The working principle of HEPA filters

HEPA (High Efficiency Particulate Air) filters are a type of high-efficiency particulate air filter,   whose working principle is primarily based on   physical interception   and adsorption.

Here is the working principle of HEPA filters:

Physical Interception: HEPA filters are composed of very fine fibers with gaps between them that are extremely small, typically at the sub-micron level.   When air passes through a HEPA filter, particulate matter such as dust, bacteria, viruses, and other particles are physically intercepted on the fibers because   their size is larger than the gaps between the fibers.

Van der Waals Force Adsorption: The fibers in a HEPA filter are charged, allowing the filter to adsorb smaller particles, including those whose size is close to or   smaller than the gaps between the fibers, through van der Waals forces (a type of weak intermolecular force).

Inertial Impaction and Diffusion: For larger particles, their inertia causes them to collide with the fibers and be intercepted as they approach. For smaller particles,   especially those less than 0.3 microns, diffusion caused by Brownian motion (random molecular motion) also leads to their capture by the fibers.

Electrostatic Action: In some HEPA filters, both the fibers and the particulate matter may carry an electric charge, increasing the probability of particle capture since charged particles are attracted to charged fibers.

Multi-layer Filtration Structure: HEPA filters are usually composed of multiple layers of fibers, increasing filtration efficiency and ensuring effective   filtration of   particles of different sizes.

HEPA filters are highly efficient, capable of capturing at least 99.97% of particles that are 0.3 microns or larger, making them very effective at removing fine particles from the air. They are widely used in various air purification equipment, including smoke purifiers, air purifiers, medical equipment, and high-efficiency   air   filtration systems.