Dissertations / Theses on the topic 'Heat transfer reduction'

This study incorporates the potential use of Variable Frequency Drives on various motors as well as areas of improved heat transfer in an older, mid-sized coal fired power plant. In power plants, fluid flow rates are often controlled using dampers or valves while the motors that power the pumps stay at full speed resulting in a significant amount of wasted electrical power; energy is also lost due to poor heat recovery prior to gases leaving the system. By examining pump usage as well as additional heat available for recovery, potential energy savings will be determined. Preliminary results of five motors suggested for variable frequency drive application show annual savings that total 31.1 GWh, resulting in a 1.66% increase in overall plant efficiency. Total project costs are near $2 million resulting in a simple payback period of less than two years assuming 0.04 $/kWh. For every degree reduction of the flue gas temperature by means of heat recovery that is reused elsewhere in the cycle, 2 Billion BTU of coal would be saved annually. One realistic scenario suggested heat recovery resulting in a 120°F degree reduction of flue gas temperature amounting to a 2.54% increase in cycle efficiency.

This dissertation focuses on the effects of heating on superhydrophobic (SHPo) surfaces. The work is divided into two main categories: heat transfer without mass transfer and heat transfer in conjunction with mass transfer. Numerical methods are used to explore the prior while experimental methods are utilized for the latter. The numerical work explores convective heat transfer in SHPo parallel plate microchannels and is separated into two stand-alone chapters that have been published archivally. The first considers surfaces with a rib/cavity structure and the second considers surfaces patterned with a square lattice of square posts. Laminar, fully developed, steady flow with constant fluid properties is considered where the tops of the ribs and posts are maintained at a constant heat flux boundary condition and the gas/liquid interfaces are assumed to be adiabatic. For both surface configurations the overall convective heat transfer is reduced. Results are presented in the form of average Nusselt number as well as apparent temperature jump length (thermal slip length). The heat transfer reduction is magnified by increasing cavity fraction, decreasing Peclet number, and decreasing channel size relative to the micro-structure spacing. Axial fluid conduction is found to be substantial at high Peclet numbers where it is classically neglected. The parameter regimes where prior analytical works found in the literature are valid are delineated. The experimental work is divided into two stand-alone chapters with one considering channel flow and the other a pool scenario. The channel work considers high aspect ratio microchannels with one heated SHPo wall. If water saturated with dissolved air is used, the air-filled cavities of SHPo surfaces act as nucleation sites for mass transfer. As the water heats it becomes supersaturated and air can effervesce onto the SHPo surface forming bubbles that align to the underlying micro-structure if the cavities are comprised of closed cells. The large bubbles increase drag in the channel and reduce heat transfer. Once the bubbles grow large enough, they are expelled from the channel and the nucleation and growth cycle begins again. The pool work considers submerged, heated SHPo surfaces such that the nucleation behavior can be explored in the absence of forced fluid flow. The surface is maintained at a constant temperature and a range of temperatures (40 - 90 °C) are explored. Similar nucleation behavior to that of the microchannels is observed, however, the bubbles are not expelled. Natural convection coefficients are computed. The surfaces with the greatest amount of nucleation show a significant reduction in convection coefficient, relative to a smooth hydrophilic surface, due to the insulating bubble layer.

This thesis work investigates techniques of reducing the thermal effects for the SIMBIO-SYS scientific suite of BepiColombo mission. SIMBIO-SYS is an integrated suite of imaging instruments and it has been selected for the European Space Agency BepiColombo mission to Mercury. It includes a stereo imaging system (STC), an high-resolution imager (HRIC) and a visible–near-infrared imaging spectrometer (VIHI). The payload will have to operate in a very harsh environment, mainly from the thermal point of view. For this reason, dedicated state-of-art heat rejection baffles and thermal control devices have to be analyzed and designed. To overcome this issue, a methodological approach has been followed. Starting from the estimation of thermal environment encountered by the payload during mission lead to a deep knowledge of the thermal environment that the instrument will face during the mission phases and provided a framework to the design of the payload baffling system. A mathematical model has been developed and simulations has been carried out to evaluate the incident fluxes on the front end of the payload for all possible hermian seasons during the orbiting of Mercury Planetary Orbiter (MPO) spacecraft around Mercury. The study allowed to identify the most critical orbits from the thermal point of view. Furthermore the mathematical model assess the Sun aspect angle of the optical axes of the three channels (HRIC, VIHI, STC) and identifies the most critical conditions among the various phases of the mission, providing input data for the design of the baffles and constraints for the verification of their geometry. The mathematical model could be applied also to other planetary observational scientific missions and allows to perform sensitivity or uncertainty analysis of incoming solar, albedo and planetary heat fluxes to orbital or attitude parameters. The geometry of the present configuration of SIMBIO-SYS baffles have been verified against direct Sun illumination and dedicated ray-casting algorithms have been implemented to calculate the angular margin to direct entry of solar rays. Thermal analyses of baffles have been afterwards carried out using lumped parameter thermal network method and implemented in ESARAD/ESATAN software. This allows to predict the main heat transfer mechanisms and temperature distribution and to estimate the performance of baffles in terms of heat rejection capability. A study on the appropriate implementation of the HRIC Stavroudis reflective baffle geometry allows to effectively model this type of baffle; furthermore this study led to the definition of a criterion to evaluate the performance of the Stavroudis and to guide the design of the most appropriate test-bed to be used to evaluate its behaviour. The lay-out of a Mercury thermal environment simulator facility has been designed on the basis of the studies carried out. It will consist of a thermal vacuum chamber with heating and cooling sources to simulate the thermal environment that the payload will face on orbit. The design and analysis methods developed had contributed to the definition of efficient baffling system for the three channels of SIMBIO-SYS scientific suite.
Il progetto di ricerca di questa tesi di dottorato è finalizzato a indagare possibili tecniche di riduzione degli effetti termici per la strumentazione scientifica SIMBIO-SYS della missione ESA BepiColombo a Mercurio. SIMBIO-SYS è una suite integrata di strumenti ottici costituita da tre canali: High Resolution Imaging Channel (HRIC), STereo Imaging Channel (STC), Visual and Infrared Hyperspectral Imager (VIHI). SIMBIO-SYS dovrà operare nell'ambiente termicamente ostile di Mercurio. E' quindi necessaria la progettazione di dedicati ed efficaci sistemi di reiezione del calore e di controllo termico per lo strumento. Il problema è stato affrontato con un approccio il più possibile metodologico al fine di individuare gli aspetti cruciali del problema progettuale. Inizialmente si è valutato l’ambiente termico che lo strumento incontrerà durante le fasi operative in orbita attorno a Mercurio. A tal fine è stato sviluppato un modello matematico in grado di valutare, per le possibili stagioni di Mercurio, i flussi solare, di albedo e planetario incidenti su una superficie orbitante attorno al pianeta secondo l’orbita e l’assetto nominali previsti per il satellite. Lo studio ha reso possibile identificare le orbite maggiormente critiche dal punto di vista termico. Il modello matematico implementato può essere applicato anche a studi riguardanti altre missioni di osservazione planetaria e consente di effettuare agevolmente studi di sensibilità dei flussi orbitali incidenti ai parametri orbitali o di assetto. Il modello matematico implementato permette inoltre di valutare l'angolo di incidenza solare rispetto agli assi ottici dei tre strumenti e ha consentito di identificare le condizioni maggiormnete critiche alla illuminazione solare diretta fornendo vincoli di progetto per le geometrie dei paraluce (baffle) degli strumenti. Le geometrie dei baffle della attuale configurazione prevista dal progetto sono state verificate all'ingresso diretto di raggi solari in orbita grazie alla implementazione di algoritmi di ray-cating ed è stato fornito un corrispettivo margine angolare per ciascun baffle. Successivamente sono stati sviluppati dei modelli termici, con approccio a parametri concentrati, dei baffle dei tre canali di SIMBIO-SYS utilizzando il software ESARAD/ESATAN, stimando così le potenze termiche scambiate, la distribuzione delle temperature e le prestazioni del sottosistema in termini di capacità di reiezione del calore. E' stato approfondito lo studio del baffle riflettente di tipo Stavroudis del canale ad alta risoluzione ed è stata individuata la geometria ottimale per la modellazione con gli attuali software commerciali disponibili di analisi termica. Questo studio ha condotto inoltre alla individuazione di criteri per la valutazione delle prestazionidel baffle Stavroudis utili a guidare il progetto di un apparato sperimentale per la caratterizzazione delle prestazioni del baffle.L'attività di ricerca è poi proseguita con il dimensionamento a livello di sistema di un apparato sperimentale finalizzato a riprodurre a terra l'ambiente termico incontrato dallo strumento in orbita attorno Mercurio. Esso è concepito per riprodurre all'interno di una camera termo vuoto l'andamento dei flussi solare e infrarosso incidenti sullo strumento e le interfacce radiative e conduttive della strumentazione con il satellite, tenendo conto della orientazione dello strumento durante il moto orbitale rispetto alle sorgenti di radiazione. I modelli matematici sviluppati e le analisi termiche eseguite hanno fornito le specifiche di progetto dell'apparato sperimentale ed utili dati numerici per la definizione del simulatore a livello di sistema. I metodi di analisi e di progetto sviluppati hanno contribuito alla definizione di efficienti sistemi di riduzione degli effetti termici per la strumentazione SIMBIO-SYS.

Firstly, I would like to show my sincere gratitude to my supervisors Dr. Ferdinando Guzzomi and Dr. Ana Vafadar for their immeasurable guidance and support throughout the duration of the project. Dr. Guzzomi and Dr. Vafadar have always had an open-door policy for me which helped me accomplish my goals on or before the deadlines. I highly appreciate Dr. Ferdinando Guzzomi for listening to and putting up with my ridiculous ideas and vision towards the project and pointing me in the right course of direction. I would like to thank Dr. Guzzomi for giving me the creative freedom and putting his trust on me with the project, allowing me to think outside the box and making my ideas a reality. I would also like to show my heartfelt appreciation towards Dr. Ana Vafadar for listening to my confusion every week and to draw meaning out of my words. Your feedback along with the constructive criticism has been highly valuable throughout this journey and has kept me in check. Your constant support and faith in me have allowed me to finish the project on time and with significant contributions to the area of my research. Dr. Kevin Hayward has also played a key role in the completion of this project. His feedback and suggestions towards my manuscripts and reports and numerous data analysis techniques have been critical in making this work presentable. From the bottom of my heart, I would like to say a big thank you to Mr. Adrian Davis, Dr. Michael Stein and Joshua Bolton for their technical and literacy support throughout my bachelors and master’s project. Without your guidance and wisdom, none of this would have been possible. A special thanks goes to my fellow researchers Aakash Shaun Hurry and Prashan Perera for all the cake and coffee I’ve had in the past 2 years and for the lovely discussions we had regarding our projects. I highly appreciate their immense support through times of doubt and uncertainty. I would also like to thank the ECU-Motorsports team specially Adam Honeycombe and Mario Leone for allowing me to use the facilities within the motorsports workshop and to be a part of the team and experience the Aus-West competition. I will cherish these memories and friendships forever. Last but not the least, my biggest gratitude goes towards my uncle and aunt for their unconditional love and support throughout my bachelors and masters. I would not be where I am without their constant support. I would also like to thank my family and friends back in India who have helped me through this journey and allowed me to accomplish my goals.

This study explores the reactions and related species of NOx pollutants in methane flames in order to understand their production and consumption during the combustion process. To do this, several analytical simulations were run to explore the behavior of nitrogen species in the pre-flame, post- flame, and reaction layer regions. The results were then analyzed in order to identify all "steady-state" species in the flame as well as the determine all the unnecessary reactions and species that are not required to meet a defined accuracy. The reductions were then applied and proven to be viable.

The subject of this study is the effect of in-cylinder selective non-catalytic reduction (SNCR) of NOx emissions in diesel exhaust gas by means of direct injection of aqueous urea ((NH2)2CO) into the combustion chamber. A single cylinder diesel test engine was modified to accept an electronically controlled secondary common rail injection system to deliver the aqueous urea directly into the cylinder during engine operation. Direct in-cylinder injection was chosen in order to ensure precise delivery of the reducing agent without the risk of any premature reactions taking place. Unlike direct in-cylinder injection of neat water, aqueous urea also works as a reducing agent by breaking down into ammonia (NH3) and Cyanuric Acid ((HOCN)3). These compounds serve as the primary reducing agents in the NOx reduction mechanism explored here. The main reducing agent, aqueous urea, was admixed with glycerol (C3H8O3) in an 80-20 ratio, by weight, to function as a lubricant for the secondary injector. The aqueous urea injection timing and duration is critical to the reduction of NOx emissions due to the dependence of SNCR NOx reduction on critical factors such as temperature, pressure, reducing agent to NOx ratio, Oxygen and radical content, residence time and NH3 slip. From scoping engine tests at loads of 40 percent and 80 percent at 1500 rpm, an aqueous urea injection strategy was developed. The final injection strategy chosen was four molar ratios, 4.0, 2.0, 1.0 and 0.5 with five varying injection timings of 60, 20, 10, 0, and -30 degrees after top dead center (ATDC). In addition to the base line and aqueous urea tests, water injection and an 80-20 water-glycerol solution reduction agent tests were also conducted to compare the effects of said additives as well. The comparison of baseline and SNCR operation was expected to show that the urea acted as a reducing agent, lowering NOx emissions up to 100% (based on exhaust stream studies) in the diesel exhaust gas without the aid of a catalyst. The data collected from the engine tests showed that the aqueous urea-glycerol solution secondary had no effect on the reduction of NOx and even resulted in an increase of up to 5% in some tests. This was due to the low average in-cylinder temperature as well as a short residence time, prohibiting the reduction reaction from taking place. The neat water and water-glycerol solution secondary injection was found to have a reduction effect of up to 59% on NOx production in the emissions due to the evaporative cooling effect and increased heat capacity of the water.

La préservation de la chaîne du froid est un paramètre particulièrement important dans le cadre de la distribution urbaine, où les fréquentes ouvertures de portes induisent une charge thermique d’infiltration. Afin de réduire les transferts de masse et de chaleur et de protéger l’ouverture, des rideaux d’air ont récemment été installés au niveau de l’ouverture des camions frigorifiques. L’objet de la présente étude est d’étudier ce type confinement. Deux modèles CFD ont été développés pour simuler les champs de températures et de vitesses dans un camion réfrigéré clos. Ils ont permis de montrer que la variation de la vitesse de soufflage ne modifie pas de manière significative la structure des écoulements. Différents conduits d’air sont modélisés. Les résultats numériques montrent que la configuration avec un conduit ouvert améliore fortement le renouvellement d’air. Puis, une étude numérique est réalisée dans le but d’étudier les infiltrations de chaleur et de masse au cours de l’ouverture des portes. Ces écoulements sont bien prédits par le modèle CFD, excepté à la transition entre les deux régimes d’infiltration. Une caisse expérimentale a été équipée d’un dispositif de rideau d’air composé d’un jet ambiant, d’un jet froid ou d’un jet double. En parallèle, un modèle numérique CFD a été développé pour étudier l’influence de différents paramètres. Une bonne concordance entre les résultats numériques et expérimentaux a été observée. L’efficacité du rideau d’air ambiant est maximale lorsque le point d’impact du rideau se situe dans le plan de l’ouverture. Le rideau double maintient efficacement l’homogénéité de la température pour de courtes ouvertures. Le rideau d’air froid est la meilleur configuration, il limite fortement l’augmentation de température de l’enceinte et permet des gains énergétiques importants
Cold chain safety is a key parameter for urban distribution where the frequent door-opening induces a heat infiltration. In order to reduce heat and mass transfer, air curtain have recently been installed to protect the doorway of refrigerated truck. The aim of this work is to study this type of door insulation. Two CFD numerical models were developed to simulate the temperature and velocity fields in a closed refrigerated truck. These models showed that modifying the blowing velocity does not modify the air flow structure inside the cavity. Different air chutes were modelled. Numerical results demonstrate that the configuration with a convergent and an open duct strongly improves the air renewal. A numerical investigation was performed in order to study heat and mass infiltration rates during the opening. The infiltration flow rate is well predicted by the CFD model, except at the transition between both flow regimes. An experimental truck was equipped with an air curtain setup, composed by an ambient air jet, a cold air jet or a double jet. In parallel, a numerical CFD model was developed to study the influence of various parameters. Experimental and numerical results were found to be in good agreement. The maximum efficiency of the ambient air curtain is reached when the impact point of the jet occurs in the door plane at the ground level. This configuration is only relevant for short opening times. The double air curtain efficiently maintains the temperature homogeneity for short openings. The cold air curtain is the best configuration which strongly limits the temperature increase during the opening and allows important energy savings

Dans cette thèse, des techniques d'homogénéisation numérique efficaces en termes de calcul sont présentées pour les phénomènes de diffusion dans des matériaux hétérogènes. Comme étape préliminaire, une réduction de modèle pour l'équation de diffusion de chaleur transitoire est effectuée à la microéchelle en utilisant la synthèse en mode composants, qui fournit une description émergente enrichie-continuum à l’échelle macroscopique. Sur la base de la localisation des variables d'enrichissement, soit sur les nœuds d'éléments finis, soit sur les points de quadrature, deux schémas de discrétisation spatiale sont analysés pour le diplacement milieu continu. La formulation du potentiel chimique et des champs de déformation est utilisée, ce qui permet l'utilisation d'éléments finis continus en C0 standard. Le problème de la micro-échelle, qui implique généralement une solution coûteuse du problème de la mécanique de diffusion de masse couplée est maintenant remplacée par un ensemble d'équations différentielles ordinaires grâce à la réduction du modèle. Enfin, une approche alternative de réduction de modèle utilisant la mécanique basée sur les données est explorée. Il repose sur une recherche directe et une interpolation à partir d'une base de données au lieu de la solution d'un problème microscopique. La base de données est construite et stockée en utilisant les calculs microscopiques dans une étape hors ligne. Il fournit également une voie pour étendre la méthode de réduction du modèle proposée au régime non linéaire
In this thesis computationally efficient numerical homogenization techniques are presented for diffusion phenomena in heterogeneous materials. As a preliminary step, a model reduction for the transient heat diffusion equation is performed at the micro-scale using component mode synthesis, which provides an emergent enriched-continuum description at the macro-scale. Based on the location of the enrichmentvariables, either on the finite element nodes or the quadrature points, two spatial discretization schemes are analyzed for the enrichedcontinuum. The proposed model reduction is also extended to the transient mass diffusion coupled to the mechanics with application to lithium-ion batteries. Chemical potential and strain fields formulation is used which allows the use of standard C0-continuous finite elements. The micro-scale problem, which usually involves an expensive solution of the coupled mass diffusionmechanics problem is now replaced by a set of ordinary differential equations through model reduction. Finally, an alternative model reduction approach using data-driven mechanics is explored. It relies on a direct search and interpolation from a database instead of the solution of a microscopic problem. The database is constructed and stored using the microscopic calculations in an offline stage. It also provides a route to extend the proposed model reduction method to the nonlinear regime

This master’s thesis focuses on effect of outer building construction on thermal load of space. The effect of translucent and non-translucent construction is discussed. The project of air-conditioning system is prepared for the two alternatives of the translucent construction, including the purchase price of the airconditioning system and glazing and the savings on summer cooling. Afterwards the period of the recovery of investment is calculated. The plan of the airconditioning system is connected to my bachelor’s thesis “Airconditioning in the car showroom”, the subject of which was the plan of the airconditioning system of the car showroom.

Une méthode non intrusive de construction d’un modèle de remplacement de l’écoulement dans une cavité de système d’air secondaire de turboréacteur est recherchée. Le modèle réduit doit pouvoir être intégré dans un modèle de l’ensemble du moteur et couplé à la thermique de la structure pour simuler son comportement thermique sur une mission complète sous aile. Pour cela, il doit prendre un grand nombre de paramètres en entrée, retourner autant de sorties et être utilisable sur des intervalles de variations étendus de ces paramètres. Plusieurs approches sont envisagées et implémentées, puis appliquées à la modélisation d’une cavité sous turbine fictive :— Création de surfaces de réponse des termes de la décomposition ANOVA des flux pariétaux.— Création de surfaces de réponse des flux pariétaux combinée avec une méthode de raffinement adaptative exploitant la trajectoire dans l’espace d’entrée issue du couplage modèle réduit - modèle de structure.— Réduction de dimension des champs d’interface échangés à partir de résultats des itérations du couplage des modèles thermiques de l’écoulement et de la structure, puis création de surfaces de réponse des coordonnées réduites.Cette dernière voie permets d'obtenir des résultats encourageants sur le cas test proposé d'abord dans le cas à conditions limites d'entrée de l'écoulement fixées, puis en incluant des variations de certaines d'entre-elles
A non intrusive method to create surrogate models describing the flow in jet engines’ secondary air system is desired. The resulting model must be integrated in a thermal model describing the whole engine during a complete mission under the wing. This requires the model to use a high number of input and output parameters and to be valid on a broad domain of variation of its parameters. Several approches are explored in this thesis and applied to a simplified turbine cavity :— Surrogate modeling of terms of the ANOVA decomposition of wall fluxes.— Surrogate modeling of wall fluxes combined with an adaptive refinement method exploiting the trajectory followed by the input parameters during the coupling between the metamodel and the structural model.— Dimensionality reduction of the interface data exchanged during the coupling between flow and structure thermal model and surrogate modeling of the resulting reduced coordinate.This last approach leads to good results on the test case considered in this thesis with fixed inlet boundary conditions and then with variations of some of the inlet parameters

Dans le contexte énergétique actuel, les pompes à chaleur (PAC) géothermiques sont parmi les technologies les plus performantes pour augmenter l’efficacité énergétique des bâtiments. Par contre le coût initial et l’encombrement des capteurs enterrés traditionnels peuvent être un obstacle à sa diffusion sur le marché des énergies renouvelables. Pour réduire ces coût et encombrement, une réflexion sur l’adjonction d’un système d’appoint et/ou de recharge thermique du sol aux capteurs enterrés est actuellement en cours de tests. Les outils actuels de modélisation des capteurs enterrés obtiennent en effet de bons résultats mais seulement pour un dimensionnement classique en régime permanent. Les modèles existants ne permettent donc pas de représenter correctement les dynamiques rapides des échanges entre le sol et les tubes et cela est d’autant plus vrai si l’on adjoint le système de recharge solaire. Par conséquence, cette thèse a pour objectif de développer les modèles fins et dynamiques nécessaires à l’analyse des phénomènes transitoires dans les capteurs enterrés eux-mêmes. Un maillage fin, sur les bases de la triangulation de Delaunay, est choisi pour le forage ainsi que pour le sol avoisinant. Une approche numérique en 3D (FVM + FEM) peut être obtenue sur les bases de la discrétisation spatiale du domaine. Cette approche appliquée brutalement induirait des temps de calcul très élevés et de toute façon incompatible avec les moyens informatiques ordinaires. Afin de répondre à l’ensemble de ces problèmes, différentes techniques ont été utilisées afin d’accélérer le temps de calcul: décomposition de domaine, emboîtement des pas de temps de calcul pour chaque sous-domaine, réduction des modèles d’états de chaque sous-domaine et finalement couplages temporels et spatiaux des équations de transferts de l’ensemble du problème. Ce dernier est développé particulièrement sur les bases de la méthode des éléments finis. Par ailleurs, un modèle hybride est développé en combinaison de différentes approches. Une approche numérique est adoptée pour la modélisation du puits et la modélisation des transferts de chaleur dans le sol environnant est faite par l’utilisation de solutions analytiques. Ainsi, ce modèle est implanté dans TRNSYS. Une plate-forme expérimentale comprenant trois puits verticaux couplés à une pompe à chaleur géothermique est également présentée. Les résultats expérimentaux sont comparés avec les résultats de la simulation aussi bien au niveau de la température du fluide qu’à la température à différentes profondeurs dans les puits. Le modèle développé donne des résultats très similaires avec ceux qui sont obtenus grâce à l’expérimentation même lors que les pas de temps sont très petits. Il y a des choses à améliorer dans ce modèle développé, mais cela concerne essentiellement l’accélération du temps de calcul. Nous avons constaté que les modèles que nous avons dévéloppés donnent des résultats meilleurs à pas de temps courts que les modèles classiques. Il faut donc bien préciser le domaine d’utilisation de chacun des modèles: consommation sur le long terme, stratégie de contrôle de la PAC, les transferts de chaleur à l’intérieur du puits et etc. De plus, une application du modèle dans le dimensionnement d’échangeurs ainsi que l’investigation de son impact sur le sol avoisinant est également envisagée. Finalement, la méthodologie de modélisation présentée dans ce travail pourrait être aussi utilisé pour différents types d’échangeurs, ouvrant aussi la porte à une analyse fine dans le domaine géothermique
Ground-source heat pump systems with vertical ground heat exchangers (GHE) are gaining popularity worldwide for their higher coefficients of performance and lower CO2 emissions. However, the higher initial cost of installing the borehole GHEs is a main obstacle to spread the systems. To reduce the required total GHE length and efficiently operate the systems, various systems such as hybrid ones (e.g. solar heat injection) have recently been introduced. Accurate prediction of heat transfer in and around boreholes of such systems is crucial to avoid costly overdesigns or catastrophic failures of undersized systems as it is for typical GCHP systems. However, unlike the traditional sizing methods, it is increasingly required to take into account detailed borehole configuration and transient effects (e.g. short circuit effects between U-tubes). Many of the existing GHE models have been reviewed. Some of these models have serious limitations when it comes to transient heat transfer, particularly in the borehole itself. Accordingly, the objective of this thesis is to develop a model that is capable to accurately predict thermal behaviors of the GHEs. A precise response to input variations even in a short time-step is also expected in the model. The model also has to account for a correct temperature and flux distribution between the U-tubes and inside the borehole that seems to be important in the solar heat injection case. Considering these effects in 3D with a detailed mesh used for describing the borehole configurations is normally time-consuming. This thesis attempts to alleviate the calculation time using state model reduction techniques that use fewer modes for a fast calculation but predict similar results. Domain decomposition is also envisaged to sub-structure the domain and vary the time-step sizes. Since the decomposed domains should be coupled one another spatially as well as temporally, new coupling methods are proposed and validated particularly in the FEM. For the simulation purpose, a hybrid model (HM) is developed that combines a numerical solution, the same one as the 3D-RM but only for the borehole, and well-known analytical ones for a fast calculation. An experimental facility used for validation of the model has been built and is described. A comparison with the experimental results shows that the relatively fast transients occurring in the borehole are well predicted not only for the outlet fluid temperature but also for the grout temperatures at different depths even in very short time-steps. Even though the current version of 3D-RM is experimentally validated, it is still worth optimizing the model in terms of the computational time. Further simulations with the 3D-RM are expected to be carried out to estimate the performance of new hybrid systems and propose its appropriate sizing with correspondent thermal impacts on the ground. Finally, the development of the model 3D-RM can be an initiation to accurately model various types of GHE within an acceptable calculation time

Atrial fibrillation is a common heart arrhythmia which is characterized by a missing or irregular contraction of the atria. The disease is a risk factor for other more serious diseases and the total medical costs in society are extensive. Therefore it would be beneficial to improve and optimize the prevention and detection of the disease.   Pulse palpation and heart auscultation can facilitate the detection of atrial fibrillation clinically, but the diagnosis is generally confirmed by an ECG examination. Today there are several algorithms that detect atrial fibrillation by analysing an ECG. A common method is to study the heart rate variability (HRV) and by different types of statistical calculations find episodes of atrial fibrillation which deviates from normal sinus rhythm.   Two algorithms for detection of atrial fibrillation have been evaluated in Matlab. One is based on the coefficient of variation and the other uses a logistic regression model. Training and testing of the algorithms were done with data from the Physionet MIT database. Several steps of signal processing were used to remove different types of noise and artefacts before the data could be used.   When testing the algorithms, the CV algorithm performed with a sensitivity of 91,38%, a specificity of 93,93% and accuracy of 92,92%, and the results of the logistic regression algorithm was a sensitivity of 97,23%, specificity of 93,79% and accuracy of 95,39%. The logistic regression algorithm performed better and was chosen for implementation in Java, where it achieved a sensitivity of 97,31%, specificity of 93,47% and accuracy of 95,25%.
Förmaksflimmer är en vanlig hjärtrytmrubbning som kännetecknas av en avsaknad eller oregelbunden kontraktion av förmaken. Sjukdomen är en riskfaktor för andra allvarligare sjukdomar och de totala kostnaderna för samhället är betydande. Det skulle därför vara fördelaktigt att effektivisera och förbättra prevention samt diagnostisering av förmaksflimmer.   Kliniskt diagnostiseras förmaksflimmer med hjälp av till exempel pulspalpation och auskultation av hjärtat, men diagnosen brukar fastställas med en EKG-undersökning. Det finns idag flertalet algoritmer för att detektera arytmin genom att analysera ett EKG. En av de vanligaste metoderna är att undersöka variabiliteten av hjärtrytmen (HRV) och utföra olika sorters statistiska beräkningar som kan upptäcka episoder av förmaksflimmer som avviker från en normal sinusrytm.   I detta projekt har två metoder för att detektera förmaksflimmer utvärderats i Matlab, en baseras på beräkningar av variationskoefficienten och den andra använder sig av logistisk regression. EKG som kommer från databasen Physionet MIT används för att träna och testa modeller av algoritmerna. Innan EKG-signalen kan användas måste den behandlas för att ta bort olika typer av brus och artefakter.   Vid test av algoritmen med variationskoefficienten blev resultatet en sensitivitet på 91,38%, en specificitet på 93,93% och en noggrannhet på 92,92%. För logistisk regression blev sensitiviteten 97,23%, specificiteten 93,79% och noggrannheten 95,39%. Algoritmen med logistisk regression presterade bättre och valdes därför för att implementeras i Java, där uppnåddes en sensitivitet på 91,31%, en specificitet på 93,47% och en noggrannhet på 95,25%.

Buildings are responsible for over a third of the energy consumption in the United States annually. This energy consumption contributes to some of the most pressing problems facing our society. Modeling of buildings and their systems is an integral part of most strategies for reduction of energy use in buildings. Modeling allows for informed building designs, optimization of systems, and greater market acceptance of new energy-saving technologies. This work addresses two particular modeling applications concerned with reduction of energy usage in buildings: convective heat transfer modeling in perimeter zones, and liquid desiccant dehumidification modeling. The first objective of this work is concerned with modeling convective transport in buildings and creation of inputs for energy modeling programs and passive pollutant removal calculations. This is accomplished through four investigations. In the first investigation, the influence of floor diffusers on convection heat transfer at perimeter zone windows in commercial buildings is measured. In the second, the impact of blinds on convection under a variety of circumstances is quantified. In the third, movement of air jets issuing from floor diffusers is predicted, and the effect of buoyancy on convective heat transfer at perimeter zone surfaces is analyzed. In the fourth investigation, convective mass transfer at indoor surfaces is investigated. Full scale experiments were conducted in support of these four investigations and semi-empirical correlations vii consistent with theory are given to predict jet movement and convective transport under a variety of circumstances. The second objective of this dissertation is concerned with modeling and analysis of liquid desiccant dehumidification systems and is pursued through three additional investigations. The first is concerned with modeling small-scale transport within the channels of a liquid desiccant absorber and regenerator. Physical and empirical models are developed which agree well with laboratory data. During the second investigation, a dynamic model of a liquid desiccant dehumidification system is developed and integrated into a full-building energy simulation. This is used to assess the potential applicability of the system in supermarkets in various climates. The models developed are used to optimize the system and develop a procedure to size components in the final investigation.
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碩士
國立臺灣大學
機械工程學研究所
94
ABSTRACT In this paper, we present a nonlinear heat-transfer macromodeling technique using the trajectory piecewise linear model order reduction (TPWLMOR) method. A 3D nonlinear heat-transfer model, which is capable of accounting for the temperature-dependent material properties as well as radiation effect, is implemented using the finite difference method (FDM). The numerical models generated by the FDM are reduced into compact models using the TPWLMOR technique, which is based on the concept of piecewise-linear approximation and an Arnoldi-based model order reduction (MOR) algorithm. Nonlinear macromodeling case studies of different MEMS thermal devices are demonstrated using the TPWLMOR technique. The calculated steady and transient characteristics of the thermal devices are discussed. In terms of computational cost, the TPWLMOR models are at least 2 orders of magnitude faster than the original nonlinear full-meshed models with negligible compromise in accuracy. The simulated results by the TPWLMOR models are also verified with the experimentally measured results. Keywords: model order reduction, piecewise linear, macromodel, system-level modeling, Arnoldi algorithm

碩士
國立中正大學
機械系
90
This thesis provides a methodology of model reduction of the heat transfer of porous media with uncertain boundary conditions and distributed parameters. It focuses on the identification of uncertain parameters, boundary conditions as well as the process of dynamical database and simplification of dynamical model, which build an important bridge from the complexity of porous media heat transfer to the availability of online operation. The kernel methodology is to formulate the governing equation and boundary conditions into a single state-space description. A set of Eigen-bases is therefore found, and a truncated model is obtained after the uncertain parameters and boundary conditions are identified in the frequency domain. A series of experiment via MATLAB simulation is performed in order to verify the methodology.

abstract: ABSTRACT The heat recovery steam generator (HRSG) is a key component of Combined Cycle Power Plants (CCPP). The exhaust (flue gas) from the CCPP gas turbine flows through the HRSG − this gas typically contains a high concentration of NO and cannot be discharged directly to the atmosphere because of environmental restrictions. In the HRSG, one method of reducing the flue gas NO concentration is to inject ammonia into the gas at a plane upstream of the Selective Catalytic Reduction (SCR) unit through an injection grid (AIG); the SCR is where the NO is reduced to N2 and H2O. The amount and spatial distribution of the injected ammonia are key considerations for NO reduction while using the minimum possible amount of ammonia. This work had three objectives. First, a flow network model of the Ammonia Flow Control Unit (AFCU) was to be developed to calculate the quantity of ammonia released into the flue gas from each AIG perforation. Second, CFD simulation of the flue gas flow was to be performed to obtain the velocity, temperature, and species concentration fields in the gas upstream and downstream of the SCR. Finally, performance characteristics of the ammonia injection system were to be evaluated. All three objectives were reached. The AFCU was modeled using JAVA - with a graphical user interface provided for the user. The commercial software Fluent was used for CFD simulation. To evaluate the efficacy of the ammonia injection system in reducing the flue gas NO concentration, the twelve butterfly valves in the AFCU ammonia delivery piping (risers) were throttled by various degrees in the model and the NO concentration distribution computed for each operational scenario. When the valves were kept fully open, it was found that it led to a more uniform reduction in NO concentration compared to throttling the valves such that the riser flows were equal. Additionally, the SCR catalyst was consumed somewhat more uniformly, and ammonia slip (ammonia not consumed in reaction) was found lower. The ammonia use could be decreased by 10 percent while maintaining the NO concentration limit in the flue gas exhausting into the atmosphere.
Dissertation/Thesis
M.S. Mechanical Engineering 2011

As the fluidic devices are miniaturized to improve portability, the friction of the microchannel becomes intrinsically high and a high pumping power will be required to drive the fluid. Since the pumping power delivered by portable devices is limited, one method to reduce this is to render the surface to become slippery. This can be achieved by roughening up the microchannel wall and form a bed of air pockets between the roughness elements, which is known as the superhydrophobic Cassie-Baxter state. While the study on superhydrophobic microchannels are focused mainly in maximizing the friction reduction effects and maintaining the stability of the air pockets, less attention has been given to characterizing the microchannel friction under a metastable state, where partial flooding of the micro-textures may be present, and under heated conditions, where the air pockets are trapped between the micro-textures. In order to quantify the frictional characteristics, microchannels with micron-sized trenches on the side walls were fabricated and tested under varying inlet pressures and heating conditions. By measuring the hydrodynamic resistance and comparing with numerical simulations, results suggest that (1) the air-water interface behaves close to a no-slip boundary condition, (2) friction becomes insensitive to the wetting degree once the micro-trenches become highly wetting, (3) the fully wetted micro-trench may be beneficial over the de-wetted ones in order to achieve friction reduction effects and (4) heating the micro-trenches to induce a highly de-wetting state may actually be detrimental to the microchannel flow due the excessive growth of the air layer. As part of the future work to characterize heat transfer in superhydrophobic microchannels, a rectangular microchannel with microheaters embedded close to the side walls was fabricated and the corresponding heat transfer rates were measured through dual fluorescence thermometry. Results suggested that significant heat is lost through the environment despite the high thermal resistance of the microchannel material. An extra insulation is suggested prior to characterizing the convective heat transfer coefficients in the superhydrophobic microchannel flow.
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Please read the abstract in the section 00front of this document
Dissertation (M Eng (Metallurgical Engineering))--University of Pretoria, 2006.
Materials Science and Metallurgical Engineering
unrestricted

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. August 8, 2014.
We study the nonlinear models arising in heat transfer in extended surfaces (fins) and in solid slab (hot body). Here thermal conductivity, internal generation and heat transfer coefficient are temperature dependent. As such the models are rendered nonlinear. We employ Lie point symmetry techniques to analyse these models. Firstly we employ Lie point symmetry methods and determine the exact solutions for heat transfer in fins of spherical geometry. These solutions are compared with the solutions of heat transfer in fins of rectangular and radial geometries. Secondly, we consider models describing heat transfer in a hot body, for example, a plane wall. We then employ the preliminary group classification methods to determine the cases of the arbitrary function for which the principal Lie algebra is extended by one. Furthermore we the exact solutions.