Agitation and Aeration – Section 2

31. Larger propellers turn at the speed of

A. 20 to 150 rpm
B. 150 to 300 rpm
C. 400 to 800 rpm
D. 1150 rpm

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32. A microbial population in a suspension culture will only be limited by oxygen availability if the dissolved oxygen

A. concentration is less than the critical concentration
B. concentration is greater than the critical concentration
C. levels are greater than the saturation concentration of oxygen
D. levels are equal to saturation oxygen level

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33. Which of the following model holds correct for the two-film theory? (where K_L is the mass transfer coefficient, D_AB diffusivity and Z_f film thickness)

A. K_L= D_AB/Z_f
B. K_L= D_AB
C. K_L = Z_f/D_AB
D. K_L= D_AB.Z_f

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34. Froude number is avoided in the calculation of power requirements for low viscosity liquid mixing systems when

A. baffled systems are used
B. Reynolds number is less than 300
C. both (a)and(b)
D. none of these

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35. A fermentation system has a K_La of 3 s^-1 and a C₀* of 5 ppm of O₂. If the bulk liquid is completely depleted of oxygen, then the oxygen transfer rate will be equal to

A. zero
B. 15 mg.l^-1.s^-1
C. 10 mg.l^-1.s^-1
D. 5 mg.l^-1.s^-1

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