Investigation on thermo-hydraulic characteristic of lead-bismuth eutectic and supercritical carbon dioxide in a straight-channel printed circuit heat exchanger

The Printed Circuit Heat Exchanger (PCHE) is considered a promising heat exchanger for Lead-Bismuth Eutectic (LBE) cooled fast reactors due to its superior pressure-bearing capacity and heat transfer efficiency. This paper introduces a conjugate heat transfer solver to investigate the thermo-hydraulic performance of a straight channel PCHE incorporating LBE and Supercritical CO2 (S-CO2). A four-equation model is implemented in the solver to capture the low Prandtl number turbulent heat transfer characteristics of LBE. Comparisons with LBE circular tube experimental results demonstrate that the solver presented enhances the resolution of LBE heat transfer simulations. This improvement in numerical resolution is crucial for understanding and predicting the behaviors of LBE-S-CO2 conjugate heat transfer process. Building on this, the present work explores the impacts of inlet mass flow rate, inlet temperature, S-CO2 pressure, and geometric parameters on the thermo-hydraulic performance of the straight channel PCHE. In terms of inlet temperature, quantitative analyses emphasize the effectiveness of augmenting the mass flow rate on the S-CO2 side to enhance overall heat transfer performance of PCHE. Adjusting the inlet temperature of S-CO2 or LBE to increase the temperature difference between the two fluids improves the average heat transfer rate, but reducing the S-CO2 inlet temperature may decrease the overall heat transfer coefficient. Furthermore, increasing S-CO2 pressure positively affects the thermal conductivity and specific heat capacity of S-CO2, thereby improving the thermo-hydraulic performance of PCHE. Additionally, geometric parameter sensitivity analyses indicate that decreasing wall thickness or increasing ridge width improves heat transfer, but increasing ridge width may significantly increase PCHE's volume. The increased channel length results in a higher pressure drop, simultaneously enhancing heat transfer. From the Performance Evaluation Criteria (PEC) perspective, lengthening the channel is advantageous for the S-CO2 side but unfavorable for the LBE side. Regarding channel width, reducing channel width yields a larger increase in PEC on the S-CO2 side compared to the LBE side. Therefore, narrower flow channels on the S-CO2 side seem more advantageous. The present work provides a numerical tool with higher numerical resolution for studying LBE-S-CO2 conjugate heat transfer process and offers valuable insights for straight channel PCHE design.