[Mr T.]

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This from the Smithsonian Institute in the US:

http://seawifs.gsfc.nasa.gov/OCEAN_PLANET/HTML/oceanography_how_deep.html

Enjoy.

 

[Dr Stevil]

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I've always thought it a bit of a coincidence that one of the guys who went down in the Trieste to Challenger Deep was called Piccard most definately to boldly go where no-one yadda yadda yadda...

 

[Dominic]

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Before anyone starts planning to dive the Titanic, here's an interesting consideration:

The Titanic is at a depth of 3,820 meters
Therefore the pressure is at 383bar down there.

So if you took a 232 bar cylinder down with you, and opened it whilst you were there, instead of air coming out, water would go in.

Scary, huh?

 

[Dr Stevil]

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<font color='#0000FF'>That's an excellent observation Dom, I'd never considered it like that.

Which makes me wonder if pressure does actually increase in strict linearity with depth, given the argument about the limits of compressibility usually given when discussing the pros  & cons of 300bar cylinders , ie at Challenger Deep,  (11,042m deep) the pressure should be about 1131 bar, wouldn't liquid start behaving like a solid under those conditions ?
Do we have any fluid-dynamics physicists on the boards ?
just curious...
Chee-az
Steve

 

[Jay]

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Quote[/b] (Steve W @ Mar. 11 2003,17:31)]Do we have any fluid-dynamics physicists on the boards ?

No but we got lots of fluidly dynamic piss artists

 

[Scoff]

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"The Titanic is at a depth of 3,820 meters
Therefore the pressure is at 383bar down there.

So if you took a 232 bar cylinder down with you, and opened it whilst you were there, instead of air coming out, water would go in."

But then, Dom, couldn't the excess pressure squeeze the tank like a toothpaste tube, and try to push out the air...??

Yeah, I failed my physics 'O'-level  

Cheers

Scoff

Now about Boyle's Law....?

 

[Mark Scott-Simons]

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Quote[/b] (Steve W @ Mar. 11 2003,17:31)]Which makes me wonder if pressure does actually increase in strict linearity with depth, given the argument about the limits of compressibility usually given when discussing the pros  & cons of 300bar cylinders , ie at Challenger Deep,  (11,042m deep) the pressure should be about 1131 bar, wouldn't liquid start behaving like a solid under those conditions ?

Even at these pressures water remains almost totally incompressible. The density would increase from 1025kg/m^3 to 1061kg/m^3 ie only a few % more so the linear relationship between depth and pressure is still pretty good.

 

[Mark Scott-Simons]

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Quote[/b] (Scoff @ Mar. 11 2003,22:51)]Therefore the pressure is at 383bar down there.
But then, Dom, couldn't the excess pressure squeeze the tank like a toothpaste tube, and try to push out the air...??

I'm fairly sure the cylinder would not have enough physical strength to resist the 383 - 232 = 151 Bar crushing force. But it wouldn't be like squeezing toothpaste. The cylinder would probably go with one hell of an implosion.

 

[Dominic]

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Quote[/b] ]But then, Dom, couldn't the excess pressure squeeze the tank like a toothpaste tube, and try to push out the air...??

Dunno. Try it and let me know how it goes  

 

[MATTBIN]

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Wouldnt your mask implode before that? Come to that you'd get a hell of a squueze on the dry-suit in the lower regions, talk about pickled walnuts.
Matt

 

[Dominic]

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The mask'd be safe... but come to think of it, you'd need a hell of a lot of air to inflate your drysuit down there... Can you imagine a 15L argon cylinder?

One of those hot water suits would probably be the way to go...

 

[Paul Thomas]

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<font color='#000080'>. . . and what mix would you use?

Even if you could breath it the mix would have to be no more than 0.28% oxygen or it would be toxic and I suspect you would be slightly narked even if you were to use hydrogen as the diluent!

(Aren't the atmospheric gasses liquified at that pressure?)

 

[Beck]

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Hey I have hear poseidon regs are good at depth but thats just ridiculous
LOL

I'm game, give me the kit to do it and i'll give it a go
LOL

 

[jasondrake]

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I once read that some people used to believe that at a certain depth the sea's density would be thick enough to stop objects sinking through them. They pictured ship wrecks suspended in the gloopy water all at the same depth above the sea bed. Oh the possibilities!

I think hard atmosphere suits would be the order of the day.

 

[angus Theape]

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Quote[/b] (Jason Drake @ Mar. 24 2003,18:47)]I once read that some people used to believe that at a certain depth the sea's density would be thick enough to stop objects sinking through them. They pictured ship wrecks suspended in the gloopy water all at the same depth above the sea bed. Oh the possibilities!

I think hard atmosphere suits would be the order of the day.

Ah the floating cannonball theory. This comes from mixing up what happens with a helium filled ballon in the atmosphere and what happens to a solid object in water.

In fact the gravity on the object will increase the deeper you go as you get nearer the centre of the Earth.

 

[Dominic]

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Quote[/b] ]In fact the gravity on the object will increase the deeper you go as you get nearer the centre of the Earth.

Eh? Gravity DECREASES as you near the center of the Earth - there's less mass below you pulling you down and more mass above you pulling you up.
In theory, the center of the Earth is at zero gravity..

 

[Rubber Johnny]

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Water density is hardly affected by depth, so an iron cannonball will never be denser than water and stop sinking. There is some increase but not as much as you would think.
 A full 232 bar cylinder would not implode on the titanic, 151 bar is not enough to crush it and in fact it would resist compession better than being overfilled on the surface. A steel cylinder would buckle but a ally would implode eventually. TThink on that when you decide which is safer.
   

The cylinder would take on water if you opened the valve and yes gravity decreases as you get nearer the core for the reason stated.  

 

[Paul Thomas]

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Quote[/b] (Jason Drake @ Mar. 24 2003,18:47)]I once read that some people used to believe that at a certain depth the sea's density would be thick enough to stop objects sinking through them.

<font color='#000080'>This doesn't happen because water is an incompressible liquid so its density does not change with pressure. (Hence one added atmosphere per 10 metres of depth, due to the weight of the column of water above the immersed object).

On the other hand the atmosphere is a mixture of gasses, which of course are compressible. The deeper you "fall" into the atmosphere the denser the air becomes (because of the variable weight of the column of air above, compressing it). This is an exponential function, as opposed to the linear function seen in liquids.

In consequence the earth's atmosphere does not have a distinct surface, it just continues to get thinner and thinner the higher you go, in an exponential manner (and it gets colder).

15,000 feet 0.70 bar
30,000 feet 0.30 bar
40,000 feet 0.18 bar
50,000 feet 0.11 bar

 

[JohnR]

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Just picked up on this thread and thought about it for awhile.

Quote[/b] ]Eh? Gravity DECREASES as you near the center of the Earth - there's less mass below you pulling you down and more mass above you pulling you up

Not sure about this as gravity directional and is a function of mass.  The centre of the earth is believed to be much more dense than the outer layers -this is why the tectonic plates "float" on the surface.  As you get closer to the core the mass is relatively little changed 'cos all the heavy stuff is in the middle, but the distance has decreased.  ie you are closer to an object with approximately the same mass.  Therefore gravitaional force will be increased.  

Once you reach the exact centre the mass/gravitational force in every direction is equal resulting in an equlibrium effect (nett force = zero).

'Course this could be a load of bollox.

Cheers,  John

 

[Finless]

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I have been trying to follow and understand the points and comments made with varying degrees of failure.

Just to be on the safe side, this means I will not be able to dive the Titanic on twin 10s + a 3 ltrs pony? Right?

Bear in mind I could get the local dive shop to pump the cylinders to 240 bar in each?

It is an awesome thought that assuming a 25 ltr per min breathing rate whilst diving on the Titanic (might be a little stressed to be at that depth with twin 10s) the cylinders would empty within 30 seconds.

Naturally I am ignoring all other factors BUT if you could breath at that depth .. wow.