So what are "rifle bearings"?

[stupoty]

I was curious about this as I had just regressed some fans that were very noisy, the bearings were cinterd bronze oil lite looking with slits in them which I hadn't seen before.

Google gave me this though

"Rifle bearing fans are similar to sleeve bearing, but are quieter and have almost as much lifespan as ball bearings. The bearing has a spiral groove in it that pumps fluid from a reservoir. This allows them to be safely mounted horizontally (unlike sleeve bearings), since the fluid being pumped lubricates the top of the shaft. The pumping also ensures sufficient lubricant on the shaft, reducing noise, and increasing lifespan."

What is rifle bearing fan?

www.overclock.net

Stu

 

[graham-xrf]

I have got it figured out. Now, there is a whole segment of "dynamic fluid" bearing fans technology that is aimed right at the noise issue. They are intended to turn much slower, and many include temperature feedback speed control tricks. They use more fan blades, usually curved, with airfoil sections suited to the slower speed. They can't shift the full 110CFM, as could be had before at 3000RPM with the three fat blades. Their ratings vary from 54CFM to about 80CFM, and most have speeds at 1600, 1800, up to 2000RPM. They also can get expensive!

Quite good ones, up to 80 CFM can be had for about $25. Gamers and computer servers drive this market. The high specification fans can run to $60 bucks! Getting enough cooling by sheer high revving speed has an air shear physics limit before noise comes on strong. Cost considerations constrain designs using bypass tricks (like fan-jet engines). Different airfoil blades, shifting air at lower speed, but with higher torque, and trading off on the shifted volume, seems to be the fashion. This coupled with better electronics, heat pipes, and efficient heat sinks, and trying not to make so much heat in the first place, is an approach that has worked.

This is why two very quiet fans, in series, to deliver ducted air right into a hot switch-mode power supply may work better than two fans side-by-side on a casing. Folk here who fit high power 3-phase VFDs into box enclosures should pay attention to the cooling airflow, and then the need to filter shop dust and oils from getting in. Much better to have a big passive heatsink on the outside of the box, (side or rear).

 

[pdentrem]

A sealed box to keep out the dirty environment can be cooled via a simple black painted enclosure and external fan blowing onto said box to as complex as heat pipes carrying the heat from the source to the enclosure walls where the heat is shed away either passively or with active cooling.
One of the reasons why enclosure size can be what we think as ridiculously large is for cooling.
Pierre

 

[homebrewed]

I've been impressed by how quiet the fan in my wife's CPAP machine is. All you can hear is the air coming out. I've been curious what the fan blades look like but I don't think she would appreciate it if I took the thing apart. Her old one was put on a recall list and it took over a year to get a replacement.....