The mechanism of nucleate boiling in pure liquids and in binary mixtures—part III

Abstract Nucleate boiling is described as a relaxation phenomenon concerning the superheating of the equivalent conduction layer at the heating surface due to the rapid growth of succeeding vapour bubbles on active nuclei. Expressions for the adherence and delay times, the bubble frequency, the departure radius, the vaporized mass and diffusion fractions at the heating surface, and the nucleate boiling peak flux, could thus be derived. The theoretical predictions are in good agreement with experimental data deduced from high speed motion pictures and from boiling curves on water-methylethylketone and water-1-butanol mixtures. In addition, a criterion for the onset of film boiling has been formulated in terms of the region of influence of a bubble. The effects of wetting and nucleation are established and incorporated in the theoretical treatment. The advantage of the present equations over correlations resulting from dimensional analysis is that they reveal a number of highly interesting phenomena, which were obscured previously. For instance, the theory predicts a coincidence of a maximal slowing down of bubble growth rate and departure size (resulting in a minimal heat transmission to individual bubbles: “boiling paradox”) and the occurrence of a maximum nucleate boiling peak flux at the same low concentration of the more volatile component in a binary system, which can be derived from equilibrium data. This is also in accordance with experimental results. In principle, the theoretical predictions include the favourable effect on peak flux by all other methods resulting in a diminished vapour production at the heating surface—which corresponds generally with an increased frequency of smaller bubbles—e.g. Surface boiling, vortex flow, the use of high pressures and the application of an electrostatic field.