55

16. You would like to determine the pressure drop in a slurry pipeline. To do this, you need to know the rheological properties of the slurry. To evaluate these properties, you test the slurry by pumping it through a 1 in. ID tube that is 10 ft long. You find that it takes a 5 psi pressure drop to produce a flow rate of 100 cm3/s in the tube and that a pressure drop of 10 psi results in a flow rate of 300cm3/s. What can you deduce about the rheological characteristics of the slurry from these data? If it is assumed that the slurry can be adequately described by the power law model, what would be the values of the appropriate fluid properties (i.e., the flow index and consistency parameter) for the slurry?

17. A film of paint, 3 mm thick, is applied to a flat surface that is inclined to the horizontal by an angle 0. If the paint is a Bingham plastic, with a yield stress of 150 dyn/cm2, a limiting viscosity of 65 cP, and an SG of 1.3, how large would the angle 0 have to be before the paint would start to run? At this angle, what would the shear rate be if the paint follows the power law model instead, with a flow index of 0.6 and a consistency coefficient of 215 (in cgs units)?

18. A thick suspension is tested in a Couette (cup-and-bob) viscometer that has having a cup radius of 2.05 cm, a bob radius of 2.00 cm, and a bob length of 15 cm. The following data are obtained:

Cup speed (rpm) Torque on bob (dyn cm)

2 2,000

4 6,000

10 19,000

20 50,000

50 150,000

What can you deduce about (a) the viscous properties of this material and (b) the best model to use to represent these data?

19. You have obtained data for a viscous fluid in a cup-and-bob viscometer that has the following dimensions: cup radius = 2 cm, bob radius = 1.5 cm, bob length = 3 cm. The data are tabulated below, where n is the point slope of the log T versus log N curve.

N (rpm)

T (dyn cm)

n

N (rpm)

T (dyn cm)

n

0 0

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