Four ways in which a particle filter works

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Four ways in which a particle filter works
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Four ways in which a particle filter works

– by Sjoerd Post – 30/11/20

How can a normal air filter eliminate as many particles as possible while simultaneously limiting the pressure drop? By removing particles from the air stream in various different ways…

Look closely and you’ll see that most air filters are made of very small fibres, all of which run into each other. The filters remove particles from the air stream as they meet and adhere to the surface of the fibre.

There are various mechanisms in which the particles are filtered out:

  1. Straining
  2. Impingement
  3. Interception
  4. Diffusion.

1. Straining

Old-fashioned-style filtering, only applicable to the biggest particles which are larger than the maze and get stuck in the filter. Remember those people sieving muddy waters in days of yore during the goldrush? That’s the idea of straining.


2. Impingement

Air running through a filter follows a certain streamline. The larger particles do not follow that line because of their large inertia. Instead they travel along a straight path until they eventually collide with a fibre and are removed from the air stream.


3. Interception

Particles that are small and light enough will follow the air streamline through the filter. However, the filter consists of fibres of different thicknesses that are crisscrossed together. As small particles follow the air stream they bend and circle in all directions, eventually hitting the surface of a fibre and getting stuck there.  


4. Diffusion

Diffusion takes care of the smallest particles, which do not strictly follow the air streamline. Because they are so small, they constantly collide with air molecules and randomly move through the filter before eventually reaching a fibre.



There is in fact one more way in which a filter picks its particles. Some filters have electrostatic charges on the media fibres to increase particle removal efficiency. The magnetic attraction of these charges causes the particles to come into contact with the fibre and attach.

Electrostatic filtering follows the principle of an ionizer. The particles are negatively charged before coming in contact with the (positively charged) filter medium.

As we have seen there are various ways to eliminate germs and other polluted particles from your HVAC system. Contact one of our engineers to discover which filter might best suit your needs. And for all things HVAC, stay tuned to

Sjoerd Post | Senior Engineer QESH

Sjoerd Post has been working at the QESH department of Heinen & Hopman since 2015. With his technical background he is responsible withing the QESH department for implementing standards and performing technical research for the company.