Further Remarks on the Stability of Boiling Heat Transfer. Report 58-5 PDF Download

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An analytical expression is presented which permits the prediction of the maximum nucleate heat flux in pool boiling of saturated or subcooled liquids. The numerical values of the empirical constants which appear in the Kutateladze and Borishanskii criteria for the burnout'' heat flux are derived from the theory. An analytical expression for the empirical function which appears in the correlation of Griffith is also derived. The hitherto unexplored features of transition boiling, i.e., the hydrodynamic instability, the well defined geometrical configuration and the frequency dependence are described, supported by experimental evidence, and used as the basis for the analytical work. The peak heat flux in transition boiling is shown to be limited by the combined effects of Taylor and Helmholtz instabilitiess whereas the minimum transitional heat flux is limited by the effect of Taylor instability ony. The analysis leads to the conclusion that because of the statistical nature of the ddsturbances and the bandwidth'' of the unstable wavelengths which govern the process, an inherent uncertainty exists in determining the exact value of the heat flux at burnout.'' The width of this uncertainty range is plus or minus 14%. The often noted poor reproducibility of experimental data on burnout'' can be inferred, therefore, from the analysis. The reason analytical attacks upon the burnout'' problem, based upon considerations of bubble agitation and other nucleate boiling characteristics, have not been successful is discussed. The literature has shown conclusively that the surface conddtions play the dominant role in determining the superheat accompanying a given heat flux. The analysis reveals, in addition, that even if the nucleating characteristics of the surface were known the problem could still not be solved from these considerations because the mechanism of the instability occurs in the fluid away from the surface. The extension of the analysis to flow systems is briefly discussed. (auth).