(Please forgive the nonsensical units with which I was crippled as a youth. The following is all probably in gross error, but it's interesting.)
The back of the envelope says that air has a mass of about 20.7 ounces per cubic foot after it is compressed to 100 PSIG. An 80 cu ft cylinder could contain air massing 1656 oz.
If you exhausted that mass through a 100 percent efficient TT at sea level in one second, you would expect to see about 140 watt-seconds of energy converted from compressed air into work at the shaft end.
(Thought experiment: TT has 24" diameter rotor. 1.29 lbs of force placed at the circumference for a torque of 1.29 lb. ft. at the shaft. That torque, for one second is about 1/426 horsepower or 1.749 watt.) At 1.749 watt seconds per cubic foot, an 80 cubic foot cylinder should contain about 139.9 watt seconds of energy if it were initially at 100 PSIG. Clearly I am assuming a massless rotor and no loss incurred in the process of measuring the power!)
So if you measured, say 70 watt - seconds of energy at the shaft, you could peg the efficiency of the TT at 50%.
Physics majors, are these *anywhere near* the real numbers?
--Winston