Question 9.4: Power Law Model Test data from a rheometer of several test ......

Solved Practical Problems in Fluid Mechanics [1011255]

Power Law Model

Test data from a rheometer of several test fluids are considered to be described by the power law relationship:

$\tau=k\dot{\gamma}^{n}$ (9.11)

If the consistency parameter k for all the fluids is 0.01 (Nsm $^{–2})^n$ , illustrate the variation of shear stress with shear rate for values of n of 0.9, 1, and 1.1 up to shear rates of 100 s $^{–1}$ .

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The calculation of the shear stress is given in Figure 9.8. With the straight line that corresponds to a Newtonian fluid (n = 1), the curve above (n > 1) corresponds to a dilatant while the curve below corresponds to a pseudoplastic (n < 1).

9.8

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