Electricity from ambient heat

[James R]

Frencheneesz:

Your engine sounds easy enough to construct.

Why don't you just build one?

If it works, then all the theoretical thermodynamics naysayers will have to eat their hats. If it doesn't, then maybe they had a point after all.

An additional up-side: if it works, and you can really generate "free" energy from ambient heat alone (more than what you need to put in to run your engine), then you'll become world famous and receive a Nobel prize for solving the world's energy problems.

Good luck!

[Frencheneesz]

"If this is to work, then the average temperature of the system must decrease over time."

You're right pete, but the equations I worked out calculate the efficiencies the machine has to work - at every instantaneous state of the system. Hypothetically, the machine could be built so that temperature of both chambers slowly decreases at the same rate.

"the discussion of why"

Exactly. Though personally I'm not convinced that the second law of thermodynamics (which is statistcal by nature) applies to situations where the statistics are deliberately tampered with. If I can successfuly prove (without the second law) that such a machine is impossible, so much the better for my understanding of physics

James R: I think you underestimate how difficult it would be to build such a device. It would take thousands of dollars and weeks of hard work to even have a chance of coming close.

An interesting point: even if the machine I propose doesn't produce energy, it may well be the most efficient refrigerator and heater in existance. Maybe?

[Pete]

You're right pete, but the equations I worked out calculate the efficiencies the machine has to work - at every instantaneous state of the system. Hypothetically, the machine could be built so that temperature of both chambers slowly decreases at the same rate.

I'm not so sure. I'll look at the equations when I have time, but for now you might like to consider what is implied about the rates of heat transfer to and from the reservoirs if it works at the desired efficiency.

[Pete]

One brief correction to my earlier post before I go off to do the maths properly:

The temperature of the system doesn't have to decrease if the cold reservoir is large enough to be considered infinite. Practically speaking, you might put the engine on a boat and use the ocean as the cold reservoir.

[Pete]

OK... things looked very interesting until I figured out that numerator of the the heat pump's coefficient of performance is the heat added to the hot reservoir (x+A), not the heat extracted from the cold reservoir (x).

Here's what I have:

Take a constant temperature hot reservoir, and an infinite cold reservoir.
A heat pump is powered by an energy source to drive heat from the cold to the hot reservoir.
A heat engine extracts energy from the hot reservoir, providing useful energy and dumping waste heat in the cold reservoir.

A = Energy from the source to drive the heat pump
x = Heat pumped from the cold to hot reservoirs
Qh = Energy extracted from the hot reservoir by the heat engine
Qc = Energy dumped to the cold reservoir by the heat engine
W = Useful work done by the heat engine.
Tc = temperature of cold reservoir
Th = temperature of hot reservoir

The constant temperature of the hot reservoir and the first law of thermodynamics means that:
Qh = A + x

Carnot's theorem says that the maximum efficiency of the heat engine is:
W/Qh <= (Th - Tc)/Th

And the maximum performance of the heat pump is:
(x+A)/A <= Th/(Th-Tc)
...or equivalently...
(Th-Tc)/Th <= A/(x+A)

Combining the previous two, we have:
W/Qh <= A/(x+A)

Now, from the first equation we know that:
x = Qh - A

...which we can substitute into the previous equation:
W/Qh <= A/(Qh + A - A)

...which immediately leads to:
W <= A

In other words, we can't get more energy out than we put in, even if we place no limits on how much heat the heat pump sucks from the cold reservoir.

[Pete]

...

A = x/Cp
where
* Cp is the coefficient of performance for the heat pump

That's the same mistake I was making.
For a heat pump, the coefficient of performance is the ratio of energy added to the hot reservoir to energy used:
A = (A+x)/Cp

The coefficient of performance of a refrigerator uses the energy extracted from the cold reservoir as the quantity of interest, and has a correspondingly lower maximum:
x/A <= Tc/(Th-Tc)

instead of:
(x+A)/A <= Th/(Tc-Th)

[Frencheneesz]

That did it, that broke the equations. Now everything's negative. So thats it. So who wants to argue about the carnot cycle now : )

[Pete]

I can't... I have a vague kind of understanding about how it follows from the ideal gas law, but mostly I'm just taking it on the authority of those who (in my experience) know what they're talking about in that domain.

It's been an interesting discussion. I really should learn thermodynamics more thoroughly.

[DRZion]

I just came across this thread on google. I am very excited. I have been working to create an ambient heat conversion device for two years..

I think it is possible to create energy from a single heat reservoir, due to the microscale fluctuations of energy.

Here is my Proof:

Suppose you have a balloon filled with helium. This balloon is anchored to the ground with a tether that has zero thermal conductivity; therefore, the balloon can only (directly) interact with the atmosphere.
[it doesn't even matter if the tether is thermally conductive, because of its high {surface area : volume} ratio it would still equalize with the atmosphere]
To this balloon is strapped a device that converts the heat of the atmosphere to electricity. This electricity is used to power a lightbulb.

Just follow the logic please..

IF the lightbulb produces light, the energy MUST be coming from the ambient heat of the atmosphere.
IF the lightbulb produces light, the thermal energy of the atmosphere MUST be lowered.
When the thermal energy of the atmosphere is lowered, entropy rises faster in the atmosphere.
This is due to the law of entropy, where : delta S = delta q / T
When energy is taken from the atmosphere, T is lowered (by a fraction of a fraction of a degree)
During this time, delta q is constant
And so, delta S increases because T drops.
The photons created by lightbulb are eventually absorbed by the atmosphere, restoring all energy.
So, even though you get useful work from a system at equilibrium, you are still creating entropy.
There is no way a demon can beat entropy, but perhaps it can create work.

The Laws that I hold true are:
2nd Law of Thermodynamics (entropy must always rise)
Conservation of Energy


This does not propose an Ambient Heat Conversion device, it only proves that such a device would not break the laws of thermodynamics.

[DRZion]

The one above is a boiled down version of this one:

Thermodynamics and Machines the Run on Thin Air

Everything so far says such a device is impossible to create, it creates energy out of nothing. They say it goes against the laws of thermodynamics. But what if the heat was taken from the atmosphere, later to be put back?


Now, I will explain my idea in several easy to understand proofs that make sense to me, at least.


When you put energy in a system at 600K, and put energy into a system at 300K, that same amount of energy is going to create more entropy in the colder system. This is freshman chemistry.


If you take heat energy out of the atmosphere and put it into accelerating a car, the car will act as a capacitor (basically a battery?) for heat and .. entropy, I believe. As the car accelerates, there is energy stored in its momentum, energy that was taken from the heat of the atmosphere. Eventually, all this energy is going to be put back as the car slows down due to air and tire friction. ALL the energy will be put back. Where else could it go?



This would mean that entropy is not created? But I would say that it is. The atmosphere-system of the earth would be cooled (going back to the first paragraph of my proof), and this regional discrepancy would have to cause extra winds, mixing of the atmosphere. And all this time, there is still heat being held in the carpacitor (ha!), meaning that the atmosphere is colder (going back to my fist statement) and more entropy is being caused by all the workings of the atmosphere. But after this, the energy from the carpacitor is still going to be released, causing a net increase in entropy.



I'm going to try to restate that. As energy is put into the carpacitor, the temperature of the earth drops. Everything that goes on in the atmosphere at this time will create MORE entropy than it would otherwise. And so, when the carpacitor slows down to a standstill, all the energy that it has been storing will be released, and the heat of the earth will return to what it has been. But that extra bit of entropy caused during global cooling will still be there! Entropy has gone up!! And yet, no energy has been used.. Very strange.

[sheik480]

Considering temperature is an absolute, and a ~150 years ago most people had no conception whatsoever of a heat engine, a mechanism that pulls energy out of the ambient environment and converts it somehow into mechanical energy should be possible some point in the future. It hasn't happened yet, so who's to say it never will?

I forgot to say, the whole system would ultimately be solar and geothermal powered; what heats the surface and atmosphere of the earth? The sun and the core. This system will never work indefinitely, especially in space, the ship would get colder and colder until you ran out of ambient heat energy. No free lunch here, just imagination and dreams.

[DRZion]

I just came across this thread on google. I am very excited. I have been working to create an ambient heat conversion device for two years..

I think it is possible to create energy from a single heat reservoir, due to the microscale fluctuations of energy.

Here is my Proof:

Suppose you have a balloon filled with helium. This balloon is anchored to the ground with a tether that has zero thermal conductivity; therefore, the balloon can only (directly) interact with the atmosphere.
[it doesn't even matter if the tether is thermally conductive, because of its high {surface area : volume} ratio it would still equalize with the atmosphere]
To this balloon is strapped a device that converts the heat of the atmosphere to electricity. This electricity is used to power a lightbulb.

Just follow the logic please..

IF the lightbulb produces light, the energy MUST be coming from the ambient heat of the atmosphere.
IF the lightbulb produces light, the thermal energy of the atmosphere MUST be lowered.
When the thermal energy of the atmosphere is lowered, entropy rises faster in the atmosphere.
This is due to the law of entropy, where : delta S = delta q / T
When energy is taken from the atmosphere, T is lowered (by a fraction of a fraction of a degree)
During this time, delta q is constant
And so, delta S increases because T drops.
The photons created by lightbulb are eventually absorbed by the atmosphere, restoring all energy.
So, even though you get useful work from a system at equilibrium, you are still creating entropy.
There is no way a demon can beat entropy, but perhaps it can create work.

The Laws that I hold true are:
2nd Law of Thermodynamics (entropy must always rise)
Conservation of Energy


This does not propose an Ambient Heat Conversion device, it only proves that such a device would not break the laws of thermodynamics.

I actually went over this this summer - its not right. By the time the carpacitor comes to rest the entropy would be the same as if it wasn't turned on. While it was on it would decrease.

The laws of thermodynamics clearly say that there is no device that could extract net useful energy from ambient heat, even if did you have such things as perfect frictionless generators and perfect insulators.

The laws of thermodynamics were written 150 years ago to describe boilers and steam locomotives. I do not think that they are very up to date. However, the concept of gibbs free energy is pretty darn useful and applicable..



Sheik, I agree. These things would not last for ever, and would not be useful in space. Especially considering that the cold sink in space is very close to 0, meaning a regular heat engine would be close to 100% efficient.

[angryScientist]

Hello,
I saw this thread and just had to make a comment because I also believe that it is possible to obtain electricity form ambient heat.

It is true that a heat engine can never be more than %100 efficient. It is also true that a heat pump is more than %100 efficient, usually %300 to %400, thanks to the transportation of the latent (hidden) heat at no cost.

I do see a problem with the original poster's thinking. If two containers are used and the heat is cycled between them by pumping the heat from the cold side and then letting it flow back through an engine then heat will disappear from the system. The reason is the heat is converted into another form of energy.

Example:
Using an engine of %30 efficiency and letting 100 units of heat flow through it only 70 units of heat will appear on the other side as 30 units will be converted into another form (mechanical, electrical or other).
Removing the heat from the cold side with a heat pump of %300 efficiency should take only (1/3)*70 = 23.33 units of energy.

As the heat moves thought the engine part of the heat disappears and the energy takes a different form. It looks like this is where you got the equation wrong.

[DRZion]

Hehehe this is the thread that started me on sciforums
I learned some interesting things here. I also found many people who do not accept radical notions in science, perhaps for the right reasons.

Anyways, I would like to go back on some of the statements I made above. I have done a simulation (2 years ago) that shows that in fact, after the last of the heat is put back the entropy would be exactly the same as if it was never removed (but not while energy is in a different form, at this point it will be lower). I also still think that its possible to produce work from ambient heat.

Just saying

[arfa brane]

I have done a simulation (2 years ago) that shows that in fact, after the last of the heat is put back the entropy would be exactly the same as if it was never removed

Which is why you can't get energy out of a closed system.

I also still think that its possible to produce work from ambient heat.

Well, it isn't possible; entropy has to increase so you can get energy from a "closed" system, or from a system with "closed" cycles.

So nyah nyah!

[angryScientist]

It's said that all our energy comes from the sun anyway. It's also said that a cold black body will absorb more energy than warm black body. Perhaps we need a super cooled black body to get any good efficiency as a solar collector.

If all the energy generated is converted to radio or light and emitted into space would that just make the system that we are looking at a lot larger?

Just thinking.

[DRZion]

Which is why you can't get energy out of a closed system.
Well, it isn't possible; entropy has to increase so you can get energy from a "closed" system, or from a system with "closed" cycles.

So nyah nyah!

So, according to you, entropy can decrease just as long as we can't get energy from that system?

It's said that all our energy comes from the sun anyway. It's also said that a cold black body will absorb more energy than warm black body. Perhaps we need a super cooled black body to get any good efficiency as a solar collector.

If all the energy generated is converted to radio or light and emitted into space would that just make the system that we are looking at a lot larger?

Just thinking.

I'm not sure if this is what you're getting at-
In another thread it was decided that photons of longer wavelengths have more entropy than those of shorter wavelengths. So, if all energy is converted to radio, then this system is more disordered than if all energy was converted to visible for instance.

What if a reaction produces a million moles of incredibly long wavelength light (so very little energy required). This would be very disordered. This should allow for something else in the reaction to become more ordered, with a net increase in entropy. Once again, this is just the gist I get from your post, I'm not sure if its what you were getting at.

[Kittamaru]

What bothers me more than anything is that I brought a question similar to this up in my 10th grade chemistry class and the entire class (including the teacher) looked at me like I was retarded, the teacher said quite flatly that it was impossible and such notions shouldn't be entertained, and then we moved on... so I dropped the idea then and there...

And here I learn that it's a thought process on par with a goddamned Physics "wiz"... it just makes me pine for the chance to have had a better primary education *sighs*

None the less - glad to see I'm not insane

[Pete]

Well, your teacher was right that it's impossible... but having the thought doesn't make you retarded or insane.

Being intelligent and creative is exploring many ideas, including wrong ones. Other parts (that many scientist wanna-bes struggle with) are in recognizing dead ends, and doing the hard work of learning the incredible idea explorations that have done already.

[Pete]

Example:
Using an engine of %30 efficiency and letting 100 units of heat flow through it only 70 units of heat will appear on the other side as 30 units will be converted into another form (mechanical, electrical or other).
Removing the heat from the cold side with a heat pump of %300 efficiency should take only (1/3)*70 = 23.33 units of energy.

The maximum efficiency of heat pumps and heat engines depends on temperature difference.

A temperature difference that a heat pump can maintain at 300% efficiency is not enough to drive an engine of 30% efficiency.

See post 25.

As the heat moves thought the engine part of the heat disappears and the energy takes a different form. It looks like this is where you got the equation wrong.

Converting heat to a different form of energy is the whole purpose of the exercise.