Childhood Invention

[One of the Few]

When I was in elementary school I thought up the greatest invention of all time, an infinite rebreather. Now that I know a bit more about physics I am realizing that with today's technological restraints, it is nigh impossible. But it was and still is fantastic all the same.

 

Simply, it separated water into hydrogen and oxygen, I assumed that the oxygen would bind to itself forming O2, secondly I knew that hydrogen was used in fusion. So my thought was that if i could make a small reactor, i could use that to power the invention, what would be required is an infitessimally small fusion reactor and an electrolysis apparatus etc. Both of which would be "hard" to come by.

 

Wouldn't it be feasible to say that with this I could live indefinately underwater?

 

Furthermore, i'm not worried about copyright imfringement or the likes, seeing as, if you can develop the technology to do this, you'll probably deserve the earnings.

 

If you have any corrections, comments, constructive criticism I would be delighted to read it.

 

With care,

One of the Few

[padren]

Nuclear submarines do this today but use fission, as you said you'd need a hydrogen based fusion reactor to avoid requiring external sources for the nuclear fuel. In nuclear submarines today, food is the largest limiting factor as far as I know - air can be produced in the manner you mentioned, water I imagine can be purified as well (ydoaPs would know better) and the fuel can last years.

 

If you want to live underwater indefinitely though, you could always just move to Seattle.

[Kyrisch]

The biggest problem with this, besides the fact that it could not be done efficiently on a small enough scale to be useful, is what happens when you decompose water like that:

 

[math]2H_2O \xrightarrow \ 2H_2 + O_2[/math]

 

As you can see, this will result in a concentration of the extremely light (so you would have to deal with buoyancy) extremely flammable (which is not a good idea if you have electrolysis going on anywhere near) diatomic hydrogen gas that would be twice as large as the oxygen gas you wish to utilize.

[insane_alien]

actually, there isn't a buoyancy issue. the gas is in a rigid container so the overall volume of the system doesn't change, you are just decreasing the liquid volume slightly and increasing the pressure. of the gaseous component.

 

but anyway, the hydrogen can just be vented out the side or used for expelling ballast water.

[CaptainPanic]

The biggest problem with this, besides the fact that it could not be done efficiently on a small enough scale to be useful, is what happens when you decompose water like that:

 

[math]2H_2O \xrightarrow \ 2H_2 + O_2[/math]

 

As you can see, this will result in a concentration of the extremely light (so you would have to deal with buoyancy) extremely flammable (which is not a good idea if you have electrolysis going on anywhere near) diatomic hydrogen gas that would be twice as large as the oxygen gas you wish to utilize.

 

You do this in a continuous reactor - so you create and also get rid of the gas at the same rate. Therefore, in time there is no accumulation of gas.

 

Also, the hydrogen appears on one electrode, oxygen on the other. If designed correctly, the two resulting gases are nearly pure and kept completely separate, so no flammability problems occur:

In a properly designed cell hydrogen will appear at the cathode (the negatively charged electrode, where electrons are pumped into the water), and oxygen will appear at the anode (the positively charged electrode). (source: wikipedia)

Edited November 23, 2009 by CaptainPanic

[Kyrisch]

actually, there isn't a buoyancy issue. the gas is in a rigid container so the overall volume of the system doesn't change, you are just decreasing the liquid volume slightly and increasing the pressure. of the gaseous component.

 

but anyway, the hydrogen can just be vented out the side or used for expelling ballast water.

 

You do this in a continuous reactor - so you create and also get rid of the gas at the same rate. Therefore, in time there is no accumulation of gas.

 

Also, the hydrogen appears on one electrode, oxygen on the other. If designed correctly, the two resulting gases are nearly pure and kept completely separate, so no flammability problems occur:

 

Interesting, thanks for the corrections!

[John Cuthber]

The radiation hazard from a personal fusion reactor might be tiresome.

[Sisyphus]

Extracting oxygen from seawater is relatively simple. It just requires electricity. They do this. If your source of electricity is cold fusion, you've built something rather more important than scuba equipment.

 

But yeah, as padren said, as long as you have a power source, you need not run out of air (or drinking water) underwater. Nuclear submarines carry enough fuel for months. With something like an ocean floor habitat, maybe you could get power from a geothermal generator or something.

[One of the Few]

Thank you for the input, and yes sisyphus if i developed cold fusion living underwater may not be the main use for it. As for the radioacticity, yes of course there's going to be a fine bunch of it, yet i think the main issue with fusion would be the electromagnetic field. If this were to be magnified to the extent you could power a city, it might have more practical uses*.

* In fact I could just make Rapture from Bioshock.

P.S. I live in the puget sound area

[Moontanman]

Thank you for the input, and yes sisyphus if i developed cold fusion living underwater may not be the main use for it. As for the radioacticity, yes of course there's going to be a fine bunch of it, yet i think the main issue with fusion would be the electromagnetic field. If this were to be magnified to the extent you could power a city, it might have more practical uses*.

* In fact I could just make Rapture from Bioshock.

P.S. I live in the puget sound area

 

No actually the electromagnetic field wouldn't be the problem, neutron radiation would be the problem. Even cold fusion, if true, would produce neutrons at a dangerous level as well.

[insane_alien]

eh just make the reactor casing out of boron.

[Moontanman]

eh just make the reactor casing out of boron.

 

Boron is going to stop neutrons from a nuclear reactor? If that is true that would make a nuclear powered space craft much lighter and more practical wouldn't it?

[One of the Few]

moontan man is right, plus it is almost as hard as diamonds(refering to moh's scale) then again it might be difficult to find it in large quantities. As for the electric field, wouldn't it fry any electrical components in the device. Ugh neutrons, that's some bad juju there.

[insane_alien]

well boron is used as a neutron absorber in nuclear reactors anyway. but for spacecraft there is a much much easier solution than heavy shielding. put the reactor out on a large truss away from the habitation section. that way you only need shielding to allow a shadow to encompass the rest of the ship. cuts your shielding weight to a 6th instantly.

[npts2020]

I can say for sure that most naval vessels (including submarines) distill their own fresh water from seawater. Also, IIRC boron is used as shielding on many reactors and even for control rods on a few of them.

[One of the Few]

I do have one more question, the massive temperatures of fusion reactions are comprised using reactors built to massive scales, isn't feasible to say that at a ten thousandth, maybe less, (note the rebreather in mind wouldn't be more than the size of bicycle handle bar.) that said temperatures would drop to a more managable temperature? Say a few hundred degrees farenheit?

[insane_alien]

if the temperatures drop then you don't get fusion. and all you have is a magnetic metallic doughnut with some slightly warm plasma going round inside it sucking up power like a hummer sucks up petrol.

 

the fact is that the bigger the fusion reactor the easier it is to deal with. the temperatures stay roughly the same as it is too problematic to have them higher than they need to be and you don't get fusion if its colder.

[One of the Few]

Alright, with this information, I will become the worlds first trillionaire. As thanks, all who responded to this thread will recieve a charming gift basket of your choice, and a lamborghini. I'll make Rockefeller look like a peasant.