Hi Bob and Gary,
I thought of the same simplification to the diffusion PMM proposal
that Gary just suggested -- eliminating the top semi-permeable
membrane. I came to the same conclusion as Bob. Getting rid of the
top membrane, although seemingly a simplification, actually would
make the device much more difficult to build and operate (assuming
it works at all). Also, due to the great vertical length of the
solution column (many meters to kilometers!), the time needed for
the solution to diffuse back to equilibrium (after each portion of
water dripped onto it) would be much much longer. So the top
membrane serves a very important purpose in this scheme by apply
downward osmotic pressure to the inside of the solution column,
thereby counteracting the bottom membrane (which generates upward
osmotic pressure). In other words, the top membrane takes the place
of that 7 kilometer high column of solution. As I mentioned in my
previous post in this thread, any dilution of solute concentration
at the top membrane will cause all cyclic flow to stop due to
lessening of the downward osmotic pressure. This is why the
critical issue for this design becomes whether or not the solution
will regain, via diffusion/Brownian motion, its initial uniform
concentration. Bob thinks that it should be possible for the
solution to become uniform again; I assert that the solution will
instead (in the absence of any imposed mixing), due to gravity,
settle into a concentration gradient with low concentration at the
top (and at an extremely slow rate on the order of months).
Getting back to Gary's one-membrane scenario, note that others have
proposed this before. Have a look at the Museum of Unworkable
Devices to see a related idea, which, although employing a different
topology, is supposed to work by exactly the same principle. They
use only one membrane, and they use the ocean as their salt solution:
The skeptics who analyze perpetual motion machines at that site
offer an explanation of why the device should not work. They got
their "refutation" completely wrong. Their explanation boils down
to the assertion that the density of the solution does not matter.
Wrong! I think that the device would actually work, but it would
not violate the second law because the high concentration of salt
solute near the membrane would de dispersed by ocean currents.
Natural sources of energy (ultimately derived from solar energy)
would power the device, not a second law violation.
Thank you gentlemen for contributing to this fascinating
discussion. Bob, I will do some more literature searches to see if
I can find real-life examples to back up my claim that the solute in
a solution settles due to gravity. If anyone knows of such
information, please let us know.
Regards, Leo Cabana
--- In firstname.lastname@example.org
, "Robert Lerwill" <bob.mo@v...>
> Hi Gary,
> Your second question is a good one. The top membrane is actually
not strictly necessary but you would need a very tall column for the
device to function without one. The osmotic pressure for a 10% sugar
solution is 7atm (700kP) and the SG is 1.01. This osmotic pressure
is enough to support a column of solution 69.3 metres high. Using
the equation I gave above for the head of water, to get enough
pressure difference to create any flow at all would need a 10% sugar
solution column at least 7km high (i.e. 69.7/(1.01 - 1). Perhaps is
might be possible in the Marianas trench, but I don't think I could
get one in my shed.
> Bob Lerwill
> ----- Original Message -----
> From: Gary S.
> To: email@example.com
> Sent: Wednesday, December 01, 2004 5:04 PM
> Subject: [free_energy] Re: Diffusion Machine Update -- REFUTATION
> Bob, I just reread your document.
If the bottom membrane is correct
> (water flows from solution to region of less concentration),
> you be better off at the top by just eliminating the upper
> altogether and just letting the drops fall into the solution?