Most airplanes rely on air cycle machines to regulate the air inside of their respective cabin. Some airplanes have two air cycle machines, whereas others have three or more air cycle machines. With air cycle machines, passengers won’t have to endure a hot and humid cabin; they will experience a comfortable environment during their flight.
What Is an Air Cycle Machine?
An air cycle machine is a system that’s designed to cool and dehumidify the air that enters an airplane’s cabin. Most commercial airplanes pump bleed air into the cabin. Bleed air is simply the excess air in jet engines. It’s “bled off” the jet engines for other purposes, such as controlling the temperature of the cabin.
How Air Cycle Machines Work
Many people assume that air cycle machines use freon or a similar refrigerant to create cool air. While air conditioning systems do, in fact, use refrigerant, air cycle machines do not. Instead, they leverage the naturally low temperature of the air in the sky at high altitudes.
Commercial airplanes can fly as high as 35,000 feet. At cruising altitudes such as this, the air is extremely cold. Air cycle machines use this naturally cold air to remove heat from the bleed air.
When bleed air leaves the jet engines, it will enter a heat exchanger. The heat exchanger will transfer heat from the hot bleed air to the cold outdoor air. From there, the air will travel to a compressor where it’s further pressurized.
The air will typically go through another heat exchanger after being pressurized. Pressurization raises the temperature of the air. Therefore, multiple heat exchangers are used in air cycle machines. Air will go through an initial heat exchanger, and after being pressurized, it will go through a second heat exchanger.
Air cycle machines don’t just cool bleed air; they dehumidify it. Dehumidification is the process of removing moisture vapor from the air. Most air cycle machines feature a cyclonic separator. The cyclonic separator will extract moisture vapor from the air so that the air pumped into the cabin isn’t too humid.
In Conclusion
Airplanes use air cycle machines to regulate their cabin air. Air cycle machines consist of various components, such as heat exchangers, that lower the temperature and humidity of bleed air. Jet engines will produce bleed air. The bleed air will travel to one or more air cycle machines where it’s cooled and dehumidified.
