Since the 1960s the idea of using supercritical carbon dioxide (s-CO2) as the working fluid in a Brayton power cycle has been entertained. But due to technical limitations of the time, the idea did not progress forward much. Presently, due to the availability of more knowledge, better technological platform, and advanced analysis tools, many believe it is time to revisit the idea of using carbon dioxide as the working fluid for power generation. Theoretically, the concept of a closed-loop s-CO2 Brayton cycle is highly attractive and promising; however, there is yet a major hurdle to be passed, namely the designing, developing, and testing of a reasonable size (10 MWe or higher) prototype of an s-CO2 Brayton-cycle-based power gas turbine. Specifically, designing a stable s-CO2 compressor is one of the main challenges that need to be addressed. In this dissertation, a supercritical CO2Brayton cycle design tool in Microsoft Excel coupled with CoolProp real gas NIST database was developed to optimize and analyze the power cycles as well as obtain the best operating conditions for an s-CO2 compressor working in a 10 MWe power cycle. Then, three s-CO2 Brayton cycles, namely simple recuperated, recompression, and dual turbine cycles were reconfigured to produce 11.11 MW (10 MWe) output net power. The results were compared to the conventional Brayton cycle as the basic s-CO2 layout. It was shown that the recompression cycle had the highest efficiency, but the highest back-work ratio and the lowest specific work. Furthermore, the reconfigured simple recuperated cycle had a thermal efficiency of 43.2% with a specific work of 125.13 kJ/kg, which is in a moderate range between the dual turbine and recompression cycles. The lower capital cost of the simple cycle suggests it could be a viable option for commercialization. Furthermore, a new compressor design procedure was introduced and developed for s-CO2 centrifugal compressors with a pinched diffuser under on-design and off-design conditions in MATLAB. The developed codes aimed to obtain a stable supercritical CO2 compressor design and to predict the performance of s-CO2 compressors by considering Span-Wagner real gas equation of state, condensation limit, as well as internal and external losses. The procedure was validated with experimental results for an air compressor and Sandia's s-CO2 compressor to examine the validity of the meanline code. The efficiency and pressure ratio obtained from the 1-D code were compared to CFD results and showed reasonable agreement with experimental data. It was found that there was an overprediction due to not considering the volute in the design at higher mass flow rates. By comparing the total-to-static efficiency of Sandia's compressor with 1-D code and CFD, it was found that while the CFD results match the experimental data, the code could not calculate the total-to-static efficiency of Sandia's compressor for the mass flow rates below 2.5 kg/s. Besides, a new impeller with a vaneless pinched diffuser was proposed, which achieved a compressor efficiency of 90.62% with an excellent operating range of 47.8%. The results matched well with simulations for different mass flow rates at the design speedline of 20,000 RPM. Additionally, the internal behavior of s-CO2 was studied at the choke condition and a new analogy between the compressor passage and a converging-diverging nozzle was made for the high limit of the performance map. Besides, a loss analysis in the proposed s-CO2 compressor was performed, revealing that 75.8% of the total enthalpy loss was due to internal losses. Finally, the condensation contours were studied and the results highlighted that condensation is unavoidable in an s-CO2 centrifugal compressor; however, the condensation does not cause damage or affect the compressor's performance.
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