Dissertations / Theses on the topic 'Stirred tanks'
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Chin, Ching-Ju. "Particle flocculation in stirred tanks." Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/21253.
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Distelhoff, Markus Friedrich Wilhelm. "Scalar mixing in stirred tanks." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265206.
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Hackett, L. A. "Gas-liquid mixing in stirred tanks." Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373092.
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Appa, Harish. "Multiphase CFD modelling of stirred tanks." Master's thesis, University of Cape Town, 2007. http://hdl.handle.net/11427/5548.
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Includes bibliographical references (p. 67-70).Stirred tanks agitated with Rushton turbines are commonly used in industry, for instance mixing processes and flotation systems. The need for more efficient systems in industries has led to the study of fluid flow within the tanks upon agitation; so that a better understanding of the phenomena can help in the optimisation of the tanks. In the recent years, efforts have been made towards the development of predictive methods using computational fluid dynamics (CFD). Among the various numerical works presented, emphasis was laid mainly on single phase systems. However, due to the various processes involving gas-liquid systems, the need for multiphase modelling of stirred tanks became increasingly important. This has led to more research studies involving multiphase flows. Most of the work reported showed good prediction of the velocity data and the power draw, reasonable turbulence parameters. But, the prediction of the gas hold-up was rarely well established. Therefore, the aim of this thesis, based on the numerical work presented by Engelbrecht (2006), is to investigate the discrepancies reported and to develop a multiphase model of a stirred tank agitated by a Rushton turbine. The commercially available CFD code FLUENT@ was used to model the agitated gas-liquid system. The results were validated with the numerical work of Engelbrecht (2006) and the experimental work presented by Deglon (1998). Two main cases were investigated, with a steady state and a transient approach. The QUICK scheme was used for the discretisation of the volume fraction and momentum and the first order upwind scheme for the discretisation of the turbulent kinetic energy and dissipation rate. The standard k - E turbulence model was used to account for the turbulent flow regime. A steady state MRF model was used for the investigation of the discrepancy reported by Engelbrecht (2006). The author reported that no convergence was achieved with such models. Solving the problem would have resulted in a good modelling approach for the prediction of gas dispersion, since steady state models are not computationally intensive. Three different boundary conditions, namely, a pressure outlet, an outflow and a velocity inlet, were used to model the outlet of the tank. The Euler-Euler multiphase model was used to simulate the gas-liquid system for the steady state model.
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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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Zipp, Robert Philip. "Turbulent mixing of unpremixed reactants in stirred tanks." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184832.
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The turbulent mixing process between two liquid streams in a standard tank stirred by a Rushton turbine has been studied. Experimental measurements of concentration and segregation (fluctuating concentration) have been made for both reacting and non-reacting flows. For the non-reacting case, one stream was marked with a fluorescent dye; the local concentration was measured using a fluorescence technique and a bifurcated fiber optic probe of custom design. Measurements were taken at two axial-radial planes within the tank. In the reacting case, the second-order reaction between sodium hydroxide and hydrochloric acid was studied, and urinine acted as a fluorescent indicator which became non-fluorescent as the reaction proceeded. Numerical studies of the mixing in the laboratory-scale vessel were made. FLUENT, a general-purpose fluid flow modelling program, was used to simulate the flow within the tank. This program uses a k-epsilon closure of the turbulent momentum equations. The program was modified to allow the inclusion of a segregation balance equation. Using this segregation balance technique, the turbulent species balance equations were solved. The results of these simulations agreed with the experimental measurements in all regions except the region near the entrance jets, where the model could not adequately predict the fluid behavior. This study has successfully predicted the behavior of reacting fluids in a bench-scale turbulently mixed stirred tank by the implementation of a segregation balance throughout the entire domain.
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Özcan-Taskin, N. Gül. "On the effects of viscoelasticity in stirred tanks." Thesis, University of Birmingham, 1993. http://etheses.bham.ac.uk//id/eprint/5407/.
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Mixing viscoelastic fluids is common to many chemical and biochemical process industries where the rheological properties of the bulk change considerably over the time course. The objectives of this study were to investigate the effects of viscoelasticity in mechanically agitated vessels (on: i- the power consumption and flow patterns in single phase and gassed systems, ii- mixing time under unaerated conditions and iii- cavities in the presence of gas) and to study the performance of InterMIGs in comparison to the classical six bladed disc turbines. Model viscoelastic fluids prepared exhibited only slight shear thinning properties (Boger fluid type), hence the effects of viscoelasticity could be studied in the absence of other rheological properties. Results obtained with these fluids were compared to those with viscous Newtonian glycerol covering the transitional flow regime (50< Re< 1000). Additionally, some work was also conducted in water for a preliminary characterisation of InterMIGs. In the relatively low range of Elasticity numbers (El < 3.5 x 10\(^-\)\(^3\)) covered, secondary flow patterns were not reversed. The power drawn under unaerated conditions was higher in viscoelastic fluids (at a given Reynolds number) for both impeller types that had to compete with mutually opposing viscoelastic forces. An experimental set-up to measure mixing times in viscous fluids (using the fluorescent dye-fibre optic technique) was installed. Reduced secondary circulations in viscoelastic fluids resulted in longer mixing times. Power consumption under aeration was also higher in viscoelastic fluids than that in Newtonian glycerol. Different from the findings under unaerated conditions, this enhancement was independent of the level of viscoelasticity. Cavities, hence the power drawn under aeration, were in general stable with respect to the variations in the gas flow rate in viscous fluids. This stability was found to be accentuated by viscoelasticity. InterMIGs underwent viscoelastic effects more severely on account of the complicated interaction of the viscoelastically driven flows with the flows associated with the inner and outer blades of these impellers. They presented a better choice in low and high viscosity Newtonian fluids and their performance was comparable to that of a single Rushton turbine in viscoelastic fluids.
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Leka, Suida. "On mixing and aeration of Rushton turbine stirred tanks." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
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The present study investigates the influence of the fluid properties on the mixing and aeration process of a Rushton turbine stirred tanks. Once the Rushton turbine agitated reactor is designed and developed following common standards, the effects of the viscosity, density, and surface tension on the bubbling process are evaluated. The size of single gas bubbles issued from a submerged nozzle is estimated at constant gas flow rate varying the orifice diameter, gas phase injected, and the liquid medium. Four orifice diameters are used: 0.6 mm, 1.0 mm, 2.0 mm, and 5.0 mm in diameter. As liquid medium, glycerine aqueous solutions at three different glycerine volume concentrations (20%, 40% and 60%), salt aqueous solution (300 g/L of salt) and surfactant solutions using Tween 20 at 0.01 mM and 0.1 mM concentrations, are employed for the experiments. Instead, air and argon are used to analyse the influence of the gas properties on the bubble size. Subsequently, the evaluations of the bubble frequency, the time rising, gas hold up and power consumption are performed considering all the investigated solutions. The mentioned experiments are carried out at three different impeller speed: 0, 185 and 315 RPM. It has been found that the fluid properties have an important role on the bubble size which largely influence the gas frequency, the time rising, and the gas hold up.
Finally, the objective is to study qualitatively the shape of the gaseous cavities in relation with the agitator speed and the gas phase flow rate in order to understand in which flow regime the different gas cavities are present. The experiments are carried out using water as liquid medium and air for the gas phase. Two different cases are investigated. In the first case, the impeller speed was varied from 150 RPM to 600 RPM, maintaining constant the gas flow rate at 0.5 L/min. In the second case, the impeller speed has been kept constant at 500RPM and the gas flow rate varied from 0.5 L/min to 1.5 L/min.
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Aoyi, Ochieng. "A hydrodynamic study of nickel suspension in stirred tanks." Doctoral thesis, University of Cape Town, 2005. http://hdl.handle.net/11427/6693.
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Many studies on solid-liquid mixing have been dedicated to low density particles at low solids concentrations. In the present work, computational fluid dynamics (CFD) simulation and experimental methods were employed to study suspension of high density particles (nickel) at high solids concentration in water. The work first focused on establishing the velocity field in a liquid-only system and then progressed to a solid-liquid system. In the liquid-only system, the influence of tank geometry and simulation strategies, including turbulence models, on fluid flow pattern and mixing was investigated in a tank stirred by a Rushton turbine. The standard k-f. model gave better overall predictions of mean velocity fields than the k-ro and RNG k-f. models. The CFD simulation and experimental results obtained with the laser Doppler velocimetry (LDV) method showed that mixing time and homogenization energy decreased with a decrease in the impeller bottom clearance. It was further shown that there is a bottom clearance range in which a draft tube can aid mixing in a tank stirred by the Rushton turbine. In the solid-liquid system, a hydrofoil impeller was used to investigate the influence of simulation strategies, particle properties and hydrodynamic operating conditions on mixing features such as the off-bottom solids suspension, cloud height, solids concentration distribution and local particle size distribution. The simulation results were compared with experimental ones, in which the off-bottom solids suspension was determined visually and an optical attenuation technique was employed to determine the cloud height and solids concentration distribution. The local particle size distribution (PSD) in the tank was measured by a laser diffraction method. A better agreement between the simulation and experimental results was obtained with drag models that account for the solids loading or free stream turbulence than those that do not. It was shown that the Stokes law applies up to a diameter of 150 ~m for the nickel particles. A CFD simulation strategy for studying mixing of high density solids is proposed and it is shown that a CFD simulation method can be used to develop empirical models that predict mixing features. A CFD simulation approach that takes particle size into account gives predictions that are more representative of practical applications than the mono-size particle simulation approach. Reactor configurations and hydrodynamic parameters that improve mixing were identified. These can also aid optimal design of mixing systems.
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Ziman, Harry John. "Computer prediction of chemically reacting flows in stirred tanks." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46632.
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Hannon, J. "Mixing and chemical reaction in tubular reactors and stirred tanks." Thesis, Cranfield University, 1992. http://dspace.lib.cranfield.ac.uk/handle/1826/11368.
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Fluid flow patterns and turbulence levels are instrumental in determining chemical reactor
performance. Parameters such as stirrer type and size, fluid physical properties, chemical
species concentrations and flow rates can strongly influence the safety, efficiency and reliability
of reactors, with consequent cost implications.
In this project, Computational Fluid Dynamics has been used to obtain insight into the
characteristics of tubular and stirred tank chemical reactors. Attention is focused on single phase
liquid isothermal turbulent flows. Turbulence theory is used to select and develop
appropriate physical models for both fluid flow and chemical reaction rates. Many previously used
models are shown to be of limited validity.
Results of simulations are compared with experimental measurements of the flow field and
progress of both simple and complex chemical reactions. Comparisons are generally favourable.
Limitations of the present approach are highlighted and future refinements and extensions
suggested.
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Bittorf, Kevin J. "The application of wall jets in stirred tanks with solids distribution." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0014/NQ59565.pdf.
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Brooks, P. C. "Liquid circulation and mixing in single and dual impeller stirred tanks." Thesis, University of Exeter, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380736.
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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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Siwale, Namwawa Alice. "Modeling of flow in impeller stirred tanks using computational fluids dynamics." Master's thesis, University of Cape Town, 2004. http://hdl.handle.net/11427/6761.
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Includes bibliographical references (leaves 63-68).The efficiency of mixing processes in impeller agitated tanks depends highly on the hydrodynamics. Computational fluids dynamics (CFD) provides a method of predicting the complex flow structures in stirred tanks. As with any approximate numerical method, CFD methods are subject to errors due to assumptions in the underlying mathematical models, as well as errors due to the numerical solution procedures. The aim of this thesis was to present a CFD method that accurately models the hydrodynamic properties of the 110w in stirred tanks. The general purpose CFD software Fluent 6. 1 was used to develop the model of a laboratory scale stirred tank. Numerical experiments were conducted to investigate the effects of the computational grid density, discretization schemes, turbulence models and impeller modelling method on the accuracy of the simulated flow. The results were validated with Laser Doppler Velocimetry data from the literature. It was found that the density of the numerical grid had more influence on the predicted turbulent quantities than on the mean velocity components. For the mean velocity components, reasonable agreement with the experimental data was observed even on relatively coarse grids. The choice of discretization scheme was found to have significant effect on the predicted turbulent kinetic energy and Power numbers. Very good agreement with experimental data was achieved for both these flow variables when higher order discretization schemes were used on fine grids. This is an important finding as it suggests that the generally reported underestimation of turbulence in literature is caused by numerical errors in the CFD simulation as opposed to inadequacies in the turbulence models as suggested by most researchers. Steady-state and time-dependent impeller models were compared and found to have little effect on the mean velocity and turbulent kinetic energy. However impeller Power numbers calculated from the time-dependent simulations were found to be in better agreement with the experimental values. A comparison was also made between the standard k-s and RNG models. It was found that the standard k-s turbulence model gave better predictions of the flow than the RNG- k-s turbulence model.
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Yu, Ziyun. "Fluid and suspension hydrodynamics in the impeller discharge flow of stirred tanks." Doctoral thesis, KTH, Chemical Engineering and Technology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3813.
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The hydrodynamics of an agitated tank have been studied byphase-Doppler anemometry. The focus is on the impeller anddischarge region of a 45o pitched blade turbine (PBT). Thestudy includes agitation of pure water as well as of a dilutesuspension of process particles. A three-dimensionalphase-Doppler anemometer is used to measure local,instantaneous, three-dimensional velocities of the fluid and ofthe suspended particles. A shaft encoding technique is used toresolve the turbulent fluctuations from the periodic velocityfluctuation due to the impeller blades, and to provide moredetailed information about the variations relative to theimpeller blade. Velocity bias is corrected for by the total3-dimensional velocity.
The mean flow field, the fluctuating velocities, and thecomplete Reynolds stress tensor, are reported for the liquidphase flow. The periodic fluctuations in the flow that aregenerated by the impeller blades are eliminated in theexamination of the turbulence. The anisotropy of the turbulenceis assessed by the invariants of the anisotropy tensor. Thetrailing vortex structure is demonstrated to be associated withhigh kinetic energy and strong anisotropy of the turbulence.The vortex is still observable 130-140 degrees behind theblade. It gradually moves down from the impeller blade but thelocation in radial direction remains essentially unchanged. Theinfluence of the periodic fluctuations is examined and it isshown that the turbulence appears more isotropic when theperiodic fluctuations are not eliminated.
The solid particle concentration is low below the impellerand is high above the impeller tip. The particles diverge fromthe liquid flow mean direction, especially below the agitatorclose to the tip where the strongest turbulence is found.Periodic fluctuations in the particle concentration relate tothe variations found in the angle-resolved mean velocity andfluctuating velocity. The ratio of the maximum to the minimumconcentration is about 2.0 in the present study.
The baffles influence on the conditions in the impellerregion, and this influence can be observed on the fluid meanvelocity field, the angle-resolved velocities, the kineticenergy, and on the behavior of larger process particles. In theimpeller region the highest kinetic energies are about 15%higher upstream of the baffle than at the middle plane betweenthe baffles. The highest energy level in the middle plane isactually the lowest value and is therefore not representativewhen rotation symmetry is assumed.
Local energy dissipation rates have been investigated, andthe integration of the local energy dissipation rates overdifferent control volumes has been compared with macroscopicenergy balance calculations. The discrepancy is significant.Different reasons have been analyzed and recommendations forfurther investigation are given. I
n the outflow region there is a significant variation alsoin the direction of the instantaneous velocity, which may leadto direction bias in the case of non-spherical measurementvolume. In order to account for this direction bias, amathematical model is developed to estimate the projected areaof the measurement volume in LDA or PDA. It is shown that theprojected area variation can lead to a significant directionbias in determination of time averaged values and localparticle concentration in a highly turbulent stirred tank flow.This bias is however negligible for an orthogonal optical setup, as is used in the present study.
Keywords:Hydrodynamics, phase-Doppler anemometer,suspension, pitched-blade turbine, anisotropy, turbulence,Reynolds stresses, trailing vortex, kinetic energy, stirredtank
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Daub, Andreas Verfasser], Jochen [Akademischer Betreuer] [Büchs, and Christian [Akademischer Betreuer] Herwig. "Hydromechanical stress in aerated stirred tanks / Andreas Daub ; Jochen Büchs, Christian Herwig." Aachen : Universitätsbibliothek der RWTH Aachen, 2016. http://d-nb.info/1129180816/34.
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Krige, Andrew Richard. "CFD analysis of reactive crystallisation in stirred tanks : a focus on nickel hydroxide." Master's thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/5303.
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Includes bibliographical references.The recovery of metal values from aqueous streams via precipitation, or reactive crystallisation, is both an economically and environmentally significant unit operation in a wide spectrum of industries. However, the control and operability of these systems is hampered by the limited fundamental basis for their design, frequently resulting in downstream processing difficulties. Previous work by Dustan (2001) considered precipitaion and subsequent dewatering as an integral system, and quantified, to a first order, the relationship between the various sub-processes. The current study is aimed at further resolving the upstream components of this intergrated model (i.e. the precipitation itself), with a particular focus, due principally to the rapid kinetics typically exhibited by precipitaion systems, on mixing and representation of time-dependent spatial inhomogeneities.
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Stone, David C. "Models for dispersion in flow injection analysis." Thesis, Loughborough University, 1987. https://dspace.lboro.ac.uk/2134/13607.
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An extensive study has been made of the factors affecting sample dispersion in flow injection analysis. This has included the effect of different manifold parameters on peak height and shape, and the use of various flow models to describe the physical processes involved. The factors investigated included sample flow-rate, tube length and diameter, sample volume, and the diffusion coefficient of the solute. The role of the detector has also been investigated, and was found to exert a strong influence on the observed dispersion behaviour of a flow injection manifold. In the light of this, a low volume flow cell was constructed which minimised the contribution of the detector to dispersion. Different modes of sample injection ("time" and "slug" injection) have been studied, and an automatic valve constructed in connection with the work. Both new and existing flow models have been evaluated in terms of their ease-of-use and ability to predict peak shape. Conditions for which the different models were valid were derived both experimentally and from consideration of the assumptions of the models. The applications of such models to the characterisation and design of flow manifolds has also been considered, and this approach compared to the purely theoretical and empirical approaches that have been described in the literature. The models examined in this thesis are the convection, diffusion, tanks-in-series, well-stirred tank, two-tanks in- parallel and two-tanks-in-series models. Finally, the practical implications of this work for the design of flow injection manifolds and the derivation of so-called "rules for dispersion" have been discussed, and suggestions made for further areas of research.
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Sossa, Jaime Alberto. "Experimental and computational study of mixing behavior in stirred tanks equipped with side entry impellers." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/42158.
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The wide applicability of mechanically stirred tanks in industry demands a comprehensive understanding of the physical and chemical phenomena controlling the performance of these fundamental units. The rheological complexity of some industrial fluids can create unfavorable mixing environments like dead zones that limit the contact area among the components being mixed. Also, the complex three dimensional nature of the flow generated by the impellers makes difficult the prediction of the flow properties, especially when the fluid viscosity is a function of the shear rate. Some research groups have investigated mixing flow of these kinds of fluids in conventional stirred tanks with top-entry impellers. But, little has been done to characterize the flow behavior in tanks with side-entry impellers.
In order to improve our understanding and provide insight into the flow mixing occurring in stirred tanks with side entry impellers, the flow field generated by different impellers in scale-down vessels filled with glycerine and carbopol solutions, was studied using the flow visualization technique, particle image velocimetry (PIV). Moreover, a computational model was built to predict flow variables and mixing characteristics unattainable with the experimental technique. The capabilities of the model were evaluated based on the velocity fields obtained experimentally. Good agreement was found between the predicted and measured macroscale flow structures and global mixing parameters. However, the models were unable to predict the symmetric flow observed during the experiments at high rotational speeds, likely due to the approach taken to simulate the flow, which provides a steady state velocity profile for one specific impeller location
Overall the results showed the formation of dead zones and segregated regions when mixing the non-Newtonian solutions. The size of the dynamic regions and the average velocity near the impeller were improved by increasing the suction area. Likewise, large pitch ratios were found to enhance the active mixing zone and the axial discharge. While, radial discharge and a strong tangential flow arose when the viscous forces dominate the flow. In conclusion, the flow features were defined by the Reynolds number in the vicinity of the impeller and the restrictions imposed by the walls of the vessel.
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Steiros, Konstantinos. "Effect of impeller design and rotation protocol on the power consumption of turbulent stirred tanks." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/50705.
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This thesis deals with topics concerning both passive and active control of stirred tanks. Regarding passive flow control, the effect of certain turbine blade modifications is investigated, most notably that of the blade perimeter increase in a fractal manner, applied on a conventional radial turbine stirring an unbaffled tank. It is found that the tested modifications show potential for applications, as by applying them, a drop in power consumption, an increase of the bulk turbulence intensity and the mass flow rate, and a suppression of the shed blade vortices' intensity and coherence is achieved. The latter, in particular, is argued to be a potential cause of the above-mentioned drop in torque/power consumption. Additional material from this section are the detailed comparison of fractal and perforated bluff bodies and a characterisation of the form drag distribution of radial turbines stirring unbaffled tanks. The latter was achieved by employing a novel pressure measuring technique. Regarding the active flow control, this thesis focuses on the prediction of stirred tank power consumption in situations where the shaft speed is not constant, but rather time dependent. The motivation for this is that such speed control has been shown to promote mixing in the tank. Employing first principles, qualitative scaling laws and empirical correlations, analytical models for the prediction of the torque response, when the shaft speed undergoes smooth, or step changes are developed. The predictions are then experimentally validated using torque measurements. The above models could find application in the design process of variable speed systems.
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Al-Wazzan, Yousef Jassim Easa. "The prediction of swirling recirculating flow and the fluid flow and mixing in stirred tanks." Thesis, Imperial College London, 1997. http://hdl.handle.net/10044/1/8329.
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Gimbun, Jolius. "Scale-up of gas-liquid stirred tanks using coupled computational fluid dynamics and population balance modelling." Thesis, Loughborough University, 2009. https://dspace.lboro.ac.uk/2134/11982.
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The main aim of the work was to produce scale-up methods for the design of aerated stirred tanks using a combined computational fluid dynamics (CFD) and population balance approach. First a modeling study of single phase stirred tanks was performed to evaluate the best model features (turbulence model, impeller's model, discretisation, grid etc). Good agreement was obtained between the CFD simulation and the LDA measurement on the time-averaged mean velocities and turbulence quantities. The angle-resolved mean velocities and turbulence quantities were also predicted very well as were the power number and the positions of the vortex cores. The next stage involved the development of a population balance model (PBM) which was carried out first using a well-mixed single compartment implemented in MATLAB to reduce the modeling complexity. The algorithm was validated for various mechanisms, namely breakage, aggregation, nucleation and growth which have an analytical solution available from literature. Tests using realistic models for bubble coalescence and breakage were also carried out with the results showing a reasonable agreement with the Sauter mean bubble sizes obtained from empirical correlations. The algorithm also responded well to changes in the turbulence dissipation rate, the initial bubble size distribution and the local gas hold-up, which suggest that the final bubble size is not affected by the initial bubble size. A fully predictive model must combine both the fluid mechanics and bubble dynamics models which can be performed either by a four-way or three-way coupling simulation. The disadvantage of the latter is that is does not consider the effect of the bubble dynamics in- the two-phase modelling. A four-way coupling (CFD-PBM) method was carried out by implementing the PBM within the CFD code. Various drag models which take into account the effect of distorted bubbles and dense gas dispersion are also considered. Mass transfer models are also implemented using the bubble sizes obtained from the PBM. The CFD-PBM model showed a reasonable prediction of the power number, local bubble sizes, gas hold-up, dissolved oxygen concentration and the mean velocities of the two-phase flow in comparison to experimental data taken from the literature. Finally, the CFD-PBM model was employed to evaluate the consequences of scale-up on the mass transfer rate in aerated stirred tanks agitated either by Rushton turbine or CD-6 impeller with operating volume ranged from 14L to 1500L. Three scale-up rules, namely a constant P IV combined with either constant Fig, Vg and VVM were studied. The simulation results suggest, that a successful scale-up may be achieved by keeping the P IV and VVM constant, which led to a slightly higher (kLa) representing a more conservative approach. In contrast, constant P/V and Vg led to a slight reduction in the rate of mass transfer at larger scale which is in agreement with experimental measurement . from the literature. Results from the CFD-PBM simulation also suggest a similar scale-up rule may be applicable for an advanced gas dispersion impeller such as the CD-6 which yielded a similar scale-up trend to that of a Rushton turbine.
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Sousa, Paulo Rogério Meneses de. "Escalonamento de tanques condicionadores utilizados na flotação de apatita." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/3/3134/tde-05122012-172154/.
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Este trabalho estudou a aplicação de oito métodos clássicos de escalonamento de tanques condicionadores, testando sua validade para dois tanques de geometria semelhante, mas com diferentes volumes (V1=10 e V2=49 decímetros cúbicos). No interior dos tanques, operavam impulsores (diâmetro D1=0,078m x D2=0,132m) que exibiam três distintos desenhos (2 pás versus 4 pás inclinadas em 45 graus versus turbina de Rushton). Sua rotação (N1 no tanque menor x N2 no tanque maior) visava à suspensão de partículas grossas de apatita (diâmetro médio = 254 micrometros) em polpas com 40% de sólidos em massa. Para balizar o escalonamento, adotou-se como variável de controle a mínima rotação do impulsor (Njs) que é capaz de fazer com que nenhuma partícula repouse no fundo do tanque por mais do que 1 ou 2 segundos (Critério 1-s), além de perfis axiais de distribuição de sólidos e a extensão da Zona Turbulenta versus Zona Quiescente no interior dos tanques. A diferença entre o valor previsto de Njs para o tanque de 49 decímetros cúbicos (N2) pelos métodos de escalonamento versus o valor de Njs (N2) determinado experimentalmente foi expressa como erro percentual (E). Consideraram-se como adequados para a aplicação que constitui o objetivo desta dissertação todos os métodos que exibiram E menor que 10%. Para o impelidor de 2 pás inclinadas, a adequação do método baseado na constância da razão potência/volume (E=2%) e também do método empírico de Rautzen (E=6%), indica a expressão N2=N1.(D1/D2) com seu expoente da relação entre os diâmetros variando entre 0,67 e 0,75 para a aplicação desejada. Considerando o impulsor de 4 pás inclinadas, a adequação do método da constância da razão potência/volume (E=4%); assim como dos métodos empíricos de Rautzen (E=0%) e Zwietering (5%), sugere o uso da expressão N2=N1.(D1/D2) com seu expoente da relação entre os diâmetros variando entre 0,67 e 0,85. Para a turbina de Rushton, o único método que exibiu E menor que 10% foi o da constância da relação potência/volume (E=8%), cuja expressão é N2=N1.(D1/D2) com seu expoente da relação entre os diâmetros igual a 0,67. Uma vez que a determinação do valor real de N2 foi baseada numa técnica experimental influenciada pelas limitações do observador, pode-se inferir que uma expressão geral de escalonamento do tipo N2=N1.(D1/D2) com seu expoente da relação entre os diâmetros igual a 0,75 atende aos propósitos desta aplicação. Por outro lado, o uso da relação P/V provê um critério mais objetivo para se balizar o escalonamento, haja vista que ele se adequou a todos os três tipos de impelidores contemplados por este estudo.This work has studied the application of eight classical methods appointed by literature to accomplish the scale-up of stirred tanks which aimed to suspend slurries of 40% of solids, containing coarse (mean diameter=254 micrometers) apatite particles. The validity of the methods was accomplished by using two tanks of similar geometry but different capacity (V1=10 e V2=49 cubic decimeter), together with impellers of different diameter (D1=0,078m versus D2=0,132m) and design (turbine of 2 or 4 blades inclined at 45 degrees and Rushton turbine). To assist the process of validation, the impeller speed (Njs) under which no particle rests on the bottom of the tank for more than 1-2 seconds (1-s Criterium) was used together with the axial profile of solids percent distribution plus the extension of the turbulent versus quiescent zones within the two tanks. For any of the eight scale-up methods, the difference between the predicted value of Njs (N2) for the 49 cubic decimeter tank and the actual value (experimental) of the same variable was determined and its magnitude was expressed in terms of the percent error (E). The methods that yielded E less than 10% were considered as suitable for the aimed application. Considering the 2-inclined blade impeller, low value of E yielded by the method based on the constancy of the ratio power/volume (E=2%) and also by the empiric method of Rautzen (E=6%) indicate that the expression N2=N1.(D1/D2) with its exponent of the relation between diameters ranging between 0,67 and 0,75 is suitable for the desired application. Regarding the 4-inclined blade impeller, because the method based on the constancy of the ratio power/volume (E=4%) and also the empiric methods of Rautzen (E=0%) and Zwietering (E=5%) yielded the lowest values of E, the expression N2=N1.(D1/D2) with its exponent of the relation between diameters ranging between 0,67 and 0,85 is suitable for the aimed application. Moreover, for the Rusthon turbine, only the method based on the constancy of the ratio power/volume (E=8%) was adequate for the aimed application and, thus, the expression N2=N1.(D1/D2) with its exponent of the relation between the diameters equal to 0,67 is suitable for the purpose of this dissertation. Once the actual value of N2 is determined by visual observation, it is not possible to get very accurate results. This way, a generic scale-up expression is proposed: N2=N1.(D1/D2) with its exponent of the relation between the diameters equal to 0,75. On the other hand, the ratio P/V may provide a more objective criterium for scale-up, because the three sort of impellers used in this study yielded E less than 10% when the power/volume method was applied for the purpose of scale-up.
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Unadkat, Heema. "Investigation of turbulence modulation in solid-liquid suspensions using FPIV and micromixing experiments." Thesis, Loughborough University, 2010. https://dspace.lboro.ac.uk/2134/6377.
Full textAbstract:
The focus of this thesis is the study of turbulent solid-liquid stirred suspensions, which are involved in many common unit operations in the chemical, pharmaceutical and food industries. The studies of two-phase flows present a big challenge to researchers due to the complexity of experiments; hence there is a lack of quantitative solid and liquid hydrodynamic measurements. Therefore, an investigation of turbulence modulation by dispersed particles on the surrounding fluid in stirred vessels has been carried out, via two-phase fluorescent Particle Image Velocimetry (FPIV) and micromixing experiments. The main property of interest has been the local dissipation rate, as well as root-mean-square (rms) velocities and turbulent kinetic energy (TKE) of the fluid. Initially a single-phase PIV study was conducted to investigate the flow field generated by a sawtooth (EkatoMizer) impeller. The purpose of this study was to gain insight into various PIV techniques before moving on to more complex two-phase flows. Subsequently stereo-, highspeed and angle-resolved measurements were obtained. The EkatoMizer formed a good case study as information regarding its hydrodynamics is not readily available in literature, hence knowledge has been extended in this area. An analysis of the mean flow field elucidated the general structure of fluid drawn into the impeller region axially and discharged radially; the latter characterised the impeller stream. The radial rms velocity was considered to represent best the system turbulence, even though the tangential rms velocity was greater close to the blade; however the radial component was more prevalent in the discharge stream. Due to differences in rms velocities, TKE estimates obtained from two and three velocity components deviated, being greater in the latter case. Integral (1-D and 2-D) length scales were overestimated by the quantity W / 2 in the impeller region. Ratios of longitudinal-to-lateral length scales also indicated flow anisotropy (as they deviated from 2:1). The anisotropy tensor showed that the flow was anisotropic close to the blade, and returned to isotropy further away from the impeller. Instantaneous vector plots revealed vortices in the discharge stream, but these were not associated with flow periodicity. Alternatively, the vortex structures were interpreted as low frequency phenomena between 0-200 Hz; macro-instabilities were found to have a high probability of occurrence in the discharge stream. Dissipation is the turbulent property of most interest as it directly influences micromixing processes, and its calculation is also the most difficult to achieve. Its direct determination from definition requires highly resolved data. Alternative methods have been proposed in the literature, namely dimensional analysis, large eddy simulation (LES) analogy and deduction from the TKE balance. All methods were employed using 2-D and 3-D approximations from stereo-PIV data. The LES analogy was deemed to provide the best estimate, since it accounts for three-dimensionality of the flow and models turbulence at the smallest scales using a subgrid scale model. (Continues...).
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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.
Full textAbstract:
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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Ochieng, A., and MS Onyango. "Homogenization energy in a stirred tank." Elsevier, 2006. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1000755.
Full textAbstract:
Mixing in stirred tanks influences conversion of reactants for fast reactions, and the efficiency of a mixing process can be determined from
the power consumption and mixing time, which are the two parameters that define homogenization energy. In this study, the computational fluid
dynamics (CFD) and laser Doppler velocimetry (LDV) techniques were employed to study the effect of the Rushton turbine bottom clearance
on the flow field, mixing time and power consumption in a stirred tank. Experimental and simulation studies were conducted in a tank with and
without a draft tube where a conductivity meter and decolourization methods were employed in validating the mixing time simulation results. A
good agreement between the experimental and simulation results for the flow field and mixing time was obtained. The results showed a reduction
in mixing time and power consumption at a low impeller clearance, with reference to the standard clearance, and a further reduction of the same
parameters was obtained for a system fitted with a draft tube. At the low clearance, there was an increase in mixing efficiency by 46%, for a system
without draft tube and 61% for that with the draft tube.
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Yapici, Kerim. "Numerical Investigation Of Stirred Tank Hydrodynamics." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/1302140/index.pdf.
Full textAbstract:
A theoretical study on the hydrodynamics of mixing processes in stirred tanks is described. The primary objective of this study is to investigate flow field and power consumption generated by the six blades Rushton turbine impeller in baffled, flat-bottom cylindrical tank both at laminar and turbulent flow regime both qualitatively and quantitatively. Experimental techniques are expensive and time consuming in characterizing mixing processes. For these reasons, computational fluid dynamics (CFD) has been considered as an alternative method. In this study, the velocity field and power requirement are obtained using FASTEST, which is a CFD package. It employs a fully conservative second order finite volume method for the solution of Navier-Stokes equations. The inherently time-dependent geometry of stirred vessel is simulated by a multiple frame of reference approach. The flow field obtained numerically agrees well with those published experimental measurements. It is shown that Rushton turbine impeller creates predominantly radial jet flow pattern and produces two main recirculation flows one above and the other below the impeller plane. Throughout the tank impeller plane dimensionless radial velocity is not affected significantly by the increasing impeller speed and almost decreases linearly with increase in radial distance. Effect of the baffling on the radial and tangential velocities is also investigated. It is seen that tangential velocity is larger than radial velocity at the same radial position in unbaffled system. An overall impeller performance characteristic like power number is also found to be in agreement with the published experimental data. Also power number is mainly affected by the baffle length and increase with increase in baffle length. It is concluded that multiple frame of reference approach is suitable for the prediction of flow pattern and power number in stirred tank.
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Forrester, Stephanie E. "Hydrodynamics of a gas-inducing impeller." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362961.
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Van, Walsum G. Peter (Gerard Peter). "Self cycling fermentation (SCF) in a stirred tank." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=56779.
Full textAbstract:
Self cycling fermentations (SCF's) were conducted in an apparatus based on a commercial model two litre stirred tank fermenter. An automated control system and peripheral vessels were used to perform cycling control, medium addition, broth removal and sampling.The apparatus was used to grow Bacillus subtilis and Acinetobacter calcoaceticus on different media. Both organisms supported a steady state SCF. Measurements of biomass, cycle time and minimum dissolved oxygen all gave repeatable results. Results were comparable to literature values for a cyclone column SCF apparatus.
A gas analyzer was installed to measure oxygen and carbon dioxide concentrations in the effluent gas. The response of the gas analyzer paralleled that of the dissolved oxygen measurements.
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Ajayi, Olukayode Oludamilola. "Prediction of the hydrodynamics in stirred tank reactors." Master's thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/5337.
Full textAbstract:
Includes bibliographical references.There have been several attempts to find a suitable set of model parameters for stirred tank reactors. In view of this, the present study investigated the performance of the standard k - ε model to predict the flow field in stirred tank reactors. The parametric analysis presented herein involves variation of the parameters in the model and an estimation of the overall error values between experimental data and the model predictions, which includes the mean velocities and the turbulent kinetic energy. The analysis also involves ascertaining the stability of the model via the moment convergence approach.
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Kennedy, Mark William. "Chlorination of magnesium carbonate in a stirred tank reactor." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=24061.
Full textAbstract:
A study was conducted on the reaction of solid MgO formed from magnesite (MgCO$ sb3),$ with Cl$ sb2$ and CO gas, in a stirred tank reactor containing a liquid bath of MgCl$ sb2.$ The reaction rate was found to be controlled by CO mass transfer from the gas to the liquid phase and was zero order with respect to the concentration of MgO. At temperatures from 743 to $824 sp circ$C, the reaction rate exhibited an activation energy of 80 kJ/mol, which is typical of a diffusion controlled reaction.The chlorinaton rate was effected by both temperature and CO/Cl$ sb2$ ratio and estimates of the optimum conditions were obtained: temperature $(856.6 sp circ$C) and ratio of CO/Cl$ sb2$ (1.24). The addition of an inert gas (N$ sb2)$ to the reagent mixture was found to decrease the reaction rate. Iron was found to have a negligible effect on reaction rate at the levels tested (up to 560 P.P.M.).
For those experiments conducted at $ rm 820 sp circ C pm 5 sp circ C,$ an overall correlation was obtained which related the MgO reaction rate, with impeller power (kW/m$ sp3),$ superficial gas velocity (cm/s) and the partial pressure of CO (atm.): rm Rate = 0.609 (P sb{g}/V sb1) sp{0.35} (v sb{s}) sp{0.64} (P sb{CO}) sp{1.14}, (kgmol/m sp3/h) eqno lbrack 55 rbrack. ixing and gas dispersion characteristics were defined for the specific impeller/tank geometry used in these experiments.
Using the results presented here, it would be possible to estimate the size and number of commercial stirred tank chlorination reactors, which would be required to produce any specified quantity of magnesium, starting from magnesite, with an accuracy of $ pm$44%, with 95% confidence.
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Thoma, Hubis Suzanne Alice. "Interactions between macro- and micromixing in stirred tank reactors /." [S.l.] : [s.n.], 1989. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=9012.
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Katsanevakis, Athanasios N. "Performance parameters for boiling and gassed stirred tank reactors." Thesis, University of Surrey, 1994. http://epubs.surrey.ac.uk/844581/.
Full textAbstract:
The flow field in two-phase boiling and gas-liquid Stirred Tank Reactors, STR, was examined in relation to cavity formation and the associated Relative Power Demand, RPD. The cavitation process has been classified in various stages for both radial and axial impellers operating in boiling water. Experiments done in a boiling reactor of 0.45 m diameter agitated by radial and axial impellers showed that the Relative Power Demand, RPD, can be correlated well with the help of a new formulation of Cavitation number named the Cavagitation number. Differences in RPD between gas-sparged and boiling reactors detected during the experiments imply that there are differences in the mechanism of cavity formation in the two systems. These differences are explained by a consistent physical model. The model was shown to be adequate for most of the features of both boiling and sparged reactors reported in the literature. The flow field in a two-phase boiling reactor has been investigated for the first time in the open literature using Laser Doppler Velocimetry, LDV, in conditions where the RPD was as low as 0.55. Measurements gave important data of the way the flow field is changed by the presence of the second phase which forms stable cavities behind impeller blades. The results also quantified the associated flow field changes in the impeller discharge stream and in the bulk of the reactor. The two-phase flow field was quantitatively described with the help of a simple model derived on the basis of energy balances calculated around the impeller. The model estimates liquid flow rates and mean liquid velocities in the two-phase system using data of the corresponding single-phase system coupled with information about the RPD. Knowledge of the void fraction seems to improve the model predictions which were shown to be in fairly good agreement with the data of mean flow rates that exist in the literature. LDV measurements done in a boiling stirred tank of 0.45 m diameter showed that flow rates can be predicted within an accuracy of around 10% and mean liquid velocities with an accuracy better than 25%, even without taking into account void fraction. Model predictions can be used as input values for numerical codes available for the calculation of flows in two-phase stirred tank reactors. Application of the model is independent of geometry and scale.
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Engelbrecht, Darnell Francois. "Development of a CFD model for stirred tank applications." Master's thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/5545.
Full textAbstract:
Word processed copy.Includes bibliographical references (leaves 86-90).
This thesis deals with the development of a multi phase model for stirred tank applications. The general purpose, commercially available CFD code, FLUENT 6.2, is used to model a Rushton turbine-agitated stirred tank with T = 0.14 m.
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Samer, Charles J. "Polymer-stabilized miniemulsion polymerization in a continuous stirred-tank reactor." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/11142.
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Lee, Hsueh-Chi. "Emulsion polymerization in a seed-fed continuous stirred-tank reactor." Diss., Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/11860.
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Mushonga, Sylvester Paul. "pH control using two continuous stirred tank reactors in series." Thesis, California State University, Long Beach, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1595785.
Full textAbstract:
The control of pH is one of the most difficult chemical control schemes in industry. Often, large tanks are used to control pH. The pH in these large tanks frequently overshoots the desired pH set-point and usually takes a long time to reach the desired set-point. In this work, a conceptual pH control process was developed and tested by using two small continuous stirred tank reactors (CSTRs). In this two-step system, the bulk of the neutralization is carried out in the first reactor and then fine-tuned in the second reactor. The conceptual neutralization model was built by analyzing the chemistry behind pH. Because pH is a nonlinear function of hydrogen ion concentration (pH= -log [H+]), the hydrogen ion concentration was chosen as the process measured variable. The slope (Gain) was calculated from a titration curve obtained from a polynomial derived from neutralization chemistry and a practical titration. The process dynamics were then fitted into the classic proportional, integral, and differential (PID) controller using the Internal Model Control (IMC) tuning method. The robust tuning parameters produced by the IMC method were able to bring the pH in the first CSTR to the desired set-point. In addition, disturbances from vibrations produced by the pump and magnetic stirrer, slight variations in reactant concentration, and pH probe lags were easily eliminated. Most importantly, pH in the second CSTR settled on the desired neutral set-point of pH 7.0 after brief oscillations. The process was repeatable when the reactors where scaled up one hundred times using synthetic waste water. Autotune variation results produced similar process dynamics to those produced by calculating the slope from the titration curve.
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Davis, Ryan Z. "Design and Scale-Up of Production Scale Stirred Tank Fermentors." DigitalCommons@USU, 2010. https://digitalcommons.usu.edu/etd/537.
Full textAbstract:
In the bio/pharmaceutical industry, fermentation is extremely important in pharmaceutical development, and in microbial research. However, new fermentor designs are needed to improve production and reduce costs of complex systems such as cultivation of mammalian cells and genetically engineered micro-organisms. Traditionally, stirred tank design is driven by the oxygen transfer capability needed to achieve cell growth. However, design methodologies available for stirred tank fermentors are insufficient and many times contain errors. The aim of this research is to improve the design of production scale stirred tank fermentors through the development of dimensionless correlations and by providing information on aspects of fermentor tanks that can aid in oxygen mass transfer. This was accomplished through four key areas. Empirical studies were used to quantify the mass transfer capabilities of several different reactors. Computational fluid dynamics (CFD) was used to assess the impact of certain baffle and impeller geometries. Correction schemes were developed and applied to the experimental data. Dimensionless correlations were created from corrected experimental data to act as a guide for future production scale fermentor design. The methods for correcting experimental data developed in this research have proven to be accurate and useful. Furthermore, the correlations found from the corrected experimental data in this study are of great benefit in the design of production scale stirred tank fermentors. However, when designing a stirred tank fermentor of a different size, further experimentation should be performed to refine the correlations presented.
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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.
Find full textAbstract:
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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Panda, Kishora Kumar. "Ozone mass transfer and reaction in In situ and stirred tank reactors /." Search for this dissertation online, 2005. http://wwwlib.umi.com/cr/ksu/main.
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com, herabudi@plasa, and Herawati Budiastuti. "Intensification of Single Stage Continuously Stirred Tank Anaerobic Digestion Process using Carriers." Murdoch University, 2004. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20051014.141638.
Full textAbstract:
The Continuously fed Stirred Tank Reactor (CSTR) is a popular design for anaerobic treatment of wastewater. This reactor type is simple in design and operation, independent of biomass type and low in capital costs. The CSTR has, however, to be operated at long Hydraulic Retention Times (HRT) of the order of 16 to 30 days since biomass is continuously lost with the effluent. Various alternate concepts of reactor design have, therefore, been developed to allow more rapid treatment. Treatment can be enhanced by retaining biomass within the digester so that the HRT is decoupled from solid biomass retention time (SRT). Unlike in continuous stirred tank digesters where the SRT is equal to HRT, the SRT in other designs are much greater than the HRT. This allows the wastewater to be treated at high throughputs while retaining the biocatalyst (or biomass) mediating the treatment within the digester.
In this study the operation of a CSTR was intensified by separating SRT from HRT while taking into account the economical aspects. The intensification of operation is defined as increasing wastewater throughput or organic loading rate while at the same time maintaining efficiency of treatment and robustness to reject disturbances (changes in wastewater concentration and flow rate). The operation of existing CSTR was intensified by addition of carriers. It is hypothesized that by providing surfaces (or carriers) for bacterial attachment within the continuous stirred tank digester, biomass will be better retained and the wastewater throughput can be increased.
The carriers or surfaces employed in this study were light carrier elements (shredded granular rubber tire having a density of 0.96 g/cm3) that move gently with the water in the reactor. This carrier material is much cheaper compared with other commercial carrier materials. This reactor type, called an Anaerobic Moving Bed Reactor (AMBR), was applied in this study to treat high strength synthetic wastewater, containing molasses as the main substrate.
The improvement of reactor performance was clearly shown by the capability of the system to be operated without any difficulties at HRT of 6 days at an OLR of 5.8 g COD/l/d or at HRT of 1 day at an OLR of 4 g COD/l/d. The carriers were shown to be effective in retaining biomass aggregates.
The AMBR was further intensified by changing the feeding strategy. It was shown that in stirred tank digester without carriers an intermittent feeding strategy resulted in better microbial capacity to degrade higher chain volatile fatty acids like propionic and butyric acids than the continuous feeding mode. An increase in degrading capacity of the intermittently fed digester was shown via degradation rates of pulse additions of propionic and butyric acids and by its capability of handling all changes in loading rates imposed. The continuously fed digester, receiving constant feed, on the other hand, suffered more when loading rates were changed, and the degradation rates of propionic and butyric acids were slower.
The intermittent feeding mode was then implemented on the AMBR, and it was operated as a sequencing batch reactor with a fill, react, settle and decant period in each cycle. The sequencing batch mode when applied to the AMBR (now called an Anaerobic Moving Bed Sequencing Batch Reactor or AMBSBR) could increase capability of the digester to handle higher shock loads. At 3.8 d HRT the AMBSBR could handle an OLR of 10.8 g COD/l/d as opposed to 7.4 g COD/l/d by the AMBR. At 2.5 d HRT the AMBSBR could handle an OLR of 6.4 g COD/l/d while the AMBR could only be loaded at an OLR of 4.2 g COD/l/d. The ratio of SRT to HRT was at least 15 for this reactor. The reactor was able to handle concentrated feed flow rates at longer cycles or more dilute feed flow rates at frequent shorter cycles.
The proposed operational strategies were verified by using a structured mathematical model which was developed based on the IWA ADM1 model. Several modifications were implemented to the model to obtain better predictions. The modified model was capable in predicting all the trends of the operating variables from both continuously and intermittently fed reactors. None of the two model versions (ADM1 and modified models) was, however, able to predict the increased propionate degradation capacity in intermittently fed digesters. The reason for this was the assumption of fixed stoichiometry of fermentative reactions for glucose mineralisation. By modifying the fractions of glucose mineralisation a better fit between experimental results and the model could be obtained.
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Budiastuti, Herawati. "Intensification of single stage continuously stirred tank anaerobic digestion process using carriers." Budiastuti, Herawati (2004) Intensification of single stage continuously stirred tank anaerobic digestion process using carriers. PhD thesis, Murdoch University, 2004. http://researchrepository.murdoch.edu.au/491/.
Full textAbstract:
The Continuously fed Stirred Tank Reactor (CSTR) is a popular design for anaerobic treatment of wastewater. This reactor type is simple in design and operation, independent of biomass type and low in capital costs. The CSTR has, however, to be operated at long Hydraulic Retention Times (HRT) of the order of 16 to 30 days since biomass is continuously lost with the effluent. Various alternate concepts of reactor design have, therefore, been developed to allow more rapid treatment. Treatment can be enhanced by retaining biomass within the digester so that the HRT is decoupled from solid biomass retention time (SRT). Unlike in continuous stirred tank digesters where the SRT is equal to HRT, the SRT in other designs are much greater than the HRT. This allows the wastewater to be treated at high throughputs while retaining the biocatalyst (or biomass) mediating the treatment within the digester.
In this study the operation of a CSTR was intensified by separating SRT from HRT while taking into account the economical aspects. The intensification of operation is defined as increasing wastewater throughput or organic loading rate while at the same time maintaining efficiency of treatment and robustness to reject disturbances (changes in wastewater concentration and flow rate). The operation of existing CSTR was intensified by addition of carriers. It is hypothesized that by providing surfaces (or carriers) for bacterial attachment within the continuous stirred tank digester, biomass will be better retained and the wastewater throughput can be increased.
The carriers or surfaces employed in this study were light carrier elements (shredded granular rubber tire having a density of 0.96 g/cm3) that move gently with the water in the reactor. This carrier material is much cheaper compared with other commercial carrier materials. This reactor type, called an Anaerobic Moving Bed Reactor (AMBR), was applied in this study to treat high strength synthetic wastewater, containing molasses as the main substrate.
The improvement of reactor performance was clearly shown by the capability of the system to be operated without any difficulties at HRT of 6 days at an OLR of 5.8 g COD/l/d or at HRT of 1 day at an OLR of 4 g COD/l/d. The carriers were shown to be effective in retaining biomass aggregates.
The AMBR was further intensified by changing the feeding strategy. It was shown that in stirred tank digester without carriers an intermittent feeding strategy resulted in better microbial capacity to degrade higher chain volatile fatty acids like propionic and butyric acids than the continuous feeding mode. An increase in degrading capacity of the intermittently fed digester was shown via degradation rates of pulse additions of propionic and butyric acids and by its capability of handling all changes in loading rates imposed. The continuously fed digester, receiving constant feed, on the other hand, suffered more when loading rates were changed, and the degradation rates of propionic and butyric acids were slower.
The intermittent feeding mode was then implemented on the AMBR, and it was operated as a sequencing batch reactor with a fill, react, settle and decant period in each cycle. The sequencing batch mode when applied to the AMBR (now called an Anaerobic Moving Bed Sequencing Batch Reactor or AMBSBR) could increase capability of the digester to handle higher shock loads. At 3.8 d HRT the AMBSBR could handle an OLR of 10.8 g COD/l/d as opposed to 7.4 g COD/l/d by the AMBR. At 2.5 d HRT the AMBSBR could handle an OLR of 6.4 g COD/l/d while the AMBR could only be loaded at an OLR of 4.2 g COD/l/d. The ratio of SRT to HRT was at least 15 for this reactor. The reactor was able to handle concentrated feed flow rates at longer cycles or more dilute feed flow rates at frequent shorter cycles.
The proposed operational strategies were verified by using a structured mathematical model which was developed based on the IWA ADM1 model. Several modifications were implemented to the model to obtain better predictions. The modified model was capable in predicting all the trends of the operating variables from both continuously and intermittently fed reactors. None of the two model versions (ADM1 and modified models) was, however, able to predict the increased propionate degradation capacity in intermittently fed digesters. The reason for this was the assumption of fixed stoichiometry of fermentative reactions for glucose mineralisation. By modifying the fractions of glucose mineralisation a better fit between experimental results and the model could be obtained.
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Zhao, Donglin. "Liquid macro- and micro-mixing in sparged and boiling stirred tank reactors." Thesis, University of Surrey, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395548.
Full text
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Dong, Jie. "Modelling of multiphase flow containing ionic liquids in a stirred tank reactor." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/46880/.
Full textAbstract:
Stirred tanks are widely used in the chemical reactions and the mixing operations for process industries to enable high product quality and process efficiency. Despite there being a large body of studies on the hydrodynamics of water in the stirred tanks, the understandings of the hydrodynamics of the ionic liquids in the stirred tanks are still very limited. In this study, Computational Fluid Dynamics (CFD) modelling is used to investigate the detailed flow characteristics of the single and multiphase ionic liquid flows in the stirred tanks which are experimentally validated using Particle Image Velocimetry (PIV). The ANSYS FLUENT was employed in this investigation to carry out the CFD simulation. Initially, the hydrodynamics of single phase flows were numerically studied where the single phase turbulent water flow and single phase transitional ionic liquid flow were modelled using a RANS and LES approach respectively in the three stirred tanks equipped with different bottom shapes and length of baffles. The simulation results indicated that the bottom shape and baffles’ length have significant effect on the flow field in a stirred tank when the water was operated in the turbulent state, where a large dead zone region was identified below the impeller. However, the magnitude of the dead zone region reduced a lot when the ionic liquid was operated in the transitional state. Before carrying out the gas-ionic liquid multiphase flow simulation in a stirred tank, the bubble size needs to be identified as it is crucial information for the accurate gas-ionic liquid multiphase flow modelling. In order to obtain the bubble size data, a high speed camera and a microscope were employed to experimentally measure the bubble size in the ionic liquid solutions. The correlations between the bubble size in the ionic liquid solutions and the impeller agitation speed were established. It showed that both the bubble breakage and coalescence has significant effect on determining bubble size in the ionic liquid. In addition, it was suggested that the surface tension of the ionic liquid is more important than the liquid viscosity on affecting the bubble size in the stirred tank. Afterward, the gas-ionic liquid multiphase flow modelling was carried out in the stirred tank at various impeller speeds and gassing rates. The simulation results indicated that the presence of gas phase did not have significant effect on changing the flow of liquid phase under the selected operation conditions due to the small bubble size, low gas flow rate and high viscosity of ionic liquid. The gas phase followed well with the liquid phase and circulated in the majority region of the stirred tank, which implied better gas holdup and mass transfer of the multiphase flow system. A correlation was proposed to predict the impeller power consumption of the gas-ionic liquid transitional flow in a stirred tank agitated by a Rushton turbine impeller. Finally, in order to validate the above single phase and multiphase flow CFD models adopted in this study, an experimental rig was established and the advanced visualization technique Particle Image Velocimetry (PIV) was used to measure the single phase water and ionic liquid flows and gas-ionic liquid multiphase flow in a stirred tank. The PIV data showed agreement with the CFD results in terms of the flow pattern and velocity components, which indicates good accuracy of the computational models and approaches presented in this investigation.
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Singh, Harminder. "Modelling of shear sensitive cells in stirred tank reactor using computational fluid dynamics." Thesis, University of Canterbury. Chemical and Process Engineering, 2011. http://hdl.handle.net/10092/5684.
Full textAbstract:
Animal cells are often cultured in stirred tank reactors. Having no cell wall, these animal cells are very sensitive to the fluid mechanical stresses that result from agitation by the impeller and from the rising and bursting of bubbles, which are generated within the culture medium in the stirred tank to supply oxygen by mass transfer to the cells. If excessive, these fluid mechanical stresses can result in damage/death of animal cells. Stress due to the rising and bursting of bubbles can be avoided by using a gas-permeable membrane, in the form of a long coiled tube (with air passing through it) within the stirred tank, instead of air-bubbles to oxygenate the culture medium. Fluid mechanical stress due to impeller agitation can be controlled using appropriate impeller rotational speeds. The aim of this study was to lay the foundations for future work in which a correlation would be developed between cell damage/death and the fluid mechanical stresses that result from impeller agitation and bubbling. Such a correlation could be used to design stirred-tank reactors at any scale and to determine appropriate operating conditions that minimise cell damage/death due to fluid mechanical stresses.
Firstly, a validated CFD model of a baffled tank stirred with a Rushton turbine was developed to allow fluid mechanical stresses due to impeller agitation to be estimated. In these simulations, special attention was paid to the turbulence energy dissipation rate, which has been closely linked to cell damage/death in the literature. Different turbulence models, including the k-ε, SST, SSG-RSM and the SAS-SST models, were investigated.
All the turbulence models tested predicted the mean axial and tangential velocities reasonably well, but under-predicted the decay of mean radial velocity away from the impeller. The k-ε model predicted poorly the generation and dissipation of turbulence in the vicinity of the impeller. This contrasts with the SST model, which properly predicted the appearance of maxima in the turbulence kinetic energy and turbulence energy dissipation rate just off the impeller blades. Curvature correction improved the SST model by allowing a more accurate prediction of the magnitude and location of these maxima. However, neither the k-ε nor the SST models were able to properly capture the chaotic and three-dimensional nature of the trailing vortices that form downstream of the blades of the impeller. In this sense, the SAS-SST model produced more physical predictions. However,this model has some drawbacks for modelling stirred tanks, such as the large number of modelled revolutions required to obtain good statistical averaging for calculating turbulence quantities. Taking into consideration both accuracy and solution time, the SSG-RSM model was the least satisfactory model tested for predicting turbulent flow in a baffled stirred tank with a Rushton turbine.
In the second part of the work, experiments to determine suitable oxygen transfer rates for culturing cells were carried out in a stirred tank oxygenated using either a sparger to bubble air through the culture medium or a gas-permeable membrane. Results showed that the oxygen transfer rates for both methods of oxygenation were always above the minimum oxygen requirements for culturing animal cells commonly produced in industry, although the oxygen transfer rate for air-bubbling was at-least 10 times higher compared with using a gas-permeable membrane. These results pave the way for future experiments, in which animal cells would be cultured in the stirred tank using bubbling and (separately) a gas-permeable membrane for oxygenation so that the effect of rising and bursting bubbles on cell damage/death rates can be quantified. The effect of impeller agitation on cell damage/death would be quantified by using the gas permeable membrane for oxygenation (to remove the detrimental effects of bubbling), and changing the impeller speed to observe the effect of agitation intensity.
In the third and final part of this work, the turbulent flow in the stirred tank used in the oxygenation experiments was simulated using CFD. The SST turbulence model with curvature correction was used in these simulations, since it was found to be the most accurate model for predicting turbulence energy dissipation rate in a stirred tank. The predicted local maximum turbulence energy dissipation rate of 8.9x10¹ m2/s3 at a rotational speed of 900 rpm was found to be substantially less than the value of 1.98x10⁵ m2/s3 quoted in the literature as a critical value above which cell damage/death becomes significant. However, the critical value for the turbulence energy dissipation rate quoted in the literature was determined in a single-pass flow device, whereas animal cells in a stirred tank experience frequent exposure to high turbulence energy dissipation rates (in the vicinity of the impeller) due to circulation within the stirred tank and long culture times. Future cell-culturing experiments carried out in the stirred tank of this work would aim to determine a more appropriate critical value for the turbulence energy dissipation rate in a stirred tank, above which cell damage/death becomes a problem.
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Ochieng, A., MS Onyango, A. Kumar, K. Kiriamiti, and P. Musonge. "Mixing in a tank stirred by a Rushton turbine at a low clearance." Elsevier, 2008. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1000754.
Full textAbstract:
Mixing efficiency in stirred tanks is an important consideration in the design of many industrial processes. Computational fluid dynamics (CFD)
techniques have been employed in the present work to study the hydrodynamics in a tank stirred by a Rushton turbine. The effect of the impeller
clearance on the velocity field and mixing has been investigated. It has been shown that at a low impeller clearance, the Rushton turbine generates
a flow field that evolves from the typical two loops to a single loop flow pattern similar to that of an axial impeller. This single loop flow pattern
resulted in an increase in axial flow and a decrease in mixing time at a constant power number. It has been found that a draft tube can be used with
a single Rushton turbine, at a low clearance to aid axial flow and mixing, and this resulted in 50% reduction in mixing time. There was a good
comparison between laser Doppler velocimetry (LDV) experimental and CFD simulation flow fields, both of which showed that the draft tube
improved mixing in the tank by suppressing secondary circulation loops.
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Hu, Windy Chiung Wen. "Anaerobic digestion of liquid wastewaters from food industry using continuously stirred tank reactors." Thesis, University of Birmingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531076.
Full textAbstract:
This thesis describes an investigation on the application of anaerobic contact process treating a variety of wastewaters from food industries (raw molasses, purge wastes, ice-cream and diary wastewaters). The raw molasses is one of the wastes produced from the sugar industries, which contains high concentrations of organic matters and high concentrations of sulphate and was firstly investigated in this work. A series of batch experiments were carried out to establish a suitable feedstock for pilot scale digesters. A 1% mass molasses medium with a COD: N: P ratio of 200: 5: 1 in a buffer system has been shown to give a successful digestion of molasses with a methane yield of 0.36 l/g CODrem and a COD removal of 89 % from the batch experiment 3. Two pilot scale digesters (14.13 1) were fed with the molasses medium that was established from the batch experiment 3 as suitable for this work. Several organic loading rates were investigated. After feeding with the molasses medium for about 30 days, both pilot digesters have reached steady-state conditions with respect to a COD removal in excess of 90 % and methane yield in excess of 0.321/g CODrem. The process kinetics of anaerobic contact reactor for treating four different wastewaters was investigated. The Monod equation and the Contois equation were used to develop two basic steady-state models. The kinetic parameters required for the application of the steady-state models were determined by using the results obtained from four individual experiments for treating four different wastewaters. Both models were evaluated with four experimental results obtained in this work and a set of routine analysis data obtained from a full scale anaerobic contact reactor treating the ice-cream wastewater for Birds Eye Walls Ltd., (Gloucester). It is found that the Contois model would be more suitable than the Monod model for express the process kinetics of the anaerobic contact process in full scale due to the reason that the Contois model considers the effect of variable influent substrate concentration into the prediction. In addition, the Contois model was found to be better than the Monod model to express the process kinetic when treating the wastewater containing the organic matters, which has a slow rate of hydrolysis (i. e. lipids/proteins).
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Adkins, Carol Leslie Jones Seinfeld John H. Flagan Richard C. "Use of a continuous stirred tank reactor for the study of aqueous aerosol chemistry." Diss., Pasadena, Calif. : California Institute of Technology, 1988. http://resolver.caltech.edu/CaltechTHESIS:12042009-080025691.
Full textAbstract:
Thesis (Ph. D.)--California Institute of Technology, 1988. UM #88-03,381.Advisor names found in the Acknowledgments pages of the thesis. Title from home page. Viewed 02/19/2010. Includes bibliographical references.
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McLachlan, Hannah Ruth. "Investigations into parameters affecting purity in the oscillatory baffled crystallizer and stirred tank crystallizer." Thesis, Heriot-Watt University, 2017. http://hdl.handle.net/10399/3381.
Full textAbstract:
Previously completed industrial trials suggested that the purity of crystals which were produced in an oscillatory baffled crystallizer (OBC) had a higher purity than those produced from the stirred tank crystallizer (STC). The results from these trials were obtained when the vessels were operated at similar experimental conditions and power densities. This thesis work initially aimed to confirm these results for a model compound (urea) and find possible scientific reasons for the noted purity differences between the two vessels. Following this the effect of the addition of a specific impurity (biuret) was investigated to see whether the OBC would still produce higher purity material and how the impurity affected the monitored system parameters. It has been shown from the work included in this thesis, that the OBC produces higher purity crystals than the STC under comparable experimental conditions. Investigations into these purity improvements were monitored using an in-situ FTIR system and the resulting data indicated that a lower supersaturation was required to induce nucleation in the OBC. This lower supersaturation corresponded to a higher nucleation temperature within the OBC. It has been proposed that the higher supersaturation in the STC leads to an increased nucleation rate consequently producing smaller single crystals which are more likely to agglomerate. In the STC this increase in the number of agglomerates led to a decrease in purity, as more mother liquor or impurity could become trapped within the crystals. This agglomeration in the STC was apparent at all three impurity levels investigated, with it being particularly apparent with 0 % added impurity. At this level of added impurity there was only evidence of mother liquor entrapment. Experiments completed with 5 wt. % added impurity also indicate impurity incorporation as well as mother liquor entrapment, leading to the production of more 'cubic' crystals with lower purities as well as agglomeration in both vessels.