CHEMICAL ENGINEERING

FLOW IN PIPES AND CHANNELS 49

25000

20000

Shear stress (N/m

2 )

15000

10000

5000

0 500 1000

Shear rate (s−^1 )

1500 2000 3000

Slope = 6.4 Ns/m^2

Intercept = 1500 N/m^2

Figure 3g.

100,000

10,000

Shear stress (N /m

2 )

1000

10 100 1000

Shear rate (s−^1 )

10,000 100,000

Figure 3h.

(b) a large pump should force the material through the present line, or

(c) a large pump should supply the liquid through a line of twice the cross-sectional

area.

Given that theflow properties of the pur ́ee can be described by the Casson equation:

Ry^1 /^2 DRY^1 /^2 C

(

 (^) c
dux
dy

) 1 / 2

whereRYis a yield stress, here 20 N/m^2 , (^) cis a characteristic Casson plastic viscosity,
5Ns/m^2 ,anddux/dyis the velocity gradient, evaluate the relative pressure drops of the
three suggestions, assuming laminarflow throughout.