An aftercooler is a mechanical heat exchanger designed to remove the heat and moisture of compression from a compressed air stream so the air is cool and dry enough for use in air-operated equipment.

A compressed air aftercooler has three primary functions:

• Cool the air discharged from the air compressor.
• Reduce the moisture in compressed air.
• Protect downstream equipment from excessive heat and moisture.

Air-Cooled Aftercoolers

Air-cooled aftercoolers use ambient air to cool the hot compressed air. Compressed air enters the air-cooled aftercooler and travels through either a spiral finned tube coil or a plate-fin coil design, while ambient air is forced over the cooler by a motor-driven fan. The cooler ambient air removes heat from the compressed air.

Most air-cooled aftercoolers are sized to cool the compressed air to within 15°F to 20°F of ambient cooling air temperature, also called approach temperature. As the compressed air cools, up to 75% of the water vapor condenses into a liquid that should be removed.

A moisture separator installed at the discharge of the aftercooler mechanically removes most of the liquid moisture and solids from the compressed air. 

The moisture separator utilizes centrifugal force, and in some cases baffle plates, to collect moisture and solids at the bottom of the separator. An automatic drain should then be used to remove the moisture and solids.