Development of Kaist-STA (system transient analysis) code and verification results for transient analysis of supercritical CO2 Brayton cycle

Abstract

Power conversion systems using CO2 as a working fluid under supercritical conditions have gained interest as one of the promising power systems and it is being developed by many countries for the next generation nuclear system application. The main reason why the Supercritical CO2 (S-CO2) cycles has high efficiency is because the cycle has reduced compressing work by compressing the CO2 near the critical point due to its high density and low compressibility. However, this also implies that the system can be operating under two-phase sub-critical condition during transients. To avoid the two-phase error near the critical point, a new system dynamic analysis code using Homogeneous Equilibrium Model (HEM) is being developed, namely KAIST-STA (KAIST-System Transient Analysis) code. Similar field equations of pre-existing system analysis code for describing 1-D single phase flow are used for the KAIST-STA code, but the quality of fluid is additionally considered by tracking the enthalpy gradient at every time step. This paper describes the current situation of the development of KAIST-STA code and presents the verification results of the code. Moreover, the validation result simulating near the critical point of CO2 is also shown.