摘要:
The first and most difficult stage in the condensation of water vapour is the increase in the size of the drops until their radius satisfies the Kelvin–Helmholtz equation for the degree of undercooling or supersaturation reached at the temperatureTcof the vapour; the second stage is the increase in size by continued addition of molecules until the vapour pressurep(v) of the drop containingvmolecules approaches the pressurep∞exerted at the same temperature by a pool of water. A gradual enlargement to visible drops follows. Consideration of the number of collisions of the molecules with the drops forming at the vapour pressurepcof steam, and the loss of molecules by virtue of the higher vapour pressure of small drops leads to the conclusion that at condensation temperatures between 0° and 50 °C. the centres of condensation in the absence of dust or ions contain fewer than a hundred molecules. When the degree of supersaturation corresponds to larger drops, condensation is bound to fail. The conclusion drawn from the theory is confirmed by the values obtained in the tests with flowing steam and with cloud chambers. At higher temperatures larger drops act as nuclei. The growth in the second stage is also extremely rapid, at least until the radius equals in size the wave-length of visible radiation. Water drops of this size, that is, drops that produce coloured diffraction rings, behave as large drops. The heat of condensation may furnish part of the work to be performed against the surface tension.
ISSN:1923-4287
DOI:10.1139/cjr44a-005
出版商:NRC Research Press
年代:1944
数据来源: NRC