The diffusion of small particle size dust (Brownian motion) is obvious, the wind speed is low, the airflow stays in the filter material for a longer period of time, and the dust has more chance to hit the obstacle, so the filtration efficiency is high. Experience has shown that for high-efficiency filters, the wind speed is reduced by half, the dust transmission rate is reduced by nearly an order of magnitude (the efficiency value is increased by a factor of 9), the wind speed is doubled, and the transmission rate is increased by an order of magnitude (efficiency is reduced by a factor of 9 ).
Similar to the effect of diffusion, when the filter material is electrostatically charged (electret material), the longer the dust stays in the filter material, 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 on the material, you should minimize the amount of air passing through each filter when designing your air conditioning system.
For large particle dusts based on the inertial mechanism, according to the traditional theory, after the wind speed is reduced, the probability of dust and fiber collision will decrease, and the filtration efficiency will decrease. However, in practice this effect is not obvious, because the wind speed is small, the rebound power of the fiber against the dust is also small, and the dust is more likely to be stuck.
The wind speed is high and the resistance is large. If the filter's service life is based on the final resistance, the wind speed is high and the filter life 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 resistance.
For high-efficiency filters, the velocity of the airflow through the filter material is generally 0.01 to 0.04 m/s. Within this range, the resistance of the filter is proportional to the amount of filtered air. For example, a 484 × 484 × 220mm high-efficiency filter with an initial resistance of 250Pa at a 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 the airflow through the filter material is in the range of 0.13~1.0m/s, and the resistance and the air volume are no longer linear, but an upward arc, the air volume is increased by 30%, the resistance It may increase by 50%. If the filter resistance is a very important parameter for you, you should ask the filter supplier for the resistance curve.