The Principle of HEPA Filter or Activated Carbon Filter(1)

There are several filtering methods of air filters. We will clarify them in 2 articles seperately.

negative ion car air purifier
negative ion car air purifier

The first thing to be clear is that all kinds of dust, TVOC, formaldehyde, no matter solid, liquid, bacteria, pollen, as long as they can be classified as particulate matter, the filter will treat them the same. Totally blocked.
The fibers are intricately arranged within the fiber layer of the filter, forming countless grids. When a particle of a certain size moves along the airflow streamline (or inertia, or random Brownian motion or some kind of field force) just to the vicinity of the fiber surface, if the flow from the streamline (also the centerline of the particle) to the fiber surface When the distance is equal to or less than the particle radius, the particles are intercepted and deposited on the surface of the fiber. This effect is called the interception effect, and the sieve effect belongs to the interception effect.


When the airflow filled with various dusts passes through the HEPA fiber layer, which is inside the car air purifier,  due to the complex arrangement of the fibers. The airflow streamline must turn violently many times. When the mass of the particles is large or the speed (which can be seen as the speed of the airflow) is large, when the streamline turns, the particles cannot follow the streamline and bypass the fiber at the same time due to inertia, so they leave the streamline and approach the fiber, and collide with the fiber. After sedimentation, if the particles do not hit the fiber surface head-on but just hit the interception effect range due to inertia, the particles are intercepted by the combined action of these two effects.

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