Movements and mechanical stresses in gas-filled flat plate solar collectors

Sealed gas filled flat plate solar collectors will have stresses in the material since volume and pressure varies in the gas when the temperature changes. Several geometries were analyzed and it could be seen that it is possible reducing the stresses and improve the safety factor of the weakest point in the construction by using larger area and/or reducing the distance between glass and absorber and/or change width and height relationship so the tubes are getting longer. Further it could be shown that the safety factor won't always get improved with reinforcements. It is so because when an already strong part of the collector gets reinforced it will expose weaker parts for higher stresses. The finite element method was used for finding out the stresses.

Design of gas filled solar collectors

With a suitable gas filling used between cover glass and absorber in a flat plate solar collector, it is possible achieving better thermal performance at the same time as the distance betweenabsorber and glass can be reduced. Though, even if there is no vacuum inside the box, there will be potential risks for exhaustion due to stresses depending on the gas volume varies as the temperature varies. This study found out that it is possible build such a collector with less material in the absorber and the tubes and still getting better performance, without risks for exhaustion.

Gas-filled, flat plate solar collectors

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.

Thermal Evaluation of a Solarus PV-T collector

Low concentrator PV-T hybrid systems produce both electricity and thermal energy; this fact increases the overall efficiency of the system and reduces the cost of solar electricity. These systems use concentrators which are optical devices that concentrate sunlight on to solar cells and reduce expensive solar cell area. This thesis work deals with the thermal evaluation of a PV-T collector from Solarus.Firstly the thermal efficiency of the low concentrator collector was characterized for the thermal-collector without PV cells on the absorber. Only two types of paint were on the absorber, one for each trough of the collector. Both paints are black one is glossy and the other is dull,. The thermal efficiency at no temperature difference between collector and ambient for these two types of paint was 0.65 and 0.64 respectively; the U-value was 8.4 W/m2°C for the trough with the glossy type of paint and 8.6 W/m2°C for the trough with dull type of paint. The annual thermal output of these two paints was calculated for two different geographic locations, Casablanca, Morocco and Älvkarleby, Sweden.Secondly the thermal efficiency was defined for the PV-T collector with PV cells on the absorber. The PV cells cover 85% of the absorber, without any paint on the rest of the absorber area. We also tested how the electrical power output influences the thermal power output of the PV-T collector. The thermal and total performances for the PV-T collector were only characterized with reflector sides, because of the lack of time we could not characterize them with transparent sides also.

Thermal Performance of a Solarus CPC-Thermal Collector

The  aim  of  this  master  thesis  is  an  investigation  of  the  thermal  performance  of  a  thermal compound parabolic concentrating (CPC) collector from Solarus. The collector consists of two troughs with absorbers which are coated with different types of paint with  unknown  properties.  The  lower  and  upper  trough  of  the  collector  have  been  tested individually. In  order  to  accomplish  the  performance  of  the  two  collectors,  a  thorough  literature  study  in  the  fields  of  CPC  technology,  various  test  methods,  test  standards  for  solar thermal  collectors  as  well  as  the  latest  articles  relating  on  the  subject  were  carried  out. In addition, the set‐up of the thermal test rig was part of the thesis as well. The thermal  performance  was  tested  according  to  the  steady  state  test  method  as  described in the European standard 12975‐2. Furthermore, the thermal performance of  a  conventional  flat  plate  collector  was  carried  out  for  verification  of  the  test  method. The  CPC‐Thermal  collector  from  Solarus  was  tested  in  2013  and  the  results  showed  four  times  higher  values  of  the  heat  loss  coefficient  UL (8.4  W/m²K)  than  what  has been reported for a commercial collector from Solarus. This value was assumed to be too large and it was assumed that the large value was a result of the test method used that time. Therefore, another aim was the comparison of the results achieved in this work with the results from the tests performed in 2013. The results of the thermal performance showed that the optical efficiency of the lower trough of the CPC‐T collector is 77±5% and the corresponding heat loss coefficient UL 4.84±0.20  W/m²K.  The  upper  trough  achieved  an  optical  efficiency  of  75±6  %  and  a  heat loss coefficient UL of 6.45±0.27 W/m²K. The results of the heat loss coefficients  are  valid  for  temperature  intervals  between  20°C  and  80°C.  The  different  absorber paintings have a significant impact on the results, the lower trough performs overall better.  The  results  achieved  in  this  thesis  show  lower  heat  loss  coefficients UL and higher optical efficiencies compared to the results from 2013. 

Thermal losses in sealed, gas-filled flat plate solar collectors

A sealed space between absorber and cover glass makes it possible reducing the influence of humidity condensate and dust at the same time as the enclosed space can be filled with a suitable gas for lowering the losses. This paper is about the size of the losses in these collectors. A calculating model of a gas-filled flat plate solar collector was built in Matlab with standard heat transfer formulas. It showed that the total loss can be reduced up to 20% when changing to an inert gas. It is also possible using a much shorter distance and still achieve low losses at the same time as the mechanical stresses in the material is reduce.

Steel Sheet Applications and Integrated Heat Management

Increasing energy use has caused many environmental problems including global warming. Energy use is growing rapidly in developing countries and surprisingly a remarkable portion of it is associated with consumed energy to keep the temperature comfortable inside the buildings. Therefore, identifying renewable technologies for cooling and heating is essential. This study introduced applications of steel sheets integrated into the buildings to save energy based on existing technologies. In addition, the proposed application was found to have a considerable chance of market success. Also, satisfying energy needs for space heating and cooling in a single room by using one of the selected applications in different Köppen climate classes was investigated to estimate which climates have a proper potential for benefiting from the application. This study included three independent parts and the results related to each part have been used in the next part. The first part recognizes six different technologies through literature review including Cool Roof, Solar Chimney, Steel Cladding of Building, Night Radiative Cooling, Elastomer Metal Absorber, and Solar Distillation. The second part evaluated the application of different technologies by gathering the experts’ ideas via performing a Delphi method. The results showed that the Solar Chimney has a proper chance for the market. The third part simulated both a solar chimney and a solar chimney with evaporation which were connected to a single well insulated room with a considerable thermal mass. The combination was simulated as a system to estimate the possibility of satisfying cooling needs and heating needs in different climate classes. A Trombe-wall was selected as a sample design for the Solar Chimney and was simulated in different climates. The results implied that the solar chimney had the capability of reducing the cooling needs more than 25% in all of the studied locations and 100% in some locations with dry or temperate climate such as Mashhad, Madrid, and Istanbul. It was also observed that the heating needs were satisfied more than 50% in all of the studied locations, even for the continental climate such as Stockholm and 100% in most locations with a dry climate. Therefore, the Solar Chimney reduces energy use, saves environment resources, and it is a cost effective application. Furthermore, it saves the equipment costs in many locations. All the results mentioned above make the solar chimney a very practical and attractive tool for a wide range of climates.

Obtenção das freqüências naturais em torres estaiadas pelo método da matriz de transferência, representando o feixe de cabos por uma rigidez horizontal dinâmica

O objetivo do presente trabalho é o estudo do comportamento, em termos de freqüências naturais de estruturas de torres estaiadas, para diversas situações de serviço. Para isso criou-se uma formulação para a determinação dessas freqüências, utilizando o método da matriz de transferência. O procedimento consiste na discretização da estrutura em elementos de barras, massas discretas, molas e amortecedores viscosos, para a representação da estrutura. Com relação aos cabos da torre estaiada, desenvolveu-se uma expressão que nos fornece a rigidez completa dos mesmos, apoiados nos extremos, com amortecimento viscoso e as propriedades físicas e geométricas uniformes. Além disso, os cabos podem ser inclinados e sujeitos à excitação horizontal harmônica no apoio superior. Nesse caso, considera-se uma deformada parabólica do cabo na posição de equilíbrio estático, e por outro lado, os deslocamentos dinâmicos são considerados pequenos. A rigidez do cabo é válida para um ângulo de inclinação que varia de zero (0) a noventa (90) graus. Esse método é aplicável a microcomputadores devido a pouca memória empregada no processamento de dados. Com esse intuito, foi elaborado um programa para microcomputadores de 16 bits, que possibilita o estudo da estrutura da torre sobre o efeito de flexão pura, torção pura ou acoplamento de ambos. Exemplos numéricos de torres estaiadas e do comportamento da rigidez de cabos foram desenvolvidos para as mais diversas situações de cálculo.

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

Construção e validação de um receptor GPS para uso espacial

Global Positioning System, or simply GPS, it is a radionavigation system developed by United States for military applications, but it becames very useful for civilian using. In the last decades Brazil has developed sounding rockets and today many projects to build micro and nanosatellites has appeared. This kind of vehicles named spacecrafts or high dynamic vehicles, can use GPS for its autonome location and trajectories controls. Despite of a huge number of GPS receivers available for civilian applications, they cannot used in high dynamic vehicles due environmental issues (vibrations, temperatures, etc.) or imposed dynamic working limits. Only a few nations have the technology to build GPS receivers for spacecrafts or high dynamic vehicles is available and they imposes rules who difficult the access to this receivers. This project intends to build a GPS receiver, to install them in a payload of a sounding rocket and data collecting to verify its correct operation when at the flight conditions. The inner software to this receiver was available in source code and it was tested in a software development platform named GPS Architect. Many organizations cooperated to support this project: AEB, UFRN, IAE, INPE e CLBI. After many phases: defining working conditions, choice and searching electronic, the making of the printed boards, assembling and assembling tests; the receiver was installed in a VS30 sounding rocket launched at Centro de Lançamento da Barreira do Inferno in Natal/RN. Despite of the fact the locations data from the receiver were collected only the first 70 seconds of flight, this data confirms the correct operation of the receiver by the comparison between its positioning data and the the trajectory data from CLBI s tracking radar named ADOUR

Avaliação do módulo de elasticidade da madeira com uso de método não-destrutivo de vibração transversal

Numerosas pesquisas têm estudado os métodos não-destrutivos de avaliação de materiais e sua aplicação àqueles de matrizes complexas, como é o caso da madeira. Um dos primeiros métodos não-destrutivos investigados para aplicação nesses casos foi o da vibração transversal. Apesar de sua concepção simples, e a despeito dos grandes avanços obtidos nessa área com outros métodos, como, por exemplo, o ultra-som, o método de vibração transversal para a determinação do módulo de elasticidade da madeira revela-se como de grande potencial de aplicação, sobretudo pela precisão do modelo matemático a ele associado e pela possibilidade de sua aplicação a peças de dimensões estruturais (in-grade testing). Neste trabalho, apresenta-se o uso desse método na determinação do módulo de elasticidade de três espécies de eucalipto. Foram ensaiados não-destrutivamente e por ensaios mecânicos convencionais de flexão corpos-de-prova de 2 cm x 2 cm x 46 cm de E. grandis, E. saligna e E. citriodora. Os ensaios não-destrutivos foram conduzidos com uso do sistema BING - Beam Identification by Non-destructive Grading, que permite a análise das vibrações do material nos domínios do tempo e da freqüência. Os resultados obtidos revelaram boa correlação entre os dois tipos de ensaios empregados, justificando o início dos ensaios com peças de dimensões estruturais, para a viabilização da técnica nas práticas de classificação estrutural.

Sistema para detecção e diagnóstico de falhas em motores elétricos de indução utilizando lógica fuzzy

Induction motors are one of the most important equipment of modern industry. However, in many situations, are subject to inadequate conditions as high temperatures and pressures, load variations and constant vibrations, for example. Such conditions, leaving them more susceptible to failures, either external or internal in nature, unwanted in the industrial process. In this context, predictive maintenance plays an important role, where the detection and diagnosis of faults in a timely manner enables the increase of time of the engine and the possibiity of reducing costs, caused mainly by stopping the production and corrective maintenance the motor itself. In this juncture, this work proposes the design of a system that is able to detect and diagnose faults in induction motors, from the collection of electrical line voltage and current, and also the measurement of engine speed. This information will use as input to a fuzzy inference system based on rules that find and classify a failure from the variation of thess quantities

Projeto, construção e levantamento de desempenho de um concentrador solar cilíndro parabólico com mecanismo automático de rastreamento solar

An cylinder-parabolic solar concentrator is presented to produce steam for different applications. This prototype was built in glass fiber with dimensions that follow a study of optimization of parameters inherent in the optical reflection of sunlight by the surface of reflection and absorption of the same by tubing that leads the fluid of work. The surface of the concentrator of 2.24 m² has been covered by layers of mirror with 1.0 m of lenght and 2.0 cm wide. The absorb tubing consists of a copper tube diameter equal to 28 mm. The concentrator is moving to follow the apparent motion of the sun. It will be presented the processes of manufacturing and assembly of the concentrator proposed, which has as main characteristics the facilities construction and assembly, in addition to reduced cost. Will be presented data from tests performed to produce steam setting up some parameters that diagnose the efficiency of the concentrator. It will be demonstrated the viabilities thermal, economic and of materials of the proposed system.The maximum temperature achieved in the vacuum tube absorber was 232.1°C and average temperature for 1 hour interval was 171.5°C, obtained in a test with automation. The maximum temperature achieved in the output of water was 197.7°C for a temperature of 200.0°C in the absorber tube. The best average result of the water exit temperature to interval of 1 hour was 170.2°C for a temperature of 171.2°C, in the absorber tube, obtained in test with automation. Water exit mean temperatures were always above of the water steaming temperature. The concentrator present a useful efficiency of 38% and a production cost of approximately R$ 450,00 ( $ 160.34)

Projeto, construção e análise de desempenho de coletores solares alternativos utilizando garrafas pet

A solar alternative system for water heating is presented. It work on a thermosiphon, consisting of one or two alternative collectors and a water storage tank also alternative, whose main purpose is to socialize the use of energy mainly to be used by people of low income. The collectors were built from the use of pets bottles, cans of beer and soft drinks and tubes of PVC, ½ " and the thermal reservoirs from a drum of polyethylene used for storage of water and garbage placed inside cylinder of fiber glass and EPS ground between the two surfaces. Such collectors are formed by three elements: pet bottles, cans and tubes absorbers. The heating units, which form the collector contains inside the cans that can be closed, in original form or in the form of plate. The collectors have an absorber grid formed by eight absorbers PVC tube, connected through connections at T of the same material and diameter. It will be presented data of the thermal parameters which demonstrate the efficiency of the heating system proposed. Relative aspects will be boarded also the susceptibility the thermal degradation and for UV for the PVC tubes. It will be demonstrated that this alternative heating system, which has as its main feature low cost, presents thermal, economic and materials viabilities

Projeto, construção e análise de desempenho de um forno solar alternativo tipo caixa a baixo custo

An alternative box-type solar oven constructed from the scrap iron of a gas conventional cook is presented, which functions principles are the effect greenhouse and the concentration. The oven of the conventional cook is the baking enclosure where the absorber (pot) of the solar oven is located, being re-covered for a glass blade for the generation of the greenhouse effect isolated lateral and having deep its and for a composite the plaster base and EPS. Segments of plain mirrors had been placed in the laterals of the oven for the concentration of the radiation and a reflecting parabola was introduced in the baking enclosure for the exploitation of the incident reflected radiation in the interior of the oven. The oven is mobile to allow one better aiming of exactly in relation to the apparent movement of the sun. The thermal economic and of materials viabilities of the stove in study will be demonstrate The average internal temperature of the absorber was around 150°C and the internal temperature around 120°C. Will demonstrate that its low cost and good thermal performance represents basic characteristics for the viability of large use of such archetype, mainly for cooking the decreases and averages temperatures. One will reveal that the archetype in study is competitive with the box-type solar cooker conceived in the whole world