Have you ever think, imagined or ask How/where the breathable air comes from, when flying in an airplane?
For a start, the modern commercial airplane cruises from approximately 10 to 12 kilometers, which is considered the “sweet spot” for flying. At that altitude, the supply of air is not a problem because there is actually enough of it, but it is not a breathable air as the pressure of the oxygen at that moment is too low to be directly inhaled by humans.
So, the question is, how do we get breathable air when flying?
This involves an in-depth explanations with terms and formulas, but let’s go for a simplified answer. As the plane flies, fast-moving air enters the jet turbine engines located on the wings of the plane. The air is compressed as it passes through the blades of the engine, however, at this stage, the temperature of the air could reach almost 100 degrees Celsius. Therefore, it has to go through a heat exchanger, which cools it down to a comfortable temperature for inhalation. Then the cool and filtered air is dispersed into the passenger cabin.
Whereas an outflow valve, which is usually located at the back of the cabin, makes sure that the used air is vented out, and so the air in the cabin is always fresh to inhale.
We all know the primary requirement for human survival is oxygen. Given that fact, traveling in a commercial airplane isn’t much different from being on land, an abundance of oxygen onboard the plane makes sure that we survive.
You might already know that ‘breathable’ air is in short supply at the altitude where most commercial planes operate. However, the word ‘breathable’ has a lot of significance in this context, because the availability of air itself at that altitude is not actually a problem. In other words, there’s ample air at 35,000 feet, and there is sufficient oxygen in it. In fact, there’s even a reasonable amount of air at the altitude where the International Space Station operates.
So, there’s plenty of air at the height where airplanes fly; it’s just that the pressure of the oxygen in that air is too low to be inhaled directly by humans.
As a plane flies, fast-moving air enters both the jet turbine engines. This fast-moving air is compressed as it passes through layers of fan blades inside the turbine. It’s at the compressor stage that a portion of the hot air is ‘bled off’ from within the turbine. The air generated at this point is therefore known as bleed air.
Bleed air is from a jet turbine; this bleed air is very hot, with a temperature in the range of a couple hundred degrees Fahrenheit, so it obviously must be cooled first. That’s why this hot bleed air is allowed to expand and passed through a heat exchanger so that it cools to a comfortable temperature. This cool, filtered air is then dispersed in the passenger cabin at a pressure that humans can comfortably breathe.
There’s also an outflow valve, usually located in the rear of the cabin, which ensures that the ‘used’ air is vented out of the airplane, thereby regulating air quality inside the cabin.
So, the two jet turbine engines you see on either side of a plane not only keep the plane airborne by providing forward thrust, but also help maintain cabin air pressure so that we remain comfortable and conscious throughout the duration of our flight.