Re: Heat through an adiabatic wall?

[Jim Green <JMGreen@SISNA.COM>]

> I like Jim Green's web page, ( http://users.sisna.com/jmgreen/FirstLaw.htm
> ) which basically says that anything that increases entropy is "heat".  By
> this definition, "energy transferred because of a temperature difference"
> is a subset of "heat", but "heat" also includes a paddle wheel turning.  In
> each of these cases, the work done microscopically from outside the system
> translates into a greater kinetic energy in the gas molecules inside the
> system.

Oops!!!  The page also says that it is a work in preparation.

I am backing off the strict coupling of "entropy change" and "Q" -- In a
non-reversible action things are much more complicated than this.  However
there is a major tendency to think of dS=Q/dT.

I know of only one action where dS=0 -- I have asked for help in
discovering other examples without success -- The one I know about is the
reversible piston in an adiabatic cylinder which contains an ideal gas. ALL
other actions that I can think of change the entropy -- at least I know of
no way to calculate dS the way I can for the piston.  And hence the web
page wants to lump all actions into Q.  I now feel that these other actions
(propeller, resistor, hot plate, etc would need to be partitioned (Joel's
word -- which I have adopted with permission) into _both_ Q & W -- but this
seems impossible -- thus I now tend to feel that the question is meaningless.

These comments may make much more sense after a look at the web page
referenced above.

As to the use of the word "adiabatic":  Energy is a _property_ of a system
and does not "flow" or move in the usual sense and Q (notice that I have
not used the evil four-letter word here) is an "action" not a fluid.  Thus
it makes no sense to use the word "adiabatic" as a limitation to the motion
of "energy" or "heat" (ugh) through a "wall" of some sort (Laplace not
withstanding)

I would use the word "adiabatic" as meaning that no "action" can pass
through a "wall" -- usually the work of microscopic collisions of molecules
-- but the point asked about is well taken -- the handle of the propeller
does pass through the wall as do the wires from the battery to the
resistor.  So I would now say that _I_ would mean by "adiabatic" that no
microscopic work is done by molecular collisions -- as _can_ be done though
the isothermal window, but that shafts and wires do not compromise the
barrier.

And in any case note that Q is not necessarily due to a temperature
difference as Joule can well attest.

I hope that at least Joel will now comment.

Jim Green
mailto:JMGreen@sisna.com
http://users.sisna.com/jmgreen