h a l f b a k e r yBaker Street Irregulars
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Water wheels can only produce power equal to the weight of the water pressing against the wheel. I'm sure someone can say that better than I just did.
So, instead of mounting "buckets" on a wheel, mount the buckets on a very long, looped chain. Half of the loop runs through a duct - say down
the side of a mountain in a creek-bed. Now, instead of just a few buckets of water pushing a wheel, you have hundreds of buckets pulling your chain (cable - whatever) so you now have thousands of pounds of pressure.
If the logistics/friction of a long bucket-equipped chain is overly daunting, one could use something like an Archimedean screw inside the duct.
Bottom line, get more water in on the action.
[link]
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This won't work. The power of the water wheel is limited by the energy in the system, which depends on speed of the water entering the system, the height of the fall, and the mass of water. Putting more buckets in the system doesn't increase the power output, any more than adding more wheels to your car would make it go faster. Modern water-powered generators use a propellor or turbine; friction is your enemy. |
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A water wheel can take kinetic energy out of the water, like one that dips into a river, or it can take potential energy out of the water, like the type mounted under a waterfall. The second type could get more force if more buckets are moving vertical. The first type isn't any good to begin with. That's why they invented turbins. The Archimedean screw gets closer to a turbin but it also transfers a lot of enrgy into rotational energy because the water column starts spinning in the screw. |
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kropotkin: So you're telling me there's no difference between standing at the top of a large building holding a rope with one water-filled bucket and holding a rope with one hundred water-filled buckets? You either sorely misunderstood my bad description or you sorely misunderstand potential energy. |
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kbecker: energy would be lost if the screw wasn't inside a duct or a tube. Since it is inside a tube, the water can't escape and must continue down through the tube where the water's weight continues to press against the screw. As opposed to a water column driving a high-speed turbine, a water column with a screw inside produces lower speed but higher torque. |
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What you're trying to do (in your idea) is keep the water for as long as possible, using up as much potential energy as possible. What [kropotkin] is saying is that the more buckets you have, the more the wheel weighs and the more energy us lose keeping the system going. |
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To use your analogy "there's no difference between standing at the top of a large building holding a rope with one water-filled bucket and holding a rope with one hundred water-filled buckets?" the answer is no (though I doubt you've ever seen a water wheel with only one bucket).
Assume there are two pools on the roof and we want to use the water from each to power water wheels - one your way and one the traditional way. Your way might empty your pool faster, but won't get any more energy out of the system than the other way. |
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I got the impression that the idea was you have multiple buckets in a stream of water, equivalent to putting multiple turbines in a stream, so that each drop of water comes into contact with multiple buckets; cljudge seemed to be suggesting that the more buckets/turbines you have the more power you'll get out. |
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This is clearly false because once the water has pushed against one bucket or turbine it loses a proportion of its energy and that energy can't then be applied to the rest of the buckets/turbines. If I'm wrong, please say. |
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The longer you hold the water, the larger the height difference between the input and output. Larger height differences give more energy. Unfortunately the further down the river you go with your chain or screw idea, the more energy you will lose to friction. |
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Waterwheels do well, because they concentrate a large height difference into a small space -- they are typically built at either natural or man-made waterfalls, and get a couple of metres of height change for a very short horizontal travel. Extend this travel further down the river and you will lose the efficiency of waterwheel in an effort to capture more energy. |
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If the river is sloping enough to make more use of its slope beyond a whaterwheel, then it would always be possible to artificially flatten the slope of the river beyond it and build another waterwheel downstream. |
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Where a chain might be useful is a long vertical drop (Niagra Falls anyone?) where a wheel would be impractical. |
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kropotkin: As long as water can still move downward because of gravity, then the water still contains potential energy. In my original, badly worded rambling, I did mention that this contraption should be placed "down the side of a mountain." What I should have stated more clearly is that a vertical displacement is necessary. Your argument about water losing its power after it has "pushed against one bucket or turbine" leads me to believe that you are picturing a horizontal tube. Make the tube vertical and you should agree that every gallon of water within the tube - whether it is near the entrance or about to exit - applies eight pounds of force against the screw. |
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[cljudge] your sense of the physics
is off. The 8 lbs of pressure (pints
a pound the world around) is there
in every gallon of water but you
also need to know the vertical
distance it is traveling, the looses
to friction on that path and the
speed at the exit. the Height or
head I think they call it is the total
potential energy. You can't extract
all of it because the water has to
keep moving to get out of the way
of the wheel, chain, turbine or
whatever. So it matters not how
long you touch the water (in fact
you'd rather touch it for less time
but slow the water more in the
process to get the most energy
extraction. As long as the device
does not have spillage and all
devices allow the water to exit at
the same speed then the only
differences would be friction
between the water and the device
and friction within the device. And
Chains would have more than
wheels. And Archimedes screws
would have the most of all I
suspect. |
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Yes it could work but it would not
offer any special advantages and
would have some significant
troubles. |
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kbecker, Pelton wheels are effective kinetic water wheels. |
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kropotkin, are we not talking about potential energy rather than kinetic? |
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cljudge, I gave you a + because you idea is sound even though few folks appear to understand this. |
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The amount of energy extracted from the falling water is a function of the weight of water and the vertical distance it travels while in the machine. So your chain idea is sound because you are increasing the vertical distance. |
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I agree an alternative would be to build a really big diameter wheel. |
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As to those who do not like the chain idea can you tell me why chain bucket pumps are so effective and apparently efficient at lifting water so why would the same principle not work in reverse? |
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