AUTHOR=Huang Xi , Pang Bo , Chai Xiang , Yin Yuan 

TITLE=Proposal of a turbulent Prandtl number model for Reynolds-averaged Navier–Stokes approach on the modeling of turbulent heat transfer of low-Prandtl number liquid metal

JOURNAL=Frontiers in Energy Research

VOLUME=Volume 10 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/energy-research/articles/10.3389/fenrg.2022.928693

DOI=10.3389/fenrg.2022.928693

ISSN=2296-598X

ABSTRACT=Thanks to their high molecular heat conductivity, low-Prandtl number liquid metal is a promising candidate coolant for various designs of advanced nuclear systems such as liquid metal cooled fast reactors and accelerator driven sub-critical system (ADS). With the fast-growing computational capacity, more and more attention has been paid to apply computational fluid dynamics (CFD) methods in thermal design and safety assessment of such systems for a detailed analysis of three-dimensional thermal-hydraulic behaviors. However, numerical modeling of turbulent heat transfer for low-Prandtl number liquid metal remains a challenging task. Numerical approaches such as wall-resolved large eddy simulation (LES) or direct numerical simulation (DNS), which can provide detailed insight into the physics of the liquid-metal flow and the associated heat transfer, were widely applied to investigate the turbulent heat transfer phenomenon. However, these approaches suffer from the enormous computational consumption and are hence limited only to simple geometrical configurations with low to moderate Reynolds numbers. Reynolds-Averaged Navier-Stokes (RANS) approach associated with a turbulent Prandtl number Pr_t accounting for the turbulent heat flux based on Reynolds analogy are still, at least in the current state in most of the circumstances, the only feasible approach for practical engineering applications. However, the conventional choice of Pr_t in the order of 0.9~unity in many commercial CFD codes is not valid for low-Prandtl number liquid metal. In this study, LES/DNS simulation results of a simple forced turbulent channel flow up to a friction Reynolds number Re_τ of 2000 at Pr of 0.01 and 0.025 were used as references, to which RANS approach with varying Pr_t was compared. It was found that the appropriate Pr_t for RANS approach decreases with bulk Peclet number Pe_b and approaches a constant value of 1.5 when Pe_b becomes larger than 2000. Based on this calibrated relation with Pe_b a new model for Pr_t used in RANS approach was proposed. Validation of the proposed model was performed with available LES/DNS results on local temperature profile in concentric annulus and bare rod bundle, as well as with experimental correlations on Nusselt number in circular tube and bare rod bundle.