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Prof Neilson wrote:

We now have two experiments breaking thermodynamics by getting work from ambient heat without a delta T. The experiments use totally different methods to achieve this.

LED converts heat into light
http://physicsworld.com/cws/article/news/48882

As I have said before - Wave Function Coupling can flow in either direction, from high energy to low or low energy to high. Now that there are two experiments of totally different means proving this - will anyone learn - or will they just KOOK OUT?

lol. if you get energy from heat, there is a "deltaT". the part you missed in the LED experiment is that heat is continually being added to the system... so no TD violation. I suggest you go down to your local university and audit a physical chemistry class.

DGDanforth wrote:

In like manner, I don't view entropy as fundamental. It is only because of the statistical nature of the objects to which it is applied that give it credence. If the marbles of a Chinese checker game are put into a corner of the board are they in a lower entropy state than if they are randomly spread over the board? Every state is just a state. No one of them is more important or special than another one. It is only when one invokes the time dependent process that governs the motion of the particles that some states stand out more than other ones. Change the process and you change the 'entropy' (probability distribution).

think of it this way... until all the marbles are in wells, they are not at their lowest energy potential and therefore not at equilibrium. unless the board is perfectly flat and level (and not subject to corriolis effect of earth's rotation, vibrations, etc), and the marbles not spheres, they will eventually find their way to the wells.

and the universe seems to "like" things being in their lowest possible energy state. space, and everything in it, seems to want to "spread out".

supamark

Please excuse my ignorance. My P Chem teacher must be mad at me. Not to mention my Engineering Thermodynamics and Heat Transfer professors. Why did they ever give me an A in their courses. I am such a dolt.

Please help me and identify the delta T in the graphene battery that I missed?

Oh, and graphene has a heat transfer coefficient 3,000 to 5,000 W / m K. See this paper cited by 219 authors. http://www.ndl.ee.ucr.edu/Balandin-APL-Thermo.pdf

The graphene was monolayer 5 mm by 5 mm. All in an liquid solution at ambient temperature. Not easy to support a delta T with a K that high. Did they use a blow torch?

Where is the delta T again?

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supamark wrote:

DGDanforth wrote:

In like manner, I don't view entropy as fundamental. It is only because of the statistical nature of the objects to which it is applied that give it credence. If the marbles of a Chinese checker game are put into a corner of the board are they in a lower entropy state than if they are randomly spread over the board? Every state is just a state. No one of them is more important or special than another one. It is only when one invokes the time dependent process that governs the motion of the particles that some states stand out more than other ones. Change the process and you change the 'entropy' (probability distribution).

think of it this way... until all the marbles are in wells, they are not at their lowest energy potential and therefore not at equilibrium. unless the board is perfectly flat and level (and not subject to corriolis effect of earth's rotation, vibrations, etc), and the marbles not spheres, they will eventually find their way to the wells.

and the universe seems to "like" things being in their lowest possible energy state. space, and everything in it, seems to want to "spread out".

I don't think you guys know how to read. I said

It is only when one invokes the time dependent process that governs the motion of the particles that some states stand out more than other ones.

That encompasses low energy states etc.

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Prof Neilson wrote:

"Work Without Delta T" - not very snappy but earthshaking to any decent student of thermodynamics.

We now have two experiments breaking thermodynamics by getting work from ambient heat without a delta T. The experiments use totally different methods to achieve this.

LED converts heat into light
http://physicsworld.com/cws/article/news/48882

The device above does indeed put out more light than you supply in input power, and that seems to be the total extent of Prof Neilson's analysis.

However, a black body at 135 degrees C without any electrical connections at all also puts out more EM radiation than it receives in electrical input power (which is zero). Does this mean it breaks the second law of thermodynamics?

In the case of the LED diode the answer is straightforward. Because the light from the LED is not coherent (i.e. is not laser light of a single frequency) then it has entropy associated with it. So the total entropy of the LED system (including light output) still increases. The second law is magically saved (as it always will be).

Another way of looking at it is that the laser diode is working as a heat pump. When you have a source of heat (a heat bath) then by applying input energy you can transfer heat elsewhere at a higher temperature within the 2nd law. That is what the LED is doing. But you can never beat Carnot efficiency. Light has a temperature and this can be used to work out a Carnot efficiency.

As usual, with attention to detail the frequent wild claims of Prof Neilson turn out to be due to lack of understanding. There's really no excuse - he has access to physicists at university! And if Prof Neilson wants a good example of something demonstrating the principle of the LED experiment then he has no need to look further than the container for his supplies of chilled beer.

There is such a richness of possibility and a flexibility of ways to put things together within the laws of physics that it seems a shame to waste time looking for effects that are only possible if the laws of physics are broken.

Regards,
Peter

Last edited Tue, 13 Mar 2012, 6:42am by Technopete

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Pete - you are straining a bit too much to save a broken law.

That you cannot see this and work up a nonsensical analysis it troubling. Then you make hand waving claims like all physicist's.

Jeesh.

But really - its much worse. You talk of heat pumps and Carnot efficiency but you have not got a clue.

I have pretty much had enough of this nonsense from you people that have no clue what a heat pump is.

Pete - I refer you to supamark and his analysis of what ails me. Audit a course. I suggest Engineering Thermodynamics. It need not be of ICI quality. Any community college will do.

Or just look at the Wikipedia page. http://en.wikipedia.org/wiki/Thermal_efficiency

"The limiting factors are the temperature at which the heat enters the engine, and the temperature of the environment into which the engine exhausts its waste heat, , "

Now to do a proper analysis, please identify Th and Tc in the LED or Graphene experiment.

A heat engine is using a Heat flux to do work. Please identify the heat flux in the LED or graphene device at ambient temperature.

The change in ambient temperature does not qualify. The starting ambient temperature is Ts not Th. The ending ambient temperature is Te not Tc. There is no heat flux into the system if you insulate it and Te is lower than Ts. If you don't insulate the system you get a heat flux into the system. This is not the Heat Engine heat flux. That requires a Qh and a Qc. This is a Qambient or some new term.

That you can't even identify a heat engine, its Th and Tc, and it Qh or Qc, then you take a run at me. Its not laughable, its sad. But what should I expect when EE's Physicists, Chemists and whatever Lens is venture outside their education?

To conclude, the LED and Graphene devices are not Heat Engines by definition. They possess no Th and no Tc, no Qh and no Qc. However, they produce work. This is impossible in the existing laws of Thermodynamics. So either the experiments are cons or the laws are broken.

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All I want to know is how much energy can you make from abandoned salt minds that are flooded with water. I saw above that salt water would work.

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However, when the researchers measured the minute power of the infrared radiation produced by the LED, they measured 70 pW of power being emitted by the LED while only 30 pW was being consumed, an efficiency of more than 200%.

As I get it, this looks like heat pump for light. You put work (electricity) in and get more light out while taking extra energy as heat from surroundings.

Second law of thermodynamics: Heat cannot spontaneously flow from a colder location to a hotter location.

All good here then as its not spontaneous.

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Prof Neilson wrote:

Pete - you are straining a bit too much to save a broken law.

The analysis that the LED system does not break any laws of thermodynamics is not mine. This is what the paper itself has to say.

Thermoelectrically Pumped Light-Emitting Diodes Operating above Unity Efficiency page 1 column 2 top paragraph :

Beginning with Tauc in 1957, a body of literature theoretically establishing the basic thermodynamic consistency of electroluminescent cooling and exploring its limits began to emerge.

PN wrote:

That you cannot see this and work up a nonsensical analysis is troubling. Then you make hand waving claims like all physicist's.

Jeesh.

But really - its much worse. You talk of heat pumps and Carnot efficiency but you have not got a clue.

I have pretty much had enough of this nonsense from you people that have no clue what a heat pump is.

Pete - I refer you to supamark and his analysis of what ails me. Audit a course. I suggest Engineering Thermodynamics. It need not be of ICI quality. Any community college will do.

Or just look at the Wikipedia page. http://en.wikipedia.org/wiki/Thermal_efficiency

"The limiting factors are the temperature at which the heat enters the engine, and the temperature of the environment into which the engine exhausts its waste heat, , "

Now to do a proper analysis, please identify Th and Tc in the LED or Graphene experiment.

A heat engine is using a Heat flux to do work. Please identify the heat flux in the LED or graphene device at ambient temperature.

I don't understand the thermodynamics of the graphene experiment in detail, so am going to stick to my knitting - in this case the LED over-unity experiment.

The separate physical synopsis behind the paper also says this.

Physics Synopsis by Don Monroe : Optical Device is More Than 100% Efficient

.. heating the light emitters increases their output power and efficiency, meaning they are like thermodynamic heat engines, except they come with the fast electrical control of modern semiconductor devices.

PN wrote:

The change in ambient temperature does not qualify. The starting ambient temperature is Ts not Th. The ending ambient temperature is Te not Tc. There is no heat flux into the system if you insulate it and Te is lower than Ts. If you don't insulate the system you get a heat flux into the system. This is not the Heat Engine heat flux. That requires a Qh and a Qc. This is a Qambient or some new term.

That you can't even identify a heat engine, its Th and Tc, and it Qh or Qc, then you take a run at me. Its not laughable, its sad. But what should I expect when EE's Physicists, Chemists and whatever Lens is venture outside their education?

To conclude, the LED and Graphene devices are not Heat Engines by definition. They possess no Th and no Tc, no Qh and no Qc. However, they produce work. This is impossible in the existing laws of Thermodynamics.

See below.

So either the experiments are cons or the laws are broken.

The third alternative is that you have not read Landsberg and Evans 1967 - Thermodynamic Limits for Some Light-Producing Devices which defines the thermodynamic quantities you are looking for above.

Here's yet another quote from the abstract

Abstract : Optical Device is More Than 100% Efficient

A heated semiconductor light-emitting diode at low forward bias voltage V<kBT/q is shown to use electrical work to pump heat from the lattice to the photon field.

and

Thermoelectrically Pumped Light-Emitting Diodes Operating above Unity Efficiency page 4 column 1 paragraph 2 :

Moreover, as sources of irreversibility are removed from the LED, it acts as a reversible Carnot-efficient heat pump operating between the lattice and the photon field.

In most people's language, including thermodynamicists, a device which pumps heat is a heat pump!

So basically the guys writing the paper, and the physicist writing the Physics Synopsis are saying the device is a heat pump and that it obeys the laws of thermodynamics - all of them.

Regards,
Peter

Last edited Tue, 13 Mar 2012, 3:51pm by Technopete

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From Physics Synopsis by Don Monroe : Optical Device is More Than 100% Efficient":

"The extra energy comes from lattice vibrations, so the device should be cooled slightly, as occurs in thermoelectric coolers."

This is very similar to the idea I stated in the E-Cat thread where phonons can supply energy thus unlimited energy can be supplied from the surroundings.

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JCatania wrote:

From Physics Synopsis by Don Monroe : Optical Device is More Than 100% Efficient":

"The extra energy comes from lattice vibrations, so the device should be cooled slightly, as occurs in thermoelectric coolers."

This is very similar to the idea I stated in the E-Cat thread where phonons can supply energy thus unlimited energy can be supplied from the surroundings.

You can pump heat (or light) from one point to another. But you have to supply input energy in order to accomplish this. That's what the laws of thermodynamics say.

Regards,
Peter

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No, light and heat propagate without energy input.

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"The graphene was monolayer 5 mm by 5 mm. All in an liquid solution at ambient temperature."

Try to manufacture a chip of graphine that big and economically and then I will believe this could be more than a curiosity. I've looked around and anything of that size has to be grown on a very clean and smooth surface.

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JCatania wrote:

No, light and heat propagate without energy input.

Of course they do, from the point where theres entropy is higher to where entropy is lower. But you have put energy in to get it in the other way.

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Pete - its really so sad - your understanding of thermo - yet you persist.

So I did the thought experiment on the LED a few days ago - perhaps you forgot it.

The thought experiment produced electricity - enough to run the LED and supply work.

But I don't feel up to the task of education today.

Just put a solar cell with 50% efficiency in the output light in the abstract. See that the energy produced by the solar cell is enough to power the LED and some additional work. Do the calculations yourself.

Show me how this is a heat engine? There is no delta T.

Any heat engine needs a delta T or it is not a heat engine.

A refrigerator is a heat pump. It is a heat engine run in reverse. Work goes in to make a delta T.

If you cannot identify a temperature difference - It is not a heat engine or pump by definition.

But make up what ever physics you like. Perhaps switch to string theory. There you can get anything published.

And bringing up blackbody radiation - beyond stupid. In a closed system, the blackbody radiation reflects back on itself. It does nothing. By definition. In an open ambient system at thermal equilibrium - it does nothing. By definition - the incoming and out going blackbody radiation is equal.

Lordy - I have had enough of this nonsense.

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I hate every time I read some posts and my selfish side tells me to leave as If I didn’t read them and leave people in the dark, while my humane/helping side says spend a little time helping people….:

Spontaneous Change: means some change that occurs without real input energy intervention. Spontaneous Change has a directionality in its definition. When delta G is negative you will have an spontaneous change!This happens very often in nature... example: just wait enough time and you will see big boulders coming down on a cliff. Nature takes care of the parameters that make the change happen and also clue us in the directionality.

Examples of spontaneous change:
1.Lets say someone or something is holding you on the high point of your swing set, and if that someone/something just lets go you will come down in motion spontaneously.
2. Hold a bottle of mustard down, and slowly but surely mustard will come down with no help, only when you get desperate and you tap it (input energy) is when you add input energy, but without input energy (i.e no tapping) mustard will spontaneously come down and move (even though it will take some time for all of it to come down even though is a case of an spontaneous change nature gives us by using one of its "forces").
3. hot body close to a warm body: heat will flow from hot body to the warm body spontaneously and not the other way around.
The concept of spontaneous change describes how without additional input there will be a change with directionality attached to it (from hot to cold, from high to low, etc, from high pressure to low pressure).
Takeaways:
1. Change can be spontaneous without additional input energy
2. It does NOT need to be fast (the speed of the change) for it to be spontaneous
3. It has a direction to it.

Spontaneous change sometimes is not as easy to assess as the bottle of mustard/ketchup case but is happens all over the place in nature.

Rationale in some reactions where there is change (where do the internal degrees of freedom come into play: vibrations {typically higher energy},and rotations{typically lower in energy}) :

Cases:
1. When the delta G is less negative than the delta H and some of the change is trapped in the internal degrees of freedom (vibrations, rotations). In this case the internal degrees of freedom are prevented from providing some of the energy they have.
2.When the delta S is positive signifying you have increased the disorder by that spontaneous change. If you increase disorder you have fewer ways to tie up the internal degrees of freedom (vibrations, rotations) and the change/energy that these contain is released/provided. This fact proof very well what the authors are saying with regards to "vibrations" (which is one type of internal degrees of freedom) in the papers since they are good scientists who learned their stuff well and this is pretty std energetic reaction (even if the change starts spontaneously) knowledge for those of us who know this stuff as to how a very well understood energetic behavior is being used to deliver energy(.i.e there is NO violation of laws here, just lack of real understanding which can be cured easily by learning assuming you are not mule stupid/ignorant and want to learn).

Last edited Tue, 13 Mar 2012, 5:25pm by BigMig

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So a solar water heater is a heat engine and solar cell isnt? They both receive photons.

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Prof Neilson wrote:

Pete - its really so sad - your understanding of thermo - yet you persist.

So I did the thought experiment on the LED a few days ago - perhaps you forgot it.

The thought experiment produced electricity - enough to run the LED and supply work.

But I don't feel up to the task of education today.

Just put a solar cell with 50% efficiency in the output light in the abstract. See that the energy produced by the solar cell is enough to power the LED and some additional work. Do the calculations yourself.

That would of course be possible - but only if a) the temperature of the solar cell is less than the temperature of the LED or b) if the light produced by the LED is monochromatic (which it isn't) and probably c) if the light is emitted in a single direction (though I'm not entirely sure about this one). If the light were monochromatic then its entropy would be low.

However, since it isn't any of the three then its entropy is higher, which means you cannot extract all the energy in it. My understanding is that this is the basic theoretical problem with your analysis, for however you try to get energy out of the spread spectrum of light, a certain proportion of the energy is thermodynamically bound to become heat in the solar cell. So you are in for a calculation before you can make any claims about possibly efficiencies. I don't understand the details - laser guys would know this stuff well.

Whereas if it is coherent and monochromatic then in theory you can convert all of it to electricity.

Show me how this is a heat engine? There is no delta T.

Any heat engine needs a delta T or it is not a heat engine.

A refrigerator is a heat pump. It is a heat engine run in reverse. Work goes in to make a delta T.

If you cannot identify a temperature difference - It is not a heat engine or pump by definition.

It's not a heat engine. It's a heat pump, which is the reverse of course, so obeys the same thermodynamic laws.

The relevant temperatures are :-

- T_cold the temperature of the LED (which would therefore cool in the case of > 100% efficiency in a perfectly thermally isolated system)

- T_hot the temperature of the light beam, which is not simply its black-body temperature but this temperature minus a function of the entropy content. The example given in Wienstein for a defined spectrum is a brightness temperature of 1794K but a thermodynamic temperature of 1527K.

But make up what ever physics you like.

I prefer physics which works and can be verified experimentally.

Perhaps switch to string theory. There you can get anything published.

And bringing up blackbody radiation - beyond stupid. In a closed system, the blackbody radiation reflects back on itself. It does nothing. By definition. In an open ambient system at thermal equilibrium - it does nothing. By definition - the incoming and out going blackbody radiation is equal.

Lordy - I have had enough of this nonsense.

Have you actually read (or skimmed) the LED paper and Landsberg and Evans? You have put me to the trouble of doing exactly that and there is no reason why you should escape doing the same.

Regards,
Peter

Last edited Tue, 13 Mar 2012, 5:40pm by Technopete

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Prof Neilson wrote:

So matt, if the self-charging battery works - you have proven that Liouville's theorem is wrong.

Now I have never really studied the Hamiltonian, but I suppose that if Liouville is wrong, the Hamiltonian is wrong too.

So Classical and Quantum mechanics get thrown out the window if the self-charging battery works. Since the second law is Classical - there goes the neighborhood.

Is this getting to be fun!

The reformulation of everything in terms of Wave Function Coupling - will work and produce surprises!

lol, you still don't understand even what they're claiming to be happening. Heat energy is going into the solution like the "0th" law says it should.

next, that heat is doing work by getting the Cu2+ cations to move around in the solution (heat is a measure of energy).

When a Cu2+ hits the graphene, some of that energy is transferred into the graphene and an e- goes into the circuit since it requires less energy than moving to the Cu ion. This should cool the soln slightly, causing more ambient heat to move into the soln.

rinse/repeat.

no laws of TD have been violated to make this thing. It is not "self charging", it is charged by heat, externally applied (via ambient room temp or heating element).

do you call yourself "professor" like fat people are called "slim" or tall people "shorty"?

Prof Neilson wrote:

Pete - you are straining a bit too much to save a broken law.

That you cannot see this and work up a nonsensical analysis it troubling. Then you make hand waving claims like all physicist's.

Jeesh.

But really - its much worse. You talk of heat pumps and Carnot efficiency but you have not got a clue.

I have pretty much had enough of this nonsense from you people that have no clue what a heat pump is.

Pete - I refer you to supamark and his analysis of what ails me. Audit a course. I suggest Engineering Thermodynamics. It need not be of ICI quality. Any community college will do.

Or just look at the Wikipedia page. http://en.wikipedia.org/wiki/Thermal_efficiency

"The limiting factors are the temperature at which the heat enters the engine, and the temperature of the environment into which the engine exhausts its waste heat, , "

Now to do a proper analysis, please identify Th and Tc in the LED or Graphene experiment.

A heat engine is using a Heat flux to do work. Please identify the heat flux in the LED or graphene device at ambient temperature.

The change in ambient temperature does not qualify. The starting ambient temperature is Ts not Th. The ending ambient temperature is Te not Tc. There is no heat flux into the system if you insulate it and Te is lower than Ts. If you don't insulate the system you get a heat flux into the system. This is not the Heat Engine heat flux. That requires a Qh and a Qc. This is a Qambient or some new term.

That you can't even identify a heat engine, its Th and Tc, and it Qh or Qc, then you take a run at me. Its not laughable, its sad. But what should I expect when EE's Physicists, Chemists and whatever Lens is venture outside their education?

To conclude, the LED and Graphene devices are not Heat Engines by definition. They possess no Th and no Tc, no Qh and no Qc. However, they produce work. This is impossible in the existing laws of Thermodynamics. So either the experiments are cons or the laws are broken.

dude, please just zip it until you at least audit a physical chem class at your local university. You simply have no understanding of thermodynamics, and yet you keep speaking as if you do.

Bloggers can't read

DW has been proven correct yet again.

And no one has answered my simple question - where is the Delta T

But I give up. Its too much like work trying to edumacate you guys.

Oh - and I am on the faculty of my local university! In the School of Engineering. Boy is the laugh on them.

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Gee a battery with a temperature dependance. What are the odds?

Robert

Prof Neilson wrote:

Bloggers can't read

DW has been proven correct yet again.

And no one has answered my simple question - where is the Delta T

But I give up. Its too much like work trying to edumacate you guys.

Oh - and I am on the faculty of my local university! In the School of Engineering. Boy is the laugh on them.

engineers are NOT scientists. since you're faculty, why don't you get one of the professors that teach TD (class will be called "physical chemistry") to explain why you're wrong if you won't believe us.

read my prior post about what the scientists claim to be happening, or better yet just read it from the scientists own mouth if you are looking for the heat change (hint "zeroth law").

Prof Neilson wrote:

supamark

Please excuse my ignorance. My P Chem teacher must be mad at me. Not to mention my Engineering Thermodynamics and Heat Transfer professors. Why did they ever give me an A in their courses. I am such a dolt.

Please help me and identify the delta T in the graphene battery that I missed?

Oh, and graphene has a heat transfer coefficient 3,000 to 5,000 W / m K. See this paper cited by 219 authors. http://www.ndl.ee.ucr.edu/Balandin-APL-Thermo.pdf

The graphene was monolayer 5 mm by 5 mm. All in an liquid solution at ambient temperature. Not easy to support a delta T with a K that high. Did they use a blow torch?

Where is the delta T again?

Let me put it in terms even an engineer could understand:

the solution is heated, ambiently or by a heating element.

that heat is translated into work - the mechanical motion of the ions in solution.

when that ion hits the graphene lattice at the proper velocity/angle it will transfer some of that mechanical energy to an e- in the graphene.

that additional energy will move the e- into the circuit. this will cause the solution to cool ever so slightly (and the circuit to heat slightly).

ambient heat, or a heating element will transfer more heat back in to the ion solution.

QED.

btw, if you ask this question again, I'll assume you've fallen to cognitive dissonance and will ignore you.

radam wrote:

JCatania wrote:

No, light and heat propagate without energy input.

Of course they do, from the point where theres entropy is higher to where entropy is lower. But you have put energy in to get it in the other way.

Sounds like your talking about something different than heat and light propagation, which do not involve entropy. What I'm talking about is ipso facto viable. No invocation of "such-and-such" law is relevant. Canned and cliched remarks from controversial figures have no place in science.

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seslaprime wrote:

as I said, like the carbon nano-tube industry that was suppose to take 20-30 years to take off only took a few years. When there is vast riches involved, the industry hath no boundaries.

It still hasn't taken off, Sesla. So far as I know, the only finished product being sold is a sort of "paper" made of tangled CNT. Nobody is selling even so much as short CNT threads, let alone the cables, structural beams, and panels which theoretically could replace most other building materials.

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Prof Neilson wrote:

So Lens

If the graphene battery is shown to work - what is the hypothetical?

Technopete explained it quite thoroughly, and in far more detail than I could. No need to gild the lily.

What continues to astonish me is that any scientifically literate person would just assume the device/process reverses entropy, as their first assumption, rather than their last. As Sherlock Holmes said: "When you have eliminated the impossible, whatever remains, however improbable, must be the truth".

But we're rather a long way here from eliminating everything except the theoretically impossible.

Prof Neilson wrote:

Hari-Kari?

No thanks. Nor hara-kiri, either.

Prof Neilson wrote:

Moving to another dimension where things work the Lensman way?

Well, since my computer still seems to be working, I presume both entropy and quantum mechanics still work according to current theory, more or less. And if you read this, then it would appear the same holds true on your end.

Last edited Thu, 15 Mar 2012, 9:50am by Lensman

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Prof Neilson wrote:

...my Engineering Thermodynamics and Heat Transfer professors. Why did they ever give me an A in their courses. I am such a dolt.

Seriously, why don't you ask them to read the abstract of the paper under discussion here, and ask what they think? I'd be interested in knowing what their response would be.

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In order for the overunity LED to break the 2nd law of thermodynamics it has to be coupled to a solar cell collector which will achieve more than 43% efficiency (as the LED is around 230% efficient, and this must be with the spectrum of light emitted by the LED.

However, this is not the only requirement. In order to fall outside the second law in a simple demonstration then the solar cell collector must be at the same temperature as the LED system, which the paper says is at 135 degrees C.

The following graph is extracted from a web article on Solar Cell Efficiency.

.

Now you have to extrapolate from the figures what you would expect the efficiency to be when the cell is at a temperature of 135 degrees C. My estimate is that the solar cell efficiency is about halved from the figure at 25 degrees C, because the current stays about constant, but the voltage decreases, and I'm assuming the voltage decrease at all currents is identical to the extrapolated reduction in open-circuit voltage (i.e. at zero current on the x axis) as it is easiest to read the voltage figures there. The relative x axis offset of the three lines at varying currents looks pretty constant so this does not seem unreasonable.

Since the solar cell efficiency does not start off at 100%, by the time you have reduced it by 50% then you are almost certain to be under 43% efficiency.

Some caveats and other points to note are:-

1) the reduction in solar cell efficiency is extrapolated based on measurements for sunlight, but the reduction for infra-red at 2.4um will be different.

2) rather than actual efficiency of the infra-red solar cell what you really need is the calculated maximum thermodynamic efficiency. The practical figures are just presented above as a guide to what might happen in theory.

3) the solar cell required to match the LED must peak in sensitivity around 2.4 um (0.5eV?), and operate at 135 degrees C (= 400K, kT = 0.033eV, ratio = 15:1). This is likely to be much less efficient and much more demanding than taking sunlight of 400-600nm (2-3eV) and expecting to operate at 25 degrees C (= 300K, kT = 0.025eV, ratio = 80:1) as the changed ratio of light temperature to kT is clearly stacked against you.

So, taking the solar cell performance into consideration it is unlikely that you can break the 2nd law, even with experimental 230% LED efficiency, and even in theory. It looks like the solar cell collector thermodynamic efficiency is what is going to stop you.

Regards,
Peter

Last edited Fri, 16 Mar 2012, 1:55pm by Technopete

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I think this is a bad extrapolation Peter.

You design any solar cell for an operating temperature. Solar cells are designed for earth ambient temps.

For this LED thought experiment - design a solar cell for max performance of the cell at 135 C.

Here is the Spectrolab data sheet for a max temp 110 C cell.

As well as I can read the data sheet - a pretty good wavelength band can reach as high as 85% efficiency at 65C.

You must have the LED spectrum and a solar cell designed to match the spectrum at that temperature.

I believe it can be done.

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