United States Industrial Environmental Research EPA-600/7-78-195
Environmental Protection Laboratory October 1978
Agency Research Triangle Park NC 27711
Effects of Charged
Particles on Cascade
Impactor Calibrations
Interagency
Energy/Environment
R&D Program Report
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EPA-600/7-78-195
October 1978
Cascade Brnpactor Calibrations
by
R. G. Patterson, Phillip Riersgard, and Seymour Calvert
Air Pollution Technology, Inc.
4901 Morena Boulevard, Suite 402
San Diego, California 92117
Contract No. 68-02-1496
ROAP 21ADL-004
Program Element No. 1AB012
EPA Project Officer: Dale L Harmon
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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ABSTRACT
Collection characteristics were determined for charged
and uncharged particles in cascade impactors. Collection
efficiency on a wide variety of substrates was found to be
greater for charged than uncharged particles.
This report was submitted in partial fulfillment of
Contract No. 68-02-1496 by Air Pollution Technology, Inc.
under the sponsorship of the U.S. Environmental Protection
Agency. This report covers the period January, 1977 to
August, 1977.
111
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CONTENTS
Page
Abstract iii
Figures v
Tables vii
List of Symbols viii
Acknowledgment x^
Sections :
1. Introduction 1
2. Conclusions 2
3. Method and Experimental Apparatus 3
Aerosol generation 3
Charger 5
Cascade impactor 7
Optical particle counter 9
Particle charge analyzer 10
4. Experimental Results 16
Single stage collection 16
Multiple stage collection 23
References 41
IV
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FIGURES
Number Page
1 Impactor calibration system 4
2 Saturation charge level on PSL aerosol
(dielectric constant, k = 2.55) 6
3 Aerosol charger .... 8
4 Radial flow aerosol charge analyzer 11
5 Ideal volt-ampere characteristic for aerosol
charge analyzer > . . 12
6 Modified electrical aerosol analyzer 15
7 Impaction characteristics with greased plate
(0. 5 ym dia. PSL) 17
8 Impaction characteristics with greased foil
(0.5 ym dia. PSL) 18
9 Impaction characteristics with glass fiber
filter (0.5 ym dia. PSL). 19
10 Impaction characteristics with ungreased
plate (0.5 ym dia. PSL) 20
11 Impaction characteristics with ungreased foil
(0.5 ym dia. PSL) 21
12 Impaction characteristics with Mylar substrate
(0.5 ym dia. PSL) 22
13 Stage 5 impaction characteristics of greased
plate (1.1 ym dia. PSL) 24
14 Stage 5 impaction characteristics of greased
foil (1.1 ym dia. PSL) 25
15 Stage 5 impaction characteristics of glass
fiber filter (1.1 ym dia. PSL) 26
-------
FIGURES (continued)
Number Page
16 Stage 5 impaction characteristics on ungreased
plate (1.1 ym dia. PSL) 27
17 Stage 5 impaction characteristics of ungreased
foil (1.1 ym dia. PSL) .".''. ..." 28
18 Stage 4 impaction characteristics of greased
plate (2.0 ym dia. PSL) 29
19 Stage 4 impaction characteristics of greased
foil (2.0 ym dia. PSL) 30
20 Stage 4 impaction characteristics of glass
fiber filter (2.0 ym dia. PSL) 31
21 Stage 4 impaction characteristics of ungreased
plate (2.0 ym dia. PSL) , . 32
22 Stage 4 impaction characteristics of ungreased
foil (2.0 ym dia. PSL) 33
23 Stage 4 impaction characteristics of Mylar
Film (2.0 ym dia. PSL) 34
24 Collection characteristics of greased Mylar
substrates with stages 1 through 6
installed (0.76 ym dia. PSL) 38
25 Collection characteristics of glass fiber
filter substrates with stages 1 through 6
installed (0.76 ym dia. PSL) 39
26 Collection characteristics for an ungreased
impaction plate with stages 1 through 6
installed (0.76 ym dia. PSL) 40
VI
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TABLES
Number Page
1 Saturation current level 14
2 Impaction characteristics for various
substrates (0.5 ym dia. PSL) 35
3 Impaction characteristics for various
substrates (1.1 ym dia. PSL) 35
4 Impaction characteristics for various
substrates (2.02 ym dia. PSL) 36
VII
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LIST OF SYMBOLS
A = area, cm2
C' = Cunningham slip correction factor =
? 0
1 + ^p 1/257 + 0.40 exp (-1.10 d /2A)
P P
d. = jet diameter, cm
d = particle physical diameter, ym
d = aerodynamic particle diameter, ymA
pa
d = aerodynamic cut diameter
d = cut diameter or diameter at which stage is 50!
Pso efficient
e = electronic charge value, 4.8 x 10"10 esu
E = applied electric field strength, kV/cm
I = current, amps
IqAT = saturation current, amp
k = dielectric constant for particle
K = inertial impaction parameter, dimensionless
K = inertial impaction cut parameter, K , at 501
P50 efficiency P
i = mean free path of gas molecules, cm
n = number density of particles, #/cm3
n = initial number density, #/cm3
n = particle charge level, elementary units
n = saturation charge level, elementary units
p = particle density, g/cm3
s = electrode spacing, cm
Q = volumetric flow rate, cm3/s
q = charge on a particle, elementary units
yG = gas viscosity, poise, g/cm-s
ymA = ym (g/cm3) 1/2
V = applied voltage
v = gas velocity, g cm/s
v. = gas (particle) velocity through jet, cm/s
Z = electrical mobility of the particle, cm2/volt-sec
Vlll
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ACKNOWLEDGMENT
A.P.T., Inc. wishes to express its appreciation for ex-
cellent technical coordination for a very helpful assistance
in support of our technical effort to Dr. Leslie Sparks of
the E.P.A. and Mr. Dale Harmon, E.P.A. Project Officer.
IX
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SECTION 1
INTRODUCTION
In the past few years considerable emphasis has been placed
on determining the performance characteristics of particulate
control devices. These investigations seek to establish the
collection efficiency as a function of the particle size. To
do this requires accurate determination of the size distri-
bution of particles at the inlet and the outlet of the control
device. Cascade impactors are routinely used in these investi-
gations for establishing the size distribution of particles
greater than 0.3 ymA diameter.
The particles which penetrate a particulate control device
employing electrostatic forces for collection can have a higher
level of charge than when they entered. Other investigators,
Smith et al. (1975) and Brink et al. (1972), have found that
the collection characteristics of cascade impactors can be
altered when sampling charged particles.
This investigation was undertaken to evaluate the effect
of charged particles on cascade impactor calibrations. The
effect of particle charge on the collection efficiency can be
expected to be a function of the charge level on the particle.
Therefore a charge level was chosen for this study that is
equivalent to that encountered on particles in electrostatic
precipitators.
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SECTION 2
CONCLUSIONS
The impaction collection efficiency was shown to be as much
as 201 greater for charged particles than Uncharged particles
with certain substrates at a given value of the impaction para-
meter K , using a University of Washington Impactor. Collection
P
on greased substrates remained relatively unchanged.
The effect that charged particles will have on the particle
size distribution measured with the cascade impactor can be de-
termined from equation (5). This equation shows that the stage
cut diameter, d , is related to K in the following way:
pc' pso
1/2
dpc charged = dpc uncharged Vso charged
Pso uncharged
The results of this investigation show that the impaction
parameter, K , increases by 5 to 171 when collecting charged
particles. The actual amount depends on the particle size and
collection substrate used. For a \1\ change in the impaction
parameter, K , the change in the stage cut diameter, d , is
Pso pc
oo,
o -a ,
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SECTION 3
METHOD AND EXPERIMENTAL APPARATUS
Impactor calibrations were performed with charged and
uncharged aerosols. The method for performing the calibration
was adapted from the "Impactor Calibration Guidelines," Calvert
et al. (1976). Figure 1 is a schematic of the impactor cali-
bration system used.
The procedure involved generating the test aerosol and
determining the collection efficiency as a function of the
flow rate through the cascade impactor. The average charge
level on the test aerosol was determined for the charged par-
ticle runs. Charge neutralization was used to assure that the
uncharged particles were electrically neutral.
AEROSOL GENERATION
Monodisperse aerosols were produced using suspensions of
polystyrene latex (PSL) microspheres. Particles of 0.5, 1.1,
and 2.0 ym diameter were used for these calibrations. This is
also the size range of most importance in fine particulate
control device evaluation.
Useful suspensions of PSL were made by diluting small
quantities of the original suspension with deionized water.
The PSL is diluted to a concentration sufficient to minimize
the occurrence of agglomeration. Dilutions of the stock 10%
solutions of PSL can be estimated from.a paper by Raabe;
however, the amount of dilution necessary depends on the speci-
fic atomizer used. Concentrations of 0.01 to 0.2 weight per-
cent for particles of 0.5 to 2.0 pm diameter were found to be
compatible with the atomizer used.
Drops containing PSL particles were produced from suspen-
sions with a Collison atomizer. The atomizer is a one-hole
design operating at 260 kPa. Number concentrations and PSL
3
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ATOMIZER
AEROSOL DRYING
SECTION
CHARGE
ANALYZER
OPTICAL PARTICLE
COUNTER
DIFFUSION BATTERY
DILUTION
AIR
NEUTRALIZER
CHARGER
CASCADE
IMPACTOR
MIXING
LENGTH
Figure 1. Impactor calibartion system.
-------
size distributions were constant throughout a run.
The aerosol is dried by passing it through a 1.8 m section
of a 3.6 cm diameter glass tube. The tube was mounted hori-
zontally with a layer of silica gel (-1.5 cm deep) spread
evenly along the bottom.
Submicron aerosols less than approximately 0.1 ym diameter
were removed by passing the dried aerosol through a diffusion
battery. Aerosol leaving the diffusion battery is mixed with
ionized air (approximately 45 &/min). The air is ionized with
a 20 mCi, PO210 alpha emitter to reduce the excess charge on
the aerosol to the Boltzman equilibrium level. The mixture
passed through 6 m of 1.3 cm diameter glass tubing to provide
adequate residence time for charge neutralization of the
aerosol.
CHARGER
The effect of particle charge on the collection charac-
teristics of cascade impactors was determined with particles
having different levels of charge. For the purposes of this
experiment the different charge levels were produced by
charging three different size aerosols to their saturation
charge level by ion bombardment. The charge levels are com-
parable to those obtained in conventional ESP's.
For a dielectric particle, such as PSL, field charging
theory predicts the following saturation charge level, White
(1963) .
I*-I\
n =
s
1 + 2
(IZOO)e
CD
ns = 2.9 x ID'2 EQ dp2 (2)
(for PSL)
The saturation charge level is seen to be proportional to the
applied field strength, E , and surface area of the particle
~d 2. Figure 2 gives the saturation charge level for field
p
charging of particles in the size range of interest in this
study.
-------
10,000
5,000
3,000
in
H
< 1,000
W
•J
w
X
u
w
1-J
CJ
H-1
H
OS
500
300
100
50
30
0.3 0.5
10 kV/cm
6 kV/cm
1.0
10
Figure 2. Saturation charge level on PSL aerosol
(dielectric constant, k=2.55).
-------
The field charger used is a modified version of the design
cited by Langer et al. (1964). The device shown in Figure 3 consists
of a small Plexiglas box with two inlets and one outlet. The
aerosol enters the charging region through the lower glass
tube. The outlet is a brass tube cut at a 45-degree angle to
the center line of the pipe. The source of the ion flux is a
small loop of platinum wire bent slightly and positioned so as
to be equidistant from the outer edge of the tube. A DC power
supply operating in the range of 0 •*• 12 kV was used for estab-
lishing the corona.
CASCADE IMPACTOR
A University of Washington Mark III source test cascade
impactor was chosen for these tests. The impactor was cali-
brated with only one jet stage installed at a time according
to the method of Calvert et al. (1976). In this manner, the
difference in collection efficiency between charged and un-
charged particles could be studied.
The inertial impaction parameter, K , is used to charac-
terize the collection efficiency for a given impaction stage.
The inertial impaction parameter is defined by:
d2 C' p v- d 2 v.
K = P P 3 = Pa 3 x 10-8
P 9 ^G dj ^G^T
Aerodynamic diameter is defined as:
d =d (C'p)2xl01*, ymA
pa p rp'
For the case where the stage is 50% efficient (i.e., the cut point)
equation 2 becomes:
d2 C' p v. d 2 v.
v _ P 5 o P 3 _ Pc 3 -v in-8 (t>~\
KP50 " 9 yG d/ - 9 £G d^ X 10 [5)
-------
ACCELERATING
GAS
INLET
oo
AEROSOL
INLET
ALUMINUM
ROD
PLATINUM
WIRE
45'
BRASS
TUBE
Figure 3. Aerosol charger.
-------
Choosing the proper jet stage depends on the particle size
being studied and knowledge of the volumetric flow rate usually
encountered in the field. For field operations this impactor is
normally operated in the range of 1.4 x 1CT2 -> 2.8 x 10'2 m3/min.
With limits set on the desired volumetric flow rate, the following
jet stages were chosen for the particle sizes used in this study:
Stage
4
5
6
dp
2.0
1.0
0.5
Hole
Dia (cm)
0.079
0.051
0.034
Number of
Holes
90
110
110
A number of impaction substrates are used for determining
size distributions in the field. The following substrates were
chosen for study to give a representative sample of the condi-
tions encountered:
1. Glass fiber filter on a metal impaction plate.
2. Greased metal impaction plate.
3. Ungreased metal impaction plate.
4. Greased aluminum foil on metal impaction plate.
5. Ungreased aluminum foil on metal impaction plate.
6. Teflon film on metal impaction plate.
7. Mylar film on metal impaction plate.
OPTICAL PARTICLE COUNTER
The number concentration of particles entering and leaving
the cascade impactor was determined with a Climet Cl 205 particle
analyzer. The Climet device has the capability of counting all
particles with diameters greater than a pre-set value (0.3, 0.5,
1.0, 3.0, 5.0, or 10.0 vim). Further discrimination is achieved
by using a potentiometer to provide a continuous particle size
selection over the range of 0.3 to 10.0 ym.
The particle counter is used within a selected band of par-
ticle diameters, centered about the known PSL diameter. This
reduces the effect of spurious counts resulting from fine impuri-
ties and agglomerates. The particle count for the larger diameter
-------
setting may be subtracted from that for the smaller diameter
setting to determine the number concentration of particles
within a desired size interval.
PARTICLE CHARGE ANALYZER
Two methods were tried for measuring the charge level of
the particles. An imposed field analyzer was constructed to
ascertain the electrical properties of the aerosol. A modified
version of the design used by Hu.rd et al. (1962) is shown in
Figure 4. The electrical mobility of the particles entering
the device can be determined from the volt-ampere characteristics
of the analyzer as shown in Figure 5. A particle entering the
device will either be intercepted on the current collecting
lower electrode or pass out of the system depending on the
imposed electric field.
The trajectory of a particle entering the system is given
by:
af • ZPS + *
and:
At low voltages, only a fraction of the particles are collected.
Those entering above a critical value of x, x , are not collected
while those entering below x will be collected. For a parti-
cular voltage, the current obtained from particles collected
on the lower electrode is given by:
I = -/ nq bEx da (8)
A
where A = area of collecting electrode
q = charge on a particle
n = number concentration of particles
10
-------
(a)
(b)
PLEXIGLAS
AIR
Figure 4. Radial flow aerosol charge analyzer
(a) Particle trajectory
(b) Analyzer configuration
-------
A
'SAT
slope =
V
SAT
V
Figure 5. Ideal volt-ampere characteristic for aerosol charge
analyzer.
-------
The inlet concentration, nQ, is maintained in the region adjacent
to the collecting electrode for every position, r. Applying this
boundary condition to equation 8 results in:
1
J
|~n q Z Al
I = M^-U- U (9)
When the voltage is raised such that all particles entering
the system are collected on the lower plate the current becomes:
1 = TSAT = no 1 Q <10)
where, Q , is the volumetric rate of gas flow. Combining equations
9 and 10 results in the saturation voltage:
VSAT ' ^ ^
from which the electrical mobility of the particle, Z , may be
determined.
The charge level of the particle, n , is related to the
electrical mobility of the particle, Z , by:
3.7T y d (300) Z
n = - E - E
p eC
(12)
The expected value of the saturation current, I , may be
o
determined by assuming the particles attain the saturation charge
level. Table 1 gives the expected value of the saturation cur-
rent for particles charged in a 6,000 V/cm field at particle
concentrations normally encountered in the experimental apparatus.
13
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TABLE 1. SATURATION CURRENT LEVEL
Particle
Diameter
(ym)
2.0
1.1
0.5
Saturation
Charge Level
(Elem Units)
701
212
44
Particle
Cone
(#/cm3)
7.1
17.7
35.3
Flow Rate
(£pm)
0.24
0.24
0.24
Saturation
Current
(amps)
1.9 x 10'13
1.4 x lO'13
5.9 x 10'1*
The actual saturation current value obtained was 2 x 10'11
amps. This measurement was made before the diffusion battery
was added to the experimental apparatus and may represent the
current carried by the submicron fraction of the aerosol. The
saturation current level was obtained at low voltages which
indicates that the majority of the charge was carried by small
particles having a high electrical mobility.
A Model 3030 electrical aerosol analyzer (EAA) was modified
for measuring the charge level on the particles. Before modi-
fying the instrument, measurements of the particle charge level
were not reproducible. This is believed to be the result of
high particle losses within the instrument.
The EAA was modified as shown in Figure 6 with the Faraday
cup remounted on the face of the instrument. The charged par-
ticles could then be collected in the Faraday cup and particle
losses in the remainder of the instrument were thus avoided.
The particle charge level can be determined from the value
of the current measured with the electrometer in the EAA and
the number concentration as measured with the optical particle
counter:
n
(13)
This method gave reproducible results after installing the dif-
fusion battery and was used for determining the particle charge
levels given in this report.
14
-------
FARADAY CUP
AEROSOL
INLET
TO VACUUM PUMP
10 Sipm MASS FLOW METER
ELECTROMETER
Figure 6. Modified electrical aerosol analyzer.
-------
SECTION 4
EXPERIMENTAL RESULTS
SINGLE STAGE COLLECTION
The collection efficiency was determined as a function of
the impaction parameter for both charged and uncharged aerosols.
Collection of charged particles in the impactor without the
impaction plate in place was found to be negligible with each
of the three jet stages used.
The electrical field strength in the charger shown in
Figure 3 was 7,000 V/cm. Actual charge levels on the particles
were somewhat less than the saturation charge because of the
short residence time in the charging section. For the PSL par-
ticles used in this study the average charge level was:
Particle Diameter Average Charge Level
(ym) (No. of elementary units)
2.0 322
1.0 201
0.5 53
Sixth Stage Results
Figures 7 through 12 are the results obtained with 0.5 ym
diameter PSL particles and the various substrates. These are
similar to the results obtained with the other particle sizes.
In all cases collection efficiencies were found to be greater
for the charged particles than the uncharged particles.
Impaction of charged particles on the greased substrates
was only slightly more efficient for a given value of the
impaction parameter, K , than with uncharged particles. The
effect was more dramatic for the other substrates with efficiency
being as much as 20 percent greater for the charged particles
for a given K value.
P
16
-------
u
z:
w
t— I
u
W
o
U
W
O
u
100
90
80
70
60
50
40
30
20
10
A Uncharged Particles
O Charged Particles
(Grounded Impactor)
•05 .10 .15 .20 .25
IMPACTION PARAMETER, K
.30
.35
Figure 7. Impaction characteristics with greased plate
(0.5 pro dia. PSL) .
17
-------
100
90
80
70
u 60
2
w
U
so
E- '
U
w 40
H-J
J
O
u
30
20
10
1 I
A Uncharged Particles
O Charged Particles
(Grounded Impactor)
i i i r
j__ i
05
10
.15
.20
.25 .30
.35
IMPACTION PARAMETER, Kr
Figure 8. Impaction characteristics with greased foil
(0.5 ym dia. PSL) .
18
-------
100
90
80
A Uncharged Particles
O Charged Particles
(Grounded Impactor)
u
2
70
60
£ 50
w
2
O
I-H
w 40
J
H-i
o
u
30
20
10
.05
Figure 9.
.10 .15 .20 .25
IMPACT I ON PARAMETER, K.
.30
.35
Impaction characteristics with glass fiber
filter (0.5 ym dia. PSL) .
19
-------
100
90
80
70
60
w
I—I
u
w 50
O
I—I
u
40
30
20
10
A Uncharged Particles
O Charged Particles
(Grounded Impactor)
.05 .10 .15 .20 .25 .30
IMPACT ION PARAMETER, K
.35
Figure 10. Impaction characteristics with ungreased plate
(0.5 \im dia. PSL) .
20
-------
u
100
90 h~
80 I
70
60
U
I—I
£ 50
w
2
O
a 40
O
U
30 I
20 \—
10
A Uncharged Particles
O Charged Particles
(Grounded Impactor)
.05 .10 .15 .20 .25
IMPACT I ON PARAMETER, K,
.30
.35
Figure 11. Impaction characteristics with ungreased foil
( 0. 5 ym dia. PSL) .
21
-------
100
90
80
70
60
2
W
^ Uncharged Particles
O Charged Particles
(Grounded Impactor)
50
2
O
t—i
H
w 40
H-l
30
20
10
.05
.10
.15 .20 .25
IMPACT ION PARAMETER, K
.35
Figure 12. Impaction characteristics with Mylar substrate
(0.5 ym dia. PSL).
22
-------
The impaction efficiency was less than 1001 for the PSL
particles and all the substrates tested because of particle
bounce. This result is similar to that found by Rao (1975).
The maximum obtainable impaction efficiency was increased by
as much as 20% for substrates other then the greased impaction
substrates.
Stage Five Results
Figures 13 through 17 are the results obtained with the 1.1
ym diameter PSL particles and the various substrates. Collection
of charged particles on the greased plate leveled off to an over-
all efficiency of 15 to 201 for low values of the impaction
parameter, K . This is a somewhat greater efficiency than the
results obtained with the 0.5 ym diameter PSL.
Figure 16 shows that collection of uncharged particles on
ungreased plate was greater than for charged particles. It is
believed that the impactor was not grounded during this run.
Stage Four Results
Figures 18 through 23 are the results obtained with the
2.0 ym diameter PSL particles and the various substrates. These
results are similar to those obtained with the 0.5 ym diameter
PSL particles on the 6th stage.
Tables 2 through 4 give the value of K and the maximum
P s o
impaction efficiency for the three particle sizes tested.
The change in the impaction parameter, K , amounted to
P s o
approximately 10% for most substrates. The effect of particle
mobility wa.s insignificant as the change in K was similar
P 5 o
for each of the PSL particle sizes tested.
MULTIPLE STAGE COLLECTION
Collection efficiencies were determined as a function of
the impaction parameter for both charged and uncharged aero-
sols. Stages 1 through 6 were installed in the cascade im-
pactor for these tests. The electrical field strength in the
charger shown in Figure 3 was 7,000 V/cm.
23
-------
100
90
80
70
60
u
2'
W
k- I
u
w
50
H
U
w 40
O
U
30
20
10
.05
1 I
A UNCHARGED PARTICLES
O CHARGED PARTICLES
(Grounded Impactor)
.10 . .15 .20 .25
IMPACTION PARAMETER, K
J L
.30
.35
Figure 13. Stage 5 impaction characteristics of greased
plate (1.1 ym dia. PSL).
24
-------
100
90
80
70
60
u
2
W
W
50
o
t—I
H
w 40
O
u
30
20
10
,05
A UNCHARGED PARTICLES
O CHARGED PARTICLES
(Grounded Impactor)
.10 ' .15 .20 .25
IMPACTION PARAMETER, K
.30
.35
Figure 14. Stage 5 impaction characteristics of greased
foil (1.1 vim dia. PSL) .
25
-------
100
90
80
70
60
W
50
w 40
i— i
-j
o
u
30
20
10
,05
A UNCHARGED PARTICLES
O CHARGED PARTICLES
(Grounded Impactor)
.10 .15 .20 .25
IMPACTION PARAMETER, K
.30
.35
Figure 15. Stage 5 impaction characteristics of glass
fiber filter (1.1 ym dia. PSL).
26
-------
100
90
80
70
60
u
2:
w
i—i
u
t—I
fi<
u<
w
50
H
U
w 40
o
u
30
20
10
.05
A UNCHARGED PARTICLES
O CHARGED PARTICLES
(Grounded Impactor)
,10 .15 .20 .25
IMP ACTION PARAMETER, K
.30
.35
Figure 16. Stage 5 impaction characteristics on ungreased
plate (1.1 ym dia. PSL).
27
-------
100
90
80
70
>
u
12;
w
60
tin
£.. 50
w '
o
i— i
H
U
w 40
>— i
,-j -
o
u
30
20
10
A UNCHARGED PARTICLES
O CHARGED PARTICLES
(Grounded Impactor)
cr
o
,05 . .10 • -.15 - .20 .25
IMPACTION PARAMETER, K^
.-30
.35
Figure 17. Stage 5 impaction characteristics of ungreased
foil (1.1 pm dia. PSL).
28
-------
100
90
80
70
60
u
2
W
PL,
E 50
w
u
w 40
o
u
30
20
10
.05
T
T
T
A UNCHARGED PARTICLES
O CHARGED PARTICLES
(Grounded Impactor)
.10 .15 .20 .25
IMPACTION PARAMETER, K
.30
.35
Figure 18. Stage 4 impaction characteristics of greased
plate (2.0 ym dia. PSL).
29
-------
100
90
80
70
2
W
l-H
U
W
?s
o
i— I
H
U
O
u
50
40
30
20
10
.05
A UNCHARGED PARTICLES
O CHARGED PARTICLES
(Grounded Impactor)
.10 .15 ',.20. ..25
IMPACTION PARAMETER, K
.30
.35
Figure 19. Stage 4 impaction characteristics of greased
foil (2.0 ym dia. PSL).
30
-------
100
90
80
70
60
w
V-H
u
O
50
H
U
w 40
I—)
30
20
10
.05
A UNCHARGED PARTICLES
O CHARGED PARTICLES
(Grounded Impactor)
.10 .15 .20 .25
IMPACTION PARAMETER, K
.30
.35
Figure 20. Stage 4 impaction characteristics of. glass
fiber filter (2.0ym dia. PSL).
31
-------
100
90
80
70
60
u
2
w
I—I
u
t—I
p-l
HH
W
50
O
H
w 40
30
20
10
.05
A UNCHARGED. PARTICLES
O CHARGED PARTICLES
(Grounded Impactor)
I
.10 .15 .20 .25
IMPACTION PARAMETER, K
.30
.35
Figure 21. Stage 4 impacticn characteristics of ungreased
plate (2.0 ym dia. PSL).
32
-------
100
90
80
70
60
50
u
z
w
I—I
u
t—I
HH
P-.
W
2
o
1—1
H
S 40
30
20
10
.05
T
T
A UNCHARGED PARTICLES
O CHARGED PARTICLES
(Grounded Impactor)
i
.10 .15 .20 .25
IMPACTION PARAMETER, K
.30
.35
Figure 22. Stage 4 impaction characteristics of ungreased
foil (2.0 ym dia. PSL).
33
-------
100
90
80.
70
60
W
P-l
P-<
W
50
H
U
S 40
30
20
10
.05
A UNCHARGED PARTICLES
O CHARGED PARTICLES
(Grounded Impactor)
I
,10 .15 .20 .25
IMPACTION PARAMETER, K
A "- —
.30
.35
Figure 23. Stage 4 impaction characteristics of Mylar
film (2.0 vim dia. PSL) .
34
-------
TABLE 2. IMPACTION CHARACTERISTICS FOR
VARIOUS SUBSTRATES (0.5 ym dia. PSL)
Substrate
Greased Plate
Greased Foil
Glass Fiber Filter
Ungreased Plate
Ungreased Foil
Mylar
K
p
Charged
0.19
0.19
0.18
0.19
0.20
0.21(1)
50
Uncharged
0.20
0.20
0.21
0.22(1)
0.22
0.22(1)
Maximum Collection
Efficiency,^
Charged
74
80
70
60
53
48
Uncharged
74
80
58
42
30
27
TABLE 3. IMPACTION CHARACTERISTICS FOR
VARIOUS SUBSTRATES (1.1 ym dia. PSL)
Substrate
Greased Plate
Greased Foil
Glass Fiber Filter
Ungreased Plate
Ungreased Foil
K
P
Charged
0.25
0. 22
0.21
0.21
0.23(1)
50
Uncharged
0.27
0.24
0.22
0.24
0.24(1)
Maximum Collection
Efficiency? %
Charged Uncharged
63
70
47
55
35
(1) Estimated by extrapolating the portion of the curve having
a strong, positive slope.
35
-------
TABLE 4.
Substrate
Greased Plate
Greased Foil
Glass Fiber Filter
Ungreased Plate
Ungreased Foil
Mylar Film
IMPACTION CHARACTERISTICS FOR
VARIOUS SUBSTRATES (2.02 ym dia. PSL)
K
Maximum Collection
Efficiency %
Charged Uncharged Charged Uncharged
Pso
0.20
0.19
0.18
0.19
0.20
0.20
0.22
0.22
0.20
0.21
0.21
0.22
90
90
78
72
68
68
90
90
66
61
51
56
36
-------
Figure 24 shows the results with a greased Mylar substrate.
This figure is similar to Figures 7, 8, 13, 14, 18, and 19 which
are for collection on various greased substrates with only one
impaction stage. The collection efficiency for a given flow
rate is somewhat greater in Figure 24 than is shown in the
other figures. This increased collection efficiency may be
attributed to particle collection on the upper stages of the
cascade impactor.
The collection characteristics for glass fiber filters is
shown in Figure 25. This figure is similar to Figures 9, 15,
and 20 which were obtained with single stages. This indicates
that collection of charged particles with glass fiber filters
is minimal on the upper stages.
An ungreased plate was used as the collection substrate
for the data shown in Figure 26. The curves for charged and
uncharged particles are quite similar to the ones found in
Figures 10, 11, 16, 17, 21, and 22 for other ungreased sub-
strates. Again this indicates that the collection of the
charged particles on the upper stages of the cascade impactor
is minimal.
37
-------
100
90
80
70
_. A UNCHARGED
w
I-H
U
I— I
UH
^
w
Z
O
4°
30
20
.00
O
CHARGED
(Grounded Impactor)
10 .15 .20 .25
IMPACTION PARAMETER, K
(SIXTH STAGE)
.30
.35
.40
Figure 24. Collection characteristics of greased Mylar
substrates with stages 1 through 6 installed
(0.76 urn dia. PSL) /
38
-------
100
90
80
70
60
fi,
w 50
O
K- 1
— A UNCHARGED
Q CHARGED
(Grounded Impactor)
O
O
30
20
10 —
.00 .05
10 .15 .20 .25
IMPACTION PARAMETER, K
(SIXTH STAGE) T
.30
.35
.40
Figure 2 5.
Collection characteristics of glass fiber filter
substrates with stages 1 through 6 installed
(0.76 pm dia. PSL).
39
-------
100
CHARGED
(Grounded Impactor)
.00 .05
10 .15 .20 .2-5
IMPACTION PARAMETER, K
(SIXTH STAGE) *
Figure 26.
Collection characteristics for an ungreased
impaction plate with stages 1 through 6 in-
stalled (0.76 ym dia. PSL).
40
-------
REFERENCES
Brink, J.A., E.D. Kennedy, and H.S. Yu. Particle Size Measure-
ments with Cascade Impactors. 65th Annual AICHE Meeting,
New York, NY, 1972.
Calvert, S., C. Lake, and R. Parker. Cascade Impactor Cali-
bration Guidelines. EPA 600/2-76-118, 1976.
Hurd, F.K., and J.C. Mullins. Aerosol Size Distribution from
Ion Mobility. J. Colloid Sci. 17_ 91-100, 1962.
Langer, G., J. Pierrard, and G. Yamate. Further Development
of an Electrostatic Classifier for Submicron Airborne
Particles. Intern. J. Air Water Poll., 8^ 167-176, 1964.
Raabe, O.G. Generation and Characterization of Aerosols. From
Inhalation Carcinogenesis, Proc. of the Biology Division,
Oak Ridge Nat. Laboratory Conf., Gatlinburg, Tennessee,
October 8-11, 1969.
Rao, A. An Experimental Study of Inertial Impactors. Particle
Technology Laboratory, Publication No. 269, University of
Minn., 1975.
Smith, W.B., K.M. Gushing, G.E. Lacey, and J.D. McCain. Par-
ticulate Sizing Techniques for Control Device Evaluation.
EPA 650/2-74-102-a, 1975.
White, H. Industrial Electrostatic Precipitation. Addition-
Wesley, Reading, Mass., 1963.
41
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TECHNICAL REPORT DATA
(Please read Intimctions on the reverse before completing)
1. REPORT NO.
EPA-600/7-78-195
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Effects of Charged Particles on Cascade Impactor
Calibrations
5. REPORT DATE
October 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
R. G. Patterson, Philip Riersgard, and
Seymour Calvert
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Air Pollution Technology, Inc.
4901 Morena Boulevard, Suite 402
San Diego, California 92117
10. PROGRAM ELEMENT NO.
1AB012: ROAP 21ADL-004
11. CONTRACT/GRANT NO.
68-02-1496
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND I
Final; 1/77 - 8/78
O PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA/600/13
15. SUPPLEMENTARY NOTES IERL-RTP project officer is Dale L. Harmon, Mail Drop 61, 919/
541-2925.
16. ABSTRACT
The report gives results of a determination of collection characteristics
for charged and uncharged particles in cascade impactors. Impaction collection
efficiency was shown to be as much as 20 percent greater for charged particles
than for uncharged particles with certain substrates at a given value of the impaction
parameter Kp, using a University of Washington impactor. Collection on greased
substrates remained relatively unchanged.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COS AT I Field/Group
Pollution
Impactors
Calibrating
Charged Particles
Collection
Dust
Pollution Control
Stationary Sources
Cascade Impactors
Particulate
13 B
131
14B
20H
11G
3. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Reporl)
Unclassified
21. NO. OF PAGES
52
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
42
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