Doctor of Philosophy / Department 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.

Significant maldistribution negatively influences performance of equipment containing dense tube bundles and, moreover, it can cause a wide range of operating issues. This thesis therefore focuses on analysis of fluid flow in complete distribution systems via computational fluid dynamics (CFD). Data obtained from simulations carried out using the software ANSYS Fluent were also statistically analysed. Influence of system arrangement, tube bundle parameters and operating parameters on flow distribution non-uniformity and pressure drop was investigated. According to the results, system arrangement is the crucial differentiating parameter in terms of flow distribution as well as pressure drop. Additionally, data obtained via the classical CFD approach were compared with those yielded by a simplified CFD model for three selected distribution systems. Simplified CFD approach can - given its low computational demand - be utilised in optimization algorithms as well as in the course of the initial stage of equipment design process. Furthermore, this thesis discusses a simulation tool which is based on the simplified CFD approach. Although this tool is still being developed, the results it yields are very promising.

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.

Tato diplomová práce se zaměřuje na modelování proudění tekutiny v paralelních distribučních systémech, kde hraje důležitou roli rovnoměrnost distribuce tekutin. Pro tento účel je vytvořen vlastní CFD kód. Kód je napsán v programovacím jazyce Java a používá ke zlepšení výkonu knihovny třetích stran, které se vyznačují přímým přístupem ke hardwarovým a systémovým prostředkům. Kód se také vyznačuje určitými zjednodušeními, u nichž se očekává, že sníží výpočetní časy. Vliv použitých zjednodušujících opatření je vyhodnocen porovnáním výsledků simulací proudění na několika geometriích s údaji získanými z podrobných modelů CFD. Geometrie použitých svazků trubek se odlišují různými uspořádáními toku a trubek a také různým počtem trubek.

This diploma thesis deals with calculation methods of heat exchanger with cross-flow tube bundle. The first part of the thesis contains summary of generally known basic calculation relations used in calculations of heat exchangers and a detailed description of a given heat exchanger.The second part of the thesis provides a description of available calculation methods of a given aparatus required for its thermal and hydraulic calculation. The final part describes application POST in 1.0 which has been formed on the basis of these calculation methods. Using this application check calculation of exchanger with cross-flow tube bundle was carried out and gained figures compared with results gained by means of professional calculation program HTRI.

Sprinkled tube bundles with a thin liquid film flowing over them are used in various technology processes where it is necessary to separate the vapour and liquid phases quickly and efficiently. The process occurs predominantly at low temperatures with a corresponding decrease of pressure around the tube bundle. Such a technology is represented for instance by an evaporator at absorption units or an evaporator for sea water desalination. In ideal conditions water boils at the whole surface of an exchanger, but in practice it must be considered that in original spots of contact between water and the exchanger wall the water will not boil at the tubes' surface but the cooling liquid will merely be heated-up. The presented dissertation thesis focuses on this issue. The objective of the thesis was to determine the heat transfer coefficient at the surface of sprinkled tube bundles of various geometries at atmospheric pressure as well as low pressure. For this purpose experiments have been carried out at tube bundles consisting of copper tubes of 12,0 mm diameter placed horizontally one above another that were heated by water. Three types of tubes (smooth, sandblasted and grooved) of four various pitches (15,0 to 30,0 mm by 5,0 mm increments) have been tested. Simultaneously individual bundles' geometries consisted of 4, 6, 8 and 10 tubes with identical surface finish. Based on the conducted experiments the mathematical model of heat transfer that involves mainly analogy criteria has been made more accurate. A temperature field at the sprinkled tube bundle surface has been scanned by a thermographic camera during the performed experiments. Influence of geometry and tube surface finish on flow mode and consequently also on heat transfer has been assessed in accordance with the compiled methodology.

Helical tube bundles are usually used in the steam generator (SG) of High-Temperature Gas-Cooled Reactors (HTGRs) as the heat transfer area. The helical tube bundle is composed of multiple-layer helically coiled tubes, which are fixed by multiple sets of supporting structures. There are ideal flow paths separated by different layers of helical tubes. The velocity non-uniformity for different flow paths will affect the heat transfer tube temperature and the outlet steam temperature uniformity of different tube layers. In the shell side of the SG, turbulent cross flow over helical tube bundles are complicated and difficult to predict due to reverse pressure gradient and boundary layer separation. Due to the huge amount of computation resources consumption, there are few numerical simulation studies on the non-uniformity of cross flow over large-volume helical tube bundles.Two cases, namely the flow past a circular cylinder and cross flow over in-line tube bundles, are simulated to validate if Partially-Averaged Navier-Stokes (PANS) model is suitable for simulations of cross flow over helical tube bundles. The simulation results of k-ω SST PANS model are well agree with the average and local experimental data. Therefore, k-ω SST PANS model is used to investigate the influences of the supporting structure and helical diameter on the non-uniformity of cross flow over ideal helical tube bundles. The helix angle of helical tube bundle is neglected. The computational domain consists of 5 rows of helically coiled tubes in the streamwise direction. Periodic boundary conditions are used for the inlet and outlet to reduce the consumption of computing resources.For cross flow over helical tube bundles, there exists significant circumferential and radial velocities, which means there are secondary flows in the plane perpendicular to the streamwise direction. The radial velocity is about 16% of the streamwise velocity. Due to the presence of secondary flow, cross flow over individual tube is inclined, and the inclination direction changes at different circumferential positions. At the same circumferential position, the flow inclination direction is the same along the streamwise direction and radial direction. For helical tube bundles, the ratio of the blocking area to the flow area (blocking area ratio) of the inner, outer and middle flow paths are different. The blocking area ratio of the inner flow path is large, and the blocking area ratio of the outer flow path is small, resulting in non-uniform velocity distribution in different flow paths.Cross flow over helical tube bundles with three helical diameters (inner wall radius Ri is 0.02 m, 0.14 m and 0.26 m, respectively) are simulated. For small helical diameter tube bundle (Ri = 0.02 m), the maximum streamwise velocity non-uniformity is 16.6%. For tube bundles with middle and large helical diameters (Ri = 0.14 m and 0.26 m), the maximum streamwise velocity non-uniformity is 6.7% and 5.8%, respectively. The results show that the flow non-uniformity becomes more obvious for small helical diameter.The supporting structures results in more complex secondary flows. The secondary flows far from the supporting structures are larger than those in the region near the supporting structures. The supporting structures causes the blocking area ratio of inner, outer and middle flow paths vary with the helical diameter, and the blocking area ratio non-uniformity is larger than that without supporting structures. In the presence of supporting structures, the maximum streamwise velocity non-uniformities of small, middle and large helical diameter tube bundles are 22.0%, 8.8% and 6.3%, respectively. The effect of supporting structures on the flow non-uniformity increases as the helical diameter decreases. / Spiralformade rörknippen används vanligtvis i ånggeneratorn (SG) i gaskylda högtemperaturreaktorer (HTGR) som värmeöverföringsområde. Det spiralformade rörknippet består av flerskikts spiralformade rör, som är fixerade av flera uppsättningar stödkonstruktioner. Det finns idealiska flödesvägar åtskilda av olika lager av spiralformade rör. Hastighetsojämnheten för olika flödesvägar kommer att påverka värmeöverföringsrörets temperatur och utloppsångans temperaturlikformighet för olika rörskikt. På skalsidan av SG är turbulent tvärflöde över spiralformade rörknippen komplicerade och svåra att förutsäga på grund av omvänd tryckgradient och gränsskiktsseparation. På grund av den enorma förbrukningen av beräkningsresurser finns det få numeriska simuleringsstudier om ojämnheten i tvärflödet över spiralformade rörknippen med stora volymer.Två fall, nämligen flödet förbi en cirkulär cylinder och korsflödet över in-line rörknippen, simuleras för att validera om PANS-modellen (Partially-Averaged Navier-Stokes) är lämplig för simuleringar av tvärflöde över spiralformade rörknippen. Simuleringsresultaten för k-ω SST PANS-modellen stämmer väl överens med genomsnittliga och lokala experimentella data. Därför används k-ω SST PANS-modellen för att undersöka påverkan av stödstrukturen och spiraldiametern på ojämnheten i tvärflödet över ideala spiralformade rörknippen. Helixvinkeln för spiralformad rörbunt försummas. Beräkningsdomänen består av 5 rader spiralformade rör i strömriktningen. Periodiska randvillkor används för inlopp och utlopp för att minska förbrukningen av datorresurser.För tvärflöde över spiralformade rörknippen finns det signifikanta perifera och radiella hastigheter, vilket innebär att det finns sekundära flöden i planet vinkelrätt mot strömriktningen. Den radiella hastigheten är cirka 16 % av den strömvisa hastigheten. På grund av närvaron av sekundärt flöde lutar tvärflödet över enskilda rör och lutningsriktningen ändras vid olika omkretspositioner. Vid samma perifera position är flödesinklinationsriktningen densamma längs strömriktningen och radiell riktning. För spiralformade rörknippen är förhållandet mellan blockeringsarean och flödesarean (blockeringsareaförhållandet) för de inre, yttre och mellersta flödesvägarna olika. Blockeringsareaförhållandet för den inre flödesvägen är stort och blockeringsareaförhållandet för den yttre flödesvägen är litet, vilket resulterar i ojämn hastighetsfördelning i olika flödesvägar.Tvärflöde över spiralformade rörknippen med tre spiralformade diametrar (innerväggsradien Ri är 0,02 m, 0,14 m respektive 0,26 m) simuleras. För rörknippe med liten spiraldiameter (Ri = 0,02 m) är den maximala strömhastighetsolikformigheten 16,6 %. För rörknippen med mellersta och stora spiralformade diametrar (Ri = 0,14 m och 0,26 m) är den maximala strömhastighetsolikformigheten 6,7 % respektive 5,8 %. Resultaten visar att flödesojämnheten blir mer uppenbar för små spiralformade diametrar.De bärande strukturerna resulterar i mer komplexa sekundärflöden. Sekundärflödena långt från stödkonstruktionerna är större än de i området nära stödkonstruktionerna. De bärande strukturerna gör att blockeringsareaförhållandet för inre, yttre och mellersta flödesvägar varierar med den spiralformade diametern, och blockeringsareaförhållandets ojämnhet är större än utan stödkonstruktioner. I närvaro av stödkonstruktioner är de maximala strömhastighetsojämnheterna för små, mellersta och stora spiralformade rörknippen 22,0 %, 8,8 % respektive 6,3 %. Effekten av stödkonstruktioner på flödesojämnheten ökar när den spiralformade diametern minskar.

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 I2M. / The 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.

This thesis is devoted to thermal-hydraulic design and rating of heat exchangers with the specialized commercial software HTRI. These heat exchangers are solved for real high-temperature applications, where the hot fluid is a flue gas with high temperature (above 500 °C). In the thesis is made a brief analysis of the conventional design of heat exchangers usable for high-temperature aplications, description of the basic relations, description and brief user manual of software HTRI. Further, work includes a comparative study of methods for calculation of pressure drop of the fluid at 180° elbows, as support analysis for solution of required applications characterized by low pressure drop of process fluids.

The master thesis is focused on analysis of specific cross-flow in-line tube bundle heat exchanger which deals with significant operational problems. Thermal, hydraulic and vibration calculation analysis of selected parts of the heat exchanger is performed based on CFD flow distribution results. Calculation is performed by using Maple software. Thermal and hydraulic calculations are compared with results obtained by commercial software HTRI.