4–2 Series 3080 Electrostatic Classifiers
Figure 4-1
Model 3081 Long Differential Mobility Analyzer
Particle-free (filtered) air enters the Sheath Flow inlet of the DMA
and passes to an annular chamber at the top of the DMA. The flow
then goes through a double screen of fine nylon (Dacron
®
) mesh to
straighten the flow. The air flows downward axially through the
classifier region. The Polydisperse Flow enters the DMA though an
inlet pipe from the top and flows in an axial direction between two
narrow concentric cylinders to evenly distribute the concentric flow
and concentration distribution. This thin annular flow is introduced
into the classifier region and smoothly merged with the laminar
sheath-air flow.
Particles with negative charge stick to the outer electrode, whereas,
noncharged (neutral) particles are removed unaffected with the
Excess Flow. Positively charged particles are carried axially
downward with the sheath airflow while also being attracted
radially toward the center electrode due to the electric field.
Particles with a narrow range of electrical mobility reach a
circumferential slit with twelve holes in the center electrode and
exit the DMA through the lower insulator as the Monodisperse
Flow. If the optional positive polarity High Voltage controller is
used, negatively charged particles with the narrow range of
electrical mobility exit the DMA through the circumferential slit.
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