Before i go on, i want to point out that i seem to have a vague memory that this has already been posted. If so, please accept my apologies and i'll delete it, but i have just searched and couldn't find it.

I'm sure we've all been stuck in a sub at the bottom of the sea with no hope of rescue. I know Doctor Who has for a start. Anyway, one of the problems they seem to encounter in that situation is that the oxygen runs out and the air fills up with carbon dioxide. On the other hand, they're surrounded with an oxygen supply either dissolved in the water or in the actual water molecules, and they have a nuclear reactor, i.e. a good source of energy.

So, either pump water through tanks at the side of the sub and extract dissolved oxygen while releasing carbon dioxide into the sea water or electolyse the actual water to release the oxygen, using the energy generated by the nuclear reactor.

Surely. Or am i missing something obvious?
-- nineteenthly, Apr 14 2013

artificial gills http://davidszondy....rwater/menfish2.htm
the gills would have to have the surface area of a bedspread-- [whlanteigne, Apr 14 2013]

Nuclear submarines can stay submerged for months at a time. They use scrubbers to extract the carbon dioxide from the air to keep it breathable. I believe they also have a means to supplement the oxygen.

Dr Who isn't a reliable source of scientific information, although they do toss in a brilliant nugget now and then. In the episode I'm thinking of, the sub's reactor was out of commission, and they only had a limited amount of battery power. Eventually, the loss of power would have meant the air scrubbers wouldn't be able to function, but nuclear sub batteries can last a good while.

They also can't launch missiles at the depth they had sunk to, but that's another issue.

I'm pretty sure the various Navies of the world have ongoing research into artificial gills for subs and divers.
-- whlanteigne, Apr 14 2013


I would imagine so too, so if it's not happened (and if it has, maybe it's a secret?), what's the obstacle?
-- nineteenthly, Apr 14 2013


The obvious obstacle is the partial pressure of oxygen vs the crushing pressure of water. Even at extreme depths, the partial pressure of air is still only about 15 psi, whereas the water pressure is tens of thousands of psi. Any membrane that passes the breathable gases and stops the water will have to withstand all that pressure.
-- whlanteigne, Apr 14 2013


Submarines can already generate oxygen with their reactors, and potable water for that matter. The limitation to staying submerged is how much food they can store, so maybe the idea should be Submarine Baleens.
-- DIYMatt, Apr 14 2013


//Dr Who isn't a reliable source of scientific information// Great. Thirty years into my career, and then this bombshell...
-- MaxwellBuchanan, Apr 14 2013


//Any membrane that passes the breathable gases and stops the water will have to withstand all that pressure.// At a pinch, you could pressurize the back-side of the membranes with nitrogen; shouldn't stop oxygen diffusing through. But, if you've got your own personal nuke, electrolysis is probably the way to go.
-- MaxwellBuchanan, Apr 14 2013


//Great. Thirty years into my career, and then this bombshell...//

I know, crushing. Even worse than finding out that Mr Spock isn't possible (as would be any kind of breeding with extraterrestrials, despite what the UFO abduction cultists believe).
-- whlanteigne, Apr 14 2013


//you could pressurize the back-side of the membranes with nitrogen; shouldn't stop oxygen diffusing through.//

That's exactly the technical problem, pressurizing the backside. As far as I know, artificial gills work only at very shallow depths.
-- whlanteigne, Apr 14 2013


"The gills are just one of the many futuristic technologies the U.S. military is funding through its Small Business Technology Transfer awards. The awards originated in 1994 as a pilot project and now extend through to 2009. Successful two-year contracts can provide as much as US$750,000 to a company for research and development."

see also link
-- whlanteigne, Apr 14 2013


//as would be any kind of breeding with extraterrestrials,

Damn, I was looking forward to that bit.

Except if it was alien tentacle shenanigans which turns up in Japanese stuff far too often.
-- not_morrison_rm, Apr 15 2013


Well if you were at the very bottom of the ocean, with those gulper eels and whatnot, this would not work. Unless you were somewhere with heliox - then it could still work. At a depth where you could oppose water pressure with air pressure I propose that removing the entire bottom of the submarine and exposing an expanse of water should work. The CO2 drifting about will dissolve into the water, and oxygen will emerge from it to equilibrate with the atmosphere. Helium, if any is around, will not dissolve and so you could maintain your pressure.

If the exposed expanse of water were not large enough, one could increase surface area via agitation - for example kicking of legs within the water, or whacking it with paddles.

This idea should be testable using bugs or other breathing critters. If the theory is true it should be possible to survive under an overturned boat without running out of air. Cage with test critters placed under vessel with end open to water. Water (outside) is open to air. Do critters live longer than critters in sealed boat? Does CO2 build up?
-- bungston, Apr 15 2013


[+] They should put shark gills on submarines even if they don't work, like fake louvres on cars.
-- FlyingToaster, Apr 15 2013


//They should put shark gills on submarines even if they don't work, like fake louvres on cars

It would be cool to have retro-submarines, done by whoever did 1950's Cadillacs. Getting the furry dice to stick on could be a challenge.
-- not_morrison_rm, Apr 18 2013



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