Ondřej Wein

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.

Periodic flows of pseudoplastic fluids in pipes

Experimental results on the flow enhancement during flow of clay slurries (n = 0.15) through oscillating pipes are compared with theoretical predictions. The agreement is fairly good, especially in the oscillating boundary layer flow regime. Flow enhancement of order 108 was found with the slurries used.

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.

AWS Viscometry—Principles and Applications

Quantitative identification of Apparent wall slip (AWS) effect, accompanying the flow of colloidal dispersions in confined geometries, requires a specific modification of common viscometric methods. Essential distinction between common and AWS viscometry is outlined—including theoretical background, calibration, data acquisition, and downstream data treatment—and demonstrated for a class of rotational viscometers.

Diagnostics of Apparent Wall Slip in Aqueous Polymer Solutions

Two experimental methods, apparent‐wall‐slip (AWS) rotational viscometry with “Morse‐taper” sensors and electrodiffusion (ED) flow diagnostics with auto‐calibrated friction probes, are used to study velocity profiles in aqueous solutions of high‐molecular polysaccharides. By comparing the velocity data from the both methods, estimates are obtained of depleted layer thickness in dependence on wall shear stress.

Wall effects in Non-Newtonian fluids

True velocity profiles near a rigid boundary were studied using both the viscometric and electrodiffusion techniques. For bentonite suspensions, both techniques gave nearly identical values of apparent slip velocity. For CMC solutions, the electrodiffusion data suggested weak slip effects, which were undetectable by viscometric methods. No slip effects were observed for PEO solutions.