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What particles in the HEPA air filter are the most difficult to stop?

2019-03-13

1. The smallest particle dust with a diameter of 0.1 micron or less will have irregular Brownian motion in the air due to its extremely small weight. There will be some differences in the direction of the airflow, so there are more opportunities to hit the fiber. This filtering action is called "diffusion," and this type of particulate matter is fairly easy to block.

2. The weight of particles larger than 0.3 microns in diameter is larger, so the principle of blocking them is different. When the air stream contacts the fiber, the airflow reverses direction and wraps around the fiber. However, some of the larger particles are too heavy to adjust direction with the airflow, so they come into contact with the fibers and are blocked by the fibers. This filtering action is called "inertial impact" and this type of particulate matter is also relatively easy to block.

3. Fine particles with a diameter of about 0.1-0.3 microns are the most difficult to block. They are the easiest to follow the airflow, around the fibers of the HEPA air filter, not easily accessible to the fibers, and because they are heavier, they do not sway in the air. These most difficult to block particles are called "most penetrating particulate matter" (MPPS).

The filtration effect of all grades of HEPA air filter is calculated according to the MPPS filtration effect. For example, the H11air filter has a filtration effect of more than 95%; this means that the most penetrating particulate matter has a filtration effect of not less than 95%, while particles smaller than 0.1 micron and particles larger than 0.3 micron have a higher filtration effect (97). %, even 99%).