Numerical Investigation of the Deteriorated Heat Transfer Phenomenon for Supercritical Water Flows in Vertical Circular Tubes

Abstract

The present paper is aimed at the in-depth thermal-hydraulic analysis of supercritical water flow at various operating conditions in vertical circular tubes. Computational fluid dramatics model using two turbulence models, Reynolds Stress Model and \\( {\\text{k}}\\,{-}\\,\\upomega \\) SST model, have been used for the analysis in this paper. Three experimental cases, which are operated at various working regimes, are chosen for the detailed analysis of deteriorated heat transfer and normal heat transfer cases. The studies are carried out for the turbulent properties and velocity profiles and their effects on the heat transfer in the vertical circular tubes. It is found that the sharp increase in the wall temperature vanishes if the gravity is neglected. Hence, it can be concluded that buoyancy plays a dominant role in deteriorating the heat transfer for the cases of a low mass flux condition. Besides, the turbulence is found to be suppressed severely for the deteriorated heat transfer and is one of the reasons for the deterioration in heat transfer. Both turbulent models predicted the suppression phenomenon. However, compared with the previous direct numerical simulation studies, which showed two peaks in the turbulent kinetic energy profile, the \\( {\\text{k}}\\,{-}\\,\\upomega \\) SST model fails to predict the proper turbulent kinetic energy profile in the near wall region, which showed only one peak or no peak for the turbulent kinetic energy in the whole flow region.