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Oil-Free Air Compressors

Part 1: Cooler Design Considerations for Centrifugal Compressors

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This is Part 1 of our Centrifugal Compressor Design Series. 

What is a Cooler?

Coolers are fundamental to the effective operation of a compressor system. These pieces of equipment cool the compressed air (which is superheated at this point) to below its dew point, allowing the removal of both moisture and water vapor from the air. Specifically, intercoolers remove heat from the air in between compressor stages, while the aftercooler assists in cooling the air discharged from the compressor.

Cooler Designs on the Market

The industry-standard design for intercoolers and aftercoolers is copper or copper-nickel tubes filled with water, where an extended surface fin design cools the hot air that is flowing past the fin/shell side. A second design consists of air flowing in the tubes with cooling water flowing around the tubes via a metal shroud. The tubes have turbulators (internal fins), and the large passage in the center of the tube bundle lets air pass into the compression stage from either the inlet filter or the previous compressor stage. 

Considerations for Performance and Cooler Design

When understanding the life cycle cost and performance of centrifugal compressors, it’s critical that the design of these coolers are taken into account to ensure ideal compressor output. To evaluate the effects of cooler design, the following should be considered:

  • Cooler approach temperature
  • Compressed air discharge temperature
  • Cooling water inlet temperature; and
  • Cooling water temperature rise (ΔT)

Water quality is critical for efficient cooling and significantly impacts the cooler cleaning interval. Cooling towers are the most common technology used in industrial/process situations, usually with some degree of chemical treatment. Closed-loop evaporative coolers are also used, as are completely closed dry cooler designs. Glycol mixture by percent and type will impact heat transfer efficiency across the cooler, affecting compressor performance.

With open cooling towers, it is common for these cooler designs to require removal and cleaning every three to five years. Life of these cooler designs is typically short compared to the rotating assemblies. Depending on the chemical treatment of the cooling water, the coolers themselves may fail before they require cleaning.

Interested in learning more about cooler design, or wish to discuss the specifics of your compressor system's cooler design? Reach out to our compressed air experts today, or tune in next week for Part 2 of our centrifugal compressor design series!

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