4–4 Series 3080 Electrostatic Classifiers
radius of 0.75 in. (1.905 cm). To reduce the effects of diffusion (by
reducing the residence time of particles in the classification zone),
the characteristic length has been reduced to 1.963 in. (4.987 cm).
The characteristic length is defined as the length between middle of
inlet slit to middle of outlet slit.
Figure 4-3
3085 Nano Differential Mobility Analyzer
The inlet to the Nano DMA is an axial
3
⁄8-inch port. The aerosol
flows through a short connecting tube that quickly widens in a
conical section to reach a narrow annular channel. The inner cone
is fixed by four narrow supports at the top of the outer cylinder.
This design promotes axisymmetric aerosol flow and reduces
distortions of the flow field. To accommodate the axial aerosol inlet,
the sheath air flow is routed through the center electrode from the
bottom before it is turned 180 degrees and passed through the
same style Dacron screen flow-straightener (P/N 1030389) as the
Long DMA.
The Nano DMA has an extra concentric cylinder below the inlet slit
that allows an increased polydisperse aerosol flow up to the inlet
slit. This increased flow reduces the particle transport time and
therefore, reduces diffusion losses up to the inlet slit. The extra
inlet flow exits the DMA as bypass flow. In addition, to match the
velocity of sheath air and aerosol flow, and to reduce electric field
penetration into the slit, the slit gap has been reduced to 0.26 in.
[0.66 mm]. The extra flow passes through a perforated ring to
provide enough pressure drop to assure a uniform and undisturbed
aerosol flow at the inlet slit.
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