(145a) Coalescence Re-Dispersion Model of Spielman and Levenspiel and Interaction By Exchange with the Mean Model of Villermaux Revisited

The CD model of Spielman and Levenspiel and interaction by exchange with the mean( IEM) model for prediction of micro-mixing effects in a CSTR are reviewed. An interpretation of the interaction parameter of the CD model is given by using the random walk theory of Chandrasekhar and the results obtained by Rao and Dunn on Monte Carlo simulation of coalescence re-dispersion phenomena to simulate mixing with homogeneous reactions in a plug flow reactor with unmixed feed. The concentration changes simulated by the CD model are proved to be identical to the concentration changes predicted by the differential equation for unsteady steady state diffusion based on Fick’s law when written in finite difference form. The application of the CD concept to the solution of the film model for diffusion with reaction in a gas-liquid film also is demonstrated. The extension of the plug flow reactor model of Rao and Dunn to predict recycle flow effect on RTD of a CSTR shows similarity in predictions of RTD data with those observed by Leitman and Ziegler. Aubry and Villermaux claimed that the results obtained by using IEM model are nearly identical to those results obtained by using the CD model if the equivalence relationship between the parameters of the models proposed by them is used. In the present work, it is observed that the effect of volumetric feed ratio of reactants fed in unmixed condition to a CSTR predicted by the two models are widely different after the equivalence relationship proposed by them is used. In addition the effect predicted by the IEM model is found to be incorrect. A set of typical results obtained in the case of a (1,1) order irreversible reaction taking place in a CSTR with unmixed feed are given in Figure 1.