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What is the principle of dust mask filtering dust

Update:01-06-2021
Summary:

The filter materials of each layer of dust masks are ge […]

The filter materials of each layer of dust masks are generally composed of non-woven fabrics, which rely on fiber filtration to achieve the filtering function. Dust masks usually have five principles of fiber filtration dust: electrostatic adsorption, gravitational deposition, inertial deposition, diffusion deposition effect and direct capture.
1. Gravity deposition
It means that some relatively large particles passing through the mask filter material deviate from the streamline direction due to gravity and deposit on the fibers when they are moving.
2. Diffusion deposition effect
The collision of particles in the airflow with gas molecules that are continuously thermally moving will produce random Brownian motion, causing small particles to move randomly. This motion will cause random collisions between particles and fibers. Dust particles are caused by the gravitational force of fiber molecules. Is adsorbed. The diffusion deposition effect is the easiest to capture small-scale particles and low-speed moving particles.


3. Direct capture
Direct capture means that the larger dust particles moving with the airflow are trapped by the mechanical sieving effect of the filter material, or when the streamline approaches the fiber, the particles come into contact with the fiber and are captured by the fiber. Generally, large-diameter particles are mainly filtered by direct capture, and particles with irregular shapes are more easily captured than spherical particles. The ratio of the particle diameter to the diameter of the filter fiber affects the interception efficiency.
4. Electrostatic adsorption
The floating particles in the air of the working environment are mostly positively or negatively charged. The filter layer fibers of modern dust masks are mostly electret fibers with polarized charges. When the charged particles in the air pass near the electret, they are strongly adsorbed on the electret fibers; while the uncharged particles in the floating particles will be polarized by induction in the electric field formed by the electret, and will also be polarized by the electret. Adsorbed to the fiber.
5. Inertial deposition
When the particles in the air flow through the curved mesh channel of the filter material, the particles with greater momentum will deviate from the direction of the flow line due to inertia, collide with the fiber and be captured, and be trapped due to the intermolecular force. This is the inertial deposition. The occurrence of inertial deposition depends on the aerodynamic diameter of the particles. Particles with larger aerodynamic diameters are more likely to impact the fibers than particles with smaller diameters. For dust masks, the inertial deposition effect is more obvious when the density of large particles in the airflow is higher and the speed is faster.

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