Дисертації з теми "Thermo-fluid dynamics"

Thesis (Ph. D.)--University of California, Riverside, 2010.
Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed May 18, 2010). Includes bibliographical references. Also issued in print.

Ice caves are classified as sporadic permafrost phenomena and consist of lava tubes or cave systems in which perennial ice forms. Ice within caves can be very old and can carry important information on permafrost conditions, climate changes and past climates. Until now, these systems have been investigated mainly with an experimental approach. A critical topic in ice cave studies is the understanding of how the internal environment interacts with the external and how these systems react to changes in the external conditions. In this thesis, a new numerical approach to understand ice cave microclimate is proposed. Numerical studies can contribute greatly to a better understanding of the processes involved in the formation and preservation of the ice in cave. Furthermore, computational fluid dynamic methods can be a valuable support to define new experimental setups and to interpret experimental results. The cave studied in this work is Leupa ice cave, located in Friuli Venezia Giulia region. Air flows inside Leupa ice caves were characterized with an integrated approach using both experimental and numerical methods. A general approach was initially adopted and three representative days were identified to investigate which circulation patterns can develop under different environmental conditions. The comparison of numerical and experimental data permitted to evaluate the quality of the simulations and to identify the main problematics that need to be investigated further. Deeper investigations were then performed for a single day to investigate the temperature and boundary conditions effect on the flow thermo-dynamics inside the cave. New insights on the fluid-dynamic behavior of Leupa ice cave are achieved, showing that numerical methods could represent a powerful tool to study ice caves, improving and integrating the information that could be obtained from standard experimental measurements.

The Pebble Bed Modular Reactor (PBMR) is a 4th generation nuclear reactor based on the HTR-Modul of Siemens currently being developed by Eskom in South Africa. The major safety characteristics of the PBMR are the fuel design and physical dimensions that make it an inherently safe reactor. This means that the reactor will not melt down like a typical Light Water Reactor (LWR) when cooling of the reactor is lost. The thermo-hydraulic analysis of the Used Fuel Tank (UFT) is of great importance in the safety analysis of the PBMR. The UFT is one of two types of tanks that will be used to store fuel that has been in the reactor for a finite time. The fuel would therefore contain fission products and would generate decay heat. This decay heat should be removed to limit the temperature of the fuel. The temperature of the fuel should be limited to prevent the release of fission products to the environment. The temperature limit on the fuel during storage is required to ensure that the graphite in the fuel does not oxidize in the presence of oxygen. The fuel is normally kept in a helium environment, but it must be shown that the fuel is safe when there is air ingress into the system. The purpose of this study is therefore to determine the temperature distribution in the fuel and the components of the used fuel tank for different scenarios. This includes the forced cooling of the tanks and the possibility of cooling the tanks with natural convection. Computational Fluid Dynamics (CFD) was used to model the various heat transfer mechanisms present. This includes convection heat transfer between the gases and the solids, conduction through the solids and thermal radiation between most of the surfaces. The effect of natural convection was also included, as the pipes through the tank cause result in high mass flow through these pipes due to the buoyancy effect. The results show that the fuel temperature will not exceed the allowable limit during forced cooling if the Heating, Ventilation and Air-conditioning (HVAC) is supplied at 6 kg/s. The possibility of cooling the tanks with passive means during upset events looks promising, but it is dependant on the design of the chimneys. The chimney cross-flow area was the most significant factor influencing the air mass flow through the system. The chimney design and the rest of the system not included in this study should be analysed in detail before the passive operation of the system can be guaranteed.
Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2004.

This PhD involved computational fluid dynamic simulations of finned generators cooling under forced convection in an oscillating water column environment. Various design changes to the upstream Wells turbine and its effect on the consequent cooling of the generator were investigated. Simulations were run in steady-state to obtain an initial condition, thereafter, unsteady simulations revealed a steadying of heat transfer over the course of multiple blade rotation cycles. This justified the use of steady-state for the remaining simulations over a range of flow coefficients. The results revealed that the heat transfer from the generator increased for tighter blade tip clearances, thicker blade profiles and greater turbine solidity. The heat transfer was found to increase with rising flow rate coefficient, which was adjusted by increasing the inlet velocity whilst maintaining the angular velocity of the turbine at a constant 2000 RPM. Additionally, the variation of turbine angular velocity at a fixed flow rate coefficient was investigated, the heat transfer was also found to increase with angular velocity, albeit by a far lesser extent. The inclusion of the Wells turbine upstream of the generator was investigated initially and was found to increase heat transfer due to the resulting impingement of airflow across the generator. In all design scenarios in which the heat transfer increases, there is also an observed increase in the mass flow rate of air, radially, towards the generator.

In this dissertation the heat flux prediction capabilities of Residual Distribution (RD) schemes for hypersonic flow fields are investigated. Two canonical configurations are considered: the flat plate and the blunt body (cylinder) problems, with a preference for the last one. Both simple perfect gas and more complex thermo-chemical non-equilibrium (TCNEQ) thermodynamic models have been considered.

The unexpected results identified early in the investigation lead to a thorough analysis to identify the causes of the unphysical hypersonic heating.

The first step taken is the assessment of the quality of flow field and heat transfer predictions obtained with RD methods for subsonic configurations. The result is positive, both for flat plate and cylinder configurations, as RD schemes produce accurate flow solutions and heat flux predictions whenever no shock waves are present, irrespective of the gas model employed.

Subsonic results prove that hypersonic heating anomalies are a consequence of the presence of a shock wave in the domain and/or the way it is handled numerically.

Regarding hypersonic flows, the carbuncle instability is discarded first as the cause of the erroneous stagnation heating. The anomalies are shown next to be insensitive to the kind and level of dissipation introduced via the (quasi-)positive contribution P to blended B schemes. Additionally, insufficient mesh resolution locally over the region where the shock wave is captured numerically is found to be irrelevant.

Capturing the bow shock in a manner that total enthalpy is preserved immediately before and after the numerical shock wave is, on the contrary, important for correct heating prediction.

However, a carefully conceived shock capturing term is, by itself, not sufficient to guarantee correct heating predictions, since the LP scheme employed (be it stand-alone in a shock fitting context or combined into a blended scheme for a shock capturing computation) needs to be immune to spurious recirculations in the stagnation point.

Once the causes inducing the heating anomalies identified, hypersonic shocked flows in TCNEQ conditions are studied.

In order to alleviate the computational effort necessary to handle many species non-equilibrium (NEQ) models, the extension of an entropic (or symmetrizing) variables formulation RD to the nS species, two temperature TCNEQ model is accomplished, and the savings in computational time it allows are demonstrated.

The multi-dimensional generalization of Roe-like linearizations for the TCNEQ model is addressed next: a study on the existence conditions of the linearized state guaranteeing discrete conservation is conducted.

Finally, the new dissipative terms derived for perfect gas are adapted to work under TCNEQ conditions; the resulting numerical schemes are free of the temperature undershoot and Mach number overshoot problem afflicting standard CRD schemes.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

This research provides an outlook on the use of biomimicry across disciplines, with a particular focus on the application of metal Additive Manufacturing (AM) to fabricate more efficient fin geometries for heat exchangers. By using functional modelling, a denticle from a shortfin mako shark was identified as geometry for a novel 3D fin for a heat exchanger. The shape of the denticle is streamlined and is known to reducing drag; therefore, indicating a possibility of enhancing fluid-to-solid contact for enhanced heat transfer when used as a fin. Initially, the thermo-hydraulic performance of the denticle was numerically evaluated with respect to a rectangular fin, cylindrical fin, and an NACA 0030 fin, using conjugate-heat-transfer simulations on ANSYS-Fluent. Then, A Markforged Metal X printer was used to fabricate the denticle fin with stainless steel 17- 4PH. Thermal and pressure drop experiments were performed to evaluate the thermos-hydraulic performance of the denticle relative to a rectangular fin. Further, a multi-objective gradient based optimisation was performed on the denticle fin by using ANSYS-Fluent. Results demonstrated that over the range of tested Reynolds numbers, 3.9x104 < Re ≤ 9.2x104, mean thermal performance factors of 1.33 and 1.09 were noted for the shape optimised denticle with respect to the rectangular fin, and initial denticle fin, respectively. Finally, the effect of using bio-inspired surface texturing as a technique to further enhance the thermo-hydraulic performance of a single NACA 63-015 fin was investigated experimentally. A mean thermal performance factor of 1.11 was noted for the range of tested Reynolds numbers, which demonstrated that the addition surface textures in the form of shark denticles to a NACA 63-015 profile increased the thermos-hydraulic performance of the fin compared to a smooth one.

Ce travail concerne l'étude thermohydraulique d'un écoulement d'hélium superfluide diphasique en conduite horizontale, comparable à celui mis en œuvre dans le refroidissement des aimants supraconducteurs du LHC au Cern. On montre que pour des vitesses de vapeur de quelques 3 à 4 m.s\mun, la phase liquide initialement stratifiée subit une atomisation qui se traduit par la présence d'un brouillard de gouttelettes transporté par la phase vapeur. Ceci a pu être montré en hélium superfluide comme en hélium normal sans différence majeure sur l'atomisation. Grâce à différents instruments et dispositifs de visualisation, plusieurs corrélations ont pu être mesurées entre la fraction de gouttelettes entraînées et la capacité frigorifique de l'écoulement diphasique, et ceci en fonction de paramètres expérimentaux comme le niveau liquide, la vitesse de la vapeur, ou encore sa densité.

Le but de ces travaux est de créer un modèle aérothermique, avec un temps de calcul court, d’un alternateur automobile intégré au sein d’une simulation complète d’un environnement sous-capot d’un véhicule. La prise en compte de leur influence au sein d'un comportement moteur est recherchée. Un modèle simplifié permettant la simulation du comportement aéraulique et thermique d’un alternateur a été développé. Il utilise une approche nodale afin de simuler les phénomènes thermiques et aérauliques du système. Différents algorithmes et une interface homme-machine permettent un paramétrage facile et rapide, et une implémentation automatique du modèle. En effet, le paramétrage du réseau nodal est fait automatiquement, l’utilisateur doit seulement rentrer les différents paramètres du système : dimensions, caractéristiques matériaux, pertes thermiques... Cela nous permet d’avoir aussi un modèle adaptable facilement à tout type d’alternateur. Le comportement aéraulique de l’alternateur est simulé via des coefficients de convection, intégrés au réseau nodal. Ces coefficients sont déterminés via des corrélations en fonction du nombre de Reynolds de l’écoulement. Pour chaque zone de l’écoulement d’air dans l’alternateur, ces corrélations ont été identifiées via une modélisation CFD de l’alternateur, lui-même validé par des essais aérauliques sur banc expérimental. Le modèle a été vérifié et validé via des essais expérimentaux thermiques. Il présente une erreur moyenne inférieure à 10%, et fonctionne sur l’ensemble des régimes d’utilisation. Il présente un temps de calcul de l’ordre de 2 minutes. Le modèle a été intégré dans une simulation simplifiée d’un environnement sous-capot. Une méthodologie de couplage a été développée, permettant l’intégration des données du modèle simplifié, au sein des simulations sous-capot. Ces simulations modélisent le comportement thermique des environnements sous-capot ainsi que le compartiment aéraulique. Les flux d’air sont simulés et le couplage du modèle simplifié permet d’intégrer l’influence thermique de l’alternateur, au sein de l’environnement sous-capot, ainsi que l’impact aéraulique de ce dernier. La méthodologie de couplage permet d’importer les valeurs de températures et de débits, estimées par le modèle simplifié, au sein du maillage d’une CAO de l’alternateur. Ces travaux sont en cours d’intégration dans les processus numériques du Groupe PSA. Différentes perspectives sont en cours d’étude, afin d’utiliser ce modèle sur d’autres éléments du sous-capot, ou d’autres machines tournantes, comme des moteurs électriques présents sur les véhicules hybrides et électriques
The objective of the thesis is to create a thermal model of an alternator, with a quickly time run. This model will integrate the influence of the alternator inside an under-hood simulation. A simplify model able to simulate the aerodynamic and thermal behaviour has developed. It use a nodal approach to simulate the aerodynamic and thermal behaviour. Different algorithms and an user’s interface able to a quickly set up and a automatically implementation. Indeed, the nodal, approach was realized automatically by the model, the user inform the dimensions of the alternator, the materials characteristics and the thermal losses. Thanks to we have a model that use with any automobile alternator. The aerodynamic of the alternator is simulate with convection coefficient via the nodal approach. These coefficients are estimated with correlations based on Reynolds of the flow. The CFD simulation of the alternator identified these correlations. The CFD model has been validate with an aerodynamics tests. The model is checked and validate by thermal tests. It has an average error lower than 10% and work to any regime of the use. The time run is equal to 2 minutes. The modal has been integrate inside an under-hood simulation. A coupling methodology has been developed to allow the integration of the data, like the temperatures and the flowrate was estimate by the simplify model, inside an under-hood simulation. The under-hood simulation modelling the aerodynamic and thermal behaviour of the engine compartment. Therefore, the coupling methodology allow integrating the aerodynamic and thermal influence of the alternator inside the compartment. The work is actually in progress inside the numerical processes of the PSA group. Many perspectives are studied, to use the model on other under-hood elements, or other electric machine, like the electric engines used inside the hybrid vehicles

Le corps humain est un système complexe, et l'œil humain n’y fait pas exception. Malgré les avancées médicales, de nombreuses questions pathologiques subsistent. Les modèles mathématiques et computationnels complètent les études cliniques en dévoilant des mécanismes physiopathologiques complexes.L'œil, accessible de manière non invasive, offre des marqueurs biologiques utiles pour diagnostiquer des maladies. Comprendre son comportement, ses pathologies et les traitements associés est donc essentiel.Cette thèse explore la modélisation et la simulation des flux oculaires, notamment le transfert de chaleur et le flux d’humeur aqueuse. Ces approches nécessitent des validations cliniques rigoureuses et tiennent compte de nombreux paramètres, spécifiques au patient ou externes. Une analyse de sensibilité globale évalue leur impact pour guider les cliniciens. Ces analyses, coûteuses en calculs, bénéficient de méthodes de réduction de modèle certifiées, permettant des simulations précises et plus rapides, favorisant l’intégration des modèles dans la pratique clinique
The human body is a complex system, and the human eye is no exception. Despite medical advances, many pathological questions remain. Mathematical and computational models complement clinical studies by revealing complex pathophysiological mechanisms.The eye, which can be accessed non-invasively, offers useful biological markers for diagnosing diseases. Understanding its behavior, pathologies and associated treatments is therefore essential.This thesis explores the modeling and simulation of ocular flows, notably heat transfer and aqueous humor flow. These approaches require rigorous clinical validation and take into account numerous parameters, both patient-specific and external. A global sensitivity analysis assesses their impact to guide clinicians. These computationally-intensive analyses benefit from certified model reduction methods, enabling accurate and faster simulations, favoring the integration of models into clinical practice

This document focuses on the procedure and results of creating a thermohydraulic model of the secondary cooling system of the SAFARI-1 research reactor at the Pelindaba facility of the South African Nuclear Energy Corporation (Necsa) to the west of Pretoria, South Africa. The secondary cooling system is an open recirculating cooling system that comprises an array of parallel-coupled heat exchangers between the primary systems and the main heat sink system, which consists of multiple counterflow-induced draught cooling towers. The original construction of the reactor was a turnkey installation, with no theoretical/technical support or verifiability. The design baseline is therefore not available and it is necessary to reverse-engineer a system that could be modelled and characterised. For the nuclear operator, it is essential to be able to make predictions and systematically implement modifications to improve system performance, such as to understand and modify the control system. Another objective is to identify the critical performance areas of the thermohydraulic system or to determine whether the cooling capacity of the secondary system meets the optimum original design characteristics. The approach was to perform a comprehensive one-dimensional modelling of all the available physical components, which was followed by using existing performance data to verify the accuracy and validity of the developed model. Where performance data is not available, separate analysis through computational fluid dynamics (CFD) modelling is performed to generate the required inputs. The results yielded a model that is accurate within 10%. This is acceptable when compared to the variation within the supplied data, generated and assumed alternatives, and when considering the compounding effect of the large amount of interdependent components, each with their own characteristics and associated performance uncertainties. The model pointed to potential problems within the current system, which comprised either an obstruction in a certain component or faulty measuring equipment. Furthermore, it was found that the current spray nozzles in the cooling towers are underutilised. It should be possible to use the current cooling tower arrangement to support a similar second reactor, although slight modifications would be required to ensure that the current system is not operated beyond its current limits. The interdependent nature of two parallel systems and the variability of the conditions that currently exist would require a similar analysis as the current model to determine the viability of using the existing cooling towers for an additional reactor.
Dissertation (MEng)--University of Pretoria, 2015.
Mechanical and Aeronautical Engineering
MEng
Unrestricted

Laser is an efficient and widely used heat source in metal processing suchas welding and additive manufacturing. It has some great advantages compared to the other conventional heat sources like electron beam and arc namely: ability of handling complicated joint geometries and producing large components. Laser beam welding encompasses many complex physical phenomena such asheat transfer, metal melting, flow and solidification, free surface deformation, evaporation and possibly vaporization. The aim of this research work istwo-fold: gain deeper process understanding and improve the model reliability. Deeper process understanding is sought on the effect of beam shaping on themelt pool. To achieve improved model reliability, a good support consists in using qualitative experimental data representing the process. Thus, 3D validation of the melt pool geometry is performed while it was usually 2D inprevious research works. Furthermore, a new calculation procedure for laser absorption is introduced. To conduct this research work, a Computational Fluid Dynamics approach is used. A solver, capable of tracking the deformation of the melt free surface, is developed in OpenFOAM. Concerning beam shaping, it is found that not only the melt pool size as previously known but also the melt flow pattern is modified through elongating the beam shape.This last result could not be revealed by former studies as the non-transparent media hinders optical observation. New in-process quantitative measurements performed by a project partner are used to test the model. Weaknesses of the former absorptivity models are highlighted, as well as the limitations of the proposed model. Finally, the results show that the proposed absorptivity model function of local surface conditions leads to much better agreement with experimental results compared to the former constant absorptivity model. The maximum discrepancy compared to the experimental measurement, which is observed for the melt pool depth, can indeed be reduced to about 10%.
Laser är en effektiv och allmänt använd värmekälla vid svetsning och additiv tillverkning. Den har några viktiga fördelar jämfört med andra konventionella värmekällor såsom elektronstråle och elektrisk ljusbåge, nämligen: den kan ofta användas till komplicerade svetsgeometrier, och den kan producera stora komponenter. Lasersvetsning involverar olika sammansatta fysikaliska fenomen såsom värmeöverföring, metallsmältning, flöde, stelning, ytdeformation, avdunstning och i vissa fall förångning. Syftet med mitt forskningsarbete är tvåfaldigt: att få en djupare processförståelse och att förbättra modellens tillförlitlighet. Fördjupad processförståelse eftersträvades för att förstå hur formen på laserstrålen påverkar svetssmältan. För att uppnå förbättrad modellsäkerhet behövs experimentella data av hög kvalitet som representerar processen. Således utfördes 3D-validering av smältgeometrin medan det vanligtvis var 2D i tidigare forskningsarbeten. Dessutom har en ny modell för laserabsorption föreslagits. I forskningen har numerisk strömningssimulering (Computational Fluid Dynamics) använts för att simulera processen och en numerisk lösare, som kan spåra deformationen av den rörliga smälta ytan, är utveckladi programvaran OpenFOAM. Beträffande laserstrålens utbredning visar resultaten att svetssmältans storlek och även svetssmältansflöde modifieras genom att laserstråleformen förlängs. Medan den förra är känd från tidigare experimentella studier upptäcktes den senare inte före denna studie eftersomdet icke-transparenta mediet hindrar optisk observation. Nya (in-process) kvantitativa mätningar utförda av en projektpartner har använts för att testa modellerna. Svagheter i den tidigare absorptionsmodellen framhävdes, liksom begränsningarna i den föreslagna modellen. Slutligen visade resultaten att den föreslagna modellen där laserabsorptionen är en funktion av lokala ytförhållanden ledde till en bättre overensstämmelse med mätningar jämfört med den tidigare modellen med konstant laserabsorbtion. Den maximala avvikelsen jämfört med experimentell mätning, som observerades med avseende på smältbassängsdjupet, kunde reduceras till cirka 10%.

Till licentiatuppsats hör 2 inskickade artiklar, som inte visas nu.

Flameless combustion can be adopted as a low-emission combustion regime in the aviation sector, which is one of the biggest contributors to NOx emissions and is expected to grow in the near future. Nevertheless, several issues must be solved before any practical applications. Effective design procedure must deal with either combustion or heat transfer phenomena occurring at extremely low—temperature conditions. To this aim, experimental and numerical analyses focused on the characterization of fuel/oxidant behaviour are strongly needed and represent an essential step for further development. Besides, the complexity of the analysed technological system requires advanced tools for the definition of the chemical kinetics, for the burner designs and more in general for the definition of aviation equipment design. In this light, the thesis has been addressed to the study of flameless combustion mechanisms within a combustion chamber prototype developed in the Faculty of Aerospace Engineering at TU Delft. In particular, the temperature and species concentration fields have been analysed. The CFD tool which will be used is Ansys Fluent together with two detailed reaction mechanisms (KIBO and RDM19).

To get an improved understanding and knowledge of the processes and phenomena during the late phase of a core melt down accident the FOREVER-experiments (Failure of Reactor Vessel Retention) are currently underway. These experiments are simulating the lower head of a reactor pressure vessel under the load of a melt pool with internal heat sources. The geometrical scale of the experiments is 1:10 compared to a common Light Water Reactor. During the first series of experiments the Creep behaviour of the vessel is investigated. Due to the multi-axial creep deformation of the three-dimensional vessel with a non-uniform temperature field these experiments are on the one hand an excellent possibility to validate numerical creep models which are developed on the basis of uniaxial creep tests. On the other hand the results of pre-test calculations can be used for an optimized experimental procedure. Therefore a Finite Element model is developed on the basis of the multi-purpose commercial code ANSYS/Multiphysics®. Using the Computational Fluid Dynamic module the temperature field within the vessel wall is evaluated. The transient structural mechanical calculations are performed applying a creep model which is able to take into account great temperature, stress and strain variations within the model domain. The new numerical approach avoids the use of a single creep law with constants evaluated for a limited stress and temperature range. Instead of this a three-dimensional array is developed where the creep strain rate is evaluated according to the actual total strain, temperature and equivalent stress for each element. Performing post-test calculations for the FOREVER-C2 experiment it was found that the assessment of the experimental data and of the numerical results has to be done very carefully. A slight temperature increase during the creep deformation stage of the experiment for example could explain the creep behaviour which appears to be tertiary because of the accelerating creep strain rate. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulation and understanding of real accident scenarios.

To get an improved understanding and knowledge of the processes and phenomena during the late phase of a core melt down accident the FOREVER-experiments (Failure of Reactor Vessel Retention) are currently underway. These experiments are simulating the lower head of a reactor pressure vessel under the load of a melt pool with internal heat sources. The geometrical scale of the experiments is 1:10 compared to a common Light Water Reactor. During the first series of experiments the Creep behaviour of the vessel is investigated. Due to the multi-axial creep deformation of the three-dimensional vessel with a non-uniform temperature field these experiments are on the one hand an excellent possibility to validate numerical creep models which are developed on the basis of uniaxial creep tests. On the other hand the results of pre-test calculations can be used for an optimized experimental procedure. Therefore a Finite Element model is developed on the basis of the multi-purpose commercial code ANSYS/Multiphysics®. Using the Computational Fluid Dynamic module the temperature field within the vessel wall is evaluated. The transient structural mechanical calculations are performed applying a creep model which is able to take into account great temperature, stress and strain variations within the model domain. The new numerical approach avoids the use of a single creep law with constants evaluated for a limited stress and temperature range. Instead of this a three-dimensional array is developed where the creep strain rate is evaluated according to the actual total strain, temperature and equivalent stress for each element. Performing post-test calculations for the FOREVER-C2 experiment it was found that the assessment of the experimental data and of the numerical results has to be done very carefully. A slight temperature increase during the creep deformation stage of the experiment for example could explain the creep behaviour which appears to be tertiary because of the accelerating creep strain rate. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulation and understanding of real accident scenarios.

Thesis (MEng)--University of Stellenbosch, 2000.
ENGLISH ABSTRACT: This study investigates the implementation of the finite volume numerical method applicable to non-orthogonal control volumes and the application of the method to calculate the thermo-flow field within the collector area of a solar chimney power generating plant. The discretisation of the governing equations for the transient, Newtonian, incompressible and turbulent fluid flow, including heat transfer, is presented for a non-orthogonal coordinate frame. The standard k - E turbulence model, modified to include rough surfaces, is included and evaluated in the method. An implicit solution procedure (SIP-semi implicit procedure) as an alternative to a direct solution procedure for the calculation of the flow field on nonstaggered grids is investigated, presented and evaluated in this study. The Rhie and Chow interpolation practice was employed with the pressurecorrection equation to eliminate the presence of pressure oscillations on nonstaggered grids. The computer code for the solution of the three-dimensional thermo-flow fields is developed in FORTRAN 77. The code is evaluated against simple test cases for which analytical and experimental results exist. It is also applied to the analysis of the thermo-flow field of the air flow through a radial solar collector. KEYWORDS: NUMERICAL METHOD, FINITE VOLUME, NON-ORTHOGONAL, k+-e TURBULENCE MODEL, SIP
AFRIKAANSE OPSOMMING: Die studie ondersoek die implementering van 'n eindige volume numeriese metode van toepassing op nie-ortogonale kontrole volumes asook die toepassing van die metode om die termo-vloei veld binne die kollekteerder area van 'n sonskoorsteen krag aanleg te bereken. Die diskretisering van die behoudsvergelykings vir die tyd-afhanlike, Newtonse, onsamedrukbare en turbulente vloei, insluitende hitteoordrag, word beskryf vir 'n nie-ortogonale koordinaatstelsel. Die standaard k - E turbulensiemodel, aangepas om growwe oppervlakrandvoorwaardes te hanteer, is ingesluit en geevalueer in die studie. 'n Implisiete oplossings metode (SIP-semi implisiete prosedure) as alternatief vir 'n direkte oplossingsmetode is ondersoek en geimplimenteer vir die berekening van die vloeiveld met nie-verspringde roosters. 'n Rhie en Chow interpolasie metode is gebruik tesame met die drukkorreksie-vergelyking ten einde ossilasies in die drukveld in die nie-verspringde roosters te vermy. Die rekenaarkode vir die oplossing van die drie dimensionele termo-vloeiveld is ontwikkel in FORTRAN 77. Die kode is geevalueer teen eenvoudige toetsprobleme waarvoor analitiese en eksperimentele resultate bestaan. Die kode IS ook gebruik om die termo-vloeiveld binne 'n radiale son kollekteerder te analiseer. SLEUTELWOORDE: NUMERIESE METODE, EINDIGE VOLUME, NIE-ORTOGONAAL, k - E TURBULENSIE MODEL, SIP

Cette thèse est une contribution à la simulation numérique des transferts de quantité de mouvement et de chaleur dans les écoulements turbulents de fluides non-Newtoniens dans une conduite cylindrique fixe. La viscosité du fluide utilisé est décrite par la loi d'Ostwald de Waele. Deux modèles sous-mailles dans l'approche des simulations des grandes échelles ont été considérés : le modèle dynamique de Germano et al. (1991) et le modèle de Smagorinsky non-Newtonien. Ils sont utilisés pour décrire les mécanismes physiques mis en jeu dans les écoulements isothermes de ces fluides à rhéologie complexe. Les transferts thermiques sont simulés avec le modèle de Smagorinsky non-Newtonien. Ces derniers sont traités en deux parties. La première concerne les échanges de chaleur sans influence sur la distribution des vitesses. Il s'agit des écoulements non-thermo dépendants ou écoulements isothermes. La deuxième partie concerne la résolution des écoulements thermo dépendants qui mettent l'accent sur les modifications induites par le couplage vitesse-température. Les champs turbulents sont analysés statistiquement en moyennant dans le temps et dans l'espace (suivant les directions périodiques) les champs instantanés de vitesse et de température pour établir les profils moyens de vitesse et de température, les rms, la tension de Reynolds, les flux de chaleur, les moments d'ordre plus élevé (coefficients de dissymétrie et d'aplatissement), les pdf (fonction de densité de probabilté), les jpdf (fonction de densité de probabilité jointe), le coefficient de frottement, le nombre de Nusselt... Ces différentes grandeurs sont analysées en fonction des divers paramètres qui gouvernent le problème: les nombres de Reynolds et de Prandtl, l’indice d'écoulement et le nombre de Pearson
This thesis is a numerical contribution of momentum and heat transfer of turbulent pipe flows of non-Newtonian fluids. The apparent viscosity of the fluid is modelled by a power-law (Ostwald de Waele model). Two models subgrid of LES were considered: the dynamic model of Germano et al. (1991) and model Smagorinsky non-Newtonian. They are used to describe the physical mechanisms involved in the isothermal flow of these complex rheology fluids. Heat transfer are simulated with the model of non-Newtonian Smagorinsky. These are processed in two parts. The first concerns the heat exchange without affecting the velocity distribution. This is non-thermo dependent flow or isothermal flow. The second part concerns the resolution of thermo dependent flows that focus on changes induced by the temperature-velocity coupling. The turbulent fields are analyzed statistically by averaging over time and space (according to the periodic directions) the instantaneous field of velocity and temperature to establish the average profiles of velocity and temperature, the root mean square of turbulent fluctuations (rms), Reynolds stress, the heat flow, the moments of higher order (skewness and flatness), the pdf (probability density function), the jpdf (attached probability density function), the coefficient of friction, the number of Nusselt ... These differents variables are analyzed for various parameters governing the problem: the Reynolds and Prandtl flow index and the number of Pearson

Il modello è una raffigurazione concettuale (molto spesso semplificata) del mondo concreto o di una sua parte, capace di spiegarne il funzionamento attraverso una serie di leggi che bene lo rappresentino. Queste leggi descrivono i principi fondamentali di una teoria e non sempre è possibile risolvere appieno in maniera analitica. Quando ciò accade si utilizzano tecniche numeriche per trovarne la soluzione per mezzo di pacchetti software dedicati allo scopo. Lo sviluppo del modello numerico si compone di tre distinte fasi: la prima (preprocessamento) è l’inserimento dei dati di input riguardanti il materiale, le condizioni al contorno del processo da descrivere e la definizione della griglia di risoluzione del dominio spaziale (mesh), la seconda (solutore) è la risoluzione delle equazioni che descrivono il fenomeno e la terza (postprocessamento) è la visualizzazione dei risultati. I modelli sono un semplice inserimento di dati fisici all’interno di un software che li utilizza per fornire un risultato, ma è determinante la qualità dei dati immessi per valorizzare o meno un modello, e la qualità di questi dati si ottiene con metodi di ricerca rigorosi, messi a punto ad hoc per ogni esperienza. Ciò che vuole essere enfatizzata da questa tesi di dottorato è che la modellistica non è semplicemente imparare ad utilizzare un software, che, pur essendo estremamente complesso, sicuramente non prepara al mondo della ricerca. Ed è questo che fa sì che lo sviluppo di un modello porti allo sviluppo e all’apprendimento di tecniche di ricerca nuove, affrontando ogni giorno sfide differenti, attraverso approcci diversi dai classici procedimenti, in modo da ampliare continuamente il bagaglio culturale personale e inserendo una metodologia innovativa e dal sicuro successo accanto a metodiche oramai consolidate. Sono state seguite con questo metodo 5 differenti ricerche, le quali mi hanno fatto affrontare problematiche relative alla loro risoluzione peculiari per ogni ricerca: • Cottura di prodotti da forno; • Supporti di appassimento uve; • Precipitazione tartrarica nel vino; • Trasmissione del calore su una padella; • Sistema di refrigerazione passiva Icepack. La cottura di un prodotto da forno è un processo estremamente complesso, dove una infinità di trasformazioni fisiche, chimiche e biochimiche avvengono. Le caratteristiche fisiche (in particolar modo la diffusività dell’acqua all’interno della matrice del biscotto) sono di difficile definizione, così come le condizioni al contorno (umidità assoluta dell’aria della camera di cottura e coefficiente di conduttanza convettiva). Anche la determinazione della mesh è stata modificata rispetto a quella automatica del software per migliorare la definizione delle grandezze che sono coinvolte. Una volta ottenuto il risultato le differenti visualizzazioni dei risultati hanno permesso di individuare l’evoluzione della temperatura e dell’umidità sia a livello spaziale che a livello temporale. Il modello è stato risolto come un simultaneo trasferimento di massa e di calore, con un infittimento della mesh nell’intorno dei punti dove maggiormente vengono modificate le grandezze. La caratterizzazione della variabili è stata fatta con sperimentazioni od hoc per l’occasione. I diversi supporti per l’appassimento delle uve che sono stati testati hanno caratteristiche completamente differenti, sia da un punto di vista del materiale (plastica, legno, bambù, resine) che da un punto di vista strutturale (cassette di diverse dimensioni e con differenti disegni tra pieno e vuoto). La grossa problematica di questo modello, che si prefiggeva lo scopo di definire il campo di velocità all’interno dei diversi contenitori, è stato definire la geometria migliore per ogni tipo di supporto. Il disegno che rappresenta la cassetta in ogni suo dettaglio risultava essere estremamente complesso e quindi con un numero di gradi di libertà talmente elevato che anche un computer di grande potenza non riusciva a completare l’elaborazione. Il modello, viste le velocità in gioco, è stato risolto ignorando i dettagli delle parti in cui il flusso di aria e la parete risultavano essere parallele. La precipitazione tartarica del vino viene fatta sfruttando i differenti livelli di solubilità in funzione della temperatura. In particolare a una diminuzione della temperatura corrisponde un decremento della solubilità. Questo processo, molto semplice impiantisticamente in quanto è un raffreddamento, è estremamente complesso per il coinvolgimento di molte specie chimiche e fenomeni secondari. Il modello è stato risolto attraverso una serie di modelli non accoppiati, ognuno dei quali si occupa di un aspetto del fenomeno. Il riscaldamento di una padella è una ricerca che è stata eseguita per enfatizzare la difficoltà della modellazione della matrice alimentare. È uno studio a differenti step, a difficoltà crescente che portano alla definizione della cottura di un disco di patata su una padella. Il primo modello riguarda la padella vuota messa a scaldare, e l’errore tra i dati sperimentali e la simulazione è intorno al 4%. Nel secondo è stato aggiunto al primo modello un disco di alluminio con proprietà note, e l’errore è passato al 4.4%. Nel terzo modello il disco di alluminio è stato sostituito con uno di patata, materiale scelto per le molte proprietà note, e l’errore è passato a circa il 22%. L’Icepack è un contenitore di polistirolo con all’interno una busta ermetica piena di acqua congelata. Sfruttando il calore latente di fusione del ghiaccio la temperatura interna del contenitore resta prossima a 0 °C fino al completo scioglimento del ghiaccio. Questo sistema è stato sfruttato per ridurre il calore di campo dai mirtilli appena dopo la raccolta. Il processo è stato semplificato non considerando la convezione interna alla scatola e ipotizzando in un primo momento una geometria più semplice rispetto a quella reale dei mirtilli. Un successivo adattamento del modello ha previsto la definizione di una geometria più simile a quella reale (mirtilli simulati per mezzo di sfere) con un incremento della accuratezza dei risultati.
The model is a conceptual representation (often simplified) of the real world or a its part, able to explain the functioning through a series of laws that represent it. These laws describe the basic principles of a theory and it is not always possible to fully solve it in an analytical way. When this happens it is possible to use numerical techniques to find the solution by means of software packages dedicated to the purpose. The development of the numerical model is composed of three distinct phases: the first (pre-processing) is the insertion of input data concerning the material, the boundary conditions of the process and the definition of the grid of resolution of the spatial domain (mesh) , the second (solver) is the resolution of equations that describe the phenomenon and the third (post-processing) is the visualization of the results. The models are a simple insertion of physical data within a software which uses them to provide a result, but is decisive the quality of the input data for the value or less of a model, and the quality of these data is obtained with rigorous research methods, developed ad hoc for each experience. The emphasis of this thesis is that modeling is not just learning to use a software, which, although extremely complex, definitely not ready for the world of research. The development of a model leading to the development and learning of new research techniques, dealing with different challenges every day, through different approaches from classical procedures, so as to continuously expand the cultural and entering a personal innovative methodology and the successful consolidated methods. There were followed with this method five different studies, which made me deal with problems relating to their specific resolution for each search: • Cooking of bakery products; • Media drying grapes; • Tartaric precipitation in wine; • Heat transfer in a pan; • Cooling system passive Icepack. The baking of a bakery product is an extremely complex process, where an infinite number of transformations physical, chemical and biochemical changes occur. The physical characteristics (particularly the diffusivity of the water within the matrix of the biscuit) are difficult to define, as well as the boundary conditions (absolute humidity of the cooking chamber and heat transfer convective coefficient). The determination of the mesh has been changed from the automatic software to improve the definition of the variables that are involved. Once the equations were solved the different views of the results have allowed us to identify the evolution of the temperature and humidity both spatial and temporally. The model was solved as a simultaneous heat and mass transfer, with a thickening of the mesh in the neighborhood of the points where the variables change more. The characterization of the variables was made with experiments specifically for the occasion. The various supports for the drying of the grapes that have been tested have completely different characteristics, both from a point of view of material (plastic, wood, bamboo, resins) that from a structural point of view (cassettes of different sizes and with different drawings between full and empty spaces). The big issue of this model, which set out the objective of determining the velocity field inside the different containers, has been to define the best geometry for each media type. The drawing representing the cassette in every detail appeared to be extremely complex and therefore with a number of degrees of freedom so high that even a large power computer could not complete the processing. The model, considering the speeds involved, has been resolved by ignoring the details of the parts where the flow of air and the wall appeared to be parallel. Tartaric precipitation of the wine is made by exploiting the different levels of solubility as a function of temperature. In particular to a reduction of the temperature corresponds to a decrease of the solubility. This process, that is a simple cooling, is extremely complex for the involvement of many chemical species and secondary phenomena. The model was solved through a series of models not coupled, each of which deals with one aspect of the phenomenon. The heating of a pan is a search which was performed in order to emphasize the difficulty of modeling the food matrix. It is a study on different steps, in increasing difficulty leading to the definition of the cooking of a disc of potato on a pan. The first model involves the empty pan on a electric heater, and the error between the experimental data and the simulation is around 4%. In the second has been added to the first model an aluminum disk with known properties, and the error is passed to 4.4%. In the third model, the aluminum disk was replaced with a potato disk, the material chosen for the many known properties, and the error is passed to about 22%. The Icepack is a polystyrene box with inside an hermetic case full of frozen water. The latent heat of fusion of ice keeps the internal temperature of the box close to 0 ° C until complete dissolution of ice. This system has been exploited to reduce the heat of the field by blueberries just after harvesting. The process has been simplified without considering the convection inside the box and assuming at first a simpler geometry than that of real blueberries. A subsequent adaptation of the model has provided for the definition of a geometry more similar to the real one (blueberries simulated by means of beads) with an increase of the accuracy of the results.

La piscine fait partie des établissements publics les plus fréquentés dans notre société. En effet, il ne s’agit pas uniquement d’un lieu de pratique d'activités physiques, mais également un espace de détente, de jeu, d’éducation et de lien familial. Il est de toute évidence essentiel, de fournir un environnement intérieur confortable et sain pour ses occupants. Cependant, en raison de sa dimension, son besoin excessif en énergie et la complexité des phénomènes physiques évoluant à l’intérieur, il est difficile de parvenir à un équilibre optimum entre : qualité de l’air intérieur, confort thermique des occupants et efficacité énergique du bâtiment. Il faut pour cela, parvenir à une description des mécanismes qui façonnent la structure de l’écoulement de l’air par une analyse profonde de ces phénomènes qui sont à l'origine des transferts de chaleur et de masse mis en jeu à l’intérieur. Ainsi, l’objectif visé de cette thèse est de présenter une étude numérique thermo aéraulique, par CFD en régime stationnaire et transitoire, qui permet d’évaluer le comportement dynamique, thermique et thermodynamique des différents phénomènes physiques qui évoluent à l’intérieur de la piscine intérieure semi-olympique de l’université Bishop’s (Sherbrooke, Canada) afin d’améliorer la qualité de l’air intérieur et le confort thermique ainsi que son rendement énergétique. Les simulations sont réalisées avec le logiciel libre OpenFOAM en utilisant une approche RANS. Une étude thermo-aéraulique par CFD a d’abord été réalisée sur une cavité rectangulaire avec plancher chauffé, afin d’appréhender les simulations thermo aérauliques. Cela a abouti à la détermination de la meilleure configuration d’aération pour une qualité de l’air et un confort thermique optimum. Plusieurs simulations CFD du flux d'air tridimensionnel avec transfert de chaleur et de masse ont été aussi effectuées ultérieurement pour la piscine, afin d’évaluer les effets des conditions climatiques extérieures et ceux des nageurs sur l'atmosphère intérieure. En adoptant plusieurs modèles de turbulence de type RANS, la comparaison des résultats obtenus avec les données expérimentales de référence a permis de valider le code OpenFOAM. Les données expérimentales ont été recueillies au préalable au sein de la piscine de l’Université Bishop’s à l’aide d’un dispositif conçu et adapté aux conditions internes propre à la piscine et qui est équipé de plusieurs capteurs pour la mesure de : température, humidité relative et vitesse. Enfin, une étude thermo-aéraulique de la piscine en régime turbulent transitoire pour une durée de 24 heures pour les jours typiques d'été et d'hiver a été réalisée afin de prédire l’évolution de la distribution des paramètres tels que la vitesse, la température et l'humidité relative. Une analyse statistique a permis de montrer que les conditions climatiques extérieures n'ont pas d'effet sur l'environnement interne de celle-ci. D’ailleurs, sa très bonne isolation thermique démontrée par un calcul détaillé des pertes thermiques à travers son enveloppe confirme ce constat. D’autre part, l’évaluation de la qualité de l'air intérieur et le confort thermique des occupants a révélé que ces derniers sont inacceptables. Suite auxquels, un ajustement des paramètres de conditionnement de l’air a été apporté pour fin d’amélioration.
Abstract : The swimming pool is one of the most popular public establishments in our society and is not just a place for physical activities but also a space for relaxation, play, education and family ties. It is therefore important to ensure a healthy and comfortable indoor environment for the occupants. However, given the size, energy requirement and complexity of the physical phenomena that take place within such space, it is difficult to achieve an optimum balance between interior air quality, thermal comfort of occupants and energy efficiency of the building. This requires a description of the mechanisms, which determine the structure of the airflow by a profound analysis of these phenomena, which are the origin of the heat and mass transfers involved inside such spaces. The objective of this thesis is to present a numerical thermo-ventilation study using CFD (computational fluid dynamic) in stationary and transient regime that allows to evaluate the dynamic, thermal and thermodynamic behaviors of the various phenomena that take place inside the semi-Olympic closed swimming pool at Bishop's University (Sherbrooke, Qc, Canada). The aim is to improve the indoor air quality and thermal comfort of occupants as well as its energy efficiency. The simulations are carried out using OpenFOAM (Open Field Operation and Manipulation) using a Reynolds-Averaged Navier-Stokes (RANS) approach. To do this, a CFD thermo-ventilation study was first carried out on a rectangular cavity with heated floor in order to understand the thermo-ventilation simulations. This has led to the determination of the best ventilation configuration for optimum air quality and thermal comfort. Several CFD simulations of the three-dimensional airflow with heat and mass transfer were also carried out later for the indoor swimming pool to evaluate the effects of outdoor climatic conditions and swimmers on the indoor atmosphere of the pool. By adopting several RANS turbulence models, the comparison of the results obtained with the experimental data allowed to validate the OpenFOAM code. The experimental data were collected in the pool at Bishop's University using a device designed and adapted to the pool’s internal conditions. The devise is equipped with several sensors to measure temperature, relative humidity and velocity. Finally, a thermo-ventilation study of the swimming pool in transient turbulent regime for a duration of 24 hours for typical days of summer and winter was conducted in order to predict the distribution of the various parameters such as velocity, temperature and relative humidity. A statistical analysis showed that the external climatic conditions have no effect on the internal environment of the swimming pool. Moreover, its good thermal insulation demonstrated by a detailed calculation of the thermal losses through building envelope confirms this observation. On the other hand, the evaluation of the indoor air quality and the thermal comfort of occupants revealed that the conditions inside the pool are unacceptable. After which, an adjustment of the air conditioning parameters was made for improvements.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
The present work aimed at investigating the biodiesel issuing from the transesterification of used frying oil with ethanol, via alkaline catalysis. Such investigation covers its thermo-oxidative stability during heating (thermal analysis and rheological properties) as well the kinetic profiles of the samples in the best oxidative induction time by the technique of Pressurized Differential Scanning Calorimetry (PDSC). The behavior of such biodiesel, as part of binary blends with fossil diesel at the proportions of 3, 5, 10, 25, 50, 75 and 100%, was also studied. The biodiesel synthesis used the ethanol route and was carried out under the following conditions: oil/alcohol molar ratio of 1:6 (m/m), 1 % de KOH, temperature of 32 °C, washing with 0.1M HCl and hot water. The reaction yield, determined by means of a mass balance aided by the technique of gas chromatography coupled to mass spectrometry, was of 90.56% and the ester content was of 99.56%. According to the physicochemical analyses, all the specifications for the biodiesel and blends met the requirements from Technical Regulation # 7 from the Brazilian National Agency of Petroleum, Natural Gas and Biofuels, with the exceptions of the odixative induction time (1.72 h) and kinematic viscosity (6.10 mm2s-1), which displayed values outside the limits established by the standard. In the thermal study, the thermogravimetric curves showed that the biodiesel blends in diesel are more volatile than the biodiesel derived from used frying oil (B100), whereas at lower concentrations (3, 5, 10 and 25%) are similar to fossil diesel. At higher concentrations (50 and 75%) the blends presented lower volatility and higher thermal stability in relation to fossil diesel and thus, biodiesel and its more concentrated blends showed higher safety in relation to transport, storage, handling and utilization. The study of the fluid dynamic properties of biodiesel and its blends showed that all the samples behave as Newtonian fluids at the studied (10, 25 and 40 ºC) temperatures. Also the results of cloud point, pour point and cold filter plugging point showed that the behavior of the blends with 3, 5 and 10% are similar to fossil diesel, therefore at these concentrations biodiesel acts as a lubricity additive to fossil diesel. The study by Pressurized Differential Scanning Calorimetry (PDSC) in the dynamic mode and the Rancimat technique revealed that the best antioxidant for the storage of biodiesel is BHT at the concentration of 2500 ppm. The determination of the kinetic parameters by the isothermal PDSC technique allowed determining the theoretical value of the shelf life of used frying oil biodiesel with 2500 ppm of the antioxidant BHT. Therefore, used frying oil biodiesel and its blends B3, B5, B10, B25, B50 and B75 may be used as an alternative source of biofuels.
O presente trabalho buscou investigar o biodiesel proveniente da transesterificação do óleo de fritura usado com álcool etílico, via catálise básica, e elucidar a sua estabilidade termo-oxidativa durante o aquecimento (análise térmica e propriedade reologicas) e estudar o perfil cinético da amostra com o melhor tempo de indução oxidativa pela técnica de calorimetria exploratória diferencial pressurizada (PDSC). Também, foi observado o comportamento do referido biodiesel, inserido em misturas binárias com o diesel fóssil nas proporções de 3, 5, 10, 25, 50, 75 e 100% também foi estudada. A síntese do biodiesel na rota etanólica processou-se sob condições de: razão molar óleo-álcool de 1:6 (m/m), 1 % de KOH, temperatura de 32 °C, lavagem com HCl 0,1 M e água quente. O rendimento reacional determinado por balanço de massa com auxilio da técnica de cromatografia gasosa acoplada a espectrometria de massa, foi de 90,56 %, com teor de esteres de 99,56 %. Nas análises físicoquímicas, todos as especificações para ambos biodiesel e blendas satisfizeram as exigências dos limites permitidos pelo Regulamento Técnico nº 7 da Agência Nacional do Petróleo, Gás Natural e Biocombustíveis. Com exceção do tempo de indução oxidativa (1,72 h) e a viscosidade cinemática (6,10 mm2s-1) que apresentaram valores fora dos limites estabelecidos pela norma. No estudo térmico, as curvas termogravimétricas evidenciaram que as blendas de biodiesel em diesel são mais voláteis em relação ao biodiesel derivado de óleo de fritura usado (B100) e em baixas concentrações (3, 5, 10 e 25%) se assemelham ao diesel fóssil. Em concentrações mais elevadas (50 e 75%) as blendas apresentam menor volatilidade e maior estabilidade térmica em relação ao diesel fóssil, e, portanto, o biodiesel e suas blendas mais concentradas apresentam maior segurança em relação ao transporte, armazenagem, manuseio e utilização. O estudo das propriedades fluído-dinâmicas do biodiesel e suas blendas, demostraram que todas as amostras comportam como fluídos newtonianos a temperatura (10, 25 e 40 ºC) e que tanto os resultados de ponto de nevoa, fluidez e ponto de entupimento de filtro a frio, apresentaram comportamento para as blendas 3, 5 e 10% semelhantes ao observado para o diesel fossil, e, portanto nestas concentrações o biodiesel atua como um aditivo de lubricidade do óleo diesel fossil. O estudo por calorimetria exploratória diferencial pressurizada no modo dinâmico e a técnica de rancimat revelou que o melhor antioxidante para o armazenamento do biodiesel é o BHT com concentração de 2500 ppm. A determinação dos parâmetros cinéticos pela técnica de PDSC isotérmica foi possível determinar teoricamente o tempo de vida de prateleira do biodiesel derivado de óleo de fritura usado com 2500 ppm do antioxidante BHT. Então, o biodiesel de fritura usado e blendas B3, B5, B10, B25, B50 e B75 podem ser utilizados como uma fonte alternativa de biocombustíveis.

The superimposition of a tangential motion on a conventional round jet has been demonstrated to significantly affect the large-scale topology of the flow. Swirling flows are widely employed, in the impinging configuration, in several industrial processes which involve both non-reacting and reacting applications. In the present dissertation, the simultaneously acquired thermal and three-dimensional velocity fields of an impinging hot jet emerging from a custom swirl generator in a cold ambient are presented. The velocity and temperature fields are experimentally measured using time-resolved Tomographic PIV and high-speed Infrared thermography in a combined system. A detailed description of a custom swirl generator is provided, and the time-averaged velocity profiles of a free swirling flow are discussed in order to estimate the swirl number. The instantaneous three-dimensional dynamics in proximity of the nozzle is discussed and the main features of a free swirling jet are investigated through the application of Proper Orthogonal Decomposition technique. The time-dependent features of velocity and temperature fields of an impinging swirling jet are investigated through the description of the time sequences of the temperature fluctuations and the synchronised instantaneous vortical structures. Taking advantage of the simultaneous acquisition and of the knowledge of the relative positioning of thermal and velocity frames, two different correlation techniques are applied, and their outcomes discussed.

Dottorato di Ricerca in Ingegneria Civile e Industriale. Ciclo XXIX SSD
The thermal power plant for the generation of electricity, which uses coal as a primary energy source, presents multiple issues linked to the emission of pollutants and greenhouse gas (CO2) into the atmosphere. Furthermore, the conventional boilers greatly contribute to the increase of these harmful substances. The aim of this work is to propose and analyze the possibility of combining two new combustion technologies: the so-called oxy and MILD combustion. The rst one, allows to capture the carbon dioxide, while the second one provides several advantages, not only because it reduces the emission of nitrogen oxides, but also because it is characterized by uniform ows in the combustion chamber. Therefore, the challenge is to combine the two technologies with applications in furnaces and a new concept of boiler. For the latter, the planned applications include the ultra-super critical plants. For this reason, numerical simulations have been carried out by means of technical CFD (Computational Fluid Dynamics) because it is hard to provide large-scale tests. The initial phase of the work involves the application of the two technologies in furnaces. The rst one focuses on the MILD combustion by analyzing di erent positions of the pulverized coal jet, while the second one focuses on the application of the combination of the two technologies in order to analyze their e ects in terms of temperature and species concentration distributions. The next phase of the work, instead, has a focus on an innovative boiler. The testing of di erent geometrical solutions and models of char combustion has also allowed to study their e ects in terms of temperature, combustion products concentrations, burnout and, above all, wall heat ux. These latter results have been compared with the ones of traditional boilers and the results reported in the literature. The nal aim of this work is to analyze the advantages deriving from the combination of two technologies into a new concept of boiler, in order to reduce pollutant emissions, greenhouse gases and obtain a better performance than the one at the current state of the art.
Università della Calabria

A numerical simulation has been carried out to understand the thermo-hydrodynamics of single phase flow with obstacle in microchannel. In this study, two different shapes of obstacle are analyzed with five different substrate materials to study the effect of thermal conductivity on the heat transfer. Uniform heating source is present at bottom wall of microchannel and remaining walls are kept adiabatic. The flow rate is maintained such that flow will be laminar theoretically. But under influence of obstacle, fluid is likely to get disturbed as it flows past the obstacle. So, both laminar and turbulent model was used in this analysis. The other factor is considered is the position of obstacle in the flow. The positions of obstacle affect the mixing of layer of fluid. Analysis revels that position of obstacle in the flow field directly affect the heat transfer. Disturbance created at the initial stage carried to long distance which enhance heat transfer coefficient. It is found that the temperature difference between wall and fluid increase along the axial direction of flow except near the obstacle. In analysis, it is found that shape of obstacle directly affect the Nusselt number, for half obstacle variation of Nusselt number increase vibrantly as compared to full obstacle. In case of laminar model, it does not take account of eddies formation near the flow. Nor it accounts the surface roughness. While in turbulent model, eddies formation near the surface can be seen which in turn increase Nusselt number, when simulating both full and half obstacle using both laminar and turbulent model, it is found that higher Nusselt number is found in case of turbulent model, hence Nusselt number is reach to maximum in turbulent in comparison to laminar model.

A two dimensional numerical analysis is carried out to understand the thermo- hydrodynamics of single phase pulsating laminar flow in a microtube with constant flux boundary condition imposed on its outer surface while the cross-sectional solid faces exposed to the surrounding are insulated. The inlet velocity to the tube is the combination of a fixed component of velocity and fluctuating component of velocity which varies sinusoidally with time, thus causing pulsatile velocity at the inlet. The working fluid is water and enters the tube at 300K. Simulations have been carried out at a range of pulsating frequency between 2-10 Hz and amplitude ratio (A) equals to 0.2. To study the effect of axial wall conduction microtube, wall to fluid conductivity ratio is taken in a very wide range (ksf = 0.344 – 715) at a flow Reynolds number of 100. Effect of pulsation frequency on heat transfer is found to be very small. Heat transfer is found to be increasing at lower thermal conductive microtube wall material (or ksf) while it is decreasing at higher ksf compared to steady flow in microtube. Again, for a particular pulsating frequency (Wo), with very low ksf leads to lower the overall Nusselt number while the time averaged relative Nusselt number remains almost constant through the entire length of microtube and it is less than the corresponding steady state Nusselt number. Higher ksf with a particular frequency again lowers overall Nusselt number slightly due to severe back conduction. From this, it is confirmed that for a particular pulsating frequency, there exist an optimum value of ksf which maximizes the overall Nusselt number while all other parameters like flow Reynolds number, microtube thickness to inner radius ratio (äsf) remaining the same.

The Existente ffortis conceded to examine the thermal- behavior of plain offset stripped fin used in heat exchanger. A simulation arrangement(geometry) built in the ANSYS FLUENT to test the behavior of offset fin.in our investigation only domain of fluid passed over the offset fin has to be taken for CFD analysis. Setup of the model had directed to define the thermal performance of the given HE by using offset fin. The surface of the fluid domain is the contact surface of fin. So in ideal condition for maximum heat trans fer of fin is possible when whole fin is at base temperature, therefore surface of fluid domain is to be maintained at isothermal condition. The project is based on the changing the offset of the fin for the passage of air. For different offset, the behavior of temperature variation and other thermal properties is investigated. One of the best method to improve the heat transfer of the HE used in airside is to transform the fin geometry. Mostly, Heat exchangers used in cryogenics and other thermal applications purpose like in automobiles chemical industries because fin is very cheap and good way for heat exchange. The different parameters is correlated by the thesis of Deepak Kumar Maiti, and validate its geometry by comparing different thermal behavior). For different s/t ratio the behavior of friction factor (f), colburn factor (j), nusselt number (Nu) for plain offset fin is investcaated. After this examination a new design of offset fin is come forward for enhancement of heat transfer, normally fin geometries are plain along the flow of fluid. Other CFD simulation work is carried out for fin having herringbone surface and wavy surface. Wide study has been done on fin and tube HEsover the last few years to comprehend the heat transfer phenomenon and heat transfer rate within heat exchanger and to determine the dimensionless parameters i.e. colburn factor “j”, heat transfer coefficient “h”, and the friction factor “f”. However, theoretical investigation done on design of the above mentioned fin often suffers from faults due to too much simplification because of complicated geometries and assumptions made.

In present work high heat and mass flux flow boiling through vertical circular tubes of diameters 24.0 mm, 15.4 mm, 10.0 mm having length 2.0 m, 2.0 m and 7.0 m respectively, subjected to constant wall heat flux was analyzed through CFD approach in order to characterize the boiling heat transfer, pressure drop, variation of vapor fraction in axial direction, wall temperature distribution and vapor velocity. Subcooled flow boiling up to critical heat flux (CHF) and past dry out were investigated to predict the heat transfer phenomena. For this purpose a detailed mathematical model of wall boiling has been discussed which includes modeling of wall heat flux partition, bubble departure diameter, frequency of bubble departure, nucleate site density, interfacial heat, mass and momentum transfer and other interactions. Commercially available ANSYS FLUENT 15.0 with user defined functions was used to solve the numerical model and analyze the results.

Liquid Propulsion Systems Centre is developing the 2000 kN thrust Semicryogenic engine for Indian Space Research Organisation to power the core stage of the Heavy Lift Launch Vehicle and the Reusable Launch Vehicle. Turbopump is a critical system which is responsible for the continuous supply of propellants from stage tanks to the thrust chamber at required pressure and flow rate. Cavitation occurring within the main pump is a serious issue which may lead to the failure of mission, so to avoid cavitation a booster pump is employed. The Semicryogenic oxidizer booster turbopump consists of an inducer pump and a partial admission gas turbine. Liquid oxygen act as the working fluid for the pump and an oxidizer rich combustion product as the turbine fluid. In the present study flow through the oxidizer booster turbopump for semicryogenic engine at nominal operation (100% engine thrust), de-rated condition (60% engine thrust) and up-rated condition (105% engine thrust) is simulated using the commercial Ansys CFX package. The pressure, temperature and velocity distribution throughout the booster pump and gas turbine is analysed. The head rise, power developed and efficiency is calculated for each operating condition. The simulation is also validated by conducting the cold flow test at the Semicryogenic test bay.

Taylor bubble flow in microchannel systems play an important role in many industrial applications such as two-phase flow micro heat exchangers, pulsating heat pipes, monolithic reactors, digital microfluidics, microscale mass transfer process, fuel cells, etc. Taylor bubble is formed in capillary tubes when gas-liquid or liquid-liquid flows with particular range of flow rate ratios. In this work, a 3D numerical study has been carried out using the volume-of-fluid (VOF) method on commercially available Ansys Fluent® for the formation of (i) isolated Taylor bubble and (ii) a train of Taylor bubbles, in a square channel of side 1.0 mm. At inlet of the capillary tube, gas and liquid flows in co-current flow arrangement neglecting the nozzle thickness. Constant thermo-physical properties are considered for solid and fluid. The flow is hydrodynamically developing at the inlet of the channel. Taylor bubble formed gets stabilized at the entry section of the fluid channel. The Taylor bubble then passes through a square channel (01 mm2 ) carved on a solid substrate of size 3×2×30 mm3 . The flow is hydrodynamically fully developed and thermally developing inside this channel. Constant heat flux is applied on the bottom wall of the substrate (3 × 30 mm2 ), while all other surfaces exposed to the ambient are insulated. To avoid the end effect, the fluid again passes through a capillary tube after it travels the full length of the substrate. Thus, three-dimensional Navier-Stokes and energy equations are solved simultaneously. No slip boundary condition is imposed on the inner walls of the channel. Sufficiently fine mesh considered near the boundary to capture liquid film surrounding a Taylor bubble interface near the wall. The liquid film is maintained without its breakup throughout the length of the channel. The numerical simulations are carried out for the substrate wall to fluid thermal conductivity ratio (ksf ∼ 10−646), ratio of substrate thickness to channel depth (δsf ∼ 1−3) and capillary number (Ca ∼ 0.005 − 0.007). The objective of this study is to explore heat transfer enhancement due to injection of Taylor bubbles in steady flow, which causes disturbance in the flow field at its head and tail, resulting in mixing in the fluid that shows reduction in wall temperature compared to single phase liquid flow in the channel. The axial variation of bulk fluid temperature shows a footprint of a Taylor bubble at its back end. The effect of bubble length and the frequency of bubble occurrence is also studied.

[ES] En la presente tesis se han desarrollados estudios sobre reactores de membrana de alta temperatura. Entre estos se puede diferenciar entre un trabajo experimental y un trabajo de simulación. En el bloque experimental se han desarrollado electrodos basados en cobre para reactores de membrana electroquímicos tubulares de alta temperatura basados en electrolitos protónicos. Para depositar estos electrodos sobre los tubos se han desarrollado diferentes técnicas. Se ha optimizado el método dip-coating para depositar un cermet basado en cobre utilizando la misma cerámica que el electrolito de los soportes tubulares. Las condiciones con las que se llevó a cabo el proceso de dip-coating provocan disminuciones de varios ordenes de magnitud en la resistencia de polarización del electrodo final. Se trata de un método que es muy sensible a posibles defectos en electrolito, como pequeñas grietas o poros, ya que el cobre del electrodo depositado se introduce por estos defectos reaccionando con el níquel del electrodo interno. Asimismo, se ha empleado el método de sputtering para depositar cobre metálico sobre soportes tubulares electroquímicos. Aumentar la temperatura de deposición genera mejores fijaciones electrodo-electrolito. Las celdas con el cobre depositado a alta temperatura mostraron resistencias de polarización inferiores a 0.1 ¿·cm^2. En el bloque de simulaciones mediante métodos de elementos finitos se han desarrollado diferentes modelos para la caracterización de los fenómenos que tienen lugar en reactores de membrana de alta temperatura. Se ha estudiado: (i) la permeación de oxígeno a través de una membrana de conducción iónica-electrónica mixta; (ii) la electrólisis del agua utilizando celdas basadas en conductores protónicos de alta temperatura; (iii) la integración de una celda protónica para la extracción de hidrógeno en un reformador de metano; (iv) la integración de una celda de conductividad co-iónica en la deshidroaromatización de metano en un reactor de lecho catalítico. El modelo de permeación de oxígeno a través de una membrana de conductividad mixta se ajustó a datos experimentales. El modelo ajustado ha permitido caracterizar la importancia del efecto dilutivo y de arrastre sobre el transporte de oxígeno a través de la membrana. Se ha observado que, aunque el efecto de arrastre tenga menor importancia que el dilutivo, su efecto es importante ya que previene la formación de concentraciones de polarización. El estudio de electrolizadores que utilizan conductores protónicos sólidos de alta temperatura ha permitido estudiar el efecto del escalado en este proceso y evaluar la eficiencia en el almacenamiento de energía. El modelo de un reactor de membrana electroquímico basado en conductores protónicos integrado en un reformador de metano ha permitido comprobar que la demanda térmica del proceso se cubre por el efecto Joule y la electrocompresión del hidrógeno. Se ha comprobado como el coarsening observado en las partículas de níquel no limita la extracción de hidrógeno para la celda estudiada. Un último modelo fue construido para estudiar un reactor de membrana para el proceso de deshidrogenación de metano utilizando una celda co-iónica. El modelo fue validado utilizando datos experimentales. Se utilizó el modelo validado para realizar estudios para analizar posibles limitaciones del proceso. Finalmente, se ha comprobado que el desplazamiento del equilibrio de reacción mediante la extracción de hidrógeno se frena debido a limitaciones cinéticas.
[CAT] Esta tesi presenta resultats sobre reactors de membrana a alta temperatura. Dos blocs diferenciades poden ser identificats: (i) treball experimental; (ii) treball de modelat. En el bloc experimental, elèctrodes basats en coure han siguts optimitzats per a tubular cells de conductor protòniques. La deposició de la capa basada en coure es va fer amb diferents tècniques. La tècnica de dip-coating ha sigut usada per a depositar una capa de cermet basada en coure. Aquesta tècnica es molt sensible a les condicions amb les que es desenvolupa la deposició perquè causa canvis de varis ordres de magnitud en la resistència de polarització del elèctrode. A més, la tècnica de sputtering ha sigut triada per a depositar coure. Per a depositar correctament la capa de coure, altes temperatures durant la deposició foren requerides. El elèctrode optimitzat presenta resistències de polarització inferiors a 0.1 ¿·cm2. En el treball de modelat, la metodologia de elements finits va ser utilitzada per a modelar diferents fenòmens concernits a reactors de membrana de elevada temperatura. La permeació de oxigen per membranes de conducció mixta ha sigut modelada per a avaluar la importància de la dilució i del arrossegament. Els resultats mostren que, encara que el efecte dilutiu es predominant, el efecte del arrossegament no pot ser depreciat. Un adequat arrossegament del oxigen permeat es necessari per evitar polaritzacions en la concentració del oxigen els quals limitarien la permeació. El efecte del arrossegament es major quan el gas portador es mes pesat. El model per estudiar un procés de electròlisis basat en conductors protòniques a elevada temperatura ha permès estudiar l'efecte de l'escalat de aquest procés i avaluar l'eficiència en l'emmagatzemament d'energia. Modelant un reformador de membrana protònica ha permès comprovar la microintegració tèrmica de tots el fenòmens que tenen lloc en aquest procés. Aquest procés compren les reaccions de reformat, extracció electroquímica de hidrogen i electrocompressió del hidrogen generat. La electrocompressió del hidrogen és un procés isoterma que allibera la energia demanda en forma de calor. El model ha permès comprovar que l'engrossiment de les partícules de níquel no limita l'extracció de hidrogen. Un últim model va ser construït per estudiar l'extracció de hidrogen en un reactor de membrana per al procés de dehidroaromatizatió de metà. El reactor de membrana utilitza materials co-iòniques per l'extracció de hidrogen de la càmera de reacció. Aquest model va ser validat amb resultats experimentals. El model va mostrar que no hi ha limitacions amb la difusió del hidrogen. A més, el desplaçament del equilibri mediant l'extracció de hidrogen està limitat per la baixa activitat cinètica del procés.
[EN] In this thesis several studies were developed about membranes reactor at high temperature. Two differentiated blocks could be identified: (i) experimental works; (ii) modelling works. In the experimental block, electrodes based on copper was developed for tubular protonic based cells. The deposition of the copper layer on the tubes was developed by different techniques. Dip-coating method was optimized to a copper-based cermet on the tube. Conditions of the dip-coating procedure has a critical impact in the final performance of the electrochemical cell whose supposes several orders of magnitude in the polarization resistance. It is a sensitive process with the defect of the tube as shows the copper spread over these defects. Additionally, sputtering technique was used to deposit copper layer on the tube. High temperature is required to achieve suitable attachments copper-tube. This high temperature deposited layer present polarization resistances lower than 0.1 ¿·cm2. In the modelling block, finite element methodology was used to build different models to study different phenomena concerning membrane reactors at high temperature. It was studied: (i) the oxygen permeation across a mixed ionic and electronic conducting membrane; (ii) water electrolysis based on high temperature protonic cells; (iii) hydrogen extraction from a steam methane reforming using a protonic cell; (iv) the intensification of the methane dehydromatization reactor using co-ionic membrane. Oxygen permeation model was built to evaluate the effect of the dilutive and the sweep contribution over the permeation process. The fitted model allowed the importance of the dilutive and sweep effect over the oxygen permeation. Although the sweep effect present lower influence in the oxygen transport across the membrane, its effect prevents concentration polarization limitations. Modelling the protonic cell based electrolysis allowed to study the effect of the scale up in this process and to evaluate the efficiency in the energy storing in form of hydrogen. Modelling protonic membrane reformer allowed checking the thermal microintegration of all the heats which take place in the setup. The electrocompression of hydrogen is an isothermal phenomenon which releases the demanded energy as heat. The model allowed to check the coarsening of the Ni particles does not limit the hydrogen extraction for the studied cell. A final model was built to study a catalytic membrane reactor for the methane dehydroaromatization using co-ionic conducting cells. The model was validated using experimental data. Additionally, different studies were performed to analyze possible limitation in the process. Results show that there are no hydrogen diffusion limitations in this process. Additionally, the shift of the equilibrium by extracting hydrogen has to be stopped because kinetic limitations.
Catalán Martínez, D. (2019). Development of electrocatalytic layers and thermo-fluid dynamic evaluation for high temperature membrane reactors [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/135278
TESIS

The efficient and enhanced mixing of heat and incoming reactants is achieved in modern gas turbine systems by employing swirling flows. This is realized by a low velocity region (internal recirculation zone -IRZ) zone resulting from vortex breakdown phenomenon. Besides, IRZ acts as effective flame holder/stabilization mode. Double concentric swirling jet is employed in plethora of industrial applications such as heat exchange, spray drying and combustion. As such, understanding essential features of vortex breakdown induced IRZ and its acoustic response in swirling flow/flame is important in thermo-acoustic instability studies. The key results of the present experimental investigation are discussed in four parts. In the first part, primary transition (sub-critical states) from a pre-vortex breakdown (Pre-VB) flow reversal to a fully-developed central toroidal recirculation zone (CTRZ) in a non-reacting, double-concentric swirling jet configuration is discussed when the swirl number is varied in the range 0.592 S 0.801. This transition proceeds with the formation of two intermediate, critical flow regimes. First, a partially-penetrated vortex breakdown bubble (VBB) is formed that indicates the first occurrence of an enclosed structure resulting in an opposed flow stagnation region. Second, a metastable transition structure is formed that marks the collapse of inner mixing vortices. In this study, the time-averaged topological changes in the coherent recirculation structures are discussed based on the non-dimensional modified Rossby number (Rom) which appears to describe the spreading of the zone of swirl influence in different flow regimes. The second part describes a secondary transition from an open-bubble type axisymmetric vortex breakdown (sub-critical states) to partially-open bubble mode (super-critical states) through an intermediate, critical regime of conical sheet formation for flow modes Rom ≤ 1 is discussed when the swirl number (S) is increased beyond 0.801. In the third part, amplitude dependent acoustic response of above mentioned sub and supercritical flow states is discussed. It was observed that the global acoustic response of the sub-critical VB states was fundamentally different from their corresponding super-critical modes. In particular, with a stepwise increase in excitation amplitude till a critical value, the sub-critical VB topology moved downstream and radially outward. Beyond a critical magnitude, the VB bubble transited back upstream and finally underwent radial shrinkage at the threshold excitation amplitude. On the other hand, the topology of the super-critical VB state continuously moved downstream and radially outwards and finally widened/fanned-out at threshold amplitude. In the final part, transition in time-averaged flame global flame structure is reported as a function of geometric swirl number. In particular, with a stepwise increase in swirl intensity, primary transition is depicted as a transformation from zero-swirl straight jet flame to lifted flame with blue base and finally to swirling seated flame. Further, a secondary transition is reported which consists of transformation from swirling seated flame to swirling flame with a conical tailpiece and finally to highly-swirled near blowout ultra-lean flame. For this purpose, CH* chemiluminescence imaging and 2D PIV in meridional planes were employed. Three baseline fuel flow rates through the central fuel injection pipe were considered. For each of the fuel flow cases (Ref), six different co-airflow rate settings (Rea) were employed. The geometric swirl number (SG) was increased in steps from zero till blowout for a particular fuel and co-airflow setting. A regime map (SG vs Rea) depicting different regions of flame stabilization were then drawn for each fuel flow case. The secondary transformation is explained on the basis of physical significance of Rom.

The efficient and enhanced mixing of heat and incoming reactants is achieved in modern gas turbine systems by employing swirling flows. This is realized by a low velocity region (internal recirculation zone -IRZ) zone resulting from vortex breakdown phenomenon. Besides, IRZ acts as effective flame holder/stabilization mode. Double concentric swirling jet is employed in plethora of industrial applications such as heat exchange, spray drying and combustion. As such, understanding essential features of vortex breakdown induced IRZ and its acoustic response in swirling flow/flame is important in thermo-acoustic instability studies. The key results of the present experimental investigation are discussed in four parts. In the first part, primary transition (sub-critical states) from a pre-vortex breakdown (Pre-VB) flow reversal to a fully-developed central toroidal recirculation zone (CTRZ) in a non-reacting, double-concentric swirling jet configuration is discussed when the swirl number is varied in the range 0.592 S 0.801. This transition proceeds with the formation of two intermediate, critical flow regimes. First, a partially-penetrated vortex breakdown bubble (VBB) is formed that indicates the first occurrence of an enclosed structure resulting in an opposed flow stagnation region. Second, a metastable transition structure is formed that marks the collapse of inner mixing vortices. In this study, the time-averaged topological changes in the coherent recirculation structures are discussed based on the non-dimensional modified Rossby number (Rom) which appears to describe the spreading of the zone of swirl influence in different flow regimes. The second part describes a secondary transition from an open-bubble type axisymmetric vortex breakdown (sub-critical states) to partially-open bubble mode (super-critical states) through an intermediate, critical regime of conical sheet formation for flow modes Rom ≤ 1 is discussed when the swirl number (S) is increased beyond 0.801. In the third part, amplitude dependent acoustic response of above mentioned sub and supercritical flow states is discussed. It was observed that the global acoustic response of the sub-critical VB states was fundamentally different from their corresponding super-critical modes. In particular, with a stepwise increase in excitation amplitude till a critical value, the sub-critical VB topology moved downstream and radially outward. Beyond a critical magnitude, the VB bubble transited back upstream and finally underwent radial shrinkage at the threshold excitation amplitude. On the other hand, the topology of the super-critical VB state continuously moved downstream and radially outwards and finally widened/fanned-out at threshold amplitude. In the final part, transition in time-averaged flame global flame structure is reported as a function of geometric swirl number. In particular, with a stepwise increase in swirl intensity, primary transition is depicted as a transformation from zero-swirl straight jet flame to lifted flame with blue base and finally to swirling seated flame. Further, a secondary transition is reported which consists of transformation from swirling seated flame to swirling flame with a conical tailpiece and finally to highly-swirled near blowout ultra-lean flame. For this purpose, CH* chemiluminescence imaging and 2D PIV in meridional planes were employed. Three baseline fuel flow rates through the central fuel injection pipe were considered. For each of the fuel flow cases (Ref), six different co-airflow rate settings (Rea) were employed. The geometric swirl number (SG) was increased in steps from zero till blowout for a particular fuel and co-airflow setting. A regime map (SG vs Rea) depicting different regions of flame stabilization were then drawn for each fuel flow case. The secondary transformation is explained on the basis of physical significance of Rom.