Sensitivity study of S-CO2 compressor impeller design for different real gas approximations

Abstract

From the efforts of many researchers and engineers related to the S-CO2 Brayton cycle technology development, the S-CO2 Brayton cycle is now considered as one of the key power technologies for the future. Since the S-CO2 Brayton cycle has advantages in economics due to high efficiency and compactness of the system, various industries have been trying to develop baseline technology on the design and analysis of the S-CO2 Brayton cycle components. According to the previous researches on the S-CO2 Brayton cycle component technology development, treatment of a thermodynamic property near the critical point of CO2 is the main concern since conventional design and analysis methodologies cannot be used for near critical point region. Since a significant thermodynamic property variation occurs near the critical point of CO2,KAIST research team has been trying to develop a S-CO2 compressor design and analysis tool, namely KAIST_TMD, to reflect real gas effects for the accurate design and performance prediction results. One of the key improvements applied to KAIST_TMD which is an in-house code for the S-CO2 turbomachinery design and analysis is updating the stagnation to static condition conversion method. Since a compressor experiences high flow velocity, the stagnation to static condition conversion process is important and it can have an impact on the design and analysis results significantly. A common process for stagnation to static conversion uses specific heat ratio which is a constant based on the ideal gas assumption. However, specific heat ratio cannot be assumed as a constant for the case of the S-CO2 compressor design and analysis because it varies dramatically. Thus, in this paper, a sensitivity study with different approaches for the stagnation to static condition conversion process will be performed to evaluate the impact of the selected approaches on the final impeller design results.