In this blog post, we’ll explore the operating principle behind the “Air Multiplier”—a bladeless fan that generates a strong breeze using only a small amount of air.
It is said that early fans took the form of large fans suspended from the ceiling, designed to swing like a pendulum using the weight of a counterweight. Later, after the development of machines that connected a windmill to a spring mechanism, electric fans became widely available in the late 1800s. However, this also led to numerous safety accidents. The main cause was accidents involving curious young children sticking their fingers into the fan blades. Although protective grilles were installed around the fan blades to prevent such accidents, safety incidents involving fan blades still occur frequently today. So, is it possible to reduce these accidents by changing the very structure of the fan itself? The British company Dyson has presented one answer to this question by developing the “Air Multiplier,” a bladeless fan.
The Air Multiplier consists of a column-like main body with a circular ring attached to its top. When turned on, air mysteriously flows out of this circular ring. While the airflow from the ring may feel slightly weaker than that of a conventional fan, it produces a much more uniform breeze compared to fans with blades. So how does air come out of an empty ring? As the product name “Air Multiplier” suggests, the core principle of this product is to amplify a small amount of air into a large volume of airflow.
First, to amplify the airflow, a device that generates air is needed. So where is this air generated? In fact, a motor and a small fan are hidden inside the column at the bottom. When this fan rotates at high speed, it draws in air from below, much like an exhaust fan sucks in surrounding air. To draw in the air, the bottom of the column is equipped with a fine mesh intake. The air generated in this way travels at a very high speed but is present in only a small volume, making it difficult to use directly as fan airflow.
How can we generate a strong breeze from such a small volume of air? After all, wind is created by the flow of air. When a large volume of air moves in one direction, the wind becomes stronger. What if we could make the air around the Air Multiplier flow in a single direction? Fluids, such as air, move from areas of high pressure to areas of low pressure. Therefore, if we can lower the pressure inside the ring, the surrounding air will naturally flow into it.
Air pressure is closely related to the number of air molecules present in a given space. As the speed of air increases, the distance between air molecules grows—similar to how the spacing between cars on a road widens as they drive faster. When the distance between air molecules increases, the number of air molecules in the same space decreases, and as a result, the pressure drops. In other words, the faster the air moves, the lower the pressure becomes.
Therefore, if the air velocity inside the ring can be increased, the pressure will drop, and as a result, air surrounding the Air Multiplier will flow into the ring. So, how can we increase the air velocity inside the ring? To achieve this, two distinctive engineering designs have been applied to the cross-section of the circular ring.
The first is a design that utilizes a very narrow gap. Air drawn up from the bottom flows along the inner wall of the ring due to the viscosity of the fluid. This is similar to the phenomenon where water flows along the surface of a teapot when pouring. The air flowing along the wall exits through a narrow gap; just as narrowing the opening of a hose causes water to spray out more rapidly, the air passing through the narrow gap is also ejected at a very high speed.
The second design features a cross-section shaped like an airplane wing. If you look at the ring’s cross-section, the upper part is relatively flat, while the lower part forms a bulging curved surface. When the pressure inside the ring drops due to air being rapidly ejected through the narrow gap, surrounding air begins to flow into the ring. As this incoming air flows along the convex curve, the pressure difference increases further, resulting in the ring drawing in more ambient air than it would without the curved surface.
When these two design elements are combined, the air surrounding the Air Multiplier is strongly channeled into the interior of the ring. Dyson explains that this principle allows the device to draw in significantly more ambient air than the amount drawn in by the internal fan, thereby greatly increasing the overall airflow. The principle behind the Air Multiplier—using a small amount of air to draw in ambient air and create a stronger breeze—is a creative, easy-to-understand, and highly intriguing piece of technology.
