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Uploaded:2019-01-24
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Bladeless fans can look like magic. How does all that air come out of that empty ring?! Well, it turns out that bladeless fans are more like a conventional fan than you might think, but that doesn't mean there isn't some really cool science behind how they work.

Hosted by: Olivia Gordon

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Sources:
http://simon.traberg-larsen.dk/website/documents/projects/2014/cfd.pdf [PDF]
https://opentextbc.ca/physicstestbook2/chapter/bernoullis-equation/
https://cosmosmagazine.com/technology/how-do-bladeless-fans-work
https://www.jameco.com/jameco/workshop/howitworks/dysonairmultiplier.html
https://www.core77.com/posts/25610/How-Does-a-Dyson-Air-Multiplier-Work
https://electronics.howstuffworks.com/gadgets/home/dyson-bladeless-fan.htm
https://media.lanecc.edu/users/driscolln/RT112/Air_Flow_Fluidics/Air_Flow_Fluidics7.html
https://archives.nbclearn.com/portal/site/k-12/flatview?cuecard=46849
♪.

Bladeless fans can look like magic. We’re so used to spinning fan blades pushing air at us that an empty, windy ring just doesn’t compute.

But the truth is… bladeless fans are a bunch of liars. There’s actually a more conventional fan hidden within every model — but the sneaky engineering isn’t what makes them cool. It’s that even though there are blades, they’re not where most of the wind comes from.

The blades that everyone looks for when they see a bladeless fan are hidden in the base, where a small fan blows outside air up toward the empty ring. The air escapes from a tiny slit cut around the inside of the ring, and it’s guided toward the front of the fan by angled walls:. The ring is slightly thicker in the back than the front, so air from the slit goes toward the thinner part.

The problem is, if that was the only reason these things worked, they wouldn’t really create a solid cylinder of air. You’d just get a circle of wind, like some sort of never-ending smoke ring. In reality, there’s wind coming from the center of the fan, too.

And that doesn’t come from the blades in the base. It comes from outside the ring. Part of the explanation has to do with pressure.

See, when you turn on your fan, a stream of fast-moving air comes out of the ring. And according to an effect known as Bernoulli’s principle, the faster a stream goes, the less pressure it exerts. That means your fan creates a zone of low pressure inside the ring.

So any air sitting behind it gets pushed toward that zone by the higher atmospheric pressure around it. This is called inducement, and it’s part of how you get air coming from the center of the fan even though the slit is in the outside of the ring. The rest of the wind comes from entrainment.

This is where the stream of air coming out of the fan drags some of the surrounding air along with it, thanks to the air’s viscosity. Basically, the molecules outside the stream try to stick to the ones inside of it, so get pulled along for the ride. Between inducement and entrainment, a bladeless fan can blow about ten or twenty times more air than it takes in through the base — all with the moving parts hidden from view.

I mean, that doesn’t make up for the fact that the “bladeless” part isn’t quite true. But the way it works is still fascinating. Thanks for watching this episode of SciShow!

If you want to learn more about the cool science behind the seemingly-ordinary things in your house, you can watch our episode about dimmer switches. Because, surprise: They’re secretly strobe lights. ♪.