[Beowulf] Desktop fan reccommendation

Vincent Diepeveen diep at xs4all.nl
Wed Jun 6 09:56:20 PDT 2012


On Jun 6, 2012, at 4:56 PM, Lux, Jim (337C) wrote:

>
>
> 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..

Yeah that was a creative way it seems to mean airspeed :)

For a small diameter  tube one needs a massive airspeed to still push  
through
some hundreds of CFM.

Note the new generation fans really improved a lot. I'm very happy  
with that
aerocool shark of 12 CM. It's 7 euro in shops here a piece (includes  
19% VAT which
soon gets btw 21% here).

Happen to have a link for the type of fan you mean that fits in a  
small tube
of around a 10CM diameter or so and which is centrifugal, big CFM and  
low noise?

Will be interesting to toy with!

V-sign!   (for the non-insiders - 6th of june is D-Day)


>
> 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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>>
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