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Author:Mohtaschemi, Mikael
Title:Modelling transient shear banding in Couette geometry
Tilapäisten leikkausvöiden mallintaminen Couette-geometriassa
Publication type:Master's thesis
Publication year:2011
Pages:vi + 58      Language:   eng
Department/School:Teknillisen fysiikan laitos
Main subject:Fysiikka (laskennallinen fysiikka)   (Tfy-105)
Supervisor:Alava, Mikko
Instructor:Puisto, Antti
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  214   | Archive
Keywords:transient shear banding
population balance equations
simple yield stress fluid
rheology
tilapäinen leikkausvyö
populaatiotasapainoyhtälöt
myötörajaneste
reologia
Abstract (eng): Long-living transient shear banding in a simple yield stress fluid has recently been observed in Couette rheometer.

Here a computational model which shows qualitatively similar behavior to the experimental findings is investigated in detail.
The model is based on population balance equations which are frequently used to model colloids.

An attempt is made to fit the experimental results and to reproduce the experimentally found relationship between the characteristic scalings between the shear rate and stress controlled fluidization times and the Herschel - Bulkley fit to the steady state flow curve.

No exact fit could be obtained and the relationship could not be unambiguously reproduced with the model.

At low shear rates deviations from the power-law scaling in the fluidization times were obtained.
These are most likely due to the geometry induced stress heterogeneity and the stress plateau in the flow curve.
Abstract (fin): Pitkäikäistä, tilapäistä leikkausjuovaisuutta (transient shear banding) on äskettäin kokeellisesti havaittu yksinkertaisissa myötörajanesteissä Couette reometrissä.

Tässä työssä on yksityiskohtaisesti tutkittu laskennallista mallia, joka osoittaa laadullisesti samanlaista käyttäytymistä kokeellisten havaintojen kanssa.
Malli pohjautuu populaatiotasapainoyhtälöihin (PBE), joita käytetään usein kolloidien mallinnuksessa.

Työssä mallia yritetään sovittaa koetuloksiin ja toistaa kokeellisesti todettu suhde nesteytymisaikojen (fluidization time) skaalauseksponenttien ja virtauskäyrän Herschel - Bulkley sovituksen parametrien välillä.
Tarkka sovitus ei ollut mahdollinen, eikä kokeellista riippuvuutta eksponenttien välillä voitu yksiselitteisesti todentaa mallilla.

Alhaisilla leikkausnopeusarvoilla havaittiin poikkeama nesteytymisaikojen potenssilakiskaalautuvuudesta.
Poikkeamat ovat peräisin todennäköisesti geometriasta johtuvasta stressin heterogeenisuudesta ja virtauskäyrän muodosta.
ED:2011-10-24
INSSI record number: 42887
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