Gee, Why can't teachers keep kids attention anymore?
Science was FUN! Look on EBAY at the old science kits and
all the damage, er a fun that you could do with one!

I'm sure Mrs. Harper would be serving time for a explosive device
detonation nowadays.

Bart

Glenn Ashmore wrote:

Back in Jr. High I had a wonderfule science teacher who had a great
experiment that she did every year to demonstrate the power of steam. She
had a cylinder with a pipe near one end for compressed air and a replaceable
cap on the other that he could mount an aluminum foil disk in to seal it up.
There was also a spring loaded pin that would puncture the foil when you
pull a lanyard.

First she would fill the cylinder to 100 PSI with compressed air and pop the
foil seal which resulted in a Whoosh!. Then she would drop in an ounce of
water and heat the cylinder to about 340F to get 100 PSI of steam. When she
broke the foil the entire school shook. I have been impressed by the power
of steam ever since. :-)

Even from 2 blocks away in senior high we would heard that BOOM! and break
out laughing knowing that Mrs. Harper was teaching thermodynamics again.


"Robert Swinney" wrote in message
...


A conversation with a friend today, brought up the question of how well a
steam engine runs on compressed air: That answer is, "It will run on air
but not very well compared to performance on steam".

My question is this: Does anyone have a simple compressed air/steam "rule
of thumb" ?

Now, I know this gets into all sorts of complex thermodynamic


calculations.


For example, the Brake HP of any engine is a direct function of pressure.
Pressure, however, in order to fit into conventional formulae must be


given


in Mean Effective Pressure (MEP). Enter hairy thermo-math here. MEP


would


be a sort of integral (mean) pressure in any heat engine. The type of
engine, amount of moisture in the steam, percentage of cut-off, insulation
of cylinder walls, size of passages including valve openings, on and on,
etc., etc., to nauseam, all enter into MEP. The old timers, at least


those


mentioned in "Modern Locomotive Construction" circa 1892 (sold by Lindsay)
commonly used 90 psi as the MEP of a representative locomotive of the


time.


So much for the math. Don't send me any formulae for calculating MEP -


I've


got that. I'm looking for shortcuts, here, thank you.

What I'd like to see is a comparison of the HP output of a steam engine
running on a given amount of input (boiler) pressure compared to the HP
output of the same engine running on the same amount of input compressed


air


pressure.

Analyze this from the standpoint of engine performance only, neglecting
boiler HP or compressor HP.

Ideas please.

Bob Swinney











--
Bart D. Hull

Tempe, Arizona

Check http://www.inficad.com/~bdhull/engine.html
for my Subaru Engine Conversion
Check http://www.inficad.com/~bdhull/fuselage.html
for Tango II I'm building.

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