Experimental investigation and mathematical modelling of dynamic equilibrium of novel thermo-fluids for renewable technology applications.

Abstract

Environmental issues such as air and water pollutions and climate change can be linked to the fossil fuels being still the main source for human activities and therefore, its intensive consumption. As a result, there is a clear need to utilise alternative and clean energy sources to address these environmental problems. Solar thermal energy has a potential to diminish the dependency on fossil fuels and reduce CO2 emissions in which solar radiation is converted to heat via a thermal fluid for power and heat generation. Medium and high-temperature solar thermal systems where concentrated collectors are employed have been utilised for power generation, whereas low-temperature solar systems where non-concentrated collectors such as flat plate are employed have been used for heat generation. A review of the literature indicates that by using an appropriate thermal fluid, the generation of power and heat is possible via low-temperature solar thermal systems. It can also be revealed from the literature that when selecting a thermo-fluid to be utilised in such systems it is important to consider thermophysical, environmental and safety aspects all together. This project is focused on the investigation of novel and environmentally friendly thermo-fluids that can be potentially utilised in low-temperature solar thermal systems for mechanical and heat energy generation. This was accomplished in three stages. Firstly, a low-temperature solar thermal system which consists of solar organic Rankine cycle and heat recovery units was designed, commissioned and tested experimentally. In the experiments, HFE 7000 refrigerant that has zero ozone depletion potential (ODP) and low global warming potential (GWP) was employed. The performance of the system was evaluated in terms of energy and exergy analyses. In the 2nd stage, the flat plate collector was mathematically modelled and simulated under various operating conditions. Then, the model was extended to the solar organic Rankine cycle to perform a simulation study where 24 organic compounds were examined according to their applicability in terms of the thermal performance of the cycle and environmental properties of the fluids such as flammability, toxicity and global warming potential. In the last stage, a numerical study of the laminar flow of HFE 7000 based nano-refrigerants at different Reynolds number and volume concentration ratio was conducted. The convective heat transfer coefficient, the pressure drop and the entropy generation of the each flow was investigated.