4 ms·

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 mac

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.

Waterluvian 8y ago
I'm curious if the numbers work out to yield you anything within the galaxy of useful.
- trentlott 8y ago
  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.
  - heavenlyblue 8y ago
    >> low-frequency waves naturally are lower energy Just to be clear here: are they really? Sound waves have an amplitude which also defines the amount of energy they contain.
    - smoyer 8y ago
      Yes ... a sinusoidal sound wave has an RMS amplitude based on the peak amplitude regardless of the frequency.
    - robocat 8y ago
      Sound waves also have a maximum amplitude (without distortion) because the minimum of the pressure wave can't be below atmospheric pressure. Although Wikipedia indicates that maximum is quite loud.
    - xelxebar 8y ago
      For a sine wave, the energy scales like E ∝α ω^2 where α is amplitude and ω is frequency. So lower frequencies need propotionally larger amplitudes to carry the same energy.
- toast0 8y ago
  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-chilling/ https://www.wired.com/2003/01/hear-that-the-fridge-is-chilli...
rubatuga 8y ago
It wouldn't be possible because you need a temperature gradient. Creating sound from plain heat is the wrong direction for entropy.
- phaedrus 8y ago
  For the idea to work for cooling, he would need to expand the air in a different location than it was compressed in. (I wonder if standing waves exhibit this effect?) IF it works out that this is possible, I imagine it would be like standing in front of a CO2 fire extinguisher (gets cold as pressure is released).
  - pontifier 8y ago
    This is essentially what the pressure waves would be... mild compression waves would travel outward as you pull a cylinder creating a vacuum. You've compressed the entire atmosphere slightly, then you let some air expand back in through a small nozzle to fill the cylinder again. Then you open a port and push the air back out without changing it's volume, and close the port to complete the cycle... It seems like there's got to be something wrong with the concept, but I can't put my finger on what exactly.
xkcd-sucks 8y ago
Maybe relevant to your nutty idea: Heat is just motion on a small scale. In solid state materials, just like there are quantized configurations of electrons, there are also quantized modes of motion. These are called "phonons". (Analagous to electron / hole model of solid state electronic structure). (It's also true for single molecules, and this is what low energy IR spectroscopy probes. But less relevant for bulk behavior in a liquid or gas state). If the material is anisotropic, probably there will be anisotropic phonons too. The existence / density of thermal modes at IR energies can also determine how much heat a material radiates into the environment versus conducts through its bulk. SO, just like materials can have an electronic bandgap, materials can have a thermal bandgap too!!! But I can no longer envision what a thermal transistor would behave like. And I'm not sure how this relates to the electronically tuned thermal materials which show you when you google "theal transistor"
aoner 8y ago
There is a company in the netherlands that uses excessive heat with a similar idea to create air conditioning (SoundEnergy BV[1]). Unfortunately I can't really find a good English article explaining the principle but it's like a sterling engine without moving parts and without pistons. [1] https://www.soundenergy.nl https://www.soundenergy.nl

Waterluvian 8y ago

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

trentlott 8y ago
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.
- heavenlyblue 8y ago
  >> low-frequency waves naturally are lower energy Just to be clear here: are they really? Sound waves have an amplitude which also defines the amount of energy they contain.
  - smoyer 8y ago
    Yes ... a sinusoidal sound wave has an RMS amplitude based on the peak amplitude regardless of the frequency.
  - robocat 8y ago
    Sound waves also have a maximum amplitude (without distortion) because the minimum of the pressure wave can't be below atmospheric pressure. Although Wikipedia indicates that maximum is quite loud.
  - xelxebar 8y ago
    For a sine wave, the energy scales like E ∝α ω^2 where α is amplitude and ω is frequency. So lower frequencies need propotionally larger amplitudes to carry the same energy.
toast0 8y ago
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-chilling/ https://www.wired.com/2003/01/hear-that-the-fridge-is-chilli...

rubatuga 8y ago

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

phaedrus 8y ago
For the idea to work for cooling, he would need to expand the air in a different location than it was compressed in. (I wonder if standing waves exhibit this effect?) IF it works out that this is possible, I imagine it would be like standing in front of a CO2 fire extinguisher (gets cold as pressure is released).
- pontifier 8y ago
  This is essentially what the pressure waves would be... mild compression waves would travel outward as you pull a cylinder creating a vacuum. You've compressed the entire atmosphere slightly, then you let some air expand back in through a small nozzle to fill the cylinder again. Then you open a port and push the air back out without changing it's volume, and close the port to complete the cycle... It seems like there's got to be something wrong with the concept, but I can't put my finger on what exactly.

xkcd-sucks 8y ago

Maybe relevant to your nutty idea: Heat is just motion on a small scale. In solid state materials, just like there are quantized configurations of electrons, there are also quantized modes of motion. These are called "phonons". (Analagous to electron / hole model of solid state electronic structure). (It's also true for single molecules, and this is what low energy IR spectroscopy probes. But less relevant for bulk behavior in a liquid or gas state). If the material is anisotropic, probably there will be anisotropic phonons too. The existence / density of thermal modes at IR energies can also determine how much heat a material radiates into the environment versus conducts through its bulk. SO, just like materials can have an electronic bandgap, materials can have a thermal bandgap too!!! But I can no longer envision what a thermal transistor would behave like. And I'm not sure how this relates to the electronically tuned thermal materials which show you when you google "theal transistor"

aoner 8y ago

There is a company in the netherlands that uses excessive heat with a similar idea to create air conditioning (SoundEnergy BV[1]). Unfortunately I can't really find a good English article explaining the principle but it's like a sterling engine without moving parts and without pistons. [1] https://www.soundenergy.nl https://www.soundenergy.nl