To see the other types of publications on this topic, follow the link: Mass transfer coefficients.
Dissertations / Theses on the topic 'Mass transfer coefficients'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Mass transfer coefficients.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Van, der Westhuizen Francois Erasmus. "Vapour phase mass transfer coefficients in structured packing." Thesis, Stellenbosch : Stellenbosch University, 2008. http://hdl.handle.net/10019.1/1966.
Full text
2
De, Oliveira Campos Leandro Dijon. "Mass transfer coefficients across dynamic liquid steel/slag interface." Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0554/document.
Full textAbstract:
Afin de prédire l’évolution de la composition chimique du laitier dans différents procédés sidérurgiques, un modèle CFD a été développé. Les coefficients de transfert de masse sont estimés à partir des modèles basés sur les paramètres physico-chimiques et hydrodynamiques, comme par exemple la diffusivité des espèces chimiques et la divergence de l’interface. Ces modèles ont été développé pour la prédiction du transfert gaz-liquide où le les nombres de Schmidt (Sc=ν⁄D) sont relativement faible (Sc≈200). Par contre, les procédés industriels ont un nombre de Sc considérablement plus importante, de l’ordre de 103 à 104. Pour évaluer la pertinence de ces modèles, l’hydrodynamique au voisinage d’une interface liquide-liquide a été étudiée. Un modèle CFD et des mesures par l’anémométrie laser (LDA) ont été utilisés pour calculer et valider les champs de vitesse d’une maquette à eau d’une lingotière de coulée continue (CC).Le modèle de transfert de masse d’une lingotière de coulée continu industriel nous a montré que les coefficients de transfert de masse ne sont pas distribués de manière homogène, et les propriétés physiques du laitier ne doivent pas y être non plus. Cette distribution non-homogène a été confirmée par des essais physiques. Les écoulements calculés numériquement ont été utilisé pour prédire les coefficients de transfert de masse entre les deux phases liquide. Ces paramètres seront utilisés comme donnée d’entré pour un modèle de thermodynamique afin de prédire l’évolution de la composition chimique du laitierIn order to characterize the mass transfer coefficients (MTC) of different species across liquid steel/slag interface, a multiphase Computational Fluid Dynamic (CFD) model was developed. MTC’s are estimated from models based on physicochemical and hydrodynamic parameters, such as mass diffusivity, interface shear and divergence strength. These models were developed for gas-liquid interactions with relative low Schmidt (Sc=ν⁄D) numbers (Sc≈200). However, the industrial processes involve mass transfer of chemical species with Sc number ranging from 103 to 104. To evaluate the applicability of these existing models, the fluid flow in the vicinity of a liquid/liquid interface is investigated. Computational Fluid Dynamic (CFD) and Laser Doppler Anemometry (LDA) were used to calculate and measure the velocity field on a continuous casting (CC) water model configuration. The work provides new insights and original measures to understand the fluid flow near liquid-liquid interfaces.The mass transfer model of an industrial continuous casting mold showed that the mass transfer coefficients are not homogeneously distributed, and slag properties should follow this trend. This non-homogeneity was confirmed by physical experiments performed with a water model of a CC configuration and its CFD representation. The calculated flow was used to predict the MTC and the interface area between phases, since the interface is constantly moving. These parameters will be the input of thermodynamic models to predict slag composition and viscosity. This methodology is currently under validation, and it will also be applied to improve steel plant performance in the desulphurization process
3
Nebrensky, J. J. "Optical measurement of local mass transfer coefficients in naturally convecting systems." Thesis, University of Edinburgh, 1996. http://hdl.handle.net/1842/12709.
Full textAbstract:
The present work covers three main areas. First, several suitable polymers (one-part silicone RTVs, including a certain silicone sealant and Dow Corning's DC 734) and swelling agents (aliphatic esters such as iso-Pentyl Ethanoate, iso-Butyl iso-Butanoate and n-Pentyl Propanoate; alkanes including n-Nonane and n-Decane) have been identified, along with effective methods of applying the rubber coatings to both flat and cylindrical substrates. The diffusion properties of these new solvent/polymer systems have also been measured. Also, various aspects of the holographic system have been examined. The fringe visibility problems mentioned above are found to stem from in the incorrect location of the optical diffusing screen and are exacerbated by an apparent design flaw in the thermoplastic holographic camera used by some workers causing the gradual re-localisation of the interference fringes after hologram development. Substantial improvements in the lifetime of the thermoplastic plates for the holocamera has resulted from surrounding the optical system with a simple plastic curtain to keep out airborne dirt and dust. The improved optical system has been used to look at natural convection mass transfer from a vertical plate, using a variety of swelling agents to cover a range of Rayleigh numbers (Ra). For the more volatile solvents the results are in fair agreement with the analytical prediction of Lorenz, Sh=0.411 Ra1/4. For the less volatile swelling agents the measured values are significantly higher than predicted; this is believed to be due to background draughts increasing mass transfer rate. Natural convection from the cylindrical surface of a vertical rod has also been investigated. Other work performed in support of the main project includes the writing of a computer program to produce simulated fringe patterns in various geometries, the demonstration of a novel swollen polymer system using water and gelatin, and the investigation of temperature distributions in vertical rod arrays in free and mixed convection using both thermocouples and liquid crystal thermography.
4
Manjo, Persis Yefon. "A fundamental approach to predicting mass transfer coefficients in bubble column reactors." Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/9120.
Full textAbstract:
Includes bibliographical references.A bubble column reactor is a vertical cylindrical vessel used for gas-liquid reactions. Bubble Columns have several applications in industry due to certain obvious advantages such as high gas-liquid interfacial area, high heat and mass transfer rates, low maintenance requirements and operating costs. On the other hand, attempts at modelling and simulation are complicated by lack of understanding of hydrodynamics and mass transfer characteristics. This complicates design scale-up and industrial usage. Many studies and models have attempted to evolve understanding of the hydrodynamic complexity in Bubble Columns reactors. A closer look at these studies and models reveals a variety of solution methods for different systems (Frössling, 1938; Clift et al., 1978; Hughmark, 1967; Dutta, 2007; Ranz and Marshall, 1952; Benitez, 2009; Buwa et al., 2006; Suzzia et al., 2009; Wylock et al., 2011). Numerous correlations (Frössling, 1938; Clift et al., 1978; Hughmark, 1967; Dutta, 2007; Ranz and Marshall, 1952; Benitez, 2009; Buwa et al., 2006) exist but to date in literature, there is no general approach to determining accurate estimates of average mass transfer coefficient values. Good estimates of the average mass transfer coefficient will improve the predictive capacity of the associated models. Recent attempts at modelling micro-scale bubble-fluid interaction resulted in the Bubble Cell Model, BCM, (Coetzee et al., 2009) which simulates the velocity vector field around a single gas bubble in a flowing fluid stream using a Semi-Analytical model. The aim of the present study is to extend the BCM applications by integrating the mass balance into the framework to predict the average mass transfer coefficient in bubble columns. A nitrogen-water steady state system was simulated in an axisymmetric grid where mass transfer occurs between the gas and liquid.
5
Davies, Stephen Nigel. "The evaluation of overall gas-liquid mass transfer coefficients in gas sparged agitated vessels." Thesis, University College London (University of London), 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263106.
Full text
6
Djebbar, Yassine. "Prediction of mass transfer coefficients of air-stripping packed towers for volatile organic compound removal." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0011/NQ38780.pdf.
Full text
7
Ahlman, Robert. "ASSESSMENT OF GOVERNING HEAT AND MASS TRANSFER COEFFICIENTS FOR CRYOGENIC NO-VENT TOP-OFF MODELING." Cleveland State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=csu1625819994533715.
Full text
8
Moeti, Lebone Tiisang. "The dependence of the continuous phase mass transfer coefficients on molecular diffusivity for liquid-liquid extraction in agitated vessels." Diss., Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/11856.
Full text
9
Miller, Jacob. "Modelling the Effect of Catalysis on Membrane Contactor Mass Transfer Coefficients for Carbon Dioxide Absorption Systems." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1627662756315225.
Full text
10
McFarland, Elizabeth Gramling. "A new method for determining diffusion and convection mass transfer coefficients in the dyeing of textile materials." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/12416.
Full text
11
Gamero, Rafael. "Transport Coefficients during Drying of Solids containing Multicomponent Mixtures." Doctoral thesis, KTH, Teknisk strömningslära, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-28897.
Full textAbstract:
This study investigated the transport coefficients involved in mass and heat transfer during the drying of a porous solid partially saturated with multicomponent mixtures. It included the coefficients governing liquid transport through the solid, the matrix of multicomponent diffusion coefficients in the liquid phase, and the effective thermal conductivity. As it is not possible to determine these coefficients by theoretical considerations alone and considerable experimental work is required to determine them in a broad range of process conditions, the principle of this study has been the use of mathematical models complemented with some empirical parameters. These empirical parameters were determined by comparison between measurements in specially designed experiments and the results of mathematical models that describe the process. In addition, the application of the multicomponent diffusion coefficients is described in two cases where liquid diffusion is important: convective evaporation of a multicomponent stationary liquid film and a falling film. To study liquid transport through the solid, isothermal drying experiments were performed to determine the transient composition profiles and total liquid content of sand samples wetted with ternary liquid mixtures with different initial compositions and temperatures. A mathematical model including mass transfer by capillary movement of the liquid and interactive diffusion in both the gas and liquid phases was developed. To simulate the capillary movement of liquid mixtures, parameters experimentally determined for single liquids were weighed according to liquid composition. A fairly good agreement between theoretical and experimental liquid composition profiles was obtained considering that axial dispersion was included in the model. To study the matrix of multicomponent diffusion coefficients in the liquid phase, the redistribution of liquid composition in a partially filled tube exposed to a longitudinal temperature gradient was analysed. Experimental work was carried out using two main ternary mixtures with different initial compositions and temperature gradients. Experimental data were compared with the results of a theoretical model that describes the steady-state liquid composition distribution in a partially filled non-isothermal tube to find the empirical exponent that modifies the matrix of thermodynamic factors. Correlations for the exponents as a function of temperature were determined for each particular multicomponent mixture. The effective thermal conductivity of a porous solid containing multicomponent liquid mixtures was studied by measuring the liquid composition, liquid content and temperature distributions in a cylindrical sample dried by convection from the open upper side and heated by contact with a hot source at the bottom side. Simulations performed at a quasi steady state were compared with experiments to estimate the adjusting geometric parameter of Krischer’s model for effective thermal conductivity, which includes the contribution of the evaporation-diffusion-condensation mechanism. The results revealed that a resistance corresponding to a parallel arrangement between the phases seems to dominate in this case. In the study of the convective drying of a multicomponent stationary liquid film, the equations describing interactive mass transfer were decoupled by a similarity transformation and solved simultaneously with a conduction equation by the method of variable separation. Variations of physical properties along the process trajectory were taken into account by a stepwise application of the solution in time intervals with averaged coefficients from previous time steps. Despite simplifications, the analytical solution gives a good insight into the selectivity of the drying process and is computationally fast. On the other hand, numerical simulations of the convective evaporation of the multicomponent falling liquid film into an inert gas with a co-current flow arrangement of the phases almost always revealed a transition from liquid-phase-controlled conditions to a process in which neither the gas nor the liquid completely controls the evaporation. The results obtained in this work would be useful in implementing models to improve the design, process exploration and optimisation of dryers by incorporating the solid-side effects to describe the drying of liquid mixtures along the whole process.QC 20110124
12
Kebe, Mouhamadou. "Incidence de traitements thermiques sur le parenchyme de Pomme (Malus Domestica) et diffusion des composés phénoliques." Thesis, Avignon, 2014. http://www.theses.fr/2014AVIG0253/document.
Full textAbstract:
La pomme (Malus Domestica Borkh.), fruit largement répandu dans les pays tempérés est beaucoup consommée. Elle représente une source importante en composés phénoliques. Cette étude s’est intéressée aux polyphénols des tissus du parenchyme. La problématique s’oriente sur les effets de la texture sur la diffusion de ces molécules. L’originalité de l’approche repose sur l’association de la texture, de la pression osmotique et la diffusion des polyphénols. Les méthodes de caractérisations physiques et biochimiques ont permis de mesurer les changements à l´échelle macroscopique et les modifications chimiques qui s’opèrent dans les matrices végétales. Les résultats de l’étude du transfert de matière ont permis de mettre en évidence les différents facteurs pouvant influer sur les valeurs des coefficients de diffusion. La texture, l’épaisseur, la variété du fruit et la pression du milieu diffusant, constituent des facteurs pouvant influencer le transfert de matière. L’étude de l’évolution de composant de la paroi a montré des changements qui s’opèrent au cours de la diffusion. Des analyses microscopiques ont relevé les modifications à l’échelle cellulaire de la diffusion de procyanidines, polyphénols majoritaires et des interactions avec les composants pariétauxApple (Malus domestica Borkh. ) fruit widespread in temperate countries, is much consumed.It represents an important source of phenolic compounds. This study was interestedin polyphenol content of apple tissue parenchyma. The problem concerns effects of texturedegradation on the diffusion of polyphenols molecules. The originality of the approach isbased on the combination of texture, osmotic pressure and polyphenol leaching. Physicaland biochemical methods were used to measure changes at macroscopic scale and chemicalchanges occurring in the parenchymateous tissue . The study of mass transfer highlightedvarious factors that may affect apparent coefficient diffusion. The result showed that thedisintegration of texture , thickness, apple variety and osmotic pressure of leaching mediacan influence mass transfer yield. The study of the Cell walls components showed changesthat occur during leaching process. Light microscopic analysis revealed changes at cellularscale, procyanidins the major polyphenols, leaching phenomena and also interactionswith cell walls matrix
13
Darolles, Danielle. "Couplages transferts de chaleur et de masse a la surface de materiaux poreux utilises en genie civil lors de sechages en ecoulements turbulents." Toulouse 3, 1987. http://www.theses.fr/1987TOU30080.
Full textAbstract:
Equations du transfert de chaleur dans le milieu poreux, et definition du coefficient d'echange de masse, avec sa relation au coefficient d'echange de chaleur. Dispositif experimental de sechage et caracteristiques mesurees de l'ecoulement. Experiences realisees de sechage et coefficients calcules d'echange de masse a la surface des echantillons, avec comparaison aux resultats obtenus par un modele de simulation monodimensionnel
14
Dowling, Irena C. "Rate of cobalt extraction by D2EHPA from aqueous forming drops : cobalt extraction from aqueous forming drops by di-2-ethylhexylphosphoric acid is studied by flow injection analysis and a computer program is used to calculate mass transfer coefficients. F." Thesis, University of Bradford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236490.
Full textAbstract:
A study of the extraction of cobalt II ions from an aqueous growing drop into a continuous medium of di-2-ethylhexylphosphoric acid (D2EHPA) is made. The apparatus for this technique is described and a flow injection analysis method for measuring the cobalt remaining in the aqueous phase has been developed. In this study the feed concentration of cobalt has varied between 8.48 x 10-3 and 16.97 x 10-3 mole 9-1. The D2EHPA held in n-heptane, has been altered between 0.143 and 2.41 mole P. Also, pH has been adjusted between 3.10 and 4.44. The principal temperature applied to this study was 25 ±0.5*C. Acetate buffers have been used, but it is shown by calculation that about 70% of the cobaltous ion is in an uncomplexed form. The kinetics of the extraction have been modelled using a method based upon reaction in an aqueous zone near to the liquid-liquid interface with diffusion of species towards and away from the interface. This model provided a fundamental parameter 01 which incorporates the chemical rate constant kR, the D2EHPA partition coefficient PHR, the acid dissociation constnat KD for D2EHPA and the metal ion diffusivity in the interface diffusion region. The results have been compared with those of other workers who studied the transfer of cobalt into an organic drop from an aqueous continuum. The diffusion controlling film is the aqueous one. The rate constant for, the extraction reaction equation is, from this work, kR - 106.34 M3 kmol-1 sec-1 which can be compared with that found by another worker using the reverse transfer system, i. e. kR - 106.18 m3 kmol-I sec-i. . Finally, the mass transfer coefficients were found to change with varying feed concentrations and pH, this is also in agreement with other workers who have studied different liquid-liquid systems.
15
Mawson, Ryan A. "Bubble Coalescence and Breakup Modeling for Computing Mass Transfer Coefficient." DigitalCommons@USU, 2012. https://digitalcommons.usu.edu/etd/1330.
Full textAbstract:
There exist several different numerical models for predicting bubble coalescence and breakup using computational fluid dynamics (CFD). Various combinations of these models will be employed to model a bioreactor process in a stirred reactor tank. A mass transfer coefficient, Kla, has been calculated and compared to those found experimentally by Thermo-Fisher Scientific, to validate the accuracy of currently available mathematical models for population balance equations. These include various combinations of bubble breakup and coalescence models coupled with the calculation of mass transfer coefficients.
16
Chau, Nguyen. "Étude et comparaison de trois contacteurs gaz-liquide a auto-aération." Vandoeuvre-les-Nancy, INPL, 1993. http://www.theses.fr/1993INPL115N.
Full textAbstract:
Une méthodologie d'étude de contacteurs gaz-liquide a été analysée et appliquée à l'étude de trois contacteurs gaz-liquide alimentés en gaz par autoaspiration selon trois mécanismes: vortex assisté par tube de tirage, turbine autoaspirante et arbre creux, éjecteur et boucle de recirculation. Le dimensionnement et la réalisation des maquettes ont été menés successivement a partir d'une base commune constituée par une cuve de dimension semi-industrielle et de capacité avoisinant les 200 l. L'hydrodynamique et les paramètres de transfert de matière gaz-liquide ont été examinés dans l'optique d'une comparaison des performances et d'une interprétation en terme de modèles de zones
17
Hou, Longfeng. "Etude numérique sur le modèle de coefficient d’absorption corrélé en multi spectral." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0068.
Full textAbstract:
Le transfert radiatif dû aux gaz joue un rôle important dans les applications industrielles comme les chambres de combustion, les sciences atmosphériques, etc. Plusieurs modèles ont été proposées pour estimer les propriétés radiatives des gaz. Le plus précis est l'approche dite Raie Par Raie (RPR). Cependant, cette méthode implique un coût de calcul excessif qui la rend inappropriée pour la plupart des applications. Néanmoins, elle reste la méthode de référence que nous utiliserons pour l'évaluation d’autres modèles approchés. Le modèle de coefficient d’absorption corrélé (Ck) est généralement suffisant pour de nombreuses applications. Cette méthode est réputée précise lorsque petits gradients de température sont rencontrés au sein du gaz. Toutefois, si le milieu gazeux est soumis à d'importants gradients de température, la méthode Ck peut conduire à des erreurs qui peuvent atteindre 50% en termes de flux radiatifs par rapport à des simulations de RPR. Le but de cette thèse est de proposer une version améliorée de la méthode Ck, appelée l'approche de coefficient d’absorption corrélé en multi spectral (MSCk). La principale différence entre les modèles Ck et MSCk est que, dans l'approche Ck les intervalles spectraux sur lesquels les propriétés radiatives des gaz sont moyennées sont choisis contiguës alors que, dans l’approche MSCk, ces intervalles sont construits afin d'assurer que le coefficient d'absorption soit corrélé sur ces intervalles. Par conséquent, l'hypothèse de corrélation dans l’approche MSCk est mieux adaptée que dans l’approche Ck. La construction de ces intervalles spectraux (en utilisant la méthode de classification automatique de données fonctionnelles) est détaillée. Cette approche est évaluée par rapport à la référence RPR dans plusieurs cas test. Ces cas traitent de mélanges de gaz (H2O-N2 et H2O-CO2-N2) dans l’intervalle de température [300-3000K]. Les résultats montrent que la méthode MSCk permet d'obtenir de meilleures précisions que les méthodes Ck tout en restant acceptable en termes de coût de calculRadiative heat transfer of gas plays an important role in industrial applications such as in combustion chambers, atmospheric sciences, etc. Several models [11] have been proposed to estimate the radiative properties of gases. The most accurate one is the Line-By-Line (LBL) approach. However, this technique involves excessive computation cost which makes it inappropriate for most applications. Nevertheless, it remains the reference approach for the assessment of other approximate models. The Correlated k-distribution method (Ck) [11] was shown to be a relevant choice for many applications. This method performs usually well, when only small temperature gradients are involved [21]. However, if the gaseous medium is subject to large temperature gradients, it may lead to errors that can reach 50% in terms of radiative heat fluxes when compared to LBL simulations [21]. The aim of the present paper is to propose an enhanced version of the Ck method, called the Multi-Spectral Correlated k-distribution approach (MSCk). The main difference between Ck and MSCk models is that in the Ck approach spectral intervals over which the radiative properties of the gas are averaged are chosen contiguous whereas, in the MSCk technique, those intervals are built in order to ensure that the absorption coefficient are scaled over them [27]. Accordingly, the usual assumption of correlated spectrum used in k-distribution approaches for the treatment of non uniformities is more acceptable in the MSCk case than in the Ck one. The building of those spectral intervals (using Functional Data Clustering, [52]) is detailed and the approach is assessed against LBL reference data in several test cases. These cases involve H2O-N2 and H2O-CO2-N2 mixtures in the [300-3000K] temperature range. Results show that the MSCk method enables to achieve better accuracies than Ck methods while remaining acceptable in terms of computational cost
18
Arduini, Tommaso. "Volumetric mass transfer coefficient in viscous batch in mechanically agitated fermenters." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
Find full textAbstract:
L’industria di processo è basata su diverse operazioni unitarie, le quali possono essere divise in due gruppi principali: il primo contenente quelle volte alla produzione vera e propria dei prodotti, mentre le rimanenti hanno come scopo la separazione dei prodotti d’interesse da quelli ritenuti di scarto. Per questo motivo, un corretto dimensionamento delle apparecchiature coinvolte è strettamente consigliato. Tuttavia, in situazioni complesse come i sistemi bifase, ciò non è sempre possibile. Infatti, lo scambio di materia che avviene tra il liquido e il gas non può essere calcolato analiticamente con formule puramente teoriche, ma al contrario, diversi dati sperimentali sono richiesti. Per questo motivo, spesso il dimensionamento di questo tipo di reattori è spesso fatto a tentativi, senza seguire una procedura ingegnerizzata. Per risolvere questo problema, diversi studi stanno cercando di costruire una corretta procedura per predire, in modo più accurato possibile il valore del coefficiente di scambio volumetrico. Il valore di questo parametro, infatti, è strettamente richiesto nella soluzione dei bilanci di materia che permettono il dimensionamento dell’apparecchiatura. In particolare, questo parametro può essere ricavato da misurazioni sperimentali. Tuttavia, diverse metodologie impiegate restituiscono risultati differenti. Per questo motivo, la letteratura contiene numerosi articoli con risultati significativamente diversi tra di loro.
Tuttavia, metodi di misurazione più efficaci sono stati introdotti. Tra questi si ricorda il Dynamic Pressure Method, il quale sarà utilizzato in questo elaborato per la valutazione del coefficiente di trasporto di materia volumetrico. Inoltre saranno proposte diverse correlazioni come un utile strumento per il dimensionamento di fermentatori industriali con più di una girante.
19
Mabrouk, Aurélie. "Caractérisation des résines échangeuses d'ions d'intérêt pour les réacteurs à eau sous pression : Application et validation d'un modèle dédié." Phd thesis, Ecole Nationale Supérieure des Mines de Paris, 2012. http://pastel.archives-ouvertes.fr/pastel-00803356.
Full textAbstract:
Dans les centrales nucléaires à eau sous pression, les Résines Echangeuses d'Ions (REI) sont utilisées dans les circuits d'épuration. Dans le cadre de cette thèse, une étude qualitative a été réalisée afin de prédire les tendances du comportement d'une REI dans le cadre de son utilisation en condition centrale nucléaire. Fort des résultats de cette étude, nous avons cherché à caractériser quantitativement le comportement des REI en colonne. Pour cela, nous avons utilisé des solutions analytiques mais ces dernières se sont révélées valables uniquement dans des cas particuliers. Afin de trouver une solution générale, nous nous sommes donc tournés vers une solution numérique : OPTIPUR. En vue de la valider et aussi de mieux comprendre la cinétique en colonne, nous avons réalisé une étude expérimentale. Cette dernière vise à caractériser la résistance au transfert de masse en colonne et à mener une étude de sensibilité sur les paramètres influençant ce phénomène. Cette étude repose sur la détermination de la fuite ionique cinétique, correspondant à une certaine concentration de polluant présente en sortie de colonne en début d'expérience. Pour cela, nous avons testé l'influence de nombreux paramètres sur la fuite ionique cinétique. Nous avons ainsi vu l'importance de la vitesse de filtre et donc des conditions hydrodynamiques sur la fuite ionique cinétique. Ces nombreux résultats de fuite cinétique, ont été modélisés à l'aide de la corrélation empirique de Dwivedi & Upadhyay afin de tester sa validité. Par la suite, nous avons simulé nos résultats de fuite ionique cinétique avec deux options du logiciel OPTIPUR : option Mass Transfer Coefficient (MTC) et Nernst-Planck (NP). Ces dernières encadrent les résultats expérimentaux. L'option MTC d'OPTIPUR donne des résultats inférieurs alors que ceux obtenus avec l'option NP sont supérieurs aux résultats expérimentaux. Nous avons vu que dans le cadre d'un échange ternaire, seule l'option NP est valide. Nous avons proposé des solutions pour mieux caler les résultats obtenus numériquement. D'autres simulations ont été réalisées afin de vérifier les capacités de prédiction de l'appareil pour des expériences plus longues (allant jusqu'à la saturation de la REI). Les tendances observées étaient celles attendues. L'outil OPTIPUR est un outil précis et robuste pour étudier la cinétique en colonne.
20
Jamnongwong, Marupatch. "Transfert de matière gaz/liquide en milieux complexes." Thesis, Toulouse, INSA, 2010. http://www.theses.fr/2010ISAT0040/document.
Full textAbstract:
L’opération de transfert de matière gaz/liquide est une étape essentielle en génie desprocédés. Elle conditionne directement les performances des contacteurs gaz/liquide en représentantbien souvent l’étape limitant l’efficacité du procédé. L'objectif de cette étude est de proposer denouvelles investigations afin d'étudier l'effet de la présence dans l'eau pure, de certains composésgénéralement rencontrés dans les procédés biologiques, sur les coefficients de diffusion de l'oxygèneet de quantifier leurs conséquences sur les coefficients de transfert de matière côté liquide. Lescoefficients de diffusion de l'oxygène DO2 ont été mesurés dans diverses phases liquides contenant dusel (NaCl), du sucre (glucose) ou des tensio-actifs (laurylsulfate de sodium). Comparé à l'eau pure,des réductions de coefficient de diffusion DO2 ont été observées, la variation de DO2 avec laconcentration C de composé a été modélisée, elle dépend de la nature du composé ajouté. Ensuite,des expériences réalisées sur un train de bulles et sur les mêmes phases liquides ont permis ladétermination des coefficients de transfert de matière côté liquide kL. Quelle que soit la solutionaqueuse étudiée, une diminution des valeurs de kL est observée avec l'augmentation de C. Cesrésultats mettent en évidence que, même si les propriétés de l'eau pure (densité, viscosité, tensionsuperficielle) ne sont pas significativement modifiées par l'ajout de sels (NaCl), les coefficients detransfert de matière côté liquide kL peuvent être modifiés. Pour les solutions aqueuses de glucose, laréduction de kL avec DO2 est bien corrélée, et principalement due à la variation de viscosité avec laconcentration. Pour les solutions de tensio-actif, les nombres de Reynolds restent presque constantspour toutes les concentrations. Le seul responsable de la réduction du coefficient de transfert dematière côté liquide kL est donc le coefficient de diffusion de l’oxygène qui diminue avec laconcentration. La présente étude a clairement confirmé la nécessité de compléter et/ou rendre comptedes données liées aux coefficients de diffusion de l’oxygène DO2 et aux coefficients de transfert dematière côté liquide kL dans des milieux complexes (solution électrolytique, solution organique ettensioactif). Ces informations sont nécessaires pour décrire et modéliser correctement lesphénomènes de transfert de matière gaz/liquideThe gas/liquid mass transfer is an essential step in process engineering. It directly affects theperformance of gas/liquid reactor in being often limiting process efficiency. The objective of this studyis to propose new investigations in order to study (i) the effect on oxygen diffusion coefficients underthe presence in clean water of some compounds usually found in biological process and (ii) quantifytheir consequences on liquid-side mass transfer coefficients. The oxygen diffusioncoefficients DO2 were measured in various synthetic liquid phases containing either salt (NaCl), sugar(glucose) or surfactant (sodium laurylsulphate). When compared to clean water, reductionsof DO2 were observed; the variation of DO2 with the compound concentration C was modeled andfound dependent on the nature of the compound added. Then, to determine the liquid side masstransfer coefficient kL, experiments on a train of bubbles rising in a quiescent liquid phase were carriedout by the same synthetic liquid phases. For all cases, whatever the aqueous solutions, a decreaseof kL with increasing C was clearly observed. These results firstly showed that, even if the properties ofclean water (density, viscosity, surface tension) were not significantly changed by the addition of salts(NaCl), the liquid-side mass transfer coefficients could be modified. For the aqueous solutions ofglucose, the reduction of kL with DO2 was well correlated, and mainly due to the change in viscositywith concentration. For surfactants, the hydrodynamic conditions (i.e. bubble Reynolds number) beingalmost kept constant for all concentrations, only the change in DO2 was thus responsible for thedecrease of kL. The present study clearly confirmed the need to complete and/or account for thedatabase related to oxygen diffusion coefficients and liquid side mass transfer coefficient in complexmedia (electrolytic solution, organic solution and surfactant). This condition is imperatively required todescribe and to model appropriately the gas-liquid mass transfer phenomena
21
Joubert, Rita. "Solid-liquid mass transfer in trickle bed reactors." Diss., Pretoria : [s.n.], 2009. http://upetd.up.ac.za/thesis/available/etd-06242009-140938/.
Full text
22
Mouawad, Charbel. "Transfert de matière dans un système solide/liquide "ions/eau/pectine" : interactions, partage ionique et simulation par dynamique moléculaire." Thesis, Vandoeuvre-les-Nancy, INPL, 2007. http://www.theses.fr/2007INPL072N/document.
Full textAbstract:
Mass transfer intervening during the process of immersion influences the final composition of the product. These transfers primarily depend on the size of the immersed products, as well as temperature, the concentration and the nature of the solution of immersion. The main objective of this work is to study the mass transfer phenomena (water loss and solid gain) in solid/liquid system constituted of vegetable product (eggplant) immerged in salt solution. We determined the kinetic studies of eggplant in different salts solutions with two concentrations (saturation and 20%) at 3°C. The physicochemical properties of solution and salt such as molar concentration, molecular weight and ionic type affected the mechanism of water loss and solid gain. Knowledge about interaction ions/vegetable pectin is important for new product formulation. Determination of partition coefficient of ion in equilibrium system showed that the main physicochemical properties of ions and solution are ionic radius, electronegativity, ionic force and molar concentration. Mathematical predictive model was developed to predict the partition coefficient of ions in food/ solution system. Molecular dynamics simulations using a dynamic force field have been carried out to investigate the absorption of ions (K+, Na+, Ca2+, Mg2+, Cl-) in pectin/water/ion/aqueous solution system. Four systems were used. The results showed that the ionic type (cation and anion) influence the type and number of interactions between pectin-ion and water-ion and then offered an explicit description transfer phenomena and distribution of ions in the system solid/liquidLes transferts de matière intervenant au cours du procédé d’immersion dépendent essentiellement de la taille des produits immergés, la température, la concentration et la nature de la solution d'immersion. L’objectif principal de ce travail porte sur l’étude des transferts dans un système solide/liquide constitué d’un produit végétal (aubergine) et d’une solution saline. Afin de parvenir à une bonne maîtrise de ces paramètres, les études cinétiques ont été conduites à 3°C sur des aubergines immergées dans des solutions salines avec deux concentrations. Les propriétés des solutions et des sels telles que la concentration molaire, la masse molaire et surtout la nature ionique influencent le mécanisme de perte et de gain. Les connaissances sur les interactions ions/pectines végétaux sont importants pour la formulation de nouveaux produits La détermination du coefficient de partage des ions à l’équilibre dans le système aubergine/solution ont montré que les principales propriétés des ions et des solutions influençant le coefficient de partage sont le rayon ionique, l’électronégativité, la force ionique et la concentration molaire. Un modèle mathématique a permis de prédire le coefficient de partage des ions dans ce système. Dans le but d’expliquer l’absorption des ions par la phase solide, une simulation par dynamique moléculaire a été menée sur un système pectine-eau-sels. Quatre systèmes ont été utilisés. Les résultats obtenus ont montré que la nature ionique influencent la nature et le nombre d’interaction entre pectine-ion et eau-ion et donc offrent une description explicite des phénomènes de transferts et distribution des ions dans le système solide/liquide
23
Ji, Xinsheng. "Parameter estimation of liquid film mass transfer coefficient and effective interfacial area for random and structured packings." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ30485.pdf.
Full text
24
Marty, Marielle. "Contribution à l'évaluation des coefficients de trainée entre phases avec prise en compte d'un transfert de masse." Aix-Marseille 1, 1994. http://www.theses.fr/1994AIX11014.
Full textAbstract:
L'objet de cette etude est la prise en compte du transfert de masse dans le calcul des coefficients de trainee entre la phase continue et la phase dispersee constituee de particules spheriques. L'ecoulement autour de la sphere etant generalement instationnaire et tridimensionnel nous avons etudie dans une premiere partie l'ecoulement bidimensionnel autour d'un cylindre sans et avec transfert de masse. Il ressort de cette etude que le transfert de masse stabilise les fluctuations de l'ecoulement. Ce resultat nous a permis de passer a l'etude de l'ecoulement autour de la sphere de facon simplifiee. Nous etablissons, dans cette seconde partie, des correlations pour les coefficients de trainee totale et visqueuse. Ces correlations sont introduites dans un code de calcul d'ecoulement physique et nous etudions l'influence du transfert de masse sur un ecoulement en tuyere. Enfin, profitant de la connaissance des valeurs des coefficients de trainee sans et avec transfert de masse, nous donnons notre opinion sur la decomposition du second membre des equations diphasiques
25
Lang, Jean Pierre. "Avaliação do efeito dos parametros operacionais e geometricos sore a eficiencia de uma coluna de destilação Higee." [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/267229.
Full textAbstract:
Orientadores: Teresa Massako Kakuta Ravagnani, João Alexandre Ferreira da Rocha PereiraDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
Made available in DSpace on 2018-08-05T04:47:12Z (GMT). No. of bitstreams: 1 Lang_JeanPierre_M.pdf: 1967050 bytes, checksum: 0383f4c0388e6e7aa19f19c4c4688052 (MD5) Previous issue date: 2005
Resumo: As colunas de recheio são equipamentos intensamente aplicados em operações de separação tais como destilação, absorção de dessorção. No entanto, a sua capacidade à transferência de massa em contracorrente é limitada devido à sua inundação. Uma nova tecnologia HIGEE ('high g¿ ¿ alta gravidade é proposta para superar esta limitação. Uma cluna HIGEE utiliza um recheio rotativo que induz acelerações centrífugas acima de 1000 vezes a aceleração da gravidade terrestre. O aumento da força motriz permite o aumento da capacidade e da eficiência da coluna. De acordo com vários autores, o tamanho do equipamento fica consideravelmente reduzido, apresentando vantagens econômicas e operacionais. A principal proposta deste trabalho é avaliar a forma como a coluna com recheio rotatico se comporta quando o raio externo do rotos é aumentado de 8 (Nascimento, 1999 e 2003) para 13cm.Os experimentos foram conduzidos em condições de refluxo total, sendo utilizando dois sistemas destilantes: n-hexano/n-heptano e etanol/água. A velocidade do rotor foi variada de 500 a 2300 rpm, criando acelerações contrifugas de 26 a256 vezes a aceleração da gravidade. O efeito da vazão de vapor, velocidade de rotação e do sistema destilante sobre o coeficiente de transferência de massa, 'K IND. y¿¿a IND. e¿ depende do fluxo de vapor, mas fracamente da velocidade do rotor...Observação: O resumo, na íntegra, poderá ser visualizado no texto completo da tese digital
Abstract: Packed colummns are equipment intensively applied in separations such as distillation, absorption and stripping , absorption and strippig. However, its for counter-current mass transfer is limited due to its flooding. A new HIGEE (high g ¿ high gravity) technology is proposal to overlap this limitation. A HIGEE column uses a rotating machine that promotes centrifugal accelerations above 1000 times the terrestrial gravity acceleration. The increase of the driving force allows the increase of column¿s capacity and efficiency. In accordance with some authors, the equipment size considerably reduced presenting economic and operational advantages. The main proposal of this work is to evaluate how the mass transfer behavior of the HIGEE column changes when the external rotor radius is increased from 8 (Nascimento 1999 and 2003) to 13 cm. The experiments had been conduced in total reflux conditions using two distilling system n-hexane/n-heptane and ethanol/ water. The rotor's speed was vaied from 500 to 2300 rpm , provided centrifugal accelerations from 26 to 556 times higher than terrestrial gravity acceleration. The effect of the vapor outflow, rotation speed and distilling system on mass transfer coefficient 'K IND. y¿¿a IND. e¿ and transfer unit area, 'AUT IND. G¿had been analyzed for each rotor size...Note: The complete abstract is available with the full electronic digital thesis or dissertations
Mestrado
Sistemas de Processos Quimicos e Informatica
Mestre em Engenharia Química
26
Chery, Olivier. "Étude hydrodynamique et transfert de matière dans un contacteur gaz-liquide à film centrifuge dans le cadre de procédés de traitement d'effluents gazeux contenant du dioxyde de soufre et/ou des oxydes d'azote." Vandoeuvre-les-Nancy, INPL, 1994. http://docnum.univ-lorraine.fr/public/INPL_T_1994_CHERY_O.pdf.
Full textAbstract:
Dans le cadre d'un programme B. R. I. T. E. De la C. C. E. , nous étudions un procédé de traitement d'effluents gazeux contenant du dioxyde de soufre et/ou des oxydes d'azote, par absorption suivie de l'oxydation de ces espèces. Dans une première phase, nous avons utilisé un contacteur gaz-liquide ayant des caractéristiques de transfert de matière élevées: le réacteur à film centrifuge. La caractérisation hydrodynamique du contacteur a permis de mettre en évidence les régimes de fonctionnement, le comportement, du réacteur piston au réacteur parfaitement agité, ainsi que les paramètres essentiels: la vitesse de rotation et la contre-pression. Nous avons ensuite déterminé les caractéristiques de transfert de matière de l'absorbeur par la mesure des coefficients volumiques de transfert de matière cote gaz et liquide. La dernière étape de cette étude a été une application du réacteur à film centrifuge à l'absorption d'un mélange dilué d'oxyde et de dioxyde d'azote dans une solution aqueuse d'urée. Il s'avère que les temps de séjour rencontrés dans le contacteur sont trop faibles pour que certaines réactions d'élimination de ces polluants puissent avoir lieu. La seconde partie a consisté à concevoir et à mettre en œuvre un réacteur à film tombant laminaire cylindrique, destiné à déterminer la cinétique de la réaction chimique suivant l'absorption du dioxyde de soufre dans une solution aqueuse acide de cérium quatre. Seules, quelques expériences ont pu être réalisées montrant que la réaction est probablement intermédiaire. D’autres expériences doivent également être menées afin de mieux caractériser ce réacteur
27
Silva, Raquel da Cunha Ribeiro da 1981. "Estudo experimental e numérico da formação de Frost em torno de três cilindros com arranjo triangular." [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265903.
Full textAbstract:
Orientadores: Carlos Teofilo Salinas Sedano, Kamal Abdel Radi IsmailTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
Made available in DSpace on 2018-08-25T08:57:38Z (GMT). No. of bitstreams: 1 Silva_RaqueldaCunhaRibeiroda_D.pdf: 3855986 bytes, checksum: dc3f065365a2224c57128ddbedffab68 (MD5) Previous issue date: 2014
Resumo: O fenômeno de formação de frost é encontrado em muitas aplicações comerciais e industriais de baixa temperatura. A camada de gelo que se forma em uma superfície fria cresce ao longo do tempo, tornando-se mais densa e por este motivo, a formação de frost em equipamentos é responsável pela queda no seu desempenho. O processo de formação de frost é um fenômeno transiente e complicado de avaliar, no qual os processos de transferência de calor e de massa ocorrem simultaneamente em um meio poroso. Neste trabalho apresentam-se medições experimentais da espessura de frost ao redor de cada um dos tubos de um arranjo triangular de cilindros verticais, realiza-se a estimação experimental de uma correlação empírica para a obtenção do número de Nusselt Global sobre o arranjo de tubos com formação de frost baseada nas medições experimentais feita numa seção de teste no interior de um túnel de vento do Laboratório de Armazenamento térmico e tubos de Calor da FEM. Para verificação é feita a estimação de uma correlação empírica para o Número de Nusselt Local em cada cilindro baseado em dados empíricos da literatura e um procedimento inverso de aproximação sucessiva utilizando a solução numérica unidimensional que simula o problema direto de formação de frost em geometria cilíndrica. O mesmo procedimento utilizando os dados experimentais deste trabalho. Encontra-se que os valores dos Números de Nusselt para as duas formas de estimação tem boa concordância. Comparações dos resultados numéricos e experimentais são realizadas e mostra-se boa concordância dos resultados das simulações numéricas para o crescimento da camada de frost utilizando ambas as correlações empíricas
Abstract: In practice, it is found the phenomenon of frost formation in a lot of commercial and industrial refrigeration applications. The layer of ice that it is formed in a cold surface grows over time, becoming more dense and bigger, and for that reason, this formation of frost in refrigeration equipment is responsible for performance decrease in this equipment. The formation of frost is a complicated and transient process, where different process of heat transfer and mass occurs simultaneously in a porous and fine layer. The convective and mass diffusive coefficients are difficult to determinate in fact of the complex physic phenomenon and the variation of the different properties that occurs over time like velocity, temperature, humidity and the geometry of this problem himself. In this work some experimental results of the frost thickness around every cylinder in a triangular arrangement of vertical cylinders are presented, an estimated experimental correlation in order to find Nusselt Global number in this triangular arrangement of cylinders is presented. This correlation is based in the experimental measurements in a wind tunnel situated in the Laboratory of Thermal storage and Fluids in FEM. In order to verify this correlation, another empiric correlation have been estimated in order to find the Nusselt number Global and Local in each cylinder. In this case, it is used data reported in the literature and an inverse method that approximates the numerical solution in one dimension that simulates this problem in cylindrical frost formation geometry. Then the same procedure has been made using the experimental results founded in this work. The different results of the two different correlations have an acceptable concordance. Different comparisons of the numerical and experimental results have been made for the frost growth always validating the results with the numerical simulations of the frost growth using both of the empirical correlations and comparing them with the experimental results that have been founded in this work and with other experimental results founded in the literature
Doutorado
Termica e Fluidos
Doutora em Engenharia Mecânica
28
Herselman, Jolandi. "Rate and yield dependency of Actinobacillus succinogenes on dissolved CO2 concentration." Diss., University of Pretoria, 2016. http://hdl.handle.net/2263/61295.
Full textAbstract:
Carbon dioxide serves as co-substrate in the production of succinic acid by Actinobacillus succinogenes. The transient concentration of dissolved CO2 in the broth (CCO2) controls the uptake of CO2 in the cell. Based on CCO2 , three distinct regimes could be identified in which the behaviour of the organism differed with CCO2 availability. When CCO2 was higher than 8.4 mM (44.4% saturated at an atmospheric pressure of 86 kPa), there was no evidence of CO2 limiting succinic acid productivity and flux to succinic acid remained constant. When CCO2 decreased below 8.4 mM a decrease in the succinic acid production and glucose consumption rates was observed to 28.01% and 19.89% of their original value respectively, at the lowest CCO2 value investigated. Below a CCO2 of 4 mM (21.16% saturated at an atmospheric pressure of 86 kPa), the productivity continued to decrease along with a shift in the total carbon flux from the succinic acid-producing pathway (C4-pathway) to the by-product-producing pathway (C3-pathway). The fraction of total carbon flux directed to the C4-pathway decreased from 0.48 to 0.33 at the lowest CCO2 value investigated. Although the by-product acetic acid concentration decreased to 88% of the original value, formic acid remained relatively stable and the ethanol concentration increased from an average of 0.26 g.L-1 to 1 g.L-1. The organism starts producing ethanol in order to satisfy the redox balance when the C4-pathway becomes less active. It was calculated that the flux shift to the C3-pathway does not favour ATP production. The organism is, however, still viable at the very low ATP production rates found at very low values of CCO2.
Since succinic acid production is not limited at relatively low values of CCO2 (44.4% saturation), adequate CO2 supply to the fermenter can be achieved without major CO2 sparging which is beneficial from an industrial processing perspective.Dissertation (MEng)--University of Pretoria, 2016.
Chemical Engineering
MEng
Unrestricted
29
Suprapto. "Étude et analyse de l'oxydation par l'ozone d'un effluent gazeux contenant de l'orthoxylène dans un réacteur gaz-liquide mécaniquement agité." Vandoeuvre-les-Nancy, INPL, 1995. http://www.theses.fr/1995INPL025N.
Full textAbstract:
Dans le but d'épurer un effluent gazeux contenant des teneurs faibles en orthoxylène, nous étudions un procédé chimique de traitement par l'ozone à température ambiante et sous la pression atmosphérique. L’air chargé en orthoxylène et l'oxygène ozone sont introduits séparément en continu dans un réacteur gaz-liquide mécaniquement agité. Le transfert de matière gaz-liquide spécifique du réacteur est étudié en déterminant d'une part le coefficient de transfert volumique partiel kLa par oxygénation dynamique de la phase liquide et d'autre part le coefficient de transfert volumique global KLa par traçage du gaz lors de l'absorption physique de l'orthoxylène dans l'eau. À partir de ces mesures, on peut estimer les coefficients de transfert volumiques kGa et KGa. La transformation chimique conduit à l'obtention de plusieurs produits non toxiques susceptibles d'être à leur tour oxydés en deux produits ultimes: l'anhydride carbonique et l'acide acétique. L’étude expérimentale portant sur l'influence de divers paramètres opératoires (concentrations des réactifs, vitesse d'agitation, débit d'air supplémentaire, température, pH du milieu réactionnel) montre que les réactions primaires ont lieu essentiellement dans le film liquide au contact des bulles d'oxygène ozone. Par suite, les étapes primaires sont limitées par le transfert gaz-liquide de l'ozone. Des améliorations du procédé ont été envisagées: en utilisant un système biphasique eau solvant fluorocarbone, en opérant en milieu aqueux en présence d'un catalyseur solide (charbon actif), enfin en stimulant la réaction par des rayonnements UV en présence ou non d'un photocatalyseur (TiO2). Les améliorations observées sont faibles et les résultats confirment le rôle prépondérant de la limitation du transfert de l'ozone sur la transformation de l'orthoxylène
30
Acunha, Júnior Ivoni Carlos. "Transferência de calor e massa de um condensador evaporativo em escala reduzida." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2010. http://hdl.handle.net/10183/27938.
Full textAbstract:
Este trabalho trata de um estudo experimental da transferência de calor e de massa de um condensador evaporativo, bem como, da relação existente entre as grandezas envolvidas durante a sua operação. Para o desenvolvimento da pesquisa foi construído um condensador evaporativo de pequeno porte com dimensões proporcionais a condensadores comercialmente fabricados no Brasil para operar com R-22 como fluido refrigerante. Este condensador tem 35 colunas e 12 fileiras de tubos de cobre de 6,35 mm de externo e opera junto a uma instalação que proporciona o escoamento de R-22 por termossifao. O distribuidor de água também foi construído em cobre e o eliminador de gotas em alumínio, assim como a estrutura do condensador. As laterais e a bandeja de recolhimento de água foram construídas em vidro para permitir a visualização do escoamento da água que e aspergida sobre os tubos. A fim de variar as condições operacionais, este condensador foi acoplado a um ventilador centrifugo acionado por um conversor de freqüência e a um circuito que permitiu a variação da vazão de água aspergida sobre os tubos. Dos ensaios resultaram 79 amostras de medição, que serviram para verificar a relação existente entre grandezas, bem como avaliar os coeficientes de transferência de calor e massa. Foram determinados os coeficientes de transferência de calor médio e local para o R-22. Alem disso, foram verificadas as regiões onde ocorrem o dessuperaquecimento, a mudança de fase e o subresfriamento do fluido refrigerante, e foram confrontados os coeficientes globais de transferência de calor obtidos a partir dos dados experimentais com aqueles obtidos por correlações para as regiões de condensação e subresfriamento. Destas investigações, resultou uma correlação para o coeficiente global de transferência de calor que visa determinar esta grandeza através das condições operacionais e das características geométricas do condensador. O Maximo desvio encontrado entre os valores provenientes dos dados experimentais e aqueles calculados pela correlação foi inferior a 10%.This work presents an experimental heat and mass transfer study of an evaporative condenser, as well as, the relationship between measured quantities obtained during its operation. A small scale evaporative condenser was built in agreement to the real size equipment geometric similarity. The small scale condenser has a bundle of 210 copper tubes, with the outer diameter equal to ¼ inch, which were arranged in 35 columns and 6 rows and operating connected to the thermosifon facility that promote R-22 flow. The spray water distributor is also built on copper and the drift eliminator on aluminum, as well as the evaporative condenser structure. This condenser bounds were constructed as a glass enclosure to allow for the spray water flow visualization. To evaluate the operational conditions, the equipment was attached to a centrifugal fan controlled by a frequency inverter and a spray water circuit which allows for water quantity changing. From the carried out tests, 79 measuring samples were obtained and used to verify the quantities relationship, as well as, to evaluate the heat and mass transfer coefficients For the R-22 were determined the local and average heat transfer coefficients. Furthermore, the dessuperheating, condensation and subcooling regions were verified and compared both, the experimental overall heat transfer coefficient and those calculated by correlations at condensation and subcooling zones. From these investigations a correlation for the overall heat transfer coefficient is proposed. Its application allows determining the coefficient using the operational conditions and the geometric condenser features. The higher deviation found between the experimental data and the presented correlation is lower to 10%.
31
Chiciuc, Igor. "Étude des paramètres affectant le transfert d'oxygène dans les vins." Thesis, Bordeaux 1, 2010. http://www.theses.fr/2010BOR14163/document.
Full textAbstract:
La micro-oxygénation des vins, par la dispersion de bulles d’oxygène, est une pratique de plus en plus utilisée dans le domaine de l’œnologie. Cette technique n’est pas toujours convenablement maitrisée par manque de connaissances scientifiques sur les paramètres régissant le transfert de l’oxygène. La recherche s'est focalisée sur l'étude des coefficients de transfert en fonction des composés du vin (CO2, éthanol, sucrose, consommateurs d’oxygène) et des conditions opératoires (type de diffuseur, température, rapport entre hauteur et diamètre du contenant de liquide). Les résultats montrent que lors de la micro-oxygénation, le dioxyde de carbone dissous et le sucrose ont une incidence négative sur le transfert alors que la présence d’éthanol améliore le transfert. En ce qui concerne les conditions opératoires, l’augmentation de débit de gaz et l’augmentation de rapport entre la hauteur et le diamètre de la cuve de micro-oxygénation joue positivement sur le transfert d’oxygène La surface spécifique des bulles et le coefficient de transfert de matière ont pu être dissociés pour les vins. La nature tensio-active des composés du vin semble être un élément important sur le transfert de matière. Les connaissances acquises ont été appliquées à la micro-oxygénation au cours de deux étapes de l'élaboration des vins : la fermentation alcoolique avec la maitrise de l’apport d’oxygène et la simulation de la technique d’élevage en barrique par micro-oxygénation couplée à l’ajout de copeaux de bois. Une nouvelle approche concerne l'étude d'un contacteur membranaire qui permet le transfert d’oxygène par diffusionMicro-oxygenation of the wines, by the dispersion of oxygen bubbles, is a practice increasingly used in oenology. This technique is not always suitably controlled for lack of scientific knowledge on the parameters governing the transfer of oxygen. Research was focused on the study of transfer coefficients in function of wine components (CO2, ethanol, sucrose, consuming oxygen) and of operating conditions (type of diffuser, temperature, relationship between height and diameter of the container of liquid). The results show that during micro-oxygenation, the dissolved carbon dioxide and the sucrose have a negative incidence on the transfer whereas the presence of ethanol improves the transfer. As operating conditions are concerned, the increase in gas output and the increase in micro-oxygenation tank height/diameter ratio positively influence oxygen transfer. For wines, the specific surface of the bubbles and the mass transfer coefficient could be dissociated. The surfactant nature of wine components seems to be the most important factor in mass transfer. The knowledge so acquired was applied to micro-oxygenation during two stages of wine making: alcoholic fermentation with the oxygen yield control and the simulation of ageing technique in barrels coupled with the wood chips addition. A new approach relates to the study of a membrane contactor application allowing the oxygen transfer by diffusion
32
Kombo, Rainah. "Qualitative analysis of flow patterns : two-phase flow condensation at low mass fluxes and different inclination angles." Diss., University of Pretoria, 2016. http://hdl.handle.net/2263/61303.
Full textAbstract:
A great deal of work has been conducted on in-tube condensation in horizontal and vertical smooth tubes. The available literature points to mechanisms governing two-phase condensation heat transfer coefficients and pressure drops, which are directly linked to the local flow pattern for both horizontal and inclined configurations. However, the work has been limited to flow pattern observations, heat transfer, pressure drops and void fractions for both horizontal and inclined tubes at high mass fluxes. No work has been conducted on the analysis of the observed flow patterns and the effect of temperature difference between the average wall temperature and average saturation temperature for different inclination angles at mass fluxes of 100 kg/m2.s and below. The purpose of this study is to carry out a qualitative analysis of flow patterns, and show the effect of temperature difference on the heat transfer coefficient for inclination angles from +90° (upward flow) to -90° (downward flow) at mass fluxes below 100 kg/m2.s. An experimental set-up provided the measurements for the two-phase condensation of R-143a in a smooth tube with an inside diameter of 8.38 mm and a length of 1.5 m. The mass fluxes were 25 kg/m2.s to 100 kg/m2.s, the saturation temperature was 40 °C and the mean qualities were 0.1 to 0.9. A high-speed camera was used to visually analyse and determine the flow patterns for both the inlet and the outlet of the test section. Through the results, eight flow patterns were observed: stratified-wavy, stratified, wavy, wavy-churn, intermittent, churn, annular and wavy-annular. The maximum heat transfer was observed for downward flow between inclination angles of -15° and -30°. The Thome-Hajal flow pattern map correctly predicted horizontal flow patterns, but failed to predict most of the inclined flow patterns. Various flow pattern transitions were identified and proposed for all the investigated inclination angles in this study. Finally, the heat transfer coefficient was found to be dependent on quality, mass flux, temperature difference and inclination angle.Dissertation (MSc)--University of Pretoria, 2016.
Mechanical and Aeronautical Engineering
MSc
Unrestricted
33
Monnerat, Sandra Mourão. "Desidratação osmotica e secagem convectiva de maçã : transferencia de massa e alterações de estrutura celular." [s.n.], 2009. http://repositorio.unicamp.br/jspui/handle/REPOSIP/256446.
Full textAbstract:
Orientador: Florencia Cecilia MenegalliTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos
Made available in DSpace on 2018-08-13T18:52:37Z (GMT). No. of bitstreams: 1 Monnerat_SandraMourao_D.pdf: 2359962 bytes, checksum: 3df7969a948ecae9b1a169de42e7087a (MD5) Previous issue date: 2009
Resumo: No presente trabalho investigou-se a desidratação osmótica de maçãs (variedade Fuji), seguida ou não de secagem convectiva com ar quente. Foram determinados perfis de concentração de água e soluto(s) em amostras de maçãs cortadas ao meio e desidratadas osmoticamente em soluções aquosas binárias (30% e 50% de sacarose, p/p) e solução ternária (50% de sacarose e 10% de cloreto de sódio, m/m), sob agitação vigorosa e temperatura constante (27°C). As amostras imersas na solução osmótica durante 2, 4 e 8 h foram fatiadas a partir da superfície plana exposta. A densidade e os teores de água, açúcares totais e redutores e cloreto de sódio foram determinados em cada fatia. O modelo matemático que descreve o transporte de cada espécie estudada (água, sacarose e cloreto de sódio) se baseia na equação de continuidade e na Lei de Fick e considera o encolhimento do tecido. O modelo foi ajustado aos dados experimentais, através do método implícito de diferenças finitas de Crank-Nicolson para determinar os coeficientes efetivos de difusão como uma função da concentração, utilizando coordenadas materiais e integrando simultaneamente as equações diferenciais de cada componente (água e sacarose ou água, sacarose e cloreto de sódio). Imagens de microscopia ótica de tecidos tratados osmoticamente, previamente pigmentados com o corante vital vermelho neutro, foram obtidas variando-se a concentração das soluções e o tempo de exposição. Os registros fotográficos retratam alterações da estrutura celular, que variam de acordo com a intensidade do processo de desidratação. A secagem convectiva com ar quente foi realizada em amostras de maçãs cortadas ao meio, frescas e previamente tratadas em solução aquosa de sacarose a 50% p/p durante 4 horas (27°C). Os perfis de umidade foram determinados a partir da superfície, após a exposição da face plana das metades das maçãs ao fluxo de ar quente (60°C ) durante 3, 6, 10 e 24 horas de secagem. O modelo matemático que descreve o transporte da água se baseia nas equações de continuidade e na Lei de Fick e considera o encolhimento do tecido e a concentração inicial não homogênea para o tecido previamente tratado. De maneira similar à desidratação osmótica, a difusividade de água na secagem também foi determinada em função da concentração, utilizando-se o método implícito de diferenças finitas de Crank-Nicolson e coordenadas materiais. Obtevese um bom ajuste dos modelos matemáticos aos dados experimentais de desidratação osmótica e de secagem. A ordem de magnitude dos coeficientes obtidos para a desidratação osmótica foi uma ou duas vezes menor que de coeficientes de difusão binários de soluções puras de sacarose e de cloreto de sódio. No caso da secagem, o comportamento da difusividade mostrou dependência significativa com a concentração de água. O tecido fresco apresentou coeficientes superiores aos do tecido pré-tratado osmoticamente além de funcionalidades distintas para diferentes tempos de secagem (inferior e superior a 6 horas). O tecido tratado apresentou um comportamento mais estável da difusividade da água no material e foi descrito por uma única função. Este fato está relacionado com as mudanças estruturais ocorridas durante a secagem, mais severas para o tecido fresco em relação ao tecido tratado
Abstract: In this study it was investigated the osmotic dehydration of apples (Fuji variety) followed or not by convective drying with hot air. Concentration profiles were determined for water and solute(s) in samples of apples cut in half and osmotically dehydrated in binary aqueous solutions (30% and 50% sucrose, w/w) and ternary solution (50% sucrose and 10% sodium chloride, w/w) under vigorous stirring and constant temperature (27°C). The samples immersed in the osmotic solution for 2, 4 and 8 h were sliced from the exposed flat surface. The density and water, total and reducing sugars and sodium chloride contents were determined in each slice. The mathematical model that describes the transport of each species studied (water, sucrose and sodium chloride) is based on the continuity equation and on the of Fick's diffusion law and considers the tissue shrinkage. The model was fitted to experimental data through the finite difference implicit method of Crank-Nicolson, to determine the effective diffusion coefficients as a function of concentration, using material coordinates and integrating simultaneously the differential equations of each component (water and sucrose or water, sucrose and sodium chloride). Light microscopy images of osmotically processed tissues previously pigmented with the vital dye neutral red, were obtained, varying the concentration of solutions and time of exposure. The photographic records show changes in cellular structure, which vary with the intensity of the dehydration process. The convective air drying was carried out on samples of apples cut in half, fresh and treated in aqueous solution of sucrose to 50% w/w for 4 hours (27°C). The moisture profiles were determined from the surface, after exposure of the flat face of half of the apples to the flow of hot air (60 ° C) during 3, 6, 10 and 24 hours of drying. The mathematical model that describes the water transport is based on the continuity equation, the Fick's diffusion law, the tissue shrinkage and the nonhomogeneous initial concentration of the previously treated tissue. Similarly to the osmotic dehydration, the water diffusivity in drying was also determined in terms of concentration, using the finite difference implicit method of Crank-Nicolson and coordinated materials. It was possible to obtained a good fit of mathematical models to experimental data of osmotic dehydration and drying. The order of magnitude of the coefficients obtained for the osmotic dehydration was one or two times lower than diffusion coefficients of pure binary solutions of sucrose and sodium chloride. For drying, the behavior of diffusivity showed significant dependence with the concentration of water. The fresh tissue showed coefficients greater than the osmotically pre-treated tissue than it needs distinct functions for different times of drying (and less than 6 hours). The treated tissue showed a more stable behavior of the water diffusivity in the material and was described by a single function. This fact is related to the structural changes during drying, more severe for the fresh tissue than for the treated tissue
Doutorado
Doutor em Engenharia de Alimentos
34
Hudjetz, Stefan. "Experimental investigation of heat exchange between thermal mass and room environments." Thesis, De Montfort University, 2012. http://hdl.handle.net/2086/9021.
Full textAbstract:
The different technologies of passive cooling concepts have to rely on a good thermal coupling between a building's thermal mass and indoor air. In many cases, the ceiling is the only surface remaining for a good coupling. Further research is necessary to investigate discrepancies between existing correlations. Therefore, the overall aim of the work described in this thesis is the investigation of heat transfer at a heated ceiling in an experimental chamber. Acoustic baffles obstruct the surface of the ceiling and impede heat transfer. However, there is nearly no published data about the effect of such baffles on heat transfer. Available results from simulations should be verified with an experimental investigation. Consequently, one of the primary aims of this work was to experimentally determine the influence of such acoustic baffles. A suitable experimental chamber has been built at Biberach University of Applied Sciences. The thesis describes the experimental chamber, the experimental programme as well as results from five different test series. With a value of ±0.1Wm⁻²K⁻¹ for larger temperature differences, uncertainty in resulting convective heat transfer coefficients for natural convection is comparable to that of results from an existing recent experimental work often recommended for use. Additionally, total heat transfer (by convection and radiation) results are presented. Results are given for natural, forced and mixed convection conditions at an unobstructed heated ceiling. Furthermore, results for acoustic baffles in both an unventilated and a ventilated chamber are shown. Natural convection results show a very good agreement with existing correlations. Under mixed convection conditions, convective heat transfer at an unobstructed ceiling decreases to the limiting case described by natural convection. Installation of acoustic baffles leads to a reduction in total heat transfer (convection and radiation) between 20% and 30% when compared to the case of an unobstructed ceiling.
35
Gonçalves, Daniel. "Estudo do processo de desterpenação de óleos essenciais cítricos: dados de equilíbrio líquido- líquido e extração em coluna de discos rotativos perfurados." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/74/74132/tde-23052013-115453/.
Full textAbstract:
Os óleos essenciais cítricos possuem uma ampla variedade de aplicações em diversos ramos das indústrias químicas, farmacêuticas, de alimentos, entre outras. Na indústria de cosméticos, mais precisamente no ramo de perfumaria, os ativos naturais cítricos (provenientes dos óleos de bergamota, limão, lima, mandarina, laranja, etc) são empregados nas formulações de colônias, cremes hidratantes e loções. Além disso, estes compostos são largamente utilizados como agentes aromatizantes nas indústrias alimentícias e farmacêuticas e empregados como matéria-prima para as indústrias de aromas. Com o objetivo de melhorar a qualidade dos óleos essenciais e sua capacidade aromatizante, alguns processos têm sido desenvolvidos para enriquecer a mistura com compostos oxigenados, os quais são reportados como os principais responsáveis pelo aroma característico da fruta. Tal processo é comumente conhecido como desterpenação e consiste na concentração destes compostos pela retirada de hidrocarbonetos terpênicos do óleo e pode ser realizado por meio da extração líquida ou extração por solvente. Neste contexto, esta dissertação de mestrado teve como finalidade estudar da viabilidade técnica do processo de desterpenação de óleo essencial cítrico modelo composto por limoneno e linalol. Os experimentos foram conduzidos em coluna de discos rotativos perfurados (PRDC) sob condição de temperatura controlada e pressão ambiente local. O equipamento operou de modo contínuo e contracorrente, utilizado como solventes soluções de etanol com teores de água de 30 e 40% (em massa), velocidade de rotação dos discos de 150, 200 e 250 rpm e razão entre a vazão mássica de solvente e alimentação de 0,5; 1,25; 2,5 e 3,0. Avaliou-se, também, o comportamento da densidade e viscosidade das fases extrato e rafinado oriundas da coluna de extração. Através deste estudo foi possível verificar que a tecnologia de desterpenação de óleos essenciais por meio da extração líquido-líquido é viável podendo ser aplicada à processos contínuos utilizando equipamento PRDC, por exemplo, sendo possível a obtenção de frações enriquecidas do composto oxigenado (linalol).Citrus essential oils are used in a wide variety of applications in various branches of the chemical, pharmaceutical, food and other industries. In the cosmetics industry, specifically in the field of perfumery, natural citrus assets (from the essential oils of bergamot, lemon, lime, mandarin, orange, etc.) are used in the formulations of colonies, moisturizing creams and lotions. Furthermore, these compounds are widely used as flavoring agents in food and pharmaceutical industries and as raw material for the flavor industry. With the aim to improve the quality of essential oils and its flavoring ability, some processes have been developed to enrich the mixture with oxygenated compounds, which are reported as the main responsible for the characteristic aroma of the fruit. Such process is commonly known as deterpenation, and consists in concentration of these compounds by the removal of terpene compounds from the essencial oil and can be performed by liquid or solvent extraction. In this context, the purpose of this dissertation of master\'s degree was to carry out a study of the technical feasibility of deterpenation process of a citrus essential oil model composed by a mixture of limonene and linalool. The experiments of deterpenation were conducted in a perforated rotating discs contactor (PRDC) under controlled conditions of temperature and local environment al pressure. The equipment was operated in continuously and countercurrently mode, using as solvents ethanol solutions with 30 and 40% of water contents (by mass), rotation of discs speed of 150, 200 and 250 rpm and the mass flow rate of the solvent and feed ratio of 0.5, 1.25, 2.5 and 3.0. The behavior of the density and viscosity of the extract and raffinate phases from the extraction column was also evaluated. It was found that the deterpenation of essential oils by liquid-liquid extraction technology is feasible and can be applied to continuous processes using PRDC column extraction type, for instance, being possible to obtain enriched fractions of oxygenated compounds (linalool).
36
Khalfi, Mohammed-Seghir. "Étude de l'influence de l'humidité de l'air sur le coefficient de transfert de chaleur d'une batterie froide en présence ou non de condensation." Nancy 1, 1998. http://www.theses.fr/1998NAN10294.
Full textAbstract:
Les objectifs de ce travail expérimental portent, d'une part, sur la caractérisation d'une batterie froide lors d'un refroidissement d'air avec ou sans condensation et d'autre part sur l'étude de l'influence de l'humidité de l'air sur le coefficient de transfert de chaleur. Son originalité consiste à explorer un nouveau paramètre susceptible d'influencer le coefficient de transfert de chaleur. Dans le but de déterminer la fraction de la surface d'échange concernée par la condensation, nous avons mis au point un modèle qui permet de calculer la température de la surface d'échange en décomposant l'échangeur en petits éléments.
37
Alghamdi, Majed Mohammed. "Investigations into long-standing problems in radical polymerization kinetics : chain-length-dependent termination rate coefficient and mode of termination." Thesis, University of Canterbury. Chemistry, 2014. http://hdl.handle.net/10092/10028.
Full textAbstract:
The present thesis investigates some long standing problems in radical polymerization (RP). The major aim is to consider the feasibility of using simple techniques to provide more insight into the kinetics of RP. This can contribute to fundamental knowledge of radical polymerizations, particularly with respect to the mode of termination (λ), average termination rate coefficient (
38
Gervais, Aroquiaradj. "Étude de l'hydrodynamique et du transfert de matière gaz/liquide dans les lits fluidises tri phasiques : application aux lits fluidises tetraphasiques." Vandoeuvre-les-Nancy, INPL, 1993. http://www.theses.fr/1993INPL084N.
Full textAbstract:
Si le design des colonnes a bulles est assez bien connu en général, celui des lits fluidises triphasiques requiert encore des études plus poussées. L'objectif de cette thèse est de mener une étude couplée de l'hydrodynamique et du transfert de matière gaz/liquide dans les lits fluidises triphasiques. Une nouvelle procédure d'étalonnage d'une sonde électroconductive dans un milieu triphasique a été mise au point. Ceci permet de déterminer les profils axiaux de rétention des phases. L'équation d'étalonnage tient compte de la composition et de la nature des phases dispersées. Quant au transfert gaz/liquide, le modèle de dispersion axiale du liquide généralement utilisé, suppose une ségrégation du réacteur en lit fluidise et freeboard. Cette hypothèse est remise en question par des expériences du traceur qui démontrent un retromélange du liquide à l'interface lit/freeboard. L'impact de ce retro-mélange sur le coefficient de transfert gaz/liquide est étudié en utilisant l'équation de dispersion axiale a coefficient k#l#a et d#z fonctions de la hauteur z. Les procédures développées pour le système triphasique sont appliqués a un lit fluidise tétraphasique gaz/slurry/particules du lit, l'objectif étant de démontrer l'efficacité d'un lit à améliorer le k#l#a d'une colonne a bulles avec slurry
39
Mouawad, Charbel Desobry Stéphane. "Transfert de matière dans un système solide/liquide "ions/eau/pectine" interactions, partage ionique et simulation par dynamique moléculaire /." S. l. : S. n, 2007. http://www.scd.inpl-nancy.fr/theses/2007_MOUAWAD_C.pdf.
Full text
40
Hudson, Neale Alan. "Investigation of mechanisms governing emission of odorants." Thesis, Queensland University of Technology, 2009. https://eprints.qut.edu.au/32001/1/Neale_Hudson_Thesis.pdf.
Full textAbstract:
The literature identifies several models that describe inter-phase mass transfer, key to the emission process. While the emission process is complex and these models may be more or less successful at predicting mass transfer rates, they identify three key variables for a system involving a liquid and an air phase in contact with it:
• A concentration (or partial pressure) gradient driving force;
• The fluid dynamic characteristics within the liquid and air phases, and
• The chemical properties of the individual components within the system.
In three applied research projects conducted prior to this study, samples collected with two well-known sampling devices resulted in very different odour emission rates. It was not possible to adequately explain the differences observed. It appeared likely, however, that the sample collection device might have artefact effects on the emission of odorants, i.e. the sampling device appeared to have altered the mass transfer process. This raised the obvious question:
Where two different emission rates are reported for a single source (differing only in the selection of sampling device), and a credible explanation for the difference in emission rate cannot be provided, which emission rate is correct?
This research project aimed to identify the factors that determine odour emission rates, the impact that the characteristics of a sampling device may exert on the key mass transfer variables, and ultimately, the impact of the sampling device on the emission rate itself.
To meet these objectives, a series of targeted reviews, and laboratory and field investigations, were conducted. Two widely-used, representative devices were chosen to investigate the influence of various parameters on the emission process. These investigations provided insight into the odour emission process generally, and the influence of the sampling device specifically.
41
Forestier, Serge. "Etude de l’évaporation d’un liquide répandu au sol suite à la rupture d’un stockage industriel." Thesis, Saint-Etienne, EMSE, 2011. http://www.theses.fr/2011EMSE0625/document.
Full textAbstract:
Ce travail de thèse s'inscrit dans le cadre d'un projet de recherche entre le CEA et ARMINES (Centre LGEI/ Ecole des Mines d'Alès). Il vise à améliorer la connaissance des mécanismes physiques se produisant lorsque qu’une nappe de liquide (inflammable et/ou toxique stocké à pression atmosphérique) s’évapore suite à la rupture de son stockage. La démarche expérimentale employée consiste à réaliser un plan d'expériences visant à exprimer le débit d'évaporation initial d’une nappe sous différentes conditions initiales de température de liquide et de sol, sous différentes vitesse d’écoulement, de température d’air et selon différentes épaisseurs initiales de liquide. Les différents flux thermiques échangés entre la nappe et son environnement, la température de la nappe et le débit d'évaporation sont mesurés et quantifiés.Les débits d'évaporation expérimentaux sont confrontés à ceux prédits par les différentes corrélations disponibles dans la littérature. Deux analyses de sensibilité sont également réalisées sur ces corrélations et les résultats confrontés à ceux du plan d'expériences afin de vérifier si les corrélations attribuent le même poids aux différents paramètres expérimentaux que le phénomène en lui-même.Les relevés de température dans l'épaisseur de la nappe mettant en évidence la présence de cellules de convection naturelle est également étudiée. Par ailleurs, la température moyenne de la surface est déterminée à partir des différents flux thermiques échangés entre la nappe et son environnement.A l'aide des résultats obtenus, l'étude de plusieurs éléments a été réalisée: l’écart de prédiction sur les résultats des équations bilan thermique et massique selon la température employée pour les incrémenter, la nette différence de température entre la surface et le coeur du liquide, rarement prise en compte dans les modèles théoriques, le rôle prépondérant de la convection naturelle dans le phénomène d'évaporation.Un dernier chapitre étudie la dispersion de la température de surface (phénomène peu étudié dans la littérature) à l'aide d'une caméra thermique. Des zones de températures homogènes apparaissent alors dans le cas de l'essai mettant en oeuvre un écoulement de cavité au-dessus du liquide. La présence de différentes zones de température implique que la cinétique d’évaporation n’est pas uniforme sur la surface de la nappe. A partir de ces résultats, le coefficient de transfert de matière est étudié en fonction de la régression du niveau de liquide dans le bac et conclut à une diminution non modélisée par les corrélations existantesThis work belongs to a research project between CEA and ARMINE (LGEI center/ Ecole des Mines d’Alès). It aims at increasing comprehension of physical mechanism generating when a liquid pool (either flammable or toxic parked under atmospheric pressure) evaporates after loss of containment. An experimental design is realized in order to express some characteristics of evaporation phenomena (initial evaporation rate, steady evaporation rate and duration of unsteady evaporation rate) as a function of initial liquid and soil temperature, wind velocity, air temperature and initial liquid thickness. Heat fluxes exchanged between the pool and its environment are either measure or computed.Experimental evaporation rates are compared to those predicted by correlations available in the literature. Two sensitivity analyses are performed and their results are confronted to those from experimental design. It allows determining if the importance of the different experimental parameters is the same from the correlations to the phenomena itself.Temperature measurements in liquid thickness highlight the presence of natural convection cells. Besides, mean surface temperature is computed from measurements of heat fluxes exchanged between the pool and its environment. From the different results, several points are investigated: the shift between heat and mass balance equations according to the temperature employed to compute them the difference between the liquid bulk and liquid surface temperature, barely taken into account in correlations the noteworthy role of natural convection in the evaporation phenomena.A last chapter studies the surface temperature distribution thanks to an infrared thermometer. Homogeneous temperatures areas appear in the case of cavity flows. The presence of different temperature areas implies that evaporation kinematic in not uniform in the whole surface. From these result the mass transfer coefficient is studied as a function of the step height between the top of the cavity and the liquid surface. It concludes to a mass transfer coefficient decrease non modeled by the different correlations in the literature
42
Darne, Raphaëlle. "Etude photophysique des transferts pariétaux." Vandoeuvre-les-Nancy, INPL, 1996. http://docnum.univ-lorraine.fr/public/INPL_T_1996_DARNE_R.pdf.
Full textAbstract:
L’objectif de la recherche est la mise au point d'un capteur photophysique pour l'étude des phénomènes de transfert de matière en milieu biphasique gaz-liquide. Le principe repose sur l'inhibition de fluorescence de molécules greffées sur le capteur, par l'oxygène dissous dans l'eau. La variation d'intensité de fluorescence est une fonction linéaire de la concentration en oxygène, celle-ci étant elle-même reliée au coefficient de transfert volumique, kLa. Dans ce but, deux actions principales ont été développées: - la réalisation et l'étude de la fixation chimique de la molécule fluorescente sur une surface plane en silice: l'acide 4-(1-pyrenyl)butyrique a été choisi comme fluorophore pour sa forte réactivité vis-à-vis de l'oxygène. Différentes conditions de greffage ont été testées pour déterminer l'influence de divers paramètres (quantité d'eau, présence de catalyseur, type de surface) et leurs actions analysées de manière qualitative (utilisations de techniques d'analyse de surface: microscopie par fluorescence, microscopie à force atomique (de cisaillement ou de friction), ) et quantitative (fluorimétrie). L’utilisation d'un post-traitement, jouant sur la désorption, a permis de dégager un modèle cinétique. - La mise au point du capteur: la détermination de la droite de Stern-Vollmer (If=f(O2)) en milieu statique et dynamique et les essais dans le milieu biphasique gaz-liquide ont permis de déterminer le coefficient kLa
43
Voisin, Laurent. "Nitration du mononitrochlorotertiobutylbenzene en reacteurs diphasiques liquide-liquide." Paris, ENMP, 1988. http://www.theses.fr/1988ENMP0102.
Full text
44
Rech, Fernanda Roberta. "Efeito do uso de glicerol residual e carreadores de oxigênio sobre a produção de lipases de Staphylococcus warneri EX17." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2011. http://hdl.handle.net/10183/29523.
Full textAbstract:
A transferência de oxigênio é um fator limitante para grande parte dos cultivos em biorreatores que operam com organismos estritamente aeróbios devido à baixa solubilidade do oxigênio em meios de cultivo. A introdução de meios não convencionais, como polidimetilsiloxanos (PDMS), em biorreatores pode ser vista como uma melhoria para o ajuste desses processos. Este trabalho propõe uma investigação do emprego de polidimetilsiloxano fluido e emulsificado, usados como carreadores de oxigênio, em meios de cultivo na produção de lipases de Staphylococcus warneri EX17, cepa capaz de utilizar glicerol residual como substrato, visando melhorar a disponibilidade de oxigênio e aperfeiçoar a produtividade. Inicialmente, foram realizados estudos para selecionar o uso de glicerol residual, oriundo da síntese química de biodiesel como fonte de carbono. A atividade lipolítica foi semelhante com glicerol comercial e residual. Após a seleção do glicerol foram realizados experimentos em incubadora rotatória horizontal nas condições previamente otimizadas em trabalhos anteriores do grupo, adicionando PDMS. Dois tipos de PDMS foram testados, fluido e emulsificado. A produção de lipase foi significativamente maior no meio contendo PDMS. Assim, ferramentas de planejamento experimental, delineamento composto central (DCC) foram utilizadas para verificar a influencia do PDMS no coeficiente de transferência de oxigênio kLa em meio de cultivo produtor de lipase livre de células. O kLa aumentou significativamente no meio de cultivo contendo PDMS. Dois novos planejamentos foram desenhados, para otimizar a produção de lipase em meio de cultivo com células. Um para PDMS fluido e outro para PDMS emulsificado. No meio contendo PDMS fluido, a atividade lipolítica foi cinco vezes maior, enquanto que no meio contendo silicone emulsificado a atividade lipolítica foi três vezes maior. Este estudo demonstrou que a lipase de S. warneri EX17 pode ser produzida utilizando glicerol residual como fonte de carbono, e polidimetilsiloxanos como carreadores de oxigênio aumentando a transferência de oxigênio no meio e elevando a produção da enzima, que apresenta diversas possibilidades de aplicação, principalmente na indústria de alimentos.The oxygen transfer is a limiting factor in many bioreactors cultivations, in which strictly aerobic organisms are grown due to the low solubility of oxygen in culture media. The introduction of unconventional media, such as polydimethylsiloxanes (PDMS) in bioreactors can be seen as a potential improvement for these processes. This work proposes an investigation of the use of polydimethylsiloxane in its two forms, fluid and emulsified, used as carriers of oxygen in culture media for the lipase production of Staphylococcus warneri EX17, strain capable of using glycerol as substrate, to improve the oxygen availability and improve enzyme productivity. Initially, studies were performed to select the use of residual glycerol, derived from the chemical synthesis of biodiesel as a source of carbon. The lipase activity was similar in both commercial and residual glycerol. Experiments were performed on orbital shaker, using conditions previously optimized in another work of the group, but with the addition of PDMS. Two types of PDMS were tested, the fluid and the emulsified. The lipase production was significantly higher in medium containing PDMS. Experimental design and central composite design (CCD) were used to evaluate the influence of PDMS on the oxygen transfer coefficient kLa in culture medium free of lipase-producing cells. The kLa increased significantly in the medium containing PDMS. Two new experimental plannings were designed to optimize the production of lipase in culture medium with cells. In the medium containing the PDMS fluid lipase activity was five times higher than medium without the oxygen carrier, while in the medium containing the emulsified silicone lipase activity was three times higher. This study showed that the lipase from S. warneri EX17 can be produced using residual glycerol as carbon source and that polydimethylsiloxanes works as interesting carrier of oxygen by increasing oxygen transfer rates, improving enzyme production, which has several possible applications, especially in the food industry.
45
Бучковец, С. А., С. Н. Романько, and С. В. Тимофеев. "Определение коэффициента массоотдачи при концентрировании серной кислоты испарением в токе воздуха." Thesis, Сумский государственный университет, 2017. http://essuir.sumdu.edu.ua/handle/123456789/66544.
Full textAbstract:
Перспективным способом концентрирования серной кислоты, особенно для
малотоннажных производств, является способ, в котором кислота нагревается через
стенку аппарата, а испарение происходит в поток нейтрального газа (воздуха) [1].
Такой способ позволяет проводить концентрирование при температуре ниже
температуры кипения кислоты и соответственно использовать низкотемпературные
теплоносители для ее нагревания [2]. Одним из основных явлений, определяющих
процесс концентрирования серной кислоты, в этом случае является массоперенос от
жидкой фазы в движущуюся газовую (парогазовую) фазу. Его особенность связана со
свойствами самой серной кислоты и наличием потока нейтрального газа (воздуха).
Интенсивность массопереноса при концентрировании серной кислоты характеризуется
экспериментально определяемым коэффициентом массоотдачи от жидкой фазы в
газовый поток.
46
Nair, Arthur William. "Investigation of the Effects of Sequential Anaerobic, Anoxic and Aerobic Zones on Dissolved Oxygen Transfer Parameters in a biological Nutrient Removal Pilot Plant." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/46264.
Full textAbstract:
Bench and pilot scale determinations of the volumetric oxygen transfer coefficient, KLa, were performed on an improved A²/O biological nutrient removal (BNR) pilot plant. Effluent from a full scale primary clarifier, used as pilot plant influent, was found to have an alpha (ratio of process to clean water KLa) of 0.71 as determined in a 21 liter bench scale reactor and an alpha of 0.332 as determined in a 0.45 m³ aeration basin of the 2.4 m³ pilot plant. Alpha of a 1:1 mixture of primary clarifier effluent with pilot plant return activated sludge was determined to be 0.94 at bench scale and 0.71 at pilot scale. An assay of alphas through the initial non aerated treatment zones of the pilot plant using the bench scale reactor indicated that alphas peaked in the effluent of the first anaerobic zone (alpha equal to 1.01) and were lower in the second anaerobic zone and first anoxic zone. An assay of alphas in the three pilot plant series sideline aeration basins indicated that alpha was maximum in the first aeration basin (alpha equal to 0.905) and were lower in the second and third aeration basins (0.716 and 0.661 respectively). A consistent increase in average surface tension was noted from the first to second to third aeration basins, however the differences were not statistically significant. A comparison of pilot plant alphas determined in the first aeration basin following anaerobic nominal hydraulic retention times of 0.0, 0.21, 0.43, and 0.64 hours yielded alpha values of 0.71, 0.94, 0.64, and 0.74 respectively. Like the assay using the bench scale reactor, the alpha values at pilot scale peaked following treatment in only one anaerobic zone (nominal HRT of 0.21 hours). The study concludes that short exposures in an initial anaerobic reactor as required for biological phosphorus removal may benefit oxygen transfer efficiency through increased alphas, however the benefits of long periods of anaerobic reaction time (over 0.43 hours) are uncertain.Master of Science
47
Lin, Kang-Yi. "The Dissolution of Iron from Automotive Steel Sheets in a Molten Zinc Bath and the Kinetics of the Nucleation and Growth of Dross Particles." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1307733545.
Full text
48
Maquinghen, Térence. "Métrologie tridimensionnelle instationnaire à l'aide de la méthode polarographique." Valenciennes, 1999. https://ged.uphf.fr/nuxeo/site/esupversions/07406958-6321-4944-97bf-22735cc5a6a8.
Full textAbstract:
L'objectif de ce travail est la mesure du frottement pariétal à l'aide de la méthode polarographie. Pour cela, une description de la méthode polarographique et du matériel nécessaire à son utilisation a été réalisée. Une étude bibliographique a été faite permettant la synthèse des travaux précédents. Devant la dispersion des résultats sur la détermination de l'inertie introduite par les sondes simples et différentielles, il a été nécessaire de compléter ces études par une modélisation numérique du comportement de ces capteurs validée par des études expérimentales. C'est pourquoi, la sensibilité des sondes au module et à la direction du gradient de vitesse a été étudiée, complétée par une étude de l'influence des défauts des surfaces actives des électrodes sur la réponse des sondes. L'inertie introduite par ces capteurs dans les mesures a été déterminée numériquement et expérimentalement. Le calcul a été réalisé dans le cas d'un écoulement tridimensionnel instationnaire. Le champ de concentration a été résolu directement sans être linéarisé. Le modèle expérimental est un dièdre insère dans un écoulement instationnaire. A l'aide de la méthode de transfert de masse inverse, le frottement pariétal au voisinage du point de décollement de la couche limite se développant sur un cylindre a été déterminé, montrant l'intérêt de cette méthode.
49
Fyferling, Mathias. "Transfert d'oxygène en condition de culture microbienne intensive." Toulouse, INSA, 2007. http://eprint.insa-toulouse.fr/archive/00000172/.
Full textAbstract:
L'objectif des travaux est la quantification et la modélisation du transfert d’oxygène en condition de production microbienne afin de contribuer à l’intensification des performances des bioprocédés. Les travaux expérimentaux sont réalisés en bioréacteur, en milieux minéraux exempt de réaction biologique, puis lors de cultures fed-batch d’Escherichia coli, Saccharomyces cerevisiae et Aspergillus niger. Le domaine d'investigation est original de par les fortes consommations volumiques d’oxygène (0,6 g. L-1. H-1) et puissances dissipées (35 kW. M-3) utilisées. Le coefficient de transfert d’oxygène est déterminé à l'aide de différents modèles non structurés (pour la prise en compte du mode d’écoulement des phases, de l’entraînement de surface et de la rétention gazeuse sur des régimes transitoires ou permanents. Il est notamment observé que, en présence de réaction biologique, (i) les valeurs du coefficient de transfert KT sont 5 à 10 fois supérieures à celles mentionnées dans la littérature relative au transfert d’oxygène, (ii) par comparaison aux milieux de culture avant ensemencement, KT et KL (la conductance de transfert) sont divisés d’un facteur 4 à 6. Les effets de l'activité cellulaire sur le transfert d'oxygène sont caractérisés par la quantification des facteurs d'accélération relatifs aux modifications chimiques du milieu, à la consommation d'oxygène, et à la présence physique de cellules. Les limites des modèles du transfert d'oxygène en culture microbienne intensive sont discutées, et des nouvelles voies d'investigation sont proposéesThis work aims to quantify and model oxygen transfer in microbial cultures with an objective of intensification of bioprocess performances. Labworks in bioreactors are achieved in mineral media, free from biological reaction, then in fed-batch cultures of Escherichia coli, Saccharomyces cerevisiae and Aspergillus niger. The fieldwork is original because of the high oxygen consumptions rates (0,6 g. L-1. H-1) and the high dissipated power (35 kW. M-3) used. The oxygen transfer coefficient is determined from continuous and dynamic methods, using several unstructured models, to take into account the profile of the dispersed gaseous flow, the gas entrained from the surface, and hold-up. Among the observations, in biological media, (i) values of the oxygen transfer coefficient KT are 5 to 10 times higher than values from the literature on oxygen transfer, (ii) compared with the initial medium prior to inoculation, KT and KL (the oxygen transfer conductance) are 4 to 6 times smaller. Effects of microbial activity on oxygen transfer are characterised and quantified according to enhancements factors related to chemical modifications of the medium, oxygen consumption, and physical presence of cells. Limits of mass transfer models in intensive microbial cultures are discussed and new areas of investigation are proposed
50
Derdar, Mawaheb M. Zarok. "Experimental and kinetic modelling of multicomponent gas/liquid ozone reactions in aqueous phase. Experimental investigation and Matlab modelling of the ozone mass transfer and multicomponent chemical reactions in a well agitatated semi-batch gas/liquid reactor." Thesis, University of Bradford, 2010. http://hdl.handle.net/10454/4872.
Full textAbstract:
Due to the ever increasing concerns about pollutants and contaminants found in water, new treatment technologies have been developed. Ozonation is one of such technologies. It has been widely applied in the treatment of pollutants in water and wastewater treatment processes. Ozone has many applications such as oxidation of organic components, mineral matter, inactivation of viruses, cysts, bacteria, removal of trace pollutants like pesticides and solvents, and removal of tastes and odours. Ozone is the strongest conventional oxidant that can result in complete mineralisation of the organic pollutants to carbon dioxide and water. Because ozone is unstable, it is generally produced onsite in gas mixtures and is immediately introduced to water using gas/liquid type reactors (e.g. bubble columns). The ozone reactions are hence of the type gas liquid reactions, which are complex to model since they involve both chemical reactions, which occur in the liquid phase, and mass transfer from the gas to the liquid phase. This study focuses on two aspects: mass transfer and chemical reactions in multicomponent systems. The mass transfer parameters were determined by experiments under different conditions and the chemical reactions were studied using single component and multicomponent systems. Two models obtained from the literature were adapted to the systems used in this study.
Mass transfer parameters in the semi-batch reactor were determined using oxygen and ozone at different flow rates in the presence and absence of t-butanol. t-Butanol is used as a radical scavenger in ozonation studies and it has been found to affect the gas¿liquid mass transfer rates. An experimental study was carried out to investigate the effects of t-butanol concentrations on the physical properties of aqueous solutions, including surface tension and viscosity. It was found that t-butanol reduced both properties by 4% for surface tension and by a surprising 30% for viscosity. These reductions in the solution physical properties were correlated to enhancement in the mass transfer coefficient, kL. The mass transfer coefficient increased by about 60% for oxygen and by almost 50% for ozone. The hydrodynamic behaviour of the system used in this work was characterised by a homogeneous bubbling regime. It was also found that the gas holdup was significantly enhanced by the addition of t-butanol. Moreover, the addition of t-butanol was found to significantly reduce the size of gas bubbles, leading to enhancement in the volumetric mass transfer coefficient, kLa.
The multicomponent ozonation was studied with two systems, slow reactions when alcohols were used and fast reactions when endocrine disrupting compounds were used.
ii
These experiments were simulated by mathematical models. The alcohols were selected depending on their volatilization at different initial concentrations and different gas flow rates. The degradation of n-propanol as a single compound was studied at the lowest flow rate of 200 mL/min. It was found that the degradation of n-propanol reached almost 60% within 4 hours. The degradation of the mixture was enhanced with an increase in the number of components in the mixture. It was found that the degradation of the mixture as three compounds reached almost 80% within four hours while the mixture as two compounds reached almost 70%. The effect of pH was studied and it was found that an increase in pH showed slight increase in the reaction. Fast reactions were also investigated by reacting endocrine disrupting chemicals with ozone. The ozone reactions with the endocrine disrupters were studied at different gas flow rates, initial concentrations, ozone concentrations and pH. The degradation of 17¿-estradiol (E2) as a single compound was the fastest, reaching about 90% removal in almost 5 minutes. However estrone (E1) degradation was the lowest reaching about 70% removal at the same time. The degradation of mixtures of the endocrine disruptors was found to proceed to lower percentages than individual components under the same conditions. During the multicomponent ozonation of the endocrine disruptors, it was found that 17¿-estradiol (E2) converted to estrone (E1) at the beginning of the reaction.
A MATLAB code was developed to predict the ozone water reactions for single component and multicomponent systems. Two models were used to simulate the experimental results for single component and multicomponent systems. In the case of single component system, good simulation of both reactions (slow and fast) by model 1 was obtained. However, model 2 gave good agreement with experimental results only in the case of fast reactions. In addition, model 1 was applied for multicomponent reactions (both cases of slow and fast reaction). In the multicomponent reactions by model 1, good agreement with the experimental results was also obtained for both cases of slow and fast reactions.Ministry of Higher Education in Libya and the Libyan Cultural Centre and Educational Bureau in London.