Artificial gills - how?

Discussion in 'Architecture & Engineering' started by CEngelbrecht, Dec 21, 2017.

  1. CEngelbrecht Registered Senior Member

    Messages:
    354
    Found a website some time ago, that claimed to have figured out how to make a gismo that allowed you to breathe oxygen from the surrounding water, and they were seeking crowd funding to get it on the market. Sounded very exciting, however, a quick readthrough of the claimed principle showed it as a massive hoax, trying to steal mo money from the gulliple of the world.

    Please Register or Log in to view the hidden image!



    But... just out of curiosity... could it be made to work? Like, you put on some kind of stormtrooper helmet, which then diffuses oxygen in and diffuses excess carbon dioxide out into the surrounding water, allowing you to breathe inside an air bubble constantly being automatically kept at set levels of O2 and CO2 (and N2?), and then you could be under water as long as you like, with limited bulky equipment and no gas limit from a SCUBA tank.

    Would there still be issues of decompression sickness and nitrogen narcosis, is what I can't figure out right now. And how deep would you be able to go before physics would still kill you? Tens of meters? Hundreds? Thousands? Provided that the diffusion issue could even be solved.

    Please Register or Log in to view the hidden image!


    (A game I played recently, where your character wore a helmet and could stay under water indefinitely.)
     
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. sideshowbob Sorry, wrong number. Valued Senior Member

    Messages:
    4,238
    Reminds me of the Beverley Hillbillies when Jethro invented an anti-smog device. The device itself was small but the filter was the size of a truck.

    The gill device might, in fact, turn out to be more unwieldy than SCUBA.
     
  4. Google AdSense Guest Advertisement



    to hide all adverts.
  5. Seattle Valued Senior Member

    Messages:
    3,434
    Pressure issues would be unchanged so no difference in decompression issues, nitrogen narcosis, oxygen toxicity, etc.

    There are already rebreathers that greatly extend your time underwater with less bulk but the same decompression obligations.

    How deep you can go isn't determined by what you are breathing (meaning the equipment). It's largely determined by how long your decompression obligation would be.

    This particular gadget however is just a joke.
     
    CEngelbrecht likes this.
  6. Google AdSense Guest Advertisement



    to hide all adverts.
  7. billvon Valued Senior Member

    Messages:
    14,165
    Sure. You would need a gas exchanger the size of several bedsheets though.
    The issues would be the same as you have today when you dive with air.
    Beyond 40 meters nitrogen narcosis would become a problem. Beyond 60 meters oxygen toxicity would be a problem.
     
    CEngelbrecht likes this.
  8. CEngelbrecht Registered Senior Member

    Messages:
    354
    Could that be folded in some design solution?

    Ah. Of course.
     
  9. billvon Valued Senior Member

    Messages:
    14,165
    Not easily. The membranes have to be very thin, which means fragile. You can increase water and air flow past them to improve performance, but that's hard to do with fragile membranes.
     
    CEngelbrecht likes this.
  10. CEngelbrecht Registered Senior Member

    Messages:
    354
    Right. The point would be, that it would happen passively and continuously.

    How much oxygen is even in sea water? Does it differ across the world? Is there enough for human metabolism?
     
  11. billvon Valued Senior Member

    Messages:
    14,165
    When water and air are equilibriated, then water contains about 35% oxygen and 60% nitrogen, as a percentage of dissolved-gas maximum (because oxygen dissolves more easily in water.) So in areas without much life there's more oxygen, as a percentage of total possible dissolved gas, than in air.

    Fish use oxygen, so that will decrease available O2. Phytoplankton release O2. Zooplankton absorb O2. So a big zooplankton bloom (caused by, for example, fertilizer) will reduce O2 significantly.

    If you were going to use such a system to dive, having a good sensor/display showing ppO2, ppN and ppCO2 would be critical.
     
    CEngelbrecht likes this.
  12. Seattle Valued Senior Member

    Messages:
    3,434
    I don't think ppCO2 sensors have been perfected for rebreathers yet.
     
  13. CEngelbrecht Registered Senior Member

    Messages:
    354
    Okay, same principle in submersibles. Submarines with a crew of 150 or whatever, keeping ppO2 etc. well below 1.6, O2 goes in, CO2 goes out, for weeks under water. Might that be possible?
     
    Last edited: Dec 21, 2017
  14. Seattle Valued Senior Member

    Messages:
    3,434
    They already do that. What are you asking specifically?
     
  15. CEngelbrecht Registered Senior Member

    Messages:
    354
    No, I mean an artificial gill system as hypothesized above, so that submarines can extract oxygen from the water around the sub, and release excess carbon dioxide into the water, so a vessle can stay submerged for weeks. Surely that doesn't already exist in subs, does it? I don't mean snorkle ventilating at the surface, but actively staying submerged, while molecules goes in and out from the body of water.
     
    Last edited: Dec 21, 2017
  16. Seattle Valued Senior Member

    Messages:
    3,434
    How do you think they currently are able to stay submerged for so long? They have an artificial (scrubber) rebreather system.
     
  17. CEngelbrecht Registered Senior Member

    Messages:
    354
    You're shittening me?

    And this can't be made chap sized?
     
  18. billvon Valued Senior Member

    Messages:
    14,165
    They do it much differently. They use CO2 scrubbers and then recycle them (they bake out the CO2) to get rid of the CO2. To get O2 they electrolyze water then vent the hydrogen. So no "permeable membranes" or gas exchange involved. (Which would be VERY hard to do at those pressures.)
     
    sideshowbob and CEngelbrecht like this.
  19. DaveC426913 Valued Senior Member

    Messages:
    9,212
    I think, in addition to area of exchange, there may also be an issue of partial pressures.

    The extracted gas that reaches your lungs must be of sufficient partial pressure to allow it to be sucked through the membrane. Oxygen in air is only 21% partial pressure.

    (In Robinson's Rad Mars series, they had masks that only let oxygen through. I have a feeling that it would not work. The crew would be sucking tremendously with each breath. Not quite the same as water, but similar.)
     
  20. Seattle Valued Senior Member

    Messages:
    3,434
    Billvon is right, it's not using the same technology that you're talking about but it's accomplishing the same thing. You want something that will allow someone to stay under water for a long time and to go to a decent depth and you want it to be portable.

    A rebreather does that. I'm a scuba diver but I have friends who have rebreather units. They scrub in a similar way to the way it's done on a sub but as billvon points out, it's not extracting oxygen from the water (nor does it need to). As the name "rebreather" implies, it scrubs the air that you have just exhaled so it can be reused (rebreathed).
     
    CEngelbrecht likes this.
  21. CEngelbrecht Registered Senior Member

    Messages:
    354
    I was basically dreaming about hanging out at 100 feet all day. But then I would have to decompress for six hours, before I could come home for tea?

    Sounds like a rebreather course is going on my bucket list.

    Is it not perceivable to have some nano membrane, that would send CO2 one way and O2 the other? How do fish gills work, how do they extract oxygen from the water and send carbon dioxide the other way, that has to be a passive system. It feels like it's a biological system just waiting to be reverse engineered.

    Please Register or Log in to view the hidden image!



    Ever had the feeling of something being just out of reach?
     
  22. Seattle Valued Senior Member

    Messages:
    3,434
    Fish don't do well in air and we don't do well underwater. It seems to be a fair trade-off.

    Please Register or Log in to view the hidden image!

    Marine mammals don't extract oxygen from water either.
     
  23. CEngelbrecht Registered Senior Member

    Messages:
    354
    They don't exactly breathe compressed air under water either. We have managed to invent that, so why not artificial gills, if it's somehow technically possible?

    We would have to breathe air in and out, though. Which means that whatever the system is and does, it would have to include an external air bubble, that you'd ventilate in and out of your lungs (like the air bubble in an upside down rowing boat under water). That external air bubble then being kept at constant safe levels of O2, CO2 and N2 by this imaginary membrane system. All kept in some oversized helmet, that also has gauge displays.

    Please Register or Log in to view the hidden image!


    (Random pic, don't really know what that's supposed to be.)

    Yeah, I know, it's getting complicated. And it's probably still impossible.
     

Share This Page