Tesi sul tema "Bubble breakup"
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Kang, In Seok Leal L. Gary Leal L. Gary. "Bubble dynamics and breakup in straining flows /". Diss., Pasadena, Calif. : California Institute of Technology, 1988. http://resolver.caltech.edu/CaltechETD:etd-11072007-112829.
Testo completoLiao, Yixiang. "Development and validation of models for bubble coalescence and breakup". Helmholtz-Zentrum Dresden-Rossendorf, 2013. https://hzdr.qucosa.de/id/qucosa%3A22180.
Testo completoLiao, 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.
Testo completoMawson, Ryan A. "Bubble Coalescence and Breakup Modeling for Computing Mass Transfer Coefficient". DigitalCommons@USU, 2012. https://digitalcommons.usu.edu/etd/1330.
Testo completoKrepper, Eckhard, e Dirk Lucas. "CFD models for polydispersed bubbly flows". Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-28052.
Testo completoKrepper, Eckhard, e Dirk Lucas. "CFD models for polydispersed bubbly flows". Forschungszentrum Dresden-Rossendorf, 2007. https://hzdr.qucosa.de/id/qucosa%3A21632.
Testo completoLiao, Y., e 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.
Testo completoPellacani, Filippo [Verfasser], Rafael [Akademischer Betreuer] Macián-Juan e 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.
Testo completoWu, Yining. "Étude des phénomènes interfaciaux à micro-échelle". Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0330/document.
Testo completoThis 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
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.
Testo completoZschau, 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.
Testo completoShukla, Rainy. "Experimental Studies on Bubble Rupture Mechanism". University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1236285097.
Testo completoHagesæther, 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.
Testo completoFluid 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.
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.
Testo completoIn 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.
Belmar, Gil Mario. "Computational study on the non-reacting flow in Lean Direct Injection gas turbine combustors through Eulerian-Lagrangian Large-Eddy Simulations". Doctoral thesis, Universitat Politècnica de València, 2021. http://hdl.handle.net/10251/159882.
Testo completo[CA] El principal desafiament als motors turbina de gas utilitzats a la aviació resideix en augmentar l'eficiència del cicle termodinàmic mantenint les emissions contaminants per davall de les rigoroses restriccions. Aquest fet comporta la necessitat de dissenyar noves estratègies d'injecció/combustió que radiquen en punts d'operació perillosos per la seva aproximació al límit inferior d'apagat de flama. En aquest context, el concepte Lean Direct Injection (LDI) sorgeix com a eina innovadora a l'hora de reduir els òxids de nitrogen (NOx) emesos per les plantes propulsores dels avions de nova generació. Sota aquest context, aquesta tesis té com a objectius contribuir al coneixement dels mecanismes físics que regeixen el comportament d'un cremador LDI i proporcionar ferramentes d'anàlisi per a una profunda caracterització de les complexes estructures de flux turbulent generades a l'interior de la càmera de combustió. Per tal de dur-ho a terme s'ha desenvolupat una metodología numèrica basada en CFD capaç de modelar el flux bifàsic no reactiu a l'interior d'un cremador LDI acadèmic mitjançant els enfocaments de turbulència U-RANS i LES en un marc Eulerià-Lagrangià. La resolució numèrica d'aquest problema multiescala s'aborda mitjançant la resolució completa del flux al llarg de tots els elements que constitueixen la maqueta experimental, incloent el seu pas pel swirler i l'entrada a la càmera de combustió. Açò es duu a terme a través de dos codis CFD que involucren estratègies de mallat diferents: una basada en la generación automàtica de la malla i en l'algoritme de refinament adaptatiu (AMR) amb CONVERGE i l'altra que es basa en una tècnica de mallat estàtic més tradicional amb OpenFOAM. D'una banda, s'ha definit una metodologia per tal d'obtindre una estrategia de mallat òptima mitjançant l'ús de l'AMR i s'han explotat els seus beneficis front als enfocaments tradicionals de malla estàtica. D'aquesta forma, s'ha demostrat que l'aplicabilitat de les ferramente de control de malla disponibles en CONVERGE com el refinament fixe (fixed embedding) i l'AMR són una opció molt interessant per tal d'afrontar aquest tipus de problemes multiescala. Els resultats destaquen una optimització de l'ús dels recursos computacionals i una major precisió en les simulacions realitzades amb la metodologia presentada. D'altra banda, l'ús d'eines CFD s'ha combinat amb l'aplicació de tècniques de descomposició modal avançades (Proper Orthogonal Decomposition and Dynamic Mode Decomposition). La identificació numèrica dels principals modes acústics a la càmera de combustió ha demostrat el potencial d'aquestes ferramentes al permetre caracteritzar les estructures de flux coherents generades com a conseqüència del trencament dels vòrtex (VBB) i dels raigs fortament arremolinats presents al cremador LDI. A més, la implantació d'estos procediments matemàtics ha permès recuperar informació sobre les característiques de la dinàmica del flux i proporcionar un enfocament sistemàtic per tal d'identificar els principals mecanismes que sustenten les inestabilitats a la càmera de combustió. Finalment, la metodologia validada ha sigut explotada a traves d'un Diseny d'Experiments (DoE) per tal de quantificar la influència dels factors crítics de disseny en el flux no reactiu. D'aquesta manera, s'ha avaluat la contribución individual d'alguns paràmetres funcionals (el nombre de pales del swirler, l'angle de les pales, l'amplada de la càmera de combustió i la posició axial de l'orifici de l'injector) en els patrons del camp fluid, la distribució de la mida de gotes del combustible líquid i l'aparició d'inestabilitats en la càmera de combustió mitjançant una matriu ortogonal L9 de Taguchi. Aquest estudi estadístic és un bon punt de partida per a futurs estudis de injecció, atomització i combustió en cremadors LDI.
[EN] Aeronautical gas turbine engines present the main challenge of increasing the efficiency of the cycle while keeping the pollutant emissions below stringent restrictions. This has led to the design of new injection-combustion strategies working on more risky and problematic operating points such as those close to the lean extinction limit. In this context, the Lean Direct Injection (LDI) concept has emerged as a promising technology to reduce oxides of nitrogen (NOx) for next-generation aircraft power plants In this context, this thesis aims at contributing to the knowledge of the governing physical mechanisms within an LDI burner and to provide analysis tools for a deep characterisation of such complex flows. In order to do so, a numerical CFD methodology capable of reliably modelling the 2-phase nonreacting flow in an academic LDI burner has been developed in an Eulerian-Lagrangian framework, using the U-RANS and LES turbulence approaches. The LDI combustor taken as a reference to carry out the investigation is the laboratory-scale swirled-stabilised CORIA Spray Burner. The multi-scale problem is addressed by solving the complete inlet flow path through the swirl vanes and the combustor through two different CFD codes involving two different meshing strategies: an automatic mesh generation with adaptive mesh refinement (AMR) algorithm through CONVERGE and a more traditional static meshing technique in OpenFOAM. On the one hand, a methodology to obtain an optimal mesh strategy using AMR has been defined, and its benefits against traditional fixed mesh approaches have been exploited. In this way, the applicability of grid control tools available in CONVERGE such as fixed embedding and AMR has been demonstrated to be an interesting option to face this type of multi-scale problem. The results highlight an optimisation of the use of the computational resources and better accuracy in the simulations carried out with the presented methodology. On the other hand, the use of CFD tools has been combined with the application of systematic advanced modal decomposition techniques (i.e., Proper Orthogonal Decomposition and Dynamic Mode Decomposition). The numerical identification of the main acoustic modes in the chamber have proved their potential when studying the characteristics of the most powerful coherent flow structures of strongly swirled jets in a LDI burner undergoing vortex breakdown (VBB). Besides, the implementation of these mathematical procedures has allowed both retrieving information about the flow dynamics features and providing a systematic approach to identify the main mechanisms that sustain instabilities in the combustor. Last, this analysis has also allowed identifying some key features of swirl spray systems such as the complex pulsating, intermittent and cyclical spatial patterns related to the Precessing Vortex Core (PVC). Finally, the validated methodology is exploited through a Design of Experiments (DoE) to quantify the influence of critical design factors on the non-reacting flow. In this way, the individual contribution of some functional parameters (namely the number of swirler vanes, the swirler vane angle, the combustion chamber width and the axial position of the nozzle tip) into both the flow field pattern, the spray size distribution and the occurrence of instabilities in the combustion chamber are evaluated throughout a Taguchi's orthogonal array L9. Such a statistical study has supposed a good starting point for subsequent studies of injection, atomisation and combustion on LDI burners.
Belmar Gil, M. (2020). Computational study on the non-reacting flow in Lean Direct Injection gas turbine combustors through Eulerian-Lagrangian Large-Eddy Simulations [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/159882
TESIS
Ahlersten, Krister. "Empirical asset pricing and investment strategies". Doctoral thesis, Stockholm : Economic Research Institute, Stockholm School of Economics [Ekonomiska forskningsinstitutet vid Handelshögskolan i Stockholm] (EFI), 2007. http://www2.hhs.se/efi/summary/726.htm.
Testo completo透, 山下, e Tohru Yamashita. "遮断器用油圧操作装置の動作時間安定化に関する研究". Thesis, https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB13045046/?lang=0, 2017. https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB13045046/?lang=0.
Testo completoWe proposed and studied a hydraulic operation stabilizing system for a hydraulic operating device of a circuit breaker to eliminate the influence of air bubbles created in hydraulic fluid. We formulated the flow of hydraulic circuit and the motion of moving parts, which were numerically simulated and experimentally confirmed. We confirmed that this stabilizing system functioned effectively and stably through the investigation: operation characteristics and stability of the stabilizing system, braking characteristics of a piston-dashpot system and operation characteristics of two hydraulic operating devices. Based on the results, we could perform an engineering development for stabilizing operation time of the hydraulic operating device.
博士(工学)
Doctor of Philosophy in Engineering
同志社大学
Doshisha University
Kang, In Seok. "Bubble Dynamics and Breakup in Straining Flows". Thesis, 1988. https://thesis.library.caltech.edu/4449/3/Kang_is_1988.pdf.
Testo completoThe dynamics and breakup of a bubble in axisymmetric flow fields has been investigated using numerical and analytical techniques. In particular, the transient bubble deformation, oscillation, and overshoot effects are considered in conjunction with the existence of steady-state solutions.
To explore the dynamics of a bubble with a high degree of deformation, a numerical technique suitable for solving axisymmetric, unsteady free boundary problems in fluid mechanics has been developed. The technique is based on a finite-difference solution of the equations of motion on a moving orthogonal curvilinear coordinate system, which is constructed numerically and adjusted to fit the boundary at any time. For example, the steady and unsteady deformations of a bubble in uniaxial and biaxial straining flows are examined for wide ranges of the Reynolds number and the Weber number. The computations reveal that a bubble in a uniaxial straining flow extends indefinitely if the Weber number is larger than a critical value (W > Wc). Furthermore, it is shown that a bubble may not achieve a stable steady state even at subcritical values of the Weber number if the initial state is sufficiently different from the steady state. Potential flow solutions for uniaxial straining flow show that an initially deformed bubble undergoes oscillatory motion if W < Wc, with a frequency of oscillation that decreases as the Weber number increases and equals zero at the critical Weber number.
In contrast to the uniaxial straining flow problem, a bubble at a finite Reynolds number in a biaxial straining flow has a stable steady state even though the deformation is extremely large. However, it is found that a bubble in a biaxial straining flow in the potential flow limit has exactly the same steady-state shape as in a uniaxial straining flow and a critical Weber number for breakup exists. Comparison of the results for the cases of high Reynolds numbers with the potential flow results suggests that the potential flow solution does not provide a uniformly valid approximation to the real flow at a high Reynolds number in the biaxial straining flow.
As a complementary analytical study to the numerical analysis, the method of domain perturbations is used to investigate the problem of a nearly spherical bubble in an inviscid, axisymmetric straining flow. The steady-state solutions suggest the existence of a limit point at a critical value of the Weber number. Furthermore, the asymptotic analysis for oscillation has provided a formula of oscillation frequency for the principal mode such as ω² = ω²₀(1 - 0.31W), where ω₀ is the oscillation frequency of a bubble in a quiescent fluid.
To include the weak viscous effect on the oscillation, a general formula for viscous pressure correction for a spherical bubble in an arbitrary axisymmetric flow has been derived in terms of the vorticity distribution. This formula has been applied to obtain the drag coefficient CD = 48/R by directly integrating the normal stress over the surface for a spherical bubble in a uniform streaming flow at a high Reynolds number, which has so far been possible only via indirect macroscopic balances. The direct method also reveals that the drag coefficient up to O(R)⁻¹ depends only on the O(1) vorticity distribution right on the bubble surface, and is independent of the vorticity distribution inside the fluid.
Finally, a voidage bubble in a fluidized bed is considered in the low Reynolds number limit. The problem has been formulated as a generalized drop problem with one additional parameter. The analysis shows that the steady and unsteady deformations in the creeping flow limit are exactly the same as the conventional drop problem even though the flow fields are different. The effect of the additional parameter on deformation first appears when inertial effects are considered.
Movassat, Mohammad. "Bubble Dynamics, Oscillations and Breakup under Forced Vibration". Thesis, 2012. http://hdl.handle.net/1807/32778.
Testo completoEvans, Geoffrey Michael. "A Study of a Plunging Jet Bubble Column". Diss., 1990. http://hdl.handle.net/1959.13/24721.
Testo completoPhD Doctorate
Evans, Geoffrey Michael. "A Study of a Plunging Jet Bubble Column". Thesis, 1990. http://hdl.handle.net/1959.13/24721.
Testo completoPhD Doctorate
Thoraval, Marie-Jean. "Drop impact splashing and air entrapment". Diss., 2013. http://hdl.handle.net/10754/293818.
Testo completo