Comparison of Gas System Analysis Code GAMMA+ to S-CO₂ Compressor Test Data

The CO₂ compressor control is one of the most important issues to operate a Supercritical CO₂ (S-CO₂) Brayton cycle with a high thermal efficiency because it is operated near the critical point to reduce the compressing work. Therefore, our research team has accumulated the CO₂ compressor data from the S-CO₂ compressor test facility called SCO2PE (Supercritical CO₂ Pressurizing Experiment). The data can be obtained under various compressor inlet conditions, especially near the critical point of CO₂.

Despite the growing interest in the S-CO2 Brayton cycle, research on the cycle transient analysis, especially in case of CO₂ compressor inlet condition variation, is still in its early stage. So, in this study, the validation and verification of the gas system transient analysis code GAMMA+ is carried out by utilizing the experimental data of SCO2PE. To simulate the SCO2PE by the GAMMA+ code, the code was revised to reflect the compressor performance and add an expansion valve option. Moreover, the NIST database was connected to the GAMMA+ code for more accurate CO₂ properties near the critical point. Prior to the transient analysis with the whole SCO2PE loop, major components such as a compressor and a heat exchanger were separately tested with the steady state data of SCO2PE. The loss of cooling water accident was assumed as the transient situation by observing the operating condition variations of the SCO2PE while the mass flow rate of water loop was decreased. Thus, the experimental data of SCO2PE was compared with the revised GAMMA+ code under the planned transient.