BEHAVIOR OF A LIQUID FILM OBSERVED ON A BOILING WALL WITH HIGH HEAT FLUXES.

The heat transfer mechanism of a thin liquid layer, termed as macrolayer, in existence between a vapor mass and a heating wall observed in nucleate boiling at a high heat rate, is studied. It is proved that heat conduction across the macrolayer and evaporation at the free surface is not a mode efficient enough to account for the major portion of heat transfer. The alternative model proposed is macrolayer primarily consumed through evaporation of much thinner microlayers at the bottoms of vapor stems penetrating the macrolayer. Analysis based upon the proposed mechanism shows the macrolayer does not totally dry out in a vapor-mass cycle before boiling crisis. Other mechanisms accountable for the consumption of the macrolayer are also discussed.