O potencial energético do gradiente térmico na plataforma continental do sul do brasil

O crescimento da demanda energética, prevista para a metade do século XXI, com números embasados no crescimento demográfico e de consumo dos países em desenvol- vimento, sugere a busca por fontes energéticas renováveis e de menor impacto ao meio ambiente, conforme os tratados da política internacional. Portanto, o fornecimento de energia suplementar se torna vital nas sociedades modernas e sua extensão até o mar tem se constituído uma recente preocupação do ponto de vista enérgico e ecológico. Várias formas de conversão de energia foram desenvolvidas no decorrer dos anos, com destaque para a energia dos gradientes térmicos. A Plataforma Continental Sul do Bra- sil (PSCB) possui alta variabilidade espacial e temporal nos campos de temperatura, de forma que existe a necessidade de uma análise das regiões de maior potencial energético com respeito ao gradiente vertical de temperatura. Neste estudo, foram utilizados dados do modelo OCCAM com uma grade de resolu- ção horizontal de 0, 25o e resolução vertical de 66 níveis, distribuídos ao longo de um sistema de coordenadas vertical. Foram utilizadas imagens de temperatura superfícial do mar (TSM) obtidas a partir do sensor AVHRR (Advanced Very High Resolution Ra- diometer) de forma a realizar a validação dos dados do modelo OCCAM. A análise da média dos dados do modelo indicou um sítio energético de maior viabilidade devido oC ao padrão médio do gradiente térmico de aproximadamente 0, 17 ao longo da coluna vertical (545 m de profundidade) no oceano. Neste local, foram coletados os dados, e aplicados a um módulo de conversão de energia térmica dos oceanos que vem sendo desenvolvido na Universidade Federal do Rio Grande - FURG. A região de estudo de- monstrou possuir um local com ótimo potencial energético, onde a produção máxima de energia pode alcançar 111, 9MW , associada com um padrão variabilidade tempo- ral dominante de 12 meses. Este sítio energético demonstra maior eficiência durante o período de verão e outono ao longo dos anos e sua média para todo o período é de 94, 3MW . Neste estudo, duas correntes: Corrente do Brasil (CB) e a Contra Corrente Costeira (CCC), com águas de origem tropical e subantártica com aportes continentais, respecti- vamente, tem alta correlação com os valores dos gradientes térmicos e com os significa- tivos eventos de conversão energética. O sítio energético demonstrou alta estabilidade à sazonalidade e à gama de eventos meteorológicos e oceanográficos, de forma que pode ser qualificado como uma fonte suplementar a matriz energética do país para um futuro próximo.

Exergetic, energetic, economic and environmental evaluation of concentrated solar power plants in Libya

The PhD project addresses the potential of using concentrating solar power (CSP) plants as a viable alternative energy producing system in Libya. Exergetic, energetic, economic and environmental analyses are carried out for a particular type of CSP plants. The study, although it aims a particular type of CSP plant – 50 MW parabolic trough-CSP plant, it is sufficiently general to be applied to other configurations. The novelty of the study, in addition to modeling and analyzing the selected configuration, lies in the use of a state-of-the-art exergetic analysis combined with the Life Cycle Assessment (LCA). The modeling and simulation of the plant is carried out in chapter three and they are conducted into two parts, namely: power cycle and solar field. The computer model developed for the analysis of the plant is based on algebraic equations describing the power cycle and the solar field. The model was solved using the Engineering Equation Solver (EES) software; and is designed to define the properties at each state point of the plant and then, sequentially, to determine energy, efficiency and irreversibility for each component. The developed model has the potential of using in the preliminary design of CSPs and, in particular, for the configuration of the solar field based on existing commercial plants. Moreover, it has the ability of analyzing the energetic, economic and environmental feasibility of using CSPs in different regions of the world, which is illustrated for the Libyan region in this study. The overall feasibility scenario is completed through an hourly analysis on an annual basis in chapter Four. This analysis allows the comparison of different systems and, eventually, a particular selection, and it includes both the economic and energetic components using the “greenius” software. The analysis also examined the impact of project financing and incentives on the cost of energy. The main technological finding of this analysis is higher performance and lower levelized cost of electricity (LCE) for Libya as compared to Southern Europe (Spain). Therefore, Libya has the potential of becoming attractive for the establishment of CSPs in its territory and, in this way, to facilitate the target of several European initiatives that aim to import electricity generated by renewable sources from North African and Middle East countries. The analysis is presented a brief review of the current cost of energy and the potential of reducing the cost from parabolic trough- CSP plant. Exergetic and environmental life cycle assessment analyses are conducted for the selected plant in chapter Five; the objectives are 1) to assess the environmental impact and cost, in terms of exergy of the life cycle of the plant; 2) to find out the points of weakness in terms of irreversibility of the process; and 3) to verify whether solar power plants can reduce environmental impact and the cost of electricity generation by comparing them with fossil fuel plants, in particular, Natural Gas Combined Cycle (NGCC) plant and oil thermal power plant. The analysis also targets a thermoeconomic analysis using the specific exergy costing (SPECO) method to evaluate the level of the cost caused by exergy destruction. The main technological findings are that the most important contribution impact lies with the solar field, which reports a value of 79%; and the materials with the vi highest impact are: steel (47%), molten salt (25%) and synthetic oil (21%). The “Human Health” damage category presents the highest impact (69%) followed by the “Resource” damage category (24%). In addition, the highest exergy demand is linked to the steel (47%); and there is a considerable exergetic demand related to the molten salt and synthetic oil with values of 25% and 19%, respectively. Finally, in the comparison with fossil fuel power plants (NGCC and Oil), the CSP plant presents the lowest environmental impact, while the worst environmental performance is reported to the oil power plant followed by NGCC plant. The solar field presents the largest value of cost rate, where the boiler is a component with the highest cost rate among the power cycle components. The thermal storage allows the CSP plants to overcome solar irradiation transients, to respond to electricity demand independent of weather conditions, and to extend electricity production beyond the availability of daylight. Numerical analysis of the thermal transient response of a thermocline storage tank is carried out for the charging phase. The system of equations describing the numerical model is solved by using time-implicit and space-backward finite differences and which encoded within the Matlab environment. The analysis presented the following findings: the predictions agree well with the experiments for the time evolution of the thermocline region, particularly for the regions away from the top-inlet. The deviations observed in the near-region of the inlet are most likely due to the high-level of turbulence in this region due to the localized level of mixing resulting; a simple analytical model to take into consideration this increased turbulence level was developed and it leads to some improvement of the predictions; this approach requires practically no additional computational effort and it relates the effective thermal diffusivity to the mean effective velocity of the fluid at each particular height of the system. Altogether the study indicates that the selected parabolic trough-CSP plant has the edge over alternative competing technologies for locations where DNI is high and where land usage is not an issue, such as the shoreline of Libya.

Características de cinzas e sua aplicação no tratamento de gases durante a gasificação de biomassa

Na procura de melhores combustíveis para a produção de energia térmica e energia elétrica, a biomassa apresenta-se como uma das fontes de energia renováveis menos prejudiciais ao meio ambiente, esta é considerada como um recurso neutro do ponto de vista de emissões de dióxido de carbono. Atualmente, a tecnologia predominante no domínio da conversão energética de biomassa por via termoquímica é a combustão. Contudo, verifica-se a procura de combustíveis de melhor qualidade produzidos a partir de biomassa, como por exemplo na forma gasosa (gás de combustível). A produção deste tipo de combustíveis gasosos envolvendo processos de gasificação carece do desenvolvimento de tecnologia que permita obter um gás combustível com características adequadas às utilizações pretendidas. Os problemas mais relevantes relacionados com a conversão termoquímica da biomassa incluem a produção de cinzas e de alcatrões, estes podem levar a vários problemas operatórios. O presente trabalho teve dois objetivos, a caracterização das cinzas resultantes do processo de combustão de biomassa e o estudo do efeito da aplicação das cinzas para melhorar as propriedades do gás produzido durante o processo de gasificação de biomassa, principalmente na redução de compostos condensáveis (alcatrões). As cinzas volantes da combustão de biomassa analisadas apresentam na sua constituição elementos químicos característicos da biomassa, onde o cálcio apresenta-se em concentrações mais elevadas. Em menores concentrações encontram-se sódio, magnésio, fósforo, enxofre, cloro, potássio, manganês e ferro. As cinzas de fundo, pelo contributo que a areia do leito tem, são caracterizadas por conterem grandes concentrações de silício. Durante os processos de gasificação de biomassa a concentração de compostos condensáveis diminuiu com o aumento da razão de equivalência. As cinzas, colocadas no reator de leito fixo, apresentam um efeito positivo sobre a qualidade do gás, nomeadamente um aumento de 47,8% no teor de H2 e de 11% de CO, consequentemente obteve-se um gás combustível com PCI (poder calorífico inferior) mais elevado.

Plasma diagnostics and ITO film deposition by RF-assisted closed-field dual magnetron system

Deposition of indium tin oxide (ITO) among various transparent conductive materials on flexible organic substrates has been intensively investigated among academics and industrials for a whole new array of imaginative optoelectronic products. One critical challenge coming with the organic materials is their poor thermal endurances, considering that the process currently used to produce industry-standard ITO usually involves relatively high substrate temperature in excess of 200°C and post-annealing. A lower processing temperature is thus demanded, among other desires of high deposition rate, large substrate area, good uniformity, and high quality of the deposited materials. For this purpose, we developed an RF-assisted closed-field dual magnetron sputtering system. The “prototype” system consists of a 3-inch unbalanced dual magnetron operated at a closed-field configuration. An RF coil was fabricated and placed between the two magnetron cathodes to initiate a secondary plasma. The concept is to increase the ionization faction with the RF enhancement and utilize the ion energy instead of thermal energy to facilitate the ITO film growth. The closed-field unbalanced magnetrons create a plasma in the intervening region rather than confine it near the target, thus achieving a large-area processing capability. An RF-compensated Langmuir probe was used to characterize and compare the plasmas in mirrored balanced and closed-field unbalanced magnetron configurations. The spatial distributions of the electron density ne and electron temperature Te were measured. The density profiles reflect the shapes of the plasma. Rather than intensively concentrated to the targets/cathodes in the balanced magnetrons, the plasma is more dispersive in the closed-field mode with a twice higher electron density in the substrate region. The RF assistance significantly enhances ne by one or two orders of magnitude higher. The effect of various other parameters, such as pressure, on the plasma was also studied. The ionization fractions of the sputtered atoms were measured using a gridded energy analyzer (GEA) combined with a quartz crystal microbalance (QCM). The presence of the RF plasma effectively increases the ITO ionization fraction to around 80% in both the balanced and closed-field unbalanced configurations. The ionization fraction also varies with pressure, maximizing at 5-10 mTorr. The study of the ionization not only facilitates understanding the plasma behaviors in the RF-assisted magnetron sputtering, but also provides a criterion for optimizing the film deposition process. ITO films were deposited on both glass and plastic (PET) substrates in the 3-inch RF-assisted closed-field magnetrons. The electrical resistivity and optical transmission transparency of the ITO films were measured. Appropriate RF assistance was shown to dramatically reduce the electrical resistivity. An ITO film with a resistivity of 1.2×10-3 Ω-cm and a visible light transmittance of 91% was obtained with a 225 W RF enhancement, while the substrate temperature was monitored as below 110°C. X-ray photoelectron spectroscopy (XPS) was employed to confirm the ITO film stoichiometry. The surface morphology of the ITO films and its effect on the film properties were studied using atomic force microscopy (AFM). The prototype of RF-assisted closed-field magnetron was further extended to a larger rectangular shaped dual magnetron in a flat panel display manufacturing system. Similar improvement of the ITO film conductivities by the auxiliary RF was observed on the large-area PET substrates. Meanwhile, significant deposition rates of 25-42 nm/min were achieved.

Análise comparativa de um sistema de refrigeração solar

Nesta dissertação são comparadas duas tecnologias de refrigeração. Uma tecnolo-gia é um sistema que usa a energia elétrica para fazer funcionar um ciclo de com-pressão de vapor, sistema comum em instalações de refrigeração. A outra solução é um sistema de absorção, em que a energia necessária para o funcionamento do sistema é energia térmica obtida através de coletores solares térmicos. Estas tecnologias são estudadas e comparadas para a refrigeração de um arma-zém de produtos agrícolas à temperatura constante de 5ºC para a região de Alque-va, região onde estão a ser desenvolvidos projetos hortofrutícolas a que estão as-sociadas necessidades de preservação dos produtos que envolvem refrigeração e em que a acessibilidade à rede elétrica é reduzida. É mostrado que a tecnologia do sistema de absorção com os coletores se apresenta a médio prazo mais vantajosa em termos económicos e ambientais; Abstract: Comparative analysis of a solar refrigeration system In this dissertation two refrigeration technologies are compared when used for the same objective. One is a technology using the electric energy to operate a vapour compression cycle, commonly used in refrigerated installations. The alternative technology is an absorption system driven by thermal energy, provided by solar thermal collectors. Both technologies are studied and compared for the refrigeration of an agricultural products warehouse at a constant temperature of 5ºC in the Alqueva region, where horticultural projects are being developed with associated needs of preservation of the products involving refrigeration, and where accessibility to the electrical grid is reduced. In the referred conditions it was shown that the absorption technology with collec-tors in the medium term surpasses the usual compression system, both from eco-nomic and environmental viewpoints.

Performance of Plate Type Heat Exchanger as Ammonia Condenser

In this study, I experimentally analyzed the performance of a commercial semi-welded plate type heat exchanger (PHE) for use with ammonia systems. I determined performance parameters such as overall heat transfer coefficient, capacity, and pressure drop of the semi-welded PHE. This was analyzed by varying different parameters which demonstrated changes in overall heat transfer coefficient, capacity, and pressure drop. Both water and ammonia flow rates to the semi-welded PHE were varied independently, and analyzed in order to understand how changes in flow rates affected performance. Inlet water temperature was also varied, in order to understand how raising condenser water inlet temperature would affect performance. Finally, pressure drop was monitored to better understand the performance limitations of the semi-welded PHE. Testing of the semi-welded will give insight as to the performance of the semi-welded PHE in a potential ocean thermal energy conversion system, and whether the semi-welded PHE is a viable choice for use as an ammonia condenser.

Effect of milling time on mechanical properties of fly ash incorporated cement mortars

Abstract. Currently, thermal energy generation through coal combustion produces ash particles which cause serious environmental problems and which are known as Fly Ash (FA). FA main components are oxides of silicon, aluminum, iron, calcium and magnesium in addition, toxic metals such as arsenic and cobalt. The use of fly ash as a cement replacement material increases long term strength and durability of concrete. In this work, samples were prepared by replacing cement by ground fly ash in 10, 20 and 30% by weight. The characterization of raw materials and microstructure was obtained by Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). The final results showed that the grinding process significantly improves the mechanical properties of all samples when compared replacing a mortar made with cement by ground fly ash and the reference samples without added fly ash. The beneficial effect of the ground fly ash can increase the use of this product in precast concrete industry

Modos projetuais de simulação: uso de ferramentas de simulação térmica no processo projetual de arquitetura

This thesis aims to describe and demonstrate the developed concept to facilitate the use of thermal simulation tools during the building design process. Despite the impact of architectural elements on the performance of buildings, some influential decisions are frequently based solely on qualitative information. Even though such design support is adequate for most decisions, the designer will eventually have doubts concerning the performance of some design decisions. These situations will require some kind of additional knowledge to be properly approached. The concept of designerly ways of simulating focuses on the formulation and solution of design dilemmas, which are doubts about the design that cannot be fully understood nor solved without using quantitative information. The concept intends to combine the power of analysis from computer simulation tools with the capacity of synthesis from architects. Three types of simulation tools are considered: solar analysis, thermal/energy simulation and CFD. Design dilemmas are formulated and framed according to the architect s reflection process about performance aspects. Throughout the thesis, the problem is investigated in three fields: professional, technical and theoretical fields. This approach on distinct parts of the problem aimed to i) characterize different professional categories with regards to their design practice and use of tools, ii) investigate preceding researchers on the use of simulation tools and iii) draw analogies between the proposed concept, and some concepts developed or described in previous works about design theory. The proposed concept was tested in eight design dilemmas extracted from three case studies in the Netherlands. The three investigated processes are houses designed by Dutch architectural firms. Relevant information and criteria from each case study were obtained through interviews and conversations with the involved architects. The practical application, despite its success in the research context, allowed the identification of some applicability limitations of the concept, concerning the architects need to have technical knowledge and the actual evolution stage of simulation tools

Qualificação de edifícios residenciais verticais em Natal/RN à luz do regulamento técnico da qualidade para o nível de eficiência energética de edificações residenciais (RTQ-R)

The goal of the research was to investigate the energy performance of residential vertical buildings envelope in the hot and humid climate of Natal, capital of Rio Grande do Norte, based in the Technical Regulation of Quality for Energy Efficiency Level in Residential Buildings (RTQ -R), launched in 2010. The study pretends to contribute to the development of design strategies appropriate to the specific local climate and the increasing of energy efficiency level of the envelope. The methodological procedures included the survey in 22 (twenty two) residential buildings, the formulation of representative prototypes based on typological and constructives characters researched and the classification of the level of energy efficiency in the envelopment of these prototypes, using as a tool the prescriptive method of the RTQ-R and the parametric analyzes from assigning different values of the following variables: shape of the pavement type; distribution of housing compartments; orientation of the building; area and shading of openings; thermal transmittance, and solar absorptance of opaque materials of the frontage in order to evaluate the influence of these on the envelopment performance. The main results accomplished with this work includes the qualification of vertical residential buildings in Natal/RN; the verification of the adequacy of these buildings to local climate based from the diagnosis of the thermal energy of the envelopment performance, the identification of variables with more significant influence on the prescriptive methodology of RTQ-R and design solutions more favorable to obtain higher levels energy efficiency by this method. Finally, it was verified, that some of these solutions proved contradictory in relation to the recommendations contained in the theoretical approaches regarding environmental comfort in hot and humid weather, which indicates the need for improvement of the prescriptive method RTQ-R and further research on efficient design solutions

Heat fluxes between the Guadalquivir river and the Gulf of Cádiz Continental Shelf

An 18-year time series of daily sea surface temperature of Gulf of Cadiz and an 18-month time series of temperature collected in the vicinity of the Guadalquivir estuary mouth have been analyzed to investigate the heat exchange between the estuary and the adjacent continental shelf. The first time identifies a continental shelf area where seasonal thermal oscillation signal (amplitudes and phase) changes abruptly. In order to explain this anomaly, the second data set allows a description of thermal fluctuations in a wide range of frequencies and an estimation of the upstream heat budget of the Guadalquivir estuary. Results show that high frequency thermal signal, diurnal and semidiurnal, and water flux signal through Guadalquivir mouth, mainly semidiurnal, apparently interact randomly to give a small exchange of thermal energy at high frequency. There is no trace, at the estuary's mouth, of daily heat exchanges with intertidal mudflats probably because it tends to cancel on daily time scales. Results also show that fluctuations of estimated air-sea fluxes force fluctuations of temperature in a quite homogeneous estuarine, with a delay of 20 days. The along-channel thermal energy gradient reaches magnitudes of 300-400 J m-4 near the mouth during the summer and winter and drives the estuary-shelf exchange of thermal energy at seasonal scale. Particularly, the thermal heat imported by the estuary from the shelf area during late fall-winter-early spring of 2008/2009 is balanced by the thermal heat that the estuary exports to the shelf area during late spring-summer of 2008. In summary, Guadalquivir river removes/imports excess of thermal energy towards/from the continental shelf seasonally, as a mechanism to accommodate excess of heat from one side respect to the other side.

Effects in ultrafast laser micromachining PMMA-based optical fibre grating

Ultrafast laser owns extreme small beam size and high pulse intensity which enable spatial localised modification either on the surface or in the bulk of materials. Therefore, ultrafast laser has been widely used to micromachine optical fibres to alter optical structures. In order to do the precise control of the micromachining process to achieve the desired structure and modification, investigations on laser parameters control should be carried out to make better understanding of the effects in the laser micromachining process. These responses are important to laser machining, most of which are usually unknown during the process. In this work, we report the real time monitored results of the reflection of PMMA based optical fibre Bragg gratings (POFBGs) during excimer ultraviolet laser micromachining process. Photochemical and thermal effects have been observed during the process. The UV radiation was absorbed by the PMMA material, which consequently induced the modifications in both spatial structure and material properties of the POFBG. The POFBG showed a significant wavelength blue shift during laser micromachining. Part of it attributed to UV absorption converted thermal energy whilst the other did not disappear after POFBG cooling off, which attributed to UV induced photodegradation in POF.

Solderjet bumping technique used to manufacture a compact and robust green solid-state laser

Solder-joining using metallic solder alloys is an alternative to adhesive bonding. Laser-based soldering processes are especially well suited for the joining of optical components made of fragile and brittle materials such as glasses, ceramics and optical crystals due to a localized and minimized input of thermal energy. The Solderjet Bumping technique is used to assemble a miniaturized laser resonator in order to obtain higher robustness, wider thermal conductivity performance, higher vacuum and radiation compatibility, and better heat and long term stability compared with identical glued devices. The resulting assembled compact and robust green diode-pumped solid-state laser is part of the future Raman Laser Spectrometer designed for the Exomars European Space Agency (ESA) space mission 2018.

Armazenamento sazonal de energia solar térmica de baixa temperatura para climatização de edifícios

Face aos padrões atuais de vida, em que despendemos a maior parte do nosso tempo no interior de edifícios, com um nível de conforto que ninguém quer abdicar, urge o desenvolvimento de tecnologias de climatização sustentáveis. Devido a uma combinação única de fatores, casas de baixo consumo de energia (e também casas passivas) em Portugal, são particularmente adequadas de explorar as vantagens da energia solar térmica, especialmente quando combinado com armazenamento sazonal de energia. No entanto nenhum exemplo documentado existe de como esta sinergia pode ser explorada com sucesso em Portugal, ilustrando assim o modo em que a necessidade de aquecimento pode ser colmatada de uma forma sustentável sem o uso de combustíveis fósseis. A energia solar é uma excelente alternativa de fonte de energia para aquecimento de edifícios. Um principal fator que limita a sua aplicação é que é uma fonte de energia com uma disponibilidade média de variação cíclica. O uso de armazenamento sazonal de energia pode reduzir substancialmente o custo do sistema solar que é capaz de fornecer até 100% das necessidades energéticas dos edifícios. Estes sistemas são projetados para armazenar a energia solar durante o verão e reter o calor armazenado para posterior utilização durante o inverno; Abstract: SEASONAL SOLAR THERMAL ENERGY STORAGE FOR LOW TEMPERATURE HEATING BUILDINGS. Given the current standards of living, where we spent most of our time inside buildings, with a level of Comfort that no one wants to give up, urges the development of sustainable climate control technologies. Due to a unique combination of factors, low energy (and also passive) houses in Portugal are particularly well suited to exploiting the advantages of solar thermal energy especially when combined with seasonal energy storage. However no documented example there of how this synergy can be exploited successfully in Portugal, illustrating the way in which the need for heating can be addressed in a sustainable manner without the use of fossil fuels. Solar energy is an important alternative energy source for heating applications. One main factor that limits its application is that it is an energy source with an average availability of cyclical variation. The use of seasonal thermal energy storage can substantially reduce the cost of solar energy systems that can supply up to 100% of buildings energy needs. Such systems are designed to collect solar energy during the summer and retain the stored heat for use during the winter.

Will insulation always bring benefits in energy saving and thermal comfort?

Building insulation is often used to reduce the conduction heat transfer through building envelope. With a higher level of insulation (or a greater R-value), the less the conduction heat would transfer through building envelope. In this paper, using building computer simulation techniques, the effects of building insulation levels on the thermal and energy performance of a sample air-conditioned office building in Australia are studied. It is found that depending on the types of buildings and the climates of buildings located, increasing the level of building insulation will not always bring benefits in energy saving and thermal comfort, particularly for internal-load dominated office buildings located in temperate/tropical climates. The possible implication of building insulation in face of global warming has also been examined. Compared with the influence of insulation on building thermal performance, the influence on building energy use is relatively small.