A standard compressed air SCUBA tank contains only about 21% usable oxygen, the rest being mainly a nitrogen filler. The filler takes up most of the space, but is required to keep the gas safe to breathe underwater.

Instead, replace the nitrogen filler with an easily liquefied gas such as a fluorocarbon. It would be contained in its own tank. Since it liquefies at a low pressure and becomes comparatively dense, the tank can be thin, small, and light. The filler is evaporated and mixed with pure O2 just before inhalation.

Condensing the filler gas in this manner reduces bulk. This can make for a lightweight apparatus with the same air time, or an extended air time apparatus with the same bulk as before.

Obviously small concentrations of other diving gases must be taken into account, but this shouldn't be too difficult.
-- Aq_Bi, May 10 2010

Triple Point http://en.wikipedia.org/wiki/Triple_point
A useful reference [8th of 7, May 11 2010]

Critical point is what you want http://en.wikipedia...28thermodynamics%29
highest possible temperature liquid can be at without boiling [metarinka, May 13 2010]

You'd still need the heavy, high pressure tank to contain the pressurised oxygen. I wouldn't be happy breathing 79% fluorocarbon. It might be OK for the small doses found in inhalers, but probably not good in large doses.
-- Twizz, May 10 2010


as we all know at standard pressure liquid nitrogen has a very low boiling point. couldn't we store it at high pressure such that it's boiling point is significantly raised?

you could also put a heat exchanger in line so that the liquid nitrogen was delivered at a more breatherable temperature.

the question is would a small pressure vessel be lighter than just the gaseous blend of air.

Also correct me if I'm wrong but doesn't the gaseous nature of liquid nitrogen play into the bouyancy of the scuba diver, would using a liquid tank be a plus or a negative?
-- metarinka, May 11 2010


Ideally, the SCUBA tank should be neutrally bouyant. The steel from which the tank itself is made has a density about 8 times that of water. The gases conatined within have densities around 1/800 times water. Pressurising to 200 Bar increases the gas density to around 1/4 of water.

Liquid fluorocarbons are typically high density (1.3 times water for R12).

A tank with liquid florocarbon would be significantly more dense than one with pressurised gas.
-- Twizz, May 11 2010


//A tank with liquid florocarbon would be significantly more dense than one with pressurised gas.//

Yes, but it would produce a far greater volume of gas.

Question: does anyone know what pressures are needed to liquefy nitrogen or oxygen at ambient temperatures?
-- MaxwellBuchanan, May 11 2010


It's not possible; if by "ambient" you mean 273 K, then both gases are above their triple point <link>, which is of the order of 60 K.

They will not liquefy or solidify whatever the pressure, until nucleon condensation effects predominate, which only occurs in collapsed supermassive stars.
-- 8th of 7, May 11 2010


8th of 7

you're confusing triple point with Critical point. Liquid nitrogen boils at 70k at atmospheric pressure. Triple point is the temperature and pressure at which all 3 states merge and is usually very low at very marginal pressures.

Liquid nitrogen's critical point is a positively bun warming temperature of 126K (-149C) at a elphant standing on a needle pressure of 33.5 Atm (3,390 KPa)

I would hate to rupture your tank of super critical liquid nitrogen at -150 degrees though... weight savings not withstanding
-- metarinka, May 13 2010


Are we not missing the point of a re-breather somewhat?
-- saedi, May 16 2010


Could we not just hire a fish?
-- MaxwellBuchanan, May 16 2010


With or without a bicycle ?
-- 8th of 7, May 17 2010


I don't think you can hire a fish with a bicycle. They usually want hard cash.

And, going back a few annotations - are people trying to tell me that, at room temperature, no amount of squashing will turn oxygen into a liquid? Are we sure about this? What happens when you squash it until the density of oxygen molecules is the same as the density of water molecules in water? I don't geddit.
-- MaxwellBuchanan, May 17 2010


Given enough gravity, you can squash down gaseous oxygen whatever the "temperature", but you're talking nuetronium/neutron star/gravtational collapse. (q.v.) and making Quark Soup*.

*Do NOT attempt to make this into a nourishing beverage by adding boiling water. Packed by mass, not volume. Contents may settle during transit. Close cover before striking.
-- 8th of 7, May 17 2010



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