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Home Biochemical Engineering Agitation and Aeration Comments

  • Question
  • The reason of using a flat disk in a Turbine is


  • Options
  • A. to create high shear conditions
  • B. to break up bubbles more efficiently than the impeller blades
  • C. to ensure that the bulk of the energy consumption occurs at the blades
  • D. all of the above

  • Correct Answer
  • to ensure that the bulk of the energy consumption occurs at the blades 


  • Agitation and Aeration problems


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    • 1. Power consumption by agitation is

    • Options
    • A. a function of physical properties
    • B. a function of operating conditions
    • C. a function of vessel and impeller geometry
    • D. all of the above
    • Discuss
    • 2. Power number is ratio of

    • Options
    • A. imposed forced to intertial force
    • B. bouyant force to inertial force
    • C. gravitation force to inertial force
    • D. imposed force to gravitational force
    • Discuss
    • 3. What is the ratio of depth of liquid in vessel to the diameter of tank (H:Dt)?

    • Options
    • A. 1 : 1
    • B. 2 : 1
    • C. 4 : 1
    • D. none of these
    • Discuss
    • 4. Which of the following best explains the reasons for using axial flow impellers in crystallization and precipitation reactions?

    • Options
    • A. Crystal and precipitates are not too small, so as to ensure easy separation of the solids from the mother liquor
    • B. Crystals and precipitates are thoroughly broken down, so as to ensure easy separation of the solids from the mother liquor
    • C. Both (a) and (b)
    • D. Axial flow impellers provide low shear, energy efficient mixing conditions
    • Discuss
    • 5. The average concentration of oxygen in the boundary layers surrounding the bubbles (Co*) in a reactor is normally determined by

    • Options
    • A. ultra-small dissolved oxygen probes
    • B. laser based photographic systems
    • C. measuring the steady state concentration of oxygen in the bulk liquid prior to inoculation of the reactor
    • D. measuring the steady state concentration of oxygen in the bulk liquid after inoculation of the reactor
    • Discuss
    • 6. Why vortexing is undesirable in the agitation of biological systems?

    • Options
    • A. The collision between the cells, impeller and air bubbles will lead to cell damage
    • B. Poor mixing despite the use of high stirrer speeds
    • C. Mixing will not be in the turbulent region
    • D. All of the above
    • Discuss
    • 7. The range of width for the baffle in the fermenter is __________ times of vessel diameter

    • Options
    • A. 1/10 to 1/12
    • B. 1/8 to 1/10
    • C. 1/5 to 1/8
    • D. none of these
    • Discuss
    • 8. Which of the following(s) is/are non-mechanically agitated reactors?

    • Options
    • A. Stirrer tank reactor
    • B. Bubble column
    • C. Air lift reactor
    • D. Both (b) and (c)
    • Discuss
    • 9. An aerated bioreactor will increase oxygen transfer rates with the addition of detergents because it

    • Options
    • A. enhances bubble coalescence
    • B. causes bubbles to expand
    • C. discourages bubble coalescence
    • D. increases the surface tension of the liquid
    • Discuss
    • 10. The average fractional gas hold up (H) can be given as (where Zf and Zl are the level of aerated and clear liquid respectively)

    • Options
    • A. H = (Zf-Zl)/Zf
    • B. H = Zf/Zl
    • C. H = Zf/ZfZl
    • D. H =(Zf+Zl)/Zf
    • Discuss


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