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Electrodynamics Electrical Precipitation Electrical precipitation is used widely in power plants for removing particles from discharging smokestacks. In the most common type, the dusty gas flows between parallel plate electrodes. The particles are charged by ions generated in a corona discharge surrounding rods or wires suspended between the plates. Figure 1 shows schematics of electrostatic precipitators.
Figure 1. Schematics of electrostatics precipitators. In the precipitators the cloud of electrons and negative ions moves towards the collecting electrodes. Particles are charged by field or diffusion charging, depending on their size. The Reynolds number is of the order of
where
Here, For
and
where
is the deposition velocity due to combined Brownian and turbulent diffusion. For
Hence,
For a length
Figure 2 shows typical collection efficiencies of electrostatic precipitators.
Figure 2. Variation of collection efficiency of an electrostatic precipitator. |
or greater and hence the flow is turbulent. The flux normal to the collecting plate is given by
, (18)
is the particle migration velocity towards the plate given by
, (19)
is the charge on the particle and 
is the intensity of the electric field.
being a constant, assuming 
remains constant, it follows that
, (20)
(21)
, (22)
, it follows that 
and deposition is controlled by diffusion.
When 
as is the case for electrical precipitators, 
. For a length 
length,
, (23)
, (24)
, 
, (25)
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