On the Nature and Location of Bubble Nuclei in Boiling from Surfaces

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Abstract
In the pool boiling of pure organic liquids from a reproducible platinum surface, an initial temperature overshoot is observed before the surface breaks into nucleate boiling. A logarithmic plot of heat flux vs temperature excess has a slope of 3.5 for the first traverse but subsequent traverses give a reproducible line having a higher slope and surface temperature. Vigorous heating in air restores the surface to its original condition. These results are explained in terms of the trapped-bubble hypothesis by assuming that many potential vapor traps on the surface are filled with liquid initially, and fill with vapor once boiling commences. The gradual increase in surface temperature for a given flux is attributed to the progressive deaeration of the nucleating centers by dilution with vapor. To reconcile the fact of surface aeration with the existence of an initial temperature overshoot, it is necessary to assume that the temperature drift is due primarily to the removal of sorbed air, resulting in decrease in contact angle, corresponding to improved wetting of the surface. These experiments also indicate that the bulk of the active nuclei are on the heating surface, rather than on dust particles in the liquid.

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