Data taken during the National Bureau of Standards Durability/Reliability (NBS D/R) Program is analyzed in depth in this report. The main thrust of the analysis is to develop methods of relating material property changes to full scale collector efficiency changes after exposure to environmental and operational conditions. To this end, results of material sample and full scale collector tests are discussed separately and then related to each other. Many of the materials tested showed no measurable change in optical properties after 480 days of exposure. Therefore, the results of six representative samples which span the range of responses observed are presented in detail. Next, a mathematical model of collector thermal performance is used to show the theoretical dependence of efficiency on property values. Actual degradation measurements of three typical collectors in the NBS D/R Program are presented. These measurements, based on ASHRAE standard 93-77 tests, show degradation between 0 and 4 percent of the original value of efficiency. Also presented is an analysis of the stagnation temperature variation with exposure time. No conclusive data resulted from the stagnation temperature analysis. Finally, the mathematical model is used with results from the material tests to predict the change in efficiency. The predictions are always within ± 3 percent of the measured 480-day efficiency. Error is estimated to be a result of uncertainty in insulation conductivity values used and other unexplained sources of error. / M.S.

The National Bureau of Standards conducted outdoor durability tests on eight different types of commercially available flat plate solar collectors. The test results for five types of collectors are analyzed. The purpose of the test program was to investigate the feasibility of determining the durability of materials by measuring collector thermal efficiency at specified intervals. The important material properties include the solar absorptance and long wave emittance of the absorber surface, solar and long wave transmittance of the cover material and the thermal conductivity of the insulation. Tests were conducted by three independent testing laboratories located in Phoenix, Arizona, Cape Canaveral, Florida, and Palo Alto, California. The test sites were chosen to investigate the effects of the various environmental conditions found in the United States on collector degradation. Three test series were considered to study the effect of various operating conditions on collector degradation. The collectors were exposed to the environment for up to 240 days. The thermal performance test results did not reveal significant degradation in the performance parameters, F_r(T_α) and F_rU_L, of the collectors considered. Any degradation that may have occurred was overshadowed by experimental uncertainty. The test results did not depend on test series, geographic location or season of the year. Referring the test results to a common set of weather conditions did not reduce the scatter in the results. / Master of Science

Presently, there exist significant discrepancies between experimental and theoretical predictions of flat-plate solar collector performance. There is a need to identify both those areas of analysis which need improvement as well as those which are already adequate. Two new methods of absorber-plate thermal analysis which can be used within the framework of existing theory were developed. The first method used the separation of variables technique in a unique manner to solve exactly for the coupled axial and transverse temperature distributions in an absorber plate-tube assembly. The conventional assumption of an overall uniform loss coefficient U_L was used in the analysis. The first method is practical only for parallel-flow collectors. The second method used two sectionally uniform loss coefficients -- U_LI for internal collector sections and U_LE for edge sections -- to evaluate collector performance. The second method is applicable for both parallel-flow and serpentine configurations. The validity of two assumptions commonly made in flat-plate collector analysis was investigated using the new methods. The first assumption that was investigated involved the approximate treatment of the effect of axial conduction on the absorber-plate temperature distributions. Results from the first new method were graphically compared to the predictions of approximate analytical treatments given by Whillier and Phillips. The comparisons showed that, for conventional flat-plate designs, the method given by Phillips yields values of the heat removal factor F_R accurate to within 1 per cent. The more commonly used method given by Whillier is accurate to within 10 per cent for conventional designs. The second assumption that was investigated dealt with the manner in heat losses from the collector peripheral area are taken into account. Results from the second new method indicated that, for typical collector designs, the conventional edge loss treatment yields values of instantaneous collector efficiency n_c accurate to within 3 per cent absolute and 15 per cent relative. Analysis of the net effect of the two improvements indicated that approximate axial and edge-loss treatments are not the primary source of error between experimental and theoretical results for typical collectors. The solution technique developed in the first new method has potential applications to a number of conduction-convection problems. The second new method has the inherent capability to better evaluate performance and design questions related to edge effects. Convenient relations between the mean plate and fluid temperatures and the heat removal factor F_R were obtained. The relations apply for parallel-flow analysis under the assumption of a uniform loss coefficient U_L. / Ph. D.

Call number: LD2668 .T4 1978 J35 / Master of Science

Orientador: Vicente Luiz Scalon / Coorientador: Alcides Padilha / Banca: Celso Luiz da Silva / Banca: Ismael de Marchi Neto / Banca: Rodrigo Correa da Silva / Resumo: A mudança na geração de energia através de fontes não renováveis para fontes renováveis é uma grande preocupação mundial e nacional, que tem impulsionado pesquisas e desenvolvimentos de tecnologias na área de energia renovável. Neste cenário, a energia solar é uma excelente alternativa, por ter um grande potencial e diversas aplicações. Com isso, este trabalho tem o objetivo de analisar melhorias na eficiência de coletor solar plano, equipamento utilizado no aquecimento de água através da energia solar, ao adicionar barreiras na cavidade de ar confinado entre a sua placa absorvedora e a sua cobertura de vidro. As barreiras bloqueiam o fluxo de ar, provocado pela convecção interna, diminuindo as perdas de calor. A análise foi realizada em quatro coletores, nos quais foram adicionados de uma a quatro barreiras e comparados com um coletor sem barreira como referência. Para isso, foi construída uma bancada de teste com todos equipamentos necessários para obter a eficiência em coletor solar plano. Os resultados dos ensaios mostraram que não houve uma variação significativa da absorção de radiação solar, já que a eficiência máxima manteve-se inalterada. Porém, houve uma diminuição da perda de calor ao adicionar as barreiras, sendo esse resultado diretamente relacionado a inclinação da curva de eficiência usada na análise de coletor solar plano. Os resultados mostram que a inclinação varia em -2,05%, -5,12% e 2,94%, para duas a quatro barreiras, respectivamente. Portanto, as barreir... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The shift in power generation from non-renewable sources to renewable sources is a major global and national concern that has driven research and development of renewable energy technologies. In this scenario, the solar energy is an excellent alternative, for having great potential and diverse applications. With this, the objective of this work is to analyze improvements in the efficiency of solar collector flat, equipment used in heating water through solar energy, by adding barriers in the confined air cavity between its absorber plate and its glass cover. The barriers block the flow of air, caused by internal convection, reducing heat losses. The analysis was performed on four collectors, in which one to four barriers were added and compared with a barrierless collector as a reference. For this, a test bench was built with all the necessary equipment to obtain the efficiency in the flat solar collector. The results of the tests showed that there was no significant variation in the absorption of solar radiation since the maximum efficiency remained unchanged. However, there was a decrease of the heat loss when adding the barriers, being this result directly related to the slope of the curve of efficiency used in the analysis of flat solar collector. The results show that the slope varies by -2.05%, -5.12% and 2.94% for two to four barriers, respectively. Therefore, the barriers reduce the heat loss to the medium, with an optimal number of barriers for each flat solar collector project. / Doutor

This work treats the thermal and mechanical performances of gas-filled, flat plate solar collectors in order to achieve a better performance than that of air filled collectors. The gases examined are argon, krypton and xenon which all have lower thermal conductivity than air. The absorber is formed as a tray connected to the glass. The pressure of the gas inside is near to the ambient and since the gas volume will vary as the temperature changes, there are potential risks for fatigue in the material. One heat transfer model and one mechanical model were built. The mechanical model gave stresses and information on the movements. The factors of safety were calculated from the stresses, and the movements were used as input for the heat transfer model where the thermal performance was calculated. It is shown that gas-filled, flat plate solar collectors can be designed to achieve good thermal performance at a competitive cost. The best yield is achieved with a xenon gas filling together with a normal thick absorber, where normal thick means a 0.25 mm copper absorber. However, a great deal of energy is needed to produce the xenon gas, and if this aspect is taken into account, the krypton filling is better. Good thermal performance can also be achieved using less material; a collector with a 0.1 mm thick copper absorber and the third best gas, which is argon, still gives a better operating performance than a common, commercially produced, air filled collector with a 0.25 mm absorber. When manufacturing gas-filled flat plate solar collectors, one way of decreasing the total material costs significantly, is by changing absorber material from copper to aluminium. Best yield per monetary outlay is given by a thin (0.3 mm) alu-minium absorber with an argon filling. A high factor of safety is achieved with thin absorbers, large absorber areas, rectangular constructions with long tubes and short distances between glass and absorber. The latter will also give a thin layer of gas which gives good thermal performance. The only doubtii ful construction is an argon filled collector with a normal thick (> 0.50 mm) aluminium absorber. In general, an assessment of the stresses for the proposed construction together with appropriate tests are recommended before manufacturing, since it is hard to predict the factor of safety; if one part is reinforced, some other parts can experience more stress and the factor of safety actually drops.

The major objective of this study was to analytically determine the effects of small transverse solar tracking errors on the concentrated intensity profile generated by a 22-inch wide, f-number one, linear Fresnel model lens. Transverse tracking error is caused by the misalignment of the lens optic axis and the center of the sun in a direction perpendicular to the lens optic axis. The analytical method consisted of extending an earlier theoretical model developed by Cosby3 in which the solar disk was perfectly tracked; thus the tracking error problem is treated as a perturbation of the basic theory. Data was obtained using extensive computer calculations.Results indicated that in the presence of transverse tracking error, lens serrations (upper half serrations) on the same side of the lens optic axis as the sun differ significantly from the lens serrations (lower half serrations) on the opposite side of the lens optic axis in their concentration characteristics. Incident angles of sunlight are greater for upper half serrations causing greater angles of refraction at the second surface. The peak concentration ratio values are observed to shift in the negative intercept direction in a linear relationship with tracking error angle. It was observed that the 90% target width monotonically increased, e.g., by 100% and 700% for transverse tracking errors of 1/2° and 2-1/2°, respectively. It is concluded that the dominant cause for the 90% target width increase is the intensity profile shift itself. Some lesser influence results from increasing intensity profile skewness and profile broadening for IR wavelengths caused by greater IR refraction with increased transverse tracking error.Ball State UniversityMuncie, IN 47306

The flat-plate solar collector is the most commonly used device for the direct utilization of solar energy, but its applicability in some places is still debatable. The performance of the solar collector varies with changes in environmental and operational conditions. In this thesis the performance ice of a flat-plate solar collector was examined in order to determine the feasibility of utilizing solar energy s an alternative energy resource for residential water and space heating purposes in East Central Indiana.Various environmental and operational data pertinent to the performance of the solar collector were collected over a period of 76 days (March 26 through June 10). Analysis of the data showed that the efficiency of the collector varies with changes in climatic and operational conditions. Negative relationships were observed between efficiency and fluid inlet temperature, wind speed, cloud cover and precipitation, while relationships between the collector efficiency and ambient temperature, solar radiation and fluid flow rate were found to be positive. Further analysis of the collector performance findings and the average energy consumption in i-iuncie, Indiana produced encouraging evidence for the utilization of solar energy for residential crater heating and space heating purposes in the area.Ball State UniversityMuncie, IN 47306

No description available.

Orientador: Vicente Luiz Scalon / Banca: Alcides Padilha / Banca: Ismael de de Marchi Neto / Resumo: Atualmente a disponibilidade de energia é uma uma grande preocupação da humanidade, pois a maior porcentagem da energia consumida é oriunda da exploração de recursos naturais, como o carvão mineral, gás natural e petróleo. Neste cenário, as energias renováveis têm um papel muito importante. As hidroelétricas, biomassa, eólica, geotérmica, solar, entre outras são a solução da disponibilidade de energia para o futuro. Dentre tais energias, a energia solar merece um destaque pelo seu enorme potencial, porém muito ainda é preciso progredir para aumentar a eficiência destas fontes. Com esse intuito, este trabalho tem como foco estudar a influência na eficiência de coletores solares planos ao introduzir barreiras em sua cavidade interna, a fim de bloquear a livre circulação do ar, desta maneira, diminuindo a perda de calor pela convecção interna. Foi realizado testes experimentais com as mesmas características térmica e geométricas dos espaços de confinamento de ar. O fluxo de calor é introduzido através de resistências elétricas e acompanhamento de um controle eletrônico para garantir que a temperatura permaneça constante ao longo de toda a base (chapa de alumínio). Com a monitoração e coleta dos dados da potência elétrica dissipada e as temperaturas do volume de controle estudado, foi analizado o comportamento do coeficiente convective natural, possibilitando a análise ao variar o número de barreiras (cavidades) assim como sua inclinação, sendo possível notar uma redução do coeficiente convectivo com o uso de barreiras / Abstract: Currently the availability of energy is a major concern of humanity, for the largest percentage of energy consumed comes from the exploitation of natural resources, such as coal, natural gas and oil. In this scenario, renewable energies have a very important role. Hydroelectric, biomass, wind, geothermal, solar, among others are the solution to the because of its enormous potential, however much progress is still needed to increase the efficiency of these sources. To this end, this work focuses on studying the influence on the efficiency of solar collector plans to its internal cavity in order to block the free flow of air, thus, reducing heat loss by internal convection. Experimental testing was performed with the same thermal and geometrical characteristics of the air spaces of confinement. The heat flow is introduced through electrical and accompanied by an electronic control to ensure that the resistance temperature remains constant over the entire base (aluminum plate). With monitoring and data collection of dissipated electrical power and temperature control volume studied was verified behavior of the coefficient of the film, allowing the analysis to vary the number of barriers (wells) and the slope, which was noticeable reduction convective coefficient using barriers / Mestre