Air filtration is not a screening. The objective is to stop the particles and keep them in the filter with a reduced pressure drop.
What are the adhesion mechanisms of the particles?
1/ Diffusion :
- The very small particles (<0.2µm) move according to a Brownian motion (oscillatory)
- If the particles approach a fiber, they will be attracted by it thanks to the Van der Waals strengths.
2/ Inertia :
- Collision on the fiber resulting in loss of kinetic energy
- Effective on fast moving heavy particles
3/ Gravity :
Effective on heavy particles
4/ Electrostatic :
- Mechanism very little present in the classic filters
- Only possible in an electrostatic type filter (used for oil filtration)
To keep the dusts in the filter, the filter must be static.
The presence of humidity significantly reduces these Van der Waals strengths. For fine filtration, it is important to control this humidity by coalescers or multiple filter stages.
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Mechanisms of particles adhesion