Heat transfer characteristics of high temperature and pressure water in vertical downward tube

In the range of pressure from 11.5 to 28 MPa,mass flow rate from 450 to 1550 kg·m-2·s-1,and heat flux at inner wall from 50 to 585 kW·m-2,an experiment was conducted to investigate the heat transfer characteristics of water in vertical downward tubes.The temperature distribution in the tube wall was obtained.The effects of heat flux at inner wall on heat transfer coefficient and temperature at inner wall were analyzed and corresponding empirical correlations were presented.The heat transfer coefficient of vertical downward flow was compared with that of vertical upward flow.The experimental results show that at subcritical and near critical pressures,dryout and departure from nucleate boiling occur in vertical downward tube.With the increase of inner wall heat flux,heat transfer deterioration occurs ahead and the peak wall temperature increases obviously after heat transfer deterioration.At supercritical pressures,the wall temperature increases slowly with fluid enthalpy when the bulk temperature is lower than the pseudo-critical temperature and increases considerably when the bulk temperature is higher than the pseudo-critical temperature.In the pseudo-critical enthalpy region,the heat transfer is enhanced.