Heat Transfer Characteristics of Printed Circuit Heat Exchanger with Supercritical Carbon Dioxide and Molten Salt

Molten salt and supercritical carbon dioxide (S-CO2) are important high temperature heat transfer media, but molten salt/S-CO2 heat exchanger has been seldom reported. In present paper, heat transfer in printed circuit heat exchanger (PCHE) with molten salt and S-CO2 is simulated and analyzed. Since S-CO2 can be drove along passage wall by strong buoyancy force with large density difference, its heat transfer is enhanced by natural convection. In inlet region, natural convection weakens along flow direction with decreasing Richardson number, and the thermal boundary layer becomes thicker, so local heat transfer coefficient of S-CO2 significantly decreases. In outlet region, turbulent kinetic energy gradually increases, and then heat transfer coefficient increases for turbulent heat transfer enhancement. Compared with transcritical CO2 with lower inlet temperature, local heat transfer coefficient of S-CO2 near inlet is lower for smaller Richardson number, while it will be higher for larger turbulent kinetic energy near outlet. Performance of PCHE is mainly determined by the pressure drop in molten salt passage and the heat transfer resistance in S-CO2 passage. When molten salt passage width increases, molten salt pressure drop significantly decreases, and overall heat transfer coefficient slightly changes, so the comprehensive performance of PCHE is improved. As a result, PCHE unit with three semicircular passages and one semi-elliptic passage has better performance.