FILM BOILING HEAT TRANSFER AND MINIMUM-HEAT-FLUX (MHF)-POINT CONDITION IN SUBCOOLED POOL BOILING.

Abstract

The minimum-heat-flux (MHF)-point condition and film-boiling heat transfer in subcooled pool boiling of water were experimentally investigated by using a horizontal cylinder and a sphere. First, collapse behavior of vapor films was observed, and it was found that collapse modes can be classified into coherent and propagative collapses. Second, the relation between the MHF-point temperature and the propagation rate of film collapse was experimentally obtained, and the MHF-point temperature at which coherent collapse occurred was defined as its true value. The experimental data obtained show that the true MHF-point temperature is not strongly dependent on liquid subcooling and it does not exceed the liquid's maximum, metastable superheat temperature even at large subcoolings. Finally, using the experimental data of subcooled film-boiling heat transfer for various liquids, a prediction technique based on Hamill's correlation was developed.