(77a) Flow Patterns and Performance Measures for Stirred Tank Mixing (process characteristics, flow patterns, measures of mixing performance)

To understand the effects of mixing on chemical reactions, it is first necessary to understand the basics of common mixing practices. The mixing done in the laboratory can be quite different from good practices in production, but understanding production requirements should influence the laboratory study. Flow patterns for basic mixing are critical. Swirling flow patterns may look violent on the surface, but provide little effective mixing where a reaction is expected to take place. The most effective flow patterns for chemical reactions place emphasis on top-to-bottom liquid motion. Angle-mounted portable mixers in unbaffled tanks and center-mounted mixers in baffled tanks can create effective mixing for chemical reactions. Mixing intensity depends on the amount and pattern of flow created by the mixer. The measure of that intensity depends more on mixer torque that power in most liquid applications.