Finned Tube Air Cooled Heat Exchanger
 

Air-Cooled Heat Exchangers are generally used where a process system generates heat which must be removed, but for which there is no local use. Air-Cooled Heat Exchangers (often simply called air-coolers) do not require any cooling water from a cooling tower. They are usually used when the outlet temperature is more than about 20 deg. F above the maximum expected ambient air temperature. They can be used with closer approach temperatures, but often become expensive compared to a combination of a cooling tower and a water-cooled exchanger.
 

Finned Tubes:
 

The Tubes can be of virtually any material available, such as carbon steel, stainless steel, Admiralty brass, or more exotic alloys. The minimum preferred outside diameter is one inch. Most of the process coolers have Tubes which are 1.0", 1.25", or 1.5" OD. The minimum tube wall thicknesses vary with the material. In some cases the design pressure and design temperature of the exchanger govern the minimum thickness.
 

The Fins are almost always of aluminum material. The most common type of Fin is the helically wrapped, L-footed type. These are used where the process temperatures are below about 350 deg. F. The API specification calls for cast zinc bands at the ends of the tubes to prevent the fins from unwrapping. Some of the better manufacturers also use cast zinc bands at the tube supports. For higher process temperatures, most customers prefer either embedded or extruded fins. The embedded fins have the highest temperature capabilities. They are made by a process which cuts a helical groove in the OD of the tube, wraps the fin into the groove, then rolls the upset metal from the tube back against the fin to lock it into place. The tube wall must be thicker with embedded fins because of the groove.