AT-84-01-4 -- Heat Transfer Analysis of Shell-and-Tube Condensers with Shell-Side Enhancement PDF

Enhanced tubes considered in this paper have small sharp fins of about 0.039 in. (1 mm) high provided with an axial pitch of 0.028 in. (0.7 mm). They are made of copper or copper alloys and designed to enhance condensation of fluorocarbon refrigerants. In the first half of the paper, the performance of this enhanced surface is summarized, indicating that the heat-transfer coefficient exceeds that of a 18 fpi (7 fins per 10 mm) low-finned surface by a factor of 3.

In applications to shell-and-tube condensers, degradation of heat-transfer enhancement is expected because of condensate inundation in the lower part of a bundle of horizontal tubes. This problem is addressed in the latter half of the paper. The laboratory experiment produced the ratio of heat-transfer coefficients with and without receiving condensate flow from above. The ratio levels off for large inundation rates at a level of 0.6. Despite this relatively large degradation, the enhanced tubes maintain a superiority over conventional low-finned tubes, leading to a reduction of about 30 percent of required heat transfer area, according to a design analysis of a condenser for R-11.