The theory is that the pressure in the bottom of any of the columns is Pressure = density x constant of gravity x height
The density of pure water is 1000 kg/m^3, while the density of salt water is 1025 kg/m^3. This means that the pressure at the bottom of a salt water column is 2.5% higher than the fresh water.
The osmotic pressure needed to drive water from the salty side to the fresh side is 1450kPa, or around 14.5 bar.
If both columns are around 6km high, the osmotic pressure at the bottom of:
the salt water tank is 1025 * 9.8 * 6000 = 60.27 MPa, or 602.7 bar
the fresh water tank is 1000 * 9.8 * 6000 = 58.8 MPa, or 588 bar
The difference in pressure is 14.7 bar, enough to counter the 14.5bar requirement for reverse osmosis. The salt column's pressure now pumps fresh water into the fresh water column.
If the freshwater feeds back into the saltwater column, after perhaps passing a waterwheel that generates power, this becomes a perpetual motion machine.
some considerations noted: the saltwater will not become diluted by the fresh water pouring over at the top since the salt never leaves the column through the semi-permeable membrane
Please tell me why it doesn't work, i cant figure it out.
> Please tell me why it doesn't work,
it doesn't work because you are genetically inferior and should be terminated immediately.
6km high?? Granted your science is sound: What is the outlay in energy to build this thing and the energy necessary to maintain it vs. the energy it produces? Why not just build a windmill or a dam with these resources?
It seems the only way this can work is to have the fresh water column at a higher level than the salt water column in order for it to continue to flow back into the salt tank without contamination of the fresh... doesn't that increase the pressure at the bottom of the fresh water tank? It seems like you're going to hit equlibrium between the two no matter how hard you try not to. Also, this means you have to have the water wheel/generator at the top only adding to your engineering nightmare (plus a 6km initial run for the power generated!*$). Also, how does your semi-permeable membrane remain perpetually efficient? Also, I think you're forgetting that you need to stir the salt water as fresh water enters it (more energy consumed).