Creating free energy by harnessing the tides.

[mark69sheer]

Just thought I would sidetrack this discussion away from the other thread...

as you were,
Methodology of creating energy using generators driven by objects using compressed air created by tidal reservoirs...

cont...

[s2art]

There more efficient ways of harnessing tidal energy.

[mark69sheer]

everyone has focussed on creating energy from waves rather than the tide itself.

[hairykrishna]

Thanks for the new thread, probably a good idea.

s2art said:

Forget the objects temperature, its a red herring. See answer above, the water cools in doing work on the object as it rises.

Ok thermal equilibrium then. Why is heat transferred from the water to the object?

[hairykrishna]

mark69sheer said:

everyone has focussed on creating energy from waves rather than the tide itself.

Not true. There's all kinds of systems using the tide. See http://en.wikipedia.org/wiki/Tidal_power

[s2art]

hairykrishna said:

Thanks for the new thread, probably a good idea.

s2art said:

Forget the objects temperature, its a red herring. See answer above, the water cools in doing work on the object as it rises.

Ok thermal equilibrium then. Why is heat transferred from the water to the object?

As described earlier, molecules of water bounce of the underside of the object. If the object rises as a consequence (buoyancy) then work is being done on the object. That energy is provided by the water molecules moving more slowly after the collision with the object. I am struggling to make this any simpler.
Just in case, note that an unmoving object (say, floating on the surface) does not extract energy.

[normalbloke]

I can see the headlines now, "Global Calming", the new doom of the world, and we'll probably have to pay tax on it somehow...

[mark69sheer]

Ah they use the tidal flow.
I am thinking of using the actual tidal rise.

ie if it will lift a ship 12ft in the air then couldn't a generator be so highly geared that a movement of 12 ft over a period of time will create energy?

[mybrainhurts]

I never doubted King Canute...

[s2art]

mark69sheer said:

Ah they use the tidal flow.
I am thinking of using the actual tidal rise.

ie if it will lift a ship 12ft in the air then couldn't a generator be so highly geared that a movement of 12 ft over a period of time will create energy?

Yes, and that is already an established technique for extracting tidal energy. Much more efficient than your proposed method.

[hairykrishna]

s2art said:

As described earlier, molecules of water bounce of the underside of the object. If the object rises as a consequence (buoyancy) then work is being done on the object. That energy is provided by the water molecules moving more slowly after the collision with the object. I am struggling to make this any simpler.
Just in case, note that an unmoving object (say, floating on the surface) does not extract energy.

The work done is by gravity. It's two masses exhanging places in a fluid (mass of displaced water, mass of object).

[s2art]

hairykrishna said:

s2art said:

As described earlier, molecules of water bounce of the underside of the object. If the object rises as a consequence (buoyancy) then work is being done on the object. That energy is provided by the water molecules moving more slowly after the collision with the object. I am struggling to make this any simpler.
Just in case, note that an unmoving object (say, floating on the surface) does not extract energy.

The work done is by gravity. It's two masses exhanging places in a fluid (mass of displaced water, mass of object).

Yes gravity is involved. The object is gaining gravitational P.E. (and some K.E.) in exchange for the loss of heat energy from the water.
Think of it as like a piston in an engine.

[hairykrishna]

s2art said:

Yes gravity is involved. The object is gaining gravitational P.E. (and some K.E.) in exchange for the loss of heat energy from the water.
Think of it as like a piston in an engine.

You're almost there. The object is gaining gravitational P.E. but the system is losing gravitational P.E. - giving it up for K.E.

Think about it, as the light object moves up it displaces it's volume of water (a heavier object) into the lower position it just vacated. The net result is a decrease in total gravitational P.E.

[Bushmaster]

There is a problems with Tidal Energy:

Wiki said:

Tidal movement causes a continual loss of mechanical energy in the Earth–Moon system due to pumping of water through the natural restrictions around coastlines, and due to viscous dissipation at the seabed and in turbulence. This loss of energy has caused the rotation of the Earth to slow in the 4.5 billion years since formation. The period of rotation has increased from 21.9 hours to the 24 hours we see now; in this period the Earth has lost 17% of its rotational energy.

GLOBAL SLOWING!

I can see the headlines now.

[s2art]

hairykrishna said:

s2art said:

Yes gravity is involved. The object is gaining gravitational P.E. (and some K.E.) in exchange for the loss of heat energy from the water.
Think of it as like a piston in an engine.

You're almost there. The object is gaining gravitational P.E. but the system is losing gravitational P.E. - giving it up for K.E.

Think about it, as the light object moves up it displaces it's volume of water (a heavier object) into the lower position it just vacated. The net result is a decrease in total gravitational P.E.

Nope. Think about what actually propels the object upwards. Its true that the overall P.E. is decreased, but that isnt the mechanism providing the lift.
Actually the overall P.E. will cancel out.

Edited by s2art on Wednesday 28th January 18:34

[hairykrishna]

s2art said:

Nope. Think about what actually propels the object upwards. Its true that the overall P.E. is decreased, but that isnt the mechanism providing the lift.
Actually the overall P.E. will cancel out.

How will the PE cancel out? It'd only cancel if the mass of the object=the mass of water it displaced i.e. it was neutrally buoyant.

If it's a heat energy transfer mechanism that provides buoyancy why does density of the object matter?

[s2art]

hairykrishna said:

s2art said:

Nope. Think about what actually propels the object upwards. Its true that the overall P.E. is decreased, but that isnt the mechanism providing the lift.
Actually the overall P.E. will cancel out.

How will the PE cancel out? It'd only cancel if the mass of the object=the mass of water it displaced i.e. it was neutrally buoyant.

If it's a heat energy transfer mechanism that provides buoyancy why does density of the object matter?

P.E. cancels out because the water was displaced in the first place by the object, which is then restored when the object is removed from the water. There is a small increase in P.E. of the object due to its increased mass (pumping in the air) and there is a temporary increase in the thermal energy of the object (due to said pumping) which will be extracted when it is deflated at the top (with normal losses).
The buoyancy is a function of its density. The movement upwards is the cause of heat energy transfer.

[mark69sheer]

Bushmaster said:

There is a problems with Tidal Energy:

Wiki said:

Tidal movement causes a continual loss of mechanical energy in the Earth–Moon system due to pumping of water through the natural restrictions around coastlines, and due to viscous dissipation at the seabed and in turbulence. This loss of energy has caused the rotation of the Earth to slow in the 4.5 billion years since formation. The period of rotation has increased from 21.9 hours to the 24 hours we see now; in this period the Earth has lost 17% of its rotational energy.

GLOBAL SLOWING!

I can see the headlines now.

So harnessing the tides will slow down the earth.

What effect will this have other than longer days?

Will gravity decrease. I guess we are heading for a situation in x billion years where the erath doesn't actually rotate at all.
Bagsy be on the sunny side.

[navier_stokes]

s2art said:

hairykrishna said:

s2art said:

Nope. Think about what actually propels the object upwards. Its true that the overall P.E. is decreased, but that isnt the mechanism providing the lift.
Actually the overall P.E. will cancel out.

How will the PE cancel out? It'd only cancel if the mass of the object=the mass of water it displaced i.e. it was neutrally buoyant.

If it's a heat energy transfer mechanism that provides buoyancy why does density of the object matter?

P.E. cancels out because the water was displaced in the first place by the object, which is then restored when the object is removed from the water. There is a small increase in P.E. of the object due to its increased mass (pumping in the air) and there is a temporary increase in the thermal energy of the object (due to said pumping) which will be extracted when it is deflated at the top (with normal losses).
The buoyancy is a function of its density. The movement upwards is the cause of heat energy transfer.

What device are we talking about here?

[hairykrishna]

navier_stokes said:

What device are we talking about here?

No device as such. A buoyant object at depth floating upwards. S2 says that this extracts heat energy from the ocean. I say that it does no such thing.

Edited by hairykrishna on Wednesday 28th January 18:59