Grant Erwin wrote:
Ned Simmons wrote:

Richard J Kinch wrote:
1. ANY EXPANSION OF COMPRESSED AIR NECESSARILY DOES WORK.

This is key to my misunderstanding. In everything I've read on the
previous (original) thread, this wasn't explained, only asserted.
So, I have to ask:

Why does any expansion of compressed air necessarily do work?
Grant

Your intuition is right, expansion of a gas doesn't
necessarily do work, but the entropy of the gas increases
as it expands.

As I've said before, the "lossy" character of regulators is
easy to demonstrate without resorting to thermodynamics.
However, understanding the energy balance of the loss is
impossible without thermo, and entropy is central to the
explanation.

I'm not looking for a demonstration, Ned. A simple explanation would
do. If you find it "impossible" to explain then that's one thing, but
could you at least try? I'm very frustrated with people who simply
assert complex facts without trying to explain them. They do teach
thermodynamics to college freshmen, and I don't usually fail to
understand concepts from freshman physics. Grant

Maybe it's a little beyond the scope of a newsgroup discussion. I don't
understand why there seems to be some sort of onus here placed on Ned and
Richard to prove or explain the basics of thermodynamics. Just because they
"teach" thermo to college freshmen doesn't mean they fully understand the
concept of entropy.