Hi all,
I just wanted to point out that a new kind of fan is appearing these days. They use what's called floating magnetic bearings and are supposed to:
- last longer
- make less noise.
Globefan, Ennermax, Sunon at least have one of them in their product lines.
As usual, I can't wait to see one of these tested according to SPCR standards !
links:http://www.globefan.com/new_product.htm
http://www.enermax.com.tw/english/image ... 12AEBS.pdf
http://www.sunon.com.tw/products/pdf/2004maglev.pdf
My two cents,
Floating Magnetic Bearing
Moderators: NeilBlanchard, Ralf Hutter, sthayashi, Lawrence Lee
Eeh, sorry I don't really get your point here. Why would that induce more turbulence noise (btw what's that ? wind noise ? Isn't that proportional to airflow only ?) ? I would have understood if you'd said "vibration noise", but here I'm stuck.
Don't get me wrong, I don't claim you're talking crap, I simply don't see what you meant.
Don't get me wrong, I don't claim you're talking crap, I simply don't see what you meant.
Turbulence noise (yes it could also be called wind noise) is actual a complicated function of airflow (my guess is a thrid or 4th order polynomial).
As the fan wiggles up and down the flow over it is disturbed causing increased turbulence. Becuase of this tip leakage (Air traveling through the fan, shroud gap) is increased as well, lowering performance as work done on the air is lost.
I would think the primary reason that fan companies want magnetic bearings is reliability, no mechanical contact means that they never wear out.
As the fan wiggles up and down the flow over it is disturbed causing increased turbulence. Becuase of this tip leakage (Air traveling through the fan, shroud gap) is increased as well, lowering performance as work done on the air is lost.
I would think the primary reason that fan companies want magnetic bearings is reliability, no mechanical contact means that they never wear out.
Ok, thanks !
But are you sure that in the special context of SPCR, where fans are run at very low air flows, turbulence is still the main source of noise. I remember many reviews where the author stated something like "when voltage drops below X volts, wind noise disappear and motor hum becomes clearly audible."
My feeling (hope) is that at low speeds this kind of fan will be more silent because there shouldn't be any motor induced noise.
But are you sure that in the special context of SPCR, where fans are run at very low air flows, turbulence is still the main source of noise. I remember many reviews where the author stated something like "when voltage drops below X volts, wind noise disappear and motor hum becomes clearly audible."
My feeling (hope) is that at low speeds this kind of fan will be more silent because there shouldn't be any motor induced noise.
Nothing even remotely so simple, I'm afraid! For those interested (I have a forlorn hope that there might be SOMEONE), there's a rather good short introduction to the problem here.bobo5195 wrote:Turbulence noise (yes it could also be called wind noise) is actual a complicated function of airflow (my guess is a thrid or 4th order polynomial).
There are also some graphic examples of just how far away turbulence is from being a polynomial function (of anything) here and a Scientific American article on turbulence here.
One of my lecturers helped invent turbulent modeling in CFD. you can actually solve the problem directly using computers but for all but the simplest problems you wont get an answer before you die.
I was talking about dominate effects in an engineering context. While you know nothing about the turbulent movement you can say how much there is and work out an model for what its doing on average.
You can approximate turbulence if you make some assumptions (like in CFD) down to a singular simple function probably a function a velocity cubed (kinetic energy: v^2 * fluid velocity: v)
Even in very low airflows turbulence still exists admittedly it does not dominate. A magnetic bearing fan is likely to have wind noise for longer and even then removing the last bit of bearing noise is often not required.
I was talking about dominate effects in an engineering context. While you know nothing about the turbulent movement you can say how much there is and work out an model for what its doing on average.
You can approximate turbulence if you make some assumptions (like in CFD) down to a singular simple function probably a function a velocity cubed (kinetic energy: v^2 * fluid velocity: v)
Even in very low airflows turbulence still exists admittedly it does not dominate. A magnetic bearing fan is likely to have wind noise for longer and even then removing the last bit of bearing noise is often not required.