Heat pipes? - copper

Bari Ari bari at onelabs.com
Mon Jun 4 21:06:30 PDT 2001

alvin at Mail.Linux-Consulting.com wrote:

>> Copper is a better conductor of heat than aluminum and a bit pricier... 
>> why not just add more surface area to your aluminum heat sinks or 
>> increase the amount of forced convection across the surface for the same 
>> effect at lower cost?
> extruded aluminum is terrible heat conductor but very cheap to make
> and good enough for slower p3-cpu

Terrible? 100W/mK - 150W/mK is terrible?

> an aluminum block that is cut is "lot better" heat conductor as its
> molecules are relatively intact ... according to those heatsink
> manufacturers .. just a few cents more to cut than to extrude ...
> but when making millions of heatsinks units...guess it adds up...
Increasing the surface area of a heatsink or increasing the amount of 
forced convection across the surface area is how the thermal resistance 
of a heatsink is reduced.

>>>>> - get a liquid cooled heatsink - copper pipes with antifreeze
>>>>> ( like a radiator ) --  seems like a fun project
>>>>> - heat pipes are expensive ?? ..as is peltier cooling
>> The least expensive approach to cooling P4s and Athlons in 1Us is by 
>> just using aluminum extrusions for heat sinks that form the top of the 
>> enclosures and using forced convection across the the units. We're using 
>> some profiles now that are only 0.08 - 0.11 degC/W at 100 CFM. These 
>> would allow the use of a P4 in an ambient of up to 68 deg C.... but I 
>> wouldn't want to be in that room :-)
> isnt 68deg still on the high side ??? ....

The 68 deg C ambient is the air temperature of the environment that the 
CPU is in. Using a heat sink with a thermal resistance of 0.08 - 0.11 
degC/W allows us to keep the P4 case temp below the 75 deg C maximum 
spec. at an ambient air temp of up to 68 deg C. So there is only a 7 deg 
C rise above ambient.

> some of ofour cpu temp measurements was around 30-35 range...hitting
> up to  40 or so when runnign heavy loads during the day...
> 	- the bigger the heatsink got... the hotter the cpu ran too
> 	cause the itty bitty fans was not good enough ...

A bigger heatsink doesn't always mean better. Surface area and the the 
profile is what counts.

What was your ambient air temp for these mesurements? 20 deg C? -10C? At 
an average room temp of 20 deg C the CPU case temp would only rise to 27 
deg C while running at the full 62W max. continuously with the heatsink 
I mentioned above.


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