Principle of air filter

1: interception

The dust particles in the air move with inertial motion or random Brownian motion of the airflow or by some field force. When the particle motion hits other objects, the van der Waals force exists between the objects (molecular and molecular, molecular group and The force between the molecular groups causes the particles to stick to the surface of the fiber. The dust entering the filter media has a greater chance of hitting the media, and it will stick if it hits the media. The smaller dust collides with each other to form larger particles and settle, and the particle concentration of the dust in the air is relatively stable. The fading of the interior and walls is for this reason.

It is wrong to treat the fiber filter like a sieve.

2: inertia and diffusion

The particulate dust moves in inertia in the airflow. When encountering the fibers arranged in disorder, the airflow changes direction, and the particles are bound by the inertia deviating from the direction and hitting the fibers. The larger the particle, the easier it is to impact, and the better the effect.

Small particle dust is used for random Brownian motion. The smaller the particles, the more intense the irregular movements, the more chances of hitting the obstacles and the better the filtering effect. Particles smaller than 0.1 micron in the air are mainly used for Brownian motion, and the particles are small and the filtering effect is good. Particles larger than 0.3 microns are mainly used for inertial motion, and the larger the particles, the higher the efficiency. It is not obvious that the diffusion and inertia are difficult to filter out. When measuring the performance of high-efficiency filters, it is often prescribed to measure the dust efficiency values ​​that are difficult to measure.

Air filter principleAir filter efficiency

3: Electrostatic action

For some reason, fibers and particles may be charged, creating an electrostatic effect. The filtering effect of the electrostatically charged filter material can be significantly improved. Cause: Static electricity causes the dust to change its trajectory and hit an obstacle. Static electricity makes the dust stick more firmly on the medium.

Materials that can carry static electricity for a long time are also called "electret" materials. The resistance of the material after static electricity is unchanged, and the filtration effect is obviously improved. Static electricity does not play a decisive role in the filtration effect, but only plays an auxiliary role.

4.: Chemical filtration

Chemical filters primarily selectively adsorb harmful gas molecules.

There are a large number of invisible micropores in the activated carbon material, which have a large adsorption area. In the activated carbon of rice size, the area inside the micropores is more than ten square meters.

After the free molecules are in contact with the activated carbon, they condense into a liquid in the micropores and remain in the micropores due to the capillary principle, and some are integrated with the material. Adsorption without a distinct chemical reaction is called physical adsorption.

Some treat the activated carbon, and the adsorbed particles react with the material to form a solid substance or a harmless gas, which is called a Huai adsorption.

The adsorption capacity of the activated carbon during the use of the material is continuously weakened, and when it is weakened to a certain extent, the filter will be scrapped. If it is only physical adsorption, the activated carbon may be regenerated by heating or steaming to remove harmful gases from the activated carbon.

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