Numerical analysis of curvature effect and buoyancy effect on heat transfer characteristics of supercritical water in cooled helical coiled tubes

The curvature and buoyancy effects on the convection of supercritical fluid in the helically coiled tubes are significant due to affected mainstream and secondary flow which causes non-uniform heat transfer. Thus, it's necessary to investigate the curvature and buoyancy effect for better understanding of heat transfer characteristics of supercritical fluid cooled in the helically coiled tube. In this work, heat transfer characteristics of supercritical water cooled in the helically coiled tube are investigated numerically using the SST k - ω model. With the effect of curvature, the centrifugal force acts on both large density and small density fluid, which moves fluid to outer part. This effect makes the outer part fluid accelerated, and the inner part fluid decelerates in mainstream direction. Due to the viscosity of fluid, secondary flow velocity is lower near the wall, while which is higher in the center. This leads to a higher HTC in the center of outside and inner side. With increasing Dean number, the non-uniformity of mainstream velocity magnitude distribution is aggravated and the influence of buoyancy decreases.