NUMERICAL SIMULATIONS OF THE FOUR PARAMETER κ-ω-κt-εt HEAT TRANSFER TURBULENCE MODEL FOR LIQUID METALS

Low Prandtl number fluids, such as heavy liquid metals, may be used as coolant for nuclear power plants for their high conductivity and neutronic properties. These fluids show a rather different convective heat transfer behavior to that of ordinary fluids, such as water or gas. In such ordinary fluids various turbulence models are available to match the experimental data for flow fields and thermal fields are computed based on similarity between velocity and thermal fields. This is assumed in almost all Computational Fluid Dynamics codes where the simple eddy diffusivity model with constant turbulent Prandtl number is implemented. In low Prandtl number fluids the standard constant turbulent Prandtl number model fails to reproduce standard correlations build from experimental data. Therefore it is important to develop new heat transfer turbulent models that are able to reproduce numerically the desired behavior. The present work addresses a new effort to improve the prediction of turbulent heat flux in vertical annular geometry by applying the four parameter κ-ω-κt-εt model. The thermal eddy heat diffusivity can be expressed in a definite manner similar to the viscous eddy diffusivity as a function of the square temperature fluctuation κt and its dissipation rate εt. These variables can be computed by solving two new transport equations. In this work a simple case is investigated using the κ-ω turbulence model for simulating the turbulent flow field right up to the wall with no wall functions. Results obtained from the four parameter κ-ω-κt-εt model are compared with the standard algebraic turbulent heat flux approximations, namely, the simple eddy diffusivity. For large range of forced flows a four parameter κ-ω-κt-εt model is a powerful tool for predicting the heat transfer in flows with no similarity between velocity and thermal fields.