Experimental investigation on boiling heat transfer of high pressure water in a SCWR sub-channel

An experiment has recently been completed to obtain the wall temperature and heat transfer coefficient of water at subcritical pressures in a SCWR sub-channel. The test section was wire-electrode cut to simulate the central sub-channel of a 2 × 2 rod bundle. Experimental parameters covered the pressures of 11-19 MPa, mass fluxes of 700-1300 kg/m2s and heat fluxes of 200-600 kW/m2. Heat transfer characteristics in single-phase and two-phase regions were analyzed with respect to the variations of heat flux, system pressure and mass flux. For a given pressure, it was found that the wall temperature increases with increasing heat flux or decreasing mass flux in the steam-water two-phase region. Departure from Nucleate Boiling (DNB) was observed from the wall temperature profiles in the sub-channel. Experimental results showed that the soaring wall temperature at DNB becomes dramatic with the increase of pressure. Correlation assessments have also been conducted against the current set of experimental data. The comparisons indicated that the Fang correlation agrees well against the two-phase heat transfer coefficient. Heat transfer difference in the sub-channel at subcritical and supercritical pressures was compared. It was concluded that the wall temperature at sub-critical pressure may be lower or higher than that of supercritical pressure depending on q/G ratio and the occurrence of DNB.