Re: Heat through an adiabatic wall?

[Jack Uretsky <jlu@HEP.ANL.GOV>]

        Of course sound propagation in a gas is an isentropic process,
although this might be close enougb to the the piston-in-cylinder
problem that you may prefer to lump the two together.
                                        Regards,
                                                Jack

Adam was by constitution and proclivity a scientist; I was the same, and
we loved to call ourselves by that great name...Our first memorable
scientific discovery was the law that water and like fluids run downhill,
not up.
                          Mark Twain, <Extract from Eve's Autobiography>

On Thu, 6 Jan 2000, Jim Green wrote:

> > 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