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# [SVC49-01] The difference between microscopic viscosity and macroscopic viscosity of crystal-bearing magmas

Material and Experimental Technique: Suspensions of plastic beads of two different radius (0.75mm, 1.5mm with density=930kg/m

^{3}) immersed in corn syrup (Karo corn syrup with density=1400kg/m

^{3}and viscosity η~7 Pa・s at 23℃) were used as analogues of crystal-bearing magmas. We prepared ten different suspensions by changing particle radius (0.75mm,1.5mm) and particle volume fractions (F

_{p}=0,5,10,20,30%). Microscopic viscosity was measured by falling stainless steel balls of three different radius (0.75mm with density=9620kg/m

^{3 }, 2.5mm with density=7960kg/m

^{3}, 4.76mm with density=7950kg/m

^{3}) into a 100ml, φ51mm glass beaker filled with the magma analogue. Macroscopic viscosity was measured using a coaxial double cylinder rotational viscometer that is of Kawanami’s own making. We changed the voltage (1.0V, 1.5V, 3.0V) applied to the motor, to investigate the shear thinning behavior.

Results: We used the viscosities measured with a rotational viscometer driven by 1V as representative macroscopic viscosities, because the effect of shere thinning looks low enough. At R

_{susp}=0.75mm, where R

_{susp}is the radius of the suspended particles, the ratio of values of microscopic viscosity to those of macroscopic viscosity, η

_{micro}/η

_{macro}, were about 0.7~0.9 under the conditions that R

_{fall}/R

_{susp}is 1.0 or 3.3, where R

_{fall}is the radius of the falling ball, and F

_{p}is less than 20%. Moreover, it is suggested that η

_{micro}/η

_{macro}is almost 1 under the condition that R

_{fall}/R

_{susp}is 6.4 and F

_{p}is less than 30%. At R

_{susp}=1.5mm, η

_{micro}/η

_{macro}is ranging from 0.6 to 0.9 under the conditions that R

_{fall}/R

_{susp}is 0.5. 1.7, or 3.2 and F

_{p}is less than 20%.

Reference

[1]Milliken WJ et al. (1989) Physicochem Hydrodynam, 11(3), 341-355.

[2]Gaudio PD et al. (2013) Geochemistry Geophysics Geosystems, 14(8), 2661-2669.