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Coalescing Principle

for the filtration of smallest aerosols up to

0.1 micron


Microfibre Filter Elements Coalescing principle

The coalescence principle

Our microfibre filter elements work according to the coalescence principle. The aim is to remove aerosols and dust particles down to a size of 0.1 µm from the air stream. To achieve this, our filter elements are constructed with two layers of special microfibres. These fibres are randomly distributed and oriented in all directions. Aerosols and dust particles, however, are much smaller than the pores of the filter material, so there is no sieving effect in this case. In the principle of coalescence, there are three different mechanisms, each of which is responsible for catching particles of a certain size.


Inertia effect

The first mechanism is the inertia effect. Large particles (light blue) do not follow the streamlines of the gas flow due to their high inertia. They flow straight ahead and collide directly with the microfibres. The inertial impaction becomes more important with increasing particle size.


The interception effect occurs with aerosols and particles of smaller size. They are light enough to follow the streamline, but hit the fibre when the radius of the particle is larger than the distance between the streamline and the edge of the fibre. They get stuck there and are removed from the air. Interception becomes more important with increasing particle size.


Diffusion plays a role when it comes to the smallest particles. These small particles do not strictly follow streamlines but Brownian motion and move randomly due to collisions with gas molecules. Because of this movement, they are likely to collide with the fibres. The smaller the particles are, the greater their freedom of movement and thus the greater the probability that they will collide with a fibre. As particle size decreases, the diffusion effect becomes more important.
The overall efficiency of the filter results from the combination of these three filtration mechanisms.

Crosssection microfibre
total filter efficiency

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R+F Filterelements GmbH_Christopher Franke_Ansprechpartner

R+F FilterElements GmbH
Wollenweberstraße 25
31134 Hildesheim

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