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1 Overview
This Andersen Sampler equipped with multi-stage, multi-orifice nozzles is used to measure
particle size distribution of airborne aerosol in air and the environment by the impactor method.
It is configured with a classifier main unit, flowmeter, pump, and shelter.
1-1 Principle
The Andersen Sampler has a structure where usually eight corrosion-resistant aluminum alloy
stages are stacked as shown in Fig. 1 on the following page. Each stage has 800, 400, and 200
nozzles (outlets) and a glass or aluminum disc-form collection plate for filtering is placed below
them.
Since the nozzle diameter becomes smaller in lower stages, when air is introduced into the
AN-200 Andersen Sampler at a constant flowrate (1 CFM = 28.3 L/min) from the upper sampled
air installation opening of the sampler, the jet airflow velocity on each stage is higher on lower
stages. Generally, impactor's inertial parameter
ψ
is defined by the ratio of aerosol particle
diameter, nozzle's cross-sectional area, and aerosol velocity. According to study of jet
impingement analysis performed by Ranz and Wong et al., the relation shown in the formula
below is established.
c
p
c
D
d
V
C
μ
ρ
18
2
⋅
⋅
⋅
=
Ψ
····························
(1)
C
: Cunningham slip correction factor
(=1.00+0.16
×
10
-4
/
d
p
)
d
p
:
Aerosol particle diameter
(cm)
μ
: Viscosity of air (1.84
×
10
-4
g/cm
sec)
ρ
:
Aerosol density
(g/cm
3
)
V
c
:
Jet airflow velocity (
cm/sec
)
D
c
: Nozzle diameter (cm)
ψ
: Non-dimensional inertial parameter
c
c
p
V
C
D
d
ρ
μ
Ψ
=
18
··························
(2)
When the suction flowrate of the air sampled by the sampler is Q (cm
3
/min) and the number of jet
openings on the stage is N, V
c
is expressed as shown below.
(
)
N
D
Q
V
c
c
2
2
/
60
π
=
·······················
(3)
