[extropy-chat] energy from osmosis

spike spike66 at comcast.net
Tue Oct 4 04:38:54 UTC 2005

> bounces at lists.extropy.org] On Behalf Of "Hal Finney"
> This is a problem for Spike's invention, because the necessary
> pressure differential for reverse osmosis will increase as the water
> becomes saltier.  Therefore as he sinks his pipe lower, the increased
> saltiness of the ocean will cause a greater pressure difference across
> the membrane, which will reduce the pressure needed on the fresh water
> side of the membrane.  As a result, his fresh water column will not grow
> as high as hoped... Hal

True, but check this:


If this salinity profile is correct and it stays linear, then
the salinity at 11km is about the same or less than on the
surface.  I do have my suspicions that all is not right
with this graph however, for I see no reason why the
salinity up top should be higher than at 500 meters.

Anybody have any ideas?

What we now need is for someone to find us a relationship
between salinity and osmotic pressure required to deionize
water.  I have seen figures as low as 20 Mpa and as
high as 50 to 60.  Don't know which is right, but it
would be easy enough to do an energy balance with
Gibbs free energy of chlorine and sodium atoms in 
solution vs chlorine and sodium atoms in an ionic bond.

But before I do that, I plant to google my lazy ass
around and see if some credible-looking PhD candidate
has already done that calculation.


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