Numerical study on the heat transfer characteristics of a microchannel heat exchanger with liquid lead-bismuth eutectic and supercritical CO2 as working fluids

The Lead-cooled Fast Reactor (LFR) is a promising option for fourth-generation nuclear energy systems, with the supercritical carbon dioxide (sCO(2)) Brayton cycle being the preferred power cycle for future nuclear energy systems. Lead-bismuth eutectic (LBE) is a more suitable reactor coolant than lead due to its lower melting point. High-efficiency microchannel heat exchanger (MCHE) may be an ideal choice for the intermediate heat exchanger (IHX) in liquid lead-bismuth fast reactors. To prevent the channels of MCHE from being blocked by liquid LBE, a new structure of MCHE is proposed, in which the liquid LBE flow channel has a large equivalent diameter and corresponds to two sCO(2) microchannels. In this study, the heat transfer characteristics of con-ventional and new structures of MCHE were investigated using numerical simulation. The results indicate that the temperature change at the inlet of the liquid LBE channel enhances the heat transfer of both liquid LBE and sCO(2). Under constant temperature and pressure, the velocity of sCO(2) has a significant effect on the convective heat transfer of sCO(2), but has little effect on liquid LBE. Based on the reliability of equipment operation, this study recommends the use of the heat exchanger form in case 5. Compared with case 3, altering the velocity of liquid LBE results in a 7.1-8.3% increase in the convective heat transfer coefficient of liquid LBE, and a similar to 38% increase in the convective heat transfer coefficient of sCO(2). Similarly, changing the velocity of sCO(2) leads to a 6.1-7.5% increase in the convective heat transfer coefficient of liquid LBE, and a 32.8-38.0% increase in the convective heat transfer coefficient of sCO(2). For sCO(2) heat transfer calculation, Yoon's heat transfer correlation is recommended, while Kirillov's heat transfer correlation is suggested for liquid LBE heat transfer calculation. The deviation between numerical calculation results and correlations is less than 18.1% and 12.7%, respectively.