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Filtration Mechanisms of HEPA Filter

18 April 2020 Bookmark and Share

American Spot Cooling - Rental Air Scrubber Mobile Air RA-650

During this pandemic and critical chapter in American history, there is unprecedented interest and frequently asked questions regarding High-Efficiency Particulate Air filters. So, we’re going to spend some time today educating you all as best we can on the subject of HEPA filtration.

HEPA filters trap particles of various size and origins via the following mechanisms:

  • Inertial Impaction - Inertial impaction happens when large particles cannot adjust immediately to the sudden shifts in streamline direction close to a filter fiber. Due to the particle's inertia, it will proceed along its initial course and collide the filter fiber. This is the most paramount filtration mechanism when the filter material has elevated gas velocities and compact fiber packing.

  • Diffusion - The gas is made of multiple molecules that are small in size when compared to the distances between them. These molecules are like corrugated orbs that move in parallel lines when they're not banging into each other. These molecules hit with each other immensely that they move in an irregular, zigzagging path which is called Brownian motion.

    Brownian motion is the cause of the diffusion mechanism of particle retention. Tiny particles that range in diameter of 0.1 μm and below are inclined to make irregular movements due to contact with spiraling gas molecules. When these small particles collide with the gas molecules, they as well start to move randomly around, bumping into other particles too. Diffusion happens with low gas velocities and smaller particles. The tinier the particle, the slower the flow as it takes longer to zigzag around, thus, providing a greater likelihood of bumping and adhering to a filter fiber.

  • Interception - Interception happens when a particle moves in accordance with a gas flow path that appears within 1 particle radius of a filter fiber. The particle in contact with the fiber becomes trapped, thereby eliminated from the gas stream. For a particular size, there are some streamlines that will travel near enough to a filter fiber in order for the particle to be trapped. Streamlines beyond 1 particle radius far from a filter fiber will not facilitate the interception mechanism.

These mechanisms make HEPA filter effective in eliminating contaminants such as bacteria, allergens, mold, and sub-micron sized dust. HEPA filters capture 0.3 microns and larger at a 99.97% rate. Negative air machines and air scrubbers with HEPA filters are excellent devices that remove impurities and purify the air. These machines are ideal in hospitals, nursing homes, and other healthcare settings.

If you have questions regarding the value of rental negative air machines and air scrubbers, contact American Spot Cooling & Power Rental.

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