Ratationship between air flow rate and air filter efficiency

- Apr 18, 2018-

In most cases, the lower air flow rate, the better the effect of air filter. Because of small size dust do diffusion action (Brownian motion), in low air flow rate,so air flow in the filter material retention time is longer, the dust will have more chance to hit obstacles, so the filtration efficiency is high.  Experience has shown that for high efficiency filter, air flow rate reduced by half, dust of transmittance decreased nearly one order of magnityde(efficiency values increase a 9)H14 Hepa filter efficiency is 99.999% become to 99.9999%,air flow rate doubled, transmittance increases and order of maginitude(efficiencyt to reduce a 9),

clean room air filter.jpg

Similar to the effict of diffusion, when the filter material is electrostatic(electret), the longer the dust stays in the filter material the grater the chace it is to be absorbed by the material.The filtration efficiency of electrostatic materials can be changed obviously by chaging the air flow rate. If you know that there is static electricity on the material, you should try to reduce the air volume of each filter as much as possible.
For large particle dust with inertial mechanism, According to the traditional theory, When the wind speed decreases the probability of dust and fiber collision will be reduced, and filtrasion efficiency will be reduced. However, in prctice,the effect is not obvious, because the air flow rate is small, and the anti-elastic force of the fiber is small, and the dust will more easily be stuck.

High air flow rate, high resistance,. The service life of the filter is based on the final resistance, the air flow rate is high, and the service life of the filter is short. It is diddicult for ordinary users to observe the effect of air flow rate on filtration efficiency, but it is much easier to observe the effect of air flow rate on resistance!

hepa fan filter unit: velocity and efficiency ralation

For high efficiency filters, the speed of the air flow through the filter material is genarally  0.01~0.04m/s. In this range, the resistance of the filter is proportional relation to filtration of air volume.For instance, a 484* 484*220mm high efficiency filter.The initial resistance at the rated air volume of 1000m3/h is 250Pa. If the actual air volume in use is 500m3/h, it's initial resistance can be reduced to 125Pa. For the general ventilation filter in the air conditioning box, the speed of the air filter material is within 0.13~1.0m/s range.Resistance and wind are no longer linear, but a rising arc: The wind volume increases by 30%,and the resistance may increase by 50%. If the filter resistance is a very impotant parameter for you , you need to ask the filter supplier for the resistance curve.