On Sat, 12 Jan 2008 04:49:47 -0800, "William Sommerwerck"
wrote:
"Arny Krueger" wrote in message
...
It doesn't take a boffin to know that if you turn a fan very slow, it
won't make much noise. Trouble is, it won't move much air, either.
Isn't the issue whether it moves _enough_?
It might be that the Noctua fans have a blade design that moves an adequate
amount of air with unusually low noise. I don't know. I do know that I wish
the fans on my computer were quieter. They're not noisy in an absolute
sense, but I'd rather they made no noise at all.
Years ago I read an engineering paper from an American fan manufacturer.
Their point was that the volume of air moved was not quite as important as
the way the air moved through the device. Their idea was that the air flow
should be broken up, so that air moved past every heat source in the device.
This was best achieved by asymmetrical fan mounting, and by pushing air into
the case rather than sucking it out.
The fans in my computer's cabinet work that way. Two at the back suck air
in, while one at the front -- NOT mounted in a line with either of the two
rear fans -- sucks it out.
Two or three small, quiet fans, will probably do a better job than one
large, "noisy" fan.
You are right. For maximum cooling it is important that the air flow
is turbulent - laminar flow will always show a slow temperature
gradient away from the source which means it effectively provides
insulation. That is most certainly not what you need for cooling.
Unfortunately turbulence implies noise. The real quiet alternative is
the fanless heat sink, usually loads of heat pipes and an awful lot of
metal.
d
--
Pearce Consulting
http://www.pearce.uk.com