A question on fan speed.

[Battousai001]

I have wondered of this thing before (almost two years ago) and I would like to know what you guys think about fan speeds:

Why is it that the newer CPU fans has a lower rpm than older fans? and that the lower the fan speed can lower the temperature of the CPU efficiently? I tried this and observed this on three CPU's, The Duron 900 has a stack fan with a speed of 7500+ RPM, The Athlon XP 1.5 has a 6300+ RPM, and the Duron 1.6Ghz has a fan speed of 2500-3000+ RPM.

I was using a 6300+ RPM fan (the fan is smaller and has lots of blades) for a Duron 1.6ghz temperature hits a maximum of 49-50 degrees. I tried replacing the fan with a 3000+ RPM fan (a little bit bigger and has less blades). at the same time I overclocked it to 1.8ghz. and surprisingly I saw the temperature at around 49 degrees!

Why is that the slower the fan the lower the temperature? I have been answered before that this could be due to fan design and size, but is it equivalent to say that when a fan is bigger and spins half the speed of a smaller fan the efficiency is the same? I was quite surprised that a fan speed of 50% less (the fan is slightly bigger and less blades though) can cool a processor much better that a fan that spins 50% faster (more blades and smaller).

 

[zagood]

This article on cow overclocking gives you some general information on fans and fan efficiency.

http://www.munters.com/www/US/home.nsf/ByKey/JHAK-63PHUT

(Other than the size of the fans and expected results, you can actually take the majority of information from this article and apply it to case cooling)

Basically it comes down to cubic feet per minute (CFM) being pushed by the fan. Larger fans, even those larger by 10mm, can produce much higher CFM while rotating more slowly.

Add to that different fan blade design, maximum air pressure, etc. and well designed slow fans are MUCH more efficient at cooling than poorly designed (or just smaller) ones that make up for it via RPM.

I'm sure someone around here has a chart or equation that can give you more technical info.

-z

 

[RallyMaster]

CPU architectures are becoming cooler and more power efficient so they produce less heat. Another change would be that the fans provide more airflow and some provide better heat transfer (such as AMD's heatpipe cooler). This means that less air is needed to cool a component and that is why you have quieter and slower spinning fans.

 

[Howard]

It's a little confusing when a heat sink is called a fan...