Thermodynamic Analysis for Supercritical Carbon Dioxide Brayton Cycle by Considering Both Thermal Efficiency and Cooler Area

Abstract

Abstract The performances of the supercritical carbon dioxide (sCO2) Brayton cycle with the recuperator were investigated by the simulation method. Evaluation criteria were proposed for system performance optimization. The calculation and analysis of the system thermal efficiency and the length of the cooler were performed. The effects of the inlet and outlet pressure of the expander, the heat transfer coefficient and the logarithmic mean temperature difference (LMTD) on the system thermal efficiency and the length of the cooler were investigated. The system thermal efficiency has a peak value with the increase of the expander inlet pressure. The peak value varies from 45% to 45.4% with different expander outlet pressures. The average heat transfer coefficient and the length of the cooler decrease with the increase of the inlet pressure, but the LMTD is on the contrary. When the expander inlet pressure is in the low-pressure stage (22–26 MPa), the thermal efficiency of the lower outlet pressure (8 MPa) is higher, which ranges from 44.3% to 45.4%. However, the length of the cooler is also larger (6.7–10.9 m). As the expander inlet pressure rises to the high-pressure stage (26–30 MPa), the higher outlet pressure (9.5 MPa) has a greater advantage in the thermal efficiency, and the range of efficiency is 44.7–45%. Similarly, the length of the cooler is the largest (4.5–8 m). Therefore, both the thermal efficiency and the length of the cooler should be fully considered in the design of the system operating conditions.