Homework II – Single Particle Motion, Diffusion, Thermal Forces (due 02/11/2010)
1.
What is the settling velocity of an asbestos fiber in the shape of a cylinder 1
μ
m in
diameter and 10
μ
m long at standard conditions?
Assume random orientation and
a density of 2.5 g/cm
3
.
Neglect slip correction. (10%)
2.
(a) Derive an expression for the collection efficiency (as a function of
particle size) for a multilayer settling chamber (see the figure below) with N
equispaced sections.
Assume a uniform flow, uniform distribution of
aerosols at the inlet, and negligible slip correction.
Neglect diffusion. (10%)
3.
A typical mass size distribution from a dieselequipped coal mine is bimodal, with
one mode for the diesel smoke particles at 0.16
μ
m, and the other for coal dust at 7
μ
m.
The saddle point between the modes is at an aerodynamic diameter of 0.8
μ
m.
If you are asked to use a singlestage impactor to separate diesel smoke from
coal dust in a sample of air from a coal mine, what nozzle diameter will you
choose if the total sample flow rate is 2.5 l/min and 8 nozzles are used? (10%)
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 Spring '08
 Wu
 Fluid Dynamics, Standard Deviation, Coal, Suspension

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