Principle and filtration efficiency parameters of high-efficiency filters without partitions
Jan 10,2022
Principle and filtration efficiency parameters of high efficiency filter without partition:
The principle of non-partition high efficiency filter by the dust particles in the air, with the air flow for inertial motion or irregular Brownian motion or by a certain field force and move, when the particle movement into other objects, the van der Waals force between the objects (is the molecule and the molecule, the force between the molecular group and the molecular group) makes the particles stick to the fiber surface.
The dust entering the filter medium has more chances to impact the medium, and it will be stuck when it hits the medium. Smaller dust colliding with each other will bond to form larger particles and settle, and the particle concentration of dust in the air is relatively stable. No partition high efficiency filters in the room and walls fade because of this reason. It is a mistake to think of a fiber filter like a sieve.
Inertia and diffusion
The particle dust of the high efficiency filter without partition makes an inertial movement in the air stream, and when the fiber is arranged in a disorderly manner, the air stream changes direction, and the particle deviates from the direction due to inertia and hits the fiber and is bonded. The bigger the particle, the easier it is to hit, the better the effect.
Small particles of dust have random Brownian motion. The smaller the particle, the more violent the irregular movement, the more chance of hitting the obstacle, and the better the filtration effect will be. The particles less than 0.1 micron in the air of the high efficiency filter are mainly Brownian motion, and the particles are small and the filtration effect is good.
The particles larger than 0.3 microns of the high efficiency filter are mainly used for inertial motion, and the larger the particles, the higher the efficiency. Both diffusion and inertia are unclear so particles are the hardest to filter out. When measuring HEPA filter performance, it is often specified to measure the most difficult dust efficiency value.
Electrostatic action
High efficiency filters without partitions will for some reason, fibers and particles may be charged, resulting in electrostatic effects. The filtration effect of the filter material with static electricity can be significantly improved.
Cause: Static electricity causes the dust to change its movement path and hit the obstacle, and 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 with static electricity remains unchanged, and the filtration effect will be significantly improved. Static electricity does not play a decisive role in the filtration effect, only an auxiliary role.
Chemical filtration
The separator free high efficiency filter mainly selectively adsorbs harmful gas molecules.
There are a large number of invisible micropores in activated carbon materials, and there is a large adsorption area. In activated carbon the size of rice grains, the inner area of micropores is more than ten square meters.
After contact with activated carbon, free molecules condense into liquid in micropores because of the capillary principle to stay in micropores, and some are integrated with the material. Adsorption without obvious chemical reaction is called physical adsorption.
Some of the activated carbon is processed, and the adsorbed particles react with the material to generate solid substances or harmless gases, which is called chemical adsorption.
Activated carbon in the use of the material's adsorption capacity continues to weaken, when weakened to a certain extent, the filter will be scrapped. If it is only physical adsorption, the harmful gas can be removed from the activated carbon by heating or steam smoking, and the activated carbon can be regenerated.
Gravity effect
When a particle passes through the fiber layer, it dislocates from the flow line of the air stream and settles on the fiber surface under the action of gravity. This effect exists only when the particle is large (>0.5um), which is because the gravity effect of the particle is too small, and when it has not settled on the fiber, it has passed through the fiber layer with the air stream. Therefore, for the filtration of particles with a particle size less than 0.5um, the gravitational settlement can be completely ignored.
Filter efficiency parameters of high efficiency filter without partition:
Standard GB/T 13554-2008 "High Efficiency Air Filter", GB/T 6165-2008 "Karma small air filter performance test method efficiency and resistance", high efficiency filter sodium flame method efficiency is:
Class A high efficiency filter, the efficiency of sodium flame method at rated air volume should not be less than 99.9%
Class B high efficiency filter, the efficiency of sodium flame method at rated air volume should not be less than 99.99%
Class C high efficiency filter, at the rated air volume of sodium flame method efficiency should not be less than 99.999%
The former refers to the general high efficiency filter, in contrast, the efficiency of the foreign generally defined high efficiency filter is ≥99.97%.
The latter refers to ultra-high efficiency filters.
Now the international common detection method is DOP detection method, which is more accurate.
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