Air filters remove particles from the air flow as particles come into contact with the surface of fibres in the filter media and adheres to them. There are various mechanisms by which the particles come into contact with the fibre in the filter media.
Theory
Below is a brief explanation of the most common methods of air filtration in use today.
Straining
The most basic form of filtration, the particle is larger than the space between two fibres, and so, cannot follow the airstream through and is captured
Interception
Only found in synthetic filters, interception occurs when a particle follows the airstream but still attaches itself to the fibre as it passes around it. This is due to electrostatics attracting the particle towards the fibre where it is retained.
Diffusion
Occurs specifically with the very small particles which follow irregular patters, in a manner similar to gases, and not necessarily following the airstream. This irregular pattern is known as Brownian motion and increases the particles chance to capture through contact with the fibres.
Impingement
The mechanism by which large, high density particles are captured is called impingement. As the particulate laden air passes through the filter media, the air tends to pass around the fibres. Inertia of the particulate causes it to separate to separate from the airstream to collide with the fibres to which they become attached.
Electrostatic Attraction
Filters utilizing on electrostatic charges on the media fibre to increase their efficiency of fine particles removal. Due to attraction of the charges, the particles make contact with the fibre and becomes attached.
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