In article , Ned Simmons
says...

I never intended to give the impression that a regulator is
the only example of lossy expansion, but that was the
subject of the original, and most of the subsequent, posts.
I certainly hope everyone following this accepts that
allowing the air to expand freely, as in your example,
lowers the potential to do mechanical work. Paradoxically,
not everyone seems to believe that if the expansion occurs
across a regulator there is also a loss.

If I might take a moment to dither about the semantics
here.

"lowering the potential to do mechanical work" is
a bit different in some sense, than "loss." Because
of the history of electrical analogy here, this may
be confusing.

Most folks think of the term 'loss' as a point loss,
ie a lumped circuit element that is dissipative. The
regulator, or the connection between the two tanks
in the case of no regulator, or even the expansion
orifice in the case where gas is expanding into
vacuum, are not analogous to electrical lumped circuit
elements like resistors. No heat appears in them
during the process. [1]

(electrical analog discussion really are
doomed to fail here...)

Sure the end result having two tanks with three times
the volume, filled at a lower pressure, has less stored
potential. But the difference does not appear in the
regulator. The energy was not lost in the regulator.

Jim

[1] aside from the turbulent flow in the regulator
as has been noted. This is a small effect.

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