9 ms·

the pressure will be distributed across the diameter of the cylinder Okay, I was skeptical about this thread when I first saw it, but now I see the awesome pot

the pressure will be distributed across the diameter of the cylinder Okay, I was skeptical about this thread when I first saw it, but now I see the awesome potential for teaching physics here. You can't "diffuse the pressure". At every point along the wall of a sealed vessel, the pressure is constant. So if, e.g., the pressure of the hole when sealed would be 100 PSI, then to stop it every square inch of the seal needs to withstand that 100 PSI. If the top of your concrete cylinder has, say, 100 times the area of the hole, then the flow of oil may end up evenly distributed over that area. But if you then try to seal the top you must now provide the same strength of seal -- it must withstand the same pressure -- over a much larger area, which is probably harder to accomplish. This seems counterintuitive, just as the lever is counterintuitive. But we use this principle all the time to lift things like elevators and cars. You push on a tiny-diameter cylinder with your arms (or with a little electric motor), and it pumps fluid into a much larger-diameter cylinder under the car, and the car rises. Of course, you have to pump up and down dozens or hundreds of times to lift the car one inch.

ImFatYoureFat 16y ago
up voted you because the opportunity to learn more about this situation was one of the main reasons I asked this question
deleted 16y ago
[deleted]
mechanical_fish 16y ago
I should also note that the idea of blocking the hole with gravel isn't exactly a bad one. You're right to point out that if you use big pebbles for your gravel the oil will just squeeze through the abundant empty spaces. So... use finer gravel! The pressure will try to push the gravel out. So maybe make it really sticky gravel, so that it glues itself together. Now there are three things to say about this plan: (a) we call this sticky, very fine gravel concrete and we use it all the time; (b) a fun educational point: Even with really fine gravel, oil can still diffuse through it. Oil diffuses through "solid" rock all the time. The oil underground is actually trapped inside rock. The rock that holds the oil is relatively porous; the oil is kept underground because above that rock is a layer of denser rock that oil can't diffuse through very well. (c) In case it isn't obvious yet: The reason your idea still doesn't work very well is that the first cupful of wet concrete you pour onto the hole will promptly get flushed away by the pressure of the leaking oil. ;) As will every successive cupful of wet concrete. Unfortunately, a giant slab of solid concrete must necessarily start out life as a thin layer of wet concrete, so the only way to put a concrete seal over a hole that is actively leaking is to cast it someplace else and then drop it on the hole.
- anigbrowl 16y ago
  Well this was why I didn't suggest pouring concrete into it...I was assuming that the cap would be cast at the same time as the cylinder :) The only point of the gravel (rather than sand) is to disperse the flow sufficiently that maneuvering is easier - same way you could wade across a stream but would be knocked over by the same volume of water aimed at your from a firehouse.
- superk 16y ago
  Actually an interesting point. What would happen if they cast a stadium sized block of concrete and dropped it on the hole.
  - stcredzero 16y ago
    It would go around.
- Tichy 16y ago
  "we call this sticky, very fine gravel concrete and we use it all the time;" I wonder if Nanotech could come up with some kind of super concrete. Ie particles that stick together extremely well?
anigbrowl 16y ago
I understand that, and apologize for my loose terminology. There are two reasons I suggest employing a larger size. The first is to do with flow, as you mention. While all of a large cap needs to be able to withstand high pressure, that is not in itself an especially tricky engineer problem. But size doesn't hurt; in my experience it's rather easier to stop up a large pipe than a small one with the same pressure, simply because it's a less delicate maneuver. In the case of a domestic plumbing crisis, it's nice to be able to exert your arm rather than just your fingers. The other reason is simply to do with bulk. The larger the cylinder, the greater it weight when finally sealed, the more room you have to anchor it, and the farther from the (presumably fragile) ground in the immediate vicinity of the gusher the circumference will be, if one is trying to bore into the ground with restraining pegs. The surgical approach has not been very successful so far. Given the urgent nature of the problem, I feel it's worth trying the crude but frequently effective approach of large mass + gravity.
pbhjpbhj 16y ago
>You can't "diffuse the pressure". I must be missing something, the parent is talking about wrapping the 21" (inch) diameter pipe in a 25' (foot) outer pipe, this is effectively 200 times the area. The force applied currently by the oil coming up is going to provide 1/200th of the pressure when applied over the end of the pipe. It's like blowing out through a straw - you can feel the pressure easily. Versus blowing out through a dustbin with a hole in the bottom. Mind you it's 4:30am ... perhaps I should go to bed and think about this another time.
- stcredzero 16y ago
  You can't diffuse static pressure, but when you deal with fluid flowing through pipes, you need to take the Bernoulli effect into account. Narrowing a pipe with a fast flow can sometimes decrease side pressure.

ImFatYoureFat 16y ago

up voted you because the opportunity to learn more about this situation was one of the main reasons I asked this question

deleted 16y ago

[deleted]

mechanical_fish 16y ago

I should also note that the idea of blocking the hole with gravel isn't exactly a bad one. You're right to point out that if you use big pebbles for your gravel the oil will just squeeze through the abundant empty spaces. So... use finer gravel! The pressure will try to push the gravel out. So maybe make it really sticky gravel, so that it glues itself together. Now there are three things to say about this plan: (a) we call this sticky, very fine gravel concrete and we use it all the time; (b) a fun educational point: Even with really fine gravel, oil can still diffuse through it. Oil diffuses through "solid" rock all the time. The oil underground is actually trapped inside rock. The rock that holds the oil is relatively porous; the oil is kept underground because above that rock is a layer of denser rock that oil can't diffuse through very well. (c) In case it isn't obvious yet: The reason your idea still doesn't work very well is that the first cupful of wet concrete you pour onto the hole will promptly get flushed away by the pressure of the leaking oil. ;) As will every successive cupful of wet concrete. Unfortunately, a giant slab of solid concrete must necessarily start out life as a thin layer of wet concrete, so the only way to put a concrete seal over a hole that is actively leaking is to cast it someplace else and then drop it on the hole.

anigbrowl 16y ago
Well this was why I didn't suggest pouring concrete into it...I was assuming that the cap would be cast at the same time as the cylinder :) The only point of the gravel (rather than sand) is to disperse the flow sufficiently that maneuvering is easier - same way you could wade across a stream but would be knocked over by the same volume of water aimed at your from a firehouse.
superk 16y ago
Actually an interesting point. What would happen if they cast a stadium sized block of concrete and dropped it on the hole.
- stcredzero 16y ago
  It would go around.
Tichy 16y ago
"we call this sticky, very fine gravel concrete and we use it all the time;" I wonder if Nanotech could come up with some kind of super concrete. Ie particles that stick together extremely well?

anigbrowl 16y ago

I understand that, and apologize for my loose terminology. There are two reasons I suggest employing a larger size. The first is to do with flow, as you mention. While all of a large cap needs to be able to withstand high pressure, that is not in itself an especially tricky engineer problem. But size doesn't hurt; in my experience it's rather easier to stop up a large pipe than a small one with the same pressure, simply because it's a less delicate maneuver. In the case of a domestic plumbing crisis, it's nice to be able to exert your arm rather than just your fingers. The other reason is simply to do with bulk. The larger the cylinder, the greater it weight when finally sealed, the more room you have to anchor it, and the farther from the (presumably fragile) ground in the immediate vicinity of the gusher the circumference will be, if one is trying to bore into the ground with restraining pegs. The surgical approach has not been very successful so far. Given the urgent nature of the problem, I feel it's worth trying the crude but frequently effective approach of large mass + gravity.

pbhjpbhj 16y ago

>You can't "diffuse the pressure". I must be missing something, the parent is talking about wrapping the 21" (inch) diameter pipe in a 25' (foot) outer pipe, this is effectively 200 times the area. The force applied currently by the oil coming up is going to provide 1/200th of the pressure when applied over the end of the pipe. It's like blowing out through a straw - you can feel the pressure easily. Versus blowing out through a dustbin with a hole in the bottom. Mind you it's 4:30am ... perhaps I should go to bed and think about this another time.

stcredzero 16y ago
You can't diffuse static pressure, but when you deal with fluid flowing through pipes, you need to take the Bernoulli effect into account. Narrowing a pipe with a fast flow can sometimes decrease side pressure.