The supercritical carbon dioxide (S-CO2) Brayton cycle is widely applied in energy conversion systems, the heat transfer characteristics of S-CO2 is an important factor affecting the cycle efficiency. The heat transfer characteristics of S-CO2 flowing upward in a vertical tube(d=4.57mm) is studied in this paper by experimental and numerical method. The numerical results are verified by experiments. And experiments are performed to analyze the parameter effects on heat transfer characteristics. The distributions of radial velocity and turbulent kinetic energy at different axial positions are obtained by numerical method to analyze the heat transfer mechanism. The results show that the effect of buoyancy flattens the velocity distribution, resulting in the weakening of turbulence intensity and the deterioration of heat transfer. Heat transfer deterioration occurs while q/G≥0.1kJ/kg. The heat transfer performance is better at higher mass flux or lower heat flux. Pressure and inlet temperature affect heat transfer only while the fluid state is near the pseudo-critical region. Based on the experimental data, a heat transfer correlation is proposed, the largest prediction deviation is less than 25%.
Keywords heat transfer characteristics, supercritical CO2, flowing upward, buoyancy effect