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The influence of wind speed on the existence of air filters
The influence of wind speed on the existence of air filtersWind speed is one of the important factors in the effectiveness of air filters. In daily use, we would say that the lower the wind speed, the better the filtering effect! The following is a brief analysis of this concept:The diffusion of small-size dust (Brownian leisure) is obvious, the wind speed is low, the airflow retention time in the filter material is longer, and the dust will have more opportunities to impact obstacles, so the filtering efficiency is high. Experience shows that for high-efficiency filters when the wind speed is reduced by half, the dust transmittance will decrease by nearly an order of magnitude (the efficiency value will increase by one 9), the wind speed will double, and the transmittance will increase by one order of magnitude (the efficiency will decrease by one 9). Similar to the effect of diffusion, when the filter material is electrostatic (electret material), the longer the dust exists in the filter material, the greater the possibility of being adsorbed by the material. With the change in wind speed, the filtering efficiency of electrostatic materials will change significantly. If you know there is the static electricity in the material, you should minimize the airflow through each filter when designing the air conditioning system. According to traditional theory, when the wind speed is reduced, the probability of collision between dust and fiber will decrease, and the filtering efficiency will decrease. But in practice, this effect is not obvious, because the wind speed is small, the fiber's elasticity to dust is also small, and dust is easier to adhere to. When the wind speed is high, the resistance is high. If the service life of the filter is based on the final resistance, the service life of the filter will be shortened when the wind speed is high. It is difficult for ordinary users to observe the effect of wind speed on filtration efficiency, but it is easier to observe the effect of wind speed on resistance. For high-efficiency filters, the air velocity through the filter material is usually 0.01-0.04m/s. Within this range, the resistance of the filter is proportional to the airflow rate. For example, the initial resistance of a 484*484*220mm high-efficiency filter is 250 Pa at a rated air volume of 1000 m3/h. If the actual air volume used is 500 m3/h, its initial resistance can be reduced to 125 Pa. For ordinary ventilation filters in air conditioning boxes, the airflow velocity through the filter material is 0.13-1.0. Ms. The relationship between resistance and air volume is no longer linear, but an upward arc. With a 30% increase in air volume, resistance may increase by 50%. If the filter resistance is a very important parameter, you should go to the air filter supplier to ask for the resistance curve. |
