# Fluid Flow – Section 1

36. A stirred tank reactor containing a fluid with a density of 2.5 g.ml-1and viscosity of 0.002 kg m-1s-1 is mixed at 120 rpm. If the fluid is mixed with an impeller having a diameter 50 cm, then the Reynolds number of the liquid in the reactor is

A. 2500
B. 100
C. 12,50,000
D. 1,000,000

37. If the viscosity of a fluid decreases with the length of time that it is being mixed, then this fluid is

A. newtonian
B. rheopectic
C. viscoelastic
D. thixotropic

38. Which of the following describes the importance of the Kolmogorov eddy size in biotechnology?

A. The Kolmogorov eddy size is a measure of the smallest eddy size in a liquid
B. When the Kolmogorov eddy size become equivalent or smaller than the cell or particle diameter, then the cell or particle will become susceptible to shear damage
C. At the Kolmogorov eddy size, much of the energy of the originating eddy will be released
D. All of the above

Correct Answer: D. All of the above

39. A thixotropic 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 mixing time
D. decreases with mixing time

Correct Answer: D. decreases with mixing time

40. Newtonian fluid is one in which the viscosity

A. remains constant with time and power input
B. increases with the level of power input
C. decreases with the level of power input
D. drastically increases with the level of power input

Correct Answer: A. remains constant with time and power input