Compressed air solubility in seawater - Compressed air ballast tank: solubility

[jorgepersan]

[color=#000000]Hi everyone,

I have run a search for technology used for main ballast tank (MBT) operation in large submarines, and there remains an issue that has puzzled me for some time now]

[interpol]

Because even at 60 bars

Because even at 60 bars of pressure, not ALL of the air will be dissolved.

The formula for calculating the ratio of solubility is

Sa = ma / mw (1)

*Sa = solubility ratio

*ma = air mass

*mw = water mass

Temperature also plays a big part, as the hotter it gets the harder it is to dissolve air into water. That is why when you heat up fresh water you see the bubbles forming before it begins to boil, as the water cannot hold the air anymore.

[petn7]

could it also be that

could it also be that the actual process of blowing the tanks is too short to let a significant amount of air to dissolve in the water?

[interpol]

Actually, I think he doesn't

Actually, I think he doesn't realize that sea water already has air in it. Or else all those nice little fishies would be dead.

So, I don't think that any of the air gets dissolved at all. Sure, it is a lot of pressure, but the water is already aerated. The pressure of the air has nothing to do with the solubility ratio, it is all dependant on the pressure of the water column above that will determine solubility of a volume of gas underwater.

[jorgepersan]

Thanks to both of you.

Thanks to both of you. I DO know that the water already contains air, but the solubility depends on temperature AND pressure, and the water pressure will be slightly less than the compressed air pressure at the air-water interface inside the ballast tank - otherwise no displacement would take place. Yes, the water is aerated, but perhaps it is not saturated with air, which means there is room for more! Please think of the carbonated soda can. The idea that it must have something to do with the speed of the process - and I suppose it actually happens very fast in a real submarine - is very appealing. But then, the tank must be sealed after the process is completed, right?

[petn7]

are you asking if the

are you asking if the ballast tanks are sealed once they are emptied to make the sub surface? well, from what i have read, American (and British too?) subs do not completely seal their main ballast tanks when surfaced. they keep the bottom openings open and seal the top openings/vents. the air inside the ballast tanks are then kept at some pressure (like 10psi) Russian and Dutch subs on the other hand seal both top and bottom main ballast tank vents and keep the air inside at atmospheric pressure.

here's where i got this information

http://www.heiszwolf.com/subs/tech/tech01.html

[mkeatingss]

Absolutly not. When tanks are

Absolutly not. When tanks are blown, at depth, the air is compressed by the water pressure. As the ship rises, the air expands as water pressure decreases. Ballast tanks are "Soft" tanks, the increasing pressure, inside of them, could rupture them. This would, of course, result in a negative impact on the subs survivabilty in the deep ocean invironment.
Mike

[JWLaRue]

Mike,

...then what are/were Kingston valves

Mike,

...then what are/were Kingston valves for?

They closed the bottom vents of the ballast tanks.

-Jeff

[mkeatingss]

Those are used only on

Those are used only on "Hard Tanks", like the negative tank. Kingstons were used on early US boats, but as depth capabilities increased, "Soft Tanks with open floods saved on cost. Soft steel vice hardened steel, as used in the pressure hull.
Mike