1. To intercept dust particles in the air and move with the flow of air in inertial motion or random Brownian motion or under the action of some field force. When particles move and bump into other objects, the van der Waals forces (forces between molecules and molecules and molecules) existing between the objects will make the particles stick to the surface of the fiber. The dust that enters filter medium has more chance of impingement medium, bump medium can be stuck. The smaller dust particles collide with each other, forming larger particles and settling down. The particle concentration of dust in the air is relatively stable. This is why the interior and walls fade. It is a mistake to treat a fibre filter like a sieve.
2. Inertia and diffused particle dust make inertial movement in the airflow. When encountering the disorderly arranged fiber, the airflow will change its direction, and the grain will be bonded by bumping into the fiber due to the deviation of inertia. The bigger the particle, the more likely it is to hit, the better. Small particles of dust perform random Brownian motion. The smaller the particle, the more violent the irregular movement, the more chance to hit obstacles, the better the filtering effect will be. Particles less than 0.1 micron in the air are mainly Brownian motion with small particles and good filtering effect. Particles larger than 0.3 micron mainly move by inertia. The larger the particle, the higher the efficiency. Both diffusion and inertia are unknown and the particles are the most difficult to filter out. When measuring the performance of hepa filters, it is often prescribed to measure the dust efficiency value which is the most difficult to measure.
3.For some reason, fibers and particles may become electrically charged, producing an electrostatic effect. The filtration effect of electrostatic filter material can be improved obviously. Reason: the static electricity makes the dust change the movement track and hit the obstacle, the static electricity makes the dust stick on the medium more firmly. Materials with permanent static electricity are also called electrets. Material with static resistance unchanged, the filtering effect will be significantly improved. Static electricity does not play a decisive role in the filtration effect, but only plays an auxiliary role.
4. Chemical filtration chemical filters mainly selectively adsorb harmful gas molecules. There are a large number of invisible micropores in activated carbon materials, which have a large adsorption area. In the activated carbon about the size of a grain of rice, the micropore area is more than ten square meters. After the free molecules contact the activated carbon, they condense into liquid in the micro pore due to the principle of capillary stay in the micro pore, and some of them are integrated with the material. Adsorption without obvious chemical reaction is called physical adsorption. Some of the activated carbon processing, adsorbed particles and materials for the reaction, the formation of solid substances or harmless gas, known as huaixue adsorption. The adsorption capacity of activated carbon in the process of use continues to decrease, when the reduction to a certain degree, the filter will be scrapped. If only for physical adsorption, heating or steam fumigation can make harmful gas from activated carbon, so that activated carbon regeneration.
