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Dissertations / Theses on the topic 'Dispersed phase'

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Published: 4 June 2021
Last updated: 19 February 2022

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1

Kemiklioglu, Emine. "Polymer Stabilized and Dispersed Blue Phases." Kent State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=kent1409153158.

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2

Lee, Woo Young. "Chemical vapor deposition of dispersed phase ceramic composites." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/11857.

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3

Ngan, K. H. "Phase inversion in dispersed liquid-liquid pipe flow." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1318099/.

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This thesis presents the experimental and theoretical investigations on the development of phase inversion in horizontal pipeline flow of two immiscible liquids. It aims to provide an understanding on the flow development across the phase inversion transition as well as the effect on pressure drop. Experimental investigation on phase inversion and associated phenomena were conducted in a 38mm I.D. liquid pipeline flow facility available in the Department of Chemical Engineering at University College London (UCL). Two sets of test pipelines are constructed using stainless steel and acrylic. The inlet section of the pipeline has also been designed in two different configurations – (1) Y-junction inlet to allow dispersed flow to be developed along the pipeline (2) Dispersed inlet to allow formation of dispersion immediately after the two phases are joined. Pressure drop along the pipeline is measured using a differential pressure transducer and is studied for changes due to redistribution of the phases during inversion. Various conductivity probes (ring probes, wire probes, electrical resistance tomography and dual impedance probe) are installed along the pipeline to detect the change in phase continuity and distribution as well as drop size distribution based on the difference in conductivity of the oil and water phases. During the investigation, the occurrence of phase inversion is firstly investigated and the gradual transition during the process is identified. The range of phase fraction at which the transition occurs is determined. The range of phase fraction becomes significantly narrower when the dispersed inlet is used. The outcome of the investigation also becomes the basis for subsequent investigation with the addition of glycerol to the water phase to reduce the interfacial tension. Based on the experimental outcome, the addition of glycerol does not affect the inversion of the oil phase while enhancing the continuity of the water phase. As observed experimentally, significant changes in pressure gradient can be observed particularly during phase inversion. Previous literatures have also reviewed that phase inversion occurs at the maximum pressure gradient. In a horizontal pipeline, pressure gradient is primarily caused by the frictional shear on the fluid flow in the pipe and, in turn, is significantly affected by the fluid viscosities. A study is conducted to investigate on the phase inversion point by identifying the maximum mixture viscosity (i.e. maximum pressure gradient) that an oil-in-water (O/W) and water-in-oil (W/O) dispersion can sustain. It is proposed that the mixture viscosity will not increase further with an increase in the initial dispersed phase if the inverted dispersion has a lower mixture viscosity. This hypothesis has been applied across a wide range of liquid-liquid dispersion with good results. This study however cannot determine the hysteresis effect which is possibly caused by inhomogeneous inversion in the fluid system. A mechanistic model is developed to predict the flow characteristics as well as the pressure gradient during a phase inversion transition. It aims to predict the observed change in flow pattern from a fully dispersed flow to a dual continuous flow during phase inversion transition. The existence of the interfacial height provides a selection criterion to determine whether a momentum balance model for homogeneous flow or a two-fluid layered flow should be applied to calculate the pressure gradient. A friction factor is also applied to account for the drag reduction in a dispersed flow. This developed model shows reasonable results in predicting the switch between flow patterns (i.e. the boundaries for the phase inversion transition) and the corresponding pressure gradient. Lastly, computational fluid dynamic (CFD) simulation is applied to identify the key interphase forces in a dispersed flow. The study has also attempted to test the limitation of existing interphase force models to densely dispersed flow. From the study, it is found that the lift force and the turbulent dispersion forces are significant to the phase distribution in a dispersed flow. It also provides a possible explanation to the observed flow distribution in the experiments conducted. However, the models available in CFX are still unable to predict well in a dense dispersion (60% dispersed). This study is also suggested to form the basis for more detailed work in future to optimize the simulation models to improve the prediction of phase inversion in a CFD simulation.
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4

Haidemenopoulos, Gregory N. "Dispersed-phase transformation toughening in ultrahigh-strength steels." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14564.

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5

Zhou, Jianyu. "Applications of Dispersed Phase Flows Through Porous Media." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1542106409444557.

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6

Hill, David Paul. "The computer simulation of dispersed two-phase flow." Thesis, Imperial College London, 1998. http://hdl.handle.net/10044/1/8733.

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7

Rusche, Henrik. "Computational fluid dynamics of dispersed two-phase flows at high phase fractions." Thesis, Imperial College London, 2003. http://hdl.handle.net/10044/1/8110.

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8

Varone, Anthony F. (Anthony Francis). "The influence of the dispersed phase on the convective heat transfer in dispersed flow film boiling." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/13996.

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9

Govan, Alastair Hamilton. "Modelling of vertical annular and dispersed two-phase flows." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/8778.

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10

Deshpande, Kiran B. "Study of transport limited heterogeneous reaction in the dispersed phase." Thesis, University of Sheffield, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.419600.

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11

Prasertmanukitch, Sitas. "Dispersed phase adsorbents : a study of their properties and behaviour." Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247501.

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12

Ioannou, Karolina. "Phase inversion phenomenon in horizontal dispersed oil/water pipeline flows." Thesis, University College London (University of London), 2006. http://discovery.ucl.ac.uk/1445603/.

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This thesis reports on experimental and theoretical investigations relevant to the understanding of the phenomenon of phase inversion and its effect on pressure drop during dispersed flow of two immiscible liquids in horizontal pipelines. Experimental studies of phase inversion and associated phenomena were carried out in the liquid flow facility in the Department of Chemical Engineering at University College London (UCL), and at the Norwegian University of Science and Technology, Trondheim, Norway (NTNU). Detailed local conductivity measurements have been obtained at UCL (using conductivity ring probes, a local needle conductivity probe and a flush probe mounted on the pipe wall), which revealed phase continuity at different locations in the pipe cross section as the system approaches phase inversion and after it. In both systems, pressure gradient was measured and phase inversion identification measurements along the pipe were enabled with the use of the conductivity ring probes. A new probe that enables phase and drop size distribution measurements was designed and developed for use at UCL. At the UCL facility, velocity ratio of the two phases, the dispersed phase droplet velocity profiles, and phase distribution at the pipe cross section and droplet chord length were also measured. This revealed a significant increase in the dispersed drop size at inversion point. The results also enabled the equal surface energy criterion validation, based on droplet size considerations. The velocity ratio of the two phases was found to have a higher value than unity at all conditions studied, while inversion from water to oil continuous mixtures results in a decrease in its value. The drop velocity was also becoming lower with increasing dispersed phase fraction and it was found to be affected by the presence of high dispersed phase concentrations. Various parameters and their effect on inversion were studied. Three types of oil (with viscosities of 1.7, 5.5 and 11 mPa s) were used while different pipe diameters and materials were tested (namely, acrylic with 32 and 60 mm ID, stainless steel with 38 and 60 mm ID and an epoxy coated stainless steel pipe with 60 mm ID). Mixture velocities from 2.5 m/s to 6.2 m/s (depending on the test section) were used, selected so that the mixture away from the inversion was dispersed. Also, two experimental routes were followed, starting from oil continuous and water continuous dispersions to investigate the existence of a possible hysteresis at the occurrence of inversion. It was found that phase inversion is accompanied with significant changes in pressure gradient it was preceded by a sharp peak when the less viscous oils were used, while no peak was recorded with the use of the more viscous oil. An ambivalent range was seen for the less viscous oil, possibly related to the creation of secondary dispersions. A mechanistic model that describes the layered structure of the flow during inversion (detected experimentally) was proposed for the prediction of flow characteristics and pressure gradient at the region of inversion. It is suggested that inversion starts when a thin layer of the dispersed phase (that is to become continuous) forms at the top or the bottom of the pipe. A clear layer of the continuous phase may also exist at the bottom or the top of the pipe respectively. Two or three layer models were used for these configurations. Results showed that the two layer model predicts pressure gradient and layer thickness well. The homogeneous model was found to agree well with the experimental results, especially in the water continuous region when considerations for the mixture velocity. The friction factor was modified to compensate for the appearance of the drag reduction in the conducted measurements. In addition, a commercial feasibility study has been carried out which confirmed the considerable and immediate potential for the commercialisation of the impedance probe developed within this research for phase and drop size distribution measurements.
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13

Jaye, Andrew Anthony. "Ultrafast dynamics in the dispersed phase of oil-in-water microemulsions." Thesis, University of East Anglia, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410121.

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14

Abrishami-Savjublagh, Yoseph. "Numerical computations of dispersed flow and gravity stratified two-phase flow." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/47736.

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15

Chen, Lu Guang, and s3064076@student rmit edu au. "Thermo-Optical Properties of Polymer Dispersed Liquid Crystals." RMIT University. Applied Science, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080206.114823.

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Polymer dispersed liquid crystal (PDLC) films, consisting of micro-sized domains of a liquid crystal dispersing in a polymer matrix, serve as the basis of a variety of high-efficiency electro-optical effects. The thermo-optical properties of the PDLCs were investigated in this thesis. The thermal properties and the morphologies of four low molar mass mesogens were studied by DSC and polarized optical microscope (POM). There were significant super cooling/heating effects on the first order phase transitions but not on the mesophase transitions. The structural effects on the transition temperature were investigated. Between the two 4-alkoxybenzoic acids mesogens, the clearing temperature of 4-(octyloxy)benzoic acid was higher than 4-(decyloxy)benzoic acid because of the increasing chain length. Trans-4-methoxycinnamic acid had the highest melting temperature among the four mesogens despite the molar mass because the carboxylic acid termini of trans-4-methoxycinnamic acid gave rise to strong intermolecular attractions. The smectic phases of 4-(octyloxy)benzoic acid were classified as head-to-head bilayer orientational smectic structures, SmA2 and SmC2, respectively, by wide angle X-ray diffraction through measuring the d spacing of the liquid crystal. The total solubility parameter was used to evaluate matching a polymer-LC-solvent combination. PDLC films were prepared by the solvent induced phase separation method and suitable morphologies were achieved by thermal induced phase separation. The phase transition temperatures of PDLCs were shifted to a lower temperature due to the polymer dispersion effects. Different mesophases were observed in PDLC films when LC exhibited different mesophases. The LC fractions in the droplets were calculated from the nematic to isotropic enthalpies through the Smith equation. Two factors, thermal cooling rate and the LC concentration, which affect the size of the droplet dispersed in the polymer matrix, were investigated in the PVC dispersed 4,4'-azoxyanisole. The phase transitions of pHEMA dispersed 4-(octyloxy)benzoic acid and PVC dispersed 4,4'-azoxyanisole were investigated by TMDSC and quasi-isothermal TMDSC. The TMDSC results were analysed by the two approaches, reversing and non-reversing heat flow and complex heat capacity. The results of the phase transitions of the two PDLCs illustrated that in the PDLCs it involved both non-reversing, melting, and reversing, clearing and the transition between two mesophases. In the non-reversing transition, the transition temperature would be affected by super cooling/heating and the results obtained in the experiments were dependent on the experimental conditions, such as the heating or cooling rate, sample size and purge gas flow rate. However, in the reversing transition process, there were no super cooling/heating effects observed and it seemed that the experimental conditions were not so critical. Results could be monitored by Lissajous figures obtained from the quasi-isothermal TMDSC. The plots of modulated heat flow versus the derivative of modulated temperature can be used to alert to unfavorable experimental conditions where loss of system linearity could be seen.
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16

Gudmundsson, Reynir Levi. "A numerical study of two-fluid models for dispersed two-phase flow." Doctoral thesis, KTH, Numerisk Analys och Datalogi, NADA, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-132.

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In this thesis the two-fluid (Eulerian/Eulerian) formulation for dispersed two-phase flow is considered. Closure laws are needed for this type of models. We investigate both empirically based relations, which we refer to as a nongranular model, and relations obtained from kinetic theory of dense gases, which we refer to as a granular model. For the granular model, a granular temperature is introduced, similar to thermodynamic temperature. It is often assumed that the granular energy is in a steady state, such that an algebraic granular model is obtained. The inviscid non-granular model in one space dimension is known to be conditionally well-posed. On the other hand, the viscous formulation is locally in time well-posed for smooth initial data, but with a medium to high wave number instability. Linearizing the algebraic granular model around constant data gives similar results. In this study we consider a couple of issues. First, we study the long time behavior of the viscous model in one space dimension, where we rely on numerical experiments, both for the non-granular and the algebraic granular model. We try to regularize the problem by adding second order artificial dissipation to the problem. The simulations suggest that it is not possible to obtain point-wise convergence using this regularization. Introducing a new measure, a concept of 1-D bubbles, gives hope for other convergence than point-wise. Secondly, we analyse the non-granular formulation in two space dimensions. Similar results concerning well-posedness and instability is obtained as for the non-granular formulation in one space dimension. Investigation of the time scales of the formulation in two space dimension suggests a sever restriction on the time step, such that explicit schemes are impractical. Finally, our simulation in one space dimension show that peaks or spikes form in finite time and that the solution is highly oscillatory. We introduce a model problem to study the formation and smoothness of these peaks.
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17

Guðmundsson, Reynir Leví. "A numerical study of two-fluid models for dispersed two-phase flow." Doctoral thesis, KTH, Numerical Analysis and Computer Science, NADA, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-132.

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In this thesis the two-fluid (Eulerian/Eulerian) formulation for dispersed two-phase flow is considered. Closure laws are needed for this type of models. We investigate both empirically based relations, which we refer to as a nongranular model, and relations obtained from kinetic theory of dense gases, which we refer to as a granular model. For the granular model, a granular temperature is introduced, similar to thermodynamic temperature. It is often assumed that the granular energy is in a steady state, such that an algebraic granular model is obtained.

The inviscid non-granular model in one space dimension is known to be conditionally well-posed. On the other hand, the viscous formulation is locally in time well-posed for smooth initial data, but with a medium to high wave number instability. Linearizing the algebraic granular model around constant data gives similar results. In this study we consider a couple of issues.

First, we study the long time behavior of the viscous model in one space dimension, where we rely on numerical experiments, both for the non-granular and the algebraic granular model. We try to regularize the problem by adding second order artificial dissipation to the problem. The simulations suggest that it is not possible to obtain point-wise convergence using this regularization. Introducing a new measure, a concept of 1-D bubbles, gives hope for other convergence than point-wise.

Secondly, we analyse the non-granular formulation in two space dimensions. Similar results concerning well-posedness and instability is obtained as for the non-granular formulation in one space dimension. Investigation of the time scales of the formulation in two space dimension suggests a sever restriction on the time step, such that explicit schemes are impractical.

Finally, our simulation in one space dimension show that peaks or spikes form in finite time and that the solution is highly oscillatory. We introduce a model problem to study the formation and smoothness of these peaks.

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18

Akritopoulos, Michail. "Combustion modelling of dispersed two-phase flows, applied in circulating fluidised beds." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414215.

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19

Mercier, David. "Large eddy simulation of coupled dispersed phase flows : a statistically-consistent formalism." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASC022.

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La simulation de sprays de carburant aux gouttes de taille variée est d’importance primordiale pour reproduction fidèle du comportement des moteurs aéronautiques. À cette fin, les méthodes de moment eulériennes offrent une stratégie intéressante car elles représentent des statistiques convergées. Ces méthodes ont déjà été utilisées avec succès pour reproduire des tendances macroscopiques telles que la forme de la flamme. Il reste toutefois de nombreux challenges à relever afin d’améliorer leur niveau de précision et de prédiction.Parmi ces challenges, le couplage réciproque entre le spray et la phase gazeuse est un élément majeur. En effet, les méthodes de moments utilisées pour la simulation de sprays de chambres de combustion reposent souvent sur le formalisme mésoscopique eulérien formalisé par Février et al. (2005). Ce formalisme s’appuie sur une moyenne d’ensemble du spray conditionnée à une réalisation de la phase gazeuse. Aucune moyenne d’ensemble n’est envisagée concernant la phase gazeuse qui reste pleinement résolue. Une telle approche est envisageable principalement dans un contexte où la phase dispersée ne rétroagit pas sur la phase gazeuse.Le travail proposé au cours de cette thèse s’attaque à cette difficulté et propose une dérivation étendue du formalisme mésoscopique eulérien qui permet de prendre en compte certains cas de couplage entre la phase dispersée et la phase gazeuse grâce à une approche de simulations aux grandes échelles (LES). Cette solution est particulièrement pertinente car comme le suggère Février et al. (2005), il est souvent observé que la phase dispersée agit en priorité sur les plus petites échelles de la phase gazeuse. C’est pourquoi, dans la lignée de Fox (2003) et Pope (2010), nous sommes amenés à considérer une moyenne conditionnelle du spray par rapport aux éléments résolus de l’écoulement. Afin d’étudier cette construction originale et difficile à approcher de façon concrète, un environnement numérique basé sur des simulations cinématiques a été développé. Les simulations cinématiques permettent de maîtriser l’espace de probabilité associé à l’ensemble des fluides turbulents, ce qui n’aurait pas été possible avec des solutions des équations de Navier-Stokes. Cet outil de simulation a été validé consciencieusement afin d’assurer la convergence des quantités d’intérêt pour l’étude proposée : notamment les moments d’ordre deux de la distribution de particules, ainsi que le contenu fréquentiel de leurs trajectoires. Cet outil a ensuite permis d’évaluer numériquement le comportement du formalisme proposé, en variant le niveau de réduction du champ fluide, de DNS à RANS. On observe alors que dès que l’on travaille avec un champ porteur réduit, ce nouveau formalisme introduit un effet diffusif sur la trajectoire de particules ponctuelles. Pour des temps asymptotiquement longs, les caractéristiques de cette dispersion sont entièrement pilotées par les propriétés du champ turbulent. En revanche, pour les temps courts, cette dispersion est directement impactée par le niveau de réduction du champ fluide. Cette observation est particulièrement intéressante car les gouttes de carburant d’une chambre s’évaporent très rapidement et sont principalement impactées par le régime initial. Pour conclure cette étude, nous étudions quelques fermetures diffusives pour la phase dispersée qui sont adaptées au nouveau formalisme que nous avons introduit et nous présentons quelques perspectives quant à la simulation d’écoulement diphasiques couplés aux grandes échelles
The simulation of the polydisperse fuel sprays is of tremendous importance for high-fidelity descriptions of aeronautical burners. To this end, the Eulerian Moment Methods are an interesting strategy, because of their intrinsic statistical convergence. Such methods have been successfully used to represent macroscopic trends such as the flame shape, but there are still some issues to be tackled in order to increase their level of fidelity and prediction.Among them, the two-way coupling between the spray and the gas phase is critical. Indeed, moment methods used to simulate sprays in burners are often based on the Mesoscopic Eulerian Formalism (MEF) of Février et al. (2005), which considers the ensemble-averaged statistics of the disperse phase conditioned to a unique gas phase. This conditioning is required in order to solve the gas phase without any ensemble averaging such as in RANS methods. Unfortunately, if the disperse phase affects the gas phase, this conditioning may be at least impossible and at most strongly restricted.In this context, the present work investigates the development of a statistical description in the case of a reduced vision of the gas phase, such as the Large Eddy Simulation (LES), and when two-way coupling is taking place between the two phases. This solution is interesting for two-way coupled disperse phase flows, as the retro-coupling can occur at the smallest scales of the flow, with limited impact on the largest scales, as suggested by Février et al. (2005). Beyond the usual description of LES, following Pope (2010) and Fox (2003), we consider a statistical framework of LES under which the statistics are taken as ensemble-averaged over the possible unresolved features. To investigate this solution, a numerical framework using synthetic turbulence is developed, based on a superposition of analytic modes. By doing so, the distribution of modes can be easily controlled, thus enabling the generation of fields with identical large scales. This framework is carefully evaluated to ensure statistical and numerical convergence of the measures of interest, such as particle dispersion. Our formalism is then investigated, focusing on the impact of choosing this framework compared to the initial MEF, from the DNS to the RANS limit. We show that the choice of the formalism has a negligible impact on the diffusion regime of particles in turbulence, but still has a clear impact on the initial transport regime, during which all physics could happen in spray combustion. We finally investigate Lagrangian LES models of the literature in this framework and propose some perspective toward two-way LES of turbulent particulate flows
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JUSTICE, RYAN SCOTT. "INTERFACE MORPHOLOGY AND PHASE SEPARATION IN POLYMER DISPERSED LIQUID CRYSTAL (PDLC) COMPOSITES." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1163783056.

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21

Pullum, Olwen J. "The fabrication and analysis of hard, Si←3N←4-based, dispersed phase composites." Thesis, University of Warwick, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357793.

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22

Lad, Bharat. "A computational method for simulating dispersed two-phase flows using the PDF approach." Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/6030.

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The thesis presents a Probability Density Function (PDF)-derived Eulerian/Eulerian model for the prediction of dispersed two-phase (solid/gas) flows. Continuum equations for the dispersed phase are formulated from the Kinetic Model (KM) PDF transport equations. The Kinetic stresses of the dispersed phase are determined from an algebraic stress model (ASM) together with a KM-based transport equation for the fluctuating kinetic energy. The continuum equations for the continuous phase are assumed to be the same as those in the Eulerian two-fluid model except for the interfacial momentum and energy transfer terms. Closures for these terms are derived from the PDF KM and mirror their counterparts in the dispersed phase equations. Also, the carrier phase turbulence is modelled by the standard k-ε model. These transport equations are solved using the numerical framework of an existing two-fluid approach. Furthermore, the current two-fluid model practice of applying wall functions to impose boundary conditions is adapted for application to the particulate phase. Such wall functions are calculated from the PDF KM itself. In this approach, the PDF equations are pre-integrated using the fully developed flow assumption along the wall to relate wall fluxes to values of the relevant variables in the interior of the flow. Such integration is utilised to create a wall functions database for a range of mean flow conditions. The model is validated against a range of both unbounded and bounded flow cases. Comparisons are made with experimental data as well as the results of other computational methods. It was found that the proposed model performs very well in capturing particulate behaviour and improves, in certain aspects, on the performance of traditional two-fluid models while retaining the practicality of the latter model for industrial applications. In particular, a reasonable capture of the particulate dispersion was observed within jet flows. Improvements were also seen in the prediction of mass flux distribution in shear layers and an accurate capture of near-wall mass distributions in bounded flows.
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23

Back, Alan Joseph. "Mass transfer and radical flux effects in dispersed-phase polymerization of highly hydrophobic monomers." Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/11295.

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24

Gudmundsson, Reymir Levi. "On stability of solutions to the two-fuid models for dispersed two-phase flow." Licentiate thesis, KTH, Numerical Analysis and Computer Science, NADA, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1503.

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In this thesis the two-fluid (Eulerian/Eulerian) formulationfor dispersed two-phase flow is considered. The inviscidformulation in one space dimension is known to be conditionallywell-posed. On the other hand the viscous formulation islocally in time well-posed for smooth initial data, but with amedium to high wave number instability. In this study weconsider two issues.

First, we study the long time behavior of the viscous modelin one space dimension, where we rely on numerical experiments.We try to regularize the problem in a standard way. Thesimulations suggest that it is not possible to regularize in astandard way.

Secondly, we analyze the inviscid formulation in two spacedimensions. Similar condition for well-posedness is obtained asfor the inviscid formulation in one space dimension.

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25

Rius, i. Riu Jaume. "Gas phase molecular relaxation probed by synchrotron radiation experiments." Doctoral thesis, KTH, Physics, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3411.

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This thesis presents experimental studies of gas phasemolecular relaxation after excitation with synchrotron photonsin the 15-35 eV and in the 70-350 eV regions.

In the 15-35 eV region, molecular relaxation by neutraldissociation processes and non

Franck-Condon effects in N2 and O2 molecules have beenstudied by means of dispersed fluorescence and photoelectronspectroscopy experimental techniques, respectively. From thedispersed fluorescence data, excitation functions for themeasured atomic fluorescence spectra have been obtained. Fromthe recorded photoelectron spectra vibrational branching ratioshave been produced. The results obtained reveal that Rydbergseries and singly and doubly excited valence states of theappropriate symmetry energetically accessible in the studiedregion and interactions between themaccount for most of theobserved effects in these two type of experiments.

In the 70-350 eV range, molecular relaxation processesresulting in fragmentation of CD4 and SF6 after absorption ofsynchrotron light have been studied by energy resolved electronion coincidence technique using a multicoincidence experimentalstation developed by our group during the last five years forsuch type of experiments. The coincidence measurements yieldedmass spectra from which information about the kinematics of thedetected fragments has been deduced by means of Monte Carlosimulations of the experimental peak shapes. The obtainedresults show completely different dissociation patternsdepending on the molecular electronic states studied. Thesepatterns reflect the bonding properties of the excited orbitalsand they permit the description and in some cases theidentification of the different molecular relaxation pathwaysobserved. The achievements presented in this thesis exemplifythe potential of the multicoincidence station used in thereported experiments.

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Albertsson, Galina. "Effect of the presence of a dispersed phase (solid particles, gas bubbles) on the viscosity of slag." Thesis, KTH, Mikro-modellering, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-133495.

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The viscosities of a set of silicone oils containing different size ranges of charcoal or paraffin particles as well as the viscosities of silicone oil foams were measured at room temperature in order to determine the effect of dispersed phase on the viscosity of a liquid and its effect on foaming ability. The effective viscosity of the samples increased with volume fraction of the second phase. The foaming ability was improved by the presence of the particles. The improved foaming effect was for the most part not a result of the increased viscosity. No connection between the particle size and the effective viscosity could be determined. On the other hand particle morphology and the particle size distribution had effect on the effective viscosity. The viscosity data were compared with a number of existing equations for the estimation of effective viscosity. Einstein-Roscoe equation is suitable for two-phase mixtures containing globular particles with narrow particle size distribution and low interfacial tension. New mathematical models are required for effective viscosity prediction, where the suspending phase viscosity, effect of the interfacial tension, as well as the particle morphology should be taken in consideration.
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27

Moss, Thomas Strong III. "The chemical vapor deposition of dispersed phase composites in the B-Si-C-H-Cl-Ar system." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/19040.

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Cho, Yong Gyun 1965. "The effect of concentration of the dispersed phase on morphology evolution in high viscosity ratio polymer blends /." Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38471.

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In order to obtain some insight into the deformation behavior of the dispersed phase in the various flows and to evaluate the effects of various variables such as concentration of the dispersed phase and viscosity ratio, affine deformation equations were derived for some stratified shear and elongational flows. It was shown by the derived deformation equations that the volume fraction of the dispersed phase is a factor affecting the deformation of the dispersed phase, and the effect depends on viscosity ratio. The results from the stratified simple shear flow model predict that, for viscosity ratio >1, the deformation rate increases with the volume fraction, and the shear stress also increases, leading to the increase of the breakup time. Therefore, the total deformation of the dispersed phase, before breakup, increases with the increase of the volume fraction, resulting in the decrease of the size of the dispersed phase particles. The prediction was verified experimentally, in both the Haake batch mixer and the Couette flow mixer, using polyethylene/polyamide-6 blends compatibilized by adding maleic anhydride grafted polyethylene, when coalescence was suppressed. In the analysis of particle size data for the verification of the volume fraction effect, an effort was made to identify the contribution of coalescence. The experimental results of particle sizes in 1 wt% blends of the Haake mixer are in reasonable agreement with the transient deformation and breakup theory for simple shear flow. This suggests that the dominant flow in the mixer was shear flow. In some reactively compatibilized blends, at high shear rate, the particle sizes showed a maximum when either the weight fraction or the shear rate was increased. This behavior may be explained by coalescence effects related to the redistribution of the produced copolymers at the interface. It was shown experimentally that, for very high viscosity ratio (>3.5∼4), the deformation of large drops between gaps i
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29

Shah, Anant Pankaj. "Development and application of a dispersed two-phase flow capability in a general multi-block Navier Stokes solver." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/36101.

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Gas turbines for military applications, when operating in harsh environments like deserts often encounter unexpected operation faults. Such performance deterioration of the gas turbine decreases the mission readiness of the Air Force and simultaneously increases the maintenance costs. Some of the major factors responsible for the reduced performance are ingestion of debris during take off and landing, distorted intake flows during low altitude maneuvers, and hot gas ingestion during artillery firing. The focus of this thesis is to study ingestion of debris; specifically sand. The region of interest being the internal cooling ribbed duct of the turbine blade. The presence of serpentine passages and strong localized cross flow components makes this region prone to deposition, erosion, and corrosion (DEC) by sand particles. A Lagrangian particle tracking technique was implemented in a generalized coordinate multi-block Navier-Stokes solver in a distributed parallel framework. The developed algorithm was validated by comparing the computed particle statistics for 28 microns lycopodium, 50 microns glass, and 70 microns copper with available data [2] for a turbulent channel flow at Ret=180. Computations were performed for a particle-laden turbulent flow through a stationary ribbed square duct (rib pitch / rib height = 10, rib height / hydraulic diameter = 0.1) using an Eulerian-Lagrangian framework. Particle sizes of 10, 50, and 100 microns with response times (normalized by friction velocity and hydraulic diameter) of 0.06875, 1.71875, and 6.875 respectively are considered. The calculations are performed for a nominal bulk Reynolds number of 20,000 under fully developed conditions. The carrier phase was solved using Large Eddy Simulation (LES) with Dynamic Smagorinsky Model [1]. Due to low volume fraction of the particles, one-way fluid-particle coupling was assumed. It is found that at any given instant in time about 40% of the total number of 10 micron particles are concentrated in the vicinity (within 0.05 Dh) of the duct surfaces, compared to 26% of the 50 and 100 micron particles. The 10 micron particles are more sensitive to the flow features and are prone to preferential concentration more so than the larger particles. At the side walls of the duct, the 10 micron particles exhibit a high potential to erode the region in the vicinity of the rib due to secondary flow impingement. The larger particles are more prone to eroding the area between the ribs and towards the center of the duct. At the ribbed walls, while the 10 micron particles exhibit a fairly uniform propensity for erosion, the 100 micron particles show a much higher tendency to erode the surface in the vicinity of the reattachment region. The rib face facing the flow is by far the most susceptible to erosion and deposition for all particle sizes. While the top of the rib does not exhibit a large propensity to be eroded, the back of the rib is as susceptible as the other duct surfaces because of particles which are entrained into the recirculation zone behind the rib.
Master of Science
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Dimitrova, Desislava Nikolova [Verfasser], Johannes [Akademischer Betreuer] Janicka, and Peter [Akademischer Betreuer] Stephan. "On the Reliability of Large-Eddy Simulation for Dispersed Two-Phase Flows / Desislava Nikolova Dimitrova. Betreuer: Johannes Janicka ; Peter Stephan." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2011. http://d-nb.info/1105562336/34.

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31

Gotteland, Delphine. "Procédé d’hydroconversion par catalyse dispersée des résidus lourds pétroliers." Thesis, Lyon 1, 2011. http://www.theses.fr/2011LYO10198.

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32

Gardner, Taylor. "Study of Water Wetting in Two-Phase Oil-Water Flow in an Annular Channel." Ohio University Honors Tutorial College / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1524844271362932.

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33

Albarzenji, Dlir. "Design, development and application of a novel seven-sensor probe system for the measurement of dispersed phase flow properties in multiphase flows." Thesis, University of Huddersfield, 2018. http://eprints.hud.ac.uk/id/eprint/34657/.

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Local measurements of the dispersed phase properties in air-water bubbly flows are of primary importance to understand the hydrodynamic characteristics of multiphase flows. One of the essential requirements in designing multiphase flow systems is to determine its flow regime since many constitutive models are flow regime dependent. In bubbly multiphase flow, the bubble diameter plays a vital role in hydrodynamics of flow. In this study, a novel invasive measuring instrumentation system has been designed and developed to determine the bubble size and shape accurately by minimising the effects of the bubble-sensor interactions. This instrumentation system has been used to determine the effects of the bubble size on the volume fraction distribution and the hydrodynamic behaviour of air-water two-phase flow. The novelty of this probe arises from the fact that the data is collected from the first bubble-sensor contact, unlike the previous methods in which the data has been collected from two points namely, first when the sensors’ tips immersed a bubble and second when the sensors’ tips left the bubble. The seven-sensor conductivity probe subsequently has been used to determine the dispersed phase local parameters. These parameters include bubble velocity, time-averaged local void fraction and bubble shape and size. The data from this probe has been acquired using National Instruments Data Acquisition (DAQ) and LabVIEW software. The experiments have comprised of two methods, namely bubble column and flow loop. For the bubble column experiments, a new image processing code has been developed for capturing the dispersed phase properties, including the void fraction from the images that have been captured by the high-speed cameras. From the comparison between both methods, the seven-sensor probe and the high-speed camera measurements, good agreement has been achieved. In the flow loop experiments, the novel seven-sensor probe system has been used for measuring the dispersed phase properties from the first bubble sensor contact; moreover, the effect of variation of gas superficial velocity, with the values of 0.05, 0.07 and 0.1 m/s, on the dispersed phase properties have been also investigated.
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34

Dehghani, Kiadehi Atena. "Development of a new technique for determining the RTD of a dispersed solid phase and its application in a deep fluidized bed." Thesis, Compiègne, 2019. http://www.theses.fr/2019COMP2491.

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L'objectif de cette thèse est le développement d’une nouvelle technique expérimentale de détermination de la distribution des temps de séjour (DTS) des particules solides dans les enceintes de manutention et de transformation de solides particulaires ainsi que le développement d’un modèle. Dans un premier temps, une nouvelle méthode optique a été développée pour mesurer la DTS des particules. Les expériences sont réalisées avec le carbure de silicium (SiC) et le pigment phosphorescent (Lumilux® Green SN-F50 WS) a été utilisé en tant que traceur. Une étude expérimentale préliminaire a été réalisée dans un lit fluidisé bouillonnant simple afin de valider la méthodologie proposée de mesure de la DTS. Dans un deuxième temps, la technique développée de la mesure de concentration a été appliquée à la détermination de la DTS dans un lit fluidisé profond. Les courbes de la DTS des particules sont déterminées expérimentalement dans différentes conditions opératoires. Dans un troisième temps, un modèle basé sur une combinaison de réacteurs idéaux est proposé pour prédire la DTS des particules du lit fluidisé étudié. Les valeurs de sortie prédites sont ensuite comparées aux données expérimentales pour l’ajustement du modèle
The aim of the present thesis is to develop a novel experimental technique for determining the residence time distribution (RTD) of solid particles in solid unit operations as well as model development. Initially, a novel optical method was developed to measure the particle RTD. Experiments are carried out with Silicon Carbide (SiC) and the pigment phosphorescent (Lumilux® Green SN-F50 WS) as tracer particle. A preliminary experimental study was conducted in a simple bubbling fluidized bed in order to validate the proposed RTD measurement methodology. In the second step, the developed technique of the concentration measurement was applied to measure the RTD of a deep fluidized bed. The particle RTD curves are determined experimentally in different operating conditions. Finally, a model consisting of the combination of the ideal reactors is proposed to predict the particle residence time distribution in the studied fluidized bed. The predicted output values are then compared with the experimental data to establish a good model fitting data
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35

Le, Touze Clément. "Couplage entre modèles diphasiques à « phases séparées » et à « phase dispersée » pour la simulation de l’atomisation primaire en combustion cryotechnique." Thesis, Nice, 2015. http://www.theses.fr/2015NICE4088/document.

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Les écoulements diphasiques jouent un rôle prépondérant dans les moteurs-fusées à ergols liquides cryogéniques, équipant par exemple les lanceurs de la famille Ariane. L'étude expérimentale de tels engins propulsifs étant complexe et onéreuse, disposer d'outils numériques à même de simuler fidèlement leur fonctionnement se révèle être un objectif aussi important qu'ambitieux. La difficulté majeure réside dans le caractère fortement multi-échelles du problème, si bien qu’aucune approche numérique existante n'est capable à elle seule de décrire parfaitement l'ensemble des échelles liquides. Partant de ce constat, les travaux présentés dans cette thèse visent à mettre en place une stratégie de couplage entre des modèles bien adaptés aux différentes topologies d'écoulement diphasique, et ce dans le cadre de la plateforme logicielle multi-physique CEDRE développée par l'ONERA. La démarche adoptée consiste précisément à coupler un modèle à interface diffuse de type ``4 équations'' pour les zones à phases séparées, et un modèle cinétique eulérien pour la phase dispersée, rendant ainsi possible la description de l’atomisation primaire. Par ailleurs, les conditions sévères qui règnent dans les moteurs cryotechniques, où de forts gradients de température, vitesse et densité sont rencontrés, mettent à l'épreuve la robustesse des méthodes numériques. Une nouvelle méthode MUSCL multipente pour maillages non structurés généraux a ainsi été développée, permettant d’améliorer la robustesse et la précision des schémas de discrétisation spatiale. L’ensemble de la stratégie de couplage est finalement appliquée à la simulation du banc Mascotte de l'ONERA pour la combustion cryotechnique
Two-phase flows play a significant role for the proper functioning of cryogenic liquid-propellant rocketengines, such as those that equip the launchers of the Ariane family. Since the experimental investigationof such propulsion devices is complex and expensive, developing numerical tools able to accuratelysimulate their functioning, is a crucial but nonetheless ambitious objective. The major difficulty is due tothe multiscale nature of the problem, as a result of which there is currently no numerical approach ableto perfectly describe all the liquid scales on its own. Based on this observation the work presented in thisthesis aims at setting up a coupling strategy between models well-adapted to each two-phase flowtopology, in the framework of the ONERA’s multiphysics CEDRE software. The approach adoptedprecisely consists in coupling a 4-equation diffuse interface model for the separated phases and aeulerian kinetic model for the dispersed phase, thus making it possible to describe primary atomization.Besides, the harsh conditions within cryogenic rocket engines, where large temperature, velocity anddensity gradients are encountered, severely challenge the robustness of numerical methods. A newmultislope MUSCL method for general unstructured meshes is thus developed in order to improve therobustness and accuracy of space discretization schemes. The whole coupling strategy is finally appliedto the numerical simulation of the ONERA’s Mascotte test bench for cryogenic combustion research
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36

Pushparajalingam, Jegan Sutharsan. "Simulations expérimentale et numérique des phénomènes de ruissellement et d’atomisation lors d’une procédure de lavage à l’eau." Thesis, Toulouse, ISAE, 2012. http://www.theses.fr/2012ESAE0005/document.

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Celui-ci a pour objectif de valider l'ensemble des modèles physiques utilisés dans un code de simulation numérique pour simuler un écoulement de type annulaire dispersé en conduite rencontré lors d'une procédure de lavage à eau utilisé dans les raffineries. Pour ce faire une banque de données expérimentale est mise en place sur des configurations représentatives de celles utilisées en condition industrielle. La géométrie retenue comporte une zone horizontale d'injection rectiligne avec un injecteur central, suivi d'un coude à 90° situé dans un plan vertical. Différentes conditions expérimentales permettent d'étudier l'influence de la vitesse du gaz, de la condition d'injection du brouillard et de la pression sur les différents processus physiques. Ces résultats comprenant des visualisations du brouillard et du film pariétale, des mesures de taille et de distribution de gouttes,des mesures de débit et d'épaisseur de film, sont analysés pour faire ressortir les principaux mécanismes d'interaction entre le gaz et la phase dispersée, le gaz et le film liquide pariétal et la phase dispersée et le film pariétal. En parallèle, des premières simulations, avec une approche RANS, sont réalisées avec le code CEDRE de l'ONERA et les résultats sont confrontés aux mesures
This work has been realised within a CIFRE contract with TOTAL. Its aim was to validate all the physical models used in a computation, which simulates an annular dispersed flow through a pipe used in a water washing process in refinery plants. That is why, a whole set of data has been gathered using experimental boundary conditions which are representative to those used in industrial configurations. The geometry is made of a horizontal pipe with a centred nozzle followed by a 90º elbow in the vertical plane. Several experimental boundary conditions enable one to study the influence of the gas velocity, the type of the spray injection and the pressure on the different physical phenomena. These results including spray and liquid film visualisations, droplets distribution and size measurements as well as liquid film thickness and mass flow measurements were analysed in order to extract the main interaction mechanism between the gas and the dispersed phase, the gas and the liquid film, and the dispersed phase and the annular liquid film. Meanwhile, simulations using a RANS approach were realized with the ONERA code named CEDRE and its results were compared to the gathered measurements
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37

Echeverri, Mauricio. "Phase Diagram Approach to Fabricating Electro-Active Flexible Films: Highly Conductive, Stretchable Polymeric Solid Electrolytes and Cholesteric Liquid Crystal Flexible Displays." University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1352949368.

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38

Keita, Sana. "Eulerian Droplet Models: Mathematical Analysis, Improvement and Applications." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37907.

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The Eulerian description of dispersed two-phase flows results in a system of partial differential equations describing characteristics of the flow, namely volume fraction, density and velocity of the two phases, around any point in space over time. When pressure forces are neglected or a same pressure is considered for both phases, the resulting system is weakly hyperbolic and solutions may exhibit vacuum states (regions void of the dispersed phase) or localized unbounded singularities (delta shocks) that are not physically desirable. Therefore, it is crucial to find a physical way for preventing the formation of such undesirable solutions in weakly hyperbolic Eulerian two-phase flow models. This thesis focuses on the mathematical analysis of an Eulerian model for air- droplet flows, here called the Eulerian droplet model. This model can be seen as the sticky particle system with a source term and is successfully used for the prediction of droplet impingement and more recently for the prediction of particle flows in air- ways. However, this model includes only one-way momentum exchange coupling, and develops delta shocks and vacuum states. The main goal of this thesis is to improve this model, especially for the prevention of delta shocks and vacuum states, and the adjunction of two-way momentum exchange coupling. Using a characteristic analysis, the condition for loss of regularity of smooth solutions of the inviscid Burgers equation with a source term is established. The same condition applies to the droplet model. The Riemann problems associated, respectively, to the Burgers equation with a source term and the droplet model are solved. The characteristics are curves that tend asymptotically to straight lines. The existence of an entropic solution to the generalized Rankine-Hugoniot conditions is proven. Next, a way for preventing the formation of delta shocks and vacuum states in the model is identified and a new Eulerian droplet model is proposed. A new hierarchy of two-way coupling Eulerian models is derived. Each model is analyzed and numerical comparisons of the models are carried out. Finally, 2D computations of air-particle flows comparing the new Eulerian droplet model with the standard Eulerian droplet model are presented.
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Farrar, B. "Hot-film anemometry in dispersed oil-water flows : Development of a hot-film anemometer based measurement technique for detailed studies of complex two-phase flows and its application.........bubbly water-kerosene and water-air flows." Thesis, University of Bradford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234685.

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40

Hantz-Brachet, Edith. "Etude d'émulsions et de vésicules unilamellaires d'intérêt biologique ou pharmaceutique par diffusion quasiélastique de la lumière et spectroscopie vibrationnelle." Paris 13, 1989. http://www.theses.fr/1989PA132009.

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41

Guibu, Pereira Gabriel. "Modélisation numérique d'écoulements turbulents avec entraînement d'air au sein d'ouvrages hydrauliques." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAD023.

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La dispersion de l'air dans l'eau est un phénomène observé fréquemment pour une large variété , d'écoulements dans des structures hydrauliques, qu'elles soient naturelles ou conçues par l'homme. Or, la présence de bulles d'air immergées dans l'eau modifie de façon significative les caractéristiques de l'écoulement. Ces modifications peuvent être bénéfiques ou nuisibles selon la situation. En particulier, dans le contexte des milieux confinés des réseaux d'eaux urbains, l'évaluation du transport d'air est un facteur important pour le dimensionnement des ouvrages, tels que les puits de chute. Le travail présenté dans cette thèse s'intéresse à l'identification et au développement des techniques de modélisation numérique tridimensionnelle, permettant de mieux évaluer les interactions eau-air et le transport diphasique dans le contexte des ouvrages hydrauliques. Une approche de modélisation diphasique hybride est implémentée, dans le but de représenter les écoulements à la fois en régime ségrégué et dispersé. Différentes méthodologies ont ainsi été appliquées pour simuler des écoulements aérés, et leurs résultats ont été confrontés à des mesures expérimentales
The mixing and dispersion of air into water is a frequently observed feature of flows occurring in nature and in man-made hydraulic structures. The addition of immersed air bubbles in the water modifies substantially the flow's characteristics, which may have a desirable or harmful effect depending on the context. Furthermore, the assessment of the air currents is of value in the study of confined spaces. For instance, this is important in the design of air vents in structures such as dropshafts in sewage systems. This thesis focuses on identifying and developing three-dimensional computational models for a better description of air-water interactions and two-phase flows in the context of hydraulic structures. A hybrid two-phase modelling approach is implemented in this thesis, thus allowing the simultaneous representation of segregated and dispersed flow regimes. The results from different methods employed for the aerated flow simulations are finally confronted with experimental data
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42

Jager, Lezer Nathalie. "Caracterisations rheologiques de systemes disperses d'interet cosmetique : correlation avec la microstructure." Paris 11, 1998. http://www.theses.fr/1998PA114813.

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43

Elsden, M. "A transport model for dispersed two - phased flows : development and implementation." Thesis, Cranfield University, 1995. http://hdl.handle.net/1826/3963.

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Two-phase flows are found in many industrial and natural processes, from the combustion chambers of aero-engines to silt transport in rivers. The interaction between the two, or more, phases is extremely complex and is not amenable to analytical solution. Though equations exist to describe the behaviour of each of the phases, the direct solution of these equations, for all but the simplest flows, is beyond current computer power. Because of this much work is being done to develop computationally tractable models which are capable of predicting the behaviour of these flows well. This thesis presents a new form of model based on a joint Eulerian-Lagrangian approach. This model is termed a transport model and consists of solving the second phase conservation equations in an Eulerian frame while introducing Lagrangian effects though a particle diffusion coefficient. This thesis consists of three parts. First the development of the method used to obtain particle diffusion coefficients is presented and tested against available experimental data. This is followed by a discussion of the Eulerian calculation procedure used for both the carrier and discrete phase. Finally the linking of the two calculation procedures is discussedin detail and the model's performance is evaluated against both experimental data and a range of other models found in the literature. The transport model is shown to perform well in predicting the chosen test-cases. Further, the results are shown to be comparable to, or better than, those of the other models considered. One of the main benefits of the model is its low computational overhead. All calculations presented here were performed on a desktop personal computer. Finally some recommendations are made for further work.
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44

Mukhopadhyay, Amartya. "Fabrication and properties of oxide nanocomposites containing uniformly dispersed second phases." Thesis, University of Oxford, 2009. https://ora.ox.ac.uk/objects/uuid:094c8b45-49b8-4518-8257-c1fd3ebbd8b2.

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The present research addresses some of the major problems pertaining to two different types of ceramic nanocomposite; viz. participate reinforced polycrystalline alumina-based nanocomposites and multiwalled carbon nanotube (MWCNT) reinforced aluminoborosilicate glass/ceramic (ABS) nanocomposites. With respect to the former, a novel and economical processing route based upon solid solution-precipitation technique is explored. Dense and homogeneous solid solutions of 10 wt.% Fe2O3 in Al2O3 were produced by pressureless sintering at 1450°C in air. Aging of the solid solutions in a reducing atmosphere at temperatures in the range 1250°C-1550°C for different durations (up to 50 h) resulted in the precipitation of FeAl2eO4 as second phase particles throughout the bulk of the samples. The optimum aging schedules resulted in a final microstructure comprising nanosized (~ 100 nm) intragranular FeAl2eO4 particles, along with coarser micro-sized particles along the matrix grain boundaries and triple point corners. The hybrid nano/micro composites possessed improved fracture toughness (by ~ 40%), flexural strength (by ~ 50%) and abrasive wear resistance (by a factor of ~ 2.5) with respect to monolithic Al2O3. With respect to the ABS-MWCNT nanocomposites, we report here the ability to develop dense nanocomposites, containing uniformly dispersed nanotubes up to a content of 10 wt.%, by an ultrasonication-assisted sol-gel technique followed by hot pressing. The optimised ABS-10 wt.% MWCNT nanocomposite possessed nearly double the strength, and a fracture toughness improvement of ~ 150% with respect to the unreinforced ABS. The carbon nanotubes have been observed to bridge crack openings of the order of ~ 100 nm which provides the major contribution towards the improvement in fracture toughness. The nanocomposites, showed an electrical percolation threshold of between 2.5 to 5 wt.% MWCNT and possessed significantly higher electrical conductivities (by a factor of 106) with respect to the unreinforced ABS glass/ceramic. Furthermore, 40% improvement in thermal conductivity (~ 1.8 W m-1 K1) over that of unreinforced ABS glass/ceramic was recorded with ABS-15 wt.% MWCNT nanocomposite.
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45

Aguirre-Puente, Jaime. "Problemes de changement de phase dans les milieux disperses contenant de l'eau." Paris 6, 1988. http://www.theses.fr/1988PA066623.

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46

Atay, N. Z. "Transport and interfacial exchange kinetics in one- and two-phase disperse systems." Thesis, University of Kent, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374831.

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47

Mfegue, Nkili Augustin. "Contribution a l'etude des ecoulements diphasiques a phase dispersee avec apport de chaleur." Paris 6, 1996. http://www.theses.fr/1996PA066290.

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Ce travail de these est consacre a l'etude d'ecoulements en conduite avec transfert de masse et de chaleur. On construit d'abord un modele monophasique qui tient compte de la geometrie de l'installation industrielle (tubes verticaux descendants et ascendants). L'apport de chaleur est une donnee experimentale. Les variables physiques sont calculees numeriquement le long de l'ecoulement, et representees graphiquement. Ainsi a partir des conditions a l'entree, nous pouvons connaitre l'evolution des variables physiques le long du tube. Dans un second temps, apres avoir donne quelques definitions concernant les ecoulements diphasiques et le formalisme qui conduit a l'ecriture des equations, nous presentons un modele tenant compte de la physique particuliere de l'ecoulement considere. La modelisation de certains termes a ete faite: on a pu ainsi donner une expression de la densite de force interfaciale dans le cas ou il y a un transfert de masse et de chaleur. Ensuite un modele diphasique unidirectionnel (d-u) a ete construit. L'etude numerique de ce modele en situation stationnaire est faite dans les deux cas suivants: sans transfert et avec transfert de masse de chaleur. Nous avons simule plusieurs ecoulements en fonction des parametres que sont la concentration initiale des bulles, le diametre des bulles, le coefficient de frottement a la paroi et le parametre intervenant dans l'expression de la force de masse ajoutee. L'influence de ces parametres sur l'evolution des variables physiques le long de la conduite a ete etudie. Le modele diphasique (d-u) a montre ses limites pour des bulles de petite taille. De plus cette etude permet de predeterminer les conditions de sortie d'un ecoulement en fonction des conditions d'entree
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48

Ciardo, Diletta. "Quantitative analysis of the regulation of the DNA replication program by the intra-S phase checkpoint in Xenopus embryos Checkpoint control of the spatio-temporal regulation of DNA replication in Xenopus early embryos Polo-like kinase 1 (Plk1) is a positive regulator of DNA replication in the Xenopus in vitro system On the Interplay of the DNA Replication Program and the Intra-S Phase Checkpoint Pathway Genome wide decrease of DNA replication eye density at the midblastula transition of Xenopus laevis Polo like kinase 1 promotes dispersed replication origin firing during S phase." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS478.

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Dans les organismes multicellulaires, plusieurs millier d’origines initient la réplication de l'ADN. Elles sont regroupées en domaines qui se répliquent tôt ou tard au cours de la phase S (origines précoces ou tardives). L'un des mécanismes régulant le programme de réplication est un point de contrôle intra phase S qui dépend des kinases ATR et Chk1. Cette voie est activée par un stress réplicatif engendré par le blocage des fourches de réplication aux origines précoces, en retour elle inhibe l’activation des origines tardives. Il a été proposé, que la protéine Polo-Like-Kinase 1 (Plk1) soit responsable du déclenchement des origines situées à proximité des fourches bloquées en cas de stress réplicatif. Cependant, aucune analyse de l’activation des origines n’a jamais été réalisée au cours d’une phase S non perturbée lorsque Plk1 est absente. Pour avoir une vue globale et unifiée du processus de réplication de l'ADN, des modèles numériques et analytiques ont été construits dans le passé, mais aucun d'eux n'intègrent le rôle de Chk1 et Plk1. L'objectif de ma thèse était d’étudier expérimentalement et analytiquement de quelle manière Chk1 peut réguler le déclenchement des origines dans l'espace et dans le temps. En particulier, de comprendre si Plk1 pouvait être impliquée dans cette régulation pendant une phase S non perturbée, à cette fin, j'ai utilisé le système réplicatif des extraits d’œuf de Xénopes. En premier lieu, j'ai intégré dans un modèle numérique l’action de Chk1 pour reproduire le programme de réplication du système Xénope. J'ai testé différents scénarios puis j’ai utilisé des données de peignage d'ADN obtenues précédemment dans des conditions d'inhibition de la kinase Chk1. Les simulations Monte Carlo obtenues ont été ajustées aux données expérimentales en optimisant les valeurs des paramètres libres des modèles. J'ai trouvé qu'il fallait ajouter deux hypothèses aux modèles de réplication développés précédemment: 1) la présence d’une forte inhibition du déclenchement des origines par Chk1 à partir du début de la phase S 2) la présence de domaines génomiques répliquant précocement et qui échappent à cette inhibition. Deuxièmement, j'ai montré expérimentalement que, Plk1 actif est recrutée sur la chromatine avant le début de la phase S non perturbée et qu'en l'absence de Plk1, la réplication de l'ADN est ralentie. De plus, l’absence de Plk1 entraîne une augmentation de la phosphorylation de Chk1 et une diminution de l’activité de la kinase Cdk2, ce qui suggère que Plk1 inhibe Chk1. En réalisant des expériences de peignage d’ADN, j'ai démontré qu’en l’absence de Plk1 on observe une baisse du niveau d’activation des origines. L'analyse de ces données par mon modèle numérique suggère que Plk1 régule négativement l’action de Chk1 levant ainsi son action inhibitrice sur l’activation globale des origines. Cet effet concorde avec mes observations expérimentales. Il semble cependant que Plk1 n’agisse pas à proximité directe des fourches de réplication, comme cela avait été proposé précédemment. Enfin, en assimilant le processus de réplication à un processus de nucléation et de croissance unidimensionnel, j'ai développé une nouvelle approche quantitative pour étudier la régulation du programme de réplication. Cette approche lie la similarité entre les profils spatiaux de réplication d'une molécule unique et les processus de régulation de la réplication de l'ADN. En analysant les données de peignage d'ADN, j'ai montré que le programme de réplication de l'ADN des embryons précoces de Xénope est régulé par deux processus exclusifs dans l'espace et dans le temps. L’un avec une fréquence faible d’activation des origines et une vitesse apparente de fourches élevée et un second, régulé par Plk1, présentant une fréquence d’activation élevée des origines avec une vitesse apparente de fourches faible
The initiation of DNA replication in multicellular organisms starts from several thousand genomic loci called replication origins. They are grouped into domains which replicate early or late during S phase. The firing of a replication origin creates two diverging replication forks that replicate flanking DNA. One of the mechanisms regulating DNA replication program is the ATR/Chk1 dependent intra-S phase checkpoint. This pathway is activated by replicative stress due to stalled replication forks at early firing origins and in turn, inhibits the late firing of origins. It has been proposed that the checkpoint recovery kinase Plk1 (Polo-Like-Kinase 1) could be responsible for allowing origin firing close to stalled forks in replication stress conditions. However, origin firing has not been analysed after Plk1 inhibition or depletion during unperturbed S phase. To assemble a comprehensive and unified view of the DNA replication process numerical and analytical models have been built in the past, but none of them integrates the role of checkpoint pathways. The goal of my thesis was to investigate experimentally and analytically how the checkpoint regulates the firing of origins in space and time and, in particular, whether the Plk1 is implicated in the regulation of origin firing during unperturbed S phase. To this end, I used the Xenopus in vitro system. First, I integrated in a numerical model the checkpoint pathway to describe the replication program in the Xenopus in vitro system. I tested different scenarios and used DNA combing data previously obtained by the laboratory after the inhibition of the checkpoint kinase Chk1. Monte Carlo simulated data were fitted to experimental data by optimizing the values of free parameters of models using a genetic algorithm. I found that two new hypothesis should be added to formerly built replication models: 1) a strong inhibition of origin firing by Chk1 from the beginning of S phase 2) the presence of early replicating genomic domains that evade the origin firing inhibition. Second, I experimentally showed that during unperturbed S phase active Plk1 is recruited to chromatin before the start of S phase and that in the absence of Plk1, DNA replication is slowed down. Moreover, Plk1 depletion led to an increase in Chk1 phosphorylation (p-Chk1) and a decrease of Cdk2 activity, suggesting that Plk1 inhibits the intra-S phase checkpoint. Performing DNA combing, I demonstrated that Plk1 depletion leads to a decrease in origin firing level. Analysis of the combing data by the developed numerical model suggested that during unchallenged S phase Plk1 down regulates the global origin firing inhibitory action of Chk1, consistent with the experimental observation of increased level of p-Chk1 in Plk1 depleted Xenopus egg extract. However, Plk1 does not seem to act close to replication forks as was proposed earlier. Finally, by considering replication process as a one-dimensional nucleation and growth process and using statistical methods, I developed a new quantitative approach to study the regulation of replication program. This approach links the similarity between single molecule replication patterns to DNA replication regulating processes. By analyzing DNA combing data, I showed that DNA replication program in Xenopus early embryos is regulated by two spatially and temporally exclusive processes. One with low frequency of origin firing and high apparent fork speed and a second, controlled by PlK1, with a high frequency of origin firing and a low apparent fork speed. Altogether my results demonstrate that Plk1 positively regulates replication origin firing during normal S phase by down regulating the replication checkpoint. The numerical model predicts the existence of replication timing domains in the Xenopus model system. Future work will show whether Plk1 regulates the replication program at the level of genomic domains
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49

Voronetska, Kateryna. "Simulation numérique directe des écoulements à phases dispersées." Thesis, Bordeaux 1, 2012. http://www.theses.fr/2012BOR14507/document.

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Dans l'industrie du pétrole et des moteurs, les écoulements de fluides non-miscibles sont fréquemment rencontrés : écoulements d'hydrocarbures dans les conduites, séparation en production, injection de carburant dans les moteurs, procédés de raffinage, etc.Pour modéliser ce type d'écoulement, deux approches sont possibles. Soit l'écoulement est décrit de façon macroscopique et les phénomènes locaux (rupture et coalescence des gouttes, glissement des phases, compaction locale, etc.) sont modélisés à l'aide de lois de fermeture analytiques ou empiriques. Soit l'écoulement est modélisé de manière directe à l'échelle de la goutte et on s'attache à décrire précisément l'interface et les interactions entre les phases. C'est cette dernière approche que nous avons proposé d'adopter pour étudier des écoulements à phase dispersée liquide-liquide, et plus particulièrement les phénomènes de rupture et coalescence, collision ou déformation de gouttes. Ainsi, le but principal de ce travail de thèse a été le développement d'un code de simulation numérique directe capable de modéliser un écoulement diphasique liquide-liquide, afin d'étudier en détail les effets de coalescence et de rupture entre les gouttes. Ce travail a nécessité l’utilisation d’une technique de suivi d’interface appropriée et le développement d’un solveur des équations de Navier-Stokes incompressible pour calculer le champ de vitesse, ainsi qu’une méthode de couplage entre ces deux solveurs pour la simulation des écoulements diphasiques. Notre outil numérique a été validé sur de nombreux cas tests académiques et appliqué à l'étude du processus de séparation liquide-liquide
The flow of immiscible fluids is a frequent issue in the petroleum industry: hydrocarbon in pipelines, separation process for production, fuel injection in engines, refinery treatment processes, etc.There are two possible approaches to model this type of flow. In the first one, the flow is described macroscopically. In this case, local phenomena (breakage or coalescence of droplets, phase slip, local compaction) are modeled thanks to analytic closure laws or empiric laws. In the second approach, the flow is simulated indirectly on a scale of droplet and we want to describe precisely the interface and the interactions between phases. We propose here to consider the second method to study liquid/liquid dispersed flows and especially the phenomena of breakage or coalescence and collision or distortion of the droplets.Thus, the main purpose of this work was the development of a direct numerical simulation code that is capable to model a liquid-liquid two-phase flow, in order to study in detail the effects of droplets coalescence and breakage. To model a two-phase flow, it is necessary to choose an appropriate interface tracking method and to develop a solver for Navier-Stokes incompressible equations to compute the velocity and pressure values. Also, a coupling method that is able to handle the discontinuous quantities at the interface has to be implemented. Our numerical tool has been validated on numerous academic test cases and applied to study the process of liquid-liquid separation
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50

Vié, Aymeric. "Simulation aux grandes échelles d'écoulements diphasiques turbulents à phase liquide dispersée." Phd thesis, Institut National Polytechnique de Toulouse - INPT, 2010. http://tel.archives-ouvertes.fr/tel-00620754.

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Les écoulements diphasiques turbulents sont présents dans de nombreux systèmes industriels (moteur à piston, turbines à gaz, moteurs fusée...). La compréhension fine de telles configurations s'avèrent de nos jours nécessaire pour limiter notamment les émissions de polluants et de gaz à effet de serre, et la consommation des énergies fossiles. Nous nous intéressons ici à la simulation aux grandes échelles des écoulements diphasiques turbulents, permettant de capturer une large partie du spectre de la turbulence, et ainsi être capable de prédire des phénomènes instables ou transitoires. La phase dispersée est ici modélisée par une approche eulérienne, en raison de ses avantages dans le contexte du calcul haute performance. Le travail de cette thèse a consisté à étendre le formalisme eulérien existant dans le code AVBP à la simulation de sprays polydisperses dans des écoulements turbulents. Pour cela, le Formalisme Eulérien Mésoscopique (FEM) a été couplé à une approche Multi-fluide. Cette nouvelle approche, intitulée Formalisme Eulérien Mésoscopique Multi-fluide (FEMM), a été évaluée sur des cas simples canoniques, permettant de bien caractériser le comportement autant en terme de dynamique turbulente que d'effets polydisperses. Les stratégies numériques disponibles dans le code de calcul AVBP sont aussi analysées, afin d'en cerner les limites pour la simulation eulérienne d'une phase liquide. Ce nouveau formalisme est finalement appliqué à la configuration aéronautique MERCATO, pour laquelle on dispose de résultats numériques obtenus avec d'autres approches (FEM et approche lagrangienne), et de résultats expérimentaux. Un accord satisfaisant avec l'expérience est montré pour toutes les approches, même si le FEM, monodisperse, obtient de moins bon résultats en terme de fluctuations. D'autres résultats expérimentaux s'avèrent nécessaires pour évaluer les approches et déterminer quelle est la plus prédictive pour cette configuration, notamment concernant la fraction massique de kerosene, autant en phase liquide qu'en phase gazeuse.
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