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Home Biochemical Engineering Agitation and Aeration Comments

  • Question
  • During aeration, a cylindrical reactor had a height of 10 m. Without aeration, the height was 7.5 m. Under these aeration and mixing conditions, the gas hold up in the reactor is


  • Options
  • A. 100%
  • B. 75%
  • C. 50%
  • D. 25%

  • Correct Answer
  • 25% 


  • Agitation and Aeration problems


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    • 1. The dynamic technique is based on the

    • Options
    • A. oxygen material balance in an aerated batch fermenter during the growth of microorganisms
    • B. change of the oxygen concentration
    • C. oxidation of the sodium sulfite to sodium sulfate
    • D. oxygen material balance in a fermenter
    • Discuss
    • 2. The addition of antifoams to an aerated bioreactor will decrease oxygen transfer rates because antifoams

    • Options
    • A. increase the tendency of bubbles to coalesce
    • B. tend to accumulate in the gas liquid interface
    • C. reduce the surface tension of the liquid
    • D. All of the above answers
    • Discuss
    • 3. In the bubble boundary layer, oxygen concentration can be determined by measuring

    • Options
    • A. the steady state oxygen concentration in a mixed aerated reactor before inoculation
    • B. the steady state oxygen concentration in a mixed aerated reactor after inoculation
    • C. the steady state oxygen concentration in the boundary layer using a micro-probe
    • D. volume of oxygen supplied
    • Discuss
    • 4. What is/are the major difference(s) between disc and turbine type stirrer?

    • Options
    • A. Blades in disc type are projected out beyond the edge of disc while blades are curved one in turbine type
    • B. Turbine type requires 50 % less air than disc type for the same yield and energy consumption
    • C. Both (a) and (b)
    • D. Number of blades in the stirrer
    • Discuss
    • 5. Larger propellers turn at the speed of

    • Options
    • A. 20 to 150 rpm
    • B. 150 to 300 rpm
    • C. 400 to 800 rpm
    • D. 1150 rpm
    • Discuss
    • 6. 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
    • 7. 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
    • 8. 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
    • 9. 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
    • 10. 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


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