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Le projet présenté ici consiste en la conception et l’étude de faisabilité d’une microturbopompe de type Rankine destinée à être opérée à haute température. Une étude préliminaire est d’abord effectuée pour déterminer la configuration globale ainsi que les matériaux possibles pour l’isolation thermique du dispositif. Il en découle la nécessité d’utiliser des matériaux isolants pour le rotor et la structure statique. Les matériaux retenus sont le quartz et le Pyrex et la surface de la structure statique doit être réduite tout en s’assurant de la solidité du dispositif. Le domaine d’application retenu est la récupération de la chaleur de gaz d’échappements automobiles pour la génération d’énergie électrique. Dans cette application, l’utilisation de panneaux de microturbines pourrait permettre d’économiser jusqu’à 2.7% du carburant consommé. Après que la configuration globale soit définie, les composants rotodynamiques sont conçus en utilisant les modèles physiques les plus actuels. La conception finale comporte la pompe centripète, la turbine à un étage, deux paliers axiaux, un palier radial anisotropique comportant quatre réservoirs ainsi que trois joints d’étanchéité (un joint d’étanchéité spiral à viscosité et deux joints d’étanchéité annulaires) permettant de découpler les écoulements des différents composants. Par la suite, une séquence de procédés est définie ainsi que le concept détaillé incluant les aménagements permettant l’instrumentation et l’opération dans un banc d’essai de la microturbopompe de démonstration. La conception des dix-huit photomasques de fabrication découle de cet exercice. Finalement, des tests de microfabrication sont effectués pour évaluer la faisabilité des principales étapes définies dans la séquence de procédés de fabrication. Les étapes de photolithographie, de gravure du silicium, de collage anodique et par fusion sont démontrées tandis que les défis inhérents à la gravure du Pyrex et du quartz sont explorés. Une approche pour compléter la fabrication d’un dispositif de démonstration est proposée à la fin de ces travaux. Cette étude définit pour la première fois la configuration détaillée d’une microturbopompe à vapeur opérant à haute température, confirmant la faisabilité de ce concept. Les jalons sont posés pour la fabrication d’un prototype de démonstration et la validation des modèles présentés ici.

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It is clear that there is no long-term solution to energy supply problems other than planned and continuous conservation. The use of low-grade energy as an unlimited resource will play an important part in maintaining the balance between the future of the world for both developed and developing countries alike. A literature survey reviewing the most promising approaches to the construction of low-grade energy engines has been conducted. The validity of each feasible system has been examined and the principles of operation described. A feasibility study concerning the adoption_of the organic Rankine cycle utilizing common suitable refrigerants (e.g. halo-carbons) as working fluids has been conducted. In particular, the use of a multiple vane expander as the prime mover has been fully investigated. A suite of computer programs has been developed to: • describe working fluid properties; • optimise the geometrical and dynamical parameters of the Rankine cycle to achieve the most efficient operation in both steady and transient states; • optimise the mechanical design of the expander depending upon the mode of operation and the source and sink characteristics. A fully flexible experimental test facility was constructed so as to be capable of testing a wide variety of prime movers. This has been operated for a real time test period in excess of 300 hours. The test results are encouraging. Efficiencies were measured in accordance with the mathematical predictions and a portfolio of suggested modifications towards a high efficiency, low-cost, robust and reliable expander capable of utilising low grade thermal energy has been produced. Fruitful links with relevant British industries have been forged. Demonstrations of the system are planned within the UK and overseas.

Heat sources such as biomass, industrial waste heat and solar thermal provide the potential to produce renewable environmentally low impact electricity. Using these resources efficiently within economic constraints is important for viability of these systems. This thesis explores a regenerative organic Rankine cycle for use in low temperature heat sources. A Bitzer model scroll expander is used for the prime mover for the system. This expander has a reliable model in which thermodynamic analysis can be done. Various working fluids are explored to investigate which one will provide the most power output and efficiency within system constraints. Using optimization, each fluid is tested within physical constraints for optimal operating conditions using system exergy efficiency as the objective function. An exergoeconomic analysis is performed to predict the cost rate of electricity of the system and is compared to current contract rates from the Ontario Power Authority. Dimethyl ether shows promising results with a system exergy efficiency of 11.76% and system energy efficiency of 2.84% at a source temperature of 120℃. The degree of superheat and pressure ratio are used as the independent variables in the optimization. Highest isentropic efficiency for the expander is 29.22%, showing large potential for improvement. Electricity cost rates for the system assuming 20 year life are 0.132 $/kWh to 0.197 $/kWh depending on the fuel input cost for dimethyl ether. At the current state the system shows merit with large potential for improvement in the expander. / UOIT

Made available in DSpace on 2018-08-02T00:02:58Z (GMT). No. of bitstreams: 1 tese_11201_LETÍCIA COSTA RIBEIRO.pdf: 2004005 bytes, checksum: e7985e810cbdfb8f6fba5d7b5b9ffcf6 (MD5) Previous issue date: 2017-03-31 / A recuperação de resíduos térmicos ou WHR (do inglês waste heat recovery) utiliza o calor que normalmente é descartado por um sistema térmico, e o transforma em uma forma útil de energia. Entre seus benefícios estão: energia adicional livre de CO2, aumento da eficiência do processo e economia de combustível. Uma das alternativas para recuperar resíduos térmicos é a aplicação de Ciclos Rankine Orgânicos, de modo a gerar mais potência sem aumentar o consumo de combustível, o que ocasionará um aumento na eficiência energética e ambiental. Neste trabalho de dissertação, é realizado a modelagem e otimização utilizando o software EES (Engineering Equation Solver) para aproveitar o calor proveniente de dois rejeitos térmicos, água de resfriamento e gás de exaustão, dos motores de combustão interna (MCI) de uma termelétrica utilizando ciclos Rankine orgânicos, com duas opções de configurações, com e sem regeneração. A otimização realizada é termoeconômica e paramétrica com o objetivo de minimizar o custo da potência gerada, e selecionar qual o fluido de trabalho que produz potência com menor custo. Para tanto, são realizadas modelagens termodinâmica e econômica para este trabalho, que levam em conta cinco variáveis de decisão, dentre elas os rendimentos isentrópicos da bomba e turbina. A principal contribuição deste trabalho é obter e ajustar equações de custo capazes de responder a essas variáveis. Os resultados mostraram que os ciclos regenerativos, para ambas as fontes de calor, apesar de aumentar a eficiência do ciclo produzem uma potência mais cara do que o ciclo simples. Na condição ótima é possível obter um aumento em torno de 7% a potência gerada pela termelétrica. Palavras-chave Ciclo Rankine Orgânico, Otimização Termoeconômica, Motor de Combustão Interna, Recuperação de Calor

Strict emissions legislation and energy security debates have spurred extensive research in alternative fuels and renewable energies. Literature research has shown the need for improvements in internal combustion engines (ICE) due to their low efficiencies. Significant gains in efficiency can be accomplished with the use of waste heat recovery (WHR) techniques. Organic rankine cycles (ORC) with turbocompounding harness the waste heat from an ICE to improve efficiency and fuel economy while reducing brake-specific emissions. A mathematical model was developed to explore the potential gains in 1st and 2nd law efficiencies. The model approaches the evaluations of the ORC from a practical and a theoretical method. The practical method in evaluation 1 limits the outlet exhaust gas temperatures from the evaporator to prevent the formation of condensation. The performance of the ORC is then evaluated and compared to the evaluation 2. In the theoretical method, in evaluation 2, the effect of pinch point on the evaporator and the entire cycle was analyzed. This analysis was conducted for R113, a dry fluid, and propane, a wet fluid, in order to analyze the differences in the two types of fluids. R113 showed a 13% – 22% and a 6% – 14.7% increase in 1st and 2nd law efficiencies, respectively. Propane showed a 9% – 17.4% and a 2% – 8.5% increase in 1st and 2nd law efficiencies, respectively. It was also shown that as the pinch point temperature decreases the 2nd law efficiencies increased. It was concluded that use of ORC with turbocompounding is an effective method for waste heat recovery in order to increase ICE efficiency.

This thesis presents the numerical and analytical study of the aerodynamic and heat transfer in laminar subsonic cascades along with the development of design guidelines and procedures to improve the design of microfabricated multistage radial turbines operating at low Reynolds number. Numerical analysis was performed on 24 cascade geometries using 2D computational fluid dynamics (CFD) for over 100 flow conditions for each cascade. Two dimensional correlations were extracted from CFD for profile and mixing losses, deviation and heat transfer. These correlations include Reynolds number and compressibility effects, and take into account incidence and various geometrical parameters (solidity, stagger, blade angles, thickness and mean-line distribution). Adaptation of losses to account for three dimensional effects and correlation for blockage were derived from analytical relationships. A turbomachinery simulation software based on mean-line analysis and conservation of rothalpy incorporating the developed correlations was programmed. The software can be adapted as for the physic it uses and the turbine configuration it analyses (axial, radial inward or outward, single or multi stage). The pressure profiles obtained from simulation were found to be in good agreement with experimental data for cold turbine tests. Design guidelines and charts are provided as well as cycle analysis considering microfabrication limitations. A considerable increase in stage isentropic efficiency compared to previous devices can result from the use of slender blades, lower solidity cascades and aspect ratios of 0.5, suggesting efficiencies as high as 85% for Re > 700. The study shows that higher power density and multistage matching can be achieved through the radial outward configuration. Two designs are presented, a single stage turbine for the next generation of microturbopump prototype and a turbine configuration with four rotors and 10 stages for closed Rankine cycle providing 50.7 W of net mechanical power.

Dissertação (Mestrado em Engenharia Mecânica) - Centro Universitário FEI, São Bernardo do Campo, 2017.

The primary objective of this work is to determine the Kalina cycle's suitability for thermal power conversion from a pressurized water reactor. Several previous papers have examined this application, but these either lack proof of concept or make unfeasible assumptions. This work expands current knowledge by simulating the Kalina cycle and comparing it to current pressurized water reactor Rankine cycles in order to identify which is more efficient. Prerequisite to the modeling is a simulation tool capable of modeling the thermodynamics of ammonia/water mixtures. Instead of using an existing program, a new one called Clearwater is used. This tool is based on a preexisting Gibbs free energy "super" equation of state. Algorithms for vapor-liquid equilibrium calculations and phase identification are presented. Clearwater will be distributed online as open-source code to aid future developers of ammonia/water power and refrigeration cycles. A comparison of single-stage Kalina and Rankine cycles driven by heat from PWR core coolant suggests that the Kalina cycle is not well suited to the application. Any benefit from the Kalina cycle's ability to match temperature profiles in the boiling region of the steam generator is outweighed by other drawbacks. These include the cycle's 1) increased turbine exhaust pressure and 2) lower average heat absorption temperature caused by its working fluid's relatively high liquid heat capacity, both of which lower efficiency. Having concluded this, an attempt is made to quantify the conditions under which the Kalina cycle produces more power than the Rankine cycle. Both cycles are optimized for a range of heat source inlet and outlet temperatures between 350 ℃ and 525 ℃. When both cycles absorb the same amount of heat from the source"”i.e., when source outlet temperature is constrained"” the Kalina cycle is less effective for small source temperature drops. When outlet temperature is unconstrained, the Kalina cycle outperforms the Rankine cycle for all but the lowest inlet temperature. This is due to the Kalina cycle's non-isothermal boiling profile, which allows it to absorb low temperature heat at relatively high pressure. Because of its isothermal boiling profile, the Rankine cycle cannot capture low temperature heat as effectively, so it performs worse over large, unconstrained source temperature drops.