Ned Simmons wrote:
In article ,
says...
Yes, I started that thread too. The reason that this has come back
is that I was never convinced the last time. Let me ask YOU, Ned, to
answer my question? I'll repeat it:

Postulate a big air tank pressurized to 180 psi, with a long (long
enough so the air has time to cool to ambient) pipe to an ideal
regulator which regulates the pressure down to 90 psi. The
regulator's output is a pipe of the same size which is connected to
a constant load of such a size as to make the cfm going into the
regulator measured to be 10 cfm @ 180 psi. What cfm will come out of
the regulator at 90 psi?


If we assume that the air behaves as an ideal gas and the
pressures are absolute, then there'll be 20 CFM @ 90 psia
flowing out of the regulator. I don't think there's ever
been any question about that. But that doesn't mean that
there isn't a loss in the potential of that air to do work.

CFM X psi for a compressible gas is not analogous to volts
X amps.

Ned Simmons

Whenever you let a confined gas expand there has to be a loss in its
potential to do work. Consider a pneumatic cylinder, it has more potential
energy in a more compressed or closed state. Is there any difference between
doubling the enclosed volume of a cylinder and expanding compressed air
through a regulator? That cylinder could do a certain amount of work
expanding, f x d. You would end up with double the amount of air at half the
psi, yet work was accomplished expanding the cylinder so there must be a
loss of potential energy in the compressed air. That's my "hand waving"
argument.