Experimental investigation of heat transfer characteristics of water in a vertically–upward tube under ultra-supercritical pressure and ultrahigh-temperature conditions

•Heat transfer of SCW under ultrahigh parameters was experimentally investigated.•Effects of pressure, mass flux and heat flux on heat transfer were investigated.•Existing heat transfer correlations for SCW under 700 °C A-USC conditions were assessed. Advanced ultra-supercritical (A-USC) steam power generation technology is characterized by main steam conditions of > 700 °C and > 35 MPa, enhanced cycle efficiency, and reduced environmental footprint, and is one of the important development goals of the thermal power plants today. However, scarce studies were conducted on the heat transfer characteristics of supercritical water (SCW) under A-USC operating conditions. An experimental platform to safely measure the heat transfer of SCW flowing in a vertical tube at temperature up to 760 °C and pressure up to 42 MPa was designed and built in this study. Experimental measurements of the heat transfer characteristics of SCW were performed on this platform in a wide range of temperature and pressure, up to a maximum bulk fluid temperature of 750 °C and a maximum pressure of 38 MPa. The effects of pressure, mass flux, and heat flux on the heat transfer characteristics of SCW in the ultrahigh enthalpy region (over 3200 kJ·kg−1) were then analyzed based on the experimental data. Results show that in the ultrahigh enthalpy region, the bulk fluid temperature and wall temperature increase approximately linearly with increasing bulk fluid enthalpy. The heat transfer coefficient decreases gently and then gradually stabilizes in the same range, with values in the range of 4–10 kW·m−2·K−1. In the ultrahigh enthalpy region, increasing the mass flux or decreasing the heat flux will improve the heat transfer performance. And at a pressure of > 35 MPa, increasing the pressure will improve the heat transfer performance moderately. By comparing with experimental data, the Gupta’s correlation has acceptable accuracy in predicting the heat transfer coefficient and inner wall temperature.