Large Eddy Simulation Of Turbulent Heat Transfer In Nuclear Sub-channels

The turbulent heat transfer of liquid metals is hard to be simulated by RANS method due to the difficulty of assumption of turbulent diffusion term. Therefore, in present study, large eddy simulation with a fine grid was employed to accurately model the fully developed turbulent heat transfer of low molecular Prandtl number (Pr) in triangular sub-channels with uniform heat flux imposed on the wall. Four cases at Pr=0.026corresponding to LBE were performed with friction Reynold number400,600,1400, P/D=1.2and with friction Reynold number600, P/D=1.05. Also, the effect of Prandtl number on the turbulent heat transfer was studied by performing four cases with four different Pandtl number (0.01,0.026,0.1and0.71) under the same flow field (Reτ=600, P/D=1.2). Periodic boundary conditions for pressure and temperature in streamwise direction are imposed and the corresponding momentum and temperature equations are explicitly deduced. A fine grid and dynamic SGS model were used in our LES calculations. The LES method was implemented by the open source code, OpenFOAM2.3.0. The time-average statistics quantities such as mean temperature, root-mean square (RMS) of the temperature fluctuation, turbulent heat flux and Nusselt number etc. were obtained and analyzed.The results show that with the increasing of Re, the temperature RMS intensity increases and its contour becomes more complex due to the stronger secondary flow motion. In a large near-wall region, the mean temperature has linear law and RMS of the temperature fluctuation is constant. Moreover, with the increasing Pr, the mean temperature has a smaller linear region and the position of the peak of curve of the temperature fluctuation RMS moves towards the wall, which means a thinner temperature sub-layer existed. The most distinct result is that the characteristics of turbulence and heat transfer of LBE in the narrow sub-channel P/D=1.05is largely different with that in the wide one P/D=1.2. At P/D=1.05, the temperature fluctuation RMS largely increases and the Nusselt number remarkably varies with the angles. Therefore, the turbulent heat transfer of liquid metal in a narrow sub-channel should be paid more attention for the safety design of nuclear reactors. Turbulent heat flux changes obviously with the various Pr while the influence of Re on it can be ignored. The Nusselt number was compared between the LES result and that of the empirical formulas, and the Ushakov correlation was recommended. The present study, it’s the beginning of the research on the turbulent transient field and turbulent heat transfer of liquid metal in the nuclear sub-channel. And, more studies related to the turbulent coherent structure will be done in the future. The authors believe that it will be helpful on the R&D of the Gen IV nuclear engineering.In addition, another numerical analysis on the turbulent heat transfer in Rectangular Flow Channels inside the First Wall of fusion Blanket Modules was done.