Rozprawy doktorskie na temat „COMPOUND PARABOLIC”

Compound Parabolic Collector (CPC) has numerous advantages such as high optical efficiency and wide applications. This thesis describes experimental and theoretical investigations of the effects of solar radiation available, design and orientation on different configurations of low concentration CPCs for Kano, Nigeria. Two solar radiation models were developed for characterizing solar radiation for regions in the northern hemisphere like Kano. Results showed that tilting the collector to the monthly optimum angle gives the maximum radiation obtainable in each month with highest increase of 28.6 and 24.8% in December and January respectively. For seasonal tilt; the best angles were 27.05° (October to March) and 0° (April to September) while for fixed collector, tilting at 12.05° (latitude) provides the highest performance. Using advanced ray tracing technique, detailed investigations of the effects of acceptance angle, receiver radius, truncation, etc. were carried out on the CPC performance. While with the truncation of 70%, results showed that compound parabolic collector can achieve daily average optical efficiencies of 86.2% and 75.4% for acceptance angles of 60° and 40° respectively. The performance of the thermosyphon (receiver) was investigated both experimentally and numerically. Using an in house solar simulator developed in this work, the performance of the developed CPC fitted with thermosyphon was experimentally investigated. Results showed that the CPC can function well with thermosyphon inclination angle up to 40° where it gives efficiency between 76% and 66%. The outcome of this work shows the potential of using this developed system in Kano environment for cooling applications.

This thesis presents a detailed design, simulation, optical performance, construction and experimental validation carried out on a novel non-imaging static symmetric reflective compound parabolic concentrator (SRCPC). By considering the seasonal variation of the sun’s position, a concentrating Photovoltaic (CPV) system with precise acceptance angle and low concentrating ratio will be an ideal alternative to conventional flat plate photovoltaic (PV) modules in harvesting the power from the sun. The SRCPC is a suitable choice well designed to achieve optimum precise acceptance angles and concentration ratio for this purpose. The optical performance theory study shows that a truncated symmetric reflective CPC with acceptance half-angles of 0° and 10° (termed as SRCPC-10) is the optimum design when compared with the symmetric reflective CPC designs with acceptance half-angles of 0° and 15° and 0° and 20° in Penryn and higher latitudes. An increase in the range of acceptance angles decreases the concentration ratio but an increase in the range of acceptance angles is achieved by truncating the concentrator profile which will reduce its cost as well. Ray tracing simulations indicates that the SRCPC-10 exhibited the maximum optical efficiency and steady slope compared with others. The simulated maximum optical efficiency of the SRCPC was found to be 94%. In addition, the SRCPC-10 was found to have a more uniform intensity distribution at the receiver and a total daily-monthly energy collection compared to the other designs. Thermal modelling of the CPV system with the SRCPC-10 concentrator shows that the solar cell operating temperature can reach up to 70°C for irradiance of 1000W/m2 at an ambient temperature of 25° at a wind velocity of 2.5m/s. The integration of the thermal management system is able to control and maintain the temperature to 29°C. The modelled thermal and electrical efficiencies were 47% and 15% respectively with a heat transfer coefficient of 54.29W/m2K thereby bringing the system efficiency to 62%. The maximum power of the SRCPC-10 when characterised in an indoor controlled environment using solar simulator was 5.96W at 1000W/m2 at a cooling flow rate of 0.0079L/s with average conversion efficiency of 8.97%. The maximum power at 1200W/m2 and 0.031L/s was 7.14W with conversion efficiency of 10.57%. The maximum increase in efficiency from non-cooling to cooling is 2.54%. The efficiency increased because of cooling is relatively 40%. The outdoor characterisation (validation) of the SRCPC-10 shows that the maximum power was 7.4W at 1206W/m2 on a sunny day. The maximum electrical conversion efficiency of the SRCPC-10 in outdoor conditions was found to be 10.96%. These results revealed that this designed SRCPC-10 is capable of collecting both direct and diffuse radiation to generate power. Therefore, the SRCPC-10 could be used to provide a solution to the increasing demand on electricity to the energy mix, leaving a clean environment for future developments.

As a low concentration concentrator with a larger acceptance angle and without a tracking requirement, compound parabolic concentrator is regarded as an attractive solution to improve the system performance and reduce the cost of photovoltaic (PV) system, solar thermal system, daylighting and lighting systems, etc. As a typical type of three-dimensional compound parabolic concentrator (CPC), dielectric crossed compound parabolic concentrator (dCCPC) has drawn a significant research attention in these years to explore its angular characteristics in solar collection for concentrating photovoltaics and daylighting control in buildings. This thesis provides a comprehensive study on dCCPC in aspect of daylighting control. The work starts from a general review that provides a detailed introduction of the background of CPC applications in solar energy. Then the fundamental property of dCCPC when it is utilized as skylights for daylighting control is investigated, and the performance of dCCPC is also compared to other types of CPC. With the consideration of actual application, the dCCPC panel should be designed as small as possible to reduce its weight and maintain the optical characters simultaneously. Several criteria relating to the dimension of dCCPC panel are proposed and investigated about their effects on the optical performance of dCCPC, followed by the experiments that are taken for validation. As ray-tracing simulation is the most common way to determine the optical performance of dCCPC which provides accurate result but requires long time to run, the multiple nonlinear regression model and artificial neural network model are put forward in the beginning of the second half of this thesis. The coefficients of determination of these models could reach 0.99 which imply the high accuracy of them. The optical performance of dCCPC can be calculated rapidly by knowing the sun position and sky condition. Afterwards, because the performance of dCCPC can be calculated easily for any time and any location with the mathematical model, a case study was taken to investigate the dCCPC effects on building energy consumption, indoor visual environment and economic benefits. This research proves the potential of dCCPC in terms of daylighting control. As a stationary skylight, the transmittance of it is adjusted automatically depending the sky condition and sun position. It also provides outstanding performance in indoor illuminance distribution. The dCCPC is suggested to be used in the locations with long hot seasons for the purpose of energy saving, and it is suggested for all locations with a view to glare control. For further work, more related criteria are encouraged to be added into the prediction models. The method of manufacturing dCCPC is suggested to be improved. Finally, the asymmetric dCCPC is expected to have high potential in daylighting control as vertical building facade, which is worth to be investigated.

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.

Neste trabalho é utilizada a Fotogrametria como ferramenta para avaliação geométrica de concentradores solares térmicos. Coletores do tipo cpc – coletores parabólicos compostos são submetidos a diversas experiências fotogramétricas e avaliados quanto à sua forma. Outros objetos com superfícies refletoras e não refletoras como concentradores solares ptc – parabolic through concentrator e fornos solares também são alvo de experiências fotogramétricas com o objetivo de estudar os efeitos de diferentes tipos de superfícies na fotogrametria. É também comparado o modelo 3D do concentrador ideal com aquele que foi obtido através da fotogrametria, para o que foi feito um estudo exaustivo, verificando as diferenças geométricas entre os dois modelos, bem como os efeitos dessas diferenças físicas na reflexão dos raios solares, ou seja, na energia captada pelo concentrador; Abstract: Geometrical assessment of reflective surfaces using photogrammetry This paper uses Photogrammetry as a tool for the geometric evaluation of solar concentrators. Collectors of the cpc type - compound parabolic collectors are submitted to several photogrammetric experiments and evaluated for their shape. Other objects with reflecting and non-reflecting surfaces such as ptc - parabolic through concentrators and solar ovens are also the subject of photogrammetric experiments to study the effects of different types of surfaces in photogrammetry. There is also a comparison between the 3D model of the ideal concentrator and that obtained by photogrammetry. An exhaustive study was done verifying the geometric differences between the two models as well as the effects of these physical differences in the reflection of the solar rays that represent the energy captured by the concentrator.

Domestic solar hot water units, if properly designed, are capable of providing all hot water needs in an environmentally friendly and cost-effective way. Despite 50 years of development, commercial technology has not yet achieved substantial market penetration compared to mainstream electric and gas options. Therefore, alternate designs are warranted if they can offer similar or greater performance for a comparable cost to conventional units. This study proved that such alternatives are possible by designing and testing two novel solar hot water systems (SHWS). The first system used compound parabolic collector (CPC) panels to concentrate solar energy and produce steam. The steam moved from a rooftop downward into a heat exchange pipe within a ground level water tank, heating the water, condensing and falling into a receptacle. The operation was entirely passive, since the condensate was pulled up due to the partial vacuum that occurred after system cooling. Efficiencies of up to 40% were obtained. The second system used an air heater panel. Air was circulated in open and closed loop configuration (air recycling) by means of a fan/blower motor and was forced across a compact heat exchanger coupled to a water tank. This produced a natural thermosiphon flow heating the water. Air recycling mode provided higher system efficiencies: 34% vs. 27%. The concurrent development of an analytical model that reasonably predicted heat transfer dynamics of these systems allowed 1) performance optimisation for specific input/starting operating conditions and 2) virtual design improvements. The merit of this model lay in its acceptable accuracy in spite of its simplicity. By optimising for operating conditions and parameter design, both systems are capable of providing over 30 MJ of useful domestic hot water on clear days, which equates roughly to an increase of 35°C in a 200 L water tank. This will satisfy, on average, daily hot water requirements for a 4-person household, particularly in low-latitude regions (eg. Queensland). Preliminary costing for these systems puts them on par with conventional units, with the passive, remotely coupled, low maintenance, CPC SHWS comparable to higher end models. The air heater SHWS, by contrast, was much more economical and easier to build and handle, but at the trade-off cost of 1) the need for an active system, 2) increased maintenance and running costs and 3) the requirement for a temperature control mechanism that would protect the panel body by dumping hot air trapped inside if stagnation were to occur.

Domestic solar hot water units, if properly designed, are capable of providing all hot water needs in an environmentally friendly and cost-effective way. Despite 50 years of development, commercial technology has not yet achieved substantial market penetration compared to mainstream electric and gas options. Therefore, alternate designs are warranted if they can offer similar or greater performance for a comparable cost to conventional units. This study proved that such alternatives are possible by designing and testing two novel solar hot water systems (SHWS). The first system used compound parabolic collector (CPC) panels to concentrate solar energy and produce steam. The steam moved from a rooftop downward into a heat exchange pipe within a ground level water tank, heating the water, condensing and falling into a receptacle. The operation was entirely passive, since the condensate was pulled up due to the partial vacuum that occurred after system cooling. Efficiencies of up to 40% were obtained. The second system used an air heater panel. Air was circulated in open and closed loop configuration (air recycling) by means of a fan/blower motor and was forced across a compact heat exchanger coupled to a water tank. This produced a natural thermosiphon flow heating the water. Air recycling mode provided higher system efficiencies: 34% vs. 27%. The concurrent development of an analytical model that reasonably predicted heat transfer dynamics of these systems allowed 1) performance optimisation for specific input/starting operating conditions and 2) virtual design improvements. The merit of this model lay in its acceptable accuracy in spite of its simplicity. By optimising for operating conditions and parameter design, both systems are capable of providing over 30 MJ of useful domestic hot water on clear days, which equates roughly to an increase of 35°C in a 200 L water tank. This will satisfy, on average, daily hot water requirements for a 4-person household, particularly in low-latitude regions (eg. Queensland). Preliminary costing for these systems puts them on par with conventional units, with the passive, remotely coupled, low maintenance, CPC SHWS comparable to higher end models. The air heater SHWS, by contrast, was much more economical and easier to build and handle, but at the trade-off cost of 1) the need for an active system, 2) increased maintenance and running costs and 3) the requirement for a temperature control mechanism that would protect the panel body by dumping hot air trapped inside if stagnation were to occur.

Baigiamajame magistro darbe suprojektuotos ir pagamintos dviejų rūšių šviesos koncentratorinės sistemos: jungtinė parabolinė ir sistema su Frenelio lęšiu. Atlikta saulės elementų efektyvumo analizė, išnagrinėtos šviesą koncentruojančių sistemų rūšys bei aptarti jų optiniai parametrai. Frenelio lęšis ir koncentratorinių sistemų laikančiosios konstrukcijos pagamintos vakuuminio formavimo būdu, ieškant pigesnės gamybos technologijos. Baigiamajame darbe atlikti optinio pralaidumo ir lūžio rodiklio, matomos šviesos bangų ilgių ruože, tyrimai bei saulės elementų, esančių šviesos koncentratorinėse sistemose,voltamperinių ir voltvatinių charakteristikų tyrimai. Iš tyrimų rezultatų nustatyti šviesos koncentravimo laipsniai. Darbe diskutuojama apie pigių optinių sistemų galimus pritaikymus ir jų tobulinimo būdus. Išnagrinėjus teorinę ir praktinę dalis, pateiktos išvados ir pasiūlymai. Darbą sudaro 8 dalys: įvadas, saulės elementų efektyvumo ribos, saulės šviesos koncentratoriai ir jų panaudojimas fotoelektrinėse sistemose, eksperimentinių tyrimų metodika, prototipų gamyba, eksperimentiniai tyrimai, išvados, literatūros sąrašas. Darbo apimtis – 82 p. teksto be priedų, 95 pav., 13 lent., 22 bibliografiniai šaltiniai. Atskirai pridedami darbo priedai.
Concentrated PV systems (compound parabolic and Fresnel CPV) have been designed and investigated. The efficiency of solar cells and the types of light concentrated systems have been analyzed and their optical parameters have been discussed. Fresnel lens and the CPV system holding structure have been fabricated by means of vacuum forming machine in this way making the technology of production less expensive. Optical transmittance and refractive index of Fresnel lens were measured in the range of visible light wavelengths. Current-voltage and voltage-power characteristics of solar cells built inside the CPV systems were investigated, based on results the degree of light concentration by Fresnel lens and compound parabolic CPV has been determined. Some discussions regarding possible applications of concentrated PV systems containing the Fresnel lens as well as possible ways of CPV design improvements are given in current work. After analysed theoretical and practical parts, conclusions and suggestions are proposed. Thesis structure: introduction, theoretical and experimental parts, results of experiments, conclusions and references. Thesis consist of: 82 p. text without appendixes, 95 pictures, 13 tables, 22 bibliographical entries. Appendixes included.

Os processos oxidativos avançados (POAs) têm sido apontados como alternativa eficiente para a degradação de poluentes recalcitrantes. Entre os POAs, a fotocatálise utilizando luz solar vem sendo muito estudada tendo em vista sua aplicação no tratamento de efluentes aquosos contendo pesticidas. No presente trabalho, estudou-se a degradação do herbicida amicarbazona (AMZ) por meio do processo TiO2/UV em um reator com coletores parabólicos compostos irradiados por luz solar. Os experimentos foram realizados segundo uma matriz Doehlert para o estudo da influência da concentração inicial de AMZ (20-100 mg L-1), da concentração de catalisador (0,1-1 g L-1) e do número de tubos expostos à luz solar (1-9). Amostras retiradas ao longo do tempo foram analisadas quanto às concentrações de AMZ e de carbono orgânico total (TOC). As medidas radiométricas realizadas indicaram que a radiação UVB-UVA correspondeu em média a ca. 4% da radiação solar total incidente entre 310-2800 nm; a actinometria de ferrioxalato indicou fluxo fotônico médio de 3,58×10-5 mol fótons m-2 s-1 para dias ensolarados típicos. O processo TiO2/UV mostrou-se eficiente para degradação do pesticida, que foi totalmente removido antes de 45 minutos de tratamento, para as seguintes condições: [AMZ]0=21,3 mg L-1; [TiO2]=0,5 g L-1; e 7 tubos. Contudo, nesse caso houve apenas ca. 24% de mineralização e na grande maioria dos casos os valores de TOC permaneceram praticamente constantes, o que indica a formação de sub-produtos recalcitrantes, cuja toxicidade e biodegradabilidade devem ser caracterizadas. A análise estatística dos resultados confirma os efeitos importantes da concentração inicial do pesticida e do número de tubos expostos (volume irradiado), cujo aumento permite compensar a menor incidência de radiação solar. Em alguns experimentos os resultados sugeriram que a degradação da AMZ foi favorecida pela maior concentração de TiO2. Na grande maioria dos casos os valores de ACM foram inferiores a 50 m2 kg-1, o que torna este parâmetro interessante para aumento de escala de processos fotocatalíticos irradiados por luz solar empregados no tratamento de efluentes aquosos contendo amicarbazona.
Advanced oxidative processes (AOP) have been considered as an efficient alternative for the degradation of recalcitrant pollutants. Photocatalysis using solar radiation has been studied for the treatment of wastewaters containing pesticides. In this work, the degradation of the herbicide amicarbazone (AMZ) by the TiO2/UV process was studied in a reactor equipped with compound parabolic collectors irradiated by solar light. The experiments were carried out according to a Doehlert matrix to study the effects AMZ initial concentration (20-100 mg L-1), catalyst concentration (0.1-1 g L-1), and number of tubes exposed to solar light (1-9). Samples were analyzed for AMZ and total organic carbon (TOC) concentrations. Radiometric measurements indicated that UVB-UVA radiation corresponded in average to about 4% of the solar radiation between 310-2800 nm; ferrioxalate actinometry resulted in an average photonic flux of 3.58×10-5 mol fótons m-2 s-1 for typical sunny days. The TiO2/UV process showed to be efficient for the degradation of the pesticide, which was completely removed before 45 minutes of treatment, for the following conditions: [AMZ]0=21.3 mg L-1; [TiO2]=0.5 g L-1; and 7 tubes. However, in this case only ca. 24% of mineralization was achieved, and in most cases TOC values remained practically constant, indicating the formation of recalcitrant by-products whose toxicity and biodegradility should be characterized. Statistical analysis of the results confirmed important effects of pesticide initial concentration and number of tubes exposed (irradiated volume), whose increase enables to compensate the lower incidence of solar radiation. Some experimental results suggested that AMZ degradation was favored by higher TiO2 concentrations. In most cases the values of ACM were lower than 50 m2 kg-1, in such a way that this parameter is interesting for scale-up of solar irradiated photocalytic processes used in the treatment of amicarbazone-containing wastewaters.

博士
國立中央大學
光電科學與工程學系
101
This paper discusses the application of the compound parabola concentrator to optical engineering. It emphasizes especially the replacement of the common design of the projection system for the acquirement of a better structure of a projector. This paper also discusses the compound parabola concentrator as the baffle of a space camera, and the baffle’s containing the environmental stray light within the margin of error tolerated by the space camera through absorbing and reflecting the stray light to acquire the point source transmittance that meets the requirements. A new type of optical engine suitable for DLP is brought up in this paper: an optical engine equipped with LEDs to replace UHP for reducing energy consumption, and the compound parabola concentrator is adopted in this engine to replace the light tube for reducing the engine’s volume. Through the verification of simulation, we acquired the results corresponding with the performance of the traditional DLP optical engine and thus proved that the optical engine designed in this paper can replace the traditional one. Furthermore, this newly-designed optical engine is smaller and saves more energy. This paper in the end presents a sort of new-type optical engine suitable for the technology of DLP projection: an optical engine using electronically-controlled colored LEDs to replace UHP for reducing energy consumption and to replace the color wheel for the electronic circuit to be able to completely control the color output of DLP, and a compound parabola concentrator is adopted in this optical engine to replace the light tube for reducing the engine’s volume. The newly-designed optical engine verified by the software can replace the traditional type. This new-type of optical engine is smaller, saves more energy and achieves higher color management.

M.Ing.
A dissertation presented on the basic solar design principles such as sun-earth geometry, energy wavelengths, optics, incidence angles, parabolic collector configurations and design, materials for solar applications, efficiencies, etc to be considered in Solar Concentrating Collector design. These principles were applied in the design and fabrication of a prototype solar collector. The solar collector was tested to verify and correct mathematical models that were generated from existing literature; as well as for optimization work.

A batch heater is an integrated collector storage unit wherein the absorber serves the dual purpose of a collector and storage unit. The present experimental work is an integration of the older concept of batch water heating with the modern trends in solar water heating technologies i.e. incorporating a concentrator in the design. The concentrator used here is the Compound Parabolic Concentrator (CPC) which is a non-imaging device having wider acceptance angle. It requires only occasional tracking and thus can be best suited for household purposes. The concentrator i.e. the reflector, in this case, is supported on a wooden cradle which comprises the two parabolas of the compound parabolic concentrator. While Batch Solar Water Heater (BSWH) facilitates easy installation, operation, and maintenance besides providing cost reduction it operates at much lower daily collection efficiencies as compared to separate storage tank facilities. The focus of the study is therefore to obtain good heat retention and better long time performance estimates and in accordance, changes have been made in the design in addition to the use of CPC concentrator. In the present work, experimental studies have been carried out and mean collector efficiency is computed on the model with an air gap introduced in the side walls (arms of the CPC). Unlike conventional systems with a large number of smaller diameter tubes, here is a single larger diameter drum which serves both as an absorber and storage unit positioned at the focus of CPC. The system works on thermosyphon principle, unlike conventionally forced circulation domestic water heating systems. The system as a whole operates at a lower temperature which reduces the overall convective and radiative losses and increases useful heat gain. The parametric study of the theoretical design by EES hovering before and after solar noon is in good agreement with experimental results with the thermal efficiency of the collector as high as 38% obtained and with water temperatures varying from 40oC to 60oC depending upon the time of the year. The key aspect is its heat retention capability which can prolong high temperatures attained for longer hours after v dusk. This model shows better performance compared to a similar model designed and developed but without an air gap. Heat loss tests performed on the collector on a 24-hour cycle period showed good long time performance estimates. Collector characterization parameters are obtained by performing thermal performance tests on the collector, under conditions meeting ASHRAE specifications for outdoor tests. The response time of collector computed and performance characteristic curve plotted to predict system response under any given conditions of solar insolation and ambient temperature. The economic figures of merit of the model are also obtained by f-chart design method and using EES software. The proposed model has low initial cost and better long time thermal performance estimates. The annual solar fraction for the model is 0.55 and the payback period is two years. Comparative studies with similar models show its competency based on collector efficiency and economic viability. Highlights  Passive system employed in comparison to the conventional active systems for household applications.  Introduction of a concentrator in domestic solar water heating system.  No usage of Transparent insulation material (TIM) or Phase change material (PCM), heat retention obtained by introducing an air gap, without adding to the cost of collector.  Better adaptability for metro cities like Delhi, where roof space is a major constraint for installation of flat plate collectors.  Economically viable