QUANTITATIVE MICROSCALE HIGH SPEED VISUALIZATION OF POOL BOILING PHENOMENA FROM ENHANCED EVAPORATOR TUBES

Experimental investigations are presented of enhanced evaporation tubes with re-entrant cavities operating in the pool boiling mode under saturation conditions of the working fluid propane.
The heat transfer coefficients of the evaporator tubes are determined for different heat fluxes and saturation temperatures. The boiling phenomena are qualitatively visualized by means of high speed video technique and the quantitative evaluations of the high speed videos, e.g. the determination of the bubble departure diameter, the bubble generation frequency, are carried out for low heat fluxes using digital image processing methods. The high speed hardware including the illumination system and the applied digital image processing (digital filtering, Fourier-frequency-analysis and correlation technique) are described. Both, the qualitative and quantitative data of the high speed visualization are discussed.