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In-tube condensers are used in many air-conditioning and refrigeration systems. While in-tube condensation "is a heat transfer process with rather high heat transfer coefficients, there are circumstances where the condensation provides the controlling heat transfer resistance. This occurs with many industrially important organic liquids as well as the common fluorocarbon refrigerants. In these cases, augmentation techniques can be used to significantly improve the performance of condensers. Smaller condensers can be specified or the average temperature differences can be reduced.

It is not possible to augment refrigerant condensation by promoting dropwise condensation since refrigerants will wet all materials. Modifications of fi1mwise condensation must thus be considered. In fi1mwise condensation in circular tubes, an annular layer of condensate is created at the cool tube wall. The ideal model, consisting of a symmetrical annular layer of the condensate and completely separated phases, has been employed in most theoretical studies. However, gravitational, interfacial shear, and pressure forces can redistribute the condensate and disrupt this ideal phase segregation. Stratification, interfacial waves, entrained liquid droplets, bubbles, and vapor slugs all can be present.

Active or passive augmentation techniques can be used to modify real film condensation processes. Active techniques require external power for operation while passive ones do not. A previous literature review describes how techniques of both types have been used to augment fi1mwise condensation [1]. Several studies have considered in-tube condensation. The present program considers only passive techniques since they are of greater practical interest.