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A new fluid dynamic model for mixing of newtonian and power‐law liquids in the transient regime
Author(s) -
Zeppenfeld Rolf,
Mersmann Alfons B.
Publication year - 1988
Publication title -
chemical engineering and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.403
H-Index - 81
eISSN - 1521-4125
pISSN - 0930-7516
DOI - 10.1002/ceat.270110122
Subject(s) - laminar flow , mechanics , power law fluid , turbulence , shear thinning , thermodynamics , power law , mixing (physics) , viscosity , non newtonian fluid , newtonian fluid , context (archaeology) , transient (computer programming) , shear rate , rheology , flow (mathematics) , fluid dynamics , materials science , physics , mathematics , computer science , geology , paleontology , statistics , quantum mechanics , operating system
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 know, 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 standardized 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.