The recent discovery of Cr4AlB4, a laminated ternary metal boride belonging to the family of layered MAB-phases, where the transition metal boride layers are interleaved by an A layer, has spurred theoretical investigation for novel M4AlB4 phases. In this study, first-principles calculations were applied in order to investigate the thermodynamical stability and mechanical properties of M4AB4 where M = Cr, Hf, Mo, Nb, Ta, Ti, V, W, Zr while the A layer was kept fixed as Al. The thermodynamical stability calculations validate the recently discovered Cr4AlB4 phase’s stability and suggest the neighboring phase Mo4AlB4 to be stable. Additionally, the phases Mo3AlB4, Mo2AlB2, Ti4AlB4 and Ti2AlB2 indicates phases close to stable with a formation enthalpy within the range of 0 < ∆H < 25 meV per atom compared to competing phases. Hence dynamical stability investigations were carried out, which indicates Mo4AlB4 to be dynamically stable. The stability of Mo4AlB4 does encourage synthesizing attempts to be kept in mind as a future project. Phase stability trends of the 111, 212, 314 and 414 compositions were discovered, where a 212, 314 and 414 composition is seen to be more stable for an M-element with lower electron configuration. Furthermore, the mechanical properties of the 414 compositions were investigated by systematically straining the unit cell in different directions. The bulk-, shear- and Young’s-modulus were derived and are presented, where Ti4AlB4 demonstrates values similar to the commended Ti2AlC MAX-phase. Finally, ductility plots are presented which purposes a linear trend between the elements of group IV, V and VI. Based on the results, further studies with a focus on the temperature and magnetization’s impact on the stability and mechanical properties are suggested.

Topic of this diploma thesis is thermodynamical recalculation of turbine TG3 for different parameters and new design of its blading. Introduction deals with theoretical basics of turbines and their components. Second part explains general reasons for retrofit and then specifically for Heating plant Olomouc, where TG3 is located. Third part includes used calculating methods and formulas. Last part presents results, which were calculated in software MS Excel. A cross section drawing is attachment of this thesis.

Made available in DSpace on 2015-04-22T22:07:27Z (GMT). No. of bitstreams: 1 IGOR_PADILHA.pdf: 1457616 bytes, checksum: 9e6a1d5bb5101370ae092f979e20432e (MD5) Previous issue date: 2006-08-11 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / In this work we will study the thermodynamics properties of the quenched decorated Ising model with competitive interactions through the effective field theory (EFT) of a one-spin cluster. The quenched decorated Ising model with competitive interactions is here used to describe the thermodynamics properties of the cooper-based oxide superconductors compounds in the insulating phase (antiferromagnetic). The model consists of planes in which the nodal spins interact antiferromagnetically (JA < 0) with their nerest-neighbors and ferromagnetically (JF > 0) with the spins that decorated the bonds, which are quenched randomly distributed over the twodimensional lattice. The planes interact antiferromagnetically with weak exchange interaction (i.e., JA´=λ JA , λ=10-5 ). By using the framework of an effective-field theory, based in the differential operator technique, we discuss beyond thermodynamics properties the antiferromagnetic-phase stability limit in the temperature-decorated bond concentration space (T-p), for λ =10-5 and various values of frustration parameter (α= JA / JF), magnetic field (H) and concentration parameter (p). For certain range of the parameter α we observe a reentrant behavior in low-temperature what it reflects in the properties behavior itself. / Neste trabalho estudaremos as propriedades termodinâmicas do modelo de Ising decorado de forma quenched (temperada) com interações competitivas através da teoria de campo efetivo (EFT) com aglomerado de um spin. O modelo de Ising decorado com interações competitivas aqui é utilizado para descrever as propriedades termodinâmicas dos compostos supercondutores baseados em planos de Cobre-Oxigênio em sua fase isolante (antiferromagnética). O modelo consiste em planos nos quais os spins nodais interagem antiferromagneticamente (JA < 0) com seus primeiros vizinhos, e ferromagneticamente (JF > 0) com os spins decoradores, os quais são distribuídos aleatoriamente de forma quenched sobre uma rede bidimensional. Os planos interagem antiferromagneticamente com uma fraca interação de troca (i.e., JA´=λ JA , λ=10-5). Utilizando o formalismo da teoria do campo efetivo, baseado na técnica do operador diferencial, discutiremos além das propriedades termodinâmicas do sistema o limite de estabilidade antiferromagnética no diagrama temperatura e concentração (T-p), para λ=10-5 e vários valores do parâmetro de frustração (α=JA / JF), campo magnético (H) e parâmetro de concentração (p). Observamos que para certos intervalos de valores do parâmetro α, o sistema apresenta um comportamento reentrante em baixas temperaturas o que se reflete nas propriedades do sistema.

The aim of this diploma thesis is a design and thermodynamical calculation of a steam condensing turbine with one controlled steam extraction and assigned technical specifications. Technical specifications are turbine inlet temperature 440,0 °C, pressure of inlet steam 38,0 bar(a), pressure in controlled steam extraction 13,0 bar(a), mass flow rate of steam in controlled steam exraction 0,0-40 t/h, temperature in deaerator 105,0 °C and temperature of cooling water in condenser 25,0 °C. Designed steam turbine works in a Rankine-Clausius cycle with a water-cooled condenser, system of low-pressure feed water heater, feed water tank with deaerator and steam boiler. Turbine was designed with regular turbine stages with reaction type of blading and with two regulation stages with impulse blading. An extraction turbine map of the steam turbine is shown in the last chapter of this work. Final parameters of steam turbine are power of 21,7 kW, internal efficiency of turbine 85,1 % and reheat factor 1,048.

Diploma thesis deals with the design of a condensing steam turbine with one controlled steam extraction. Its working range is 0 to 10 t/h. The first part contains the design of the heat balance scheme. The turbine has two unregulated steam extractions for low-pressure feedwater heater and outlet steam is cooled by water condenser. The main part is the design of the turbine flow channel with one regulative stage using impulse blading and 26 regular stages using reaction blading. The turbine rotating speed is 8500 rpm, which is strength suitable even in critical points. The following chapters are describing the design of the compensation piston and bearings. The consumption characteristic of the steam turbine is shown in the last chapter. Drawing of the turbine section is attached to this thesis. Final turbine power is 9259,7 kW and thermodynamic efficiency 85,5 %.

Utilizamos o modelo de Bose-Hubbard para estudar as estabilidades dinâmica e termodinâmica dos condensados numa rede óptica periódica circular. O nosso principal objetivo foi investigar a existência de condensados metaestáveis no sistema. Deduzimos e resolvemos a equação de Gross-Pitaevskii e, a partir da análise das soluções, foi possível mostrar que o sistema se condensa em estados com momento modular bem definido. Esses estados formam uma base que diagonaliza o termo que descreve o tunelamento atômico no hamiltoniano de Bose-Hubbard. No contexto da teoria de Bogoliubov deduzimos para cada condensado, o hamiltoniano efetivo cuja diagonalização determina o espectro das excitações coletivas do sistema. Identificamos corretamente o modo de energia zero, conseqüência da violação da conservação do número de átomos, e verificamos que este possui momento modular igual ao do condensado. No estudo da estabilidade vimos que todos os condensados com momento modular nos 2º e 3º quadrantes são termodinamicamente instáveis e as respectivas condições de estabilidade dinâmica dependem dos parâmetros de controle do sistema. Por outro lado os condensados com momento modular nos 1º e 4º quadrantes são todos dinamicamente estáveis enquanto que, nesse caso, é a estabilidade termodinâmica que depende dos parâmetros de controle do sistema. Nessa análise verificamos que o condensado com momento modular zero, que corresponde ao mínimo global da energia, é sempre estável. Determinamos exatamente o intervalo nos parâmetros de controle a partir do qual podemos encontrar condensados metaestáveis no sistema. Examinamos como a competição entre as intensidades dos termos de tunelamento e repulsão local afeta a estabilidade dos condensados. Essa competição define dois regimes distintos: Rabi, onde a coerência entre estados localizados nos sítios é mantida, e Fock, onde não há mais essa coerência e a aplicabilidade da aproximação de Bogoliubov é questionável. / We use the Bose-Hubbard model to study the dynamical and thermodynamical stabilities of condensates in a circular periodic optical lattice. Our main goal was to investigate the existence of metastable condensates in the system. We derive and solve the Gross-Pitaevskii equation, and from the analysis of the solutions it was possible to show that the system condenses in states with well-defined modular momentum. These states constitute a basis that diagonalizes the term of the Bose-Hubbard Hamiltonian which describes the dynamics of atomic tunneling. In the framework of Bogoliubov theory we determine, for each condensate, the effective Hamiltonian whose diagonalization give us the collective excitation spectrum of the system. We show that the mode associated to a zero eigenvalue, which is a consequence of the violation of atoms number conservation, has the same modular momentum of the condensate. The condensates with modular momentum in the 2nd and 3rd quadrants are all thermodynamically unstable whereas the dynamical stability depends on the control parameters. On the other hand, the condensates with modular momentum in the 1st and 4th quadrants are all dynamically stable whereas the thermodynamical stability depends on the control parameters. Our analysis shows that the condensate with modular momentum zero, which corresponds to a global minimum of energy, is always stable independently of the control parameters. We determine, exactly, the range on the control parameters where it is possible to detect metastability in the system. We have studied how the competition between the intensities of the tunneling and local interaction terms affects the stability of the condensates. This competition defines two distinct regimes: Rabi, where the coherence between states localized in the sites is achieved, and Fock, where this coherence is not achieved and the validity of Bogoliubov approximation is questionable.

A significant part of world energy consumption balance, approx. 40 %, is utilized in buildings. Maintenance of comfortable conditions and improvement in the living, working or recreational environment is a desire for every human. Therefore it is no surprise that there has been a sudden increase in scientific research in the field of building’ energy efficiency. Despite the relevance of the problem there is no sustaining methodology for evaluating building’ energy efficiency by applying sustainable energy development approach. The majority of the researchers don’t assess different potential of the analyzed energy flows nor systems operational regimes. The aim of the work is to evaluate the possibilities for applying exergetical process and system integration method in the design, operation and normalization of the office building service systems: to prepare design solutions that increase buildings’ service systems’ thermodynamical efficiency and covers individual processes and elements’ chain systems. The thesis is divided into the introduction and three main chapters, conclusions, a list of literature and a list of publications. In this work the building service systems’ analysis incorporates three interconnected methods: system analysis, life cycle and thermodynamical analysis. Application of system analyses enables an estimation of service system’s elements (subsystems) and their interconnections. Life cycle analysis allows estimation of total exergy demand through the... [to full text] / Ženklią dalį pasauliniame galutinės energijos vartojimo balanse, apie 40 %, užima energijos dalis, suvartojama pastatuose. Komfortinių sąlygų palaikymas ir gerinimas gyvenamojoje, darbo ar poilsio aplinkoje yra natūralus kiekvieno žmogaus poreikis. Pastaruoju metu stebimas ryškus mokslinių tyrimų suaktyvėjimas didininat energijos vartojimo pastatuose efektyvumą. Nepaisant aktualios problematikos, nuoseklios, darnia energetikos plėtra grindžiamos pastatų energetinio efektyvumo vertinimo metodikos iki šiol nėra. Daugelio tyrėjų naudojami metodai neįvertina skirtingų analizuojamų energijos srautų kokybinių potencialų, nekreipiamas dėmesys į skirtingus sistemų veikimo režimus jų eksploatavimo metu. Darbo tikslas – įvertinti galimybes taikyti procesų ir sistemų integracijos metodą viešųjų pastatų mikroklimato sistemų projektavime, naudojime bei normavime, sukuriant individualius procesus ir visą įrenginių sistemą aprėpiantį priemonių kompleksą, kurio dėka būtų padidintas energijos vartojimo pastate termodinaminis naudingumas. Disertaciją sudaro įvadas, 3 skyriai, pagrindinės išvados, naudotos literatūros sąrašas. Disertaciniame darbe pastato inžinerinių sistemų tyrimui panaudoti trys metodai: sisteminė analizė, gyvavimo ciklo analizė ir termodinaminė (ekserginė) analizė. Sisteminės analizės naudojimas leidžia apibrėžti pastato inžinerinių sistemų elementus bei jų tarpusavio ryšius. Pasitelkus gyvavimo ciklo analizę nustatomi eksergijos poreikiai per visą sistemos gyvavimo... [toliau žr. visą tekstą]

Ce travail de recherche est motivé par les contraintes environnementales qui imposent une réduction des émissions de gaz à effet de serre. L'objectif de cette thèse est d'explorer les possibilités de réduction de consommation des moteurs à combustion interne en les munissant d'un dispositif de récupération de chaleur. Cette étude est focalisée sur la valorisation des rejets thermiques d'installations de faible puissance. Le cycle de Rankine est la technologie qui a été sélectionnée. Une installation d'essais a été construite. Un générateur de gaz chaud simule le moteur thermique ; une part de cette chaleur est collectée par le système de récupération de chaleur et partiellement convertie en énergie mécanique. L'échangeur de chaleur a été conçu et construit en interne ainsi que la machine de détente à piston. Un modèle numérique statique validé expérimentalement pour l'évaporateur a été développé. Celui-ci permet d'explorer les performances du cycle de Rankine sur un large champ de fonctionnement. Avec des hypothèses restrictives le modèle numérique fait apparaître qu'un gain de consommation de l'ordre de 3 % à 4 % sur un tracteur agricole serait possible. Un modèle dynamique de moteur à piston adapté aux cycles de Rankine de faibles puissances a été développé pour aider à son dimensionnement. Ce modèle a permis de mettre au point un concept de machine de détente à piston avec un mécanisme de distribution simplifié. Bien qu'offrant des performances en retrait sur les machines de détente à piston à distribution commandée ce concept est à approfondir pour les systèmes de faible puissance nécessitant une simplicité de construction et un faible coût. / This research was motivated by environmental constraints which impose a reduction in greenhouse gas emissions. The aim of the thesis was to explore the possibility of reducing the consumption of an internal combustion engine using a bottom waste heat recovery system. The study focused on waste heat recovery for low power installations. The Rankine cycle technology was selected to exploit the heat source. An experimental test bench was designed and set up. A hot gas generator simulates an internal combustion engine. Part of the thermal power is absorbed by the evaporator and partially converted into mechanical power. The heat exchanger and piston expander were designed and built in-house. A numerical static model with experimental validation of the evaporator was developed. The model was used to explore the performances of the Rankine cycle over a large operating range. Under restrictive hypotheses, the numerical model showed that is possible to reduce the consumption of a tractor by about 3 to 4 %. A piston expander dynamic model was developed to assist in sizing the expander. The model was used to define a piston expander concept with a simple distribution mechanism. Although a classical distribution mechanism offers better performances, this concept is promising for systems that are simple, small-scale and low-cost.

Utilizamos o modelo de Bose-Hubbard para estudar as estabilidades dinâmica e termodinâmica dos condensados numa rede óptica periódica circular. O nosso principal objetivo foi investigar a existência de condensados metaestáveis no sistema. Deduzimos e resolvemos a equação de Gross-Pitaevskii e, a partir da análise das soluções, foi possível mostrar que o sistema se condensa em estados com momento modular bem definido. Esses estados formam uma base que diagonaliza o termo que descreve o tunelamento atômico no hamiltoniano de Bose-Hubbard. No contexto da teoria de Bogoliubov deduzimos para cada condensado, o hamiltoniano efetivo cuja diagonalização determina o espectro das excitações coletivas do sistema. Identificamos corretamente o modo de energia zero, conseqüência da violação da conservação do número de átomos, e verificamos que este possui momento modular igual ao do condensado. No estudo da estabilidade vimos que todos os condensados com momento modular nos 2º e 3º quadrantes são termodinamicamente instáveis e as respectivas condições de estabilidade dinâmica dependem dos parâmetros de controle do sistema. Por outro lado os condensados com momento modular nos 1º e 4º quadrantes são todos dinamicamente estáveis enquanto que, nesse caso, é a estabilidade termodinâmica que depende dos parâmetros de controle do sistema. Nessa análise verificamos que o condensado com momento modular zero, que corresponde ao mínimo global da energia, é sempre estável. Determinamos exatamente o intervalo nos parâmetros de controle a partir do qual podemos encontrar condensados metaestáveis no sistema. Examinamos como a competição entre as intensidades dos termos de tunelamento e repulsão local afeta a estabilidade dos condensados. Essa competição define dois regimes distintos: Rabi, onde a coerência entre estados localizados nos sítios é mantida, e Fock, onde não há mais essa coerência e a aplicabilidade da aproximação de Bogoliubov é questionável. / We use the Bose-Hubbard model to study the dynamical and thermodynamical stabilities of condensates in a circular periodic optical lattice. Our main goal was to investigate the existence of metastable condensates in the system. We derive and solve the Gross-Pitaevskii equation, and from the analysis of the solutions it was possible to show that the system condenses in states with well-defined modular momentum. These states constitute a basis that diagonalizes the term of the Bose-Hubbard Hamiltonian which describes the dynamics of atomic tunneling. In the framework of Bogoliubov theory we determine, for each condensate, the effective Hamiltonian whose diagonalization give us the collective excitation spectrum of the system. We show that the mode associated to a zero eigenvalue, which is a consequence of the violation of atoms number conservation, has the same modular momentum of the condensate. The condensates with modular momentum in the 2nd and 3rd quadrants are all thermodynamically unstable whereas the dynamical stability depends on the control parameters. On the other hand, the condensates with modular momentum in the 1st and 4th quadrants are all dynamically stable whereas the thermodynamical stability depends on the control parameters. Our analysis shows that the condensate with modular momentum zero, which corresponds to a global minimum of energy, is always stable independently of the control parameters. We determine, exactly, the range on the control parameters where it is possible to detect metastability in the system. We have studied how the competition between the intensities of the tunneling and local interaction terms affects the stability of the condensates. This competition defines two distinct regimes: Rabi, where the coherence between states localized in the sites is achieved, and Fock, where this coherence is not achieved and the validity of Bogoliubov approximation is questionable.

Solid oxide fuel cells (SOFC) are mainly used as large stationary elec- tricity sources, therefore an every little improvement in their performance leads to considerable savings. In order to understand the fundamentals of the SOFC operation, we have developed a new model describing the main physical processes. The thermodynamical model of SOFC, developed in this thesis, concerns the gas transport, the transport of the charged particles in- cluding the thermoelectric effect and the electrochemical reactions. Linear irreversible thermodynamics is the key modelling framework, in which the dusty gas model and the Butler-Volmer equations are used. A new relation between the electrochemical affinity and the overpotential is introduced into the Butler-Volmer equation. A weakly formulated statinonary system en- dowed with boundary conditions is solved with the finite element method in one dimensional approximation. 1