NOTES
Operational Characteristics of the Vibrating Orifice Aerosol Generator James B. Wedding' University of Illinois at Urbana-Champaign,Urbana, 111. 61601
A universal scaling parameter has been recognized which allows the researcher to ascertain the monodisperse frequency range of the Vibrating Orifice Aerosol Generator by simply optically sizing the aperture used and selecting a reasonable flow rate. The need for experimentally establishing the correct modulation frequency has been eliminated for two commonly used aperture sizes which allow aerosols in the 0.8-3Op size range to be produced. In an earlier paper [Wedding, J. B., Stukel, J. J., Enuiron. Sci. Technol., 8 (5),456 (1974)], a general relationship was published to allow determination of the correct disturbance wavelength (A) for production of monodisperse aerosol when applied to a jet of liquid of constant velocity. T h e expression, given by
still required fma. to be determined experimentally which = r for fm,). Then, allowed D, to be calculated (as A&D, by use of plot in the earlier paper, jmln could he determined to establish the overall operating frequency range for monodisperse aerosol. This procedure, which requires considerable experimental effort, would be acceptable except for the fact that tolerances on commercially produced electron microscope beam apertures may he as much as
through the aperture. Figure 1 shows DA/Dj, AID, plotted vs. VA.T h e AID, plots are for two commonly used aperture sizes of 9-lop and 21-22p. While the lower limit is r, it is seen that the upper limit varies widely. These plots are not precise and are to serve only as a guide in selecting operating frequencies using Equation 1. The procedure for generating these plots was entirely experimental. I t consisted of collecting numerous samples of particles using millipore filter paper of 0 . 2 2 ~pore size for different aperture flow rates allowing a range of V A to be established. Each collected sample was individually sized using an optical microscope a t lOOOX and a Leitz traveling hair (Filar) eyepiece until the monodisperse (bg = 1.06) frequency range was estahlished. Then D, was calculated and the upper and lower bounds for X were determined for all cases. The particles were made of uranine dye (sold commercially under the name fluorescein) dissolved in water. T h e results for the ratio of DalD, are linear and range from about 0.84-0.96 for a velocity range of 700 cmlsec to 2500 cmlsec. With this plot, the maximum operating frequency may be determined using the left-hand side of Equation 1 (where Ami,,,max apply to the left- and righthand side of the inequality, respectively) and the value of
10%. The missing element here is a scaling parameter that the ratio D d D , and AID, may be referenced to, enabling one easily to calculate the monodisperse operating frequency for a given aperture size and flow rate without necessitating experimental calibration of each new aperture individually, when a replacement or size change becomes necessary. The best scaling parameter appears to be the jet velocity Engineering Research Center, Foothills Campus, Colorado State University, Fort Collins, Colo. 80523.
Volume 9.Number 7. July 1975 673
DA/D, obtained from the plot for the particular velocity used, again recalling that AmlnID, = T and by making the V,. Thus, f m a x is deterreasonable assumption that V.4 mined without the time-consuming and error-prone experimental calibrating previously required. One must be careful in sizing the aperture, however, and in ensuring a constant velocity through the aperture as by using a n infusion pump (good quality one available from Harvard Apparatus, Milas, Mass.). The upper limit of X may he approximately determined by the upper dashed curves for AID, and the value just found for D,. Then the lower limit on disturbance frequency may he calculated by applying the right-hand side of the inequality. Within this overall operation envelope, an optimum frequency will exist at which aerosol quality is best.
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An example of Aerosol quality following this procedure is given in Figure 2. Nomenclature A, = area of the jet, = 7rDj2/4,cm2 D A = diameter of aperture, cm D, = diameter of the jet, cm fmax,min = monodisperse operating frequency maximum and minimum, respectively Q = volume flow rate through aperture, cm3 V A , ~= velocity through the aperture, jet, respectively Greek Letters
h = disturbance wavelength for monodisperse operation x =
3.1416.. .
Receiced for recieu, October 4, 1974. Accepted February 7 , 1975
Facile Incorporation of Chlorine into Aromatic Systems During Aqueous Chlorination Processes Robert M. CarIson,* Robert E. Carlson, Herbert
L. Kopperman, and Ronald Caple
Department of Chemistry, University of Minnesota, Duluth, Minn. 558 12
I t has been observed t h a t chlorine is readily incorporated into aromatic compounds under those conditions utilized for water renovation. The extent of chlorine incorporation varies with p H and contact time.
production of polychlorinated biphenyls (PCBs) a t waste treatment facilities known t o receive biphenyl ( 2 1 ) . Experimental
Typical Procedure (Table I). All reactions were carried out in a 500-ml volumetric flask. T o each flask was added 12.72 ml of the 3.84-mg/ml NaOCl solution, HC1 (for p H There is a mounting awareness that there may be enviadjustment), and the test solution. T h e reaction temperaronmentally deleterious chlorine-containing chemicals ture was maintained a t 25 i 0.2OC using a constant tem(other than chloramines) produced during a water renovaperature bath. A 20-ml aliquot was taken a t 20 min and tion process (1-7). The present report deals specifically added immediately to a flask containing 15 ml of 0.00543N with the aqueous chlorination of aromatic systems and the Na&Oa solution, 5 ml of HOAc, 2 ml of KI (50% aqueous) examination of the relationship of chlorine incorporation to and 1-2 ml of freshly prepared starch solution. This was tip H and contact time. trated to a faint purple color using 0.096 mg/ml of NaOCl Within the typical ranges of p H found during the course solution. of most water treatment processes (pH 5-9), the active Typical procedure (Table 11). T o five of the bottles conchlorine species could range from entirely hypochlorite taining 100 ml of distilled water and saturated biphenyl, (-OC1) to entirely hypochlorous acid (HOC1 pK, = 7.5 a t 100 ppm of Ca(OC1)2 were added, and t o another five bot20°C). It has been observed that chlorine is more readily tles, 100 ppm of Ca(OC1)Z were added. The remaining five incorporated into aromatic systems a t lower p H values (8), bottles, containing water and biphenyl only, served as cona result which parallels the observation of increasing disinfection capability with decreasing p H ( 1 ) . The active chlorinating species has not yet been determined although it is known not to be the C1+ ion (9). Table I Monosubstituted aromatics were exposed to low concentrations of aqueous chlorine (‘7 X M , 20 min, Table I), PH with the extent of chlorine incorporation following well3 7 10.1 recognized trends whereby aromatics containing “activat(9.5 i 0.6 x M ) % CI (uptake) % CI % CI ing” groups such as hydroxyl, ether, amine derivatives, or Phenol 97.8 z 0.1 97.6 i 0.1 97.6 = 0.2 alkyl undergo electrophilic aromatic substitution faster Anisole 80.7 z 0 . 2 11.4 0.4 2.8 0.3 than those containing “deactivating” groups such as nitro, Acetan i 1 ide 55 3 z 0 . 5 3.4 1 0 . 2 chloro, nitrile, and carbonyl ( I O , 1 1 ) . Phenol is unique in Toluene 11.1 i 0.1 2.9 z 0.4 being readily chlorinated a t high pH values in that, alBenzyl alcohol 2.3 i 0 . 2 though the chlorinating agent is hypochlorite, the substrate Benzonitrile 2.1 i 0.2 is the very reactive phenolate anion. Nit1 obenzene 1.8 10.1 A detailed analysis of the aqueous chlorination process Chloi obenzene 1 8 10.1 was also accomplished using biphenyl as the aromatic Methyl benzoate 1.8 t 0.2 species. Biphenyl was chosen for study owing to the availBenzene 1.5 r 0.1 ability of methodology for isomer recognition and the conC h l o r i n e ( 7 . 0 x I O - ~ J I ) , 20 m i n , 25‘C. siderable interest that has recently centered on the possible 674
Environmental Science & Technology
