How Cyclonic Separation Works

Power of the Cyclone

Cyclonic separation at work in a Dyson vacuum cleaner.
Cyclonic separation at work in a Dyson vacuum cleaner.
Image courtesy Dyson

Let's start with the basics. Cyclonic separation can eliminate particulates, such as dirt and dust, from a stream of air, gas or liquid. Engineers sometimes call these tornadic dust busters centrifugal separators. That's because at the root of these machines is something called centrifugal force [source: University of Delaware].

Think back to your high school physics class. Centrifugal force is the tendency of an object following a curved path to fly away from the center of the curvature. Remember the ball and string experiment? Sure you do. You swung a ball on a string over your head. What happened when you released the string? The ball flew off on a path that was tangential to its radius at the point of release. That's centrifugal force, which is not to be confused with centripetal force, the moving of an object toward a center or axis (or what compels the ball to keeping moving in a circle over your head until you release it).

Yet, centrifugal force is not a real force, but a form of inertia, the tendency of an object to move in a straight line until another force acts upon it. In a cyclonic separator, typically air laden with dirt and dust is pumped through the top of a vertical cylinder with a conical bottom. The fast-moving air enters the chamber at the top of the cylinder and begins rotating violently. As that happens, a mini tornado or cyclone forms [source: Wacharawichanant].

The air and dust spin wildly in a circular, spiraling motion. Because the particulates have more mass than air molecules, a greater force is needed to keep the debris moving in a circle. But there is no such force inside the cyclonic chamber. As the whirling mass of air spins, the heavier particles start to diverge and move toward the wall of the chamber. Because these large, dense particulates have too much inertia to follow the curvature of the air, they're thrown against the sides. Smack, the particles slam into the wall, sliding to the bottom of a dust trap or bin [sources: Wacharawichanant, University of Delaware].

Finally, the "clean air" near the bottom of the cyclone changes direction and moves up the center of the cylinder to an exhaust tube or outlet, which is usually connected to a filter that catches any remaining fine particles [source: University of Delaware].