Suggested placement of after-coolers
The after-cooler should be placed as close as manageable to the compressor discharge.

Types of after-coolers
Basically there are two kinds of air after-coolers :-

• Air-Cooled
• Water-Cooled.
  

The after-cooler type you opt depends on the specific preference and demand.

Compressor makers may add after-coolers within the compressor assemblage. Generally, these compressors are adverted as integral after-coolers. A freestanding or stand-alone after-cooler is a detached unit, which is set in the bottom of the compressor.

Air Cooled after-coolers (fig. AC1-2) make the use of ambient air for cooling the hot compressed air. The compressed air then passes into the air cooled after-cooler. The closed air moves via either corrugated aluminum sheets or finned tubes or of the after-cooler while ambient air is pushed over the cooler by the motor-driven fan. The ambient air and cooler take away the heat from the compressed air.

Belt Guard Air Cooled After-cooler

The belt guard air-cooled after-coolers are mounted to the compressor's v-belt protector or guard. The compressor's belt pulley incorporates fins, which are configured to propel ambient air over the air cooled after-cooler and compressor. The air passing via the after-cooler aids the heat transfer. The pulley also directs the air over the compressor and assists in keeping accurate operating temperature.

Water-Cooled Pipe Line After-cooler

The water-cooled pipe line after-coolers are available in various styles. The most common variety for compressed air work is a Tube Heat Exchanger/After-cooler and Shell(fig. AC1-3). The pipe line after-cooler are comprised of the shells with the packet of tubes contoured inside. Typically the compressed air flows via the tubes in single direction when the water flows towards the shell side in the other way. Heat from the compressed air is transferred to the water. Water vapor is gathered as the compressed air gets cooled. The moisture is abstracted by the drain valves and moisture extractor. A modulating structure is suggested to manage a consistent temperature and cut down the water ingestion. The tube bundles come with the benefit that they can be fixed or removed. Fixed tube collections value less but they are more challenging to keep than bundles, which can be abstracted for cleaning purpose.

The drawbacks of the water-cooled aftercooler are difficult heat recovery and high water utilization. Advantages to utilizing a water-cooled after-cooler are finer heat transfer and zero electricity requirement.

Aftercooling sizing considerations

Most air after-coolers are particularly sized to cool the air to inside 5 to 20°F (2.7°C to 11°C) of cooling water temperature or ambient air. This is also identified as the approach temperature. Always sized for the warmest day with 100% relative humidity, the sizing is based on the air temperature that comes from the compressor. Commonly, air exiting compressor is between 180°F (82.2°C) to 350°F (176.6°C).

To choose an aftercooler, it should be determined that the approached temperature demand (temperature more than the cooling medium utilized) for the compressed air. Particularize 5, 10, 15, or 20°F (2.7°C, 5.5°C, 8.3°C, or 11°C) all over the cooling medium temperature. There is also a necessity of considering the temperature demands of downstream instrumentality such as dryers and the climate of the location. Then, dependent on the compressed air temperature and compressor's CFM (cubic feet per minute), opt for an aftercooler.

These have maximum operating temperatures provided for industrial usage. Before you buy or install any compressed air part, do check the real maximum operating temperature for that specific product.

Figure AC1-4

The oversized aftercooler is normally cost-effective; and offer cooler air with low moisture and reduced demands for the air dryer. In addition, a large aftercooler will incorporate a reduced pressure drop, diminishing the essential discharge pressure from the mechanical device. For the flawless results, the sizing of the aftercooler for a 1 to 2 psi pressure drop is necessary.
 
Maintenance demands

Aftercooler (water-cooled): Routinely inspection is needed, cleaning is essential.
Review of approach temperature and pressure drop is must, monitoring of water quality is requisite.

Aftercooler (air-cooled): Inspection of parts and their cleaning should be done on a regular basis. The drain valves should be checked every day.

Correct maintenance will manage the efficiency of aftercooler. A dirty aftercooler bring out both warmer air temperatures as well as accrued pressure drop.

Thumb Rules :-

• The after-coolers are organized to cool the air to an approach temperature of 5 to 20°F (2.7°C to 11°C) of close air temperature.
• Sized for the hot temperature days with 100% relative humidity.
• Compressed air after-coolers are directly placed in the compressor downstream.
• Proper maintenance will continue the efficiency of aftercooler. A dirty aftercooler can bring out disturbances in the operation and can result in warm air temperatures and exaggerated pressure drop.
• For every 20°F (11.1°C) the ascent is done in compressed air temperature, the moisture complacent of the air multiples.