Дисертації з теми "Coalescence and breakup"
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1
Vold, Truls Chr. "Droplet breakup and coalescence in compact wellstream seperation." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for kjemisk prosessteknologi, 2000. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-2323.
2
Hunt, William E. "Breakup and coalescence in turbulent two-phase flows." Thesis, Virginia Tech, 1995. http://hdl.handle.net/10919/40633.
Анотація:
Many engineering processes involve a gas and a liquid or two immiscible liquids in
turbulent flow. The turbulent flows present in two-phase systems will cause the bubbles
or drops of a dispersion to undergo breakup and coalescence, and the resulting changes in
the dispersion may significantly affect the engineering process under consideration. For
this reason, many researchers have studied breakup and coalescence in turbulent two phase
flows. Models that can be used to simulate changes in a dispersion over time have
been proposed, but these models contain constants that change with experimental
conditions and empirical equations that can only be considered valid for certain
experimental setups. The goal of this study was to develop general models that could be
used to predict changes in bubble or drop size distributions over time for turbulent flows
in agitated vessels and pipes.
Computer programs were written to reproduce the results of three agitated vessel
studies. These programs used existing population balance models to approximate the
changes in a dispersion over time measured in previous experiments. A new model for
breakup in agitated vessels was then developed and verified with existing experimental
data. A new model for coalescence in agitated vessels was also developed and verified
with existing experimental data. Both of these models are based on theory and are more
readily extendible than previous breakup and coalescence models. The work for agitated
vessels was then extended to turbulent two-phase pipe flow. Since there was only a
limited amount of experimental data available for breakup and coalescence in pipes, the
model for turbulent pipe flow could not be verified.
Master of Science
3
Liao, Yixiang. "Development and validation of models for bubble coalescence and breakup." Helmholtz-Zentrum Dresden-Rossendorf, 2013. https://hzdr.qucosa.de/id/qucosa%3A22180.
Анотація:
A generalized model for bubble coalescence and breakup has been developed, which is based on a comprehensive survey of existing theories and models. One important feature of the model is that all important mechanisms leading to bubble coalescence and breakup in a turbulent gas-liquid flow are considered. The new model is tested extensively in a 1D Test Solver and a 3D CFD code ANSYS CFX for the case of vertical gas-liquid pipe flow under adiabatic conditions, respectively. Two kinds of extensions of the standard multi-fluid model, i.e. the discrete population model and the inhomogeneous MUSIG (multiple-size group) model, are available in the two solvers, respectively. These extensions with suitable closure models such as those for coalescence and breakup are able to predict the evolution of bubble size distribution in dispersed flows and to overcome the mono-dispersed flow limitation of the standard multi-fluid model.
For the validation of the model the high quality database of the TOPFLOW L12 experiments for air-water flow in a vertical pipe was employed. A wide range of test points, which cover the bubbly flow, turbulent-churn flow as well as the transition regime, is involved in the simulations. The comparison between the simulated results such as bubble size distribution, gas velocity and volume fraction and the measured ones indicates a generally good agreement for all selected test points. As the superficial gas velocity increases, bubble size distribution evolves via coalescence dominant regimes first, then breakup-dominant regimes and finally turns into a bimodal distribution. The tendency of the evolution is well reproduced by the model. However, the tendency is almost always overestimated, i.e. too much coalescence in the coalescence dominant case while too much breakup in breakup dominant ones. The reason of this problem is discussed by studying the contribution of each coalescence and breakup mechanism at different test points. The redistribution of the gaseous phase from the injection position at the pipe wall to the whole cross section is overpredicted by the Test Solver especially for the test points with high superficial gas velocity. Besides the models for bubble forces, the simplification of the Test Solver to a 1D model has an influence on the redistribution process. Simulations performed using CFX show that a considerable improvement is achieved with comparison to the results delivered by the standard closure models. For the breakup-dominant cases, the breakup rate is again overestimated and the contribution of wake entrainment of large bubbles is underestimated. Furthermore, inlet conditions for the liquid phase, bubble forces as well as turbulence modeling are shown to have a noticeable influence, especially on the redistribution of the gaseous phase.
4
Liao, Yixiang. "Development and validation of models for bubble coalescence and breakup." Forschungszentrum Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-134760.
Анотація:
A generalized model for bubble coalescence and breakup has been developed, which is based on a comprehensive survey of existing theories and models. One important feature of the model is that all important mechanisms leading to bubble coalescence and breakup in a turbulent gas-liquid flow are considered. The new model is tested extensively in a 1D Test Solver and a 3D CFD code ANSYS CFX for the case of vertical gas-liquid pipe flow under adiabatic conditions, respectively. Two kinds of extensions of the standard multi-fluid model, i.e. the discrete population model and the inhomogeneous MUSIG (multiple-size group) model, are available in the two solvers, respectively. These extensions with suitable closure models such as those for coalescence and breakup are able to predict the evolution of bubble size distribution in dispersed flows and to overcome the mono-dispersed flow limitation of the standard multi-fluid model.
For the validation of the model the high quality database of the TOPFLOW L12 experiments for air-water flow in a vertical pipe was employed. A wide range of test points, which cover the bubbly flow, turbulent-churn flow as well as the transition regime, is involved in the simulations. The comparison between the simulated results such as bubble size distribution, gas velocity and volume fraction and the measured ones indicates a generally good agreement for all selected test points. As the superficial gas velocity increases, bubble size distribution evolves via coalescence dominant regimes first, then breakup-dominant regimes and finally turns into a bimodal distribution. The tendency of the evolution is well reproduced by the model. However, the tendency is almost always overestimated, i.e. too much coalescence in the coalescence dominant case while too much breakup in breakup dominant ones. The reason of this problem is discussed by studying the contribution of each coalescence and breakup mechanism at different test points. The redistribution of the gaseous phase from the injection position at the pipe wall to the whole cross section is overpredicted by the Test Solver especially for the test points with high superficial gas velocity. Besides the models for bubble forces, the simplification of the Test Solver to a 1D model has an influence on the redistribution process. Simulations performed using CFX show that a considerable improvement is achieved with comparison to the results delivered by the standard closure models. For the breakup-dominant cases, the breakup rate is again overestimated and the contribution of wake entrainment of large bubbles is underestimated. Furthermore, inlet conditions for the liquid phase, bubble forces as well as turbulence modeling are shown to have a noticeable influence, especially on the redistribution of the gaseous phase.
5
Mawson, Ryan A. "Bubble Coalescence and Breakup Modeling for Computing Mass Transfer Coefficient." DigitalCommons@USU, 2012. https://digitalcommons.usu.edu/etd/1330.
Анотація:
There exist several different numerical models for predicting bubble coalescence and breakup using computational fluid dynamics (CFD). Various combinations of these models will be employed to model a bioreactor process in a stirred reactor tank. A mass transfer coefficient, Kla, has been calculated and compared to those found experimentally by Thermo-Fisher Scientific, to validate the accuracy of currently available mathematical models for population balance equations. These include various combinations of bubble breakup and coalescence models coupled with the calculation of mass transfer coefficients.
6
Lee, Joshua. "Experimental Investigation of Breakup and Coalescence Characteristics of a Hollow Cone Swirling Spray." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5974.
Анотація:
Atomization can be achieved by discharging liquid at relative high velocities into a slow moving environment (hydraulic nozzles) or by discharging liquid at low velocities into a fast moving gas flow (air-blast nozzles). These two types of injector nozzles are featured in majority of the industry applications such as power generation, food or pharmaceutical powder formation, spray painting, petroleum refining, and thermal sprays. The most common atomizer used in combustion engines is the pressure-swirl nozzle (Simplex nozzle) to obtain a homogenous mixture at different equivalence ratios. The experimental studies performed with pressure-swirl nozzles have reported contradictory results over the last few years. Thus, the fundamentals of spray dynamics, such as spray formation, liquid breakup length, droplet breakup regimes, and coalescence still need to be understood for a pressure-swirl nozzle.
An experimental study of the breakup characteristics of various liquids and fuels with different thermal physical properties emanating from hollow cone hydraulic injector nozzles induced by pressure-swirling was investigated. The experiments were conducted using two nozzles with different orifice diameters 0.3mm and 0.5mm and injection pressures (0.3-4MPa) which correspond to Rep = 7,000-31,000 depending on the liquids being tested. Three laser-based techniques, i.e., Shadowgraph, Particle Image Velocimetry (PIV) and Phase Doppler Particle Anemometry (PDPA) were utilized in this study. Although each technique had its limitation in different flow regimes, the results were cross-validated, and generally showed correct trends in axial and radial measurements of velocity and diameter for different nozzles, Weber and Reynolds numbers.
The spatial variation of diameter and velocity arises principally due to primary breakup of liquid films and subsequent secondary breakup of large droplets due to aerodynamic shear. Downstream of the nozzle, coalescence of droplets due to collision is also found to be significant. Different types of liquid film break up was considered and found to match well with the theory. The spray is subdivided into three zones: near the nozzle, a zone consisting of film and ligament regime, where primary breakup and some secondary breakup take place; a second zone where the secondary breakup process continues, but weakens, and the centrifugal dispersion becomes dominant, and a third zone away from the spray where coalescence is dominant. Each regime has been analyzed in detail to understand the effect of surface tension and viscosity. Surface tension and viscosity were engineered to mimic fuels, which were then compared with real fuels such as Ethanol, Jet-A and Kerosene. Results show similarity in the diameter in the beginning stages of breakup but in the coalescence regime, the values deviate from each other, indicating that the vapor pressure also plays a major role in this regime.Ph.D.
Doctorate
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering
7
Regnault, Paul. "Front-Tracking mesh adaptation for the simulation of two-phase flows with coalescence and breakup." Electronic Thesis or Diss., Université Gustave Eiffel, 2023. http://www.theses.fr/2023UEFL2076.
Анотація:
Dans le cadre des écoulements diphasiques à phases séparées, ce travail porte sur la gestion dynamique du maillage de l'interface (constitué de triangles en 3D) et son impact sur l'approximation des propriétés géométriques que sont la position et la courbure. Les équations de conservation de la mécanique des fluides sont résolues sur des grille fixes, décalées et structurées. L'interface est suivie de façon lagrangienne au cours du temps avec un maillage mobile et déformable : on parle de méthode de type « Front-Tracking ». En plus des opérations de remaillage classiques (suppression et échange d'arêtes, insertion de sommets notamment), on étudiera l'adaptation du maillage à la courbure de l'interface et l'utilisation d'une approximation polynomiale pour améliorer l'insertion de sommets ou la suppression d'arêtes. Ces méthodes sont évaluées sur des surfaces analytiques mobiles et déformables, sans résolution des équations de Navier-Stokes ni changement topologique. Dans les écoulements diphasiques, des changements topologiques peuvent avoir lieu : la coalescence et la rupture. Nous proposons une méthode de coalescence et une méthode de rupture d'interface. Ces deux méthodes sont activées selon des critères de distance et sont basées uniquement sur le maillage de l'interface, sans recourir au maillage eulérien. Ces méthodes sont utilisées sur des configurations numériques et expérimentales de la littérature pour apprécier leur robustesse et leurs performancesIn the context of two-phase flows with separated phases, this work focuses on dynamic management of the interface mesh (made up of connected triangles in 3D) and its impact on the approximation of geometrical properties that are position and curvature. The conservation equations of fluid mechanics are solved on fixed, staggered and structured grids. The interface is tracked in a Lagrangian fashion with a moving and deformable mesh: this method is known as the"Front-tracking" method. In addition to classical remeshing operations (edgesplitting, collapsing and swapping for instance), we will study the adaptation of the mesh to the curvature of the interface and the use of polynomial approximation to improve edge splitting and collapsing. These methods are evaluated on analytical, mobile and deformable surfaces, with neither the resolution of the Navier-Stokes equations nor topological changes. In two-phaseflows, topological changes may happen: coalescence and breakup. We propose a method for coalescence and a method for breakup. These two methods are activated by distance criteria and rely only on the interface mesh, without resorting to the Eulerian mesh. These methods are employed on numerical and experimental configurations from the literature to appreciate their robustness and performances
8
Suwa, Akihiko 1972. "Simulation of phase domain breakup and coalescence in strong shear and transient flows using lattice-Boltzmann method." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50408.
9
Krepper, Eckhard, and Dirk Lucas. "CFD models for polydispersed bubbly flows." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-28052.
Анотація:
Many flow regimes in Nuclear Reactor Safety Research are characterized by multiphase flows, with one phase being a continuous liquid and the other phase consisting of gas or vapour of the liquid phase. In dependence on the void fraction of the gaseous phase the flow regimes e.g. in vertical pipes are varying from bubbly flows with low and higher volume fraction of bubbles to slug flow, churn turbulent flow, annular flow and finally to droplet flow. In the regime of bubbly and slug flow the multiphase flow shows a spectrum of different bubble sizes. While disperse bubbly flows with low gas volume fraction are mostly mono-disperse, an increase of the gas volume fraction leads to a broader bubble size distribution due to breakup and coalescence of bubbles. Bubbles of different sizes are subject to lateral migration due to forces acting in lateral direction different from the main drag force direction. The bubble lift force was found to change the sign dependent on the bubble size. Consequently this lateral migration leads to a de-mixing of small and large bubbles and to further coalescence of large bubbles migrating towards the pipe center into even larger Taylor bubbles or slugs. An adequate modeling has to consider all these phenomena. A Multi Bubble Size Class Test Solver has been developed to investigate these effects and test the influence of different model approaches. Basing on the results of these investigations a generalized inhomogeneous Multiple Size Group (MUSIG) Model based on the Eulerian modeling framework has been proposed and was finally implemented into the CFD code CFX. Within this model the dispersed gaseous phase is divided into N inhomogeneous velocity groups (phases) and each of these groups is subdivided into Mj bubble size classes. Bubble breakup and coalescence processes between all bubble size classes Mj are taken into account by appropriate models. The inhomogeneous MUSIG model has been validated against experimental data from the TOPFLOW test facility.
10
Krepper, Eckhard, and Dirk Lucas. "CFD models for polydispersed bubbly flows." Forschungszentrum Dresden-Rossendorf, 2007. https://hzdr.qucosa.de/id/qucosa%3A21632.
Анотація:
Many flow regimes in Nuclear Reactor Safety Research are characterized by multiphase flows, with one phase being a continuous liquid and the other phase consisting of gas or vapour of the liquid phase. In dependence on the void fraction of the gaseous phase the flow regimes e.g. in vertical pipes are varying from bubbly flows with low and higher volume fraction of bubbles to slug flow, churn turbulent flow, annular flow and finally to droplet flow. In the regime of bubbly and slug flow the multiphase flow shows a spectrum of different bubble sizes. While disperse bubbly flows with low gas volume fraction are mostly mono-disperse, an increase of the gas volume fraction leads to a broader bubble size distribution due to breakup and coalescence of bubbles. Bubbles of different sizes are subject to lateral migration due to forces acting in lateral direction different from the main drag force direction. The bubble lift force was found to change the sign dependent on the bubble size. Consequently this lateral migration leads to a de-mixing of small and large bubbles and to further coalescence of large bubbles migrating towards the pipe center into even larger Taylor bubbles or slugs. An adequate modeling has to consider all these phenomena. A Multi Bubble Size Class Test Solver has been developed to investigate these effects and test the influence of different model approaches. Basing on the results of these investigations a generalized inhomogeneous Multiple Size Group (MUSIG) Model based on the Eulerian modeling framework has been proposed and was finally implemented into the CFD code CFX. Within this model the dispersed gaseous phase is divided into N inhomogeneous velocity groups (phases) and each of these groups is subdivided into Mj bubble size classes. Bubble breakup and coalescence processes between all bubble size classes Mj are taken into account by appropriate models. The inhomogeneous MUSIG model has been validated against experimental data from the TOPFLOW test facility.
11
Castellano, Simone. "Multiscale study and modeling of dispersion properties relevant for liquid-liquid extraction : adaptation of breakup and coalescence kernels to industrial processes." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1243.
Анотація:
Ce projet de thèse porte sur l'étude de l'hydrodynamique des dispersions dans les extracteurs liquide-liquide utilisés dans l'industrie du recyclage nucléaire. Dans la première partie du projet, un modèle de bilan de population homogène (0D-PBM), basé sur l'évaluation des taux moyens en volume de coalescence et de rupture, est proposé. La méthode tient compte des inhomogénéités spatiales dans le mélange, notamment de la fonction de densité de probabilité de la dissipation de l’énergie cinétique turbulente dans l’appareil. Le modèle est capable de reproduire les expériences de dispersion liquide-liquide turbulentes à faible viscosité. Dans la deuxième partie de cette étude, un modèle généralisé pour les noyaux de rupture et coalescence, valable pour l’ensemble du spectre de la turbulence, est proposé et validé. La plupart des noyaux disponibles dans la littérature sont basés sur la fonction de structure de second-ordre de Kolmogorov, qui n'est valable que dans le domaine inertiel. Cependant, dans des nombreuses situations rencontrées au niveau industriel, la plupart des gouttes peuvent avoir une taille dans le domaine dissipatif, où la fonction de structure de second-ordre de Kolmogorov ne s'applique pas. Le modèle généralisé est basé sur la fonction de structure de second ordre de Davidson, valable dans tout le spectre de la turbulence. Dans la dernière partie de l'étude, un modèle permettant de simuler le comportement hydrodynamique d'une colonne pulsée est proposé. Le modèle est basé sur un bilan de population 1D, dont les termes source ont été modélisés à l'aide des noyaux de Coulaloglou et Tavlarides généralisés. Les inhomogénéités turbulentes dans la colonne pulsée ont été prises en compte par la fonction de densité de probabilité du taux de dissipation turbulent. Un bon accord modèle-expérience est obtenu en ce qui concerne le diamètre et la concentration moyenne des gouttes dans un compartimentThis PhD project deals with the study of the hydrodynamics of the dispersions in the liquid-liquid extractors employed in the nuclear recycle industry. In the first part of the project, a zero-dimensional homogenous Population Balance Model (0D-PBM), based on the evaluation of the volume-averaged coalescence and breakup rates, is adopted to fit low-viscosity turbulent liquid-liquid dispersion experiments. The method accounts for the spatial inhomogeneities in mixing, namely for the probability density function of the turbulent kinetic energy dissipation in the apparatus. In the second part of this study, a generalized model for the breakage and coalescence kernels, valid for the entire spectrum of turbulence, is proposed and validated. Most of the available kernels in literature indeed are based on the Kolmogorov second-order structure function, which is only valid in the inertial subrange. However, in many industrially encountered situations, most of the droplets may have size in the dissipation range, where the Kolmogorov second-order structure function does not apply. The generalized model is based on the Davidson second-order structure function, valid in the entire spectrum of turbulence. In the last part of the study, a model that allows to simulate the hydrodynamic behavior of a pulsed column is proposed. The model is based on a 1D Population Balance Equation (1D-PBE), whose source terms were modeled through the generalized Coulaloglou and Tavlarides kernels. The turbulent inhomogeneities in the pulsed column were accounted through the probability density function of the turbulent dissipation rate. The model well reproduces the experimental Sauter mean diameters and the dispersed phase volume fractions in a compartment of the pulsed column
12
Wu, Yining. "Étude des phénomènes interfaciaux à micro-échelle." Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0330/document.
Анотація:
Cette thèse a étudié de façon systématique les processus de la rupture et de la coalescence impliquant une interface liquide-liquide (gouttelettes) ou gaz-liquide (bulles) en présence ou pas d’un champ magnétique dans des dispositifs microfluidiques, à l’aide d’une caméra rapide. Les mécanismes de la rupture d’une interface ferrofluide sous différents champs magnétiques ont été étudiés et comparés. On a constaté que la structure morphologique et la vitesse d’amincissement du cou peuvent être contrôlées activement par la force magnétique. Ainsi, le volume et la fréquence de formation de gouttelettes de ferrofluide peuvent être pilotés aisément. La rupture de l'interface liquide-liquide a généralement conduit à la formation de gouttelettes satellites avec sa taille proportionnelle au nombre capillaire de la phase continue. La coalescence des gouttelettes ont aussi été étudiée avec l’analyse de l'évolution du cou reliant deux gouttelettes. Il a été constaté que la formation du pont ou du cou liquide pouvait se produire dans la gamme de l'ordre de dizaines de micromètres entre les bords d'attaque sous champ magnétique. L'inertie d’origine d'attraction magnétique sur des gouttelettes de ferrofluide devenait la force motrice pour la coalescence lors de la première étape au détriment de la force capillaireThis thesis systematically investigates the breakup and coalescence processes of the involved droplet (bubble) interface under magnetic field or not in two-phase microfluidic flow, by using a high speed digital camera. The whole breakup processes of ferrofluid interface under different magnetic fields were investigated and compared. It was found that the morphological structure and necking velocity of the interface can be actively controlled by the magnetic force. Thus the volumes and the formation frequencies of ferrofluid droplets can be actively adjusted. The breakup of Liquid-Liquid interface usually leads to the formation of satellite droplet with its size proportional to the capillary number of the continuous phase. The coalescences of droplets were investigated. The evolution of the neck connecting two droplets was analyzed. It was found that the formation of liquid bridge or neck could occurs with a visible gap in the order of tens of micrometers between the leading edges under magnetic field and the inertia of the ferrofluid originating from the magnetic attraction fields becomes the driving force at the initial stage of coalescence instead of capillary force
13
Liao, Y., and D. Lucas. "Entwicklung und Validierung von Modellen für Blasenkoaleszenz und -zerfall." Forschungszentrum Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-113883.
Анотація:
Ein neues, verallgemeinertes Modell für Blasenkoaleszenz und –zerfall wurde entwickelt. Es basiert auf physikalischen Überlegungen und berücksichtigt verschiedene Mechanismen, die zu Blasenkoaleszenz und –zerfall führen können. In einer ausführlichen Literaturrecherche wurden zunächst die verfügbaren Modelle zusammengestellt und analysiert. Es zeigte sich, dass viele widersprüchliche Modelle veröffentlicht wurden. Keins dieser Modelle erlaubt die Vorhersage der Entwicklung der Blasengrößenverteilungen entlang einer Rohrströmung für einen breiten Bereich an Kombinationen von Volumenströmen der Gas- und der Flüssigphase.
Das neue Modell wurde ausführlich in einem vereinfachten Testsolver untersucht. Dieser erfasst zwar nicht alle Einzelheiten einer sich entlang des Rohres entwickelten Strömungen, erlaubt aber im Gegensatz zu den CFD-Simulationen eine Vielzahl von Variationsrechnungen zur Untersuchung des Einflusses einzelner Größen und Modelle. Koaleszenz und Zerfall kann nicht getrennt von anderen Phänomenen und Modellen, die diese widerspiegeln, betrachtet werden. Es bestehen enge Wechselwirkungen mit der Turbulenz der Flüssigphase und dem Impulsaustausch zwischen den Phasen. Da die Dissipationsrate der turbulenten kinetischen Energie ein direkter Eingangsparameter für das neue Modell ist, wurde die Turbulenzmodellierung besonders genau untersucht.
Zur Validierung des Modells wurde eine TOPFLOW-Experimentalserie zur Luft-Wasser-Strömungen in einem 8 m langen DN200-Rohr genutzt. Die Daten zeichnen sich durch eine hohe Qualität aus und wurden im Rahmen des TOPFLOW-IIVorhabens mit dem Ziel eine Grundlage für die hier vorgestellten Arbeiten zu liefern, gewonnen. Die Vorhersage der Entwicklung der Blasengrößenverteilung entlang des Rohrs konnte im Vergleich zu den bisherigen Standardmodellen für Blasenkoaleszenz und -zerfall in CFX deutlich verbessert werden. Einige quantitative Abweichungen bleiben aber bestehen.
Die vollständigen Modellgleichungen sowie eine Implementierung über „User-FORTRAN“ in CFX stehen zur Verfügung und können für weitere Arbeiten zur Simulation polydisperser Blasenströmungen genutzt werden.
14
Yao, Juncheng. "Characterization and Prediction of Water Droplet Size in Oil-Water Flow." Ohio University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1470741069.
15
Pellacani, Filippo [Verfasser], Rafael [Akademischer Betreuer] Macián-Juan, and Vicent Sergio [Akademischer Betreuer] Chiva. "Development and Validation of Bubble Breakup and Coalescence Constitutive Models for the One-Group Interfacial Area Transport Equation / Filippo Pellacani. Gutachter: Sergio Chiva Vicent ; Rafael Macián-Juan. Betreuer: Rafael Macián-Juan." München : Universitätsbibliothek der TU München, 2012. http://d-nb.info/104199480X/34.
16
Hagesæther, Lars. "Coalescence and Break-Up of Drops and Bubbles." Doctoral thesis, Norwegian University of Science and Technology, Department of Chemical Engineering, 2002. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-2148.
Анотація:
Fluid particle break-up and coalescence are important phenomena in a number of industrial processes.
A Lagrangian momentum balance model for the collision process between two fluid particles has been developed and tested favorably against experimental data. It is based on an earlier model developed in our department. Oscillations were introduced and the volume balances that are solved avoid earlier approximations. Film drainage was also implemented into the model based on a literature review given. It is believed this approach will lead to a more fundamental modeling of the coalescence process.
An improved break-up model has been developed. It is an extension of earlier work at the department and it introduces an additional criterion for break-up. This criterion gives a lower limit for the daughter fragment sizes in binary break-up, thus also limiting the break-up of smaller fluid particles, and is a more consistent model than the earlier one.
Two break-up models, original model by Luo (1993) and improved model, and a coalescence model have been implemented in a population balance as algebraic sink and source terms. This population balance is in turn included in an in-house CFD-code. The models have been tested against experimental data from a bubble column in our laboratory, and the improved break-up model compares favorably with the experimentally obtained accumulated mass distribution. Too few bubbles are predicted in the lower population classes, but it is shown that this may as well be a result of the coalescence model used as the improved break-up model.
17
Kracht, Gajardo Willy Andrés 1979. "Effect of frother on bubble coalescence, break-up, and initial rise velocity." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=111911.
Анотація:
Frothers are used in flotation to aid generation of small bubbles, but little is known about the mechanisms that take place in the flotation machine to produce such an effect. Coalescence prevention is the common explanation, although the exact mechanism is obscure and almost no attention has been paid to a frother effect on bubble break-up, the other possible mechanism. This thesis presents a technique to study the effect of frothers on bubble coalescence at the generation stage (at a capillary tube) and a technique to study the effect of frothers on bubble coalescence and break-up in a turbulent field. The first technique is based on the sound bubbles emit when they form and coalesce. The sound signal was linked to bubble formation and coalescence events using high-speed cinematography. The technique has a resolution capable of detecting coalescence events that occur within 1-2 ms. The second technique allows discriminating between coalescence and break-up and is based on the exposure of a mono-size distribution of bubbles to a turbulent field generated by a three-bladed axial flow impeller. Analysis of bubble size distributions after contact with the turbulent field gives the coalescence and break-up fraction. The results show frothers reduce coalescence and alter the bubble size distribution of bubbles generated by break-up.In the course of high-speed imaging an effect of frother on bubble shape and motion after formation was detected. Analysis of this forms the third major component of the work. A dependence of velocity on bubble aspect ratio is shown, which is in line with recent literature.
18
Bagley, Justin C. "Understanding the Diversification of Central American Freshwater Fishes Using Comparative Phylogeography and Species Delimitation." BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/5296.
Анотація:
Phylogeography and molecular phylogenetics have proven remarkably useful for understanding the patterns and processes influencing historical diversification of biotic lineages at and below the species level, as well as delimiting morphologically cryptic species. In this dissertation, I used an integrative approach coupling comparative phylogeography and coalescent-based species delimitation to improve our understanding of the biogeography and species limits of Central American freshwater fishes. In Chapter 1, I conducted a literature review of the contributions of phylogeography to understanding the origins and maintenance of lower Central American biodiversity, in light of the geological and ecological setting. I highlighted emerging phylogeographic patterns, along with the need for improving regional historical biogeographical inference and conservation efforts through statistical and comparative phylogeographic studies. In Chapter 2, I compared mitochondrial phylogeographic patterns among three species of livebearing fishes (Poeciliidae) codistributed in the lower Nicaraguan depression and proximate uplands. I found evidence for mixed spatial and temporal divergences, indicating phylogeographic “pseudocongruence” suggesting that multiple evolutionary responses to historical processes have shaped population structuring of regional freshwater biota, possibly linked to recent community assembly and/or the effects of ecological differences among species on their responses to late Cenozoic environmental events. In Chapter 3, I used coalescent-based species tree and species delimitation analyses of a multilocus dataset to delimit species and infer their evolutionary relationships in the Poecilia sphenops species complex (Poeciliidae), a widespread but morphologically conserved group of fishes. Results indicated that diversity is underestimated and overestimated in different clades by c. ±15% (including candidate species); that lineages diversified since the Miocene; and that some evidence exists for a more probable role of hybridization, rather than incomplete lineage sorting, in shaping observed gene tree discordances. Last, in Chapter 4, I used a comparative phylogeographical analysis of eight codistributed species/genera of freshwater fishes to test for shared evolutionary responses predicted by four drainage-based hypotheses of Neotropical fish diversification. Integrating phylogeographic analyses with paleodistribution modeling revealed incongruent genetic structuring among lineages despite overlapping ancestral Pleistocene distributions, suggesting multiple routes to community assembly. Hypotheses tests using the latest approximate Bayesian computation model averaging methods also supported one pulse of diversification in two lineages diverged in the San Carlos River, but multiple divergences of three lineages across the Sixaola River basin, Costa Rica, correlated to Neogene sea level events and continental shelf width. Results supported complex biogeographical patterns illustrating how species responses to historical drainage-controlling processes have influenced Neotropical fish diversification.
19
Mira, Joele Paulus. "Production of Li, Be and B nuclei in the interaction of 12C with 12C at incident energies of 200 and 400 MeV." Thesis, Online Access, 2008. http://etd.uwc.ac.za/usrfiles/modules/etd/docs/etd_gen8Srv25Nme4_7059_1260783023.pdf.
20
Zschau, Jochen, Winfried Zippe, Cornelius Zippe, Horst-Michael Prasser, Dirk Lucas, Ulrich Rohde, Arnd Böttger, et al. "Strömungskarten und Modelle für transiente Zweiphasenströmungen." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-29111.
Анотація:
Experimente mit neuartigen Messverfahren lieferten Daten über die Struktur von transienten Flüssig-keits-Gas-Strömungen für die Entwicklung und Validierung von mikroskopischen, d.h. geometrieunabhängigen Konstitutivbeziehungen zur Beschreibung des Impulsaustauschs zwischen Flüssig-phase und Gasblasen sowie zur Quantifizierung der Häufigkeit von Blasenkoaleszenz und -zerfall. Hierzu wurde eine vertikale Testsektion der Zweiphasentestschleife MTLoop in Rossendorf genutzt, wobei erstmals Gittersensoren mit einer Auflösung von 2-3 mm bei einer Messfrequenz von bis zu 10 kHz angewandt wurden. Dabei wurde die Evolution von Gasgehalts-, Geschwindigkeits- und Bla-sengrößenverteilungen entlang des Strömungsweges und bei schnellen Übergangsprozessen aufge-nommen und so die für die Modellbildung erforderlichen Daten bereitgestellt. Für den Test der Mo-dellbeziehungen wurde ein vereinfachtes Verfahren zur Lösung der Strömungsgleichungen entlang des Strömungswegs erstellt. Es basiert auf der Betrachtung einer größeren Anzahl von Blasengrö-ßenklassen. Die erhaltenen numerische Lösungen haben erstmals gezeigt, dass der bei Erhöhung der Gasvolumenstromdichte stattfindende Übergang von einer Blasenströmung mit Randmaximum zu einem Profil mit Zentrumsmaximum und anschließend zu einer Pfropfenströmung ausgehend von einem einheitlichen Satz physikalisch begründeter und geometrieunabhängiger Konstitutivgleichun-gen modelliert werden kann. Die Modellbeziehungen haben sich in einem abgegrenzten Gebiet der Volumenstromdichten als generalisierungsfähig erwiesen und sind für den Einbau in CFD-Modelle geeignet. Weiterhin wurden Arbeiten zur Kondensation durchgeführt, die direkten Bezug zu den Kon-densationsmodellen haben, die in Thermohydraulik-Codes enthalten sind. Die Untersuchung liefert darüber hinaus experimentelle Daten für die Modellvalidierung hinsichtlich des Verhaltens und des Einflusses nichtkondensierbarer Gase. Hierfür wurden spezielle Sonden für die Bestimmung der Konzentration und für die Lokalisierung von Pfropfen nichtkondensierbarer Gase entwickelt und bei transienten Kondensationsversuchen in einem leicht geneigten Wärmeübertragerrohr eingesetzt.
21
Zschau, Jochen, Winfried Zippe, Cornelius Zippe, Horst-Michael Prasser, Dirk Lucas, Ulrich Rohde, Arnd Böttger, et al. "Strömungskarten und Modelle für transiente Zweiphasenströmungen." Forschungszentrum Rossendorf, 2003. https://hzdr.qucosa.de/id/qucosa%3A21738.
Анотація:
Experimente mit neuartigen Messverfahren lieferten Daten über die Struktur von transienten Flüssig-keits-Gas-Strömungen für die Entwicklung und Validierung von mikroskopischen, d.h. geometrieunabhängigen Konstitutivbeziehungen zur Beschreibung des Impulsaustauschs zwischen Flüssig-phase und Gasblasen sowie zur Quantifizierung der Häufigkeit von Blasenkoaleszenz und -zerfall. Hierzu wurde eine vertikale Testsektion der Zweiphasentestschleife MTLoop in Rossendorf genutzt, wobei erstmals Gittersensoren mit einer Auflösung von 2-3 mm bei einer Messfrequenz von bis zu 10 kHz angewandt wurden. Dabei wurde die Evolution von Gasgehalts-, Geschwindigkeits- und Bla-sengrößenverteilungen entlang des Strömungsweges und bei schnellen Übergangsprozessen aufge-nommen und so die für die Modellbildung erforderlichen Daten bereitgestellt. Für den Test der Mo-dellbeziehungen wurde ein vereinfachtes Verfahren zur Lösung der Strömungsgleichungen entlang des Strömungswegs erstellt. Es basiert auf der Betrachtung einer größeren Anzahl von Blasengrö-ßenklassen. Die erhaltenen numerische Lösungen haben erstmals gezeigt, dass der bei Erhöhung der Gasvolumenstromdichte stattfindende Übergang von einer Blasenströmung mit Randmaximum zu einem Profil mit Zentrumsmaximum und anschließend zu einer Pfropfenströmung ausgehend von einem einheitlichen Satz physikalisch begründeter und geometrieunabhängiger Konstitutivgleichun-gen modelliert werden kann. Die Modellbeziehungen haben sich in einem abgegrenzten Gebiet der Volumenstromdichten als generalisierungsfähig erwiesen und sind für den Einbau in CFD-Modelle geeignet. Weiterhin wurden Arbeiten zur Kondensation durchgeführt, die direkten Bezug zu den Kon-densationsmodellen haben, die in Thermohydraulik-Codes enthalten sind. Die Untersuchung liefert darüber hinaus experimentelle Daten für die Modellvalidierung hinsichtlich des Verhaltens und des Einflusses nichtkondensierbarer Gase. Hierfür wurden spezielle Sonden für die Bestimmung der Konzentration und für die Lokalisierung von Pfropfen nichtkondensierbarer Gase entwickelt und bei transienten Kondensationsversuchen in einem leicht geneigten Wärmeübertragerrohr eingesetzt.
22
Bannari, Rachid. "Mathematical modeling of cellulase production in an airlift bioreactor." Thèse, Université de Sherbrooke, 2009. http://savoirs.usherbrooke.ca/handle/11143/1930.
Анотація:
Fossil fuel is an important energy source, but is unavoidabiy running out. Since the cellulosic material is the most abundant source of organic matter, the ethanol, which is produced from cellulosic waste materials, is gaining more and more attention. These materials are cheap, renewable and their availability makes them superior compared to other raw materials. The cellulose must be hydrolyzed to glucose before it can be fermented to ethanol. The enzymatic hydrolysis of cellulose using cellulase enzymes is the most widely used method. The production cost of cellulase enzymes is the major cost in ethanol manufacture. To optimize the cost of ethanol production, enzyme stability needs to be improved through maintaining the activity of the enzymes and by optimizing the production of the cellulase. The aim of researchers, engineers and industrials is to get more biomass for the same cost. The filamentous fungus Trichoderma reesei has a long history in the production of the cellulase enzymes. This production can be influenced strongly by varying the growth media and culture conditions (pH, temperature, DO, agitation,... ). At present, it is my opinion that no modelling study has included both the hydrodynamic and kinetic aspects to investigate the effect of shear and mass transfer on the morphology of microorganisms that influence the rheology of the broth and production of cellulase. This thesis presents the development of a mathematical model for cellulase production and the growth of biomass in an airlift bioreactor. The kinetic model is coupled with the methodology of two-phase flow using mathematical models based on the bubble break-up and coalescence to predict mass transfer rate, which is one of the critical factor in the fermentation. A comparison between the results obtained by the developed model and the experimental data is given and discussed. The design proposed for the airlift geometry by Ahamed and Vermette enables us to get a high mass transfer and production rate. The results are very promising with respect to the potential of such a model for industrial use as a prediction tool, and even for design.
23
Melhus, Christoffer. "Effects of microbial community coalescence in lake water at ice break-off." Thesis, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-386529.
Анотація:
The period of ice break-off in spring is a key event for many biogeochemical processes in lakes globallly. The biogeochemical processes occurring at ice break-off have the potential of influencing characteristics of lakes throughout spring and summer, including algal blooms and greenhouse gas emission. This makes it important to study lakes in the period of ice break-off. At ice break-off, soil bacteria from the catchment area usually enter the lake via spring floods and mix with the bacteria already occurring in the lake water. In this study, the effects of mixing soil- and lake microbial communities during ice break-off-like conditions were tested by performing an experiment under controlled conditions in the laboratory. In the experiment, light, microbial community composition and concentration of soil-derived organic matter were manipulated to simulate different conditions associated with ice break-off. The variables investigated were bacterial activity and functionality, measured as cell abundance and enzymatic activity, as well as primary production and concentration of dissolved organic matter. The results showed that a mix of soil and lake microbial communities had enzymatic activity patterns resembling lake communities, and then shifted to being more similar to soil communities. The experiment also showed that degradation of measured dissolved organic matter was not linked to biotic processes, and that the observed decrease was most likely due to photo degradation. Finally, the experiment showed that primary production, here measured as chlorophyll a, was only stimulated by the mixed community with light and added soil dissolved organic matter. The results found in this study are important as they show that microbial communities do alter their function and enzymatic activity based on composition. Furthermore, the result that primary production was only seen in the presence of light, soilderived organic matter and a mixed community of lake and soil bacteria may be seen as an indication that primary producers in lake ecosystems to some extent depend on the inflow of terrestrial microbes and organic matter. It also possible that the coalescence of microbial communities enables the communities to perform tasks they were unable to prior to coalescence (i.e. perform tasks that allows primary production to take place). These results give the basis for further, more detailed studies.
24
Wang, Chih-Wei. "Flow-directed solution self-assembly of block copolymers in microfluidic devices." Thesis, 2012. http://hdl.handle.net/1828/3984.
Анотація:
The self-assembly of polystyrene-stabilized cadmium sulfide nanoparticles (PS-CdS) with amphiphilic stabilizing chains of polystyrene-block-poly(acrylic acid) (PS-b-PAA) into colloidal quantum dot compound micelles (QDCMs) is studied on two-phase gas-liquid segmented microfluidic reactors. The resulting particle sizes are found to arise from the interplay of shear-induced coalescence and particle breakup, depending on a combination of chemical and flow conditions. Variation of water content, gas-to-liquid ratio, and total flow rate, enable control of QDCM sizes in the range of 140 – 40 nm.
The flow-variable shear effect on similar microfluidic reactors is then applied to direct the solution self-assembly of a PS-b-PAA block copolymer into various micelle morphologies. The difference between off-chip and on-chip morphologies under identical chemical conditions is explained by a mechanism of shear-induced coalescence enabled by strong and localized on-chip shear fields, followed by intraparticle chain rearrangements to minimize local free energies. Time-dependent studies of these nanostructures reveal that on-chip kinetic structures will relax to global equilibrium given sufficient time off-chip. Further investigations into the effect of chemical variables on on-chip shear-induced morphologies reveal a combination of thermodynamic and kinetic effects, opening avenues for morphology control via combined chemical (bottom-up) and shear (top-down) forces. An equilibrium phase diagram of off-chip micelle morphologies is constructed and used in conjunction with kinetic considerations to rationalize on-chip mechanisms and morphologies, including cylinders and vesicles, under different chemical conditions.
Finally, we extend our strategy of two-phase microfluidic self-assembly of PS-b-PAA to the loading of fluorescent hydrophobic probes (pyrene and naphthalene) with different affinities for the PS core. The on-chip loading approach provides a fast alternate to the slow off-chip method, with implications for the potential development for point-of-care devices for drug loading. On-chip loading results indicate that loading efficiencies are dependent on water content and, to a lesser extent, on flow rate; the results also suggest that the on-chip morphologies of the PS-b-PAA micelles are an important factor in the loading efficiencies.Graduate