New approach using nanoparticle alloys allows heat to be focused or reflected just like electromagnetic waves

Jan 11, 2013 by David Chandler
How to treat heat like light
Thermal lattices. Image courtesy of the researchers

An MIT researcher has developed a technique that provides a new way of manipulating heat, allowing it to be controlled much as light waves can be manipulated by lenses and mirrors.

The approach relies on consisting of nanostructured semiconductor alloy . is a of matter—technically, a vibration of the atomic of a material—just as sound is. Such vibrations can also be thought of as a stream of phonons—a kind of "virtual particle" that is analogous to the that carry light. The new approach is similar to recently developed photonic crystals that can control the passage of light, and phononic crystals that can do the same for sound.

The spacing of tiny gaps in these materials is tuned to match the of the heat phonons, explains Martin Maldovan, a research scientist in MIT's Department of and author of a paper on the new findings published Jan. 11 in the journal .

"It's a completely new way to manipulate heat," Maldovan says. Heat differs from sound, he explains, in the frequency of its vibrations: consist of lower frequencies (up to the kilohertz range, or thousands of vibrations per second), while heat arises from higher frequencies (in the terahertz range, or trillions of vibrations per second).

In order to apply the techniques already developed to manipulate sound, Maldovan's first step was to reduce the frequency of the heat phonons, bringing it closer to the sound range. He describes this as "hypersonic heat."

"Phonons for sound can travel for kilometers," Maldovan says—which is why it's possible to hear noises from very far away. "But phonons of heat only travel for nanometers [billionths of a meter]. That's why you could't hear heat even with ears responding to terahertz frequencies."

Heat also spans a wide range of frequencies, he says, while sound spans a single frequency. So, to address that, Maldovan says, "the first thing we did is reduce the number of frequencies of heat, and we made them lower," bringing these frequencies down into the boundary zone between heat and sound. Making alloys of silicon that incorporate nanoparticles of germanium in a particular size range accomplished this lowering of frequency, he says.

Reducing the range of frequencies was also accomplished by making a series of thin films of the material, so that scattering of phonons would take place at the boundaries. This ends up concentrating most of the heat phonons within a relatively narrow "window" of frequencies.

Following the application of these techniques, more than 40 percent of the total heat flow is concentrated within a hypersonic range of 100 to 300 gigahertz, and most of the phonons align in a narrow beam, instead of moving in every direction.

As a result, this beam of narrow-frequency phonons can be manipulated using phononic crystals similar to those developed to control sound phonons. Because these crystals are now being used to control heat instead, Maldovan refers to them as "thermocrystals," a new category of materials.

These thermocrystals might have a wide range of applications, he suggests, including in improved thermoelectric devices, which convert differences of temperature into electricity. Such devices transmit electricity freely while strictly controlling the flow of heat—tasks that the thermocrystals could accomplish very effectively, Maldovan says.

Most conventional materials allow heat to travel in all directions, like ripples expanding outward from a pebble dropped in a pond; thermocrystals could instead produce the equivalent of those ripples only moving out in a single direction, Maldovan says. The crystals could also be used to create thermal diodes: materials in which heat can pass in one direction, but not in the reverse direction. Such a one-way heat flow could be useful in energy-efficient buildings in hot and cold climates.

Other variations of the material could be used to focus heat—much like focusing light with a lens—to concentrate it in a small area. Another intriguing possibility is thermal cloaking, Maldovan says: materials that prevent detection of heat, just as recently developed metamaterials can create "invisibility cloaks" to shield objects from detection by visible light or microwaves.

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User comments : 32

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gblaze41
2.3 / 5 (3) Jan 11, 2013
How about using at as a heat ray?
prof-art
not rated yet Jan 11, 2013
Could these crystals have the ability to cause heat to follow a path downwards(in this case, hot air)? Could it reduce the cost of heating and air conditioning in some way?

Used on microprocessors, made to specification, could it stop any overheating from being possible?

Have you thought about making something similar to a welder by focusing the heat?

Where can I learn more about Phonons?

One more thing, Would it work as a coating on firefighters coats to protect from overheating?
Uzza
not rated yet Jan 11, 2013
I wonder if it would be possible to use this to concentrate the heat to a smaller area, increasing the temperature there.

The specific application would be thermoelectric power plants using steam, where instead of letting steam pass over steam turbines, it is instead moved and concentrated for use in a high temperature cycle like brayton. This would allow you to gain the benefits of higher thermodynamic efficiencies without having to design the entire plant around the higher temperatures.

A perfect example would be nuclear plants, where the higher temperatures would require a redesign of the entire reactor to accommodate a high temperature cycle. If my idea works, only the power conversion part would have to be changed to allow higher thermodynamic efficiency.
italba
2 / 5 (4) Jan 11, 2013
You can't concentrate a low temperature heat source in a higher temperature target. That would be a negative entropy operation.
jade39339
not rated yet Jan 11, 2013
I'm thinking if it is possible to create a plasma gun, converting the heat of the chemical reaction of a standard projectile and transferring the heat into the bullet.
antialias_physorg
4.3 / 5 (3) Jan 11, 2013
You can't concentrate a low temperature heat source in a higher temperature target.

Funny, solar concentrators do seem to work rather well (so well in fact that whole powerplants work on that principle)

The thing about entropy is that you have to remember a couple of things:
- it only always increases in a CLOSED system
- heat is not the only energy form and entropy always needs to be considered over ALL energy forms present. So even in a closed system you can make a seemingly contrary (from the point of entropy) move in one energy form by offsetting that in other energy forms.
italba
2.5 / 5 (6) Jan 11, 2013
No solar concentrator can give you a temperature higher than the sun's surface! The sun is the source.
Uzza
5 / 5 (1) Jan 11, 2013
You can't concentrate a low temperature heat source in a higher temperature target. That would be a negative entropy operation.

It is possible. The second law of thermodynamics gives that energy cannot move from a cold body to a hot body, unless work is performed.
That is how heat pumps work. You perform work to move energy from the cold outdoors to the warmer indoors.

Additional work would be required to move the energy in my idea, so the question is as follows: is the energy expended outweighed by the potential increase in efficiency?
italba
1 / 5 (1) Jan 11, 2013
is the energy expended outweighed by the potential increase in efficiency?

Surely no! You cannot have a more efficient Carnot cycle by using two Carnot cycles in series!
Manitou
5 / 5 (2) Jan 11, 2013
"Heat also spans a wide range of frequencies, he says, while sound spans a single frequency."
There are many frequencies of sound, so what does this sentence from the article mean?
Uzza
5 / 5 (1) Jan 11, 2013
is the energy expended outweighed by the potential increase in efficiency?

Surely no! You cannot have a more efficient Carnot cycle by using two Carnot cycles in series!

If that's the case, I suppose power plants using combined cycles are just marketing hoaxes?

http://en.wikiped...ed_cycle
italba
1 / 5 (1) Jan 11, 2013
The combined cycles power plant are a completely different case. If you read the Wikipedia article carefully, the problem is that we can't build a single steam turbine whit a 1400° steam temperature. So we use a gas turbine for the first stage and a steam turbine, heated by the gas turbine exausts, for the second stage. We can have a better efficiency in this way, albeit lower than the theoretical high temperature single steam turbine.
Steven_Anderson
1 / 5 (1) Jan 11, 2013
Can someone comment on the dimensional aspects of this solution. Is it really small. Does it scale to large sizes? What about the material costs of this? also curious about the efficiency of this design.
packrat
1 / 5 (1) Jan 11, 2013
The combined cycles power plant are a completely different case. If you read the Wikipedia article carefully, the problem is that we can't build a single steam turbine whit a 1400° steam temperature. So we use a gas turbine for the first stage and a steam turbine, heated by the gas turbine exausts, for the second stage. We can have a better efficiency in this way, albeit lower than the theoretical high temperature single steam turbine.


I guess you've never heard of a supercritical steam plant? Also most steam turbine plants run from max psi all the way down below 0 psi with multiple turbines (normally a high psi turbine with it's exhaust feeding a low psi turbine system) before the water is returned to the boiler feed system.
hyongx
not rated yet Jan 11, 2013
So first of all, this is a theory paper. The author did not perform experiments; he did calculations and simulations that showed that this should be feasible.
The paper is here http://prl.aps.or.../e025902

Also,
he says, while sound spans a single frequency.
is completely ridiculous. Humans can perceive sound with frequencies from ~20 Hz to ~ 20,000 Hz.
italba
1 / 5 (1) Jan 11, 2013
I guess you've never heard of a supercritical steam plant?...

Yes I read about supercritical steam plant, but this is not the point. If you read the previous messages, I was answering to Uzza who proposed to raise the coolant temperature from, for instance, a nuclear reactor with a sort of heat pump in order to get more power from it. I wrote this is impossible, climbing to a hill and riding down is not more efficient than taking a plain route.
packrat
1 / 5 (1) Jan 11, 2013
I did read them, I just didn't understand the point there you were trying to make. Now that you cleared that up I pretty much agree with you on your statement. It wouldn't be impossible but not very useful either and it would probably cost more than it's worth to do. He does have an interesting idea but I don't see how it could be really useful except in one manner and that would be adding solar heat to the feed water for the boiler. That could save a bit of money over time on fuel.
Caliban
5 / 5 (1) Jan 11, 2013
I wonder if it would be possible to use this to concentrate the heat to a smaller area, increasing the temperature there.

The specific application would be thermoelectric power plants using steam, where instead of letting steam pass over steam turbines, it is instead moved and concentrated for use in a high temperature cycle like brayton. This would allow you to gain the benefits of higher thermodynamic efficiencies without having to design the entire plant around the higher temperatures.

A perfect example would be nuclear plants, where the higher temperatures would require a redesign of the entire reactor to accommodate a high temperature cycle. If my idea works, only the power conversion part would have to be changed to allow higher thermodynamic efficiency.


From the article:


Other variations of the material could be used to focus heat—much like focusing light with a lens—to concentrate it in a small area.


So -apparently, the answer is yes.

PhyOrgSux
1 / 5 (2) Jan 11, 2013
(oops I have to take back my comment...sorry for this interruption)
davidgro
not rated yet Jan 11, 2013
The crystals could also be used to create thermal diodes: materials in which heat can pass in one direction, but not in the reverse direction.


Isn't that Maxwell's demon? Meaning it's impossible for certain? If so, I wonder how many of the other claims in this article are compatible with the laws of thermodynamics.
kaypee
not rated yet Jan 12, 2013
The paper is behind the APS paywall, so I can't get to it, but thermal "diodes"? I think that this has got to be a case of poor wording because the use of the word "diode" implies a near-total restriction of flow in one of two directions. The only way to stop the "flow" of phonons in a macroscopic solid is with a vacuum boundary. Furthermore, a "phonon" is a whole-system phenomenon, so when people talk of phonons "flowing", what's really being described is the time-evolution of "wave packets" created by linear combinations of phonons. Unless I'm guessing incorrectly what they are doing, it would be better to say that they are engineering a material or a device that has a macroscopic directionally-dependent thermal conductivity that can be controlled externally. Modifying a uniform distribution of phonons into one with a non-uniform character reduces the system entropy and thus requires an external energy source to accomplish.
Caliban
not rated yet Jan 12, 2013
@kaypee,

I think he's talking about this "transform" heat energy that has been reduced in frequency, so transmission can be stymied via restricting bandgap for the particular frequency of the heat
energy.
italba
1 / 5 (1) Jan 12, 2013
@Caliban:
From the article:


Other variations of the material could be used to focus heat—much like focusing light with a lens—to concentrate it in a small area.


So -apparently, the answer is yes.


Please do not mistake heat with temperature! The second thermodynamics law states that you can't, without external work, move heat from a lower to a higher temperature object. In the same way you can't create, in an object, a hot spot with a temperature higher than the starting one. You could indeed, with this new material, move the heat of an object in one side, so that side will stay warm for a longer time, but the temperature of the warm side will anyway be lower or equal the starting one.
Osiris1
1 / 5 (1) Jan 12, 2013
Expanding on gblaze, why not use a device incorporating this tech in fusion ignition. Beautifully tailor made for this. Also maybe in rocket nozzles for VASIMR so velocities of up to a million miles/hour exhaust can be kept at bay from the walls of the rocket body, protecting the rocket engines from forces that would tear it apart or melt it in microseconds. Maybe allow VASIMR to achieve high enuf thrust to take rockets off from the earth's surface. Make a true space shuttle....and a true interplanetary exploration ship that is not some artillery shell shot into the cosmos on a wish and a prayer and billions to some oil magnate who cares nothing for the astronauts he/she would kill or maim.
Tausch
1 / 5 (1) Jan 12, 2013
The transport equations for thermal energy [is] Fourier's law.

The same laws that govern the transfer of light govern the radiant/conductive transfer of heat.

http://en.wikiped...transfer

Imagine hearing thermal noise.

When you look at a phononic crystal you are looking at a physical, passive noise-cancelling control unit - the crystallographic 'headphones' for heat.

Heat is thermal noise.
Atomic lattices are for the phonons what the atoms are for gases when view as propagation of density fluctuations.

We label the propagation of density fluctuations in gas sound.
The sun has acoustical descriptions. Are there phonons there too?

Can the sound of heat 'sound' at one frequency only?

"Heat also spans a wide range of frequencies, he says, while sound spans a single frequency."

There are many frequencies of sound, so what does this sentence from the article mean? - Manito


I tried to give the sentence meaning. Still in the dark though.
Tausch
1 / 5 (1) Jan 13, 2013
For those in the life sciences think of thermocrystals as a tonotopy landscape to route the frequencies of the carriers (phonons)of thermal noise (heat).
Caliban
not rated yet Jan 13, 2013
@Caliban:
From the article:


Other variations of the material could be used to focus heat—much like focusing light with a lens—to concentrate it in a small area.


So -apparently, the answer is yes.


Please do not mistake heat with temperature! The second thermodynamics law states that you can't, without external work, move heat from a lower to a higher temperature object. In the same way you can't create, in an object, a hot spot with a temperature higher than the starting one. You could indeed, with this new material, move the heat of an object in one side, so that side will stay warm for a longer time, but the temperature of the warm side will anyway be lower or equal the starting one.


@italba,

I understand the Second Law. I am not personally claiming that these guys are correct. I was pointing out what they said, as it is related in the article.

Thus the quote, which would appear to be an answer in the affirmative to Uzza's question.

Caliban
1 / 5 (1) Jan 13, 2013
@Caliban:
From the article:


Other variations of the material could be used to focus heat—much like focusing light with a lens—to concentrate it in a small area.


So -apparently, the answer is yes.


Please do not mistake heat with temperature! The second thermodynamics law states that you can't, without external work, move heat from a lower to a higher temperature object. In the same way you can't create, in an object, a hot spot with a temperature higher than the starting one. You could indeed, with this new material, move the heat of an object in one side, so that side will stay warm for a longer time, but the temperature of the warm side will anyway be lower or equal the starting one.


It's what Maldovan said --not me. Uzza asked the question, and I picked the answer to it out of the article.

And yes, at least superficially, it would appear to be a violation of the Second Law.
Caliban
not rated yet Jan 13, 2013
Apologies to all for the double post. The first comment didn't appear, which resulted in a do-over while the first was in limbo.
PPihkala
5 / 5 (1) Jan 16, 2013
"Heat also spans a wide range of frequencies, he says, while sound spans a single frequency."
There are many frequencies of sound, so what does this sentence from the article mean?

What they probably meant is that the frequency range of sound is much narrower than the frequency range of heat. So if one compares those ranges, it might appear that sound range is so narrow that it looks as it was a single frequency.
Tausch
1 / 5 (1) Jan 19, 2013
Frequency range is medium dependent. The sinusoids are finite.
Atoms for sound. Lattices for phonons.
The sum is a single frequency.
Tausch
1 / 5 (1) Jan 28, 2013
Phononic crystals to realize sasers.
Photonic crystals to realize lasers.

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