Compression and Expansion of Cabin Air
The Lear series corporate jets have an emergency pressurization system where air can be tapped off between the high and low pressure compressors, and fed directly into the cabin. So this air does not going through an ECU, and doesn't have any temperature control except the engine rpm. While testing on the ground, if one puts the throttles up to a mid point, the air coming in is quite warm, though not at an excessive rate or speed, even in the winter.
So here is my dilemma; the air starts out at -20 degrees C, and maybe 1 atmosphere of pressure. It gets compressed to a higher pressure and temperature, and then reduces pressure to gently enter the cabin. The flow is smooth and seemingly of a pressure very close to ambient, ie 1 atmosphere again. However, the temperature of the incoming air has not cooled to - 20 degrees C, it is maybe 35 deg C. Shouldn't the amount of heating due to compression equal the amount of cooling due to expansion?
Sorry for what seems a simple question. Anyone with ideas?
Hawk