Biochemical Engineering Objective Questions { Fluid Flow }

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8. If the viscosity of a fluid decreases with increasing stirrer speed, then the nature of the fluid is

B. pseudoplastic

9. A pseudoplastic fluid is one in which the viscosity

A. is constant regardless of the stirrer speed or mixing time

B. changes during mixing but returns to its original state after mixing

C. increases with increasing stirrer speed

D. decreases with increasing stirrer speed

10. A viscoelastic fluid is one in which the viscosity

A. is constant regardless of the stirrer speed or mixing time

B. changes during mixing but returns to its original state after mixing

C. increases with increasing stirrer speed

D. decreases with increasing stirrer speed

11. Mixing in stirred tank reactors can

A. be described as either laminar, transient or turbulent

B. achieve turbulent conditions by increasing the stirrer speed

C. induce laminar flow conditions by the addition of baffles

D. all of the above

12. In animal cell bioreactor, bubble damage can be minimized by

A. the addition of a shear protectorant

B. using a bubble free oxygen delivery system

C. headspace aeration

D. all of the above

13. The viscosity of a fluid changes with either stirrer speed or mixing time. But when mixing ceases, the viscosity returns to its original state. This fluid is best described as

C. viscoelastic

14. In sparged mammalian cell bioreactors, the cell damage is caused because of

A. shear stress arising during mixing of the cell culture fluid

B. shear stresses arising from the breakup of bubbles at the liquid surface

C. shear stresses between bubbles in foam at the liquid surface

D. all of the above

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