EPA-600/2-75-025
June 1975
Environmental Protection Technology Series
PARTICLE DETECTOR
BY
MECHANICAL
IMPACT SENSING
-------
EPA-600/2-75-025
PARTICLE DETECTOR
BY
MECHANICAL
IMPACT SENSING
by
Michel Benane and Jean-Pierre Quetier
Institut Nat'l de Recherche Chimique Appliquee
91710 Vert-le-Petit, France
Grant No. 802424
ROAP No. 26AAM-36
Program Element No. 1AA010
EPA Project Officer: John S. Nader
Chemistry and Physics Laboratory
Office of Research and Development
Research Triangle Park, N. C. 27711
Prepared for
US ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, D. C. 20460
June 1975
-------
EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental Protection
Agency and approved for publication. Approval does not signify that
the contents necessarily reflect the views and policies of the Environ-
mental Protection Agency, nor does mention of trade names or commer-
cial products constitute endorsement or recommendation for use.
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environ-
mental Protection Agency, have been grouped into series. These broad
categories were established to facilitate further development and applica-
tion of environmental technology. Elimination of traditional grouping was
consciously planned to foster technology transfer and maximum interface
in related fields. These series are:
1. ENVIRONMENTAL HEALTH EFFECTS RESEARCH
2. ENVIRONMENTAL PROTECTION TECHNOLOGY
3. ECOLOGICAL RESEARCH
4. ENVIRONMENTAL MONITORING
5. SOCIOECONOMIC ENVIRONMENTAL STUDIES
6. SCIENTIFIC AND TECHNICAL ASSESSMENT REPORTS
9. MISCELLANEOUS
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to
develop and demonstrate instrumentation, equipment and methodology
to repair or prevent environmental degradation from point and non-
point sources of pollution. This work provides the new or improved
technology required for the control and treatment of pollution sources
to meet environmental quality standards.
This document is available to the public for sale through the National
Technical Information Service, Springfield, Virginia 22161.
Publication No. EPA-650/2-75-025
11
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ABSTRACT
Particulate impact is used for the detection and measurement o'f
raindrops and micrometeorites since several decades. Aerosols
might be detected in the same way if the suspension is expanded
rapidly when it enters through a capillary in a nearly evacua-
ted vessel.
If the accelerating capillary is relatively long and the pres-
sure inside the vessel below 1 torr, particulate beams are
obtained. They enable the study of particle velocities, their
rebound properties, etc. in good conditions. For particulate
beam conditions, impact sensing is mass concentration propor-
tional, grain size and substance independent, and sensitivity
may rate from the detection of single particle to the range
-3
of mg m .
With short nozzles and chamber pressure above 1 torr, impact
sensing remains possible but marked grain size dependence and
possible substance dependence complicate the phenomenon.
iii
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TABLE OF CONTENTS
Page
LIST OF FIGURES V
CONCLUSIONS VI1
RECOMMENDATIONS l'X
1. INTRODUCTION 1
2. PARTICIPATE BEAMS 3
3. PARTICULATE BEAM IMPACT SENSING 9
3.1 Theory 9
3.2 Single particle detection by SCHORMANN ''
3.3.1 Continuous concentration monitoring general
and theoretical part 11
3.3.2 Particulate beam impact sensing - experimental 13
3.3'2.1 Preliminary experiments 13
3.3*2.2 The experimental setup 18
3.3.2.3 The yield of the intake 22
3.3.2.4 The influence of the grain size distri-
bution 27
3.3.2.4.1 The calibration of the device 27
3.3.2.4.2 Results : grain size independence 29
3.3.2.4.3 The influence of the nature of the
particulates 41
4. RESONANT MODE SENSING 44
4.1 General considerations 44
4.2 Some results of the resonant mode sensing 50
5. IMPACT SENSING OUTSIDE PARTICULATE BEAM CONDITIONS 56
6. INFORMATION ABOUT PARTICLE ADHESION AND BOUNCING 59
REFERENCES 63
iv
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Figure 1 :
Figure 2 :
Figure 3 :
Figure 4 :
Figure 5 :
Figure 6 :
Figure 7 :
Figure 8 :
Figure 9 :
Figure 1O:
Figures 11
Figure 21:
Figrue 22:
Figure 23:
Figure 24:
LIST OF FIGURES
Schematic diagram of a participate beam source, after
MURPHY and SEARS (1964)
Measured stop distance vs. reciprocal pressure, after
DAHNECKE and FRIEDLANDER (19?O)
Measured stop distance vs. reciprocal pressure, after
DAHNECKE and FRIEDLANDER (1970)
Oscilloscope trace of a latex particle impacting on a
membrane, after HOLLANDER and SCHORMANN (1974a)
Schematical view of the quartz microbalance impact
detection.
Grain size distribution (number and weight) of the
"silica J" test-dust.
Preliminary results with the spring microbalance
detector.
Schematical cutoff of an early version impact
detector.
Schematical cutoff of an impact detector with
roughing chamber.
Calibration of the detector with dust dispersed by
a fluidized bed; comparison with a p-ray absorption
device.
-2O : Grain size distributions (number and weight)
of the test dusts.
Measured force vs. impacting particulate mass for
three different test dusts.
Pulsating supersonic air jets, after HARTMANN (1939)
Schema of air jets with pressure waves.
Schema of an early model resonant device.
Page
4
7
8
12
14
15
17
20
23
24
30 - 39
40
45
46
47
-------
49
Figure 25: Scale cutoff view of a resonant detector.
Figures 26, 27 and 28: Sinusoidal response in case of the
resonant mode sensing, at various particulate
51 - 53
loadings.
Figure 29: Amplitude vs. concentration for silica dust with a
resonant type detector.
vi
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CONCLUSIONS
The limits and the possibilities of the particulate sensing
by mechanical impact were explored.
Three modes of particulate impact sensing were identified :
(1) Impact sensing in particulate beam conditions.
(2) Impact sensing outside particulate beam conditions. This
report contains no details about this mode, which has
been explored earlier.
(3) Resonant mode impact sensing.
The conditions of the impact sensing in particulate beam con-
ditions are :
( la)A good focusing of the beam, which can be attained
either by a long capillary, or by a succession of shorter ones,
separated by fore-pumping chambers.
(lb) A good vacuum in the measuring chamber, of the order
of 0.1 Torr or better.
When these conditions are met, impact sensing is grain size and
material independent, for hard dusts at least. For sticky, tarry,
semiliquid or liquid particles, an influence of the elastic
properties of the substance is being felt. The empirical rule is;
visible deposit on the impacting surface : dependence on the
material. No visible deposit : good"mass concentration propor-
tionality.
There are two contradictory requirements for particulate beam
conditions : on one hand the diameter of the inlet capillary
must be as large as possible, to avoid obstructions by large
vii
-------
particles or by agglomerates; on the other hand, the pumping
rate (the dimension of the pumping unit) which has to maintain
the working vaccum, must increase with the inlet diameter.
(2) Impact sensing outside particulate beam conditions is
not mass-proportional, but may eventually be used in indicating
devices with external calibration.
(3a) The resonant mode of impact sensing in mass-proportio-
nal under particulate beam conditions.
(3b) Its sensibility is about hundred times (order of
magnitude) greater than that of the direct impact sensing. It
is reasonable to think, that its sensitivity might be further
increased by orders of magnitude through synchronous detection.
(3c) We did not succeed in the technical definition of an
easily built resonant node detector. In each case, hand tuning
was employed and such devices seem to be very failure-prone.
viii
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RECOMMENDATIONS
Particle detection by impact sensing is a technically feasible
proposition.
The transducer aspect of the question, i.e. the transformation
of the position of (or of the force exeited on) the impacting
surface into an electrical output was not subject to scrutiny.
To obtain particulate beam conditions, which guarantee in most
cases for a mass concentration proportional detection, a rather
powerful pumping unit must be used. This could be a cost limi-
ting factor of the usefulness of the detector.
A very sensitive mode of detection (the "resonant mode") was
discovered. Notwithstanding that the expended man-hours alone
on this topic were considerably larger than the total amount
of the grant, the detectors on this principle never gave a
reliable operation. It could be, that here another, quite
promising side-path was discovered. It should be stressed,
on basis of our experience, that this is not a quick and easy
way for the development of an industrial device.
ix
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1. INTRODUCTION
Information about particulates may be obtained through obser-
vation their momentum mv (m, mass; v, velocity). That seems
obvious and is being already used in two fields for some time:
(1) where the particles, as raindrops, have a comparatively
important mass and (2) as micrometeorite sensor. Although of
slight mass, micrometeorites are moving at very high veloci-
ties. (Raindrop detection by purely mechanical sensing :
VOEGELMANN, 1913; STRAUB, 1923; by sensing through a micro-
phone membrane : MAULARD, 1951; through piezoelectric sensing:
KATZ, 1952; SHVANG and FEDOROV, 1954; WELLHONER, 1960; momentum
transducer for sensing micrometeoroid impacts: DUBIN, I960;
ROGALLO and NEUMAN, 1965).
In order to extend the momentum sensing technique to airborne
suspended matter, in the range from tenths to tens of micron
of diameter, the particles must have high velocities. A con-
venient way to imprint the needed velocities is to allow the
airborne suspension to expand into an evacuated vessel, through
a nozzle or a tube. This is a well known procedure to obtain
molecular beams since the 195O's (about molecular beams see
e.g. ROSS, 1966); when instead of macroions or molecules,
particulate matter is accelerated in this manner, "particulate
beams" would be a convenient name for the phenomenon.
Particulate beams were observed independently and almost simul-
tanously in two laboratories : by BENARIE (1963,1964), AVY and
BENARIE (1964) and by MURPHY and SEARS (1964). The properties
of particulate beams as velocity characteristics, were studied
-------
more thoroughly by ISRAEL and FRIEDLANDER (1967), by DAHNECKE
and FRIEDLANDER (197°) and by DAHNECKE and FLACHSBART (1972).
In the paper of AVY and BENARIE (1964) two distinct means are
indicated for the detection of particles :
(1) The mechanical sensing of the impacting particles, e.g.
by displacement or deformation of a (microphone) membrane.
The development and the potential uses of this method will be
the main topic of this report.
(2) As the particles are expulsed from a high velocity flow,
audible sounds may be produced. This phenomenon was studied and
usefully implemented as acoustic particle sensor by LANGER
(1965, 1966, 1968 a,b, 1972), by KARUHN (1973) and evaluated
by REIST and BURGESS (1968) and by HOFMANN and MOHNEN (1968).
Since the effect of the particles is to modify the pressure
conditions in a capillary, the pressure differential may be
used as on-line concentration monitor, provided the particu-
late loading is high enough. This variant, oriented rather
towards the pneumatic transport of powders was studies by
EARTH et al. (1957). The acoustic or pressure-wave mode of
detection will not be discussed in this paper.
- 2 -
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2. PARTICULATE BEAMS
Raindrop and micrometeorite detection are the proof that impact
sensing is perfectly feasible in other conditions than those of
particulate beams. Further below, this will be also shown for
the case of solid, airborne particulates. Nevertheless, as in
particulate beams the geometrical and the mechanical conditions
of the process are well defined, they represent ideal means
for the basic, quantitative study. To begin with, we shall
make a short review of the generation and properties of par-
ticulate beams, a topic intimately related to impact sensing.
To obtain particulate beams, the particles must be - as an
aerosol or a smoke - initially at or near atmospheric pressure.
The aerosol is admitted to the high vacuum vessel through a
sequence of individually pumped preliminary chambers that are
connected by coaxial capillaries. The capillaries offer almost
no resistance to particle flow but substantial resistance to
the flow of carrier gas. The participate beam is mainly confi-
ned to a very small solid angle about the capillary axis; appro-
ximately one out of ten particles entering the first chamber,
with velocity nearly that of the carrier gas molecules, is
found in the final beam.
The number of coaxial capillaries might be from one to four;
their length/diameter ratio depends on their number (i.e. must
be higher in the case of a single capillary and can be around
1O if four capillaries are used) and the available vacuum pumps.
Evacuation in several steps - as shown by Fig.l. - has definite
- 3 -
-------
7"
CAPILLARIES ^ ^=:"»
I mm 1.0.
x
Tmm.O.D
INPUT CAPILLARY
FROM GENERATOR
.25mm 1.0.
TO ROUGH PUMP A
TO ROUGH PUMP B
TO DIFFUSION
PUMPC
TO DIFFUSION
PUMP 0
200/i SLIT ON
f JOINT
DEFLECTING PLATES
SPACED I cm.
MICROSCOPE SLIDE
Fig.l Schematic diagram of a particulate beam source,
The smoke generator (not shown) is above the
apparatus; the beam is finally defined by the
200 -11 slit in the highest vacuum region.
After MURPHY and SEARS (1964)
- 4 -
-------
advantages. MURPHY and SEARS (1964) expanded a mixture of air
and molybdenum oxide (MoO.) smoke at pressure ranging from 50
to 300 mm Hg through a capillary (i.d., 0.25 mm and length,
1O cm) into an evacuated vessel. The core of the beam was pas-
sed through three successive capillaries (i.d., 1 mm and length,
2 cm), separating successive chambers, each evacuated by its
own pumping system. In the final stage this procedure resulted
in a beam of MoO particles expanding into a solid angle of
-4
2.5 x 1O steradians (sr.).
The velocity of the particles can be evaluated in several ways:
by the "ballistic11 method; from the stop distance of the par-
ticles or through direct distance/time measurements.
The ballistic method consists in the observation of the downward
deflection by gravity, of an originally horizontal beam. Its use
(BENARIE 1964, MURPHY and SEARS 1964, ISRAEL and FRIEDLANDER
1967) has shown that following experimental conditions, particle
velocities between 2O and 2OO ms may be observed.
It was established by DAHNECKE and FRIEDLANDER (197O), in accor-
dance with their theoretical prediction, that horizontal parti-
cle beams of monodisperse spheres stop in a well defined stop
distance and settle to the bottom of the deceleration chamber
where a deposit becomes readily visible in a few minutes. It
can be shown by an order of magnitude comparison of the hori-
zontal and vertical equations of motion that the trajectory of
the beam is effectively horizontal until the particle velocity
is very small. The leading edge of the uncoilimated beam assumes
the form of a parabole (for the larger particles which experien-
- 5 -
-------
ced little Brownian motion while settling) probably resulting
from the velocity profile of the carrier gas in the capillary.
The length of the deposit varies from a few mm to a few cm as
stop distance varies from 1O to 1OO cm. The stop distance will
be directly proportional to particles diameter and inversely
proportional to deceleration chamber pressure. Measurements of
the stop distance will allow to calculate the initial velocity
of the particle beam. These conclusions were verified by various
experimental results, as shown by Figs. 2 and 3-
Direct measurement of beam velocities was accomplished by
DAHNECKE (19?1) and HOLLANDER and SCHORMANN (19?4a), recording
the light signals of single particles which cross two laser
beams separated by a known distance. Velocities around 15O ms
were generally measured.
Other uses than impact sensing of the particulate beams should
be mentioned for the sake of record only. They are : (1) Parti-
culate spec 1rometry, i.e. separation in size classes : BENARIE
(1964), DAHNECKE and FLACHSBART (1972); (2) study of the elastic
rebound properties of particles and their capture by surfaces
at high velocities (for more details, see sect. 6. of this
report).
- 6 -
-------
r
150
L, cm.
100
d = i.305yu.
SOURCE PRESSURE
Fig.2 Measured stop distance vs. reciprocal
pressure. After DAHNECKE and FRIEDLANDER
(1970)
- 7 -
-------
IT i i -f [
L, cm. _
= O. 365
i
s
J
A
SOURCE PRESSURE
80 torr.
20
torr
-I
30
Fig. 3. Measured stop distance vs. reciprocal
pressure. After DAHNECKE and FRIEDLANDER
(1970)
- 8 -
-------
3. PARTICULATE BEAM IMPACT SENSING
3.1 - THEORY
The reponse of a transducer (membrane, flexible beam or similar
device) to an impact is available to simple analysis if the
duration of impact t. is short as compared to the natural period
L/"M~
of the transducer 2
-------
2 M2V2
l/2Kx0 = l/2kmv . 2-- (2)
x0 = maximum displacement of the mass.
Solving Eq. (2) for x0, we have
MV ,, »
x0 = (3a)
N/KM"
or in terms of the particle momentum
kmv i *
*o = (3b)
VKM
It can be seen from Eqs. (3a) and (3b) that the peak deflection
is directly proportional to the particle momentum. Following the
peak deflection, the system will oscillate in a decaying sinu-
soidal transient with the equation of motion
d2*
M -j£2 + C ^ + Kx = f (t) (4)
C = damping coefficient ( (force/time)).
The solution of Eq.(4) shows that for an impulse the maximum
amplitude of the envelope of the decaying exponential is direc-
tly proportional to the input momentum.
- 1O -
-------
3.2 - SINGLE PARTICLE DETECTION BY SCHORMANN (
The single particle experiment was realized by HOLLANDER and
SCHORMANN ( 19?4a) : a typical recording of their oscilloscope
output can be seen in Fig. 4.
3-3.1 - Continuous concentration monitoring - general and theo-
retical part.
The opposite extreme to the particle by particle impact is the
case when their arrival in the beam appears like a continuous
jet. The number of particles hitting the obstacle per time unit
is very high and the frequency of the impacts is higher by orders
of magnitude than the resonant frequency of the receiving surface.
For this case, the same considerations apply as for the impulse
of fluid jets. If the beam carries the mass q per second during
the time differential dt, the total mass
m = qdt (5)
will impact as
,, dv m , . ,^
F = m dT = at ' dv = qdv <6)
With an impacting jet velocity v and the mean perpendicular
rebouncing velocity -kv, the force which acts on the receiving
surface will be
F = 2kqv (7)
- 11 -
-------
Fig. 4. Oscilloscope display of a 1.84 nm latex
particle (lower beam) impacting on a membrane
at 180 m s-1. Upper beam : time signals for
particle velocity measurement. After
HOLLANDER and SCHORMANN (19?4a)
- 12 -
-------
Using a sensitive spring microbalai. ^. an air inlot rate of
3 -1
7.5 cm s equivalent to
-7 -1 -3 ^i
3-75 10 gs at 5O mg m / source concentra-
q = ^ S" tion at atmosphe-
-6 -1 -3
7.5 1O gs at 10OO mg m J ric pressure
with silica dust of grain size between 1 and 2O lim, an effective
v around 150 ms , BENARIE et al. (1973) measured mass-concentra-
-3 -2 dynes
tion proportional forces between 0.5 10 and 10 , with an
average error of _+_ 2O %. The distance of the receiving microba-
lance plate (impacting surface) was about 1O cm from the inlet
capillary and the vacuum chamber pressure around 0.1 torr. Lack
of information about the real density of silica particles and
the indirect estimation of velocity did not allow an accurate
evaluation of k, which seemed to be in the range of O.5 to l.O.
3«3«2 - Particulate beam impact sensing - Experimental.
3.3*2.1 - Preliminary experiments.
made
The preliminary experiments were with the glass apparatus
schematized in Fig. 5* The inlet glass capillary had about
0.25 mm diameter and 6 cm length. The pumping unit (a double-
stage rotational roughing pump followed by a ROOTS of 10 I/sec)
maintained a chamber pressure of about 0.1 torr. From the par-
ticle diameters (silica dust; see grain size distribution in
Fig. 6) and the working conditions, it was inferred following
DAHNECKE and FRIEDLANDER - (197O) that the impact velocities
were around 150 ms .
- 13 -
-------
STAINLESS STEEL SPRING
TO VACUUM
CAPILLARY
Figure 5. Schematical view of the quartz microbalance impact detection.
- 14 -
-------
5 6 /
SILICA
Figure 6. Grain size distribution (number and weight) of the "silica J' test-dust.
- 15 -
-------
The particulate beam impacted against a horizontal mica lamella,
suspended on a quartz spiral microbalance having the sensitivity
of 0.1 dyne cm" (*). The :
experiments are in Fig. ?
of 0.1 dyne cm (*). The results of this preliminary series of
The particulate mass concentration at the intake was measured
by the aid of filters. The incertitude in the abscissa gives
an idea about the unsteadiness of the concentration with time
and about the sampling and weighing error. The spread in the;
ordinate accounts for the error in reading the vertically oscil-
lating spring microbalance. There are even slight horizontal os-
cillations, which make the estimation of the equilibrium position
at times only a few tenth of mm from the zero, an uneasy pro-
position. Moreover, the spring microbalance is quite sensitive
of outside perturbations (vibration, temperature change) so
that little gain could be hoped from following further this path.
On one hand the quartz spiral microbalance is perhaps the most
easily calibrated dynamometric device. The slope in Fig. 7 is
4 -1 -1
2 1O cm s . Admitting that the impact velocity v is 15O m s ,
4 -1
i.e. 2v = 3.1O cm s , the value of K See Eq. 7 page 11 is about
O.7, which is quite possible.
(*) Note. These quartz spiral microbalances and others with
different caracteristics are currently manufactured in our
laboratory, also for sale. The O.I dyne cm is rather fra-
gile and does not support well shipment.
- 16 -
-------
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On the other hand, the errors in optical reading of a sensitive
micro-balance are rather great. The distance from the inlet
end of the capillary must be important as to avoid the influence
of the air molecules. Thus the centering of the device becomes
critical. Also quite critical is the vibration-free positioning
of the instrument. Especially mechanical pumps must not be too
near; but too long vacuum manifolds do not allow the high pum-
ping speeds which are needed to maintain molecular beam condi-
tions .
In conclusion, the quartz microbalance detector is a demonstra-
tion device at its best. Quantitative evaluations should not be
expected from it.
3.3.2.2 - The experimental setup.
The experiments described in the previons section have shown,
that Eq.(7) is a fair working formula for further development.
The mass flow q (g s ) through the capillary or through the
orifice is the product of the concentration c (g cm ) by the
-3 -1
volume flow Q (cm s ):
q (g s'1) = cQ (g s'1) (8)
with the efficiency f of particle beam hitting the target
and considering for the time being k approximately O,7, from
(7) and (8) one has :
F = 1.4 f c Q (gs"1) v (cm s"1) (9)
- 18 -
-------
-4 -1
For the order of magnitude f = 1, v = 10 cm s and a par-
ticulate concentration
- 3 6 -1
c = 1 g m =1O gem
~2
F a$ 1.4 1O Q dynes
One must keep the entering volume flow as high as possible,
to arrive at a well measurable dynamometric effect. On the
other hand, the chamber working pressure must be below 1
torr (this is an upper limit; it is preferable to work at O.I
torr) to obtain particulate beam conditions. Expressed the
other way round, at a higher pressure, the influence of the
molecular air jet on the impaction surface will be too important
and introduce perturbations into the measurement of the force
exerced by the particulate beam.
3 -1
With e.g. Q = 1O cm s at atmospheric pressure, the volume
delivery of the pumping unit must be at or above 1OO liters/
second, leaks not counted, which is anything but a small pump.
A given volume flow may be either delivered by an orifice in
a thin wall, acting as critical orifice or by a capillary of
some length. The latter, the capillary, is a good focusing
device for the aerosol beam, while in the case of a critical
orifice, the particles spread out in a larger solid angle.
The apparatus developed following the conclusions of the
preliminary experiments and the above considerations was 1
presented in Fig. 8 which is approximately on 1 : 1 scale
- 19 -
-------
g
00
*
Crt
dl :Capillary inside diameter
d 2 :caplllary lengh
d 3 -.distance from capillary outlet to dynamometer
to
rt
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PI
n
rt
o
it,
(D
ft)
-
§
O
rt
0
rt
dynamometer
to vacuum
pump
gas tight seal
eye-piece micrometer1
capillary tube
to m anomet er
-------
(inner orifices, etc., exagerated for better visibility). As
microdynametric device, a vinyl lamella was used, about O.I mm
thick, approximately of the form of a miniature tennis racket,
suspended by its handle. (Calibration of the lamella, see
below).
After boosting the aspiration of the vacuum manifold to
30O liters/second, we experimented with different capillary
lengths and diameters in view to obtain particulate beam con-
ditions .
With steel capillaries of 0.8 mm I.D. (d3) in Fig.13 of length
from 10 to 5O cm, the vacuum did not attain the sought low
values. The lowest working pressures were around 1 torr, clearly
insufficient, shown also by the fact that even after gradually
increasing d (the distance from the and of the capillary to
Ct
the impacting surface) to 12 cm, an aerodynamic jet influence
(fluttering) of the plastic lamella was perceived.
On the other hand, using the silica dust of grain size repre-
sented in Fig.6, obstructions of long (i.e. longer than 15 cm)
capillaries occured, but were not all too frequent.
After some experiments with O.6 and O.5 mm I.D. capillaries, we
went over to O.3 mm I.D. which gave full satisfaction as far cham-
and
ber vacuum vibrationless lamella behaviour were concerned. But,
in very favorable case, such capillaries gave fifteen minutes
obstructionless operation. Mostly even this "limit" was not
attained, and after only a few minutes experiments, time-consu-
- 21 -
-------
ming disassembly, cleaning, etc. was needed. Obviously, this
is not a good way for accumulating quantitavie results.
After a several intermediate trials, the arrangement shown in
Fig. 9 was adopted. A forepumping chamber was attached before
the capillary inlet. A critical orifice of O.5 mm diameter,
at O.5 cm from the capillary inlet and centered against it,
acts as particulate intake. The chamber A was evacuated by a
double-stage oil rotation pumps of 3 liters/second, but the
vacuum here was not measured. A capillary diameter of 0,5 mm
and length of 14 cm gave good, obstruction and trouble free
performance during the whole series of experiments wich will be
described below. The distance d2 from the capillary outlet to
the impacting surface was 5 cm.
3.3.2.3 - The yield of the intake.
It was checked and rechecked, that with a single capillary, all
the particulates entering the intake, hit the target, within a
circle of 5 mm, if the latter was well aligned. So, in the
case of the single capillary, f in Eq (9) is unity and dynamical
calculations as in sect. 3-1 may be made.
In the case of the setups of Fig.9 - i.e. a the presence of a
roughing chamber, f is not necessarily unity and its experimental
determination becomes necessary.
The setups used can be seen in Fig.lO; it is the same as that
which was used for the measurement of the mass-concentration
proportionality and will be described with more detail below.
- 22 -
-------
I
CO
s
II
(0
o
s
ft
O
MI
Hi
O
i-h
I
P9
O
0-
(D
rt
8
I
TO
t o v a cu u m pump A
d1: distance from critical orifice to capillary inlet
d2:distance from capillary outlet to dynamometer
d3: capillary inside diameter
d/,: critical orifice diameter
I : caprllary length
d;ynamomel.er
to vacuum
pum p E
gas tight seal
eye-piece micrometer
to manomet er
d1
-------
SAPHYMCMRCHAf dust meter
exhaust
f lurch's ed bed
Figure 10. Calibration of the detector with dust dispersed by
a fluidized bed; comparison with a B-ray absorption
device.
- 24 -
-------
The principle, which is of concern here, consists of coating the
impactor surface with a thin layer of sticky silicone grease and
feeding into the intake a particulate suspension of known concen-
tration during a measured interval of time. The mass difference
of the lamella (impactor surface) before and after the experi-
ment, divided by the actually aspirated particulate mass, gives
the intake yield.
On different days, following yields were measured : Table 1
- 25 -
-------
Table 1
Measured yields of the intake of the device illustrated on Fig. 15
Particulate
concentration
mg/1
Sampling
duration
seconds
Samples
volume
liter
Particulate
mass, in
mg
Particulate mass,
collected on the
target mg
Intake
yield
%
115^15
63.+ 1
1.05.+0.03
121+19
20.2+0.1
17.2+2.6
23^4
9O+1
1.50+0.01
34^6
8.4^0.1
27 .O+6.0
36±5
6o+_i
1.00^0.01
36±5
8 . 3 +0 . 1
23.5+3.5
10+2
3oq+_i
3.00^0.01
30^6
6.5.+.0.1
23 . 2^5 . 3
11+2
24O+1
2.40_+0.01
26.5.+5
5.2+0. 1
20 . 5.+ 4 . 2
18±2
120^+1
1.20+0.01
2 1 . 6 + 2 . 6
5 . 2_+ 0 . 1
24.5^3.5
26^3
90^1
1.50+0.01
39.0±5
9.0_0.l
23 .5O.5
I
to
-------
The first of these values, around 17 %, is very probably too
low because of the thickness of the deposit, some particle
rebounce took place. Some of the differences in the span from
2O.5 to 27.O per cent may be real and due to imperfect centering
of the pieces after disassembly and cleaning. The major part
of the relative error is due to the particulate mass concentra-
tion measurement made in this case by weighing of control fil-
ters; the estimate of the relative standard deviation for the
concentration is 15 % Taking into account these sources of
error, one may estimate the intake yield of the sensor of
geometry defined in Fig. 9 at 23 %
3.3.2.4 - The influence of the grain size distribution.
3-3.2.4.1 - The calibration of the device. The impact-sensing
instrument is shown in Fig. 9; it was partly described in the
previous section. The inlet is a O.5 mm dia critical orifice
mounted on a rough-pumping chamber A. In its axis, at 5 mm
distance is the inlet capillary of 14 cm length and O.5 mm
I.D. The vacuum in the main chamber is maintained as nearly
as possible at O.I torr. The particle velocities were not
directly monitored, but from published evidence it may be infer-
red, that they were in the 2OO to 3OO m s~ range. The results
shown below prove, that this velocity was uniform for all par-
ticle dimensions concerned and did not vary appreciably from one
experiment to the other.
At a distance of five cm from the capillary outlet was the
impaction sensing lamella. This was cut out from vinyl foil
O.O3 mm thick, a circle about 12 mm diameter with a "handle" of
3 mm width.
- 27 -
-------
The dynamometric calibration of the lamella ..a& done in the
following way : the apparatus in fig.9, normally used in the
horizontal position, as shown, was set up vertically, i.e.
the lamella horizontally. The lamella remained perpendicular to
the tube axis, which showed that its weight represented but a
negligible fraction of the elastic restoring force of the
"handle", which acted as a beam fixed at one of its ends.
Microanalytic weight pieces (platinum wire) were charged as
near as possible to the center of the circular receptor sur-
face and the deflections observed on the eye-piece micrometer
of a long objective working distance microscope . Pour such
points, gave a straight dynamometric calibration curve, pro-
vided that the deflections were kept below 1O°. This was attai-
ned by chosing the appropriate "suspension beam" width, as the
thickness was already given by the vinyl sheet.
As already explained, the impact measuring device was used with
its axis horizontal, i.e. the lamella pending. A zero-deflection
was observed, i.e. a deflection from the vertical, partly due
to the laminating tensions sometimes present in the lamella,
and partly to the air jet as the pumps were on. This deflection
is shown in an exaggerated way on Fig.9. Due to this deflection,
the impact of the particulate beam was not perpendicular to the
lamella. If the receiving surface deviates from the vertical by
a degress, the flexing force is proportional to cos a. The
appropriate correction to the readings was applied when a >10°;
below this limit, the correction factor is less than 1.5%> which
is certainly below the precision of the measurement.
- 28 -
-------
Strictly speaking, in cas3 of angular deviation from the ver-
tical, the restoring momentum of the pendulum formed by the
lamella should also have been considered. But, as it was already
exposed when speaking about calibration, the weight of the
lamella may be neglected before the elastic force; thus this
correction was not applied to the data.
3.3*2.4.2 - Results ; grain size independence. The apparatus used
for the measurement, is schematized in Fig. 10. A fluidized bed,
containing O.3 mm dia glass beads and the test dust, generates
the particulate cloud. The intakes of the impact sensing device
and of a SAPHYMO-IRCHA p - absorption dust monitor, operating in
the 1 minute sampling mode are horizontal and about 1O cm dis-
tant inside a 1O liter flask. The position of the impact-sensing
lamella is read microscopically.
The following hard test-dusts were used :
Silica, density 2.7, grain size distribution Fig.6
Aluminium oxide, density 3-6, grain size distributions Figs.
11 and 12.
Silicon carbide, density 3*2, grain size distributions,
Figs. 11 - 2O.
A summary of the results is shown in Fig. 21. Here three par-
ticulates as different in grain size as possible (silice J
Fig. 6 Aloxite 40 Fig. 11 and silicone carbide W25, Fig. 19)
- 29 -
-------
Figure 11. Grain size distributions (number and weight)
of the test dusts.
- 30 -
-------
4 5 6 7 8 V 10
Figure 12. Grain size distribution (number and weight) of the
test results.
- 31 -
-------
. -i
4 567
suMBta,.Jit. Pillion
Figure 13. Grain size distributions (number and weight) of the
test results.
-------
o/
6 7
W10 POWDER
;
Figure 14. Grain size distributions (number and weight) of
test results.
the
- 33 -
-------
Figure 15. Grain size distributions (number and weight) of the
test results.
- 34 -
-------
W16 POWDER
Figure 16. Grain size distributions (number and weight) of the
test results.
- 35 -
-------
I 11 P
-------
567
Figure 18. Grain size distributions (number and weight) of the
test results.
- 37 -
-------
5 6 /
W25 PQWDER!
; .NUMBER OFPAJlTICLES_fc
PAJRTICui DJAMtTEfi | MiqHQNS
Figure 19. Grain size distributions (number and weight) of the
test results.
-------
Figure 20. Grain size distributions (number and weight) of the
test results.
- 39 -
-------
O
I
2
M
rt
S" f?
i-( o>
m co
ro c
*
Ou ID
t* a
ro o
i n
n r>
9 n>
rt
rt CD
m
co
a-a
c PI
CD n
1
O
en
l-h
O
e m a ss
per sec id on
the Ian ell a
-------
were compared. The abscissae are expressed in two ways: as
particulate concentration at the sampling orifice and as par-
ticulate mass, effectively hitting the lamella, i.e. taking
into account the ^ 23% efficiency.There is no visible segrega-
tion of the point3 which could be attributed to substance or
grain size differences. The scatter is due mainly to three
reasons: partly reading and parallax errors, but mostly vibra-
tion of the receptor surface. This latter error is estimated
to be about ten per cent, which may be even greater at low
angular deviations. Finally it is also possible that the
particulate beam velocity varied slightly from one experiment to
the other.
3.3.2.4.3 - The influence of the nature of the particulate. The
experiment exposed above and summarized in Fig. 21 was repeated
with all the particulates of which the grain sizes were given
in the Figs. 6 and 11 to 2O, measuring ten to thirty concentra-
tions for each. The total of 253 points shows the same regres-
sion line.
F (dyne) = 2.38 1Q4 (cm s'1) q (g s'1) (1O)
where q is the particulate mass impacting on the target per
second; with a regression coefficient of O.6?, highly signi-
ficant at the quoted 251 D.L. level.
The same experiment, with the same apparatus was repeated with
coal dust, carbon black, asbestos dust, dust from power plant
electrical precipitator, road dust, lycopodium spores, finely
ground sugar, heavy oil spray and water spray. No exact grain
- 41 -
-------
size measurements are available about these particles. The
"constant" in Eq. (1O) contains in fact the particle velocity
_4
and the restitution parameter k, and which is 2.38 1O for hard,
irregular particles, takes the following values other particu-
lates Table 2 :
Table 2
Values of the restitution parameter for various substances
Coal dust
Carbon black
Asbestos dust
Electrical precip.
dust
Road dust
Lycopodium
Ground sugar
Oil spray
Water spray
Values of the cons
tant in
-4 - 1
1O (cm s )
2.32
1.56
2.35
2.37
2.24
2.79
2.3O
1.9O
1.7O
Observations
Adhering speck obser-
ved on the lamella.
Adheres when wet.
Thin film of cons-
tant thickness ob-
served on the lamel-
la; most of the
liquid blown away.
particulates experiencing high-velocity reflection, show quite
similar behaviour. On the other hand, adhering particles show a
- 42 -
-------
k value O.5 even if they adhere only for a relatively short
time and are then blown away (e.g. non - viscous liquids, as
water) .
-------
4. RESONANT MODE SENSING
4.1 - GENERAL CONSIDERATIONS
By Eq.(4) we anticipate still an other mode of impact detection.
Tf the particles arrive just at the resonant frequency of the
springmass-system, a very high sensitivity can be expected in
the harmonically filtered output. Such a timing in the arrival
is quite difficult to obtain with individual particles but it
might be done by clusters.
It was shown by HARTMANN (1939) that a jet of air, issuing from
an orifice, contains longitudinal compression waves. Instead of
theoretical developments, Figs. 22 and 23 illustrate adequately
the phenomenon. Particulate matter introduced into this standing,
longitudinal wave-system is a) transported by the jet, b) locally
condensed and rarified just as it occurs in case of the "powder
figures" of KUNDT, a classical physics-textbook experiment.
This idea was tested with the device schematized in Fig.24 which
is a development of the basic one shown in Fig.5- The slotted
disc obturates the particulate cloud, but not the air intake.
Its rotation was adjusted to the frequency of the spring-mass
system (about 2 Hz). Qualitative, preliminary experiments have
shown, that a more sensitive detection may be obtained than with
direct, uninterrupted beam. After a few more preliminary cons-
tructions, this approach was found too fragile and perturba-
tion-prone, and was replaced by clustering by a sonic effect, as
- 44 -
-------
Fig. 22. Structure of pulsating supersonic air
jets at different flow rates and orifice
diameters. After HARTMANN (1939)
-------
TUBE
CONICAL WAVE
AIR PRESSURE
3-5 kg/cm
DIAGRAM OF THE
STATIC PRESSURE
Fig. 23- Schema of air jets with pressure waves.
- 46 -
-------
stainless steel spring
to vacuum
(spinning speed
according to natural frequency of spring)
dusl
d: capillary inside diamet»r
d;d-.d ; diameters of holes
di -.distance from capillary outlet to first hoi?
"> .1» '.distances betv/een haifs
P .cap i:iarv leng! r>
Figure 24. Schema of an early model resonant device.
- 47 -
-------
outlined in the above paragraph.
The schema of the instrument with the vibrating lamella is
shown in Fig. 25 The plexiglass envelope allows the observa-
tion of the lamella.
The vibrating mode is obtained by adjusting the distance
between the lamella and the grounded detector body, from
which the particle stream emerges through a critical orifice.
Part of this body may be finely adjusted by a differential
screw (see Fig. 25). Vibrating mode is not difficult to obtain
with (metallized) mica impaction lamellae; but very difficult
to obtain with thin metallic foils, as stainless steel. If
these are out with scissorlike instruments, the edges are
always microscopically bent and the lamella will not be plane.
Tf the lamella is cut by sand blasting or by chemical etching,
the release of internal tensions in the (always rolled) sheet
warps the lamella by a few microns, which is enough to hinder
a successful vibrating mode. Heat-treatment made the metal to
loose its indispensable resilience. Very numerous unsuccessful
trials were made to obtain good metallic lamellae, before
finally settling with mica.
The vibrating mode and the vibration frequency of the lamella
were ascertainded in three ways :
1) The vibrating lamella emits a clearly audible pitch. A
headphone was fed with a variable sinusoidal frequency from a
generator and the two tones matched by the ear.
- '18 -
-------
8
Ui
cn
n
ft
n
*
o
i-h
Hi
O
Ml
P)
cn
O
rt
(D
O
rr
O
VIBRATING DEVICE
stainless steel or met allrz edrnica
-------
2) Through the plexiglass envelope, the lamella vibrations
were synchronized with the light of a stroboscope. The "stop-
ping" of the lamella was visually followed.
3) The vibrating lamella, connected to the imput of an oscil-
loscope, (high impedance, 1O m Sc ) gives the sinusoidal res-
ponse shown in the Figs. 26, 27 and 28.
The frequencies measured by these three means were within
very narrow limits the same. The amplitude variations in func-
tion of the particulate loading are clearly visible with strobos-
copic lightning, but as quantitative measuring means, the optical
way was not adopted in this case.
'..2 - SOME RESULTS OF THE RESONANT MODE SENSING.
Ft was seen early, that the resonant mode sensing, while a
sensitive way of particulate detection, is not yet a prac-
tical one. Before each experiment, the distance of the orifice
(detector body) from the lamella must be carefully tuned. The
lamella must be plane within a few microns and paralell to the
surface containing the orifice, within a fraction of a degree,
at least crosswise. In the lengh axis of the lamella the para-
lellism is somewhat less critical, as its elasticity will
allow some adjustement once the vibrations are started, but
more than a few degrees slope will hinder the process to start.
To sum up the difficulties, it was rather the rule and not the
exception, to adjust and to test a "vibrating detector" two
clays for half an hour of satisfactory measurement. Then, more
often as not, the vibrating mode was lost, perhaps because of
- 50 -
-------
Fig. 26. Example of sinusoidal response
-------
o
'ig. 27 . Sinusoidal response with 15 mg m~ particulates.
- 52 -
-------
_
Fig. 28. Sinusoidal response with 30 mg m particulate
loading
- 53 -
-------
a slight deformation in some part of the device and the
"tuning" had to be recommenced. Although, by its sensitivity,
this seems a promising device (and perhaps the sensibility
may be pushed further by synchronous detection) it is still
not technically mature.
A series of res^ults are given in Fig. 29. The amplitudes, as
in Figs. 26, 27 and 28 (and others, not presented here as
oscilloscope recordings) are plotted against the particulate
concentrations, monitored by the SAPHYMO-IRCHA (3-ray appa-
ratus .
-------
s
I
0) T3
O M
» H-
IB rt
3 C
ft O.
(D
rt
*^ <
T) a
-------
5. IMPACT SENSING OUTSIDE PARTICULATE BEAM CONDITIONS
With a relatively short nozzle - generally with a length/dia-
meter ratio of 1O or less - the necessary conditions for the
particulate beam formation were not realized. The velocity
attained by the particles will neither be uniform nor indepen-
dent of their grain size. The particle velocities will not ap-
proach sonic velocity; they will be rather around a few tenths
_ i
of ms , carrying lesser impact momentum. Nevertheless, their
detection is feasible, provided a sufficiently sensitive device
exists.
A device of this kind might be produced -by a very thin lamella,
on condition that it should be quite near (a few tenths of
mm) the intake nozzle. The lamella together with the nozzle
body thus forms a condenser, the capacitance of which is a
function of the distance separating the lamella from the body.
Other kinds of proximity sensing (magnetic, inductive, etc..)
were also experimented with.
The problem to be solved is the maintaining of a thin, flexible
lamella, very near albeit not in contact with a surface. This
is hard to do because of a nozzle traversing the said surface and
from which a high-velocity particle stream is spurting. A possi-
ble solution was suggested by BENARIE and QLJETIER ( 197O) . A
surface is attracted to an other if an airstream is blown
from a central nozzle into the space separating the two sur-
faces. The air has the highest velocity in the circular zone
- 56 -
-------
around the nozzle and decreases with increasing radius. As on
the rim and on the outside surface the pressure is ambient, a
depression must be found (ECK 1957? -p.27) in the high velocity
zone. The effect of this depression is counteracted by the
dynamic pressure in the center and eventually by the weight
or a spring-loading of the surface. Vibrations caused by this
effect, when the damping of the surface is weak, are well
known in any plumbing systems' taps.
The system is seducing by its constructive simplicity. Its
potential for particulate matter detection, in the ten-to
hundred milligram per cubic meter range, was demonstrated.
Nevertheless, compared to the technically more exacting parti-
culate beam impact sensing, its several drawbacks should also
be noted :
(1) The particle trajectory, albeit very short, does not
occur in vacuum. Behind the nozzle acting as critical orifice,
about half of the atmospheric pressure is maintained. This
fact in addition to the shortness of the nozzle, induces a grain
size-sensitivity of the output.
(2) The nearness of the sensing lamella to the earthed detec-
tor body, makes any kind of proximity detection easy, but at
the same time, because of electrically charged particles, very
parasite-prone. It was observed in some cases that electrical
charges accumulating on the lamella, obviated the possibility
of capacitative detection.
- 57 -
-------
(3) The low particle velocities which may be attained in relati-
vely short nozzles, restrict the impact momentum and in conse-
quence, the lower detection limit.
(') The abovementioned problems, concerning nozzle and resis-
tance, coupled perhaps with other less known parasitic effects,
foreclose the use of the devise in Its present form for mass-
monitoring. Individual calibrations become unavoidable.
-------
6. INFORMATION ABOUT PARTICLE ADHESION AND BOUNCING
In this section, we will discuss the important factor k of Eq.
(1): the momentum transfer parameter.
It is well known from jet impactors and conimeters operating
at fairly high speeds, that particles rebound from the receiving
surfaces if those are not adhesive-coated (BIRSE and ROBERTS,
1948; JORDAN 1954).
Some experiments on particle collection efficiency (= adhesion
probability) were carried out with WO, aerosols of 0.013 -
-* _ i
O.O18 lim mass median diameter at 2OO ms by ISRAEL (1967). He
found that about 75% of the WO particles were reflected from
the formwar or carbon coated electron microscope grids. When
the target was covered with a thin layer of silicone fluid,
the number of reflected particles was less than 7%> ISRAEL
concludes that even very small particles are reflected to a
high degree from a target, unless this surface is coated with
an adhesive.
A theoretical approach to particle adhesion in beam condition
(v > 1OO ms ) colliding with a target surface, was made by
DAHNECKE (1971). His conclusions were that at velocities of
this order, hard, rigid impaction surfaces, as well as thin,
flexible membranes will reflect silica and similar particles
above 1 |lm diameter.
HOLLANDER and SCHORMANN (1974b) provided results of measure-
ments on single aerosol particles of various origin, bouncing
from different surfaces. Latex particles show elastic rebound
- 59 -
-------
for velocities < [JO ms . For increasing velocities the ine-
lastic losses during the impact increases in such a way that
the rebound velocity v is nearly constant and independent
of v. the incident velocity. The velocity v does not depend
significanly on the particle diamter D for . 5V-m < D < 2.O2y,m,
There is no significant difference between different hard
targets (e.g. polished brass and glass).
Irregular shaped particles from crystalline solids (coal,
SiO , Asbestos) also rebound but have a larger spread in
velocity. This is probably caused by the different deformation
energy due to different contact conditions and the different
amount of rotation energy.
With plastic coated microscope slides, the thicker the film,
the faster is the rebound velocity of the particles, regard-
less of their size, shape and material. This "mattress" -
effect can be explained by the fact that the deceleration
during impact is less and stress is distributed over a larger
area, both effects resulting in a reduced plastic flow.
Liquid DOP droplets and soft carnauba wax particles did not
rebound for initial velocities > 22O ms but adhered to all
tested targets. DOP droplets burst during impact; parts of
them .ire possibly scattered into all directions.
Crystalline materials rarely adhere on smooth, cleaned sur-
faces when they have irregular shape (adhesion probability,
A 74 5%). Spherical latex particles practically always rebound.
- 60 -
-------
Adhesion significantly increases (A «r 50°i) for the combina-
tion of an irregular solid particle and coated surface. Coa-
ting with vacuum grease retains practically all particles
regardless of the shape.
Some results obtained by HOLLANDER and SCHORMANN are abs-
tracted in the following Table 3«
Table 3
Information about rebound properties of particles. After
HOLLANDER and SCHORMANN (I974h)
Aerosol
Latex 1. IV-m
Latex 2.02Tlm
Coal
Asbestos
Carnauba wax
1. 1 Tim
DOP 1 . 1 Tim
SiO O.62 V-m
£*
Latex
1. 1 Tim
Coal
Asbestos
Target
clean
micros-
slide
polished
brass
matted
glass
*
Coated
cope
silicon
grease
Number
of
experi-
ments
48
50
29
58
60
16
22
13
42
43
57
Mean rebound
velocity at
15O
-------
* A cleaned microscope slide once immerged into a 4 % polyi-
sobutylene solution in toluene
During our own experimentation with solid dusts, no deposit
was observed on the lamella, even after protracted impacting.
On the other hand, with very hard particulates (e.g. Al 0 )
^ j
erosion on the target became visible. With thin (& lOp-m)
lamellae, this effect may continue until neat perforation
of the target. That means that in some cases at least, disrup-
tion of the target material is possible by the particle beam-
a not at all surprising phenomenon after all that is known
about technical sandblasting.
- 62 -
-------
REFERENCES
AVY A.P. and BENARIE M. 1964 : Akustischer Nacheweis von
Staubteilchen Staub J24_ p.343-344.
EARTH W., NAGEL R. and VAN WAVEREN K. 1957 : Neues Verfahren
zur Bestimmung der augenblicklich gefdrderten Gutmengen im
Luftstrom bei pneumatischer Fdrderung. Chemie-Ing. Techn. 29
p.599-602
BENARIE M. 1963 : Die Niederdruckelutriation als Trenn - und
Korngro'ssenmessmethode fur Feinstaube - Schwebstofftechnische
Arbeitstagung, 24/25 Okt. Mainz - Staub J24 (1964) 23
BENARIE M. 1964 : Precede et appareil pour la separation gra-
nulometrique des poussieres fines. French Pat. N°l.405-297
BENARIE M. and QUETIER J.P 197O : Etude d'une methode micro-
dynamometrique pour la mesure de la concentration des pous-
sieres. Aerosol Sci. _1 p.77-lO9
BENARIE M., GRUDZINSKI A. and QUETIER J.P. 1973 : Developpe-
ments recents concernant le principe des detecteurs de parti-
cules par observation mecanique de leur impaction (Micrody-
namometrie). Meeting of the Ges. f. Aerosolforschung, Oct.
Bad Soden, Germany, p.8-12
BIRSE E. and ROBERTS J. 1948 : The action and the design of
mechanical filters for dust and smoke. Trans. Farad. Soc.
jt4_ p.273-278
- 63 -
-------
COOPER D.F 1951 : Austr. J. Appl. Sci. £ p.43
DAHNECKE D. 1971 : The capture of aerosol particles by sur-
faces .
J. Coll. Interface Sci. 37_ p.342-353
DAUNECKE D.E. and FLACIISHART H. 1972 : An aerosol beam
spectrometer Aerosol Sci. 3_ P-345-349
DAHNECKE 13. E. and FRIEDLANDER S.K. 197O : Velocity characte-
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TECHNICAL REPORT DATA
(Please read JaOmclions on the reverse before completing)
1 REPORT NO.
EPA-6QO/2-75-025
3 RECIPIENTS ACCESSION-NO.
4 TITLE AND SUBTITLE
Particle Detector by Mechanical Impact Sensing
5 REPORT DATE
,lune 1975
6. PERFORMING ORGANIZATION CODE
7 AUTHOR(S)
Michel Benarie and Jean-Pierre Quetier
8. PERFORMING ORGANIZATION REPORT NO
9 PERFORMING ORGANIZATION NAME AND ADDRESS
Institut Nat'l de Recherche Chimique Appliquee
91710 Vert-le-Petit, France
10 PROGRAM ELEMENT NO.
1AA010
11. CONTRACT/GRANT NO.
802424
12 SPONSORING AGENCY NAME AND ADDRESS
Chemistry and Physics Laboratory
National Environmental Research Center
Research Triangle Park, N. C. 27711
13 TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15 SUPPLEMENTARY NOTES
16. ABSTRACT
Particulate impact is used for the detection and measurement of raindrops
and micrometeorites since several decades. Aerosols might be detected in the
same way if the suspension is expanded rapidly when it enters through a
capillary in a nearly evacuated vessel.
If the accelerating capillary is relatively long and the pressure inside the
vessel below 1 torr, particulate beams are obtained. They enable the study
of particle velocities, their rebound properties, etc. in good conditions.
For particulate beam conditions, impact sensing is mass concentration propor-
tional, grain size and substance independent, and sensitivity may rate from
the detection of single particle to the range of mg nr3.
With short nozzles and chamber pressure above 1 torr, impact sensing remains
possible but marked grain size dependence and possible substance dependence
complicate the phenomenon.
17
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b IDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Particle Detector
Mass Monitor
Particle Counter
Impact Sensing
18 DISTRIBUTION STATEMENT
Release Unlinitfl
19. SECURITY CLASS (This Report)
Unclassified
21 NO. OF PAGES
65
20 SECURITY CLASS {This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
67
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