Does physics forbid such a device; a heat destroyer

[Deeviant]

Hello physics forum crew, I would like some help coming up with one of those "is this possible" type questions.

Basically, I'm writing a sci-fi story that is has the strict limitation that all technology must be feasible within the laws of physics as we currently know them. However, there is some leeway as you can assume that man has advanced our technology for many thousands of years and might find a way to use old physics any new ways.

Anyways, the question is this: can a "heat destroyer" be made?

As I define it, this device takes simply converts heat into some other form of energy, either EM or perhaps electricity. Of course, this can already be done in many ways today, but what we're talking about is a matter of degree. The amount of power it generates is not important, nor is the efficiency, but the important part is it can do so "infinitely" i.e. you turn the device on and it brings itself to near absolute zero, I suppose a somewhat higher minimum cap is ok. Another limitation is, other than the heat, it can't be fed any other energy, except maybe for some control or other higher level stuff, but the key here is it's not like you have to feed this thing a huge amount of energy for it to work, it just "eats" the heat.

My only lead is the carnot's work, perhaps the formula making clear that close delta T's make for very little work.

But it it specifically talks about work and efficiency. I can't find a way to use the limit to definity rule out such a device.

Any input is much appreciated.

Thanks!

 

[Muphrid]

I suggest looking at http://en.wikipedia.org/wiki/Coefficient_of_performance to get an idea about the theoretical limits on a heat engine being used to cool a reservoir. The bottom line is that it takes an infinite amount of energy to get all the way to absolute zero, but you can get arbitrarily close with merely finite amounts of energy.

Either way, though, you need energy to do this. You're moving heat from a cold reservoir to a hot one. This is like trying to push a ball up a hill. Energy is required to do this. It certainly can't suck all the heat out of a region and produce energy in the process.

Rather, perhaps the solution to your problem is to use the concept of negative temperature. A system with a negative temperature is actually hotter than any system with a positive temperature, and heat will naturally want to flow from it to a positive temperature reservoir. Thus, the usual concepts of a heat engine producing energy apply--it makes the negative temperature reservoir colder and yet it extracts heat from the system and can do work.

The downside is that most systems don't experience negative temperatures. You couldn't apply this idea to any arbitrary material or reservoir of gas, only very specific objects that could experience such a phenomenon.

 

[Deeviant]

I can see where you are coming from, but I don't think that answers the fundamentals for this problem.

It isn't a heat exchanger problem. The primary thought here is that the is machine converting heat to another form of energy, and can do this "perfectly", so any kinetic energy in the form of heat that hits the business end of this machine is converted to electric current. Converting energy from one form to another doesn't exactly "take" energy, but there are losses; so the question is does physics disallow the converting of increasingly up to (nearly)infinitely smaller quanta of kinetic energy.

Here's an example: let's say you you have some sort of exotic "gas", let's not worry too much about what the gas is, but it's some sort of monoatomic or subatomic ion or subatomic particle, the gas is contained within some sort of nano-mechanic system that is basically is series of nano-magnetic structures in a conductive matrix. Every time a ion passes through the field it would general some(very small) amount of current, and loss some of it's kinetic energy, as it successive passes through more nano-magnetic structures, it would lose all of it's energy. I can't find a specific law that would forbid this time of system.

Or am I missing something?

 

[johnbbahm]

Within the right conditions you might be able to get a blend of gasses to absorb a select
spectrum of heat, and then other gasses in the blend radiate it in a different spectrum.
This may not sound like much, but a microwave oven does this in reverse. (A narrow spectrum heats the water molecules, which then transfer the heat to other portions of the heated object.
Also look at the breaks on a modern locomotive. The drive motor is reversed and the current generated is converted to heat via a resistor. The large resistor is air cooled.
So no wearable parts!

 

[TobyC]

You can't convert heat into any other form of energy freely without putting something (energy not in the form of heat) in. It is impossible for any machine to just take heat from a reservoir at a single temperature and convert it into work, that's one way of stating the 2nd law of thermodynamics.

Imagine you could do what you're suggesting, then if you wanted you could put your machine in a cold reservoir say and turn loads of its heat into some form of work, say making a wheel rotate. You can then use this rotating wheel to drive a conveyor belt in a hot reservoir against friction, producing heat in the hot reservoir and raising its temperature. You have now built a machine which takes heat from a cold reservoir to a hot reservoir at no cost, and that is definitely forbidden.

I know you don't talk about two reservoirs in your example, but once you've turned heat into work, there's nothing stopping you from turning it back into heat again and dumping it wherever you want to, and nature can't give you the option to do that or you'd violate the 2nd law in the form it's more usually stated in.

I think that's right anyway, if I've understood what you're saying right and thermodynamics right.

 

[Deeviant]

You can't convert heat into any other form of energy freely without putting something (energy not in the form of heat) in. It is impossible for any machine to just take heat from a reservoir at a single temperature and convert it into work, that's one way of stating the 2nd law of thermodynamics.

I'm not sure I agree. Conversion does not "take" energy, but there are always losses. A photovoltaic cell for instance, converts light into electrical energy. It doesn't take any energy other than the photon striking the cell in order to generate the electricity, although some of the energy is converted into heat, rather than electrical energy. The loss can be reduced considerably, for instance if the wavelength of the light carried exactly the energy required to knock the electron into the conduction band and if the circuit was super conducting; in this case the vast majority of the energy of the photon would be converted into electrical energy, without any outside force.

I am also not sure I understand your second example, but if I understand it correctely, in your example the transfer was not "for free" as the temperature of the cold reservoir decreased, energy was taken from it and not all of it was transferred to the hot reservoir as there would certainly be losses due to friction, entropy, etc, so it is doubly not for free.

 

[Dale]

I can see where you are coming from, but I don't think that answers the fundamentals for this problem.

It isn't a heat exchanger problem. The primary thought here is that the is machine converting heat to another form of energy, and can do this "perfectly", so any kinetic energy in the form of heat that hits the business end of this machine is converted to electric current. Converting energy from one form to another doesn't exactly "take" energy, but there are losses; so the question is does physics disallow the converting of increasingly up to (nearly)infinitely smaller quanta of kinetic energy.

Here's an example: let's say you you have some sort of exotic "gas", let's not worry too much about what the gas is, but it's some sort of monoatomic or subatomic ion or subatomic particle, the gas is contained within some sort of nano-mechanic system that is basically is series of nano-magnetic structures in a conductive matrix. Every time a ion passes through the field it would general some(very small) amount of current, and loss some of it's kinetic energy, as it successive passes through more nano-magnetic structures, it would lose all of it's energy. I can't find a specific law that would forbid this time of system.

Or am I missing something?

I would suggest a much simpler resolution. Just have your device somehow be in thermal contact with deep space. Then your Tc is just 2.7 K. It isn't "perfect", but it is pretty close, and it is the kind of thing which doesn't violate any known laws of thermo. You can sweep the details about how the device is in thermal contact with deep space under the "future tech" rug.

 

[TobyC]

I'm not sure I agree. Conversion does not "take" energy, but there are always losses. A photovoltaic cell for instance, converts light into electrical energy. It doesn't take any energy other than the photon striking the cell in order to generate the electricity, although some of the energy is converted into heat, rather than electrical energy. The loss can be reduced considerably, for instance if the wavelength of the light carried exactly the energy required to knock the electron into the conduction band and if the circuit was super conducting; in this case the vast majority of the energy of the photon would be converted into electrical energy, without any outside force.

No that part of my post I am certain of. There are only two ways of taking heat out of a reservoir, or 'destroying' the heat to use your terminology. The first is if you have an even colder reservoir handy, in which case just put the two in contact and it will happen. If you don't have that then the only possibility you have left is to use a heat pump where you take the heat from your reservoir and dump it still as heat in a hotter reservoir, you also have to then put yet more extra energy into do this which is why freezers need to be plugged in. The greater the difference in temperatures, the more extra energy you will have to put into power your heat pump. Those are the only two ways of getting rid of heat. It is impossible to do it without a second reservoir, you can't simply convert heat to some form of energy that isn't heat at no cost, for the reasons I outlined in my first post.

I am also not sure I understand your second example, but if I understand it correctely, in your example the transfer was not "for free" as the temperature of the cold reservoir decreased, energy was taken from it and not all of it was transferred to the hot reservoir as there would certainly be losses due to friction, entropy, etc, so it is doubly not for free.

Well if your machine worked there would be nothing in principle stopping my example from being 'for free'. All those little losses like friction all end up as heat, and so even the losses are heating up the hot reservoir while cooling the cold reservoir, which shouldn't be allowed. Even if it did only transfer 1% of the energy to the hot reservoir and the rest somehow found its way back to the cold one, that's still a result that is forbidden by the 2nd law, because a process has occurred which has the sole net result of taking some heat from a cold reservoir and transferring it to a hotter one.

I really like DaleSpam's suggestion though, that seems like a really neat way of building exactly the machine you want to build.

 

[Deeviant]

I would suggest a much simpler resolution. Just have your device somehow be in thermal contact with deep space. Then your Tc is just 2.7 K. It isn't "perfect", but it is pretty close, and it is the kind of thing which doesn't violate any known laws of thermo. You can sweep the details about how the device is in thermal contact with deep space under the "future tech" rug.

This is actually won't work. You can't be "in contact" with deep space, there is nothing to contact with. Although the average temperature of deep space probably what you state, it is not very effective at thermal dissipation, the (pretty much)only way an object cools off in space is via black body radiation. Thus a spaceship with a very energetic power source, let's say a fusion generator, would actually have quite a problem, the heat would need to be dissipated and space doesn't help much at all, it has zero thermal conductivity, you would have to construct some rather massive fins, and gain as much surface area on the ship as possible to maximize black body bleed off.

No that part of my post I am certain of. There are only two ways of taking heat out of a reservoir, or 'destroying' the heat to use your terminology. The first is if you have an even colder reservoir handy, in which case just put the two in contact and it will happen. If you don't have that then the only possibility you have left is to use a heat pump where you take the heat from your reservoir and dump it still as heat in a hotter reservoir, you also have to then put yet more extra energy into do this which is why freezers need to be plugged in. The greater the difference in temperatures, the more extra energy you will have to put into power your heat pump. Those are the only two ways of getting rid of heat. It is impossible to do it without a second reservoir, you can't simply convert heat to some form of energy that isn't heat at no cost, for the reasons I outlined in my first post.
Well if your machine worked there would be nothing in principle stopping my example from being 'for free'. All those little losses like friction all end up as heat, and so even the losses are heating up the hot reservoir while cooling the cold reservoir, which shouldn't be allowed. Even if it did only transfer 1% of the energy to the hot reservoir and the rest somehow found its way back to the cold one, that's still a result that is forbidden by the 2nd law, because a process has occurred which has the sole net result of taking some heat from a cold reservoir and transferring it to a hotter one.

I really like DaleSpam's suggestion though, that seems like a really neat way of building exactly the machine you want to build.

You are may be correct about the specifics of thermo dynamics to to heat reservoir but this case does not simplify to the scenario that the thermo that you cite describes. You state that there are only two ways to remove heat from a reservoir, first of all, this problem as stated above, doesn't simplify to a simple heat reservoir; there are many more ways that I can think of off to remove heat from the theoretical machine that I can think of off the top of my mind, I feel this is probably a pretty strong indication the reservoir model doesn't fit well here.

For example, all objects above absolute zero emit black-body radiation. A object that represents the "cold reservoir" in your example would be emitting photons, it is entirely conceivable for a cold reservoir to emit a photon which would then strike the object that represents the "hold reservoir" which is then absorbed and converted into thermal energy. I think this is not the best example, but in the case an assertion is made (that this situation is accurately described by a simple hot/cold reservoir problem) and can be contradicted, the assertion may be invalid.

 

[Dale]

This is actually won't work. You can't be "in contact" with deep space

I didn't say "in contact", I said "in thermal contact". And yes, you can be in thermal contact with deep space. Heat transfer in deep space is via radiation to a 2.7 K thermal bath called the cosmic microwave background radiation.

Although the average temperature of deep space probably what you state, it is not very effective at thermal dissipation, the (pretty much)only way an object cools off in space is via black body radiation. Thus a spaceship with a very energetic power source, let's say a fusion generator, would actually have quite a problem, the heat would need to be dissipated and space doesn't help much at all, it has zero thermal conductivity, you would have to construct some rather massive fins, and gain as much surface area on the ship as possible to maximize black body bleed off.

Yes, that is just an engineering problem, not a fundamental violation of known physics. So you can just sweep it under the "future tech" rug as I said earlier: they develop some elegant way to increase the effective surface area for thermal contact. The point is that it doesn't violate known physics like a "heat destroyer" would.

Look, it is your story. You can accept or reject your "feasible within the laws of physics as we currently know them" rule at your own whim. But what you described simply does not fit that rule. Either the device or the rule has to go, they are incompatible.

 

[Deeviant]

I didn't say "in contact", I said "in thermal contact". And yes, you can be in thermal contact with deep space. Heat transfer in deep space is via radiation to a 2.7 K thermal bath called the cosmic microwave background radiation.

Yes, that is just an engineering problem, not a fundamental violation of known physics. So you can just sweep it under the "future tech" rug as I said earlier: they develop some elegant way to increase the effective surface area for thermal contact. The point is that it doesn't violate known physics like a "heat destroyer" would.

Look, it is your story. You can accept or reject your "feasible within the laws of physics as we currently know them" rule at your own whim. But what you described simply does not fit that rule. Either the device or the rule has to go, they are incompatible.

I haven't seen any evidence that the "heat destroyer" violates physics, nor has anybody presented me with conclusive evidence of such. There was a reason the "heat destroyer" was in quotes, if you read the first post, you would see that it is somewhat of a misnomer because it doesn't set out to destroy heat, we all know that is impossible, but to convert it to other forms of energy.

Going back to your other statement, whether you are "in contact or in thermal contact" is the same thing in this case, there is nothing to be in contact with or in "thermal contact" with. Heat transfer(which is not an accurate term at all for this) is much more accurately said to be as I said it was: energy lost to black-body radiation, I have no idea what you are getting at. You are obviously going pointy-side-up, which frankly is a very bad sign for intelligent discourse, so I very much doubt any productive discourse is to be had between us.

 

[Dale]

I haven't seen any evidence that the "heat destroyer" violates physics, nor has anybody presented me with conclusive evidence of such.

It violates the second law of thermo.

There is a reason the "heat destroyer" was in quotes, if you read the first post, you would see that it is somewhat of a misnomer because we aren't set out to destroy heat, we all know that is impossible, but to convert it to other forms of energy.

A device which converts heat to other forms of energy is called a heat engine. They obey the second law of thermo and it's consequences. Including the equation that you cited in the OP.

http://www.google.com/url?sa=t&rct=...5e3LBg&usg=AFQjCNEL8xQOFVNbAEw6LOJLTB8buZGkCg

 

[Deeviant]

It violates the second law of thermo.

A device which converts heat to other forms of energy is called a heat engine. They obey the second law of thermo and it's consequences. Including the equation that you cited in the OP.

http://www.google.com/url?sa=t&rct=...5e3LBg&usg=AFQjCNEL8xQOFVNbAEw6LOJLTB8buZGkCg

Wrong, a heat engine is, and I quote, "heat engine is a system that performs the conversion of heat or thermal energy to mechanical work"

 

[Drakkith]

Wrong, a heat engine is, and I quote, "heat engine is a system that performs the conversion of heat or thermal energy to mechanical work"

Which converts the thermal energy to another form, such as kinetic energy for example.

 

[jobsism]

I'll give my thoughts on this, but it's up to the OP and other physicists to decide if I'm right (or wrong for that matter).

I'm not a physicist, and I apologise for the potential blunders I might make in the following statements.

A point I'd like to address is that the conversion of energy does indeed involve, or as I might say, "take" energy. Otherwise, there would be a spontaneous interconversion of energy. For example, I possesses chemical energy (please pardon the poor wording;physically this might be incorrect, but you get the idea), and I have a system that readily converts some of this chemical energy to mechanical energy (a bicycle). If it didn't "take" energy for the interconversion, why isn't there a sporadic conversion of chemical energy to mechanical? Without me even attempting to pedal?

Let's take your example: you have plenty of photons (light energy) and also a system capable of converting light energy to electrical energy (a solar cell). Then why doesn't the conversion take place instantaneously? It is imperative that the photons MUST be directed and made to strike on the solar cell, and I believe this involves energy of some sort.

Just my thoughts on the problem.

 

[Deeviant]

Which converts the thermal energy to another form, such as kinetic energy for example.

From the wiki entry on perpetual motion:

"There is a scientific consensus that perpetual motion in an isolated system violates either the first law of thermodynamics, the second law of thermodynamics, or both. The first law of thermodynamics is essentially a statement of conservation of energy. The second law can be phrased in several different ways, the most intuitive of which is that heat flows spontaneously from hotter to colder places; the most well known statement is that entropy tends to increase (see entropy production), or at the least stay the same; another statement is that no heat engine (an engine which produces work while moving heat from a high temperature to a low temperature) can be more efficient than a Carnot heat engine.

In other words:

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."

 

[Dale]

Wrong, a heat engine is, and I quote, "heat engine is a system that performs the conversion of heat or thermal energy to mechanical work"

I would just drop the pretense that you want to stick to the laws of physics as we currently know them. It is clearly not something that you really want to do.

 

[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."
________________________________________________________________________________________________________________

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 question is this: the ion goes through the channel, loses some of it's energy as 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 in which. What part of such a mechanism is disallowed by physics.

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]

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.

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.

 

[Dale]

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.".

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]

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

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]

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.

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

 

[Dale]

see the wiki article I already cited, twice, it's fine if you feel it is wrong

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.

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".

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.

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.

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]

You are may be correct about the specifics of thermo dynamics to to heat reservoir but this case does not simplify to the scenario that the thermo that you cite describes. You state that there are only two ways to remove heat from a reservoir, first of all, this problem as stated above, doesn't simplify to a simple heat reservoir; there are many more ways that I can think of off to remove heat from the theoretical machine that I can think of off the top of my mind, I feel this is probably a pretty strong indication the reservoir model doesn't fit well here.

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.

For example, all objects above absolute zero emit black-body radiation. A object that represents the "cold reservoir" in your example would be emitting photons, it is entirely conceivable for a cold reservoir to emit a photon which would then strike the object that represents the "hold reservoir" which is then absorbed and converted into thermal energy. I think this is not the best example, but in the case an assertion is made (that this situation is accurately described by a simple hot/cold reservoir problem) and can be contradicted, the assertion may be invalid.

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.

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.

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 into 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-knowledge-cools-entropy.html

 

[mfb]

1.) Thermal energy is mechanical energy

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.@$\tau$: 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]

I can see where you are coming from, but I don't think that answers the fundamentals for this problem.

It isn't a heat exchanger problem. The primary thought here is that the is machine converting heat to another form of energy, and can do this "perfectly", so any kinetic energy in the form of heat that hits the business end of this machine is converted to electric current. Converting energy from one form to another doesn't exactly "take" energy, but there are losses; so the question is does physics disallow the converting of increasingly up to (nearly)infinitely smaller quanta of kinetic energy.

Here's an example: let's say you you have some sort of exotic "gas", let's not worry too much about what the gas is, but it's some sort of monoatomic or subatomic ion or subatomic particle, the gas is contained within some sort of nano-mechanic system that is basically is series of nano-magnetic structures in a conductive matrix. Every time a ion passes through the field it would general some(very small) amount of current, and loss some of it's kinetic energy, as it successive passes through more nano-magnetic structures, it would lose all of it's energy. I can't find a specific law that would forbid this time of system.

Or am I missing something?

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.

 

[Dale]

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.

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.

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).

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.

 

[Deeviant]

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.

Multiple times I have asked you if you simply meant that an object loses energy due to black-body radiation, and you have never said "yes that is what I meant", this threw my off course. With further reading, I now understand how you are using the term, and I agree is used correctly and that there is "thermal contact" between objects and space, but I am still completely baffled by your responses. A spaceship is obviously always in thermal contact with space, it happens by default, and in the case, is to not nearly sufficient rate of heat loss, hence the whole idea of the thought experiment in which to create a process that has a faster rate of heat loss. Really, the term "thermal contact", though accurate, is really not helpful at all; speaking directly to black-body radiation rather that "thermal contact" immediately elicits the exact mechanism and even leads to easy finding of the exact mathematical description of the phenomenon (i.e. Planck's law of black-body radiation).

I think the main problem that I have digesting the rather consistent feedback from you guys is that objects already do what I what I want to accomplish here(albeit I want to accelerate the process somehow within the rules the universe has laid out): all objects turn their heat into electromagnetic energy and cast it out into space. It is trivially easy to see then, that converting heat(or whatever you would like to call it) into electromagnetic energy(in this case with 100% efficiency with no outside energy) does not break any laws of physics, this happens everyday; as you read this you are literally using converted heat energy that was converted into electromagnetic energy from the sun. So the cooling of an object by converting it's heat energy into electromagnetic energy without using additional energy is not against the laws of physics, it just isn't, if it was, we wouldn't be here right now.