5 ms·

That is amazing! I’d never thought of leveraging the pressure of ocean depth for this, it’s a great idea. For anyone reading, the energy that OP is talking abou

That is amazing! I’d never thought of leveraging the pressure of ocean depth for this, it’s a great idea. For anyone reading, the energy that OP is talking about would actually force the fresh water above the surface of the ocean without pumps. I didn’t get to the whole paper, but I imagine the challenges of keeping that membrane clean are remarkable.

Metacelsus 3y ago
Yeah, I thought of it a few years ago, then realized I'd been scooped by ~40 years. But given the advances in technology maybe it's possible today?
- tinus_hn 3y ago
  Technology will never advance enough to enable the perpetuum mobile device, which is what this is, unfortunately.
  - hwillis 3y ago
    No it isn't. This is just like putting a filter at the bottom of a dam, except the filter also blocks salt. The top of the dam is at sea level, so you have to bring the water back up to the surface.
    - postalrat 3y ago
      Water without salt is less dense so that column of water would have less pressure at depth and would be pushed up.
  - AnotherGoodName 3y ago
    Adding salt water is endothermic and separating them is exothermic fwiw. That is separating salt from water releases energy. There's nothing perpetual motion about a process that separates fresh water and salt and also gives energy. I'm not sure if the above works or not but physically there's no issue with this.
  - gadilif 3y ago
    Not exactly, the pressure is an external force working on the system (so, open system). Perpetuum mobiles is a closed system with no energy loss.
    - IshKebab 3y ago
      No he's right, the idea of extracting work from the pressure of the ocean is as impossible as perpetual motion.
      - quertered 3y ago
        It is clearly not impossible, the paper clearly states that it's thermodynamically feasible, even if not practical at 1970s
        waveBidder 3y ago
        where are we extracting the energy from? is it effectively geothermal power?
        MarkMarine 3y ago
        It’s solar powered. Ok, I’m being brief but you seem genuinely curious, so, lemme explain what I mean: In thermo, you would draw a line around a closed system, and say basically conservation of energy applies in this system. Energy in = work out + losses. In a system where one input is the ocean, you basically just consider that infinite because of the size differences. One dinky little pipe compared to the mass flow into the system from the ocean, that math would be silly to bother with. That said, to swat down the stupid “this is perpetual motion” comments from people with Reddit engineering degrees, you also have to add in the energy input into the system of the sun, which is keeping the water from freezing over the course of 1 million years as it runs someone’s sarcastic water wheel.
        lazide 3y ago
        Your comment is literally word salad. Mind taking another pass?
IshKebab 3y ago
It's not amazing, it's obviously delusional. Think about it - if it really worked you have invented a perpetual motion machine, since you could just feed the fresh water through a little water wheel back into the ocean. You don't need to do any maths at all to know that his maths has gone drastically wrong somewhere.
- MostlyStable 3y ago
  In the absence of the sun (which is what ultimately drives ocean mixing), eventually this would lead to a layer of pure fresh water on top of a layer of salt. The energy is being driven by osmotic pressure of salt water. Once you have extracted the water out of the salt, that pressure is exhausted. Thus it is not perpetual.
- roflc0ptic 3y ago
  Take a long tube with an osmotic filter on it. Put it in the sea with one end out. Pressure is going to fill the tube up, no, just like a snorkel? Probably back up to sea level, possibly minus whatever force reduction caused by the filter? Boom, water filtration with no expenditure of energy. It may be wrong but it really isn't "obviously delusional."
  - postalrat 3y ago
    You forgot the part where the water in the pipe is less dense and would be pushed up.
- MarkMarine 3y ago
  This isn’t a closed system. It’s not perpetual motion, there is an EXTRAORDINARY amount of energy added to the system by the sun. Saying “maths” instead of just math sounds quite odd, why are you making it plural? Is solving one equation “a math” and solving multiple equations “maths”?
  - xdex 3y ago
    “Math” is used in USA and Canada. “Maths” is used by the rest of the English speaking world.

Metacelsus 3y ago

Yeah, I thought of it a few years ago, then realized I'd been scooped by ~40 years. But given the advances in technology maybe it's possible today?

tinus_hn 3y ago
Technology will never advance enough to enable the perpetuum mobile device, which is what this is, unfortunately.
- hwillis 3y ago
  No it isn't. This is just like putting a filter at the bottom of a dam, except the filter also blocks salt. The top of the dam is at sea level, so you have to bring the water back up to the surface.
  - postalrat 3y ago
    Water without salt is less dense so that column of water would have less pressure at depth and would be pushed up.
- AnotherGoodName 3y ago
  Adding salt water is endothermic and separating them is exothermic fwiw. That is separating salt from water releases energy. There's nothing perpetual motion about a process that separates fresh water and salt and also gives energy. I'm not sure if the above works or not but physically there's no issue with this.
- gadilif 3y ago
  Not exactly, the pressure is an external force working on the system (so, open system). Perpetuum mobiles is a closed system with no energy loss.
  - IshKebab 3y ago
    No he's right, the idea of extracting work from the pressure of the ocean is as impossible as perpetual motion.
    - quertered 3y ago
      It is clearly not impossible, the paper clearly states that it's thermodynamically feasible, even if not practical at 1970s
      - waveBidder 3y ago
        where are we extracting the energy from? is it effectively geothermal power?
        MarkMarine 3y ago
        It’s solar powered. Ok, I’m being brief but you seem genuinely curious, so, lemme explain what I mean: In thermo, you would draw a line around a closed system, and say basically conservation of energy applies in this system. Energy in = work out + losses. In a system where one input is the ocean, you basically just consider that infinite because of the size differences. One dinky little pipe compared to the mass flow into the system from the ocean, that math would be silly to bother with. That said, to swat down the stupid “this is perpetual motion” comments from people with Reddit engineering degrees, you also have to add in the energy input into the system of the sun, which is keeping the water from freezing over the course of 1 million years as it runs someone’s sarcastic water wheel.
        lazide 3y ago
        Your comment is literally word salad. Mind taking another pass?

IshKebab 3y ago

It's not amazing, it's obviously delusional. Think about it - if it really worked you have invented a perpetual motion machine, since you could just feed the fresh water through a little water wheel back into the ocean. You don't need to do any maths at all to know that his maths has gone drastically wrong somewhere.

MostlyStable 3y ago
In the absence of the sun (which is what ultimately drives ocean mixing), eventually this would lead to a layer of pure fresh water on top of a layer of salt. The energy is being driven by osmotic pressure of salt water. Once you have extracted the water out of the salt, that pressure is exhausted. Thus it is not perpetual.
roflc0ptic 3y ago
Take a long tube with an osmotic filter on it. Put it in the sea with one end out. Pressure is going to fill the tube up, no, just like a snorkel? Probably back up to sea level, possibly minus whatever force reduction caused by the filter? Boom, water filtration with no expenditure of energy. It may be wrong but it really isn't "obviously delusional."
- postalrat 3y ago
  You forgot the part where the water in the pipe is less dense and would be pushed up.
MarkMarine 3y ago
This isn’t a closed system. It’s not perpetual motion, there is an EXTRAORDINARY amount of energy added to the system by the sun. Saying “maths” instead of just math sounds quite odd, why are you making it plural? Is solving one equation “a math” and solving multiple equations “maths”?
- xdex 3y ago
  “Math” is used in USA and Canada. “Maths” is used by the rest of the English speaking world.