Analysis of the Thermal–Hydraulic Characteristics of Supercritical CO2/Kr Mixtures in the Straight-Channel Printed Circuit Heat Exchanger

The supercritical carbon dioxide recompression Brayton cycle (SCO2RBC) has attracted much attention as one of the most promising thermal power conversion systems. As the component with the largest volume and quantity in the cycle, the heat exchanger has a crucial impact on the cycle efficiency. Printed circuit heat exchanger (PCHE) is widely utilized as regenerator and precooler in the Brayton cycle. CO2/krypton has shown great potential for development as the working fluid of Brayton cycle. In this work, PCHE is analyzed as the high-temperature regenerator for Brayton cycle with CO2/krypton mixtures as the heat transfer fluid in both hot and cold channels. Thermal properties of CO2/Kr vary with temperature, and mass fraction of Kr is explored. The thermal–hydraulic characteristics of S-CO2/Kr mixture flow in straight-channel PCHE are investigated. The effects of krypton mass fraction, channel diameter, and Reynolds number on heat transfer and friction features are discussed via numerical analysis. The results show that the Nusselt number of cold and hot channel increases by 1.09 and 0.87% when the molar fraction of krypton varies from 0 to 0.25 while the change of Fanning friction factor can be neglected. The channel diameter and Reynolds number have important effects on the thermal–hydraulic performance of cold and hot channels. New correlations are developed for the flow and heat transfer performance of CO2/krypton (mass fraction 0.75/0.25) PCHEs with errors of less than ± 5%.