TABLE OF CONTENTS The most expensive and most critical component of any air-cooled heat exchanger is the heat transfer surface area. Owing to the low heat transfer coefficient on the air side, extended surfaces or fins are required to increase the surface area density. This improves the overall conductance and results in a lighter and more compact heat exchanger. These reductions of heat exchanger mass and volume are important for propulsive plants (automobile, truck, aircraft, etc.), cryogenic, refrigeration, and air-conditioning systems. In air-cooled heat exchangers found in power plants and chemical processing complexes, it is important to have low-cost finned surfaces that resist corrosion, can be cleaned readily, and have adequate mechanical strength. A service life of more than 25 years must often be guaranteed. Although nonmetallic materials have been evaluated for possible use in air-cooled heat exchangers, no large unit incorporating such materials has been built according to both Pollack and Guyer.
Finned tubes may be round, elliptical, flattened, or otherwise stream-lined to reduce the flow resistance on the air side. Different types and shapes of fins are either an integral part of the tube or attached to the tube by mechanical means only. In addition, they can be attached by soldering, brazing, galvanizing, or welding.
To improve the heat transfer characteristics, the fin surface may be roughened, cut, corrugated, or perforated. In certain applications, sections of the surface are stamped out to create spaces separating the adjacent fins. Examples of finned surfaces are shown in Figure...
