Overview about Studies of Turbulent Mixing in Sub-Channel Analysis

In the sub-channel analysis,the turbulent mixing is one of the important parts of lateral mixing between coolant channels.It is non-directional cross-mixing due to the natural eddy diffusion during the fluid pulsation.The strength of turbulent mixing will affect the local thermal parameters of the sub-channel,thus affecting the critical heat flux prediction.It is an important input parameter for the reactor thermal hydraulic design and analysis.This paper aims to review the state-of-the-art studies of turbulent mixing in sub-channel analysis,in order to provide some reference during the fuel assembly design and sub-channel code development.Key issues in the turbulent mixing research were summarized,including the mechanism and models,turbulent mixing coefficient,experimental methods,CFD calculation methods and models in sub-channel code.The main theoretical model of turbulent mixing is in analogy to the molecular diffusion theory.Turbulent mixing coefficient β is a function of the sub-channel geometry and flow conditions of the coolant,and it can be obtained through experiments or CFD calculations.Turbulent mixing models in sub-channel code vary greatly.In practical applications,the choice of model depends on the specific object and the condition.