The bladeless fan seems to work by magic. It appears to be a plain hoop on a fat stick, but when you switch it on, air blows from the hoop even though you see no fan blades. It's not magic, though. It's simply a clever application of the same basic aerodynamic principles that enable jet planes to fly.
It Has Blades
The "bladeless" fan actually has blades driven by a 40-watt electric motor concealed in the base of the unit. The motor-driven impeller fan sucks air through vent holes in the base and pushes it into the hollow hoop. The back of the hoop has a 1.3 mm-wide slot running completely around the hoop and facing forward. Air is blown through the toward a Coanda adhesion airfoil that channels the air into a straight forward-moving annular jet stream.
How It Works
The bladeless fan dramatically increases air circulation. As air is forced from the relatively fat hoop through the thin slot, it speeds up and its pressure drops. The high-velocity, low-pressure annular air stream sucks room air in from behind and alongside the hoop. This has the effect of multiplying the circulation of air, as it puts out 15 units of air for every unit of air drawn into the fan's base. The basic 10-inch table fan moves up to 5.28 gallons of air per second, equal to 40 cubic feet of air per minute.
Advantages
Bladless fans offer tilt, oscillation and multi-speed features similar to bladed fans. Conventional fans need unsightly cages to keep children and pets away from the spinning blades. The blades of the "bladeless" fans are concealed in a base housing that's inaccessible unless you break the fan apart. Conventional fan blades and their cages become coated with airborne dust and dirt and are hard to clean. Bladeless fans can simply be wiped clean. The airstream from bladeless fans is smooth, without the buffeting created by bladed fans.
Drawbacks
The Dyson company introduced the original "Air Multiplier" bladeless fan in October 2009 and sold it for $300, a price that put off some potential buyers. Within a year, imitators were selling similar machines for less than a third that price. Apart from the price of some machines, the major complaint about bladeless fans is the noise, which resembles the sound of a tiny vacuum cleaner when the fan is at full speed. The noise isn't very noticeable, however, when the fan is run at half-speed.
Tags: annular stream, bladed fans, bladeless fans, , thin slot, through thin, through thin slot