In article , Richard J Kinch
says...

I continue to assert that there is little power or energy loss in a
regulator. (don)

Astonishingly, amazingly stubborn. Equivalent to belief in perpetual
motion, and denial of energy conservation.

And yet, Don is correct. The energy did *not*
show up in the body of the regulator.

Take the example where you start with one volume
of gas at some large pressure. Then allow the
gas to expand, through a regulator, to twice the
volume and a lower pressure.

Now compare the energy of the original and final states:
One tank of gas at a large pressure, compared with
*two* tanks (represening three times the original
volume) at the new, lower pressure. Remember there's
still gas left in the supply tank, at the outlet
tank's pressure, you have to account for that
energy.

Sure, there's less potential energy in the
final, stored gas of that two-tank system, than
in the original, one-tank configuration.
Don's point: energy does *not* appear as
heat "in the regulator" during the gas transfer.

- He's correct.

The gas regulator does not get hot.

That's not perpetual motion - it's just physics.

Doing the conservation of energy math properly
requires you to consider a bunch of things, like
the thermal (heat) energy *in* the gas, the kinetic
energy during the flow, the amount of heat
that is given up to, or from, the surroundings
to the volumes of gas, and any actual mechanical
work done during the expansion.

This subject is actually pretty well understood
and was, even a long time ago. Basically thermodynamics
came about because folks wanted to build steam engines.
Granted the physicists would say that the theory came
first, but we all know better.

It's a tolerably complicated subject; a proper
treatment has all kinds of equations and funny symbols
littering the discussion. Some here have complained
that putting stuff like that in a post is needlessly
complicated. I agree. But to *really* understand what
goes on when somthing as blastedly simple as 'one
tank of compressed air gets hooked up to an empty
tank' the rigorous treatment is the ONLY way to get
the correct answer.

Jim

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