This is an excerpt from a post by Bill Beaty which refers to a cascade
produced noise that ties in with acoustic emissions from your celestial
cars and cold, if you have the time, it might be of interest to read the
whole thing, this is just an excerpt about the electronic cooling device
and the noise and vibration sections;
http://www.madsci.org/posts/archives/may98/895429513.Ph.r.html
These devices are called TE modules (TE = thermoelectric) or Peltier
coolers, and are based on the "Peltier effect" from physics. They are
commonly sold as part of CPU fans for cooling your PC's processor, and
as 6-pack coolers which are powered by the 12V jack in your car.
They can be used in reverse: if one side is heated and the other is
cooled, they generate electrical energy (a couple volts DC.) In this
form they are used in the hot-plutonium thermoelectric generators used
in deep-space probes.
You can buy them for about $20 from various surplus electronics sources
(see my SUPPLIERS page, try ALL and H&R.) Some science education
suppliers also have them, try Arbor Scientific. (Note to experimenters:
the device is held together by low-temp solder, so be careful when
experimenting with flames, your TE module might melt!)
Charges going over the waterfall make "noise"
If two pieces of different conductor materials are touched together,
there is a "step" at the spot where they join. This "step" is a
difference in the energy levels of their charge fluids. If this
composite conductor is used as a wire in a circuit, then their charges
can be forced to flow over this energy "step".
It's like a waterfall. If the electrons are forced to flow from the
higher energy to the lower energy, each electron gives off a pulse of
vibration as it falls down the step. (It's a lot like the electron
of an atom jumping down in orbital level and emitting light.) In metals,
the jump in energy is small, and the vibration is a heat vibration
rather than a photon of light.
So, whenever an electric current goes down an energy step as it travels
from one type of material to another, it gives off energy. If the step
is small, this energy will take the form of a rise in temperature.
A backwards waterfall is a vibration-sucker
If the direction of current is reversed, how can the charges get up the
"step"? Backwards waterfalls don't REALLY work in real life. But in
conductors, the electrons always have quite a bit of motion.
They are jangling around in the materials. If something pushes them
towards the energy step, many can easily jump up it. But when they do,
they lose a lot of speed. Imagine a bouncing ball which bounces
repeatedly off the floor, then by chance bounds up onto a tabletop.
This can greatly slow the ball, even stop it. Same with the charges
being forced across the junction between differing materials.
The ones which don't bounce "high enough" cannot proceed across the
junction, but those that do will be slowed. But why would this cool down
the metals? Because the moving electrons ARE THE HEAT. The motion of the
jangling electrons are actually the heat vibrations in the material.
Yes, the protons wiggle too (as do the entire atoms.) But electrons
cause protons to vibrate, and vice versa, and entire atoms share their
vibrations with protons and electrons. These vibrations are heat
vibrations, and if something slows down the electrons (or the protons,
or the atoms), the material gets cooled.
-- Jerry Wayne Decker / jdecker@keelynet.com http://keelynet.com / "From an Art to a Science" Voice : (214) 324-8741 / FAX : (214) 324-3501 KeelyNet - PO BOX 870716 - Mesquite - Republic of Texas - 75187