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Effect of low wind speed on the filtration effect of air filter

Nov 15, 2019

Everyone knows that the filtering effect of the air filter has a certain relationship with the wind speed. Most people may think that the higher the wind speed, the better the filtering effect of the air filter, but the reality is just the opposite. The smaller the wind speed, the better the filter will be. The following is a description of the effect of low wind speed on the filtration effect of the air filter by the North Filter:

 

The diffusion of small particle size dust (Brownian motion) is obvious, the wind speed is low, the airflow stays in the filter data for a longer period of time, and the dust has more opportunities to hit the obstacle, so the filtration efficiency is high. According to the experience, 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 (the efficiency is reduced by a factor of 9).

Similar to the effect of diffusion, when the filter material is electrostatically charged, the longer the dust stays in the filter material, the more likely it is to be adsorbed by the material. When the wind speed is changed, the filtration efficiency with electrostatic materials will be significantly changed. If you know that there is static on the material, you should reduce the amount of air passing through each filter as much as possible when stopping the design of the air conditioning system.

Regarding the large particle dust mainly based on the inertial mechanism, according to the conventional theory, after the wind speed is lowered, the probability of the dust colliding with the fiber is reduced, and the filtration efficiency is lowered. However, in theory, 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 service life of the filter is based on the final resistance, the wind speed is high and the service life of the filter is short. It is difficult for ordinary users to see the effect of wind speed on filtration efficiency, but it is much easier to see the effect of wind speed on resistance.

Regarding the high-efficiency filter, 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 air filter is proportional to the amount of filtered air. For example, a 484×484×220mm KLC high-efficiency filter has an initial resistance of 250Pa at a rated air volume of 1000m3/h. If the applied air volume is 500m3/h, its initial resistance can be reduced to 125Pa. Regarding the ordinary ventilation filter in the air-conditioning box, the speed of the airflow through the filter material is in the range of 0.13 to 1.0 m/s, and the resistance and the air volume are no longer linear, but an upward arc, the air volume is increased by 30%, and the resistance is increased. 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.


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