Single Particle Motion. Reading: Chaps 3 & 5. Want to be great athletes? Study aerosol science & engineering because you surely need to know how to control particle movement in the air!. V.
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Reading: Chaps 3 & 5
Want to be great athletes? Study aerosol science & engineering because you surely need to know how to control particle movement in the air!
CD = 0.44 (sphere) for 103 < Rep < 2×105
Delivery van 0.04
Sports car 1.0
For a spherical particle, L = dp,
Q: Choose a combination of dp and V when the Newton’s Law can be applied.
Stokes’ Law: negligible inertial force compared to viscous force (Rep < 1); in a laminar flow for a spherical particle
Q: How does FD change wrt V and dp in the laminar regime?
Q: Under what scenario will you expect to apply Newton’s law instead of Stokes’ Law?
Q: How does CD change wrt Re from 10-3 to 105?
Q: What is the physical meaning of B?
Q: Does a smaller or a larger particle
have larger mobility?
0.1 mmTerminal Settling Velocity of unit-density spheres
: mean free path (Chap 2.3)
0.066 mm for air @STP
(Re < 1)
Q: So is the corrected VTS larger or smaller?
Q: How long do you have to wait for 0.1 mm particles to completely settle in this classroom (4 m high)?
Kn = 2/dp
Q: Kn for a 10 mm particle? In which regime?
de: equivalent volume diameter
Q: Does an irregular particle experience a larger or smaller force (compared to a particle with the same volume)?
Cunningham factor should be included if dp < 1 mm
Q: Can we design an instrument by applying settling velocity?
Q: Can it be vertical?
Q: Can we make the acceleration > g?
Cheng et al., 1988
Time for unit density particles to reach their terminal velocity
Q: Stk << 1? Stk >> 1?
Uniform streamlines in the jet
Streamlines are arcs of a circle with
the centers at A
Q: How to collect smaller particles
using an impactor?
(Chap 3.4, Pdin kPa, dp in um)
Q: (low pressure impactor) Advantages? Disadvantages?
Q: Again, how to collect smaller particles using an impactor?
Aerosol flow In
Clean air out
Collection efficiency & internal loss
curves for a virtual impactor
Q: Comparison with an impactor?
Time of Flight (TOF) vs Time in Beam (TIB)
TSI Operating Manual, 2004