Heat Transfer Characteristics of Internally Ribbed Tube for a Boiler With Annular Furnace at Subcritical and Near Critical Pressure

Within the range of pressure from 12 to 22.5 MPa, mass flux from 170 to 420 kg/(m2·s) and inner heat flux from 150 to 366 k W/m2, an experiment was conducted to investigate on the heat transfer characteristics of vertical upward internally ribbed tube. The experimental results show that dryout occurs at subcritical pressure. With the increase of inner wall heat flux and pressure, dryout occurs ahead and the peak wall temperature after dryout goes up. The effect of mass flux is non-monotonic and there exists a critical mass flux. When mass flux goes up, dryout appears ahead if it is lower than the critical mass flux and is delayed if it is above the critical mass flux. At subcritical pressure in near critical pressure region, departure from nucleate boiling(DNB) occurs at high heat flux. The increase of inner wall heat flux and the decrease of mass flux can delay the DNB and lead to higher peak wall temperature after heat transfer deterioration. At supercritical pressure in near critical pressure region, the heat transfer performs well and the heat transfer is enhanced in the pseudo-critical enthalpy region. The heat transfer characteristic is similar to that in subcritical pressure region.