Maximum Heat Fluxes for Pool Boiling on Partly III-Wettable Heating Surfaces : (Part 1, On the Visual Observation of Boiling and the Temperature Profiles of Heating Surface)

Abstract

The current study presents some experimental results for examining the maximum heat fluxes in pool boiling of saturated water at atmospheric pressure on partly ill-wettable heating surfaces. The experiment was carried out on the electrically heated horizontal strip, at the center of which an artificially ill-wettable portion was installed. The boiling regime on the ill-wettable portion at very low heat fluxes is nucleate boiling whose behavior closely resembles a transition one. Alternatively stable vapour film is formed on this portion at comparatively low heat fluxes of 5×104kcal/m2hr to 105 kcal/m2hr that depend on the geometrical dimension of ill-wettable area and thereafter the simultaneous nucleate-film boiling is realized. Accordingly, in such a system, while the maximum heat fluxes are prescribed by the transition to film boiling for large sizes of ill-wettable part, the formation of stable vapour film is not clear for small sized ill-wettable part on account of drastic hydrodynamic interaction of nucleate boiling. Parallel to the experimental measurements of heating surface temperature at the center of ill-wettable portion for simultaneous nucleate-film boiling regime, simple analytical calculations were performed and, in consequence, favorable consistencies were obtained for the wide ranges of heat fluxes and ill-wettable dimensions of interest.