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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Investigation of the Turbulent Flow and Heat Transfer around a Heated Cube Cooled by Multiple Impinging jets in a Cross-Flow

Johansson, Robert January 2016 (has links)
The fast development in electronics has resulted in faster and faster computers. Furthermore, the electronic components trend to get smaller and smaller by the year. With more processing power combined with smaller components the heat generation rapidly increases. The scope of this study is to examine a spot cooling technique consisting with different geometry of multiple impinging jets in combination with a cross-flow by the use of CFD. The case is limited to a heated wall mounted cube cooled by a impinging jet as well as an multiple impinging jets in a low velocity cross-flow. This study can be divided into two parts a verification study and a detailed study. The verification study consist of comparison between RSM model and measured values for both the turbulent flow and the surface temperature. The single impinging mesh consists of 934 k elements while the plus 1439 k and cross consists of 2809 k elements. All the meshes are created in ANSYS fluent and this paper contains a detailed guide to create them. The verification study proved that RSM can predict the complicated flow with good agreement with the single impinging jet. The heat transfer coefficient differ substantially between the cases. The PIV compared to the UDF for the inlet velocity profiles had a 21\% increase in heat transfer coefficient in the top layer of the cube. In all the simulations the cross had at least an increase of 18\% on average \(h\). While there was no real verification study for the multiple impinging jets I would still argue that cross is better than the plus sign geometry in terms of heat transfer.
2

Application of Sequential Microwave/Aeration Process for the Removal of Ammonia from Landfill Leachate

Dong, Sainan January 2015 (has links)
Application of microwave (MW) radiation followed by aeration (A) for the purpose of ammonia removal from both synthetic solutions and landfill leachate was investigated in this study. Four sets of experiments: water bath (WB), microwave (MW), sequential microwave/aeration process (MW+A), and sequential water bath/aeration process (WB+A) were conducted using synthetic solution. MW and MW+A tests were applied on the landfill leachate as well. For each test, either 100 mL of synthetic solution or landfill leachate was used. All the tests were conducted with three replicates in batch scale. For both economic and safety concerns, the samples’ temperature were maintained below the boiling point. One-way ANOVA tests and T-tests were conducted to analyze the differences of ammonia removal efficiencies among different methods. Both thermal and non-thermal effects for the sequential microwave/aeration process were investigated. Factorial design and response surface methodology (RSM) were applied to evaluate and optimize the effects of pH, MW energy level and microwave power output. Results confirmed that the sequential microwave/aeration process was an effective approach for removal of ammonia from aqueous systems. Maximum ammonia removal of 81.7 % for synthetic solution and 70% for landfill leachate was achieved by applying 7.8 KJ MW energy output/L sample and 10 minutes aeration. When apply the sequential microwave/aeration process to synthetic solution, at optimum condition of pH 10.5, 7.8 KJ MW energy output/L sample and 10 minutes aeration time, the contribution of thermal process was 39%, while 61% for non-thermal processes (33% for aeration and 28% for EMF). Statistical analysis of synthetic solution tests data using RSM showed that ammonia removal efficiency strongly depended on pH and MW energy output. R square of 0.941 indicates that observed results fitted well with the model prediction. Optimum pH and MW energy output level for ammonia removal was 11 and 7.8 KJ MW energy output/L sample respectively, and under this condition, maximum ammonia removal efficiency predicted for synthetic solution was 76.3%.
3

Contribution à l'étude du procédé de dégradation des colorants synthétiques par les méthodes d'oxydation chimique et d'oxydation avancée UV/H2O2

Olya, Mohammad Ebrahim 19 February 2009 (has links)
Cette étude a porté sur la dégradation des colorants synthétiques par les méthodes d’oxydation chimique en utilisant le permanganate de potassium et d’oxydation avancée UV/H2O2. Les résultats obtenus montrent que la décoloration des colorants étudiés est très rapide par l’effet oxydant du permanganate de potassium dans les conditions opérationnelles optimales mais la minéralisation des colorants est incomplète. L’étude de procédé de minéralisation des colorants dans les réacteurs photochimique annulaires par UV/H2O2 montre que ce procédé est très efficace pour dégrader ces colorants. Dans ce procédé, le choix des conditions opératoires et la configuration des réacteurs sont importants. L’étude d’un procédé hybride d’oxydation chimique par KMnO4 et d’oxydation avancée UV/H2O2 a montré une efficacité accrue par rapport au procédé UV/H2O2 seul. L’estimation de la consommation d’énergie électrique pour le taux de minéralisation équivalent, présente une diminution considérable du coût de procédé. La méthodologie de surface de réponse (RSM) a été utilisée afin d’optimiser et modéliser les procédés. / This work is about the degradation of some synthetic dyes by the chemical oxidation method using KMnO4 and UV/H2O2 advanced oxidation process. Decolourisation of the dyes by potassium permanganate under optimal condition is very rapid but a complete dye mineralization is not obtained. The results show that despite of its high cost; UV/H2O2 is an effective method to achieve the dyes mineralization. So, an appropriate combination of these two methods could granite high amount of mineralization with a reasonable cost. The operational conditions and hydrodynamic behaviour of the reactors are very important to optimise the process. Efficiency study of the combined method KMnO4/UV/H2O2, as well as the economic calculations show, this process can be used to increase the rate of dyes degradation and reduce notably the cost of electrical energy consumed for the process. Response surface methodology (RSM) was used as a modelling and optimizing method.
4

Tracking Sediment Bypassing, Geomorphological Analysis, and Regional Sediment Management at Tidal Inlets

Beck, Tanya M. 01 July 2019 (has links)
Tidal inlets on sandy shorelines separate barrier islands and serve as a conduit for transport of sand and water between embayments and oceans, seas, or other tidally influenced waterbodies. Tides and waves induce currents along the coastline that transport sediment across-shore and alongshore. Coastal managers must optimize barrier-inlet system stability while conserving limited sediment resources, and often base management decisions and engineering design upon geomorphic and numerical models that predict the morphological behavior of tidal inlets on short-to-medium timescales (years to decades). The overall goal of this study was threefold. First, to provide science-based practical guidance for regional sediment management in the vicinity of tidal inlets. Secondly, to enhance the understanding of the temporal and spatial scales of sediment pathways in these regions through numerical simulation of traced sediment transport. And, third, to combine these lessons learned in both regional sediment management and analysis of morphodynamic and sediment bypassing pathways with application to a common practical management practice of inlet shoal mining and adjacent beach placement. The temporal and spatial scales controlling the morphodynamics of barrier-inlet systems were reviewed within a regional sediment management context. Next, the application of regional sediment management methods to case studies of multiple barrier-inlet systems in West-Central Florida led to the development of a decision-support tool for regional sediment management (RSM) as applied to barrier-inlet systems. Connecting multiple barrier islands and inlets at appropriate spatio-temporal scales is critical in developing an appropriately scoped sediment management plan for a barrier-inlet system. Evaluating sediment bypassing capacity and overall inlet morphodynamics can better inform regional sand sharing along barrier-inlet coastlines; particularly where sediment resources are scarce and a close coupling between inlet dredging and beach placement is vital to long-term sustainable management. Continued sea-level rise and anthropogenic activities may intensify the need for investigating longer-term processes and expanding regional planning at a centennial timescale, and are acknowledged as challenging tasks for RSM studies going forward. A regionally focused, multi-inlet study was necessary to improve the management plans for the case study inlets (from north to south): John’s Pass, Blind Pass, Pass-a-Grille Inlet, and Bunces Pass. Key recommendations based on the case studies include: 1) allow the natural sediment bypassing to be re-established at Blind Pass inlet through reduced ebb-tidal delta mining, 2) reduce the interruption to sediment bypassing at John’s Pass and Pass-a-Grille inlets through an improved design of the dredged mining areas located along sediment bypassing pathways, 3) allow for continued natural sediment bypassing at Bunces Pass, and, 4) incorporate the cyclic sediment bypassing through swash-bar attachment into the management plan at Bunces Pass and adjacent barrier-islands. Similar systems in other regions may benefit from the lessons derived in this case study of an adaptively managed multi-inlet system. A numerical model that computes hydrodynamics, sediment transport, and morphodynamics including bed layering was incorporated in this study to analyze sediment transport pathways between littoral sources from adjacent beaches and the geomorphic features of an idealized tidal inlet designed to imitate the John’s Pass tidal inlet in West-central Florida, USA. This study developed a methodology to numerically trace sediment transport, deposition and erosion. This method was applied to investigate sediment-bypassing pathways under varying temporal and spatial scales. The analyses of the adjacent beach’s contribution to tidal inlet sediment bypassing demonstrated variable temporal scales on sediment transport and exchange. High-energy wave events dominated the temporal scale for sand to be transported from the updrift beach to the ebb-tidal delta, whereas cyclical tidal processes had a significant influence on the spatial pattern of exchange between the shoals and channel features of the tidal inlet. The ability to simulate burial and erosion of tracers allowed identification of offshore sedimentation hotspots such as terminal lobe as well as zones of deposition and active transport in shallow water, such as the updrift channel margin linear bar and the downdrift platform of the ebb-tidal delta. The general sediment-bypassing pathway reflected a tidal-driven redistribution following event-driven pulses of wave-induced sediment mobilization. Sediment was transported along the beach during these energetic wave events. Flood- and ebb-tidal currents transported the sediment mobilized by high waves into the inlet channels. This was followed by subsequent gradual redistribution of the deposited channel sediments over the ebb-tidal delta features during fair-weather conditions. The modeling methods were then applied to investigate the sediment pathways and bypassing processes for three validated numerical models of coastal tidal inlets that span a range of forcing conditions. The processes that influence sediment transport along various pathways between the several morphological features of each inlet and its adjacent beaches were examined. The sediment tracing methodology employed in this study allowed for an evaluation of the sediment transport pathways between the various morphologic features of a tidal inlet, as well as their respective processes that drive the exchange of sediments. Characterizing and correlating the sediment pathways between tidal inlet morphologic features can improve the inlet reservoir model, which is a predictive model of inlet shoal volumes based on empirical formulae. The results of this study illustrate the value of including sediment-tracking techniques in simulating sediment bypassing and the potential of this application to inform coastal engineering and design modifications to sediment reservoirs of tidal inlets. And, finally, the spatial patterns of transport and erosion and deposition of traced, littoral source sediment, were investigated using the same modeling framework to evaluate the design of ebb-tidal delta mining on sediment bypassing dynamics of a tidal inlet system based on an idealized model of John’s Pass, Florida. Seven mining areas were simulated with traced sediment sources from the updrift beach, downdrift beach, and adjacent shoals. The tracers’ migration pattern and mining area infilling were analyzed to depict the sediment bypassing pathways and their contributions to mining area infilling. Mining area recovery rates were highest along the channel margin linear bar, and decrease offshore and downdrift. Updrift sand sources contributed more to mining area infilling than downdrift sand sources. The position of the mining area in relation to the updrift or downdrift morphological features dictates whether it will receive primarily updrift- or downdrift-originating littoral sediment from the beach. The source of sedimentation within the mining areas is a combination of inlet-ward transport of beach sediment and nearby shoal sediment. Proximity to the inlet channel determined the degree to which sedimentation had originated from longshore transported beach sediment. This methodology can improve confidence in management decisions concerned with the sand-sharing capacity of barrier-inlet systems in a local and regional context.
5

Developed Hybrid Model for Propylene Polymerisation at Optimum Reaction Conditions

Khan, M.J.H., Hussain, M.A., Mujtaba, Iqbal M. 28 January 2016 (has links)
Yes / A statistical model combined with CFD (computational fluid dynamic) method was used to explain the detailed phenomena of the process parameters, and a series of experiments were carried out for propylene polymerisation by varying the feed gas composition, reaction initiation temperature, and system pressure, in a fluidised bed catalytic reactor. The propylene polymerisation rate per pass was considered the response to the analysis. Response surface methodology (RSM), with a full factorial central composite experimental design, was applied to develop the model. In this study, analysis of variance (ANOVA) indicated an acceptable value for the coefficient of determination and a suitable estimation of a second-order regression model. For better justification, results were also described through a three-dimensional (3D) response surface and a related two-dimensional (2D) contour plot. These 3D and 2D response analyses provided significant and easy to understand findings on the effect of all the considered process variables on expected findings. To diagnose the model adequacy, the mathematical relationship between the process variables and the extent of polymer conversion was established through the combination of CFD with statistical tools. All the tests showed that the model is an excellent fit with the experimental validation. The maximum extent of polymer conversion per pass was 5.98% at the set time period and with consistent catalyst and co-catalyst feed rates. The optimum conditions for maximum polymerisation was found at reaction temperature (RT) 75 °C, system pressure (SP) 25 bar, and 75% monomer concentration (MC). The hydrogen percentage was kept fixed at all times. The coefficient of correlation for reaction temperature, system pressure, and monomer concentration ratio, was found to be 0.932. Thus, the experimental results and model predicted values were a reliable fit at optimum process conditions. Detailed and adaptable CFD results were capable of giving a clear idea of the bed dynamics at optimum process conditions.
6

Lois de paroi adaptatives pour un modèle de fermeture du second ordre dans un contexte industriel / Adaptive wall treatment for a second order turbulence model in an industrial context

Wald, Jean François 29 June 2016 (has links)
Les calculs de CFD industriels pour les écoulements turbulents commencent par une phase complexe de réalisation de maillage (calculs de fond de cuve, de plénum supérieur ou d’assemblages combustibles par exemple dans le domaine nucléaire). Les premières contraintes prises en compte sont le plus souvent géométriques (complexité, détail, intuition ou retour d'expérience concernant les endroits « importants » où le maillage doit être raffiné). On doit cependant respecter des contraintes inhérentes aux modèles de turbulence RANS (Reynolds Averaged Navier Stokes) utilisés notamment la taille de la première cellule de calcul à la paroi. Si on utilise un modèle dit « Haut-Reynolds » (k- ε standard, SSG, …), on ne devrait trouver que des cellules de paroi ayant un centre à une distance adimensionnelle au moins égale à 20 pour pouvoir d’une part justifier l'utilisation de la loi « universelle » logarithmique pour la vitesse et d’autre part, ce qui souvent occulté, respecter le fait que ces modèles ne sont pas conçus pour des distances plus basses. En revanche, si on utilise un modèle dit « Bas-Reynolds » (BL-v²/k, EB-RSM, …), on devrait partout avoir des cellules de paroi ayant un centre à une distance adimensionnelle de la paroi très faible. Si ces modèles sont utilisés avec une partie des cellules en paroi ayant une distance adimensionnelle nettement supérieure, les résultats peuvent être catastrophiques (le calcul peut ou bien diverger ou bien donner des résultats avec une physique totalement fausse). Cette thèse propose le développement d'un nouveau modèle de turbulence avec lois de paroi adaptatives qui donne des résultats satisfaisants quelque soit le type de maillage utilisé, en particulier quand ce dernier contient à la fois des cellules dont le centre est à une distance « Bas-Reynolds » et « Haut-Reynolds ». Étant donné les écoulements complexes des configurations industrielles, ce nouveau modèle s'appuie sur l'utilisation d'un modèle du second ordre connu pour son bon comportement : le modèle EB-RSM. Ce modèle permet de reproduire l'anisotropie de la turbulence et comble certaines lacunes des modèles du premier ordre. Ce modèle est disponible dans Code_Saturne, code open source développé par EDF et au sein duquel les développements ont été réalisés. / CFD computations of turbulent flows always begin with a complex meshing process (upper plenum, fuel assembly in the nuclear industry for example). Geometrical constraints are the first ones to be satisfied (level of details, important zones to refine regarding “user experiences”). One has however to satisfy constraints that are inherent to the RANS model (Reynolds Averaged Navier Stokes) used for the computation. For example, if a « High-Reynolds » (k-ε standard, SSG, …) model is used one should only have wall cells with a dimensionless distance to the wall greater or equal to 20 to justify the use of the universal “law of the wall”. On the other hand, if a « Low-Reynolds » (BL-v²/k, EB-RSM, …) model is used, one should only find wall cells with a dimensionless distance to the wall below 1. If those models are used in an inappropriate way the results could be dramatic (computations can either diverge or give unphysical results). This thesis proposes the development of a new turbulence model with adaptive wall treatments that gives satisfactory results on all types of meshes. In particular, the model will be able to cope with meshes containing both « High-Reynolds » and « Low-Reynolds » wall cells. Given the complex flows encountered in the nuclear industry this thesis will use a model known for its good behavior: the EB-RSM model. This model is able to reproduce the anisotropy of the turbulence and give more satisfactory results than eddy viscosity models in different configurations. This model is available in Code_Saturne, an open source code developed at EDF. Al the developments are made in this code.
7

Bioconversion of paper mill lignocellulosic materials to lactic acid using cellulase enzyme complex and microbial cultures

Mukhopadhyay, Achira January 1900 (has links)
Master of Science / Department of Grain Science and Industry / Praveen V. Vadlani / Paper mill sludge is a solid waste generated from the paper-making industry. Cellulose in the sludge can be hydrolyzed into glucose using a cellulase enzyme complex, which can then be fermented to produce value added chemicals, such as lactic acid. The enzyme requirement for hydrolysis of the cellulose in paper sludge was benchmarked against paper pulp. Enzymatic requirements for complete conversion of cellulose in paper pulp was found to be 12 fpu cellulase, supplemented with 5 egu of beta-glucosidase per gram of cellulose. However, beta-glucosidase supplementation had to be increased to 38 egu to obtain a similar level of hydrolysis in the case of paper sludge indicating a decrease in enzyme activity due to sludge components. Response Surface Methodology (RSM) was used to study the lactic acid yield from paper sludge using enzyme dosage and temperature as parameters and operating in simultaneous saccharification and fermentation (SSF) mode. Maximum lactic acid yield of 0.75 g/g glucose was obtained within 36 hours using 10 fpu cellulase supplemented with 32 egu beta-glucosidase at a temperature of 39 degree C. Using the optimization function of the software, the optimal operational conditions for paper sludge hydrolysis were found to be 9 fpu cellulase, 12.5 egu beta-glucosidase at 40 degree C which resulted in a lactic acid yield of 0.58 g /g glucose. Lactic acid producing microbial cultures, Lactobacillus plantarum and Rhizopus oryzae were evaluated for fermentation of the pulp and sludge hydrolyzate at 125-ml shake flask and 2-L fermenter levels. In paper pulp media, the yields obtained by bacterial and fungal fermentations were 0.89 and 0.36 g/g glucose, respectively. In the case of paper sludge, the yield remained same, but inhibition of bacterial growth occurred. This resulted in lower substrate uptake and productivity than those obtained in paper pulp. On the other hand, fungal growth rate was enhanced due to the high solids content of paper sludge. The yield of lactic acid from paper sludge using L. plantarum and R. oryzae was 0.88 and 0.72 g/g glucose, respectively. Microbial cultures native to the sludge were isolated and evaluated for their performance of lactic acid production.
8

Extended Rasch Modeling: The eRm Package for the Application of IRT Models in R

Mair, Patrick, Hatzinger, Reinhold 22 February 2007 (has links) (PDF)
Item response theory models (IRT) are increasingly becoming established in social science research, particularly in the analysis of performance or attitudinal data in psychology, education, medicine, marketing and other fields where testing is relevant. We propose the R package eRm (extended Rasch modeling) for computing Rasch models and several extensions. A main characteristic of some IRT models, the Rasch model being the most prominent, concerns the separation of two kinds of parameters, one that describes qualities of the subject under investigation, and the other relates to qualities of the situation under which the response of a subject is observed. Using conditional maximum likelihood (CML) estimation both types of parameters may be estimated independently from each other. IRT models are well suited to cope with dichotomous and polytomous responses, where the response categories may be unordered as well as ordered. The incorporation of linear structures allows for modeling the effects of covariates and enables the analysis of repeated categorical measurements. The eRm package fits the following models: the Rasch model, the rating scale model (RSM), and the partial credit model (PCM) as well as linear reparameterizations through covariate structures like the linear logistic test model (LLTM), the linear rating scale model (LRSM), and the linear partial credit model (LPCM). We use an unitary, efficient CML approach to estimate the item parameters and their standard errors. Graphical and numeric tools for assessing goodness-of-fit are provided. (authors' abstract)
9

Extended Rasch Modeling: The eRm Package for the Application of IRT Models in R

Mair, Patrick, Hatzinger, Reinhold January 2007 (has links) (PDF)
Item response theory models (IRT) are increasingly becoming established in social science research, particularly in the analysis of performance or attitudinal data in psychology, education, medicine, marketing and other fields where testing is relevant. We propose the R package eRm (extended Rasch modeling) for computing Rasch models and several extensions. A main characteristic of some IRT models, the Rasch model being the most prominent, concerns the separation of two kinds of parameters, one that describes qualities of the subject under investigation, and the other relates to qualities of the situation under which the response of a subject is observed. Using conditional maximum likelihood (CML) estimation both types of parameters may be estimated independently from each other. IRT models are well suited to cope with dichotomous and polytomous responses, where the response categories may be unordered as well as ordered. The incorporation of linear structures allows for modeling the effects of covariates and enables the analysis of repeated categorical measurements. The eRm package fits the following models: the Rasch model, the rating scale model (RSM), and the partial credit model (PCM) as well as linear reparameterizations through covariate structures like the linear logistic test model (LLTM), the linear rating scale model (LRSM), and the linear partial credit model (LPCM). We use an unitary, efficient CML approach to estimate the item parameters and their standard errors. Graphical and numeric tools for assessing goodness-of-fit are provided. (author's abstract) / Series: Research Report Series / Department of Statistics and Mathematics
10

Contribution à l'étude de dégradation des colorants organiques par le procède d'oxydation avancée UV/Fe-ZSM5/H2O2 / Contribution to the study of organic dyes degradation by advanced Oxidation process “uv/fe-zsm5/h2o2”

Bagherzadeh Kasiri, Masoud 01 May 2009 (has links)
L’utilisation de colorants synthétiques se développe depuis de nombreuses années dans des différentes industries. Les procèdes les plus couramment utilises pour le traitement des eaux usées colorées sont les traitements biologiques mais ils ont leurs limites. Les techniques d’oxydation chimique traditionnelle quant a elles conduisent à la coupure de la molécule au niveau du chromophore ne peuvent pas minéraliser totalement des colorants alors que la dépollution complète de ces effluents l’exigerait. Le procède photo-fenton homogène est une technique de traitement qui peut dégrader les effluents colores efficacement. Mais il y a quelques inconvénients majeurs qui limitent l’application industrielle de cette technologie. L’objectif de ce travail de recherche était d’étudier la décoloration et la dégradation des solutions des colorants: acide orange 7 acide orange 8 acide rouge i4 acide rouge 73 et acide bleu 74 par le procède d’oxydation avancée: photo-Fenton heterogene. Dans ce procède la zeolite fe-zsm5 a été utilisée comme un catalyseur heterogene. L’application de ce système nous a permis d une part de diminuer la quantité de boue formée au cours du traitement ainsi que la consommation d’énergie électrique engendrée par l’utilisation d’UV estimée à l aide de la méthode figures-of-merit et d’autre par d’étendre l’application du procède type photo-fenton aux ph plus élevés. La modélisation des procèdes étudies a été faite par deux méthodes à la méthodologie de surface de réponse (RSM) et les réseaux neuronaux artificiels (ANNS) - afin d optimiser la performance de système et également d'évaluer les effets simples et combines des différentes variables sur l’efficacité du traitement. / Large amounts of dyes are annually produced and applied in different industries. The biological methods are widely used for treatment of coloured ef fluents, but they have some limitations. Traditional chemical oxidations that destroy the chromophore of the molecule could not also result the complete mineralisation of the dyes. Homogeneous photo-fenton is a promising technique for treatment of the effluents but there are still some drawbacks that limit the industrial applications of this method. The aim of this work was to study the decolourisation and the degradation of coloured solution containing acid orange 7 acid orange 8 acid red I4 acid red 73 or acid blue 74 by an advanced oxidation process: heterogeneous Photo-fenton. In this study zeolite fe-zsm5 was used as a heterogeneous catalyst. Application of this system not only allowed us to diminish the quantity of sludge formed during the process but also reduced the consummation of electrical energy process keeps its high efficiency even at neutral phs. The modelling of the process was done by two methods - response surface methodology (RSM) and artificial Neural networks (ANNS) in order to optimise the performance of the system and to evaluate the simple and the combined effects of different variables on the process efficiency.

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