Dust is everywhere, yet it seems like the ONE place where it would NOT accumulate is on the blades of my ceiling fan, which I never turn off. In fact, last time the power went out (the only time I can recall it was ever not spinning) there was think dust all over the front (windward) portion of the blades. WHY? HOW? I’ll be dissapointed if the answer to this question has to do with ‘static electricity’ or something like that. I see no way for dust to attatch itself to a moving fan. I have it on a pretty high speed, too. I’m sure someone knows the answer to this… thanks in advance.
-in case I don’t see your post. First of all, static electricity does play a part in it. The motor probably has brushes that continuously spark as the fan rotates. They’re inside where you can’t see them but the motor case is most likely vented somehow and the brush sparks would release ions, contributing to some amount of static electricity.
A second reason is that dust is heavier than air. If you turned the fan off, the dust would eventually settle. As the fan rotates, the air moves faster than the dust and dust that happens to drift close to the fan blades gets caught on imperfections on the surface. - If the fan blades were airfoil shaped instead of flat, the dust would accumulate on the back side instead of the front. - MC
MC, sorry to stick a pin in your balloon, but the motors that run ceiling fans are AC induction motors. No commutators, no brushes. That shoots the legs out from under your static electricity theory…or does it?
Air moving over a surface will create a static charge in the surface, and the very slight amount of oils and greases in household air will build up on the blades, and cause any dust(depends upon your housekeeping habits as to how much) in the air to adhere to the blade. If it were merely static electricity creating the adhesion, the dust would fall off as soon as the charge on the fan blade was bled off by touching it.
Guess what, vertical oscillating fans have the same problem. I think FixedBack is mostly right. As evidence of this, look at your air conditioning vents, they will tend to collect dust for the same reason. Another factor contributing to both the static buildup and general dust collection is the electric field of the motor, which is pretty large for your typical ceiling fan, but also explains why dust is attracted to your TV, stereo, computer, and other electronic equipment. Static electricity acts like a magnet to dust.
for some innate reason i have a hard time believe it is static (or only static)… i’m sure someone would have come out with a ‘dustless’ fan/ac vent/etc a long time ago.
Yes, vertical oscillating fans, air conditioner vents, they all collect dust, and they all have air moving across them at relatively high speeds. See, the thing is, if there is some dust on my counter, i can blow very gently and it will come off all over the place. So, it would make sense to me that if i was constantly blowing on my counter 24/7 that dust would never accumulate there.
Because 90% of dust in a household are dust mites, not an inatimate object, i.e. little dirt specks. Gross, but true. They look like little teeny ticks. Swear. And they can settle anywhere.
Forget static electricity. Think of laminar flow. In any streamlined (or, at any rate, non-turbulent) airflow, the air tends to separate into layers. The layer closest to the surface actually is non-moving. A bit of dust that falls on the fan when it is not moving will not be blown off when the fan blade begins to move because it is in the non-moving layer immediately next to the surface. As the blade moves, since it is (somewhat) aerodynamic, the laminar effect kicks in immediately and the settled dust just hangs on for the ride.
The reason that dust stirs when someone blows on it is that it is turbulent, non-laminar flow. There is no “laminate” layer at the lowest level in which the dust can hide. Actually, even there a small laminate field will exist so that you can never blow all the dust away. However, enough dust projects up into the air so that the turbulence carries a lot of the visible dust away. Try blowing all over a flat, dusty surface. Then go back with a rag. Look at how much dust never got blown away.
This effect is similar to trying to wash your car with a hose and no brush/rag/sponge. You can hit that car with the fanciest “turbo” nozzle you wish. When you are done, a light wipe with a rag or sponge will come away dirty.
I don’t discount the effects of laminar air flow that prevents the dust from getting blown off of the fan blades, but static electricity still plays a pretty major effect… as evidenced by the fact that your electronic equipment will not have a laminar air flow. Most TVs and stereos don’t even have forced air flows and the fans on most PCs are designed and placed to generate non-laminar air flow over the components.
JoeyBlades, certainly collecting dust includes static electricity. Once it has clung to an object, however, the OP wondered why it was not blown off the moving fan blade. For that you need to look at laminar flow.
The build-up of dust around the ventilation ports of electronic equipment (or anywhere else) includes static electricity. As you noted, however, most equipment does not even have forced air–putting it outside the OP’s question.