[Beowulf] Desktop fan reccommendation

[Daniel Pfenniger]

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