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Home Biochemical Engineering Agitation and Aeration Comments

  • Question
  • Small propellers turn at the speed of either


  • Options
  • A. 20 or 150 rpm
  • B. 150 or 300 rpm
  • C. 400 or 800 rpm
  • D. 1150 rpm or 1750 rpm

  • Correct Answer
  • 1150 rpm or 1750 rpm 


  • Agitation and Aeration problems


    Search Results


    • 1. Main reason for using baffles in stirred tank reactors are

    • Options
    • A. baffles permit turbulence conditions to arise at low stirrer speed
    • B. baffles will allow axial mixing to occur even with radial flow impellers
    • C. both (a) and (b)
    • D. baffles prevent turbulent conditions in stirred tank reactors
    • Discuss
    • 2. Which of the following would be best described as a radial flow impeller?

    • Options
    • A. An impeller with blades pitched at 45° to the vertical
    • B. A Rushton turbine
    • C. Both (a) and (b)
    • D. An impeller which directs liquid flow towards the base of the reactor
    • Discuss
    • 3. Power number (Np) is also known as

    • Options
    • A. Froude's number
    • B. Bond's number
    • C. Newton's number
    • D. Rayleigh's number
    • Discuss
    • 4. When the height of an aerated bioreactor is increased, it will increase the oxygen transfer rate by

    • Options
    • A. increasing the partial pressure of oxygen at the base of the reactor
    • B. decreasing the saturation concentration of oxygen in the reactor
    • C. decreasing the gas-holdup
    • D. all of the above
    • Discuss
    • 5. A cylindrical reactor has a liquid volume of 100,000 litres. It has an aspect ratio the ratio of the channel height to width of 1:1. The height of the liquid in the reactor will be approximately:

    • Options
    • A. 1.0 m
    • B. 3.0 m
    • C. 5.0 m
    • D. 7.0 m
    • Discuss
    • 6. A microbial population in a suspension culture will only be limited by oxygen availability if the dissolved oxygen

    • Options
    • 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
    • Discuss
    • 7. Which of the following model holds correct for the two-film theory? (where KL is the mass transfer coefficient, DAB diffusivity and Zf film thickness)

    • Options
    • A. KL = DAB/Zf
    • B. KL = DAB
    • C. KL = Zf/DAB
    • D. KL = DAB.Zf
    • Discuss
    • 8. Higher temperatures affect oxygen transfer rates by

    • Options
    • A. increasing KLa but lowering C*o
    • B. lowering KLa but increasing C*o
    • C. increasing KLa and increasing Co
    • D. lowering KLa and lowering Co
    • Discuss
    • 9. In the design of a paddle agitator, the ratio of paddle diameter to tank diameter is normally taken as

    • Options
    • A. 0.1
    • B. 0.8
    • C. 0.25
    • D. 0.5
    • Discuss
    • 10. The maximum solubility of the alkane in the medium is 5 ppm. If the actual dissolved concentration of the alkane in the medium is 1 ppm. what conclusion may be drawn?

    • Options
    • A. The growth rate is limited by the rate of mass transfer of the alkane into the fermentation medium
    • B. The growth rate is limited by the intrinsic kinetic properties of the cells and not by mass transfer
    • C. The growth rate is neither mass transfer nor kinetically limited
    • D. No conclusion on the growth rate can be withdrawn
    • Discuss


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