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Scientists Watch as Heat Moves at the Speed of Sound

scientificamerican.com

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Re: Scientists Watch as Heat Moves at the Speed of Sound

#11

Post by pontifier »

This is so strange. Just 2 days ago I realised that although excessive sound production is usually a symptom of a machine that is not working properly, if a machine is designed to produce sound to dissipate energy, that energy would not be converted into heat within the machine. The energy is carried away at the speed of sound.

I have been thinking about using a similar process to make a "middle of the room" air conditioner that creates a localised cold spot, and sends the heat absorbed out of the room through the walls and into the surrounding atmosphere using low frequency pressure waves.

All of these processes are likely related, and macroscopic systems based on these principles almost seem magical.

Re: Scientists Watch as Heat Moves at the Speed of Sound

#12

Post by teh_infallible »

rfrey wrote: post #2

As I understood the article, in one part of the experiment they set up alternate regions of heat and cold within a sample of graphite using interference patterns from two laser sources. When they turned off the lasers, instead of the hot regions dispersing their energy until the troughs were the same temperature, the hot regions "overshot", becoming cooler than the (former) troughs, with wave-like behaviour. This see…

Sounds like this would explain the Mpemba effect:

https://en.m.wikipedia.org/wiki/Mpemba_effect

Re: Scientists Watch as Heat Moves at the Speed of Sound

#13

Post by sp332 »

arithma wrote: post #3
rfrey wrote: post #2

As I understood the article, in one part of the experiment they set up alternate regions of heat and cold within a sample of graphite using interference patterns from two laser sources. When they turned off the lasers, instead of the hot regions dispersing their energy until the troughs were the same temperature, the hot regions "overshot", becoming cooler than the (former) troughs, with wave-like behaviour. This see…

Not a "Real Physicist" but the information is not being lost, it's only being kept static-ish. This is the same as that waves don't violate the 2nd law (it's telling that they being called the phenomenon second sound.) > The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time. So instead of entropy increasing, it's hanging around for a while. No violation, sti…

Heat often correlates with entropy, but they are not the same thing. Increasing heat doesn't always mean increasing entropy.

Re: Scientists Watch as Heat Moves at the Speed of Sound

#14

Post by Waterluvian »

pontifier wrote: post #11

This is so strange. Just 2 days ago I realised that although excessive sound production is usually a symptom of a machine that is not working properly, if a machine is designed to produce sound to dissipate energy, that energy would not be converted into heat within the machine. The energy is carried away at the speed of sound. I have been thinking about using a similar process to make a "middle of the room" air cond…

I'm curious if the numbers work out to yield you anything within the galaxy of useful.

Re: Scientists Watch as Heat Moves at the Speed of Sound

#15

Post by ricardobeat »

turdnagel wrote: post #10
hannasanarion wrote: post #8

The effect appears at 120 Kelvin, or -240°F, so the article's assertion that this could revolutionize microelectronics seems like a stretch

Right, and the article says you wouldn't need to do it at "cryogenic" temperatures. I thought this was funny: "Nobody ever thought that you would actually be able to do this at such high temperatures."

-150℃ is almost halfway up to ambient temperature though, so it halves the energy requirement.

Re: Scientists Watch as Heat Moves at the Speed of Sound

#16

Post by trentlott »

Waterluvian wrote: post #14
pontifier wrote: post #11

This is so strange. Just 2 days ago I realised that although excessive sound production is usually a symptom of a machine that is not working properly, if a machine is designed to produce sound to dissipate energy, that energy would not be converted into heat within the machine. The energy is carried away at the speed of sound. I have been thinking about using a similar process to make a "middle of the room" air cond…

I'm curious if the numbers work out to yield you anything within the galaxy of useful.

Yeah, that's the actual question and probably a reason why it's not an established technique

Also, low-frequency waves naturally are lower energy. Why not bury the output and increase the frequency?

It would have the added benefit of supposedly keeping away ground-dwelling pests; supposedly.

Re: Scientists Watch as Heat Moves at the Speed of Sound

#17

Post by rubatuga »

pontifier wrote: post #11

This is so strange. Just 2 days ago I realised that although excessive sound production is usually a symptom of a machine that is not working properly, if a machine is designed to produce sound to dissipate energy, that energy would not be converted into heat within the machine. The energy is carried away at the speed of sound. I have been thinking about using a similar process to make a "middle of the room" air cond…

It wouldn't be possible because you need a temperature gradient. Creating sound from plain heat is the wrong direction for entropy.

Re: Scientists Watch as Heat Moves at the Speed of Sound

#18

Post by renholder »

Asking because it's an interesting phenomenon and I don't know enough to understand the question I'm putting forth:

If conductive heat is radiated through quanta, phonons[0], why would it be limited to the speed of sound? Is there a limitation to waveforms in matter that limits the speed at which it travels or is it purely dependent on the energy "type"? (Thinking of light travelling in waveform, when I posit this, which is the reason the ridiculous ask.)

[0] - https://en.wikipedia.org/wiki/Phonon#Acoustic_and_optical_ph...

Re: Scientists Watch as Heat Moves at the Speed of Sound

#19

Post by EngineerBetter »

sp332 wrote: post #13
arithma wrote: post #3

Earlier quoted context omitted.

Not a "Real Physicist" but the information is not being lost, it's only being kept static-ish. This is the same as that waves don't violate the 2nd law (it's telling that they being called the phenomenon second sound.) > The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time. So instead of entropy increasing, it's hanging around for a while. No violation, sti…

Heat often correlates with entropy, but they are not the same thing. Increasing heat doesn't always mean increasing entropy.

I'd highly recommend Arieh Ben-Naim's books on entropy for anyone looking for more on this point.

TLDR he makes the argument that entropy is a measure of the probability of probability distributions.

Re: Scientists Watch as Heat Moves at the Speed of Sound

#20

Post by toast0 »

Waterluvian wrote: post #14
pontifier wrote: post #11

This is so strange. Just 2 days ago I realised that although excessive sound production is usually a symptom of a machine that is not working properly, if a machine is designed to produce sound to dissipate energy, that energy would not be converted into heat within the machine. The energy is carried away at the speed of sound. I have been thinking about using a similar process to make a "middle of the room" air cond…

I'm curious if the numbers work out to yield you anything within the galaxy of useful.

I recall reading an article about thermoacoustic cooling years ago, but couldn't find anything more current than this old wired article [1]. More recent articles about Ben and Jerry's refrigerators have been about changing refrigerants, so I suspect the research didn't work out.

Also, sort of sound and heat related, piezo fans seem to be a niche way to move air around without a spinning blade.

[1] https://www.wired.com/2003/01/hear-that-the-fridge-is-chilli...

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