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Home Biochemical Engineering Agitation and Aeration Comments

  • Question
  • In aerobic microorganisms cultures radial flow impellers are used because


  • Options
  • A. they provide energy efficient high turbulent mixing conditions
  • B. they provide low shear mixing conditions
  • C. they provide high shear mixing conditions
  • D. they ensure that bubble size is maximized leading to high oxygen transfer rates

  • Correct Answer
  • they provide high shear mixing conditions 


  • Agitation and Aeration problems


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    • 1. Impeller damage can be minimized by

    • Options
    • A. using specially designed axial flow impellers
    • B. using radial flow impellers
    • C. using Intermig impellers
    • D. all of the above
    • Discuss
    • 2. A fermentation system has a KLa 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

    • Options
    • A. zero
    • B. 15 mg.l-1.s-1
    • C. 10 mg.l-1.s-1
    • D. 5 mg.l-1.s-1
    • Discuss
    • 3. During fermentation, the saturation concentration of oxygen was reduced from 7 ppm. to 1 ppm. Which one of the following conclusions can be drawn?

    • Options
    • A. Microbial growth is oxygen limited since the oxygen concentration is lesser than the saturation concentration
    • B. Microbial growth is not oxygen limited since the oxygen concentration is lesser than the saturation concentration
    • C. Experimental error leads to the reduction
    • D. No conclusion can be drawn
    • Discuss
    • 4. For aerated mixing vessels in an aqueous solution, the mass transfer coefficient (kL) co-relating power consumption (Pm) and fermenter volume (V) can be expressed as

    • Options
    • A. kL ? (Pm/V)0.33
    • B. kL ? (Pm/V)0.66
    • C. kL ? (Pm/V)0.50
    • D. kL ? (Pm/V)
    • Discuss
    • 5. Flooding is a condition/phenomenon which occur in a bioreactor when

    • Options
    • A. The air escapes without being distributed by the agitator
    • B. The fermenter medium spills out the reactor due to foaming
    • C. The volume of foam is more than the volume of broth
    • D. None of the above
    • Discuss
    • 6. A fermentation system has a KLa of 3 s-1 and a C0* of 5 ppm of O2. If the bulk liquid is saturated with oxygen then the oxygen transfer rate will be equal to

    • Options
    • A. zero
    • B. 3 mg.l-1.s-1
    • C. 5 mg.l-1.s-1
    • D. 15 mg.l-1.s-1
    • Discuss
    • 7. If the stirrer speed is too slow, bubbles will accumulate and coalescese under the impeller. This phenomenon is known as a

    • Options
    • A. coalesced impeller
    • B. flooded impeller
    • C. river impeller
    • D. dry impeller
    • Discuss
    • 8. A reactor has a total volume of 50,000 litres. If it has a headspace volume of 10,000 litres, then volume of liquid in the reactor will be

    • Options
    • A. 10,000 l
    • B. 20,000 l
    • C. 30,000 l
    • D. 40,000 l
    • Discuss
    • 9. Reynolds (Rei) number for the impeller is given by (where Di, stirrer diameter; N, stirrer speed, ?, density of fluid and ?, viscosity of fluid)

    • Options
    • A. DiV?/?
    • B. Di2N?/?
    • C. Di2V?/?
    • D. DiN? /?
    • Discuss
    • 10. The advantage of axial flow impellers over radial flow impellers is that axial flow impellers

    • Options
    • A. provide better lift of solids
    • B. provide high shear conditions
    • C. provide low shear conditions
    • D. are cheaper to build
    • Discuss


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