intercept
The dust particles in the air are moved by the inertia or random Brownian motion of the airflow or by the action of some field force. When the particles collide with other objects, the van der Waals forces (forces between molecules and molecules) existing between the objects 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.
Inertia and diffusion
Particle dust in the air flow for inertia movement, when the disorderly arrangement of fibers, the air flow changes direction, due to the inertia of the particles deviate from the direction, bump into the fiber and be bonded. 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.
Electrostatic interaction
For some reason, fibers and particles can 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.
Chemical filter
Chemical filters 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 treatment, adsorbed particles and materials for the reaction, the formation of solid substances or harmless gas, known as chemisorption.
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.
Gravity effect
When the particles pass through the fiber layer, under the action of gravity, they will move out of the airflow flow line and settle on the fiber surface. This effect only exists when the particles are large (>0.5um). This is because the particle gravity effect is too small, and it has passed through the fiber layer with the airflow before settling on the fiber. Therefore, for the filtration of particles with particle size less than 0.5um, the gravity deposition can be completely ignored.
