Environ. Sci. Technol. 1996, 30, 271-276
Design Methodology for Multiple Inlet Cyclones MURRAY E. MOORE† AND ANDREW R. MCFARLAND* Aerosol Technology Laboratory, Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843
Correlations were developed to model the performance of two types of multi-inlet aerosol sampling cyclones. The body of one cyclone had the Lapple conventional geometry and the other had a shorter design, which was one-half the length of the Lapple geometry. Four cyclones of each type were constructed, with body diameters of 38.1, 57.2, 88.9, and 139.7 mm. Each cyclone was tested at several flow rates, with the range of flow rates for the entire data set being from 9.4 L/min to 1027 L/min. Aerodynamic particle cutpoint diameters, D0.5, were determined for several sets of test conditions, consisting of a given cyclone type and a fixed flow rate. The range of cutpoints determined in the experiments was 3.9-17.1 µm aerodynamic diameter. Experimental data were correlated to a logarithmiclinear relationship: C0.51/2D0.5/dc ) ln a + b ln Ref where C0.5 is Cunningham’s slip correction for the cutpoint size; dc is the cyclone diameter; and, Ref is the flow Reynolds number, which is characterized by the air inlet velocity and the width of the channel between the cyclone body and the outlet tube. The correlation coefficients, r 2, for data of the long and short multiinlet cyclones to the log-linear model were 0.984 and 0.991, respectively. The log-linear relationship between the size parameter and the flow Reynolds numbers was re-arranged to provide working relationships for designers. Fractional efficiencies were measured for each cyclone, and sigmoid curves were fitted to the data that provide a relationship between fractional efficiency and dimensionless particle size, (Da - D0.5)/D0.5, where Da is the aerodynamic particle diameter.
Introduction Cyclones are used as aerosol sampling devices because they are simple, require relatively low pressure drops, and are relatively easy to fabricate; however, they must be cleaned regularly so that the buildup of collected particulate matter will not affect cyclone performance by allowing previously * Corresponding author fax: 409-862-2418. † Present address: ESH-4, Los Alamos National Laboratory, Los Alamos, NM 87545.
0013-936X/96/0930-0271$12.00/0
1995 American Chemical Society
collected particulate matter to either be re-entrained or to collect fine particulate matter from the flowing airstream. In many applications, it is desirable for a cyclone to provide a sample that is nearly omni-directional. Cecala et al. (1) found that the orientation of the inlet of a cyclone sampler could adversely affect its performance. They noted that an inlet facing away from incoming incident air could undersample ambient particulate matter. At the present time, there are de facto standard designs for single inlet cyclones (2, 3) and there are models for predicting their performance (4-12); however, there are neither generalized design criteria for multiple inlet cyclones nor models to predict either the cutpoint (particle size for which the efficiency is 50%) or the fractional efficiency (variation of efficiency with particle size) of a multi-inlet cyclone. In this study, we present generalized designs for two multi-inlet cyclones that can provide samples that are nearly omnidirectional, and we have developed correlations that can be used to predict the performances of the cyclones. Models of Single-Inlet Cyclone Performance. Lapple (3), in a study of industrial cyclones, developed a model that is essentially equivalent to the fractionation process being represented by a constant cutpoint Stokes number. The cutpoint Stokes number, Stk0.5, is defined as
Stk0.5 )
FwC0.5D0.52Ui 9µdc
(1)
where: C0.5 ) Cunningham’s slip correction (13) based on the cutpoint aerodynamic diameter (AD); Fw is the density of water at 4 °C (1000 kg/m3); D0.5 is the cutpoint aerodynamic particle diameter; Ui is the inlet air velocity; µ is the dynamic viscosity of air; dc is the characteristic dimension for cyclone scaling (in this case, dc is the cyclone body diameter). Lapple also included an empirical parameter that specified the number of turns that the fluid stream would trace out along the cyclone inner wall. The constant Stokes number model was developed for industrial cyclones where the Reynolds numbers are generally large; however, it is not successful in predicting the general performance of small sampling cyclones (11). Chan and Lippmann (4) considered the Lapple model to be of the general form of D0.5 ) KQ-n, where Q is the volumetric flow rate through the cyclone. The factor K could vary with cyclone dimensions and the number of spiral turns of the internal fluid flow path, and n could vary with cyclone type and flow rate. In turn, flow rate would take into account the degree of turbulence in the internal flow field. John and Reischl (6) used the model of Chan and Lippmann to relate cutpoint particle size to cyclone flow rate for a particular cyclone that they tested. Their study resulted in a relationship between cutpoint and flow rate, D0.5 ) 52.5Q-0.99 (with particle size in units of µm and flow rate in units of L/min). Beeckmans and Kim (5) suggested that performance differences with regard to flow rate and cyclone size could be rationalized by including consideration of a cyclone body Reynolds number, Rec, which is defined as
Rec )
FUidc µ
(2)
where F is the density of air.
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A form of the Reynolds number based on the cyclone outlet tube, Reo, was utilized by Saltzman and Hochstrasser (7) and Burkholz (8) for characterizing the effect of flow parameters on the performance of sampling cyclones. In terms of volumetric flow rate, Q, rather than velocity, this parameter is defined as
Reo )
4FQ πµdo
(3)
where do is the inside diameter of the cyclone outlet tube. Saltzman and Hochstrasser constructed a semiempirical log-linear model relating the ratio of the cutpoint particle diameter and the cyclone body diameter, D0.5/dC, to the outlet tube Reynolds number:
( )
Reo D0.5 ) Kd dc 1000
n
25200 Rec2.72-0.119 ln Rec
FUi(rc - ro) µ
(5)
(6)
Here rc is the cyclone body radius, and ro is the cyclone outlet tube radius. Based on both the theory of Dring and Suo (15) and the previous success of Saltzman and Hochstrasser (7), Moore and McFarland used the ratio of the cutpoint diameter to the cyclone body diameter, D0.5/ dc, as the dependent variable in developing a correlation for cyclone performance. They obtained a least squares fit to the function:
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The correlation coefficient for the fit of their data to this model was r2 ) 0.994. Multiple Inlet Cyclones. Several researchers have fabricated and tested multiple inlet sampling cyclones. Chan and Lippmann (16) tested cyclones with two tangential inlets separated by a 180° angle. These devices generally had a cutpoint particle diameter of approximately 3.5 µm. Smith (17) built a multiple port inlet cyclone that used flat turning vanes to impart a tangential velocity to the incoming air flow. This cyclone was principally used for flow visualization and velocity measurement studies. Wedding et. al. (18) developed a cyclonic fractionator for ambient aerosol sampling that used multiple inlet vanes.
Experimental Methodology
This correlation allowed for direct calculation of cyclone parameters for design purposes. For example, if the particle cutpoint diameter and cyclone flow rate were specified, the determination of cyclone body diameter was possible through solution of a transcendental equation. In a later study, Moore and McFarland (12) found that a different form of the Reynolds number could be used to describe the effect of changing the ratio of the cyclone outlet tube to the cyclone body diameter in a single inlet cyclone. They used a flow Reynolds number, Ref, that had been employed by Pui, et al. (14) in studies of particle deposition in tube bends where the flow Reynolds number is defined as
Ref )
(7)
(4)
They correlated 60 data points for 18 different cyclone types, with the coefficients Kd and n being experimentally determined for each cyclone type. Li and Wang (10) developed a theoretical method for predicting the slope of the cyclone collection efficiency curve. Their approach utilized a constant cutpoint Stokes number assumption, and their predictions fit well to the experimental data of Dirgo and Leith (9), who had used a 305 mm (1 ft) diameter cyclone in their studies. Moore and McFarland (11) compared their experimental results with the theories of Beeckmans and Kim (5), John and Reischl (6), and Saltzman and Hochstrasser (7). By correlating the results of the particle cutpoint Stokes number, Stk0.5, with the Reynolds number based on body diameter, Rec, they were able to describe the performance of four proportionally similar single inlet cyclones of the Lapple design as a quadratic logarithmic function:
Stk0.5 )
D0.5 ) ln a + b ln Ref ln Dc
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The multiple inlet cyclones of this study were tested in a low-velocity wind tunnel (Figure 1) that has a 600 mm × 600 mm cross section. To experimentally characterize cyclone performance, it was necessary to minimize bias that would result from aerosol entering the cyclone in a non-uniform manner; hence, we chose the 2 km/h wind tunnel speed, which is smaller than the range of inlet velocities (3-25 km/h) at which we operated the cyclones. Also, Cecala et al. (1) had shown that for a dual inlet sampling cyclone there were no significant sampling differences due to velocity or sampler orientation for air velocities less than 5.5 km/h. Aerosol output from a vibrating jet atomizer (TSI Incorporated, St. Paul, MN) was introduced into the tunnel inlet. The aerosol was generated from a solution of alcohol and oleic acid tagged with an analytical tracer (sodium fluorescein), and it was passed by a 10-mCi Kr-85 radioactive source to neutralize electrical charge. Because vibrating jet atomizers can exhibit variations in particle size due to oscillations in liquid flow rate, the infusion pump of the vibrating jet atomizer was replaced with a flow system driven by a constant air pressure. The size of the aerosol particles was determined by first impacting a sample onto a glass slide that had been coated with an oil-phobic fluorocarbon (3M Chemical FC-721, 3M Co., St. Paul, MN) and then measuring the size of the droplets under a microscope. Because of gravitational effects, liquid aerosols are flattened to oblate spheroids on the slide; however, through use of the flattening factor of Olan-Figueroa et al. (19), the original diameter of the spherical droplets could be calculated. Aerodynamic diameter of the aerosol particles was then determined from
CaDa2 )
Fp C D2 Fa p p
(8)
where Fp is the actual particle density; Cp is the Cunningham’s correction based on the actual particle diameter; and Dp is the actual particle diameter. An aerosol sample was taken before and after each test, where a test typically lasted 5 min. If either the aerosol size or homogeneity changed during the course of the test, that test was rejected. Mixing baffles were used in the wind tunnel to ensure that the aerosol was uniformly distributed across the region of the test section where sampling was performed (center two-thirds of the wind tunnel cross section) (20). The test
FIGURE 1. Apparatus used to test sampling cyclones.
setup (Figure 1) was configured so that a cyclone inlet was positioned in the center of the test section of the wind tunnel. The cyclone outlet tube was fitted into a larger diameter transport tube, which in turn was attached to a filter holder assembly that was located in the bottom of the tunnel. A total of eight different cyclone devices were utilized in this study. Four of these cyclones were constructed according to the Lapple conventional cyclone geometry (Figure 2a) but with an inlet that had six ports circumferentially distributed around the perimeter of the cyclone cylindrical section. This cyclone will be referred to as the long multi-inlet cyclone geometry. The remaining four cyclones were constructed with a shortened length, as shown in Figure 2b, with the cylinder and cone lengths being equivalent to one cyclone diameter instead of two. This cyclone will be referred to as the short multi-inlet cyclone. Both long and short cyclones were constructed with body diameters of 38.1, 57.2, 88.9, and 139.7 mm. Thinwalled aluminum was used for the outlet tubes, with inside diameters of 17.3, 26.7, 42.9, and 68.3 mm and outside diameters of 19.0, 28.4, 44.4, and 69.8 mm, respectively. The six individual subinlets on each cyclone were scaled to the cyclone body diameter in the proportions of inlet width, w ) 0.083dC, and inlet height ) 0.25dC. For each set of experimental conditions (cyclone geometrical configuration, flow rate, and particle size), three replicate wind tunnel tests were conducted. A sharp-edged
isokinetic probe, fitted with a filter holder that contained a glass fiber filter, was used to provide reference samples. The isokinetic probe was operated in the wind tunnel aerosol for 3 min, the vacuum pump and wind tunnel blower were stopped, and the probe was removed from the wind tunnel test section. The cyclone to be tested was then placed in the wind tunnel test section with the outlet tube directed downward, and a special filter holder was fitted to the bottom of the test cyclone apparatus. Air was then pulled through the cyclone for a complementary 3 min test period. The six filters from the set of three replicate tests were then placed in separate measured solutions of equal parts of alcohol and distilled water to elute the collected aerosol particles. One droplet of sodium hydroxide was added to each test solution to ensure the stability of subsequent fluorescent measurements. The solutions were then quantitatively analyzed in a Sequoia-Turner Model 450 fluorometer (Sequoia-Turner Corp., Mountain View, CA). The collection efficiency for each test was calculated from knowledge of the ratio of aerosol concentration at the cyclone exit and the free stream aerosol concentration in the wind tunnel. The experimental fractional efficiency results were plotted with respect to the aerodynamic particle diameter. An example of such a graph is shown in Figure 3, where results for tests with the 88.9-mm body diameter short multiinlet cyclone are presented. The fractional efficiency curves were interpolated from a spline fit to a third-order polynomial to determine the value of the cutpoint aerodynamic diameter. The operation of the cyclones with the outlet tube facing downward was based on two considerations. First, in field applications where cyclones with larger cutpoints (∼10 µm AD) are used, a filter collector can be placed in a straight line below the cyclone outlet tube, thereby minimizing sample losses in comparison with those associated with an upward-facing outlet tube connected by a 180° elbow to an upward-facing filter. Second, for small particle collection with cyclones (e.g., 2.5 µm AD), the ratio of the centrifugal force to the gravitational force on particles in the cyclone is of the order of 100, so the orientation of the cyclone will not effect the collection characteristics.
FIGURE 2. Geometrical configurations of multi-inlet cyclones used in the testing program. (a) Long multi-inlet cyclone: The lengths of the cylindrical and conical sections are both two body diameters. (b) Short multi-inlet cyclone: The cylindrical and conical sections are both one cyclone diameter in length.
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C0.5 ) 1 +
2.52λ D0.5
(10)
where λ is the mean free path of air molecules, which can be calculated (in units of m) from
λ ) 1.71 × 10-7(T/P)
FIGURE 3. Example of the type of fractional efficiency plots that were used to establish the cutpoint sizes. Spline fit computer curves were drawn through the data, and the cutpoint was determined by interpolation. Error bars represent ( 1 SD, but if the error bars are smaller than the size of the plotting symbol they are omitted.
Here P is the air pressure at cyclone entrance (in units of mmHg), and T is the air temperature (in units of K). For comparative purposes, the single inlet cyclone models of Moore and McFarland (12) Li and Wang (10) are included in Figure 4. It may be noted the slopes of the curves for the long and short multi-inlet cyclones and the single inlet cyclone of Moore and McFarland all differ. The model of Li and Wang produces a straight line relationship; however, it predicts quite different results than the model of Moore and McFarland. The latter model was shown to have a correlation coefficient with its database of r2 ) 0.994. The values of the coefficients a and b, obtained by fitting the experimental data to eq 10, are given in Table 1. Also given in Table 1 are the correlation coefficients, r2, which are 0.984 and 0.991 for the long and short multi-inlet cyclones, respectively. Again, for comparative purposes, the coefficients a and b are given for the single inlet long cyclone model of Moore and McFarland (12). Working Equations for Design of Sampling Cyclones. Equation 9 can be rearranged to accommodate three different modes of design for either multi-inlet sampling cyclones that are proportioned as shown in Figure 2, panels a and b, or for the single inlet cyclones of Moore and McFarland (12). First, if the flow rate, geometrical form (i.e., single inlet cyclone or long or short multi-inlet cyclone), and the body diameter are known, the cutpoint diameter can be calculated from
D0.5 )
FIGURE 4. Results that show the experimental data plotted on a basis of a cutpoint size parameter (C0.51/2D0.5/dc) as a function of flow Reynolds number. Lines through the data points are regression fits. The single inlet models of Li and Wang (10) and Moore and McFarland (12) are shown for comparison.
x
-2.52λ 1 + 2 2
(
)
C0.51/2D0.5 ln ) ln a + b ln Ref dc
(9)
Cunningham’s correction for the cutpoint size is included in this relationship based on a re-examination of the arguments of Dring and Suo (15). Although they did not include Cunningham’s correction, presumably because the particle sizes of interest to them did not warrant the refinement, it is implicit in their derivation. For sampling cyclones operated at approximately ambient pressure, Cunningham’s correction for the cutpoint size can be expressed as
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(2.52λ)2 + 4a2
(2FQ µ )
2b
dc2(1-b) (12)
Alternatively, if the cutpoint size and flow rate are given, the corresponding size of a cyclone is
dc )
Results Cutpoint Correlations. A comparison of results for the different cyclone geometries is presented on a basis of C0.51/2D0.5/dc as a function of Ref in Figure 4. The straight lines through the data are linear regressions fitted to the functional form:
(11)
[
]
xD0.5(D0.5 + 2.52λ) a
(2FQ µ )
b
1/(1-b)
(13)
Third, if a particular cutpoint size is desired for a cyclone with a given diameter, the flow rate associated with those criteria is
Q)
µdc 2F
[
]
xD0.5(D0.5 + 2.52λ) adc
1/b
(14)
The performance (e.g., cutpoint) of an existing cyclone can be somewhat modified by changing the cyclone outlet tube diameter, do, from the proportions given in Figure 2a,b. In the previous study of Moore and McFarland (12), the ratio of the outlet tube diameter to the cyclone body diameter was varied for single inlet cyclones, which produced a corresponding change in the cutpoint aerodynamic particle diameter, as predicted by eq 9. For fixed cyclone body diameter and prescribed values of flow rate and cutpoint
TABLE 1
Coefficients for Use in Equation 9 for Modeling Performance of Various Cyclones correlation coefficient, r2
cyclone type
coeff a
coeff ba
long multi-inlet short multi-inlet single inlet (12)b
0.1314 0.0274 0.0517
-0.943 ( 0.065 -0.717 ( 0.021 -0.812 ( 0.038
0.984 0.991
a The ( values give the 95% confidence intervals for a and b. Data from ref 12 have been modified to account for Cunningham’s correction. b
diameter, the appropriate value of the outlet tube is
do )
[ (
µdc2 4FQ 4FQ µdc
)]
xD0.5(D0.5 + 2.52λ) adc
1/b
(15)
This equation is of particular value where it is desired to modify the cutpoint of an existing cyclone. In many instances, replacement of the outlet tube will provide the appropriate cutpoint, negating the need for machining a completely new cyclone. Fractional Efficiency Equations. The fractional efficiency values from tests with the multi-inlet cyclones are shown in Figure 5a,b as functions of relative particle size (difference between particle diameter and cutpoint diameter divided by the cutpoint diameter). For comparison, fractional efficiency data for single inlet cyclones determined by Moore and McFarland (12) are given in Figure 5c. Because these fractional efficiency data have sigmoid shapes, they were fitted by least squares technique to a sigmoid function, which is of the form:
η)
a1
(
)
x - b1 1 + exp c1
(16)
where x ) ln [(Da - D0.5)/D0.5]; η is the fractional efficiency; and a1, b1, and c1 are coefficients fitted by the least squares method. Values of the coefficients used in eq 16 and the correlation coefficients for the least squares regression processes are given in Table 2. These functional forms can be used to estimate the collection of aerosol particles of sizes other than the cutpoint diameters. Solid Particle Carryover. With cyclones, there is a question of whether solid particles can be carried over as a result of re-entrainment or bounce. The multi-inlet cyclones were challenged with large (∼20 µm AD) solid ammonium fluorescein particles, and the measured aerosol penetration (1 - η) was small, as shown in Table 3. The long multi-inlet cyclones were tested over a range of cyclone body diameters, and the 57.2-mm body diameter short multi-inlet cyclone was tested over a range of cyclone air flow rates. These tests were conducted with the outlet tube facing downward for the reason that this orientation can be used in environmental monitoring, where a filter placed in the airstream from the outlet tube does not have to be inverted. The average solid particle penetration was 1.3%, even though the result for one case with the 57.2-mm long multi-inlet cyclone was a penetration of 6.1%. If this were an anomalous result, the remaining seven cases would have an average penetration of 0.6% for solid aerosol particles.
Discussion If a designer were to seek to employ a different geometry than those of the cyclones in this study, we believe the
FIGURE 5. Fractional efficiencies of various cyclones. Curves drawn through the data are regression fits to a sigmoid model (eq 16). (a) Long multi-inlet cyclone. (b) Short multi-inlet cyclone. (c) Single inlet cyclone data of Moore and McFarland (12).
same methodology and governing equations could be utilized to simplify the design process. For example, if a designer wished to use a round inlet (or multiple round inlets), a prototype cyclone could be constructed and tested at different flow rates (to vary the flow Reynolds number) and at different particle sizes (to vary the size parameter). A least squares process would then be used with eq 9 to
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Acknowledgments
TABLE 2
Coefficients for Use in Equation 16 for Calculating Fractional Efficiencies of Various Cyclones cyclone type
a1
b1
c1
correlation coefficient, r2
long multi-inlet short multi-inlet single inlet (12)
0.925 1.025 0.962
-0.01303 -0.00993 -0.01419
0.1624 0.1299 0.1698
0.924 0.950 0.968
Literature Cited
TABLE 3
Tests of Multi-Inlet Cyclones with Solid Particlesa cyclone type long multi-inlet
short multi-inlet
body flow aerodynamic diameter, rate, particle (mm) (L/min) size, Dp (µm) 38.1 57.2 88.9 138.9 57.2 57.2 57.2 57.2
13.0 34.9 110 342 27.5 36.7 36.7 45.8
18.7 18.1 17.9 17.7 19.6 20.1 19.1 20.1
a Aerosol was monodisperse ammonium fluorescein. are the mean ( 1 SD.
penetration (%)b 0.9 ( 0.4 6.1 ( 1.2 1.1 ( 0.1 0.1 ( 0.01 1.0 ( 0.11 0.4 ( 0.03 0.21 ( 0.01 0.3 ( 0.05 b
The values
determine new values for a and b. The equation could then be used to design other cyclones as long as they are of the same proportional design. Although this study presents a basis for design and testing of multi-inlet sampling cyclones, it should be noted that a working inlet in the ambient atmosphere would generally require an external wind decelerator. High-velocity wind acting on the cyclone inlets could cause there to be nonuniform velocities in the inlets and thereby bias the sampling. Also, the correlation was developed based on tests conducted at laboratory temperature and a barometric pressure of approximately 750 mmHg. The flow field associated with operation of cyclones at other pressures and temperatures should be modeled correctly by the flow Reynolds number; however, the particle dynamics could be different at significantly different temperatures where the viscosity of air would be different from that of the test conditions.
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The authors wish to express appreciation to Carlos Ortiz and Bruce Gamble for their technical assistance. Funding for this study was provided by the U.S. Environmental Protection Agency under Grant R-811315-01. The opinions, conclusions, and suggestions that are presented are those of the authors and do not necessarily represent the policies of the U.S. Environmental Protection Agency. This paper is Aerosol Technology Laboratory Report 5101/05/95/MEM.
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(1) Cecala, A. B.; Volkwein, J. C.; Timko, R. J.; Williams, K. L. Report Investigations RI 8764. U.S. Department of Interior, Bureau of Mines: Pittsburgh, PA, 1983. (2) Stairmand, C. J. Trans. Inst. Chem. Eng. 1951, 29, 356-383. (3) Lapple, C. E. Chem. Eng. 1951, 58 (5), 144-151. (4) Chan, T.; Lippmann, M. Environ. Sci. Technol. 1977, 11, 377382. (5) Beeckmans, J. M.; Kim, C. J. Can. J. Chem. Eng. 1977, 55, 640664. (6) John, W.; Reischl, G. J. Air Pollut. Control Assoc. 1980, 30, 872876. (7) Saltzman, B. E.; Hochstrasser, H. M. Environ. Sci. Technol. 1983, 17, 418-424. (8) Burkholz, A. Ger. Chem. Eng. 1985, 8, 351-358. (9) Dirgo, J.; Leith, D. Aerosol Sci. Technol. 1985, 4, 401-415. (10) Li, E.; Wang, Y. Am. Inst. Chem. Eng. J. 1989, 35, 666-669. (11) Moore, M. E.; McFarland, A. R. Am. Ind. Hyg. Assoc. J., 1990, 51, 151-159. (12) Moore, M. E.; McFarland, A. R. Environ. Sci. Technol. 1993, 27, 1842-1848. (13) Fuchs, N. A. The Mechanics of Aerosols; Pergamon Press: New York, 1964. (14) Pui, D. Y. H.; Romay-Novas, F.; Liu, B. Y. H. Aerosol Sci. Technol. 1987, 7, 301-315. (15) Dring, R. P.; Suo, M. J. J. Energy 1978, 2, 232-237. (16) Lippmann, M.; Chan, T. L. Am. Ind. Hyg. Assoc. 1974, 35, 189202. (17) Smith, J. L., Jr. Trans. Am. Soc. Mech. Eng. J. Basic Eng. 1962, 84, 602-608. (18) Wedding, J. B.; Weigand, M. A.; Carney, T. A. Environ. Sci. Technol. 1982, 16, 602-606. (19) Olan-Figueroa, E.; McFarland, A. R.; Ortiz, C. A. Am. Ind. Hyg. Assoc. J. 1982, 43, 395-399. (20) McFarland, A. R.; Ortiz, C. A. Atmos. Environ. 1982, 16, 29592965.
Received for review May 4, 1995. Revised manuscript received August 18, 1995. Accepted August 18, 1995.X ES950302E X
Abstract published in Advance ACS Abstracts, November 15, 1995.
