Sub-Saharan Africa has an underutilised solar resource that is available to provide distributed-scale power to rural communities that are not reached by the current grid systems that are in place. Renewable power generation systems are typically infeasible for this purpose due to their high manufacturing and maintenance costs. This research proposes to address this by experimentally investigating the performance of a micro-scale, solar thermal Rankine cycle with direct steam generation using an affordable solar collector design. The intended power generation range is between 0.1 and 1 kW, which can be used for the direct mechanical pumping of rural irrigation systems or municipal water supplies. The study focuses on the performance of the solar collector (the solar reflector and the solar receiver) under realistic solar thermal conditions in sub-Saharan Africa, as it is considered to be one of the most important components in the solar thermal Rankine cycle. The performance of the solar collector was first characterised in an optical analysis of the new faceted dish reflector design, which comprised six Mylar membranes stretched over the elliptical rims of television satellite dishes. The optical analysis was conducted with the main goal of determining how much concentrated solar radiation would intercept the experimental receiver aperture during solar testing. This was determined by measuring the reflectivity of the reflector facets through ultraviolet and visible light (UV-VIS) spectroscopy and producing an intercept factor trend as a function of receiver aperture size through photographic lunar flux mapping. Based on the spectroscopy analysis, the spectral reflectivity of the clean Mylar facets was determined to be 97% for the visible light spectrum. The intercept factor was determined to be 87% for the designed receiver aperture diameter of 135 mm. The thermal testing took place on a clear, sunny day with low wind velocities. The solar collector followed the arc of the sun throughout the day with a 1° tracking error. During the testing, municipal water was passed through the receiver at 0.284 g/s and the temperature and pressure within the receiver were recorded. A 91-minute testing period occurred, where the inlet and outlet process flows obtained relatively constant operating temperatures with the inlet temperature at 54 °C and the outlet temperature at 343 °C. The total solar irradiance dropped from 801 to 705 W/m2 during this testing period. Using a reflector with a total incident area of 2.73 m2, the total radiation intercepted at the aperture dropped from 1 845 to 1 625 W during this period. The total power capture by the working fluid averaged at approximately 861 W and the total rate of heat loss was determined to be between 1 000 and 750 W. An average collector efficiency of 42% and an average receiver efficiency of 49% were determined for the testing period. An analysis of the heat loss showed that approximately 84% of the heat was lost through the aperture, of which, 31% was from reflected radiation. The second-law analysis showed that most of the irreversibility in the solar collector was caused by absorption of the concentrated radiation at the coil surface. This was because of the large temperature difference between the sun and the receiver coils. The experimental thermal analysis highlighted the design challenges of the micro-scale thermal Rankine cycle. However, the analysis showed that a solar collector can be constructed using locally sourced, affordable materials and can be used to produce power at a micro-scale. With appropriate attention given to optimising the collector design and determining the optimum operating conditions of the solar receiver, the power cycle would be able to compete with current technologies to provide decentralised power to communities in need. / Dissertation (MEng)--University of Pretoria, 2019. / Technology Innovation Agency (TIA); National Research Foundation (NRF); Department of Science and Innovation (DSI) / Mechanical and Aeronautical Engineering / MEng (Mechanical) / Unrestricted

Uncertainty analysis is crucial to any thorough analysis of an engineering system. Traditional uncertainty analysis can be a tedious task involving numerous steps that can be error prone if conducted by hand. If conducted with the aid of a computer, these tasks can be computationally expensive. In either case, the process is quite rigid. If a parameter of the system is modified or the system configuration is changed, the entire uncertainty analysis process must be conducted again giving more opportunities for calculation errors or computation time. Modular uncertainty analysis provides a method to overcome all these obstacles of traditional uncertainty analysis. The modular technique is well suited for computation by a computer which makes the process somewhat automatic after the initial setup and computation errors are reduced. The modular technique implements matrix operations to conduct the analysis. This in turns makes the process more efficient than traditional methods because computers are well suited for matrix operations. Since the modular technique implements matrix operations, the method is adaptable to system parameter or configuration modifications. The modular technique also lends itself to quickly calculating other uncertainty analysis parameters such as the uncertainty magnification factor, and the uncertainty percent contribution. This dissertation will focuson the modular technique, the extension of the technique in the form the uncertainty magnification factor and uncertainty percent contribution, and the application of the modular technique to different type of energy systems. The modular technique is applied to an internal combustion engine with a bottoming organic Rankine cycle system, a combined heat and power system, and a heating, ventilation, and air conditioning system. The results show that the modular technique is well suited to evaluate complex engineering systems. The modular technique is also shown to perform well when system parameters or configurations are modified.