Let's say I have a container and it has an opening. I drop it into the

[D9 XTC]

Let's say I have a container and it has an opening. I drop it into the ocean and let it sink to the bottom of the deepest part about 36k feet down. Now it's at the bottom and full of water and I seal it then I bring it back to the surface. If I open it will it decompress pretty violently since the pressure at the bottom of the ocean is 8 tons psi and at sea level it's 14.7 lbs psi?

Sorry if this is obvious...

 

[Mapes]

The container will be pressurized to some extent when you bring it to the surface, assuming no leaks. But the container will deform in response to this pressure, so the pressure inside will no longer be as high. The geometry and material of the container will determine the extent of this equalization. Also, the water will have compressed much less than an equal amount of gas. For both of these reasons, there's no guarantee that decompression (upon opening the container) will be "violent." Does this make sense?

 

[sophiecentaur]

The violence of the explosion will depend upon the amount of strain energy that is involved. The stored energy will be proportional to the product of the pressure change and the volume change. If the container just contains water then the amount of expansion will be fairly small so the energy involved will not be a lot. If you use a gas, the energy stored would be much much more - that could cause a nasty accident if the container fails.

When they pressure test diving cylinders, they fill them with water and measure how much they expand under the test pressure. If the cylinder does, actually, rupture, there is not much harm done. If they did the test with compressed air, there would be mand MJ of stored energy and it could take out the workshop!

 

[D9 XTC]

Very interesting and thanks for the answers guys. My goal is to see if a violent jet of water can be shot out of a container just by using hydrostatic pressure.

So going off from your input tell me how this scenario would go.

Let's say we have a large non deformable container in the shape of a cylinder. One side has a door that can be opened and closed to the ocean. The cylinder is divided in half internally by a movable wall (basically like a cylinder head). On the side of the divided cylinder that has no door a highly pressurized gas is pumped in so now the cylindar head travels closest to the side that the door is at. Phew...

Okay, so we drop it into the ocean to 36k feet. The hydrostatic pressure should compress the already highly compressed gas even further. Depending on how big the surface area is of the movable wall the amount of hydrostactic pressure pushing on it could be huge.

So we seal it up and bring it back to sea level and open a special alternate door built into the door that narrows the flow of water to make a jet.

Would this be a nasty jet of water then if the gas pressure is huge on the other side of the moveable wall and is pushing the water out?

 

[sophiecentaur]

Yes, of course you would get a squirt of water at very high pressure - there would be a lot of stored energy in the compressed gas.
I have a feeling that you may be thinking you would get all this energy for free. In fact you wouldn't because more work would be put into raising the compressed container up than any energy you may have been able to store up whilst lowering it. The upthrust / buoyancy would be less on the way up than on the way down.

Your scenario of an incompressible container is not real, either. The material would compress somewhat. Nothing - including all liquids and solids - has an infinite modulus. It would be much greater than the gas it contains, though.

I didn't quite get the point of pre-compressing the gas first?

 

[pallidin]

Of course, if the pre-compression is equal to the compression potential of being 36 thousand feet underwater, there would be no additional compression.

 

[Mapes]

My goal is to see if a violent jet of water can be shot out of a container just by using hydrostatic pressure.

You might be interested in http://en.wikipedia.org/wiki/Water_jet_cutter" (no ocean required!).