Assessment and simulation on the thermal mixing phenomenon with CFD method in a 45° horizontal T-junction

In this paper, the detailed thermal mixing characteristics of the two-phase stratified flow in a 45° T-junction were studied with complicated direct contact condensation. The feasibility of CFD model on the two phase mixing process was validated against the experimental data obtained from the XJTU-ECCS apparatus. Results show that the established two-phase CFD model can predict the mixing process correctly during the ECC safety injection with the matched grid, exact boundary conditions and a proper set of mathematical model. Moreover, with a comparison between the condensation rate and the experimental data under different Rt numbers, it was found that the error range of numerical results turned out to be lower than 28%. The condensation rate during the ECC injection was closely related to the Rt number, and the linearity degree between the condensation rate and Rt number was high when the cooling capacity of injection coolant was insufficient. This study summarized a fitting correlation according to simulation results, which can be used to predict the condensation rate in case that the Rt number is lower than 0.55.