ambient heat conversion

Is it possible to get energy from a single heat well? I say yes.

Harnessing the thermal radiation emitted by every object could lead to nearly limitless amounts of energy that can be recycled over and over again.

Consider a block of infrared glass a meter cubed. .01% of volume of this block is radiating particles (dopant). The surface area of radiating particles would be HUGE! Link this with planck's radiation laws and you get ENORMOUS amounts of energy. Then, substitute these laws with near-field radiation laws and the energy radiated is ASTRONOMICAL .

The potential is there.

 

Log in or Sign up to hide all adverts.

Yeah- E=MC2.

 

Log in or Sign up to hide all adverts.

Log in or Sign up to hide all adverts.

The second law of thermodynamics is empirical, not absolute. There are fluctuations in the second law described by 'fluctuation theorem'. In these cases violation of the second law is spontaneous even at room temperature.

 

Just out of curiosity, what if I put a random room-temperature object in a box that's lined with IR-active photovoltaic cells so as to catch the black-body radiation coming off the object?

 

In theory this should produce electricity.

However, there are other parameters such as the temperature of the box that have to be included. The band-gap of the photovoltaic cell is also important.

But because thermal radiation at room-temperature is weak, and because infrared photovoltaics are not well developed you could get more energy by building a solar cell using the same money.


In theory it seems to me that this box (as long as it is at room temperature) would be producing electricity whether or not there was any object in it due to thermally-induced electron-hole recombination.

This thermally-induced recombination accounts for the noise that many infrared sensors experience. Most of the time sensors have to be cooled in order to be precise.

 

Yes, of course. My point is that it seems like a way ot convert ambient heat into usable energy, which isn't supposed to be possible, so I assume I'm probably missing something.

Actually forget the box, suppose I just lay an IR active photocell that's connected to a battery on the floor, so it starts absorbing the black-body radiation of my surroundings. Am I not converting ambient heat into usable chemical potential energy? If I have a battery with an infinite capacity and leave my photocell there for an infinitely long time, can't I convert ALL of the thermal energy in my surroundings into stored energy in this way? (assuming I'm in a closed system)

 

Assuming you are in a closed system (where the sun won't engulf your photocell after several billions of years) I would say this is possible to a certain extent. However, once enough energy is absorbed the temperature of the earth will be lowered to the point where your photocell would not be able to harness the photons produced through thermal radiation.

I do not think ambient heat conversion is impossible.

Please Register or Log in to view the hidden image!

Thermal radiation is produced by nano-fluctuations in the energies of single molecules. Even the wikipedia says:
"Thermodynamics is a theory of macroscopic systems and therefore the second law applies only to macroscopic systems with well-defined temperatures. For example, in a system of two molecules, there is a non-trivial probability that the slower-moving ("cold") molecule transfers energy to the faster-moving ("hot") molecule. Such tiny systems are not part of classical thermodynamics, but they can be investigated by quantum thermodynamics by using statistical mechanics. For any isolated system with a mass of more than a few picograms, probabilities of observing a decrease in entropy approach zero.[3]"

 

Yes you are. The loss of energy removed from the radiating box will cool it assuming the surrounding are cooler. It is just the same as if you placed it in thermal contact with these cooler surroundings. If however, the surrounding are at the same temperature as the radiating box, then they will be radiating to the box and the net flux between then in the space separating them will be zero. (No net transport of energy either way.)

Now in addition to temperature's fourth power law controlling the rate of IR photon leaving there is also the surface characteristics called "emissivity," (often "e" is used to represent it.) or absorption "a" (e & a are identical coefficients). I.e. e = a but one must understand that this is true wave length by wavelength. Thus, a given surface can have near unity e and a at one wavelength and near zero at another.

If we assume, for this discussion that the box and walls are not transparent (t = 0 ) and call the reflection probability "r" the generally true relationship
e+r+t = 1 (or a+r+t =1) colapse to a+r =1

Assume that the walls and box have come to the same temperature. Now as the walls and box inside them are different one can have a large and the other e small. Thus, if box has large e (or a as they are the same) and the walls small a (or e) then the r of the box is small and the r of the walls high. So the box will be radiating many more photons per unit area than the walls. However when they come to the walls most will be reflected as there r is high.

Likewise as the walls have low e, they do not radiate much. If you ask how many photons are coming away from the walls surrounding the box (both those reflected and those radiated by the box) you have that same answer as if you had asked how many are leaving the internal box. I.e. there is no net transport of energy either way when the temperature is the same.

If the temperature is not the same then no matter what the choice of surface a and r you have made or whether or not they are vastly different as in the case of the prior paragraph or not, there is a net radiative transfer of energy from the hotter surface to the colder one.

Unless you believe that energy can be created, instead of conserved, this thread is nonsense. The walls, no matter what they are made of (photo cells included), will come to the temperature of the box they contain (assuming that the walls have perfect external insulation or are contained in an even larger set of walls at the same temperature). Then as explained in detail above there is an equal flux of photons going between the central box and the walls with ZERO net energy being exchanged.

If this were not true, then the one (walls or box) which was absorbing more photons when both were at the same temperature would become hotter. Then one could operate a heat engine between them and produce unlimited quanties of energy - this should convince you it is necessary that there be no net exchange of energy between the box and the walls surrounding it, even if you do not know any thermodynamics.

SUMMARY: This thread is nonsense. Ambient energy cannot be converted into useful energy if there is not some colder surface. If there is a colder regions to absorb heat then only the fraction {1 -(t/T)} can be converted into useful energy and the fraction (t/T) is converted to heat at the lower temperature, t. (T is the higher temperature source of energy.)

PS James R said the same in post 3 with less detail in his post and not quite so bluntly.

 

You did not gvie the Wiki link so I can not be sure, but bet you added the two words (hot and cold) I made bold above. Wikï makes many errors, but this one to too gross even for Wiki. The slow molecule is not "cold" - it has less kinetic energy than the fast moving one. The concept of temperature is nonsense if applied to single atoms.

If you did not add these words, then this is just another example of Wiki seriously misleading its readers. What is the link?

 

Well yes, if it was widely believed that converting ambient heat to electricity is possible we wouldn't even try solar panels. Unfortunatley the second law of thermodynamics seems to make such a process impossible and so most people do not even consider it. After an in-depth analysis it should be clear that thermodynamics is not permenently violated. I am saying that in the long run entropy will be created even with ambient heat conversion, as a direct response to the process of converting enthalpy to electricity.

http://en.wikipedia.org/wiki/Second_law_of_thermodynamics#Microscopic_systems
it seems that the words are already there. Indeed, single molecules do not radiate thermal energy, but when they collide with each other quantum mechanics does allow for thermal radiation. I would say that temperature on the monatomic scale can only be defined as kinetic energy.. it is not established in science as of yet

Please Register or Log in to view the hidden image!

I agree with you that the box lined with infrared photopanels would thermally equalize with the object inside of it. Also, if the emissivity was the same for the panel as the object inside of the box, the rate of photon emission would likely be the same (planck's laws are very hard to violate, but there have been claims of it being done using photonic crystals).

However, the energy for this emission may come from different sources. The object in the box would only radiate its thermal energy. The photopanel could radiate either from it's thermal energy, or from it's electron-hole pairs recombining (both sources of potential energy).

The fact that electron hole pair recombination generally produce one wavelength (the wavelength of the band-gap) makes it likely that a semiconductor radiates from its thermal energy rather than electron-hole pair recombination. If it was in fact electron hole pair recombination one should note a very strong peak in thermal radiation at the wavelength of the bangap in most semiconductors. I do not have the data, this is only a speculation. I could be wrong. Recombination does indeed interact with heat in the form of phonons.

So, the objects could be at the same temperature and radiating equal amounts of thermal energy, with energy still leaving the box. Extra energy would be taken from the environment (this is Ambient Heat Conversion after all). Conservation of energy is very much respected.

 

This won't work. Let's look at three cases.

1. The photocell is initially warmer than the surroundings,
2. The photocell is in thermal equilibrium with its surroundings, and
3. The photocell is initially cooler than the surroundings.

In case (1), the photocell will emit more photons than it absorbs. The photocell will drain power from the battery. In this case the photocell acts as a (terribily inefficient) flashlight. This is definitely not a way to collect energy from the surroundings.

In case (2), the photocell will emit and absorb the same amount of thermal radiative energy. If the photovoltaic process was 100% efficient, nothing of interest would happen. Since the photovoltaic process is less than 100% efficient, this situation represents a slow way to drain the battery. So, still not a good situation for collecting energy from the surroundings.

In case (3), the photocell will emit less energy than it absorbs. It will initially convert some but not all of the incoming photons to electricity. The remainder will warm the photocell up to ambient temperature, eventually bringing the cell up to ambient temperature. See case (2) above.

Suppose you keep the photocell cooler than the ambient temperature. The photocell will then continue to convert incoming radiation to electricity. Problem solved, right? Wrong. It takes energy to keep the photocell cooler than ambient temperature. The only source of energy available is the energy stored in the battery. Since no process is 100% efficient, this still represents slow way to drain the battery.


Photocells work because sunlight is essentially blackbody radiation from a temperature source that is a whole lot warmer than ambient temperature.

Nonsense. See the above.

 

I'm not saying you're wrong, but this doesn't seem to jive with my understanding of how either semiconductors or radiant cooling work. What exactly is the mechanism by which the radiant cooling of the photocell will drain the battery?

I understand that if the solar cell is warmer than its surroundings it will undergo radiant cooling until it gets back into equilibrium with its surroundings, but the energy source for that radiant cooling would seem to be not the battery, but rather the vibrational excited states in the material.

Draining the battery to emit light would imply that the electrons and positive holes in the depletion region of the photocell are recombining. My understanding of how p-n junctions work is that as the temperature decreases, the depletion region will get bigger and the density of the excess electrons and holes will get smaller, leaving you with the same overall number of electrons and holes on each side of the junction, assuming that both sides of the depletion region cool evenly. (You can cause electron/hole recombination and emit light/drain a battery if you have a temperature gradient across the depletion region, but there's no clear reason why you would necessarily have such a gradient.)

Edit:
Intuitively it seems to me that as the photocell captures ambient thermal radiation and stores the energy in a battery, the temperature of the entire system would decrease. In order for that to not happen, there needs to be some mechanism by which the energy stored in the battery (or capacitor, or whatever) will drain out to replace the energy that is lost when the photocell captures an IR photon and uses its energy to charge the battery. In other words, there needs to be some mechanism by which the energy in the battery will be converted back into heat at the same rate that the photocell adds energy into it. The nature of that mechanism is what I'm confused about.

 

This is my response exactly. Electron-hole recombination is not the only source of energy for thermal radiation in this case. Due to the electric field inside of a photo panel, negative electrons will drift away from the negative 'N' junction as soon as they are generated. This may lead to a lower rate of recombination.

As an example, I will use infrared photo detectors.
http://en.wikipedia.org/wiki/Infrared_detector
Here it says that photovoltaic detectors have to be cooled, but only to reduce noise. If you wanted to harvest energy, this noise wouldn't matter very much. On the whole page, re-radiation was never mentioned.

To Nasor:
The idea is that you plop down a unit in your back yard and connect it to you house. Assume that any electricity you do not use in the house is released back as heat.

In this house, you will have lots of things that use energy - lightbulbs, computers, refrigerator, microwave, etc. All of these essentially turn electricity back to heat.

This way, it get colder in your back yard and warmer in your house. The house loses this heat just like any other heat, by releasing it into your back yard.

This could, perhaps, on a very large scale, lead to negative environmental consequences.

 

Indeed, I came to this conclusion before. But this would lead to some more interesting conclusions. In this case, it would seem that the physical world is incredibly inter-connected, to the point where the base parameters of even a semiconductor are linked to the 2nd law of Thermodynamics. Most laws are not this exact.


My counterpoint: earth's radiation is essentially the sun's radiation re-radiated. Photons have the tendency to try to escape from wherever they are held down as heat. . . like the sun. The sun is radiating. The earth intercepts some of this re-radiation, adding a bit of its own thermal energy to the mix of photons emitted. This radiation is also trying to escape from the earth. Think of this device as some sort of 'sail' that tries to capture this never ending flow of radiation.

 

D.H. has already give adequate reply to both DRZion and Nasor, both of whom are mainly working from their intutions but DRZion has been searching and posting also recently. I will repeat part of my post 9 and expand it to sepcifically speak of band gap solids: In post 9 I said:

"... there is also the surface characteristics called "emissivity," (often "e" is used to represent it.) or absorption "a" (e & a are identical coefficients). I.e. e = a but one must understand that this is true wave length by wavelength. Thus, a given surface can have near unity e and a at one wavelength and near zero at another. ..."


Now a photon with less than the band gap energy lacks the needed energy to promote an electron from the valence band up across the band gap energy into the conduction band where it is free to move so the absorption coefficient for that wavelength is low. Likewise e is low as it is always the same as a for the same wavelength. However only a small decrease in wavelength (increase in photon enegry) will greatly increase both a & e. I.e. now the slightly more energetic photon can lift bound electron up to the conduction band. Thus the photo electric cell is very "black" for photons of or a little above the band gap energy; however this also means that for those wave length it is an near perfect emmitter of radiation. If you like you can say that some electrons in the conduction band and near its bottom are falling down into the valence band. However, these must be a hole (unoccupied energy level) there for them to fall into and become bound.

At any normal temperature found on Earth there are these holes being constantly made thermally. If the PV cell is warmer than the box you are trying to collect IR energy from, the energy flow is going the other way - i.e. from the PV cell to the box as at the band gap energy the PV cell is essentially a black body radiator an that is the maximium possible radiation for that temperature. As it is unlikely that the box has near unity e at that wavelenght even if the box were at the same temperature as the PV cell, there would be a net flux of band gap photons from the PV cell to the box (if we were to neglect those that left the PV cell, went to the box and reflected backoff the box surface.) But of course the actual flux coming off the box does include the both those emitted by the box and those reflected by the box.

Thus when any two bodies are at the same temperature, as I explained in detail in post 9, THERE IS NO NET ENERGY TRANSPORT BETWEEN THEM.* Without any net energy flux from the box at any wavelength when they are are the same temperature, how do you expect there to be energy sent to the PV cell by the box? This is the last time I will explain why this thread is nonsense.
-----------------
*There is a well known and very clever conceptual attempt to violate this, known as "Maxwell's Demon." - It takes some very careful analysis to prove in detail (not just an appeal to the laws of thermodymanics) that this Demon too does not permit two chambers initially at the same temperature to divide in to one hotter than the other.

If that were possible, one could run heat engine forever on the sustainalbe temperature difference, so everyone knew the demon could not do his job, but it is hard to quantatively demonstrate in detail why a "Maxwell's Demon" approach is not possible.

 

Well then, I stand totally rebutted.

Please Register or Log in to view the hidden image!

Given that this idea will revolutionize the air conditioning industry, I suggest that you try to patent your device. I also suggest that you build a working copy first because the patent office will reject your claims out of hand if you don't have a working copy. They have these silly bureaucratic, conspiratorial rules that discriminate against patents on over-unity devices.

One last thing: I suggest you google the term "dark current".

Here is one search result, from google books:http://books.google.com/books?id=5P...s62yCQ&sa=X&oi=book_result&ct=result&resnum=4

Edit:
Billy T, I was not replying to your post when I sarcastically said that I stand totally rebutted. I was replying to the two who are posting nonsense.

 

No you still do not get it. It is so "inter-connected" in ALL CASES. It is not something special about PV cells. It true of all substances that a = e for any and all given wavelengths; True of popcorn, true of pennies, true of nails, true of water, true of X.

If there were ANY substance for which, at the same wavelength, the coefficient of absorption did not exactly equal coefficient of emission then what this thread is trying to suggest would be possible and net enegy could be produced from nothing (in a closed cycle , for example)

This actually follows from the reversibility in time of the processes envolved in emission and absorption. I.e. emission is time reversed absorption - like a movie played backward does not have different scenes.

 

Well fuck, I apologize for trying to learn something.

 

No apologies needed. You did learn something, didn't you?