Numerical Study of Heat Transfer and Flow Instability of Water at Supercritical Pressure in a Vertical Tube

The parameters of water in the steam generator of high-temperature gas-cooled reactor could be increased to supercritical then the reactors and the supercritical steam generators can work with the supercritical steam turbine unit considering the high efficiency, no phase change heat transfer at the supercritical pressures, so the heat transfer and the flow instability of water at supercritical pressure is very important and was studied numerically in this paper. The comparison between the numerical results with the experimental data showed that the RNG k- model with enhanced wall treatment performed well in the steady-state calculation and was also adopted in the transient state calculation. The flow and heat transfer characteristics at various moments, and the effects of fluid inlet enthalpy were then studied. The results show that the flow rates oscillate intensely once the fluid enters the unsteady zone, and the wall temperature can increase dramatically due to the very low flow rate at some moments. The flow rate and the heating power at the unstable initial points decrease as the inlet fluid enthalpy increases, whereas NTPC relatively increases.