Gas and Ocean: How Pressure Affects Expansion

[D9 XTC]

Alright, so let's say you've got two air tanks. They both have the same capacity. So, let's say we bring the tanks down into the ocean where the atmosphere is 4x that at sea level and fill both of the air tanks to about their max capacity. (They hold 4x the air that they did at sea level because of their depth)

The difference between the tanks is that one is very sturdy and one is not.

Now, we bring both tanks to sea level and the sturdy one doesn't blow up and the other one does but only because one is much more solid than the other.

My question is does the air in both tanks expand equally even though one was solid enough to withstand the pressure changes?

 

[rcgldr]

Air only expands if a tank expands. If a tank is rigid (doesn't expand) then the air inside doesn't expand. For the other part of the question, a tank could be very expandable, like a strong balloon, and still not rupture even with lage expansion of air.

 

[D9 XTC]

Very good to know! Thanks for the answer!

 

[Studiot]

Hello D9XTC

You seem to have a bit of a misunderstanding about pressure, or you haven't described your tanks very well.

If you were to fill a rigid walled tank that "was solid enough to withstand the pressure changes" with a gas (air) you would get the same amount in the tank regardless of whether you 'filled' it at the surface 10m, 100m 0r 1000m depth.

The amount you get into the tank will depend solely on the pressure of the reservoir you fill it from, not on the local environmental pressure of atmosphere or ocean.

 

[D9 XTC]

You're right I didn't understand. I was looking at this webpage

http://www.onr.navy.mil/focus/blowballast/sub/work4.htm"

and saw that the diver's lungs could hold much more air at lower depths because the air was compressed at lower depths... or that's how I understood it anyway.

Which is basically what you're saying... in the slide show they just didn't say that the air going into the diver was compressed.

 

[Studiot]

Yes the diver's lung walls are flexible, not rigid.

The external pressure due to the water depth is balanced by breathing air at the same pressure as the water. This is accomplished automatically by a 'regulator' in the diver's airline.

If you take a deep breath and do a duck dive, your lungs and the air in them will actually be compressed at depth. It is possible to damage your lungs this way if you go too deep.

Divers reckon that the pressure increases by one atmosphere for every 10 metres depth.

go well

 

[Integral]

Yes the diver's lung walls are flexible, not rigid.

...

If you take a deep breath and do a duck dive, your lungs and the air in them will actually be compressed at depth. It is possible to damage your lungs this way if you go too deep.

Divers reckon that the pressure increases by one atmosphere for every 10 metres depth.

go well

Not sure that I am reading this right. If you do a surface dive with your lungs filled with air at 1 atm I do not believe it is possible to damage your lungs. IIRC some of the pearl divers free dive to about 100' they are not subject to lung damage.

Where lungs can be damaged is if you are scuba diving and attempt to free ascend while holding your breath. The air in your lungs expands as you ascend, if held in it will certainly damage your lungs. Scuba divers are taught to continuously exhale as you ascend.

 

[Studiot]

Sorry If I gave anyone the wrong impression.

I did not mean to imply that 10 metres, or any particular depth, was too deep.

Too deep depends upon the individual.

http://www.impulseadventure.com/freedive/lung-squeeze.html

Yes indeed the expansion of air can also cause damage on ascent in several different ways.