Дисертації з теми "Bundle of tubes"
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1
Mazzone, Robert Walter. "Enhanced condensation of R-113 on a small bundle of horizontal tubes." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/43769.
Анотація:
Condensation of r-113 was studied using an evaporator condenser test platform. the condenser section contained four horizontal tubes (nominal outer diameter 15.9 mm)forming a vertical in line column with a pitch-to-diameter ratio of 2.25 and a condensing length of 1.2 m. the condenser tubes could be operated either individually (ie. as a single tube apparatus) or as a small tube bundle. this allowed investigation of the effects of condensate inundation on different types of condenser tubes. tubes tested were smooth copper tubes, copper/nickel korodense roped tubes, korodense tubes wrapped with wire, and copper /nickel finned tubes (26 fpi). the outside heat transfer coefficient was calculated by experimentally determining the overall heat transfer coefficient and then using a modified wilson plot procedure. great care was taken to ensure the results were not vitiated by the presence of non condensibles. results obtained with smooth copper tubes are in agreement with published data and verify satisfactory operation of the test platform. furthermore, problems associated with the apparatus encounted by previous workers were successfully overcome. in comparison to the top smooth tubes, the copper nickel to korodense tube yielded about a 22% increase.
2
Mabrey, Burlin Davis. "Condensation of refrigerants on small tube bundles." Thesis, Monterey, California. Naval Postgraduate School, 1988. http://hdl.handle.net/10945/22984.
Анотація:
Approved for public release; distribution is unlimitedThe construction of an apparatus for the condensation performance testing of a horizontal bundle of four tubes with various refrigerants was completed. The apparatus was instrumented, and data reduction software was developed to provide bundle and single tube condensation data. Two tube bundles were tested, smooth copper tubes and low integral-fin copper-nickel tubes, with two refrigerants, R-114 and R-113. An enhancement ratio of about 2.0 for the overall heat transfer coefficient was demonstrated for the finned tubes over the smooth tubes. Internal contamination, possibly due to a breakdown of the refrigerant molecules when subjected to high temperatures in the boiling chamber, inhibited further meaningful data collection. Recommendations for improvement of the test apparatus are made.
http://archive.org/details/condensationofre00mabr
Lieutenant, United States Navy
3
Beech, Philip Michael. "Filmwise condensation of high velocity downward flowing steam on a bundle of horizontal tubes." Thesis, Queen Mary, University of London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309675.
4
Bazin, Clément. "Numerical and experimental studies of two-phase flows interacting with a bundle of tubes." Electronic Thesis or Diss., Institut polytechnique de Paris, 2023. http://www.theses.fr/2023IPPAX106.
Анотація:
Les générateurs de vapeur (GV) des centrales nucléaires sont composés de faisceaux de tubes soumis à des écoulements diphasiques eau-vapeur. Les vibrations liées à cette interaction peuvent induire des dommages (fatigue et usure par frottement et chocs) pouvant entraîner de graves conséquences pour la sûreté nucléaire.Dans le cadre de la prévention des risques vibratoires des tubes de GV des études expérimentales sont réalisées à l'aide de faisceaux analytiques de tubes droits soumis à un écoulement transverse diphasique.En parallèle, il est également important de développer un outil de simulation numérique permettant d'accéder à des données et des informations difficilement mesurables.L'objectif de cette thèse est donc de simuler l’interaction entre un fluide diphasique et une structure rigide (tube unique ou faisceau de tubes), à l'aide du code NEPTUNE_CFD. Ces simulations doivent permettre de reproduire le chargement mécanique exercé par le fluide sur les tubes. La modélisation employée dans cette thèse repose sur un modèle à deux-fluides - trois-champs, comprenant un champ liquide continu, un champ de gaz dispersé, composé de bulles peu déformées, et un champ hybride dispersé-continu pour tenir compte des bulles très déformées et des poches de gaz. La première partie de ce travail s'est concentrée sur la validation du couplage diphasique-turbulence liquide ainsi que sur la modification et l'adaptation de la modélisation pour mieux prendre en compte la présence d'une structure immergée. De nouvelles modélisations pour la force de dispersion turbulente, les termes sources de coalescence et fragmentation, la masse ajoutée et le critère d'activation du champ continu ont été proposées. Dans la deuxième partie de ce travail, nous avons simulé l’écoulement diphasique autour d’un tube unique fixe, afin d'en extraire une physique sous-jacente et d'identifier ses limites et lacunes. Enfin, dans la dernière partie de ce travail, nous avons simulé l’interaction d’un écoulement diphasique avec un faisceau de tubes rigides. Les résultats numériques ont été comparés aux mesures expérimentales. Cette approche nous a permis de justifier l'intérêt de notre modélisation, de trouver des similitudes entre les résultats numériques et expérimentaux, tout en proposant des pistes d'améliorationThe steam generators (SG) in nuclear power plants are made up of bundles of tubes subjected to two-phase water-steam flows. Vibrations related to this interaction can cause damage (fatigue, wear due to friction and shocks) that can lead to serious consequences for nuclear safety.In the context of preventing vibrational risks in SG tubes, experimental studies are conducted using analytical bundles of straight tubes subjected to transverse two-phase flow. In parallel, it is also important to develop a numerical simulation tool to access data and information that are difficult to measure.The goal of this work is to simulate the interaction between a two-phase fluid and a rigid structure (single tube or bundle of tubes) using the NEPTUNE_CFD code. These simulations aim to reproduce the mechanical loading exerted by the fluid on the tubes. The modeling used in this work is based on a two-fluid - three-field model, including a continuous liquid field, a dispersed gas field made up of slightly deformed bubbles, and a dispersed-continuous hybrid field to account for highly deformed bubbles and gas pockets. The first part of this work focused on the validation of the two-phase liquid-turbulence coupling as well as the modification and adaptation of the modeling to better account for the presence of an immersed structure. New models for turbulent dispersion force, source terms of coalescence and break-up, added mass, and the activation criterion of the continuous field were proposed. In the second part of this work, we simulated the two-phase flow around a fixed single tube to extract underlying physics, and identify its limitations and shortcomings. Finally, in the last part of this work, we simulated the interaction of a two-phase flow with a bundle of rigid tubes. The numerical results were compared to experimental measurements. This approach allowed us to justify the relevance of our modeling, find similarities between numerical and experimental results, while also suggesting areas for improvement
5
Ramadan, Abdulghani. "Numerical And Experimental Investigation Of Forced Filmwise Condensation Over Bundle Of Tubes In The Presence Of Noncondensable Gases." Phd thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/3/12607831/index.pdf.
Анотація:
The problem of the forced film condensation heat transfer of pure steam and steam-air mixture flowing downward a tier of horizontal cylinders is investigated numerically and experimentally. Liquid and vapor-air mixture boundary layers were solved by an implicit finite difference scheme. The effects of the free stream non-condensable gas (air) concentration, free stream velocity (Reynolds number), cylinder diameter, temperature difference and angle of inclination on the condensation heat transfer are analyzed. Inline and staggered tubes arrangements are considered. The mathematical model takes into account the effect of staggering of the cylinders and how condensation is affected at the lower cylinders when condensate does not fall on to the center line of the cylinders. An experimental setup was also manufactured and mounted at METU workshop. A set of experiments were conducted to observe the condensation heat transfer phenomenon and to verify the theoretical results.
Condensation heat transfer results are available in ranges from (U
= 1 - 30 m/s) for free stream velocity, (m1,&
#61605
= 0.01 -0.8) for free stream air mass fraction, (d = 12.7 -50.8 mm) for cylinder diameter and (T&
#61605
-Tw =10-40 K) for temperature difference. Results show that
a remarked reduction in the vapor side heat transfer coefficient is noticed when very small amounts of air mass fractions present in the vapor. In addition, it decreases by increasing in the cylinder diameter and the temperature difference. On the other hand, it increases by increasing the free stream velocity (Reynolds number). Average heat transfer coefficient at the middle and the bottom cylinders increases by increasing the angle of inclination, whereas, no significant change is observed for that of the upper cylinder. Although some discrepancies are noticed, the present study results are inline and in a reasonable agreement with the theory and experiment in the literature. Down the bank, a rapid decrease in the vapor side heat transfer coefficient is noticed. It may be resulted from the combined effects of inundation, decrease in the vapor velocity and increase in the non-condensable gas (air) at the bottom cylinders in the bank. Differences between the present study results and the theoretical and the experimental data may be resulted from the errors in the numerical schemes used. These errors include truncation and round off errors, approximations in the numerical differentiation for interfacial fluxes at the vapor-liquid interface, constant properties assumption and approximations in the initial profiles. Mixing and re-circulation in the steam-air mixture at the lower tubes may be the other reasons for these deviations.
6
Marcel, Thibaud. "Simulation numérique et modélisation de la turbulence statistique et hybride dans un écoulement de faisceau de tubes à nombre de Reynolds élevé dans le contexte de l'interaction fluide-structure." Thesis, Toulouse, INPT, 2011. http://www.theses.fr/2011INPT0109/document.
Анотація:
La prédiction des instabilités fluide-élastique qui se développent dans un faisceau de tubes est importante pour la conception des générateurs de vapeur dans les centrales nucléaires, afin de prévenir les accidents liés à ces instabilités. En effet, ces instabilités fluide-élastique, ou flottements, conduisent à une fatigue vibratoire des matériaux, voire à des chocs entre les tubes, et par la suite, à des dégâts importants. Ces aspects sont d'une grande complexité pour les applications scientifiques impliquant l'industrie nucléaire. Le présent travail est issu d'une collaboration entre l'EDF, le CEA et l'IMFT. Elle vise à améliorer la simulation numérique de cette interaction fluide- structure dans le faisceau de tubes, en particulier dans la gamme de paramètres critiques favorisant l'apparition d'un amortissement négatif du système et de l'instabilité fluide-élastiqueThe prediction of fluid-elastic instabilities that develop in a tube bundle is of major importance for the design of modern heat exchangers in nuclear reactors, to prevent accidents associated with such instabilities. The fluid-elastic instabilities, or flutter, cause material fatigue, shocks between beams and damage to the solid walls. These issues are very complex for scientific applications involving the nuclear industry. This work is a collaboration between EDF, CEA and IMFT. It aims to improve the numerical simulation of the fluid-structure interaction in the tube bundle, in particular in the range of critical parameters contribute to the onset of damping negative system and the fluid-elastic instability
7
Belghazi, Mourad. "Condensation d'un fluide pur et de mélanges zéotropes à l'extérieur d'un faisceau de tubes à surface améliorée." Université Joseph Fourier (Grenoble), 2001. http://www.theses.fr/2001GRE10055.
8
Blanc, Philippe. "Condensation des fluides frigorigènes HFC134a et HFC22 à l'extérieur d'un faisceau de tubes horizontaux améliorés." Université Joseph Fourier (Grenoble ; 1971-2015), 1994. http://www.theses.fr/1994GRE10221.
Анотація:
L'utilisation de nouveaux fluides frigorigenes respectueux de notre environnement remet en cause les connaissances etablies pour le dimensionnement des installations frigorifiques et de conditionnement d'air. Les condenseurs de type tema x, largement utilises dans de telles applications, sont composes d'un faisceau de tubes horizontaux ameliores a l'exterieur desquels vient se condenser la vapeur de fluide frigorigene. Le dimensionnement optimal d'un tel echangeur necessite la prise en compte de l'effet d'inondation du condensat le long des rangees de tubes du faisceau. L'approche experimentale reste dans ce domaine un moyen privilegie d'amelioration des connaissances. L'experimentation est realisee sur une maquette simulant une partie du condenseur. Les mesures locales effectuees pour deux fluides frigorigenes et deux geometries de tubes ameliores ont permis d'etablir un nombre important de donnees experimentales. Leur confrontation avec divers modeles de la litterature permet de choisir le mieux adapte au cas de la condensation de fluides frigorigenes. Par la suite, afin de mettre a disposition des fabricants et utilisateurs d'echangeurs les principaux resultats de ce travail, le logiciel cetuc a ete etendu au cas des condenseurs de type tema x
9
Mansur, Sergio Said. "Amélioration des échangeurs thermiques tubulaires par l'utilisation d'inserts hélicoïdaux à l'extérieur des tubes." Grenoble 1, 1993. http://www.theses.fr/1993GRE10192.
Анотація:
Ce travail propose une etude numerique et experimentale du comportement thermohydraulique des echangeurs multitubulaires munis de bandes vrillees a l'exterieur des tubes. Des lois de frottement et d'echange thermique au sein de cette geometrie ont ete determinees experimentalement et programmees dans le logiciel trio developpe au commissariat a l'energie atomique, cea , avec une modelisation du type milieu poreux. Des mesures de pression et de vitesse, ainsi que des visualisations de l'ecoulement ont ete realisees sur un echangeur construit en plexiglas transparent. Les resultats obtenus dans cette etape ont permis d'evaluer la distribution du debit a l'interieur de l'appareil et de degager les elements necessaires a la validation des calculs. L'adequation du modele pour une description macroscopique de l'ecoulement a ete confirmee par des nombreuses comparaisons entre donnees numeriques et experimentales. Une analyse comparative entre differents types d'echangeurs, realisee a l'aide de la simulation, a mis en evidence la performance thermohydraulique satisfaisante de ce nouveau type d'echangeur. Enfin, l'aspect de la diffusion turbulente a l'interieur du faisceau tubulaire a ete aborde par une experience simple de visualisation. D'un point de vue qualitatif, ces essais ont clairement montre que la presence des inserts favorise le melange et la dispersion des proprietes transferables au sein du fluide, qualifiant ainsi les bandes helicoidales en tant de promoteurs de turbulence
10
Adom, Ebenezer. "Investigation of boiling heat transfer on small diameter tubes and tube bundles." Thesis, Heriot-Watt University, 2007. http://hdl.handle.net/10399/2067.
Анотація:
Boiling heat transfer on the outside of small diameter tubes in the range of 1.8-3.0mm has been investigated. Pool boiling was investigated at nominal atmospheric pressure for each of the tubes iIi isolation. The experiment was varied by investigating the effect of bubbles from a second tube mounted below by varying the heat flux on the upper tube. The upper tube diameter was changed from 3.00 to 2.32 and 1.83mm and in each case the lower tube was 3.00mm. Experimental results showed that the upper tube heat transfer coefficient was enhanced due to the combined mechanism of translating bubbles and turbulent convection at low to moderate heat fluxes. A compact tube bundle made up of 30 stainless steel tubes of outer diameter 3nun, pitch diameter ratio 1.5 and heating length of 50nun was designed to. permit the measurement of flow boiling heat transfer coefficient from tubes within the bundle. The heat flux tested was in the range of 4-21 kW/m2 and mass flux of 5.6-32.8 kg/m2s using distilled water, R-l13 and Flutec PPI at nominal atmospheric pressure as the working fluids. Results obtained showed that the heat transfer coefficient was predominantly dependent on the heat flux as opposed to mass flux. Macro scale models were compared with the experimental results and none of these models predicted the experimental results well. The Confinement number (Co) developed for flow boiling inside micro channels was applied to compact tube bundles and it was shown that confinement is expected ~o be significant for Co>0.63. Photographic studies. also showed that the diameter of the bubbles that were generated within the,bundle were greater than the tube diameter. As such, the sliding bubbles mechanism played less significant role in contributing to the heat transfer coefficient. The recent three-state correlation developed by Thome et al for flow boiling .he.at transfer in micro .channels was modified to predict the experimental results obtained using a compact tube bundle and it has been shown that the thin film evaporation was the dominant mechanism compared to the nucleate boiling. The results from the twin tube and compact bundle arrangement showed two regions coexist at any point in time; that part of the tube covered with liquid subject to nucleate boiling and the other part completely enveloped with vapour. This latter part is designated by the introduction of a factor p and this has been demonstrated experimentally and theoretically corroborated by a model based on a liquid part (i-p) and vapour part p.
11
Ortega, Del Rosario Maria de los Ángeles. "Système de stockage et transfert d'énergie par chaleur latente adaptable au rafraîchissement d’air en bâtiments : conception et analyse thermique." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0197/document.
Анотація:
Ces travaux de thèse visent à concevoir et étudier une unité d'échangeur de chaleur air-MCP en tant que solution passive a la problématique du contrôle de confort thermique dans les bâtiments pendant l'été, fournissant des directives de conception et une intégration facile aux bâtiments. Les MCP présentent une grande capacité de stockage par unité de volume, ce qui leur permet de contribuer à la réduction de la consommation d'énergie liée aux applications de rafraîchissement. Bien qu'ils présentent certains inconvénients, en tant que faible conductivité thermique, notamment dans les PCM commerciaux, une conception bien détaillée est nécessaire pour atteindre des performances thermiques adéquates.La première partie de cette thèse examine les systèmes existants à travers une étude bibliographique, mettant en évidence la relation géométrique avec la physique et la performance thermique. Cette recherche a fourni les bases pour le développement d'une conception d'une unité air-MCP, suivant une méthodologie de résolution de problèmes développée par le laboratoire I2M. Une matrice de mots-clés a été obtenue à partir des phénomènes physiques et de l'analyse fonctionnelle de l'unité. A partir de cette matrice, l'analyse des brevets a inspiré la conception qui a abouti à un échangeur de chaleur air-PCM à faisceau tubulaire avec des tubes verticaux alignés perpendiculairement au flux d'air.Le développement d'outils de conception et d'intégration dans les bâtiments a été recherché au moyen d'une modélisation permettant de prédire avec précision les performances thermiques du système. Les modèles simplifiés sont préférés pour cette tâche. Néanmoins, ils peuvent sous-estimer les performances réelles si les phénomènes physiques impliqués ne sont pas correctement comptabilisés. Alors,des approches expérimentales locales et globales ont été utilisées pour parvenir à une compréhension de la physique associée aux cycles de charge et de décharge dans l'unité air-MCP. Pour cela, un banc d'essai a été installé, mesurant la température et le débit d'air dans différentes conditions d'entrée, accompagné d'un suivi visuel à travers des images numériques. Les traitements d'images et des données ont été utilisés pour obtenir des indicateurs de performance thermique et des corrélations équivalentes en utilisant des nombres adimensionnels connus pour les mécanismes de transfert de chaleur convectifs-conducteurs dans le PCM.Ces découvertes ont permis de développer des modèles de résistance thermique et d'enthalpie qui rendent compte de la complexité des phénomènes impliqués dans l'unité pour la prédiction de la performance. Enfin, la performance thermique du système a été testée dans deux applications de bâtiments : en tant qu'unité mobile dans une maison PEH à Gradignan dans un bureau du labo I2MThe present work aims to design and study an air-PCM heat exchanger unit as a passive solution for thermal comfort assessment in buildings during summertime, providing tools to ease the design and building integration. The PCM present a large storage capacity per volume unit where by, they can contribute to the reduction of the energy consumption related to cooling applications. Although, theyshow some drawbacks, as a low thermal conductivity in commercial PCM, so a wellthought design of these kind of systems is necessary to achieve adequate thermal performances.The first part of this thesis surveys the existing systems through a literature review,highlighting the geometry relation with the physics and thermal performance. This search provided the bases for the development of an air-PCM unit design, following a problem-solving methodology developed by the I2M laboratory. A keyword matrix was obtained from the physical phenomena and functional analysis of the unit. From this matrix, the patents analysis provided inspiration for the design resulting in a tubebundle air-PCM heat exchanger with vertical tubes aligned perpendicular to the airflow.The development of design and integration in buildings tools was sought through a modeling that can accurately predict the thermal performance of the system.Simplified models are preferred for this task. Nevertheless, they can under predict the actual performance if the physical phenomena involved is not properly accounted. Then, local and global experimental approaches were used to achieve anunderstanding of the physics associated with charging and discharging cycles in theunit. For this, a test bench was installed, measuring temperature and airflow underdifferent in let conditions, accompanied by a visual tracking through digital images.Image and data processing were used to obtain thermal performance indicators and equivalent correlations using known dimensionless numbers for convective conductive heat transfer mechanisms in the PCM.These findings allowed the development of thermal models based on energy balances, that accounted the complexity of phenomena involved in the unit for performance prediction. Finally, the thermal performance of the system was tested intwo buildings applications: as a mobile unit in a PEH house in Gradignan and as anactive façade in a building in Talence
El presente trabajo tiene como objetivo diseñar y estudiar una unidad intercambiador de calor aire-PCM como presentan una solución pasiva al conforttérmico en edificios durante el verano, proporcionando herramientas para facilitar el diseño y la integración en edificios. Los PCM una gran capacidad de almacenamiento por unidad de volumen, por lo que pueden contribuir a la reducción del consumo de energía relacionado con las aplicaciones de refrigeración. Estos materiales presentan algunos inconvenientes en cual su uso, como una baja conductividad térmica, típica en PCM comerciales, por lo es necesario un diseño que tome en cuenta esta problemática para lograr rendimientos térmicos adecuados. La primera parte de esta tesis examina los sistemas existentes a través de unarevisión de la literatura, destacando la relación de geometría con los fenómenos físicos y el rendimiento térmico. Esta búsqueda proporcionó las bases para el desarrollo de un diseño de unidad aire-PCM, siguiendo una metodología de resolución de problemas desarrollada por el laboratorio I2M. Se obtuvo una matrizde palabras clave a partir de los fenómenos físicos y el análisis funcional de launidad. A partir de esta matriz, el análisis de patentes proporcionó inspiración para el diseño que dio como resultado un intercambiador de calor PCM de aire y haz detubos verticales alineados perpendicularmente al flujo de aire.El desarrollo del diseño y la integración en herramientas de edificios se buscó através de un modelo que pudiese predecir con precisión el rendimiento térmico delsistema. Los modelos simplificados son los preferidos para esta tarea. Sin embargo,su poder de predicción puede verse afectada si los fenómenos físicos involucradosno se contabilizan adecuadamente. Es por ello que se utilizaron enfoques experimentales locales y globales para lograr una comprensión de la física asociadacon los ciclos de carga y descarga en la unidad. Se realizó una instalación de unbanco de pruebas, que permitió mediciones de temperatura y flujo de aire en diferentes condiciones de entrada, acompañado de un seguimiento visual a travésde imágenes digitales. El procesamiento de imágenes y datos se utilizó para obtener indicadores de rendimiento térmico y correlaciones a partir de números adimensionales relacionados con mecanismos de transferencia de calor porconvección y conducción en el PCM.Estos hallazgos permitieron el desarrollo de modelos térmicos para la predicción delrendimiento, basados en balances de energía de cada volumen de control.Finalmente, el rendimiento térmico del sistema se probó en dos aplicaciones deedificios: como una unidad móvil en una casa PEH en Gradignan y dentro de una oficina del laboratorio I2M
12
Havlů, Michal. "Algoritmus automatického výběru vhodného typu zařízení z databáze výměníků tepla." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2009. http://www.nusl.cz/ntk/nusl-228730.
Анотація:
Thesis is devoted to development of an database algorithm for selection (or necking selection) of suitable type of heat exchanger for given industrial application. Database creates a part of multipurpose calculation system containing three individual modules: (i) module for selection (or necking selection) of type of heat exchanger for given application, (ii) module for thermal-hydraulic design or rating of heat exchanger, (iii) module for calculation of investments and operating cost. Thesis describes details of method for selection of suitable heat exchanger type for given application and presents and discuss individual criteria for selection process which influence values in tables of priorites for given equipment. These tables are unavoible part of selection algorithm. Details of software application of selection algorithm are also presented in the thesis. Description of behaviour of individual types of heat exchanger creates important part of thesis. Practical application of developed selection algorithm is demonstrated on several industrial examples.
13
Gidi, Alejandro. "Two-phase flow-induced vibrations in a heated tube bundle." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0031/NQ66267.pdf.
14
Ahmad, Hussain Hamed. "Boiling of immiscible systems over tube bundles." Thesis, Heriot-Watt University, 1989. http://hdl.handle.net/10399/966.
15
Gorgy, Evraam. "Experimental evaluation of heat transfer impacts of tube pitch on highly enhanced surface tube bundle." Diss., Kansas State University, 2011. http://hdl.handle.net/2097/11995.
Анотація:
Doctor of PhilosophyDepartment of Mechanical and Nuclear Engineering
Steven J. Eckels
The current research presents the experimental investigation of the effect of tube pitch on enhanced tube bundles’ performance. The typical application of this research is flooded refrigerant evaporators. Boosting evaporator’s performance through optimizing tube spacing reduces cost and energy consumption. R-134a with the enhanced tube Turbo BII-HP and R-123 with Turbo BII-LP were used in this study. Three tube pitches were tested P/D 1.167, P/D 1.33, and P/D 1.5. Each tube bundle includes 20 tubes (19.05 mm outer diameter and 1 m long each) constructed in four passes. The test facility’s design allows controlling three variables, heat flux, mass flux, and inlet quality. The type of analysis used is local to one location in the bundle. This was accomplished by measuring the water temperature drop in the four passes. The water-side pressure drop is included in the data analysis. A new method called the EBHT (Enthalpy Based Heat Transfer) was introduced, which uses the water-side pressure drop in performing the heat transfer analysis. The input variables ranges are: 15-55 kg/m².s for mass flux, 5-60 kW/m² for heat flux, and 10-70% for inlet quality. The effect of local heat flux, local quality, and mass flux on the local heat transfer coefficient was investigated. The comparison between the bundle performance and single tube performance was included in the results of each tube bundle. The smallest tube pitch has the lowest performance in both refrigerants, with a significantly lower performance in the case of R-134a. However, the two bigger tube pitches have very similar performance at low heat flux. Moreover, the largest tube pitch performance approaches that of the single tube at medium and high heat fluxes. For the R-123 study, the smallest tube bundle experienced quick decease in performance at high qualities, exhibiting tube enhancement dry-out at certain flow rates and high qualities. The flow pattern effect was demonstrated by the dry-out phenomena. At medium and high heat fluxes, as the tube pitch increases, the performance approaches that of the single tube. All tube bundles experience quick decrease in performance at high qualities. Evidently, P/D 1.33 is the optimum tube pitch for the studied refrigerants and enhanced tubes combinations.
16
McIlwain, Stuart Russell. "Improved prediction methods for finned tube bundle heat exchangers in crossflow." Thesis, University of Strathclyde, 2003. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21526.
Анотація:
Previous methods for predicting the heat transfer and pressure drop performance of crossflow heat exchangers with finned tubes have concentrated on developing correlations. These correlations have been based on the researchers observations of what geometric parameters may affect the performance, and then dimensionless groups developed to allow a correlation to be developed. This work shows that many of these models are limited either by design or by their databases, and often are not general enough to cater for air-cooled heat exchangers as well as the generally larger scale heat recovery bundles. The most recent prediction methods have been developed as more aerodynamically based models, although these still encompass an element of empiricism to account for effects that are not readily understood. This new work develops from these physically based models. An improved method for the prediction of the pressure drop of staggered finned tube bundles is presented, based on high quality test data and the results of a CFD (Computational Fluid Dynamics) study. This is shown to perform better than previous models, and also correct a defect in the formulation of a previous method. A new prediction scheme for inline finned tube bundles is also presented. Experimental work was performed on nine inline air coolers to determine their performance characteristics and, along with open literature data, develop a reliable databank for prediction method development. The models incorporate a new approach to the pressure drop prediction using a sophisticated gap flow model, and a multiple term heat transfer model, that considers heat transfer and flow mixing between the main flow streams. This method is shown to significantly improve on previous methods. Experiments were conducted on an isothermal staggered air-cooler bundle that allowed differing wall sealing devices (corbels) to be used, or allow a bypassing lane. Flow visualization tests were performed on this bundle, and observations of the flow patterns compared with a simple two-dimensional CFD model. From the test results a new method of predicting the pressure drop performance of staggered bundles with various corbels was developed. Using the bypassing air-cooler data and new data taken from a heat recovery bundle an iterative method to predict the pressure drop when a bypassing lane is present is presented. This method is shown to be both simple and computationally cheap, and is used in conjunction with the new staggered bundle pressure drop method. The experimental inline air cooler results were used in conjunction with CFD to provide data to investigate the effect on heat transfer with an increasing number of rows through the bundle. It was found that the key factors in determining this are turbulence and the temperature difference between the tubeside and crossflow fluids, and also that the fin frequency plays a key role. A model is presented to predict the local heat transfer coefficient, which uses sub-models to express the two contributory factors. The results of this approach are shown to be very good, and promote better understanding of tube row heat transfer duty than previously developed models.
17
Nelson, Peter Jonathan. "Boiling the immiscible water/n - nonane system from a tube bundle." Thesis, Heriot-Watt University, 1986. http://hdl.handle.net/10399/1060.
18
Omar, Hossin. "Numerical Simulations of Fluidelastic Instability in Tube Bundles." Thesis, University of New Brunswick, 2010. http://hdl.handle.net/1882/1089.
Анотація:
Flow-Induced Vibration (FIV) is a major issue in designing shell and tube heat exchangers. Amongst FIV behaviour, fluidelastic instability (FEI) is the most damaging excitation mechanism since it can cause catastrophic failure of tube arrays. This study investigates unsteady flow in tube bundles and the fluid forces which can lead to large tube vibration amplitudes associated with FEI. The fluidelastic forces are approximated by the combining of the unsteady-flow model and a computation fluid dynamics (CFD) flow model. The unsteady flow through tube arrays is simulated using a two-dimensional CFD model. The CFD model solves the Reynolds-Average Navier-Stokes (RANS) equations for unsteady turbulent flow, and is cast in an Arbitrary Lagrangian-Eulerian (ALE) form to handle any motion associated with moving tubes. One tube was forced to oscillate at a prescribed amplitude and frequency and the resulting unsteady forces were obtained by integrating the pressure around the moving and surrounding tubes. The predicted forces were utilized to calculate added damping and stiffness coefficients. The predicted fluid force coefficients were then used in the theoretical framework of the unsteady flow model.
The ability to predict the tube array FEI threshold from the numerically derived coefficients for two array configurations (normal square and normal triangle) and assuming single and fully flexible tube arrays was assessed. The FEI threshold was predicted for each configuration over a mass damping parameter (MDP) range of 1 to 1000. The predicted fluid force coefficients and FEI threshold are then compared with the available experimental data. The comparison demonstrates that the unsteady-flow model utilized in conjunction with a 2D RANS based CFD model is a viable approach for calculating the stability map for a given tube array. The effect of the pitch-to-diameter (P/d) ratio, Reynolds number and neighbouring tubes on the FEI threshold was also investigated.
19
Scoones, David John. "Boiling on plain and low-finned tube bundles." Thesis, Heriot-Watt University, 1986. http://hdl.handle.net/10399/2134.
20
Andrews, Patrick Rowan. "Boiling on in-line and staggered tube bundles." Thesis, Heriot-Watt University, 1985. http://hdl.handle.net/10399/1608.
21
Teixidó, Roman Miguel. "A cotangent bundle Hamiltonian tube theorem and its applications in reduction theory." Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/288376.
Анотація:
The Marle-Guillemin-Sternberg (MGS) model is an extremely important tool for the theory of Hamiltonian actions on symplectic manifolds. It has been extensively used to prove many local results both in symplectic geometry and in symmetric Hamiltonian systems theory. It provides a model for a tubular neighborhood of a group orbit and puts in normal form the group action and the symplectic structure.
The main drawback of the MGS model is that it is not explicit. Only it existence and main properties can be proved. Moreover, for cotangent bundles, this model does not respect the natural fibration.
In the first part of the thesis we build an MGS model specially adapted to the cotangent bundle geometry. This model generalizes previous results obtained by T. Schmah for orbits with fully-isotropic momentum. In addition, our construction is explicit up to the integration of a differential equation on G. This equation can be easily solved for the groups SO(3) or SL(2), hence giving explicit symplectic coordinates for arbitrary canonical actions of these groups on any cotangent bundle.
In the second part of the thesis we apply this adapted MGS model to describe the structure of the symplectic reduction of a cotangent bundle. We show that the base projection of any momentum leaf is a Whitney stratified space. Moreover, we can refine the orbit-type stratification of the symplectic reduced space so that each piece is a fibered space. We prove that each of those pieces is endowed with a constant rank presymplectic form and that there is always one unique piece which is open and dense. Furthermore, this maximal piece is symplectomorphic to a vector subbundle of a certain cotangent bundle.El model de Marle-Guillemin-Sternberg (MGS) és una eina extremadament important per la teoria de les accions Hamiltonianes en varietats simplèctiques. Ha estat utilitzada per provar molts resultats te tipus local tant en geometria simplèctica com en la teoria de sistemes Hamiltonians simètrics. Proporciona un model per un entorn tubular de una òrbita de la acció de forma que fica en forma normal tant l'acció del grup com l'estructura simplèctica. El principal problema del model MGS és que no és explícit. Només es poden provar la seva existència i les seves propietats principals. Per altra banda, en el cas de que la varietat sigui un fibrat cotangent la el model MGS no respecta la fibració natural. En la primera part de la tesis construïm un model MGS especialment adaptat a la geometria dels fibrats cotangents. Aquest model generalitza els resultats obtinguts per T. Schmah per òrbites amb moment completament isotròpic. Addicionalment, la nostra construcció és explicita excepte per la integració d'una equació diferencial sobre el grup G. Aquesta equació pot ser solucionada de forma explícita per els grups SO(3) o SL(2), per tant podem donar explícitament coordenades simplèctiques per a accions arbitraries d'aquests grups sobre qualsevol fibrat cotangent. En la segona part de la tesis apliquem aquest model MGS cotangent per descriure l'estructura de les reduccions simplèctiques de fibrats cotangents. Mostrem que la projecció sobre la base de una fulla de moment és un espai estratificat de Whitney. També podem refinar l'estratificació de l'espai simplèctic reduït de forma que cadascuna de les peces és un espai fibrat. Demostrem que cadascuna d'aquestes peces està dotada d'una forma pre-simplèctica de rang constant i que sempre hi ha una única peça que es oberta i densa en l'espai reduït. A més aquesta peca maximal és simlpectomorfa a un subfibrat vectorial de un cert fibrat cotangent.
22
Chilman, Scott V. "Nucleate boiling characteristics of R-113 in a small enhanced tube bundle." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28404.
23
Castiglia, Davide. "Fluid flow and heat transfer in unconventional tube bundle arrangements in crossflow." Thesis, King's College London (University of London), 2002. https://kclpure.kcl.ac.uk/portal/en/theses/fluid-flow-and-heat-transfer-in-unconventional-tube-bundle-arrangements-in-crossflow(19f17b5f-6ea1-4f6c-9168-8e809d2495f7).html.
24
Shire, Neil Frank. "Heat transfer and hydrodynamics of boiling over tube bundles." Thesis, Heriot-Watt University, 1995. http://hdl.handle.net/10399/769.
25
Balabani, Stavroula. "An experimental investigation of the crossflow over tube bundles." Thesis, King's College London (University of London), 1996. https://kclpure.kcl.ac.uk/portal/en/theses/an-experimental-investigation-of-the-crossflow-over-tube-bundles(27c20ab8-798a-4a07-b1cd-b31fbd77578e).html.
26
MacIver, Alasdair. "The application of enhanced surfaces to boiling over tube bundles." Thesis, Heriot-Watt University, 1993. http://hdl.handle.net/10399/1472.
27
Penner, Lloyd Alan. "Two-dimensional flow predictions in a tube bundle using orthogonal and non-orthogonal grids." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/mq23452.pdf.
28
Haas, Russell E. "Nucleate pool boiling of R-114/oil mixtures in a small enhanced tube bundle." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/23733.
29
Angula, Ester. "Numerical performance evaluation of a delugeable flat bare tube air-cooled steam condenser bundle." Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/97151.
Анотація:
Thesis (MEng)--Stellenbosch University, 2015.ENGLISH ABSTRACT: In this study, one and two-dimensional models are developed for the evaluation of the thermal performance of a delugeable flat tube bundle to be incorporated in the second stage of an induced draft hybrid (dry/wet) dephlegmator (HDWD) of a direct air-cooled steam condenser (ACSC). Both models are presented by a set of differential equations. The one-dimensional model is analysed analytically by using three methods of analysis which are: Poppe, Merkel, and heat and mass transfer analogy. The two-dimensional model is analysed numerically by means of heat and mass transfer analogy method of analysis whereby, the governing differential equations are discretised into algebraic equations using linear upwind differencing scheme. The two-dimensional model’s accuracy is verified through a comparison of the two dimensional solutions to one dimensional solutions. Satisfactory correlation between the one and two-dimensional results is reached. However, there is a slight discrepancy in the solutions, which is mainly due to the assumptions made in one-dimensional model. The effect of tube height, tube pitch, tube width, deluge water mass flow rate, frontal air velocity, steam, and air operating conditions on the heat transfer rate and air-side pressure drop for both wet and dry operating modes are investigated. The long tube height, large tube width, small tube pitch, and high frontal air velocity are found to increase the tube bundle’s performance. However, this performance is associated with a high airside pressure drop. The performance of the deluged flat tube bundle is found to be less sensitive to the changes in the deluge water mass flow rate and air operating conditions. Furthermore, the best configuration of a delugeable flat tube bundle is identified through a comparison to round tube bundle presented by Anderson (2014). The performance of the round tube bundle is found to be around 2 times, and 1.5 times of that of flat tube bundle, when both bundles operate as an evaporative and dry air-cooled condenser respectively.
AFRIKAANSE OPSOMMING: In hierdie studie is een en twee-dimensionele modelle ontwikkel vir die evaluering van die termiese prestasie van 'n benatbare plat buis bundel in die tweede stadium van 'n geïnduseerde ontwerp hibriede (droë / nat ) deflegmator van 'n direkte lugverkoelde stoom kondensator. Beide modelle is aangebied deur 'n stel van differensiaalvergelykings. Die een-dimensionele model is analities ontleed deur die gebruik van drie metodes van analise wat: Poppe, Merkel, en die hitte en massa-oordrag analogie. Die twee-dimensionele model is numeries ontleed deur middel van hitte en massa-oordrag analogie metode van analise waardeur , die regerende differensiaalvergelykings gediskretiseer in algebraïese vergelykings met behulp van lineêre windop differensievorming skema. Die tweedimensionele model se akkuraatheid is geverifieer deur 'n vergelyking van die twee dimensionele oplossings te een dimensionele oplossings. Bevredigende korrelasie tussen die een en twee-dimensionele resultate bereik word. Maar daar is 'n effense verskil in die oplossings, wat is hoofsaaklik te wyte aan die aannames wat gemaak in een-dimensional model. Die effek van buis hoogte, buis toonhoogte, buis breedte, vloed water massa-vloeitempo, frontale lug snelheid, stoom, en in die lug werktoestande op die hitte oordrag snelheid en lug - kant drukval vir beide nat en droë maatskappy modi word ondersoek. Die lang buis hoogte, groot buis breedte, klein buisie toonhoogte, en 'n hoë frontale lug snelheid gevind die buis bundel se prestasie te verhoog. Tog is hierdie prestasie wat verband hou met 'n hoë lug - kant drukval. Die prestasie van die oorstroom plat buis bundel gevind word minder sensitief vir die veranderinge in die vloed water massa-vloeitempo en lug werktoestande. Verder is die beste opset van 'n benatbare plat buis bundel geïdentifiseer deur 'n vergelyking met ronde buis bundel aangebied deur Anderson (2014). Die prestasie van die ronde buis bundel gevind word om 2 keer, en 1.5 keer van daardie plat buis bundel , wanneer beide bundels funksioneer as 'n damp en droë lugverkoelde kondensor onderskeidelik.
30
Sadikin, Azmahani. "An experimental study of two-phase flow in idealised tube bundles." Thesis, Heriot-Watt University, 2013. http://hdl.handle.net/10399/2898.
Анотація:
This thesis reports on an experimental study of air-water mixtures flowing through idealized shell and tube, in-line and staggered heat exchangers. The measured void fractions in the maximum and minimum gaps between the tubes are reported at near atmospheric conditions, to give local variations for different tube diameters and tube bundle arrangements. The void fraction measurements were made using a gamma-ray densitometer. The pressure drops in the tube bundles are also reported. These data are compared with the correlations available in the open literatures to investigate the void fraction and pressure drop prediction methods for these heat exchangers. The in-line 38 mm tube bundle is shown to provide no significant effect on void fraction or drag force when compared with the 20 mm tube diameter bundle. A new void fraction model is therefore proposed by modifying the characteristic length of an existing slip ratio method. A new pressure drop model is presented. The acceleration pressure drop between the tubes from the separation to re-attachment is shown to be responsible for some of the frictional pressure drop with a liquid film on the tubes responsible for the remainder. The staggered bundle shows the bundle arrangement gives different void fraction and different pressure drop data when compared to the in-line bundle.
31
Li, Fang. "Heat Transfer in a High-pressure Gas-solid Fluidized Bed with Horizontal Tube Bundle and Continuous Addition of Fines." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/38002.
Анотація:
Climate change is becoming more severe than ever in human history and the emission of green house gas urgently needs to be reduced while global energy consumption remains booming. Large-scale application of clean fossil fuel combustion shall be considered as a priority for its economical advantages as well as reliability in meeting global energy needs. Oxygen-fired pressurized fluidized bed combustor technology with downstream carbon capture and sequestration is considered a key approach to clean coal combustion. In such technology, the fluidized bed combustor operates at elevated pressures and houses an in-bed heat exchanger tube bundle. It is essential to understand the rate of heat transfer between the immersed heat exchange surface and the fluidized bed as it is a key parameter in heat exchanger design. The goal of this work was to investigate the impact of pressure and presence of fine particles (i.e., surrogate for pulverized fuel) on the overall tube-to-bed heat transfer coefficient.
Experiments were conducted in a pilot-scale fluidized bed with an inner diameter of 0.15 m under cold flow conditions. A tube bundle consisting of five horizontal staggered rows was completely submerged in the bed. One of the tubes was replaced by a heating cartridge housed in a hollowed copper rod. Five thermocouples distributed at 45º intervals along the copper rod circumference measured the surface temperature and ensured that local effects were included. The bed material was large glass beads of 1.0 mm in diameter while the fines were glass beads of 60 µm in diameter and thus susceptible to entrainment. The fine particles were continuously fed to the fluidized bed and then captured downstream by a filter system. Fluidization was conducted at 101, 600 and 1200 kPa with excess gas velocities (Ug - Umf) of 0.21, 0.29 and 0.51 m/s. Fine particle feed rates were 0, 9.5 and 14.4 kg/h. Two heating rod positions (2nd row and 4th row) were studies.
Overall, the heat transfer coefficient approximately doubled when pressure was increased from 101 to 1200 kPa. At atmospheric conditions, where the slug flow regime occurred, the maximum heat transfer coefficient was at the bottom of the rod, while it moved to the side of the rod at high pressures where the bubbling regime occurred. As the heating rod moving from 2nd row to the 4th row, the averaged heat transfer coefficient increased by respectively 18%, 9% and 6% at 101, 600 and 1200 kPa. The addition of fine particles decreased the average heat transfer coefficient by 10 to 20 W/m2 K where the time – averaged heat transfer coefficient was approximately 220 and 450 W/m2K at 101 kPa and 1200 kPa respectively. There was no effect on the angular profile across the tube surface. The results showed that average heat transfer coefficients matched the correlation developed by Molerus et al. (1995) within a 5% difference across all conditions when fines were not present.
32
Cui, Xingdong. "Prediction of critical heat flux in bundles using tube look-up table." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0002/MQ28415.pdf.
33
Kanizawa, Fábio Toshio. "Estudo teórico e experimental sobre padrões de escoamento, fração de vazio e perda de pressão durante escoamento bifásico água-ar cruzado ascendente externo a banco de tubos." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/18/18147/tde-30032015-080832/.
Анотація:
O presente trabalho envolve um estudo teórico e experimental do escoamento bifásico externo a banco de tubos. Inicialmente, apresenta-se uma ampla revisão da literatura sobre padrões de escoamento, fração de vazio e perda de pressão, durante escoamentos monofásicos e bifásicos externos a banco de tubos. Nesta análise são também descritos os métodos de previsão destes parâmetros. Verificam-se diferenças significativas entre as estimativas proporcionadas por eles, fato que indica a inexistência de métodos generalizados. Posteriormente é apresentada uma descrição detalhada da bancada experimental projetada e construída durante o doutoramento. O aparato completo compõe-se da seção de testes, circuito de água, sistema de compressão e condicionamento de ar, e seções de injeção dos fluxos e condicionamento do escoamento. A seção de testes consiste em um banco de tubos distribuídos segundo configuração triangular normal, com os tubos apresentando diâmetro externo de 19,1 mm, comprimento de 381 mm, e espaçamento transversal de 24 mm. Os experimentos foram realizados para escoamento vertical ascendente de misturas água-ar e velocidades superficiais da fase líquida e gás de 0,020 a 1,500 m/s e de 0,10 a 10,00 m/s, respectivamente. Neste estudo foram desenvolvidas técnicas inéditas para determinação experimental da fração de vazio superficial no interior do banco de tubos baseadas em sistemas óptico e de sensoriamento capacitivo. Os padrões de escoamento foram identificados subjetivamente através de visualização de imagens e vídeos do escoamento, e objetivamente com o auxílio do método de agrupamento de dados k-means utilizando parâmetros baseados no sinal de perda de pressão e do sensoriamento capacitivo. Identificou-se subjetivamente os padrões de escoamento bolhas, bolhas dispersas, bolhas grandes, agitante, intermitente e anular. Constatou-se equivalência entre os padrões de escoamento identificados através dos métodos objetivo e subjetivo. Resultados experimentais para fração de vazio foram obtidos através de técnicas óptica e capacitiva. Constatou-se que o traçador rodamina B utilizado no método óptico altera as condições do escoamento, ainda que em concentrações reduzidas. A partir dos resultados obtidos com o sensoriamento capacitivo estimou-se a fração de vazio para o padrão bolhas. Resultados para a parcela friccional da perda de pressão também foram levantados. Constata-se o incremento da fração de vazio e da parcela friccional da perda de pressão com as velocidades superficiais das fases líquida e gás. Os resultados para fração de vazio foram comparados com métodos de previsão da literatura, e de maneira geral os métodos preveem as tendências dos resultados experimentais apenas para vazões de líquido reduzidas. Analogamente, os resultados para perda de pressão foram comparados com estimativas segundo métodos da literatura, concluindo que os métodos não preveem satisfatoriamente os resultados obtidos. Desta forma, foram propostos novos métodos de previsão para padrões de escoamento, fração de vazio e parcela friccional da perda de pressão, desenvolvidos a partir de análises dos mecanismos dominantes do escoamento, e adotando parâmetros adimensionais para correlacionar os dados. Os métodos propostos preveem satisfatoriamente os resultados experimentais deste estudo e da literatura para escoamentos bifásicos água-ar.The present thesis concerns a theoretical and experimental study of external two-phase flows across tube bundles. Initially, a comprehensive literature review covering flow patterns, void fraction and pressure drop for single and two-phase flows across tubes bundle is presented. The review also describes predictive methods for these parameters. A comparison of these methods reveals reasonable disagreement among their predictions, indicating the absence of generalized methods. Subsequently, the apparatus and instrumentation designed and built to obtain the experimental data are described. The experimental apparatus comprises the test section, a water loop, air compression and conditioning systems, and sets for fluid flow injections and conditioning. The test section is a normal triangular tube bundle, with 19.1 mm OD tubes, 381 mm long and transversal pitch of 24 mm. The experiments were performed for air-water upward vertical flow, for superficial liquid and gas velocities ranging from 0.020 to 1.500 m/s and 0.10 to 10.00 m/s, respectively. Innovative techniques to evaluate the void fraction within the bundle were developed based on capacitive and optical methods. The flow patterns were identified subjectively and objectively by k-means clustering method, using as clustering parameters the pressure drop and the capacitive signals. Bubbles, dispersed bubbles, large bubbles, churn, intermittent and annular flow patterns were identified subjectively. The data groups identified by the objective method are representative of the flow patterns. Void fraction measurements were obtained for bubbly flow using both techniques (optical and capacitive). The void fraction data based on the optical method had its experimental range limited due to changes in the flow characteristics caused by the addition of the fluorescent dye Rhodamine B. The experimental results indicate that the void fraction increases with increasing the superficial velocities of both phases. In general, the void fraction predictive methods available in the literature capture the trends of the experimental results only for reduced liquid flow rates. According to the experimental results, the frictional pressure drop increases asymptotically with increasing the flow rates of both phases. None of the predictive methods from literature evaluated in the present study predicted satisfactorily the experimental results. Methods for prediction of flow patterns, void fraction and frictional pressure drop parcel were also developed in the present study. These methods provided reasonable predictions of the experimental results obtained in the present study, and also from the literature for air and water flows across tube bundles.
34
Schlup, Jason. "Two phase flow visualization in evaporator tube bundles using experimental and numerical techniques." Thesis, Kansas State University, 2013. http://hdl.handle.net/2097/16237.
Анотація:
Master of ScienceDepartment of Mechanical and Nuclear Engineering
Steven Eckels and Mohammad Hosni
This research presents results from experimental and numerical investigations of two-phase flow pattern analysis in a staggered tube bundle. Shell-side boiling tube bundles are used in a variety of industries from nuclear power plants to industrial evaporators. Fluid flow patterns in tube bundles affect pressure drop, boiling characteristics, and tube vibration. R-134a was the working fluid in both the experimental and computational fluid dynamics (CFD) analysis for this research. Smooth and enhanced staggered tube bundles were studied experimentally using a 1.167 pitch to diameter ratio. The experimental tube bundles and CFD geometry consist of 20 tubes with five tubes per pass. High speed video was recorded during the experimental bundle boiling. Bundle conditions ranged in mass fluxes from 10-35 kg/m[superscript]2.s and inlet qualities from 0-70% with a fixed heat flux. Classification of the flow patterns from these videos was performed using flow pattern definitions from literature. Examples of smooth and enhanced bundle boiling high speed videos are given through still images. The flow patterns are plotted and compared with an existing flow pattern map. Good agreement was found for the enhanced tube bundle while large discrepancies exist for the smooth tube bundle. The CFD simulations were performed without heat transfer with non-symmetrical boundary conditions at the side walls, simulating rectangular bundles used in this and other research. The two-phase volume of fluid method was used to construct vapor interfaces and measure vapor volume fraction. A probability density function technique was applied to the results to determine flow patterns from the simulations using statistical parameters. Flow patterns were plotted on an adiabatic flow pattern map from literature and excellent agreement is found between the two. The agreement between simulation results and experimental data from literature emphasizes the use of numerical techniques for tube bundle design.
35
Liang, Chunlei. "Large eddy simulation of the turbulent flow and heat transfer in tube bundles." Thesis, King's College London (University of London), 2005. https://kclpure.kcl.ac.uk/portal/en/theses/large-eddy-simulation-of-the-turbulent-flow-and-heat-transfer-in-tube-bundles(73e0ff53-1135-4620-bb66-7eb3d091a7a6).html.
36
Tuma, Juergen. "The enhancement of heat transfer to gases in longitudinal flow in tube bundles." Thesis, University of Brighton, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280462.
37
Almeshaal, Mohammed Abdulrahman. "An experimental and numerical study of two-phase flow in horizontal tube bundles." Thesis, Heriot-Watt University, 2013. http://hdl.handle.net/10399/2900.
Анотація:
An effective design for a kettle reboiler is dependent on fitness for purpose while reducing costs. Thus, accurate information concerning two-phase flow behaviour within it is important. Experimental and numerical studies have been carried out in this research to gain a more detailed understanding of the phenomena associated with two-phase flow in a thin-slice kettle reboiler. The kettle reboiler contained 241 electrically heated tubes arranged as 17 rows of 17 columns in an in-line layout with an outside diameter of 19 mm and a pitch-to-diameter ratio of 1.34. The working fluids used in this investigation were pentane and the refrigerant R113. They were boiled at atmospheric pressure at uniform heat fluxes in the range of 10 to 40 kW/m2. The patterns of flow inside the kettle reboiler were investigated experimentally using ordinary and high speed cameras. Visual observation of the flow patterns showed that the flow in the tube bundle was two-dimensional at heat fluxes of 20 kW/m2 and above. The quantity of foam and recirculation above the tube bundle were found to depend on both the heat flux and the working fluid used. Observations of the two-phase flow pattern in the shell indicated that the movement of fluid from the centre column of the bundle was affected by the down flow into the top of the tube bundle. Two flow patterns in the tube bundle were identified: bubbly and intermittent. At low heat fluxes, bubbly flow dominated, then, with increasing heat flux, bubble coalescence led to the development of vapour slugs and intermittent flow was observed. Pressure drop measurements were made in three columns within the tube bundle. The results showed that at heat fluxes below 20 kW/m2, the pressure drop remained nearly constant and equal to the all-liquid value. At a heat flux of 20 kW/m2 and above, the pressure drop was found to increasingly fall below the all-liquid value as the bundle row number increased. This effect was especially evident in the centre of the bundle. A change in the flow pattern caused the pressure distribution up the tube bundle to change from roughly constant to decaying with height. Based on a number of assumptions, the two-fluid model has been applied. The two-fluid model’s drag coefficient and tube resistance were deduced from a one-dimensional model. The two-fluid model predictions show good agreement with the experimental results for the pressure distribution and flow distribution. Grid sizes of 10, 8 and 4 mm for the bundle and the pool were considered. It was found that the predicted bundle results were not affected by changing the grid size. However, in the pool region, a small grid size was needed. A grid size of 10 mm was used in the bundle while 4 mm was used in the pool. The pool velocity predictions compared well with measured values available in the open literature. The results indicated that the bundle flow is not significantly affected by the pool flow. This allows the two-fluid model to be further refined: simplifying it and reducing the computational time. A bundle-only two fluid model has been developed to accurately predict two-phase flow behaviour in the kettle reboiler tube bundle. Information available from earlier studies has been used to develop this model because of the difficulties associated with measuring the void fraction and velocities within the tube bundle. The model uses two different boundary conditions: (1) static liquid pressure in the pool and (2) variation of pressure in the pool based on the flow pattern transition. The results predicted by the model have been compared with experimental data and with one and two-fluid models at different heat fluxes. Boundary condition (1) was found to be in good agreement with experimental data and the one and two-fluid models at a heat flux of 10 kW/m2. This was because the transition flow pattern was not achieved and the bundle was surrounded by a static pool. Boundary condition (2) is based on the Kutateladze number (Ku), which sets the transition point from bubbly to intermittent flow at a certain height in the bundle. For Ku ≤ 1.09, the bundle flow would be surrounded by liquid, and if Ku > 1.09, the bundle flow would be surrounded by two-phase flow. At heat fluxes of 20 kW/m2 and above, boundary condition (2) has been found to be in good agreement with experimental data and the values predicted from the one and two-fluid models for liquid velocities, vertical mass flux and void fraction. The bundle-only model accurately predicts the trend line of constant and decaying pressure drop measured at low and high heat fluxes, respectively, and the observed flow phenomena in the kettle reboiler. The key feature of the model presented is that it allows two-phase flow in the kettle reboiler to be simulated by only modelling the tube bundle. Thus the model is simplified and less computational time is required. A central column model was developed using the minimum pressure gradient approach. The predicted results from this model were compared with experimental data and the values predicted by the two-fluid model and the bundle-only model. Reasonable agreement was obtained indicating that the flow distribution may be linked to the minimum pressure gradient.
38
Wu, Tzu-Yu. "Design of Confocal Microendscopy for Fallopian Tube Imaging and Detection of Esophageal Cancer." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/347227.
Анотація:
This work presents several major developments related to a fluorescence confocal microendoscope technology that can provide instantaneous cellular level images from selected depths of tissue inside the human body. The confocal microendoscope systems discussed employ fiber-optic based imaging catheters coupled to custom built slit-scan confocal microscopes. One major new development involves the design, development, and testing of a new flexible confocal microgastroscope (CMG) system for imaging the esophagus. This new system has the potential to aid in the early detection of esophageal cancer. It consists of a new optical scan unit mounted on an endoscopy cart and a new flexible catheter that can be inserted through the instrument channel of a commercial gastroscope. The CMG system has higher spatial resolution and larger field of view than the previous generation clinical confocal microendoscopes in our lab. In addition, the new CMG system can be operated over a greater wavelength range than its predecessor. Central to the CMG system is the design, construction, and testing of a new distal miniature objective that enables high-quality microendoscopy. The miniature objective, built with all glass spherical surfaces, achieves diffraction-limited performance over a 486 to 1000 nm spectral range. The wide achromatic range of this lens allows the CMG system to be used with a variety of contrast agents including agents in the NIR region. In addition, the new miniature objective can be mounted on existing confocal microendoscopes in our lab such as the ovarian clinical confocal microlaparoscope and our laboratory based experimental system. Finally, a new confocal microlaparoscope with an articulating catheter capable of imaging inside the distal portion of fallopian tubes is presented. This instrument is intended to allow the detection of early stage ovarian cancer originating inside the fallopian tube. The new microlaparoscope is compatible with 5 mm trocars and includes a thin 2.2 mm diameter articulating distal tip consisting of a bare fiber bundle and an automated dye delivery system. The distal tip of this new endoscope can be articulated through simple wrist movements and locked in place at a given angle if desired. The thin distal tip and the ability to control the angle of the tip provide the size and flexibility needed to image inside the curved and delicate structures of the fallopian tube. Preliminary imaging results from the new CMG system, the achromatized miniature objective, and the new articulating confocal microlaparoscope are presented to demonstrate the performance and the potential of each system towards the overall goal of in vivo imaging and disease diagnosis.
39
Bahaidarah, Haitham M. S. "A numerical study of heat and momentum transfer over a bank of flat tubes." Texas A&M University, 2004. http://hdl.handle.net/1969.1/2782.
Анотація:
The present study considers steady laminar two-dimensional incompressible flow over both in-line and staggered flat tube bundles used in heat exchanger applications. The effects of various independent parameters, such as Reynolds number (Re), Prandtl number (Pr), length ratio (L/Da), and height ratio (H/Da), on the pressure drop and heat transfer were studied.
A finite volume based FORTRAN code was developed to solve the governing equations. The scalar and velocity variables were stored at staggered grid locations. Scalar variables (pressure and temperature) and all thermophysical properties were stored at the main grid location and velocities were stored at the control volume faces. The solution to a one-dimensional convection diffusion equation was represented by the power law. The locations of grid points were generated by the algebraic grid generation technique. The curvilinear velocity and pressure fields were linked by the Semi-Implicit Method for Pressure Linked Equations (SIMPLE) algorithm. The line-by-line method, which is a combination of the Tri-Diagonal Matrix Algorithm (TDMA) and the Gauss-Seidel procedure, was used to solve the resulting set of discretization equations.
The result of the study established that the flow is observed to attain a periodically fully developed profile downstream of the fourth module. The strength increases and the size of the recirculation gets larger as the Reynolds number increases. As the height ratio increases, the strength and size of the recirculation decreases because the flow has enough space to expand through the tube passages. The increase in length ratio does not significantly impact the strength and size of the recirculation.
The non-dimesionalized pressure drop monotonically decreased with an increase in the Reynolds number. In general, the module average Nusselt number increases with an increase in the Reynolds number. The results at Pr = 7.0 indicate a significant increase in the computed module average Nusselt number when compared to those for Pr = 0.7. The overall performance of in-line configuration for lower height ratio (H/Da = 2) and higher length ratio (L/Da = 6) is preferable since it provides higher heat transfer rate for all Reynolds numbers except for the lowest Re value of 25. As expected the staggered configurations perform better than the in-line configuration from the heat transfer point of view.
40
Ahlinder, Stefan. "On modelling of compact tube bundle heat exchangers as porous media for recuperated gas turbine engine applications." [S.l.] : [s.n.], 2006. http://se6.kobv.de:8000/btu/volltexte/2006/15.
41
Ahlinder, Stefan [Verfasser]. "On Modelling of Compact Tube Bundle Heat Exchangers as Porous Media for Recuperated Gas Turbine Engine Applications / Stefan Ahlinder." Aachen : Shaker, 2006. http://d-nb.info/1170538037/34.
42
Musa, Mohd Nor. "Condensation of a binary vapour of immiscible liquids on a horizontal tube bundle under the influence of vapour shear." Thesis, Heriot-Watt University, 1987. http://hdl.handle.net/10399/1046.
43
Beccacece, Lorenzo. "Electromagnetic interaction between multi-walled carbon nanotube bundles." Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS268.
Анотація:
L’utilisation des matériaux 1D et 2D dans les dispositifs électroniques suscite un intérêt dans la communauté scientifique et industriel. Grâce à leurs propriétés uniques, les chercheurs envisagent la miniaturisation de dispositifs électroniques fabriqués. Les nanotubes de carbone font partie des matériaux 1D. Après avoir fait l’état de l’art concernant le matériau et son intégration dans les dispositifs électroniques, on a pu déterminer de nouveaux axes de recherche. Ce travail de thèse porte sur la synthèse, caractérisation, modélisation et intégration des fagots verticaux de nanotubes de carbone multi-parois (VAMWCNTs), dans des dispositifs hyperfréquences. L’objectif a été d’améliorer la compréhension du comportement électrique du matériau dans le domaine hyperfréquence, et d’étudier l’interaction électromagnétique entre deux fagots de VAMWCNTs. Ces objectifs font que ce travail de thèse propose une étude novatrice. Des caractérisations avancées ont été réalisées sur ce matériau, et ceci afin de déterminer leurs caractéristiques. Deux modèles électriques équivalents ont été proposés et implémentés par des simulations numériques afin de calculer leurs impédance électrique complexe. Ces résultats de caractérisation ont été utilisés a posteriori pour valider, et aussi pour améliorer ces modèles. Un procédé de fabrication en salle blanche a été optimisé dans le but de synthétiser les fagots de VAMWCNTs directement sur les pistes métalliques.Un dispositif hyperfréquence a été conçu pour étudier le couplage électromagnétique entre deux fagots verticaux de VAMWCNTs. Les mesures montrent l’existence d’un effet qui peut être attribué aux couplages capacitif et magnétiqueThe use of 1D and 2D materials in electronic devices is a matter of interest for the scientific and industrial communities. Thanks to their unique properties, the researchers want to reach the device miniaturization. The carbon nanotubes are part of the 1D materials. After the study of the state of the art on this material and on its integration in electronic devices, we defined new research issues on the matter. The work performed in this Ph.D. covered the synthesis, characterization, modeling and integration of vertically aligned multi-walled carbon nanotube (VAMWCNT) bundles, in microwave devices. The goal was to have a better comprehension of the electrical behavior of the synthetized material in the microwave spectrum, and to test the electromagnetic interaction between two large VAMWCNT bundles. This subject has never been previously explored. Advanced characterizations have been achieved on the material, to determine their quality and properties. Two equivalent electrical models, implemented with numerical experiments, were proposed to have the frequency-dependent behavior of the complex electrical impedance. The characterization results were used as feedback to validate and also to improve the models. A clean room fabrication process was optimized, in order to synthetize the VAMWCNT bundles directly on the metallic lines of the devices, and to study the impact of the synthesis. Finally, a microwave device was designed to study the electromagnetic coupling between two large VAMWCNT bundles. The measurements permitted to observe an effect which can be attributed to their capacitive and magnetic coupling
44
Akcasayar, Nezih. "Nucleate pool boiling performance of finned and high flux tube bundles in R-114/oil mixtures." Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/27168.
Анотація:
Approved for public release; distribLUion is unlimitedThe heat transfer characteristics of pure R-114 and R-114/oil mixtures during nucleate pool boiling from a small bundle of finned and High Flux tubes were measured. The bundles had 5 instrumented and 10 additional heated tubes of 15.8 mm outside diameter which were arranged in an equilateral triangular pitch of 19.1 mm giving a pitch-to-diameter ratio of 1.2. Pure refrigerant with York-C lubrication oil mass con-centrations of 1, 2, 3, 6 and 10% was used. All experiments were performed at 2.2C corresponding to a pressure slightly below atmospheric. Data sets were taken using decreasing heat flux only in order to avoid the boiling hysterisis phenomenon. An enhancement in heat-transfer performance of the finned tube bundle due to oil applications was observed. The enhancement increased with up to 3% oil concentration over all heat flux ranges. Further oil additions showed better performances than pure R-114 at high heat flux levels but poorer performance was obtained at lower heat fluxes. High flux tube experiments indicated that the heat transfer performance of the bundle was approximately 2.5 times better than the finned tube bundle performance for pure R-114. No positive performance enhancement was observed from the High Flux tube bundle due to oil addition. The performance immediately degraded with 1% oil and stayed almost constant with 2% and 3% oil additions. A decrease of performance became significant at high heat flux levels with oil concentrations of 6% and 10%. The performance of these two tube bundles was compared to smooth tube operation.
45
Anderson, Carl Lee. "Nucleate pool boiling performance of smooth and finned tube bundles in R-113 and R-114/oil mixtures." Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/27169.
46
Eraydin, Hakan. "Nucleate pool boiling performance of small High Flux and Turbo-B tube bundles in R-114/oil mixtures." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA241936.
Анотація:
Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, December 1990.Thesis Advisor(s): Marto, Paul J. ; Memory, Steve. "December 1990." Description based on title screen as viewed on March 30, 2010. DTIC Identifier(s): Pool Boiling. Author(s) subject terms: Heat Transfer, Pool Boiling. Includes bibliographical references (p. 102-104). Also available in print.
47
Chýlek, Martin. "Tok látek v nestandardních procesních a energetických zařízeních." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-377756.
Анотація:
Flow distribution has big importance in equipment with limited tube rows because it provides correct operation and sometimes specific flow distribution for technology purposes is needed. This thesis is focusing on flow analysis in these units using computational fluid dynamics (CFD). For analysis of such systems models with varying tube rows and varying perforated segment lengths were created. Analysis showed significant impact of flow manifold layout along with tube layout and number of tubes. Simplified 1D model using static pressure regain coefficient was created which provides much shorter computational times. Comparison of 1D and CFD models was made to determine field of their usage.
48
Kubíček, Ondřej. "Návrh ohříváku topné vody pro vyvedení tepla z teplárny o výkonu 5,5 MW." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-232145.
Анотація:
The Master thesis deals with the water-heater design for heat-exchange station with total power output 5,5 MW. The goal of the thesis is to make thermal and hydraulic calculation in the extent of the assignment and to develop a projection drawing of the heater along with a correct dimensioning of the shell and flanges. Thesis goals were met according to the assignment. The introductory part of the thesis briefly introduces to the heat-exchanger problematic and selected topics about heat-transfer. Following the basic mass and energy flows calculation inside the heater together with the thermal and hydraulic design determines the size of the heat transfer surface of pipes. After that the design calculations were made, whose results are used to determine the basic dimensions of selected parts and checking the accuracy of designed dimensions. In the last part of the work the design process is more described also with a more detailed description of selected parts.
49
Pomarède, Marie. "Investigation et application des méthodes d'ordre réduit pour les calculs d'écoulements dans les faisceaux tubulaires d'échangeurs de chaleur." Thesis, La Rochelle, 2012. http://www.theses.fr/2012LAROS355/document.
Анотація:
Cette thèse s’intéresse à la faisabilité de la mise en place de modèles d’ordre réduit pour l’étude des vibrations sous écoulement au sein de faisceaux tubulaires d’échangeurs de chaleur. Ces problématiques sont cruciales car les systèmes étudiés sont des éléments majeurs des centrales nucléaires civiles et des chaufferies embarquées dans les sous-marins.Après avoir rappelé le fonctionnement et les risques vibratoires existants au sein des échangeurs de chaleur, des calculs complets d’écoulement et de vibrations sous écoulement ont été effectués, d’abord pour un tube seul en milieu infini, puis pour un faisceau de tubes. Ces calculs ont été menés avec l’outil CFD Code_Saturne. La méthode de réduction de modèle POD (Proper Orthogonal De-composition) a été appliquée au cas des écoulements avec la structure laissée fixe.Les résultats obtenus montrent l’efficacité de la méthode pour ces configurations, moyennant l’introduction de méthodes de stabilisation pour l’écoulement au sein du faisceau. La méthode POD-multiphasique, permettant d’adapter la méthode POD à l’interaction fluide-structure, a ensuite été appliquée. Les grands déplacements d’un cylindre seul dans la zone d’accrochage (lock-in) ont été correctement reproduits par cette méthode de réduction de modèle. De même, on montre que les grands déplacements d’un cylindre en milieu confiné dans un faisceau de tubes sont fidèlement reconstruits.Enfin, l’extension de l’utilisation de la réduction de modèle aux études d’évolution paramétrique a été testée. Nous avons d’abord utilisé la technique considérant une base POD unique pour reproduire des écoulements à divers nombres de Reynolds autour d’un cylindre seul. Les résultats confirment la prédictivité bornée à une gamme de paramètres de cette méthode. Enfin, l’interpolation de bases POD pré-calculées pour une famille de paramètres donnés, utilisant les variétés de Grassmann et permettant de générer de nouvelles bases POD, a été testée sur des cas modèlesThe objective of this thesis is to study the ability of model reduction for investigations of flow-induced vibrations in heat exchangers tube bundle systems.These mechanisms are a cause of major concern because heat exchangers are key elements of nuclear power plants and on-board stoke-holds.In a first part, we give a recall on heat exchangers functioning and on vi-bratory problems to which they are prone. Then, complete calculations leaded with the CFD numerical code Code_Saturne are carried out, first for the flow around a single circular cylinder (fixed then elastically mounted) and then for the case of a tube bundle system submitted to cross-flow. Reduced-order method POD is ap-plied to the flow resolution with fixed structures. The obtained results show the efficiency of this technique for such configurations, using stabilization methods for the dynamical system resolution in the tube-bundle case.Multiphase-POD, which is a method enabling the adaptation of POD to fluid-structure interactions, is applied. Large displacements of a single cylinder elastically mounted under cross-flow, corresponding to the lock-in phenomenon,are well reproduced with this reduction technique. In the same way, large displace-ments of a confined moving tube in a bundle are shown to be faithfully recon-structed.Finally, the use of model reduction is extended to parametric studies. First,we propose to use the method which consists in projecting Navier-Stokes equations for several values of the Reynolds number on to a unique POD basis. The resultsobtained confirm the fact that POD predictability is limited to a range of parameter values. Then, a basis interpolation method, constructed using Grassmann mani-folds and allowing the construction of a POD basis from other pre-calculated basis,is applied to basic cases
50
Volná, Kateřina. "Vliv zanášení svazku trubek v kotli na jeho životnost." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-377757.
Анотація:
Fouling of tube bundles in boilers on the flue gas side affects not only the service life, but also the boiler heat output and increases maintenance and operating costs. Therefore, it is necessary to minimize or completely eliminate this process. This thesis focuses on comparison of the service life and the heat output of the tube bundles with and without deposit in the coal fired boiler. Simulations of flue gas flow in area of tube bundles with and without deposit are performed using ANSYS Fluent software, which shows that the surface of tube bundles with deposit is much less heated than the surface without deposit. The thermal loads of tubes obtained by the CFD analysis are applied to the model, which is created in the program ANSYS Mechanical, where the calculation of the temperature field in the cross section of the pipe is realized. The effect of fouling on creep life and heat output is then evaluated based on simulation results. The results show that fouling increases creep life, but significantly reduces heat output of heavily fouled tubes. Hence the flue gas flows at a higher temperature to the rest of the tube bundle, and the service life of those tubes will therefore probably decrease.