A first principle flotation model has been derived from the basic mechanisms involved in the bubble-particle and bubble-bubble interactions occurring in flotation. It is a kinetic model based on the premise that the energy barrier (E1) for bubble-particle interaction can be reduced by increasing the kinetic energy (Ek) for bubble-particle interaction and by increasing the hydrophobic force in wetting films. The former is controlled by energy dissipation rate (𝜀), while the latter is controlled by collector additions. The model consists of a series of analytical equations to describe bubble generation, bubble-particle collision, attachment and detachment, froth recovery, and bubble coalescence in froth phase. Unlike other flotation models that do not consider role of hydrophobic force in flotation, the first principle model developed at Virginia Tech can predict flotation recoveries and grades from the chemistry parameters such as 𝜁-potentials, surface tension (𝛾), and contact angles (𝜃) that may represent the most critical parameters to control to achieve high degrees of separation efficiencies. The objectives of the present work are to i) validate the flotation model using the experimental data published in the literature, ii) incorporate a froth model that can predict bubble coarsening due to coalescence in the absence of particles, iii) develop a computer simulator for a froth model that can predict bubble coarsening in the presence of particles, and iv) study the effects of incorporating a regrinding mill and using a stronger collector in a large copper flotation circuit. The model validation has been made using the size-by-class flotation rate constants (kij) obtained from laboratory and pilot-scale flotation tests. Model predictions are in good agreement with the experimental data. It has been found that the flotation rate constants obtained for composite particles can be normalized by those for fully liberated particles (kmax), which opens the door for minimizing the number of flotation products that need to be analyzed using a costly and time-consuming liberation analyzer. A bubble coarsening froth model has been incorporated into the flotation model to predict flotation more accurately. The model has a limitation, however, in that it cannot predict bubble-coarsening in the presence of particles. Therefore, a new computer simulator has been developed to predict the effects of particle size and particle hydrophobicity on bubble coarsening in froth phase. In addition, the first principle flotation model has been used to simulate flotation circuits that are similar to the Escondida copper flotation plant to study the effects of incorporating a re-grinding mill and using a more powerful collector to improve copper recovery. The flotation model developed from first principles is useful for predicting and diagnosing the performance of flotation plants under different circuit arrangements and chemical conditions. / Master of Science

Dual process theories of mind have been developed over the last decades to posit that humans use heuristics or mental shortcuts (automatic) and analytical (reflective) reasoning while consuming information. Can such theories be used to support users' information consumption in the presence of problematic content in online spaces? To answer, I merge these theories with the idea of affordances from HCI to into the concept of dual process cognitive affordances, consisting of automatic affordance and reflective affordance. Using this concept, I built and tested a set of systems to address two categories of online problematic content: misinformation and filter bubbles. In the first system, NudgeCred, I use cognitive heuristics from the MAIN model to design automatic affordances for better credibility assessment of news tweets from mainstream and misinformative sources. In TransparencyCue, I show the promise of value-centered automatic affordance design inside news articles differentiating content quality. To encourage information consumption outside their ideological filter bubble, in NewsComp, I use comparative annotation to design reflective affordances that enable active engagement with stories from opposing-leaning sources. In OtherTube, I use parasocial interaction, that is, experiencing information feed through the eyes of someone else, to design a reflective affordance that enables recognition of filter bubbles in their YouTube recommendation feeds. Each system shows various degrees of success and outlines considerations in cognitive affordances design. Overall, this thesis showcases the utility of design strategies centered on dual process information cognition model of human mind to combat problematic information space. / Doctor of Philosophy / Over the last several decades, billions of users have moved to the internet for everyday information gathering, allowing information flow around the globe at a massive scale. This flow is managed by algorithms personalized to each users' need, creating a complicated trio of producer-algorithm-consumer. This has resulted in some unforeseen challenges. Bad information producers takes the advantage of system to promote problematic content, such as, false information, termed as misinformation. Personalized algorithms have created filters of what people see oftentimes isolating them from diverse perspectives of information, creating a distorted perception of reality. Augmenting the online technology infrastructure to combat these challenges has become crucial and the overall goal of this thesis. Cognitive psychologists theorize that two cognitive processes are at play when people consume information, also known as dual process theories. Can we design new tools to combat these challenges by tapping into each of these processes? In this thesis, I answer this question through a series of studies. In each of these studies, I combine this theory from psychology with design guides from Human-Computer Interaction to design socio-technical design. I evaluated each of these systems through controlled experimentation. The result of these studies informs ways we can capitalize on users' information processing mechanism to combat various types of problematic information online.

京都大学 / 新制・課程博士 / 博士(経済学) / 甲第25077号 / 経博第684号 / 京都大学大学院経済学研究科経済学専攻 / (主査)教授 関口 格, 准教授 陳 珈惠, 教授 渡辺 誠 / 学位規則第4条第1項該当 / Doctor of Economics / Kyoto University / DFAM

Bubble curtains offer a potential solution for hindering downstream migrating fish from passing through the turbines of hydropower plants, by instead guiding them to a safe passage. Compared to the conventional method of using low-inclined bar racks close to the turbine intake, bubble curtains are considerably cheaper, especially for large scale hydropower plants. In this work bubble curtains are evaluated through an experimental parametric study, mainly regarding two quantities, defined here as the overall bubble coverage of the background, as well as the occurrence of large tears in the curtain. The examined parameters cover the design of the device that generates the bubbles, the positioning of the device, as well as the flow condition of the water. The bubble curtain was filmed with underwater cameras and image analysis was performed using image segmentation in MATLAB. Results indicate that the total air flow should be chosen high, around 200-500 nl/min/m. The number of holes the air is distributed across is of little importance, except in the area closest to the air outlets, where permanent tears may occur inbetween holes if the distance is to great. Smaller holes (<1mm) are preferable to larger holes (>1 mm), but the difference is small compared to the effect of the total air flow. In flowing water, a smaller angle of attack against the current is better based on the defined quantities, but it will also result in a longer and therefore more expensive device. The bubble curtain should not be placed where mean water velocities exceed 0,75 m/s, since it will result in an inclination with the current close to that of bar racks designed to guide fish towards the surface. Furthermore, at these water velocities some fish may have difficulties following the curtain, due to their limited swimming capabilities.

La simulation de réacteurs à bulles en régime industriel est un grand défi. L'objectif principal de ce travail est la prédiction de la taille des bulles à l’aide d’un modèle numérique de bilan de population, basé sur la modélisation des phénomènes de brisure et de coalescence, et pouvant être couplé aux conditions hydrodynamiques présentes dans les réacteurs. Différentes données expérimentales sont obtenues pour valider le modèle. La taille des bulles est mesurée à l'aide d'une technique innovante de corrélation croisée. Les essais, réalisés en eau du réseau (partiellement contaminée) et en eau déminéralisée avec ajout éventuel d'éthanol, montrent que les additifs réduisent la coalescence et diminuent la taille moyenne des bulles. Deux distributeurs du gaz différents sont utilisés pour découpler l'étude de la brisure et de la coalescence. Les données expérimentales sont utilisées initialement pour valider des simulations CFD 3D transitoires Eulériennes-Eulériennes. La loi de traînée est corrigée par un facteur de swarm pour intégrer l’effet d’une fraction de gaz élevée. Différents modèles de turbulence sont testés. La contribution de la turbulence induite par les sillages de bulles au mélange de scalaires est évaluée. Enfin, pour prédire la taille des bulles, un bilan de population est couplé au modèle hydrodynamique préalablement validé et est résolu par la méthode de quadrature des moments (QMOM). Un set original de kernels de brisure et coalescence est proposé, capable de prédire la taille des bulles pour différentes conditions opératoires. Le comportement du modèle lors de l’extrapolation des réacteurs est également examiné / The simulation of bubble column reactors under industrial operating conditions is an exciting challenge. The main objective of this work is to predict the bubble size, in turn interconnected to the reactor hydrodynamic conditions, with computational models, by modelling bubble breakage and coalescence. Experimental data is collected for model validation, including bubble size measurements with an innovative cross-correlation technique. Experiments are carried out with tap water and demineralized water, with or without the addition of ethanol, and gathered results show that additives reduce coalescence and lower the mean bubble size. Two different spargers are used, in order to decouple the investigation of breakage and coalescence. The experimental data set is used to validate out unsteady three-dimensional Eulerian-Eulerian CFD simulations. A drag law for oblate bubbles is considered, together with a swarm factor, that accounts for the swarm effect. Several turbulence models are tested. The contribution of bubble induced turbulence (BIT) to scalar mixing is assessed. To predict bubble size, a population balance model is coupled to the hydrodynamic model and is solved with the quadrature method of moments. A set of breakage and coalescence kernels is proposed, capable of predicting the bubble size for different operating conditions. Scale-up effects are also investigated

Adsorption layers of soluble surfactants enable and govern a variety of phenomena in surface and colloidal sciences, such as foams. The ability of a surfactant solution to form wet foam lamellae is governed by the surface dilatational rheology. Only systems having a non-vanishing imaginary part in their surface dilatational modulus, E, are able to form wet foams. The aim of this thesis is to illuminate the dissipative processes that give rise to the imaginary part of the modulus. <br><br> There are two controversial models discussed in the literature. The reorientation model assumes that the surfactants adsorb in two distinct states, differing in their orientation. This model is able to describe the frequency dependence of the modulus E. However, it assumes reorientation dynamics in the millisecond time regime. In order to assess this model, we designed a SHG pump-probe experiment that addresses the orientation dynamics. Results obtained reveal that the orientation dynamics occur in the picosecond time regime, being in strong contradiction with the two states model. <br><br> The second model regards the interface as an interphase. The adsorption layer consists of a topmost monolayer and an adjacent sublayer. The dissipative process is due to the molecular exchange between both layers. The assessment of this model required the design of an experiment that discriminates between the surface compositional term and the sublayer contribution. Such an experiment has been successfully designed and results on elastic and viscoelastic surfactant provided evidence for the correctness of the model. <br><br> Because of its inherent surface specificity, surface SHG is a powerful analytical tool that can be used to gain information on molecular dynamics and reorganization of soluble surfactants. They are central elements of both experiments. However, they impose several structural elements of the model system. During the course of this thesis, a proper model system has been identified and characterized. The combination of several linear and nonlinear optical techniques, allowed for a detailed picture of the interfacial architecture of these surfactants. / Amphiphile vereinen zwei gegensätzliche Strukturelemente in einem Molekül, eine hydrophile Kopfgruppe und ein hydrophobe, meist aliphatische Kette. Aufgrund der molekularen Asymmetrie erfolgt eine spontane Adsorption an der Wasser-Luft Grenzfläche. Die Adsorptionsschicht verändert die makroskopischen Eigenschaften des Materials, z.B. die Grenzflächenspannung wird erniedrigt. Amphiphile sind zentrale Bauelemente der Kolloid- und Grenzflächenforschung, die Phänomene, wie Schäume ermöglichen. <br><br> Eine Schaumlamelle besteht aus einem dünnen Wasserfilm, der durch zwei Adsorptionsschichten stabilisiert wird. Die Stabilität der Lamelle wird durch die Grenzflächenrheologie entscheidend geprägt. Die wesentliche makroskopische Größe in diesem Zusammenhang ist das so genannte Grenzflächendilatationsmodul E. Es beschreibt die Fähigkeit des Systems die Gleichgewichtsgrenzflächenspannung nach einer Expansion oder Dilatation der Adsorptionschicht wieder herzustellen. Das Modul E ist eine komplexe Größe, in dem der Imaginärteil direkt mit der Schaumstabilität korreliert. <br><br> Diese Arbeit widmet sich der Grenzflächenrheologie. In der Literatur werden zwei kontroverse Modelle zur Interpretation dieser Größe diskutiert. Diese Modelle werden experimentell in dieser Arbeit überprüft. Dies erfordert die Entwicklung neuer experimenteller Aufbauten basierend auf nichtlinearen, optischen Techniken. Mit diesen Experimenten konnte eines der Modelle bestätigt werden.

Les colonnes à bulles sont largement utilisées dans les domaines du génie chimique et biologique, grâce à leur configuration simple, exempte de toute partie mobile. Néanmoins, leur extrapolation aux échelles industrielles engendre des modifications de l’hydrodynamique globale (vitesse du liquide, taille des bulles) qui sont encore difficile à prédire avec les outils numériques disponibles.La thèse a pour objectif d’établir une base de données sur l’évolution radiale et axiale de l’hydrodynamique locale (taux de vide, taille de bulles, vitesse liquide), dans différentes tailles de colonnes allant de 0.15 à 3 m de diamètre, pour des vitesses superficielles gaz comprises entre 3 et 35 cm/s, générant des taux de vide atteignant les 35%. Les mesures de taux de vide local, de vitesse de bulles et de la taille verticale des bulles sont réalisées à l’aide d’une sonde optique 1C. De plus, une nouvelle méthode pour mesurer la taille horizontale des bulles à fort taux de vide et en écoulement fortement multidirectionnel est proposée dans cette thèse. Cette méthode est basée sur la corrélation croisée spatiale de signaux provenant de deux sondes optiques placées parallèlement à la même élévation, et à une distance l’une de l’autre devant nécessairement être plus faibles que les bulles les plus petites présentes dans l’écoulement. Les mesures de taille de bulles sont validées en les comparant à un traitement d’images par endoscopie. Pour des vitesses superficielles de gaz supérieures à 9 cm/s, un bon accord est trouvé entre les trois méthodes (sonde optique 1C, corrélation croisée et endoscopie). La taille des bulles augmente légèrement lorsque la vitesse superficielle gaz augmente, par contre elle n’est pas impactée de manière significative par le diamètre des colonnes. Une plus grande ségrégation radiale est tout de même visible dans les plus grandes colonnes testées.Un modèle 1D radial développé pour un écoulement invariant le long de l’axe de la colonne est utilisé pour tester différents formalismes de forces de trainée, utilisant les données expérimentales de taille moyenne de bulles. Les simulations montrent que pour prédire correctement le flux gazeux expérimental, il est nécessaire d’introduire un « swarm factor » (Simonnet et al, 2008) diminuant le coefficient de trainée à fort taux de vide. De plus, des simulations 3D URANS avec Fluent® sont réalisées avec la loi de trainée validée par le modèle 1D précédemment cité. Un bon accord est observé entre les valeurs expérimentales et simulées des profils radiaux de taux de vide et de vitesse liquide, pour des diamètres de colonne allant de 0.4 m à 3 m, et pour des vitesses superficielle gaz de 3 à 35 cm/s. / Bubble columns reactors are widely used in chemical and biological engineering due to its simple configuration without mobile parts. However, the scale-up prediction of a bubble columns reactors is still a challenging process, due to the lack reliable experimental data and models.The present work aims to construct detailed database of the radial and axial evolution of local hydrodynamics properties (gas hold-up, bubble size and velocity, liquid velocity) acquired in several bubble columns in a scale factor of 20 (from 0.15 to 3 m in diameter), for a superficial gas velocity from 3 to 35 cm/s, yielding gas hold-ups up to 35 %. Measurements of local gas hold-up, bubble velocity and bubble vertical size are performed by a 1C mono-fiber optical probe. Moreover, a novel method to measure mean horizontal diameter of bubbles at high void fraction and in a multi-directional flow is proposed. This method is based in the spatial-cross correlation of signal of two optical probes placed parallel side by side, at a given distance from each other, at the same elevation in the column. The validation of the bubble size measurements are performed through a comparison of the results with an endoscopic imaging method. For superficial gas velocities higher than 9 cm/s, a good agreement is found between the three methods (1C mono-fiber optical probe, cross-correlation and endoscopic imaging). A slight increase is registered with the increase of the superficial gas velocity, however there is no significant variation with the column diameter.A 1-D radial model of a bubbly flow (Ueyama and Miyauchi, 1979) developed for a invariant flow along the column axis, is used to benchmark several classic formalisms of the drag force, using experimental average bubble size. Results show that to correctly predict the experimental gas flowrate, it is necessary to use a Swarm factor (Simonnet et al, 2008) that reduces the drag coefficient for high gas hold-up values. Moreover, Fluent® 3D URANS simulations are performed using the previously validated drag force formalism. A good agreement is found between experimental and simulated radial profiles of gas holdup and liquid velocity for column diameters ranging from 0.4 m up to 3 m in diameter in a range of superficial gas velocities from 3 cm/s to 35 cm/s.

The bubble flow is used for different application in steel production and refining processes. It plays in indispensable role in the ladle refining process such as for homogenization and inclusion removal. Hence, it is important to understand the effect of the nozzle outlet geometry on the bubble formation. Three different nozzles with different outlet geometries were examined using a physical model. These geometries were: a) Circle, b) Square with round edges and c) Elliptical. All three nozzles had the same nozzle design and similar outlet cross-section areas. Therefore, the only tested parameter was the outlet geometry. The physical model is a water/air model, that consist of water tank ,the nozzles, gas gauge and a high speed camera. Each nozzle was tested under five different gas flow rates: starting from 10 L/min of air gas flow rate, until a 30 L/min of gas flow rate by incriminating with 5 L/min per experimental trial. Therefore, each nozzle was studied using a 5 experimental sets, so in total 15 experiments were made. For each set, 3000 photos were captured by the high speed camera. The photos were then analyzed using mainly the ImageJ software and the naked eye. After analyzing the photos for the experimental sets the following were found: a) The frequency of bubble formation was for the most part constant with an average of 11 bubbles per second. b) The elliptical nozzle produced for the most part the largest bubbles, while the circular produced the smallest ones. The square nozzle had similar bubble sizes comparable to the elliptical nozzle. c) The circular nozzle resulted in the bubbles with most stable surface, while the elliptical nozzle had the most unstable bubble boundary. The study had a drawback, which is the presence of a jetting flow which reduced the accuracy of the results. Thus, it is recommend that future work can solve this issue by finding at which gas flow rate pure bubbling flow stops for each nozzle geometry. / Bubbelinjektion används för olika tillämpningar inom stålproduktion och raffineringsprocesser. Det spelar en oumbärlig roll i raffineringsprocesser som homogenisering och borttagning av inneslutningar. Därför är det viktigt att förstå effekten av utloppsgeometrin hos munstycket på bubbelbildningen. Tre olika munstycken med olika utloppsgeometrier undersöktes med hjälp av en fysisk modell. Dessa geometrier är: a) Cirkel, b) Fyrkantig med rundade kanter och c) Elliptisk. Alla tre munstyckena har samma munstycksdesign och liknande utloppstvärsnittsarea. Därför är den enda parametern som testas utloppsgeometrin. Den fysiska modellen bestod av en vattentank, munstyckena där var och en undersöks separat, en gasmätare, en höghastighetskamera och modellen använde vatten/luft. Varje munstycke testades under fem olika gasflöden: startande från 10 L/min luftgasflöde, tills 30 L/min gasflöde stegvis 5 L/min per experimentuppsättning. Därför har varje munstycke 5 experimentuppsättningar, så totalt 15 experiment togs. För varje uppsättning togs 3000 bilder med höghastighetskameran. Bilderna analyserades sedan med främst ImageJ-programvara och blotta ögat. Efter att ha analyserat bilderna från experimenten så visade resultaten följande: a) Frekvensen av bubbelbildning var mestadels konstant med ett genomsnitt på 11 bubblor per sekund. b) Det elliptiska munstycket producerade mestadels de största bubblorna, medan det cirkulära producerade de minsta bubblorna. Det fyrkantiga munstycket resulterade i en liknande bubbelstorlek som det elliptiska munstycket. c) Det cirkulära munstycket resulterade i bubblorna med den mest stabila ytan, medan det elliptiska munstycket hade den mest instabila bubbelgränsen. Studien hade en nackdel, vilket är närvaron av ett jetflöde som minskade noggrannheten i resultatet. Det rekommenderas att framtida arbete kan lösa detta problem genom att hitta vid vilken gasflödeshastighet rent bubblande flöde stoppar för varje munstycke

The economic prosperity of the late 1990s was characterized by a perceived expansive growth that increased the expectations of a company's performance. WorldCom, a telecommunications company, was a victim of these expectations that led to the evolution of a fraud designed to deceive the public until the economic outlook improved. Through understanding what led to the fraud, how the fraud grew, and what its effects were, lessons can be derived to gain a better understanding of the reasons behind a fraud and to prevent future frauds from occurring or growing as big as the WorldCom fraud did.

This paper describes the modelling of bubbly flow in a bubble column considering non-drag forces, polydispersity and bubble induced turbulence using the Eulerian two-fluid approach. The set of used closure models describing the momentum exchange between the phases was chosen on basis of broad experiences in modelling bubbly flows at the Helmholtz-Zentrum Dresden-Rossendorf. Polydispersity is modeled using the inhomogeneous multiple size group (iMUSIG) model, which was developed by ANSYS/CFX and Helmholtz-Zentrum Dresden-Rossendorf. Through the importance of a comprehensive turbulence modeling for coalescence and break-up models, bubble induced turbulence models are investigated. A baseline has been used which was chosen on the basis of our previous work without any adjustments. Several variants taken from the literature are shown for comparison. Transient CFD simulations are compared with the experimental measurements and Large Eddy Simulations of Akbar et al. (2012).