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What factors are affected by the filter?
- 2019-08-22-

1. Influence of filtering wind speed The wind speed increases the resistance and the wind speed decreases the resistance. For large particles dominated by inertial motion, the wind speed is increased, the inertia of the particulate matter is increased, and the possibility of hitting an obstacle is increased, so the filtration efficiency is improved. However, the inertia is large, and the rebounding force of the obstacle on the particulate matter is also increased. If the van der Waals force cannot overcome the rebounding force, the particulate matter will run away. Therefore, sometimes the wind speed is increased, and the filtering efficiency of the filter on the large particulate matter is lowered.
For small particles mainly composed of diffusion movement, the filtration efficiency depends on the residence time of the particles in the filter medium, the residence time is shortened (increasing the wind speed), the probability of the particles hitting the obstacle is reduced, and the filtration efficiency is lower. If the material is electrostatically charged, the filtration efficiency depends on the residence time of the gas stream in the material. The lower the filtration wind speed, the higher the filtration efficiency, both for large and small particles.
Electrostatic materials are very sensitive to the filtered wind speed. For example, at a wind speed of 1 cm/s, the transmittance of 0.3 μm dust is 0.01% (filtration efficiency is 99.99%), and when the filtration wind speed is increased to 5.3 cm/s, the measured transmittance is 1.5% (filtering) The efficiency is only 98.5%), and the transmission rate is two orders of magnitude.
2, the impact of humidity Under normal circumstances, changing the humidity will not affect the efficiency and resistance of the filter. However, when the air humidity is high, the filter medium may condense, and the surface of the contact between the particles and the obstacle has a water film. The contact surface between the two is large, the adhesion is also large, and the large particles are no longer so easy to rebound, so The filtration efficiency of large particles may be improved.
In reality, if the water is wet to the filter, the performance of the filter may undergo various unpredictable changes. For example, for filter paper made from vegetable fiber, if the paper is poor in water resistance, water makes the paper soft, the fiber is compressed, and the resistance of the filter increases rapidly until the filter is blocked. For another example, the high-efficiency filter carries water, and the dust is transported by water to the leeward side of the material. After drying, the filter becomes a dust collector.