Pressure Harvesting - from ocean depths

Discussion in 'General Science & Technology' started by Quantum Quack, Mar 8, 2020.

  1. Quantum Quack Life's a tease... Valued Senior Member

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    22,494
    Something to get creative about?
    Ample resource
    No waste product


    Average depth of the oceans is about 3600 meters
    At this depth the pressure is 36000kPa (360 atm or 5263 psi)

    What could you do with an endless supply of 36000 kPa?

    Extracting pressure using appropriate two chamber systems seems too easy...
    Why haven't we?
     
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  3. billvon Valued Senior Member

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    Because it doesn't work. You might as well get a lot of rocks, pile them on a piston, and "harvest the endless supply of pressure." That won't work either, but same idea.
     
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  5. Quantum Quack Life's a tease... Valued Senior Member

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    there are so many problems with your analogy I don't know where to begin...
    Oceans are liquid for starters and water pressure is omni directional and continuous whether pressure ( volume) is extracted or not.
    There is no need to pile water on top of a compressible volume as the ambient pressure is already and always present...
     
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  7. origin In a democracy you deserve the leaders you elect. Valued Senior Member

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    What exactly do you think you could do with it?
    How would you extract pressure.
     
  8. Quantum Quack Life's a tease... Valued Senior Member

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    Anything driven using pressure.... pneumatic devices, tools, manufacturing, electricity generator turbines, ships, cars, trucks.etc
    In simple terms, sink a chamber with air that can trap the pressure (compressed air) then float it back to the surface.

    For example: 1000 cubic meters of compressed air at 100 atm is a lot of stored potential energy.

    How do you think harvesting pressure could be done?
    At what ever scale you wish.

    For general info:
    https://en.m.wikipedia.org/wiki/Air_compressor
     
    Last edited: Mar 8, 2020
  9. DaveC426913 Valued Senior Member

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    billvon is correct. You might as well pile some rocks up and compress your air. It is exactly the same principle.

    The pressure at the bottom of the sea is there because it is at its lowest potential (like rocks fallen to the ground at the base of a cliff). You can't get a net gain of energy by taking something from low potential and moving it to high potential.

    It takes energy to lift that compressed air (since it's not buoyant). Turns out it takes as much (in fact more) energy to lift it back up to a place of higher potential energy than you gain from it.

    It is identical to "harvesting" rocks at the bottom of a cliff by schlepping them back to the top of the cliff.
     
    Last edited: Mar 8, 2020
  10. Quantum Quack Life's a tease... Valued Senior Member

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    I am not sure whether I can agree.
    compressed air can be buoyant...and is used all the time in submarines etc...
    Flood ballast with water to sink then flood ballast with compressed air to purge water to surface.
    The only difference is that you have pressure cargo on the upward journey that didn't cost you or the environment anything.
    https://science.howstuffworks.com/transport/engines-equipment/submarine1.htm

    So you design a crew less automated submersible with ballast tanks and cargo tanks and deliver harvested pressure to the surface, transfer to more suitable chambers and you have pressure energy cells. A percentage of which could be used for ballast on the next journey...
    or that's the thought any way...
    or you could position your collecting over a geothermal vent and use the hot water to aid your ascent...

    but maybe there are other ways to capitalize on the extreme pressures available.

    I am confident there would be a way to harvest serious pressure economically.
     
    Last edited: Mar 8, 2020
  11. DaveC426913 Valued Senior Member

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    14,562
    No.
    Compressed air is not buoyant - because it is compressed. i.e. high weight in small volume.
    Once you decompress it - by venting into into ballast tanks - its volume increases, making it buoyant, but rendering it useless for your purpose.

    If you have a geothermal vent at your disposal, then just draw the energy from it directly.
    This is key: Unlike water pressure, geothermal vents are a source of energy.

    It is not a matter of cost. It is a matter of thermodynamics.

    Engineers look at these type of problems as if they are black boxes: it doesn't matter what happens inside, you only need to look at what goes in and what comes out.

    You are trying to extract energy from a system that already has the lowest potential energy possible. To get that state to somewhere where you could use it, takes more energy than you get. Exactly like rocks at the bottom of a cliff.

    You're essentially saying there should be an efficient way to lug those rocks back up to the top of the cliff where you could the extract more energy from them.

    The engineer simply looks at the system as a black box. It doesn't matter what mechanism is invented - no matter how creative or efficient to get the rocks to the top of the cliff - you can't even in principle - turn this into a net-energy-positive system.
     
    Last edited: Mar 8, 2020
  12. Quantum Quack Life's a tease... Valued Senior Member

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    well...what way would you suggest?
    solar powered cable and winch?
     
  13. Quantum Quack Life's a tease... Valued Senior Member

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    I didn't think weight was the issue but displacement was?
     
  14. DaveC426913 Valued Senior Member

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    Think about the rocks at the bottom of the cliff problem and the system as a black box.
    You can't cheat thermodynamics.
     
  15. Quantum Quack Life's a tease... Valued Senior Member

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    Unfortunately you are mistaken.
    The potential of compressed gases is a well known source of energy and if water pressure allows you to extract that pressure then water pressure is also a source of energy....
     
  16. DaveC426913 Valued Senior Member

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    Yes it is. (Nor did I suggest it wasn't.)

    If you plunge a hollow pipe tap down into a pocket of compressed gas what does it do? It erupts upward with a spray of compressed gas.

    If you plunged a hollow tube down a mile into the open ocean of water to let "all that pressure escape", do you get a perpetual geyser? No.

    Do the ocean depths ever erupt with water jets from all that pressure below? Do Earth's oceans explode all the time from all that pressure? No.

    Unlike gas, water is virtually incompressible.

    It doesn't.
     
    Last edited: Mar 8, 2020
  17. Quantum Quack Life's a tease... Valued Senior Member

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    I am confident even running a diesel powered winch arrangement to raise the chamber with large amount of compressed air will be cost effective.
    So yes water pressure can indeed be a source of energy.
    And that is the point of this thread..
    Pressure harvesting the ocean depths... it ain't rocket science... you could even use your back yard swimming pool if you wanted to...

    For some reason I get the impression that you and Billvon are stuck on the idea that this is a pseudo Perpetual motion or energy thread. It isn't.
     
  18. DaveC426913 Valued Senior Member

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    No it ain't. It's a violation of energy laws.

    I don't want to poop on your desire to come up with alternate sources of energy, but this is the energy analogy of perpetual motion machines - they look like they could work - to those who don't understand the cold, hard laws of thermodynamics.
     
  19. Quantum Quack Life's a tease... Valued Senior Member

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    22,494
    lol... see my edit to my last post:
     
  20. Quantum Quack Life's a tease... Valued Senior Member

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    being a bit cynical are we...? lol

    I could design a simple cylinder with a ratchet ram/plunger that I could throw it into the deep with a cable attached, retrieve it by hand and have a vessel with some seriously compressed air in it.
    Nothing perpetual about it...
    ah except, that I could do the above for eternity and still not depleted the resource. Maybe that's the bit that is throwing you... lol
     
  21. DaveC426913 Valued Senior Member

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    14,562
    Look, the simplest way to set up your "pressure harvesting" system is to simply plunge a rigid tube straight down into the open ocean a mile deep.
    That pressurized water - at hundreds or thousands of atmospheres - should just come shooting right up the pipe under high pressure, right?

    With such a geyser you would be able to put a turbine over it, right?

    Do you know how high that geyser would shoot?

    Exactly zero inches. It would be the height of sea level.

    A rigid tube, open at the bottom, where the pressure is hundreds - or thousands - of atmospheres will have a surface level the same as the sea level.
     
  22. Quantum Quack Life's a tease... Valued Senior Member

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    now you are being silly.... hardly worth the effort typing that dribble...

    the simplest way is described in my post #17
     
  23. DaveC426913 Valued Senior Member

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    No it isn't.

    The point is that your idea fails it fails for the same reason - a lack of application of basic thermodynamics. The fact that you must put energy in to your system to get energy out. And PMM-inventors always discount the amount of energy required to put in. As you are doing.
     

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