Engineering:Air multiplier

thumb|The Dyson Air Multiplier

An air multiplier, sometimes called bladeless fan, is a fan which blows air from a ring with no external blades. Its vanes are hidden in its pedestal and direct the collected airflow through a toroid, blowing a thin high-velocity smooth airflow from a continuous slot across the surface of the tube or toroid.

History

The first concept was created by Toshiba in 1981. Industrial designer James Dyson used the technique in a consumer fan, terming it the air multiplier.

Design

The design places fan blades inside the base. The air is drawn in by a compressor and directed up into a ring. It comes out of a slit around the ring and passes over a shape like that of an aircraft wing (Coandă effect). This design generates airflow up to 55 miles per hour (25 m/s).

The fan's pedestal contains a brushless electric motor that rotates nine asymmetrically, aligned blades attached to a rotor. Usually, the upper frame of this fan is ring-shaped. The frame's cross-section curves at a 16-degree angle slope.

Air flows through the channel in the pedestal. and upwards into the ring. Then the air is shot out through a 16-mm slit at the edge of the ring. This air flows smoothly, rather than turbulently as with a conventional fan. The curvature of the inner wall creates an area of negative pressure like an airplane wing to draw more air into the flow, hence "multiplying" it. This action is called entrainment. The ambient air surrounding the ring flows with the direction of the air exiting the slit (is "entrained" to it). Dyson claims that the fan's air output is at least 15 times greater than the air volume entering the pedestal.

Performance

The Spanish consumer advocate Organización de Consumidores y Usuarios tested Dyson's first Air Multiplier (AM01) and remarked on the further-reaching and stabler stream. It was found to use 40W and move 2700m³/h at its maximum setting. However, it was noisier and much more expensive (€300–€400 versus €20) than bladed fans. Another test found the AM01's power consumption to be variable between 2-3W and 31W.

Geek.com performed airflow, noise level, and power measurements on the AM06 and, aside from the first setting, was found to achieve similar levels of air speed and air volume moved per second while being quieter (2–10dB) and more energy efficient per volume of air moved (6–3×) depending on the setting. The highest setting reportedly produced 1150ft³/min (1950m³/h) and 548ft/min (2.7m/s). The volume was on par with an $80 regular fan and about twice as much as a $15 fan, while the air speed was roughly on par with both. At this setting, the AM06 produced 10dB less noise than either regular fan and used 20W, versus 60W and 40W used by the regular models. It concludes that while "there is more to the air multiplier than a bit of fancy plastic", "this data probably won’t convince anyone to buy a Dyson AM06". "The Dyson is for doctor’s offices, executive suites, and other places where air flow is nice to have, but design is paramount."