Blocking effect

The blocking effect or blocking effect ( English interception ) is an important physical effect for the filtration . It is also referred to as interception in German-language specialist literature .

mechanism

The blocking effect is based on the fact that the movement of the center of gravity of a particle to be separated leads past the filter fiber, but due to its geometric expansion the particle nevertheless hits the fiber and remains stuck by adhesion .

The greater the particle diameter, the greater the likelihood of particle-fiber contact. This describes the blocking effect parameter  R :

${\displaystyle R={\frac {D_{\mathrm {P} }}{D_{\mathrm {F} }}}}$

With

• the particle diameter ${\displaystyle D_{\mathrm {P} }}$
• the fiber diameter . ${\displaystyle D_{\mathrm {F} }}$

Especially in the case of surface filters with an existing filter cake , the barrier effect is the dominant separation mechanism. But it is also important for depth filters . There it is perceptible as a separation mechanism for particle diameters greater than approx. 0.1  µm and, together with the inertia , is the predominant mechanism from a particle diameter greater than approx. 0.4 µm.

Other uses of the term

In semiconductor technology, the Schottky effect (or barrier layer effect or rectifier effect ) is sometimes referred to as the blocking effect .

Furthermore, the z. B. Nafion occurring selective conductivity for protons and other cations (barrier effect for anions), d. H. a diffusion behavior depending on the ionic charge.

Individual evidence

1. ↑ ^{a b c} Albert Hellmann, Kilian Schmidt, Siegfried Ripperger, Christoph Thelen, Carsten Möhlmann: Determination of the separation effect of fibrous filter media against ultrafine particles . In: Hazardous substances - cleanliness. Air . 72, No. 11/12, 2012, ISSN  0949-8036 , pp. 484-488.
2. ↑ Orest Lastow, Albert Podgorski: Single-Fiber Collection Efficiency. In: Kvetoslav R. Spurny : Advances in Aerosol Filtration. Lewis Publishers, Boca Raton 1998, ISBN 0-87371-830-5 , p. 27.
3. ↑ ^{a b c} VDI 3677 sheet 2: 2004-02 Filtering separators; Depth fiber filters (filtering separators) . Beuth Verlag, Berlin. P. 14.
4. ↑ VDI 3677 sheet 1: 2010-11 Filtering separators; Surface filters (Filtering separators; Surface filters) . Beuth Verlag, Berlin. P. 7.