Principles of automotive air filters

The particulate pollutants suspended in the air are composed of solid or liquid particles. Atmospheric dust can be divided into narrowly defined atmospheric dust and broadly defined atmospheric dust: narrowly defined atmospheric dust refers to solid particles in the atmosphere, that is, real dust; the modern concept of atmospheric dust includes both solid particles and polydispersed aerosols of liquid particles, is Specially refers to the suspended particles in the atmosphere, the particle size is less than 10μm, this is the general atmospheric dust. For particles larger than 10μm, because of their heaviness, after a period of irregular Brownian motion, they will gradually settle to the ground under the action of gravity, which is the main target of ventilation and dust removal; 0.1--10μm in the atmosphere Dust particles also make random movements in the air. Because of their light weight, they tend to float with the airflow and are difficult to settle to the ground. Therefore, the concept of atmospheric dust in air cleaning technology is different from the concept of dust in general dust removal technology.
The dust filtered by nylon mesh air filter, metal mesh filter and foam sponge filter for ventilation and dust removal, because the pore size of the filter material is large, generally greater than 10μm, mainly to filter dust greater than 10μm, so for 0.1~~10μm Particles, the filtration efficiency is very low; if there is a certain degree of cleanliness requirements for the purification of the environment, the air filtration technology in the clean technology must be adopted to meet the purification requirements. The main task of air purification is to adopt air filtration technology to capture 0.1--10 μm suspended dust particles and microorganisms in the atmosphere according to the production process of various products, different processes, and the air cleanliness level of various rooms, so as to clean The concentration of dust particles or bacteria in the room or local purification area should be controlled within the allowable range to ensure the level of cleanliness.
In addition to tiny droplets in the shape of suspended particles in the air, other particles are crystalline, flake, block, needle, chain, etc., it is difficult to measure its size from the geometric shape. In the clean technology, the meaning of particle size refers to the passage of a certain length within the particles, which does not contain the meaning of regular geometric shapes, but only a "nominal size" that is convenient for comparing particle sizes.
Airborne particles are divided into non-biological particles and biological particles: non-biological particles are produced by the breaking, evaporation, combustion, and condensation of solids and liquids, and their formation process has physical or chemical effects. Biological particles include microorganisms, plant pollen, trifles, and villi. Microorganisms generally include viruses, Rickettsia, bacteria, fungi, protozoa, and algae. Among them, bacteria and fungi are more directly related to purification. The microorganisms in the air mainly adhere to the dust, so filtering the dust in the air can effectively remove the microorganisms in the air, which is also the main theoretical basis of biological purification.
According to the statistics of particles in atmospheric dust in different countries and times, the number of particles in atmospheric dust decreases significantly with the increase of particle size, that is, on a double logarithmic coordinate graph, the number and particle size have a linear relationship, especially for 0.1- --5μm; the distribution relationship between quantity and mass, the proportion of the number of sub-micron particles in the total is close to 100%, and the weight is only 2%--3% of the total; this is also the standard for cleanliness that can be used in different countries Theoretical basis.
Statistics show that the concentration of dust in rural areas is about 100,000 grains/liter, the concentration of dust in suburbs is about 200,000 grains/liter, and the concentration of dust in cities is about 300,000 grains/liter. It reached more than 1 million grains/liter.
1. Air filtration technology mainly adopts filtration and separation methods: by setting air filters with different performances, the suspended dust particles and microorganisms in the air are removed, that is, the dust particles are trapped and retained through the filter material to ensure the cleanness of the air volume Degree requirements. The filter material it uses is finer diameter fiber, which can not only make the air flow pass smoothly, but also effectively collect dust particles.
2. The dust filtered by the clean technology control is generally 0.1--10μm dust particles, the particle size is small, including solid particles and liquid particles; the organic particles suspended in the atmosphere are microorganisms, plant pollen, floc and fluff, microorganisms Generally include viruses, Rickettsia, bacteria, fungi, protozoa and algae. Air purification is mainly controlled by bacteria, fungi and viruses. Because microorganisms are mainly attached to dust particles, the effective control of dust particles in the air can also effectively control bacteria, fungi and viruses in the air. To do this, it must pass through a particulate filter with barrier properties before it can be filtered. In general, the efficiency of ordinary high-efficiency filters on bacteria can reach 99.996%, which can basically meet the requirements of filtration and purification of biological clean rooms. .
The filter layer of the air filter has 5 main functions of capturing particles:
1. Interception effect: When a particle of a certain size moves near the surface of the fiber, the distance from the center line to the surface of the fiber is less than the particle radius, and the dust particles will be intercepted by the filter material and deposited.
2. Inertial effect: When the mass of the particles is large or the speed is large, it is deposited due to the inertia impacting on the fiber surface.
3. Diffusion effect: The particles with small particle size have strong Brownian motion and easily collide with the fiber surface.
4. Gravity effect: When particles pass through the fiber layer, they are deposited on the fiber due to gravity settling.
5. Electrostatic effect: Fibers or particles may be charged, generating an electrostatic effect that attracts particles, and attracts particles to the fiber surface.
As more and more dust is collected, the filtration efficiency of the filter layer also decreases, and the resistance increases; when a certain resistance value or efficiency drops to a certain value, the filter needs to be replaced in time to ensure Purification cleanliness requirements.
The most common forms of filter materials for air filters are: non-woven fabrics, chemical fiber materials, glass fiber materials; they have less resistance and higher efficiency at rated air volume, are easy to replace and maintain, and have a wide range of applications. The system has extremely high use value and application fields.