Flow resistance analysis of non-isothermal supercritical CO2. (October 2022) - Zhu, Meng
Highlights: Supercritical CO2 turbulent flow in gas-like region was studied. Friction factor of supercritical CO2 decreases with the increase of heat flux. The density and turbulence fluctuation are the key to thermally-induced mechanism. Proposed dimensionless number can evaluate thermally-induced and inertial forces. Proposed correlation of supercritical CO2 friction factor has excellent accuracy. Abstract: Supercritical carbon dioxide power cycle is considered as one of the promising systems of next generation power cycle. Nevertheless, the hydraulic characteristics of typical heat source components under operating conditions (gas-like region) are not clear, and the present conclusions for flow characteristics of non-isothermal fluids are also not consistent. In this work, the turbulent flow of supercritical CO2 in a vertical upward tube was studied experimentally and numerically. The range of experiment parameters was set as 750–2800 kg/(m 2 s) of mass flux, 10–28 MPa of pressure, 200–410 kW/m 2 of heat flux and 65–500 °C of bulk flow temperature. Furthermore, the feasibility of SST k-omega model was verified by experiment results. The effects of mass flux and pressure on friction pressure drop under non-isothermal conditions are basically consistent with those under isothermal conditions. However, the increase of heat flux leads to the decrease of friction pressure drop and friction factor. Under high heat flux condition, both the viscous shear stress and Reynolds shear stress decrease. The viscous shear stress contributes slightly to the mechanical energy dissipation, hence the Reynolds shear stress is the crux to the change of friction pressure drop. Further studies show that the decrease of density in near-wall region and the decrease of turbulence fluctuation in core region are critical to the decrease of mechanical energy dissipation. According to the theoretical and dimensional analysis, the dimensionless number Xi that can be qualitatively analyzed for the ratio of thermally-induced force to inertial force was obtained. Finally, a high-precision correlation of friction factor was proposed. The proportion of calculated value within 10% and 30% error ranges is 76.65% and 100%, respectively.