Performance analysis of heat transfer for supercritical water cooled in various inclined tubes

Abstract

In this paper, the heat transfer performance of supercritical water (SCW) cooled in various inclined tubes was investigated numerically. The simulation was conducted using the shear stress transport (SST) k-ω model and it was verified using measured data. The inclination angle ranges from vertically downward flow (θ = -90°) to vertically upward flow (θ = 90°). The effects of mass flux, operating pressure and inclination angle on SCW heat transfer were presented. The analysis indicated that buoyancy had little influence on the flow heat transfer in the gas-like region (Tb > Tpc) and it became more significant in the liquid-like region (Tb < Tpc), especially at low mass flux. The secondary flow induced by buoyancy distorted the velocity field, achieving better heat transfer performance at the top surface. It sharpened the velocity field and intensified the heat transfer in the upward flow. The inclined flow with θ = 60° provided the best heat transfer performance among the various inclined flows. Moreover, the buoyancy effect could be alleviated and the heat transfer could be improved with increasing of mass flux. When the mean bulk enthalpy was slightly superior to the pseudo-critical enthalpy (Hb > Hpc), the heat transfer coefficient reached peak. Not only did the specific heat increase but also the velocity gradient and turbulent kinetic energy increased with decreasing pressure, which enhanced the heat transfer. The buoyancy effect was evaluated using the empirical parameters Gr/Re2 and Gr/Re2.7, and results showed that the Gr/Re2.7 had better prediction accuracy.