Tesi sul tema "Cycle de Stirling"

Stirling cycle cryocoolers are used widely in military applications. The regenerator is the key element of Stirling cycle cryocoolers. It is known that performance of the regenerator directly affects the cryocooler performance. Therefore, any improvement on the regenerator will lead to a more efficient cryocooler. Thus, it is essential to have an idea about regenerator parameters and their effects on the system. In this study Stirling engine regenerator, which is constructed by wire mesh screens, is accepted as a porous medium. Using energy balance and continuity equation, matrix and fluid thermal equations are derived. Simplified versions of these equations are obtained for not only the ideal case, but also two other cases which take into account the effects of longitudinal conduction and the effects of regenerator wall. A computer code is developed in Matlab to solve these equations using finite difference method. The developed code is validated by using Sage. Afterwards, effects of all regenerator parameters on regenerator performance are investigated in detail and results are presented. To make this investigation easier, a graphical user interface is also built (in Matlab) and used.

In this dissertation the analysis of the Stirling engine is presented, this research topic falls within the category of thermal energy conversion. The research that was conducted is presented in three chapters of which the topics are: the effects of allocation of volume on engine performance, the GPU-3 (Ground Power Unit - developed by GM) Stirling engine analysis, and the optimisation of a 1000 cm³ Stirling engine with finite heat capacity rates at the source and the sink. The Stirling engine has many advantages over other heat engines, as it is extremely quiet, has multi-fuel capabilities and is highly efficient. There is also significant interest in using Stirling engines in low to medium temperature solar thermal applications, and for waste heat recovery. To develop high-performance engines that are also economically viable, advanced mathematical models that accurately predict performance and give insight into the different loss mechanisms are required. This work aims to use and adapt such a model to analyse the effects of different engine parameters and to show how such a model can be used for engine optimisation using the Implicit Filtering algorithm. In the various analyses that are presented, the dynamic second order adiabatic numerical model is used and is coupled to equations that describe the heat and mass transfer in the engine. The analysis shows that the allocation of volume has a significant effect on engine performance. It is shown that in high-temperature difference (HTD) engines, increasing dead-volume ratio increases efficiency and decreases specific work output. In the case of low-temperature difference (LTD) and medium-temperature difference (MTD) engines, there is an optimal dead-volume ratio that gives maximum specific work output. It was also found that there are optimal swept volume ratios and that the allocation of heat exchanger volume has a negligible effect on engine performance - so long as the dead-volume ratio is optimal. The second order model with irreversibilities included was used to perform an exergy analysis of the GPU-3 Stirling engine. This model compared well with experimental results and the results from other models found in the literature. The results of the study show the two different approaches in modelling the engine losses and the effect that the various engine parameters have on the GPU-3 power output and efficiency. The optimisation of the 1000 cm³ Stirling engine was performed using a model with finite heat capacity rates at the source and the sink, fixed number of heater and cooler tubes, and four different regenerator mesh types. The engine geometry was optimised for maximum work output using the implicit filtering algorithm, and the results show the dominant effect that the regenerator has on engine performance and the geometry that gives maximum work output. The critical insights obtained from this research are the importance of the dead-volume ratio in engine analysis, the merits of the novel Second law Stirling engine model, and the importance of regenerator mesh choice and geometry. The Implicit filtering algorithm is also shown to be a suitable choice of optimisation algorithm to use with Stirling engine mathematical models.

This dissertation discusses Stirling’s cycle and its contribution using different approaches. There are calculation of Schmidt’s theory and distinctiveness between ideal and real cycle described. Based on my previous research, this work provides a detailed summary of different methods which are used to stimulate Stirling’s cycles as well as the motor as a whole. Attention is particularly dedicated to current utilization of this machine which is not broadly known within general public.

Dans le contexte économique et énergétique actuel, la mise en œuvre de technologies à l'aide de l'énergie renouvelable comme source de chauffage offre un double avantage: la réduction de la pollution et des coûts de carburant. Il y a un besoin de promouvoir les sources renouvelables d'énergie comme les sources significatives de production d'énergie pour les systèmes décentralisés. Une première étude bibliographique a été fait sur les technologies existantes pour la production d'énergie électrique à partir du solaire. Cette étude consiste dans la recherche d’une nouvelle solution de conversion de l’énergie solaire pour la production d’électricité de faible puissance. L'un des objectifs de cette thèse a été la construction d'un moteur Stirling de type gamma fonctionnant à basse différence de température, adapté à un circuit solaire (capteur plan). Le moteur Stirling a été testé en vue de comparer les résultats expérimentales avec les résultats d’un model Schmidt, fait dans le logiciel, Matlab. Un autre cycle thermodynamique étais étudie dans cette travail, le Cycle Organique Rankine (ORC). Un modèle mathématique a été développé et vérifie dans les logiciels, Thermoptim et EES (Engineering Equation Solver) avec les résultats expérimentaux pour étudier les performances d'installation avec des différentes températures de fonctionnement. La méthode exergétique et la méthode du Pincement sont utilisée pour évaluer les performances du système comme irréversibilité, destruction d’exergie et phénomènes qui se produisent dans toutes les composantes du système ORC pour améliorer son fonctionnement
In the current economic and energy context, implementation of technologies using renewable energy as heat source has two advantages: reducing pollution and fuel costs. There is a need to promote renewable energy sources such as significant sources of power generation for decentralized systems. In the first part, it was made a literature review on existing technologies for the production of electricity with solar energy. One of the objectives of this thesis was to build a Stirling engine gamma type suitable to use solar energy (flat plate collator). The Stirling engine was tested to compare the experimental results with the results of Schmidt model, realized in the software, Matlab. Another thermodynamic cycle was studied in this work, the Organic Rankine Cycle (ORC). A mathematical model was developed and verified in software, Thermoptim and EES (Engineering Equation Solver) with experimental results to study the installation performance function of different operating temperatures. The entire system and each subsystem are analyzed according to the first and the second law of thermodynamics. The exergy method and Pinch analysis are used to evaluate the performance of the system like irreversibility and exergy destruction, phenomenon that occurs in all components of the ORC system. This analysis is to improve the operation

Bolivia is a developing country in South America. Many rural communities still lack access to electricity. The extension of the National Grid System to all rural communities is not feasible due to economic and topographic challenges as well as the environmental problems that may arise. To tackle these problems, Off-grid solutions are implemented. Photovoltaic (PV) panels combined with batteries are a viable option for areas located close to the equator and high altitudes such as Bolivia. Almost always a controlled source of energy such as Diesel generators must complement the PV system due to the stochastic nature of solar energy. The use of fossil fuel can be detrimental to the environment and more environmentally friendly solutions are being investigated. The use of wood pellets in Stirling engines is a viable replacement for Diesel generators.  The purpose of this study is to investigate and compare the environmental impacts caused by two Off-grid hybrid systems. The first one is composed of a Diesel generator, PV panels, and batteries. The second one is composed of a Stirling engine, PV panels, and batteries. The study area chosen for this work is the community El Carmen, Pando, in Bolivia. A Life Cycle Assessment (LCA) model is carried out for the systems according to the 4 phases of the LCA methodology. First, individual LCA models for all midpoint impact categories are generated. Secondly, a comparative LCA between the two systems, both at midpoint and endpoint, is created. Finally, a sensitivity analysis is conducted to determine the robustness of the models.  The individual midpoint analysis of both systems showed that the controlled part of the electricity production (i.e., the Diesel generator and the Stirling engine) generated the greatest impact in the categories Global warming, Stratospheric ozone depletion, Ionizing radiation, Ozone formation, Fine particulate matter formation, Terrestrial acidification, Human carcinogenic toxicity, Land use, Fossil fuel scarcity, and Water consumption. All the processes related to the PV panels generated a greater impact in all Ecotoxicity categories (terrestrial, marine, and freshwater), Eutrophication (freshwater and marine), and Human non-carcinogenic toxicity.  The midpoint results of the comparative LCA are inconclusive. Each system received higher scores in certain categories and lower scores in others. No firm conclusion could be drawn regarding the identification of the more environmentally friendly alternative. The Diesel/PV/Batteries system dominated the Global warming, Tropospheric ozone formation, Fine particulate matter formation, Terrestrial acidification, and Fossil resource scarcity categories. The Stirling/PV/Batteries system showed a greater impact on Stratospheric ozone depletion, Ecotoxicity, Eutrophication, Human carcinogenic toxicity, Human non- carcinogenic toxicity, and Mineral resource scarcity.  The endpoint damage assessment showed that the emissions and midpoint categories described had a greater impact on Human health and Resource scarcity in the case of the Diesel/PV/Batteries system. On the other hand, the Stirling/PV/Batteries system caused greater damage to the Ecosystem category.  The sensitivity analysis was conducted in two scenarios for each system. In the first scenario, alteration of fuel transport distance, no significant changes were detected in all endpoint categories. In the second scenario, alteration of Diesel/Stirling Contribution, the model showed an increasing trend (~30% for the first system and ~25% for the second one) in all categories when the contribution of the controlled part of the electricity production was increased.
Bolivia är ett utvecklingsland i Sydamerika där många landsbygdssamhällen fortfarande saknar tillgång till elektricitet. En anslutning till det nationella kraftsystemet är inte genomförbar på grund av de ekonomiska och topografiska svårigheterna samt miljöproblemen som kan uppstå. För att ta itu med problemet måste decentraliserade lösningar hittas. Solcellspaneler i kombination med batterier utgör ett möjligt alternativ för avlägsna områden som befinner sig nära ekvatorn och vid höga höjder. Ett sådant system behöver dock ytterligare en kontrollerad energikälla för att tillgodose efterfrågan på grund av den ojämna tillgången på solenergi. Det vanligaste alternativet är dieselgeneratorer. Men förbränning av fossila bränslen påverkar klimatet och mer miljövänliga lösningar undersöks. Stirlingmotorer som använder träpellets skulle kunna ersätta dieselgeneratorn i kampen för en bättre miljö.  Syftet med denna studie är att undersöka och jämföra miljöpåverkan av två hybridsystem. Det ena systemet består av en dieselgenerator, PV-paneler och batterier medan det andra systemet består av en Stirlingmotor, PV-paneler och batterier. Det utvalda studieområdet är samhället El Carmen, Pando, i Bolivia. En livscykelanalys (LCA) utförs för de två systemen enligt LCA-metodiken. Först, utförs individuella LCA för vardera system för alla påverkanskategorier vid midpoint. Sedan utförs en jämförande LCA mellan de två systemen för alla påverkanskategorier både vid midpoint och endpoint. Slutligen, utförs en känslighetsanalys för att testa systemens robusthet.  Den individuella analysen vid midpoint för båda systemen påvisade att den kontrollerade delen av elproduktion, det vill säga dieselgeneratorn och Stirlingmotorn, genererade den största miljöpåverkan i kategorierna Global uppvärmning, Uttunning av ozonskiktet, Joniserande strålning, Bildning av marknära ozon, Bildning av partiklar, Försurning, Cancerframkallande humantoxicitet, Landanvändning, Brist på fossila resurser och Vattenförbrukning. Alla processerna kopplade till PV-elproduktionen genererade en större miljöpåverkan i kategorierna Ecotoxicitet (mark, söt- och havsvatten), Övergödning (såväl söt- som havsvatten) och Icke cancerframkallande humantoxicitet.  Resultaten vid midpoint för den jämförande LCA är inte övertygande. Vardera system fick högre poäng i vissa kategorier men lägre poäng i andra. Ingen tydlig slutsats kunde dras angående identifieringen av det mer miljövänliga alternativet. Diesel/PV/Batteri-systemet dominerar kategorierna Global uppvärmning, Bildning av marknära ozon, Bildning av partiklar, Försurning och Brist på fossila bränslen medan Stirling/PV/Batteri-systemet påvisade större miljöpåverkan i kategorierna Uttunning av ozonskiktet, Ekotoxicitet, Övergödning, Cancerframkallande humantoxicitet och Brist på mineraltillgångar.  Skadebedömningen vid endpoint påvisade att de redovisade utsläppen och midpoint- katergorierna har en större påverkan på människors hälsa och resursbrist i Diesel/PV/Batteris fall. Däremot påvisade det Stirling/PV/Batteri-systemet en större påverkan på ekosystemet.  Känslighetsanalysen utfördes i två scenarier. I det första scenariot ändrades avståndet för bränsletransport. Ingen signifikant skillnad påvisades i någon av de tre endpoint- kategorierna. I det andra scenariot, Diesel/Stirling insats, påvisades en ökande trend (~30% för första systemet och ~25% för det andra) i alla endpoint-kategorier med ökandet av insatsen från den kontrollade delen av elproduktion.

En France, on estime que plus de 27 TWh de chaleur à une température comprise entre 100 et 200°C sont perdus chaque année. La récupération de cette chaleur perdue est donc un enjeu important pour réduire la consommation globale d'énergie. La récupération de la chaleur peut se faire à l'aide de machines de Stirling, qui sont des machines thermodynamiques réversibles convertissant la chaleur en mouvement mécanique - lequel pourrait ensuite être converti en électricité - à partir de deux sources de température suffisamment différentes. La récupération de la chaleur produite par les systèmes électroniques pourrait être faite avec une machine de Stirling miniaturisée capable de produire de l'électricité à partir de n'importe quelle source de chaleur. Une telle micro-machine peut aussi fonctionner en mode "réfrigérateur" (transport de la chaleur d'une source chaude vers une source froide grâce à un travail mécanique) et pourrait être utilisée pour refroidir des composants électroniques. Le rendement énergétique des machines Stirling peut atteindre 38% (avec une source chaude à 200°C) et leur entretien est réputé être minimal. Cependant, aucune machine Stirling n'a encore été démontrée avec un volume inférieur à un centimètre cube. En 2015, une architecture de micromachine Stirling triphasée pouvant être miniaturisée grâce aux technologies MEMS a été proposée et testée avec succès en macro-volume (avec une taille d'une vingtaine de centimètres). Le présent travail de thèse a été consacré à la miniaturisation de ce nouveau concept de micromachine Stirling pour la récupération de chaleur entre 50 et 200°C, en utilisant les technologies MEMS. Cette approche permettrait la production simultanée de grandes quantités de micro-machines et donc la création éventuelle de réseaux de micromachines à faible coût par watt d'électricité produite. Les micromachines sont constituées d'un empilement de tranches de silicium et de verre. Leurs défis de conception ont été étudiés en détail et leur puissance mécanique de sortie attendue a été estimée. Les procédés de fabrication nécessaires ont été développés et la caractérisation de chaque élément a été effectuée avant l'assemblage. Elles comportent notamment des membranes hybrides de 5 mm de diamètre et de 200 microns d'épaisseur qui jouent le rôle des pistons en micro-volumes et sont des éléments clés de la micro-machine. Ces membranes sont constituées de pièces en silicium (spirales et disques) noyées dans une membrane souple en élastomère de silicone dont les propriétés mécaniques ont donc été étudiées en détail. Des simulations numériques du comportement mécanique et dynamique de ces membranes hybrides ont été présentées. L'accord entre les simulations numériques et les caractérisations a été considéré comme très satisfaisant. Ces membranes se sont révélées très robustes et le déplacement de leur centre peut atteindre 1 à 2 mm sans dommage. Leurs fréquences de résonance vont de 850 Hz à 2800 Hz et il a été montré qu'elles peuvent fonctionner à 200°C sans vieillissement. De plus, l'optimisation d'un procédé d'assemblage par thermocompression d'or (Au) a permis d’obtenir des contraintes de rupture en traction d'environ 20 à 30 MPa, parmi les meilleures rapportées dans la littérature. Des prototypes de micromachines triphasées de 20x20x8mm ont été assemblés, mais leur fonctionnement en mode moteur n'a pas pu être observé, même pour une différence de température de 100 °C. Cependant, en insérant des aimants pour provoquer le déplacement des membranes par excitation électromagnétique, il a été possible d'observer un effet de refroidissement encourageant. Grâce aux travaux réalisés, les principaux éléments de base sont maintenant disponibles et devraient permettre des optimisations ultérieures dans des conditions beaucoup plus favorables
In France, it is estimated that more than 27 TWh of heat at a temperature between 100 and 200°C is lost each year. The recovery of this lost heat is therefore an important issue in reducing overall energy consumption. Heat recovery can be done using Stirling machines, which are reversible thermodynamic machines that convert heat into mechanical motion, which could then be converted into electricity from two sufficiently different temperature sources. The recovery of the heat produced by electronic systems could be done with a miniaturized Stirling machine capable of producing electricity from any heat source. Such a micro-machine can also operate in "refrigerator" mode (transporting heat from a hot source to a cold source through mechanical work) and could be used to cool electronic components. The energy efficiency of Stirling machines can reach 38% (with a hot source at 200°C) and their maintenance is considered minimal. However, no Stirling machine has yet been demonstrated with a volume of less than one cubic centimeter. In 2015, a three-phase Stirling micromachine architecture that can be miniaturized using MEMS technologies has been proposed and successfully tested in macro-volume (with a size of about twenty centimeters). The present thesis work was devoted to the miniaturization of this new Stirling micromachine concept for heat recovery between 50 and 200°C, using MEMS technologies. This approach would allow the simultaneous fabrication of large quantities of micro-machines and thus the possible creation of micromachine networks at low cost per watt of electricity produced. The studied micromachines are made up of a stack of silicon and glass wafers. Their design challenges have been studied in detail and their expected mechanical output power has been estimated. The necessary manufacturing processes were developed and the characterization of each element was carried out prior to assembly. In particular, they include hybrid membranes 5 mm in diameter and 200 microns thick that act as micro-volume pistons and are key elements of the machine. These membranes are made up of silicon parts (spirals and discs) embedded in a flexible silicone elastomer membrane whose mechanical properties have therefore been studied in detail. Numerical simulations of the mechanical and dynamic behavior of these hybrid membranes were presented. The agreement between the numerical simulations and the characterizations was considered to be very satisfactory. These membranes proved to be very robust and the displacement of their center can reach 1 to 2 mm without damage. Their resonance frequencies range from 850 Hz to 2800 Hz and it was shown that they can operate at 200°C without aging. In addition, the optimization of a gold thermocompression assembly process has resulted in tensile breaking stresses of about 20-30 MPa, among the best reported in the literature. Prototype of 20x20x8mm three-phase micromachines were assembled, but their operation in motor mode could not be observed, even for a temperature difference of 100°C. However, when magnets were inserted to induce the displacement of the membranes by electromagnetic excitation, it was possible to observe an encouraging cooling effect. As a result of the work carried out, the main basic elements are now available and should allow further optimization under much more favorable conditions

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The current paper develops an experimental Stirling engine Gama type. Different settings of this type of engine are presented (alpha, beta and gamma), along with the Stirling Cycle Definition and the mathematical modeling for each setting. It´s been Proceed a mathematical analysis based on the Stirling Theory, which is the method based upon the isothermical compression and expansion of an ideal gas, put to analysis by a computer software, determining the dependency between the engine s construction and functioning parameters. Bibliography used takes over the main Stirling engine settings and various working conditions, fed by a numerous types of fuels. The experimental part of the paper is assembling of a Stirling engine gamma type containing no regenerator, therefore, having the air as its working fluid, using electrical resistances as heat source, also a water jet at ambiance temperature to cool down the compression and heat exchanger. Engine tests were performed at atmospheric pressure, temperatures from 100 to 600 °C, 100 to 400 rpm rotations. The results are presented in graphics and are questioned.
O presente trabalho consiste no desenvolvimento experimental de um motor Stirling tipo gama. São apresentadas inicialmente as diferentes configurações deste tipo de motor (alfa, gama e beta), a definição do ciclo de Stirling e a modelagem matemática para cada configuração. Uma análise matemática é feita através da teoria de Schmidt, que é um método baseado na compressão e expansão isotérmica de um gás ideal, implementada em programa computacional permitindo determinar a dependência entre os parâmetros construtivos e de funcionamento do motor. A revisão bibliográfica contempla as principais configurações de motores Stirling e várias condições de funcionamento, alimentados por diversos tipos de combustíveis. A parte experimental do trabalho é a montagem de um protótipo de motor Stirling tipo gama sem regenerador tendo o ar como fluido de trabalho, utilizando resistências elétricas como fonte de calor e um fluxo de água a temperatura ambiente para o resfriamento do trocador de calor de compressão. Os testes do motor serão realizados a pressão atmosférica, para temperaturas de 100 a 600 °C e rotações de 100 a 400 rpm, os resultados são apresentados em gráficos e discutidos.

Dans cette étude, un système combiné d'un moteur Striling à piston libre (MSPL) et d'un Moteur linéaire synchrone à aimants permanents (MLSAP) est étudié. Tout d'abord, un modèle linéaire (un modèle déjà développé dans la littérature) et un modèle non linéaire (un nouveau modèle appliqué dans la présente étude) du MSPL sont développés, et les résultats de ces modèles sont comparés. Ensuite, le meilleur modèle, qui est adapté à la présente étude, est choisi. Il est démontré que le modèle linéaire ne peut pas identifier le comportement réaliste de l'MSPL ; par conséquent, le modèle non linéaire devrait être utilisé. Ensuite, le modèle non linéaire de l'MSPL est validé avec les résultats expérimentaux disponibles. Après avoir validé le modèle MSPL, deux scénarios, dont un découplé (déjà existant dans la littérature) et un couplé (une méthode nouvellement introduite dans cette étude), sont considérés pour étudier la perte par pompage enthalpique sur le système MSPL. Ensuite, le meilleur scénario pour le pompage d'enthalpie, qui est le scénario couplé, est choisi sur la base des résultats. Après cela, le système MSPL est couplé avec le modèle MLSAP présenté. Afin de combiner le modèle thermodynamique du MSPL et le modèle électrodynamique du MLSAP, leurs équations dynamiques sont combinées. Ensuite, les équations thermo-électro-dynamiques sont résolues, et le système couplé est contrôlé dans MATLAB Simulink®. Le contrôle d'un tel système permet d'éviter les conditions conduisant à l'instabilité de l'MSPL. De plus, il est possible de contrôler le système dans des modes de fonctionnement transitoires pour obtenir les meilleures performances. Après avoir combiné MSPL avec MLSAP, deux méthodes de contrôle des performances sont introduites, et leurs résultats sont comparés. Ces méthodes de contrôle sont basées sur l'identification des paramètres de référence. Enfin, pour montrer l'application d'un tel système, il est utilisé comme une récupération de chaleur dans un système de tri-génération. La source d'énergie de ce système de tri-génération est une pile à combustible à oxyde solide (SOFC) qui est combinée avec un refroidisseur à absorption à double effet (DEACH) pour la production de froid et un échangeur de chaleur pour fournir les besoins thermiques. De plus, une étude de sensibilité est réalisée sur le système combiné MSPL-MLSAP. L'utilisation de cette analyse de sensibilité fournit des informations concernant la sensibilité d'un tel système à différents paramètres
In this study, a combined system of an FPSE and a PMLSM is investigated. First, a linear model (an already developed model in literature) and a nonlinear model (a new applied model in the present study) of the FPSE are developed, and the results of these models are compared. Then the most suitable model for the study, is chosen. It is shown that the linear model cannot identify the realistic behavior of the FPSE; thus, the nonlinear one should be used. After that, the nonlinear FPSE model is validated with available experimental results. After validating the FPSE model, two scenarios, including a decoupled one (an already existed one in literature) and a coupled one (a newly introduced method in the present study), are considered to study the enthalpy pumping loss on the FPSE system. Then the best scenario for the enthalpy pumping, which is the coupled one, is chosen based on the results. After that, the FPSE system is coupled with the presented PMLSM model. In order to combine the thermodynamic model of the FPSE and the electrodynamic model of the PMLSM, their dynamic equations are combined. Then, the thermo-electro-dynamic equations are solved, and the coupled system is controlled in MATLAB Simulink®. Controlling such a system makes it possible to avoid conditions leading to FPSE instability. Moreover, it is feasible to control the system in transient operating modes to get the best performance. After combining FPSE with PMLSM, two control methods are introduced, and their results are compared. These control methods are based on identifying the reference parameters. Then, an application of such a system is presented. This system is used as a waste heat recovery in a tri-generation system. The power source of this tri-generation system is a Solid Oxide Fuel Cell (SOFC) which is combined with a Double Effect Absorption Chiller (DEACH) for cooling production and a heat exchanger for providing the thermal needs. Finally, a study of the sensitivity to the parameters of such a system is performed. Using this analysis provides information concerning the sensitivity of such a system to different parameters

This paper deals with the thermodynamic cycle of Striling engine. Analysis of the ideal cycle, Schmidt analysis and second-order method with loss correction by PROSA 2.4 software is applied. The results are compared with experimental data of two model engines.

Ce travail traite la modélisation et l'optimisation des centrales solaires thermodynamiques à concentration produisant de l'électricité pour l'électrification des zones rurales isolées et mal raccordées au réseau électrique. D’abord, un modèle optique et thermique détaillé des concentrateurs solaires cylindro-paraboliques est présenté permettant l'identification de capteurs existants et la création de corrélations qui peuvent être injectées dans un modèle plus global. Dans un second temps, un modèle original d'un stock de chaleur stratifié de type « lit de roche » est développé. Le nouveau modèle proposé permet de déterminer analytiquement le profil de température dans le stock à n'importe quel instant dans le cas d'une température d'entrée régulée. Ensuite, deux alternatives de bloc moteur sont modélisées : le moteur Stirling et le Cycle Organique de Rankine (ORC acronyme anglais pour Organic Rankine Cycle). Concernant le moteur Stirling, une revue critique des modèles existants a été effectuée. Certains de ces modèles ont été implémentés et complétés par des modèles originaux des pertes par fuite de matière et par effet navette. Le cycle organique de Rankine, lui, est modélisé par un modèle orientée vers l'optimisation. Enfin, une optimisation mono et multicritère d’une centrale solaire est effectuée. La configuration étudiée est équipée d’un stock de chaleur et d’une chaudière d’appoint. Elle est optimisée selon trois critères : le coût moyen actualisé de l'électricité (LCOE acronyme anglais pour Levelized Cost Of Electricity), le rendement énergétique de la centrale et la quantité de CO2 émise par Kilowatt heure d'électricité produite
This work deals with the modelling and the optimization of thermodynamic solar power plants intended to supply electricity to isolated locations. Firstly, a state of the art of solar collectors is achieved and a model for parabolic trough collectors is proposed. This model is used for actual collectors identification. It is used also to propose correlations to be introduced in the whole system model. In a second time, a state of the art of energy storage technologies is conducted and an original model of a packed bed storage tank is proposed. This model gives an explicit solution of the temperature inside the tank without using a time step based numerical resolution. Two alternatives for the power block are given: Stirling engines and Organic Rankine Cycles. For Stirling engines, a critical review of existing models is performed. Some losses occurring in Stirling engines are not well documented in the literature as leakage losses at the power piston and displacer gap losses. Therefore, original models are proposed to estimate these losses. When compared to former models in the literature, the new model of the displacer gap losses demonstrates clearly that it is very important to use decoupled models with caution. Concerning the ORC, an optimization-oriented model is proposed. Finally, a mono and multi-objective optimization of a solar power plant is performed. The optimized system is composed of a solar field, a packed bed heat storage, a power block and an auxiliary fired heater. Objective functions used in this study are: the Levelized Cost of Electricity (LCOE), the energetic efficiency of the power plant and CO2 emission per kilowatt hour of electricity

Le sujet choisi a nécessité une étude bibliographique pour les études de recherche publiées dans les domaines de la Thermodynamique à Vitesse Finie (TVF) et Thermodynamique en Temps Fini (TTF), et pas seulement. Le premier chapitre est dédié à l’état de l’art bibliographique en ce qui concerne le sujet. Une synthèse des aspects énergétiques du Monde, les principales considérations sur les machines de Stirling, les principales méthodes d’analyse et optimisation thermodynamique sont présentés. La comparaison entre la TVF et TTF est présentée, car le développement original s’appuie sur deux méthodes, une de la TVF et l’autre de la TTF, ou plutôt en Dimension Finie. Le deuxième chapitre est dédié aux contributions originales dans le domaine de la TVF: l’adaptation de la Méthode Directe à l’étude et optimisation des machines à cycle inverse avec des irréversibilités internes et externes; amélioration de la méthode de Schmidt en considérant la cinématique effective de la machine considérée ; présentation d’une étude de sensibilité qui permet de séparer les irréversibilités par causes et analyser les effets séparément ; adaptation de la Méthode Directe à l’étude et optimisation de moteurs de Stirling solaires et des ensembles solaire récepteur – concentrateur - moteur Stirling solaire- générateur électrique ; validation de schéma par la comparaison avec les données expérimentales; mise en valeur de la recherche par une application pratique: système de génération d’énergie électrique à partir de l’énergie solaire et hydrogène comme vecteur d’énergie. Le troisième chapitre est dédié aux contributions originales dans le domaine de la TTF. Un modèle thermodynamique pour l’étude et optimisation des machines thermiques est proposé et appliqué pour le cycle de Carnot, pour plusieurs cas, pour des lois de transfert de chaleur linéaires et non linéaires convectif et radiatif. L‘existence des données expérimentales a fait possible la simulation du fonctionnement avec le modèle analytique et la validation. Les conclusions générales et perspectives attendues sont présentées
The stated subject needed an important bibliographic research for the publications in the field of Thermodynamics with Finite Speed (TFS) and Thermodynamics in Finite Time (TFT), and more than that. The first chapter is dedicated to the current status in the chosen subject. A synthesis of worldwide energetic aspects, main considerations on Stirling machines, main methods for analysis and optimization are presented. An important paragraph is the comparison between TFS and TFT, since the original contributions represent two methods, one from TFS and the other one from TFT. The second chapter is dedicated to the original contributions in the field of TFS: adjustment of the Direct Method to the study and optimization of reverse cycle machines with internal and external irreversibilities; correction of the Schmidt method by considering the effective kinematics of the studied machine; development of a sensitivity study to analyze the effects of each irreversibility; adaptation of the Direct Method to the study and optimization of Stirling solar engines and solar assemblies receiver – concentrator - Stirling engine - electric generator; validation of the proposed scheme par comparison with experimental data; research practical utilization: a proposed solar system for electric energy and hydrogen (as an energy career) production. The third chapter is dedicated to the original contributions in the field of TFT. A thermodynamic model pour for the study and optimization of thermal machines is proposed and applied to the Carnot cycle, for more cases, for linear and non linear convective and radiative heat transfer laws. Existence of experimental data allowed the operating simulation and validation of the model. The general conclusions and perspectives are presented

Thèse de doctorat : Mécanique, Energétique : Nancy 1 : 2007. Thèse de doctorat : Mécanique, Energétique : Université Politehnica de Bucarest : 2007.
Thèse soutenue en co-tutelle. Titre provenant de l'écran-titre. Bibliogr.

Cette thèse porte sur le développement d’un cogénérateur résidentiel constitué d’un générateur linéaire asynchrone entraîné par deux moteurs Stirling fonctionnant en mode ‘piston libre double effet’. Les critères caractérisant un tel cogénérateur sont décrits ainsi que ses différents modes d’utilisation dans le domaine résidentiel. Les différentes technologies sont passées en revue.Les équations de la mécanique sur lesquelles se fondent le contrôle du couplage thermoélectrique du cogénérateur et sa stabilité y sont définies. Le générateur électrique est modélisé en vue de calculer les grandeurs électriques des équations à bobines couplées et les grandeurs du schéma électrique équivalent, ce schéma permet d’inverser le modèle.Les résultats des modèles analytiques sont validés par des mesures faites sur des maquettes spécialement conçues. Une étude paramétrique de la structure du générateur a permis d’optimiser ses performances. Les équations de la mécanique et le modèle électrique sont utilisés pour poser les bases d’une optimisation ‘système’ du cogénérateur
This thesis focuses on the development of a residential cogenerator which consists of a linear induction generator driven by two Stirling engines, free-piston double-acting operating mode. The criteria characterizing such cogenerator are described and its various modes of use in the residential sector. The various technologies are reviewed.The equations of mechanics that underlie the control of the coupling of thermoelectric cogeneration and stability are defined.The electric generator is modeled to calculate the electrical coil coupled equations and the magnitudes of the equivalent circuit, this scheme allows us to reverse the pattern. The results of analytical models are validated by measurements on specially designed models. A parametric study of the structure of the generator has optimized its performances. The equations of mechanical and electrical model are used to lay the groundwork for optimization of all the cogenerator, considered as a system

This dissertation about the Stirling engine deals with the history and formation of the heat engine. At the beginning of this work, fundamental parts and their functions are described, elucidating the principle of operation explained by the thermodynamic cycle and subsequently comparing the ideal and the real Stirling cycle and last but not least provides various modifications whilst describing their differences. The mathematical model of the Stirling engine is processed by Schmidth’s theoretical analysis and thereafter is created in PScad v46. The process of creating a model is shown in one of the chapters of this dissertation. The results were taken into account in the design of 3D models in Inventor Professional by Autodesk. The work concludes with the evaluation of the computational model and its functionality as well as the documentation of the 3D model.

Chip scale refrigeration system is critical for the development of electronics with the rapid increase of power consumption and substantial reduction of device size, resulting in an emergent demand on novel cooling technologies with a high efficiency for the thermal management. In this thesis, active refrigeration devices based on Stirling cycle and an electrocaloric material, are designed and investigated to achieve a high cooling performance. Firstly, a new Stirling micro-refrigeration system composed of arrays of silicon MEMS cooling elements is designed and evaluated. The cooling elements are fabricated in a stacked array on a silicon wafer. A regenerator is placed between the compression (hot side) and expansion (cold side) diaphragms, which are driven electrostatically. Under operating conditions, the hot and cold diaphragms oscillate sinusoidally and out of phase such that heat is extracted to the expansion space and released from the compression space. A first-order of thermodynamic analysis is performed to study the effect of geometric parameters. Losses due to regenerator non-idealities and chamber heat transfer limitation are estimated. A multiphysics computational approach for analyzing the system performance that considers compressible flow and heat transfer with a large deformable mesh is demonstrated. The optimal regenerator porosity for the best system COP (coefficient of performance) is identified. To overcome the computational complexity brought about by the fine pillar structure in the regenerator, a porous medium model is used to allow for modeling of a full element. The analysis indicates the work recovery of the system and the diaphragm actuation are main challenges for this cooler design.The pressure drop and friction factor of gas flow across circular silicon micro pillar arrays fabricated by deep reactive ion etch (DRIE) process are investigated. A new correlation that considers the coupled effect of pillar spacing and aspect ratio, is proposed to predict the friction factor in a Reynolds v number range of 1-100. Silicon pillars with large artificial roughness amplitudes is also fabricated, and the effect of the roughness is studied in the laminar flow region. The significant reduction of pressure drop and friction factor indicates that a large artificial roughness could be built for pillar arrays in the regenerator to enhance the micro-cooler efficiency. The second option is to develop a fluid-based refrigeration system using an electrocaloric material poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer. Each cooling element includes two diaphragm actuators fabricated in the plane of a silicon wafer, which drive a heat transfer fluid back and forth across terpolymer layers that are placed between them. Finite element simulations with an assumption of sinusoidal diaphrahm motions are conducted to explore the system performance detailedly, including the effects of the applied electric field, geometric dimensions, operating frequency and externally-applied temperature span. Multiphysics modeling coupled with solid-fluid interaction, heat transfer, electrostatics, porous medium and moving mesh technique is successfully performed to verify the thermal modeling feasibility. The electrocaloric effect in thin films of P(VDF-TrFE-CFE) terpolymer is directly measured by infrared imaging at ambient conditions. At an electric field of 90 V/μm, an adiabatic temperature change of 5.2 °C is obtained and the material performance is stable over a long testing period. These results suggest that application of this terpolymer is promising for micro-scale refrigeration.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
Recently, tapered granular chains have been studied for the development of impact-absorbing devices (shock waves). The characteristic of this system to mitigate shock waves (pulses of linear momentum), makes this material an excellent candidate for such absorbers. Therefore, many studies have been conducted in this direction, but most are numeric character, and some analytical. However, the analytical approximations presented do not show good fits with numerical solutions. In this work we study analytically the propagation of linear momentum and kinetic energy in one-dimensional tapered chains of spherical grains that interact according to the Hertz potential. We apply the binary approximation, based on the supposition that the energy transferred along the chain occurs through successive collisions between two particles. Four settings taper were studied: forward linear, forward exponential, backward linear and backward exponential. With the Binary Theory, we correctly anticipate the trends of increase and decrease the propagation of linear momentum and kinetic energy. However, to capture the correct values of the amplitudes of the pulses of these quantities we developed a numericalanalytic correction to the velocities of particles. Compared the results with numerical solutions of the equations of motion, where we use the Runge-Kutta fourth order. The results show: good agreement between the analytical and numerical theories; forward exponentially tapered chains are the most suitable in the design of absorbers (present exponential decay of linear momentum); a weaker scenario for the propagation of kinetic energy (due to quadratic dependence with the velocity), but the linear momentum is the quantity relevant in the context of impacts.Furthermore, we found good agreement with experimental results presented by F. Melo et al (2006). Thus, we present analytical expressions that capture correctly the propagation of linear momentum and kinetic energy in tapered granular chains. These systems actually demonstrate be excellent for absorbing shock waves, attenuating pulses of linear momentum and saturating kinetic energy. An extension of this work is to study tapered decorated chains and with precompression, allowing the absorption in chains composed of a number smaller grains (short chains).
Recentemente, cadeias granulares afiladas tem sido objeto de estudo para o desenvolvimento de dispositivos absorvedores de impacto (ondas de choque). A caracterıstica deste sistema em atenuar ondas de choque (pulsos de momento linear), torna este material um excelente candidato para tais absorvedores. Assim, vários estudos neste sentido foram realizados, por´em a maioria são de caráter numérico e, alguns, anal´ıticos. Todavia, as aproximaçoes analıticas apresentadas não demonstram bons ajustes com soluções numericas. Neste trabalho estudamos analiticamente a propagação do momento linear e energia cinetica em cadeias afiladas unidimensionais de graos esfericos que interagem segundo o potencial de Hertz. Aplicamos a aproximaçao binaria, baseada na suposiçao que a energia transferida ao longo da cadeia ocorre atraves de colis oes sucessivas entre duas part´ıculas. Estudamos quatro configuraçoes de afilamento: linear para frente, exponencial para frente, linear para tras e exponencial para tras. Com a Teoria Binaria, prevemos corretamente as tendencias de aumento e diminuiçao das propagaçoes do momento linear e energia cinetica. Contudo, para capturarmos os valores corretos das amplitudes dos pulsos dessas grandezas desenvolvemos uma correçao numerico-analıtica para as velocidades das partıculas. Confrontamos os resultados com soluçoes numericas das equaçoes de movimento, onde utilizamos o metodo de Runge-Kutta de quarta ordem. Os resultados demonstram: bom acordo entre as teorias analıtica e numerica; as cadeias afiladas exponencialmente para frente são as mais indicadas nos projetos de absorvedores (apresentam decaimento exponencial do momento linear); um cen´ario mais fraco para a propagação da energia cinetica (devido a dependencia quadratica com a velocidade), porem o momento linear e a grandeza relevante no contexto de impactos. Alem disso, obtivemos bom acordo com resultados experimentais apresentados por F. Melo e colaboradores (2006). Dessa forma, apresentamos expressoes analıticas que capturam corretamente as propagaçoes de momento linear e energia cinetica em cadeias granulares afiladas. Estes sistemas, realmente demonstram serem excelentes para absorver ondas de choque, atenuando pulsos de momento linear e saturando pulsos de energia cin´etica.Uma extensao deste trabalho sera estudar cadeias decoradas afiladas com pre-compressao, que permitem a absorçao de ondas de choque com numero menor de graos nas cadeias (cadeias curtas).

Cette thèse s'inscrit dans le cadre du projet collaboratif MICROSOL, mené par Schneider Electric, et qui oeuvre pour le développement de micros centrales solaires thermodynamiques destinées à la production d'électricité en sites isolés (non connectés au réseau électrique) en exploitant l'énergie thermique du soleil. Le but de cette thèse étant le développement de lois de commande innovantes et efficaces pour la gestion de l'énergie de deux types de micros centrales solaires thermodynamiques : à base de moteur à cycle de Stirling et à base de machines à Cycle de Rankine Organique (ORC). Dans une première partie, nous considérons une centrale solaire thermodynamique à base de machine à cycle de Stirling hybridée à un supercondensateur comme moyen de stockage d'énergie tampon. Dans ce cadre, nous proposons une première loi de commande validée expérimentalement, associée au système de conversion d'énergie du moteur Stirling, qui dote le système de performances quasi optimales en termes de temps de réponse ce qui permet de réduire la taille du supercondensateur utilisé. Une deuxième loi de commande qui gère explicitement les contraintes du système tout en dotant ce dernier de performances optimales en terme de temps de réponse, est également proposée. Cette dernière loi de commande est en réalité plus qu'un simple contrôleur, elle constitue une méthodologie de contrôle applicable pour une famille de systèmes de conversion de l'énergie.Dans une deuxième partie, nous considérons une centrale solaire thermodynamique à base de machine à cycle de Rankine Organique (ORC) hybridée à un banc de batteries comme moyen de stockage d'énergie tampon. Etant donné que ce système fonctionne à vitesse de rotation fixe pour la génératrice asynchrone qui est connectée à un système de conversion d'énergie commercial, nous proposons une loi de commande prédictive qui agit sur la partie thermodynamique de ce système afin de le faire passer d'un point de fonctionnement à un autre, lors des appels de puissance des charges électriques, le plus rapidement possible (pour réduire le dimensionnement des batteries) tout en respectant les contraintes physiques du système. La loi de commande prédictive développée se base sur un modèle dynamique de la machine ORC identifié expérimentalement grâce à un algorithme d'identification nonlinéaire adéquat
This Ph.D thesis was prepared in the scope of the MICROSOL project, ledby Schneider Electric, that aims at developing Off-grid solar thermodynamic micro powerplants exploiting the solar thermal energy. The aim of this thesis being the development of innovative and efficient control strategies for the energy management of two kinds of solar thermodynamic micro power plants: based on Stirling engine and based and Organic RankineCycle (ORC) machines.In a first part, we consider the Stirling based solar thermodynamic micro power planthybridized with a supercapacitor as an energy buffer. Within this framework, we propose afirst experimentally validated control strategy, associated to the energy conversion system ofthe Stirling engine, that endows the system with quasi optimal performances in term of settlingtime enabling the size reduction of the supercapacitor. A second control strategy that handlesexplicitly the system constraints while providing the system with optimal performances interm of settling time , is also proposed. This control strategy is in fact more than a simplecontroller, it is a control framework that holds for a family of energy conversion systems.In a second part, we consider the Organic Rankine Cycle (ORC) based thermodynamicmicro power plant hybridized with a battery bank as an energy buffer. Since this system worksat constant speed for the asynchronous generator electrically connected to a commercial energyconversion system, we propose a model predictive controller that acts on the thermodynamicpart of this system to move from an operating point to another, during the load power demandtransients, as fast as possible (to reduce the size of the battery banks) while respecting thephysical system constraints. The developed predictive controller is based upon a dynamicmodel, for the ORC power plant, identified experimentally thanks to an adequate nonlinearidentification algorithm

With a view to maximize efficiency by reducing power consumption, a quasi halbach magnetized armature in a slotted stator forming a linear motor, has been used to drive a Stirling cycle based cryocooler. The developed cryocooler has been analyzed so as to find out the undamped natural frequency of the system. An experimental as well as a numerical approach has been taken to find out the stiffness contributed by the flexure bearings used herein. An analytical approach has been taken to calculate the variation of the gas spring stiffness offered by the working fluid during the cycle. Thus, the undamped natural frequency of the system has been found. The performance of the developed cryocooler has been found and an analysis has been performed using Schmidt’s proposed analysis.

碩士
國立成功大學
航空太空工程學系碩博士班
97
The present study is aimed at performance measurement of a beta-type Stirling engine with rhombic drive mechanism. The cyclic variation of pressure and volume of the working medium in the cylinder can be predicted by using the analytical model proposed by Cheng and Yu [26], and the influence on performance of the geometric parameters of Stirling engine is evaluated. In addition a 10-W Stirling engine with rhombic drive is made in this study. The working medium used in the the engine is air, and engine is heated by an electric heater in the experiment. By installing a pressure transducer and a laser displacement sensor, the variation of pressure inside the cylinder and trajectory of piston is measured. Meanwhiles, the rotational speed of the engine can be obtained by a rotary encoder connected to the shaft of the flywheel. Displacers with different outside diameter and flywheels with different moments of inertia are tested. And various heat sources are considered during the test of engine. In the experiments, a comparison in performance based on different operating parameters is attempted. Results show that an increase in the heat source temperature yields a great increase in the power output of the Stirling engine. A similar trend is found both in the experiments and the simulation. The Stirling engine produces the highest rotational speed when the regenerative channel width (G) is settose 0.0006 m. The highest rotational speed is around 3140 rpm. When G =0.0004 m, the Stirling engine exhibits maxium power output and the maximum power output is 11.2 W. A change in the flywheel moment of inertia leads to no appreciable difference in the cyclic variation of pressure in the cylinder. The experimental data for the thermal efficiency of the engine basically agree with the predictions from the anslytical model proposed by Cheng and Yu [26].

博士
淡江大學
機械與機電工程學系博士班
97
Energy and environmental protection issues have become the most important targets of global investigation and development. The solar energy can be collected in a variety of different ways and it also called Concentrating Solar Power (CSP) systems emerging as one of the most promising sources of renewable energy. Some of them combined with Stirling engines as the key component to transfer energy and generate electricity. On this dissertation the author discusses the technical advantages of a technology with Stirling cycle engine which may combine to the solar-thermal-electric or CSP technology. Furthermore, it focuses on integrating the Wankel mechanism of rotary internal combustion engine with Stirling cycle in order to fabricate a new engine type. Some advantages like there exists no waste gas discharged for the system in working and it won’t contaminate the environment. It could be also according to the variety of heat source and with simpler mechanism as general Stirling engines. Besides, the shaft transmission is without using the crank. This dissertation includes the simulation analysis by FLUENT CFD software. It could relate to the design initially and provide criterions for improving the prototype by analyzing the factors of heat source temperature, operate pressure, phase angle of rotors, rotation speed, and porosity of regenerator. The simulation results show that better efficiency of system related to the higher temperature of heat input and higher operation pressure. Phase angle of rotors, and rotate speed effects are also discussed in this dissertation. In addition, the effect of porosity on regenerators shows efficiency increases with fill rate increased and decreased with porosity. The author additionally fabricated the prototypes and performed the preliminary test. Some factors of boundary conditions for simulation should be modified by comparing with the experimental data. Considering the physical properties of materials and manufacture limits, the experience of procedure from design to fabrication with results of simulation could bring up a suitable Rotary Stirling Cycle Engine (RSE) design. It can be helpful for future similar work and apply to solar-thermal-electric power generator scopes.

碩士
國立成功大學
航空太空工程學系
105
This study is aimed at development of a numerical model for predicting thermodynamic cycle and thermal efficiency of thermal-lag Stirling engine. Thermal-lag Stirling engine is working through the principle of thermal-lag instability phenomenon. In thermal-lag engine, piston is the only moving part. So, the configuration of this engine is simpler when compared to other traditional Stirling engine. A computational fluid dynamics (CFD) numerical simulation method is used to predict the transient variations of pressure, temperature and working fluid mass in the individual working spaces of the engine. A parametric study of the effect of working gas pressure, heating temperature, cooling temperature, regenerator porosity and rotation speed on the performance of thermal-lag Stirling engine is carried out. Also, the numerical simulation of engine power output, torque and the thermal efficiency has been computed with the different operating speed, heating temperature, cooling temperature and the working gas pressure. The optimum engine speed at which the engine can reach the maximum power output and thermal efficiency has been determined. With the help of numerical simulation, the thermal-lag engine performance was analyzed with the different operating conditions.

Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia
Stirling and Ericsson engines are external heat engines that offer the ability to use many different heat sources to provide reliable and sustainable power. In this thesis, we compare the Stirling and Ericsson cycles in order to determine in which situations one engine produces more net work output than the other. The net work output equations are derived and are analyzed for three different scenarios: (i) equal mass and temperature limits, (ii) equal mass and pressure or volume, and (iii) equal temperature and pressure or volume limits. The comparison is performed by calculating when both cycles produce the same net work output and then analyzing which one produces more net work output based on how the parameters are varied. In general, the results demonstrate that Stirling engines produce more net work output at higher pressures and lower volumes, and Ericsson engines produce more net work output at lower pressures and higher volumes. For certain scenarios threshold values are calculated to illustrate precisely when one cycle produces more net work output than the other. This thesis can be used to inform the design of the engines and particularly to determine when either a Stirling or Ericsson should be selected for a particular application.Stirling and Ericsson engines are external heat engines that offer the ability to use many different heat sources to provide reliable and sustainable power. In this thesis, we compare the Stirling and Ericsson cycles in order to determine in which situations one engine produces more net work output than the other. The net work output equations are derived and are analyzed for three different scenarios: (i) equal mass and temperature limits, (ii) equal mass and pressure or volume, and (iii) equal temperature and pressure or volume limits. The comparison is performed by calculating when both cycles produce the same net work output and then analyzing which one produces more net work output based on how the parameters are varied. In general, the results demonstrate that Stirling engines produce more net work output at higher pressures and lower volumes, and Ericsson engines produce more net work output at lower pressures and higher volumes. For certain scenarios threshold values are calculated to illustrate precisely when one cycle produces more net work output than the other. This thesis can be used to inform the design of the engines and particularly to determine when either a Stirling or Ericsson should be selected for a particular application.
Os motores Stirling e Ericsson são motores de calor externos que oferecem a capacidade de usar muitas fontes de calor diferentes para fornecer energia confiável e sustentável. Nesta tese, comparamos os ciclos Stirling e Ericsson para determinar em quais situações um motor produz mais trabalho do que o outro. As equações de trabalho são derivadas e são analisadas para três cenários diferentes: (i) limites de massa e temperatura iguais, (ii) massa e pressão ou volume iguais, e (iii) igual temperatura e pressão ou limites de volume. A comparação é realizada calculando quando ambos os ciclos produzem o mesmo trabalho e, em seguida, analisando em que situações um produz mais trabalho baseado em como os parâmetros são variados. Em geral, os resultados demonstram que os motores Stirling produzem mais trabalho com pressões mais altas e menores volumes, e os motores Ericsson produzem mais trabalho com pressões mais baixas e volumes maiores. Para certos cenários, os valores de limiar são calculados para ilustrar precisamente quando um ciclo produz mais trabalho do que o outro. Esta tese pode ser usada para informar o design dos motores e particularmente para determinar quando um Stirling ou Ericsson devem ser selecionados para uma aplicação específica.Os motores Stirling e Ericsson são motores de calor externos que oferecem a capacidade de usar muitas fontes de calor diferentes para fornecer energia confiável e sustentável. Nesta tese, comparamos os ciclos Stirling e Ericsson para determinar em quais situações um motor produz mais trabalho do que o outro. As equações de trabalho são derivadas e são analisadas para três cenários diferentes: (i) limites de massa e temperatura iguais, (ii) massa e pressão ou volume iguais, e (iii) igual temperatura e pressão ou limites de volume. A comparação é realizada calculando quando ambos os ciclos produzem o mesmo trabalho e, em seguida, analisando em que situações um produz mais trabalho baseado em como os parâmetros são variados. Em geral, os resultados demonstram que os motores Stirling produzem mais trabalho com pressões mais altas e menores volumes, e os motores Ericsson produzem mais trabalho com pressões mais baixas e volumes maiores. Para certos cenários, os valores de limiar são calculados para ilustrar precisamente quando um ciclo produz mais trabalho do que o outro. Esta tese pode ser usada para informar o design dos motores e particularmente para determinar quando um Stirling ou Ericsson devem ser selecionados para uma aplicação específica.

In its theoretical part, this thesis sums up the basic knowledge concerning permutations. Besides the representation of permutations and determination of their fundamental characteristics, the theoretical part is, first of all, aimed at results concerning the decomposition of permutations into disjoint cycles and at finding the number of permutations with a certain characteristic. We introduce the fundamental bijection that is useful for solving many problems concerning the permutations. Further on, we focus on the number of permutations without a fixed point, Eulerian numbers expressing the number of permutations with a given number of descents, and the number of permutations with a given number of excedances, Stirling numbers of the first kind expressing the number of permutations with a given number of cycles, and Catalan numbers representing the number of permutations avoiding a chosen pattern of length three. Attention is also paid to the Gilbreath permutations and their characteristics. The practical part consists of 14 solved problems. The solutions rely on the results presented in the theoretical part, and there are deduced some further interesting results concerning random permutations.