ABSTRACT
The onset of nucleate boiling on a heater submerged in a pool of liquid is characterized by the appearance of vapor bubbles at discrete locations on the heater surface. These bubbles form on surface imperfections, such as cavities and scratches. The gas/vapor trapped in these imperfections serves as nuclei for the bubbles. After inception, the bubbles grow to a certain size and depart from the surface. The effect of increased surface roughness is to shift the nucleate boiling curve to the left. This, in turn, corresponds to a higher heat flux at a given wall superheat for a rougher surface. Physicochemical changes on a boiling surface can take place in several ways: deposition of inert matter contained in the host liquid, slow chemical reaction of the surface with gases dissolved in the liquid or with vapor, and strong chemical reaction of the metal with concentrated solutions of electrolytes.
