On Tue, 11 Oct 2005 21:14:20 -0700, Winston
wrote:

Robert Swinney wrote:
Winston sez: " Please post again when you have performance and efficiency
curves."

Not liable to happen. How are you going to test the efficiency of a heat
engine -- on air?

(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?

Probably not. Ya gotta include thermodynamics because temperature is
not constant when there is expansion and pressure is affected by
temperature.

When the term "entropy" appears, my eyes glaze and I quietly
retreat.