CORRESPONDENCE
SIR: The paper “Venturi Scrubber Performance Model” by Yung, Calvert, Barbarika, and Sparks [ES&T, 12,456-9 (1978)] represents a significant step forward in the on-going effort to produce better performance models for Venturi scrubbers. However, all recent models continue to suffer from certain fundamental defects. The distribution of drop sizes in a gas-atomized spray is ignored and instead a Sauter mean diameter is used to represent the spray. By means of sample calculations, Licht and Radhakrishnan ( I ) have shown that a significant difference in grade efficiency and in the overall penetration may be obtained when a drop size distribution is used rather than a Sauter mean. Unfortunately, the only data available for size distributions have been determined on preformed sprays, that is, for pneumatic nozzles (see, e.g., Nukiyama and Tanasawa ( 2 ) , Kim and Marshall ( 3 ) ,Licht ( 4 ) ) .I t is not only unrealistic to apply these to the gas-atomized sprays which are to be found in Venturi scrubbers, but also it involves a transition to a vastly different range of operating conditions than those which were used in the experimental work. The only drop-size measurements on a full-scale prototype Venturi are those of Boll ( 5 ) ,in which only Sauter mean sizes were determined. Licht and Radhakrishnan ( 1 )have shown that these are low by as much as 50% of the values obtained from the widely cited Nukiyama and Tanasawa equation, for comparable gas velocity and liquidlgas flow ratio. In fact, the question of which mean drop size to use to represent the spray in the collection performance model has never been fully explored. There is no proof that the Sauter mean would necessarily be the correct one. Instead, in the related case of an equation to model the pressure drop across a Venturi, where the Sauter mean is also usually recommended, the mass mean drop size would seem to be far more logical, as has been suggested by Yoshida et al. (6). Research into these aspects of the Venturi model is ongoing a t the University of Cincinnati. Literature Cited (1) Licht, W., Radhakrishnan, E., AIChE S y m p . Ser., 74 (No. 1751, 28 (1978).
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(2) Nukiyama, S., Tanasawa, Y., Nippon Kikai Gakkai Rombunshu, 4,86 (438); 5,63 (1939). (3) Kim. K. Y.. Marshall, W. R., Jr., AIChE J., 17,575 (1971). (4) Licht, W., AIChE J., 20,595 (1974). (5) Boll, R. H., et al., J. Air Pollut. Control Assoc., 24,934 (1974). ( 6 ) Yoshida, T., et al., Kagaku Kogaku, 3,232 (1965).
William Licht Department of Chemical and Nuclear Engineering University of Cincinnati Cincinnati, Ohio 45221
S I R Morishima and Yoshida ( I ) performed a mathematical analysis to determine the influence of liquid drop size distribution on the particle impaction and diffusion collection efficiency. The technique is based on calculating the average collection efficiency from the following equation:
5=
J m
rl
f(dd) ddd
where 7 is the collection efficiency of a single drop and f(&) is the drop size distribution function. Then instead of using 7 and dd in the efficiency equations, i j and a d are used. However, in carrying out this calculation, they concluded that the difference between using rl and 7 is insignificant unless the drop size distribution is quite wide. This technique is very complicated and one must use a numerical technique for solving the equation. Our feeling is that given: (a) the absence of reliable data on drop size distribution, (b) the complicated technique for calculating penetration, and (c) an insignificant gain in most cases, the model developed by us is a step forward and should be used as reported. Literature Cited (1) Morishima, N., Yoshida, T., Kagaku Kogaku, 1114-9 (1967).
Seymour Calvert Air Pollution Technology, Inc. 4901 Morena Boulevard Suite 402 San Diego, Calif. 92117
0013-936X/79/0913-0354$01 .OO/O @ 1979 American Chemical Society
