A new fluid dynamic model for mixing of newtonian and power-law liquids in the transient regime

✍ Scribed by Dipl.-Ing. Rolf Zeppenfeld; Prof. Dr.-Ing. Alfons B. Mersmann

• Publisher: John Wiley and Sons
• Year: 1988
• Tongue: English
• Weight: 653 KB
• Volume: 11
• Category: Article
• ISSN: 0930-7516
• DOI: 10.1002/ceat.270110122

✦ Synopsis

In the description of mixing processes influenced by viscosity in pseudoplastic (power-law) fluids, a definition of representative viscosity is normally used which takes into account the variable flow behaviour of the stirred material as a result of different shear stresses. In this context, the Metzner and Otto concept, which postulates that a representative shear rate is proportional to stirring speed, has become widely known, although the power calculation is inaccurate, particularly in the transient regime between the laminar and turbulent flow. A new model of fluid dynamics in the mixing vessel is presented, based on the increase of the mean flow velocity standarized with the stirrer's tip velocity in the transition regime. It provides a physical explanation for the above deviations. A suitable definition of representative viscosity substantially improves the accuracy of calculations of the stirring power in power-law fluids.

* Modified version of a paper presented at the "GVC Working Party on Mixing", Trier, 4./5. May 1987.