B–14 Series 3080 Electrostatic Classifiers
Figure B-7 allows calculation of the particle diameters that pass
through the exit slit of the Electrostatic Classifier, if the number of
charges on the particle is known. Table B-1 shows that the majority
of the aerosol in charge equilibrium exists as singly charged
particles. However, a fraction of the particles exist as multiply
charged particles.
A particle with a certain mobility may exist as a small particle with
a single charge or as a larger particle with multiple charges. Either
has the same mobility and is removed by the system with the
monodisperse airflow. Refer to Wang and Flagan [1990] for the
effect of multiply charged particles on the data analysis. Figure B-7
shows the relationship between the diameter of particles with a
single charge and collector rod voltage for a Model 3081 Long DMA.
Particle Diameter,
Dp, µm
Collector Rod Voltage V, Volts
Figure B-7
Collector Rod Voltage as a Function of Particle Diameter for Normal Operating
Conditions of the Long DMA [Agarwal and Sem, 1978]
The Equations listed above do not account for diffusion broadening.
This is an important factor in particles below 50 nm. For the more
comprehensive formulas, refer to work by Stoltzenburg [1988].
Once the particles are classified according to electrical mobility,
their concentration is measured by a CPC or Electrometer.
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