Design and Assessment of Lead–sCO2 Intermediate Heat Exchanger for LFRs

Lead–sCO2 intermediate heat exchanger (IHX) was designed for lead-cooled fast reactor (LFR). The reactor coolant is lead and flowing through a circular straight channel, meanwhile, sCO2 is heated through 5 channels with different geometries were investigated respectively, including straight channel, zigzag 52° channel, S-shaped fins, offset rectangular fins, and airfoil fins. Considering the thermal-hydraulics characteristics, mechanical structure, corrosion, and flow blockage in the IHX designs, the performance, total cost, and power density of several heat exchanger designs were evaluated and compared. Finally, a printed circuit heat exchanger (PCHE) design using the circular straight (lead) - offset rectangular fins (sCO2) channels was proposed. The straight and S-shaped channels for sCO2 flow were recommended as alternative designs under certain circumstances. However, S-shaped fins and zigzag channels will dramatically increase the cost while straight and airfoil channels will greatly increase the volume.

Optimization and Comparison of Two Combined Cycles Consisting of CO2 and Organic Trans-Critical Cycle for Waste Heat Recovery

CO2-based trans-critical and supercritical cycles have received more and more attention for power generation in many applications such as solar and nuclear energy due to the desirable thermal stability and properties of CO2 and the high efficiency and compact size of the plant. In this study, two combined cycles driven by the flue gas exhausted from the LM2500+ gas turbine, CO2-TC+OTC (organic trans-critical cycle) and CO2-TC/OTC, which can achieve a good trade-off between thermal efficiency and utilization of the waste heat, are investigated. Parameters optimization is carried out by means of genetic algorithm to maximize the net power output of the combined cycle and the effects of the key parameters on the cycle performance are examined. Results show that the exergy efficiency of CO2-TC+OTC is about 2% higher than that of CO2-TC/OTC. In CO2-TC+OTC, the recuperation process of CO2 causes the largest exergy loss; in CO2-TC/OTC, the largest exergy loss occurs in the heat recovery vapor generator, followed by the intermediate heat exchanger due to the larger variation of the specific heat capacity of CO2 and organic fluid in the heat addition process.