A study on geometric shape factors for turbulent mixing coefficents in rod bundles

摘要

The sub-channel analysis code is widely used in order to predict the thermal hydraulic performance in the core. Turbulent mixing presenting the influence of fluctuating velocity is one of the mechanisms of the lateral flow between sub-channels. The previous research on the turbulent mixing was focusing on the center to center sub-channels. In this study, based on the previous work, the turbulent mixing between different kinds of sub-channels is studied by CFD simulations. The results show that the coefficient beta do not change much, if different kinds of sub-channels are considered. The coefficient beta(E) and beta(M) change in different ways because the distribution of temperature and velocity change in different ways. It is found that the influence of the hydraulic diameter is only related to Re number. The geometric shape factors are defined and their values are recommended according to the calculation results. Finally, when applied in the sub-channel code, the coefficients calculated by CFD method and the geometric shape factors have better performance than the previous turbulent mixing coefficient.