Re: [Phys-l] physics of dissipation

[John Denker <jsd@av8n.com>]

On 01/15/2010 08:09 AM, chuck britton asked:

> Are there counterexamples available where quick make less entropy than slow?

Yes.

For example, consider an ordinary automobile engine.
There is some tach where it is most efficient.  Running 
it appreciably faster *or* slower than that makes it 
less efficient.

One obvious source of inefficiency is heat leakage into
engine block.  Any energy that goes into the engine
block is unavailable for doing P dV work.  This leakage
becomes more of a problem as the tach becomes lower.

> Thanks for some great discussions folks ! ! !

:-)

> Time is indeed a variable that doesn't get a lot of attention in the 
> Thermo field.

We agree time is all-too-often slighted, but sometimes it
does get mentioned.  For example, Feynman on page 1 of his 
Stat Mech book defines equilibrium as "when all the fast 
things have happened and the slow things have not".

Any worthwhile theory of thermodynamics needs to take time
seriously.  Any device that is complicated enough to be
interesting, such as a refrigerator or a heat engine, needs
for some of its parts to be in equilibrium and some not.
This depends critically on time-scales;  not too fast and 
not too slow.