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Old 14-04-2017, 06:28   #46
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Re: Another way to create drinkable seawater?

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Originally Posted by RaymondR View Post
I don't believe there is any endothermic reaction involved in the reverse osmosis method of separating the Na and Cl ions from the water if it is a filtration process. You are not trying to recombine the ions, just filter them out of the water phase.

Might take a fair bit of salt to raise the temperature to boiling point and I'm sure the folks down stream would get pretty pissed off with you.

Mixing salt with ice to reduce the temperature in order to make ice cream was once a common practice.
Nothing to do with entropy or the Laws of Thermodynamics. Don't confuse enthalpy with entropy.
It's completely explainable by the lower freezing point, phase transition and the latent heat of fusion of ice/water.
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Old 14-04-2017, 09:09   #47
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Re: Another way to create drinkable seawater?

StuM, I understand that capillary action can create tremendous pressure, and in fact create higher pressure than the osmotic pressure of seawater. The problem is that capillary action only works while water is confined to small tubes and the smaller the tube the more powerful the capillary action. The pores in graphene oxide membranes are perhaps the smallest a water molecule can fit through so the capillary pressure would be at or near it's maximum theoretical value. The problem is that capillary pressure only works while the water molecules are confined inside the tube and water does not accumulate at the open end of the tube. Tall trees like redwoods do this by evaporating the water at their tops and consuming water in the process of photosynthesis in their leaves, both of which remove water from the top of the tree. If water accumulated there even as drops the capillary action would stop. If the capillary tube is short and water accumulates on the "fresh water" side the there is no more capillary action. You could conceivably evaporate the water off of the fresh water side at a high rate to keep the capillary action going, but if your purpose is to use that fresh water, evaporating it away seems to be counter productive, not to mention energetically expensive. As soon as water starts accumulating on the "fresh water" side of the graphene membrane, capillary action stops and osmotic pressure becomes the dominant physical force. At that point the graphene membrane is now no different than any other semipermeable membrane.


Zboss's video from China demonstrated nano filtration of fresh water, not desalinization of sea water. It stated that it reduced TDS and salinity. Given that the salinity is already very low in "fresh water" i'm not surprised at all that they might have seen a reduced salinity in their product water. It looked to me like their head pressure was about a half a meter. That would mean that they could reduce their salinity until the osmotic pressure at the bottom was about 1 PSI lower than the water poured into the top. That is a reduction, which is all they claimed, and it should be noted they did not provide before and after numbers.
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Old 20-04-2017, 19:28   #48
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Re: Another way to create drinkable seawater?

In addition to the posted effort to use graphene to separate sea water from it's component parts, there is another interesting effect recently (?) demonstrated by a high school senior science student using graphene.

She demonstrated how sea water (or any fluid containing enough free salts) passing over the surface of a graphene membrane will generate electricity! How about that for the all purpose utility power supply conveniently located in a small cavity below the waterline?!

Apparently, though the experiment and demonstration was very small, the application has been shown to scale well, and could be a real breakthrough for those who travel near or in moving water. Perhaps the water wheel of old will resurface for the benefit of all.
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Old 20-04-2017, 21:15   #49
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Re: Another way to create drinkable seawater?

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Originally Posted by GeneK10 View Post
In addition to the posted effort to use graphene to separate sea water from it's component parts, there is another interesting effect recently (?) demonstrated by a high school senior science student using graphene.

She demonstrated how sea water (or any fluid containing enough free salts) passing over the surface of a graphene membrane will generate electricity! How about that for the all purpose utility power supply conveniently located in a small cavity below the waterline?!

Apparently, though the experiment and demonstration was very small, the application has been shown to scale well, and could be a real breakthrough for those who travel near or in moving water. Perhaps the water wheel of old will resurface for the benefit of all.
Here's a 3 year old report on the original research:

https://phys.org/news/2014-04-team-e...-graphene.html
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