The use of S-CO2 as working fluid in a power cycle has been growing in recent years due to associated benefits such as highly compact power plant and high cycle thermal efficiencies for application including waste heat, solar thermal and nuclear power plants. Many authors have presented studies on S-CO2 cycle and its modifications and there also exists many patents which claim different embodiments of the S-CO2 cycle for different heat sources. Each author of the S-CO2 cycle embodiment uses some specific tool to analyze the cycle performance with assumed values of component efficiencies. In the S-CO2 cycle the ratio of turbine work to compressor work is relatively small and its variation may cause a significant influence on cycle performance estimation accuracy. Exact prediction of the S-CO2 cycle performance requires defining exact turbomachinery efficiency magnitudes. However, S-CO2 turbines and compressors are in development stage except for several low power scale prototypes and hence it is very difficult to make assumptions on efficiency and they need to be designed.

To enable design of cycle from concept to detailed design of the turbomachinery, the authors in this work have developed a flexible design system which is starting from heat balance calculation, continues with sizing of turbomachinery flow path, through 1D/2D/3D aero and structural multidisciplinary optimization. Such a design process is iterative because a refinement of the turbomachinery efficiencies lead to change in cycle boundary conditions for turbomachinery design and the design needs to be refined by recalculation of the cycle. In the present work, four different embodiments of S-CO2 thermodynamic cycles were analyzed using assumed component efficiencies and based on the actual design of the turbomachinery components the cycle was recalculated and accurate performance of the cycle was predicted. It is observed that the turbine efficiency has significant influence on the overall cycle performance compared to the compressor efficiency.

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