The Principle of HEPA Filter or Activated Carbon Filter (2)

We described both interception and inertia of air filters in the last article. Let’s share another 3 functions, namely diffusion, gravity and electrostatic interaction.

Car Air Purifier Refresher Portable
Car Air Purifier Refresher Portable

The Brownian motion of the particles is generated due to the collision of the thermal motion of the gas molecules with the particles, and the smaller the particles, the more significant the effect is. At room temperature, it is several times to dozens of times larger than the distance between fibers, which makes the particles have a greater chance to move to the fiber surface and deposit, while the Brownian motion of particles larger than 0.3pm is weakened, which is generally not enough to rely on Brownian motion. Leave the streamline and collide with the fiber.


When the particles pass through the fiber layer, they are displaced from the streamline under the action of gravity, that is, they are deposited on the fibers due to gravity sedimentation. Since the time for the airflow to pass through the fiber filter, especially the filter paper filter is much less than 1s, for particles with a diameter less than 0.5pn, they have passed through the fiber layer before they settle into the fiber, so the gravity sedimentation can be completely ignored.

Electrostatic Interaction

Due to various reasons, such as friction, both positive and negative electrons in the air, fibers and particles can be charged, creating an “electrostatic effect” that attracts particles

The above five functions explain the filtering mechanism of the filter, and also make it clear why we need to replace the filter in time under the condition of long-term use. Remember to replace the filter, it is a good habit. A good car air purifier supplier offers you wonderful HEPA filter that is endurable for a long time.

Links: Smart Wall Mount UV-C Air Sterilizer

car air purifier market