Includes references (sheets 167-194)

Thesis (Ph.D)--Cyprus International University Institute of Graduate Studies and Research Energy Systems Engineering Department

ABSTRACT
Humanity is required to move a vast majority of its energy needs to sustainable and renewable energy sources. Therefore, it is important that we continually improve the energy production and cost efficiencies of these renewable energy sources.
Solar thermal collectors can help to solve both domestic thermal application and industrial electricity consumption. While significant progress has been made in solar collector engineering; the invention of nanofluids presents a unique opportunity to improve the thermal performance of solar collectors considerably. It is therefore important to find the most ideal heat transfer nanofluid that optimizes thermodynamic performance, cost and material availability. This study contributes to this goal by investigating the thermophysical properties of different novel hybrid nanofluids. The study also presents intelligent ways to predict the thermal conductivity of the hybrid nanofluids using adaptive neuro-fuzzy inference system and multilayer perceptron artificial neural network. In addition, the study presents a simulation analysis to find out the effects of the nanofluid particle mixture ratio on the thermal efficiency of the FPC. To ensure accuracy in simulation, correlation models were developed for thermal conductivity, viscosity, and the specific heat capacity properties of the hybrid nanofluids. Metrological data, obtained for Nicosia Cyprus was used to observe the effects of temperature, volumetric concentration, mass flow rate, and nanoparticle mixture ratios on the thermal efficiency of the FPC as well as the economic viability of using nanofluids in the system. Al2O3-ZnO water nanofluid and Al2O3-Fe water nanofluid were used in these investigations. These particles were used because they are chemically inert, cheap and can be obtained from the environment. Al2O3 is also commonly used in literature, which allows us to validate the results between the hybrid nanofluid and Al2O3 nanofluid. The results from this study as particularly significant in that the hybrid nanofluids show an unexpected phenomenon when the mixture ratio of the particles present the hybrid nanofluid are equal. This unique effect observed in the thermophysical properties allows hybrid nanofluid to perform better as heat transfer fluids in collectors. When compared to water, the average thermal efficiency enhancement of the Al2O3-ZnO water hybrid nanofluid at 1:1, 1:2 and 2:1 mixture ratio was 7%, 5%, and 4.5% respectively at fluid inlet temperatures between 250C and 500C.