Originally Posted by
FE Hoppy
Pressurise and COOL!
err........
Yes, because when you pressurize the temp will go up, so you might need to cool it before it goes into the cabin. I know it is -56deg C outside, but the temperature increase will be bigly...
From NASA (who are a lot smarter than me):
T2 / T1 = (p2 / p1) ^ [(gamma - 1)/gamma]
During the compression process, as the pressure is increased from p1 to p2, the temperature increases from T1 to T2 according to this exponential equation. "Gamma" is just a number that depends on the gas. For air, at standard conditions, it is 1.4. The value of (1 - 1/gamma) is about .286.
So:
Altitude FL400, so p1 = 19KPa, T2 = -56deg C = 220K
Cabin 6,000ft so p2 = 81KPa
T2/220 = (81/19)^0.286
T2 = 220x(81/19)^0.286
T2 = 333 or 60deg C so a little warmer than I prefer my cabin....