Evaporation of macrolayer in nucleate boiling near burnout

The mechanism of nucleate boiling heat transfer near burnout has been investigated by studying the evaporation of the liquid macrolayer underneath the vapor mass. 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 a macrolayer primarily consumed through evaporation of much thinner microlayers at the bottom of vapor stems penetrating the macrolayer. Analysis based upon the proposed mechanism shows that 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.