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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/m3) immersed in corn syrup (Karo corn syrup with density=1400kg/m3 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 (Fp =0,5,10,20,30%). Microscopic viscosity was measured by falling stainless steel balls of three different radius (0.75mm with density=9620kg/m3 , 2.5mm with density=7960kg/m3, 4.76mm with density=7950kg/m3) 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 Rsusp=0.75mm, where Rsusp is the radius of the suspended particles, the ratio of values of microscopic viscosity to those of macroscopic viscosity, ηmicro/ηmacro, were about 0.7~0.9 under the conditions that Rfall/Rsusp is 1.0 or 3.3, where Rfall is the radius of the falling ball, and Fp is less than 20%. Moreover, it is suggested that ηmicro/ηmacro is almost 1 under the condition that Rfall/Rsusp is 6.4 and Fp is less than 30%. At Rsusp=1.5mm, ηmicro/ηmacro is ranging from 0.6 to 0.9 under the conditions that Rfall/Rsusp is 0.5. 1.7, or 3.2 and Fp is less than 20%.
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