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Unglazed transpired solar collectors (UTSCs) preheat makeup ventilation air for buildings, thereby reducing energy used for heating. The performance of the UTSC is dependent on the heat loss from the absorber plate, which is strongly affected by the wind speed. To date, correlations to determine UTSC heat loss are limited to flat or sinusoidal plate corrugations. In reality, trapezoidal corrugations have been added to UTSCs to provide them with structural stiffness. These corrugations prevent the attachment of the flow to the absorber plate and cause flow separation which increases the heat loss. In this study, a numerical simulation of a UTSC with trapezoidal shape corrugation has been performed to investigate the heat loss in the developing region due to wind on the UTSCs. It has been found that heat loss from new configuration is up to three times greater than the heat loss from a perforated flat absorber plate. A correlation of heat loss due to the wind speed and suction velocity was developed. This study also includes an evaluation of the effectiveness in the asymptotic region. In this case, wind speed had no effect. A correlation was derived in terms of suction velocity.

Thesis (Ph.D.)--Australian National University, 2004.

Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 131-132).

M.Ing. / The focus of the document is the development and use of an algorithm that controls a heliostat, and the high level design of that heliostat. The heliostat is only controlled by the algorithm and had a specified accuracy requirement equal to or better than 0.5 degrees. The algorithm uses the elevation and azimuth angle of sun calculated to an accuracy of 0.0003 degrees as input. The algorithm positions the heliostat to ensure a continuous reflection of sunlight into a predetermined direction for the purpose of indoor illumination. The position of the sunlight reflected into the predetermined direction is marked on a vertical grid-board placed orthogonal to the intended reflection direction. Ideally the sunlight positions marked throughout the day will all be in one location. The reflected sunlight deviated from the intended direction by only 0.28 degrees.

The concept of a cavity absorber for use with a focusing parabolic trough is developed in this paper. A mathematical model is formulated and used to compare different absorber geometries. Limitations of the model are discussed and within the range of materials and fabrication methods available, the choice of a cylindrical cavity is substantiated. Relative sizes of the gap and cylinder are chosen for a given mirror arc length, focal length, and alignment error. The model is used to optimize these parameters and predict absorber and collector efficiency. The processes of building and testing the absorber are detailed, and test results are reported. Observed performance is significantly below that predicted. Mirror alignment errors are considered the most likely reason for the discrepancy. Other possible improvements to the experiment are suggested.

Two types of solar collecting systems are frequently employed--flat plate collectors with spectrally selective windows which trap sunlight with the "greenhouse effect" and focusing systems with curved mirrors which concentrate the sun's rays on an absorbing surface. The flat plate collector is the simpler of the two designs, but cannot readily provide temperatures as high as the focusing collector. Both of the collectors are candidates for absorption cycle solar air conditioning systems. This role dictates higher temperature than are normally required of solar collectors, particularly the flat plate design. Focusing systems of interest here are those which are fixed in orientation and require no elaborate solar tracking mount. Such collectors might be economically competitive with flat plate configurations if the higher energy "quality" or delivery temperature they can provide permitted a smaller installation than would be possible with a flat plate collector. An analysis of the two collector candidates is undertaken here to assess the merits of a fixed orientation focusing collector and a more traditional flat plate system. This analysis indicates that the focusing design is superior to the flat plate for solar air conditioning. The study of the two designs includes selection of system configurations and the development of their mathematical descriptions. The analytical approach was to incorporate mathematical models of the collectors into a computer program which predicts the performance of both the flat plate and focusing systems. The program has been designed to permit convenient variation of important parameters so that their effect on collector performance may be determined. The results of the collector analysis and the computer program are presented with sufficient information to permit the reader to use the program for his own analyses.

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.

A cylindrical-parabolic solar collector was thermally optimized for a winter season using a weather model and an extension of the present state-of-the-art collector theory. An accurate model for the cover transmittance and a seasonal performance model was developed. The optimum collector dimensions and materials were found to be a strong function of the design operating temperatures. The optical and thermal losses of a cylindrical-parabolic collector were compared and the results showed that the major loss for process heating temperatures was heat lost by natural convection. Reflection and cover losses were the next largest losses. Comparison of a flat-plate collector with a cylindrical-parabolic collector showed that a cylindrical-parabolic collector appears better suited for process heating than domestic hot water or space heating. Glass and plastic covers were analyzed and the optimum collector slope was obtained. The investigation resulted in a better understanding of how different collector dimensions and materials affect collector performance. / Master of Science

An analytical and experimental investigation was undertaken to evaluate a proposed method for determining the thermal degradation of materials used in flat-plate solar collectors. The proposed method is based on measuring stagnation (no-flow) temperatures of the absorber plate. A comparison of the advantages and limitations of the proposed method is made with the conventionally used existing method which is based on measuring the energy output from the collector. Previous investigations have shown that the existing test method may not be sufficiently sensitive to detect expected changes in material properties, is influenced by the test environment, and is relatively expensive to perform. The material properties of interest are primarily the cover transmittance, the solar absorptance of the absorber, the infrared emittance of the absorber, and the thermal conductivity of insulation. Experimental results were obtained from both on and off-campus test sites. The data includes those from solar simulator tests and indoor tests using a highly instrumented solar collector. This indoor collector was equipped with electrical strip heaters mounted on the backside of the absorber plate to simulate the absorbed solar radiation in a controlled environment. The experiments included an investigation of four techniques for measuring the absorber stagnation temperature. Steady-state and transient analytical models are developed to evaluate stagnation temperature test methods. These models are validated using extensive experimental data. The proposed method is based on measuring stagnation temperatures before and after prolonged exposure to prevailing environmental conditions. While these measurements are simpler than those required in the energy output method, other.factors, such as transient effects, are important for outdoor tests. Test methods using instantaneous and allday integrated stagnation temperatures are considered. Both of these test methods were shown to be highly sensitive to environmental conditions. Wind speed was shown to potentially have the most serious influence on results. The measured temperature distribution of the absorber plate was shown to be highly nonisothermal as a result of collector edge heat losses and thermal stratification of the air underneath collector covers. Instantaneous measurements were observed to be very sensitive to transients as a result of intermittent cloud cover. All-day integrated measurements were not affected by such transients. The investigation revealed that proposed stagnation temperature test methods have potential in determining collector property changes after environmental exposure. Results indicate that the proposed method is more sensitive to small property changes than the current energy output method. However, variations in environmental conditions should be limited or taken into account when using stagnation temperature test methods. / Ph. D.