On Jun 6, 2012, at 4:56 PM, Lux, Jim (337C) wrote: > > > On 6/6/12 6:36 AM, "Vincent Diepeveen" <[email protected]> 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 >>> _______________________________________________ >>> Beowulf mailing list, [email protected] sponsored by Penguin >>> Computing >>> To change your subscription (digest mode or unsubscribe) visit >>> http://www.beowulf.org/mailman/listinfo/beowulf >> >> _______________________________________________ >> Beowulf mailing list, [email protected] sponsored by Penguin >> Computing >> To change your subscription (digest mode or unsubscribe) visit >> http://www.beowulf.org/mailman/listinfo/beowulf > _______________________________________________ Beowulf mailing list, [email protected] sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
