Termodinâmica aplicada

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Experimentos didáticos em fenômenos de transporte e operações unitárias para a Engenharia Ambiental

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Termodinâmica aplicada: conceitos e definições

Apresenta a definição e revisão de alguns conceitos básicos sobre termodinâmica aplicada: sistema termodinâmico e volume de controle, exemplo de sistemas abertos, fechados, isolados e volume de controle; estado e propriedades de uma substância – fases (sólida, líquida ou gasosa), propriedades termodinâmicas extensivas e intensivas com apresentação de exemplos, definição de propriedade específica; Equilíbrio termodinâmico, processos e ciclos; energia potencial, cinética e interna; definições de calor e trabalho; lei da conservação da energia; definição e exemplo de cálculo de pressão; pressão manométrica, pressão absoluta, pressão manométrica; temperatura, lei zero da termodinâmica, equilíbrio térmico; descrição das unidades das grandezas físicas envolvidas nos processos – Sistema Internacional de Unidades (SI).

Leis da termodinâmica e suas aplicações

Apresenta a definição e aplicação dos principais conceitos relacionados aos balanços de energia (Primeira Lei da Termodinâmica) para sistemas fechados e abertos, discutindo todos os tipos de energia que neles são incluídos. Descreve o experimento de Joule. Demonstra como estes sistemas interagem com as vizinhanças, trocando energia nas formas de calor e trabalho. Discute simplificações dos balanços de energia para processos com uma variável termodinâmica constante (p, v ou T) e processos que ocorrem com gases ideais. Posteriormente, apresenta correlações para o cálculo de capacidades caloríficas e calores latentes de vaporização, e também como usá-las nos cálculos de variação de entalpia.

Vórtex

Este modelo é parte de um conjunto de modelos 3D produzidos pela equipe de audiovisual da SEaD/UFSCar para o jogo de realidade virtual “O Laboratório de Química”.

Estudo e avaliação das componentes térmicas na utilização de energia em edifícios

Este trabalho tem por objectivo desenvolver eimplementar metodologias relacionadas com a temática de térmica de edifícos, no sentido dequantificar e optimizar as perdas e ganhos decalor e os consumos de energia associados aosedifícios. Com base na teoria de transferência de calor e massa, foram construídos programas de cálculo numérico para simular, em regime estacionário (permanente) e não estacionário (transiente), os fluxos de calor e a distribuição das temperaturas em diferentes tipos de paredes comummente encontradas em Portugal e em particular na Região Autónoma da Madeira. Estes resultados permitiram analisar a eficácia dos diversos tipos de paredes estudadas bem como o risco de condensação em algumas dessas situações. Para além deste estudo houve a preocupação de desenvolver uma metodologia de análise económica relacionada com a espessura de isolamento a aplicar. Foram igualmente estudadas algumas medições simples de conservação de energia cuja implementação em edifícios será facilmente ustificada atendendo aos baixos períodos de retorno de investimento geralmente associados a estas medidas. Como resultado deste trabalho foi desenvolvida uma ferramenta de cálculo cuja aplicaçãovai permitir não só estimar o risco decondensação mas igualmente o campo de temperaturas no interior das paredes ao longo do período de tempo considerado, visando a optimização de soluções de isolamento térmico versus condições de conforto recomendadas.

A influência do tipo de envidraçados e da inércia térmica dos materiais na prevenção de situações de sobreaquecimento no verão: uma análise baseada no RCCTE

A importância dos vãos envidraçados deve-se não só à sua contribuição para o isolamento térmico da habitação, mas também, por permitirem obter uma otimização dos ganhos solares, maximizando-os no inverno e minimizando-os no verão, contribuindo deste modo para a melhoria das condições de conforto e diminuição dos consumos energéticos. Sendo os vãos envidraçados elementos bastante favoráveis às trocas de calor, tornase necessário conhecer de que forma as diferentes soluções envidraçadas existentes no mercado, e proteções solares/oclusão noturna, podem influenciar o desempenho térmico dos edifícios. Com a crescente tendência de utilização do vidro na construção torna-se ainda mais importante uma escolha criteriosa das soluções para os vãos envidraçados. Este trabalho contribui para a avaliação da influência do tipo de envidraçados e da inércia térmica dos materiais, na prevenção de situações de sobreaquecimento no verão, com base no RCCTE (Regulamento das Características de Comportamento Térmico dos Edifícios), bem como para identificar a melhor relação custo/benefício das soluções. Como caso de estudo, considerou-se uma moradia unifamiliar, simulando diferentes soluções envidraçadas e analisado o seu impacto na moradia. A metodologia consistiu numa análise paramétrica e económica, sustentada no RCCTE e direcionada para a influência dos envidraçados na prevenção do sobreaquecimento no verão. Para a análise da viabilidade económica das soluções propostas, recorreu-se à metodologia definida pela ADENE (Agência para a Energia), pelo cálculo dos custos de exploração e períodos de retorno do investimento, e também o método VAL (Valor Atual Líquido) que pressupõe uma análise do investimento ao longo do tempo. Com este trabalho, conclui-se que um projeto cuidado dos vãos envidraçados e uma seleção criteriosa dos elementos construtivos, aliados a uma análise inerente ao custo/benefício, contribui significativamente para a escolha adequada das soluções construtivas a adotar, de forma a privilegiar o conforto térmico, o desempenho energético dos edifícios e a conservação de energia.

Ventilação e prescrições urbanísticas: uma aplicação simulada para a Orla da Praia do Meio em Natal/RN

This work analyses a study on natural ventilation and its relation to the urban legislation versus the building types in an urban fraction of coastal area of Praia do Meio in the city of Natal/RN, approaching the type or types of land use most appropriate to this limited urban fraction. The objective of this study is to analyse the effects of the present legislation as well as the types of buildings in this area on the natural ventilation. This urban fraction was selected because it is one of the sites from where the wind flows into the city of Natal. This research is based on the hypothesis stating that the reduction on the porosity of the urban soil (decrease in the set back/boundary clearance), and an increase in the form (height of the buildings) rise the level of the ventilation gradient, consequently causing a reduction on the wind speed at the lowest part of the buildings. Three-dimensional computational models were used to produce the modes of occupation allowed in the urban fraction within the area under study. A Computational Fluid Dynamics (CFD) software was also used to analyse the modes of land occupation. Following simulation, a statistical assessment was carried out for validation of the hypothesis. It was concluded that the reduction in the soil porosity as a consequence of the rates that defined the minimum boundary clearance between the building and the boundary of the plot (and consequently the set back), as well as the increase in the building form (height of the buildings) caused a reduction in the wind speed, thus creating heat islands

A influência de decisões arquitetônicas na eficiência energética do Campus vol. 1/UFRN

Building design is an effective way to achieve HVAC energy consumption reduction. However, this potentiality is often neglected by architects due to the lack of references to support design decisions. This works intends to propose architectural design guidelines for energy efficiency and thermal performance of Campus/UFRN buildings. These guidelines are based on computer simulations results using the software DesignBuilder. The definition of simulation models has begun with envelope variables, partially done after a field study of thirteen buildings at UFRN/Campus. This field study indicated some basic envelope patterns that were applied in simulation models. Occupation variables were identified with temperature and energy consumption monitoring procedures and a verification of illumination and equipment power, both developed at the Campus/UFRN administration building. Three simulation models were proposed according to different design phases and decisions. The first model represents early design decisions, simulating the combination of different types of geometry with three levels of envelope thermal performance. The second model, still as a part of early design phase, analyses thermal changes between circulation halls lateral and central and office rooms, as well as the heat fluxes and monthly temperatures in each circulation hall. The third model analyses the influence of middle-design and detail design decisions on energy consumption and thermal performance. In this model, different solutions of roofs, shading devices, walls and external colors were simulated. The results of all simulation models suggest a high influence of thermal loads due to the incidence of solar radiation on windows and surfaces, which highlights the importance of window shading devices, office room orientation and absorptance of roof and walls surfaces

Desempenho térmico de coberturas: Um estudo comparativo entre as telhas de material reciclado, de fibra e betume, fibrocimento e cerâmica

This study aims to compare the thermal performance of tiles made from recycled material (waste packaging cardboard with aluminized film) with the tiles of fiber and bitumen, fiber cement and red ceramic with the aim of verifying the suitability of tile to be used in hot and humid climate of low latitude. The samples were selected according to the availability from Natal - RN market, as they are sold to the consumers. The methodology was based on studies that used experimental apparatus composed of thermal chambers heated by banks of incandescent bulbs, to analyze the thermal performance of materials. The tiles in the study were submitted to analysis of thermal performance, thermophysical properties and absorptance, using chambers of thermal performance, measuring the thermophysical properties and portable spectrometer, respectively. Comparative analysis of thermal performance between two samples of the recycled material with dimple sizes and different amounts of aluminum were made, in order to verify, if these characteristics had some interference on the thermal performance of them; the results showed no significant performance differences between the samples. The data obtained in chambers of thermal performance and confirmed by statistical analysis, showed, that the tile of recycled material have similar thermal performance to the tile of fiber cement. In addition to these tests was carried out the automatic monitoring of a building covered with tiles of recycled material, to verify its thermal performance in a real situation. The results showed that recycled shingles must be used with technical criteria similar to those used for fiber cement tiles, with regard to the heat gain into the building. Within these criteria should be taken into account local characteristics, especially in regions with hot and humid climate, and its use must be associated, according to the literature, to elements of thermal insulation and use of passive techniques such as vented attics, ceilings and right foot higher

Ventilação e prescrições urbanísticas: uma aplicação simulada no bairro de Petrópolis em Natal/RN

The present work studies the natural ventilation and its relationship with the urban standards, which establishes the form of occupation and use of the land in our cities. The method simulates the application of the urban standards of the City Master Plan over the last three years. The simulation takes place in the District of Petrópolis, in the city of Natal , Brazil and analyses the effects of the standards of natural ventilation. The formulated hypothesis states that the reductions in the urban spaces between buildings rises up the vertical profile of ventilation, reducing, therefore, the velocity of the wind at the lower levels of the buildings. To develop the study, occupation models were built, using computerized, three-dimensional models. These occupation models were analyzed using the CFD (Computational Fluid Dynamics) code. The conclusion is that the more we reduce the urban space between buildings, the more we reduce the wind speed in constructed areas, increasing, therefore, the possibility to generate heat islands

Estudo da síntese e sinterização de pós compósitos do sistema Ta-Cu

Ta-Cu bulk composites combine high mechanical resistance of the Ta with high electrical and thermal conductivity of the Cu. These are important characteristics to electrical contacts, microwave absorber and heat skinks. However, the low wettability of Ta under Cu liquid and insolubility mutual these elements come hard sintering this composite. High-energy milling (HEM) produces composite powders with high homogeneity and refines the grain size. This work focus to study Ta-20wt%Cu composite powders prepared by mechanical mixture and HEM with two different conditions of milling in a planetary ball mill and then their sintering using hydrogen plasma furnace and a resistive vacuum furnace. After milling, the powders were pressed in a steel dye at a pressure of 200 MPa. The cylindrical samples pressed were sintered by resistive vacuum furnace at 10-4torr with a sintering temperature at 1100ºC / 60 minutes and with heat rate at 10ºC/min and were sintered by plasma furnace with sintering temperatures at 550, 660 and 800ºC without isotherm under hydrogen atmosphere with heat rate at 80ºC/min. The characterizations of the powders produced were analyzed by scanning electron microscopy (SEM), x-ray diffraction (XRD) and laser granulometry. After the sintering the samples were analyzed by SEM, XRD and density and mass loss tests. The results had shown that to high intense milling condition produced composite particles with shorter milling time and amorphization of both phases after 50 hours of milling. The composite particles can produce denser structure than mixed powders, if heated above the Cu melting point. After the Cu to arrive in the melting point, liquid copper leaves the composite particles and fills the pores

Estudo da moagem de alta energia e sinterização de pós compósitos W-Cu

The Tungsten/copper composites are commonly used for electrical and thermal objectives like heat sinks and lectrical conductors, propitiating an excellent thermal and electrical conductivity. These properties are dependents of the composition, crystallite size and production process. The high energy milling of the powder of W-Cu produces an dispersion high and homogenization levels with crystallite size of W very small in the ductile Cu phase. This work discusses the effect of the HEM in preparation of the W-25Cu composite powders. Three techniques of powder preparation were utilized: milling the dry with powder of thick Cu, milling the dry with powder of fine Cu and milling the wet with powder of thick Cu. The form, size and composition of the particles of the powders milled were observed by scanning electron microscopy (SEM). The X-ray diffraction (XRD) was used to analyse the phases, lattice parameters, size and microstrain of the crystallite. The analyse of the crystalline structure of the W-25Cu powders milled made by Rietveld Method suggests the partial solid solubility of the constituent elements of the Cu in lattice of the W. This analyse shows too that the HEM produces the reduction high on the crystallite size and the increase in the lattice strain of both phases, this is more intense in the phase W

Desenvolvimento de tubulação em compósito polimérico revestida externamente com poliuretano de alta densidade

Pipelines for the transport of crude oil from the production wells to the collecting stations are named production lines . These pipes are subjected to chemical and electrochemical corrosion according to the environment and the type of petroleum transported. Some of these lines, depending upon the composition of the fluid produced, may leak within less than one year of operation due to internal corrosion. This work aims at the development of composite pipes with an external protecting layer of high density polyurethane for use in production lines of onshore oil wells, meeting operational requirements. The pipes were manufactured using glass fibers, epoxy resin, polyester resin, quartz sand and high density polyurethane. The pipes were produced by filament winding with the deposition of high density polyurethane on the external surface and threaded ends (API 15 HR/PM-VII). Three types of pipes were manufactured: glass/epoxy, glass/epoxy with an external polyurethane layer and glass/epoxy with an intermediate layer of glass fiber, polyester, sand and with an external polyurethane layer. The three samples were characterized by Scanning Electronic Microscopy (SEM) and for the determination of constituent content. In addition, the following tests were conducted: hydrostatic test, instant rupture, shorttime failure pressure, Gardner impact, transverse stiffness and axial tension. Field tests were conducted in Mossoró RN (BRAZIL), where 1,677 meters of piping were used. The tests results of the three types of pipes were compared in two events: after two months from manufacturing of the samples and after nine months of field application. The results indicate that the glass/epoxy pipes with an intermediate layer of fiber glass composite, polyester e sand and with an external layer of high density polyurethane showed superior properties as compared to the other two and met the requirements of pressure class, axial tensile strength, transverse stiffness, impact and environmental conditions, for onshore applications as production lines

Caracterização de compósitos Nb-20%cu obtidos por moagem de alta energia e sinterizados por fase líquida

In this work, was studied the formation of a composite of the refractory metal niobium with copper, through the process of high-energy milling and liquid phase sintering. The HEM can be used to synthesize composite powders with high homogeneity and fine size particle distribution. It may also produce the solid solubility in immiscible systems such as Nb-Cu, or extend the solubility of systems with limited solubility. Therefore, in the immiscible system Cu-Nb, the high-energy milling was successfully used to obtain the composite powder particles. Initially, the formation of composite particles during the HEM and the effect of preparation technique on the microstructure of the material was evaluated. Four loads of Nb and Cu powders containing 20%wt Cu were synthesized by MAE in a planetary type ball mill under different periods of grinding. The influence of grinding time on the metal particles is evaluated during the process by the withdrawal of samples at intermediate times of milling. After compaction under different forces, the samples were sintered in a vacuum furnace. The liquid phase sintering of these samples prepared by HEM produced a homogeneous and fine grained. The composite particles forming the sintered samples are the addition of a hard phase (Nb) with a high melting point, and a ductile phase (Cu) with low melting point and high thermal and electrical conductivities. Based on these properties, the Nb-Cu system is a potential material for many applications, such as electrical contacts, welding electrodes, coils for generating high magnetic fields, heat sinks and microwave absorbers, which are coupled to electronic devices. The characterization techniques used in this study, were laser granulometry, used to evaluate the homogeneity and particle size, and the X-ray diffraction, in the phase identification and to analyze the crystalline structure of the powders during milling. The morphology and dispersion of the phases in the composite powder particles, as well the microstructures of the sintered samples, were observed by scanning electron microscopy (SEM). Subsequently, the sintered samples are evaluated for density and densification. And finally, they were characterized by techniques of measuring the electrical conductivity and microhardness, whose properties are analyzed as a function of the parameters for obtaining the composite