A 25cfm fan will cool 125W of CPU? Well so can a 5 cfm fan. Question is,
is it enough. It's pretty easy to figure out if your statement could
possibly be true.
The heat capacity of air (STP) is ~ 24 Watt seconds per cu. ft. per K, so a
1 k rise would require, for a 125 Watt CPU dissipation, 125/24 * 60 ~ =
300 cu. ft. per minute, or 30 cfm for a 10 K rise. But then there is the
thermal resistance of the spreader plate, the heatsink base, and the fin
interface... even pure copper is going to have a significant thermal
resistance for the die size and thermal spreader size of a Pentium 4
Prescott. So say case air temperature is a balmy 30 degrees C; add 15
degrees C for all thermal resistance, then the 10 degrees C for the air
temperature rise, and you get 30 + 15 + 10 = 55 C CPU temperature... not
what overclockers would be thrilled with. A dissipation level of 215 Watts
with the same die size and thermal spreader size would end up with a CPU die
temperature of more like 65 degrees C with the same input air temperature
and a 43 cfm fan. Within Intel specs, but on the edge of throttling, and
again, not thrilling to overclockers. Real world results will be even
worse. So I have to doubt the usefulness of your pronouncement.
--
Phil Weldon, pweldonatmindjumpdotcom
For communication,
replace "at" with the 'at sign'
replace "mindjump" with "mindspring."
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"Dorothy Bradbury" wrote in message
news:8A19c.14$le4.5@newsfe1-win...
60mm, 80mm & 92mm fans usually have the same hub size.
Choose a good heatsink like the SLK, then either size fan.
However, keep cfm scaled proportional to thermal load:
o A 25cfm fan will cool 125W of CPU
o A 43cfm fan will cool 215W of CPU
So either is beyond the hottest P4-Prescott - and L spec Panaflo.
Instead ensure you are removing hot air from the CPU cooler area
rather than recirculating it. If your CPU-cooler recirculates 50% of
its air then a 75W CPU that requires 15cfm now needs 30cfm. That
is easiest with an exhaust fan near the CPU on the rear of the case.
You don't need screamers, just design a system level solution.
--
Dorothy Bradbury
www.stores.ebay.co.uk/panaflofan for fans, books & other items
http://homepage.ntlworld.com/dorothy...ry/panaflo.htm (Direct)