As the name suggests an air filter is a device that purifies the air by filtering disease-causing contaminants from the air. In this context we mean allergens in the air. Many air borne allergies can be avoided by filtering the air. In this article we give the classification of air filters, explaining the principle of working.
Air Filters are broadly classified as:
- Mechanical Air Filter
- Electronic Air Filters
Mechanical Air Filters:
Mechanical air filters have fibers in the filter media which actually filter the air. When sub-micron particles in the air come in contact with the surface of fibers they adhere to the fibers. There are 4 ways or mechanisms by which the filter media filters the particles or allergens from the air. They include:
Impaction: The mechanism is based on inertia. Larger particles have higher mass. Compared to smaller particles they are harder to turn. Due to inertia, the particles continue to travel in a straight line even though the air stream is turning past the fiber. They come in contact with the fiber and are attached to the fiber. Thus are filtered.
Sieving: This method is used for separating large particles. The particles get struck in the filter media and can’t make their way through the filter media. Impaction and sieving are the methods to filter larger particles.
Interception: In the method of interception, a particle is intercepted. It is an advanced method where smaller particles are filtered. When the inertia is not strong enough for the particle to continue in a straight line, a distance equal to one radius of itself is crucial for filteration. At this distance the particle gets attached to the fiber.
Diffusion: Very small particles do not follow the air stream precisely. Instead they “vibrate.” This is called Brownian motion. This erratic movement is used to increase the probability of the particles to come in contact with the fibers. The mechanism is called diffusion.
Electronic Air Filters:
These filters have external power source to impose a charge on the particles. A set of parallel plates are placed onto which the particles are collected after getting charged. According to the principle of electronics, the charged particle are attracted to a plate of the opposite charge. Here the plates require maintenance by regular cleaning in order to retain maximum efficiency.
