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Главная Архив Thermal Letter Оргкомитет Будущие конференции AIHTC
International Heat Transfer Conference 12

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

Separation in Reflux Condensers

David R. Webb
Department of Chemical Engineering UMIST University of Manchester Manchester M60 1QD United Kingdom.

S. B. Al-Shammari
Dept of Chem Eng, UMIST, Sackville St., Manchester, M60 1QD

DOI: 10.1615/IHTC12.5510
6 pages

Аннотация

Reflux condensation is used to give some separation of a vapour mixture. It is often carried out in a cooled vertical tube with the vapour stream in counter-current flow to its condensate. A natural separation occurs whereby the more volatile components remain in the vapour phase. This is enhanced by an additional rectification effect. The condensate formed at the top of the condenser is richer in the more volatile components and as it falls towards the vapour inlet they may evaporate, improving the separation achieved. It is this rectification that is the major potential advantage of the device. This benefit should compensate for the disadvantages, principally lowthroug hput, caused by the necessity to operate below the flooding point where the vapour carries the condensate from the top of the device and the separation effect is lost.

The extent to which the condensate is mixed is crucial to the design. If the rate of mixing of the condensate is low, the surface composition is defined by the local rates of condensation and the behaviour of the condenser would be similar to that of a horizontal condenser where the condensate is separated from the remaining vapour. The rectification effect can only be realised and the choice of a vertical reflux condenser justified if the mixing rate of the condensate is fast enough. The condensate film in a reflux condenser is usually in laminar flow though the surface is disturbed by capillary waves. Thus the film is mixed principally by diffusion. It has not been clear whether this is fast enough to promote the rectification effect. Additionally the rate processes in the gas film may limit the extent of rectification.

This paper treats the problem from an analytical viewpoint. It should help designers resolve the problems that they face in design of reflux condensers. Recommendations are made on howto predict the performance of reflux condensers.

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