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Home Biochemical Engineering Agitation and Aeration Comments

  • Question
  • 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

  • Correct Answer
  • A bubble with a diameter of 1 mm 


  • Agitation and Aeration problems


    Search Results


    • 1. 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
    • 2. 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
    • 3. 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
    • 4. 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
    • 5. 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
    • 6. The effect of increasing the stirrer speed in an unbaffled stirred tank reactor is that

    • Options
    • A. a small increase in stirrer speed will cause the liquid to enter the turbulent flow regime
    • B. as the stirrer speed increases, the liquid will continue to circulate and then become turbulent
    • C. as the stirrer speed increases, the liquid will continue to circulate. Eventually a vortex will form.
    • D. A vortex will form at low stirrer speeds. As the stirrer speed increases the liquid will start to circulate
    • Discuss
    • 7. Bioreactors, where vortex is formed, another dimensionless number, __________ is useful.

    • Options
    • A. Stanton
    • B. Rayleigh
    • C. Bond
    • D. Froude
    • Discuss
    • 8. Turbulent flow range of mixing speed is obtained for

    • Options
    • A. Rei<10
    • B. 10<Rei<104
    • C. Rei>104
    • D. None of these
    • Discuss
    • 9. Which device is commonly used for measuring the rate of rotation (rpm) of the stirrer shaft?

    • Options
    • A. Anemometer
    • B. Manometer
    • C. Tachometer
    • D. Barometer
    • Discuss
    • 10. Axial flow impellers

    • Options
    • A. provide high shear conditions for breaking up bubbles
    • B. provide low shear conditions and are suited for use in shear sensitive procesess
    • C. provide direct flow towards the walls of the reactor
    • D. none of the above
    • Discuss


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