# Viscosity Problem using power law for non-newtonian fluids

1. Apr 2, 2012

### jetpacks

Problem Statement:
Blood is a pseudoplastic fluid that has a variable viscosity at 37 °C that depends on the percent composition of hematocrit and plasma. It will usually range between 3 x 10^-3 to 4 x 10^-3 Pa s. A small sample of blood is tested in a viscometer and the following results are obtained:

(Shear stress (Pa), Shear rate (s^-1))
(0.0235, 2.25)
(0.0396, 4.5)
(0.0787, 11.25)
(0.1324, 22.5)
(0.2227, 45)
(0.3746, 90)
(0.7447, 225)
(1.2524, 450)

Determine the viscosity of the blood sample using the power law for non-Newtonian fluids:

τ=ηγ^n

where τ is shear stress, η is viscosity, γ is shear rate, and n is the flow behavior index.
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I have no idea where to start, since I have two unknowns in this problem. It also seems like the sample would have a different viscosity at each point, but the problem only asks for one value. I am truly lost. Any help or insight would be greatly appreciated!