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| Titel |
How crystals affect magma rheology |
| VerfasserIn |
Sebastian Mueller, Edward W. Llewellin, Heidy M. Mader |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250041127
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| Zusammenfassung |
| The presence of solid particles in a liquid melt inevitably affects its flow behaviour: the
crystals increase the bulk viscosity of the magma, and may impede flow at low driving
stresses and cause shear thinning at increasing strain rates. Despite a multitude of theoretical
and experimental investigations on suspension rheology no comprehensive flow model exists
that satisfactorily accounts for the effects of particle concentration, particle shape and strain
rate.
We here present the data of an analogue experimental study, aimed to cover a broadest
possible parameter space. We have measured suspensions of monodisperse particles of
varying aspect ratio, from oblate to prolate, and covering particle volume fractions Ï from
dilute to highly concentrated. Rheology is characterized by fitting the experimental data to the
model of Herschel & Bulkley (1926), yielding three rheometric parameters: consistency K
(cognate with viscosity); flow index n (a measure of shear-thinning); yield stress Ï0. We
develop models to predict these three parameters in dependence of particle aspect
ratio.
We relate our rheological observations to the underlying particle motions via Jeffery’s
(1922) theory. We extend Jeffery’s work to calculate, numerically, the Einstein
coefficient for a suspension of many, initially randomly oriented particles. This
provides a physical, microstructural explanation of our observations, including
transient oscillations seen during run start-up and changes of rheological regime as Ï
increases. |
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