The use of mathematical models in studies on scale-up and impeller geometries in a continuous flow reactor

A modified version of the single loop recirculation model is proposed for the simulation of the dynamics of turbine and propeller agitated continuous systems. The model predictions characterise experimentally determined responses for a variety of operating conditions and a wide range of impeller speeds. The model is verified, using thin fluids, for various diameter impellers placed in vessels of different diameter. Analytical expressions are obtained for batch mixing time using a matrix technique, having formulated batch conditions by a reduction, of the continuous flow model. Experimentally determined batch mixing times appear to match the analytical solutions more favourably than the predictions of various empirical correlations. A new approach, based: on the intensity function, is suggested for the assessment of continuous mixing time. The continuous flow model parameter (q/Q), the ratio of impeller pumping capacity to system throughput, is proposed as the first dynamic scale-up rule. If held constant this criterion ensures identical residence time distributions in the laboratory and pilot plant vessels. A variance analysis assesses the merits of different feed inlet positions, for the continuous case, and shows that inlet feed directed away from the outlet stream and impeller region produces the most effective mixing. Scale-up using constant impeller tip speed is shown to provide an economic optimum for the scale-up of continuous systems.