Dust masks are designed to prevent dust from entering the human respiratory system. How is this anti-dust function achieved? Let's take a look at the filtration mechanism of the dust mask to find out.
1. Impact effect, inertial effect - surface filtration
Impact: When the dusty airflow approaches the fiber, the dust particles with large particle size and high wind speed contact or collide with the fiber , intercepted by fibers.
Inertia: When the dust-laden airflow passes through the curved mesh channel of the filter material, the dust particles with large momentum will deviate from the direction of the streamline due to inertia, collide with the fiber and be intercepted. For masks, the inertial deposition of dust particles with larger particle size, higher density and faster speed is obvious. (Supplementary note: Momentum refers to the product of the mass and velocity of an object; particle size refers to the diameter of dust particles)
Second, diffusion - deep filtration
Dust particles in the airflow Collisions with gas molecules produce random Brownian motion, which results in irregular movement of particles; when a dusty airflow approaches or passes through the filter material, this motion causes the particles to diffuse and randomly collide with fibers, thereby being collected (deposited) on fiber cotton. When the particle size and wind speed are low, the diffusion deposition is obvious.
3. Electrostatic action (molecular action) 3354 electrostatic filtration
When the distance between the dusty airflow and the fiber surface is less than or equal to the dust particle radius r, due to the molecular attraction with the fiber ( Molecular interaction), dust particles with smaller particle size are adsorbed and captured by fibers. In other words, dust particles will generate charges due to mutual friction during crushing and movement, and the polarities of charges carried by different substances are also different. Dust particles with different charges attract each other to form larger new particles, which are easier to be intercepted; on the other hand, dust particles with the same charge are easier to catch because they repel each other and spread (Brownian motion).
According to the charged characteristics of dust particles, we can use electrostatic fibers as filter materials for dust masks. When the dust-laden airflow touches the filter material, the airflow continues to move forward after passing through the filter material, and the dust particles with positive and negative charges will be captured by the electrostatic fiber. The greater the amount of charge carried by the filter material, the higher the dust blocking efficiency.
4. Modified filtration
When the dusty airflow is in contact with the high-energy composite dustproof material (a filter material), the airflow passes through, and the respirable dust will adhere and Agglomeration, less than 10m dust.
To sum up, when the dust-laden airflow passes through the filter material of the dust mask, under the joint action of various filtering mechanisms, the greater part is due to inertia or impact. Being intercepted, smaller particles are deposited on the fiber due to diffusion or static electricity, or become new large particles due to static electricity, and are intercepted in the airflow due to collision with the fiber or deposited under the action of inertia.