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)

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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 5×10^4kcal/m^2hr to 10^5 kcal/m^2hr 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.
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