CFD modelling of discharging process in a two-tank molten salt thermal storage system

Canadian Nuclear Laboratories (CNL) has established a lab-scale experimental facility to address the potential solidification at local cold spots, and/ or stratification in a two-tank molten salt thermal storage system, which severely influences the system's performance and safety. In the experiment design, a preliminary similarity analysis and computational fluid dynamics (CFD) simulations of the heat transfer performance during the transient discharging process have been undertaken. Reynolds number and Péclet number were chosen for the similarity criteria, and a bounding range for the inlet mass flow rate was determined based on the geometry and kinematic scaling ratio. Since the flow is mixed convection during the process, the significance of the forced convection was determined for different inlet mass flow rates. In smaller inlet flow rate cases, natural convection was found to be dominant over forced convection, resulting in stratification with a high risk of solidification. However, enhanced mixing from larger inlet mass flow rates contributed to lower temperature deviation, i.e., a better thermal mixing performance. This study was used to support the CNL operating conditions of the test facility and materials, and appropriate inlet flow rates to reproduce the corresponding flow and heat transfer phenomena in the full-scale facility.