Does physics forbid such a device; a heat destroyer

Drakkith

Deeviant I have no idea what you are trying to get at. A heat engine converts thermal energy into work, as you said. However this also necessitates the conversion of that energy into other types of energy as well, otherwise no work could have been done.

Deeviant

I repeat:

In other words(2nd law of thermo says...):

1. In any isolated system, one cannot create new energy (first law of thermodynamics)

2. The output power of heat engines is always smaller than the input heating power. The rest of the energy is removed as heat at ambient temperature. The efficiency (this is the produced power divided by the input heating power) has a maximum, given by the Carnot efficiency. It is always lower than one

3. The efficiency of real heat engines is even lower than the Carnot efficiency due to irreversible processes.

The statements 2 and 3 only apply to heat engines. Other types of engines, which convert e.g. mechanical into electromagnetic energy, can, in principle, operate with 100% efficiency."
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In the ionic gas and nano-magnetic structure example, heat can simply be looked as mechanic energy(the ions are moving, that's all heat is, the more heat, the higher the average kinetic energy of the ions). The ions are moving, a moving charge creates a magnetic field(a moving magnetic field), somehow* the moving charges are channeled or in some way pass by the conductive surface of the chamber,the interior of the chamber could consist of some sort of porous material that exposes a huge amount of surface area to the gas, thus converting some of the energy into electric current reducing the kinetic energy of the ion, thus the average kinetic energy of the ion gas, thus the heat of the system.

In this case, other that circuit/voltage/etc losses the conversion is 100% efficient, no energy is required to reduce the heat of the system as others have said in this thread before. No laws of thermo have been broken as still others have asserted.

The question is this: the ion goes through the channel, loses some of it's energy which it is converted into electrical current and continues to bounce around until it is runs past another conductor, has some more of it's kinetic energy converted into electrical energy and so on, until it reaches some limit, of which I do not know what is the limiting factor, what part of such a mechanism is disallowed by physics?




*one assumption made is that any engineering issues can be assumed to be solved, as long as they do not violate fundamental laws.

Drakkith

The general idea is feasible, however I don't see how this applies to your device in your original post. This requires charged particles, so unless you are going to place it next to a star you're going to have to use energy to ionize whatever you want to use for power.

Deeviant

That's an engineering problem. One idea is that it could simply be proton gas. If it is held in a vessel constructed of a material jealously holds on to it's electrons, the gas only needs to be create once, captured and contained within the machine.

DaleSpam

You have already stated that you are converting thermal energy into other forms. That conversion is limited in efficiency by the Carnot limit.

The fact that other types of energy can be converted with 100% efficiency does not get you around the limit. If you want to convert heat to electrical then you hit the Carnot limit converting heat to mechanical and then 100% conversion to electrical, with the net result that heat to electrical is limited to the Carnot efficiency. Similarly with any other form of energy.

If you are converting it from thermal energy then the best you can do is the Carnot limit. That is the second law of thermo. That is the laws of physics as we currently understand them.

Btw, your ion idea is essentially a variant of Maxwells demon:
http://en.wikipedia.org/wiki/Maxwell's_demon

Deeviant

I actually like that direction and I think that is valuable feedback, although I disagree on two fronts:

1.) Thermal energy is mechanical energy, the theoretical device would convert the kinetic motion of the the ion gas into electrical energy. This type of conversion does not obey the laws in which you are stating it does(the term "carnot limit" doesn't seem to be defined btw, perhaps you are talking about carnot efficiency? Which does not apply to mechanical -> electrical energy conversion).

Specifically, the 2nd law of thermo is talking about heat transfer and of entropy. It is not a general description of "everything there is to do with heat"(see the wiki article I already cited, twice, it's fine if you feel it is wrong, but I love to see you prove it wrong). The type of system you are trying to force onto this idea is a system in which heat is converted into mechanical energy(although heat is mechanical energy and what were actually talking about is a system in which turns the mechanical energy of heat directly into work) which is then converted into electrical energy.

You can not refute my point that heat inside "the machine" can be described by the average kinetic energy of the ion gas, which in turn, is mechanical energy. The only thing thermo says about such a conversion is that you can not create energy with such a conversion, Carnot efficiencies are ilrelevant(see quoted wiki article and prove it wrong, or me wrong I guess, but please don't just ignore it), it is not a "heat engine".

2.) Maxwell's demons is about entropy. In the Maxwell's demons case, entropy is reduced. I think this would be the most valid observation, one that I have to think about and study more before I can intelligently respond to. But my first response is that the "heat destroy" is perfectly happy not getting any work out of the heat, and it is also perfectly happy re-radiating the heat in the form of electromagnetic radiation, a case in which would certainly not result in lower entropy.

Drakkith

I know of no such material. Why not invent one for your story?

DaleSpam

I don't feel it is wrong. I feel you are misunderstanding it. It doesn't support the point you are making. Specifically, that you can get energy out of heat more efficiently than the Carnot efficiency limit. If you would read it correctly you would realize that the only point where it talks about exceeding the Carnot limit specifically refers to OTHER forms of energy, not thermal.

It is a heat engine, it is taking disorganized microscopic KE (thermal energy) and converting it to organized macroscopic energy. That is a heat engine. I am sorry if you don't like it, but that is how it is understood by current science.

Lowering the entropy of the energy is exactly what you are trying to do. You want to take it from high entropy thermal energy to low entropy EM energy. That IS a change in entropy. Your proposal to reduce entropy with devices sensitive to the microscopic motion is precisely the key idea in Maxwell's demon. Also, EM energy does have an entropy, so if you are re-radiating it with any spectrum different from the original black-body spectrum then you are decreasing its entropy.

TobyC

Reservoir is just a fancy term for wherever it is that the heat is. There must be at least one reservoir in your example, and that is just the system you are removing heat from. I'm not clear whether that is the machine itself or something external that you attach the machine to, but you have at least one reservoir in your example. You don't talk about a second reservoir, but as I explained, that doesn't matter. The same thermodynamics still applies. Once you have converted the heat from your one reservoir into some other form of energy there would then be nothing stopping you using it to heat up a hotter reservoir, and that most definitely violates the 2nd law of thermodynamics. You can't be left with the option to do that, and you in fact aren't.

It's true that objects above absolute zero emit blackbody radiation, but they also absorb radiation. If they are put near a hotter body then that too will be emitting radiation and although at the microscopic level you could trace heat moving both ways between the two systems, at a macroscopic level all you observe is a net transfer of heat from the hotter body to the colder body, because the hot body emits more than it absorbs while the cold body absorbs more than it emits.

The machine you have described is not compatible with the 2nd law, that seems to be the question you came here to ask and it has been answered by different people. A neat way around it seems to be the putting it in thermal contact with deep space idea.

I see in some later posts you've claimed that heat is just mechanical energy and that you're allowed to remove that. But just because heat is mechanical energy at a microscopic level does not mean that it is not still heat. Heat doesn't really describe a 'type' of energy in the same way that the words 'kinetic' and 'potential' or 'mechanical' and 'electrical' do. Heat is (essentially) just a word used to describe energy in any of these forms which is distributed randomly. That's what makes it heat. By converting this randomly distributed energy, heat, into a non-randomly distributed form, as you want to do, you are lowering the entropy of your system, and this violates the 2nd law unless you raise entropy somewhere else, which can be done by putting more energy in or dumping the heat in an even colder reservoir. You seem to want to avoid both those things, which makes your machine impossible according to the currently understood laws of physics.

Ok so do you accept that if you did get work out of your machine, then it would be a heat engine and would violate the 2nd law?

The only other alternative is you leave the energy as heat and dump it somewhere else, by radiating it for example. But you have to dump it somewhere, and that somewhere will have a temperature. If you want to avoid putting extra energy in to power your machine, the only way this process is allowed is if the place you are dumping the heat has a lower temperature than the system you are extracting the heat from. That is required by the 2nd law. If you could do what you are describing then that certainly would lower overall entropy.

6.28318531

What about something based on this; '
http://phys.org/news/2011-06-quantum...s-entropy.html

mfb

Thermal energy is unordered mechanical energy. It is the only energy form discussed here which corresponds to a high entropy.

Converting high-entropy thermal energy to low-entropy energy (electromagnetic, moving macroscopic objects, ...) and nothing else would decrease entropy and therefore violate the second law of thermodynamics. This is very fundamental and does not care about the specific way the energy is stored. Your device needs some entropy dump. If you want to generate useful energy, this has to be a low-temperature material (where the entropy to energy ratio is even larger) - radiators in spaceships.


@[itex]\tau[/itex]: You cannot continue to "delete" data (which actually looks like the opposite - get more knowledge on the tape) without reversing the process sometimes.

NdotA

As to the physics involved with such a machine I think everything is said before.

But here, as I understand it, we are talking about SciFi story that is placed some considerable time from now. Maybe the technology is advanced in those future days to place the colder reservoir in the past or in the future ? Would contribute to some climatical effects then.

I fear, if you need such a machine in the plot of your story you will have to enter some 'improbabilities' that would strain the current view on physics to some extent.

QuantumPion

It is possible to use magnetic fields and lasers to cool atoms to very close to absolute zero. However, the electricity required to run those is obviously greater than the heat energy removed from the molecules. The source of that power generation would ultimately have to dump waste heat into its environment.

Darwin123

What you are missing is that there is no specific form of energy that is called heat. Furthermore, there is no specific form of energy called work. You can only use Carnot's formula if you know which packets of energy are called heat and which are called work.
In your example, you discriminated between kinetic energy that is heat and kinetic energy that is not heat. You claimed that the kinetic energy going in was heat. Furthermore, you are not telling us whether the electric current going out is also heat. Maybe the electric current going out is still heat.
Heat is energy that is transferred on a macroscopic scale by heat conduction. Heat is the temperature times the change in entropy. The designation heat has nothing to do with what form the energy takes on an atomic level.
I assume your machine absorbs heat by heat conduction. I will also assume that the electric current is work. By Carnot's theorem, it is impossible to turn all the energy absorbed by heat conduction into work.
So basically, your machine can't work because of the Second Law of Thermodynamics. If the second law is correct, you can't make a machine that automatically takes all the energy that comes into it by heat conduction and turns it into something else.
If the energy does not enter by heat conduction, then the energy is work. One form of work can be changed into another form of work. However, such machines already exist.
The weasel word here is "heat". "Heat energy" is conceptually ambiguous because heat is not a perfect differential. On an atomic level, heat is a mixture of many types of energy (kinetic, potential, etc.) So the minute that you say "kinetic energy that is heat", you run into an ambiguity.
Ahh, but that doesn't solve your literary problem. You are looking for some techno-babble that would sound plausible to a scientist. One thing you must avoid in a fantasy is ambiguity. Real life may be ambiguous, but at least it is real. A fantasy has to be extra specific to make up for the fact that it is a fantasy. Ambiguity can only weaken a SF story. I suggest that you describe your device in terms of entropy rather than heat energy.
Entropy is actually better defined than heat energy. Entropy is a perfect differential. Entropy acts a lot like an indestructible gas, where temperature is the pressure of the gas. I recommend that you hypothesize what the machine does to the entropy, rather than hypothesize what what the machine does to the heat energy. Whether or not your concept is viable, you will have avoided ambiguity.
The phrase "heat energy" is always ambiguous. Avoid it in science and in literature.

Deeviant

"A neat way around it seems to be the putting it in thermal contact with deep space idea."

This doesn't make any sense to me. You can not be in "thermal contact" with deep space, there is no contact with space, there is is no thermal interaction between the two at all(or am I missing some subtly here.) Or are you trying to just say put it in space and let it lose it's energy via black body radiation(I've asked this question several times regarding this and never got an answer). This would work equally well anywhere has sufficiently low ambient temperature, deep space has nothing to do with it.

mfb

Radiators can exchange thermal energy with deep space. As they are usually much warmer than 3K, their blackbody radiation as emission is a good description of this "exchange". Close to stars, you have to consider the stellar radiation, too.

DaleSpam

Yes, you can, I don't know why you keep on making this incorrect assertion when I have corrected it multiple times. If you could not be in thermal contact with deep space then the earth would be as hot as the sun since it couldn't get rid of all the heat that the sun dumps on it, and the earth wouldn't cool off at night.

While it is losing energy via blackbody radiation to deep space it is also gaining energy via blackbody radiation at 2.7 K from deep space. That is thermal contact with deep space.