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Re: Earth thermodynamics




On Sun, 15 Jun 1997 13:56:51 brian whatcott <inet@intellisys.net> writes:
At 14:56 6/11/97 PST, Tom Wayburn wrote:

... we have no proven sustainable
alternative energy technology, i.e., a technology that has a
non-negative availability efficiency when indirect availability costs
are counted,
we are not doing the research to find out just how
desperate our situation is as the petroleum era draws to a close
...
Tom

P.S. Help!!!!


Despite goodwill on my part, I have found it difficult to tell
what sort of help would prove useful to you.
There is a suspicion that your text is at a level that is relatively
inaccessible to me at least - and if so, to whom could it be directed?

Your concern appears to be identical to that of the group of people
called
the "Club Of Rome", some of whom wrote a popular account of the future
for
energy consumption on Earth in the next century or two.
This was called "The Limits to Growth" Meadows, Meadows, Randers,
Behrens , Pan Books 1972

Their predictions though dire were not based on a strictly
mathematical-physics approach. Rather, they used a world model, which
was
inevitably full of estimated fitting parameters, and with dynamic
linkages
which were not justified in a rigorous way.

In this connection, it has been noted within the last year or two
that
world weather models have run into trouble with the energy balance
calculations they adopted; in particular, the effective albedo of the
Earth's cloud cover, and the flux of heat energy due to clouds.

You noted that some texts which were relevant to your task were too
formidable for the small contribution required from this topic.
A text in this category which came to mind was Chandrasekhar's
classic monograph "Stellar Structure" (1937)
In the first few chapters, he treats thermodynamics strictly at
the level of detail which you seem to need, though he makes no mention
of Prigogine.

As to the transfer of solar energy to the biosphere, it seems to me
that
whereas a thermodynamic efficiency of (3000 - 3)/3000 x 100% could be
approached for some direct conversion method - the heat gain at 300 K
represents a thermodynamic efficiency of less than (300 - 270)/300
x 100% for the thermal range available in an average diurnal cycle.

As to the solar constant, I have no difficulty with the dictionary
definition of
"The flux of solar energy passing normally through unit area at the
earth's
mean orbital distance."

I only wish I could have provided something of more direct help.

Regards
brian whatcott <inet@intellisys.net>
Altus OK

Thank you, Brian,

I agree with your criticism of the Club of Rome, nevertheless they did
a great deal to point out that there *was* a problem. Unfortunately, it
is fashionable nowadays to disparage their work, which some people who
oppose *all* change in society can do by pointing out that they were not
infallible. Ha.
The book by Chandrasekhar might turn out to be just the thing. I think I have barely enough background to read it; however, if I rightly
remember, his book on black holes is immense. (I recall seeing an equally prolix disquisition on the I formation, a well-known offensive
technique in American football, so what am I complaining about?)
I am confused by your mention of a "method" such that "a thermodynamic efficiency of (3000 - 3)/3000 x 100% could be approached". Is that
not the efficiency of a Carnot engine receiving heat (reversibly) at
3000 K (from the sun?) and rejecting heat at 3 K (again reversibly) (to
outer space?)? I cannot imagine such a thing. Where did the number 3000
come from? Presumably, living plants are not heat engines that accept heat (reversibly) during the day and reject heat reversibly at night -
at least I don't *think* they are, so I don't understand the pertinence
of the 300 K and 270 K.
I think you are right about the solar constant representing energy
flux, but radiant energy is not like heat conduction. Where is the
gradient? We are dealing with quantum weirdness. I believe I wrote, in a previous posting, that, in twelve thermo books, I did not find a
single Second-Law problem with a radiation term in it. Also, the
dictionary may call something energy that isn't really energy. Energy
is even more confusing than entropy. I hope, though, that the solar
constant is approximately equal to the average frequency of the photons times Plank's constant times the number of photons per unit time that "
pass normally through unit area at the earth's mean orbital distance."
But, why the earth's mean orbital distance? Isn't that the distance
between the *center* of the sun and the *center* of the earth? That's
too large, isn't it? Don't we want the average number of photons that
pass through unit area at the hypothetical sphere that includes the
earth and its atmosphere - 100 miles above the surface of the earth,
say?
The book on exergy analysis by Szargut, Morris, and Steward is confusing and almost all the references are in Polish or Russian, however they
do devote nine pages to black-body radiation, which is a good
approximation for the sun's input but not so good for the earth's
rejection of infra-red junk radiation to outer space - as the earth is
not a black body. I think most of their equations remain valid,
though, when multiplied by emissivity. But, exergy is a clumsy
concept. The exergy of gasoline, say, is the availability minus the availability of the same atomic species reduced to their lowest energy
state - even going so far as to consider the products of combustion *after* diffusion to the concentrations of carbon dioxide and water at the
concentration at which they are normally found in atmospheric air.
(The oxygen required for combustion is considered "free".) Moreover,
they have an unfortunate practice of representing nearly every variable as B sub something. Thus, the important variables can be distinguished
only with a magnifying glass when you are my age.

Best regards and thanks for your input (I hope there is more),
Tom Wayburn