Naked Science Forum
Non Life Sciences => Technology => Topic started by: FULKRAM on 30/06/2011 14:38:28
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Ok, this has been hanging around in my head for a few days.
If you put a cone with a hole at the top into water but not standing on the bottom, with the top of the cone just above the top of the water. Then cap the bottom of the cone and then pump out the water. When you remove the cap, water would rush up the cone trying to equalise water level between outside the cone and inside the cone.
However, as the water is entering from the bottom end of the cone, as it rises the speed it would rise at would increase due to the decreasing area available. The result would be a water spout from the top end.
Ok, so as a large scale version. Build a massive cone somewhere where the water is very deep in the oceans, pump out the water. Put a disk at the bottom slightly above the pumped out water level. Open the water gates and let in the water at the bottom. as the water rises it pushes the disk up the cone and excelerating in speed. By the time the disk reaches the top of the cone the speed would be enough to launch an object very high in the atmosphere. Such as a space ship, which then might further use rockets to achieve orbit.
So please shoot this one down in flames. I'm no engineer and don't quite have the grasp of how the water would react.
What do you think?
P.S. could use wave/wind power to pump out the water prior to launch.
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You would use more energy to pump out the water than you can ever expect to get back.
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Need to think about that one, here's a bit of a clue. If it was a pipe of constant diameter rather than a cone as you suggest, when the water got to the top of the pipe it have no kinetic energy at all. I think it would rise to the level of the ocean surface and stop when it got there.
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You would have to do some tests, but I don't think the cone would give you the acceleration that you wish for.
Your water pressure would be greatest at 10km depth, and then would decrease as one moves towards the surface.
If you had a set of pipes of different diameters. 6", 1', 2', 3', etc. I would anticipate the water to rise in the pipes at nearly the same rate near the bottom of each pipe. The biggest problem is cumulative friction which your cone would eliminate. But, other than friction, as your cone decreases in diameter, it would become similar to the speed water would enter near the opening of the next smaller size of pipe.
Another problem with ocean water, in particular, is the temperature and salinity gradients. The water temperature at the bottom of the ocean is near the maximum density, and the salinity is higher too, so the densest, heaviest water is near the bottom. And, thus with your pipe/cone, you would be displacing light water with heavy water from the bottom, and would get even less filling velocity, although perhaps this would be somewhat insignificant.
Anyway, you would likely quickly reach a maximum velocity, after which you would begin to loose velocity as the pressure gradient decreases.
This isn't to say you couldn't use water pressure to perform work. For example, you might put a balloon filled with air 10km deep. That could deliver a constant air pressure of about 15,000 psi for a very large volume of air. You could make quite an air cannon with that.
Hmmm, thinking about this a bit more.
The question is whether the two cones at different levels have fundamentally the same pressures, or different pressures near the water level in the cone.
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I think you could eliminate the lower flooded section of the cone, and thus the two are the same, but perhaps that isn't the proper way to consider the problem.
Nonetheless, as Geezer pointed out, the maximum velocity would be far below the surface of the ocean.
The other issue you would run into is air friction which would likely limit you to around Mach 5 or so near the surface, and cause significant slowing of your vehicle, but you would need to achieve Mach 10 to Mach 15 at higher altitudes. This would mean that you would need an additional boost to achieve orbit, but it might reduce the amount of fuel burned. I think this is one of the main limitations of using something like a mag-lift on earth, whereas the atmospheric resistance becomes insignificant on the moon, at least up until much higher velocities.
The most common liquid rocket fuel used is Hydrogen+Oxygen which can be generated with renewable energy. Other fuels are likely synthesized with lots of electricity too.
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Thank you for your replies. I had not considered the salinity of deep water and it's subsequent density.
I dont mind being shot down in flames.
I suppose my question is about how to use constant natural mass to create enough energy to launch from our dear planet to atleast escape velocity. Fluids I know so little about. water as pure, oil? I assumed that Sea water had the same salinity at all depths. that is a failing on my behalf.
I was more worried about the dynmic of the water as it rises through the cone. If it were a purified water system, we would also have drag on the uplift of water to the top. hence losing energy.
So, In my humble ability. I accept. this posit is dead.
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Should I learn a bit of fluid dynamics?
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Yes, this can be a most enjoyable study. May I suggest the Royal College of Boozers, where you can study single fluids (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.freesmileys.org%2Fsmileys%2Fsmiley-eatdrink005.gif&hash=8623effd8f7905b21b2e58c5bcc10958) (http://www.freesmileys.org/smileys.php) or you can shtudy mutiplllle flooooidsh ***HIC*** (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.freesmileys.org%2Fsmileys%2Fsmiley-eatdrink048.gif&hash=1a29116b950efd292558fd33415610ec) (http://www.freesmileys.org/smileys.php)
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I might recommend the University of Getting Sloshed, previously the Polytechnic of Being P*****d and earlier still known as the The College of Binge Drinking
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I might recommend the University of Getting Sloshed
That's the one in Holland my daughter went to for six months. They run a pretty good course in Applied Marijuana.
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Here's a preliminary test you can do. Fill a tub with water. Get an adequately sized funnel with a good smooth rim. Get a slick flat object such as a sheet of processed lumber, that will cover the rim. Put the sheet onto the rim, turn it over, quickly immerse. Yank the sheet sideways, quickly opening the mouth. See what happens. (Note: the system will tend to be buoyant and difficult to handle, which might require some additional structure.)
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One other thought: The Bournelli principle applies: You are funneling a fluid at a certain pressure and velocity into a restriction, often called a nozzle. That results in a drop of pressure below its static value, and increase of velocity.
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One other idea.
I had thought of the funnel as having a fixed depth, in which case the pressures on both sides of the funnel should generally equalize, although perhaps not as much as I had thought since it is a dynamic system, rather than static.
However, what would happen if you designed the funnel to be very heavy, and then would drop it, say from a depth of 5km to 10km deep. You would likely hit a terminal velocity (or a velocity where the funnel would tend to exclude water, rather than capture it) very quickly, but perhaps you could increase the rate the water entered the device.
Personally I would think of something more like an enormous cannon for the first stage of the rocket.
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Another option: Place the projectile in the small end of the funnel, and seal the end . Then immerse the funnel wide-end down until the small end just reaches the surface of the ocean. The funnel, while descending, will first exclude the entry of water by reason of the air pressure inside, which is contained by the closed small end, but as the funnel descends, the pressure will rise, compressing the air. When th funnel reaches its lowest depth, the wide end will be partly filled with water, overlaid with compressed air. The pressure of the air will be essentially that of the water at the surface inside the funnel. Then, pop the seal off, and the compressed air will immediately apply the full pressure to the projectile, shooting it out. The advantage of this system is that it does not depend on moving water to do much; full pressure is immediately available in the air. Whether this would reach orbit, however, is another question.
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archimedis principal maybe