Sensitivity Study of Turbulent Prandtl Number Model for Lead-Bismuth Eutectic Cooled Bare 19-Rod Bundle Based on OpenFOAM

Liquid lead-bismuth eutectic (LBE) has a low Prandtl number ( Pr ), leading to inaccuracies in heat transfer calculations when using the constant turbulent Prandtl number ( Pr_\mathrmt ) model, which is commonly employed in computational fluid dynamics (CFD) simulations. To improve the numerical accuracy of heat transfer calculations for LBE, researchers both domestically and internationally have developed several Pr_\mathrmt models for liquid metals. To assess the applicability of these liquid metal Pr_\mathrmt models in the commonly used triangular arrangement of fast reactor rod bundles, this study incorporates multiple liquid metal Pr_\mathrmt models into the steady-state heat transfer solver buoyantSimpleFoam from the open-source CFD software OpenFOAM. A numerical study was then conducted on the fully developed turbulent heat transfer process within a smooth 19-rod bundle for Prandtl numbers of 0.01 and 0.025, and the resulting Nusselt number ( Nu ) was compared to the heat transfer correlation for triangular rod bundles proposed by Mikityuk et al.Nucl Eng Des, 2009, 239(4): 680. The results show that when using the \mathrmS\mathrmS\mathrmTk-\omega turbulence model, the Nu results calculated using the Pr_\mathrmt model developed by Aoki et al.Bull Tokyo Inst Tech, 1963, 54:63, based on global flow parameters, and the Pr_\mathrmt model constructed by Kays et al.ASME Journal of Heat Transfer, 1994, 116: 284, based on local turbulence parameters, demonstrate good agreement with the Mikityuk correlation. In contrast, the Pr_\mathrmt = 0.85 model produced significant errors and should be applied with caution in engineering calculations. Additionally, molecular heat conduction in LBE has a substantial impact on the temperature and heat flux fields, and the use of an appropriate Pr_\mathrmt model can improve the accuracy of CFD heat transfer simulations.