Numerical Modeling for a Supercritical CO2-Liquid Sodium Hybrid Compact Heat Exchanger

As research continues into the generation IV advanced nuclear reactors, exploration of liquid sodium as a coolant, or Sodium Fast Reactors (SFRs), coupled to supercritical CO2 (sCO2) Brayton cycles are currently underway. Liquid sodium offers unique and beneficial fluid properties that can achieve higher efficiencies and longer equipment lifespans compared to conventional water cooled reactors. Coupling sodium with sCO2 matches well with sodium’s temperature profile and is less reactive with sodium when compared to water used in standard Rankine cycles. To achieve commercial viability, methods for developing diffusion-bonded Hybrid Compact Heat Exchangers (H-CHX) to couple SFRs with sCO2 Brayton cycles are being developed. This paper includes thermal-hydraulic analysis of these fluids to quantify thermal and pressure stresses within the H-CHX for use in determining a structurally sound design. Two models for predicting the temperature profiles within a practical H-CHX channel design are presented. The first is a 1-D heat transfer model employing heat transfer correlations to provide both bulk fluid and wall temperatures. The second is a 3-D computational fluid dynamics model (CFD) providing a three-dimensional temperature profile, but at a significantly increased simulation time. By comparing the results of the two models for specific design conditions, significant temperature deviation is shown between the models at a short channel length of 10 cm. However, for longer channel lengths, although the 1-D model neglected the strong axial conduction on the sodium side, it generally shows good agreement with the CFD model. Thus, for any practical H-CHX designs, the findings reveal both simulation methods can be used to extrapolate the temperature gradient along the channel length for use in designing a H-CHX, as well as predicting the overall size and mass of the heat exchanger for component costing.