Bladeless Fans - Air Multipliers

Dyson fans are advertised as bladeless fans or air multipliers. The technology behind it is quite fascinating.

Overview

The first thing that you notice is a large ring shape and no fan blades. There are small slit openings facing the front, where air is exhausted from the device.

The second thing is the whirring located at the base of the unit. This is where the impeller or intake fan is housed. Air flows in from teh base and is pushed out of the ring.

Science Of How It Works

Ring

The ring has small slits in the front, where air is pushed out from the unit. The ring surface is curved convex (outwards) at a small angle, ~15 degrees. This results in the Coanda Effect, where air “clings” to the surface of an air foil. The combination of these two effects produces an area of low pressure in the middle of the ring. High pressure air from behind the unit flows in (inducement). So the ring shape is not a coincidence, it’s very important to the design.

See this video for visual explanation of the effect.

Fan

The fan in the base pushes air into the ring. Because it’s enclosed in duct, the airflow is directed in the same direction. A small fan can efficiently achieve significant flow rates.

Airflow

The airflow that leaves the unit is directed and smooth. Surrounding air is pulled into the low pressure (fast moving) currents. This is called entrainment.

Conventional fans do not experience this because their airflow is more turbulent:

• fan blade and motor are directly in the path of airflow
• output air is not channeled in the same direction

Compared to Conventional Fans

Air multipliers seem really cool and not just gimmicky. Their airflow is smooth and efficient. The ring has a clear opening for air to flow without obstruction.

The conventional fan blade causes turbulence because the tangential velocity of the blade tip is higher (faster and pushes more air) than the middle of the blade. This makes the air flow less targeted.

The impeller is housed in a sealed section, allowing for efficient and contained intake. A small fan is sufficient to power the entire unit. This is what allows the small footprint or narrow body designs.

Conventional fans must be spun faster or have wider radius, to achieve higher airflow. Air multipliers use smaller fans, which can be noisy. This is more-so a design trade-off, small footprint for louder noise.