[Tfug] peltier?

[John Gruenenfelder]

On Thu, Sep 27, 2007 at 05:09:25PM -0700, Sean Warburton wrote:
>
>Now, I heard of an interesting physical property called the peltier effect,
>which is (as I understand it) the direct conversion of electricity into
>temperature changes.  This makes sense, because  when I overclock my CPU, I
>force more power than normal into it, and a higher temperature is achieved.
>This system must work the other way, where it can make things cold. Some
>research yielded a product that looks like a ceramic plate and one side gets
>cold while the other gets hot when a current is applied. Furthermore, the
>temperature difference is dependent on the ambient temperature, right?

Actually, your CPU generates heat as a waste product when transistors (all the
many millions of them in the chip) switch off and on and some due to
resistance in the tiny wires.  The peltier effect is fundamentally different,
but in broad terms, yes, you supply a current and the plate starts cooling.

But, there are a number of reasons why you don't see them in PCs very often.
One is that they are very inefficient, no more than 10%, so you're wasting a
lot of electricity with them.  And waste generally means waste heat.

Also, they can work *too* well.  The amount of heat transfer depends on how
much current you give the device, but you can get one side *very* cold and the
other side *very* hot.  The problem is that the cold side can form frost if
you're not careful.  You definitely don't want that.  I've read that some
people will make an airtight foam seal around whatever that put the cold side
on, but that will depend on how your cooler is designed.

And then once the heat is off the CPU and onto the other side of the cooler,
you still need to get rid of it ASAP.  I think most people who have gone to
the trouble of using peltiers use water cooling for this.

As for your continuing heat issues, your probably on to something with regards
to the reservoir size.  Have you tried putting a thermometer in the water to
see how warm it is?  The more it rises above room temperature the less heat
its going to remove from your CPU.  Alternatively, again depending on design,
you might try a reservoir with more surface area or putting a heatsink on the
reservoir itself.


-- 
--John Gruenenfelder    Research Assistant, UMass Amherst student
                        Systems Manager, MKS Imaging Technology, LLC.
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