Heat transfer characteristics of supercritical pressure water in vertical upward rifled tube

In the range of pressure from 22.5 MPa to 30 MPa,mass flow rate from 430 kg·m-2·s-1 to 1200 kg·m-2·s-1,and heat flux at inner wall from 284 kW·m-2 to 719 kW·m-2,an experiment was conducted under supercritical pressure to investigate the heat transfer characteristics of water in a vertical upward rifled tube.The temperature distribution in the tube wall was obtained.The effects of pressure,heat flux at inner wall and mass flow rate on heat transfer coefficient and temperature at inner wall were analyzed,the enhancement mechanism for heat transfer was discussed,and the corresponding empirical correlations were presented.The experimental results show that the supercritical pressure water in the vertical upward rifled tube presents very good heat transfer characteristics.The wall temperature in the rifled tube increases slowly with fluid enthalpy when the bulk temperature of fluid is lower than the pseudo-critical temperature and increases considerably when the bulk temperature is above the pseudo-critical temperature.At the temperature near the pseudo-critical temperature,the thermophysical properties of water under supercritical pressure change abruptly.Therefore,the heat transfer is enhanced in the pseudo-critical enthalpy region.With the increase of pressure and heat flux of inner wall and with the decrease of mass flow rate,the temperature of inner wall increases and the heat transfer coefficient decreases obviously,the enhancement on heat transfer is weakened and the heat transfer may be deteriorated.