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I'm curious as to how the Dyson air multiplier fan works. So far I understand that it creates negative air pressure that causes air behind and around the device to be sucked into the air stream and blown out. My question is how is the negative air pressure created? I haven't found an explanation for that yet.

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The negative pressure is to be understood with respect to atmospheric pressure. As people pumping up water from very low sources know very well, there is a limit on how "negative" a pressure can be. Planes fly with that kind of negative pressure created above the wings. –  babou Jun 30 '13 at 21:10

3 Answers 3

air moving along the inner surface of the fan naturally creates a lower pressure inside... bernoulli's principle.

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3 down-votes and no comments..? Too bad of these guys. I'd say that, It's better to comment and start arguing rather than posting an answer & getting down-voted..! –  Waffle's Crazy Peanut Oct 21 '12 at 5:54
    
This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post. –  Manishearth Nov 24 '12 at 13:53

For your first question, think of the air kind of like sand. If you just slide you hand across the surface, some grains beneath the surface will move due to friction between the sand grains transferring the energy of your hand to other sand grains. The same thing happens in the air inside the ring, as air shoots out of the slit surrounding the ring it collides with the air particles already inside the ring and transfers some energy to them, thus pushing them out of the front of the fan.

Second, the low pressure area. As the air inside the ring is getting pushed out of the center of the ring by the air blowing out of the slit, then there will be a void, for lack of a better term, in the center of the ring. Think of this void as the low pressure zone, as the void grows in size, the air at the back of the fan wants to flow into the void and there fore gains momentum towards the front of the fan and it gets accelerated from the friction as it flows past the slit in the ring.

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There seems to be a lot of B.S. in the ads for this product, making it seem much more complicated than it really is.

It seems that the fan contains an ordinary fan in its base, and squirts out high speed jets of air from around the big ring. These jets of air push on the ambient air. This slows down the individual jets but pushes along a greater volume of air.

This link seems to have a more reasonable explanation than many other sites, which tend to simply reproduce press-release hyperbole: http://www.pocket-lint.com/news/27887/how-dysons-air-multiplier-works

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Thanks for your reply. Still a couple things I don't understand. First, why does friction in the air create entrainment? Second, how does "air that gets pushed away from the ring towards your beautiful face creates an area of low pressure"? I don't understand how that area of low pressure cone about. Thanks –  rabbid Feb 20 '12 at 12:22
    
it's the same principle as any fan (at least any i know of) works: it propels the air in one direction, and because there are then less air molecules behind (because they moved towards you), the pressure is lower than the average room air pressure, which causes the air molecules behind to move towards the fan to equalize that pressure gradient. –  nonchip yesterday

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