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A thick glass sphere full of air and water at 1 atmosphere of pressure is placed at least 200 metres under the sea. A glass pipe extends from the centre of the sphere, through the bottom, and as far again down into the sea. At the bottom of the pipe is a semipermeable membrane which lets pure water
in. Further up at the bottom of the sphere is another to let it back out into the sea.
The higher density of seawater means the pressure across the bottom of the pipe is higher than across the bottom of the sphere, so one can overcome osmotic pressure while the other can't. The water inside the sphere will have to come most of the way up the pipe.
Ideally the membranes are transparent along with everything else. There is a glass spiral staircase down the outside of the pipe in the sphere for the water to run down.
If divers and dolphins can go down deep enough they can see it too. If the glass pipe and steps are too hard to see it should be tinted until it's visible.
An optional extra slightly detracts from the appearance but provides illumination: A glass turbine in the pipe powers a friction oven element which glows red hot or better.
Inspired by Supersimple reverse osmosis, the related 8000m idea in the comments, and the Windmill powered friction oven.
Supersimple reverse osmosis
[caspian, Nov 19 2004]
Windmill powered friction oven
[caspian, Nov 19 2004]
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||I have been contacting academic authorities all over the world to ask them why this concept won't work (it must not work, or someone would have done it by now), but I have not received any knowledgable responses.
||I don't know about the fountain idea, but I believe the idea of a pump has value. The question is, how much energy is required to pump water from a depth of 2,000 feet vs how much energy is required to force reverse osmosis at sea level?
||Also remember that it will be necessary to constantly pump the water out from the bottom of the pipe. Once even a little fresh water starts to accumulate at the bottom of the pipe, the pressure difference deteriorates and the reverse osmosis stops.
||Hurricaine - for much edifying discussion of this topic see the linked "supersimple" idea below. I learned a lot from the annotations on that one.
||if on the surface, mirrored ponds could evaporate off the fresh water therefore help driving the gradient
||could a material (menger sponge) be used to attract salts and therefore make a higher than normal salt density at the top of the tube to aid fresh water flow .