Environmental Letters
ISSN: 0013-9300 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/lesa17
Particle Sizing of Arc Smokes by Forward Light Scattering P. W. Chan , O. Apichatonon & C. Y. She To cite this article: P. W. Chan , O. Apichatonon & C. Y. She (1975) Particle Sizing of Arc Smokes by Forward Light Scattering, Environmental Letters, 10:1, 69-76, DOI: 10.1080/00139307509435809 To link to this article: http://dx.doi.org/10.1080/00139307509435809
Published online: 02 Sep 2009.
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ENVIROXMENTAL LETTERS, 1 0 ( 1 ) , 69-76 (1975)
PARTICLE SIZING OF ARC SMOKES BY FORWARD LIGHT SCATTERING
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Key Words: Arc Smoke P a r t i c u l a t e s , S i z e D i s t r i b u t i o n , Two-angle R a t i o , P o l a r i z a t i o n R a t i o , L i g h t S c a t t e r i n g P. W. Chan, 0. Apichatonon Department of E l e c t r i c a l Engineering and C. Y. She Department o f P h y s i c s Colorado S t a t e U n i v e r s i t y , F o r t C o l l i n s , Colorado
80523
ABSTRACT The p o l a r i z a t i o n r a t i o method sinilar t o that proposed by K i r k e r e t a l . h a s been a p p l i e d t o o b t a i n s i z e d i s t r i b u t i o n f o r s e v e r a l t y p e s of metallic smoke p a r t i c u l a t e s g e n e r a t e d by a d c e l e c t r i c arc.
R e s u l t s are p r e s e n t e d f o r carbon, t u n g s t e n and
aluminum arc smokes.
These r e s u l t s a r e compared w i t h t h e a v e r a g e
s i z e of t h e p a r t i c u l a t e s measured by t h e two-angle r a t i o method of Hodkinson and are found t o b e c o n s i s t e n t and w i t h i n e x p e r i m e n t a l error.
The o p t i c a l system w a s c a l i b r a t e d w i t h s t a n d a r d l a t e x
spheres i n both cases.
It is believed t h a t t h e parameters of t h e
arc smoke p a r t i c u l a t e systems should b e u s e f u l f o r environmental particulate research. INTRODUCTION Among t h e v a r i o u s o p t i c a l methods f o r measuring p a r t i c l e s i z e , l i g h t s c a t t e r i n g p o s s e s s e s t h e most p o t e n t i a l i n s p i t e of i t s r e l a t i v e
69 Copyright 0 1975 hy Marcel Ikkker, Inc. All Rights Reserved. Neither this work 1ror any part m3y he reproduced or transmitted in any form or by any means, electronic or mech~nical,including photocopying. microfilming. and recording. or hy any inform~tionstorage and retrieval system. without permision in writing from the publisher.
70
CHAN, APICHATONON, AND SHE
c o m p l i c i t y as compared w i t h e x t i n c t i o n measurement. two-angle i n t e n s i t y r a t i o method o f Hodkinson
Recently t h e
has a t t r a c t e d
c o n s i d e r a b l e a t t e n t i o n i n a i r p o l l u t i o n c o n t r o l systems
('I. The
method, due t o t h e n a t u r e of forward s c a t t e r i n g , i n t h e Fraunhofer
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l i m i t , is e s s e n t i a l l y independent of t h e r e f r a c t i v e index of t h e p a r t i c u l a t e system and t h u s making s i z e measurement p o s s i b l e w i t h o u t
a knowledge of t h e i n d e x of r e f r a c t i o n .
K i r k e r et a l . ( 3 ) w a s t h e
f i r s t t o s u g g e s t t o measure t h e p o l a r i z a t i o n r a t i o a t s e v e r a l s c a t t e r i n g a n g l e s t o measure p a r t i c l e s i z e d i s t r i b u t i o n (average s i z e and s t a n d a r d d i r e c t i o n ) of sub-micron range.
T h i s method h a s been
s u c c e s s f u l l y employed by M a t i j e v i c e t a l . ( 4 ) i n o b t a i n i n g a e r o s o l s i z e d i s t r i b u t i o n g e n e r a t e d from o c t a n o i c a c i d w i t h r e a l r e f r a c t i v e i n d e x down t o 0.4pm.
The t e c h n i q u e r e q u i r e s a knowledge o f t h e
r e f r a c t i v e i n d e x of t h e p a r t i c l e s i n g e n e r a l .
However, i f t h e s c a t t e r i n g
is chosen i n t h e forward d i r e c t i o n ( s a y less t h a n 4 0 " ) ,
the polarization
r a t i o is a g a i n i n s e n s i t i v e t o r e f r a c t i v e i n d e x as i n t h e two-angle r a t i o method.
Thus t h e t e c h n i q u e c a n b e used t o supplement t h e two-
a n g l e r a t i o method f o r measuring p a r t i c l e s i z e d i s t r i b u t i o n (average s i z e and s t a n d a r d d e v i a t i o n ) .
I n t h i s paper w e r e p o r t a n e x p e r i m e n t a l
i n v e s t i g a t i o n of t h e s i z e d i s t r i b u t i o n of m e t a l l i c arc smoke p a r t i c u l a t e system u s i n g b o t h t h e p o l a r i z a t i o n r a t i o and t h e two-angle i n t e n s i t y r a t i o methods u s i n g small forward s c a t t e r i n g a n g l e s . THEORETICAL BACKGROUND The b a s i c concept of forward l i g h t s c a t t e r i n g is based on t h e f a c t , f i r s t noted by Hodkinson")
t h a t t h e a n g u l a r d i s t r i b u t i o n of
t h e s c a t t e r e d l i g h t w i t h i n t h e forward l o b e is p r i m a r i l y due t o Fraunhofer d i f f a c t i o n and as such, is n e a r l y independent of t h e index of refraction.
I f t h e r a t i o of t h e s c a t t e r e d f l u x a t two
PARTICLE SIZING OF ARC SMOKES
71
a n g l e s is c a l c u l a t e d , i t 2s a known f u n c t i o n of t h e p a r a n e t e r of nd a = -where
X
d is t h e p a r t i c l e d i a m e t e r , X is t h e wavelength of
i n i t i a l l i g h t f o r any p a i r of a n g l e s O1 and 0 2 . c u r v e s can b e c a l c u l a t e d " ) . y i e l d t h e s i z e parameter a.
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Conparison of e x p e r i m e n t a l r e s u l t s The t e c h n i q u e g i v e s a mean v a l u e of
It becomes r a t h e r i n s e n s i t i v e f o r a51 f o r a l l
p a r t i c l e diameter. p a i r s of a n g l e s (1)
Thus a f a m i l y of
.
The p o l a r i z a t i o n r a t i o method was f i r s t proposed by K i r k e r e t a l . (')
The r a t i o of t h e p a r a l l e l and t h e p e r p e n d i c u l a r components of
t h e s c a t t e r e d l i g h t p(O);$, angles.
(0)/11(0)
According t o Mie t h e o r y ,
Ji,(ek(a)da
is measured a t s e v e r a l s c a t t e r i n g
p(O)E$
(0)/11(0)
=
Ji,, (O)p(a)da/
where p ( a ) is t h e s i z e d i s t r i b u t i o n , a = r a d i u s ,
(O),
i (0) are, r e s p e c t i v e l y , t h e s c a t t e r e d i n t e n s i t y p a r a l l e l and
1
p e r p e n d i c u l a r t o t h e p l a n e of i n c i d e n c e .
The procedure from h e r e on i s
t o assume a s i z e d i s t r i b u t i o n and compare t h e e x p e r i m e n t a l measured v a l u e of p ( 0 ) w i t h t h e t h e o r e t i c a l p r e d i c t i o n by v a r y i n g t h e c h a r a c t e r i s t i c r a d i u s and t h e s t a n d a r d d e v i a t i o n of t h e d i s t r i b u t i o n u n t i l a good f i t
is o b t a i n e d .
A z e r o t h o r d e r l o g a r i t h m i c d i ~ t r i b u t i o n ' ~ is ) assumed i n
t h i s work w i t h aMa s t h e n o d a l v a l u e of t h e s i z e parameter a and u
the logarithmic standard deviation.
APPARATUS AND EXPERIMDJTAL METHODS The b a s i c a p p a r a t u s c o n s i s t s of a 2mW He-Ne laser s o u r c e , s l i g h t l y focused a t t h e c e n t e r of a c y l i n d r i c a l snoke chamber. S c a t t e r e d l i g h t w a s c o l l e c t e d by a l e n s and d e t e c t e d by a RCA 1P22 p h o t o m u l t i p l i e r whose o u t p u t was connected t o a d c microvoltmeter. The e n t i r e c o l l e c t i o n o p t i c s was mounted on a r i g i d r o t a t a b l e bench c e n t e r e d a t t h e smoke chamber r o t a t a b l e through 10' t o 40' t o t h e forward d i r e c t i o n .
relative
I n t e r f e r e n c e f i l t e r s and s l i t a p e r t u r e s
72
CHAN, APICHATONON, AND SHE
were used t o improve s i g n a l a g a i n s t n o i s e background.
A t each
a n g u l a r p o s i t i o n , t h r e e r e a d i n g s of t h e s c a t t e r e d l i g h t i n t e n s i t y , namely, t h e t o t a l i n t e n s i t y , t h e h o r i z o n t a l i n t e n s i t y and t h e v e r t i c a l i n t e n s i t y as s e l e c t e d by p o s i t i o n i n g a p o l a r i z e r i n t h e h o r i z o n t a l and v e r t i c a l d i r e c t i o n w e r e r e c o r d e d a t 2.5" i n t e r v a l .
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The t r a n s m i t t e d l i g h t w a s monitored t o e n s u r e a t t e n u a t i o n o f t h e i n c i d e n t beam and was k e p t t o less t h a n t e n p e r c e n t t o avoid c o m p l i c a t i o n s due t o n u l t i p l e s c a t t e r i n g . ( 6 )
The smoke p a r t i c l e s were
g e n e r a t e d between a p a i r of e l e c t r o d e s of d i f f e r e n t m a t e r i a l s under An arc w a s i n i t i a t e d between t h e e l e c t r o d e s .
study.
The a r c s p a c i n g
w a s k e p t a t a d i s t a n c e of 2m and i t c a r r i e d 7 Amps ( d c ) .
After
a l l o v i n g t h e arc t o b u r n f o r 1 minute, t h e a r c smokes were d i s p e r s e d by a f a n f o r a n hour b e f o r e e x p e r i m e n t a l d a t a were o b t a i n e d a s described.
The w a i t i n g p e r i o d is due t o t h e r a p i d c o a g u l a t i n g smoke
systems under i n v e s t i g a t i o n .
A t l e a s t two r u n s were t a k e n and t h e
s c a t t e r i n g a n g l e s were s e l e c t e d a t random. t o be
A
The r e p r o d u c i b i l i t y w a s found
20% between r u n s when p r e c a u t i o n s were t a k e n t o c l e a n t h e arc
e l e c t r o d e s and a d j u s t t h e e l e c t r o d e spacing. For s y s t e n c a l i b r a t i o n , a d i l u t e s o l u t i o n of s t a n d a r d l a t e x i n d i s t i l l e d water w a s used.
S i n c e t h e s i z e d i s t r i b u t i o n of t h e l a t e x
i s a c c u r a t e l y known, t h e e x p e r i m e n t a l a c c u r a c y can be checked. EXPERIMENTAL RESULTS, ANALYSES AND DISCUSSIONS The e x p e r i m e n t a l r e s u l t s of p a r t i c l e s i z e f o r l a t e x s p h e r e s , carbon, t u n g s t e n and aluminum arc smokes a s measured by b o t h t h e twoa n g l e r a t i o o r t h e p o l a r i z a t i o n r a t i o methods are p r e s e n t e d .
The
e x p e r i m e n t a l c o n d i t i o n s f o r a r c smoke g e n e r a t i o n were as d e s c r i b e d i n t h e last section.
The l a t e x s p h e r e s a r e manufactured by Dow Chemical
Co. (Batch 2G6J) w i t h m a n u f a c t u r e r ' s g i v e n mean d i a m e t e r
d
=
0.234~
73
PARTICLE S I Z I N G OF ARC SMOKES and s t a n d a r d d e v i a t i o n o = .0026!~m. The s o l u t i o n (10% by weight) i s d i l u t e d 1000 times i n d i s t i l l e d water.
The methods of a n a l y s i s are s t r a i g h t f o r w a r d .
For t h e two-angle
r a t i o method, t h e measured i n t e n s i t y r a t i o f o r t h r e e p a i r s of a n g l e s
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over two i n d i v i d u a l r u n s were averaged and compared t o t h e i n t e n s i t y r a t i o c u r v e s a l r e a d y c o r r e c t e d f o r t h e geometric f a c t o r a s g i v e n by
-
from which t h e a v e r a g e v a l u e s of a =
Hodkinson")
nd are A
obtained.
The r e s u l t s a r e t a b u l a t e d i n Table 1. For t h e p o l a r i z a t i o n r a t i o method, t h e t h e o r e t i c a l p o l a r i z a t i o n r a t i o p ( 0 ) a c c o r d i n g t o >lie t h e o r y i s computed w i t h a CDC 6400 Computer f o r a n e x t e n s i v e a r r a y of t h e a 40" i n s t e p s of 2.5'.
f o r a range of a n g l e s from 10" t o
a.
The v a l u e of the r e f r a c t i v e i n d i c e s were 0
t a k e n from l i t e r a t u r e f o r A = 6328 A = m m
carbon
=
6.9ic8).
2.0
-
0 . 6 6 i , (6)
tungsten
latex
= 3.4
i n t h e forward d i r e c t i o n , s m a l l e r r o r s i n m For l a t e x s p h e r e s , t h e r a n g e of
Table 1.
1 . 2 ( r e l a t i v e t o w a t e r ) (5)
- 2.7i,
These v a l u e s are only approximate.
important.
=
(7) aluminum
=
1.1 -
Since the s c a t t e r i n g is
are n o t expected t o b e
yl i s
v a r i e d from 0.5 t o
Average P a r t i c l e Diameters ?Ieasured by Two-Angle R a t i o Forward S c a t t e r i n g Techniques.
Average
Type of Smoke Particulates
u = nd/A
Average Diameter d (urn)
Latex
1.25
t 0.25
.25
2
0.04
Tungsten
3.75
2
0.70
.75
2
0.15
Carbon
5.30
2
1.06
1.07
5 0.21
Aluminum
6.00
1.20
1.'19
5
0.24
CHAN, APICHATONON, AND SHE
74
2.4 i n s t e p s of 0 . 1 and uo from 0.005 t o 0.145 i n s t e p s o f 0.005. t h e arc smokes, t h e r a n g e of or u
Fbr
is v a r i e d f r o n 3 t o 5.9 i n s t e p s of 0 . 1
from 0.10 t o 0.30 in s t e p s of 0.01.
Each t h e o r e t i c a l v a l u e of
~ ( 0 is ) compared t o t h e e x p e r i n e n t a l p ( 0 ) f o r t h e 13 a n g l e s measured.
The f i n a l v a l u e s of a
II
and u
were s e l e c t e d from t h e b e s t s o l u t i o n
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a c c o r d i n g t o t h e minimum v a l u e of t h e s q u a r e of t h e d i f f e r e n c e between t h e t h e o r e t i c a l and e x p e r i m e n t a l p o l a r i z a t i o n r a t i o .
The p r o c e d u r e i s
i d e n t i c a l t o t h a t used by K i r k e r (3) and t h e program used i n t h i s work w a s provided by K i r k e r w i t h s l i g h t n o d i f i c a t i o n s .
The r e s u l t s are
summarized i n T a b l e 11. It should be p o i n t e d o u t that a l t h o u g h t h e f i t was v e r y good
f o r t h e c a s e of t h e l a t e x s p h e r e ( n o n d i s p e r s e s y s t e m ) , t h e f i t f o r t h e arc smokes are o n l y f a i r . cause t h i s .
There are two r e a s o n s which could
The l a r g e s t a n d a r d d e v i a t i o n of t h e s e smokes tend t o
d e c r e a s e t h e . s e n s i t i v i t y of t h e p o l a r i z a t i o n method.
In addition,
f o r forward s c a t t e r i n g , t h e o s c i l l a t o r y f e a t u r e of p ( 0 ) is smeared o u t , t h u s making t h e d a t a f i t no:
good a l t h o u g h t h e r e s u l t s o b t a i n e d
by t h e s e two methods a g r e e t o 2301; which is probably q u i t e good f o r c o m p l e x . p a r t i c u l a t e systems such a s a r c smokes.
Theoretically
t h e modal d i a m e t e r dH is l a r g e r t h a n t h e mean d i a m e t e r
T a b l e 11.
Type of Particulates
a.
However,
P a r t i c l e S i z e Measurement by P o l a r i z a t i o n R a t i o Method
Model Diameter dH (um)
I
Log. Standard Deviation
Standard D e v i a t i o n u = oodrr(um)
U 0
& .02
.0 1
.003
.80
2
.20
.16
.13
.80
2
.20
.16
.13
1.18
5
.24
-25
.30
Latex
.24
Tungsten Carbon Aluminum
PARTICLESIZING OF ARC SMOKES
75
t h i s d i f f e r e n c e amounts t o l e s s t h a n 14% even f o r u 4 . 3 . and i s thus w i t h i n t h e e x p e r i n e n t a l e r r o r .
CONCLUSION
I n summary, two forward s c a t t e r i n g r a t i o t e c h n i q u e s have been
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used t o d e t e r m i n e s i z e and size d i s t r i b u t i o n f o r p o l y d i s p e r s e arc smoke p a r t i c u l a t e systems and t h e r e s u l t s are f a i r l y s a t i s f a c t o r y or a g r e e w i t h e a c h o t h e r w i t h i n e x p e r i m e n t a l e r r o r
(A
3 0 % ) . Both
methods are s i m p l e t o a p p l y and may b e a p p l i e d t o s i z e o t h e r t y p e s of p a r t i c u l a t e systems.
However, t h e p o l a r i z a t i o n method h a s achieved
only l i m i t e d s u c c e s s f o r p o l y d i s p e r s a l systems because t h e t h e o r e t i c a l f i t s are n o t v e r y good as compared t o t h e case of l a t e x .
Both
t e c h n i q u e s f a i l f o r smaller p a r t i c l e s i z e ( a < l ) as they become insensitive.
It is b e l i e v e d t h a t arc smoke d a t a o b t a i n e d may b e of
i n t e r e s t to workers i n r e s p i r a t o r y , p l a n t and a n i m a l pathology and
particle behavior research.
Real-time p a r t i c l e s i z i n g t e c h n i q u e s based
on t h e above s c a t t e r i n g methods are being i n v e s t i g a t e d .
ACKNOWLEDGNENTS T h i s work w a s s u p p o r t e d by t h e EPA under Grant No. 800150. REFERENCES
5,
1.
Hodkinson, J. R.
2.
G r a v a t t , C. C. Measurements
3.
K i r k e r , M., M a t i j e v i c E., Espenscheid, Farone, W. A. and K i t a n i s . (1964), J. C o l l . S c i . 2,213-222.
4.
5.
.
(1966), Applied O p t i c s
839-843.
(1974), Proc. of t h e Conference on Aerosol
M a t i j e v i c , E., K i t a n i s and K i r k e r , M. 223-237.
19,
K i r k e r , M. (1969). P r e s s , N. Y.
(1964).
J. C o l l . S c i .
The S c a t t e r i n g o f L i g h t Chap. 7 , Academic
Downloaded by [University of Florida] at 01:15 07 November 2015
16
CHAN, APICHATONON, AND SHE
6. Schwiesow, R. L. (1972) Remote Spectral Sensing'of Pollutants Chap. 24, U. S . Department of Comerce, NOAA and University of Colorado. 7.
Hodkinson, J. R. (1966) in Aerosol Science, ed. Academic Press, London and New York.
C.
N. Daores,
8. Hass, G. and Hadley, L. (1972) in American Institute of Physics Handbook, EIcGraw Hill, New York.
Received Efarch 31, 1975 Accepted April 2 3 , 1975
ISSN: 0013-9300 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/lesa17
Particle Sizing of Arc Smokes by Forward Light Scattering P. W. Chan , O. Apichatonon & C. Y. She To cite this article: P. W. Chan , O. Apichatonon & C. Y. She (1975) Particle Sizing of Arc Smokes by Forward Light Scattering, Environmental Letters, 10:1, 69-76, DOI: 10.1080/00139307509435809 To link to this article: http://dx.doi.org/10.1080/00139307509435809
Published online: 02 Sep 2009.
Submit your article to this journal
Article views: 1
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=2esa20 Download by: [University of Florida]
Date: 07 November 2015, At: 01:15
ENVIROXMENTAL LETTERS, 1 0 ( 1 ) , 69-76 (1975)
PARTICLE SIZING OF ARC SMOKES BY FORWARD LIGHT SCATTERING
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Key Words: Arc Smoke P a r t i c u l a t e s , S i z e D i s t r i b u t i o n , Two-angle R a t i o , P o l a r i z a t i o n R a t i o , L i g h t S c a t t e r i n g P. W. Chan, 0. Apichatonon Department of E l e c t r i c a l Engineering and C. Y. She Department o f P h y s i c s Colorado S t a t e U n i v e r s i t y , F o r t C o l l i n s , Colorado
80523
ABSTRACT The p o l a r i z a t i o n r a t i o method sinilar t o that proposed by K i r k e r e t a l . h a s been a p p l i e d t o o b t a i n s i z e d i s t r i b u t i o n f o r s e v e r a l t y p e s of metallic smoke p a r t i c u l a t e s g e n e r a t e d by a d c e l e c t r i c arc.
R e s u l t s are p r e s e n t e d f o r carbon, t u n g s t e n and
aluminum arc smokes.
These r e s u l t s a r e compared w i t h t h e a v e r a g e
s i z e of t h e p a r t i c u l a t e s measured by t h e two-angle r a t i o method of Hodkinson and are found t o b e c o n s i s t e n t and w i t h i n e x p e r i m e n t a l error.
The o p t i c a l system w a s c a l i b r a t e d w i t h s t a n d a r d l a t e x
spheres i n both cases.
It is believed t h a t t h e parameters of t h e
arc smoke p a r t i c u l a t e systems should b e u s e f u l f o r environmental particulate research. INTRODUCTION Among t h e v a r i o u s o p t i c a l methods f o r measuring p a r t i c l e s i z e , l i g h t s c a t t e r i n g p o s s e s s e s t h e most p o t e n t i a l i n s p i t e of i t s r e l a t i v e
69 Copyright 0 1975 hy Marcel Ikkker, Inc. All Rights Reserved. Neither this work 1ror any part m3y he reproduced or transmitted in any form or by any means, electronic or mech~nical,including photocopying. microfilming. and recording. or hy any inform~tionstorage and retrieval system. without permision in writing from the publisher.
70
CHAN, APICHATONON, AND SHE
c o m p l i c i t y as compared w i t h e x t i n c t i o n measurement. two-angle i n t e n s i t y r a t i o method o f Hodkinson
Recently t h e
has a t t r a c t e d
c o n s i d e r a b l e a t t e n t i o n i n a i r p o l l u t i o n c o n t r o l systems
('I. The
method, due t o t h e n a t u r e of forward s c a t t e r i n g , i n t h e Fraunhofer
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l i m i t , is e s s e n t i a l l y independent of t h e r e f r a c t i v e index of t h e p a r t i c u l a t e system and t h u s making s i z e measurement p o s s i b l e w i t h o u t
a knowledge of t h e i n d e x of r e f r a c t i o n .
K i r k e r et a l . ( 3 ) w a s t h e
f i r s t t o s u g g e s t t o measure t h e p o l a r i z a t i o n r a t i o a t s e v e r a l s c a t t e r i n g a n g l e s t o measure p a r t i c l e s i z e d i s t r i b u t i o n (average s i z e and s t a n d a r d d i r e c t i o n ) of sub-micron range.
T h i s method h a s been
s u c c e s s f u l l y employed by M a t i j e v i c e t a l . ( 4 ) i n o b t a i n i n g a e r o s o l s i z e d i s t r i b u t i o n g e n e r a t e d from o c t a n o i c a c i d w i t h r e a l r e f r a c t i v e i n d e x down t o 0.4pm.
The t e c h n i q u e r e q u i r e s a knowledge o f t h e
r e f r a c t i v e i n d e x of t h e p a r t i c l e s i n g e n e r a l .
However, i f t h e s c a t t e r i n g
is chosen i n t h e forward d i r e c t i o n ( s a y less t h a n 4 0 " ) ,
the polarization
r a t i o is a g a i n i n s e n s i t i v e t o r e f r a c t i v e i n d e x as i n t h e two-angle r a t i o method.
Thus t h e t e c h n i q u e c a n b e used t o supplement t h e two-
a n g l e r a t i o method f o r measuring p a r t i c l e s i z e d i s t r i b u t i o n (average s i z e and s t a n d a r d d e v i a t i o n ) .
I n t h i s paper w e r e p o r t a n e x p e r i m e n t a l
i n v e s t i g a t i o n of t h e s i z e d i s t r i b u t i o n of m e t a l l i c arc smoke p a r t i c u l a t e system u s i n g b o t h t h e p o l a r i z a t i o n r a t i o and t h e two-angle i n t e n s i t y r a t i o methods u s i n g small forward s c a t t e r i n g a n g l e s . THEORETICAL BACKGROUND The b a s i c concept of forward l i g h t s c a t t e r i n g is based on t h e f a c t , f i r s t noted by Hodkinson")
t h a t t h e a n g u l a r d i s t r i b u t i o n of
t h e s c a t t e r e d l i g h t w i t h i n t h e forward l o b e is p r i m a r i l y due t o Fraunhofer d i f f a c t i o n and as such, is n e a r l y independent of t h e index of refraction.
I f t h e r a t i o of t h e s c a t t e r e d f l u x a t two
PARTICLE SIZING OF ARC SMOKES
71
a n g l e s is c a l c u l a t e d , i t 2s a known f u n c t i o n of t h e p a r a n e t e r of nd a = -where
X
d is t h e p a r t i c l e d i a m e t e r , X is t h e wavelength of
i n i t i a l l i g h t f o r any p a i r of a n g l e s O1 and 0 2 . c u r v e s can b e c a l c u l a t e d " ) . y i e l d t h e s i z e parameter a.
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Conparison of e x p e r i m e n t a l r e s u l t s The t e c h n i q u e g i v e s a mean v a l u e of
It becomes r a t h e r i n s e n s i t i v e f o r a51 f o r a l l
p a r t i c l e diameter. p a i r s of a n g l e s (1)
Thus a f a m i l y of
.
The p o l a r i z a t i o n r a t i o method was f i r s t proposed by K i r k e r e t a l . (')
The r a t i o of t h e p a r a l l e l and t h e p e r p e n d i c u l a r components of
t h e s c a t t e r e d l i g h t p(O);$, angles.
(0)/11(0)
According t o Mie t h e o r y ,
Ji,(ek(a)da
is measured a t s e v e r a l s c a t t e r i n g
p(O)E$
(0)/11(0)
=
Ji,, (O)p(a)da/
where p ( a ) is t h e s i z e d i s t r i b u t i o n , a = r a d i u s ,
(O),
i (0) are, r e s p e c t i v e l y , t h e s c a t t e r e d i n t e n s i t y p a r a l l e l and
1
p e r p e n d i c u l a r t o t h e p l a n e of i n c i d e n c e .
The procedure from h e r e on i s
t o assume a s i z e d i s t r i b u t i o n and compare t h e e x p e r i m e n t a l measured v a l u e of p ( 0 ) w i t h t h e t h e o r e t i c a l p r e d i c t i o n by v a r y i n g t h e c h a r a c t e r i s t i c r a d i u s and t h e s t a n d a r d d e v i a t i o n of t h e d i s t r i b u t i o n u n t i l a good f i t
is o b t a i n e d .
A z e r o t h o r d e r l o g a r i t h m i c d i ~ t r i b u t i o n ' ~ is ) assumed i n
t h i s work w i t h aMa s t h e n o d a l v a l u e of t h e s i z e parameter a and u
the logarithmic standard deviation.
APPARATUS AND EXPERIMDJTAL METHODS The b a s i c a p p a r a t u s c o n s i s t s of a 2mW He-Ne laser s o u r c e , s l i g h t l y focused a t t h e c e n t e r of a c y l i n d r i c a l snoke chamber. S c a t t e r e d l i g h t w a s c o l l e c t e d by a l e n s and d e t e c t e d by a RCA 1P22 p h o t o m u l t i p l i e r whose o u t p u t was connected t o a d c microvoltmeter. The e n t i r e c o l l e c t i o n o p t i c s was mounted on a r i g i d r o t a t a b l e bench c e n t e r e d a t t h e smoke chamber r o t a t a b l e through 10' t o 40' t o t h e forward d i r e c t i o n .
relative
I n t e r f e r e n c e f i l t e r s and s l i t a p e r t u r e s
72
CHAN, APICHATONON, AND SHE
were used t o improve s i g n a l a g a i n s t n o i s e background.
A t each
a n g u l a r p o s i t i o n , t h r e e r e a d i n g s of t h e s c a t t e r e d l i g h t i n t e n s i t y , namely, t h e t o t a l i n t e n s i t y , t h e h o r i z o n t a l i n t e n s i t y and t h e v e r t i c a l i n t e n s i t y as s e l e c t e d by p o s i t i o n i n g a p o l a r i z e r i n t h e h o r i z o n t a l and v e r t i c a l d i r e c t i o n w e r e r e c o r d e d a t 2.5" i n t e r v a l .
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The t r a n s m i t t e d l i g h t w a s monitored t o e n s u r e a t t e n u a t i o n o f t h e i n c i d e n t beam and was k e p t t o less t h a n t e n p e r c e n t t o avoid c o m p l i c a t i o n s due t o n u l t i p l e s c a t t e r i n g . ( 6 )
The smoke p a r t i c l e s were
g e n e r a t e d between a p a i r of e l e c t r o d e s of d i f f e r e n t m a t e r i a l s under An arc w a s i n i t i a t e d between t h e e l e c t r o d e s .
study.
The a r c s p a c i n g
w a s k e p t a t a d i s t a n c e of 2m and i t c a r r i e d 7 Amps ( d c ) .
After
a l l o v i n g t h e arc t o b u r n f o r 1 minute, t h e a r c smokes were d i s p e r s e d by a f a n f o r a n hour b e f o r e e x p e r i m e n t a l d a t a were o b t a i n e d a s described.
The w a i t i n g p e r i o d is due t o t h e r a p i d c o a g u l a t i n g smoke
systems under i n v e s t i g a t i o n .
A t l e a s t two r u n s were t a k e n and t h e
s c a t t e r i n g a n g l e s were s e l e c t e d a t random. t o be
A
The r e p r o d u c i b i l i t y w a s found
20% between r u n s when p r e c a u t i o n s were t a k e n t o c l e a n t h e arc
e l e c t r o d e s and a d j u s t t h e e l e c t r o d e spacing. For s y s t e n c a l i b r a t i o n , a d i l u t e s o l u t i o n of s t a n d a r d l a t e x i n d i s t i l l e d water w a s used.
S i n c e t h e s i z e d i s t r i b u t i o n of t h e l a t e x
i s a c c u r a t e l y known, t h e e x p e r i m e n t a l a c c u r a c y can be checked. EXPERIMENTAL RESULTS, ANALYSES AND DISCUSSIONS The e x p e r i m e n t a l r e s u l t s of p a r t i c l e s i z e f o r l a t e x s p h e r e s , carbon, t u n g s t e n and aluminum arc smokes a s measured by b o t h t h e twoa n g l e r a t i o o r t h e p o l a r i z a t i o n r a t i o methods are p r e s e n t e d .
The
e x p e r i m e n t a l c o n d i t i o n s f o r a r c smoke g e n e r a t i o n were as d e s c r i b e d i n t h e last section.
The l a t e x s p h e r e s a r e manufactured by Dow Chemical
Co. (Batch 2G6J) w i t h m a n u f a c t u r e r ' s g i v e n mean d i a m e t e r
d
=
0.234~
73
PARTICLE S I Z I N G OF ARC SMOKES and s t a n d a r d d e v i a t i o n o = .0026!~m. The s o l u t i o n (10% by weight) i s d i l u t e d 1000 times i n d i s t i l l e d water.
The methods of a n a l y s i s are s t r a i g h t f o r w a r d .
For t h e two-angle
r a t i o method, t h e measured i n t e n s i t y r a t i o f o r t h r e e p a i r s of a n g l e s
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over two i n d i v i d u a l r u n s were averaged and compared t o t h e i n t e n s i t y r a t i o c u r v e s a l r e a d y c o r r e c t e d f o r t h e geometric f a c t o r a s g i v e n by
-
from which t h e a v e r a g e v a l u e s of a =
Hodkinson")
nd are A
obtained.
The r e s u l t s a r e t a b u l a t e d i n Table 1. For t h e p o l a r i z a t i o n r a t i o method, t h e t h e o r e t i c a l p o l a r i z a t i o n r a t i o p ( 0 ) a c c o r d i n g t o >lie t h e o r y i s computed w i t h a CDC 6400 Computer f o r a n e x t e n s i v e a r r a y of t h e a 40" i n s t e p s of 2.5'.
f o r a range of a n g l e s from 10" t o
a.
The v a l u e of the r e f r a c t i v e i n d i c e s were 0
t a k e n from l i t e r a t u r e f o r A = 6328 A = m m
carbon
=
6.9ic8).
2.0
-
0 . 6 6 i , (6)
tungsten
latex
= 3.4
i n t h e forward d i r e c t i o n , s m a l l e r r o r s i n m For l a t e x s p h e r e s , t h e r a n g e of
Table 1.
1 . 2 ( r e l a t i v e t o w a t e r ) (5)
- 2.7i,
These v a l u e s are only approximate.
important.
=
(7) aluminum
=
1.1 -
Since the s c a t t e r i n g is
are n o t expected t o b e
yl i s
v a r i e d from 0.5 t o
Average P a r t i c l e Diameters ?Ieasured by Two-Angle R a t i o Forward S c a t t e r i n g Techniques.
Average
Type of Smoke Particulates
u = nd/A
Average Diameter d (urn)
Latex
1.25
t 0.25
.25
2
0.04
Tungsten
3.75
2
0.70
.75
2
0.15
Carbon
5.30
2
1.06
1.07
5 0.21
Aluminum
6.00
1.20
1.'19
5
0.24
CHAN, APICHATONON, AND SHE
74
2.4 i n s t e p s of 0 . 1 and uo from 0.005 t o 0.145 i n s t e p s o f 0.005. t h e arc smokes, t h e r a n g e of or u
Fbr
is v a r i e d f r o n 3 t o 5.9 i n s t e p s of 0 . 1
from 0.10 t o 0.30 in s t e p s of 0.01.
Each t h e o r e t i c a l v a l u e of
~ ( 0 is ) compared t o t h e e x p e r i n e n t a l p ( 0 ) f o r t h e 13 a n g l e s measured.
The f i n a l v a l u e s of a
II
and u
were s e l e c t e d from t h e b e s t s o l u t i o n
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a c c o r d i n g t o t h e minimum v a l u e of t h e s q u a r e of t h e d i f f e r e n c e between t h e t h e o r e t i c a l and e x p e r i m e n t a l p o l a r i z a t i o n r a t i o .
The p r o c e d u r e i s
i d e n t i c a l t o t h a t used by K i r k e r (3) and t h e program used i n t h i s work w a s provided by K i r k e r w i t h s l i g h t n o d i f i c a t i o n s .
The r e s u l t s are
summarized i n T a b l e 11. It should be p o i n t e d o u t that a l t h o u g h t h e f i t was v e r y good
f o r t h e c a s e of t h e l a t e x s p h e r e ( n o n d i s p e r s e s y s t e m ) , t h e f i t f o r t h e arc smokes are o n l y f a i r . cause t h i s .
There are two r e a s o n s which could
The l a r g e s t a n d a r d d e v i a t i o n of t h e s e smokes tend t o
d e c r e a s e t h e . s e n s i t i v i t y of t h e p o l a r i z a t i o n method.
In addition,
f o r forward s c a t t e r i n g , t h e o s c i l l a t o r y f e a t u r e of p ( 0 ) is smeared o u t , t h u s making t h e d a t a f i t no:
good a l t h o u g h t h e r e s u l t s o b t a i n e d
by t h e s e two methods a g r e e t o 2301; which is probably q u i t e good f o r c o m p l e x . p a r t i c u l a t e systems such a s a r c smokes.
Theoretically
t h e modal d i a m e t e r dH is l a r g e r t h a n t h e mean d i a m e t e r
T a b l e 11.
Type of Particulates
a.
However,
P a r t i c l e S i z e Measurement by P o l a r i z a t i o n R a t i o Method
Model Diameter dH (um)
I
Log. Standard Deviation
Standard D e v i a t i o n u = oodrr(um)
U 0
& .02
.0 1
.003
.80
2
.20
.16
.13
.80
2
.20
.16
.13
1.18
5
.24
-25
.30
Latex
.24
Tungsten Carbon Aluminum
PARTICLESIZING OF ARC SMOKES
75
t h i s d i f f e r e n c e amounts t o l e s s t h a n 14% even f o r u 4 . 3 . and i s thus w i t h i n t h e e x p e r i n e n t a l e r r o r .
CONCLUSION
I n summary, two forward s c a t t e r i n g r a t i o t e c h n i q u e s have been
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used t o d e t e r m i n e s i z e and size d i s t r i b u t i o n f o r p o l y d i s p e r s e arc smoke p a r t i c u l a t e systems and t h e r e s u l t s are f a i r l y s a t i s f a c t o r y or a g r e e w i t h e a c h o t h e r w i t h i n e x p e r i m e n t a l e r r o r
(A
3 0 % ) . Both
methods are s i m p l e t o a p p l y and may b e a p p l i e d t o s i z e o t h e r t y p e s of p a r t i c u l a t e systems.
However, t h e p o l a r i z a t i o n method h a s achieved
only l i m i t e d s u c c e s s f o r p o l y d i s p e r s a l systems because t h e t h e o r e t i c a l f i t s are n o t v e r y good as compared t o t h e case of l a t e x .
Both
t e c h n i q u e s f a i l f o r smaller p a r t i c l e s i z e ( a < l ) as they become insensitive.
It is b e l i e v e d t h a t arc smoke d a t a o b t a i n e d may b e of
i n t e r e s t to workers i n r e s p i r a t o r y , p l a n t and a n i m a l pathology and
particle behavior research.
Real-time p a r t i c l e s i z i n g t e c h n i q u e s based
on t h e above s c a t t e r i n g methods are being i n v e s t i g a t e d .
ACKNOWLEDGNENTS T h i s work w a s s u p p o r t e d by t h e EPA under Grant No. 800150. REFERENCES
5,
1.
Hodkinson, J. R.
2.
G r a v a t t , C. C. Measurements
3.
K i r k e r , M., M a t i j e v i c E., Espenscheid, Farone, W. A. and K i t a n i s . (1964), J. C o l l . S c i . 2,213-222.
4.
5.
.
(1966), Applied O p t i c s
839-843.
(1974), Proc. of t h e Conference on Aerosol
M a t i j e v i c , E., K i t a n i s and K i r k e r , M. 223-237.
19,
K i r k e r , M. (1969). P r e s s , N. Y.
(1964).
J. C o l l . S c i .
The S c a t t e r i n g o f L i g h t Chap. 7 , Academic
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16
CHAN, APICHATONON, AND SHE
6. Schwiesow, R. L. (1972) Remote Spectral Sensing'of Pollutants Chap. 24, U. S . Department of Comerce, NOAA and University of Colorado. 7.
Hodkinson, J. R. (1966) in Aerosol Science, ed. Academic Press, London and New York.
C.
N. Daores,
8. Hass, G. and Hadley, L. (1972) in American Institute of Physics Handbook, EIcGraw Hill, New York.
Received Efarch 31, 1975 Accepted April 2 3 , 1975
