HIGH SPEED FLOW VISUALIZATION OF POOL BOILING FROM STRUCTURED TUBULAR HEAT TRANSFER SURFACES

Experimental investigations of pool boiling from novel tubular heat transfer surfaces (structured tubes with re-entrant cavities) are carried out with the hydrocarbon propane as working fluid operating under moderate heat fluxes (<100 W/m2) and saturation conditions. The heat transfer coefficients determined by thermocouple measurements are presented. The evaporation phenomena are visualized by a high speed video system and by means of digital image processing techniques (e.g. Fourier-analyses, correlation-techniques). The bubble departure diameter at the surface, the bubble generation frequency at corresponding nucleation sites and the bubble upward flow velocity are quantitatively determined.