Boiling: Difference between revisions

Revision as of 16:03, 10 October 2007

Revision as of 16:04, 10 October 2007

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'''Mike cozzBoiling''', a type of [[phase transition]], is the rapid [[evaporation|vaporization]] of a [[liquid]], which typically occurs when a liquid is heated to its [[boiling point]], the [[temperature]] at which the [[vapor pressure]] of the liquid is equal to the pressure exerted on the liquid by the surrounding environmental pressure. Thus, a liquid may also boil when the pressure of the surrounding atmosphere is sufficiently reduced, such as the use of a [[vacuum pump]] or at [[high altitude]]s. Boiling occurs in three characteristic stages, which are ''nucleate'', ''transition'' and ''film boiling''. These stages generally take place from low to high surface temperatures, respectively.

''Nucleate boiling'' is characterized by the incipience and growth of bubbles on a heated surface, which rise from discrete points on a surface, whose temperature is only slightly above the liquid’s saturation temperature. In general, the number of [[nucleation]] sites are increased by an increasing surface temperature. An irregular surface of the boiling vessel (i.e. increased surface roughness) can create additional nucleation sites, while an exceptionally smooth surface, such as glass, lends itself to [[superheating]]. Under special conditions, a heated liquid may show [[boiling delay]] when heated over its boiling point, by starting to boil suddenly and violently.