Heat transfer characteristics of lead-bismuth eutectic and CO2-based mixtures in straight-channel printed circuit heat exchangers

Lead-cooled fast reactors coupled with supercritical CO 2 Brayton cycles represent a highly promising energy conversion technology for next generation nuclear power system. The overall thermal performance of these systems can be further enhanced by introducing CO 2 -based mixtures, however, investigations on the heat transfer and flow characteristics of lead-bismuth eutectic (LBE) and CO 2 -based mixtures in the intermediate heat exchanger between the primary and secondary loops remain scarce. In this work, numerical simulations were conducted to investigate the heat transfer and flow characteristics of LBE and CO 2 -based mixtures in straight-channel printed circuit heat exchangers (PCHEs). The performance of CO 2 -propane, CO 2 -krypton and CO 2 -xenon at different mixing mole fractions was compared. The results show that, among the investigated CO 2 -based mixtures, the CO 2 -propane mixture provides the most favourable heat transfer performance when coupled with LBE. Compared with pure CO 2 under the same operating conditions, the overall heat transfer coefficient of the CO 2 -propane/LBE PCHE increases by up to 40%. In addition, the impact of key parameters ( e.g. , inlet velocity, mass flow rate, inlet temperature, and pressure) on the heat transfer characteristics of CO 2 -propane mixtures was analysed. Finally, correlations for the Nusselt number and friction factor were derived using the simulation results, with prediction errors within ±3% for CO 2 -propane mixtures with a propane mole fraction in the range of 0.05-0.30. This study provides a theoretical foundation for designing and optimizing PCHEs with LBE and CO 2 -based mixtures serving as heat transfer media.