Scale-up in laminar and transient regimes of a multi-stage stirrer, a CFD approach

A multi-stage industrial agitator system adapted to the mixing of a mixture whose viscosity varies during the process has been characterized by using CFD. In the entire study the mixture is supposed to have a Newtonian behavior even though it is rarely the case. It is shown that the well-adapted propeller is able to e7ciently blend high viscous media provided the Reynolds number is not too low. A scale-up study of the agitated system has also been carried out by respecting the classical scale-up rules such as the geometrical similarity and the conservation of the power per volume in the particular case of viscous media. Using an Eulerian approach, the hydrodynamics of three di9erent scales with geometrical similarity have been numerically characterized by the energy curve (power number versus Reynolds number) and by the Metzner and Otto constant in which both are required for scale-up procedure. Experimental power measurements have been carried out at the smaller scale so that simulations have been partially validated. New hydrodynamic criteria have also been introduced in order to quantify the =ows in the case of a multi-stage stirrer running at low Reynolds number. It has been shown how this hydrodynamic di9ers dramatically from one scale to another when scale-up at constant energy per volume is applied. From the CFD results, recommendations about the widely used scale-up rules have been suggested and modi>cations of stirring geometry have been proposed in order to reduce the =ow pattern variations during scale-up. ? 2002 Elsevier Science Ltd. All rights reserved

CFD analysis of industrial multi-staged stirred vessels

This paper presents tools for analysis of CFD results adapted for flows in multi-stage stirred vessels through out two industrial cases. Those tanks fitted with double-flow impellers are used first to cool down highly viscous resins and subsequently for indirect emulsification. Since the simulation of these processes in their whole complexity would be unrealistic, it considers single-phase flows without heat transfer. The result analysis in order to prove that the mixing and the circulation are effective is not usual; in these cases, the circulation and impeller numbers are not adapted. The average axial flow numbers are relevant of the circulation in the whole tank and of the connection between the flows produced by the propellers in the given configuration. The velocity profiles give relevant results, but are not sufficient whereas the particle tracking validates that the propellers do not work together in one case and do work together in a second one

Modelling and simulation of batch and semi-batch emulsion copolymerization of styrene and butyl acrylate

International audienceThis work deals with modelling of emulsion polymerization processes using batch and semi-batch reactors. Speciÿc attention is paid to copolymerization of the system styrene/butyl acrylate. The main key parameters of the model are identiÿed on the basis of batch experimental data in order to describe the complete sketch of emulsion polymerization. The model is then used to simulate, under several operating conditions, the polymerization rate, the global monomers conversion, the number and weight average molecular weights as well as the particle size distribution and the glass transition temperature. Then, the model is generalized to the use of semi-batch processes and validated for this application.