Half a croissant, on a plate, with a sign in front of it saying '50c'
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Localised production of fresh water from sea water

Localised production of fresh water from sea water
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(+6, -2)
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Ok, imagine sea water pumped up to the top of a frame and then allowed to trickle down and through a sheet of membrane that is not air proof.

The warm desert wind blows through the membrane and evaporates off some water. The rest of the water is returned to the sea at slightly higher levels of salt concentration.

The membrane is close to a parallel sheet of non-permeable tubes, another feed of salt water travels down (and on the inside) these tubes, causing the [warmer] evaporated water to condense on the outside, and eventually trickle down to a collecting tank.

The pump itself is powered by a small local solar / wind turbine generator and the wind turbine is run from the same wind that evaporates the water through the membrane.

The whole set-up need only be a very local (family / village level) installation and does not require any infrastructure outside of itself e.g. mains power or water and hopefully maintenance

If the wind is blowing the wrong way, then the membrane and tube sheets swivel

Anyone know if you'd get enough water to make it viable.

eldon, Feb 09 2005

Solar still on a very small scale http://www.txses.org/epsea/stills.html
[Klaatu, Feb 10 2005]

Danvest wind/diesel desalination plants http://www.danvest.com/
baked [willard_b_trophy, Feb 15 2005]

[link]






       A desert next to an ocean is less than 1% of the planet's locations. The length of pipe to move the water from the ocean to where the people would safely live is prohibitive compared to taping into a mountain fed stream/river/lake. The condenser is the costly part in this and similar systems. With an RO membrane, you want to use it to the recommended psi and water temperature for maximum efficiency all the time, coupled with a regular back wash. What is the minimum size reservoir, shape and height to create @ 60 psi? The reservoir would be a cone starting ten feet off the ground, one foot in diameter tapering to half/inch pipe, or 100 ft. of vertical pipe I'm estimating. The wind could power a pump to fill the reservoir otherwise.
mensmaximus, Feb 09 2005
  

       As described, I am not sure there needs to be a "membrane". You could use old burlap sacks. The idea is that water evaporates from them and blows over to the pipes where it condenses.   

       I love this sort of thing so I will give a bun. The problem is that it is an open system. If you get a gusty day, a lot of your vapor will be carried off into the desert by that warm desert wind. You want to reclaim all of your vapor. If you put the membrane and the tubes very close together I would worry about salt water (or dry salt) also blowing across and contaminating your freshwater.   

       I wonder if you could do something like this but eliminate the membrane completely. Consider - wind off the ocean has probably picked up some water, just as wind through the membrane would. If you could funnel this wind through your condensing system perhaps you could reclaim that moisture that way.
bungston, Feb 10 2005
  

       mensmaximus, 60psi is approx 4 bar, or forty metres (120ft) of water. 100ft of pipe seems a reasonable estimate. However, no high-pressure system is mentioned. Agreed that this needs relatively unusual conditions - desert next to a water source - to function.
david_scothern, Feb 10 2005
  

       I've seen several ideas like this, all very nice, all with catches. So I give you a bun, even though it's baked, but just not baked enough.   

       I've even seen one where you can put in a little dinghy and float behind you as you're out at sea.
sophocles, Feb 11 2005
  

       I imagine seran wrap would work quite nicely. If any of you have ever built a water collector with one, you know what I'm talking about. I'll try to find a link.
Blumster, Feb 15 2005
  
      
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