dusty fans!

March 9, 2006 7:15 AM

how do fans get so dusty?

so fans are always very dusty how does a moving object collect so much dust? i know they come in contact with more air because thats what they do but the only thing i could think of is a static electricity type of attraction

posted by BSummers to Home & Garden (9 answers total)

Not all dust is dry. Some dust has a little bit of oil or something else on it, and the fast-moving fan blades hit the sticky dust particles with greater frequency than things that stand still. Then, of course, the sticky dust is there on the fan blade, and some dry dust is bound to stick to the sticky dust.
posted by cerebus19 at 7:22 AM on March 9, 2006

Response by poster: wet sticky dust! who knew
posted by BSummers at 7:23 AM on March 9, 2006

Also -- boundary layers. While the air near the fan is (in effect) moving very quickly, the air right next to the fan blades moves along with the blades. So, despite what you'd think, there isn't much airflow to move the dust that sticks to the blades.

That's why the dust sticks when the fan spins, but a can of compressed air blows the dust right off.
posted by eriko at 7:28 AM on March 9, 2006

You can see for yourself. If you have a fan that you can open up to clean the blades, open it up and wipe the dust off a blade with a clean white paper towel, but don't wipe too hard. Now take another paper towel and wipe the area you just dusted again, and you should see a slightly greasy smear on the paper towel.
posted by cerebus19 at 7:29 AM on March 9, 2006

Also, plastic or metal fan blades passing through the air do create static charges.

Also, also, some particles are fibrous and get tangled with other fibers as they pass by, then still other particles get caught in the tangles. Next thing you know you've got a fuzzy fan.
posted by Pollomacho at 7:31 AM on March 9, 2006

About this boundary layer idea: why, then, are fans noisy? Shouldn't the boundary layer conform to the most efficient, ie. least noisy, shape?
posted by five fresh fish at 9:49 AM on March 9, 2006

Also, if you are talking about equipment with ventilation fans, most equipment with fans is poorly designed and the fans are installed in such a way it creates a negative pressure in the item. Pressure (positive or negative) in a (somewhat) sealed container causes dust to settle everywhere (especially the fans, it seems). Positive pressure fans, with a filter, are somewhat better than negative pressure fans. But only somewhat.

Properly designed equipment (like high end telco stuff) has fans pushing air in one side, and the equivalent amount of fans pushing the same amount of air out the other side, leaving the pressure inside neutral.

Or, at least, that's my guess...
posted by shepd at 10:20 AM on March 9, 2006

Isn't this kind of the same thing as asking "why do windshields get a bunch of dirt and crap on them in the summer even when it hasn't rained a drop?"
posted by Rhomboid at 2:27 PM on March 9, 2006

Why fans get dusty.
posted by BitterOldPunk at 8:12 PM on March 9, 2006