<div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Actually, not all fans are set up to suck out of the box. </blockquote><div><br></div><div>Ha!</div>
<div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">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.<br>
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And a lot of higher performance PCs (like the Dell sitting on my desk) use centrifugal fans (with variable speed, to boot)<br>
<span class="HOEnZb"><font color="#888888"><br>
Jim Lux<br>
</font></span><div class="HOEnZb"><div class="h5"><br>
-----Original Message-----<br>
From: <a href="mailto:beowulf-bounces@beowulf.org">beowulf-bounces@beowulf.org</a> [mailto:<a href="mailto:beowulf-bounces@beowulf.org">beowulf-bounces@beowulf.org</a>] On Behalf Of Daniel Pfenniger<br>
Sent: Wednesday, June 06, 2012 10:33 AM<br>
To: <a href="mailto:holway@th.physik.uni-frankfurt.de">holway@th.physik.uni-frankfurt.de</a><br>
Cc: Beowulf Mailing List<br>
Subject: Re: [Beowulf] Desktop fan reccommendation<br>
<br>
<a href="mailto:holway@th.physik.uni-frankfurt.de">holway@th.physik.uni-frankfurt.de</a> wrote:<br>
><br>
>> The Dyson bladeless and silent fans are based om a different<br>
>> principle, a cylindrical thin air layer carries along the inner air<br>
>> column, the air flow is then laminar (<a href="http://www.dyson.com/store/fans.asp" target="_blank">http://www.dyson.com/store/fans.asp</a>).<br>
><br>
> Which is not good if your trying to cool stuff.....<br>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
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<br>
Dan<br>
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</div></div></blockquote></div><br><br clear="all"><div><br></div>-- <br>- - - - - - - - - - - - - - - - - - - - - <br>Nathan Moore<br>Winona, MN<div>- - - - - - - - - - - - - - - - - - - - -</div><div>- - - - - - - - - - - - - - - - - - - - -</div>
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