SENSITIVITY STUDY OF S-CO2 COMPRESSOR DESIGN FOR DIFFERENT REAL GAS APPROXIMATIONS

Abstract

With the efforts of many researchers and engineers on the Supercritical CO2 (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 S-CO2 Brayton cycle has advantages in economics due to high efficiency and compactness of system, various industries have been trying to develop technologies on the design and analysis of S-CO2 Brayton cycle components. Among various technical issues on the S-CO2 Brayton cycle technology development, treatment of thermodynamic property near the critical point of S-CO2 is very important since the property shows non-linear variation which causes large error on design and analysis results for ideal gas based methodologies. Due to the special behavior of thermodynamic property of CO2 near the critical point, KAIST research team has been trying to develop a S-CO2 compressor design and analysis tool to reflect real gas effect accurately for better design and performance prediction results. The main motivation for developing an in-house code is to establish turbomachinery design methodology based on general equations to improve accuracy of design and analysis results for various working fluids including S-CO2. One of the key improvements of KAIST_TMD which is an in-house tool for S-CO2 turbomachinery design and analysis is the conversion process between stagnation condition and static condition. Since fluid is moving with high flow velocity in a compressor, the conversion process between stagnation and static condition is important and it can have an impact on the design and analysis results significantly. A common process for the conversion is based on the specific heat ratio which is typically a constant from ideal gas assumption. However, specific heat ratio cannot be assumed as a constant for the case of S-CO2 compressor design and analysis because it varies dramatically near the critical point. Thus, in this paper, sensitivity study results on the state condition conversion between stagnation and static conditions with different approaches will be presented and further analysis on impact of the selected approaches on the final impeller design results will be discussed.