Aircraft travel at 40,000 feet above sea level and the temperature of the air at that height is – 60-degree centigrade, pretty cold air. Aircraft’s turbine blades which are near the combustion chamber become very hot. A coolant is a must to cool these blades.
What is your proposal for coolant? Cold air right? Sadly no.
Instead of going for the cold air readily available in the atmosphere, engineers prefer compressed hot air at a temperature of 900 Kelvin for cooling these blades. Very “hot” air is used as “coolant,” weird right?
The problem with the cold air is that it can’t provide necessary pressure for circulation and thus can’t be used as a coolant. I guess only mechanical and aerospace engineers know about that.