Dissertations / Theses on the topic 'Liquid-liquid dispersion'
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Bucciarelli, Elia. "Liquid-liquid dispersion in mechanically agitated vessel." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
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L’argomento trattato è lo studio di due liquidi immiscibili all’interno di un recipiente agitato.
Una nuova tecnica di misura delle dimensioni delle particelle viene presentata, la tecnica sperimentata è non invasiva in quanto tutti gli strumenti di misura sono stati posizionati esternamente al vessel.
Il recipiente conteneva una dispersione di olio siliconico in acqua, i test sono stati condotti in assenza di coalescenza.
Il sistema è agitato in un primo test da una girante Rushton e in un secondo da una girante con denti; esso consiste in un recipiente cilindrico dal diametro T=300mm in vetro, questo vessel è stato inserito in un secondo recipiente, anch’esso in vetro ma dalla geometria cubica, riempito di acqua per ridurre problemi legati alla distorsione ottica dovuta alla cilindricità delle pareti del vessel agitato.
Il recipiente è stato posto tra una fotocamera ad alta velocità e una lampada avente lo scopo di illuminare la dispersione. Sono state quindi relazionate le reali dimensioni in mm delle gocce, con i pixel della fotocamera nella fase di calibrazione; la taratura è stata effettuata tramite l’utilizzo di speciali sfere solide monodimensionali.
L’analisi della dispersione in esame consisteva nella cattura di più set di immagini ad intervalli di tempo prestabiliti, solo dopo che la dispersione fosse arrivata all’equilibrio.
La foto sono state quindi salvate in stack ed analizzate da un apposito codice che è stato scritto per il programma di analisi di immagini utilizzato: ImageJ. La possibilità di implementare macro in ImageJ rende molto flessibile questo programma, caratteristica fondamentale in questo lavoro in quanto lo studio di questi liquidi ha richiesto un notevole numero di test per ottenere una corretta interpretazione delle dimensioni delle gocce.
Segue infine l’analisi dei dati ottenuti, alcune correlazioni riportate in letteratura sono state verificate statisticamente a partire dai risultati ottenuti.
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Rajapakse, Achula, and s9508428@student rmit edu au. "Drop size distribution and interfacial area in reactive liquid-liquid dispersion." RMIT University. Civil Environmental and Chemical Engineering, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080717.163619.
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Emulsion explosives have become the preferred choice as blasting agents for numerous industries including mining, agriculture, and construction. One of the most important components in such an emulsion is an emulsifier, which controls the emulsification properties of the explosive. The present study involves the production of one such emulsifier, which is produced by reacting two immiscible liquids, PIBSA (polyisobutylene succinic anhydride) and MEA (monoethanolamine). The study examines the effect of design variable such as the impeller speed, impeller type and the dispersed phase volume fraction on interfacial area. Experiments were carried out in a 0.15 m diameter fully baffled stirred tank using a 6-bladed Rushton turbine impeller and a marine propeller. Drop size was determined using a microscope with a video camera and image processing system. The transient concentration of PIBSA was determined using FTIR analysis and used to estimate the volume fraction of the dispersed phase (Ö). The effective interfacial area was calculated using the Sauter mean drop diameter, d32 and Ö. Impeller speeds ranging from 150 to 600 rpm and dispersed phase volume fractions, Ö ranging from 0.01 to 0.028 were examined in the experimental study. It was found that that the evolution of Sauter mean drop diameter, d32 has four different trends depending on Ö and impeller speed. At high impeller speeds and high Ö, d32 values decrease initially and reach constant values after a long period of time. This trend is consistent with the findings in previous investigations. Under certain operating conditions, d32 values increase initially with stirring time to reach a maximum value and then decrease to reach a steady state value. The presence of these trends has been attributed to the effect of changing physical properties of the system as a result of chemical reaction. Results indicate that, in general, Sauter mean drop diameter d32 decreases with an increase in agitation intensity. However a decrease in the dispersed phase volume fraction is found to increase d32. These trends are found to be the same for both impeller types studied. Comparing the drop size results produced by the two impellers, it appears that low-power number propeller produces s ignificantly smaller drops than the Rushton turbine. It was found that the concentrations of reactants decrease with time for all impeller speeds thereby leading to a decrease in interfacial area with the progress of the reaction. Interfacial area values obtained at higher impeller speeds are found to be lower in spite of lower d32 values at these speeds. Also, these values decrease with time and become zero in a shorter duration indicating the rapid depletion of MEA. The interfacial area values obtained with the propeller at a given impeller speed are lower as compared to those for Rushton turbine. They also decrease and become zero in a shorter duration as compared to those for Rushton turbine suggesting propeller¡¦s performance is better in enhancing the reaction rate.
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Rodgers, Andrew Norman John. "Dispersion, assembly and electrochemistry of graphene at the liquid-liquid interface." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/dispersion-assembly-and-electrochemistry-of-graphene-at-the-liquidliquid-interface(c2ffd27a-cf5f-45c2-a471-60dcab788e12).html.
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The dispersion of graphene in 1,2-dichloroethane (DCE), its subsequent attachment at the water-DCE interface and the reduction of oxygen at the water-DCE interface proceeding via interfacial graphene have been investigated. Using addition of an electrolyte which screens surface charge, it was found that electrostatic repulsions play a significant role in determining the kinetic stability of lyophobic non-aqueous graphene dispersions. The onset of aggregation was determined and it was found that dispersions prepared from higher-oxygen content graphite were more stable than those prepared from lower-oxygen content graphite, indicating that oxygen content is important in determining the surface charge on graphene in non-aqueous dispersion. The presence of organic electrolyte was also found to promote assembly of graphene into a coherent film at the liquid-liquid interface. Measurement of the liquid-liquid interfacial tension and three-phase contact angle revealed that the energetics of particle attachment did not change in the presence of organic electrolyte, thus indicating a mechanism of inter-particle electrostatic repulsion minimisation through surface charge screening. Interfacial graphene was found to display a catalytic effect toward the oxygen reduction reaction at the water-DCE interface. A bipolar cell was developed which showed that this reaction occurs heterogeneously, with graphene acting as a conduit for electrons across the water-DCE interface.
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Haam, Seungjoo. "Multiphase research on solid-liquid dispersion /." The Ohio State University, 1996. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487935958846755.
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Young, C. H. "High flux mass transfer and axial dispersion in agitated liquid-liquid contactors." Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234762.
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Salih, M. A. "Effects of antifoams on gas-liquid dispersion." Thesis, Swansea University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638752.
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The use of antifoam solution to control any foaming tendency is a very important aspect of fermentation processes. However, an antifoam solution will affect the mass transfer characteristics of a fermentation broth as well as suppressing foam so that both mass transfer and foam behaviour have been studied in the present work. The behaviour of a transient foam, which is produced by the antifoam itself, was investigated by means of a small two-dimensional bubble column. This bubble column consisted of two glass plates separated by a 10 mm thick frame of PTFE. Bubbles were produced from sintered-glass spargers of two pore sizes. Measurements of the average bubble diameters in the foam for different concentrations of solution were carried out from still photographs of the foam using an image analyzer. Two types of antifoams were investigated, polypropylene glycol (PPG) and a silicone oil emulsion. The two PPG concentrations used were 0.05 and 0.15 g/l both with and without adjustment of the pH and the addition of an electrolyte, NaCl. The silicon emulsion concentration was 0.015 g/l. Bovine serum albumen BSA as a foaming agent at a concentration of 0.20 g/l was investigated by itself, and with each of the antifoams. In each experiment, the height of foam layer was recorded as a function of the superficial gas velocity. A constant flow tank has been designed to allow the foam to overflow and to enable measurements of the mass transfer characteristics of the froth (or broth) layer only. These characteristics are: volumetric mass transfer coefficient KLA, Sauter mean bubble diameter b, gas hold-up g, interfacial area A, and mass transfer coefficient KL. The value of KLA was calculated from a mass balance of steady-state dissolved oxygen. The gas hold-up was estimated from the differences in heights of gassed and ungassed solution. A photographic technique was applied to measure the bubble diameter. Thus, the interfacial area A was simply calculated using the formula (A = 6 g / b). Finally, the value of KL value was determined.
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Wonderly, Hugh Alan. "Electro-optical effects of liquid crystals with dielectric dispersion." Kent State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=kent1291069300.
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Krishnardula, Venu Gopal. "Transient liquid phase bonding of ferritic oxide dispersion strengthened alloys." Auburn, Ala., 2005. http://repo.lib.auburn.edu/2005%20Fall/Dissertation/KRISHNARDULA_VENU_19.pdf.
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Baker, S. A. "Liquid dispersion in two-phase flow in a packed column." Thesis, Swansea University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636015.
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This study presents the results of an investigation of liquid flow and dispersion in the bulk and wall region as well as liquid dispersion in the whole cross-section in a packed column with and without counter-current gas flow. In the study a column of 30 cm in diameter packed with 2.54 cm Rashig rings was used. Water was uniformly distributed at the top while air was introduced and distributed uniformly at the bottom of the packed column. Using a point injector, an input pulse of sodium choride solution was introduced at the axis of the column through a small diameter injection tube at a bed height of 25 cm. The responses were measured at four radial positions, using conductivity cells attached to the supporting plate, and were recorded simultaneously with the input pulse, which was recorded as a pressure signal using a pressure transducer. The dispersion equation was solved analytically, and the axial and radial dispersion coefficients in the bulk region were estimated by a non-linear optimization technique. The values of interstitial liquid velocity in the bulk region were estimated from the first moment of the input and output pulses. A plane tracer injector was used to introduce an input pulse of sodium chloride solution to the whole cross section area of the column at bed height of 15 cm. The responses were measured at four radial positions, simultaneously using the four conductivity cells. The input pulse was recorded as a pressure signal. A dispersion equation was solved analytically and total dispersion coefficients were estimated by a non-linear optimization technique. The values of the interstitial liquid velocity in the bulk and wall region were estimated from the first moment on the input and output pulses. The responses in the bulk and wall region were used separately in a dispersion equation which was solved analytically to estimate the axial dispersion coefficients in the bulk and wall region respectively. The operation was repeated at eight different heights up to 150 cm, and the total dispersion coefficients were estimated at each height for different liquid and gas flow rates. The above results were used to study the validity of Gunn's (1980) theoretical analysis, which was based on the assumption that the total dispersion coefficients in a packed column has two important contributions, local dispersion in the packing and axial dispersion due to the differences in liquid flow conditions between the wall and bulk regions of packing. By this treatment, a two-dimensional formulation of dispersion may be reduced to a one-dimensional axisymmetric formulation of dispersion for the limit of long dispersion times. Good agreement between experiment and theory was found.
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Wei, Suwan. "Transient liquid phase bonding of an oxide dispersion strengthened superalloy." Thesis, Brunel University, 2002. http://bura.brunel.ac.uk/handle/2438/7861.
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Oxide dispersion strengthened (ODS) alloys have been developed with unique mechanical properties. However, in order to achieve commercial application an appropriate joining process is necessary which minimizes disruption to the alloy microstructure. Transient liquid phase (TLP) bonding is a promising joining method, but previous work has shown that the segregation of dispersoids within the joint region results in bonds with poor mechanical strengths. This research work was undertaken to further explore particulate segregation at the joint region when TLP bonding and to develop bonding techniques to prevent it. A Ni-Cr-Fe-Si-B interlayer was used to bond an alloy MA 758. The effects of parent alloy grain size, bonding temperature, and external pressure on the TLP bonding process were investigated. Three melting stages were identified for the interlayer, and the bonding temperature was chosen so that the interlayer was in the semi-solid state during bonding. This novel bonding mechanism is described and applied to counteract the segregation of Y203 dispersoids. The grain size of the parent alloy does not alter the particulate segregation behaviour. It is concluded that a low bonding temperature with moderate pressure applied during bonding is preferable for producing bonds with less disruption to the microstructures of the parent alloy. Joint shear tests revealed that a near parent alloy strength can be achieved. This study also shed some light on choosing the right bonding parameters suitable for joining the complicated alloy systems. A Ni-P interlayer was also used to bond the ODS alloy. Microstructural examination indicated that a thin joint width and less disruption to the parent grain structure were achieved when bonding the alloy in the fine grain state. The time for isothermal solidification was found to be shorter when compared with bonds made with the parent alloy in the recrystallized state. All these observations were attributed to the greater diffusivity of P along the grain boundaries than that of the bulk material. A high Cr content within the parent alloy changes the mechanism of the bonding process. The diffusion of Cr into the liquid interlayer has the effect of raising the solidus temperature, which not only accelerates the isothermal solidification process, but also reduces the extent of parent alloy dissolution.
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Vilt, Michael Edward. "Supported Liquid Membranes with Strip Dispersion for Recovery of Cephalexin." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1283447020.
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Kanel, Jeffrey Scott. "Minimum impeller speeds and power requirements for complete dispersion of non-Newtonian liquid-liquid systems in baffled vessels." Thesis, Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/11256.
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Herbelin, Armando L. "Dispersion and gradients in flow injection /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/11548.
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Costa, Elisabete Fernandez Reia Da. "Liquid moulding of carbon nanoparticle filled composites." Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/7276.
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This thesis focuses on the incorporation of carbon nanoparticles within continuous fibre reinforcements by liquid composite moulding processes, in order to provide enhanced electrical and delamination properties to the multiscale composites. The mechanisms controlling the flow and filtration of these nanoparticles during liquid composite moulding are studied, in order to develop a predictive 1-D model which allows design of the processing of these composite materials. Five different carbon nanoparticles at 0.25 wt% loading, three unmodified and one surface modified carbon nanotube systems and one carbon nanofibre system, were utilised to modify a commercial two-component epoxy resin utilised to impregnate carbon and glass reinforcements at high fibre volume fraction by resin transfer moulding. The dispersion of the nanofillers in the prepolymer was carried out by ultrasonication, high shear mixing or triple roll milling or a combination of the three. Electrical conductivity measurements of the carbon nanoparticle liquid suspensions during dispersion, alongside optical microscopy imaging and rheological analysis of these allowed the selection of the concentration of nanofiller and the appropriate dispersion technique for each nanoparticle system. The resin transfer moulding process required adaptation to incorporate the dispersion and modify degassing steps, especially when utilising unmodified carbon nanoparticles suspensions, due to their higher viscosity and tendency to be filtered. Nanoparticle filtration was identified by electrical conductivity measurements and microscopy of specimens cut at increasing distances from the inlet. Cake filtration was observed for some of the unmodified systems, whereas deep bed filtration occurred for the surface modified CNT material. Property graded composites were obtained due to filtration, where the average electrical conductivity of the carbon and glass composites produced increased by a factor of two or one order of magnitude respectively. The effect of filler on the delamination properties of the carbon fibre composites was tested under mode I. The results do not show a statistically significant improvement of delamination resistance with the presence of nanoparticles, although localised toughening mechanisms such as nanoparticle pull-out and crack bridging as well as inelastic deformation have been observed on fracture surfaces. Particle filtration and gradients in concentration resulted in non-linear flow behaviour. An 1-D analytical and a finite difference model, based on Darcy’s law accompanied by particle mass conservation and filtration kinetics were developed to describe the flow and filtration of carbon nanoparticle filled thermosets. The numerical model describes the non-linear problem by incorporating material property update laws, i.e. permeability, porosity and viscosity variations on concentration of retained and suspended particles with location and time. The finite difference model is consistent and converges to the analytical solution. The range of applicability of the analytical model is limited to lower filtration coefficients and shorter filling lengths, providing an approximate solution for through thickness infusion; whereas the numerical model presents a solution outside this range, i.e. in-plane filling processes. These models allow process design, with specified carbon nanoparticle concentration distributions achieved via modifying the nanofiller loading at the inlet as a function of time.
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Biasi, Verner de. "The application of low dispersion liquid chromatography in the pharmaceutical industry." Thesis, Open University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259485.
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Muskett, M. J. "Gas-liquid dispersion in stirred tanks : scale-up and agitator comparison." Thesis, Cranfield University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245784.
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MASSARI, PHILLYPE DE LIMA. "EXPERIMENTAL EVALUATION OF GAS DISPERSION IN OSCILLATORY CROSS FLOW OF LIQUID." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2017. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=30692@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROEste trabalho apresenta uma investigação experimental do escoamento induzido pela interação entre uma pluma de bolhas e um escoamento cruzado oscilatório. Condições de escoamento similares podem ser encontrados em processos de aeração artificial utilizados na mitigação da poluição nos rios e na representação de vazamento de gás natural no fundo dos oceanos. No presente trabalho, ondas superficiais controladas foram inseridas em um canal de água para gerar oscilações na corrente do escoamento cruzado. As ondas foram geradas a partir de uma placa móvel na superfície da água e determinadas condições de escoamento instável foram selecionadas para a investigação. O ar foi injetado pelo fundo do canal para formar a pluma de bolhas. A técnica Particle Image Velocimetry (PIV) foi empregada para medir a velocidade do escoamento. Antes da estimativa da velocidade, as imagens foram pré-processadas aplicando-se rotinas desenvolvidas no Matlab a fim de distinguir as partículas traçadoras das bolhas de ar e criar máscaras dinâmicas para as imagens do sistema PIV. Assim, o campo vetorial de velocidade foi estimado utilizando algoritmos padrão do PIV. Além disso, as propriedades das bolhas, como tamanho e velocidade, também foram estimadas a partir das imagens adquiridas. Finalmente, foi analisada a interação entre a pluma de bolhas com o escoamento cruzado instável.
This work presents an experimental investigation of the flow field induced by the interaction between a bubble plume and an oscillating cross flow. Similar flow conditions can be found in artificial aeration processes used for mitigation of pollution contamination in rivers and submarine outfalls in coastal areas. The mixing zone is highly dependent of the flow field near the plume hence the efficiency of aeration processes. In the present work, controlled surface waves were introduced to generate oscillations in streamwise and wall normal components of the cross flow. The waves were excited with a moving paddle and unsteady flow conditions were selected for the investigation. Air was injected in the bottom wall of the water channel to form the bubble plume. Particle Image Velocimetry (PIV) techniques were employed to measure the velocity flow field. Prior to velocity estimation, images were pre-processed using Matlab routines in order to distinguish tracer particles from air bubbles and to create a dynamic mask for the PIV images. Thus, the velocity vector field was estimated using standard PIV algorithms. In addition, properties of the bubbles, such as size and velocity, were also estimated from the acquired images. Finally, the interaction between the bubble plume with the unsteady cross flow was analyzed.
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Meloy, John R. "Modelling the motion and dispersion of liquid and particles in foams." Thesis, University of Manchester, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.681983.
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A model has been developed for the simulation of the motion of unattached particles through foams. The model uses previous work on the bulk drainage of liquid through foams (Verbist et al., 1996) in addition to a velocity profile equation which describes the local variation in liquid velocity over the Plateau border cross section (Sparrow and Loeffler, 1959). These descriptions of the liquid flow on two separate scales are combined with realistic foam structures (provided by Kraynik, 2004) to form a description of the liquid flow through the foam. This liquid flow description is used as a basis for the simulation of particle motion through the interconnected network of Plateau borders and vertices of the foam. The results of the particle motion simulation model have been used to calculate the dispersion of particles through the foam. The model was used to replicate experiments performed by Lee (2004) on the forced drainage of liquid and particles in a laboratory scale foam column. From the results of this replication it is possible to predict axial dispersion coefficients which are validated with experimental data. It is also possible to use the model to perform a sensitivity analysis to determine which parameters have the greatest effect on the particle motion and dispersion and therefore merit further investigation. For instance, the model has been used to calculate the effect of particle size on axial dispersion through the foam. Finally, a geometric dispersion coefficient has been calculated for the three› dimensional, random, monodisperse foam structure used in the simulations. This is an improvement on the previous coefficient calculation method which used a two› dimensional, regular foam structure. The calculated value of the geometric dispersion coefficient corresponds closely to a value predicted based solely on the foam structure used in the simulations. This further highlights the already known dependence of geometric dispersion on foam structure.
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Sultan-Mohammadi, Mansur. "Polyatomic London dispersion forces and NMR gas to liquid chemical shifts." Thesis, Aston University, 1986. http://publications.aston.ac.uk/11761/.
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Craig, Glenn R. "DISPERSION OF CARBON NANOTUBE CLUSTERS VIA THE RAPID VAPORIZATION OF INTERSTITIAL LIQUID." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1396476339.
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Jagannadh, Satyavolu V. S. "A study of liquid drop dispersion in a turbulent four-roll mill /." The Ohio State University, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487671640056881.
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Castellano, Simone. "Multiscale study and modeling of dispersion properties relevant for liquid-liquid extraction : adaptation of breakup and coalescence kernels to industrial processes." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1243.
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Ce projet de thèse porte sur l'étude de l'hydrodynamique des dispersions dans les extracteurs liquide-liquide utilisés dans l'industrie du recyclage nucléaire. Dans la première partie du projet, un modèle de bilan de population homogène (0D-PBM), basé sur l'évaluation des taux moyens en volume de coalescence et de rupture, est proposé. La méthode tient compte des inhomogénéités spatiales dans le mélange, notamment de la fonction de densité de probabilité de la dissipation de l’énergie cinétique turbulente dans l’appareil. Le modèle est capable de reproduire les expériences de dispersion liquide-liquide turbulentes à faible viscosité. Dans la deuxième partie de cette étude, un modèle généralisé pour les noyaux de rupture et coalescence, valable pour l’ensemble du spectre de la turbulence, est proposé et validé. La plupart des noyaux disponibles dans la littérature sont basés sur la fonction de structure de second-ordre de Kolmogorov, qui n'est valable que dans le domaine inertiel. Cependant, dans des nombreuses situations rencontrées au niveau industriel, la plupart des gouttes peuvent avoir une taille dans le domaine dissipatif, où la fonction de structure de second-ordre de Kolmogorov ne s'applique pas. Le modèle généralisé est basé sur la fonction de structure de second ordre de Davidson, valable dans tout le spectre de la turbulence. Dans la dernière partie de l'étude, un modèle permettant de simuler le comportement hydrodynamique d'une colonne pulsée est proposé. Le modèle est basé sur un bilan de population 1D, dont les termes source ont été modélisés à l'aide des noyaux de Coulaloglou et Tavlarides généralisés. Les inhomogénéités turbulentes dans la colonne pulsée ont été prises en compte par la fonction de densité de probabilité du taux de dissipation turbulent. Un bon accord modèle-expérience est obtenu en ce qui concerne le diamètre et la concentration moyenne des gouttes dans un compartimentThis PhD project deals with the study of the hydrodynamics of the dispersions in the liquid-liquid extractors employed in the nuclear recycle industry. In the first part of the project, a zero-dimensional homogenous Population Balance Model (0D-PBM), based on the evaluation of the volume-averaged coalescence and breakup rates, is adopted to fit low-viscosity turbulent liquid-liquid dispersion experiments. The method accounts for the spatial inhomogeneities in mixing, namely for the probability density function of the turbulent kinetic energy dissipation in the apparatus. In the second part of this study, a generalized model for the breakage and coalescence kernels, valid for the entire spectrum of turbulence, is proposed and validated. Most of the available kernels in literature indeed are based on the Kolmogorov second-order structure function, which is only valid in the inertial subrange. However, in many industrially encountered situations, most of the droplets may have size in the dissipation range, where the Kolmogorov second-order structure function does not apply. The generalized model is based on the Davidson second-order structure function, valid in the entire spectrum of turbulence. In the last part of the study, a model that allows to simulate the hydrodynamic behavior of a pulsed column is proposed. The model is based on a 1D Population Balance Equation (1D-PBE), whose source terms were modeled through the generalized Coulaloglou and Tavlarides kernels. The turbulent inhomogeneities in the pulsed column were accounted through the probability density function of the turbulent dissipation rate. The model well reproduces the experimental Sauter mean diameters and the dispersed phase volume fractions in a compartment of the pulsed column
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Lobry, Emeline. "Batch to continuous vinyl chloride suspension polymerization process : a feasibility study." Phd thesis, Toulouse, INPT, 2012. http://oatao.univ-toulouse.fr/11498/1/lobry.pdf.
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Continuous processes present the benefit to be safer and more cost saving than batch processes. Many researches have been carried out in fine chemistry but few contributions refer to polymerization. We focus on the vinyl chloride suspension polymerization. This process has been extensively studied in batch with lots of improvement regarding the formulation and the technologies. This polymerization process is highly complex due to the toxic nature of the monomer, the good manage of heat transfer and stirring. Moreover the reaction step remains the only batch step of the PVC production. According to the PVC grain formation, the process can be divided into three steps (i) a liquid-liquid dispersion step in which the monomer droplet (30-50 µm) are generated and stabilized, (ii) a controlled agglomeration step of the reacting droplets exhibiting a sticky behaviour, (iii) a reaction step until the conversion rate is around 80-90% and the particles size is stable. In this study, the different technologies suitable for the different steps are pointed out. Based on the state of the art of the grain behaviour depending on the reaction conversion and on the literature concerning polymerization continuous process, static mixers and different co-current pulsed columns are proposed. Three technologies with different model system were chosen to study the liquid-liquid dispersion step. Static mixers allow the control of the droplet size under turbulent flow. In the range of the operating conditions, the dispersed phase concentration does not have a significant effect on the droplet size. The interfacial tension appears to be the most significant physico-chemical parameters. Correlation to predict the mean droplet size is proposed depending on different dimensionless numbers based on the hydrodynamics and on the systems: the Reynolds and Weber numbers. Given the promising results, static mixers are implemented at pilot scale to load the batch prior to polymerization. Their use demonstrates a noticeable reduction of the loading time and a better homogenisation of the different suspending agents and initiator inside the PVC grain. The two co-current pulsed columns design studied are the discs and doughnuts pulsed column and the COBR (continuous oscillatory baffled reactor, Nitech). For the first one, the effect of the packing materials (type and height), of the physico-chemical parameters (dispersed phase concentration, surfactant) and of hydrodynamic parameters (flowrate and oscillation conditions) on the droplet size are investigated where as for the second one the study is limited to the hydrodynamic parameters. A mean droplet size correlation is proposed based on the characteristic dimensionless numbers. The three continuous contactors used for liquid-liquid dispersion are compared in term of energy dissipation rate. The reaction is carried out in a continuous tubular reactor (the pulsed column). The column is suitable to transport solid-liquid suspension. Vinyl acetate suspension polymerization is performed to demonstrate the feasibility and particularly to study the encrusting and fouling problem. The first results are very promising.
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Wahle, Markus [Verfasser]. "Microstructured fibers with liquid crystals: tuning of optical transmission and dispersion / Markus Wahle." Paderborn : Universitätsbibliothek, 2017. http://d-nb.info/1128210959/34.
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Shi, Jun-Mei, Horst-Michael Prasser, and Ulrich Rohde. "Turbulent dispersion of bubbles in poly-dispersed gas-liquid flows in a vertical pipe." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-28046.
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Turbulence dispersion is a phenomenon of practical importance in many multiphase flow systems. It has a strong effect on the distribution of the dispersed phase. Physically, this phenomenon is a result of interactions between individual particles of the dispersed phase and the continuous phase turbulence eddies. In a Lagrangian simulation, a particle-eddy interaction sub-model can be introduced and the effect of turbulence dispersion is automatically accounted for during particle tracking. Nevertheless, tracking of particleturbulence interaction is extremely expensive for the small time steps required. For this reason, the Lagrangian method is restricted to small-scale dilute flow problems. In contrast, the Eulerian approach based on the continuum modeling of the dispersed phase is more efficient for densely laden flows. In the Eulerian frame, the effect of turbulence dispersion appears as a turbulent diffusion term in the scalar transport equations and the so-called turbulent dispersion force in the momentum equations. The former vanishes if the Favre (mass-weighted) averaged velocity is adopted for the transport equation system. The latter is actually the total account of the turbulence effect on the interfacial forces. In many cases, only the fluctuating effect of the drag force is important. Therefore, many models available in the literature only consider the drag contribution. A new, more general derivation of the FAD (Favre Averaged Drag) model in the multi-fluid modeling framework is presented and validated in this report.
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Shi, Jun-Mei, Horst-Michael Prasser, and Ulrich Rohde. "Turbulent dispersion of bubbles in poly-dispersed gas-liquid flows in a vertical pipe." Forschungszentrum Dresden-Rossendorf, 2007. https://hzdr.qucosa.de/id/qucosa%3A21631.
Full textAbstract:
Turbulence dispersion is a phenomenon of practical importance in many multiphase flow systems. It has a strong effect on the distribution of the dispersed phase. Physically, this phenomenon is a result of interactions between individual particles of the dispersed phase and the continuous phase turbulence eddies. In a Lagrangian simulation, a particle-eddy interaction sub-model can be introduced and the effect of turbulence dispersion is automatically accounted for during particle tracking. Nevertheless, tracking of particleturbulence interaction is extremely expensive for the small time steps required. For this reason, the Lagrangian method is restricted to small-scale dilute flow problems. In contrast, the Eulerian approach based on the continuum modeling of the dispersed phase is more efficient for densely laden flows. In the Eulerian frame, the effect of turbulence dispersion appears as a turbulent diffusion term in the scalar transport equations and the so-called turbulent dispersion force in the momentum equations. The former vanishes if the Favre (mass-weighted) averaged velocity is adopted for the transport equation system. The latter is actually the total account of the turbulence effect on the interfacial forces. In many cases, only the fluctuating effect of the drag force is important. Therefore, many models available in the literature only consider the drag contribution. A new, more general derivation of the FAD (Favre Averaged Drag) model in the multi-fluid modeling framework is presented and validated in this report.
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Allsford, K. V. "Gas-Liquid Dispersion and Mixing in Mechanically Agitated Vessels with a Range of Fluids." Thesis, University of Birmingham, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.512063.
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This study aims at understanding the effect of fluid rheology on gas dispersion and mixing in mechanically agitated vessels. Bulk flow is linked with the two-phase flow in the impeller region and the power drawn by the rotating agitator(s). A base case study using a Rushton Disc Turbine in water is initially reported. Model Newtonian, viscoelastic and shear-thinning fluids (corn syrup, Boger fluids and Carbopol solutions respectively) and a typical fluid (CMC solution) were then used to determine the effects of fluid rheology on flow phenomena and power consumption for single agitators (Disc Turbines and Angle-Bladed Impellersl dual combinations thereof, and InterMIGs under gassed and ungassed conditions in a 0.61 m diameter vessel. Similar experiments were performed in smaller vessels. The relative effectiveness of all the agitator configurations studied at achieving bulk liquid mixing was also determined using a redox reaction technique. The most energy efficient configuration proved to be a large Disc Turbine combined with an equisized Angle-Bladed Impeller (pumping upwards) in both the gassed and ungassed cases. The results presented in this thesis are also related to process design considerations and a technique which predicts the agitator rotational speed and diameter required for achieving optimal mass transfer is developed.
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Lin, Xing Jun 1960. "Simulation of odour dispersion around natural windbreaks." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=102997.
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The research objective was to calibrate a model to simulate odour dispersion downwind from natural windbreaks and then, use this model to observe the effect of windbreak characteristics and climatic conditions on the size of the odour dispersion plume. Computational fluid dynamic (CFD) models were used for the simulations because of their capability in reproducing turbulent wind conditions. The model was initially calibrated to ensure the proper velocity recovery ratio (VRR), and then to reproduce odour plumes measured in the field by three groups of four panellists.The visual and statistical analysis of the field panellist observations indicated that a windbreak with an optical porosity of 0.35 could reduce by 21% the length of the odour dispersion plume, as compared to a site without a windbreak. Also, these analyses indicated that the site with a windbreak offering an optical porosity of 0.55 had no significant impact on the length of the odour plume, as compared to the site without a windbreak.
The models selected for the simulations were the Fluent 6.2 standard k-epsilon and SST k-o models. Their odour dispersion calibration indicated that both models can accurately reproduce the field measured odour hedonic tone and odour concentration by transforming the odour mass fraction computed by the models into the hedonic tone with a power function, and then into the odour concentration with an exponential function. The correlations between the simulated and measured absolute HT and between the simulated and measured odour concentrations were statistically significant (P < 0.01). However, the SST k-o was preferred over the standard k-epsilon because it could physically better reproduce the high turbulence conditions created by the windbreak.
The SST k-o model simulations indicated that odour plume length was mostly affected by windbreak porosity and height, as well as distance from the source. In terms of climatic conditions, odour plume size was mostly affected for atmospheric stability conditions which generally established ambient wind speed and rate of change of temperature. Wind direction has an impact on the length of the odour plume and the formation of a fin intensifying odour concentration near the windbreak, where an angle of 45º produces the shortest odour plume and the largest fin.
Key words: Simulation; odour; dispersion; natural Windbreak; CFD.
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Felis-Carrasco, Francisco. "Atomisation et dispersion d'un jet liquide : approches numérique et expérimentale." Thesis, Ecole centrale de Marseille, 2017. http://www.theses.fr/2017ECDM0001/document.
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L'atomisation d'un jet circulaire d'eau typique des applications agricoles est présentée dans cette étude. Maîtriser la dispersion de l'eau à des fins d'irrigation ou de traitements phytosanitaires implique de réduire la consommation d’eau et la pollution de l'environnement. Un cas d'étude simplifié est construit : une buse ronde dn=1.2 mm et d'une longueur Ln=50dn y est considérée. La vitesse d'injection est fixée à UJ=35 m/s et alignée avec la gravité, plaçant le jet liquide dans un régime d'atomisation turbulent. L'écoulement est statistiquement axisymétrique. L'approche est à la fois expérimentale et numérique.Un modèle multiphasique Eulérien de mélange décrit l'écoulement constitué de deux phases. Plusieurs modèles de turbulence U-RANS sont utilisés: k-ε et RSM. Une attention particulière est alors portée à la modélisation des effets de masse volumique variable issus de la formulation du fluide de mélange. Un solveur numérique spécifique est développé à l'aide du code CFD OpenFOAM. Une série de cas d'étude est construite pour tester l'influence de la modélisation de la turbulence et des fermetures de premier/second-ordre des flux massiques turbulents.Les techniques optiques (LDV et DTV) sont déployées pour recueillir des informations statistiques des phases liquide et gazeuse du spray. La campagne expérimentale est réalisée de x/dn=0 jusqu'à x/dn=800. En ce qui concerne la LDV, des gouttelettes d'huile d'olive (~1 µm) permettent d'analyser la phase gazeuse. Une distinction entre les gouttes de liquide et ces traceurs est obtenue par une configuration spécifique de la source laser et le paramétrage de la détection des bouffées Doppler (Filtre-BP et le SNR). Dans la zone dispersée, les mesures par DTV permettent d'estimer les vitesses et les tailles des gouttes. Une attention particulière est portée à l'estimation de la profondeur de champ (DOF) afin d'obtenir une corrélation taille-vitesse des gouttes moins biaisée.Les résultats numériques et expérimentaux concordent pour le champ de vitesse moyenne. Une forte dépendance au modèle de turbulence est trouvée. Cependant, le modèle RSM ne simule pas le comportement du tenseur de Reynolds. En effet, ni l'anisotropie trouvée expérimentalement (R22/R11≈0.05), ni la vitesse de glissement liquide-gaz ne peuvent être reproduites; même avec une fermeture au 2nd-ordre des flux massiques turbulents. Le fort rapport de masse volumique (eau/air), la directionnalité de l'écoulement et la production d'énergie cinétique turbulente peuvent être à l'origine d'une faible dispersion et d'un faible mélange entre les deux fluides. Ce mécanisme n'est pas encore clarifié du point de vue de la modélisation RSMA typical water round-nozzle jet for agricultural applications is presented in this study. The dispersion of a liquid for irrigation or pesticides spraying is a key subject to both reduce water consumption and air pollution. A simplified study case is constructed to tackle both scenarios, where a round dn=1.2 mm nozzle of a length Ln=50dn is considered. The injection velocity is chosen to be UJ=35 m/s, aligned with gravity, placing the liquid jet in a turbulent atomization regime. The flow is considered statistically axisymmetric. Experimental and numerical approaches are considered.An Eulerian mixture multiphase model describes the original two-phase flow. Several U-RANS turbulence models are used: k-ε and RSM; where special attention is taken to the modelling of variable density effects from the mixture formulation. A custom numerical solver is implemented using the OpenFOAM CFD code. A series of study cases are constructed to test the influence of the turbulence modeling and first/second-order closures of the turbulent mass fluxes. LDV and DTV optical techniques are used to gather statistical information from both the liquid and the gas phases of the spray. The experimental campaign is carried out from x/dn=0 to x/dn=800. Concerning the LDV, small (~1 µm) olive-oil tracers are used to capture the gas phase, where a distinction between the liquid droplets and tracers is achieved by a specific set-up of the laser power source and the burst Doppler setting (BP-Filter and SNR). On the dispersed zone, DTV measurements are carried out to measure velocities and sizes of droplets. Special attention to the depth-of-field (DOF) estimation is taken in order to obtain a less biased droplet’s size-velocity correlation.Numerical and experimental results show good agreement on the mean velocity field. A strong dependence on the turbulence model is found. However, the RSM does not capture the same behaviour on the calculated Reynolds stresses. Indeed, neither the experimental anisotropy (R22/R11≈0.05), nor the liquid-gas slip-velocity can be reproduced, even with a second-order closure for the turbulent mass fluxes. The strong density ratio (water/air), flow’s directionality and production of turbulent kinetic energy may be the cause of a weak dispersion and mixing between the two fluids. This mechanism is not yet clarified from a RSM modeling point-of-view
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Larsen, Kyle F. "Investigation of particle velocity and drag with spherical and non-spherical particles through a backward facing step. /." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd1975.pdf.
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Liu, Ning. "Soil and Site Characterization Using Electromagnetic Waves." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/26627.
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Success in geotechnical analysis, design, and construction invariably requires that we have proper knowledge and understanding of (1) the strength, (2) the fluid flow properties, and (3) the stress-deformation behavior of the earth materials. These important engineering properties are primarily determined by the components and structure of a soil, which also dictate the soilâ s responses in an electromagnetic field. As a nondestructive technique, the electromagnetic property measurement offers a promising approach to characterize earth materials and identify the effects of changes in environments.
However, despite many investigations in the last several decades, the relationship between the frequency-dependent electromagnetic properties of soils and their components and structure are still not well understood. Hence, estimation of engineering properties of a soil in a quantitative way from electromagnetic measurements can be uncertain.
In this research several tasks have been accomplished:
(1) Development of a physically based model that provides a means of investigating the coupled effects of important polarization mechanisms on soil electromagnetic properties, and a means of relating the electromagnetic properties of a soil to its fines content, clay mineralogy, anisotropy, degree of flocculation and pore fluid chemistry;
(2) Proposal of a practically applicable method to determine the volumetric water content, specific surface area and pore fluid salt concentration simultaneously from the dielectric spectrum;
(3) Deduction of the wide-frequency electromagnetic properties of a soil by measuring its responses to a step pulse voltage using time domain reflectometry (TDR);
(4) Establishment of the relationships between the specific surface area and compressibility, residual shear strength and hydraulic conductivity.
This study establishes a framework for quantifying soil engineering properties from their electromagnetic properties. If properly determined and interpreted, the electromagnetic properties can also provide insights into the causes of soil property changes over time and can be very useful in studying the effects of biological factors in geotechnical engineering, a field that may offer great potential for future advances.Ph. D.
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Li, Yan. "High-efficiency Blue Phase Liquid Crystal Displays." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5399.
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Blue phase liquid crystals (BPLCs) have a delicate lattice structure existing between chiral nematic and isotropic phases, with a stable temperature range of about 2 K. But due to short coherent length, these self-assembled nano-structured BPLCs have a fast response time. In the past three decades, the application of BPLC has been rather limited because of its narrow temperature range. In 2002, Kikuchi et al. developed a polymer stabilization method to extend the blue-phase temperature range to more than 60 K. This opens a new gateway for display and photonic applications. In this dissertation, I investigate the material properties of polymer-stabilized BPLCs. According the Gerber's model, the Kerr constant of a BPLC is linearly proportional to the dielectric anisotropy of the LC host. Therefore, in the frequency domain, the relaxation of the Kerr constant follows the same trend as the dielectric relaxation of the host LC. I have carried out experiments to validate the theoretical predictions, and proposed a model called extended Cole-Cole model to describe the relaxation of the Kerr constant. On the other hand, because of the linear relationship, the Kerr constant should have the same sign as the dielectric anisotropy of the LC host; that is, a positive or negative Kerr constant results from positive or negative host LCs, respectively. BPLCs with a positive Kerr constant have been studied extensively, but there has been no study on negative polymer-stabilized BPLCs. Therefore, I have prepared a BPLC mixture using a negative dielectric anisotropy LC host and investigated its electro-optic properties. I have demonstrated that indeed the induced birefringence and Kerr constant are of negative sign. Due to the fast response time of BPLCs, color sequential display is made possible without color breakup. By removing the spatial color filters, the optical efficiency and resolution density are both tripled. With other advantages such as alignment free and wide viewing angle, polymer-stabilized BPLC is emerging as a promising candidate for next-generation displays. However, the optical efficiency of the BPLC cell is relatively low and the operating voltage is quite high using conventional in-plane-switching electrodes. I have proposed several device structures for improving the optical efficiency of transmissive BPLC cells. Significant improvement in transmittance is achieved by using enhanced protrusion electrodes, and a 100% transmittance is achievable using complementary enhanced protrusion electrode structure. For a conventional transmissive blue phase LCD, although it has superb performances indoor, when exposed to strong sunlight the displayed images could be washed out, leading to a degraded contrast ratio and readability. To overcome the sunlight readability problem, a common approach is to adaptively boost the backlight intensity, but the tradeoff is in the increased power consumption. Here, I have proposed a transflective blue phase LCD where the backlight is turned on in dark surroundings while ambient light is used to illuminate the displayed images in bright surroundings. Therefore, a good contrast ratio is preserved even for a strong ambient. I have proposed two transflective blue phase LCD structures, both of which have single cell gap, single gamma driving, reasonably wide view angle, low power consumption, and high optical efficiency. Among all the 3D technologies, integral imaging is an attractive approach due to its high efficiency and real image depth. However, the optimum observation distance should be adjusted as the displayed image depth changes. This requires a fast focal length change of an adaptive lens array. BPLC adaptive lenses are a good candidate because of their intrinsic fast response time. I have proposed several BPLC lens structures which are polarization independent and exhibit a parabolic phase profile in addition to fast response time. To meet the low power consumption requirement set by Energy Star, high optical efficiency is among the top lists of next-generation LCDs. In this dissertation, I have demonstrated some new device structures for improving the optical efficiency of a polymer-stabilized BPLC transmissive display and proposed sunlight readable transflective blue-phase LCDs by utilizing ambient light to reduce the power consumption. Moreover, we have proposed several blue-phase LC adaptive lenses for high efficiency 3D displays.Ph.D.
Doctorate
Optics and Photonics
Optics and Photonics
Optics
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Khoury, Joe Farid. "Liquid Dispersions and Fiber Spinning of Boron Nitride Nanotubes Combined With Polyvinyl Alcohol." Cleveland State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=csu1623868708786823.
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Nakamatsu, Sandra. "Dispersão de nanopartículas de látex em um cristal líquido liotrópico." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-27112008-125412/.
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Neste trabalho, estudamos a dinâmica de formação e dispersão de agregados de látex quando inseridos num cristal líquido liotrópico. Esse cristal líquido é um sistema ternário composto de laurato de potássio, cloreto de decilamônia e água; e apresenta fases nemáticas uniaxiais calamítica e discótica (NC e ND, respectivamente) e biaxial (NB). As partículas de látex possuem diâmetro de 100nm e partículas com diferentes tipos de recobrimentos foram testadas. Observamos que nas fases NC e NB há formação de aglomerados de partículas, porém na transição para a fase ND as partículas se dispersam no meio. Verificamos que esse processo de aglomeração e dissociação das partículas está relacionado com a transição de fase NB - ND e foi observado em dois sistemas hospedeiros por resfriamento e por aquecimento. No intervalo de temperatura que corresponde à fase nemática biaxial para o cristal líquido puro, observa-se que há um aumento na dimensão dos aglomerados, que se tornam anemométrico e orientados na direção de orientação do meio. Dois diagramas de fases foram construídos, variando-se a concentração de partículas dispersas no meio, e a composição relativa de surfactantes do sistema hospedeiro. Experimentos de espalhamento de raios X indicam que a distância média entre as micelas que formam o meio hospedeiro não é alterado pela inserção de partículas no cristal líquido e permanece a mesma em todas as fases nemáticas. Foram também realizados estudos de reologia que mostram que a viscosidade do sistema é alterada pela presença das partículas de látex. Os fenômenos observados são interpretados levando-se em conta as flutuações de orientação das micelas nas diferentes fases nemáticas.In this work, we studied the dynamics of agglomeration and dissociation of latex particles when inserted into a lyotropic liquid crystal. This liquid crystal is a ternary system formed by potassium laurate, decilamonium chloride and water, presenting uniaxial calamitic and discotic nematic phases (NC e ND, respectively) and a biaxial nematic phase NB. The latex particles have diameter of 100 nm and particles with different surface treatments were tested. It was observed that in the NC e NB phases the latex particles form agglomerates, however in the transition to the ND phase, the particles disperse in the medium. In the temperature domain of the biaxial nematic phase the agglomerates increase in size, become anisometric and oriented along parallel to the orientation of the medium. Two phase diagrams were built by varying the particle concentration dispersed in the liquid crystal and by varying the relative composition of surfactants of the liquid crystal. X rays diffusion experiments have shown that the average distance between the micelles in the host medium are not affected by the presence of the latex particles and remain the same in all nematic phases. Rheology studies were also performed and it was found that the viscosity of the system is affected by the presence of the particles. The observed phenomenon are interpreted taking into account the orientational fluctuations of miceles in the different nematic phases.
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Veit, Max David. "Designing a machine learning potential for molecular simulation of liquid alkanes." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/290295.
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Molecular simulation is applied to understanding the behaviour of alkane liquids with the eventual goal of being able to predict the viscosity of an arbitrary alkane mixture from first principles. Such prediction would have numerous scientific and industrial applications, as alkanes are the largest component of fuels, lubricants, and waxes; furthermore, they form the backbones of a myriad of organic compounds. This dissertation details the creation of a potential, a model for how the atoms and molecules in the simulation interact, based on a systematic approximation of the quantum mechanical potential energy surface using machine learning. This approximation has the advantage of producing forces and energies of nearly quantum mechanical accuracy at a tiny fraction of the usual cost. It enables accurate simulation of the large systems and long timescales required for accurate prediction of properties such as the density and viscosity. The approach is developed and tested on methane, the simplest alkane, and investigations are made into potentials for longer, more complex alkanes. The results show that the approach is promising and should be pursued further to create an accurate machine learning potential for the alkanes. It could even be extended to more complex molecular liquids in the future.
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Mirzaei, Javad. "Optical and Electro-optical Properties of Nematic Liquid Crystals with Nanoparticle Additives." The Royal Society of Chemistry, 2011. http://hdl.handle.net/1993/30280.
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Liquid crystals (LCs) are an interesting class of materials that are attracting significant attention due to their ever-growing applications in a wide variety of fields such as liquid crystal display (LCD) technology, materials science and bioscience. In recent years, along with the developments of materials at the nanoscale, doping LCs with nanoparticles (NPs) has emerged as a very promising approach for improving LC properties. Nanoparticle additives can introduce novel effects on optical and electro-optical properties of nematic liquid crystals (N-LCs), such as altered molecular alignment, faster response time and increased efficiency. This thesis studies the impacts that the inclusion of metallic NPs made of gold or semiconductor CdSe quantum dots (QDs), have on optical and electro-optical properties of N-LCs. Using polarized optical microscopy and detailed capacitance and transmittance measurements of nematic mixtures in electro-optic test cells, characteristics such as optical texture, phase transition temperatures, switching voltages and dielectric anisotropy are investigated in pure as well as doped samples. Surface ligands in NPs and their chemical functionalization play an important role in the LC-NP interactions, largely by determining the dispersibility of NPs and stability of the nanocomposites. One important objective of this thesis is to investigate and prepare a series of gold nanoparticles (Au NPs) with specially formulated robust coatings that maximizes solubility and stability in LC medium. Silanization of NPs is developed as a method to overcome the stability challenge. The functionalization of silanized NPs with aliphatic ligands or liquid crystalline molecules, provides chemically and thermally stable NPs with hydrophobic and structurally compatible surfaces required for dispersion in N-LCs. After complete characterization the synthesized particles are used to make the new nematic nanocomposites.
By analysis of the structure-property relationships governing LC-nanomaterial composites and by comparison of new results and data from previous studies on other types of NPs, this thesis will further reveal the mechanism of the interrelations between host LC molecules and NP, considering the role of variables such as core composition, size and surface chemistry of NPs (e.g. siloxane shell, aliphatic ligand vs. liquid crystalline ligand) in achieving stable LC composites with desired optical and electro-optical properties.
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Gu, Mingxia. "Effects of Dielectric Relaxation on Director Dynamics in Uniaxial Nematic Liquid Crystals." Kent State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=kent1236368118.
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Sully, Vicky Ann. "Characterisation of the discharge flowrate and dispersion of non-flashing liquid releases through failed pipe flanges." Thesis, London South Bank University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369883.
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Thiriet, Maud. "Nanobâtonnets de NaYF4 à upconversion : synthèse, dispersion colloïdale et propriétés électro-optiques." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX071/document.
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Les nanoparticules de fluorures dopées avec des ions lanthanides ont connu un développement croissant ces dernières années. Elles présentent en effet des propriétés optiques d’upconversion remarquables et très intéressantes pour de multiples applications allant du photovoltaïque à l’imagerie médicale. Dans cette thèse, on a élaboré des nanobâtonnets de NaYF4 dopés Yb/Er/Gd, aux propriétés d’émission optimisées. Leur alignement par un champ électrique a ensuite été étudié, nous permettant de tirer parti de leur anisotropie et des propriétés physiques en découlant : biréfringence et luminescence polarisée.Les nanocristaux sont synthétisés par voie solvothermale, à haute température (200 °C) et sous haute pression (20 bars). Leur morphologie et leur structure cristalline sont contrôlées par un choix approprié des paramètres de synthèse comme le dopage en gadolinium ou les conditions de chauffage. A l’issue de la synthèse, l’état d’agrégation des particules de NaYF4 produites limite leur dispersion dans les solvants organiques usuels. Une fonctionnalisation bien spécifique avec des ligands possédant des groupements carboxylate ou phosphonate se révèle alors indispensable. Le greffage des particules avec un ion citrate ou une molécule d’alendronate permet d’obtenir des suspensions colloïdales très stables dans le DMSO. Par ailleurs, la réactivité de l’amine porté par l'alendronate nous a permis de greffer une deuxième molécule active : une rhodamine B, un colorant test, ainsi qu’un cristal liquide cyanobiphényl à tête carboxylique. Grâce à cette fonctionnalisation, de nouveaux matériaux hybrides organo-minéraux ont été développés. La réponse électro-optique des suspensions colloïdales soumises à un champ électrique haute fréquence suit une loi de type effet Kerr, avec une relation quadratique entre la biréfringence induite et l’amplitude du champ appliqué. Les constantes de Kerr sont de l’ordre de 10 8 m/V2 en cohérence avec ce qui a été observé sur d’autres systèmes. La biréfringence observée est majoritairement induite par la structure cristalline anisotrope des particules. Le mécanisme de réorientation de nos particules sous champ est largement dominé par la polarisation de leur nuage électronique. Une luminescence polarisée est finalement décrite, ouvrant la voie à l’usage des nanobâtonnets de NaYF4 comme sondes d’orientation dans des systèmes biologiques ou au sein de fluides en écoulementFluorides nanoparticles doped with lanthanides have seen an increase in interest the last years. They offer outstanding optical properties with a very attractive upconversion for multiple applications from photovoltaics to medical imaging. In this work, we use NaYF4 nanorods doped with Yb/Er/Gd and optimized emission properties. Their alignment by an electric field allows us to access their anisotropic physical properties like polarized luminescence and birefringence.Nanocrystals are synthesized by a hydrothermal route, at high temperature (200 °C) and high pressure (20 bar). Morphology and crystalline structure can be controlled by varying gadolinium doping and heating conditions. At the end of the synthesis, the aggregation of the particles limits their dispersion in all common organic solvents. A particular functionalization with ligands having carboxylate or phosphonate functions is shown to be necessary. The grafting of particles with ions like citrate or alendronate allows to obtain very stable colloidal suspensions in DMSO. Furthermore, the reactivity of the amine function carried by alendronate enables us to graft a second active dye like rhodamine B or a cyanobiphenyl liquid crystal with a carboxylic group. New organo-mineral materials can be produced with this functionalization. The electro-optical response of colloidal suspensions submitted to a high-frequency electric field follows the Kerr law, with a quadratic relation between induced birefringence and the amplitude of the applied field. The system exhibits Kerr constants of the order of 108 m/V2, in agreement with the literature. The birefringence is induced by the anisotropic crystalline structure of the colloid, not by its shape. The mechanism of reorientation of colloids under an electric field is widely dominated by the polarization of their ionic cloud. A polarized luminescence is finally described, which will allow the use of NaYF4 nanorods as orientation probes in biological systems or fluid flows
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Gopalkrishnan, Prasad. "INTER-PARTICLE LIQUID BRIDGES: A BUILDING BLOCK TO MODEL COMPLEX MIXING PHENOMENA." online version, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=case1085169849.
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Khalid, Perveiz. "Effects on seismic properties of thermoelastic relaxation and liquid/vapor phase transition." Pau, 2011. http://www.theses.fr/2011PAUU3002.
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Deux sources d'atténuation et de dispersion sismiques liées à la présence de fluide dans le milieu poreux sont examinées : la relaxation thermique, due à des variations de température différentes dans le fluide saturant et les minéraux au passage de l'onde de pression, et la transition liquide-vapeur en milieu partiellement saturé, consistant en une condensation de la vapeur lors de la compression et une vaporisation du liquide lors de la détente. L'analyse des temps de relaxation montre que ces phénomènes sont pertinents dans la bande sismique et augmentent la valeur de la compressibilité effective du fluide par rapport aux valeurs non relaxées communément adoptées, à savoir la compressibilité adiabatique prévalant en l’absence de milieu poreux dans le premier cas, et la moyenne de Wood des compressibilités du liquide et du gaz dans le deuxième cas. Pour des fréquences suffisamment faibles telles que le fluide et le minéral sont en équilibre thermique, la compressibilité effective est la moyenne des compressibilités adiabatique et isotherme du fluide pondérées par les capacités thermiques du fluide et des minéraux, respectivement. Par ailleurs, la compressibilité effective du fluide dans la limite thermodynamique des basses fréquences varie au passage du point de bulle de façon discontinue, alors que la moyenne de Wood varie de façon continue. Ce résultat, démontré dans le cas des fluides purs par Landau et Lifshitz, reste valide pour les fluides de réservoir. Ces deux processus de relaxation conduisent à une différence de module du fluide entre les régimes relaxé et non relaxé pouvant aller de 0,5 à 1 GPa, selon le type de fluide et le taux de saturation en gazTwo fluid-related sources of seismic attenuation and velocity dispersion are examined: thermal relaxation, which originates from the contrasted temperature variations in the rockforming minerals and in the saturating fluid at the passage of the pressure wave, and the liquid-vapor phase transition in partially saturated rocks, which consists in vapor condensation at pressure peaks and liquid vaporization at pressure troughs. An analysis of the relaxation times shows that these processes are relevant in the seismic frequency band and drive the effective fluid compressibility towards values higher than the unrelaxed values commonly adopted in practice, namely the adiabatic fluid compressibility in the first case, and Wood’s average of liquid and gas compressibilities in the second case. Under full thermal relaxation between fluid and mineral, i. E. , at low enough frequency, the effective fluid compressibility is equal to the average of the fluid adiabatic and isothermal compressibilities weighted respectively by the heat capacities of the fluid and the mineral. On the other hand, at the crossing of bubble point conditions, there is in the low-frequency or thermodynamic limit a discontinuous variation in fluid compressibility, whereas Wood’s average varies sharply but continuously. These features, analysed first by Landau and Lifshitz for pure fluids, hold for reservoir fluids as well. In these two relaxation processes, the difference in fluid bulk modulus between the unrelaxed and relaxed regimes, which is directly related to P-wave velocity dispersion, can be as large as 0. 5–1 GPa, depending on the fluid type and gas saturation
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Utting, Anita A. "Liquid filled hard gelatin capsules : an investigation of thermosoftened drug/poloxamer solid dispersion formulations in relation to drug release mechanisms." Thesis, University of Sunderland, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327315.
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Fernandes, Ricardo M. Ferreira. "Dispersing Carbon Nanotubes: Towards Molecular Understanding." Doctoral thesis, KTH, Tillämpad fysikalisk kemi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-176443.
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Carbon nanotubes (CNTs) exhibit unique and fascinating intrinsic electrical, optical, thermal or mechanical properties that lead to a plethora of potential applications in composite materials, electronics, energy storage, medicine, among others. However, the manipulation of nanotubes is not trivial and there are significant difficulties to overcome before achieving their full potential in applications. Because of their high aspect ratio and strong tube-to-tube van der Waals interactions, nanotubes form bundles and ropes that are difficult to disperse in liquids. In this thesis, the topic of dispersing carbon nanotubes in water was addressed by several experimental methods such as nuclear magnetic resonance (NMR) diffusometry and light/electron microcopy. The main goal was to obtain molecular information on how the dispersants interact with carbon nanotubes. In dispersions of single-walled carbon nanotubes (SWNTs) in water, only a small fraction of the polymeric dispersant (Pluronic F127) was shown to be adsorbed at the CNT surface. Regarding dynamic features, the residence time of F127 on the SWNT surface was measured to be in the order of hundred milliseconds, and the lateral diffusion coefficient of the polymer along the nanotube surface proved to be an order of magnitude slower than that in the solution. The surface coverage of SWNTs by F127 was also investigated and the competitive adsorption of F127 and the protein bovine serum albumin, BSA, was assessed. F127 was found to bind stronger to the CNT surface than BSA does. Low molecular weight dispersants, viz. surfactants, were also investigated. Using carefully controlled conditions for the sonication and centrifugation steps, reproducible sigmoidal dispersibility curves were obtained, that exhibited an interesting variation with molecular properties of the surfactants. Various metrics that quantify the ability of different surfactants to disperse CNTs were obtained. In particular, the concentration of surfactant required to attain maximal dispersibility depends linearly on alkyl chain length, which indicates that the CNT-surfactant association, although hydrophobic in nature, is different from a micellization process. No correlation between dispersibility and the critical micellization concentration, cmc, of the surfactants was found. For gemini surfactants of the n-s-n type with spacer length s and hydrophobic tail length n, the dispersibility of multiwalled carbon nanotubes (MWNTs) also followed sigmoidal curves that were compared to those obtained with single-tailed homologues. The increase in spacer length caused an increase in the dispersion efficiency. The observations indicate a loose type of monolayer adsorption rather than the formation of micelle-like aggregates on the nanotube surface. With the future goal of embedding nanotubes in liquid crystal (LC) phases and thereby creating nanocomposites, the effect of the spacer length on the thermotropic behavior of the gemini 12-s-12 surfactant was investigated. Different mesophases were observed and a non-monotonic effect of the spacer length was found and rationalized within a model of the surfactant packing in the solid state. The relative binding strength of simple surfactants to CNTs was assessed by the amount of F127 they displace from the CNT surface upon addition. Anionic surfactants were found to replace more F127, which was interpreted as a sign of stronger binding to CNT. The data collected for all surfactants showed a good correlation with their critical dispersibility concentration that suggests the existence of a surface coverage threshold for dispersing nanotubes. On the macroscopic scale, the formation of weakly bound CNT aggregates in homogeneous dispersions was found to be induced by vortex-shaking. These aggregates could quickly and easily be re-dispersed by mild sonication. This counterintuitive behavior was related to the type of dispersant used and of the duration of mechanical agitation and was explained as a result of loose coverage by the dispersant.This Ph.D thesis was completed under the Thesis Co-supervision Agreement between KTH Royal Institute of Technology and the University of Port. QC 20151105
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Sukhawipat, Nathapong. "Synthesis of natural rubber based cationic waterborne polyurethane dispersion for adhesive applications." Thesis, Le Mans, 2018. http://www.theses.fr/2018LEMA1013/document.
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Synthèse de nouveaux WPU (waterborne polyurethane) cationiques à partir du caoutchouc naturel (NR), et évaluation de leurs propriétés adhésives pour des surfaces de type cuir. Ces WPU ont été obtenus par réaction du caoutchouc liquide hydroxy téléchélique (HTNR), de toluene-2,4-diisocyanate (TDI), N-methyl diethanol amine (NMDEA, en tant qu’émulsifiant) et d’éthylène glycol (EG, extenseur de chaîne). Ces structures biosourcés sont développés comme alternatives aux WPU issus des ressources fossiles à fort impact environnemental. Les effets de cinq paramètres ont été étudiés, à savoir la quantité d'émulsifiant (de 0 à 2,25 mole), celle d’éthylène glycol (de 0 à 3 moles), le Mn du HTNR (de 100 à 3000 g/mole), l'indice NCO (de 100 à 150) et le taux d’époxydation des HTNR précurseurs (de 0 à 30%). Il a été en outre démontré que la stabilité des dispersions aqueuses pour les formulations optimales dépassait les 10 mois. La géométrie des particules dispersées a été étudiée, démontrant un aspect sphérique et une taille à l'échelle nanométrique. Ainsi, plusieurs facteurs ont été étudiés pour évaluer les propriétés adhésives optimales sur bandes de cuir (Mn, pourcentage d’'époxyde). Des tests standard (Peel test et Lap Shear test) ont été utilisés et les valeurs obtenues comparées avec celles issus de formulations adhésives commerciales avec ou sans solvants. Au bilan, une formulation optimale a été déterminée (Mn = 3000 g/mole, LR epoxydation = 10%, NMDEA 5.67%wt, NCO index de 100 et 1 mole d’EG) avec cuisson préalable des systèmes à 70°C. Ce WPU a montré une force d’'adhésion supérieure à toutes les formulations commerciales testéesNovel cationic waterborne polyurethane (cWPU) based on natural rubber (NR) have been prepared by the polymerization reaction of hydroxyl telechelic natural rubber (HTNR), toluene-2,4-diisocyanate (TDI), N-methyl diethanol amine (NMDEA, as emulsifier), and ethylene glycol (EG, chain extender). The polyol structures have been developed as alternative to produce cWPUs derived from a renewable resource. The effects of five parameters were studied – amount of NMDEA (0 – 2.25 mole), amount of EG (0 – 3 mole), molecular weight of HTNR (~1000 – 3000 g/mole), NCO index (100 – 150), and epoxide content on eHTNR soft segment (0 – 30%). The appearance of cWPU dispersion was milky-blue with long shelf life time, more than 10 months. Particle of prepared cWPU were spherical shape in the nano range size. The adhesive properties of cWPUs on the real leather surface, taking into account of the different molecular weights of HTNR and different degree of epoxide content on HTNR, were tested by lap shear test and 180 degree peel test and compared with commercial adhesives. Overall, to balance the stability and adhesive strength, the best conditions for preparing cWPU adhesive for leather application in this study was from the composition of HTNR3000 with epoxide content of 10%, NMDEA 5.67%wt, NCO index of 100 and 1 mole of EG. in condition of curing at 70 °C. In comparison to non-solvent based and solvent based commercial adhesives, the adhesive strengths of these synthesized cWPU adhesive were superior
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Samasiri, Peeradon. "Mixing in axisymmetric gravity currents and volcanic conduits." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/280120.
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The first part of this thesis investigates the mixing of ambient fluid into axisymmetric high Reynolds number gravity currents. A series of laboratory experiments were conducted in which small scale gravity currents travelled along a wedge shaped channel with an increasing width in the downstream direction. The channel was filled with fresh water and the current was generated using saline solution introduced either by a rapid release of a known finite volume from behind a lock gate or by pumping at a constant rate into the apex of the channel. The distribution and evolution of the density of the flow with distance downstream was measured using a light attenuation technique. Additional experiments were performed by injecting parcels of dye in different regions of the flow in order to visualise the motion of fluid in and surrounding the gravity current. Unlike currents introduced by the release of a finite volume of fluid, where most mixing occurs in the head of the flow, currents produced from a steady source develop a steady tail region behind the front which is also found to entrain a significant amount of ambient fluid. In both types of current, we estimate the fraction of displaced ambient fluid that is entrained into the flow. We then derive a new class of self-similar solutions for gravity currents produced from a finite volume release of fluid. The second part of this thesis develops the experimental method of measuring mixing using light attenuation to investigate the mixing of liquid in a vertical conduit which results from a continuous stream of high Reynolds number gas bubbles. The experiments identify that the mixing in the wake of the bubbles leads to a net dispersive transport along the conduit. The process provides an explanation for the heat transfer within a volcanic conduit in the case of a gas-slug flow regime as occurs in the near surface region of volcanic conduits connected to surface lava lakes. We derive a theoretical model to estimate the heat flux associated with such a system using the empirical law for the dispersive mixing. The predicted heat flux associated with the bubbles is found to be comparable to the heat loss at the surface of lava lakes associated with radiative and convective heat loss. Given values for the gas flux, the lake area and the temperature at the surface of the lake, the model enables new predictions for the size of the volcanic conduit.
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Segovia, Mera Alejandro. "Effets de la dispersion de nanoparticules dans un cristal liquide ferroélectrique sur les propriétés ferroélectriques et de relaxations diélectriques." Thesis, Littoral, 2017. http://www.theses.fr/2017DUNK0461/document.
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Ces travaux de thèse ont porté sur des matériaux constitués de dispersions de particules colloïdales nanométriques, issues d'un matériau ferroélectrique, dans un cristal liquide chiral à phase smectique ferroélectrique. Ils ont pour but d'étudier les effets occasionnés par ces dispersions sur les propriétés du nanocolloïde, notamment celles liées à leur ferroélectricité. Cette étude a montré que les comportements mésomorphes et ferroélectriques de ces matériaux sont conservés. Une baisse de polarisation spontanée ainsi qu'un recul des températures des transitions ont été mis en évidence pour des faibles concentrations en NPs. Une "transition" de ces comportements a été observée pour une concentration critique au-delà de laquelle les particules s'agrègent pour former des amas au sein du milieu cristal liquide. Nous nous sommes intéressés ensuite à deux modes de relaxation diélectriques. Le premier lié aux mouvements de distorsions de l'hélice dans la phase ferroélectrique, le second aux mouvements de compression des couches smectiques de part et d'autre de la transition ferroélectrique-paraélectrique. Les comportements observés semblent être gouvernés par les modifications des propriétés visco-élastiques des nanocolloïdes, occasionnés par l'intercalation des nanoparticules entre les couches smectiquesThe present thesis work concerns materials made of dispersions of nanometric colloidal particles, from a bulk ferroelectric material, dispersed within a chiral smectic phase of a ferroelectric liquid crystal. The goal of this work is to study the effect of the dispersed nanoparticles over the nanocolloïd properties, specially the ones related to ferroelectricity. This study showed no change over mesomorphic and ferroelectric behavior of the materials. A decrease in spontaneous polarization and phase transition temperatures was found for low nanoparticle concentrations. A "transition" of these behaviors was observed for a critical concentration, beyond which, nanoparticles aggregate and form clusters inside the liquid crystal matrix. Afterwards, we have studied two dielectric relaxation modes. The first one related to distorsions of the helix in the ferroelectric phase and the second one to the compression movements of the smectic layers around the ferroelectric-paralectric transition. The observed behaviors seem to be due to modifications of the visco-elastic properties of nanocolloids, produced by intercalation of nanoparticles between the smectic layers
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Donnadille, Philippe. "Comportement de gouttes en écoulement turbulent instationnaire : simulation numérique, modélisation, experimentation." Valenciennes, 1992. https://ged.uphf.fr/nuxeo/site/esupversions/65515773-7bc6-415c-8beb-98e07fbcb3d7.
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Le travail présenté dans cette thèse concerne l'étude de l'influence de fortes instationnarités d'écoulement sur la dispersion de gouttes. Le sujet est abordé selon les trois aspects suivants: simulation numérique, modélisation, expérimentation qui sont appliqués à deux géométries de base: marche descendante, zone de mélange. Des moyens originaux de visualisation, traitement d'image, et mesure sont utilisés pour caractériser l'écoulement: trajectographie de gouttes par vidéo rapide, anemogranulométrie par technique phase doppler. La simulation numérique: approche déterministe instationnaire lagrangienne pour la phase liquide, couplés a un calcul instantané de la phase gazeuse, est validée par l'expérience. Cinq approches stochastiques sont ensuite mises en œuvre pour la phase liquide (couplées à un calcul k-) et comparées aux approches précédentes. Une première analyse relative aux performances de ces différents modèles est présentée.
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Ridell, Annika. "Characterisation of Aqueous Solutions, Liquid Crystals and Solid State of Non-ionic Polymers in Association with Amphiphiles and Drugs." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ-bibl. [distributör], 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3607.
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Deshpande, Kiran B. "Studies On Phase Inversion." Thesis, Indian Institute of Science, 2001. http://hdl.handle.net/2005/285.
Full textAbstract:
Agitated dispersions of one liquid in another immiscible liquid are widely used in chemical industry in operations such as liquid-liquid extraction, suspension polymerisation, and blending of polymers. When holdup of the dispersed phase is increased, in an effort to increase the productivity, at a critical holdup, the dispersed phase catastrophically becomes the continuous phase and vice versa. This phenomenon is known as phase inversion.
Although the inversion phenomenon has been studied off and on over the past few decades, the mechanism of phase inversion (PI) has yet not become clear. These studies have however brought out many interesting aspects of PI, besides unravelling the effect of physical and operational variables on PL Experiments show that oil-in-water (o/w) and water-in-oil (w/o) dispersions behave very differently, e.g water drops in w/o dispersions contain oil droplets in them, but oil drops in o/w dispersions contain none, dispersed phase hold up at which inversion occurs increases with agitation speed for w/o dispersions but decreases for o/w dispersions.
A common feature of both types of dispersions however is that as agitation speed is increased to high values, inversion holdups reach a constant value. A further increase in agitation speed does not change inversion hold up. Although this finding was first reported a long time ago, the implications it may have not received any attentions. In fact, the work reported in the literature since then does not even mention it. The present work shows that this finding has profound implications. Starting with the finding that at high agitation speed inversion hold up does not change with agitation speed, the present work shows that inversion hold up also does not change with agitator diameter, type of agitator and vessel diameter. In these experiments, carried out in agitated vessel, energy was introduced as a point source. The experiments carried out with turbulent flow in annular region of two coaxial cylinders, inner one rotating, in which energy is introduced nearly uniformly throughout the system, show that the inversion holdup remains unchanged. These results indicate that constant values of inversion holdups for a given liquid-liquid systems (o/w and w/o) are properties of the liquid-liquid systems alone, independent of geometrical and operational parameters. A new hypothesis is proposed to explain the new findings.
Phase inversion is considered to occur as a result of imbalance between breakup and coalescence of drops. Electrolytes, which affect only coalescence of drops, were therefore added to the system to investigate the effect of altering coalescence of drops on phase inversion. The experiments performed in the presence of electrolyte KI at various concentrations indicate that addition of electrolyte increases the inversion holdup for both o/w and w/o dispersions for three types of systems: non polar-water, polar-water and immiscible organic-organic. Higher the concentration of electrolyte used, higher was the holdup required for phase inversion. These findings indicate that while the addition of electrolyte increases coalescence of drops in lean dispersions, it has exactly opposite effect on imbalance of breakage and coalescence of drops at high holdups near phase inversion point. The opposite effect of electrolytes in lean and concentrated dispersions could be explained qualitatively, but only in part in the light of a new theory, involving multi-particle interactions.
The phase inversion phenomenon is quantified in a simple manner by testing the
breakage and coalescence rate expressions available in literature. It has been found
that, equilibrium drop size (where breakage and coalescence events are in dynamic
equilibrium) approaches infinity near phase inversion holdup which is not an ex
perimentally observed fact. To capture the catastrophic nature of phase inversion,
two steady state approach is proposed. The two steady states namely the stable
steady state and unstable steady state, are achieved by modifying the expression
for coalescence frequency on the basis of (i) shear coalescence mechanism and, (ii)
recognising the fact that at high dispersed phase holdup the droplets are already in
contact with each other at all times and hence rendering the second order coales
cence process to a first order one. Using two steady states approach, catastrophic
phase inversion is shown to occur at finite drop size.
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Souidi, Kaïes. "Effet de la configuration des agitateurs dans une colonne à faible entrefer mécaniquement agitée sur la dispersion du gaz en foisonnement : approches expérimentale et numérique." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2012. http://tel.archives-ouvertes.fr/tel-00836761.
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Cette thèse est dédiée à l'étude de l'effet de la configuration des agitateurs (pales planes) et la nature du tensioactif sur la dispersion de gaz dans un liquide en vue d'obtenir un produit foisonné. Cette étude est menée à deux échelles pilote et locale. Le premier chapitre est dédié à une étude à l'échelle pilote. Les résultats ont montré qu'à conditions opératoires fixées, lorsque les agitateurs sont collés et décalés, l'aspect distributif de la dispersion de gaz est amélioré. L'aspect dispersif (taille des bulles), en revanche, reste peu sensible à la configuration des agitateurs. Les protéines sériques" WPI " comme agent tensioactif améliore l'efficacité de la rétention de gaz alors que le Tween 20 la réduit et provoque l'augmentation de la taille des bulles. Le deuxième chapitre concerne une approche locale qualitative (observation optique) et quantitative (détermination de capillaire critique). L'étude qualitative a montré que l'ajout d'un angle de décalage modifie l'écoulement du liquide et les bulles suivent la trajectoire imposée par le liquide. Lorsque les protéines WPI est utilisé comme agent tensioactif, sous l'action de la contrainte de cisaillement, les bulles subissent une déformation qui se termine par une rupture par extrémité. Un système couette a permis de déterminer un nombre capillaire critique correspondant à cette rupture. Par contre, en présence du Tween 20, la déformation ne conduit jamais à une rupture par extrémité. Le troisième chapitre de ce travail est dédié à une étude numérique de l'hydrodynamique de l'écoulement. Cette étude a permis de confirmer les résultats obtenus par l'approche qualitative. A titre d'exemple, un décalage entre deux agitateurs collés conduit à la multiplication des zones de vortex, à l'apparition des élongations supplémentaires et d'effet venturi favorables à l'aspect distributif de la dispersion. L'étude numérique montre également que le gradient maximal et moyen de vitesse reste indépendant de la configuration, ce qui explique pourquoi la taille moyenne est indépendante de la configuration.