problem. The DT has been validated against several experimental case studies and found to be very reasonably accurate. / Thesis / Doctor of Philosophy (PhD) / This study is focused on investigating heat transfer and fluid flow inside a self-contained drum motor drive system (SCDMDS). The problem of interest involves multiple heat sources enclosed inside a tight space of the rotating drum. There is an electrical motor, gearbox and a multiphase (oil/air) flow inside the rotating drum of the SCDMDS. In this thesis, experimental test rigs were constructed to investigate the effect of a number of operating and geometrical parameters. In addition, numerical analysis of the multiphase oil/air flow was carried out using Ansys - CFX. The KISSsoft and KISSsys software packages were used to determine various types of heat losses within the geartrain. Due to the presence of multiple heat sources inside a confined space, overheating of a number of SCDMDS has been reported. The overheating problem worsened even more when rubber lagging is used to increase traction between the drive drum and the belt. Several correlations have been developed for various heat transfer mechanisms governing the overall thermal performance of the entire SCDMDS. An analytical model (a digital twin) has been developed using Visual Basics and Excel. The digital twin estimates the temperature distribution and the amount of heat generated and dissipated inside the SCDMDS. It has been validated against many case studies provided by the industrial partner. The model identifies the possibility of overheating and provides the user with several potential modifications to resolve it. Hence, the model can be used as a performance and design tool of various models of SCDMDS.

Les contacteurs centrifuges, basés sur les écoulements de Taylor-Couette, sont bien adaptés pour la mise en œuvre de réactions chimiques ou biochimiques, y compris en milieu polyphasique. Ils possèdent particulièrement plusieurs propriétés favorables à la mise en œuvre des opérations d'extraction liquide-liquide. Un dispositif expérimental a été conçu avec cette idée en tête. Il est constitué de deux cylindres concentriques avec le cylindre intérieur entraîné en rotation et l'externe fixe. L’écoulement de Taylor-Couette se produit dans l’espace annulaire entre eux. Il présente la particularité d’évoluer vers la turbulence par apparition successive d’instabilités. La dispersion axiale ainsi que le mélange, sont extrêmement sensibles à ces structures d’écoulement, ce qui rend difficile la modélisation du couplage entre l’hydrodynamique et le transfert de matière. Ce point particulier a été étudié expérimentalement et numériquement. L’écoulement et le mélange ont été caractérisés par des mesures simultanées de PIV (Vélocimétrie par Imagerie de Particules) et PLIF (Fluorescence Induite par Laser). Les champs de concentration PLIF ont permis d’identifier les différents mécanismes de transport intra et inter-vortex. Pour les régimes ondulatoires (WVF et MWVF), le mélange intra-vortex est contrôlé par l’advection chaotique, directement lié aux caractéristiques du champ de vitesse, qui confère aux vortex une capacité plus importante à convecter et à étirer les filets de fluide. En revanche, l’apparition des vagues brisent les frontières qui séparent les vortex ce qui favorise le transport inter-vortex. La combinaison de ces deux mécanismes contrôle principalement la dispersion axiale. Nous avons également mis en évidence le comportement non monotone des propriétés de mélange en fonction de l’histoire de l’écoulement. Notamment l’état d’onde (la longueur d’onde axiale et l’amplitude de la vague). Nous avons calculé le coefficient de dispersion axiale Dx à l’aide des mesures de distribution de temps de séjour (DTS) et de suivi Lagrangien de particules (DNS). Les deux résultats numériques et expérimentaux ont confirmé l’effet significatif des structures de l’écoulement et de l’histoire sur la dispersion axiale. / Taylor-Couette flows between two concentric cylinders have great potential applications in chemical engineering. They are particularly convenient for two-phase small scale devices enabling solvent extraction operations. An experimental device was designed with this idea in mind. It consists of two concentric cylinders with the inner one rotating and the outer one fixed. Taylor-Couette flows take place in the annular gap between them, and are known to evolve towards turbulence through a sequence of successive instabilities. Macroscopic quantities, such as axial dispersion and mixing index, are extremely sensitive to these flow structures, which may lead to flawed modelling of the coupling between hydrodynamics and mass transfer. This particular point has been studied both experimentally and numerically. The flow and mixing have been characterized by means of flow visualization and simultaneous PIV (Particle Imaging Velocimetry) and PLIF (Planar Laser Induced Fluorescence) measurements. PLIF visualizations showed clear evidences of different transport mechanisms including « intravortex mixing » and « inter-vortex mixing ». Under WVF and MWVF regimes, intra-vortex mixing is controlled by chaotic advection, due to the 3D nature of the flow, while inter-vortex transport occurs due to the presence of waves between neighbouring vortices. The combination of these two mechanisms results in enhanced axial dispersion. We showed that hysteresis may occur between consecutive regimes depending on flow history and this may have a significant effect on mixing for a given Reynolds number. The axial dispersion coefficient Dx evolution along the successive flow states was investigated thanks to dye Residence Time Distribution measurements (RTD) and particle tracking (DNS). Both experimental and numerical results have confirmed the significant effect of the flow structure and history on axial dispersion. Our study confirmed that the commonly used 1-parameter chemical engineering models (e.g. the « well-mixed stirred tanks in serie » model) are not valid for Taylor-Couette reactors modelling : two parameters are at least required for an efficient description of mixing in Taylor-Couette flows.

Le projet e-MECA : electro-Mécanique Embarquée à Compacité Améliorée, dont l’objectif est de concevoir une machine ultra compacte et ultra rapide à une puissance utile de 12Kw, trouve son application dans les véhicules mild et full hybrides. Ce type de machine présente en effet un fort potentiel de déploiement industriel en très grandes séries à des prix abordables. Pour ces machines, les pertes de charge liées aux écoulements dans le jeu constituent des enjeux essentiels pour les constructeurs. La présente étude porte sur le moyen d’identifier de ces pertes des machines électriques ultra-compactes et ultra-rapides (50 000 rpm).Cette thèse a pour objet l’étude des pertes aérauliques dans l’espace entre le rotor et le stator d’une machine électrique ultra-rapide (≈ 250 m/s) et ultra-compacte (0,5mm - 2mm d’entrefer), en cherchant à répondre aux spécifications élaborées par nos partenaires dans le cadre du projet e-MECA. / The project e-MECA: electromechanical engineering Embarked in Improved Compactness, the objective of which is to design a machine with a small gap and high speed rotor with a useful power of 12Kw, finds its application in mild and hybrid vehicle. This type of machine indeed presents a high potential in the industrial deployment in very big series to affordable prices. The losses in these machines are linked to the flow in the gap has a significant importance for the manufacturers. This study aims to identify these losses for the ultra-compact and ultrafast electric machines (50 000 rpm).This thesis is a study of the air losses in the space between the rotor and the stator of an ultra-fast electric machine (≈ 250 m/s) and ultra-compact (0,5mm - 2mm of air-gap). This study was done to meet the specifications that had been elaborated by our partners in the e-MECA project.

Outbreaks of food-born illness associated with the consumption of unpasteurized juice and apple cider have resulted in a rule published by the U.S. Food and Drug Administration (FDA) in order to improve the safety of juice products. The rule (21 CFR120) requires manufacturers of juice products to develop a Hazard Analysis and Critical Control Point (HACCP) plan and to achieve a 5-log reduction in the number of the most resistant pathogens. Ultraviolet (UV) disinfection is one of the promising methods to reach this 5-log reduction of pathogens. The absorption coefficients of juices typically vary from 10 to 40 1/cm and can be even higher depending on brand and processing conditions. Thin film reactors consisting of two concentric cylinders are suitable for inactivating pathogens in juices. When the two concentric cylinders are fixed, the flow pattern in the gap can be laminar Poiseuille flow or turbulent flow depending on flow rates. If the inner cylinder is rotating, and the rotating speed of the inner cylinder exceeds a certain value, the flow pattern can be either laminar or turbulent Taylor-Couette flow. UV disinfection between concentric cylinders in laminar Poiseuille flow, turbulent flow and both laminar and turbulent Taylor-Couette flow was investigated experimentally and numerically. This is the first systematic study done on UV disinfection between concentric cylinders in all three flow patterns. The present work provides new experimental data for pathogen inactivation in each of the three flow patterns. In addition, the present study constitutes the first systematic numerical CFD predictions of expected inactivation levels. Proper operating parameters and optimum gap widths for different flow patterns are suggested. It is concluded that laminar Poiseuille flow provides inferior (small) inactivation levels while laminar Taylor-Couette flow provides superior (large) inactivation levels. The relative inactivation levels are: laminar Poiseuille flow < turbulent flow < laminar Taylor-Couette flow.

A high resolution spectrally accurate three-dimensional flow solver is developed in order to simulate convection dominated fluid flows. The governing incompressible Navier Stokes equations along with the energy equation for temperature are discretized using a second-order accurate projection method which utilizes Adams Bashforth and Backward Differentiation formula for temporal discretization of the non-linear convective and linear viscous terms, respectively. Spatial discretization is performed using a Fourier/Chebyshev spectral method. Extensive tests on three-dimensional Taylor Couette flow are performed and it is shown that the method successfully captures the different states ranging from formation of Taylor vortices to wavy vortex regime. Next, the code is validated for convection dominated flows through a comprehensive comparison of the results for two dimensional Rayleigh Benard convection with the theoretical and experimental results from the literature. Finally, fully parallel simulations, with efficient utilization of computational resources and memory, are performed on a model three-dimensional axially homogeneous Rayleigh Benard convection problem in order to explore the high Rayleigh number flows and to test the scaling of global properties.

Ce travail est une étude expérimentale permettant de mettre en évidence la cartographie générale de l’ensemble des états d’écoulement obtenus entre le régime laminaire de Couette et la turbulence. L’ensemble des expériences a été réalisé dans un dispositif appelé système Taylor-Couette (STC), composé de deux cylindres concentriques avec le cylindre intérieur tournant. Ces différentes instabilités (SPI, TVF, WVF, MWVF, TTVF), qui dépendent principalement du nombre de Taylor (Ta), seront obtenues avec ou sans débit axial dans le STC selon des protocoles d’analyse bien définis et nous notons que le nombre de Reynolds axial (Reax) a un effet de stabilisation de l’écoulement. Les vortex de Taylor toroïdaux, ondulés ou ondulés modulés, ont été caractérisés en termes de gradient pariétal de vitesse, de nombre d’ondes, de longueur d’ondes axiales et azimutales, de la vitesse de déplacement axial, de fréquence et de la vitesse de révolution ; la polarographie sera utilisée comme technique de mesure. La vitesse du cylindre intérieur (Ta) est essentiellement le seul phénomène agissant sur l’évolution de ces paramètres. L’utilisation de la sonde tri-segmentée dans la caractérisation des structures tourbillonnaires a contribué à la compréhension des mécanismes d’interaction vortex-paroi et à la détermination des composantes azimutale et axiale du gradient pariétal de vitesse. / This work is an experimental study to highlight general mapping of the set of states obtained from the Couette laminar flow to turbulence. All experiments were performed in a device called Taylor-Couette system (TCS) which consists of two concentric cylinders with the inner cylinder rotating. The flow regimes (SPI, TVF, WVF, MWVF, TTVF), which depend mainly on the Taylor number (Ta), were obtained with or without axial flow in the TCS according to well-defined experimental protocols. We noted that the axial Reynolds number (Reax) has astabilizing effect on the flow. Using electrodiffusion method and analysis of films, the toroidal Taylor vortices, wavy or wavy modulated flow, were characterized in terms of the wall velocity gradients, wave number, axial and azimuthal wavelength, the axial velocity of vortex displacement, and there frequencies. The Taylor number has substantial effect on the evolution of these parameters in the investigated range. The use of three-segment electrodiffusion has contributed to the understanding of the mechanisms of vortex-wall interaction and the determination of the azimuthal and axial components of the wall velocity gradient.

Implanter une machine électrique dans un véhicule hybride pose avant tout des problèmes d’encombrement. Sous-dimensionner la machine semble légitime compte tenu de l’usage qui en est fait sur véhicule. Par contre, cela suppose que les aspects thermiques soient pris en compte non seulement lors de l’utilisation, mais aussi lors de la conception de la machine. Le phénomène majeur limitant la densité de puissance massique des machines électriques est l’échauffement interne des bobines et des aimants. La modélisation thermique de la machine est complexe compte tenu de la diversité des sources de chaleur et de la coexistence de différents modes de transferts thermiques : conduction dans la matière, convection avec l’eau de refroidissement, conduction, convection et rayonnement dans l’entrefer. En termes de géométrie, si une première approche peut être réalisée en ne considérant que des flux de chaleur radiaux, la composante axiale doit nécessairement être prise en compte dès lors qu’on veut tenir compte aussi des extrémités de machine, et notamment de la chaleur produite par les roulements et les têtes de bobines. Ainsi pour pouvoir analyser pertinemment les transferts thermiques dans la machine, des méthodes numériques de type CFD ont été utilisées pour caractériser le transfert thermique par convection. La caractérisation des échanges thermiques par convection naturelle et forcée a été réalisée à l’intérieur d’une machine synchrone à aimants permanents internes (MAPI). Des relations empiriques ont été proposées afin de prendre en compte le couplage entre la thermique et l’aérodynamique dans les cavités des machines électriques totalement fermées. Afin de valider la pertinence des modèles numériques dans le cadre de ce travail, des mesures thermiques à l’aide des moyens d’essais de l’UTC ont été réalisées. Les résultats de cette étude sont utilisés pour construire des circuits thermiques équivalents qui prennent en compte les phénomènes thermiques complexes dans les machines électriques fermées utilisées dans les véhicules hybrides et électriques. Ces recommandations de conception permettront l’optimisation de l’effort investi pour le refroidissement de la machine électrique dans ses différentes phases de fonctionnement. / The integration of an electrical machine into modern hybrid vehicles is associated with new technical constraints such as the integrability into small volume without losing certainly in performance. Therefore, the development of compacter electrical machines is a well-founded argument for car manufacturers as well as electrical machine designers. On the other hand, this finding assumes that the thermal aspects are undertaken not only during the operation of the electrical machine, but also during the design process. The internal heat generated in different areas impacts strongly the power density and the magnet health which deeply reduce the electrical machine reliability. Heat transfer modeling inside electrical machines is a tricky task because of the strong coupling between the different physics governing their operations. Indeed, the generated losses spread inside the electrical machine through three heat transfer modes which are: conduction (heat diffusion), convection(heat transport) and radiation (heat scattering). In terms of geometry, if a first approach can be carried out by considering only radial heat fluxes, the axially-transferred heat must be undertaken when it is also necessary to consider end caps effects, and particularly the heat released by the bearings. In order to carry out relevantly the thermal analysis of a permanent magnets synchronous machine, CFD based methods are used to characterize the convective heat transfer inside this machine over a large operating range. Both natural and forced convection are analyzed and the corresponding heat transfer coefficients are numerically-estimated. Empirical equations are proposed in order to take into account the coupling between thermal and fluid dynamics inside the cavities of the studied totally-enclosed machine. These correlations are integrated then into a detailed and reduced thermal network. Experimental tests are carried out using a test bench in order to measure temperature distribution in different areas of the electrical machine. Afterward, a comparison between estimated and measured temperatures shows that the results of the numerically-enhanced thermal network are in a good agreement with measurements. Thus, the proposed recommendations based on CFD modeling allow the convective heat transfer to be characterize quickly and precisely. These correlations are useful for upcoming studies dealing with convection inside automotive electrical machines as well as high speed electrical machines.