In message <[EMAIL PROTECTED]>, Peter Jeremy writes
:
>> How about these Peltier (sp ?) cooling devices I have heard about ?
>
>A Peltier cell is just a semiconductor heat pump. It effectively just
>reduces the junction-to-heatsink thermal resistance, allowing you (in
>theory) to use a less efficient heatsink (or have the CPU run cooler
>with the same heatsink.
This is actually not true, quite the contrary in fact: You need
a better heat-sink with a Peltier because of the significant
electrical power you pump into it.
As a general rule you can expect to *raise* your CPU temperature if
you put a peltier under anything less than a *very good* heat-sink.
Example:
A Celeron 500 disipates about 25W
An average heatsink is about .8 C/W
delta-T becomes 25W * .8C/W = 20C
At 30C ambient that becomes 50C CPU temperature.
Now, add a peltier. To remove 25W and keep a 25C
temperature difference we need to feed it about 50W
Now the heatsink has to deal with 25 + 50 W and the
delta-T becomes: (25W + 50W) * .8C/W = 60C
Subtract the 25C difference from the peltier and add
the ambient temperature and we find:
30C + 60C - 25C = 65C
We just raised our CPU temperature about 15 C :-(
--
Poul-Henning Kamp FreeBSD coreteam member
[EMAIL PROTECTED] "Real hackers run -current on their laptop."
FreeBSD -- It will take a long time before progress goes too far!
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