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Heat pipe for downward heat transfer

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Posted by David Delaney on March 3, 2004, 3:25 am
Steve Baer's 1969 patent on a heat pipe for
downward heat transfer seems never to have been
exploited. Perhaps it has never even been the
subject of a demonstration, since Steve says in
the short article on downward heat pipes in his
book, Sunspots (1979), that he never built one.
Steve has given me permission to post that short
article from Sunspots on my web site.

The article may be seen at

The article should suggest several applications to
readers of this news group.

It should be fairly easy to build demonstration

David Delaney, Ottawa

Posted by William P.N. Smith on March 3, 2004, 6:26 pm

Although I obtained a patent on this heat transport device (United
States Patent No. 3,561,525), I am ashamed to say I never once tried
out the idea.

Your tax dollars at work.  8*)  You can only pump as high as the
osmotic pressure across the membrane will raise the working fluid, you
have to make sure the distillate flow doesn't reduce the salt
concentration in the bottom, and he makes no comparison to the
capillary action of conventional heat pipes.

Please let us know your results!

William Smith
ComputerSmiths Consulting, Inc.    www.compusmiths.com

Posted by David Delaney on March 4, 2004, 1:33 am
 On Wed, 03 Mar 2004 13:26:05 -0500, William P.N.
Smith <> wrote:

This is not an important limitation for
applications of interest to this group.  Osmotic
pressure can be large. Have you ever seen the
photographs of mushrooms bursting through
ashphalt? The hydraulic pressure of the mushrooms
is generated by osmosis. I have a copy of Fermi's
Thermodynamics, the book that Baer mentions as
having inspired the invention. I can understand
why it did. From p. 122 of the Dover edition: "For
example, a normal solution, that is, a solution
containing one [gram] mole of solute per liter of
water, has, at 15C, an osmotic pressure Pnormal =
<snip> = 23.7 atm."

Yes, but a 2 kW heat pipe using water as its
solvent would only need to move solvent through
the membrane at a rate of 1 gm/s. The bouyancy of
the lower solution will be increased by the
solvent (distillate) flow, decreased by the
thermal expansion of the hot upper solution, and
increased by the evaporative cooling at the upper
surface. I suspect there would be a
concentration-restoring thermosyphon. I can think
of ways to enhance a concentration-restoring
thermosyphon. The obvious way is to use a very
strong solution having a much higher osmotic
pressure than needed to hold up the column of
solution. This would reduce the rate needed for
the concentration-reducing thermosyphon, increase
the buoyancy of solvent entering the solution, and
increase downward diffusion of the solute. One
might also have a solution-up channel heated by an
adjacent vapor-down channel, and a solution-down
channel insulated from the vapor-down channel and
from the heat source.

Actually, He does mention that the wicks of
conventional heat pipes (of 1979, the date of
writing) limit downward heat transfer by
conventional heat pipes to inches.
Also, the text of the patent says "As is well
known, the passage of [a] solvent through [a]
semipermeable membrane into [a] solution creates
an osmotic or pumping pressure considerably
stronger than the usual capillary action caused by
the surface tension of the fluid."

You probably won't see experimental results from
me, since I live in an apartment, and my wife is
resistant to experiments being performed here, and
to the construction of experimental apparatus.

David Delaney, Ottawa

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