Experimental study on heat transfer and flow resistance performance of an air-cooled fluoride salt heat exchanger

The air-cooled fluoride salt heat exchanger (ASHX) plays a crucial role in maintaining optimal operating temperature in the reactor core and enhancing the economic efficiency of nuclear power plants. However, there remains a notable gap in structural design and comprehensive experimental research on ASHX performance. To address this, this study developed an "S"-shaped tubular ASHX integrated with airflow guide plates and conducted experimental evaluations of its heat transfer and flow resistance performance. Experiments were performed in a scaled simulation fluoride salt cooled nuclear reactor (SF0), using liquid fluoride salt as the tube-side working fluid and air as the shell-side coolant. The results demonstrate that the empirical model, derived from classical Darcy analysis, accurately predicts the flow resistance coefficient, with deviations within +/- 4 %. For heat transfer performance, traditional correlations based on Nusselt analysis provided reasonable approximations but exhibited a maximum prediction error of 10 %. To improve accuracy, a modified convective heat transfer correlation was developed, specifically accounting for the tube array in crossflow with high temperature fluoride salt inside the tubes. This new correlation, validated for Reynolds numbers (Re) ranging from 1949 to 9077, significantly improves consistency with experimental data, with deviations limited to within 5 %. The outcomes of this study may offer valuable insights for improving ASHX designs in Molten Salt Reactors, contributing to enhanced thermal management and operational efficiency.