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Home Biochemical Engineering Agitation and Aeration Comments

  • Question
  • 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? /?

  • Correct Answer
  • Di2N?/? 


  • Agitation and Aeration problems


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    • 1. 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
    • 2. 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
    • 3. 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
    • 4. 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
    • Discuss
    • 5. 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
    • 6. 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
    • 7. In a bioreactor, if at a particular time the oxygen transfer rate is 23 kg.h-1, then the oxygen uptake will be

    • Options
    • A. 23 kg.h-1
    • B. less than 23 kg.h-1
    • C. greater than 23 kg.h-1
    • D. 2.3 kg.h-1
    • Discuss
    • 8. In a two-phase system where the continuous phase remains in place, the gas hold up can be expressed as (where Vs and Vt are the superficial gas velocity and bubble rise velocity)

    • Options
    • A. H = Vs/(Vs-Vt)
    • B. H = Vs/(Vs+ Vt)
    • C. H = Vs/(Vs.Vt)
    • D. H = (Vs+Vt)/Vs
    • Discuss
    • 9. For turbulent flow, Reynolds number is correlated with power number as (where K, a constant which depends on the container geometry and shape of stirrer; Rei, is Reynolds number for agitator; Di, stirrer diameter and N, stirrer speed)

    • Options
    • A. Np = K(Rei)-1
    • B. Np = N2Di(Rei)-1
    • C. Np = K
    • D. Can't be correlated
    • Discuss
    • 10. Which of the following will have the largest interfacial area per unit volume?

    • Options
    • A. A bubble with a diameter of 1 mm
    • B. A bubble with a diameter of 5 mm
    • C. A bubble with a diameter of 15 mm
    • D. A bubble with a diameter of 50 mm
    • Discuss


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