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Old 01-12-2018, 11:46 AM   #1
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Default Hydrodynamics question (Hydroelectric power)

Water behind a dam flows out the bottom under pressure and powers a turbine generator to produce electricity. This can be used to create heat. Water then flows to the ocean eventually.

So, the water at high altitude has stored potential energy. Some of which is extracted as electricity. Eventually the water reached sea level and has zero potential energy.

Now, compare to water flowing without the restriction of the damn and generator. It too eventually reaches sea level and has zero potential energy. Where did the original energy go? Does water heat up as it flows to the ocean? Does the generator cool the water?
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Old 01-12-2018, 12:29 PM   #2
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The energy dissipates as it levels out on it's decent. All our city water comes from reservoirs upstate, it flows down to us under it's own pressure (I may be over simplifying it) and comes out our faucets.
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Old 01-12-2018, 12:29 PM   #3
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Kinetic energy. If you didn't have the dam then the water would be flowing a lot faster.
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Old 01-12-2018, 12:42 PM   #4
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The potential energy of water at elevation is what moves the water down to sea level along the entire course of the river. It does not dissipate as heat, but rather is the force that continues to drive the flow.
Some of energy of moving water also moves sand and rocks, carves curves in rivers along the way.
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Old 01-12-2018, 12:50 PM   #5
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Energy is dissipated through interactions with the environment ie friction with the ground/stream bed. So, say water that is going down a stream. The water flows and hits a rock, stick, etc that slows it down. It causes erosion to the rock and yes heat is generated through the friction with the environment that heat is minimal. The amount of kinetic energy that a kilogram of water has does not change based on wether it flows down a stream or interacts with a turbine.

The other extreme from the dam is you can imagine a giant slip and slide, the water going down would be traveling much quicker because there is minimal fraction.

So to answer your question, when it got to the end of its run it would dissipate its energy into the body of water it was entering but the energy would not be lost. It would just be so spread out that it would be immeasurable. For example, if you want to call a lake at sea level, zero potential energy. Say the lake is 1 million gallons, and you Rana stream at a million gallons into it. Then you would have potential energy stored in the lake because the lake would be higher than it was before. The same thing happens in the ocean but a stream running into the ocean is such a small change in the potential energy that, like I said, it is immeasurable.

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Old 01-12-2018, 01:08 PM   #6
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Quote:
Originally Posted by Fish Haid View Post
Water behind a dam flows out the bottom under pressure and powers a turbine generator to produce electricity. This can be used to create heat. Water then flows to the ocean eventually.

So, the water at high altitude has stored potential energy. Some of which is extracted as electricity. Eventually the water reached sea level and has zero potential energy.

Now, compare to water flowing without the restriction of the damn and generator. It too eventually reaches sea level and has zero potential energy. Where did the original energy go? Does water heat up as it flows to the ocean? Does the generator cool the water?
Hydro electric dams use penstock and head pressure to capture the energy from falling water. Penstock has less friction than a natural stream bed. The energy that would be used to move the water thru a natural stream bed is captured by the turbine.



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Old 01-12-2018, 01:35 PM   #7
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Quote:
Originally Posted by Fish Haid View Post
Water behind a dam flows out the bottom under pressure and powers a turbine generator to produce electricity. This can be used to create heat. Water then flows to the ocean eventually.

So, the water at high altitude has stored potential energy. Some of which is extracted as electricity. Eventually the water reached sea level and has zero potential energy.

Now, compare to water flowing without the restriction of the damn and generator. It too eventually reaches sea level and has zero potential energy. Where did the original energy go? Does water heat up as it flows to the ocean? Does the generator cool the water?
the kinetic energy in converted into heat.

Think about how It takes a flowing creek longer to freeze than a still pond.
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Old 01-12-2018, 02:14 PM   #8
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ehhhhh I'm not right into that one. I scuba dive and with that I ice dive as well. It is nothing to see flowing water in the winter time being well below 32° F. If your theory was correct then I would say the water would remain warmer than 32° and hence why it is not frozen.

For a water molecule to freeze there needs to be a stabilization of motion and that allows two molecules to bond together. Create motion and the bonding process is greatly hampered.

Heat and temperature are not the same thing.
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Old 01-12-2018, 02:21 PM   #9
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the kinetic energy in converted into heat.

Think about how It takes a flowing creek longer to freeze than a still pond.
that's not how it works..... that's not how any of this works
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Old 01-12-2018, 02:23 PM   #10
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that's not how it works..... that's not how any of this works
How does it work?
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Old 01-12-2018, 02:24 PM   #11
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Did anyone pay attention during physics classes?
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Old 01-12-2018, 02:38 PM   #12
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Did anyone pay attention during physics classes?
So what is your explanation?
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Old 01-12-2018, 03:05 PM   #13
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How does it work?
Garett already explained it to you

Quote:
For a water molecule to freeze there needs to be a stabilization of motion and that allows two molecules to bond together. Create motion and the bonding process is greatly hampered.
Solid materials have to form some kind of structure. The turbulence of flowing water makes a crystalline lattice structure nearly impossible to obtain. On the flip side of this, and this is a fun little party trick... A bottle of water that's been sitting in your car all night when the low is in the 20s won't necessarily be frozen. Give it a quick shake and it will freeze up almost instantaneously because it had a bubble to grab onto and begin the crystalline structure.


Last edited by Kenny Powers; 01-12-2018 at 03:12 PM.
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Old 01-12-2018, 03:29 PM   #14
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Garett already explained it to you



Solid materials have to form some kind of structure. The turbulence of flowing water makes a crystalline lattice structure nearly impossible to obtain. On the flip side of this, and this is a fun little party trick... A bottle of water that's been sitting in your car all night when the low is in the 20s won't necessarily be frozen. Give it a quick shake and it will freeze up almost instantaneously because it had a bubble to grab onto and begin the crystalline structure.

https://www.youtube.com/watch?v=ThKMcQf94VM
Heat is energy.

It takes energy to create motion. The same kinetic energy that creates the motion that keeps the water turns into thermal energy because of friction in the water and has to be transferred as heat before the water will freeze.
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Old 01-12-2018, 03:33 PM   #15
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So what is your explanation?
Some of the potential energy in the water is converted to kinetic energy by the turbine which is mechanically connected to the generator which produces electricity. The inefficiency of the process produces some heat as waste. The way the electricity is used determines into exactly what kind of energy the electricity is converted. It could be used to pump water upward which would be mostly back to kinetic or used to power strip heaters which would be almost entirely converted to heat. But at no point in time during this process is all of the potential energy ever extracted from the water.
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Old 01-12-2018, 03:38 PM   #16
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http://galileo.phys.virginia.edu/classes/152.mf1i.spring02/Joule.htm
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Old 01-12-2018, 03:54 PM   #17
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Some of the potential energy in the water is converted to kinetic energy by the turbine which is mechanically connected to the generator which produces electricity. The inefficiency of the process produces some heat as waste. The way the electricity is used determines into exactly what kind of energy the electricity is converted. It could be used to pump water upward which would be mostly back to kinetic or used to power strip heaters which would be almost entirely converted to heat. But at no point in time during this process is all of the potential energy ever extracted from the water.
The water had potential energy when it was held behind the dam.

When the gates opened and let the water start moving the potential energy was converted into kinetic energy.

The turbine Took some of the kinetic energy from the moving water and turned it into mechanical energy that turned a generator.


The water Downstream of the dam is still has some energy and is moving through the riverbed.

There is friction between the moving water and the riverbed and some of the kinetic energy is being transformed into heat.
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Old 01-12-2018, 04:02 PM   #18
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Quote:
Originally Posted by Wood boat builder View Post
The water had potential energy when it was held behind the dam.

When the gates opened and let the water start moving the potential energy was converted into kinetic energy.

The turbine Took some of the kinetic energy from the moving water and turned it into mechanical energy that turned a generator.


The water Downstream of the dam is still has some energy and is moving through the riverbed.

There is friction between the moving water and the riverbed and some of the kinetic energy is being transformed into heat.
What part of what I said are you disagreeing with?
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Old 01-12-2018, 04:36 PM   #19
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H=v^2/2g
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Old 01-12-2018, 07:34 PM   #20
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Fwiw-
Torquing up bolts w/2-1/2" drive 9-1/2" AF socket-Water wheel(turbine) Niagara Moses power dam.
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