Each layer of filter material of dust mask is generally composed of nonwovens, and the filtration function is realized by fiber filtration. Generally, the principle of fiber dust filtration has five aspects: electrostatic adsorption, gravity deposition, inertial deposition, diffusion deposition effect and direct capture
(1) electrostatic adsorption
most of the floating particles in the air of the working environment have positive or negative charges. The filter layer fiber of modern dust mask is electret fiber with polarization charge. When these charged particles in the air pass near the electret, they are strongly adsorbed on the electret fiber; The uncharged particles in the floating particles will be polarized by induction in the electric field formed by the electret, and will also be adsorbed on the fiber
(2) gravity deposition
refers to the deposition of some relatively large particles passing through the mask filter material on the fiber due to gravity deviation from the streamline direction< (3) inertial deposition when the particles in the air pass through the curved network channel of the filter material with the air flow, the particles with larger momentum will deviate from the streamline direction due to the inertial effect, collide with the fiber, and be trapped due to the intermolecular force, which is called inertial deposition. The occurrence of inertial deposition depends on the aerodynamic diameter of particles. Particles with larger aerodynamic diameter are easier to impact on the fiber than particles with smaller diameter. For the mask, the effect of inertial deposition is more obvious when the density of large particles in the air is higher and the velocity is faster (4) diffusion deposition effect the collision between particles in the air stream and continuously moving gas molecules will produce random Brownian motion, leading to irregular motion of small particles, which will lead to random collision between particles and fibers, and dust particles will be absorbed due to the gravitational action of fiber molecules. The diffusion deposition effect is easy to capture small-scale particles and low-speed particles (5) direct capture direct capture means that the larger dust particles moving with the air flow are intercepted by the mechanical screening of the filter material, or when the streamline is close to the fiber, the particles contact with the fiber and are captured by the fiber. Generally, large particles are mainly filtered by direct trapping, and irregular particles are easier to be trapped than spherical particles. The ratio of particle diameter to filter fiber diameter affects the interception efficiency when the filter material filters the polydisperse particles in the air, under the joint action of several filtration mechanisms, the smaller particles deposit on the fiber first due to diffusion, so when the particle size increases from small to large, the diffusion efficiency gradually decreases, while the larger particles deposit under the action of interception and inertia in this way, the filtration efficiency curve related to the particle size has a lowest point, and the total efficiency under the particle size is the smallest, so this kind of particle is the least easily trapped in the filter material by testing the filtration efficiency of various dust mask filter materials for the polydisperse particles in the air flow, it is found that the filtration efficiency of 0.31 μ m particles is always the lowest. Therefore, 0.3 μ m particle size is usually used as the particle size index to detect the filtration efficiency of filter media this article is a reprint of 1nternet media, which only represents the author’s point of view and has nothing to do with this website. 1f the information column articles and comments violate your legal rights, please call to let us know and we will deal with them in time