Study on Ex-Vessel Cooling of Reactor Pressure Vessel : Model Analysis of Critical Heat Flux on Inclined Plate and Hemisphere Facing Downward(<Special Issue>International Conferences on Power and Energy System)

Critical heat fluxes (CHFs) on inclined plates and hemispheres in the case of saturated pool boiling were investigated analytically. In the present model, the most dangerous wavelength and propagation velocity in the Kelvin-Helmholtz instability on the liquid-vapor interface were calculated to determine the length and the velocity of the coalesced bubbles at CHF. The time period for which the coalesced bubble covered the heated surface was calculated as the length divided by the velocity. In close to the surface oriented downward, the characteristic length was provided by the length of the heater; the characteristic velocity was given by the correlation of the rising velocity of a spherical cap bubble with 17 to 40mm the equivalent diameter. The predictions agreed well with previous experimental data obtained for an inclined plate in overall inclination angle. The model given as a function of the inclination angle was developed for the CHF on a hemisphere. The extended model well represented the experimental data on hemispheres.