Right. Bob's original question had to do with an expansion engine
running on air vs running on steam, both coming from an external source at
given pressure without regard to how it got there. The Carnot limit,
dealing with efficiency, is irrelevant here.

"Gary Coffman" wrote in message
...
On Mon, 13 Sep 2004 10:08:50 +0000 (UTC), "Don Foreman"
wrote:
Sure it can, if pressure is higher than ambient at ambient temp as in
most
compressed air systems. Air tools get cold while in use, right? They
typically use vanes rather than pistons, but expansion is still going on.

A compressed air system has external mechanical input to create higher
than ambient pressure at ambient temperature. A heat engine, such as
a steam engine, doesn't.

Gary

"Gary Coffman" wrote in message
.. .


Outlet temp can't be below ambient unless external work is applied to
the piston to expand the gas below ambient pressure. Otherwise, you'd
be violating the Carnot limit.

Gary