Re: multi-step reasoning and Joule-Thompson

[Hugh Haskell <hhaskell@MINDSPRING.COM>]

At 12:10 -0500 8/22/02, Joseph Bellina wrote:
> Thanks to all who pointed out that the Joule-Thompson gedanken is a case
> in which the volume changes but no work is done, at least in the case
> where one has a perfect vacuum on one side...I'm not so sure about the
> real case where there is no perfect vacuum.
I think that a vacuum where the mean free path of the particles is
very large compared to the size of the chamber can constitute a
pretty good approximation to a perfect vacuum. I believe that the
folks who do the electron and positron trapping work have achieved
such. I recall hearing about a single trapped positron that was
transported from, I believe, Boulder to Cambridge, by truck. I think
it was lost on the return trip when the cooling system failed. If a
positron can be kept from colliding with any real matter for a period
of several days, I suspect that should qualify as a long enough mean
free path.

Hugh
--

Hugh Haskell
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<mailto:hhaskell@mindspring.com>

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