Numerical study of the effect of buoyancy force and centrifugal force on heat transfer characteristics of supercritical CO2 in helically coiled tube at various inclination angles

The fully developed turbulent flow of supercritical CO2 in a heated helically coiled pipe is investigated by numerical simulation. The supercritical CO2 in the helically coiled tube is heated under constant heat flux with the inclination angles range from −90° to 90°. This work analyzes the effects of the heat flux, pressure, mass flux, flow direction, buoyancy force and centrifugal force on the convection heat transfer characteristics of supercritical CO2. Results show that the non-uniformity of the circumferential heat transfer coefficients is more evident with the decrease of the incline angle. When the helically coiled tube is oriented vertically, the heat transfer coefficient firstly increases and then decreases, exhibiting a maximum near the pseudo-critical temperature. When the helically coiled tube is positioned at horizontal or inclined angles, the heat transfer coefficient (HTC) oscillates dramatically as a result of the fact that the buoyancy force becomes a dominant factor compared to the centrifugal force.