Abstract:

ESDU 89038 summarises the advantages and disadvantages of reflux condensation in vertical tubes, in which the vapour enters the heat exchanger tube bundle at the bottom and the condensate flows down under gravity. The mechanism of flooding, when the condensate is carried upwards rather than draining to the bottom, is discussed and available flooding data are compared with two successful correlations to establish their accuracy. Limitations of the recommended correlation are stressed and methods of improving the flooding performance are suggested. Data for condensate film heat transfer are also compared with an existing correlation for co-current flow of vapour and condensate and suggest that the correlation can be used in the reflux situation. Pressure drop is discussed, and it is concluded that under most operating conditions it will be low and often negligible. A step-by-step calculation procedure for the design of a reflux condenser, or for performance rating an existing condenser, is given for either a single- or a multi-component vapour and is illustrated with a worked example.