The filtering principle of the air filter separates the liquid water and liquid oil drops in the compressed air, and filters the dust and solid impurities in the air, but cannot remove the gaseous water and oil.

The removal technologies of particulate matter in the air mainly include mechanical filtration, adsorption, electrostatic precipitation, negative ion and plasma method, electrostatic stationary filtration and so on.

Mechanical filtration generally catches particles through the following three ways: direct interception, inertial collision and Brownian diffusion mechanism. It has good collection effect for fine particles but large wind resistance. In order to obtain high purification efficiency, the filter element needs to be dense and replaced regularly.

Adsorption is the use of large surface area and porous structure of materials to capture particulate pollutants, which is easy to block, and the removal effect of gas pollutants is more significant;

Electrostatic precipitator (ESP) is a dust collecting method that uses high voltage electrostatic field to ionize the gas, so that the dust particles can be charged and adsorbed on the electrostatic precipitator. Although the wind resistance is small, the trapping effect on larger particles and fibers is poor, which will cause discharge, and the cleaning is troublesome and time-consuming. It is easy to produce ozone and form secondary pollution.

The working principle of negative ion and plasma method to remove indoor particulate pollutants is similar. They both make the particles in the air charged, coalesce to form larger particles and settle. However, the particles are not actually removed, but are attached to the nearby surface, which is easy to cause dust again.

Electrostatic static filter can effectively block particulate pollutants in the air, such as dust, wool, pollen, bacteria, etc. at the same time, the ultra-low impedance ensures the stable operation of air conditioning and refrigeration effect.

The traditional standard filter media can remove more than 10 micron particles effectively. When the particle size is in the range of 5 μ m, 2 μ m or even submicron, the mechanical filtration system of * will become more expensive and the wind resistance will increase significantly. Through the electrostatic air filter material filtration, it can achieve high capture efficiency with low energy consumption, and has the advantages of electrostatic dust removal and low wind resistance, but it does not need to be connected to the external voltage, so it will not produce ozone, and because of its composition of polypropylene material, it is very convenient for disposal.

intercept

The dust particles in the air move with the air flow in inertial motion or irregular Brownian motion or under the action of a certain field force. When the particles collide with other objects, the van der Waals force (the force between molecules or between molecular clusters) makes the particles stick to the fiber surface. The dust entering the filter medium has more chances to hit the medium, and it will be stuck when it hits the medium. The smaller dust particles collide with each other to form larger particles and settle. The concentration of dust particles in the air is relatively stable. This is why the interior and walls fade.

It's wrong to think of fiber filters as sieves.

Inertia and diffusion

The particle dust makes inertial motion in the air flow. When encountering the disordered fibers, the air flow changes direction, and the particles are stuck because of the inertial deviation. The bigger the particle, the easier it is to impact, and the better the effect.

Small particles of dust make irregular Brownian motion. The smaller the particles are, the stronger the irregular movement is, the more chances of hitting obstacles are, and the better the filtering effect is. The particles smaller than 0.1 μ m in the air mainly make Brownian motion, and the particles are small, so the filtering effect is good. Particles larger than 0.3 μ m are mainly in inertial motion, and the larger the particles are, the higher the efficiency is. Diffusion and inertia are not obvious particles can be filtered out. When measuring the performance of the filter, people often specify the dust efficiency value which is difficult to measure.

Electrostatic action

For some reason, fibers and particles may be charged, resulting in electrostatic effect. The filtering effect of the filter material with static electricity can be obviously improved. Cause: static electricity makes the dust change the track of movement and hit obstacles, static electricity makes the dust stick more firmly on the medium.

Materials that can carry static electricity for a long time are also called electret materials. When the material is static, the resistance will not change and the filtration effect will be improved obviously. Static electricity does not play a decisive role in the filtration effect, but only plays an auxiliary role.

Chemical filtration

Chemical filter mainly selectively adsorbs harmful gas molecules.

There are a large number of invisible micropores in activated carbon materials, which have large adsorption area. In the activated carbon with the size of rice grain, the area of micropore is more than ten square meters.

Some of them are in contact with the active molecules in the capillary, and some of them are in contact with the active molecules in the capillary. Adsorption without obvious chemical reaction is called physical adsorption.

In some cases, activated carbon is treated and the adsorbed particles react with the material to produce solid substances or harmless gases, which is called chemical adsorption.

In the process of using activated carbon, the adsorption capacity of the material is constantly weakening. When it weakens to a certain extent, the filter will be scrapped. If it is only physical adsorption, the harmful gas can be separated from the activated carbon by heating or steam fumigation, and the activated carbon can be regenerated.

Gravity effect

When the particles pass through the fiber layer, under the action of gravity, they move away from the airflow streamline and settle on the fiber surface. This effect only exists when the particles are larger (> 0.5um). This is because the gravity effect of the particles is too small. When they have not settled on the fiber, they have passed through the fiber layer with the airflow. Therefore, for the filtration of particles with particle size less than 0.5um, gravity sedimentation can be completely ignored.