Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2005. / Parabolic trough solar collectors (PTSCs) constitute a proven source of thermal energy for industrial process heat and power generation, although their implementation has been strongly influenced by economics. In recent years, environmental concerns and other geopolitical factors have focused attention on renewable energy resources, improving the prospects for PTSC deployment. Further work is needed to improve system efficiencies and active areas of research include development of advanced heat collecting elements and working fluids, optimisation of collector structures, thermal storage and direct steam generation (DSG). A parabolic trough collector, similar in size to smaller-scale commercial modules, has been developed locally for use in an ongoing PTSC research programme. The aim of this study was to test and fully characterise the performance of the collector. Specialised logging software was developed to record test data and monitor PTSC performance in real-time. Two heat collecting elements were tested with the collector, one unshielded and the other with an evacuated glass cover. Testing was carried out according to the ASHRAE 93-1986 (RA 91) standard, yielding results for the thermal efficiency, collector acceptance angle, incidence angle modifier and collector time constant. Peak thermal efficiency was 55.2 % with the unshielded receiver and 53.8 % with the glass-shielded unit. The evacuated glass shield offered superior performance overall, reducing the receiver heat loss coefficient by 50.2 % at maximum test temperature. The collector time constant was less than 30 s for both receivers, indicating low thermal inertia. Thermal loss tests were conducted and performance of the trough’s tracking system was evaluated. The measured acceptance angles of 0.43° (unshielded) and 0.52° (shielded) both exceeded the tracking accuracy of the PTSC, ensuring that the collector operated within 2 % of its optimal efficiency at all times. Additionally, experimental results were compared with a finite-volume thermal model, which showed potential for predicting trough performance under forced convection conditions.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2000. / A solar chimney power plant consists of a central chimney that is surrounded by a transparent canopy located a few meters above ground level. The ground beneath this canopy or collector as it is known is heated by the solar radiation that is effectively trapped by the collector. This in turn heats the air in the collector, which flows radially inwards towards the chimney. This movement is driven by the difference between the hydrostatic pressure of the air inside- and outside the solar chimney system. The energy is extracted from the air by a turbine driven generator situated at the base of the chimney. The performance of such a solar chimney power plant is evaluated in this study making use of a detailed mathematical model. In this model the relevant discretised energy and draught equations are deduced and solved to determine the performance of a specific plant referred to as the "reference plant". This plant is to be located at a site near Sishen in the Northern Cape in South Africa where meteorological data is available. The performance characteristics of this plant are presented using values from the 21 st of December as an example. These characteristics include the instantaneous and integrated power output, as well as the absorption of the solar radiation of each of the parts of the collector. The air temperatures throughout the plant and the convective heat transfer coefficients in the collector in the region of developing and fully developed flow are presented. The pressure of the air throughout the system is presented as well as the pressure drop over the turbine. Temperature distributions in the ground below the collector are also presented and discussed.

Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2002. / This project investigates the performance of solar chimney power plant turbines. A solar chimney power plant consists of a tall chimney surrounded by a transparent deck or solar collector. The sun heats the air in the collector through the greenhouse effect. A turbine extracts energy from the hot air rising up the chimney. An investigation of the requirements and operation of such turbines is needed. Correct matching of the turbine to the plant requires the determination of the turbine operational range and other requirements. An air-standard cycle analysis is extended to include component and system losses. Simple steady-state and transient collector models are added to take into account the coupling effect of the collector air temperature rise and mass flow rate on the turbine operation. The predicted turbine operational range for a representative day shows that the expected pressure drop in a full-scale solar chimney turbine is significantly higher than has previously been predicted. A turbine design method is developed and used to design a turbine for the representative day. The methods can easily be extended to include more operating points for a full year of operation. A turbine layout is suggested that uses the chimney support pillars as inlet guide vanes (IGVs). These introduce pre-whirl to the turbine and reduce the amount of exit whirl thus decreasing the kinetic energy at the turbine exit. Non-radial inlet guide vanes add to the torsional stiffness of the chimney base. A matrix throughflow method is used to design the radial to axial duct between the IGVs and rotor. The turbine blade profiles are simulated using a surface-vortex method. This is coupled to an optimisation scheme that minimises both the chord length and maximum flow velocity of the profile to reduce blade drag. An experimental program investigates the performance of the turbine. Volume flow, pressure drop, torque and speed are measured on a scale model turbine to map the turbine performance over a wide range. The velocity and pressure profiles are measured at two design points to investigate the flow through the turbine in more detail. These are compared to the design predictions and used to improve the design method. The experiments show that the design of a solar chimney turbine with a total-to-total efficiency of 85 % - 90 % and total-to-static efficiency of 75 % - 80 % is possible. Analysis of the experimental results shows that the turbine efficiency can be improved.

A novel and original category of low-cost static solar-daylighting-collectors named Keywo solar energy, solar collectors, daylighting systems, nonimaging optics, Refractive Integrated Nonimaging Solar Collectors (RINSC) has been designed and thoroughly tested. The RINSC category is based on nonimaging optics and integrates several optical elements, such as prismatic arrays and light guides, into a single-structured embodiment made of solid-dielectric material. The RINSC category is sub-divided in this thesis into four distinctive and original sub-categories/systems: Prismatic Solar Collectors (PSC), Multi-Prismatic Solar Collectors (MPSC), Integrated Multi-Prismatic Solar Collectors (IMPSC) and Vertically Integrated Nonimaging Solar Collectors (VINSC). The optical configuration and compact embodiment of these systems allows them to be integrated into a building façade without creating any protrusion, indicating that they can lead to solar collector systems with high building integration potential. Laboratory and outdoor experimental tests conducted with a series of demonstration prototypes made of clear polymethyl-methacrylate (PMMA) and manufactured by laser ablation process, yield peak transmission efficiencies TE varying from 2% to 8%. Computer simulations indicated that transmission efficiencies TE > 30% are possible. The design and development of the innovative optical systems introduced in this thesis were backed-up with extensive computer ray-tracing analysis, rapid-prototyping, laboratory and outdoor experimental tests. Injection moulding computer simulations and surface analysis concerning the development of the RINSC systems were also conducted. Basic theory and comprehensive literature review are presented. This research has also resulted in the design and prototyping of a novel optical instrumentation named Angular Distribution Imaging Device (ADID), specially developed to analyse the spatial distribution of light emerging from the exit aperture of solar collectors/concentrators. The systems and knowledge described in this thesis may find application in areas such as solar collector systems to harvest sunlight for natural illumination in buildings, solar-photovoltaic and solar-thermal.

Abstract not available

This research investigates the collection of concentrating solar energy and its transmission through optical fibres for use in high temperature applications such as lunar in-situ resource utilisation (ISRU) programmes, solar power generation and solar surgery. A prototype collector, known as the Fibre Optic Concentrating Utilisation System (FOCUS), has been developed and is capable of delivering high energy fluxes to a remote target. Salient performance results include flux concentrations approaching 1000 suns with an overall optical efficiency of 13%, measured from the inlet of the collector to the fibre outlet. The system comprises a novel solar concentrator designed to inject solar energy into a four metre long fibre optic cable for the transmission of light to the target. A nonimaging reflective lens in the form of a 600 mm diameter ring array concentrator was chosen for the collection of solar energy. Advantageous characteristics over the more common parabolic dish are its rearward focusing capacity and single stage reflection. The ring array comprises a nested set of paraboloidal elements constructed using composite material techniques to demonstrate a low-cost, effective fabrication process. At concentrator focus, a fibre optic cable of numerical aperture 0.37 is positioned to transport the highly concentrated energy away from the collector. The cable is treated to withstand UV exposure and high solar energy flux, and allows flexibility for target positioning. A computational analysis of the optical system was performed using ray tracing software, from which a predictive model of concentrator performance was developed to compare with experimental results. Performance testing of FOCUS was conducted using energy balance principles in conjunction with a flat plate calorimeter. Temperatures approaching 1500°C and flux levels in the region of 1800 suns were achieved before injection to the cable, demonstrating the optical system's suitability for use in high flux applications. During testing, peak temperatures exceeding 900°C were achieved at the remote target with a measured flux of 104 W/cm2 at the cable outlet. The predicted optical efficiency was 22%, indicating that further refinements to the ray trace model are necessary, specifically with regard to losses at the inlet to the cable. FOCUS was able to demonstrate its usefulness as a test bed for lunar in-situ resource utilisation technologies by successfully melting a lunar soil simulant. The system permits further terrestrial-based ISRU research, such as oxygen production from regolith and the fabrication of structural elements from lunar soil. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

The Monte Carlo-type statistical ray-tracing method was used to investigate the performance of the line-focusing Fresnel mirror solar concentrator. An optical model of the line-focusing Fresnel mirror concentrator using the statistical ray-tracing approach was developed. Many rays of sunlight from the solar disk were selected at random and traced through the concentrator in this model. This optical model permits calculation of the local and geometric concentration ratios. The latter requires an energyloss analysis. Small sun-tracking errors of the diurnal or transverse type were included in the model.Based on the optical model and the Monte Carlo-type statistical ray-tracing method, a computer program was written implementing the model and computations using Pascal. To facilitate performance comparisons, a baseline concentrator design was adopted. To study the effects of imperfect tracking, performance data were generated for small tracking errors up to approximately two and one-half degrees. The selected mirror configuration permitted comparisons between the statistical approach and previous applications of the "extreme ray" analysis for an imperfectly tracking mirror concentrator.Simulation results demonstrated that the concentration characteristics are highly sensitive to the tracking error. The geometric concentration ratio dramatically decreases when the tracking error increases, which is the same as the "extreme ray" analysis. Results of some typical numerical calculations are presented graphically and discussed. / Department of Physics and Astronomy

The solar concentration performance of a tracking, flat-base, line-focusing Fresnel mirror was investigated in this study. The Fresnel mirror consists of flat mirror strips situated on a base and oriented at appropriate angles to focus incident light to a desired line. Simple optical ray tracing and energy conservation were used to develop a mathematical model of the concentrator assuming small or zero diurnal tracking errors. The model analyzed the concentrator design and provided detailed expressions for the geometric evaluation of the concentrated sunlight rays in the focal plane above the mirror. The local concentration ratio and the geometric concentration ratio were introduced to describe the intensity profile in the focal plane and the average concentration of sunlight on a target absorber. Included in the model were losses of incident sunlight due to imperfect reflection, nonreflecting portions of the base, and blockage by adjacent mirror strips when imperfect tracking occurs.Based on the analytical model and using the Ada high level language, a computer program was written to simulate the concentrator. To facilitate performance comparisons, a baseline concentrator design was adopted. To study the effects of imperfect tracking, performance data were generated for small tracking errors up to approximately two and one-half degrees. The effects of design variations were studied by varying the concentrator focal length, strip width, and base width.Simulation results demonstrated that the concentration characteristics were highly sensitive to tracking error. Intensity profile shifts relative to the target caused the highest losses in intercepted sunlight.Design decisions were found to dramatically affect the concentration character- istics. For the baseline concentrator under perfect tracking conditions, an optimum focal length was identified. Except for the disadvantage of added costs, decreased strip widths was found to be a way to increase both the maximum and average concentration ratio for the absorber. Using smaller strip widths might, however, critically affect the energy intercepted by the target under imperfect tracking. Increasing the concentrator base width increased the total amount of power in the focal plane, with a higher maximum concentration ratio and additional tailing of the intensity profile. / Department of Physics and Astronomy

Tez (Yüksek Lisans) - Süleyman Demirel Üniversitesi, Fen Bilimleri Enstitüsü, Makina Eğitimi Anabilim Dalı, 2008. / Bibliyografya var.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Sheldon Jeter; Committee Member: Sam Shelton; Committee Member: Srinivas Garimella