# Q1: Which of the following will have the highest surface area available for oxygen transfer?

B A standing test tube
C A non-sparged stirred tank reactor agitated at 400 rpm
D A sparged stirred tank reactor agitated at 400 rpm

# Q2: Vortexing in stirred tank reactors can be prevented by

A installing baffles in the reactor
B shifting the impeller to an off-centre position
C Both (a) and (b)
D using axial flow impellers

# Q3: The oxygen transfer rate in a bioreactor will increase if

C detergent like molecules are added
D increase in the reactor temperature

A H = (Zf-Zl)/Zf
B H = Zf/Zl
C H = Zf/ZfZl
D H =(Zf+Zl)/Zf

B turbines
C propellers
D none of these

A 64 h-1
B 32 h-1
C 16 h-1
D 8h-1

# Q7: Which of the following is most likely to cause an increase in the rate of oxygen transfer into a particular aerated fermentation system?

B Increase in temperature
C Increase in stirrer speed
D Both (a) and (b)

# Q8: Henry's law relates

A the partial pressure of oxygen and the saturation concentration of oxygen in the liquid
B the oxygen transfer rate and the bubble size
C the oxygen transfer rate and the temperature
D the oxygen transfer rate to the partial pressure of oxygen in the liquid

# Q9: Power consumption by agitation is

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

# Q10: A flooded impeller will lead to poor oxygen transfer rates because

A bubbles tend to coalesce under the impeller
B bubbles tend to break down too rapidly under high shear conditions
C bubbles tend to move too quickly through the bulk liquid
D the cells clog up the surface of the bubble

A 0.793atml/mmol
B 0.207atml/mmol
C 1.26 atml/mmol
D 8.74 atml/mmol

A Mig
B Intermig
C Turbine
D All of these

# Q13: Gas hold up, characterizing the hydrodynamics in a fermenter, mainly depends on the

A superficial gas velocity
B power consumption
C Both (a) and (b)
D gas concentration

# Q14: A typical ceiling fan would be best described as a(n)

B axial flow impeller
C intermig impeller
D Rushton turbine

A Rei<10
B 10<Rei<104
C Rei>104
D None of these

# Q16: Which have the maximum resistance while transferring carbon dioxide from the bulk liquid to an air bubble?

A Moving through the gas liquid interface
B Moving through the bubble boundary layer
C Moving across the cell membrane
D Moving through the bulk liquid

# Q17: The reason of using a flat disk in a Turbine is

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

A 1 : 1
B 2 : 1
C 4 : 1
D none of these

# Q19: The volume of liquid (VL)in a cylindrical reactor can be calculated from the liquid height (HL) and tank diameter (Dt) using the following equation

A VL = 4/3 x π x HL x Dt3/8
B VL=HL x π x Dt2/4
C VL=HL x π x Dt2
D VL= 4 x π x Dt2

# Q20: If liquid density and viscosity remains constant, then the Reynolds number in a stirred tank reactor will vary with the

A impeller diameter
B square root of the impeller diameter
C square of the impeller diameter
D cube of the impeller diameter

# Q21: Why vortexing is undesirable in the agitation of biological systems?

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

A 1 : 3
B 2 : 1
C 4 : 1
D 1 : 5

# Q23: Penetration theory assumes that turbulent eddies travel from the bulk of the phase to the interface where they remain constant for a constant exposure time (te). The model correlatingKL, mass transfer coefficient and DAB, diffusivity can be expressed as

A KL = 2(DABte)0.25
B KL = 2(DABte)0.5
C KL = 2(DABte)0.75
D KL = 2(DABte)

# Q24: Swirling and vortex formation can be prevented by

A using baffles
B using diffusion ring with turbines
C both (a) and (b)
D none of these

# Q25: Which of the following(s) is/are non-mechanically agitated reactors?

A Stirrer tank reactor
B Bubble column
C Air lift reactor
D Both (b) and (c)

# Q26: The average concentration of oxygen in the boundary layers surrounding the bubbles (Co*) in a reactor is normally determined by

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

A provide high shear conditions for breaking up bubbles
B direct flow towards the walls of the reactor
C Both (a) and (b)
D provide low shear conditions and are suited for use in shear sensitive procesess

# Q28: Surface renewal theory predicts that the mass transfer coefficient is

A directly proportional to the square root of the molecular diffusivity
B inversely proportional to the square root of the molecular diffusivity
C directly proportional to the cube root of the molecular diffusivity
D indirectly proportional to the cube root of the molecular diffusivity

# Q29: Turbine impeller consists of flat impeller blades with

A a vertical pitch welded directly to the shaft
B a angled pitch welded directly to the shaft
C a vertical pitch welded to a horizontal disk
D a angled pitch welded to a horizontal disk

# Q30: Power number is ratio of

A imposed forced to intertial force
B bouyant force to inertial force
C gravitation force to inertial force
D imposed force to gravitational force

# Q31: Which of the following would be best described as an axial flow impeller?

A An impeller with blades pitched at 45° to the vertical
B An impeller which directs liquid flow towards the base of the reactor
C Both (a) and (b)
D An impeller with blades pitched at 75° to the vertical

# Q32: An aerated bioreactor will increase oxygen transfer rates with the addition of detergents because it

A enhances bubble coalescence
B causes bubbles to expand
C discourages bubble coalescence
D increases the surface tension of the liquid

# Q33: Which of the following is not considered among the three best-known theories of interphase mass transfer?

A two-film theory
B penetration theory
C surface renewal theory
D Calderbank and Moo-Young theory

A P0 / N2Di3ρ
B P0 / N3Di5ρ
C P0 / N3Di3ρ
D P0 / N2Di2ρ

# Q35: When liquid is pumped through cooling coil in a stirred tank reactor to cool. Which of the following is not correct?

A If the stirrer speed is increased, the rate will be faster
B Baffles in the tank will increase the rate of cooling
C Faster cooling rates at a slower rate of pumping
D Faster cooling rates at a faster rate of pumping

# Q36: Which of the following impellers will provide radial flow?

D All of the above

A 1/10 to 1/12
B 1/8 to 1/10
C 1/5 to 1/8
D none of these

# Q38: The power consumption in a stirring vessel can be assessed by using a

A dynamometer
B strain gauge attached to agitator shaft
C watt meter attached to agitator motor
D all of these

# Q39: The rate limiting step in the movement of oxygen from the gas phase in a bubble to the cell is the movement of oxygen molecules through

A gas-liquid interface
B bubble boundary layer
C bulk liquid
D gas phase

# Q40: Which of the following best explains the reasons for using axial flow impellers in crystallization and precipitation reactions?

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

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