Submitted by Maicon Juliano Schmidt (maicons) on 2015-07-15T13:18:20Z No. of bitstreams: 1 Fábio Ricardo de Oliveira de Souza.pdf: 10103280 bytes, checksum: 4e2fd0c8307348f7e9098749cafe8b73 (MD5) / Made available in DSpace on 2015-07-15T13:18:20Z (GMT). No. of bitstreams: 1 Fábio Ricardo de Oliveira de Souza.pdf: 10103280 bytes, checksum: 4e2fd0c8307348f7e9098749cafe8b73 (MD5) Previous issue date: 2013-01-31 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / PROSUP - Programa de Suporte à Pós-Gradução de Instituições de Ensino Particulares / Este trabalho apresenta um estudo numérico sobre características de escoamento e transferência de calor em tubo evacuado. A abordagem numérica foi realizada com o software comercial ANSYS-CFX. O modelo numérico adotado é tridimensional e é composto pelas equações da conservação da massa, quantidade de movimento e energia. A malha computacional é do tipo hexaédrica, com refinamento nas regiões de maiores gradientes térmicos e fluidodinâmicos. O modelo implementado foi validado com resultados numéricos da literatura e um estudo de caso foi realizado, considerando variações do ângulo de inclinação do tubo, da variação da taxa de transferência de calor para o tubo e da variação da temperatura da água proveniente do reservatório térmico. Também foram avaliadas duas hipóteses: uma considerando propriedades físicas da água constantes e a outra com propriedades variáveis com a temperatura. Comparações são apresentadas para campos de velocidade e temperatura, vazão mássica e números de Nusselt e de Reynolds. O comparativo entre os resultados obtidos com a hipótese de propriedades constantes, com aqueles obtidos com propriedades variáveis mostra diferenças significativas entre eles, apontando a importância do uso de propriedades variáveis neste tipo de simulação numérica. Os resultados dos estudos paramétricos indicam que o incremento da vazão mássica e da temperatura média de saída do fluido é diretamente proporcional ao incremento do ângulo de inclinação, da taxa de transferência de calor e da temperatura do reservatório térmico. / This work presents a numerical study on characteristics of flow and heat transfer in an evacuated tube. The numerical approach was performed with the commercial software ANSYS-CFX. The numerical model adopted is three-dimensional and consists of the mass, momentum and energy equations. The computational mesh is hexaedrical, with refinement in regions of higher thermal and fluid gradients. The implemented model was validated with numerical results of literature and a case study was conducted considering inclination angle, rate of heat transfer and water temperature from the thermal reservoir. Also were evaluated two hypotheses: one considering constant physical properties of water and the other with properties varying with temperature. Comparisons are presented for velocity and temperature fields, mass flow and Nusselt and Reynolds numbers. The comparison between the results obtained with the hypothesis of constant properties, with those obtained with variable properties, shows significant differences between them, pointing out the importance of using variable properties in this type of numerical simulation. The results of the parametric studies indicate that the increment of the mass flow and average temperature of the fluid is directly proportional to the inclination angle, the rate of heat transfer and the temperature of the thermal reservoir.

The thesis presents background on solar thermal energy and addresses the structural challenges associated with the deployment of concentrating solar power fields in urban areas. Two potential structural systems and urban locales of deployment are proposed and investigated to determine whether they have the potential to be a cost-effective renewable energy solution for urban areas. The structural issues explored in the thesis include flutter, the wind loading of open frame structures, performance-based design, and the design of flexibly mounted equipment on a building.

Solar thermal collectors at high latitudes have been studied, with emphasis on concentrating collectors. A novel design of concentrating collector, the Maximum Reflector Collector (MaReCo), especially designed for high latitudes, has been investigated optically and thermally. The MaReCo is an asymmetrical compound parabolic concentrator with a bi-facial absorber. The collector can be adapted to various installation conditions, for example stand-alone, roof- or wall mounted. MaReCo prototypes have been built and outdoor-tested. The evaluation showed that all types work as expected and that the highest annually delivered energy output, 340 kWh/m2, is found for the roof MaReCo. A study of the heat-losses from the stand-alone MaReCo lead to the conclusion that teflon transparent insulation should be placed around the absorber, which decreases the U-value by about 30%. A method was developed to theoretically study the projected radiation distribution incident on the MaReCo bi-facial absorber. The study showed that the geometry of the collectors could be improved by slight changes in the acceptance intervals. It also indicated that the MaReCo design concept could be used also at mid-European latitudes if the geometry is changed. A novel method was used to perform outdoor measurements of the distribution of concentrated light on the absorber and then to calculate the annually collected zero-loss energy, Ea,corr, together with the annual optical efficiency factor. A study using this method indicated that the absorber should be mounted along the 20º optical axis instead of along the 65º optical axis, which leads to an increase of about 20% in Ea,corr. The same absorber mounting is suggested from heat loss measurements. The Ea,corr at 20º absorber mounting angle can be increased by 5% if the absorber fin thickness is changed from 0.5 to 1 mm and by 13% if two 71.5 mm wide fins are used instead of one that is 143 mm wide. If the Ea,corr for the standard stand-alone MaReCo with 143 mm wide absorber mounted at 65º is compared to that of a collector with a 71.5 mm wide absorber mounted at 20º, the theoretical increase is 38%.

Three different green technologies are compared in terms of net energy and carbon savings for a theoretical Toronto rooftop. Embodied energy values are calculated through Life Cycle Analysis and compared to the estimated energies produced and/or saved by each technology. Results show that solar photovoltaics displace the most carbon per m2 of roof space and solar thermal (for hot water) displaces the most energy. An in-depth analysis of an intensive green roof for growing food indicates that the high embodied energy of the materials is not quickly repaid by the sum of six energy savings that were examined (direct and indirect cooling, run-off treatment, transport of food, on-farm energy use, and activities that would otherwise be carried out). However, the energy and carbon benefits are not insignificant, but depend strongly on various assumptions. The methodology used is replicable and therefore useful for other locations.

Three different green technologies are compared in terms of net energy and carbon savings for a theoretical Toronto rooftop. Embodied energy values are calculated through Life Cycle Analysis and compared to the estimated energies produced and/or saved by each technology. Results show that solar photovoltaics displace the most carbon per m2 of roof space and solar thermal (for hot water) displaces the most energy. An in-depth analysis of an intensive green roof for growing food indicates that the high embodied energy of the materials is not quickly repaid by the sum of six energy savings that were examined (direct and indirect cooling, run-off treatment, transport of food, on-farm energy use, and activities that would otherwise be carried out). However, the energy and carbon benefits are not insignificant, but depend strongly on various assumptions. The methodology used is replicable and therefore useful for other locations.

This master’s degree project concerns the combination of a multi dwelling passive house with solar energy for the generation of electricity and domestic hot water (DHW). Different alternatives with either solar thermal systems or photovoltaic (PV) systems are compared with two reference alternatives producing DHW from electricity or district heating. The economical comparison uses a life cycle cost (LCC) perspective based on the present value of expenditures for investment, energy and annual operating and maintenance. The energy yields from the solar energy systems were calculated by hand and with simulation software. Calculation and dimensioning of PV systems were carried out with a software called PVSYST. Solar thermal systems were calculated by hand and with the software Winsun Villa Education. Both softwares use hourly weather data for the calculations. The LCCs are lower for the two reference alternatives than for the solar energy alternatives. The reference alternative with district heating generates the lowest LCC. The alternatives with solar thermal energy replace more energy and have significantly lower LCCs than the PV alternatives. The study also shows the importance of using cheap and environmentally friendly backup energy for producing DHW. When aiming for a quantitative energy use target, the DHW-circulation losses ought to be taken into account as these can be extensive.

Traditionally, energy capture by non-concentrating solar collectors is calculated using the Hottel-Whillier Equation (HW): Q(u)=A(c)*F(r)*S-A(c)*F(r)*U(l)*(T(fi)-Tₐ), or its derivative: Q(u)=A(c)*F(r)*S-A(c)*F(r)*U(l)*((T(fi)-T(fo))/2-Tₐ). In these models, the rate of energy capture is based on the collector's aperture area (A(c)), collector heat removal factor (F(r)), absorbed solar radiation (S), collector overall heat loss coefficient (U(l)), inlet fluid temperature (T(fi)) and ambient air temperature (Tₐ). However real-world testing showed that these equations could potentially show significant errors during non-ideal solar and environmental conditions. It also predicts that when T(fi)-Tₐ equals zero, the energy lost convectively is zero. An improved model was tested: Q(u)=A(c)F(r)S-A(c)U(l)((T(fo)-T(fi))/(ln(T(fo)/T(fi)))-Tₐ) where T(fo) is the exit fluid temperature. Individual variables and coefficients were analyzed for all versions of the equation using linear analysis methods, statistical stepwise linear regression, F-Test, and Variance analysis, to determine their importance in the equation, as well as identify alternate methods of calculated collector coefficient modeling.

[pt] Este trabalho tem por objetivo principal a avaliação de desempenho de um sistema piloto de preaquecimento dos motores da central termelétrica Gera Maranhão, via energia solar térmica, em Miranda do Norte, Maranhão, através de uma simulação numérica. Cinco subsistemas independentes, cada um responsável pelo preaquecimento de um motor Wartsila 20V32 de 8,73 MW, foram construídos, somando um total de 500 coletores solares instalados e uma superfície de captação solar total de 1000 metros quadrados. Uma estação meteorológica com sensores de radiação solar global, difusa, direta e temperatura ambiente foi posicionada do lado dos sistemas para medir as condições ambientais na região. A simulação do desempenho do sistema solar foi efetuada ao longo de um ano com dados de radiação solar da estação meteorológica de Buriticupu, no Maranhão, dados que mais se aproximam dos dados disponíveis de Miranda do Norte. Correlações para transformar a radiação global medida numa superfície horizontal para uma superfície inclinada foram selecionadas após uma revisão bibliográfica dentre as disponíveis na literatura. Diferentes cenários de controle do acionamento das bombas de água foram comparados a fim de determinar a melhor configuração de operação. A influência da temperatura de preaquecimento dos motores no desempenho do sistema solar foi avaliada também. Os resultados da simulação foram comparados com os resultados obtidos via o método F-CHART. Uma participação média anual da energia solar de 11,5 por cento foi encontrada para o preaquecimento dos motores levando a uma redução de 24693 kg/ano de óleo combustível usado na caldeira do sistema de preaquecimento dos motores da usina termelétrica. / [en] The present work has as main objective the performance evaluation of a pilot system for preheating the engines of Gera Maranhão power plant, in Miranda do Norte, state of Maranhão, via thermal solar energy using a numerical simulation. Five independent subsystems, each one responsible for the preheating of a Wartsila 20V32 internal combustion engine of 8.73 MW, were installed. These systems amount five hundred solar collectors, with a total solar collecting area of 1000 square meters. A meteorological station with sensors for global, diffusive and beam solar radiation, as well as ambient temperature recorders, was placed by the side of the system in mode to measure ambient condition in the area. The simulation of the solar system performance was processed over a year with data of solar radiation for a meteorological station of Buriticupu, state of Maranhão, Brazil. Correlations to transform the global radiation measured on a horizontal plane to a sloped plane were selected, following a selection from a literature review. For the control of the water pumps, different scenarios were compared in order to determine the best operational configuration. The influence of engine preheating temperature in the performance of the solar system was also evaluated. Simulation results were compared with results obtained with the F-CHART method. An annual average solar energy contribution of 11.5 percent was found for the preheating of the engines. This resulted in a reduction of 24693 kg per year of fuel oil used in the boiler of the traditional preheating system of the power plant.

abstract: Recently, nanostructured metamaterials have attracted lots of attentions due to its tunable artificial properties. In particular, nanowire/nanohole based metamaterials which are known of the capability of large area fabrication were intensively studied. Most of the studies are only based on the electrical responses of the metamaterials; however, magnetic response, is usually neglected since magnetic material does not exist naturally within the visible or infrared range. For the past few years, artificial magnetic response from nanostructure based metamaterials has been proposed. This reveals the possibility of exciting resonance modes based on magnetic responses in nanowire/nanohole metamaterials which can potentially provide additional enhancement on radiative transport. On the other hand, beyond classical far-field radiative heat transfer, near-field radiation which is known of exceeding the Planck’s blackbody limit has also become a hot topic in the field. This PhD dissertation aims to obtain a deep fundamental understanding of nanowire/nanohole based metamaterials in both far-field and near-field in terms of both electrical and magnetic responses. The underlying mechanisms that can be excited by nanowire/nanohole metamaterials such as electrical surface plasmon polariton, magnetic hyperbolic mode, magnetic polariton, etc., will be theoretically studied in both far-field and near-field. Furthermore, other than conventional effective medium theory which only considers the electrical response of metamaterials, the artificial magnetic response of metamaterials will also be studied through parameter retrieval of far-field optical and radiative properties for studying near-field radiative transport. Moreover, a custom-made AFM tip based metrology will be employed to experimentally study near-field radiative transfer between a plate and a sphere separated by nanometer vacuum gaps in vacuum. This transformative research will break new ground in nanoscale radiative heat transfer for various applications in energy systems, thermal management, and thermal imaging and sensing. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2017

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / This dissertation presents the experimental result of a system to absorb solar energy to heat up a desalination tower with heat recovery mechanism and a change made in the heated water distribution at the heat storage tank. The system to absorb solar energy consists of solar thermal flat plate collectors for high temperatures and it responsible for the conversion of solar radiation in thermal energy to heat up the water to be desalinated. The change made in the storage tank consists of the installation of a stainless steel pipe with holes equally spaced and arrangement to allow a better distribution of the hot water from the solar collectors in the heat storage tank. The desalination unit has two components: two high temperatures solar collectors and a desalination tower with six stages. In its operation, water is heated in the solar collectors and moves by natural convection to the storage tank, to the bottom of the tower. In the tank, the water transfers heat to the salty water in the first stage of the tower. This heated water transfer heat by evaporation, convection and radiation to the second stage and part of its energy is lost to the ambient. The condensed vapor on the walls of the stages flows down by gravity to be collected in a reservoir installed under the desalination tower. The heat received by the second stage is used to heat up the ater in this stage and the process is repeated in all stages. The performance of the desalination unit was satisfactory. The temperature in the storage tank reached values near 85ÂC and the water temperatures at the outlet of the solar collector were near 100ÂC. The daily production was 31 liters of desalinated water and the GOR-value (gain output ratio) was 1,54