no free lunch
on our helicopters we had a high pressure turbine that was driven off bleed air from the main turbines
it used the hp air to spin a turbine very fast and build pressure then this clean hp air was allowed t expand and loose pressure across a condensor
MAN on MAN did it ever make some cold air, and lots of it,
but it took tons of bleed air to drive it.....and when we was in the sand box it took to much power from the main engines, so you got warm in the cabin
no free lunch