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Electrodiffusion Diagnostics of Apparent Wall Slip in Polymer Solutions
Wein, Ondřej ; Tovčigrečko, Valentin ; Večeř, M. ; Sobolík, Václav
Two substantially improved experimental methods, the apparent wall slip (AWS) rotational viscometry with a Morse-taper sensor and electrodiffusion (ED) flow diagnostics with autocalibrated friction probes, are used to study near-to-wall velocity profiles in aqueous solutions of high-molecular polysaccharides under viscometric flow conditions. By comparing the velocity data from the both methods, estimates of the depleted layer thickness in dependence on wall shear stress are obtained. The ED data support the two-layer model of AWS effect, with the constant enhanced fluidity across the depleted layer.
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Teorie elektrodifuzních čidel třeni v mikrodisperzních kapalinách 8. Vliv zdánlivého skluzu na směrové charakteristiky
Wein, Ondřej
Insulated insertions between individual segments of direction-sensitive electrodiffusion friction probes attenuate the directionalsensitivity. Quantitative study of this effect by Wein and Wichterle (1989) for Newtonian liquids has been extended in a recent research report (Wein 2007) for the microdisperse liquids, displaying the Apparent Wall Slip, i.e. a non-linear velocity profile close to solid surfaces. In the present research report, this theory is used to the simulation calculations of directional characteristics for a class of 3-segment electrodiffusion friction probes with the insulating insertions. Rather realistic model of non-ideal 3-segment direction-specific probes is tested by comparison of the predictions with experimental data about an actual 3-segment probe in both homogeneous and microdisperse liquids.
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Směrové charakteristiky vícesegmentových ED čidel pod vlivem zdánlivého skluzu při stěně
Wein, Ondřej
The direction-sensitive electrodiffusion (ED) probes consist of three working electrodes (segments), separated by thin insulated insertions. In common, the directional characteristics, ie. the ratios of individual limiting diffusion currents, are determined experimentally, using a suitable calibrator that generates a steady viscometric flow. It has been shown in that, at high enough Peclet number, the directional characteristics can be calculated from a front photograph of the probe via the linear theory of convective diffusion. In the present contribution, the original theory for a constant wall shear rate is generalized for a class of non-linear velocity profiles.
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