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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.
2
Boyd, Jonathan W. R. "Sound measurement as a means of sizing gas bubbles in an aerated agitated vessel." Thesis, University of Reading, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265712.
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Bentham, Erik James. "Conjugate transfer processes in a pilot-scale unbaffled agitated vessel with a plain jacket." Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/12381/.
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Conjugate flow and heat transfer has been investigated in an unbaffled pilot-scale stirred tank reactor with a plain jacket. The vessel volume was 25 litres with a nominal capacity of 20 litres. Experiments and three-dimensional CFD simulations have been conducted on this vessel. The experiments involved heating, boiling, and cooling of methanol as well as water. The heat transfer medium in the jacket was an oil mixture called ‘DW-Therm’. The CFD simulations of some aspects of these experiments have been broken down into jacket-only and process-only simulations, followed by a fully conjugate simulation. The link between flow patterns, pressure drop and heat transfer in conventional jackets of stirred tank reactors has been analysed. The experiments and CFD simulations have been performed using a range of DW-Therm inlet temperatures. The CFD results were compared with experimental data of temperature measurements and with the use of engineering correlations found in the literature to predict heat transfer coefficients from the experimental data. The simulations produced values of total heat transferred by the jacket within 10% of the experimental results. The simulations of boiling inside the vessel approximated a constant process temperature which was used to investigate the jacket-only phenomena. The process-only and the conjugate simulations simulated heating of water inside the vessel. Mathematical analysis as well as and industrially and academically used correlations from the literature were used to estimate heat transfer coefficients for boiling and external heat loss. These correlations for overall heat transfer coefficients overlook maldistribution of heat transfer coefficients in jackets that use a liquid heat transfer medium. This is industrially important because it provides new information to consider when maintaining highly temperature-dependent processes, in which adequate heat transfer to or from the process is required. This could be for a variety of reasons, from maintenance of product quality to preventing runaway reactions.
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Carrillo, De Hert Sergio. "Drop size distribution analysis of mechanically agitated liquid-liquid dispersions." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/drop-size-distribution-analysis-of-mechanically-agitated-liquidliquid-dispersions(02a0af25-3d1c-47e0-8a4e-8b2cc98cdaea).html.
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Many daily life products consist of mixtures of oil and water. When an immiscible material is dispersed an interface in-between the two phases is created which gives rise to rheological phenomena which can be exploited for product formulation; this is the case in products such as hand-creams and food products. Furthermore emulsions are used to transport hydrophobic materials, for example, many pharmaceuticals are injected as emulsions into the bloodstream. The performance of such products depends on their microstructure, which is determined by its formulation and how its constituents are mixed together; therefore the microstructure depends on the properties of the dispersed phases, the emulsifier used, the equipment used and its processing conditions. Emulsified products are seldom mono-dispersed due to the complex drop breakup mechanism in the turbulent fields inside the equipment in which the phases are forced together. The chaotic breakup mechanism of highly viscous dispersed phases yield complex and broad drop size distributions (DSD) as a result of the dominating viscous cohesive stresses inside the parent drop. Former studies have used the Sauter mean diameter and/or the size of the largest drop as the characteristic measure of central tendency of the DSD to correlate their results and to prove mechanistic or phenomenological models; however these parameters in isolation are insufficient to characterise the whole DSD of highly polydisperse emulsions. In this dissertation a vast amount of silicon oils of different viscosity were used as dispersed phase to study the effect of various processing conditions and formulations on the resulting DSD. The effect of several formulation and processing parameters were studied for two different mixing devices: stirred vessels and in-line high-shear mixers. (1) For stirred vessels, the effect of stirring speed, continuous phase viscosity and dispersed phase volume fraction were studied in combination with the viscosity of the dispersed phase for steady-state systems. (2) For in-line high-shear mixers a model that links batch and multi-pass continuous emulsification for multimodal DSD was derived from a transient mass balance. Processing parameters such as time and volume, flow rate and number of passes through the mixer, and stirring speed were studied for a wide dispersed phase viscosity range. The analytical methodology implemented included the use of one or more probability density functions to describe the shape of the DSD. The models proposed gave reasonable approximations of the Sauter mean diameter and allowed to study the drop size changes and the relative amount of different types of drops resulting from different breakup mechanisms.
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Iamonaco, Mark A. "Determination of impeller pumping capacity from laser doppler anemometer (LDA) measurements in an agitated vessel /." Online version of thesis, 1991. http://hdl.handle.net/1850/11005.
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Mehauden, Karin. "Evaluation of the thermal and mixing performance of an agitated vessel for processing of complex liquid foodstuffs." Thesis, University of Birmingham, 2009. http://etheses.bham.ac.uk//id/eprint/297/.
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Thermal treatment is the most common method used by industry to ensure food is safe for consumption and to increase its storage life. To ensure safety, food is often overprocessed which can significantly affect its nutritional value as well as taste and flavour attributes. In this study, the heating and mixing efficiency of a bespoke vessel used for heat treatment of complex foodstuffs (250 litre ‘Vesuvio’ vessel manufactured by Giusti Ltd) was investigated. Enzymatic Time Temperature Integrators (TTIs) were used to determine the heat treatment efficiency. TTIs are small unattached measurement devices which contain a thermally labile enzyme: determination of the degree of degradation of the enzyme at the end of the thermal process enables the integrated temperature history to be obtained. TTIs can be used for process validation, particularly when the processing environment is inaccessible for fixed devices such as thermocouples. The reliability and accuracy of the TTIs was determined by exposure to various non isothermal industrially relevant temperature profiles using a Peltier stage and Polymerase Chain Reaction (PCR) device. The integrated temperature histories obtained by the TTIs’ correlated generally well with data obtained from thermocouples installed in parallel, although the error increases with holding time of the heat treatment. The work showed that the TTIs can be used reliably over a range (e.g. Enzymatic TTI made from the α-amylase from the Bacillus Licheniformis can reliably used from 5 to 30 minutes at 85°C) which is relevant for conditions of thermal pasteurisation of interest to this study. The range of time temperature profiles that enzymatic TTIs can monitor depends on the thermal resistance of the enzyme. The heat treatment efficacy of the ‘Vesuvio’ vessel was evaluated using TTIs and two thermocouples fixed onto the vessel wall and impeller shaft at the centre of the vessel. In addition to the plain or ‘free’ TTIs, a new TTI was developed where it was placed at the centre of an open structure to prevent intimate contact between the surface of the TTI and the vessel wall (‘Golf Ball’ and ‘Tie Clip’ TTIs). The food fluid could, however, penetrate the structure. The parameters examined in the study were fluid rheology, fill level (100% and 120% filling level) and the heating options (steam heating via wall jacket or direct injection). The study showed that the thermal process efficiency is lowered as the fluid viscosity increases when the wall jacket was used alone; this was observed by greater differences between the temperatures recorded by the thermocouples between the centre and the vessel wall. This was overcome by using direct steam injection into the vessel contents. Overfilling the vessel was also found to affect performance. The ‘free’ TTIs were found to have a higher thermal treatment than the TTIs which could not directly contact the wall. Under perfect mixing conditions, the ‘free’ TTIs and the TTIs placed inside the open structure should both give close results. However, this is not the case and it can be seen that the discrepancy increases when the mixing conditions worsen (increase of the fluid viscosity, no use of steam injection). The reliability of the TTIs as a validation tool is dependent upon their following the same path as the food fluid, i.e. they should be isokinetic and follow the fluid streamlines. To investigate this issue, the flow of both fluid and TTIs was examined on a reduced scale version of the ‘Vesuvio’ vessel using Particle Image Velocimetry (PIV) and Positron Emission Particle Tracking (PEPT). The effect of changing fluid rheology, agitation speed and filling level were investigated on the basis of a scaling at constant power per unit mass. The PIV experiments showed that the flow was laminar/transitional through bulk of vessel, with significant flow instabilities at the free surface and at the trailing edge of the impeller. Bulk mixing can therefore be expected to occur by laminar mechanisms with some mixing by eddy diffusion present at the free surface. The mixing pattern was not affected by rheology or agitation speed, however, overfilling of the vessel appeared to move the centre of the fluid rotation to above the impeller shaft, as verified using PEPT. PEPT was also applied by inserting either the free tracer into the fluid or placing it within a TTI. Significant differences in the path taken by the TTI and the fluid were observed when the TTI had a significant settling velocity in the fluid. Hence TTIs cannot be assumed to give reliable results in low viscosity fluids (e.g. water).
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Chiti, Fabio. "Lagrangian studies of turbulent mixing in a vessel agitated by a Rushton turbine : positron emission particle tracking (PEPT) and computational fluid dynamics (CFD)." Thesis, University of Birmingham, 2008. http://etheses.bham.ac.uk//id/eprint/1607/.
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Stirred vessels are used in a wide variety of process industries such as fine chemicals, pharmaceuticals, polymers and foods. In order to design efficient mixing vessels, a deep understanding of the blending processes is required. In cases where the fluid is not completely transparent, traditional optical laser based techniques are ineffective. One of the most promising techniques to study opaque systems is based on the detection of a tracer that emits gamma rays. Positron Emission Particle Tracking (PEPT) has been developed at the University of Birmingham and has been used in a wide range of applications including stirred tanks. However, for agitated vessels, any attempt of validation of the PEPT technique versus other techniques cannot be found. Hence, this work aims to validate and explore the potential of Lagrangian data in a well known mixing system such as a standard baffled vessel stirred by a Rushton turbine. As part of the validation, comparison with Eulerian PIV/LDA data has been also undertaken and some underestimation of the high velocities in the system was found in the impeller region. By using a selective interpolation algorithm of the tracer locations, this problem was greatly reduced although a perfect match with optical technique is not feasible. As further contribution to Lagrangian studies of mixing processes, Computational Fluid Dynamics (CFD) simulations have been undertaken to give both Eulerian and Lagrangian velocities and particle paths. However, it has been shown that traditional approaches to Lagrangian numerical simulation are unable to produce good trajectories that can be compared to experimental data. A novel three-step approach was suggested and implemented in order to achieve good paths, which then have been compared to the experimental trajectories. Qualitative and quantitative analysis of experimental Lagrangian data showed that the trajectories are erratic and follow random paths; furthermore, frequency analysis applied to portions of trajectories does not reveal any dominant low frequency in the system. Finally, circulation studies were undertaken in order to characterise mixing processes. This focused on tracking the tracer every time it leaves and returns a control volume proving the value of analysing time and return length distributions, since it was possible to compare the circulation times achieved in PEPT with published work. The trajectography approach used in this work is the first attempt at using trajectories from PEPT as a tool to characterise mixing performance rather than only using the data to find Eulerian velocities and vector plots.
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Torré, Jean-Philippe. "Quenching runaway reactions : hydrodynamics and jet injection studies for agitated reactors with a deformed free-surface." Phd thesis, Toulouse, INPT, 2007. http://oatao.univ-toulouse.fr/7658/1/torre.pdf.
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To quench a thermal runaway reaction in a chemical rector, an efficient approach is the introduction of a small quantity of a liquid inhibiting agent, named a “killer”, into the mixing vessel. In this thesis, an experimental approach has been coupled tightly with numerical modelling using Computational Fluid Dynamics (CFD). The first part of this thesis is devoted to a study of the hydrodynamics of partially-baffled mixing vessels, including the free-surface deformation caused by the central vortex. The use of an inhomogeneous, multiphase approach allowed simulation of the free-surface deformation. The capability of this novel method was demonstrated by very good agreement between the numerical predictions and experimental data. In the second part, liquid jet injection at the free-surface was coupled with the vessel hydrodynamics. Numerical results, obtained using an Eulerian-Lagrangian approach, have again shown good agreement with experimental data. These results allowed the jet trajectory to be modelled and its penetration into the agitated vessel was quantified. New mixing criteria were introduced that are specific to this application. Finally, the numerical methods validated at the pilot scale were applied at the industrial scale and allowed the proposal of practical improvements to the safety of the synthesis reactors studied
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Koutsakos, Erineos. "Solids suspension in mechanically agitated vessels." Thesis, University College London (University of London), 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318399.
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Mak, Andrew Tsz-Chung. "Solid-liquid mixing in mechanically agitated vessels." Thesis, University College London (University of London), 1992. http://discovery.ucl.ac.uk/1317906/.
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Experimental data are reported for solids suspension and distribution in four geometrically similar vessels with diameters equal to 0.31, 0.61, 1.83 and 2.67 m. Agitation was provided by a series of pitched blade turbines with impeller to vessel diameter ratios from 0.3 to 0.6 and pitched angles between 30° and 90°. The effect of impeller clearance on solids suspension was examined for a clearance range of T/4 to T/8. Dual impeller systems were also studied, covering two combinations (dual pitched and flat/pitched) and impeller spacing of half to two diameters apart. The majority of the experiments were carried out with 150-210 μm round-grained sand (density: 2630 kg m-3 and settling velocity: 0.015 m s-1) and tap water. Solids concentration was varied between 0.1 to 40% by weight. Four parameters were measured; impeller speed, using an optical tachometer, power input, calculated from the shaft torque given by strain gauges, just suspension speed, ascertained both visually and by use of an ultrasonic Doppler flowmetering (UDF) technique and the local solids concentration, measured by a in-house solids concentration probe. In addition extensive flow visualisations were made with the 0.61 m vessel in order to establish both liquid and particles flow patterns during the experiments. Results from this study were compared with previous publications in order to examine the effects of some of the important geometrical variables on solids suspension and distribution. This work revealed that for the range of parameters covered, the smallest (D/T=0.3) and the largest (D/T=0.6) impellers are the most and least efficient ones for solids suspension. Distribution tests with the three geometrically similar impellers show that the results are neither correlated in terms of tip speed nor power input but are best described by the thrust force generated by the impellers. In general, dual impeller systems improve solids distribution but require more power to just suspend solids compared with a single impeller. The scaling effect proposed by Zwietering (1958) for solids suspension has been confirmed by this study for vessel up to 2.67 m in diameter. The constant tip speed rule for solids distribution, which is based on one-dimensional dispersion models was found to underestimate the power requirement in large scale applications. This study indicates that equal power per unit volume is required to achieve the same degree of homogeneity.
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Zolfagharian, Akramolmoolouk. "Solid suspension in rotary-stirred and in liquid-jet stirred vessels." Thesis, University College London (University of London), 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318665.
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Patel, Ashvin G. "Surface movement in mechanically agitated gas-liquid reactors." Thesis, University of Bath, 1989. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234684.
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Bolour-Froushan, Abol Hassan. "Prediction of single-phase turbulent flow in agitated mixing vessels." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/37946.
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Rapisarda, Andrea. "Hydrodynamic characterization of two/three phase flow regimes in stirred tank." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
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Questo progetto di ricerca riguarda i processi di miscelazione in sistemi multifase meccanicamente agitati(regime turbolento). I sistemi studiati sono: gas-liquido, solido-liquido e gas-solido-liquido. Lo scopo è quello di analizzare il movimento delle particelle solide all'interno di un recipiente agitato, calcolandone la velocità(n) alle quali si è ottenuto lo stato di estrazione delle particelle(nJD), della completa dispersione(nCD) e del loading(nloading), attraverso l'uso di due diversi valori di diametro delle particelle.
Le misure sono state effettuate utilizzando due giranti su un albero e condotte con 6 diverse portate di gas e (da 3 a 6) concentrazioni X di particelle solide.
La presente ricerca dimostra che i valori di nloading non dipendono dalla concentrazione X di particelle nel sistema con acqua come fase liquida per entrambi i diametri di particelle dp, nel sistema con 0.4 Kmol/m3 di NaCl per dp1 e nel sistema con 0.8 Kmol/m3 di NaCl per dp2.
Nei sistemi con acqua e 0.4 Kmol/m3 di NaCl come fase liquida, i valori di nCD aumentano con l'aumento della concenrtrazione di particelle.
I valori di nJD aumentano significamente con l'aumento della concentrazione solida, per entrambi i diametri di particelle nel sistema a coalescenza(con acqua) e non coalescenza con concentrazione di elettrolita 0.8 Kmol/m3 di NaCl. La stessa dipendenza di nJD=f(X) è osservata per 0.4 Kmol/m3 di NaCl per dp2.
Per l'intera gamma di concentrazioni solide X, per lo stesso valore ddel diametro delle particelle, si ottengono valori inferiori di velocità di nloading, nCD, nJD per la configurazione delle giranti CD6-PBT.
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Guida, Antonio. "Positron emission particle tracking applied to solid-liquid mixing in mechanically agitated vessels." Thesis, University of Birmingham, 2010. http://etheses.bham.ac.uk//id/eprint/935/.
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Mechanically agitated vessels are widely used for various mixing operations within a wide range of industries including the chemical, pharmaceutical, food and petroleum industries. They are used for liquid blending, solid-liquid mixing, gas dispersion in liquids, heat/mass transfer enhancement and chemical reaction. Mixing is intrinsically a Lagrangian process and, whilst Eulerian data are essential, Lagrangian information is necessary for its complete description. Possible approaches of generating Lagrangian data can, in principle, employ numerical simulations or experimental techniques based on Lagrangian tracking to provide the trajectories of fluid elements or solid particles. In this work a set of tools are developed for the analysis and theoretical validation of Lagrangian single and multi-phase flow data obtained from tracer trajectories in mechanically agitated vessels. Whilst theoretical procedures developed here exploit a large range of mathematical and statistical concepts with Shannon entropy being an example, the computational data analysis often involved handling and sequential processing of multidimensional matrices containing several millions of data points. Computational codes were developed for performing Lagrangian statistical data analysis, Lagrangian-Eulerian data conversion, Shannon entropy analysis, multi-phase mixing studies and detailed Eulerian multi-plane investigations. The implementation and power of these tools are demonstrated by analysing a wide range of measurements acquired using the technique of positron emission particle tracking (PEPT) during the mixing of Newtonian and non-Newtonian fluids, as well as the mixing of highly concentrated solid-liquid systems. These multi-phase suspensions included monodisperse, binary and polydisperse solid-liquid suspensions. Experimental measurements obtained in these systems are unique and valuable in their own right as, for the first time, it has been possible to determine the full 3D velocity and concentration fields of liquid and solid phases within opaque dense slurries of this type containing up to 40 wt% solids.
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Muhr, Laurence. "Étude du procédé de fabrication des graisses au lithium complexe." Vandoeuvre-les-Nancy, INPL, 1993. http://www.theses.fr/1993INPL151N.
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Les procédés de fabrication de graisses de lubrification se sont souvent développés de façon empirique dans l'industrie pétrochimique. Face aux difficultés rencontrées lors du développement de nouveaux produits, une recherche plus fondamentale a été entreprise avec pour objectif d'améliorer la conduite du procédé de fabrication des graisses, dans le cas présent des graisses au lithium complexe. Dans un premier temps, une étude critique et explicative du procédé a été réalisée afin d'identifier les séquences susceptibles d'influer fortement sur la qualité du produit final. Il s'est avéré qu'une connaissance plus fondamentale des phénomènes lies à l'ébullition de fluides non newtoniens en cuve agitée était requise. L'étude envisagée dépassait donc le cadre strict de la fabrication des graisses. En effet, les problèmes d'ébullition en milieu fluide visqueux non newtoniens sont fréquents dans l'industrie et ont fait l'objet de très peu d'études jusqu'à maintenant. Dans un second temps, le transfert thermique au cours de ces opérations a été étudié de façon expérimentale sur des fluides modèles puis sur des graisses. Des résultats nouveaux quant à l'influence des propriétés rhéologiques de la charge sur les différents régimes d'ébullition en présence de convection forcée ont été obtenus
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Davies, Stephen Nigel. "The evaluation of overall gas-liquid mass transfer coefficients in gas sparged agitated vessels." Thesis, University College London (University of London), 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263106.
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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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Lo-Yim, Mei Yee Aideo. "Theoretical and experimental studies of drop breakage in two-liquid phase dispersions in mechanically agitated vessels." Thesis, University College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300088.
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Assirelli, Melissa. "Micromixing studies in turbulent stirred baffled and unbaffled vessels agitated by a Rushton turbine : an experimental study." Thesis, University of Birmingham, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.626864.
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The parallel-competing iodide-iodate reaction scheme has been used to study micromixing phenomena in baffled and unbaffled vessel of 0.29 m diameter (T) agitated by a Rushton turbine (D=1/3T) under turbulent conditions in a semi-batch mode. Firstly it was confirmed that by using successive injections, this reaction scheme is very efficient for such a study. Using this technique for the rest of the programme of work the first experiments were undertaken in the “standard baffled geometry”. Four agitator speeds giving mean specific energy dissipation rates, T ε , from ~0.2 W/kg to ~1.2 W/kg were used. For a given speed, addition at five different static feed locations, one just above the liquid surface and four submerged, were investigated. The four sub-surface feeding positions were associated with different local specific energy dissipation rates, εT, ranging from less than T ε , very close to the top of the liquid, to much greater close to the impeller. The point closest to the impeller was chosen to be such that feeding was estimated to be at the point of (εT)max. For the maximum speed, the segregation index, Xs, as a measure of the amount of 'waste product', was ~20% with feed onto the top of the liquid (as preferred industrially because of its convenience) or if slightly submerged. This 'waste' was reduced to ~5% by feeding at (εT)max. The distribution of εT was estimated from numerical solutions of the incorporation model combined with relationships arising from turbulence concept. A comparison was also made with results reported in the literature using the same reaction for two new devices developed for improved micromixing. By feeding at the carefully chosen position close to the impeller, the results with the Rushton turbine were as good as or better than with the special devices even at the comparatively low T ε of ~1.2 W/kg. It was estimated that the ratio of T T ε /ε (=φ) gave a maximum circumferentially averaged value of φ of ~90. The iodide-iodate technique was then used to ascertain the effectiveness of micromixing in a standard baffled reactor when feeding with pipes rotating with the impeller and discharging continuously into the region of (εT)max. The results when compared with those obtained using the fixed pipe at the equivalent position showed a significant intensification. Overall, a seven-fold reduction in ‘waste product’ was found between the most convenient fixed feed pipe position above the liquid surface and the rotating pipes, even at the modest T ε of ∼1.0 W/kg. This study is the first to use feeding continuously into the region of (εT)max. Thus an angular resolved (εT)max could be estimated from the incorporation model compared to a circumferentially averaged (εT)max obtained with a fixed pipe. The former was ∼3.0 times the latter, in close agreement with recent PIV based measurements. Finally the same geometry but without baffles was studied. The power number Po was measured and found to be Po=0.8, much less than Po=4.3 for the baffled tank. Visual decolourisation to give the macromixing time θm revealed evidence of a poor mixing region corresponding to the forced vortex region. The poor mixing in this region was confirmed by micromixing experiments. At the same T ε of 0.18 W/kg in the two cases, the values of segregation index, Xs, were found to be from ∼50% to 40% less than those III obtained with the baffled configuration except in the region close to the impeller where similar Xs values were found. These results are considered surprising, the unbaffled vessel proving much more effective for micromixing then expected. However, these improvements are limited by the very low maximum specific power input of 0.18 W/kg achievable with this configuration. Using the same micromixing model, all local (εT) values were > T ε . Clearly, this result is wrong. It is postulated that the swirling vortex flow past the fixed feed tube may give rise to a high very localised εT value. Clearly, further experimental and modelling work is required to gain a better understanding of the flow structure and micromixing in unbaffled vessels.
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Moeti, Lebone Tiisang. "The dependence of the continuous phase mass transfer coefficients on molecular diffusivity for liquid-liquid extraction in agitated vessels." Diss., Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/11856.
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De, Renzis Diletta. "Fluid dynamic analysis in three-phase stirred tanks." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
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The aim of this study is to measure the three characteristic agitator speeds (loading speed, complete dispersion speed and just drawdown speed) in a mechanically agitated vessel containing three phases (gas, solid and liquid phases).
The gas phase is air, the liquid phase is a water solution with 15% (by weight) concentration of glucose and the solid phase is made by particles of polyethylene that present two different mean values of diameter (dp = 3,025mm and dp = 4,025mm).
The first system considered was a vessel agitated by only one impeller (Smith turbine) and the second system was one vessel agitated by two impellers (Smith turbine and pitched blade turbine).
The aim of the experiment was to understand how the solid concentration, the volumetric gas flow rate and the mean diameter of the solid particles can affect the 3 characteristic speeds in the two different mechanically agitated systems.
A comparison between the two system was made in different conditions of:
- solid particles concentration
- volumetric gas flow rate
- diameter of the solid particles
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Chen, Ting Xuan, and 陳庭璿. "Numerical simulation of solid suspension and gas dispersion in a gas-liquid-solid three phase Rushton turbine agitated vessel." Thesis, 2019. http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi/login?o=dnclcdr&s=id=%22107CGU05063042%22.&searchmode=basic.
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Lin, Po-Yen, and 林柏岩. "Effects of Baffle Configuration and Vessel Size on Effects of Baffle Configuration and Vessel Size on Effects of Baffle Configuration and Vessel Size on Effects of Baffle Configuration and Vessel Size on Effects of Baffle Configuration and Vessel Size on Effects of Baffle Configuration and Vessel Size on Effects of Baffle Configuration and Vessel Size on Effects of Baffle Configuration and Vessel Size on Effects of Baffle Configuration and Vessel Size on Effects of Baffle Configuration and Vessel Size on Effects of Baffle Configuration and Vessel Size on Effects of Baffle Configuration and Vessel Size on Effects of Baffle Configuration and Vessel Size on Spherical Agglomerates of Dimethyl Fumarate in a Spherical Agglomerates of Dimethyl Fumarate in a Spherical Agglomerates of Dimethyl Fumarate in a Spherical Agglomerates of Dimethyl Fumarate in a Spherical Agglomerates of Dimethyl Fumarate in a Spherical Agglomerates of Dimethyl Fumarate in a Spherical Agglomerates of Dimethyl Fumarate in a Spherical Agglomerates of Dimethyl Fumarate in a Spherical Agglomerates of Dimethyl Fumarate in a Spherical Agglomerates of Dimethyl Fumarate in a Spherical Agglomerates of Dimethyl Fumarate in a Spherical Agglomerates of Dimethyl Fumarate in a Spherical Agglomerates of Dimethyl Fumarate in a Spherical Agglomerates of Dimethyl Fumarate in a Spherical Agglomerates of Dimethyl Fumarate in a Spherical Agglomerates of Dimethyl Fumarate in a Spherical Agglomerates of Dimethyl Fumarate in a Common Agitated Tank Common Agitated Tank Common Agitated Tank Common Agitated TankCommon Agitated Tank Common Agitated Tank Common Agitated TankCommon." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/cuc8w3.
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碩士國立中央大學
化學工程與材料工程學系
103
The aim of this thesis is to study the effects of baffle configuration and different vessel sizes on the spherical agglomeration process. Spherical agglomeration was operated in the 0.5 L-, 2 L-, 10 L-sized stirred vessels with the standard dimensions and the arrangement of impeller diameter, impeller location and liquid level. The stirred vessel installed with the standard US vertical baffle type or the European baffle type, or the Kawashima baffle type was used to prepare the spherical agglomerates of dimethyl fumarate. Initial solvent screening was used to establish the form space of dimethyl fumarate for selecting the useful solvent combination in spherical agglomeration process. It was found that the particle size distribution of agglomerates prepared in the stirred vessel installed with different baffle types at the same operating conditions could vary significantly, and plenty of powders did not assemble into granules in the large size of vessel under the same operating conditions. The polymorphism of spherical agglomerates did not transform after cohering the powders into the granules, but the crystallinity of the agglomerates was slightly altered. The size-related properties, such as dissolution profile and flowability, of granules from the same size cut remained unchanged. The interior structure-related properties, such as density and mechanical property, of granules from the same size cut upon baffle change and scale up were decayed. However, granules could become denser and stronger by prolonged maturation time.
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Wu, Shiang-Yu, and 吳翔愈. "Free-Surface and Vortex Shape Modeling in Unbaffled Agitated Vessels." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/c5j5u7.
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碩士國立臺北科技大學
能源與冷凍空調工程系碩士班
98
In this study, numerical simulations of turbulent flows with free-surface vortex in unbaffled agitated vessels, by Rushton turbine, and propeller impeller were presented. The predictions were obtained using the Fluent 6.3 computational fluid dynamics by a finite-volume method. The flow was assumed as a quasi-steady state, and this study applied a Multiple Reference Frame to calculate flow field. A rotational frame was used to calculate the flow of the impeller swept region, and the surrounding flow. A stationary frame was use to calculate the flow of the remaining region near the fence or the wall. The turbulent model used a Reynolds Stress Model (RSM); and wall function was used to calculate the flow near the wall. A Eulerian multiphase model was used to determine the free-surface and shape of the vortex. In order to assess the accuracy of the vortex shape, as identified above, this study used experimental data for analysis of the free-surface. Five parameters were changed to observe the transform of the vortex shape and depth in the stirred tanks, including angle of the impeller blades, clearance between the bottom of the vessel and the midsection of the impeller disk, eccentric distance between the stirring shaft and the Z-axis, and increasing the fence and diameter of the tank. It was shown that in the standard case, the predicted general vortex shape of the liquid free-surface is in good agreement with measurements, and the predicted vortex depth is good. The CVRMSE is less than 2.3%. In addition, the fence settings can increase the vortex depth and the turbulence kinetic energy. It can be used in large-diameter agitated vessels when the increased rotational velocity is able to maintain the vortex shape without losing its mixing efficiency.