Ind. Eng. Chem. Fundam. 1980, 19, 327
0 EXPERIMENTAL RTD
- - I STIRRED TANKS IN SERIES MODEL
527
reactor in the agitation condition no. 1 is almost perfectly macromixed and micromixed for both values of experimented space times. It is likely that such systematic errors also exist in derivations relative to agitation conditions 2 to 5 and that the results and the conclusions of Hanley and Mischke have to be revised.
Literature Cited Buffham, B. A., Gibilaro, L. G., AIChE J., 14, 805 (1968). Danckwerts, P. V., Cbem. Eng. Sci., 8, 93 (1958). Hanley, T. R., Mischke, R. A., Ind. Eng. Chem. Fundam., 17, 51 (1978). Olsson, H., 2.Phys. Cbem., 118,99 (1925). Olsson, H., 2.Pbys. Chem., 133, 233 (1928). SaMick, J., Hammet, L. P.,J . Am. Chem. Sac., 72,283 (1950). Tommila, E.,Koivisto, A., Lyyra, J. P., Antell, K., Heimo, S., An. Acad. Sci. Fennicae, AM47, 3 (1952). Villermaux, S., Gibert, R., Villermaux, J., Malenge, J. P.,Rev. Inst. Fr. Pet.,
1. 114 (1967).
Figure 3. Comparison of the experimental RTD (agitation condition no. 1; y = 8.86 min) and the model of stirred tank in series.
Warder, L., J . Am. Cbem. Sac., 3, 203 (1881). Zoulalian, A., Villerrnaux, J., Adv. Chem. Ser.. No. 133,348 (1974). Zoulalian, A., PhD Thesis, Universit6 de Nancy I, 1973. Zwleterlng, T. N., Chem. Eng. Sci., 11, 1 (1959).
could be expected, the points are very close to those for a single perfect macromixer, in contrast to what is shown in Figure 12 of Hanley and Mischke. (3) Conclusion. It results from this discussion that the
Laboratoire des Sciences d u Genie Chimique CNRS-ENSIC Nancy, France
Sir: In their critique, David and Villermaux focus on two particular areas of calculation assumption: the temperature dependency of the rate constant, k, and the method for evaluation of residence time distribution curves. They present data to substantiate use of an alternate rate constant equation and suggest that the residence time curves be altered by inserting an undefined “small” time delay into experimental data. Based on a partial analysis of the experimental data, they conclude that the reactor in agitation condition one is perfectly micromixed as well as perfectly macromixed and suggest that the conclusions be seriously revised. The rate constant equation for calculation was chosen on the basis of best substantiated data available at the time of the investigation. From the review of the literature, the results of Warder appeared to be the best available. The data presented by David and Villermaux, mostly from foreign publications, certainly appear to be better than those of Warder and obviously necessitate a recalculation of the results. This also answers some questions in the minds of the authors, as the new rate constant predicts near perfect micromixing, a condition anticipated in the study. This application lends credence to the results in agitation condition one and should affect other condition results favorably. The increased k value will essentially predict more micromixing in each mixing condition, as the k value affects all calculated values.
The calculation made from Figure 9 by introducing a small time delay in the data is not consistent. Time for delay was allowed in the experimental data based on entrance and exit flow lengths and subsequent flow times. To choose one RTD for alteration without adjusting all other curves by the same amount is not consistent. However, since this calculation has a small effect when compared to the effect of the rate constant change, it should perhaps be considered insignificant. Only with a recalculation of all results can this effect be fully measured. The results are being recalculated and will be available on completion. It is the authors’ opinion that this recalculation will substantiate the results and conclusions. The major conclusion of this paper involved the use of concentration fluctuations as the RTD response to characterize micromixing. Although the numbers will obviously change (increased micromixing),the conclusion of relation is still valid.
0196-4313/80/1019-0327$Ol.OO/O
R. David J. Villermaux*
Department o f Chemical Engineering Rose-Hulman Institute o f Technology Terre Haute, Indiana 47803
Thomas R. Hanley*
Department of Chemical Engineering Virginia Polytechnic Institute and State University Blacksburg, Virginia 24061
Roland A. Mischke
0 1980 American
Chemical Society
