From: behnke@FNALF.FNAL.GOV (M.L. 'Broomen' Behnke)
Subject: Re: Peltier Effect Heat Pumps
Organization: Fermi National Accelerator Lab
Lines: 66
Reply-To: behnke@FNALF.FNAL.GOV
NNTP-Posting-Host: fnalf.fnal.gov

In article <2745@snap>, paj@uk.co.gec-mrc (Paul Johnson) writes:
>
>I was having a look through a couple of components catalogues when I
>came across a range of Peltier Effect heat pumps intended for cooling
>components.  For those who have not heard of this effect, you put a
>current through one of these devices, and it pumps heat from one side
>to the other.  Reverse the current and you reverse the effect.  I
>think a temperature difference can give you an EMF as well.
>
>Anyway, it struck me that you could make a nice cool/hot box for
>picnics with one of these, a power regulator, a thermostat and a
>couple of heat sinks.  The biggest device can shift 60W with an
>efficiency of 80-90%, which ain't bad (although it would flatten my
>car battery in about half an hour).
>
 So-Called Cool-Hot boxes have been advetised for several years.  I recall
Damark advertising them in a recent catalog.  Problem with the units is they do
a sh***y job of keeping food cold/warm.  The peliter devices used just don't
seem to have enough punch to keep up.  If you want something hot, you need to
heat it up before you put it in the box, and end up hours later with food thats
only moderately warm.  Same goes for cold items.

>Unfortunately the catalogue didn't list anything more than the basic
>specs as a heat pump.  I imagine that you would get a back-EMF as the
>temperature gradient across the device increases.  If so, presumably
>its power decreases as the back-EMF increases, until eventually we
>have a steady state with no current being consumed (assuming no
>leakage).  If so, then the final temperature difference between the
>two sides could be set by the supply voltage and nothing more
>(although that would be a lousy way to control it).
>
>What I would like to know is:
>
>1: Are the above guesses correct?
>
>2: What is the open-circuit thermal resistance of a typical device?
>   (I just want to be sure that my coolbox is not going to get warm
>   too fast when I unplug it)

 You'de probably be better off getting a good Coleman(tm) cooler and stocking
up on "blue ice" blocks.

>
>3: How does a Peltier Effect heat pump actually work?  It looks like
>   magic!
>
>4: Why don't they use these things in domestic fridges/freezers?
>
 Same as above.  Not enough "punch" in them to keep/get things cold/hot.
>
>Thanks in advance,
>
>Paul.
>
>Paul Johnson (paj@gec-mrc.co.uk).	    | Tel: +44 245 73331 ext 3245
>--------------------------------------------+----------------------------------
>These ideas and others like them can be had | GEC-Marconi Research is not
>for $0.02 each from any reputable idealist. | responsible for my opinions
Mike Behnke             | Senior Tech/Advisor | Quid est illuidin aqua??
Fermi Nat Accel Lab     | Equipment Suuport   |
Batavia, Il.            | Computing Div       | PISTRIX!!  PISTRIX!!
BEHNKE@FNALF.FNAL.GOV   |                     |

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