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From: cberry@muddcs.UUCP (Craig Berry)
Newsgroups: net.physics
Subject: Re: TPMMTP (Thermodynamic PMM to ponder)
Message-ID: <319@muddcs.UUCP>
Date: Mon, 6-May-85 03:08:33 EDT
Article-I.D.: muddcs.319
Posted: Mon May  6 03:08:33 1985
Date-Received: Thu, 9-May-85 01:40:31 EDT
References: <517@terak.UUCP> <3676@alice.UUCP>
Reply-To: cberry@muddcs.UUCP (Craig Berry)
Organization: Harvey Mudd College, Claremont, CA
Lines: 58

In article <3676@alice.UUCP> jhc@alice.UUCP (JHCondon) writes:

>In some places of the world, the Bay of Biafra is one, sunlight causes
>heating and evaporation which results in first tens of feet of
>water being more saline and warmer than the water several hundred feet down.
>
>Take a 200 foot long pipe and suspend it vertically with its top end
>about ten feet below the surface. Now start and upward flow in the pipe
>by exhaling air into the bottom end, the bubbles rising in the pipe will
>drag the water along with it. As the less saline water warms
>by thermal conduction through the wall of the pipe it becomes less
>dense than the more saline water on the outside of the pipe. This density
>difference then maintains the flow once started.

[...]

> you can put a turbine with electric generator
>on the end of the pipe. Any excess power should be converted into matter
>in the form of rocks in case you need to restart.
>
>Is this a perpetual motion machine?

 Sorry, no.  Consider that this system is not in thermal equilibrium;
we have warm water at the surface and cold water below.  It is this
temperature difference which drives the "heat engine" you have described.
Note, however, that your pipe, and the entire warm water / cold water
interface, continuously conduct heat from the warm layer to the cold layer
as long as there is a temperature difference between the layers.  As soon
as this temperature difference has been eliminated, your PMM shuts down.

 Of course, in your system the sun will continuously pump additional
energy into the upper layer.  This will allow the system to operate as
long as the sun continues to shine.  An interesting side note to this
observation is that power plants which extract power from ocean thermal
energy conversion (OTEC) systems similar in principle to the one you
describe have actually been built and seem to work quite well, although
some problems still remain which prevent scaling them up to a really
useful level of power output.  Using the sun to power a PMM is clearly
cheating, however, since any net power you pull out of such a PMM is
obviously "paid for" by the nonreversible fusion of solar hydrogen.

 Somebody else pointed out recently that if you think you can describe
the operation of a PMM using currently known physics, then what you
have is not a PMM, since known physics excludes PMMs.  Your system
is another illustration of the value of this heuristic.  If PMMs ever
exist, they will operate on principles which cannot be explained using
physics as it is currently understood.  Rather a depressing thought,
really.

 Oh well, enough for now.  I promised my research director that I would
have the circle squared by tomorrow afternoon, and I've hit some unexpected
snags... :-)

                               Craig Berry

{allegra!scgvaxd | ucla-cs}!muddcs!cberry
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