EFFECT OF SURFACE WETTABILITY ON ACTIVE NUCLEATION SITE DENSITY DURING POOL BOILING OF WATER ON A VERTICAL SURFACE

Pool boiling of saturated water at 1 atm pressure has been investigated. In the experiments, copper surfaces prepared by following a well-defined procedure were used. The cumulative number density of the cavities and their shapes were determined with an optical microscope. The surface had a mirror finish and had a surface R(a) (centerline average) value of less than 0. 02 mum. The wettability of the surface was changed by controlling the degree of oxidation of the surface. In the experiments with the primary surface, the wall heat flux and superheat were determined with the help of thermocouples embedded in the test block. The density, spatial distribution, local distribution, and nearest-neighbor distance distribution of active nucleation sites in partial and fully developed nucleate boiling were determined from still pictures.