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1
Murphy, Terry 1955. "Residence time distribution of solid particles in a CSTR." Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=79251.
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When mixing in a tank is insufficient solid particles are known to form a concentration gradient along the height. The one-dimensional sedimentation dispersion model provides a relationship between mixing parameters and the solids concentration gradient. An investigation of the relationship between the solid mixing properties and the solids residence time distribution, as derived from the sedimentation dispersion model has been conducted. Experimental results show that the solids residence time distribution was a function of particle size and differed from that for the liquid phase. An empirical correlation for the solids Peclet number to predict the residence time distribution of the particles is proposed. A single parameter model to predict the solids residence time distribution as a function of particle size is presented. The influence of the particle concentration gradient on the mean conversion obtained in the reactor for two different cases is examined.
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Nadeau, Patrice. "Measurement of residence time distribution by laser absorption spectroscopy." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=22666.
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The residence time distribution was measured at ambient temperature and pressure in a tubular reactor with radial injection at very short space times (0.04-0.7 s). A technique using infrared laser absorption spectroscopy was developed and used to provide the required rapid response for concentration measurements. The equipment comprised an infrared He-Ne laser emitting at a wavelength of 3.39$ mu m$ and a lead selenide detector. Methane, which absorbs strongly at the laser wavelength, was used as the tracer. The absorption of the laser light was related to the tracer concentration by Beer-Lambert law. The laser beam passed through the diameter of the reactor at different axial locations. The residence time distributions were obtained from the response to quasi-step inputs. An axial dispersion model was used to describe the reactor.
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Hopley, Alexandra. "Liquid Residence Time Distribution in Micro-reactors with Complex Geometries." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37111.
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Micro-reactors, enabling continuous processes at small scales, have been of growing
interest due to their advantage over batch. These advantages include better scaling, as well as improved mass and heat transfer, though many new challenges arise due to the small scales involved such as non-negligible entrance effects and significant pressure drops.
The flow in coils, rectangular channel serpentine plates, mix-and-reside plates, and
complex liquid-liquid mixing plates was investigated and characterized using residence time
distribution (RTD) tests. A pulse test was used to determine the RTD curve shape of these
reactors at flowrates ranging from 20 to 100 g/min. A semi-empirical, multi-parameter model was used to describe the asymmetrical curves, while the axial dispersion model was used to describe the symmetrical ones.
The Peclet number is given in function of the Reynolds number for the liquid-liquid plates
that were found to be near-plug flow (Pe > 100). In a continuous mixing plate, the Pe ranged from 190 to 475 with Pe increasing as Re increased. The effect of straight channel sections in micro-reactors is also evaluated. Longer straight segments between micromixers resulted in the development of unidirectional flow and the occurrence of tailing in the RTD.
Finally, the suitability of a liquid-liquid plate for a reactive liquid-solid system is
evaluated. The plugging is determined visually and by measuring pressure increase; pressure started to increase after 5 minutes and the experiment had to be halted after 10 minutes due to plugging. Parallels between the particle size distribution and the residence time distribution curves are drawn. The particle size distribution of silver chloride at low flow rates is much wider than at high flowrates. The average particle size at high flowrates was also much lower (≈69nm) than at low flowrates (≈112nm).
4
TANYEL, ZEYNEP. "Residence Time Distribution of Multiple Particles in Four Configurations of Holding Tubes." NCSU, 2004. http://www.lib.ncsu.edu/theses/available/etd-08102004-124311/.
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Residence time distributions of multiple particles (as affected by process and system parameters) were investigated during non-Newtonian tube flow. Process parameters included flow rate, particle type, carrier fluid viscosity, and particle concentration. The system parameter of interest was the holding tube configuration. Polystyrene and acrylic particles were used as model food particles. Digital imaging analysis was used to obtain residence time data of particles. A novel type of holding tube (chaotic holding tube) was constructed. Comparisons among the straight, single helical, double helical, and chaotic holding tube were performed in terms residence time distribution (RTD) of particles. In addition, the effect of inclination angle (0 º and 45 º) of the chaotic holding tube was investigated. It was found that the narrowest RTD of particles was obtained in the single helical holding tube. RTstd in the chaotic holding tube was greater than that in the single helical holding tube, but lower than those in the straight and double helical holding tubes. The most significant process parameter affecting RTD was flow rate. The effect of flow rate was more pronounced for high density (acrylic) particles. Carrier fluid viscosity, particle type, and particle concentration did not have significant effects on the overall RTstd. Trends observed in the chaotic holding tube were similar to those observed in the single helical holding tube. However, there were some cases where use of chaotic holding tube resulted in narrower RTD of particles. Changing the inclination angle from 0 º to 45 º in the chaotic holding tube resulted in wider RTD of both types of particles.
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Higgins, Philip Richard. "The characterisation of the hydrodynamic vortex separator using residence time distribution analysis." Thesis, Liverpool John Moores University, 2000. http://researchonline.ljmu.ac.uk/5534/.
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The hydrodynamic vortex separator (HDVS) is currently employed at wastewater treatment works and in the sewerage system as a combined sewer overflow (CSO) for the separation of solids from an incoming waste stream. This project presents the first stage in developing and aiding the existing design methodology for the optimisation of kinetic processes within the HDVS. The kinetic process design methodology combines hydraulic and kinetic principles by using the true mixing regime characteristics of a system and batch reactor data to determine a kinetic processes efficiency. This project used residence time distribution (RTD) analysis to extensively characterise the mixing regime within a model and prototype HDVS. The HDVS was operated with and without a baseflow component and with and without the sludge hopper for a range of inlet flow rates and flow splits covering design flow rates for a number of existing applications. The RTD was obtained using a pulse tracer injection method and described using the complete range of data analysis techniques typical employed in RTD studies. This includes the axial dispersion model (ADM), tanks-in-series model (TISM), RTD indices and a RTD combined mathematical model. The combined model is configured to quantify the inactive flow behaviour within the HDVS i. e. stagnant and dead volumes. The HDVS has a complex imperfect plug-flow mixing regime. This non-ideal flow behaviour is associated with both dispersion and dead volumes and results in short-circuiting. At low flow rates the HDVS operating without a baseflow contains fluid elements which conduct flow slower than the mean velocity. At high flow rates the inactive flow behaviour is associated with dead volumes and subsequently short-circuiting. The flow rate at which this change in mixing characteristics occurs is termed the transition flow rate and is approximately 151/min and 901/min for the model and prototype HDVS respectively. At all flow rates above the transition flow rate the HDVS has a very stable mixing regime, which is associated with both the inactive flow behaviour and the plug-flow mixing characteristics. The ADM and TISM parameters increase as the flow rate decreases and therefore, the HDVS has improved plug-flow mixing characteristics and reduced dispersion at low flow rates. Removing the sludge hopper reduces the inactive flow behaviour and improves the plug-flow mixing characteristics. The inactive flow behaviour within the model HDVS operating with no baseflow occupies approximately 20-40% of the total volume and similarly for the prototype HDVS 5-25% and increases as the inlet flow rate increases. The inactive flow behaviour occupies a smaller fraction of the total volume and the plug-flow mixing characteristics are also improved as the HDVS is scaled-up in size. Hence, the scale-up of the HDVS will provide a mixing regime with less short-circuiting and improved plug-flow mixing characteristics and therefore, more conducive for certain kinetic processes and particularly chemical disinfection processes. The introduction of a baseflow component alters the total mixing regime within the HDVS. The baseflow component introduces an element of plug-flow mixing and subsequently the total plug-flow mixing characteristics of the HDVS operating with a baseflow component are greater than the HDVS operating without a baseflow. The baseflow component plug-flow mixing characteristics increase and the overflowcomponent decrease as the inlet flow rate increases. Short-circuiting of the baseflow and overflow component occurs as the inlet flow rate decreasesa nd increasesr espectively. Hence, there are different mixing regimes within the HDVS associated with the overflow and baseflow component. The HDVS operating with a baseflow component has improved plug-flow mixing characteristics when the sludge hopper is included. This project was also extended to include an experimental kinetic process analysis, by investigating the first-order decomposition of hydrogen peroxide (H202) using catalase. This was undertaken to compare the actual kinetic process performance within the HDVS to that estimated using the RTD. The H202 decomposition results showed that the design of the HDVS for kinetic processes can be achieved using only the RTD and relevant batch reactor data. This enables the HDVS to be optimised for kinetic process applications and eliminates the need for costly and time consuming pilot trials. The characterisation of the HDVS using RTD analysis creates scope for significant future research. This includes: alternative experimental RTD techniques, development of the RTD combined mathematical model to include a baseflow component and kinetic process principles, extensive kinetic process batch reactor investigations, application of both the hydraulic and kinetic data into chemical reactor design computer software and finally the scaling of the HDVS using the RTD and therefore the kinetic process optimisation. This work is a proactive response by practitioners and Hydro International Plc to pressure from the regulators and EU Directives, placing emphasis on the use of sophisticated treatment processes based on good scientific principles, to meet current and future stringent water quality standards.
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Kennedy, Dennis Lee. "Redesign of Industrial Column Flotation Circuits Based on a Simple Residence Time Distribution Model." Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/35510.
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The potential for improved selectivity has made column flotation cells a popular choice for upgrading fine coal. Unfortunately, recent production data from full-scale column plants indicate that many industrial installations have failed to meet original expectations in terms of clean coal recovery. Theoretical studies performed using a simple dispersion model showed that this inherent shortcoming could be largely minimized by reconfiguring the columns to operate in series as a cell-to-cell circuit. Follow-up field data showed that this low-cost modification increased flotation recovery as predicted by the dispersion model. This study presents the key findings obtained from the field investigation and provides generic guidelines for designing multi-stage column circuits.Master of Science
7
Choi, Mee H. "Residence time distribution as a measure for stochastic resonance in a bistable system." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/29349.
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Chen, Dong. "An on-line measurement of residence time distribution in a twin-screw extruder /." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61235.
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The importance of the residence time distribution (RTD) in polymer extrusion has been recognized for along time, however, it is very difficult to measure. In this project, an optical on-line RTD measurement technique based on extrudate transmittance changes was investigated. A He-Ne laser beam was the light source, and carbon black was the tracer and detection was performed by a photomultiplier.The RTD of a ZSK-30 twin-screw extruder was measured with and without an in-line rheometer installed. Various operating conditions were used to examine their effects on the RTD curve. It was found that the mean residence time of the system decreased linearly with screw speed and exponentially with the feed rate. The temperature effect was minuscule. The in-line rheometer increased the mean residence time of the system by 80%.
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Tiev, Visoth. "Vegetation and discharge effects on the hydraulic residence time distribution within a natural pond." Thesis, University of Warwick, 2011. http://wrap.warwick.ac.uk/49201/.
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Results are presented from sets of field and laboratory experiments conducted to measure and quantify the Hydraulic Residence Time Distribution in treatment ponds containing vegetation. The field measurements were taken in the Lyby field pond (Sweden) with complementary experiments on a distorted, laboratory scale model pond designed and built in the University of Warwick’s engineering laboratory. Rhodamine WT Dye tracer experiments were used in both the Lyby field pond and the distorted physical scale model to investigate vegetation and discharge affects on HRTD characteristics and the technique of PIV (Particle Image Velocimetry) was used in the distorted physical scale model to investigate how surface flow profiles were affected by different vegetation and discharge configurations. The results show that the distorted physical scale pond did not reflect the HRTD characteristics of the field site, with the actual residence time, (tm), for the distorted physical scale pond ranging from 85 % to 125% of its nominal residence time. For the distorted scale model, pond vegetation and discharge did not affect the relative HRTD centroid, em, or the actual residence time, tm. This finding is attributed to the unique pond geography and associated aspect ratios However, flow rates did have a significant effect on the HRTD e0 (time of first dye arrival at the outlet) and ep (time of peak dye concentration). Changes in vegetation were found to have little effect on e0 and ep. For the laboratory pond, vegetation had a significant control on the surface flow field whereas, flow rates did not – the latter suggests that surface flow fields are not representative of the internal flow field in different layers of the pond. The experiments demonstrate that the specific shape of the distorted physical scale pond in this study enables optimal actual resident times to be achieved over a wide range of vegetation and flow rate configurations. If full scale field ponds based upon this design give the same stable centroid results, then this would be a substantial breakthrough in pond design, which would aid the design and management of pond treatment and allow more robust optimisation of treatment efficiency.
10
Salengke, C. "Residence time distribution of model food particles in the curved section of holding tube." The Ohio State University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=osu1301602949.
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Payne, Robert R. U. Tatarchuk Bruce J. "Electrochemical characterization and modelling of fuel cells via AC impedance and residence time distribution." Auburn, Ala., 2008. http://hdl.handle.net/10415/1420.
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Al-hengari, Salah. "Process intensification : a study of micromixing and residence time distribution characteristics in the spinning disc reactor." Thesis, University of Newcastle Upon Tyne, 2012. http://hdl.handle.net/10443/1771.
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Micromixing phenomena (i.e. mixing at molecular level) play a very important role in the chemical industry when the time scale of the chemical reaction involved have the same magnitude or smaller than the time scale of mixing process. The study of micromixing is very critical to the understanding of important processes such as polymerization, precipitation, crystallization and competing fast chemical reactions. It has long been recognised that the intense mixing characteristics of thin films in the spinning disc reactor (SDR), play an important role in improving the selectivity, yield, and quality of final products of a chemical reaction. However, to date, there has been no systematic study of micro and macro mixing in SDR thin films. The first part of this study reports on the fundamental study undertaken to characterise micromixing in the thin films formed in 10 cm and 30 cm SDRs operating under a wide range of operating conditions. A well-established parallel-competitive reaction test scheme was adopted to quantify micromixing in terms of the segregation index (Xs) or micromixedness ratio (α), the power dissipation (ε) and micromixing time(tm). The micromixing data obtained from 10cm and 30cm SDRs were benchmarked against both a 1.37 l conventional semi-batch reactor (SBR) and continuous tubular flow reactors in the form of narrow channels (NCRs) of 1.0 mm diameter and three different lengths namely 5 cm, 10 cm and 15 cm (Y and T shape junctions). The effects of various operating parameters such as disc rotation rates, disc size, disc surface configurations, feed flowrates, feed distribution systems, liquid feed concentrations and viscosities were investigated. It was observed that, at an acid concentration of 1 M, the lowest segregation index of 0.05 was achieved for a feed of 0.001Ns/m2 viscosity at the highest flowrate of 5ml/s (corresponding to Refilm=72) and highest rotational speed of 2400 rpm in the 10cm diameter disc. Greatly improved micromixing was obtained on the larger disc of 30 cm diameter, especially at the lower Refilm of 15 and 42, in comparison to the smaller disc. Under optimised conditions, the micromixing time(tm) in the water-like film on the 30cm diameter disc was estimated to be as low as 0.3ms with corresponding power dissipation (ε) of 1025 W/kg. In contrast, the SBR could only achieve, under optimised conditions, segregation indices of no lower than 0.13 corresponding to a micromixing time of above 1ms with power dissipation of no more than about 21 W/kg. On the other hand, the NCRs could only achieve, under optimised conditions, a micromixing time of about 19 ms corresponding to power dissipation (ε) of about 208 W/kg. Therefore, when compared with other mixing devices such as conventional SBRs or NCRs, the SDR is shown to give significantly better micromixing performance which highlights its potential as an alternative device for processes where a high degree of mixing is critically important. In the second part of this study, the residence time distribution (RTD) of the liquid flow in the 30 cm SDR was characterised for a range of operating conditions including disc rotational speeds, disc configuration (smooth vs. grooved), total flow rate of liquid and viscosity in order to determine the conditions for which plug flow profile became more prevalent in the SDR films. The dispersion number from the RTD results and Peclet number were also estimated for the purpose of further characterising the extent of axial dispersion in the thin film flow on the rotating disc. All the mentioned operating conditions were found to have a profound influence on the overall Mean Residence Time, ( ), variance, , dispersion number and Peclet number, (Pe). More specifically, the lowest value for the of 10.1 s was achieved for a feed of 0.001 Ns/m2 viscosity at the highest flowrate of 15ml/s and highest rotational speed of 1200 rpm on the smooth disc with corresponding of 2.16. The dispersion number and Pe were 0.010 and 100 respectively, showing that the degree of axial dispersion was very small. A considerable reduction in the dispersion number and Pe was observed when the smooth disc was replaced by grooved disc. Thus, under the above mentioned hydrodynamic conditions, whilst the was almost unchanged at 10.10 s on grooved disc, the corresponding variance of 1.03 was significantly lower, indicating even more reduced axial dispersion in the film on the grooved disc. This is further substantiated by dispersion number and Pe of 0.005 and 200 respectively. In general the RTD curves become narrower and the values of and decreased as the disc rotational speed and flowrates increased and as the feed viscosity decreased. For the given operating conditions used in this research, it was confirmed that the 30 cm SDR approaches plug-flow regime which had a positive influence on the micromixing intensity on the SDR.
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Wales, Nadine Jenifer. "The effect of prewetting on the residence time distribution and hydrodynamic parameters in trickle bed reactors." Pretoria : [s.n.], 2007. http://upetd.up.ac.za/thesis/available/etd-09042008-123057/.
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Parker, Brian Mark. "The Simulation and Analysis of Particle Flow Through an Aggregate Stockpile." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/35932.
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For many aggregate mining facilities, the stockpile is the preferred method of storing rock. In many aggregate mines, as well as other mines using stockpiling techniques, understanding the timing and flow of particles through a stockpile is important for correctly timing samples, making proper process adjustments and overall stockpile safety. Because much of the research of today lacks important information regarding actual interior particle movement within a stockpile, a series of Real Time Distribution (RTD) analyses and stockpile flow models have been prepared and analyzed for this study in order to better understand the flow characteristics of a stockpile.
A series of three RTD analyses performed on three separate stockpiles provides information leading to the assumption that stockpiles tend to operate similar to a plug flow system. While conveyor loading techniques may lead to separation of rocks prior to traveling through the stockpile, the majority of the rock particles entering the pile remain near the point of entry, or within the â actionâ area, and will travel through the pile in a plug flow, rather than a mixed flow, manner. High Peclet number results for each analysis prove this assumption to be accurate.
A series of models on three separate stockpiles have been created using PFC3d. Mainly, the simulations prove PFC3d is capable of showing how stockpile particles move in three dimensions while monitoring specific particles within the pile. In addition, these models provide simulation results similar to the results obtained within the RTD analyses. Results show that particles located directly above the discharge point, or â actionâ area, travel through the pile at a faster rate than particles surrounding this area. Velocity results obtained from the simulations show particles accelerating as they get closer to the discharge points while also providing evidence of â archingâ during the simulation process. These findings provide a better understanding of internal flow within the stockpile and ways to possibly predict future stockpile flow issues that may be encountered.Master of Science
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Yim, Samson Sau Shun. "The effect of flow stability on residence time distribution of Newtonian and non-Newtonian liquids in couette flow." Thesis, University College London (University of London), 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264191.
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Cox, Shane Joseph Chemical Sciences & Engineering Faculty of Engineering UNSW. "Design and analysis of a photocatalytic bubble column reactor." Awarded by:University of New South Wales, 2007. http://handle.unsw.edu.au/1959.4/37818.
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The current work has developed a CFD model to characterise a pseudo-annular photocatalytic bubble column reactor. The model development was divided into three stages. Firstly, hydrodynamic assessment of the multiphase fluid flow in the vessel, which incorporated residence time distribution analysis both numerically and experimentally for validation purposes. Secondly, the radiation distribution of the UV source was completed. The final stage incorporated the kinetics for the degradation the model pollutant, sodium oxalate. The hydrodynamics were modelled using an Eulerian-Eulerian approach to the multiphase system with the standard k- turbulence model. This research established that there was significant deviation in the fluid behaviour in the pseudo-annular reactor when compared with traditional cylindrical columns due to the nature of the internal structure. The residence time distribution study showed almost completely mixed flow in the liquid phase, whereas the gas phase more closely represented plug flow behaviour. Whilst there was significant dependence on the superficial gas flow rate the mixing behaviour demonstrated negligible dependence on the liquid superficial velocity or the liquid flow direction, either co- or counter- current with respect to the gas phase. The light distribution was modelled using a conservative variant of the Discrete Ordinate method. The model examined the contribution to the incident radiation within the reactor of both the gas bubbles and titanium dioxide particles. This work has established the importance of the gas phase in evaluating the light distribution and showed that it should be included when examining the light distribution in a gas-liquid-solid three-phase system. An optimal catalyst loading for the vessel was established to be 1g/L. Integration of the kinetics of sodium oxalate degradation was the final step is developing the complete CFD model. Species transport equations were employed to describe the distribution of pollutant concentration within the vessel. Using a response surface methodology it was shown that the reaction rate exhibited a greater dependency on the lamp power that the lamp length, however, the converse was true with the quantum efficiency. This work highlights the complexity of completely modelling a photocatalytic system and has demonstrated the applicability of CFD for this purpose.
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Agizza, Maria Angela [Verfasser], Andreas Akademischer Betreuer] Dreizler, Tiziano [Akademischer Betreuer] [Faravelli, and Giancarlo [Akademischer Betreuer] Sorrentino. "Residence Time Distribution modeling of combustors through Chemical Reactor Network / Maria Angela Agizza ; Andreas Dreizler, Tiziano Faravelli, Giancarlo Sorrentino." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2020. http://d-nb.info/1211088650/34.
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Agizza, Maria Angela [Verfasser], Andreas [Akademischer Betreuer] Dreizler, Tiziano [Akademischer Betreuer] Faravelli, and Giancarlo [Akademischer Betreuer] Sorrentino. "Residence Time Distribution modeling of combustors through Chemical Reactor Network / Maria Angela Agizza ; Andreas Dreizler, Tiziano Faravelli, Giancarlo Sorrentino." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2020. http://d-nb.info/1211088650/34.
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Fangueiro, Gomes Leonel. "Etude du couplage hydrodynamique/adsorption : application au lit mobile simulé." Thesis, Ecully, Ecole centrale de Lyon, 2015. http://www.theses.fr/2015ECDL0031.
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Modèle monodimensionnel de type Piston-Dispersion. Le terme de dispersion axiale englobe alors toutes les imperfections de l'écoulement : injection des fluides non homogène dans l’espace et étalée dans le temps, effet de parois, et enfin volumes morts derrière les obstacles noyés dans le tamis (poutres, conduites...) dans le cas des Lits Mobiles Simulés. Cette représentation, quoique très simpliste, s'avère généralement suffisante tant que l’étalement des fronts de concentration est d'abord induit par les limitations au transfert externe, interne (macro/microporeux) et par la thermodynamique du système. Par contre, lorsque l’adsorbant employé présente d’excellentes performances de transfert, une approche aussi simple s'avère extrêmement risquée. En effet, les phénomènes dispersifs associés à l’adsorbant (transfert et thermodynamique) et à l’hydrodynamique ont des contributions de même ordre de grandeur sur la dispersion des fronts de concentration. Dans ce cas, une description plus réaliste de l'écoulement est requise afin de mieux appréhender son effet sur les performances de séparation.Dans ce contexte, l’objectif de ce projet de thèse est de mettre en place une méthodologie pour prendre en compte ces phénomènes hydrodynamiques lors de l’extrapolation d’un procédé de séparation par adsorption. Pour cela, nous proposons une étude du couplage entre les phénomènes hydrodynamiques et le phénomène d’adsorptionHydrodynamics inside industrial Simulated Moving Bed (SMB) adsorption columns can be complex due to the presence of internal distribution devices, free flow chambers and heterogeneous injections. These have to be taken into account in SMB numerical models to scale-up purposes. In the present thesis, a CFD approach is adopted as an intermediate step to develop a 1D model simple enough to be used for cyclic SMB simulations while being able to represent realistic hydrodynamics. This model results from the interpretation of the moments of the fluid age distribution, transported by CFD according to the method developed by Liu and Tilton (2010) that allows to estimate the degree of mixing (Liu, 2011) of the adsorption columns. The resulting 1D model consists in the two examples provided by Zwietering (1959) of a completely segregated system and a maximum mixedness system. This model is able to reproduce the residence time distribution of the CFD model of an adsorption column, while being representative of the internal flow patterns. This results in a good representation of the coupling of adsorption and hydrodynamics by the 1D model. When integrated in a SMB simulator and compared to the traditionally used dispersed plug flow model, the new 1D model demonstrates that for most of the adsorption column geometries considered a detailed hydrodynamic description is mandatory. Such detailed hydrodynamic description is even more important when employing adsorbents with better mass transfer performances than those currently used for the p-xylene purification, which is expected in the upcoming years
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Singh, D. P. "Flow and mixing studies in a co-rotating intermeshing twin screw extruder." Thesis, Brunel University, 1988. http://bura.brunel.ac.uk/handle/2438/5548.
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The basic understanding of mixing in the process of polymer melt extrusion by twin screw extruder is limited by their geometrical complexity and the interactions of the process parameters. Mixing and flow in a 100mm diameter, trapezoidal channeled, intermeshing co-rotating twin-screw extruder have been characterised by determination of residence time distribution (RTD) and of the paths taken by tracers added to the melt. The axial mixing and the effects of varius parameters on it were established by studying RTD using tracer techniques. As the tail of the distribution is of paramount importance, the reproducibility of the RTD curve was extensively studied. Radioactive NnO2 was used as a tracer and detected by gamma ray spectroscopy giving more reproducible results than added barytes estimated gravimetrically after ashing. Shock cooling of the extruder and sectioning of the solidified compound in the screw channels was used to-study the flow mechanism. The maximum throughput achieved, polymer melting mechanism, filled volume and axial mixing Are interrelated, and are dependent on the configuration and position of segmented mixing discs present in the screw profile. In the upstream position these act as melting discs and their efficiency is increased in a closed configuration. Initial melting is achieved over a remarkably short distance along the screw profile. The screw speed affects the axial mixing which is shown to be related to the net relative pressure change at the screw tips. A flow model is proposed such that the overall material flow taking place in an anticlockwise direction along the screw channel comprises two separate flow regimes. The upper regime rotates anti-clockwise and is made up of main and small tetrahedron flow and calender flow. The lower flow regime rotates clockwise and is made up of main and small side leakage flows and a portion of the main tetrahedron flows together with a central flow. The flow studies show conclusively that the melt from a particular site ahead of the intermeshing zone occupies a predestined site after passing through the intermeshing zone.
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Lizima, Louis. "Hydraulic Evaluation of a Community Managed Wastewater Stabilization Pond System in Bolivia." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4360.
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This work explores the hydraulic performance of a wastewater lagoon system located in San Antonio, Bolivia. The system consists of one facultative pond and two maturation ponds in series and is managed through a locally elected water committee. A tracer study was performed on the primary facultative pond and an analysis of the solids accumulation on the bottom of the facultative lagoon was also performed. The results were used to generate residence time distribution curves and provide an estimate of mean residence time in the system. The data was used to examine hydraulic efficiency as it relates to short-circuiting and dead zones. A sludge study accumulation study was performed using the white towel method and the resulting measurements were interpolated to determine a total estimated sludge volume of 169 m3 (which is 8% of the facultative pond volume). An orange study was also performed to assess the surface flow pattern in the system. The results were compared with a computational 2-d model. The 2-d model incorporated the estimated sludge distribution and provided a good fit for the tracer dye concentrations measured in the field over the 12 day study period. Simple models such as the Tanks in Series and the Completely mixed model were evaluated and abandoned because of their inability to model the physical behavior in the system. The Completely mixed model did however perform better than the Plug flow model. After comparing the tracer results from the reactor models that were considered: Tanks in Series, Completely mixed fluid, manual interpolation and the results from the 2-d cfd flow simulation, the results that provided the best fit for the data over 12 days was the manual interpolation method at a flow rate of 98 m3/day and configuration D at 60 m3/day. However, because of uncertainty as to what depth to obtain a representative area for the 2-d simplification and sensitivity to flow; all four configurations were considered for estimating the MHRT at the lowest measured flow rate of 60 m3/day. The results at a flow rate of 60 m3/day varied between 10.88 and 13.04 days for the MHRT with a hydraulic efficiency that varied between 33-51.6% (accounting for sludge volume). This is much shorter than the actual nominal retention time of 37 days and the design nominal retention time of 26 days. As a result it was concluded that short-circuiting was occurring in the facultative lagoon.
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Alhamdan, Abdullah M. "Particle Residence Time Distribution and Bulk Heat Transfer Coefficients of Two-Phase Flow in Scraped Surface Heat Exchanger and Holding Tubes /." The Ohio State University, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487929230742153.
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D'Orazio, Antonio. "Computational Fluid Dynamics Modelling of Incompressible Flow and Mixing in Continuous Microreactors." Thesis, Université d'Ottawa / University of Ottawa, 2021. http://hdl.handle.net/10393/42033.
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Continuous milli-scale and micro-scale structures such as FlowPlate® microreactors have emerged as a promising element of process intensification due to their inherently effective rates of mass and heat transfer. These microfluidic devices have proven to be a preferred solution in place of energy-intensive batch processes for certain pathways of fine chemical and pharmaceutical synthesis, most notably fast reactions taking place on the scale of milliseconds to seconds. Computational fluid dynamics (CFD) has become an increasingly valuable tool in the field of microreactor design and optimization for its ability to locally map complex fluid flow patterns and resolve microscopic scales of reactive mixing that are challenging to characterize experimentally. The primary objective of this research was thus to develop and validate a mathematical model for the simulation of chaotic flow and homogeneous mixing in continuous microreactors. The model needed to be versatile enough to handle transition between flow regimes within a given reactor as well as the coexistence of both chaotic and laminar flow patterns in the micromixing elements that comprise said reactors. This was successfully achieved through the implementation of a k-ω SST (shear-stress transport) turbulence model that accounts for the impact of small-scale temporal and spatial fluctuations generated in the micromixer geometries studied herein; be it a liquid-liquid mixer (LLM), a serpentine (SZ) or a tangential (TG) mixer. In a first CFD study, the computational predictions were validated based on excellent agreement with experimental pressure loss (R^2 > 0.997) and residence time distribution (RTD) data (R^2 > 0.97) in several LL microreactors at Reynolds numbers ranging from 210 to 2140. Furthermore, the local velocity distribution and streamlines were mapped across the 3D domain of these reactors and it was discovered, based on the emergence of advective recirculation zones and turbulent dispersion, that a drastic change in flow behaviour occurred in these mixing elements at a Reynolds number of about 640. The interspacing of LLM elements with straight microchannels proved to be a suitable approach to modulating pressure loss while concurrently maintaining the chaotic secondary flow patterns generated from the mixers. In a second CFD study, the impact of micromixer geometry on the local velocity fields and advective transport performance was investigated both from a macromixing and micromixing perspective. Like the LLM, the SZ and TG mixers conferred chaotic secondary flow patterns at characteristic Reynolds numbers between 500 and 1000. As such, it was concluded that it would be ideal to operate these mixers at water flow rates of at least 30 ml/min. Contour plots of the velocity magnitude coupled with the computation of RTD showed that the SZ virtually mimics a plug-flow profile over a volume of 77 mm3 or greater at 50 g/min. The RTD of the LLM and TG resembles that of a mixed flow pattern given that approximately 65-80% of their fluid volume is occupied by recirculation zones. As such, it required 65 LLMs in series (3105 mm3) and 80 TGs (1142 mm3) to approach the same pattern as 10 SZs (77 mm3) from a macromixing perspective. Micromixing time distributions (MTD) were also characterized by locally computing the decay time of small-scale segregation (t_SSS) as a function of flow rate, wherein higher flow rates generated lower characteristic mixing times. The TG and LLM conferred the broadest range of mixing times, spanning nearly four orders of magnitude in the range of [0.02 ms, 10 ms], whereas the SZ generated a much narrower MTD ranging between [0.024 ms, 0.69 ms]. Finally, the impact of geometry and flow conditions on reaction yield was assessed by characterizing the extent of a finite-rate reaction relative to an infinitely fast reaction taking place in parallel. The calculated yield for the competitive-parallel reaction scheme showed that the second Damköhler number (Dall) computed based on the mean tSSS provides useful information about whether the process will be limited by the intrinsic rate of reaction or by the rate of mass transfer, even though the reaction process is controlled by a combination of the RTD as well as loss of LSS and SSS. It was concluded that the change in MTD as a function of power dissipation should coincide with the reaction yield response, and that any deviation in that relationship is because of macroscopic blending of reactants in the entrance region.
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Langarkhorshid, Alimuhammad Rezaeipour. "A study of heat transfer, pressure drop and residence time distribution for two-phase, two component flow in a plate and frame heat exchanger." Thesis, University of East London, 1985. http://roar.uel.ac.uk/1228/.
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This thesis presents a literature review and the results of the present investigation for the upward flow of mixtures of air and water, water or air only in the channel of two Alfa-Laval plate heat exchangers. The flow patterns and their areas in the channel were identified photographically and visually. For both single-phase and two-phase flow, the embossed section of the channel was occupied by the slow and fast zones of flow. The ratio of the areas of these zones varied from nearly one to negligibly small as the flow rate of the phase(s) was increased gradually. These data were correlated empirically with the flow variables of the phase(s). High speed photography was used to analyse mixing in the channel as well as each cell formed by the herringbone patterns of the plates. The data on the flow patterns were used to develop a mathematical model of mixing in the channel to predict the exit concentration profiles of the phase(s). The residence time distribution of the phase(s) predicted by the present model compared very well with the experimental data for both singlephase and two-phase flow of the phases. However, the fit between the experimental and predicted exit concentrations was exceptionally good at high flow rates of the phase(s). The fractional volume of air occupied in the mixture of two-phase flow derived from the mean residence time of twophase flow were correlated empirically with dimensionless groups. The mixing parameters of the gamma distribution model were also correlated with the single-phase and two-phase flow dimensionless groups. The mean heat transfer film coefficients of water (hsL) and mixtures of air and water (htp) for the clean plates were correlated empirically. A Nusselt type equation was used to correlate the mean heat transfer film coefficients for water. The ratio (htp/hsL) was also correlated empirically against single-phase and two-phase dimensionless groups by two correlations which suggest the presence of two widely different flow patterns and mixing characteristics in the channel. Within the range of the variables investigated the values of htp increased by 53 to 340 percent over those for hsL. The pressure drop data for both metal and perspex plate heat exchangers were analysed with the Fanning friction factor (fr) v. Reynolds Number of water or air type of relationships. For air and water two different curves were obtained for the fr: Re relationships. For the analysis of the two-phase pressure data, an empirical approach incorporating the use of the dimensionless groups viz. the ratio of the liquid to gas superficial Reynolds Numbers and the Lockhart & Martinelli parameter (XLM) was found to correlate the twophase friction factor data extremely well. Finally, the pressure drop data were correlated equally well by a Lockhart & Martinelli (12) plot similar to that presented for the tubes.
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Monchatre, Benjamin. "Contribution à l'étude expérimentale d'un outil de mélange de type co-malaxeur : application aux polymères." Thesis, Saint-Etienne, 2015. http://www.theses.fr/2015STET4013/document.
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L’objectif de ce travail de thèse est la compréhension du mode de fonctionnement des co-malaxeurs, outils de mélange dont la connaissance est lacunaire par rapport à d’autres types de mélangeur comme l’extrudeuse mono-vis ou bi-vis. Ce manuscrit porte sur plusieurs études expérimentales relatives au co-malaxeur. L'influence de la vitesse de vis et du débit a été explorée par des mesures de distribution des temps de séjours (DTS), de température matière, de pression, de taux de remplissage, ainsi que de dispersion de fibres de verre. L'influence de la viscosité du polymère à l'état fondu sur la distribution des temps de séjour, la pression filière et la température à l'intérieur du co-malaxeur, a également été traitée, par variation de la température de régulation ou de la masse molaire du polymère. La distribution des temps de séjour ne dépend pas de la viscosité, malgré des différences de pression filière et de température matière. L'influence du profil local sur la DTS a été étudiée par des expériences interchangeant localement les types d'éléments (transport et mélange). Une méthode de mesure de la pression par extrusion micro-capillaire aux emplacements de doigts le long du fourreau a été développée, les gradients de pression sont similaires à ceux obtenus en extrudeuses bi-vis. Enfin une série d'expériences a porté sur la gélification du PVC, déterminée de façon qualitative et quantitative, et a montré l'influence primordiale de la température matière sur l’état de gélificationThe aim of this PhD work is to gain a better understanding of the co-kneading process, whose knowledge is still lacking compared to other types of mixer such as the single screw extruder or the twin-screw extruder. This manuscript features several experimental studies about the co-kneader. The influence of screw speed and throughput was explored by measurements of the residence time distribution, material temperature, die pressure, filling rate, as well as dispersion of glass fibers. The influence of the viscosity of the polymer melt on the residence time distribution, die pressure and temperature within the co-kneader, was also investigated by varying the barrel temperature or the molecular weight of the polymer. The RTD is similar regardless of the viscosity, despite differences in pressure and material temperature. The influence of the screw profile on the RTD was obtained by experiments interchanging locally the types of elements (conveying and mixing). A method of measurement of the pressure along the barrel by micro-capillary extrusion through the location of pins in the barrel was developped, pressure gradients are similar to those obtained in twin-screw extruders. Finally, a series of experiments was dedicated to the gelation of PVC evaluated both qualitatively and quantitatively, and showed that the temperature governs the gelation rate
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Sarang, Sanjay S. "OHMIC heating for thermal processing of low-acid foods containing solid particulates." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1197669208.
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Zhang, Xian-Ming. "Simulation par CFD et mesure en ligne de la distribution des temps de séjour et la qualité de mélange dans une extrudeuse bi-vis." Thesis, Vandoeuvre-les-Nancy, INPL, 2008. http://www.theses.fr/2008INPL066N/document.
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Aujourd’hui le développement de nouveaux matériaux polymères ayant de bonnes propriétés repose de plus en plus sur des procédés de mélange ou de compoundage de polymères au lieu de recourir à la synthèse de nouvelles molécules. L’action du mélange peut fortement influer sur la morphologie des matériaux polymères multi-constituants. Les extrudeuses bi-vis (TSE) sont souvent utilisées comme mélangeurs/réacteurs pour des procédés de mélange, de compoundage et d’extrusion réactive. Cependant, l’étude sur la qualité du mélange dans les TSE demeure un grand défi en raison de la complexité géométrique et du caractère transitoire de l’écoulement. Cette thèse a pour objet de développer un nouvel instrument en line pour mesurer en temps réel la distribution des temps de séjour (DTS) qui caractérise la performance du mélange axial et la capacité de convoyage de différents types d’éléments de vis basées sur l’analyse de l’écoulement transitoire et l’évaluation systématique de la théorie de mélange dans les TSE. Le mélange distributif des polymères fondus est caractérisé par la génération de l’aire des interfaces, un paramètre difficile à mesurer expérimentalement. Alors on fait appel à des simulations numériques de type CFDThe development of new materials with improved properties seems to rely nowadays more on blending and compounding than on the synthesis of chemically new polymers. Mixing may have a great effect on the morphology and structure of multi-component polymer materials. Twin-screw extruders (TSE) are widely used as mixers/reactors for blending, compounding, and reactive processing. This work aimed at developing a new instrument to measure in real time the residence time distribution (RTD) which characterizes the axial mixing and transport abilities of different screw elements based on the analysis of the transient flow pattern and systematic evaluation of mixing theory in TSE. Distributive mixing of polymer melts is characterized by the generation of interfacial area, which is experimentally much more difficult to measure. This 3D numerical simulation based on CFD is adopted
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Gai, Jing-Gang. "Etudes théoriques et expérimentales de la processabilité du polyéthylène à ultra-haute masse molaire." Thesis, Vandoeuvre-les-Nancy, INPL, 2009. http://www.theses.fr/2009INPL039N/document.
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Aujourd’hui le développement de nouveaux matériaux polymères ayant de bonnes propriétés repose de plus en plus sur des procédés de mélange ou de compoundage de polymères au lieu de recourir à la synthèse de nouvelles molécules. L’action du mélange peut fortement influer sur la morphologie des matériaux polymères multi-constituants. Les extrudeuses bi-vis (TSE) sont souvent utilisées comme mélangeurs/réacteurs pour des procédés de mélange, de compoundage et d’extrusion réactive. Cependant, l’étude sur la qualité du mélange dans les TSE demeure un grand défi en raison de la complexité géométrique et du caractère transitoire de l’écoulement. Cette thèse a pour objet de développer un nouvel instrument en line pour mesurer en temps réel la distribution des temps de séjour (DTS) qui caractérise la performance du mélange axial et la capacité de convoyage de différents types d’éléments de vis basées sur l’analyse de l’écoulement transitoire et l’évaluation systématique de la théorie de mélange dans les TSE. Le mélange distributif des polymères fondus est caractérisé par la génération de l’aire des interfaces, un paramètre difficile à mesurer expérimentalement. Alors on fait appel à des simulations numériques de type CFDThe development of new materials with improved properties seems to rely nowadays more on blending and compounding than on the synthesis of chemically new polymers. Mixing may have a great effect on the morphology and structure of multi-component polymer materials. Twin-screw extruders (TSE) are widely used as mixers/reactors for blending, compounding, and reactive processing. This work aimed at developing a new instrument to measure in real time the residence time distribution (RTD) which characterizes the axial mixing and transport abilities of different screw elements based on the analysis of the transient flow pattern and systematic evaluation of mixing theory in TSE. Distributive mixing of polymer melts is characterized by the generation of interfacial area, which is experimentally much more difficult to measure. This 3D numerical simulation based on CFD is adopted
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LINAK, WILLIAM PATRICK. "THE EFFECT OF COAL TYPE, RESIDENCE TIME AND COMBUSTION CONFIGURATION ON THE SUBMICRON AEROSOL COMPOSITION AND SIZE DISTRIBUTION FROM PULVERIZED COAL COMBUSTION (STAGED, FLYASH, SPECIES ENRICHMENT)." Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/188070.
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Pulverized samples of Utah bituminous, Beulah (North Dakota) low Na lignite, Beulah high Na lignite and Texas (San Miguel) lignite coals were burned at a rate of 2.5 kg/hr in a laboratory furnace under various (overall fuel lean) combustion conditions. Particle size distributions (PSD) and size segregated particle filter samples were taken at various positions within the convection section. Temperature and gas concentrations were measured throughout. The evolution of the submicron PSD within the convection section for the four coals was similar, although the location of the initial particle mode at the convection section inlet varied with coal type. While staged (.8/1.2) combustion of the Utah bituminous coal had a variable effect on the volume of submicron aerosol produced, staged combustion of two of the three lignites (Beulah low Na and Texas) caused a definite increase in the submicron aerosol volume. Vapor enhancement due to a localized reducing atmosphere, which would effect coals of higher ash volatility or higher inherent ash content, is thought to explain this behavior. Depressed combustion temperatures associated with the high moisture content of the Beulah high Na lignite are thought to offset the effects of staging. Increased combustion temperatures (through oxygen enrichment) caused staged volume increases for the Beulah high Na lignite. Combustion temperatures are a controlling factor even at more extreme staging conditions. Chemical analysis of the size segregated particle samples show the trace elements, As, Pb, Zn and the major elements, Na and K to be enriched in the submicron aerosol. Auger depth profiles show these small particles to be comprised of a core enriched in Fe, Si, Ca and Mg and surface layers enriched in Na and K. These results point to a mechanism of homogeneous nucleation of low vapor pressure species followed by successive layering of progressively more volatile species. Volatile species are enriched in the submicron aerosol due to the large surface areas provided. Modeling efforts show that while coagulation may be the dominant mechanism to describe the aerosol evolving within the convection section, it cannot be used solely to predict the PSD. Another mechanism, presumably surface area dependent growth (condensation) must be included.
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Dedewanou, Myriam. "Vulnérabilité spécifique des forages vis-à-vis des phytosanitaires : moélisation et application au Val d'Orléans." Thesis, Orléans, 2014. http://www.theses.fr/2014ORLE2020/document.
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Les évaluations de vulnérabilité spécifiques pour les ressources d'eau souterraine sont des méthodes SIG qui établissent des indices qualitatifs spatiaux qui déterminent la sensibilité à l'infiltration de polluants superficiels. D'autre part, les fonctions de transfert, comme la Distribution de Temps de Séjour (DTS), sont utilisées pour prévoir le changement temporel de qualité de l'eau au forage, mais ils ne permettent pas de relier les concentrations aux pratiques observées sur le bassin versant. Basé sur une approche analytique, un modèle pour le transport souterrain des produits phytosanitaires liant la vulnérabilité spécifique SIG à la DTS a été développée. L’idée étant de relier les notions de vulnérabilité aux méthodes de prédiction des chroniques de la qualité des eaux. L'outil estime la qualité de l'eau à partir de l'ensemble de données des cartes de vulnérabilité. La validation de cette méthode de vulnérabilité spécifique est possible à partir des données de suivi de la qualité de l’eau au forage. Une formulation de paramètres équivalents a été proposée pour prendre en compte les caractéristiques hydrodynamiques des compartiments de sol (zone saturée et zone non saturée). Une validation théorique de l'approche est faite à l’aide de modèles souterrain à différence finie : HYDRUS et MODFLOW. Une application a été réalisée sur l'aquifère karstique du Val d'Orléans. Elle a permis de déterminer la DTS des concentrations en pesticides dans l'eau souterraine et a mis en évidence la présence non négligeable des métabolites du métazachlore dans le forage. En même temps, le modèle DTS, lié au SIG rend possible la localisation des zones contributrices dans le bassin versantThe specific vulnerability estimations for the groundwater resources are GIS methods that establish spatial qualitative indices which determine the sensitivity of infiltration from surface contaminants. On the other hand, the transfer functions, using the Residence Time Distribution (RTD), are used to predict temporal water quality change in a borehole, but they do not integrate the spatial variability of the land use. Based on an analytic (advection / dispersion equation) approach, a simple GIS-linked RTD model for groundwater transport has been developed. The tool estimates the water quality from the vulnerability map dataset. This method enables to validate the specific vulnerability maps with the water quality monitoring at the borehole. It links the impacts of land use with the temporal evolution of the water quality. A equivalent formulation parameters is proposed to take into account the hydrodynamic characteristics of the soil compartments (unsaturated zone and Saturated Zone). A theoretical validation of the approach is made from finite-difference groundwater models: HYDRUS and MODFLOW. Also, an application of the RTD compilation was realized on the Val d’Orléans karstic aquifer. This last methodology allowed to determine the RTD of pesticides into the groundwater and highlighted the not insignificant presence of the metabolite of the metazachlor in the groundwater drilling. At the same time, the GIS-linked RTD model makes possible the localization of the contributing zones in the watershed
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Wang, Zhiguo. "Experimental studies and CFD simulations of conical spouted bed hydrodynamics." Thesis, University of British Columbia, 2006. http://hdl.handle.net/2429/61.
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Conical spouted beds have been commonly used for drying suspensions, solutions and pasty materials. They can also be utilized in many other processes, such as catalytic partial oxidation of methane to synthesis gas, coating of tablets, coal gasification and liquefaction, pyrolysis of sawdust or mixtures of wood residues.
The main objectives of this work include both the experimental research and mathematical modelling of the conical spouted bed hydrodynamics.
For experimental research, pressure transducers and static pressure probes were applied to investigate the evolution of the internal spout and the local static pressure distribution; optical fibre probes were utilized to measure axial particle velocity profiles and voidage profiles; the step tracer injection technique using helium as the tracer and thermal conductivity cells as detectors was used to investigate the gas mixing behaviour inside a conical spouted bed. It was found that many factors might affect calibration of the effective distance of an optical fibre probe. Therefore, a new calibration setup was designed and assembled, and a comprehensive sensitivity analysis was conducted to calibrate the optical probes used in this study.
For mathematical modelling, a stream-tube model based on the bed structure inside a conical spouted bed was proposed to simulate partial spouting states. By introducing an adjustable parameter, this model is capable of predicting the total pressure drop under different operating conditions, and estimating axial superficial gas velocity profiles and gauge pressure profiles.
A mathematical model based on characteristics of conical spouted beds and the commercial software FLUENT was also developed and validated using measured experimental data. The proposed new CFD model can simulate both stable spouting and partial spouting states, with an adjustable solids-phase source term. At stable spouting states, simulation results agree very well with almost all experimental data, such as static pressure profiles, axial particle velocity profiles, voidage profiles etc. A comprehensive sensitivity analysis was also conducted to investigate the effect of all possible factors on simulation results, including the fluid inlet profile, solid bulk viscosity, frictional viscosity, restitution coefficient, exchange coefficient, and solid phase source term.
The proposed new CFD model was also used successfully to simulate gas mixing behaviours inside a conical spouted bed, and simulate cylindrical packed beds as well as cylindrical fluidized beds in one code package.
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Fortes, Nilo Henrique Meira. "Estudo da distribuição do tempo de residência em um processo de pasteurização assistido por micro-ondas." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/3/3137/tde-01112018-115416/.
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O processo de pasteurização tem como objetivo garantir a segurança e qualidade nutricional do alimento e aumentar sua vida de prateleira. O conhecimento da distribuição do tempo de residência (DTR) do alimento em cada etapa do processo contínuo é importante para uma avaliação adequada do processo e das alterações que causa no alimento. Este trabalho tem como objetivo estudar a DTR em um processo de pasteurização contínuo assistido por micro-ondas aplicado a alimentos líquidos e propor modelos de escoamento para representá-la. Para isso, foram realizados experimentos de estímulo-resposta com alimentação tipo pulso por técnica condutimétrica utilizando uma solução saturada de NaCl como traçador. Com isso, foram obtidas as curvas de DTR do sistema completo, dos trocadores de calor das seções de pré-aquecimento e resfriamento, de seis tubos de retenção com diferentes diâmetros e comprimentos (volumes entre 40 e 125 mL) e do sistema de aquisição de dados de condutividade elétrica. Os experimentos foram realizados em quatro vazões volumétricas (0,5, 0,7, 0,9 e 1,1 L/min), a temperatura ambiente (19 a 26 °C) e como fluido de trabalho foi utilizada uma corrente de alimentação de água com concentração 0,5 g/L de NaCl para estabilizar a leitura de condutividade elétrica. Foram realizadas três repetições por vazão para o processo completo, trocadores de calor e tubos de retenção, e cinco repetições por vazão para o sistema de aquisição de dados, dada a maior sensibilidade. Observou-se a necessidade de realizar o procedimento de convolução numérica para avaliar a distorção na curva de DTR do processo causada pelo escoamento na célula do sistema de aquisição de dados. Foram testados cinco modelos de escoamento: dispersão axial, compartimentado PFR+CSTR, tanques em série, convecção generalizada e y-laminar. O critério de ajuste dos modelos foi a minimização do erro quadrático entre valores experimentais e calculados da curva E(t). Os modelos de dispersão axial e y-laminar foram o que apresentaram melhor ajuste para os tubos de retenção e o modelo de convecção generalizada apresentou melhor ajuste para os trocadores de calor. O regime de escoamento durante os experimentos variou entre laminar e de transição (valores de Reynolds entre 1259 e 4238). Os resultados para o sistema completo e trocadores de calor foram satisfatórios, para os tubos de retenção foi observada uma grande incerteza nos valores dos parâmetros e foi observada a importância da convolução numérica em sistemas de pequeno volume.Pasteurization process aims to ensure the safety and nutritional quality of the food and increase its shelf life. The knowledge of residence time distribution (RTD) of the food in each step of continuous processes is important to evaluate the process and changes that it causes in foods. This work aims to study the RTD in a continuous pasteurization process assisted by microwave applied to liquid foods and propose flow models to represent it. For this reason, stimulus-response experiments by pulse injection were conducted by conductimetric technique using a saturated solution of NaCl as a tracer. Thus, it was obtained the RTD of the complete process, heat exchangers of preheating section and cooling section, six retention tubes with different diameters and lengths (volumes between 40 and 125 mL) and of the electrical conductivity data acquisition system. The experiments were carried out at four volumetric flow rates (0.5, 0.7, 0.9 and 1.1 L/min), at room temperature (19 to 26 °C) and water with 0.5 g/L of NaCl was used as the work fluid to stabilize the electrical conductivity reading. Three repetitions per volumetric flow rate were performed for the complete process, heat exchangers and holding tubes, and five repetitions per volumetric flow rate were performed for the data acquisition system, given the higher sensibility. It was observed the need to apply the numerical convolution procedure to evaluate the distortion in the RTD curve of the process caused by the flow through the data acquisition system. Five flow models were tested: axial dispersion, PFR+CSTR association, tanks in series, generalized convection and y-laminar. The adjustment criterion of the parameters was the minimization of the quadratic error between experimental and calculated E(t) values. The axial dispersion and y-laminar models provided the best adjustments for the holding tubes and the generalized convection model provided the best adjustment for the heat exchangers. The flow regime during the experiments varied between laminar and transition (Reynolds values between 1259 and 4238). The results for the complete system and heat exchangers were satisfactory, for the holding tubes was observed a great uncertainty in the parameters values and was observed the importance of numerical convolution in small volume systems.
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Gutierrez, Carola Gean Carla Cavero. "Distribuição do tempo de residência em processo de pasteurização com trocador de calor a placas." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/3/3137/tde-30052008-155723/.
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É apresentado um estudo de distribuição do tempo de residência nas etapas de um processo de pasteurização contínuo por trocador de calor a placas (aquecimento, resfriamento, regeneração e retenção). Para o estudo experimental, foi adotada a técnica condutimétrica usando cloreto de sódio em solução aquosa como traçador. Foram verificadas as influências da vazão, da configuração do trocador de calor a placas (número de passes para o arranjo em série) e do tipo de tubo de retenção (tubo em \"S\" e tubo helicoidal). Modelos de distribuição foram usados para representar o comportamento experimental (dispersão axial, tanques em série, laminar modificado, combinado PFR+CSTR). Este estudo foi aplicado para as condições de pasteurização HTST de leite, visando a futura implementação de uma modelagem matemática rigorosa do processo, para otimização do projeto e operação do processo.It is presented a study of residence time distribution in the steps of a process of continuous pasteurization by plate heat exchanger (heating, cooling, regeneration and holding). For the experimental study, it was adopted a conductimetric technique using sodium chloride in aqueous solution as a tracer. It was also studied the influence of the flow rate, the configuration of the plate heat exchanger (number of passes in series arrangement) and the type of holding tube (\"S\"- shaped tube and helicoidal tube). Distribution models were used for representing the experimental behavior (axial dispersion, tank in series, modified laminar, combined PFR+CSTR). This study was applied for the conditions of HTST pasteurization of milk, targeting the future implementation of a rigorous mathematical modeling of the process, which can be applied for the process operation and optimization of the project design.
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Pegoraro, Paula Rossato. "Distribuição do tempo de residência e letalidade no processamento térmico contínuo de líquidos com escoamento laminar não ideal em trocadores bitubulares." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/3/3137/tde-10052012-122241/.
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Os trocadores de calor tubulares são muito utilizados para o processamento térmico de alimentos líquidos viscosos por possuírem um maior diâmetro hidráulico em comparação aos trocadores de calor a placas. O cálculo da letalidade neste tipo de trocador está diretamente relacionado ao perfil de velocidade e à distribuição do tempo de residência (DTR). Para escoamento laminar de fluidos viscosos, Newtonianos e não-Newtonianos, geralmente adota-se um perfil de velocidade laminar e de lei de potência, respectivamente. No entanto, algumas características do equipamento como irregularidades na tubulação, a corrugação do tubo ou as curvas podem modificar o perfil de velocidade ideal. Esse desvio da idealidade pode ser caracterizado através da determinação experimental da distribuição do tempo de residência do processo. Este trabalho teve como objetivo a determinação experimental da DTR de fluidos viscosos em um equipamento bitubular de processamento térmico e o ajuste do perfil de velocidade associado. Modelos clássicos de DTR foram ajustados aos dados, assim como foram propostos e testados novos modelos generalizados de DTR, a fim de caracterizar o escoamento laminar não ideal em tubos. A determinação da DTR experimental foi realizada para vazões entre 10 e 50 L/h utilizando água, solução de carboximeticelulose 1,0% (pseudoplástico) e mistura glicerina/água 80%. Os dados de DTR foram obtidos através de duas técnicas: condutimétrica e colorimétrica. A primeira técnica baseia-se na injeção de solução saturada de cloreto de sódio e detecção online por um condutivímetro, porém, não apresentou resultados satisfatórios mostrando que o método não é adequado para fluidos viscosos. Já a segunda técnica utilizada se baseia na injeção de corante e posterior detecção em espectrofotômetro. Os modelos que melhor se ajustaram aos dados experimentais para os três fluidos estudados foram os modelos generalizados y-laminar e exponencial. A letalidade foi calculada a partir da distribuição de temperatura no trocador de calor em estado estacionário e do tempo médio de residência obtido experimentalmente e permitiu detectar o sobreprocessamento no processo estudado.Tubular heat exchangers are widely used for thermal processing of viscous liquid foods because they have larger hydraulic diameters than the plate heat exchangers. The calculation of lethality in this type of exchanger is directly related to velocity profile and the residence time distribution (RTD). For the laminar flow of viscous fluids, Newtonian and non-Newtonian, generally laminar and power law velocity profiles are used, respectively. However, some features of the equipment as irregularities in the pipe, the corrugation of the pipe or the presence of curves can change the ideal velocity profile. This ideality deviation can be characterized through the experimental determination of the residence time distribution of the process. The aim of this work was the experimental determination of the RTD of a viscous fluid in a bitubular thermal processing equipment and the determination of the associated velocity profile. Classic models of RTD were fitted to the data, as well as were proposed and tested new generalized models of RTD, in order to characterize the non ideal laminar flow in tubes. The experimental determination of RTD was performed to volumetric flow rates between 10 and 50 L/h using water, carboximeticelulose solution 1,0% (pseudoplastic) and glycerin/water mixture 80%. The RTD data were obtained through two techniques: conductimetric and colorimetric. The first technique is based on injection of saturated solution of sodium chloride and online detection with a conductivimeter however, unsatisfactory results showed that the method was not suitable for viscous fluids. The second technique is based on the injection of dye and subsequent detection with a spectrophotometer. The best fitted models to the experimental data for the three studied fluids were: ylaminar and exponential generalized models. The lethality was calculated from the temperature distribution in the heat exchanger at steady state and average residence time obtained experimentally and allowed the evaluation of the overprocessing of this process.
35
Colin, Baptiste. "Modélisation de la torréfaction de plaquettes de bois en four tournant et validation expérimentale à l’échelle d’un pilote continu de laboratoire." Thesis, Ecole nationale des Mines d'Albi-Carmaux, 2014. http://www.theses.fr/2014EMAC0015/document.
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La torréfaction est un traitement thermique à basse température (250 à 300 °C) en atmosphère inerte qui permet de modifier les propriétés de la biomasse. La biomasse torréfiée est alors plus dense énergétiquement, plus hydrophobe et plus fragile. Dans cette étude, un modèle numérique de torréfaction en four tournant à une dimension a été développé. Le transport des plaquettes de bois, les transferts thermiques, le séchage ainsi que les cinétiques de torréfaction ont été modélisés séparément. Après confrontation aux résultats expérimentaux, ces différents sous-modèles ont été assemblés dans un modèle global. Le modèle prédit alors l’évolution de la température et de la perte de masse des plaquettes le long du four. Les résultats numériques montrent une adéquation satisfaisante avec les valeurs obtenues lors d’expériences de torréfaction sur un four tournant pilote. Les solides torréfiés ont été analysés et leurs propriétés ont été corrélées à la perte de masse. Il a en particulier été démontré que l'énergie de broyage de la biomasse torréfiée était fortement réduiteTorrefaction is a thermal treatment at low temperature (250-300°C) used to improve biomass properties. Torrefied biomass has a higher energy density, it is more hydrophobic and more brittle. In this study, a one-dimensional numerical model of torrefaction in a rotary kiln has been developed. The wood chips flow, the thermal transfers, the drying step and the torrefaction kinetics have been modelled separately. These submodels have been experimentally validated before being implemented together. The model can thus predict the temperature and the mass loss of wood chips along the kiln. These results are in good agreement with values obtained during torrefaction experiments in the pilot-scale rotary kiln. In parallel, torrefied biomass has been analysed in terms of composition, heating value and structural properties with emphasis on the decrease of grinding energy consumption
36
Do, Nascimento Arrais Murilo Rricardo. "Vers une meilleure distribution des fluides dans les réacteurs polyphasiques." Electronic Thesis or Diss., Université de Toulouse (2023-....), 2024. http://www.theses.fr/2024TLSEP066.
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La maldistribution des phases dans les réacteurs millistructurés de type monolithe est un inconvénient majeur pour les réactions gaz-liquide, qui freine le déploiement de cette technologie à l'échelle industrielle. En effet, ce problème est d'autant plus gênant pour les réacteurs monolithes, qui sont plus efficaces que les réacteurs classiques pour les réactions catalytiques si la distribution des fluides est uniforme.Afin de résoudre ce problème, un distributeur gaz-liquide original avec une géométrie basée sur une jonction en T, et conçu au LGC pour un monolithe à 84 canaux, a été construit par fabrication additive (stéréolithographie) et testé avec un système air-eau.Pour caractériser la distribution de gaz et de liquide effectuée, un capteur résistif spécifique a été développé, qui permet de mesurer la fréquence des bulles, la vitesse des bulles et la rétention de gaz dans tous les canaux simultanément. Cet outil est constitué de circuits imprimés et de 84 paires d'électrodes, qui délivrent à haute résolution temporelle la résistivité équivalente du mélange gaz-liquide traversant chaque canal. Le capteur a été évalué avec une précision de ± 10 % pour la fréquence des bulles et de ± 20 % pour la rétention de gaz et la vitesse des bulles, par référence à l'ombroscopie, utilisée comme technique de référence.Des essais expérimentaux ont été réalisés pour plusieurs régimes d'écoulement avec le distributeur innovant et le capteur spécifique. Elles ont été comparées à celles réalisées avec un distributeur conventionnel, de technologie basée sur des plateaux perforés. Un critère combinant la fréquence des bulles et l'existence d'un écoulement gaz-liquide dans les canaux est choisi pour évaluer la maldistribution. Le distributeur proposé présente une distribution des fluides plus homogène que celui du distributeur conventionnel, avec une maldistribution de 20% pour tous les régimes, à l'exception du régime à bulles (32%). Ainsi, le distributeur conventionnel donne en moyenne une maldistribution de 61%.Pour le distributeur innovant, l'impact du matériau et de sa rugosité, l'impact de la géométrie interne du distributeur, ainsi que la stabilité des flux distribués tout au long des canaux monolithiques, ont été étudiés.Parallèlement, une approche de distribution du temps de séjour est proposée pour modéliser le comportement global de l'écoulement - quantifier la dispersion - au sein du monolithe. Pour des couples donnés de débits globaux de gaz et de liquide, cette approche combine la représentation DTS de l’écoulement de Taylor – attendu au sein des canaux – et la maldistribution observée en sortie du distributeur (ou à l’entrée du monolithe). Pour des maldistributions allant jusqu’à 20 % sur la vitesse de bulles et/ou le taux de gaz et, le degré de mélange est augmenté jusqu'à 60 % pour le nombre de Péclet or jusqu'à 160 % pour le coefficient de dispersion axiale, par rapport à ceux d'une distribution uniforme de débits équivalents.Le modèle DTS résultant peut ensuite être couplé à une cinétique de réaction afin de prédire l'avancement de la réaction à la sortie du réacteur, et permet d'explorer l'impact de maldistributions réalistes sur les performances du réacteur. Pour des maldistributions allant jusqu’à 20% sur la vitesse de bulles et/ou le taux de gaz et en considérant une cinétique de réaction de pseudo premier ordre couplée au transfert de masse d'un réactif issu de la phase gaz, la performance du réacteur est réduite d'un facteur pouvant atteindre 20%, par rapport à une distribution uniformeMaldistribution of phases in milli-structured reactors of monolith type is a major drawback for gas-liquid reactions, which hinders the deployment of this technology on industrial scale. Indeed, this problem is all the more troublesome for monolith reactors, which are more efficient than conventional reactors for catalytic reactions if the fluid distribution is uniform.In order to solve this problem, an original gas-liquid distributor with a T-junction based geometry, previously designed in the laboratory for an 84-channel monolith, has been built by additive manufacturing (stereolithography), and tested with air-water system.To characterize the performed gas and liquid distribution, a specific sensor was developed, which allows measuring bubble frequency, bubble velocity, and gas holdup simultaneously in all channels. This tool consists of printed circuit boards and 84 pairs of electrodes, which deliver at high temporal resolution the equivalent resistivity of the gas-liquid mixture passing through each channel. The sensor was assessed with an accuracy of ± 10% for bubble frequency and of ± 20% for gas holdup and bubble velocity, with respect to the shadowgraphy as reference technique.Experimental essays have been carried out for several flow regimes with the innovative distributor and the specific sensor. They were compared to those performed with a conventional one of showerhead type. A criterion combining bubble frequency and the occurrence of gas-liquid flow is chosen to assess maldistribution. The proposed distributor is found to induce a more homogeneous distribution than the showerhead one, with a maldistribution of 20% for all regimes, except for bubbly flows (32%). The showerhead distributor gives an average of 61% of maldistribution.For the innovative distributor, the impact of the material and its roughness, the impact of the inner distributor geometry, as well as the stability of the distributed flows all along the monolith channels are investigated.Alongside, a Residence Time Distribution approach is proposed to model the overall flow behaviour - i.e. to quantify its dispersion - within the monolith. For a given set of gas and liquid global flow rates, this approach combines the RTD representation of the Taylor flow – which is expected within the channels – and the observed maldistribution at distributor outlet (or at monolith inlet). For experimental maldistributions of up to 20% for bubble velocity and/or gas holdup, mixing degree is increased by up to 60% for the Peclet number (or by up to 160% for the axial dispersion coefficient), as compared to a uniform distribution.The resulting RTD model can then be coupled to reaction kinetics in order to predict the reaction yield at reactor outlet, and allows exploring the impact of realistic maldistributions onto the reactor performance. For experimental maldistributions of up to 20% for bubble velocity and/or gas holdup and considering a pseudo first-order reaction kinetics with gas-liquid mass transfer, the reactor yield is reduced by up to 20%, as compared to a uniform distribution
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Yucel, Cakal Gaye O. "Dynamic Behavior Of Continuous Flow Stirred Slurry Reactors In Boric Acid Production." Phd thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12605047/index.pdf.
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One of the most important boron minerals, colemanite is reacted with sulfuric acid to produce boric acid. During this reaction, gypsum (calcium sulfate dihydrate) is formed as a byproduct. In this study, the boric acid production was handled both in a batch and four continuously stirred slurry reactors (4-CFSSR&rsquos) in series system. In this reaction system there are at least three phases, one liquid and two solid phases (colemanite and gypsum). In a batch reactor all the phases have the same operating time (residence time), whereas in a continuous reactor all the phases may have different residence time distributions. The residence time of both the reactant and the product solids are very important because they affect the dissolution conversion of colemanite and the growth of gypsum crystals. The main aim of this study was to investigate the dynamic behavior of continuous flow stirred slurry reactors. By obtaining the residence time distribution of the solid and liquid components, the non-idealities in the reactors can be found. The experiments performed in the continuous flow stirred slurry reactors showed that the reactors to be used during the boric acid production experiments approached an ideal CSTR in the range of the stirring rate (500-750 rpm) studied. The steady state performance of the continuous flow stirred slurry reactors (CFSSR&rsquo
s) in series was also studied. During the studies, two colemanites having the same origin but different compositions and particle sizes were used. The boric acid production reaction consists of two simultaneous reactions, dissolution of colemanite and crystallization of gypsum. The dissolution of colemanite and the gypsum formation was followed from the boric acid and calcium ion concentrations, respectively. The effect of initial CaO/ SO42- molar ratio (1.00, 1.37 and 2.17) on the boric acid and calcium ion concentrations were searched. Also, at these initial molar ratios the colemanite feed rate was varied (5, 7.5, 10 and 15 g/min) to change the residence time of the slurry. Purity of the boric acid solution was examined in terms of the selected impurities, which were the magnesium and sulfate ion concentrations. The concentrations of them were compared at the initial molar ratios of 1.00 and 1.37 with varying colemanite feed rates. It was seen that at high initial CaO/ SO42- molar ratios the sulfate and magnesium ion concentrations decreased but the calcium ion concentration increased. The gypsum crystals formed in the reaction are in the shape of thin needles. These crystals, mixed with the insolubles coming from the mineral, are removed from the boric acid slurry by filtration. Filtration of gypsum crystals has an important role in boric acid production reaction because it affects the efficiency, purity and crystallization of boric acid. These crystals must grow to an appropriate size in the reactor. The growth process of gypsum crystals should be synchronized with the dissolution reaction. The effect of solid hold-up (0.04&ndash
0.09), defined as the volume of solid to the total volume, on the residence time of gypsum crystals was investigated and the change of the residence time (17-60 min) on the growth of the gypsum was searched. The residence time at each reactor was kept constant in each experiment as the volumes of the reactors were equal. The growth of gypsum was examined by a laser diffraction particle size analyzer and the volume weighted mean diameters of the gypsum crystals were obtained. The views of the crystals were taken under a light microscope. It was observed that the high residence time had a positive effect on the growth of gypsum crystals. The crystals had volume weighted mean diameters of even 240 µ
m. The gypsum crystal growth model was obtained by using the second order crystallization reaction rate equation. The residence time of the continuous reactors are used together with the gypsum growth model to simulate the continuous boric acid reactors with macrofluid and microfluid models. The selected residence times (20-240 min) were modeled for different number of CSTR&rsquo
s (1-8) and the PFR. The simulated models were, then verified with the experimental data. The experimentally found calcium ion concentrations checked with the concentrations found from the microfluid model. It was also calculated that the experimental data fitted the microfluid model with a deviation of 4-7%.
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Caldas, Pereira Silveira Arlan. "Caractérisation expérimentale et comportement de constituants protéiques et minéraux laitiers en concentration sous vide." Thesis, Rennes, Agrocampus Ouest, 2015. http://www.theses.fr/2015NSARB269/document.
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Les évaporateurs à flot tombant (EFT) sont largement utilisés dans les industries chimiques, de la réfrigération, du raffinage du pétrole, et alimentaires. Dans l'industrie laitière, les EFT sont appliqués pour la concentration de solutions avant l'étape de séchage. Malgré l'importance économique du procédé d'évaporation sous vide dans la fabrication de produits laitiers déshydratés, la connaissance du procédé est essentiellement empirique. Des recherches visant à améliorer l'efficacité du procédé sont donc nécessaires. L'objectif de ce projet de doctorat est de caractériser expérimentalement un EFT lors de la concentration de produits laitiers, par des approches thermo et hydro-dynamiques, afin d'étudier les interactions entre les propriétés des produits et les paramètres opérationnels. Un évaporateur à flot tombant, simple effet, à l’échelle pilote, qui décrit le même processus que celui à l'échelle industrielle, d'un point de vue hydrodynamique, a été instrumenté et utilisé pour établir les bilans massiques et énergétiques. La capacité évaporatoire et le coefficient global de transfert de chaleur ont été calculés à partir des données expérimentales. Une méthodologie pour la détermination expérimentale des fonctions distribution des temps de séjour (DTS) a été développée. En effet, les fonctions de DTS fournissent des informations essentielles sur l'écoulement des produits lors de la concentration dans un EFT. L'augmentation de la concentration, du débit massique et de la distance parcourue par le produit entraîne une augmentation de la dispersion des particules dans le flux. Ces fonctions ont été modélisées par une combinaison de réacteurs en cascade, parfaitement agités. D’après l'interprétation de ce modèle, deux flux, un principal et un secondaire, correspondant à deux couches superposées de produit circulant à travers des tubes d'évaporateur, a été proposé. La méthodologie développée pour le calcul des fonctions de DTS a été appliqué pour la concentration de produits laitiers (lait écrémé, lactosérum doux et acide). Par la suite, l'étude a été étendue à la formation de l'encrassement pendant la concentration par évaporation sous vide. Il a été montré que le temps de séjour moyen était plus sensible pour identifier l'encrassement que le coefficient global de transfert de chaleur et la capacité évaporatoire. Ainsi, cette étude a souligné le rôle crucial de l’importance de la caractérisation des EFT sous vide afin d’en améliorer leurs performances et la qualité des produits qui en sont issuFalling film evaporators (FFE) are widely used in the chemical, refrigeration, petroleum refining, desalination and food industries. In the dairy industry FFE is applied for the concentration of solutions prior to the drying step. Despite the economic importance of the vacuum evaporation process in the manufacture of dairy dried products, the knowledge about the process is mostly empirical. Research aiming to improve the efficiency of the process is therefore necessary. The objective of this PhD project was to characterize experimentally a FFE during the concentration of dairy products by means of thermodynamic and hydrodynamic approaches, in order to study the interactions between the products properties and the operating parameters. A pilot-scale, single-stage falling film evaporator that describes the same process as that of an industrial scale from a hydrodynamic point of view was instrumented and used to establish the mass and energy balances. The evaporation rate and the overall heat transfer coefficient were calculated from the experimental data to follow up the process. A methodology for the determination of the experimental residence time distribution (RTD) functions was developed. RTD functions provide global information about the flow of the products during concentration in a FFE. Increasing of the concentration of skim milk, mass flow rate and the distance covered by the product resulted in an increase in the dispersion of the products particles. The experimental RTD functions were modelled by a combination of two perfectly mixed reactor tanks in series. From the interpretation of this model, two different flows, a main and a minor flow, were identified. The RTD methodology developed on skim milk was applied to sweet whey and lactic acid whey and the study was extended to the formation of fouling during a 5-hour concentration. The mean residence time was more sensitive to identify fouling than the overall heat transfer coefficient and the evaporation rate. This study emphasized the crucial role of process characterization to improve the performance of FFE and product quality
39
Dülle, Matthias [Verfasser], and Claudia S. [Akademischer Betreuer] Leopold. "Investigations on the powder behaviour and the residence time distribution within a production scale rotary press with special focus on its geometric and parametric setups / Matthias Dülle ; Betreuer: Claudia S. Leopold." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://d-nb.info/1193650763/34.
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Skalak, Katherine Joanne. "Fine-grained channel margin deposits in a typical gravel bed river spatial and temporal controls on the distribution, quantity, and residence time and implications for centennial-scale sediment and mercury cycling /." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 437 p, 2009. http://proquest.umi.com/pqdweb?did=1885693201&sid=5&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Varinot, Christelle. "Contrôle de la distribution granulométrique en broyage fin continu." Vandoeuvre-les-Nancy, INPL, 1996. http://www.theses.fr/1996INPL109N.
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Compte tenu des exigences de plus en plus draconiennes sur la qualité des poudres utilisées dans l'industrie pharmaceutique, les cosmétiques, les céramiques etc qui doivent être de plus en plus fines avec des diamètres moyens précis, le contrôle de la distribution granulométrique dans les opérations de réduction de taille est devenu une préoccupation majeure. Dans ce travail de thèse qui porte sur l'étude du broyage du carbone dans un broyeur à billes agité humide, nous nous sommes donc attachés à définir les conditions de fonctionnement permettant d'obtenir des produits de granulométrie déterminée. Pour cela, une étude de l'influence des paramètres opératoires sur la cinétique de fragmentation et l'écoulement à travers le broyeur a été réalisée. Elle a permis la mise au point d'un modèle du broyage continu dont les paramètres peuvent être utilisés pour calculer les fonctions de sélection et de broyage à partir desquelles il est possible d'identifier les mécanismes de fragmentation mis en jeu. Une étude par analyse d'images et des mesures de potentiel de surface et de tension superficielle ont montré qu'ils ont une influence importante sur la forme et les propriétés de surface des fragments produits. Enfin, l'allure de la distribution granulométrique du produit obtenu ne pouvant être modifiée que de façon limitée en jouant sur les paramètres opératoires du procédé de broyage, l'étude théorique d'une boucle de broyage-sélection a été réalisée et a conduit à la mise au point d'un élutriateur centrifuge permettant la récupération de la fraction fine et le recyclage en continu de la fraction grosse
42
Treguer, Véronique. "Recherche des conditions optimales de mise en contact de particules solides et de gouttelettes dans un réacteur à jets : application au craquage catalytique." Vandoeuvre-les-Nancy, INPL, 1995. http://docnum.univ-lorraine.fr/public/INPL_T_1995_TREGUER_V.pdf.
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Les réacteurs à impact de jets, contenant ou non des phases dispersées, constituent une classe mal connue de réacteurs. Dans le cas du procédé de craquage catalytique trois phases sont mises en jeu : du gaz, des particules de catalyseur et des gouttelettes de charge pétrolière. La zone de mise en contact initiale des jets de réactifs semble particulièrement déterminante pour le rendement global de la réaction. L’objet de ce travail est donc l'étude expérimentale du comportement global des phases continues ou dispersées au cours de leur mise en contact qui s'effectue en des temps de l'ordre de quelques dizaines de millisecondes. À partir de mesures de distributions de temps de séjour sur des maquettes froides le comportement hydrodynamique de la phase continue est déterminé, l'éventuelle influence de la présence des solides étant aussi envisagée. Une étude sur l'efficacité des transferts de chaleur au cours de la mise en contact des particules et de la phase gazeuse est ensuite menée. Par ailleurs l'efficacité de la mise en contact des phases dispersées est caractérisée par l'étude des interactions entre des particules modèles, réactives ou non, et des gouttelettes d'eau. Une réaction test est mise au point et un modèle simple décrivant le comportement des phases dans le réacteur y est associé. L’existence d'une fraction de solides ne participant pas à l'impact des particules et des gouttelettes a ainsi pu être mise en évidence. Ce phénomène est quantifié par certains paramètres dont l'évolution est étudiée en fonction des conditions expérimentales. Il en ressort un certain nombre de conclusions mais aussi de possibilités d'études futures pour une meilleure connaissance des phénomènes.
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Gatehouse, Hazel A. W. "Ecology of the naturalisation and geographic distribution of the non-indigenous seed plant species of New Zealand." Diss., Lincoln University, 2008. http://hdl.handle.net/10182/1009.
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The naturalisation and subsequent spread of non-indigenous plant species (NIPS) is a major problem for most regions of the world. Managing plant invasions requires greater understanding of factors that determine initial naturalisation and distribution of wild NIPS. By the year 2000, 2252 NIPS were recorded as wild (1773 fully naturalised and 479 casual) in New Zealand. From published literature and electronic herbaria records, I recorded year of discovery of wild populations, and regional distribution of these wild NIPS. I also recorded species related attributes hypothesised to affect naturalisation and/or distribution, including global trade, human activities, native range and biological data; and regional attributes hypothesised to affect distribution, including human population densities, land use/cover, and environmental data. I used interval-censored time-to-event analyses to estimate year of naturalisation from discovery records, then analysed the importance of historical, human activity, biogeographical and biological attributes in determining patterns of naturalisation. Typically, NIPS that naturalised earlier were herbaceous, utilitarian species that were also accidentally introduced and/or distributed, with a wide native range that included Eurasia, naturalised elsewhere, with a native congener in New Zealand. In the year 2000, 28% of wild NIPS occupied only one region, 18% occupied two regions, decreasing incrementally to 2.5 % for nine regions, but with 13.5% occupying all ten regions. I used generalised linear models (GLMs) with binomial distribution to determine predictors of whether a wild NIPS occupied ten regions or not, and GLMs with Poisson distribution for wild NIPS occupying 0 – 9 regions. As expected, the dominant effect was that species discovered earlier occupied more regions. Utilitarian wild NIPS that were also accidentally introduced and/or distributed, and wild NIPS with a native congener tended to be more widely distributed, but results for other attributes varied between datasets. Although numbers of wild NIPS recorded in regions of New Zealand were sometimes similar, composition of wild NIPS was often very different. I used nonmetric multidimensional scaling (NMDS) to determine dissimilarity in composition between regions. Then, after reducing correlation between predictor variables using principal components analyses (PCAs), I tested the importance of regional variables in determining the regional composition of wild NIPS using metaMDS. The density of human populations best explained the dissimilarity in composition, but temperature gradients and water availability gradients were also important. In the year 2000 more than 1100 (60%) of the 1773 fully naturalised NIPS in mainland New Zealand had each been recorded in Northland/Auckland and Canterbury, and at the other end of the scale, Southland and Westland each had fewer than 500 (30%). I used GLMs to analyse the importance of people and environment in determining the numbers of wild NIPS in each region. Because I conducted multiple tests on the same dataset I used sequential Bonferroni procedures to adjust the critical P-value. Only human population density was important in explaining the numbers of NIPS in the regions. Overall, humans were the dominant drivers in determining the patterns of naturalisation and spread, although environment helps determine the composition of NIPS in regions. Incorporating human associated factors into studies of wild NIPS helps improve the understanding of the stages in the naturalisation and spread process.
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Ortwein, Andreas. "Modellierung der Hochdruck-Partialoxidation von Heiz- und Schweröl." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2012. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-88104.
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Für die Modellierung der Hochdruck-Partialoxidation von Heiz- und Schweröl werden zunächst Untersuchungen des Einsatzstoffes durchgeführt, um deren Verdampfungs- und Pyrolyseverhalten zu bestimmen. Dazu wird das Verfahren der Hochdruck-Thermogravimetrie verwendet. Mit Hilfe der numerischen Strömungsmechanik unter Anwendung von detaillierten Reaktionsmechanismen und eines umfangreichen Partikelmodells werden die Zustände im Reaktor modelliert. Die Validierung mit Verweilzeitmessungen wird demonstriert und damit verbundene Probleme aufgezeigt. Anhand von Untersuchungen am Vergasungsrückstand kann die Existenz von Cenosphären (Tropfenrückstände) und von in der Flamme gebildetem Ruß nachgewiesen werden.
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Matsumoto, Danielle. "Modelagem e simulação de reator solar usando fluidodinâmica computacional." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/3/3137/tde-06072014-220539/.
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Este estudo apresenta a modelagem fluidodinâmica de um reator solar utilizado para Processos Oxidativos Avançados (POA). Desenvolveu-se um modelo que considera a fluidodinâmica, o campo de radiação e cinética da reação de actinometria química (ferrioxalato), em regime transiente. Essa modelagem foi feita utilizando-se o código de fluidodinâmica computacional PHOENICS. Para análise dos resultados de simulações com o modelo, consideraram-se os dados experimentais de actinometria química para um trecho do reator, constituído de dois tubos (hairpin), e de distribuição de tempos de residência (DTR), para o reator completo, constituído de dez tubos. Os dados experimentais foram obtidos por RIBEIRO (2009). O resultado da análise da distribuição do tempo de residência do reator completo mostrou que o modelo baseado em escoamento laminar apresentou uma maior aderência aos dados experimentais de DTR. Como os experimentos de actinometria foram realizados em trecho com dois tubos do reator, construiu-se a geometria do hairpin que apresentou uma DTR mais aderente aos modelos teóricos. Outra simplificação foi necessária para a modelagem do campo de radiação de forma mais precisa, adaptando-se o hairpin para um tubo reto simples. A partir dos resultados de actinometria química foi possível estimar, pelo modelo, a taxa de fótons incidentes na parede do reator.This study consists of the fluid dynamic modeling of a solar reactor used in Advanced Oxidation Processes (AOP). The model was developed by considering fluid dynamics, radiation field and the kinetics of the chemical actinometry reaction (ferrioxalate) in transient regime. This modeling was developed using computational fluid dynamics (CFD) in PHOENICS. Simulation results based on the model were analyzed by comparing them with a set of chemical actinometry experimental data obtained by RIBEIRO (2009). This considered a reactor section constituted by two pipes (hairpin), and the residence time distribution (RTD) of the complete reactor, composed of ten pipes. Residence time distribution results showed that the laminar flow model presented a better fitting to experimental data. Since the actinometry experiments were carried out in a reactor section with two pipes, a new geometry was designed, which resulted in a better fitting of RTD results with theoretical models. In order to obtain a more precise radiation field model, another simplification was necessary, which consisted of assuming a straight cylindrical pipe geometry. The use of the chemical actinometry and the radiation field model enabled the estimation of the incident photons rate at reactor wall.
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Charlou, Christophe. "Caractérisation et modélisation de l’écoulement de boues résiduaires dans un sécheur à palettes." Thesis, Ecole nationale des Mines d'Albi-Carmaux, 2014. http://www.theses.fr/2014EMAC0004/document.
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Le séchage est une opération incontournable pour la valorisation énergétique des boues résiduaires. La flexibilité pour ajuster la teneur en matière sèche finale de la boue est un critère important pour le choix d'une technologie. Cet objectif est difficile à atteindre pour les sécheurs à palettes. La modélisation du processus est alors essentielle. Malheureusement, le comportement rhéologique des boues est complexe et la mécanique des fluides numérique est hors de portée. La notion de Distribution des Temps de Séjour est employée ici pour caractériser l'écoulement. Un protocole fiable et reproductible a été établi et mis en œuvre sur un pilote de laboratoire. Des injections Dirac d'oxyde de titane et de sels métalliques, avec la spectrométrie de fluorescence X comme méthode de détection, ont été employées pour caractériser les DTS du solide anhydre et de la boue humide. Pré-Mélanger la boue pâteuse, pour disperser le traceur par exemple, modifie la structure du matériau. Ceci a été mis en évidence par des mesures de distribution en taille des particules et par des caractérisations rhéologiques. Cependant, des expériences de séchage en batch ont montré que ce pré-Mélange n'a aucune influence sur la cinétique et sur la phase plastique. Nous avons montré que le solide anhydre et le solide humide s'écoulent de la même manière. Une seconde méthode, basée sur une détection par conductimétrie, a alors été développée. Plus facile à mettre en œuvre et moins onéreuse, cette méthode s'avère tout aussi fiable que la première. L'influence de la durée de stockage de la boue, avant séchage, a été évaluée. Le temps de séjour de la boue dans le sécheur double quand la durée de stockage passe de 24h à 48h. Finalement, un modèle d'écoulement, basé sur la théorie de chaînes de Markov, a été développé. L'écoulement du solide anhydre est décrit par une chaîne de n cellules parfaitement mélangées, n correspondant au nombre de palettes. Les probabilités de transition entre les cellules sont régies par deux paramètres : le ratio de recyclage interne, R, et la masse de solides retenus, MS. R est déterminé par la relation de Van der Laan et MS est identifié par ajustement du modèle aux données expérimentales. Le modèle décrit de manière satisfaisante les DTS. La masse de solides retenus identifiée est toujours plus faible que la quantité mesurée expérimentalement. Une partie de la boue, collée aux parois du sécheur et au rotor, agit comme un volume mortDrying is an unavoidable operation prior to sludge valorization in incineration, pyrolysis or gasification. The flexibility to adapt the solid content of the dried sludge to the demand is a major requirement of any drying system. This objective is difficult to reach for paddle dryers. Modeling the process is thus essential. Unfortunately, sludge rheological behavior is complex and computational fluid dynamics is out of reach for the time being. The concept of Residence Time Distribution (RTD) is used here to investigate sludge flow pattern in a paddle dryer. A reliable and reproducible protocol was established and implemented on a lab-Scale continuous dryer. Pulse injections of titanium oxide and of salt metals, with X-Ray fluorescence spectroscopy as detection method, were used to characterize the RTD of anhydrous solid and wet sludge, respectively. Premixing the pasty sludge, for tracer powder dispersion for instance, changes the structure of the material. This was highlighted through the measurements of particle size distributions and characterization of rheological properties. However, drying experiments performed in batch emphasized that premixing does not have any influence on the kinetic and the sticky phase. The RTD curves of the anhydrous solid are superimposed on those of the moist sludge. Consequently, a simpler protocol, based on pulse injection of chloride sodium and offline conductivity measurements, was established. Easier to implement in industry and cheaper, this method proves to be as reliable as the first one. The influence of storage duration prior to drying was assessed. The mean residence time doubles when the storage duration changes from 24h to 48h. Finally, a model based on the theory of Markov chains has been developed to represent the RTD. The flow of anhydrous solids is described by a chain of n perfectly mixed cells, n corresponding to the number of paddles. The transition probabilities between the cells are governed by two parameters: the ratio of internal recirculation, R, and the solids hold-Up, MS. R is determined from the Van der Laan's relation and MS is identified by fitting the model to the experimental RTD. The model describes the flow pattern with a good accuracy. The computed hold-Up is lower than the experimental one. Part of the sludge is stuck to the walls of the dryer, acting as dead volumes in the process
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Peres, José Carlos Gonçalves. "Análise de um reator fotoquímico anular usando a fluidodinâmica computacional." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/3/3137/tde-15052013-184542/.
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Os processos oxidativos avançados são promissores para a degradação de compostos orgânicos resistentes aos tratamentos convencionais, como o fenol. A fluidodinâmica computacional (CFD) tornou-se uma poderosa ferramenta para analisar processos fotoquímicos por resolver os balanços acoplados de quantidade de movimento, de massa e de radiação. O objetivo deste trabalho é investigar o processo UV/H2O2 num reator fotoquímico anular usando CFD e um modelo cinético mais realista. O modelo em CFD foi criado de forma progressiva. Inicialmente, foram determinados os campos de velocidade para três vazões (30, 60 e 100 L/h). Considerou-se dois diâmetros de lâmpada para reproduzir a configuração experimental do sistema. A discretização foi feita com malhas tetraédricas variando entre 390 000 e 1 200 000 elementos. Quatro modelos de turbulência RANS foram analisados: k-e, k-w, o shear stress transport (SST) e o modelo de tensões de Reynolds (RSM). O campo de velocidades foi validado comparando a DTR com seu levantamento experimental. A próxima etapa foi incluir o mecanismo de degradação de fenol proposto por Edalatmanesh, Dhib e Mehrvar (2008) no modelo em CFD. Trata-se de um modelo cinético baseado em equações dinâmicas para todas as espécies. O campo de radiação foi calculado pelo modelo radial e pela solução da equação de transporte de radiação através do método discrete transfer. As simulações reproduziram dados experimentais abrangendo uma larga gama de concentrações iniciais de fenol, razões molares H2O2/fenol e três potências de emissão das lâmpadas. O campo de velocidades obtido era dependente da vazão: o fluido pode manter movimento helicoidal sobre toda a extensão do reator ou se desenvolver como um escoamento pistonado. O modelo k-e não reproduziu bem o escoamento por não ser adequado para escoamentos rotativos. Os outros modelos geraram curvas de DTR com bom ajuste aos dados experimentais, especialmente o modelo k-w. O desvio médio entre as simulações de degradação de fenol e os dados experimentais é inferior a 8%. Verificou-se que, devido ao escoamento rotativo, os reagentes ficavam concentrados próximos à parede externa e migravam para a região da lâmpada ao longo do reator. A elevada intensidade de radiação na superfície da lâmpada criou uma camada ao seu redor na qual a fotólise do H2O2 ocorreu com grande taxa. Os radicais OH gerados nessa camada eram transportados para a região das paredes por convecção. Isso fez com que a maior parte do fenol fosse atacada na segunda metade do reator e gerou acúmulo do radical próximo à lâmpada na seção de saída do reator, já que o poluente já fora oxidado nessa área. O método discrete transfer previu intensidades de radiação maiores que o modelo radial, e, consequentemente, maior concentração de radicais OH. Os resultados satisfatórios indicam que CFD foi uma ferramenta adequada para analisar este escoamento reativo.Advanced oxidation processes are a promising technology for degradation of organic compounds resistant to conventional treatments such as phenol. Computational fluid dynamics (CFD) has recently emerged as a powerful tool that allows a deeper understanding of photochemical processes in reactor engineering by solving the coupled momentum, mass and radiation balances. This work aimed to investigate the UV/H2O2 process in an annular photoreactor using CFD and a more realistic kinetic model. A progressive approach was used to develop the CFD reactor model. First, the velocity fields were determined for three volumetric flow rates (30, 60 and 100 L/h). Two lamp diameters were considered to reflect the experimental configuration of the system. Tetrahedral meshes varying form 390,000 to 1,200,000 elements were analyzed to achieve grid independence. For accounting turbulence effects, four RANS models were tested: k-e, k-w, the Shear Stress Transport (SST) and the Reynolds Stress models (RSM). The velocity field was validated through comparison to RTD experimental data. Next step was introducing the mechanism of phenol degradation proposed by Edalatmanesh, Dhib and Mehrvar (2008) into the CFD model. This kinetic model is based on dynamic equations for all species. The fluence rate field was calculated by the radial model and by solving the radiation transport equation with the discrete transfer method. Simulations reproduced experimental data spanning a wide range of initial phenol concentrations, H2O2/phenol molar ratios and three values for lamp power. It was found that the velocity field depends on the volumetric flow rate: either it maintains a swirling motion through the whole reactor or might develop like a plug flow. The k-e model did not represent the RTD data accurately, and the velocity field therefore, since it is not appropriate for swirling flows. The other turbulence models showed good match of RTD, especially the k-w model. Simulations of phenol degradation deviated less than 8% from experimental data. It was possible verified that, due to the swirling inlet effects, reactants got concentrated close to the outer wall and migrated on the lamp direction along the reactor path. High radiation intensities close to the lamp surface created a layer around it where photolysis of H2O2 took place with higher rates. OH radicals were generated in that layer and transported towards the outer wall by convection. This caused most of phenol to be consumed in the second half of the reactor and accumulation of the radical near the lamp and the reactor outlet, since the pollutant in this area was already oxidized. The discrete transfer method predicted higher incident radiation intensity than the radial model, and higher concentrations of OH radicals as a consequence. Satisfactory results indicated that CFD was an appropriate tool for analyzing this reactive flow.
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Harris, A. T. "Residence time distributions in circulating fluidised beds." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603761.
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The major focus of the work is on the measurement and simulation of the particle residence time distribution in the square cross section riser of a laboratory scale, cold model, circulating fluidised bed. To this end, a novel measurement technique was developed using phosphorescent tracer particles and a light based tracer injection and detection system. Experimental results confirm that the RTD is sensitive to changes in superficial gas velocity, external solids flux and the geometry of the riser exit. Simulations made using a novel stochastic particle RTD model are in good agreement with the experimental results. The measurements of the particle RTD, separately confirm the findings of a study of the riser exit using local pressure measurements, that demonstrate the influence of the riser exit on the solids flow pattern can be significant. A series of dimensionless correlations were developed to predict this influence. The effect of the exit has been shown to be dependent upon only one dimensionless group, the riser exit Froude number, FrR. A dimensionless correlation was also developed for predicting the thickness of the annular film present at the wall of CFB risers operating in the fast fluidisation regime. This correlation is superior to those published in the literature. A further series of correlations were developed to predict the size, shape, decent velocity, solids concentration and wall coverage of the particle clusters that are a characteristic feature of the gas-solid suspension in a CFB riser.
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Nakama, Caroline Satye Martins. "Modelagem estocástica da dispersão axial: aplicação em um reator tubular de polimerização." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/3/3137/tde-30062016-082711/.
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Reatores tubulares de polimerização podem apresentar um perfil de velocidade bastante distorcido. Partindo desta observação, um modelo estocástico baseado no modelo de dispersão axial foi proposto para a representação matemática da fluidodinâmica de um reator tubular para produção de poliestireno. A equação diferencial foi obtida inserindo a aleatoriedade no parâmetro de dispersão, resultando na adição de um termo estocástico ao modelo capaz de simular as oscilações observadas experimentalmente. A equação diferencial estocástica foi discretizada e resolvida pelo método Euler-Maruyama de forma satisfatória. Uma função estimadora foi desenvolvida para a obtenção do parâmetro do termo estocástico e o parâmetro do termo determinístico foi calculado pelo método dos mínimos quadrados. Uma análise de convergência foi conduzida para determinar o número de elementos da discretização e o modelo foi validado através da comparação de trajetórias e de intervalos de confiança computacionais com dados experimentais. O resultado obtido foi satisfatório, o que auxilia na compreensão do comportamento fluidodinâmico complexo do reator estudado.The velocity profile of polymerization tubular reactors may be very distorted. Based on this observation, a stochastic model based on the axial dispersion model was proposed for the mathematical representation of the fluid dynamics of a tubular reactor for polystyrene production. The differential equation was built by inserting randomness in the dipersion coefficient, which added a stochastic term to the model. This term was capable of simulating the experimentally observed fluctuations. The stochastic differential equation was discretized and solved by the Euler-Maruyama method adequately. An estimator function has been developed to calculate the parameter of the stochastic term, while the parameter of the deterministic term was estimated by a least squares method. A convergence analysis was carried out in order to determine the number of elements needed for the time discretization. The model was validated through comparisons of sample paths and computational confidence intervals with experimental data. The result was considered satisfactory, allowing a better understanding of the complex fluid dynamic behaviour of the analised reactor. Key-words: modelling, simulation, stochastic differential equation, polymerization tubular reactor, time residence distribution.
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Urmès, Caroline. "Expérimentation et modélisation dynamiques de réacteurs catalytiques : vers une meilleure description du processus catalytique." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1226/document.
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L'étude cinétique d'une réaction catalytique permet une meilleure compréhension du mécanisme réactionnel et du fonctionnement du catalyseur. Elle est nécessaire pour le dimensionnement des réacteurs et des procédés. Les modèles micro-cinétiques sont constitués d'une séquence d'étapes élémentaires sans hypothèses sur les étapes cinétiquement déterminantes. Ces modèles sont applicables sur des plages de conditions opératoires plus larges que celles des modèles plus classiques de type Langmuir-Hinshelwood (LH) ou d'Hougen-Watson. Lorsqu'ils sont implémentés dans un modèle de réacteur, ils permettent d'obtenir une plus grande précision vis-à-vis du dimensionnement du catalyseur et du réacteur. Cependant, cette approche nécessite un nombre d'expériences plus élevé pour estimer les nombreux paramètres cinétiques qui le constituent. Ce travail de thèse porte sur le développement de modèles micro-cinétiques de systèmes catalytiques en exploitant les informations obtenues lorsque le catalyseur fonctionne en régime transitoire. En effet, l'expérimentation en régime transitoire, en comparaison avec celle classiquement réalisée en régime stationnaire, permet d'accéder à plus d'informations par une meilleure sensibilisation des réactions mises en jeu. Les études cinétiques en régime permanent sont plutôt adaptées pour des modèles cinétiques globaux qui considèrent un nombre limité d'étapes cinétiquement déterminantes (en général une seule). De ce fait, la compréhension du mécanisme réactionnel [1], la connaissance du nombre de types de sites actifs mis en jeu ou encore la détermination des vitesses de réaction des étapes élémentaires restent imprécises. Afin d'accéder aux différentes vitesses de réaction des étapes élémentaires, il est nécessaire de réaliser un grand nombre d'expériences en régime permanent, ce qui est très coûteux en temps et en argent. L'expérimentation en régime transitoire est donc une alternative qui permet d'accéder à des informations cinétiques détaillées dans un délai plus rapide. Cependant, l'interprétation des expériences est plus fastidieuse puisqu'elle nécessite le développement de modèles dynamiques de réacteur. Ces études consistent à réaliser des perturbations sous forme de pulses, d'échelons ou bien d'oscillations périodiques d'un certain nombre de paramètres d'état tels que la concentration des réactifs, la pression ou encore la température. Dans ces travaux, des oscillations périodiques de concentration sont réalisées en entrée de réacteur. Ce choix permet de réaliser des variations autour de l'état stationnaire, dans des conditions proches des celles utilisées dans l'industrie. La mise en place et la validation de cette méthodologie ont été réalisées pour un système catalytique réactionnel d'intérêt industriel : l'hydrogénation sélective de l'acétylène. Cette réaction a lieu en phase gaz au contact d'un catalyseur solide et présente l'avantage de mettre en jeu peu de composés facilement analysables. Une voie importante pour la production d'éthylène est le vapocraquage. L'éthylène produit par ce procédé contient de faibles quantités d'acétylène qu'il faut éliminer car il constitue un poison pour les procédés catalytiques en aval. Cette élimination se fait par l'hydrogénation sélective de l'acétylène, en présence d'éthylène, en employant un catalyseur à base de palladium. C'est une réaction rapide dont le mécanisme réactionnel n'est pas encore complètement connu.La cinétique transitoire permet non seulement d'étudier les réactions chimiques mais également de caractériser le transport des réactifs et des produits, de l'échelle du lit catalytique à l'échelle des pores du catalyseur. Un modèle de réacteur incluant un modèle cinétique a été développé pour expliquer les données expérimentales obtenues sur un réacteur pilote. Des manipulations en régime transitoires et une modélisation dynamique de l'unité pilote incluant un modèle micro-cinétique sont réalisées [etc...]Kinetic experiments performed under stationary conditions mainly give information on the rate determining step. Numerous experiments must be done to estimate a limited number of parameters. Unsteady-state experiments, on the other hand, give more detailed information about the kinetics of the different elementary steps with a small number of experiments. In order to work under dynamic conditions, a perturbation of a process variable (concentration, pressure, temperature, etc.) is introduced at the reactor entrance (pulse, step, oscillation ...). This study explores periodic sinusoidal variations of the flow to obtain kinetics for heterogeneous catalytic processes. The kinetic information is contained in the phase lag and the gain change of the oscillations. The oscillations can be kept small and can be performed around steady-state operation, thus studying the kinetics under relevant conditions. First a model able to directly estimate the gain and phase lag has been created. Secondly, simple cases of adsorption have been performed in order to validate the model and to test the experimental set up. To finish, the approach has been applied to the selective hydrogenation of acetylene. Kinetic modeling was carried out in both stationary and dynamic conditions in order to compared the two methodologies