Power Dissipation and Power Number Correlations for a Retreat-Blade Impeller under Different Baffling Conditions

Glass-lined tanks/reactors provided with a torispherical (dish) bottom and equipped with a retreat-blade impeller (RBI) are commonly used in the industrial syntheses of Active Pharmaceutical Ingredients (APIs). The power, P, dissipated by the RBI in the liquid in the tank is critical to many mixing processes, especially since the power per unit liquid volume, P/V, controls many mixing phenomena. Despite their common industrial use, limited information on P for RBIs and the corresponding nondimensional Power number, Po, is available. Here, P values for an RBI in liquids of very different viscosities at different agitation speeds and for different baffling configurations, i.e., unbaffled, partially baffled (with a single "beavertail" baffle), and fully baffled (four rectangular baffles), were measured experimentally in a scaled-down version of a typical reactor for API synthesis. The corresponding Po values were obtained for a large range of the Reynolds number, Re (1 < Re < 400,000). Po was found to vary significantly with baffling type and Re. Equations correlating Po with Re and baffling type are presented.