Numerical investigation on cooling heat transfer and flow characteristics of supercritical CO2 in spirally fluted tube at various inclination angles

Abstract

The convective flow and heat transfer characteristics of supercritical carbon dioxide cooling in various inclined spirally fluted tubes, which is used under high pressure conditions for power plants, are investigated by numerical simulation in this study. Using the examined computational model, the distributions of the turbulent kinetic energy and the fluid velocity in each side of the groove varied with the inclination angles δ range from −90° to 90° are analyzed. The results show that the components of the buoyancy force in the mainstream and perpendicular to the mainstream have different effects on the flow behavior, especially near the cooling surface. The variation of the local heat transfer coefficient is also issued. In the gas-like region, the fluid velocity plays the main role, and the heat transfer coefficient increases with the decreasing δ. In the liquid-like region, the dominant impact factor is the velocity gradient, and the variation of the heat transfer coefficient with δ is opposite to that in the gas-like region, where the buoyancy has a more significant effect. The buoyancy effect will be more important with the increase of the helix angle and increase as the inclined upward flow. The optimal inclination angle corresponding to the maximum heat transfer coefficient is obtained, and it varies from −45° to 45° as the helix angle increases.