P. Mitschka

SHEAR RATES ON TURBINE IMPELLER BLADES

Shear rates on the front side of a turbine impeller blade have been measured by an electrochemical method. The values obtained for water, CMC solutions and a kaoline suspension have been found to be in general higher than assumed so far. The data agree (for ReM > 10) satisfactorily with the predictions from the laminar boundary layer solutions for the flow of power-law fluids around rotating disks

SHEAR STRESSES ON THE WALLS OF AGITATED VESSELS

Abstract Characteristics of flow near the walls of baffled vessels equipped with a six blade Rushton type turbine were measured by an electrochemical method. A directionally sensitive probe was used for determination of velocity gradient vector fields. It was found that the flow conditions near the wall could be described by a meridional profile of the friction coefficient. An extensive set of experimental data obtained by the limiting current technique showed that the profile depends on the Reynolds number, on the flow index of the (power-law) fluids and on the d/D simplex. The maximum values of the friction coefficient characterizing flow near the impeller plane can be correlated by a simple relation of the laminar boundary layer type.

DIAGNOSTICS OF SLIP EFFECTS IN NON-NEWTONIAN MEDIA VIA ELECTROCHEMICALLY DRIVEN TRANSIENT CONVECTIVE DIFFUSION

Abstract True velocity profiles in the close vicinity of a wall can be determined by measuring the transient limiting diffusion currents after applying a step change of electrode overpotential. Slip effects in a bento-nite slurry under viscometric flow conditions were investigated by using this novel experimental technique. Electrochemically determined apparent slip velocities were found to be in excellent agreement with the results of conventional viscometric experiments.

Automorphous models of viscoelasticity

Abstract Automorphy is introduced as an algebraic property of functions or functionals which represents the necessary and sufficient condition for a dimensionally consistent formulation of a rheological model having a single dimensional parameter. Automorphous rheological models are shown to represent the true behaviour of polymer systems satisfactorily at high shear rates. It is shown, with an example (plate start-up problem), how the assumption of automorphy may simplify the solution of rheodynamic problems.