Transition from film boiling to nucleate boiling in forced convection vertical flow

摘要

The mechanism of collapse of forced cnnvection annular vertical flow film boiling, with liquid core, is investigated using liquid nitrogen at low pressures. The report includes the effect of heat flux from the buss bar. Tests include runs with mass fluxes varying from 44,000 lbm/hr-ft2 2 2 to 186,000 lbm/hr-ft , and buss bar heat fluxes from 0 to 107,000 BTU/hr-ft The channel was a 0.4 inch I. D. by 0.5 inch O.D. by 8 feet long Inconel 600 tube. Two modes of collapse were isolated, in the absence of rewet by dispersed cooling within the mist flow region. These were axial conduction controlled collapse originating at the entrance to the test section for zero or negative buss bar heat flux; and impulse cooling collapse originating downstream of the entrance for heat into the test section from the buss bar. Collapse heat flux was found to be a function of mass flux, but the collapse wall temperature difference (T - T ) was independent w S of mass flux and could be successfully predicted within 6% by pool boiling minimum transition correlation (e.g. Berenson [5]).