Effect of Condensation on Performance and
Design of Extended Surfaces
VIRGIL J. LUNARDINI AND ABDUL AZIZ
INTRODUCTION
Extended surfaces or fins have been traditionally employed to reduce the convective
resistance associated with low values of the heat transfer coefficient h such as those
encountered in convection to and from gases. In condensation, the typical values of h are
high and the need for and the effectiveness of fins for augmentation may not be immedi-
ately apparent. However, in the past 50 years, several engineering situations have been
identified where augmenting condensation can be beneficial. Consider, for example, the
condensation of organic vapors where the poor thermophysical properties result in com-
paratively low values of h and consequently offer room for enhancement. Even with
fluids having favorable thermophysical properties, the condensing side resistance may be
significant and warrant reduction, especially if the cold side is augmented. The wide-
spread use of integral fin tubes in surface condensers for the refrigeration and so-called
process industries clearly demonstrates the usefulness of fins for enhancing condensa-
tion. The use of finned tubes in the cold regions of the world will almost always occur
with condensation and the effects of the condensed liquid must be carefully examined.
Vapor on a surface condenses if the temperature of the surface is kept below the vapor
saturation temperature. Although four basic mechanisms (homogeneous, direct contact,
drop, and film) occur, most condensers are designed to operate under the film condensa-
tion mode. The process is characterized by the formation of a thin film of liquid that
drains under the action of gravity or surface tension or both. The presence of a film creates
a barrier between the vapor and the cooled surface and thus retards the condensation
process. If condensation is to be enhanced, the film thickness must be reduced. This
reduction can be achieved by using, among other methods, finned surfaces instead of
plain surfaces.
The purpose of this report is to serve as a comprehensive review of the published
literature on condensation on extended surfaces. The authors hope that the review will be
useful to researchers and practicing engineers alike. The report contains several examples
that serve to demonstrate the applicability of the material to engineering analysis and
design.
To facilitate a systematic presentation, the report has been organized as follows. First,
the theory of film condensation on extended surfaces is introduced. The theory utilizes
the well-known Nusselt model for the heat transfer coefficient to analyze condensation on
three fin configurations: horizontal cylindrical (pin) fin, vertical cylindrical fin, and verti-
cal rectangular fins. This is followed by a discussion of conjugate conductioncondensa-
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