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Electric and Air driven cooling motors and filters

Why Aftercoolers

The compressed air discharged from an air compressor is hot. Typically piston compressor outlet temperature can be 300*, that of a rotary screw 200*. Compressed air at these temperatures contains large quantities of water in vapor form. As the compressed air cools this water vapor condenses into a liquid form. As an example if an aftercooler is not used, a 200 scfm compressor operating at 100 psig introduces 45 gallons of water into the compressed air system each day.
 

Rotary Screw Compressor

Much more efficient and even simpler -- is the screw compressor. The screw compressor is also driven by electric motors. The main difference from the piston type is that the screw compressor uses two large intermeshing screws to squeeze the air inside a large chamber. In order to keep the screws from being damaged, oil must be injected to keep the entire system lubricated. The oil is mixed with the air upon entrance into the compression chamber and is passed between to two rotating screws. After exiting the chamber, the air and oil pass through a large oil separator where the air passes readily through a small orifice filter. The oil is cooled and reused while the air goes on to the reservoir tanks to be utilized in work.

Air cooled aftercooler
Aftercoolers are heat exchangers for cooling the discharge from a air compressor. They use either air or water and are an effective means of removing moisture from compressed air. Aftercoolers reduce the amount of water vapor in a compressed air system by condensing the water vapor into liquid form. Aftercoolers combined with a separator are an excellent way to reduce moisture in a compressed air system. In a distribution or process manufacturing system, liquid water causes significant damage to equipment.

An aftercooler is necessary to ensure the proper functionality of pneumatic or air handling devices that are a part of process manufacturing systems. Aftercoolers can use either air-cooled or water-cooled mechanisms.

Air cooled aftercoolers
Air cooled aftercoolers use ambient air to cool the hot compressed air. The compressed air enters the air cooled aftercooler. The compressed air travels through either finned tubes or corrugated aluminum sheets of the aftercooler while ambient air is forced over the cooler by a motor-driven fan. The cooler, ambient air removes heat from the compressed air.
 
Aftercooling sizing considerations
Most air aftercoolers are sized to cool the air to within 5 to 20°F (2.7°C to 11°C) of ambient air or cooling water temperature. This is called the approach temperature. Always size for the hottest day with 100% relative humidity. Sizing is dependent on the temperature of the air coming from the compressor. Typically air exiting a compressor is between 180°F (82.2°C) to 350°F (176.6°C).
 
To select an aftercooler, determine the approach temperature requirement (temperature above the cooling medium used) for your compressed air. Specify 5, 10, 15, or 20°F (2.7°C, 5.5°C, 8.3°C, or 11°C) over the cooling medium temperature. Consider the temperature requirements of downstream equipment like dryers and your location's climate. Then, based on your compressor's CFM (cubic feet per minute) and compressed air temperature, choose an aftercooler.
 
Rules of Thumb
·        Most aftercoolers are sized to cool the air to an approach temperature of 5 to 20°F (2.7°C to 11°C) of ambient air temperature.
·        Size for the hottest day with 100% relative humidity.
·        Compressed air aftercoolers are located directly downstream of the compressor.
·        Proper maintenance will keep the aftercooler efficient. A dirty aftercooler results in both warmer air temperatures and increased pressure drop.
·        For every 20°F (11.1°C) rise in compressed air temperature, the moisture content of the air doubles.
 
An oversized aftercooler is usually cost-effective; it will produce cooler air with less moisture, reducing the requirements for the air dryer. Additionally, a larger aftercooler will have a lower pressure drop, lowering the necessary discharge pressure from the compressor. For the best results, size the aftercooler for a 1 to 2 psi pressure drop.