Science Buddies: "Ask an Expert"

My project topic is Thermoacoustic Refrigeration of a Computer by Use of Ambient Sound and I was wondering if it were viable to produce.

The sounds that will be used to produce the oscillations, which would otherwise be produced by a motor, is taken from the surrounding environment and focused by a parabola-shaped device focused onto a point. The air then moves the shapes inward concentrating the gases and producing more excited molecules.
From the temperature gradient, two tube carrying water would flow through. The one carrying the heated water would be carried to a water tower device to cool down the water. The tube carrying the cooled water would circulate back into the computer to further cool the case.

Basically, my questions are:
Is it were possible to create a device that is powered by ambient noise focused by a parabolic disc?

Is this a project that a high school student would be able to pursue?

Thank you for your help.

Interesting idea. This is not really my field, but a search of Google yielded this patent, which might be of interest.

http://www.freshpatents.com/Abient-nois ... 218052.php

An interesting, intriguing, and mystifying project. I too am stumped by your question. Have you examined this site:

http://www.acs.psu.edu/thermoacoustics/ ... efault.htm

It is presented by Steven L. Garrett, United Technologies Corporation Professor of Acoustics at the Pennsylvania State University and his research group. It appears that he is the world's foremost expert on Thermoacoustic Refrigeration. They even sell an inexpensive (US$14) kit for science fair projects.

The kit requires electrical energy for a heating element, presumably to generat the accoustic energy in the device. I am not sure that pointing a parabolic dish and focusing sound waves would work, but I suppose you could try. What little I am able to understand is that a standing wave of acoustic energy is set up in the devices "stack," and that somehow sets up the refrigeration effect. Whether ambient noise can be used to do the same thing is not clear to me.

I assume you have already searched the web with Google. There is a reasonable amount of information out there. Ben and Jerry's even created a unit to cool their ice cream!
http://www.benjerry.com/our_company/sounds_cool/

Try these search terms:
"Thermoacoustic Refrigeration" science fair project

You can look up the 22 patents that heve the term "thermoacoustic refrigeration" in them:
http://patft.uspto.gov/netacgi/nph-Pars ... D2=&d=PTXT
They have some gnarly physical chemistry in them, so you may be in for a rough ride.

Sorry I couldn't be of more help. If I find something else, I'll let you know.

To compensate for my evident ignorance, I wrote to the lab which appears to be the world's foremost authority on Thermoacoustic Refrigeration. Here is the reply. He had already received an inquiry from SRysling, which he answers in his message:

Good initial thoughts. The challenges with using environmental sound are two--first the levels are low (which you'd be looking to address with your concentrator) and they are typically not at both a constant phase and frequency. More on this. But first, let's talk scale.

The average pressure in the atmosphere is around 100,000 Pascals. These are units like lbs per square inch, as you'd use for tire inflation. In this case it is Newtons per square meter.
The sound pressure level for a really, really loud, on the verge of ear damaging sound, is on the scale of 2 Pascals. Now the kind of the kind of temperature fluctuations that can produce is very small--
It is about 2.4 thousandths of a degree Celsius. That is why, while you might, so to speak, feel like you are "chillen" with loud music, it would be a big technical challenge to even measure those temperature changes. Even that sound power level would only correspond to about a watt of sound energy per square meter. A typical, modern home refrigerator would need, I would guess, about 120 Watts of power, if you could perfectly capture all of the sound power, roughly speaking. Our ears are just amazingly super sensitive sound sensors.

So, you could try to concentrate the sound. One problem here is that there is a "diffraction limit" which says something how much you can do that. The same thing happens with lens that you use for light--the spot can only be made so small by a given size concentrator. That size depends on the wavelength and the size of the concentrator --but it is hard to ever get things smaller than about a 6th of the wavelength. In air, middle C on a piano has a wavelength of about 4 feet. So, that makes things a bit tough as well.

Also, the best way anybody knows of to do thermoacoustics requires a single frequency. Doesn't matter a lot which, but you do have to pick one when you design. So you'd need something that is producing all the power you need at one pitch.

Last, the acoustic pressures at your concentrator need to add in-phase. So even if you had lots of sources at the same pitch, when you add them at the focus of your concentrator, the "timing" of the sound has to be set up so that at the focus, all the sources are producing a pressure maximum at the same instant, and a minimum at the same instant. Sometime you may have heard this called "constructive interference" in a science class.

In our machines the sound is very loud, but it all happens inside of steel containers that have as much as 1/2 inch thick wall.

I assume you have been to our website, and poked around there, and seen http://www.acs.psu.edu/thermoacoustics/ ... erdemo.htm I'd suggest you build one of these, and take it from there.

Keep thinkin' Sxxxx,

Bob Smith

Robert W. Smith, P.E.
Research Engineer
Physical Acoustics Group
Penn State Applied Research Laboratory
P.0. Box 30
Rear North Atherton Street
State College PA 16804