# The Naked Scientists Forum

### Author Topic: Will this buoyancy engine-based generator work?  (Read 75308 times)

#### Geezer

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##### Will this buoyancy engine-based generator work?
« Reply #200 on: 25/11/2011 22:22:56 »
but the gearing ratio is vital in determining the average energy available throughout the year for the Buoyancy Engine.

What do you mean by "average energy"? Do you mean energy in time? If so, you are talking about units of power, not energy.

#### Geezer

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##### Will this buoyancy engine-based generator work?
« Reply #201 on: 26/11/2011 08:47:28 »
Your 1:1 ratio would take 25 tides based on 2m tidal range - this would result in a much cheaper solution but the average energy available throughout the year would be too low to be worthwhile.

No, assuming there is no difference in efficiency, it wouldn't make the slightest difference to the total energy output during the year, or to average power output during the year.

What it would do is reduce mechanical inefficiency in the pulley system at the expense of a much larger turbine and storage vessel. As the storage vessel would have to be as large as the displacement of the pontoon, it would probably cost a bit more than the pontoon, so it would hardly be "a much cheaper solution".

#### Mootle

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##### Will this buoyancy engine-based generator work?
« Reply #202 on: 26/11/2011 11:05:42 »

In terms of thermodynamics, the gearing ratio is irrelevant when discussing the energy density of the 'working fluid' since the working fluid is that which drives the turbine.

In terms of thermodynamics the gear ratio is everything to do with the energy density of the working fluid in the turbine. It's the gear ratio that determines the energy density of the working fluid in the turbine by multiplying the tidal head by the gear ratio to produce the turbine head.

If you are only interested in the relationship between the turbine and the working fluid in the turbine you are confusing fluid dynamics with thermodynamics.

Interesting, then perhaps you would care to provide a reference to support your assertion?

Why don't you simply explain why the gearing ratio and the energy density of the turbine working fluid are irrelevant in terms of thermodynamics? Should we assume that you have invented a system that is is exempt from the laws of thermodynamics? That's what your statement implies.

I didn't think you would be able to provide a reference for your assertion but rather than concede the point you choose to paraphrase? Unless we can agree on the meaning of the thermodynamic terms the discussion will continue to be an argument in semantics i.e., utterly pointless.

#### Mootle

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##### Will this buoyancy engine-based generator work?
« Reply #203 on: 26/11/2011 11:09:25 »
but the gearing ratio is vital in determining the average energy available throughout the year for the Buoyancy Engine.

What do you mean by "average energy"? Do you mean energy in time? If so, you are talking about units of power, not energy.

When ever I use the term 'average energy' you should regard it as defined in all reputable thermodynamic references.

#### Mootle

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##### Will this buoyancy engine-based generator work?
« Reply #204 on: 26/11/2011 11:15:40 »
Your 1:1 ratio would take 25 tides based on 2m tidal range - this would result in a much cheaper solution but the average energy available throughout the year would be too low to be worthwhile.

No, assuming there is no difference in efficiency, it wouldn't make the slightest difference to the total energy output during the year, or to average power output during the year.

What it would do is reduce mechanical inefficiency in the pulley system at the expense of a much larger turbine and storage vessel. As the storage vessel would have to be as large as the displacement of the pontoon, it would probably cost a bit more than the pontoon, so it would hardly be "a much cheaper solution".

Typically, there are (2) tides per day.

The ocean depth is a function of the tidal range.

The gearing ratio has to be matched to achieve the desired depth in one tide if optimum average energy output is to be achieved. Gear it too low and several tides are required before a generation phase can be run, i.e., the machine is under utilised. Gear it too high and the cost of the Pontoon and speed of descent is overrated.

#### Bored chemist

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##### Will this buoyancy engine-based generator work?
« Reply #205 on: 26/11/2011 16:07:40 »
Mootle,
You cannot change the tidal range (for any given location) and so, for any give size of pontoon the energy available per tide is fixed.
The gearing cannot change the energy.
Averaging that energy, for example over the course of the year to allow for neap and spring tides, doesn't change it.
The gearing doesn't enter into it.

#### Geezer

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##### Will this buoyancy engine-based generator work?
« Reply #206 on: 26/11/2011 21:27:25 »
but the gearing ratio is vital in determining the average energy available throughout the year for the Buoyancy Engine.

What do you mean by "average energy"? Do you mean energy in time? If so, you are talking about units of power, not energy.

When ever I use the term 'average energy' you should regard it as defined in all reputable thermodynamic references.

I'm sure they do, but the average energy of your system better be zero, or some very interesting things are going to happen.

#### Mootle

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##### Will this buoyancy engine-based generator work?
« Reply #207 on: 26/11/2011 21:59:41 »
Mootle,
You cannot change the tidal range (for any given location) and so, for any give size of pontoon the energy available per tide is fixed.
The gearing cannot change the energy.
Averaging that energy, for example over the course of the year to allow for neap and spring tides, doesn't change it.
The gearing doesn't enter into it.

I'm not saying the input average energy is changed, I'm only interested in the output average energy. You clearly understand the theory so perhaps I've taken your ability to apply this to this application for granted.

If the ratio is not properly matched to the prevailing tidal range, desired depth, generating duration etc., much of the available energy will not converted. The aim is to complete each system cycle (descent, generation, ascent, purge,) with each tidal cycle in order to optimise the convertion of energy. If the ratio is too small several tidal cycles will be necessary to complete one system cycle this will greatly reduce the average energy.
« Last Edit: 26/11/2011 22:08:26 by Mootle »

#### Mootle

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##### Will this buoyancy engine-based generator work?
« Reply #208 on: 26/11/2011 22:00:38 »
but the gearing ratio is vital in determining the average energy available throughout the year for the Buoyancy Engine.

What do you mean by "average energy"? Do you mean energy in time? If so, you are talking about units of power, not energy.

When ever I use the term 'average energy' you should regard it as defined in all reputable thermodynamic references.

I'm sure they do, but the average energy of your system better be zero, or some very interesting things are going to happen.

Why?

#### Bored chemist

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##### Will this buoyancy engine-based generator work?
« Reply #209 on: 27/11/2011 10:11:28 »
The average energy is zero because it stores energy from the tide but gives it up to the generator.
The input and output have to balance so the net stored energy is zero.
However this talk of "average energy" is meaningless, for a start, average with respect to what?

There's still absolutely nothing that gearing can do to affect the energy provided by the tide.
All it can do is waste a bigger or smaller part of that energy..

#### Mootle

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##### Will this buoyancy engine-based generator work?
« Reply #210 on: 27/11/2011 16:17:53 »
The average energy is zero because it stores energy from the tide but gives it up to the generator.
The input and output have to balance so the net stored energy is zero.
However this talk of "average energy" is meaningless, for a start, average with respect to what?

There's still absolutely nothing that gearing can do to affect the energy provided by the tide.
All it can do is waste a bigger or smaller part of that energy..

Geezer managed that without moving his fingers.

You're describing energy balance and I think we've already covered this and are in violent agreement.

I've already agreed that gearing will not affect the energy input but that is irrelevant since the question was to do with average energy output.

The success or failure of the system would in practical terms depend on the average energy output since it is this which determines the available revenue. It is in this respect that the selection of the gearing ratio has a huge impact.

We can continue with circular arguments of semantics or we can move forward by discussing something which actually matters. If the answer is let's argue about nothing some more then I think it would be better to draw the thread to a close.

If there are any new questions about the schematic animation or concept design then I'm all eyes.

If you have questions about the detailed design I would be happy to speculate but if it's hard facts you're looking for I'm afraid that would have to wait until the design has been developed.
« Last Edit: 27/11/2011 16:19:47 by Mootle »

#### Bored chemist

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##### Will this buoyancy engine-based generator work?
« Reply #211 on: 27/11/2011 16:58:26 »
"I've already agreed that gearing will not affect the energy input but that is irrelevant since the question was to do with average energy output. "

Do you really not see the contradiction there?
The energy input is the same as the energy output. Averaging doesn't make any difference (or, indeed, very much sense).
(or have you really given up on thermodynamics?)

#### Mootle

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##### Will this buoyancy engine-based generator work?
« Reply #212 on: 27/11/2011 17:39:40 »
"I've already agreed that gearing will not affect the energy input but that is irrelevant since the question was to do with average energy output. "

Do you really not see the contradiction there?
The energy input is the same as the energy output. Averaging doesn't make any difference (or, indeed, very much sense).
(or have you really given up on thermodynamics?)

I don't think the continuation of this thread to be a worthwhile use of 'our' time at this stage.

Thank you to everyone for their valued input.

Signing off,

Mootle

#### Geezer

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##### Will this buoyancy engine-based generator work?
« Reply #213 on: 27/11/2011 18:37:12 »
Mootle,

This is not a debate about semantics. If you consult those reputable books about thermodynamics you will appreciate that you have to define the complete system! Your system includes the pontoons, the gearing system, the storage vessel and the turbine.

The gearing absolutely will affect the power output because it affects the energy that can be recovered by the storage vessel.

You better have a equation somewhere that accounts for all the energy flowing in and out of your system (and it better average to zero in some timeframe) so that you can evaluate the effect of any changes you make. Any change affects the entire system, and you must account for the impact any change has on other parts of the system.

If you change the gearing, you absolutely will change its efficiency, and that means you will have more or less energy available to do useful work on the generator. If you lose more energy in the gearing system, you can still get the same amount of energy out of the generator, but you will have to make the pontoon even bigger to compensate for that loss. Considering how expensive the pontoon is going to be, that might not be a very good idea.

You continually take a microscopic view of one part of your system rather than a top down view of the entire system. If you don't do a total energy balance for the system as a whole you cannot possibly determine what the optimum gear ratio is.

#### Mootle

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##### Will this buoyancy engine-based generator work?
« Reply #214 on: 27/11/2011 19:25:39 »
Mootle,

This is not a debate about semantics. If you consult those reputable books about thermodynamics you will appreciate that you have to define the complete system! Your system includes the pontoons, the gearing system, the storage vessel and the turbine.

You should appreciate from my prior replies that I fully intend to define the complete system. Apologies for any frustration caused by a unwillingness to prematurely enter into detailed design elements but if you're of the mind to continue this later I will return once the scaled animation is complete.

The gearing absolutely will affect the power output because it affects the energy that can be recovered by the storage vessel.

I would concede that there are any number of tunes we could play but this is not the way I would look at it. The gearing will affect the average energy output but the only impact on power output is the availability. It is the working head and flow rate that governs the power output for this system so for the 2m tidal range and 50m desired depth if we choose a 1:12.5 ratio it would take two tidal cycles rather than one (@25:1) for the Storage Vessel to reach the desired depth, i.e., the average energy output would be halved or in other words the same power output would be available for half the time.

You better have a equation somewhere that accounts for all the energy flowing in and out of your system (and it better average to zero in some timeframe) so that you can evaluate the effect of any changes you make. Any change affects the entire system, and you must account for the impact any change has on other parts of the system.

During the course of the first few pages of this thread we have looked at three check calculations which all served to demonstrate that the energy balance is theoretically sound. As the design develops I will aim to calculate realistic efficiency losses for each element of the system and if you are of a mind to check over my work that would be much appreciated.

If you change the gearing, you absolutely will change its efficiency, and that means you will have more or less energy available to do useful work on the generator. If you lose more energy in the gearing system, you can still get the same amount of energy out of the generator, but you will have to make the pontoon even bigger to compensate for that loss. Considering how expensive the pontoon is going to be, that might not be a very good idea.

It is true that it gets harder to maintain efficiency as the gearing ratio increases but the efficiency of the pulley system will depend (within certain bounds,) on the engineering. It is essential that the best fit is found in terms of revenue, cost and efficiency for the given arrangement.

You continually take a microscopic view of one part of your system rather than a top down view of the entire system. If you don't do a total energy balance for the system as a whole you cannot possibly determine what the optimum gear ratio is.

Thanks for the summary. I thought we'd covered this (somewhat fractiously,) within the first few pages of the thread but in anycase I would once again thank you for your input. As with BC above we're covering old ground so propose to bid you adieu for now.

Signing out,

Mootle

« Last Edit: 27/11/2011 19:38:17 by Mootle »

#### Bored chemist

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##### Will this buoyancy engine-based generator work?
« Reply #215 on: 27/11/2011 20:02:15 »
It may be some sort of progress that he's talking about gears, but I think it was mentioned some time ago.
It seems much simpler to hang a big heavy float in the sea and let it rise and fall with the tide. Tie a rope to it and then connect that rope to a pulley. Have the other end of the pulley connected to a spring (or a counterweight).
When the tide falls it pulls the rope and turns the pulley. When the tide falls the spring or counterweight pulls the rope and turns the pulley the other way.
With this system there is less rope, it's all above water (and so is everything else apart from some sort of frame to hold it in place.)
Your system looks unduly complicated. Why have 6 ropes + pulleys when you can just put a gearbox on the generator shaft?

I wonder if I will ever get an answer to that question.

#### Geezer

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##### Will this buoyancy engine-based generator work?
« Reply #216 on: 27/11/2011 22:51:39 »
Quote
The gearing will affect the average energy output but the only impact on power output is the availability.

Average energy means there are changes in energy in time. In other words, between time x and time y there was a change of z joules. A change in energy in a certain amount of time is a measurement of power. It might be joules per second (watts), joules per hour, BTUs per month, or calories per tide, but it's still a measure of power.

Therefore we can rewrite your statement as;

"The gearing will affect the average energy power output, but the only impact on power output is the availability."

#### The Naked Scientists Forum

##### Will this buoyancy engine-based generator work?
« Reply #216 on: 27/11/2011 22:51:39 »