Q.1 Which scale‑up criterion maintains the same power input per unit volume (P/V) when moving from a laboratory to a pilot‑scale bioreactor?
Constant tip speed
Constant Reynolds number
Constant power per volume (P/V)
Constant impeller diameter
Explanation - Keeping P/V constant ensures that the energy supplied to the fluid per unit volume is the same, which helps maintain similar mixing and mass‑transfer conditions during scale‑up.
Correct answer is: Constant power per volume (P/V)
Q.2 When scaling up a bioreactor, which dimensionless number is most directly related to the ratio of inertial to viscous forces and thus to mixing intensity?
Reynolds number (Re)
Damköhler number (Da)
Sherwood number (Sh)
Biot number (Bi)
Explanation - Re = (ρND^2)/μ represents the balance between inertial and viscous forces; a higher Re indicates more turbulent flow and better mixing.
Correct answer is: Reynolds number (Re)
Q.3 In a stirred‑tank bioreactor, which parameter is most commonly used to estimate the oxygen transfer rate (OTR)?
KLa (volumetric mass‑transfer coefficient)
P/V (power input per volume)
Tip speed
Impeller clearance
Explanation - OTR = KLa (C* – C), where KLa quantifies how quickly oxygen moves from the gas phase into the liquid; it is the key design parameter for oxygen supply.
Correct answer is: KLa (volumetric mass‑transfer coefficient)
Q.4 Which geometric similarity rule should be followed when scaling up a cylindrical bioreactor to keep the liquid‑filled height to diameter ratio constant?
Maintain the same impeller diameter
Keep the same H/D ratio
Keep the same tip speed
Maintain the same P/V
Explanation - Geometric similarity requires all linear dimensions to scale proportionally; preserving the height‑to‑diameter (H/D) ratio maintains the same aspect ratio.
Correct answer is: Keep the same H/D ratio
Q.5 What is the primary disadvantage of using constant tip speed as a scale‑up criterion for large‑volume bioreactors?
Excessive shear stress on cells
Reduced oxygen transfer
Increased power consumption
Difficulty in maintaining temperature
Explanation - Tip speed scales with impeller diameter; at larger scales the same tip speed can generate high shear, potentially damaging shear‑sensitive cells.
Correct answer is: Excessive shear stress on cells
Q.6 Which impeller type is most commonly used in large‑scale mammalian cell culture bioreactors to minimize shear?
Rushton turbine
Pitched‑blade turbine
Marine impeller
Axial flow (hydrofoil) impeller
Explanation - Hydrofoil or axial flow impellers provide gentle mixing with lower shear compared to radial impellers like Rushton turbines, making them suitable for fragile cells.
Correct answer is: Axial flow (hydrofoil) impeller
Q.7 When scaling up a bioreactor based on the constant volumetric mass‑transfer coefficient (KLa), which operating condition is typically adjusted?
Impeller clearance
Aeration rate
Impeller diameter
Reactor wall material
Explanation - KLa is strongly influenced by gas flow; increasing aeration can compensate for the loss of surface area when scaling up while keeping KLa constant.
Correct answer is: Aeration rate
Q.8 The dimensionless number Damköhler (Da) compares which two phenomena in a bioreactor?
Mass transfer to reaction rate
Inertial forces to viscous forces
Heat transfer to conduction
Diffusion to convection
Explanation - Da = (reaction rate)/(mass‑transfer rate); it indicates whether the process is reaction‑limited or mass‑transfer‑limited.
Correct answer is: Mass transfer to reaction rate
Q.9 In scale‑up, why is the ratio of impeller diameter to tank diameter (D/T) often kept between 0.3 and 0.5?
To ensure adequate power consumption
To avoid vortex formation
To maintain similar flow patterns
To maximize surface area for gas exchange
Explanation - A D/T ratio in this range provides comparable flow structures and mixing zones across scales, preserving process performance.
Correct answer is: To maintain similar flow patterns
Q.10 Which of the following is a key advantage of using Computational Fluid Dynamics (CFD) during bioreactor scale‑up?
Eliminates need for experimental validation
Predicts temperature gradients and shear zones
Reduces power consumption automatically
Increases the KLa without hardware changes
Explanation - CFD models fluid flow, temperature, and shear stress, allowing engineers to identify problematic regions before building the larger reactor.
Correct answer is: Predicts temperature gradients and shear zones
Q.11 During scale‑up, which factor most directly influences the formation of a vortex at the liquid surface?
Aeration rate
Impeller clearance
Impeller speed (N)
Reactor height
Explanation - Higher impeller speeds increase the centrifugal forces that can draw liquid up the impeller shaft, leading to vortex formation.
Correct answer is: Impeller speed (N)
Q.12 If a lab‑scale bioreactor operates at 1 kW m⁻³ (P/V) and the target pilot scale volume is 100 L, what is the required total power input?
100 W
1 kW
10 kW
0.1 kW
Explanation - P/V = 1 kW/m³ = 1 W/L. For 100 L, total power = 1 W/L × 100 L = 100 W.
Correct answer is: 100 W
Q.13 Which scale‑up strategy is most appropriate when the bioprocess is limited by oxygen transfer?
Constant impeller diameter
Constant tip speed
Constant KLa
Constant Reynolds number
Explanation - Maintaining the same volumetric mass‑transfer coefficient ensures that oxygen availability per unit volume does not become a bottleneck.
Correct answer is: Constant KLa
Q.14 What is the effect of increasing the impeller clearance (distance from impeller to tank bottom) on mixing time?
Mixing time decreases
Mixing time is unchanged
Mixing time increases
Mixing time first decreases then increases
Explanation - Larger clearance reduces the impeller’s ability to sweep the lower region of the tank, leading to slower homogenization.
Correct answer is: Mixing time increases
Q.15 For a bioreactor using a 4‑blade marine impeller, which parameter is most likely to be kept constant during scale‑up to preserve shear conditions?
Tip speed
Impeller diameter
Impeller clearance
Gas sparger design
Explanation - Tip speed is directly related to shear; keeping it constant helps avoid excessive shear stress on cells at larger scales.
Correct answer is: Tip speed
Q.16 Which of the following best describes the relationship between Reynolds number (Re) and flow regime in a stirred‑tank bioreactor?
Re < 10 000 → Turbulent flow
Re > 10 000 → Laminar flow
Re < 10 000 → Laminar flow
Re > 10 000 → Transitional flow
Explanation - Typically, Re < 10 000 indicates laminar flow, 10 000–10 0000 transitional, and >10 0000 turbulent flow in stirred tanks.
Correct answer is: Re < 10 000 → Laminar flow
Q.17 When scaling up a bioreactor, which factor most strongly influences the scale‑up of heat removal capacity?
Impeller type
Cooling jacket surface area
Aeration rate
Impeller speed
Explanation - Heat removal depends on the area available for heat exchange; larger reactors need proportionally larger cooling surfaces.
Correct answer is: Cooling jacket surface area
Q.18 In the context of scale‑up, what does the term "geometric similarity" imply?
All dimensionless numbers are identical
All linear dimensions are scaled by the same factor
Power consumption is identical
Shear rates are identical
Explanation - Geometric similarity means the shape of the reactor is preserved; each dimension is multiplied by the same scaling factor.
Correct answer is: All linear dimensions are scaled by the same factor
Q.19 Which scale‑up criterion is most suitable for processes that are highly sensitive to shear stress?
Constant power per volume (P/V)
Constant tip speed
Constant Reynolds number
Constant impeller clearance
Explanation - Tip speed correlates with shear; keeping it constant limits shear exposure across scales.
Correct answer is: Constant tip speed
Q.20 If the volumetric oxygen transfer coefficient (KLa) in a 5 L bioreactor is 0.2 s⁻¹, what KLa should be targeted in a 500 L pilot reactor to keep oxygen transfer per volume constant?
0.02 s⁻¹
0.2 s⁻¹
2 s⁻¹
0.004 s⁻¹
Explanation - Maintaining the same KLa value ensures that the oxygen transfer rate per unit volume remains unchanged, independent of total volume.
Correct answer is: 0.2 s⁻¹
Q.21 Which of the following is a common method to increase KLa in a large‑scale bioreactor without changing the impeller design?
Increase liquid viscosity
Decrease sparger hole size
Reduce aeration rate
Increase temperature
Explanation - Smaller sparger holes produce finer bubbles, increasing interfacial area and thus raising KLa.
Correct answer is: Decrease sparger hole size
Q.22 When scaling up a bioreactor, the term "scale‑up factor" usually refers to:
The ratio of impeller speeds
The ratio of reactor volumes
The ratio of power inputs
The ratio of gas flow rates
Explanation - Scale‑up factor = V_large / V_small; it defines how many times larger the new reactor is compared to the original.
Correct answer is: The ratio of reactor volumes
Q.23 In a bioreactor, the term "mixing time" is defined as:
Time required to reach steady‑state temperature
Time required for a tracer to become uniformly distributed
Time required to achieve the target pH
Time required for cells to reach maximum density
Explanation - Mixing time is measured by introducing a tracer (e.g., dye) and recording the time for its concentration to become uniform throughout the vessel.
Correct answer is: Time required for a tracer to become uniformly distributed
Q.24 Which factor most directly affects the tip speed (U_tip) of an impeller?
Impeller diameter (D)
Reactor height
Aeration rate
Liquid viscosity
Explanation - U_tip = π D N; it depends on both impeller diameter and rotational speed.
Correct answer is: Impeller diameter (D)
Q.25 During scale‑up, if the power number (Np) for a given impeller remains constant, what does this imply about the flow regime?
The flow is laminar
The flow is turbulent
The flow is transitional
The flow is stagnant
Explanation - In turbulent flow, Np becomes independent of Reynolds number and stays roughly constant for a given impeller geometry.
Correct answer is: The flow is turbulent
Q.26 What is the typical effect of increasing the gas sparger height above the liquid surface on oxygen transfer in a bioreactor?
KLa decreases
KLa remains unchanged
KLa increases
Shear stress dramatically rises
Explanation - A higher sparger promotes better gas dispersion and bubble residence time, which enhances the volumetric mass‑transfer coefficient.
Correct answer is: KLa increases
Q.27 If a bioreactor operates at a constant Reynolds number during scale‑up, which of the following will change proportionally?
Impeller speed (N)
Impeller diameter (D)
Liquid density (ρ)
Viscosity (μ)
Explanation - Re = (ρ N D²)/μ; keeping Re constant while increasing D requires reducing N proportionally.
Correct answer is: Impeller speed (N)
Q.28 Which of the following statements about the Damköhler number (Da) is correct for a bioprocess limited by substrate diffusion?
Da > 1 indicates diffusion limitation
Da < 1 indicates diffusion limitation
Da = 1 means reaction and diffusion rates are equal
Da does not apply to diffusion processes
Explanation - Da = (reaction rate)/(mass‑transfer rate). When Da = 1, both phenomena proceed at comparable rates; Da > 1 shows reaction‑limited, Da < 1 shows diffusion‑limited.
Correct answer is: Da = 1 means reaction and diffusion rates are equal
Q.29 When scaling up a bioreactor, why is it often necessary to redesign the sparger geometry?
To increase reactor pressure
To maintain the same bubble size distribution
To reduce impeller clearance
To change the reactor material
Explanation - Bubble size influences gas‑liquid interfacial area; preserving it across scales helps keep KLa consistent.
Correct answer is: To maintain the same bubble size distribution
Q.30 Which scaling principle is most appropriate when the bioprocess is limited by heat removal rather than mass transfer?
Constant P/V
Constant surface‑to‑volume ratio (A/V)
Constant tip speed
Constant Reynolds number
Explanation - Heat removal is proportional to the area available for heat exchange; keeping A/V constant helps maintain similar thermal conditions.
Correct answer is: Constant surface‑to‑volume ratio (A/V)
Q.31 If the pilot‑scale bioreactor has an impeller diameter of 0.5 m and the laboratory reactor has a diameter of 0.1 m, what is the geometric scale factor?
5
0.2
10
0.5
Explanation - Scale factor = D_pilot / D_lab = 0.5 m / 0.1 m = 5.
Correct answer is: 5
Q.32 During scale‑up, which parameter is most directly related to the formation of dead zones (areas with low mixing) in a stirred tank?
Impeller clearance
Gas flow rate
Reactor wall material
Temperature set point
Explanation - If the impeller is too far from the tank bottom, a region near the bottom may experience insufficient agitation, forming a dead zone.
Correct answer is: Impeller clearance
Q.33 Which of the following is NOT a typical reason for scaling up a bioreactor?
Increasing product yield
Reducing equipment cost per unit volume
Improving cell viability
Validating a new fermentation strain
Explanation - Strain validation is usually performed at small scale before scale‑up; the other options are primary motivations for scale‑up.
Correct answer is: Validating a new fermentation strain
Q.34 When scaling up, if the volumetric power input (P/V) is kept constant, how does the impeller speed (N) change with increasing impeller diameter (D) assuming constant fluid properties?
N increases with D
N decreases with D
N stays the same
N varies unpredictably
Explanation - P/V ∝ N³ D²; keeping P/V constant while increasing D requires a lower N.
Correct answer is: N decreases with D
Q.35 In a scale‑up study, the measured KLa in a 10 L reactor is 0.15 s⁻¹ at an aeration rate of 0.5 vvm. What aeration rate (vvm) would you initially try in a 100 L reactor to achieve a similar KLa, assuming all other factors remain the same?
0.05 vvm
0.5 vvm
5 vvm
0.25 vvm
Explanation - If geometry and agitation are maintained, the same vvm (volumes of gas per volume of liquid per minute) often yields similar KLa.
Correct answer is: 0.5 vvm
Q.36 Which of the following statements best describes why constant tip speed is sometimes unsuitable for scaling up high‑viscosity processes?
Viscous fluids require higher tip speeds for mixing
Tip speed does not affect shear in viscous fluids
Maintaining tip speed can lead to excessive power consumption
Viscous fluids are insensitive to tip speed
Explanation - High viscosity raises the torque needed; keeping tip speed constant can demand impractically high power, making the criterion unsuitable.
Correct answer is: Maintaining tip speed can lead to excessive power consumption
Q.37 In a bioreactor, the term "specific oxygen uptake rate (qO₂)" refers to:
Oxygen dissolved per unit time per volume
Oxygen consumed per cell per unit time
Oxygen transferred from gas to liquid per minute
Oxygen concentration in the inlet gas
Explanation - qO₂ is a cell‑specific parameter (e.g., mmol O₂·g⁻¹·h⁻¹) that indicates the metabolic demand of the culture.
Correct answer is: Oxygen consumed per cell per unit time
Q.38 Which of the following scale‑up criteria directly controls the shear environment experienced by cells?
Constant P/V
Constant tip speed
Constant KLa
Constant surface‑to‑volume ratio
Explanation - Shear stress correlates with tip speed; keeping it constant helps maintain a comparable shear environment.
Correct answer is: Constant tip speed
Q.39 If the Reynolds number in a lab‑scale reactor is 8 000 (laminar‑to‑transitional) and the impeller diameter is doubled for the pilot scale, what must happen to the impeller speed to keep Re the same?
Increase speed by a factor of 4
Decrease speed by a factor of 2
Increase speed by a factor of 2
Decrease speed by a factor of 4
Explanation - Re ∝ N D²; if D doubles (×2), to keep Re constant N must be reduced by (1/2).
Correct answer is: Decrease speed by a factor of 2
Q.40 Which measurement technique is most commonly used to determine mixing time in a stirred bioreactor?
Thermocouple temperature response
pH probe response
Conductivity tracer method
Optical density monitoring
Explanation - A small amount of conductive salt is added, and the time for the conductivity signal to stabilize indicates mixing time.
Correct answer is: Conductivity tracer method
Q.41 During scale‑up, why might a bioprocess engineer choose to increase the number of impellers rather than the impeller diameter?
To reduce the overall reactor height
To lower the overall power consumption
To improve axial mixing without increasing shear
To increase the reactor’s surface‑to‑volume ratio
Explanation - Multiple smaller impellers can provide better axial flow while keeping tip speed (and shear) lower than a single large impeller.
Correct answer is: To improve axial mixing without increasing shear
Q.42 Which of the following best describes the relationship between gas hold‑up (ε) and aeration rate in a stirred bioreactor?
ε decreases as aeration rate increases
ε is independent of aeration rate
ε increases with aeration rate
ε is only affected by impeller speed
Explanation - Higher gas flow introduces more bubbles, raising the volumetric gas hold‑up in the liquid.
Correct answer is: ε increases with aeration rate
Q.43 When scaling up a bioreactor, which factor most strongly influences the choice of material for the reactor vessel?
Desired power per volume
Compatibility with the product (sterility, corrosion)
Reactor geometry
Impeller type
Explanation - Material must meet regulatory and process requirements; scaling up does not change this primary consideration.
Correct answer is: Compatibility with the product (sterility, corrosion)
Q.44 Which parameter is most directly related to the formation of foam in aerobic bioreactors?
Impeller clearance
Gas flow rate
Liquid viscosity
Reactor wall color
Explanation - Higher gas flow introduces more bubbles that can stabilize into foam, especially when surfactants are present.
Correct answer is: Gas flow rate
Q.45 In a scale‑up based on constant P/V, if the pilot reactor volume is 10 times the lab reactor volume, how does the total power input change?
It stays the same
It increases by 10‑fold
It decreases by 10‑fold
It doubles
Explanation - P_total = (P/V) × V; with constant P/V, total power scales linearly with volume.
Correct answer is: It increases by 10‑fold
Q.46 Which of the following is a typical consequence of operating a large‑scale bioreactor at too high a tip speed?
Reduced oxygen solubility
Cell lysis due to shear
Lower temperature gradients
Decreased power consumption
Explanation - Excessive tip speed generates high shear forces that can damage or rupture delicate cells.
Correct answer is: Cell lysis due to shear
Q.47 What is the primary advantage of using a dual‑impeller configuration in large‑scale bioreactors?
It eliminates the need for sparging
It reduces the required reactor volume
It enhances both radial and axial mixing
It eliminates heat removal requirements
Explanation - A combination of radial (e.g., Rushton) and axial (e.g., pitched‑blade) impellers provides comprehensive mixing throughout the vessel.
Correct answer is: It enhances both radial and axial mixing
Q.48 Which of the following equations correctly defines the tip speed (U_tip) of an impeller?
U_tip = π D N
U_tip = N / (π D)
U_tip = 2π D N
U_tip = D / N
Explanation - Tip speed is the linear speed at the outer edge of the impeller: circumference (π D) multiplied by revolutions per second (N).
Correct answer is: U_tip = π D N
Q.49 When scaling up a bioreactor for a shear‑sensitive mammalian cell line, which combination of scale‑up criteria is most appropriate?
Constant P/V and constant KLa
Constant tip speed and constant impeller clearance
Constant Reynolds number and constant surface‑to‑volume ratio
Constant tip speed and constant KLa
Explanation - Tip speed limits shear, while KLa maintains oxygen supply—both crucial for delicate mammalian cells.
Correct answer is: Constant tip speed and constant KLa
Q.50 In scale‑up, what does the term "pilot‑scale" typically refer to?
A reactor smaller than laboratory scale
A reactor of the same size as commercial production
An intermediate‑size reactor used to bridge lab and full scale
A theoretical model without physical hardware
Explanation - Pilot scale provides a test platform larger than lab but smaller than full‑scale, allowing validation of scale‑up strategies.
Correct answer is: An intermediate‑size reactor used to bridge lab and full scale
Q.51 If the volumetric power input (P/V) in a 2 L lab reactor is 0.8 kW m⁻³, what is the power input per liter?
0.4 W L⁻¹
0.8 W L⁻¹
0.16 W L⁻¹
1.6 W L⁻¹
Explanation - 0.8 kW m⁻³ = 0.8 W L⁻¹ (since 1 m³ = 1000 L).
Correct answer is: 0.8 W L⁻¹
Q.52 Which of the following best describes why the specific power (P) per kilogram of biomass often decreases with scale‑up?
Larger reactors have higher mixing efficiency
Shear forces are reduced at larger scales
Oxygen transfer becomes unlimited
Power consumption grows slower than biomass yield
Explanation - As scale increases, the total power scales with volume, but biomass productivity often increases more proportionally, lowering specific power per kg.
Correct answer is: Power consumption grows slower than biomass yield
Q.53 In a scale‑up scenario, which parameter is most directly influenced by the choice of impeller blade angle?
KLa
Reactor wall thickness
Gas hold‑up
Temperature uniformity
Explanation - Blade angle determines the axial versus radial flow component, impacting bubble dispersion and thus the mass‑transfer coefficient.
Correct answer is: KLa
Q.54 What is the main purpose of using antifoam agents in large‑scale bioreactors?
Increase dissolved oxygen
Reduce shear stress
Prevent foam buildup that can cause overflow
Enhance mixing efficiency
Explanation - Antifoams destabilize foam, preventing it from blocking sensors or causing operational issues.
Correct answer is: Prevent foam buildup that can cause overflow
Q.55 If a bioreactor is scaled up using constant Reynolds number, which of the following statements is true?
Impeller speed remains unchanged
Power input per volume remains unchanged
Shear rate scales directly with reactor size
Impeller speed must be adjusted according to D²
Explanation - Re = ρ N D² / μ; to keep Re constant when D changes, N must vary inversely with D².
Correct answer is: Impeller speed must be adjusted according to D²
Q.56 Which scale‑up criterion would you select for a process where product formation is limited by nutrient diffusion rather than oxygen?
Constant tip speed
Constant nutrient concentration gradient
Constant KLa
Constant P/V
Explanation - Maintaining similar concentration gradients ensures that nutrient diffusion rates remain comparable across scales.
Correct answer is: Constant nutrient concentration gradient
Q.57 In a stirred‑tank bioreactor, which of the following best describes the effect of increasing the impeller diameter while keeping speed constant?
Decreases Reynolds number
Increases tip speed
Reduces power consumption
Lowers shear stress
Explanation - Tip speed U_tip = π D N; larger D at constant N raises tip speed, potentially increasing shear.
Correct answer is: Increases tip speed
Q.58 Which dimensionless group is most useful for comparing heat transfer performance between lab‑scale and pilot‑scale bioreactors?
Biot number (Bi)
Reynolds number (Re)
Damköhler number (Da)
Péclet number (Pe)
Explanation - Bi = h L_c / k relates convective heat transfer to conductive resistance within the fluid, aiding heat‑transfer scaling.
Correct answer is: Biot number (Bi)
Q.59 When scaling up a bioreactor for a high‑viscosity broth, which scale‑up criterion becomes less reliable?
Constant tip speed
Constant Reynolds number
Constant P/V
Constant impeller clearance
Explanation - Reynolds number loses significance in highly viscous flows where laminar conditions dominate; other criteria are more appropriate.
Correct answer is: Constant Reynolds number
Q.60 If the gas flow rate in a bioreactor is doubled while all other conditions remain the same, which of the following is most likely to increase?
Mixing time
KLa
Impeller clearance
Liquid viscosity
Explanation - More gas flow raises bubble surface area and interfacial renewal, enhancing the volumetric mass‑transfer coefficient.
Correct answer is: KLa
Q.61 Which of the following best explains why pilot‑scale studies often use a lower impeller speed than the lab scale when scaling up by constant P/V?
To reduce temperature gradients
To maintain the same tip speed
Because larger impellers require less speed to achieve the same power density
To increase gas hold‑up
Explanation - Power per volume ∝ N³ D²; a larger D means N can be reduced while keeping P/V constant.
Correct answer is: Because larger impellers require less speed to achieve the same power density
Q.62 During scale‑up, the term "scale‑down experiment" refers to:
Testing a smaller reactor to mimic large‑scale conditions
Reducing the number of impellers in a large reactor
Operating the reactor at lower temperature
Using less media to cut costs
Explanation - Scale‑down models intentionally reproduce large‑scale stressors (e.g., gradients) in a smaller, controllable system for troubleshooting.
Correct answer is: Testing a smaller reactor to mimic large‑scale conditions
Q.63 Which factor most directly affects the formation of concentration gradients (e.g., nutrient, pH) in a large‑scale bioreactor?
Impeller clearance
Mixing time
Reactor wall material
Sparger shape
Explanation - Longer mixing times allow zones to develop where nutrients or pH differ from bulk values, leading to gradients.
Correct answer is: Mixing time
Q.64 If the volumetric power input (P/V) is kept constant during scale‑up, how does the impeller torque (T) change with reactor size (assuming constant fluid properties and geometry)?
T remains constant
T increases proportionally to the reactor volume
T decreases as reactor size increases
T is independent of P/V
Explanation - P = 2π N T; with constant P/V, total power (P) grows with volume, so torque must increase accordingly.
Correct answer is: T increases proportionally to the reactor volume
Q.65 Which scale‑up criterion is most appropriate for processes where the product is a gas‑phase volatile compound that must be removed efficiently?
Constant KLa
Constant tip speed
Constant Reynolds number
Constant surface‑to‑volume ratio
Explanation - A higher surface‑to‑volume ratio promotes gas removal; maintaining this ratio helps control volatile product stripping.
Correct answer is: Constant surface‑to‑volume ratio
Q.66 When using CFD to assist scale‑up, which output is most valuable for assessing potential shear damage to cells?
Velocity magnitude contours
Pressure distribution maps
Shear‑rate fields
Temperature gradients
Explanation - CFD provides local shear‑rate data, allowing engineers to identify high‑shear zones that could harm cells.
Correct answer is: Shear‑rate fields
Q.67 Which of the following statements about the power number (Np) is true for a Rushton turbine in turbulent flow?
Np increases with increasing Reynolds number
Np is independent of Reynolds number
Np decreases as impeller diameter grows
Np is zero in turbulent flow
Explanation - In turbulent regime, Np for a given impeller geometry remains approximately constant.
Correct answer is: Np is independent of Reynolds number
Q.68 Which of the following is a common method to evaluate the scale‑up of oxygen transfer performance?
Measuring pH drift
Conducting a dynamic gassing‑out experiment
Recording temperature rise
Measuring foam height
Explanation - A gassing‑out test determines KLa by monitoring dissolved oxygen decay after gas supply is stopped.
Correct answer is: Conducting a dynamic gassing‑out experiment
Q.69 In a scale‑up from 10 L to 1000 L, which of the following parameters is most likely to be limited by the mechanical design of the agitator shaft?
Impeller tip speed
Gas sparger location
Reactor wall thickness
Cooling jacket flow
Explanation - The shaft must transmit torque at higher speeds; maintaining tip speed may exceed shaft strength or cause excessive vibration.
Correct answer is: Impeller tip speed
Q.70 Which scale‑up approach would you use if the target process is highly exothermic and heat removal is the main limitation?
Constant P/V
Constant KLa
Constant surface‑to‑volume ratio (A/V)
Constant tip speed
Explanation - Heat removal scales with the area available for cooling; keeping A/V constant helps preserve heat‑transfer capacity.
Correct answer is: Constant surface‑to‑volume ratio (A/V)
Q.71 If a bioreactor operates at a gas flow of 1 vvm and the liquid volume is 200 L, how many liters of gas per minute are supplied?
200 L min⁻¹
20 L min⁻¹
2 L min⁻¹
0.2 L min⁻¹
Explanation - vvm = volume of gas per volume of liquid per minute; 1 vvm × 200 L = 200 L min⁻¹.
Correct answer is: 200 L min⁻¹
Q.72 Which factor most directly influences the choice of impeller clearance in a scale‑up design?
Desired gas hold‑up
Desired mixing time
Desired shear rate near the tank bottom
Desired temperature uniformity
Explanation - Clearance determines how close the impeller approaches the bottom, affecting shear and mixing in that region.
Correct answer is: Desired shear rate near the tank bottom
Q.73 When scaling up a bioreactor, the term "hydrostatic pressure increase" refers to:
Higher pressure due to increased liquid column height
Increased gas pressure from sparging
Higher pressure from impeller rotation
Higher pressure from temperature rise
Explanation - Larger reactors often have greater liquid depth, leading to higher hydrostatic pressure at the bottom.
Correct answer is: Higher pressure due to increased liquid column height
Q.74 Which of the following is a key consideration when scaling up a bioreactor that uses a shear‑sensitive filamentous fungus?
Maintaining constant tip speed
Maximizing KLa
Using the smallest possible impeller
Increasing aeration rate dramatically
Explanation - Filamentous fungi are sensitive to shear; constant tip speed helps avoid damaging the hyphae.
Correct answer is: Maintaining constant tip speed
Q.75 Which dimensionless number compares the rate of heat conduction within the liquid to the rate of thermal convection?
Reynolds number (Re)
Péclet number (Pe)
Biot number (Bi)
Sherwood number (Sh)
Explanation - Pe = (U L)/α, relating advective transport to diffusive (conductive) heat transport.
Correct answer is: Péclet number (Pe)
Q.76 If the pilot‑scale bioreactor has a tip speed of 1.2 m s⁻¹ and the lab‑scale tip speed was 3.0 m s⁻¹, what can be inferred about the shear environment in the pilot scale?
Shear is higher in the pilot scale
Shear is lower in the pilot scale
Shear is unchanged
Shear cannot be inferred from tip speed
Explanation - Tip speed is directly related to shear; a lower tip speed indicates reduced shear stress.
Correct answer is: Shear is lower in the pilot scale
Q.77 Which of the following is the most common method to experimentally determine the power number (Np) of an impeller?
Measuring temperature rise due to viscous dissipation
Measuring torque on the shaft and calculating power
Measuring dissolved oxygen concentration
Measuring pH change
Explanation - Torque (T) is measured, then power P = 2π N T; with known geometry, Np can be derived.
Correct answer is: Measuring torque on the shaft and calculating power
Q.78 When scaling up a bioreactor for a process that is limited by substrate diffusion, which of the following scale‑up criteria is most appropriate?
Constant tip speed
Constant Reynolds number
Constant substrate concentration gradient
Constant KLa
Explanation - Maintaining the same concentration gradient ensures similar diffusion fluxes across scales.
Correct answer is: Constant substrate concentration gradient
Q.79 In a stirred‑tank bioreactor, which design change most directly increases the volumetric mass‑transfer coefficient (KLa) without altering gas flow rate?
Increasing impeller diameter
Decreasing impeller clearance
Increasing impeller speed
Increasing reactor height
Explanation - Higher impeller speed improves bubble breakup and liquid turbulence, raising KLa.
Correct answer is: Increasing impeller speed
Q.80 Which of the following best explains why scale‑up of a bioreactor often requires a larger cooling capacity than predicted by simple geometric scaling?
Heat generation per cell decreases with scale
Heat removal is less efficient in larger vessels due to lower surface‑to‑volume ratio
Viscosity increases dramatically at larger scale
Gas sparging removes heat directly
Explanation - Larger reactors have proportionally less surface area for heat exchange, demanding enhanced cooling systems.
Correct answer is: Heat removal is less efficient in larger vessels due to lower surface‑to‑volume ratio
Q.81 Which of the following scale‑up criteria is least appropriate for a highly viscous (μ > 10 cP) fermentation broth?
Constant Reynolds number
Constant tip speed
Constant P/V
Constant impeller clearance
Explanation - Re becomes very low for viscous fluids, making it a poor indicator of mixing performance; other criteria are preferred.
Correct answer is: Constant Reynolds number
Q.82 When scaling up a bioreactor, which parameter is most directly affected by increasing the number of baffles?
Gas hold‑up
Mixing time
KLa
Impeller torque
Explanation - Baffles disrupt vortex formation and improve radial flow, thereby reducing mixing time.
Correct answer is: Mixing time
Q.83 In a scale‑up study, the engineer decides to keep the same surface‑to‑volume ratio (A/V). Which aspect of the reactor is being preserved?
Impeller diameter relative to tank diameter
Cooling jacket surface area relative to reactor volume
Gas sparger hole size relative to liquid height
Number of impellers relative to volume
Explanation - A/V refers to the external surface area (often the cooling jacket) available for heat exchange per unit volume.
Correct answer is: Cooling jacket surface area relative to reactor volume
Q.84 Which of the following statements about the Sherwood number (Sh) is true in the context of bioreactor scale‑up?
Sh relates to heat transfer only
Sh is proportional to KLa multiplied by a characteristic length
Sh is independent of flow conditions
Sh decreases with increasing gas flow
Explanation - Sh = k L / D, where k is the mass‑transfer coefficient (related to KLa) and L a characteristic length; it links convective to diffusive mass transfer.
Correct answer is: Sh is proportional to KLa multiplied by a characteristic length
Q.85 During scale‑up, if the pilot reactor experiences higher than expected foam formation, which corrective action is most likely to be effective?
Increase impeller speed
Decrease gas flow rate
Add antifoam agent
Increase cooling water flow
Explanation - Antifoams reduce foam stability, directly addressing excessive foam without altering process fundamentals.
Correct answer is: Add antifoam agent
Q.86 Which of the following is the most reliable indicator that a scale‑up has preserved adequate oxygen supply?
Constant dissolved oxygen concentration (DO) profile
Unchanged impeller clearance
Same reactor height
Identical gas flow rate
Explanation - Maintaining similar DO levels indicates that oxygen transfer (KLa) and consumption are balanced across scales.
Correct answer is: Constant dissolved oxygen concentration (DO) profile
Q.87 In a scale‑up from 10 L to 100 L, if the pilot reactor uses the same impeller type but double the impeller diameter, what is the expected change in tip speed if impeller speed is kept constant?
Tip speed doubles
Tip speed halves
Tip speed remains unchanged
Tip speed quadruples
Explanation - U_tip = π D N; doubling D at constant N doubles tip speed.
Correct answer is: Tip speed doubles
Q.88 Which parameter is most directly used to calculate the mixing time in a stirred‑tank bioreactor using the empirical correlation t_m = k (V/N D³)?
Impeller diameter (D)
Reactor volume (V)
Impeller speed (N)
All of the above
Explanation - The correlation incorporates V, N, and D, indicating all three affect mixing time.
Correct answer is: All of the above
Q.89 When scaling up a bioreactor for a process with high heat generation, which scale‑up criterion would you prioritize?
Constant tip speed
Constant KLa
Constant surface‑to‑volume ratio (A/V)
Constant Reynolds number
Explanation - Heat removal scales with the cooling surface; preserving A/V helps maintain effective temperature control.
Correct answer is: Constant surface‑to‑volume ratio (A/V)
Q.90 What is the typical effect on the Reynolds number when both impeller diameter and speed are increased proportionally during scale‑up?
Re remains constant
Re decreases
Re increases
Re becomes zero
Explanation - Re ∝ N D²; proportional increases in both N and D lead to a larger product, thus higher Re.
Correct answer is: Re increases
Q.91 Which of the following scale‑up strategies would be least effective for a process that is limited by gas–liquid mass transfer?
Constant tip speed
Constant KLa
Constant P/V
Constant surface‑to‑volume ratio
Explanation - Tip speed influences shear more than gas–liquid mass transfer; KLa directly addresses the limitation.
Correct answer is: Constant tip speed
Q.92 During scale‑up, if the pilot reactor exhibits longer lag phases in microbial growth, which of the following is a likely cause?
Higher dissolved oxygen concentration
Inadequate mixing leading to substrate gradients
Excessive antifoam addition
Lower impeller clearance
Explanation - Poor mixing can create zones of low substrate, delaying microbial adaptation and extending the lag phase.
Correct answer is: Inadequate mixing leading to substrate gradients
Q.93 Which of the following is an advantage of using a pitched‑blade impeller for scale‑up of shear‑sensitive cultures?
Higher KLa values
Lower power consumption
Reduced axial flow
Gentle radial flow with lower shear
Explanation - Pitched‑blade impellers create a balance of axial and radial flow with relatively low shear, suitable for delicate cells.
Correct answer is: Gentle radial flow with lower shear
Q.94 When scaling up a bioreactor, which of the following is the most direct way to keep the volumetric mass‑transfer coefficient (KLa) constant?
Increase impeller clearance
Decrease gas sparger hole size
Reduce impeller diameter
Increase cooling jacket thickness
Explanation - Smaller sparger holes generate finer bubbles, increasing interfacial area and maintaining KLa across scales.
Correct answer is: Decrease gas sparger hole size
Q.95 Which of the following statements correctly describes the effect of increasing the number of baffles on the power number (Np) of an impeller?
Np decreases because flow becomes more laminar
Np increases due to higher turbulence
Np remains unchanged
Np becomes zero
Explanation - Baffles disrupt vortex formation, increasing turbulence and the power required to turn the impeller, thereby raising Np.
Correct answer is: Np increases due to higher turbulence
Q.96 If a bioprocess requires a shear rate below 100 s⁻¹ to avoid cell damage, which scale‑up criterion would best help guarantee this condition?
Constant tip speed
Constant P/V
Constant KLa
Constant surface‑to‑volume ratio
Explanation - Shear rate is closely related to tip speed; maintaining it ensures the shear threshold is not exceeded.
Correct answer is: Constant tip speed
Q.97 Which of the following is a common reason for performing a scale‑down experiment after a pilot‑scale run?
To verify the reactor material
To reproduce large‑scale gradients in a controllable lab system
To increase the reactor volume further
To reduce the number of impellers
Explanation - Scale‑down models intentionally create gradients (e.g., pH, substrate) observed at large scale, allowing detailed study and troubleshooting.
Correct answer is: To reproduce large‑scale gradients in a controllable lab system
Q.98 In scale‑up, which of the following is the most appropriate method to estimate the required agitator torque for a new reactor size?
Use the same torque as the lab reactor
Scale torque linearly with volume
Calculate using P = 2π N T and the desired P/V
Assume torque is proportional to impeller clearance
Explanation - Knowing the target power per volume, impeller speed, and geometry allows direct calculation of the required torque.
Correct answer is: Calculate using P = 2π N T and the desired P/V
Q.99 Which of the following is the most direct effect of increasing the gas sparger depth in a bioreactor?
Decreased KLa
Increased gas hold‑up
Reduced impeller torque
Higher liquid viscosity
Explanation - Deeper spargers release bubbles further into the liquid, increasing the volumetric gas hold‑up.
Correct answer is: Increased gas hold‑up
Q.100 When scaling up a bioreactor, which criterion would you prioritize for a product that is heat‑sensitive and must be kept below 30 °C?
Constant tip speed
Constant surface‑to‑volume ratio (A/V)
Constant KLa
Constant impeller clearance
Explanation - Maintaining A/V ensures adequate cooling capacity to keep temperature under control for heat‑sensitive products.
Correct answer is: Constant surface‑to‑volume ratio (A/V)
Q.101 Which parameter directly influences the Reynolds number in a bioreactor?
Gas flow rate
Impeller tip speed
Reactor wall color
Cooling jacket material
Explanation - Re = (ρ U_tip D)/μ; tip speed is a key component of the inertial forces affecting Re.
Correct answer is: Impeller tip speed
Q.102 If the volumetric power input (P/V) is kept constant during scale‑up, how does the mixing time typically change with reactor size?
Mixing time decreases
Mixing time stays the same
Mixing time increases
Mixing time becomes zero
Explanation - Larger volumes require longer times for homogenization even if power density is constant, because the distance for mixing grows.
Correct answer is: Mixing time increases
Q.103 Which of the following statements about the Damköhler number (Da) is true for a bioprocess where the reaction rate is much faster than mass transfer?
Da << 1
Da ≈ 1
Da >> 1
Da is independent of reaction speed
Explanation - Da = reaction rate / mass‑transfer rate; a fast reaction relative to mass transfer yields a large Da.
Correct answer is: Da >> 1
Q.104 In scale‑up, which design feature most directly reduces the formation of dead zones near the tank bottom?
Increasing impeller clearance
Adding more baffles
Using a larger sparger
Increasing cooling jacket thickness
Explanation - Baffles improve radial flow, breaking up stagnant regions near the bottom and enhancing mixing.
Correct answer is: Adding more baffles
Q.105 When scaling up a bioreactor, why is it important to keep the same impeller blade angle?
To maintain identical gas flow patterns
To preserve the balance of axial and radial flow
To keep the same power consumption
To ensure the same reactor height
Explanation - Blade angle determines the flow direction generated by the impeller; keeping it constant helps maintain similar mixing characteristics.
Correct answer is: To preserve the balance of axial and radial flow
Q.106 Which of the following is a primary reason for using a dual‑stage sparger in large‑scale bioreactors?
To reduce power consumption
To increase gas hold‑up and improve mass transfer
To simplify cleaning procedures
To lower impeller speed requirements
Explanation - A dual‑stage sparger introduces gas at two depths, enhancing bubble dispersion and KLa.
Correct answer is: To increase gas hold‑up and improve mass transfer
Q.107 Which of the following statements best describes why constant P/V is often used for scaling up chemically‑driven processes?
Chemical reactions are insensitive to shear
Power input directly influences temperature control
P/V correlates with mixing and mass transfer, affecting reaction rates
Maintaining P/V reduces gas hold‑up
Explanation - Power density influences turbulence, which in turn impacts mixing and mass transfer—key factors for chemical reaction kinetics.
Correct answer is: P/V correlates with mixing and mass transfer, affecting reaction rates
Q.108 If the pilot‑scale bioreactor has a volumetric oxygen transfer coefficient (KLa) that is 25 % lower than the lab scale, which adjustment is most likely to restore KLa?
Decrease impeller speed
Increase gas flow rate
Reduce impeller diameter
Increase reactor height
Explanation - Higher gas flow introduces more bubbles and raises interfacial area, thus increasing KLa.
Correct answer is: Increase gas flow rate
Q.109 Which of the following scale‑up criteria is most appropriate for a process where the product yield is limited by substrate diffusion rather than oxygen transfer?
Constant tip speed
Constant substrate concentration gradient
Constant KLa
Constant P/V
Explanation - Maintaining similar concentration gradients ensures substrate diffusion rates remain comparable across scales.
Correct answer is: Constant substrate concentration gradient
Q.110 During scale‑up, which of the following measurements would you monitor to verify that shear stress has not increased beyond acceptable limits?
Dissolved oxygen concentration
Cell viability assay
Reactor temperature
Gas flow rate
Explanation - Shear‑sensitive cells will show reduced viability if shear stress exceeds tolerable levels; this is a direct indicator.
Correct answer is: Cell viability assay
Q.111 In a scale‑up study, which of the following is the most common reason to increase the number of impellers when moving to a larger reactor?
To reduce the total power consumption
To improve axial mixing and reduce dead zones
To increase the surface‑to‑volume ratio
To lower the gas flow rate
Explanation - Multiple impellers spaced along the shaft enhance axial flow, minimizing regions of poor mixing.
Correct answer is: To improve axial mixing and reduce dead zones
Q.112 Which of the following best explains why constant tip speed may lead to higher power consumption in larger reactors?
Larger impellers require more torque at the same tip speed
Tip speed is independent of power consumption
Gas sparger efficiency decreases with tip speed
Cooling requirements increase with tip speed
Explanation - Power P = 2π N T; maintaining tip speed with a larger impeller often means higher torque, raising power consumption.
Correct answer is: Larger impellers require more torque at the same tip speed
Q.113 Which dimensionless group would you use to compare the relative importance of convective to diffusive mass transfer in a bioreactor?
Reynolds number (Re)
Sherwood number (Sh)
Biot number (Bi)
Péclet number (Pe)
Explanation - Sh = k L / D reflects the ratio of convective mass transfer to diffusion, directly relating to KLa.
Correct answer is: Sherwood number (Sh)
Q.114 When scaling up a bioreactor for a highly shear‑sensitive algae culture, which impeller type is least suitable?
Rushton turbine
Marine impeller
Pitched‑blade turbine
Axial flow (hydrofoil) impeller
Explanation - Rushton turbines generate high radial flow and shear, which can damage shear‑sensitive algae.
Correct answer is: Rushton turbine
Q.115 If the pilot‑scale reactor requires a higher gas sparger pressure than the lab scale to achieve the same KLa, what is the most likely cause?
Increased liquid viscosity at larger scale
Larger bubble size due to higher pressure
Reduced gas hold‑up because of larger reactor volume
Higher temperature in pilot scale
Explanation - Larger volumes dilute gas bubbles, lowering hold‑up; higher pressure compensates by creating more bubbles.
Correct answer is: Reduced gas hold‑up because of larger reactor volume
Q.116 Which of the following is a key benefit of using scale‑down models after successful pilot‑scale runs?
They eliminate the need for full‑scale production
They allow detailed investigation of scale‑induced gradients
They increase the reactor’s power input
They reduce the need for process monitoring
Explanation - Scale‑down experiments replicate large‑scale gradients in a controllable environment, facilitating root‑cause analysis and optimization.
Correct answer is: They allow detailed investigation of scale‑induced gradients
Q.117 Which of the following statements correctly describes the effect of increasing the number of baffles on the power number (Np) for a Rushton turbine?
Np decreases because flow becomes smoother
Np stays the same because Np is geometry‑independent
Np increases due to higher turbulence and reduced vortex formation
Np becomes zero
Explanation - Baffles disrupt vortex formation, forcing the impeller to work harder, which raises the power number.
Correct answer is: Np increases due to higher turbulence and reduced vortex formation
Q.118 In a scale‑up where constant KLa is maintained, which of the following process parameters is most likely to stay unchanged?
Impeller speed (N)
Aeration rate (vvm)
Impeller clearance
Reactor wall thickness
Explanation - Maintaining KLa often requires keeping the gas flow per volume (vvm) constant, assuming other variables remain similar.
Correct answer is: Aeration rate (vvm)
Q.119 Which of the following is the most direct measurement to assess whether a scaled‑up bioreactor maintains adequate mixing?
Measuring dissolved oxygen (DO) fluctuations
Recording impeller torque
Measuring temperature uniformity
Monitoring pH drift
Explanation - Rapid, stable DO signals indicate effective mixing and mass transfer throughout the reactor.
Correct answer is: Measuring dissolved oxygen (DO) fluctuations