[AReU] Recap of August AReU meeting

[Terry Petrash]

Hello all again,

This past meeting was one of our more thought provoking
technical ones.  Tony, W4TAS, brought in a little thing called a
Peltier Junction device.  For those of us less learned ones, for
which I claim membership, it is a semiconductor device that acts
like a small air conditioner or refrigeration device.  He
demonstrated it and showed how by just applying a DC current to
the device, which is made like a small soda cracker sandwich, it
would get cold on one side and hot on the other.  

This little thing was really neat and something that I had never
seen or heard about before.  Ever since I moved down to Florida
I have been interested in and worked with air conditioning and
refrigeration.  However, all the systems I was familiar with
were our common moving refrigerant type systems.  This thing has
no moving parts or refrigerant per say.  How does it work?  

Well, no one at the meeting really had a handle on the “how to”
of the device, only the fact the one side cools and the other
side heats.  So, I got on the Internet and started searching to
find out more.  To my amazement most of the articles found went
no further other than to say that the device gets cool on one
side and hot on the other when a DC current is supplied.  Some
articles even reiterated the same frustration that the internal
workings of this device are always ignored or skipped over.  So,
I dug and surfed further.

I got into a few technical physics dissertations, which went
into great math detail and sub-atomic structure details on the
inner actions of particle physics.  After scratching my head and
butt for a day or three I finally came up with this
interpretation for us less learned ones.

The Peltier Junction works on the principal of electrons moving
from a P type material to an N type material or visa verse.  

First, let me give you the definition of the P & N materials as
they are referred to here so we stay on the same track. An N
type material would be one that has an abundance of electrons
like we learned in our electronic study.  The P type material
would be one that has fewer electrons or consists of holes where
electrons would be in N type material.  

Taking this concept one step further, another analogy would be
like comparing P & N type semiconductor material to a gas and a
liquid.  A gas comparison would be similar to P type material
where electrons float all around and bump into each other ever
now and then with wide spaces between them.  The liquid
comparison would be similar N type material where the electrons
are packed densely and have less room to move around.  Similar
to what we learned in school about molecular density of liquids
and gasses but here it is taken one step further and applied
also to the electrons.  

 Now back to the Peltier Junction.  In this process the electron
not only takes on its electrical charge that we are familiar
with as hams but also takes on a unit of heat charge like a
molecule in a gas or liquid.  Are you starting to see the
picture?  

In conventional refrigeration the refrigerant media changes
phase from a gas to a liquid and then back to a gas again in a
system engineered to taking on or giving off heat energy at the
designed cooling side or heat exhaust side.  In a Peltier
Junction, the same process takes place but instead of using a
refrigerant, the electrons are used!  And, the DC power source
acts as the compressor.

Electrons going from P material to N material get hot and are
forced to give off heat.  Electrons going from N material to P
material get cool and can absorb heat.  And there you have the
cooling function and the secret of the Peltier Junction.

Well, you say, doesn't every semiconductor then have this
feature?  The answer is YES!  But, we don’t emphasize this
particular feature when we want a switching or RF transistor for
manipulating electrical frequency or logic.  If we did their
construction would have to be made physically different.   Hmmm

 now there’s a thought.  Integrated Peltier characteristics with
electronic functions that would result in electronic systems
that wouldn't’t need any peripheral cooling!

So, there you have it in a nutshell.  If you want to research
this topic further I would suggest starting with the Wikipedia
link of: 

http://en.wikipedia.org/wiki/Peltier-Seebeck_effect
   
And then following other links mentioned from that article
including the Thompson Effect.

In addition to this topic we discussed the finer intricacies of
atomic batteries and how their construction compares with atomic
bomb devices.  Dave, AI4CR, also told us some knuckle biting
stories of his experiences working on 1000 ft plus commercial
towers and their failing and falling elevator systems.
   
Our next AreU meeting is scheduled for Tuesday, September 5th. 
So, if you’re not too exhausted from the holiday come by and
join us.

Hope to see you all there!

73
Terry Petrash
WA4BYK

PS: Don’t forget about TARC fest this Saturday, August 26.

  



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