Mechanical filtration generally captures particles in the following 3 ways: direct interception, inertial collision, Brown diffusion mechanism, which has a good effect on fine particle collection but large wind resistance, in order to obtain high purification efficiency, the filter element needs to be dense and replaced regularly. The main technologies for removing particulate matter in the air are mechanical filtration, adsorption, electrostatic fine bubble diffuser dust removal, negative ion and plasma methods, and electrostatic electret filtration.  Adsorption is the use of large surface area and porous structure of the material to capture particulate pollutants, which is easy to block, and the effect of gas pollutant removal is more significant; Electrostatic precipitator is the use of high-voltage electrostatic field to ionize the gas so that the dust particles are charged to the electrode dust collection method, although the wind resistance is small, but the effect of capturing larger particles and fibers is poor, it will cause discharge, and cleaning trouble is time-consuming, easy to produce ozone, the formation of secondary pollution.
The influence of wind speed on the air filter, the diffusion effect disc air diffuser of small particle size dust (Brownian motion) is obvious, the wind speed is low, the air flow remains in the filter material for a longer time, and the dust has more opportunities to hit obstacles, so the filtration efficiency is high. Experience has shown that for HEPA filters, the wind speed is reduced by half, the dust transmittance is reduced by nearly an order of magnitude (the efficiency value is increased by a 9), the wind speed is doubled, and the transmittance is increased by an order of magnitude (efficiency is reduced by a 9). Similar to the effect of diffusion, when the filter material is electrostatic (electret material), the longer the dust remains in the filter media, the more likely it is to be adsorbed by the material. Changing the wind speed, the filtration efficiency of the electrostatic material will change significantly. If you know that there is static electricity on the material, the air conditioning system should be designed to minimize the airflow through each filter. For large particle dust based on inertia mechanism, according to traditional theory, after the wind speed is reduced, the probability of dust colliding with fibers will be reduced, and the filtration efficiency will be reduced. But in practice, this effect is not obvious, because the wind speed is smaller, the rebound force of the fibers to the dust is also smaller, and the dust is more likely to be stuck. The wind speed is high, and the rapid sand filters resistance is large. If the service life of the filter is based on the final resistance and the wind speed is high, the service life of the filter is short. It is difficult for the average user to actually observe the effect of wind speed on filtration efficiency, but it is much easier to observe the effect of wind speed on drag. For high-efficiency filters, the speed of air flow through the filter material is generally 0.01 ~ 0.04m /s, in this range, the resistance of the filter is proportional to the filter air volume. For example, a 484×484× 220mm hePA filter, the initial resistance of 250Pa at the rated air volume of 1000m3/h, if the actual air volume in use is 500m3/h, its initial resistance can be reduced to 125Pa. For the general ventilation filter in the air conditioning box, the speed of air flow through the filter material is in the range of 0.13 ~ 1.0m / s, the resistance and air volume are no longer linear relationship, but an upward arc, the air volume increases by 30%, the resistance may increase by 50%, if the filter resistance is a very important parameter for you, you have to ask the filter supplier for a resistance curve.