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# Re: McMath

```Dave Lawson pointed out a small error in my numbers:  incorrect T2i in
the calculation of T2.  The two methods actually come out pretty close
(too close for coincidence).

Since efficiency is a pretty basic definition in thermodynamics, it
would follow that the compressor efficiency = (ratio of ideal to actual
temperature gain) equation might just work because we're assuming an
ideal gas.  Indeed, that's the case!  So, don't mess w/ the complicated
version, use Dave Lawson's method.  The turbo mfrs do... :-)  To
understand what's going on, you need to recognize that the cold side
wheel does "useful" work to compress the air, and "useless" work that
just heats it up.  Efficiency is the percentage of total work done on
the air that's useful.  From there, it's "plug and chug".

For the derivation, see alt.math.complicated.  Hint for masochists:
R = cp - cv.

Sorry for the confusion!

Dave Weiss
'91 V8 5-spd
'93 90 CS UnQ

```