Air-cooled heat exchangers in very cold climates and/or involving viscous or high pour-point fluids may require winterization for freeze protection and process temperature control. To prevent process fluids from freezing and to protect the exchanger, the exchanger is equipped with automatic louvers and recirculation chambers to mix warm exhaust air with cold inlet air and plenum heaters for start-up.

Extruded fins are applied by forming the fins from the metal of a tubular aluminum sleeve into which the fluid handling tube has been inserted. The extruded finning machine literally squeezes the fins out in a close spiral shape from the material of the aluminum sleeve. This extrusion raises the fins to their required height, leaving a substantial thickness of aluminum totally encasing the fluid handling tube. This design offers excellent resistance to corrosion as the aluminum fin completely encloses the metal of the tube and provides the best bond between fin and process tube.

Extruded Serrated fins are formed by taking the standard extruded finned tubes and cutting longitudinal serrations along the entire length of the finned tubes. The serrations improve the heat transfer rate and allow for smaller footprint designs.

Embedded fins are applied by first plowing or rolling a continuous spiraling groove into the outer surface of the tube. A strip of fin material is then wound on edge into this groove followed by a mechanical process that either peens or rolls the tube material against the inserted fin. The integrity of this process can only be verified by a fin pull test. Preferred design for cyclical temperatures and high temperature service.

Wrap-on fins are applied by feeding a thin strip of heat conducting metal (usually aluminum) into a machine which first forms a small “foot” at one edge of the strip (L-Base). The strip is wound tightly around the tube and retained by staples at both ends of the tube. Most economical option and offers some protection from corrosion. Not recommended for severe service.

The plug box header consists of tube sheet, plug sheet, top, bottom, and end plates welded together to form the header. Holes are drilled and grooved in the tube sheet so that the tubes can be rolled in place. Holes are drilled and threaded in the plug sheet opposite each tube to allow access to the tubes. Partitions are welded in the headers to establish the tube-side flow pattern, which generates suitable velocities in as near countercurrent flow as possible for maximum mean temperature difference. Partitions and stiffeners (partitions with flow openings) also act as structural stays. Horizontally split headers may be required to accommodate differential tube expansion in services having high fluid temperature differences per pass.

Bolted removable cover plates are used for improved access to headers in severe fouling services or where complete access to the inside of the header boxed is desired. The removable cover header is constructed similarly to the plug box header except that a flanged and gasketed solid cover plate replaces the plug sheet. Cover plate headers are limited to approximately 400 psi in design pressure.

Pipe and U-bend headers are utilized for very high pressure applications. These designs are more expensive and difficult to access the tubes, but necessary for design pressures above approximately 5000 psi.

A rolled tube-to-tubesheet joint is standard but seal-welded and strength-welded construction is also available.

The air moving device for an air-cooled heat exchanger is commonly an axial flow, propeller type fan that either forces the air across the bundles (forced draft) or pulls it across (induced draft). To provide redundancy in case a mechanical unit falls and to provide the basic control achievable by running one fan or two, a bundle or set of bundles is usually provided with two fans. Depending on design requirements and customer preference, a Fin-Fan® may be supplied with Hudson Tuf-Lite® fiberglass fans or Cofimco aluminum fans.

Fans are typically driven by electric motors according to customer specifications. Speed reduction is typically accomplished with high-torque positive type belt drives, which uses sprockets that mesh with the timing belt cogs. Also available for high horsepower applications or according to customer preference, are right angle gear drives. Bearings for fan shafts are specially made for severe duty use in Fin-Fan® exchangers.