National Repository of Grey Literature 74 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Factors Influencing Apparent Wall Slip of Colloidal Dispersions.
Pěnkavová, Věra ; Tihon, Jaroslav ; Wein, Ondřej
This lecture is dedicated to memory of professor Ondřej Wein without him it cannot be possible to penetrate such deep into secrets of wall phenomena.
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Detection of Apparent Wall Slip in Microdispersion Liquids
Pěnkavová, Věra ; Tihon, Jaroslav ; Wein, Ondřej
Zdánlivý přístěnný skluz je možno detekovat přímo různými vizualizačními technikami, pokud je mikrodisperzní kapalina dostatečně transparentní, nebo nepřímo pomocí viskozimetrie, kdy je měření prováděno v minimálně dvou různých geometriích senzoru. Z rozdílných tokových křivek naměřených v různých geometriích je možno pomocí statistického zpracování vyhodnotit jak viskozitu v objemu disperze, tak skluzový příspěvek podél stěny.
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Models of AWS Material Functions
Wein, Ondřej ; Pěnkavová, Věra
New classes of 4-parameter models of fluidity for the shear-thinning non-Newtonian liquids are introduced, including their local pseudosimilarity representation. The models cover both purely-viscous (PV) and visco-plastic (VP) flow behavior. New 4-parameter model of slipidity (Navier slip coefficient) is introduced, as well as its modification for retarded AWS (slipidity decreasing with rising shear stress) and wall dilatancy (negative slipidity). Their asymptotic behavior, as well as their asymptotic sub-models are identified and prepared for implementation in the software AWSWork.
Edge Effects in Rotational Viscometry III. ZZ and KK Sensors, Total Slip Pseudosimilarity
Wein, Ondřej
This report presents a next step of our effort in developing a system of corrections on edge effects in rotational AWS viscometry. In the previous two reports [4, 5], the edge corrections are given for Newtonian and pseudoplastic liquids with no-slip (adherence) boundary conditions at solid walls (BC).
Edge Effects in Rotational Viscometry VI. ZZ- and KK- Type Sensors: No-slip Pseudosimilarity for Inertialess Flow (Revisited)
Wein, Ondřej ; Havlica, Jaromír
This report should serve as a manual to the program Prog_cL_m.exe for calculating the correction cL on edge effects in narrow-gap rotational viscometry with almost cylindrical or conical spindles. Referring to the previous Research Report ICPF 2004/8, which deals with the same subject, it includes, in addition, also computation of cL for the entire ZZ and KK sensors with an arbitrary front of bottom semi-sensors (FLAT, CONE, HUB, HAAKE). Detailed attention is paid to numerical aspects: extrapolation/interpolation of the related fields (angular velocity, shear stress, dissipation, local torque contribution) towards the boundaries, including the analytical smoothing at singularities. The source codes for Prog_cL_m.exe, the results of numerical simulations, as well as the resulting correlations for cL , are available on the attached CD, which is an integral part of this report. The inertia effect was computed using commercial software FLUENT 12 for the Z40DIN sensor and applied in an approximate way also for the KK35/23 sensor.
A New Look on the Nernst Model in Electrochemistry
Wein, Ondřej
The present paper is inspired by the electrodiffusion (ED) flow measurement, utilizing the limiting-diffusion regime (LDR) in two-electrode ED cells. The electrochemical testing and calibrations of the ED cells is based on two standard electrochemical techniques - quasi-steady voltammetry and voltage-step transient. Recently published theory of the voltage-step transient under simultaneous effect of Faradaic and Ohmic resistances is based on a suitably extended Nernst model. An analogous theory of the voltammetric experiment is presented here.
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AWS Viscosimetry of Microdispersions - Detection of Apparent Wall Slip
Pěnkavová, Věra ; Večeř, M. ; Wein, Ondřej
The rheometric data measured using three various sensor geometries (PP60, ZZ40DIN and KK-sensor) are compared in this contribution at the case of water solution of polymer welan. The KK-sensor, constructed at our department, combines advantages of geometry both plate-plate and concentric cylinder geometry. It is shown that KK-sensor is comparable to commercial sensors. It is presented for water kaolin dispersions that apparent wall slip does not disappeared neither for low consistent dispersions. The values of slip coefficients are even higher in the case of less consistent samples.
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AWS Viscometry – Principles and Applications
Wein, Ondřej
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.
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Voltage-step Transient in Redox Systems III. Effect of the Current Primary Distribution via Nernst Model
Wein, Ondřej
In addition to the common transient diffusion (Cottrell), there are further transport results that cannot be neglected: Faradic resistance at surface of the working electrode, and Ohmic resistance in the bulk of streaming electrolyte solution between the working and counter electrodes. These additional resistances are analyzed here for the voltage-step transient (VST) process using the Nernst model of a two-electrode cell (no reference electrode). The Faradic resistance is considered for a single redox couple O + ne- = R according to Butler-Volmer electrode kinetics. The effect of Ohmic and Faradic resistances in VST is accounted for using two models: the recently updated 1D approximation and a new model that accepts primary current distribution for a circular electrode. It is shown that the 1D approximation introduces unacceptable errors.
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