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1
Morillo, Sebastian. "Engineering solutions to water quality problems in lakes." University of Western Australia. Centre for Water Research, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0153.
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Lake restoration and management strategies focus on reducing the negative impacts of enriched or polluted inflows. These strategies become of paramount importance when lakes are used for recreational and/or drinking water purposes. Long term control of eutrophication and turbidity problems associated with large inflow loads is usually oriented to catchment management. Although it has been suggested that this is the correct long term approach, public concerns usually require a short term solution. In addition, due to political and economic costs related to changes in catchment management, in-lake restoration technologies have been emerging as a viable pretreatment option, complementary to water treatment plants, both reducing the operational costs of the water treatment plant and ameliorating the water residing in the lakes. This research investigates the effects of two in-lake technologies on the dynamics of inflowing rivers, where basin shape plays a significant role. The three lakes in this study suffer from eutrophication combined with a distinctive water quality problem: from turbidity in Silvan Reservoir (Australia), to heavy metal loads in Coeur d'Alene Lake (USA) and industrial wastes in Lake Como (Italy). Firstly, the influence of basin morphology, wind speed, and wind direction on the fate and transport of two rivers flowing into the L-shaped Coeur d'Alene Lake was examined, and it was shown that transport and mixing patterns in a lake can be greatly influenced by the shape of the lake, leading to important consequences for the plankton ecology in the lake. Secondly, in Silvan Reservoir we investigated the potential to modify the basin shape using vertical barriers, increasing the retention time and hence the barrier capacity to microbial pollution. A final in-lake technology was tested for Lake Como, using a downward pointing impeller to remove polluted water from the coastal margin. Lessons from these three examples indicate that there is significant potential for in-lake remediation at relatively low cost, over relatively short timescales.
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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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Munkebye, Knut-Arne Rademacher. "Residence time distribtion: Konduktivitetsmålinger på eksperimentell tubulær blandetank reaktor." Thesis, Norges Teknisk-Naturvitenskaplige Universitet, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-21119.
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Denne oppgaven har gått ut på å bygge en forsøksrigg til bruk på felleslab, ved Institutt for kjemisk prosessteknologi ved NTNU.Det skulle kjøres forsøk på oppholdstidsdistribusjoner/Residence time distributions. Alt av nødvendig utstyr er anskaffet, og satt sammen. Instrumentene er programmert il å brukes via en PC. Utstyret fungerer som det er ment å fungere, med noen justeringer. Det er gjort enkle lab forsøk, med bruk av metoden.
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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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Matthews, Samuel Aaron 1962. "High pressure biomass liquefaction in a short-residence time autoclave." Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/277800.
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The University of Arizona has developed an advanced extruder-feeder biomass liquefaction reactor system. This 11-year project successfully provided an alternative energy process for converting biomass to a crude oil, which can be hydrotreated and ultimately processed into liquid transportation fuels. In order to provide support studies for this process, a short-residence time autoclave capable of providing very brief heat-up and quenching periods in comparison to the time at reaction temperature has been designed and operated. Wood liquefaction in the presence of carbon monoxide, water, and sodium carbonate catalyst has been conducted at residence times of 1.75-60 minutes at temperatures of 340-400°C. Results indicate that the primary thermal decomposition reactions reach completion in less than 1.75 minutes. As a consequence, this research concentrated mostly on the effects of secondary reactions, and even shorter residence times are required to study the primary reactions.
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Ball, Jason. "Investigating the importance of residence time in controlling catchment hydrochemistry." Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286915.
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Dauben, Verena. "Phytoplankton induced changes of air bubble residence time in seawater." Thesis, University of Southampton, 2005. https://eprints.soton.ac.uk/41356/.
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Air bubbles in the ocean, naturally induced by breaking waves or artificially entrained by ships, remain in the water for different periods of time. Knowledge of the factors accounting for the differences in air bubble residence time (BRT) is essential for understanding processes of air sea-gas exchange as well as for the detection of underwater ship wakes in defence applications. Reasons for the differences in BRT have been found mainly with respect to physical and chemical properties of seawater, such as temperature, salinity and gas saturation level. The impact of biological factors on the behaviour of air bubbles in seawater has not previously been investigated. It is hypothesised that phytoplankton influence BRT through the production of dissolved organic material (DOM) and oxygen. Laboratory experiments were carried out in a seawater mesocosm tank system to investigate the influence of phytoplankton growth on the BRT of artificially injected air bubbles of a wide size range (10-1000 µm diameter) using both natural phytoplankton populations from Kiel Firth and phytoplankton monocultures. BRT was determined acoustically and several phytoplankton growth-related parameters (chlorophyll concentration, dissolved inorganic nutrients, dissolved organic carbon (DOC), oxygen saturation, bacteria numbers) as well as physico-chemical parameters (surface tension and viscosity) were monitored. BRT showed statistically significant covariation with oxygen saturation and chlorophyll a concentration during phytoplankton growth periods in the tank. Increases in BRT of a factor of > 2 were found during the chlorophyll maxima, provided that the water was sufficiently supersaturated with oxygen (~>110%). When the seawater was undersaturated with oxygen, BRT changed only marginally regardless of the chlorophyll a concentration. No clear relationship was evident between BRT and measurements of DOC, surface tension and viscosity. Investigations of the influence of dissolved oxygen on BRT through variation of oxygen saturation of deionised water showed that oxygen saturation alone has no apparent effect on BRT. The influence of phytoplankton on the rheological properties of an air/water interface was investigated in small scale experiments using different phytoplankton monocultures. An increase in surface shear viscosity was detected for only one of the four species of microalgae tested, Nitzschia closterium. Dependency of BRT on the combination of oxygen supersaturation and other phytoplankton growth-related parameters are discussed.
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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).
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He, Youzhang. "Residence time distributions of liquids and particulates in a holding tube." Thesis, University of Reading, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308106.
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Glasser, Mary. "Migration through time : a residence history analysis of a rural population." Thesis, University of Leicester, 2002. http://hdl.handle.net/2381/30399.
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Previous studies of human migration have tended to use information drawn either from cross-sectional snapshots at a particular time, or from data that focuses only on a small sub-section of the community. A longitudinal approach to understanding migration decision-making through time, such as a residence history analysis, permits an account of how those same individuals may behave throughout their lives with respect to more than one move. Few previous studies have examined migration variability throughout a lifetime with regard to the geographical context in which they were made or examined the same individual's migratory patterns through their lives and during historical times. The aim of this thesis is to examine lifetime migration using residence history analysis in a rural context. The sample of residence histories as drawn from two rural areas: Tynedale in Northumberland and Rutland in Leicestershire. Following a questionnaire survey of 250 households to establish broad patterns of lifetime migrations, in-depth interviews of 40 of those households were used to examine the decision-making behind those moves in more detail. The lifetime residence histories were subdivided into three different age cohorts, those under 40 (Cohort A), those aged between 40 and 59 (Cohort B) and those aged over 60 (Cohort C) at the time of interview. The moves made by individuals in these cohorts were analyzed in three broad categories; younger years (moves in teens and twenties), middle years (moves in thirties and forties) and later years (moves in fifties, sixties and seventies). Individuals in all three age cohorts behaved in a remarkably similar fashion, irrespective of the temporal or spatial context in which decisions were made. Notably, however, the youngest age cohort made more moves during their twenties than their older counterparts. The first independent moves of Cohort A were also made over greater distances. Moves in the younger years not only generated the greatest volume of migration but in the course of subsequent moves it was these moves that tended to be particularly important in creating ties to areas and yielding information about possible alternative residences.
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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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Saruchera, Thomas. "Measurement and modelling of particle residence time in a return-flow cyclone." Thesis, University of Canterbury. Chemical and Process Engineering, 1999. http://hdl.handle.net/10092/7212.
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Cyclones find wide applications in industry as drying apparatus or as chemical reactors. For these applications it is necessary to know and predict the residence time of the particles in the reactor for product quality control. In the present study the residence time of granular particles (210 μm < dp < 850 μm) was measured by the stimuli-response technique using a moving impactor method. The experimental data was analysed by the moments, Laplace transform and the least squares methods. The axially dispersed plug flow model was found to be a valid representation of flow of these particles in the cyclone. The parameters of this diffusion model were the mean particle residence time and the particle Peclet number.
A simple mathematical model based on the particle momentum equation was developed to model the flow of a single particle in the cyclone by the experimentally observed mechanism of bouncing and sliding on the walls. This is the first known bouncing particle model for modelling passage of granular particles through process equipment. The coefficient of restitution and friction for input into the model were obtained from simple bouncing tests. The model was used to predict the residence time of the particles in the cyclone. The experimental results were compared with the model-predicted results. Good agreement between model and experimental results was obtained with regard to trends of residence time with cone angle. However there was deviation with regard to particle size and density, where the model gave opposite trends compared to the experimental results.
The phenomenon of roping was studied with the aid of a high frame rate camera. The incidence of roping was found to increase with increase in cone angle. When the total included cone angle was large > 36° the solids in the rope behaved independently of the gas flow and discharged at a rate controlled by the feed into the cyclone. The discharge of a rope was found to be transient in nature.
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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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Holland, Jeff F. "Nonideal and Pulsed Flow: Applying Residence Time Distributions to Stormwater Treatment Wetlands." The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1406812534.
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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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Glover, II Leslie James. "The Influence of Residence Time and Organic Acids on the Desorption of Goethite." Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/33478.
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Trace metal concentrations in soil solution, and hence trace metal bioavailability and toxicity, are primarily controlled by sorption/desorption reactions at the mineral-water interface. While numerous studies have been conducted to understand the initial adsorption of these metals to soil minerals, less in known about long-term adsorption/ desorption processes. The objective of this study was to examine the influence of residence time and organic acids on the desorption of Pb2+and Cd2+ from goethite. Adsorption experiments were conducted at pH 6.0. Lead adsorption was nearly completed after 4 hours, with very little additional sorption during a 20-week period. In contrast cadmium showed a continuous slight increase in the amount of adsorption over the 20-week period. Desorption experiments were conducted at pH 4.5 and similar to previous studies examining trace metal desorption from oxide surfaces, the desorption kinetics for Pb2+and Cd2+ were slow compared to the sorption reaction. None of the experiments were completely reversible after an eight-hour desorption period. For all experiments except long-term Pb2+ desorption, the quantity of metal desorbed from goethite followed the order salicylate >NaNO3 > oxalate. Based on differences in cation affinity for the iron oxide surface one would expect a greater quantity of Cd2+ to be removed compared to Pb2+, for each of the extracting solutions. However at a pH of 4.5 we did not find a statistically significant trend. We observed a difference between the amount of metal removed for short and long-term experiments in five of six experiments, but these differences were only significant for Pb2+ experiments in the presence of salicylate. Two first order rate equations best fit the kinetics of trace metals desorption, with R2 values greater than 0.910 in all cases. Although our results show a decrease in rate coefficients (expect k1 for oxalate) with increased residence time, statistical analysis indicates that these results were only significant for Pb2+ experiments in the presence of salicylate. However raw and transformed data both suggest that desorption values are diverging as a function of aging time. Similar to other researchers we believe that Pb2+ and Cd2+ are sequestered by the goethite surface with an increase in residence time. These results suggest that residence time effects observed by many researchers are much less prevalent at low pH values. Therefore a reduction in soil pH created by natural anthropogenic processes may reduce the ability of soils to naturally sequester metals over time.Master of Science
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Gibson, Borbor Auzzel Kwaku Kudar. "Residence time investigation of artificial silver ores in heap leaching using cyanide lixiviant." Master's thesis, Faculty of Engineering and the Built Environment, 2020. http://hdl.handle.net/11427/32642.
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Heap Leaching has gained much relevance in the processing of low-grade mineral resources - ores considered uneconomical for beneficiation through conventional concentration and tank leaching. However, it is at the same time characterized by extended leaching periods due to slow mineral conversion and low rates of recovery as a major challenge. Interactions within the heap bed are not fully understood as chemical leaching and hydrodynamics interact in a complex manner. To study these interactions, a number of investigations have focused on the hydrodynamic interaction using conventional residence time distribution (RTD) studies in laboratory columns. In these RTD studies, the flows of tracer exiting through the effluent stream provide information of its paths, where some flows might relate to fast movement, slow convoluted channels, or micro/macro stagnated regions. This information is usually interpreted through simplified reactor models representing the bed as a combination of plug flow reactors (PFRs), continuous stirred tank reactors (CSTRs) and dead zones. Using columns as reactors to approximate heap leaching on a laboratory scale, it is anticipated that the RTD flow distribution response should be similar to the distribution of a PFR with associated dead zones. While some literature sources have alluded to the response in columns being similar to a plug flow response, recent sources using a similar hydrodynamic RTD approach reported column reactor distribution resembling flow more typical of a continuous stirred tank, CSTR, system instead of plug flow. Given that packed ore beds are not agitated, this appears paradoxical. It is hypothesised that the CSTR-like response is a result of the distribution of convoluted flow channels through the ore bed, which perform overall like a bundle of PFRs of different lengths. To discern the two patterns the use of a reactive leaching on a well characterized ore material is proposed. Therefore, this work aims to study simultaneously the flow and leach performance of a laboratory column reactor, utilizing a novel reactive leaching approach with a lixiviant amendable to a well-characterized homogeneous solid material. The objective of this work is to establish flow distribution performance in packed bed columns and correlate such performance to the ultimate extraction from the packed bed. The study was performed using a nonreactive solution tracer (potassium nitrate) to characterise flow through a column packed with an artificial silver ‘ore' (silver grains embedded in concrete), followed by a reactive leaching study using sodium cyanide which would leach the silver. The artificial silver ore was developed with the aim to exhibit four ideal properties, namely homogeneous porosity, uniform grain size, homogenous dispersion of the grains throughout the ore, and even grade distribution of the different size fractions after crushing. Leaching and micro-XCT characterization studies were performed in order to determine the leaching properties of the artificial silver ore and validate the ore corresponds to these ideal properties. This validation was indeed achieved; however, the inner-particle pores were not found to be continuous at the scale of resolution of the instrument (4.8 microns). Poor extraction from the coarse particles in both the leaching characterization and reactive column leaching investigations suggested that this network was not well established and may exist only at the sub-micron scale. Leach tests were performed on individual particle sizes in both shake flask and circulating bed reactor tests. Extraction from the leaching of the coarse synthetic silver ore particles was observed to be very low relative to dissolution from pure silver metal grains. Diagnostic shrinking core and the extended mixed topology models were used to determine the controlling dissolution mechanism. Both models demonstrated that a diffusion-reaction mechanism governed the dissolution extraction from the large particles. RTD column leaching studies were performed utilizing flow rate and PSD as investigated parameters. The nonreactive tracer produced a step-change flow response that was more similar to a characteristic plug flow type distribution but showed distinct deviations towards CSTR behavior, especially for the beds containing a higher degree of fines. Reactive column leaching experiments were performed under similar conditions as the nonreactive RTD, introducing a step-change of the cyanide reagent. Rapid silver leaching occurred initially, but equally rapidly declined to very low rates. The leach curves were interpreted by translating the information obtained from the nonreactive RTDs into a distribution of parallel plug flow channels. The extent of reaction for each of these channels is derived from the surface reaction model for the individual size classes, put together for the corresponding PSD in each experiment. RTD specific PSDs tested using this approach assumed that longer residence times correspond to the prevalence of finer material. The validity of the approach was tested by comparing the extraction determined from the particle leaching kinetics studies to the reactive column data through modelling. The model is based on the weighted average leaching from a population of particles, calibrated against kinetic models formulated for individual size classes. This model is further linked to a distribution of flow channels determined from the RTD studies. The prediction of the model did not compare too well against the raw silver dissolution data of the columns. This was attributed to the model having been calibrated against kinetic data that did not fully consider the smaller size classes below -4/+2.8 mm – considered to be the key source of rapid surface reaction in the packed bed. Although the concept proposed in this project was not fully proven, further test work is recommended to expand on the approach presented here.
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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.
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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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Mu, Yan, and Yan Mu. "Slurry Mean Residence Time Analysis and Pad-Wafer Contact Characterization in Chemical Mechanical Planarization." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/621459.
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This dissertation presents a series of studies related to the slurry mean residence time analysis and the pad-wafer contact characterization in Chemical Mechanical Planarization (CMP). The purpose of these studies is to further understand the fundamentals of CMP and to explore solutions to some of CMP's challenges. Mean residence time (MRT) is a widely used term that is mostly seen in classical chemical engineering reactor analysis. In a CMP process, the wafer-pad interface can be treated as a closed system reactor, and classical reactor theory can be applied to the slurry flow through the region. Slurry MRT represents the average time it takes for fresh incoming slurry to replace the existing slurry in the region bound between the pad and the wafer. Understanding the parameters that have an impact on MRT, and therefore removal rate, is critical to maintain tight specifications in the CMP process. In this dissertation, we proposed a novel slurry injection system (SIS) which efficiently introduced fresh slurry into the pad-wafer interface to reduce MRT. Results indicated that SIS exhibited lower slurry MRT and dispersion numbers but higher removal rates than the standard pad center slurry application by blocking the spent slurry and residual rinse water from re-entering the pad-wafer interface during polishing. Another study in this dissertation dealt with the effect of pad groove width on slurry MRT in the pad-wafer interface as well as slurry utilization efficiency (η). Three concentrically grooved pads with different groove widths were tested at different polishing pressures to experimentally determine the corresponding MRT using the residence time distribution (RTD) technique. Results showed that MRT and η increased significantly when the groove width increased from 300 to 600μm. On the other hand, when the groove width increased further to 900μm, MRT continued to increase while n remained constant. Results also indicated that MRT was reduced at a higher polishing pressure while η did not change significantly with pressure for all three pads. In the last study of this dissertation, the effect of pad surface micro-texture on removal rate during tungsten CMP was investigated. Two different conditioner discs ("Disc A" and "Disc B") were employed to generate different pad surface micro-textures during polishing. Results showed that "Disc B" generated consistently lower removal rates and coefficients of friction than "Disc A". To fundamentally elucidate the cause(s) of such differences, pad surface contact area and topography were analyzed using laser confocal microscopy. The comparison of the pad surface micro-texture analysis on pad surfaces conditioned by both discs indicated that "Disc A" generated a surface having a smaller abruptness (λ) and more solid contact area which resulted in a higher removal rate. In contrast, "Disc B" generated many large near-contact areas as a result of fractured and collapsed pore walls.
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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
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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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Wei, Xiaomin. "FUNDAMENTAL CHARACTERIZATION OF TRIBOLOGICAL, THERMAL, FLUID DYNAMIC AND WEAR ATTRIBUTES OF CONSUMABLES IN CHEMICAL MECHANICAL PLANARIZATION." Diss., The University of Arizona, 2010. http://hdl.handle.net/10150/195125.
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This dissertation presents several studies relating to fundamental characterization of CMP consumables in planarization processes. These are also evaluated with the purposes of minimizing environmental impact and reducing cost of ownership (COO).The first study is conducted to obtain the retaining ring wear rate in a typical ILD CMP process and is specifically intended to investigate the effect of retaining ring materials and slot designs during the CMP process. The results show that retaining ring materials have effect on the COF, pad temperature and retaining ring wear rate, while retaining ring slot designs affect the pad surface abruptness. The second study is performed to compare the effect of different retaining ring slot designs on the slurry film thickness within the pad-wafer interface. A novel non-intrusive optical technique, dual emission UV-enhanced fluorescence (DEUVEF), was applied to accurately measure the film thickness of the slurry underneath the wafer during polishing. It is indicated that the optimized retaining ring slot design can significantly reduce the COO of CMP processes by increasing slurry utilization.A COF method is applied to measure the slurry mean residence time (MRT) during CMP. This technique uses transient COF data induced by a shift in slurry concentration to determine MRT. Variations in consumables as well as sliding velocity, pressure and slurry flow rate can affect the slurry MRT. One study in this dissertation focus on the effect of retaining ring slot designs on the slurry MRT. Another study compares the slurry MRT under same polishing conditions using pads with different groove width. Both studies are conducted on multiple sliding velocity, pressure and slurry flow rate variations to understand the characteristics of consumable designs. The method of measuring MRT during polishing presented in this dissertation can be easily applied in general CMP processes.The subsequent studies focus in the diamond conditioner discs characterization techniques. A newly developed method for determining active diamonds and aggressive diamonds on a diamond conditioner disc under a certain vertical load is elaborated in this dissertation. Later, this technique together with scanning electron microscopy (SEM) imaging is implemented to analyze diamond pullout and fracture in CMP. Five different types of diamond conditioner discs are subjected to a novel accelerated wear test respectively to compare the extent of diamond pullout and fracture under the same conditioning condition
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Ajibode, Oluyomi Marriet. "Effect of Residence Time on Microbial and Chemical Quality of Reclaimed Water In Urban Infrastructures." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/228512.
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The goal of this study was to assess the effect of residence time on the chemical and microbial quality of reclaimed water in two distribution systems located in southern Arizona. Utility A produced Class A water and utilized chlorine as a means of disinfection whereas Utility B produced Class A+ water and utilized UV radiation as a means of disinfection. Water-based pathogens were consistently detected in both distribution systems beyond the point of compliance, while microbial indicators like Escherichia coli was only detected in Utility B suggesting that treatment eliminated waterborne pathogens. Heterotrophic plate concentrations in samples from both utilities initially increased rapidly with increased distance from the point-of-compliance and were as high as 10⁹ CFU/100ml. Regardless of the initial level of treatment, the microbial quality deteriorated with increased residence time in the distribution systems. The second study was designed to evaluate the effect of reclaimed water storage on microbial and chemical quality of two classes of reclaimed water (Class A and Class A+). In Class A water, nitrification was observed during both field scale trials resulting in concentrations greater than 10mg/L while nitrification was not observed in Class A+. Chlorine residuals rapidly decreased within 48hours of storage. HPC concentration were as high as 10⁷ - 10⁸ /100ml. In both field scale trials, there was no observed growth of HPC during storage and waterborne indicator bacteria were rarely detected, and if detected, only at low concentrations. Based on this data, deterioration of microbial water quality during storage is minimal.
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Huang, Lumeng. "Transport through Georeservoirs: Spatial Entropy in Hydraulic Properties, and Temporal Entropy in Residence Time Distributions." Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1275920344.
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Rosenthal, Daniel Jay. "The critical properties of thermally stable and unstable fluids using a low residence time flow method." Diss., Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/10223.
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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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Dokoupil, Jan. "Residence Erasmus - příprava, realizace a řízení stavby." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2013. http://www.nusl.cz/ntk/nusl-226481.
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This diploma thesis deals with the construction of a residential building The Erasmus Residence. This work includes a technical report of the issue solved, construction site installations of three phases of construction, which are groundwork, rough top construction and finishing. The work includes drawings of construction site installations for all these stages. The thesis also includes technological specification for thermal insulation systems including scaffolding construction, timing of construction, inspection and quality test plan and itemized budget.
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Kumar, Rajesh. "Non-traditional grains in low and high moisture extrusion applications –residence time, physico-chemical properties and resistant starch." Thesis, Kansas State University, 2017. http://hdl.handle.net/2097/38210.
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Master of ScienceDepartment of Grain Science and Industry
Sajid Alavi
Sorghum, millets and teff are important staple crops worldwide, especially in semi-arid regions of Africa and India because of their drought tolerance. However, lack of research and other limitations have restricted their usage in food products. This study is focused on extrusion processing of low and high tannin sorghum varieties, millet and teff for high and low moisture applications, and to investigate process characteristics such as residence time distribution and specific mechanical energy, physico-chemical properties of resultant food products (such as pre-cooked pasta and expanded snacks) and their resistance starch content. Results from preliminary lab scale extrusion, including optimization of starch type and level for pre-cooked pasta and in-barrel moisture for expanded snacks, were used to design pilot-scale studies on a twin-screw extruder. In the first pilot-scale experiment, decorticated white sorghum blends prepared with addition of mono-glycerides (0.5%, 1% and1.5%) and salt (1%) were processed at three different in-barrel moisture contents 40%, 44% and 48% (wet basis) for processing of precooked pasta. The optimum formulation containing 1% mono-glycerides and process conditions corresponding to 48% in-barrel moisture were also used to develop precooked teff and millet pasta. The non-traditional grain based pastas were investigated for cooking quality, thermal characteristics using differential scanning calorimeter, pasting properties using rapid visco analyzer and texture profile analysis. In general, increasing in-barrel moisture led to reduction in solid losses (ranging from 4.0-8.2% for all treatments), indicating improvement in cooking quality. On the other hand, increase in mono-glycerides concertation led to higher cooking losses, and also affected pasting and textural properties significantly. Sorghum-based precooked pasta was of best quality while millet pasta was poorest in cooking quality, visual and textural attributes. Cooking loss for control pre-cooked pasta produced in this experiment using semolina was 4.5%, and commercial semolina pasta was 3.2%. Residence time distribution in pilot-scale twin screw extruder, during high moisture process conditions used for pre-cooked pasta, was also investigated at three different in-barrel moistures (40%, 44% and 48%) and monoglycerides/ lipid (0.5, 1% and 1.5%) concentrations. Increase in in-barrel moisture significantly decreased mean residence time. For example, mean residence time was 4.47 min at 40% moisture, 3.89 min at 44% and 3.74 min at 48%. On the contrary, residence time significantly increased with lipid level. For example, mean residence time was 3.87 min at 0.5% concentration of mono-glycerides, 4.48 min at 1% and 4.70 min 1.5%. In the second experiment focusing on low moisture applications, pilot-scale twin screw extrusion was used to process decorticated white sorghum and high tannin sumac sorghum for expanded snacks. The addition of sumac bran decreased the specific mechanical energy input (366-578 kJ/kg) and expansion ratio (6.4-7.9), and resulted in higher piece density of extrudates. Use of sumac bran and sumac flour led to increase in resistant starch content, although it was less than 1% for all treatments. Therefore, extrusion with ingredients having high tannin content does not provide value, despite tannins being associated with resistant starch at least in raw materials.
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Haile, Estifanos. "CHEMICAL EVOLUTION AND RESIDENCE TIME OF GROUNDWATER IN THE WILCOX AQUIFER OF THE NORTHERN GULF COASTAL PLAIN." UKnowledge, 2011. http://uknowledge.uky.edu/ees_etds/2.
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This study aims to integrate groundwater geochemistry and mathematical modeling to determine the dominant geochemical processes and groundwater residence time within the Wilcox aquifer in the northern Gulf Coastal Plain. Groundwater samples were collected and analyzed for major ion chemistry, stable isotopes (18O, 2H, and 13C), and radioisotope 36Cl content. Geochemical modeling enabled the identification of major sources and sinks of solutes in the aquifer. A two-dimensional, finite-difference, numerical model was used to determine the deep groundwater flow rate and transport of 36Cl in the aquifer. Major ion chemistry shows a chromatographic pattern along the flow path in which a gradual increase of Na+ and decrease of Ca2+ and Mg2+ is evident. The most plausible inverse models in the downgradient section of the aquifer indicate that oxidation of organic matter (OM), which may be associated with discontinuous lenses of lignite, and consequent release of CO2 sustain the reduction of Fe(III) (oxyhydr)oxides and sulfate and the dissolution of carbonate minerals (calcite and, in some instances, siderite). These processes, in turn, result in pyrite precipitation and exchange of Ca2+ for Na+ on clay-mineral surfaces. Models constrained with 13C are consistent with mole transfers between pairs of wells in close proximity, but not for the entire flow path. The observed range of δ13C of dissolved inorganic carbon (-7.3‰ to -12.4‰) is interpreted as a result of both oxidation of OM and dissolution of carbonates. Calculated values of 36Cl/Cl show an abrupt discontinuity between the upgradient and downgradient sections that was also observed in δ18O and δ2H data. The gradual enrichment of 18O and 2H along the flow path could be the result of diffusion. The distinct differences in δ18O and δ2H between the upgradient and downgradient Wilcox aquifer suggest that the latter preserves a paleoclimatic signal.
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Zhao, Xiaofei. "Harvesting Microalgae-Development of a Short Residence Time Method Using Rapid-response Temperature-sensitive Semi-IPN Hydrogels." University of Toledo / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1434501731.
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Sonnenwald, Frederick C. "Identifying the residence time distributions of urban drainage structures from solute transport data using maximum entropy deconvolution." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/5468/.
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Solute transport, the processes of water carrying particles through flow, is affected by the bulk mixing that the flow experiences. Improved understanding of solute transport can therefore lead to improved understanding of bulk mixing processes. The Residence Time Distribution (RTD) is a non-parametric model that more fully describes solute transport than traditional models, and therefore can provide additional insight into the underlying mixing processes. As a predictive model, a downstream concentration profile can be expressed as the convolution of an upstream concentration profile with an RTD. Maximum entropy deconvolution is an optimisation method that can be used to reverse the convolution process and obtain an RTD from paired experimental upstream/downstream concentration profiles. This thesis focuses on the application of maximum entropy deconvolution to solute transport. As maximum entropy deconvolution is a relatively new method as applied to solute transport data, it has been tested thoroughly. An initial investigation of the effects of outlet angle on short-circuiting (as a mixing process) in surcharged manholes was undertaken to guide further work on maximum entropy deconvolution. Maximum entropy deconvolution was found to make repeated comparisons between recorded and predicted data through a constraint function. A study evaluating 12 potential correlation measures was undertaken, finding 8 measures potentially suitable for inclusion in maximum entropy deconvolution as a constraint function. 3 correlation measures were found to be additionally suitable for independent model evaluation. Several other configuration settings to maximum entropy deconvolution (number and distribution of sample points, and number of iterations) were also found to impact on the deconvolved RTD. These were examined with different types of input data (e.g. storage tank vs manhole) in order to determine a robust combination of settings for all data types. Two novel extensions to maximum entropy deconvolution are proposed and examined. The first novel extension involves changing interpolation function and number of sample points to give a smoother RTD. The smoother shape is more realistic and allows for easier interpretation of the RTD. The use of alternative interpolation functions also reduces the impact of over-sampling. The second novel extension is the deconvolution of raw data, i.e. data without pre-processing, reducing potential sources for error and making deconvolution easier to apply. Synthetic raw data was examined to produce guidelines for raw data quality. When the quality limits are exceeded, some minimal pre-processing then becomes necessary. A large data set, covering both benched and unbenched manholes with 0°, 30°, 60°, and 90° outlet angles at a range of surcharge depths and flow rates, has been re-analysed (as raw data) with deconvolution. The data was previously analysed with Advection Dispersion Equation and Aggregated Dead Zone models. 6 characteristic RTD shapes were observed, from which different flow fields have been inferred. Deconvolved RTDs are shown to provide new insight into mixing processes occurring.
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Séguin, Marc-André. "Fuel Residence Times for Clean Combustion of Coal in a Pressurized Fluidized Bed - Cold Flow Study." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36244.
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Anthropogenic Climate Change is amongst the greatest challenges of human civilization. A key area that will play a large role in mitigating its effects are clean fossil fuel applications. Clean coal combustion is one such application with an urgent timeline. This can be achieved with an oxygen-fired pressurized fluidized bed combustor with downstream carbon capture and sequestration. In relation to pressurized fluidization processes, understanding the influence of pressure on bed hydrodynamics and in turn their effect on parameters including fuel residence time is essential. For the proposed combustor, the heat exchanger boiler tubes are submerged in the fluidized bed such that the effect of a horizontal tube bank on the fuel residence time is also of great importance. The main focus of present work was to evaluate the impact of gas velocity, pressure, presence of a tube bank and fuel feed rate on the average fuel residence time. Experiments were conducted under cold flow conditions in a pilot-scale pressurized fluidized bed with an inner diameter of 0.15 m. The fluidization material was relatively large glass beads (1.0 mm in diameter) while the fuel particles were simulated with smaller glass beads (40 to 138 μm in diameter), susceptible to entrainment. Operating pressures and superficial gas velocities tested were between 101.3 and 1200 kPa and 0.4 and 1.1 m/s respectively. To simulate coal combustors, experiments were then conducted in a continuous mode where the fuel particles were continuously fed to the fluidized bed of large particles over a desired period of time. Downstream, entrained particles were continuously captured to determine the entrainment rate and mass of fuel particles inside the fluidized bed at steady state, which yielded the average fuel residence time. The combination of elevated pressure with the tube bank present was found to enhance gas bubble break up and reduce the average gas bubble size. In turn, this increased the average fuel residence time of 83 μm particles by nearly 3 fold to a value of 77 s in comparison to 27 s at atmospheric pressure. The effect of gas velocity was not found to be statistically significant under the range tested. Similarly the effect of increased fuel feed rate by 50% neither had a statistically significant impact.
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Mendes, Ana Lúcia Mesquita. "Fito-ETAR uma tecnologia aplicada ao tratamento de águas residuais: análise do comportamento hidráulico." Master's thesis, ISA, 2010. http://hdl.handle.net/10400.5/3352.
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Mestrado em Engenharia do Ambiente - Instituto Superior de AgronomiaIt became increasingly necessary to promote the use of low-cost technologies (in the construction and maintenance) on the implementation of sanitation in small agglomerations, yet never failing to ensure appropriate treatment efficiencies. The construction of constructed wetlands, in these rural areas allows the reproducing of mechanisms of degradation of pollutants that occur in natural wetlands, in a system for waste water purification. The process consists of passing the wastewater through a medium (usually after being pre-sedimented), where, roots of macrophytes and microbial communities that degrade organic matter in wastewater assimilating the nutrients existing in it, grow. The study of the hydraulic behavior of these alternative systems of sanitation was based on the analysis of constructed wetland of Barroca D'Alva in Alcochete with a subsurface horizontal flow. The performance evaluation and effectiveness of the tracer (potassium bromide) introduced, the measurement of water level inside the bed and the analysis of the hydrographs of the flow, allowed a study of the hydraulic behavior and also the development of a simplified one-dimensional model applied to the transport that occurs within the bed, which allows to model the detention times of a non reactive solute.
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McClintock, Samuel Alan. "Effects of temperature and mean cell residence time on the performance of high-rate biological nutrient removal processes." Diss., This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-08252008-162825/.
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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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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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Bremm, Alessandra Baldissarelli. "Habitar a escola : minúcias de encontros entre arte e educação." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2017. http://hdl.handle.net/10183/170335.
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A pesquisa parte de inquietações docentes cotidianas de uma professora de Arte de escola básica da rede pública, que, ao relacionar seus processos artísticos com questões da docência e com os estudos dos conceitos de ―vida como obra de arte‖ (NIETZSCHE, 2012) e ―estética da existência‖ (FOUCAULT, 2004a), percebe a arte como um modo de pesquisar em educação. Com a realização de uma residência artística em uma escola básica da rede pública de Porto Alegre – RS, buscou-se produzir outros tempos e espaços para problematizar as emergências dos encontros entre arte e escola, a partir da seguinte problematica: De que modos uma residência artística pode vir a problematizar os tempos e os espaços da escola, a partir dos encontros entre arte e educação?. As experiências da residência artística na escola permitiram tensionar, de modo artístico, questões relacionadas ao cotidiano escolar, à docência e seus desafios no mundo contemporâneo. A arte permeou a pesquisa, em sentido expandido, a partir dos referenciais teóricos, como postura diante da vida, bem como, através de produções artísticas desenvolvidas na residência e de trabalhos de artistas que contribuem para pensar as questões emergentes neste trabalho. Os encontros entre arte e escola fizeram emergir questões relacionadas às minúcias da escola, entendidas, aqui, como potências para pensá-la nas seguintes linhas de força: a escola como espaço de alteridade, no(s) outro(s) como estrangeiro(s) e os tempos e os espaços escolares em relação aos tempos da arte Os modos de fazer pesquisa na escola são relacionados com noções de residência artística, bem como, das pesquisas educacionais baseadas em arte (PEBA), no intuito de salientar a especificidade de uma pesquisa de cunho artístico realizada no campo educativo. Também buscou-se operar na potência dos entremeios, produzindo fissuras entre as fronteiras que delimitam o que é considerado arte e o que é considerado educação. A escola foi pensada como potência de criação em sua multiplicidade de práticas, sem o intuito de realizar diagnósticos ou prescrições. O caráter de troca permeou todas as ações da residência, em que o próprio lugar da pesquisadora&professora&artista esteve em constante movimento na escola, possibilitando afirmar a potência dos espaços ―entre‖ para além de delimitações. No entrecruzamento entre as experiências vividas na residência artística e a escola, afirma-se a potência da arte como um outro tempo e espaço para pensar as relações entre escola, arte e educação no mundo contemporâneo.The research is based on daily teaching concerns of an art teacher from a public elementary school who, by relating her artistic processes to teaching issues and to the studies of the concepts of "life as a work of art" (NIETZSCHE, 2012) and "aesthetics of existence" (FOUCAULT, 2004a), perceives art as a way of researching in education. With the development of an artistic residence in a elemetary public school of Porto Alegre - RS, the aim was to try to produce other times and spaces to problematize the emergencies of the encounters between art and school, from the following problematic: In what ways a residence can problematize the times and spaces of the school, from the encounters between art and education?. The experiences of the artistic residence in the school allowed problematize, in an artistic way, questions related to the school routine, teaching and its challenges in the contemporary world. The art permeated the research, in an expanded sense, from the theoretical references, as an attitude to life, as well, through artistic productions developed in the residence and works of artists that contribute to think the emerging issues in this work. The encounters between art and school have raised questions related to the minutiae of the school, understood here as powers to think of it in the following lines of force: the school as a space of alterity, in the other(s) as foreign(s) and the times and the school spaces in relation to the times of art The ways of doing research in the school are related to notions of artistic residency, as well as of art-based educational research, in order to emphasize the specificity of an artistic research carried out in the educational field. At the same time, we tried to operate on the power of the interstices, producing fissures between the boundaries that delimit what is considered art and what is considered education. The school was conceived as a creative power in its multiplicity of practices, without the intention of performing diagnoses or prescriptions. The character of exchange permeated all the actions of the residence, in which the researcher & teacher & artist's place was in constant movement in the school, making it possible to affirm the potency of spaces "between" beyond delimitations. In the intersection between the experiences lived in the artistic residence and the school, the power of art is affirmed as another time and space to think the relations between school, art and education in the contemporary world.
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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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Wan, Shaolong. "Characterization of early stage coal oxidation and effects of gas residence time on NO(x) reduction in oxy-coal combustion /." Full text available from ProQuest UM Digital Dissertations, 2009. http://0-proquest.umi.com.umiss.lib.olemiss.edu/pqdweb?index=0&did=1839607861&SrchMode=1&sid=5&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1268676055&clientId=22256.
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Thesis (Ph.D.)--University of Mississippi, 2009.Typescript. Vita. "May 2009." Major professor: Dr. Wei-Yin Chen Includes bibliographical references (leaves 121-132). Also available online via ProQuest to authorized users.
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Lin, Joyce T. Camassa Roberto. "An experimental and mathematical study on the prolonged residence time of a sphere falling through stratified fluids at low Reynolds number." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2009. http://dc.lib.unc.edu/u?/etd,2488.
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Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2009.Title from electronic title page (viewed Oct. 5, 2009). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Mathematics." Discipline: Mathematics; Department/School: Mathematics.
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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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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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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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Pacheco, Ruiz Santiago. "Submerged anaerobic membrane bioreactor for wastewater treatment : effect of mean cell residence time on membrane flux, mixed liquor characteristics and overall reactor performance." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/403002/.
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Mean cell residence time (MCRT) is a major operational parameter in all biological treatment systems because of its relationship to growth rate and thus to metabolic activity. Due to their mode of operation, submerged anaerobic membrane bioreactors (SAnMBR) offer a homogenous system in which MCRT can be simply controlled through volumetric wastage. Although a number of studies using SAnMBR have been reported, however, little information is available regarding the effect of MCRT on operational performance, mixed liquor characteristics and the influence of these on membrane performance. In this research an innovative SAnMBR using gravity-induced transmembrane pressure to maintain flux was developed and tested for first time. This configuration was then used to evaluate the impact of MCRT on membrane flux, mixed liquor characteristics and overall performance of SAnMBR treating low-to-intermediate strength wastewater. Long-term experimental periods of more than 240 days allowed steady-state conditions under different MCRTs, in which the mixed liquor suspended solids (MLSS) adjusted to the applied load, making possible to assess the influence of this growth and metabolism-dependent kinetic parameter. The SAnMBRs were monitored for membrane flux, overall process efficiency and mixed liquor characteristics when operating at 36 oC and 20 oC. The results of this work showed that at both operational temperatures, the MCRT has a significant effect on the mixed liquor characteristics, particularly on the filterability which was higher at short MCRTs. This resulted in improved membrane flux at relatively short MCRT, although no advantages were observed if the MCRT was further reduced. Higher specific methane production was observed at longer MCRT, most probably due to a higher fraction of carbon incorporated into biomass as a result of higher microbial growth rates. Overall, the results of this research showed that the MCRT has a considerable effect on the mixed liquor characteristics and thus on the membrane fouling and overall reactor performance. It is clear that there is a trade-off to be made between enhanced membrane performance, specific methane production and sludge yield when considering the most suitable operational MCRT. Further studies are required to identify the optimum MCRT for a wider range of wastewater and other operational parameters and to fully understand the causes of these effects.
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Zhou, Tiya. "Residence time and survival studies for Enterococcus faecium as a surrogate for Salmonella during preconditioning and extrusion processing of dry expanded pet food." Thesis, Kansas State University, 2016. http://hdl.handle.net/2097/32905.
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Master of ScienceFood Science
Sajid Alavi
Validation studies on process equipment are an important step for effective pathogenic control during dry expanded pet food manufacturing. The preconditioner is used to hydrate, mix and pre-cook raw materials before extrusion of pet food. The High-Intensity-Preconditioner (HIP) was designed with two independently driven shafts, thus offering control of both shaft speed and rotational direction with potential for improving residence time and thus pathogen inactivation. Residence time distribution (RTD) of raw dog food mix was impacted by the HIP process parameters (average residence time varying between 104-178 s for dry experiment and 65-177 s with steam addition) depending on shaft speed and direction. In general, increase in shaft speed resulted in shorter residence time with the larger shaft having a greater impact than the smaller shaft. Rotational direction of shafts also had an effect on average residence time (a maximum difference of 37 s was noticed between treatments with different shaft directions and the same speed). The uniformity of residence time distribution (difference of 97-132 s between 15 and 85 percentiles of the cumulative RTD) also varied considerably with process conditions, with uniformity increasing with shaft speed. Enterococcus faecium (ATCC® 8459™) was chosen as a surrogate for Salmonella for microbial inactivation studies on the HIP. Both HIP shaft speed (200 and 300 rpm) and process temperature (67-70°C and 89-91°C) impacted E.faecium survival. Lower shaft speed (corresponding to longer residence time) or higher temperature led to greater E.faecium inactivation. A 5 log CFU/g of E.faecium was reduced using selective agar (m-Enterococcus or mE agar) after treatment with high temperature, but approximately 3.5 log CFU/g of E.faecium reduced on non-selective agar (Brain Heart Infusion or BHI agar). Uneven heat distribution, inadequate residence time and system instability might have negatively affected the inactivation. Microbial inactivation, with E.faecium as surrogate, was also studied for the complete dry expanded pet food process using a pilot-scale single-screw extruder with a regular double shaft preconditioner. Meal was inoculated with E.faecium at 6 log CFU/g and processed. Preconditioner downspout temperature ranged from 89-94°C and extrusion die temperature was between 120-140°C. Complete inactivation was observed after extrusion.