No description available.

Microplastics are tiny particles that due to their small size, durability, and widespread usage have become a huge threat to the world and the environment. Aquatic environments like rivers and oceans have faced some irreparable problems such as the extinction of various marine species. Field sampling and numerical modeling are two methods that can help researchers have a better understanding of the situations to come up with the best solutions. Machine learning methods have drawn considerable attention in most engineering fields recently, which can be used in conjunction with field sampling and numerical simulation. In this study, by generating a fine mesh and using bathymetry, water level, and discharge data, a three-dimensional hydrodynamic modeling of the domain of study was conducted using TELEMAC 3D, which is a model that was used to simulate the behavior of the Fraser River in x, y, and z directions. The results were implemented to track the movements of microplastic particles in the lower part of the Fraser River. CaMPSim-3D, which is a three-dimensional Lagrangian particle tracking model was employed to track microplastic particles. This model, in addition to calculating the horizontal location of particles, computes their vertical movements too. The release locations of microplastic particles were chosen based on the locations of the wastewater treatment plants and combined sewer overflows and in the end, nine scenarios were conducted for this study. An unsupervised branch of machine learning is clustering which helps to cluster points by relying on their different properties. The OPTICS algorithm, which is a density-based clustering algorithm, was used to find the accumulation zones of microplastic particles in the lower part of the Fraser River. It should be mentioned that in all parts available measured data and information were used for validation. The results of the clustering algorithm indicated that there are eight accumulation zones in the study area and the breakwater in the upper branch of the Fraser River is an ideal place for microplastic particles to accumulate. A reasonable agreement was obtained between the model results and measured data.

Yes / Positron emission particle tracking (PEPT) was used to visualise the flow patterns established by mixing in two laboratory-scale anaerobic digesters fitted with mechanical mixing or gas mixing apparatus. PEPT allows the visualisation of flow patterns within a digester without necessitating the use of a transparent synthetic sludge. In the case of the mechanically-mixed digester, the mixing characteristics of opaque sewage sludge was compared to a transparent synthetic sludge at different mixing speeds. In the gas-mixed apparatus, two synthetic sludges were compared. In all scenarios, quasi-toroidal flow paths were established. However, mixing was less successful in more viscous liquids unless mixing power was increased to compensate for the increase in viscosity. The robustness of the PEPT derived velocities was found to be significantly affected by the frequency with which the particle enters a given volume of the vessel, with the accuracy of the calculated velocity decreasing in regions with low data capture. Nevertheless, PEPT was found to offer a means of accurate validation of computational fluid dynamics models which in turn can help to optimise flow patterns for biogas production. / The first author was funded via an EPSRC CASE award in conjunction with Severn Trent Water. The second author was funded via a University of Birmingham Postgraduate Teaching Assistantship award.

Single particle tracking has become a ubiquitous class of tools in the study of biology at the molecular level. While the broad adoption of these techniques has yielded significant advances, it has also revealed the limitations of the methods. Most notable among these is that traditional single particle tracking is limited to imaging the particle at low temporal resolutions and small axial ranges. This restricts applications to slow processes confined to a plane. Biological processes in the cell, however, happen at multiple time scales and length scales. Real-time feedback-driven single particle tracking microscopes have emerged as one group of methods that can overcome these limitations. However, the development of these techniques has been ad-hoc and their performance has not been consistently analyzed in a way that enables comparisons across techniques, leading to incremental improvements on existing sets of tools, with no sense of fit or optimality with respect to SPT experimental requirements. This thesis addresses these challenges through three key questions : 1) What performance metrics are necessary to compare different techniques, allowing for easy selection of the method that best fits a particular application? 2) What is a procedure to design single particle tracking microscopes for the best performance?, and 3) How does one controllably and repeatably experimentally test single particle tracking performance on specific microscopes?. These questions are tackled in four thrusts: 1) a comprehensive review of real-time feedback-driven single particle tracking spectroscopy, 2) the creation of an optimization framework using Fisher information, 3) the design of a real-time feedback-driven single particle tracking microscope utilizing extremum seeking control, and 4) the development of synthetic motion, a protocol that provides biologically relevant known ground-truth particle motion to test single particle tracking microscopes and data analysis algorithms. The comprehensive review yields a unified view of single particle tracking microscopes and highlights two clear challenges, the photon budget and the control temporal budget, that work to limit the two key performance metrics, tracking duration and Fisher information. Fisher information provides a common framework to understand the elements of real-time feedback-driven single particle tracking microscopes, and the corresponding information optimization framework is a method to optimally design these microscopes towards an experimental aim. The thesis then expands an existing tracking algorithm to handle multiple particles through a multi-layer control architecture, and introduces REACTMIN, a new approach that reactively scans a minimum of light to overcome both the photon budget and the control temporal budget. This enables tracking durations up to hours, position localization down to a few nanometers, with temporal resolutions greater than 1 kHz. Finally, synthetic motion provides a repeatable and programmable method to test single particle tracking microscopes and algorithms with a known ground truth experiment. The performance of this method is analyzed in the presence of common actuator limitations. / 2024-01-16T00:00:00Z

Particle-laden supersonic jets impinging on a flat surface are of interest to cold gas-dynamic spray technology. Solid particles are propelled to a high velocity through a convergent-divergent nozzle, and upon impact on a substrate surface, they undergo plastic deformation and adhere to the surface. For given particle and substrate materials, particle velocity and temperature at impact are the primary parameters that determine the success of particle deposition. Depending on the particle diameter and density, interactions of particles with the turbulent supersonic jet and the compressed gas region near the substrate surface can have significant effects on particle velocity and temperature. Unlike previous numerical simulations of cold spray, in this dissertation we track solid particles in the instantaneous turbulent fluctuating flow field from the nozzle exit to the substrate surface. Thus, we capture the effects of particle-turbulence interactions on particle velocity and temperature at impact. The flow field is obtained by direct numerical simulations of a supersonic rectangular particle-laden air jet impinging on a flat substrate. An Eulerian-Lagrangian approach with two-way coupling between solid particles and gas phase is used. Unsteady three-dimensional Navier-Stokes equations are solved using a six-order compact scheme with a tenth-order compact filter combined with WENO dissipation, almost everywhere except in a region around the bow shock where a fifth-order WENO scheme is used. A fourth-order low-storage Runge-Kutta scheme is used for time integration of gas dynamics equations simultaneously with solid particles equations of motion and energy equation for particle temperature. Particles are tracked in instantaneous turbulent jet flow rather than in a mean flow that is commonly used in the previous studies. Supersonic jets for air and helium at Mach number 2.5 and 2.8, respectively, are simulated for two cases for the standoff distance between the nozzle exit and the substrate. Flow structures, mean flow properties, particles impact velocity and particles deposition efficiency on a flat substrate surface are presented. Different grid resolutions are tested using 2, 4 and 8 million points. Good agreement between DNS results and experimental data is obtained for the pressure distribution on the wall and the maximum Mach number profile in wall jet. Probability density functions for particle velocity and temperature at impact are presented. Deposition efficiency for aluminum and copper particles of diameter in the range 1 micron to 40 microns is calculated. Instantaneous flow fields for the two standoff distances considered exhibit different flow characteristics. For large standoff distance, the jet is unsteady and flaps both for air (Mach number 2.5) and for helium (Mach number 2.8), in the direction normal to the large cross-section of the jet. Linear stability analysis of the mean jet profile validates the oscillation frequency observed in the present numerical study. Available experimental data also validate oscillation frequency. After impingement, the flow re-expands from the compressed gas region into a supersonic wall jet. The pressure on the wall in the expansion region is locally lower than ambient pressure. Strong bow shock only occurs for small standoff distance. For large standoff distance multiple/oblique shocks are observed due to the flapping of the jet. The one-dimensional model based on isentropic flow calculations produces reliable results for particle velocity and temperature. It is found that the low efficiency in the low-pressure cold spray (LPCS) compared to high-pressure cold spray (HPCS) is mainly due to low temperature of the particles at the exit of the nozzle. Three-dimensional simulations show that small particles are readily influenced by the large-scale turbulent structures developing on jet shear layers, and they drift sideways. However, large particles are less influenced by the turbulent flow. Particles velocity and temperature are affected by the compressed gas layer and remain fairly constant in the jet region. With a small increase in the particles initial temperature, the deposition efficiency in LPCS can be maximized. There is an optimum particle diameter range for maximum deposition efficiency. / Ph. D.

The analysis of turbulent flows provides a unique scientific challenge whose solution remains central to unraveling the fundamental nature of all fluid dynamics. Measuring and predicting turbulent flows becomes even more difficult when considering a two-phase flow, which is a commonly encountered engineering problem across many disciplines. One such example, the ingestion of foreign debris into a gas turbine engine, provided the impetus for this study. Despite more than 40 years of research, operation with a particle-laden inlet flow remains a significant problem for modern turbomachines. The purpose, therefore, is to develop experimental methods for investigating multi-phase flows relevant to the cooling of gas turbine components. Initially, several generic components representing turbine cooling designs were evaluated with a particle-laden flow using a special high temperature test facility. The results of this investigation revealed that blockage was highly sensitive to the carrier flowfield as defined by the cooling geometry. A second group of experiments were conducted in one commonly used cooling design using a Time Resolved Digital Particle Image Velocimetry (TRDPIV) system that directly investigated both the carrier flowfield and particle trajectories. Traditional PIV processing algorithms, however, were unable to resolve the particle motions of the two-phase flow with sufficient fidelity. To address this issue, a new Particle Tracking Velocimetry (PTV) algorithm was developed and validated for both single-phase and two-phase flows. The newly developed PTV algorithm was shown to outperform other published algorithms as well as possessing a unique ability to handle particle laden two-phase flows. Overall, this work demonstrates several experimental methods that are well suited for the investigation of wall-bounded turbulent two-phase flows, with a special emphasis on a turbine cooling method. The studies contained herein provide valuable information regarding the previously unknown fluid and particle dynamics within the turbine cooling system. / Ph. D.

No description available.

Ces travaux de thèse s’intègrent au sein du projet Biocarb lancé par le Commissariat à l’Énergie Atomique dont l’objectif est de développer des procédés de production de carburants liquides ou gazeux à partir de gaz de synthèse riche en H2 et CO obtenu par gazéification de la biomasse lignocellulosique. L’objectif de cette étude est d’étudier le comportement de particules de biomasse millimétriques lors de la pyrolyse dans des conditions types de gazéifieurs industriels tels que les réacteurs à lit fluidisé ou à flux entraîné, qui fonctionnent pour des flux de chaleur élevés (105 – 106 W⋅m-2) et pour de hautes températures (>800°C). Tout d’abord, des expériences de pyrolyse sont menées à 800 et 950°C dans un four à chute de laboratoire sur des particules de bois entre 350 et 800 μm. Les résultats montrent que dans les conditions de l’étude, l’augmentation de la taille de la particule augmente seulement la durée de la pyrolyse mais ne modifie pas les rendements ou la composition du solide et du gaz au cours de la pyrolyse. Par ailleurs, des mesures basées sur la technique de PTV (Particle Tracking Velocimetry) sont réalisées à température ambiante pour caractériser la taille et la densité des particules de bois brut et de résidu, et valider une corrélation donnant le coefficient de traînée qui sert à calculer le temps de séjour des particules dans le réacteur. On constate à la fin de la pyrolyse une diminution de la densité comprise entre 70 et 80% ainsi qu’une diminution de la taille des particules entre 25 et 40%. Les résultats montrent également que la vitesse de glissement de la particule et l’évolution de ses propriétés doivent être prises en compte lors du calcul de sa vitesse. Enfin, à partir des résultats expérimentaux, un modèle unidimensionnel à coeur rétrécissant est développé pour décrire le comportement d’une particule de bois lors de sa pyrolyse. Le modèle est capable de prévoir l’évolution du rendement en solide, en gaz total et en goudrons au cours de la pyrolyse ainsi que la vitesse de glissement de la particule et son temps de séjour dans le réacteur.L’analyse de sensibilité du modèle montre que même pour des particules millimétriques, une connaissance précise de la chaleur de réaction associée à la pyrolyse, de la densité du bois et de la conductivité thermique du résidu solide est essentielle / The present work is part of a project of the French energy research centre Commissariat à l’Energie Atomique. The goal of the project is to develop processes of production of gaseous or liquid fuel from synthesis gas obtained by gasification of lignocellulosic biomass. The objective of the present work is to study the pyrolysis behaviour of millimetric biomass particles under the operating conditions encountered in fluidized bed or entrained flow gasifiers, namely high external heat flux (105 – 106 W⋅m-2) and high temperature (> 800°C). First, pyrolysis experiments are conducted at 800 and 950°C in a lab-scale drop tube reactor on wood particles between 350 and 800 μm. The results show that under the explored conditions, the increase of the particle size only increases the time required for pyrolysis but does not affect the product distribution during pyrolysis. Since in the pyrolysis experiments, the particle residence time cannot be directly measured, PTV (Particle Tracking Velocimetry) measurements are performed at room temperature to characterize the evolution of the particle size and density along pyrolysis and to validate a drag coefficient correlation for the particle residence time calculation. The optical measurements show that at the end of pyrolysis there is a decrease of particle density of 70 – 80% and of particle size of 25 – 40%. It is also proven that the particle slip velocity cannot be neglected and that the change of these particle properties must be taken into account for the calculation of the particle slip velocity and residence time. Finally, based on these experimental results, a 1D shrinking-core model is developed that is able to predict the solid/gas/tar yields and the residence time of a single particle along pyrolysis in the drop tube reactor. It is validated on both the pyrolysis and optical experiments. The model sensitivity analysis shows that even for millimetric particles, the accurate knowledge of the heat of pyrolysis, of the wood density and of the char thermal conductivity is essential

La turbulence est connue pour sa capacité à disperser efficacement de la matière, que ce soit des polluantes dans les océans ou du carburant dans les moteurs à combustion. Deux considérations essentielles s’imposent lorsqu’on considère de telles situations. Primo, l’écoulement sous-jacente pourrait avoir une influence non-négligeable sur le comportement des particules. Secundo, la concentration locale de la matière pourrait empêcher le transport ou l’augmenter. Pour répondre à ces deux problématiques distinctes, deux dispositifs expérimentaux ont été étudiés au cours de cette thèse. Un premier dispositif a été mis en place pour étudier l’écoulement de von Kàrmàn, qui consiste en une enceinte fermé avec de l’eau forcé par deux disques en contra-rotation. Cette écoulement est connu pour être très turbulent, inhomogène, et anisotrope. Deux caméras rapides ont facilité le suivi Lagrangien des particules isodenses avec l’eau et petites par rapport aux échelles de la turbulence. Ceci a permis une étude du bilan d’énergie cinétique turbulente qui est directement relié aux propriétés de transport. Des particules plus lourdes que l’eau ont aussi été étudiées et montrent le rôle de l’anisotropie de l’écoulement dans la dispersion des particules inertielles. Un deuxième dispositif, un écoulement de soufflerie ensemencé avec des gouttelettes d’eau micrométriques a permis une étude de l’effet de la concentration locale de l’eau sur la vitesse de chute des gouttelettes grâce à une montage préexistant. Un modèle basé sur des méthodes théorique d'écoulements multiphasiques a été élaboré enfin de prendre en compte les effets collectifs de ces particules sedimentant dans un écoulement turbulent. Les résultats théoriques et expérimentaux mettent en évidence le rôle de la polydispersité et du couplage entre les deux phases dans l’augmentation de la sédimentation des gouttelettes. / Turbulence is well known for its ability to efficiently disperse matter, whether it be atmospheric pollutants or gasoline in combustion motors. Two considerations are fundamental when considering such situations. First, the underlying flow may have a strong influence of the behavior of the dispersed particles. Second, the local concentration of particles may enhance or impede the transport properties of turbulence. This dissertation addresses these points separately through the experimental study of two different turbulent flows. The first experimental device used is the so-called von K\'arm\'an flow which consists of an enclosed vessel filled with water that is forced by two counter rotating disks creating a strongly inhomogeneous and anisotropic turbulence. Two high-speed cameras permitted the creation a trajectory data base particles that were both isodense and heavier than water but were smaller than the smallest turbulent scales. The trajectories of this data base permitted a study of the turbulent kinetic energy budget which was shown to directly related to the transport properties of the turbulent flow. The heavy particles illustrate the role of flow anisotropy in the dispersive dynamics of particles dominated by effects related to their inertia. The second flow studied was a wind tunnel seeded with micrometer sized water droplets which was used to study the effects of local concentration of the settling velocities of these particles. A model based on theoretical multi-phase methods was developed in order to take into account the role of collective effects on sedimentation in a turbulent flow. The theoretical results emphasize the role of coupling between the underlying flow and the dispersed phase.

Die Analyse von Kollisionen zwischen Partikeln und Blasen in einer turbulenten Strömung ist ein grundlegendes Problem von hoher technologischer Relevanz, z. B. für die Abtrennung wertvoller Mineralpartikel durch Schaumflotation. Dieser Relevanz steht ein Defizit an experimentellen Daten und Erkenntnissen über den Kollisionsprozess gegenüber. Ein Hauptproblem ist die geringe Anzahl der verfügbaren Messtechniken zur direkten Beobachtung der Kollisionen zwischen Partikeln und Blasen. Daher besteht das Ziel dieser Dissertation darin, neue Methoden zu entwickeln, um die Wechselwirkung zwischen Blasen und Partikeln unter definierten hydrodynamischen Bedingungen zu messen. Diese Methoden beruhen auf der Verfolgung von einzelnen Partikeln mit 4D Particle Tracking Velocimetry (PTV) und Positron Emission Particle Tracking (PEPT), um die Lagrangeschen Partikeltrajektorien in der Nähe einer Blase zu bestimmen und die kollidierenden Partikel zu klassifizieren. In zwei Versuchsaufbauten werden diese Messmethoden angewandt, um die Wechselwirkung zwischen Blasen und Partikeln in turbulenten Strömungen zu untersuchen. In einer Blasensäule wird die Turbulenz im Nachlauf einer frei aufsteigenden Blasenkette erzeugt, während in einem Wasserkanal die Turbulenz durch die Umströmung eines Gitters produziert wird. In beiden Fällen wird das vorhandene turbulente Strömungsfeld um die Blasen mittels Tomographic Particle Image Velocimetry (TPIV) charakterisiert. Zunächst wird der Einfluss des Blasennachlaufs auf die Blasen-Partikel-Kollision für beide Versuchsaufbauten mit dem 4D-PTV-Verfahren analysiert. Es wird gezeigt, dass in beiden Versuchsanordnungen die Kollision von feinen Partikeln nicht nur an der Vorderseite, sondern auch an der Hinterseite der Blase stattfindet. Diese Ergebnisse werden mit der gemessenen turbulenten kinetischen Energie und der Dissipationsrate um die Blase korreliert. Anschließend werden die experimentell ermittelte turbulente kinetische Energie und Dissipationsrate genutzt, um die Kollisionsfrequenz vorherzusagen. Dafür werden bestehende Modelle angewendet und deren Vorhersagen den experimentellen Ergebnissen gegenübergestellt. Weiterhin wird der Wasserkanal genutzt, um den Einfluss der turbulenten Flüssigkeitsströmung auf die Kollision zwischen einer stagnierenden Blase und den Modellpartikeln zu verdeutlichen. Neben der Untersuchung in einer verdünnten Feststoffsuspension wird auch die Blasen-Partikel-Wechselwirkung in einer dichten Strömung mit dem PEPT-Verfahren untersucht. Das PEPT-Verfahren hat das Potenzial, Suspensionen mit einem hohen Feststoffanteil zu messen, was mit optischen Trackingverfahren, wie 4D-PTV, nicht möglich ist. Für den Nachweis einzelner Partikel mit dem PEPT-Verfahren wurden radioaktive Tracerpartikel entwickelt, welche repräsentativ für die Modellpartikeln sind. Die Trajektorien der markierten Partikel werden verwendet, um die durchschnittliche Partikelverteilung im turbulenten Feld zu bestimmen und die Blasen-Partikel-Wechselwirkung zu beschreiben. Insgesamt bieten die entwickelten Methoden eine Möglichkeit die Kollision zwischen Partikeln und Blasen in einer turbulenten Strömung direkt zu untersuchen. Die gewonnenen experimentellen Daten ermöglichen es, bestehende Kollisionsmodelle zu überprüfen und das Verständnis über die Rolle von Turbulenzen in der Schaumflotation zu verbessern. / The analysis of collisions between particles and bubbles in a turbulent flow is a fundamental problem of high technological relevance, e.g. for the separation of valuable mineral particles by froth flotation. That relevance contrasts with an apparent lack of experimental data and insights into this collision process. A major issue is the limitation of available measurement techniques to directly observe the collisions between particles and bubbles. In this dissertation, novel methodologies are developed to measure the interaction between bubbles and particles under defined hydrodynamic conditions. These methodologies comprise particle tracking techniques such as 4D PTV and PEPT to triangulate the Lagrangian particle trajectories in the vicinity of a bubble and classify those which are colliding. In two experimental setups, these techniques are applied to investigate the bubble-particle interaction in turbulent flows. In a bubble column, turbulence is generated in the wake of a freely rising bubble chain, whereas in a water channel, a fluid passing through grid produces a turbulent flow upstream of a stagnant bubble. Accordingly, the turbulent flow field around these bubbles is characterized by TPIV. Firstly, the influence of the bubble wake on the bubble-particle collision is analyzed for both experimental setups with 4D PTV. It is shown that the collision of fluorescent fine particles take place not only at the leading edge but also at the trailing edge of the bubble, independently of the experimental setup. These findings are correlated with the measured TKE and dissipation rates around the bubble and in the bubble wake. Subsequently, the experimental TKE and dissipation rates are applied to existing models for collision frequency, and their predictions are discussed. Secondly, the impact of the turbulent liquid flow on the collision between a stagnant bubble and model particles is studied for a range of turbulent length scales. Besides the investigation in a dilute solid suspension, the bubble-particle interaction is also examined in a dense flow with PEPT. PEPT has the potential to measure suspensions with a high solid fraction, which could not be achieved with optical particle tracking methods. For the detection of individual particles with PEPT, radioactive tracer particles were designed to represent the bulk particles. The trajectories of the labeled particles are used to determine the average particle distribution in the turbulent field and describe the bubble-particle interactions. Overall, the developed methodologies in this dissertation provide a framework to investigate directly the collision between particles and bubble in a turbulent flow. The gained experimental validation data allows to verify existing collision models and to advance our understanding of the role of turbulence in froth flotation.