Could this work?

[stoupidmonkey]

So I was sitting in a class and we were talking about reverse osmosis and the pressure needed to force H2O through the organic membrane, approximately 26 ATM of pressure. Thats alot of pressure and I know that the powerful pumps are expensive and require alot of energy to produce the water. As a diver, I know that 10 meters of depth equal a pressure of 1 ATM, so you can achieve 26 ATM by going 260 meters down in the ocean. Well, even if you did have a tube with only air and a membrane that was down that far, the energy to bring the clean water up would roughly equal the power and pump requirements of forcing water at 26 ATM. Not useful at all. What could work to bring up the water is a series of capilaries (hundreds even) that would through capilary action bring the fresh water up without any energy requirements at all. Could work, if the system was anchored firmly to the ocean floor and balanced properly. Not really useful, though because of the huge system needed to produce a fairly small amount of water per time frame. What could be a good idea, if in a situation that would nececiate a small amount of fresh water is if someone was DIW and out in the ocean. What could work is a small, metal device that has a membrane and air inside, could be lowered to 260m and left there for the pressure to fill the tube with fresh water. When recovered, there would be a 1 way valve that would discharge the air (as the pressure increased in the tube from air expanding) and leave the collected fresh water inside for drinking. I know, its an odd idea and has limited application, but its 2am and my mind is wandering. And Im a little drunk.

Interesting concept.

[martinworswick]

is the metal box full of air at 1atm? ie filled on the surface
if so there would be no extra air inside to expand and need to expand

or am i reading it wrong

[martinworswick]

filled with water obviously-duh!

just reread it!

I don't want to be redundant, but just so I am sure I understand the idea.
You would have a tube going down 260 meters This tube would include at least one, one-way valve, probably one at each 10 meters. This intake hose would be fed by a pump. It would feed into a box with a membrane. From this box, a tube would run from the output side of the membrane, and back to the surface, and a storage tank of some sort. There would also be a pump on the output side to ensure negative pressure on that side of the system. How am I doing?

[stoupidmonkey]

actually, by tube, I mean a cylinder or anything that is stand alone. Its just on a cable.

[S/V Elusive]

You'd sure need that water after playing out and then retrieving 260' of line! Interesting idea though ... maybe some of that air that is pressuring the water through the membrane could then also feed a balloon on the 'finished' side that would help float the device up to the surface?

Interesting. So there would be a direct feed to the membrane at 260 meters, then a suction pump to create the negative pressure on the output side. I like it. Have to add this contraption to the "Why a Mono is better than a Multi" thread All that gear would add a few pounds.

[bill good]

Do'nt forget the salt concentrate has to be dealt with!! What were you drinking?
Bill

[ShadowRWolf]

yall are nuking it.
since im bord to deth here on duty on the big ship il bust out my fancy MS paint and draw up the idea i can see what hes thinking of...
RUN GET YOURE PATTENT NOW!

one oddity is thow that working on subs is that they dont use that system they use pumps... il ask my neabor he is a 2 star on one of the subs. maby he knos y.


now with this idea theres 2 options.
watter pressure will force the drinking wtr to the surface, so if you want to run a hose to the boat you can. a cheep wtr. pupm that takes little pwr. can be used.

option 2 is that it just fills the rezavor in the tube then you lift it to the surface and empty it in to youre tanks.

[Tellie]

You have to take into account that it is not only pressure that is needed to create RO but flow as well. Membranes will quickly fail if pressure alone is used without proper flow across the membrane. Roughly for example, it takes ten gallons of salt water to make one gallon of fresh water. Watermakers send the remaining nine gallons overboard as brine yet even that nine gallons contains mostly hydrogen and oxygen or fresh water. What would be needed in your concept is a pump large enough to send both pressure and flow down to your membrane on the sea floor. If you have that then you already have the capabilities of RO at the surface. But I like any ideas that try to beat the energy needed. That's why Spectra watermakers have the rest beat in energy usage and recovery.

[Fishspearit]

Along with Tellies point about needing flow past the membrane, not just pressure, I think a few of the base numbers are off. The 26 ATM works for fresh water RO, but to RO salt water you need at least 50 ATM or more. At 11 meters per atmosphere, you would need to drop it down more like 550 meters.

[James S]

Once the now fresh water passes through the membrane it will create pressure on the top…the more of it that passes through and collects in the tube the more pressure acting against the membrane.
We would need to continually remove the fresh water to maintain the pressure up from the bottom….the energy to remove this would be equal to the energy required to push the water through the membrane to start with…..I think.

[ShadowRWolf]

not necasarly, the pressure on the hose should help it.

[svHyLyte]

Guy's--someone needs to repeat high school physics.

The pressure at depth is due to the weight of the water column above. Accordingly, to lift the water column to the surface will require the same pressure--or vacuum--as the pressure at a given depth. (Think drinking straw.)

Moreover, it is the pressure across the membrane that permits "reverse osmosis". If one requires 800 PSI for "reverse osmosis" one must provide a vacuum of 800 PSI!