(13) Smith, W. H., Microb. Ecol., 3,231-9 (1977). (14) Smith, W. H., Staskawicz, B., Harkov, R., Trans. Br. M Y C OSOC., ~.
in press. (15) Staskawicz, B., Smith, W. H., Proc. Am. Phytopathol. SOC.,2,
loa.
Received for review December22,1976. Accepted May 26,1977. Research supported by a grant from the Consortium for Environmental Forestry Studies through the Pinchot Institute for Environmental Forestry Research, U.S. Department of Agriculture, Forest Seruice.
CORRESPONDENCE
SIR: The paper, “Particle Collection Efficiencies of Air Sampling Cyclones: An Empirical Theory” by Tai Chan and Morton Lippmann [ES&T 11 (4), 377 (1977)],contains several serious errors with reference to the theory of Leith and Licht as cited. In Table I and in the discussion, this is classed as a “semiempirical theory” with the comments “empirical fit of cyclone collection efficiency data” and “weak dependence of D,, to Q predicted”. It is also stated that this theory “make(s) an analogy to electrostatic collection of particles”. The facts are: (a) there is nothing whatever empirical about the theory, and there are no empirical constants in it; (b) the dependence of D,, on Q is precisely the same as that given for the “conventional” (Type I) theories, namely, D,, = K-Q-l’*, and this is clearly stated in the cited reference; (c) there is no analogy whatever drawn with electrostatic collection in the explanation of the theory. The line purporting to represent the Leith and Licht theory in Figure 1 is incorrect. It must have a slope of -Yz on a plot of log D,, vs. log Q, and therefore be parallel to the lines for the other Type I theories represented. Our theory was developed for use in the design of industrial size cyclones and without reference to its possible application to the very small cyclones used for respirable dust sampling. We are naturally very interested in any investigation of the relevance of the theory to this small scale of cyclone operation. However, any conclusions drawn from such an investigation must a t least be based upon a correct knowledge of our theory.
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Flgure 1. Comparison of experimental data vs. theoretical predictions for 10-mm nylon cyclone. Data from Blachman and Lippman (1974).Data for Beeckmans’ theory obtained from Beeckmans (1974)
The Leith and Licht theory should be classified under semiempirical theories since the original equation (5) includes an empirical constant n , termed the vortex component. The Leith and Licht equation was written as:
William Licht Dept. of Chemical and Nuclear Engineering University of Cincinnati Cincinnati. Ohio 45221
SIR: I t has come to our attention that there were computational errors in the data presented in Figure 1 in our recent paper ( I ) corresponding to the Leith and Licht theory ( 2 ) .The corrected version is presented here, showing a slope of -0.5 for the Leith and Licht theory. Although most cyclone theories in Figure 1 seemed useful in predicting performances of air cleaning cyclones, they were shown to be unsatisfactory in describing the collection characteristics in the miniature air sampling cyclones. For the industrial size air cleaning cyclones, the high loading factor improves collection efficiencies due to kinematic coagulation (31, but also favors losses due to particle rebound and reentrainment. In contrast, the operating conditions of the air sampling cyclones are quite different since the concentration of the airborne particulates hardly exceeds a few mg/m3. Particle reentrainment effects were shown to be negligible a t dust concentrations below 300 kg/m3, although particle rebound is probable ( 4 ) . The empirical theory presented in our paper includes these complicating factors.
where C = cyclone design number, $ = inertial deposition parameter, and n = vortex component.
We regret the misinterpretations of the Leith and Licht theory which were unfortunately based on faulty arithmetic computations.
Literature Cited (1) Chan, T., Lippmann, M., Enuiron. Sci. Technol., 11 (4), 377 (1977). (2) Leith, D., private communication, 1977. (3) Fuchs, N. A., “The Mechanics of Aerosols”,p 319, Pergamon, New York, N.Y., 1964. (4) Lippmann, M., Chan, T., Am. Znd. Hyg. Assoc. J., 35, 189 (1974). (5) Leith, D., Mehta, D., Atmos. Enuiron., 7,527 (1973).
Tai Chan Morton Lippmann New York University Medical Center Institute of Environmental Medicine 550 First Avenue New York, N.Y. 10016
Volume
11,
Number
10,
October
1977
1021
