Theory of Operation B-3
Figure B-1
Classifier Shown with Impactor Installed on Inlet
Impaction
Nozzle or
Jet
Stream Lines
Impaction
Plate
Figure B-2
Cross-Sectional View of an Inertial Impactor [Hinds, 1982]
The impaction plate deflects the flow to form a 90° bend in the
streamlines. Particles with sufficient inertia are unable to follow the
streamlines and impact on the plate. Smaller particles follow the
streamlines, avoid contact with the plate and exit the impactor. The
impactor is used in the SMPS
™ spectrometer to remove particles
larger than a known aerodynamic size. The aerodynamic particle
size at which the particles are separated is called the cut-point
diameter. The cut-point diameter is a function of the impactor flow
rate and nozzle diameter.
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