EXPERIMENTAL STUDY ON THE CO2 TO WATER HEAT EXCHANGER PERFORMANXCE NEAR THE CO2 CRITICAL POINT

Abstract

Supercritical CO2 (S-CO2) cycle is considered as one of the promising candidates for the next generation nuclear reactor power conversion system due to relatively high efficiency at low turbine inlet temperature. It also has simple layout and small footprint due to compact turbomachinery and heat exchangers. The major characteristic of a S-CO2 cycle is the small compression work due to dynamic thermodynamic property variation near the critical point. As the S-CO2 cycle efficiency is highly dependent on the compressor inlet condition, the performance of precooler must be investigated thoroughly as the precooler conditions the compressor inlet condition. For such application, conventional shell and tube heat exchanger can be considered. To investigate the CO2 heat transfer near the critical point to the water acting as the ultimate heat sink, the experimental data obtained from S-CO2 Pressurizing Experiment (SCO2PE) were utilized. SCO2PE is composed of a canned motor type CO2 compressor, an expansion valve and a spiral tube heat exchanger. The conventional LMTD method was utilized for the spiral tube heat exchanger design evaluation. However, the heat exchanger performance differs from the design point as the CO2 specific heat changes vigorously near the critical point. To assess the CO2 heat transfer more precisely, the average Nusselt number is calculated and compared with the existing correlations.