Numerical simulation study on the coupled heat transfer characteristics of liquid sodium and supercritical carbon dioxide

Abstract

Among fourth-generation nuclear technology, the Sodium-cooled Fast Reactor (SFR) is one of the most mature reactors, offering high thermal efficiency and inherent safety advantages. The adoption of supercritical carbon dioxide (S-CO₂) as the secondary-loop heat transfer medium in SFR has gained significant attention due to its potential to reduce heat exchanger size and improve thermal-to-electric conversion efficiency. Furthermore, the coupled system of an S-CO₂ Brayton cycle with an SFR effectively eliminates sodium-water reaction risks while achieving higher cycle efficiency compared to the steam Rankine cycle. Meanwhile, the Printed Circuit Heat Exchanger (PCHE), known for its compact structure and superior heat transfer performance, is considered as a promising candidate for thermal coupling between sodium and S-CO₂. However, studies on heat transfer between sodium and S-CO₂ in PCHE remain scarce, and the associated technologies are still immature, necessitating further investigation into their thermal interaction and fundamental design guidelines. This study numerically investigates the heat transfer characteristics of liquid sodium and S-CO₂ through geometric modeling and simulation of a PCHE. Parameter-controlled simulations were performed to assess the impact of flow conditions and channel geometry on temperature and pressure distributions. The results indicate that temperature fields are primarily influenced by the inlet mass flow rates and temperatures of both fluids, while S-CO₂ outlet pressure, channel cross-section, and horizontal spacing show negligible effects (the variation in outlet temperature remains below 8 K). In contrast, pressure drop is mainly affected by the inlet mass flow rate of each fluid and the channel cross-sectional area, with an increase in channel diameter from 1.6 mm to 2.4 mm reducing the pressure drop by over 80%. The heat transfer coefficient is highly sensitive to changes in S-CO₂ mass flow rate and channel cross-sectional area; within the studied ranges, it increased by 58% and decreased by 44% respectively, both leading to significant performance variation. This study provides valuable insights for the design of sodium-S-CO₂ heat exchangers and supports the development of SFR technology.