[Beowulf] Desktop fan reccommendation

[Nathan Moore]

>
> Actually, not all fans are set up to suck out of the box.


Ha!


> Blowing in works better for heat transfer (you're pushing cold dense air,
> rather than sucking warm undense air)..  Most test equipment uses the "suck
> in through a filter and pressurize the box" design approach.  I think PCs
> evolved the other way because the single fan was in the power supply, and
> you didn't want to blow hot air, preheated by the power supply, through the
> rest of the system.   So it is set up as an "exhaust from PS box" fan.
>
> And a lot of higher performance PCs (like the Dell sitting on my desk) use
> centrifugal fans (with variable speed, to boot)
>
> Jim Lux
>
> -----Original Message-----
> From: beowulf-bounces at beowulf.org [mailto:beowulf-bounces at beowulf.org] On
> Behalf Of Daniel Pfenniger
> Sent: Wednesday, June 06, 2012 10:33 AM
> To: holway at th.physik.uni-frankfurt.de
> Cc: Beowulf Mailing List
> Subject: Re: [Beowulf] Desktop fan reccommendation
>
> holway at th.physik.uni-frankfurt.de wrote:
> >
> >> The Dyson bladeless and silent fans are based om a different
> >> principle, a cylindrical thin air layer carries along the inner air
> >> column, the air flow is then laminar (
> http://www.dyson.com/store/fans.asp).
> >
> > Which is not good if your trying to cool stuff.....
>
> Well, the fans we are discussing expel air *out* of the box so the heat
> carried by the air doesn't care about the downstream laminar or turbulent
> state of the airflow.
>
> However noise generation does depend on the airflow state, since the
> acoustic power is proportional to the 8th power of the turbulence eddy
> speed (Lighthill 1952, 1954).  This is why jet planes are noisy, as their
> turbulence is almost sonic.  The airplane or helicopter propeller tips, or
> the fan blade ends move closer to the sound speed, so most of the sound is
> generated there.
>
> The conclusion is that to keep a computer quiet one has advantage to use
> large fans rotating at low speed.  For the same air/heat output one gets
> much less noise, especially if the airflow is laminar.
>
>
>        Dan
>
>
>
>
>
>
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Nathan Moore
Winona, MN
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