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The science behind bladeless fans

The Dyson Air Multiplier, released in 2009, is a fan that claims to be quieter, more efficient and also a lot safer than your average cooling fan — and this in large part because it has no blades. Just how do these mysterious, bladeless fans actually work? Let us take a look.

The bladed fan that most of us are familiar with employs several blades attached to a central rotating hub to circulate air around the room. The Dyson Air Multiplier and other bladeless fans work very differently.

In these fans, air enters in through small slits at the base of the fan. The air is directed by a tiny fan powered by a small electric motor (so the bladeless fan aren’t technically bladeless after all!), up a tube to the topmost region of the fan where it enters another hoop-like tube, and eventually, is forced out of another narrow slit into the surroundings. science behind bladeless fansHere is the essential bit. What is pivotal to the operation of the bladeless fan is the effect of the shape of the loop, so let’s take a closer look. At its base, the hoop-like tube is wide. But towards the top it tapers and narrows, thereby ‘squeezing’ the air that passes through it and thus accelerating it, much the same way water sprays out of a hose faster when you place a finger over the nozzle. This accelerating effect ensures the air is propelled efficiently around the room. A second effect of the tube’s shaping is that it multiplies the amount of ar involved in the fan’s action – hence the name, ‘Dyson Air Multiplier’. You see, the inside of the hoop shaped tube is curved upwards similar to an aeroplane’s wing, which means that as air exits through the top slit, it adheres to the curved surface creating a vacuum. This induces surrounding air to be sucked through the hoop also and then pulled along with the electrically propelled air as the latter exits the fan. Similarly, the air around the edge of the tube is drawn through and caught up (‘entrained’) in the same movement as the electrically driven air exiting the tube.

These simple thermodynamic effects together (acceleration, ‘inducement’, and ‘entrainment’), allow the Air Multiplier to ‘multiply’ the original air intake about 15 fold. According to Dyson, their fans draw in about 20 litres of air every second. But because of the multiplier effect, they pump out a much more impressive 300 litres every second. And of course, because these fans are bladeless, another upshot is that there is no need to worry about stray fingers or hair being chopped off by the whirring blades. They also make a lot less noise than their bladed brethren.

There you have it then. The seemingly mysterious, magical action of the bladeless fan can actually be explained by simple physical principles and thermodynamics. The Dyson Air Multiplier has now been demystified for you.

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