[Beowulf] Desktop fan reccommendation

Lux, Jim (337C) james.p.lux at jpl.nasa.gov
Wed Jun 6 07:56:22 PDT 2012



On 6/6/12 6:36 AM, "Vincent Diepeveen" <diep at xs4all.nl> wrote:

>How much airflow per square centimeter do they generate?

That's not typically how fans are rated..

You'll have a curve of volume/time (e.g. Cubic feet/minute or cubic
meters/hour) for a given back pressure (usually in "inches of water
column")

Fan ratings at zero backpressure are almost worthless.  There's huge
variation from the freeflow number to a backpressure number. You need the
number at some decent backpressure (0.25" water column, for instance)


A EBM Papst 4182 NX is nominally 105.9 CFM..at 0.1" it's about 90 CFM, at
0.2" it's about 50, and at the max backpressure for that fan.



>
>As for the cluster here plenty of space available. To rent office
>space is around a 50 euro a square meter a year over here,
>not sure about there. So the cluster, some cardboard and huge fans of
>14 and 18 CM are diong the job to cool the nodes
>and switch, mellanox of course. now as i understand the square meters
>they reserve for datacenters is always far too limited,
>causing space each node eats as important as well, yet that's not the
>problem here in my office.
>
>The thing that worries me more is the airflow to outside (and
>inside). Usually only have limited amount of square centimeters of
>tube there. The 'industrial' fans that have massive airflow, they're
>very very noisy.


Not true... You can get VERY quiet fans that push a lot of air through a
large duct. It's all about the air speed.

You might want to look at a centrifugal blower rather than a axial fan.
Axial fans don't do as well against high static pressures, and if you're
doing a scheme with ducting, a centrifugal fan is usually a better choice.

>
>I'm already wondering about using some massive cardboard box and blow
>in air there using 8 fans (@ 100CFM each) or so
>and then behind them a second layer of fans, around 6 @ 100CFM,
>creating a massive overpressure, hoping that this will
>generate more airpressure, enough to blow in and blow out through
>some meters of tubing, but seems not like a perfect solution to me.


That sort of works, but the problem is that unless your "taper" is very,
very long, you're basically just creating a pressurized plenum, and the
fans will be inefficient working against that backpressure.  What you are
trying to do is combine multiple low speed flows into one high speed flow,
and that's a tricky aerodynamics problem.   That said, it does allow you
to put a noisy fan somewhere else.

IN general, high pressure fans are more noisy than low pressure fans, for
the same flow or horsepower rating.

Stacking fans doesn't work very well.  The flow coming off the fan is
twisting (unless you've got vanes to recover the rotational energy) so the
second fan in the stack is working against a spiraling flow.  Counter
rotating sequential fans does work, but is trickier to design, and there's
a lot fewer fans available with reverse rotation.


>
>On Jun 6, 2012, at 2:42 PM, Prentice Bisbal wrote:
>
>>
>> On 06/06/2012 05:38 AM, Daniel Pfenniger wrote:
>>> Nathan Moore wrote:
>>>> All,
>>>>
>>>> This is barely beowuf related...
>>>>
>>>> New desktop machine is a Shuttle SX79R5,
>>>> http://us.shuttle.com/barebone/Models/SX79R5.html
>>>>
>>>> In the past, shuttles have been very quiet, but this one has a
>>>> fairly loud
>>>> variable speed fan on the CPU heat exchanger.  I normally buy
>>>> replacement parts
>>>> from vendors like newegg, but their selection of 90mm case fans
>>>> mainly seems to
>>>> be described by CFM and whether the fan has LED lights mounted in
>>>> it (FYI, that
>>>> is not a selling point).
>>>>
>>>> So, is there an engineer's version of newegg that ya'll know
>>>> about? There must
>>>> be a super quiet 90mm fan out there that I can pick up for $10...
>>> I remind ads for quiet and more efficient rotor-less fans for PC's
>>> but
>>> cannot find such products anymore.
>>>
>>> The idea was to maximize the air flow area by displacing the
>>> central motor
>>> to the blade edges.  Not only the larger central area would allow
>>> a lower,
>>> quieter blade speed, but the blades being accelerated at their
>>> extremities
>>> by the circular motor would be mechanically more stable, less
>>> subject to
>>> vibrations.  My guess is that such fans, although technically
>>> better, were
>>> too expensive in regard of the advantages.
>>>
>> I had one of these fans on one of my CPU heatsinks a few years ago. It
>> was much quieter than the fan it replaced,but still not all that quiet
>> when compared to a Dell or HP tower. I forget the name of the
>> manufacturer or the model. The last time I looked, I couldn't find
>> them
>> anywhere.
>>
>> --
>> Prentice
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