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| Titel |
The effect of crystal shape, size and bimodality on the maximum packing and the rheology of crystal bearing magma |
| VerfasserIn |
Pranabendu Moitra, Helge Gonnermann |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250095092
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| Publikation (Nr.) |
 EGU/EGU2014-10533.pdf |
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| Zusammenfassung |
| Magma often contains crystals of various shapes and sizes. We present experimental
results on the effect of the shape- and size-distribution of solid particles on the
rheological properties of solid-liquid suspensions, which are hydrodynamically
analogous to crystal-bearing magmas. The suspensions were comprised of either a
single particle shape and size (unimodal) or a mixture of two different particle
shapes and sizes (bimodal). For each type of suspension we characterized the dry
maximum packing fraction of the particle mixture using the tap density method. We then
systematically varied the total volume fraction of particles in the suspension, as well as the
relative proportion of the two different particle types in the bimodal suspensions. For
each of the resultant mixtures (suspensions) we performed controlled shear stress
experiments using a rotational rheometer in parallel-plate geometry spanning 4
orders of magnitude in shear stress. The resultant data curves of shear stress as a
function of shear rate were fitted using a Herschel-Bulkley rheological model. We
find that the dry maximum packing decreases with increasing particle aspect ratio
(ar) and decreasing particle size ratio (λ). The highest dry maximum packing was
obtained at 60-75% volume of larger particles for bimodal spherical particle mixture.
Normalized consistency, Kr, defined as the ratio of the consistency of the suspension
and the viscosity of the suspending liquid, was fitted using a Krieger-Dougherty
model as a function of the total solid volume fraction (Ï). The maximum packing
fractions (Ïm) obtained from the shear experimental data fitting of the unimodal
suspensions were similar in magnitude with the dry maximum packing fractions of the
unimodal particles. Subsequently, we used the dry maximum packing fractions of the
bimodal particle mixtures to fit Kr as a function of Ï for the bimodal suspensions. We
find that Kr increases rapidly for suspensions with larger ar and smaller λ. We
also find that both the apparent yield stress and the shear thinning behavior of the
suspensions increase with increasing ar and become significant at Ï/Ïm ≥ 0.4. |
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