Theoretical Investigation on the Printed Circuit Heat Exchanger (PCHE) Based S-CO2 Brayton Cycle

Abstract The supercritical CO2 (S-CO2) Brayton cycle is considered to be one of the most promising cycles for the fourth-generation nuclear power system. In this study, the printed circuit heat exchanger (PCHE) is introduced into the S-CO2 Brayton cycle as the recuperator, the thermodynamic performance of S-CO2 Brayton cycle configuring with both Re-heating and Inter-cooling processes are analyzed. To accurately describe the drastic variations of properties in the recuperator, the segmental calculation method combining conventional heat transfer correlation equations is employed in the simulation of the compact printed circuit heat exchanger, and the thermal hydraulic performance prediction model is utilized to estimate the size of the heat exchanger. In addition, one-dimensional radial-flow turbine model is employed to conduct the turbine calculation. With the reactor outlet temperature of 550°C and compressor outlet pressure of 25MPa, the thermal efficiency of the S-CO2 Brayton cycle is 36.12%, and the length of the PCHE is 1.734m. For the basic S-CO2 Brayton cycle configuring with Re-heating and Inter-cooling processes, both cycle layouts can improve the system efficiency, the Re-heating cycle performs better, with the thermal efficiency increases from 36.12% to 38.26% while the length of the PCHE increases from 1.734m to 1.852m. For the Inter-cooled cycle, the secondary compression ratio plays an important role in cycle performance. With a medium compression pressure ratio, the thermal efficiency of the S-CO2 Brayton cycle is reduced to 35.8%, compared with the high compression pressure ratio at 36.14% and low compression pressure ratio at 36.18%. Nevertheless, system complexity and heat exchanger cost of the low/high compression pressure ratio S-CO2 Brayton cycle is not competitive.