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I n d . E n g . Chem. Res. 1988,27, 1744
Response to Comments on “Ultrasonic Technique for Dispersed-Phase Holdup Measurements” Sir: We wish to address the comments by Sovova and Havlicek in regard to our paper in 1987 (Bonnet and Tavlarides, 1987). The first comment states that we cited the work of HavliEek and Sovovl(1984) incorrectly. We acknowledge this error. In our Review section, the word “velocity” should be replaced by “the pulse transmission time” in the statement “A linear relationship between the “velocities” of the sound in the dispersion ...correlate the data.” Their second comment provides information regarding the drop size range they studied (0.1-2.0 mm) and the frequency of ultrasound they employed (2 MHz) in their work and indicates that the maximum ratio of sound wavelength to drop diameter was of the order of 10, which is in the region of our experimentation. This information is not provided by the authors in their work nor is it possible to deduce this information from details provided. Coupled with their comments regarding Kuster and Toksoz’s work (1974), they conclude that the propagation of sound through liquid dispersions differs significantly than through suspension of solids. It is our contention that, at the time of our work, no conclusions could be drawn, without additional experimentation and comparison, as to which model appropriately describes the acoustical characteristics of a liquidliquid dispersion. Toward this goal, we compared our data with the homogeneous model by Wood (1955)’ the timeaverage model proposed by Kuster and Toksoz (1974), the scattering theory model of Chaban (1974)’ and the fluiddynamic model of Ahuja (1973) as shown in Figure 3 of our work. From these comparisons, we concluded that the time-averaged model represents our data. These pertinent literature references escaped the attention of HavliEek and Sovovb. We note that their eq 6 is the time-average model proposed by Kuster and Toksoz (1974), who proposed the applicability of the model for “a fluid matrix with spherical inclusions”. The third comment by the authors delineates the history of the development of their immersed ultrasonic probe technique. The objective of our work is clearly stated in the Review section of the paper: viz., to develop a “reliable technique of measurement of dispersed-phase holdup profiles in extraction columns using instrumentation that can be located on the outside of the vessel or column wall.’’ It is noted that intrusive and invasive ultrasonic instruments to measure concentration of solutions, emulsions,
Q888-5885/8S/2627-1744$01.50JQ
and suspensions as well as flow rates of single phases have been commercially available in the US since the 1960s (Greenspan and Tschiegg, 1957; Allison, 1958). Our objective differs in a significant way from the direction taken by HavliEek and Sovovl. Regarding the final comment, we point out that our noninvasive and nonintrusive technique is not only suitable for laboratory use but also for industrial application. The ultrasonic technique using an oscilloscope requires a sharp signal in order to maintain a good signal recognition. The procedure to achieve this quality on the signal is clearly indicated on p 812 of our paper. This knowledge has permitted us to recently develop an electronic data acquisition system which obviates the need for an oscilloscope and permits automatic evaluation of holdups at different locations in the reactor using the same technique. Accordingly, one has the choice to choose between a noninvasive-nonintrusive technique or one with probes immersed in liquid, both of which offer automatic evaluation of transmission time for monitoring and control of industrial scale equipment. Literature Cited Ahuja, A. S. J . Appl. Phys. 1973, 44(11), 4863. Allison, P. A. J . Colloid Sei. 1958, 13, 513. Bonnet, J. C.; Tavlarides, L. L. Ind. Eng. Chem. Res. 1987,26, 811. Chaban, I. A. Sou. Phys.-Acoust. (Engl. Transl.) 1974, 19(6), 600. Greenspan, M.; Tschiegg, E. E. Reu. Sci. Instrum. 1957,28(11), 897. HavliEek, A.; Sovovfi, H. Collect. Czech. Chem. Commun. 1984,49, 378. Kuster, G. T.; Toksz, M. N. Geophysics 1974, 39(5), 607. Wood, A. B. A Textbook of Sound, 3rd ed; Bell: London 1955.
Lawrence L. TavlaridesY Department of Chemical Engineering and Materials Science Syracuse University Syracuse, N e w York 13244-1190
Julio C. Bonnet Escuela d e Zng. Quimica Uniuersidad Central d e Venezuela A p a r t a d o 50656-50361 Sabana Grande Caracas 1040-A, Venezuela
0 1988 American Chemical Society
