CFD ANALYSIS OF TURBULENT MIXED CONVECTION UPWARD FLOW OF SUPERCRITICAL WATER IN A VERTICAL TUBE

摘要

A Computational Fluid Dynamics (CFD) model is developed for the prediction of heat transfer to supercritical water (SCW) flowing upwards in vertical tubes under the conditions of turbulent mixed convection. The model is validated using experimental data obtained under the operating conditions typical for SCW cooled reactors (SCWRs), namely: at a pressure of 24 MPa, an inner tube diameter of 10 mm, an inlet temperature of 320 or 350 °C and a heated tube length of 4 m. Four values of the mass flux (200, 500, 1000 and 1500 kg/m~2s) and various values of the wall heat flux (ranging from 129 to 729 kW/m~2) are considered. The physical properties of SCW are calculated by using the REFPROP software from National Institute of Standards and Technology (NIST). The model has been incorporated into the commercial general-purpose CFD software, PHOENICS. Various turbulence models and numerical grid settings are tested. The study has demonstrated a good agreement between the CFD predictions and the experimental data on the inside tube wall temperature and heat transfer coefficient with use of a two-layer low-Reynolds-number k-e turbulence model and a proper numerical grid spacing. However, this good agreement deteriorates appreciably under the influence of strong buoyancy forces at the lowest mass flux value of 200 kg/m~2s. Further research is required to improve the model's performance under these conditions. Practical recommendations are made regarding potential model applications in 3D analyses of SCWRs.