(94b) Power Numbers and Power Correlations for a Retreat-Blade Impeller Under Different Baffling Conditions

Glass-lined tanks and reactors are commonly used in the in pharmaceutical API synthesis because of their corrosion resistance, cleanability, and reduced contamination level. A retreat-blade impeller with a low impeller clearance off the tank bottom is commonly used in glass-lined reactors provided with a torispherical vessel bottom. The power, P, dissipated by the impeller is critical to many mixing processes to achieve the desired mixing effect, especially since the power per unit volume, P/V, controls directly mass transfer processes and other mixing phenomena. Despite their common use in industry little information is available on power dissipation and the corresponding power number Po for this type of system is available in the literature.

In this study the power, P, dissipated by a retreat-blade impeller in different fluids of different viscosities at different agitation speeds and the non-dimensional Power Number, Po, were obtained experimentally in a scaled-down version of a typical glass-lined reactor for pharmaceutical API synthesis. Additionally, P and Po were obtained for an unbaffled system and a fully baffled system (four rectangular baffles) and for a large range of the Reynolds Number (1<Re<1,000,000). Po was found to vary significantly with baffling type and Re.

Equations correlating Po with Re and baffling type were obtained. These equations can be used by industrial users to help quantify and optimize pharmaceutical mixing processes typically involving the synthesis of APIs in this type of reactors.