Heat transfer to supercritical water in circular tubes with circumferentially non-uniform heating

Abstract

Heat transfer was numerically investigated for flow of supercritical water in a vertical circular tube which was heated on one side. The Shear-Stress Transport k-ω (SST) model was employed and preliminarily validated against experimental results under both circumferentially uniform and non-uniform heating. Numerical studies were performed for a pressure of 24.82 MPa, mass velocity of 404 kg/(m2s) and heat flux between 158 and 370 kW/m2. Within the range studied, empirical Nusselt correlations for uniform heating can adequately predict the circumferentially maximum wall temperature of a one-side heated tube. The circumferential difference of inner wall temperature was large (>60 K at high heat flux) due to poor mixing of fluid between the hot and cold side. At low heat flux, maximum wall temperature barely differed from that under uniform heating. While at high heat flux, maximum wall temperature dropped significantly compared with the uniformly heated case. With further heat input, buoyancy-induced local deterioration of heat transfer occurred, though not as severe as uniformly heated cases. Detailed axial velocity and turbulence show that turbulent quantities in the region, which is similar to the law of the wall region for isothermal flow, play an important role in heat transfer. Local deterioration did not happen when turbulent diffusion of this region was intense. Results also indicate that in a one-side heated tube, buoyancy effect is much stronger in upward flow than in downward flow.