Comparative CFD Investigation of Laminar and Transition-SST Models in a Molten Salt Natural Circulation Loop

A two-dimensional computational fluid dynamics (CFD) analysis of a molten-salt natural circulation loop (MSNCL) was developed to investigate the flow and heat transfer behavior under buoyancy-driven conditions. Both laminar and Transition-SST models were employed in this study to observe how the two models interpret local phenomena inside an MSNCL system. The simulation results were validated against benchmark experimental data. Both models captured the overall temperature rise with increasing heater power, but the laminar model systematically underpredicted the flow velocity and Reynolds number due to its inability to represent turbulence-enhanced transport. This phenomenon is explained by examining the local distribution of velocity vectors and eddy-viscosity ratio and demonstrates the presence of secondary flow. The secondary local circulation appears to be stronger in the vertical leg as reported by several previous studies. Due to this condition, the Transition-SST model demonstrated superior capability in reproducing both global circulation and local flow phenomena compared to the laminar model. This study emphasizes the importance of turbulence modeling in accurately predicting molten-salt natural circulation behavior.