Fluidized Bed Coating MCQs With Answer

Introduction: This blog presents a focused set of Fluidized Bed Coating MCQs with answers tailored for M.Pharm students studying MIP 203T – Pharmaceutical Production Technology. The questions emphasize core principles, equipment types (e.g., Wurster/top-spray/bottom-spray), critical process parameters (air velocity, spray rate, atomization, droplet size, inlet/outlet temperature), formulation factors (binder, plasticizer, solids content), scale-up considerations, in-process monitoring and common defects with troubleshooting. These MCQs aim to reinforce conceptual understanding, help prepare for exams and viva voce, and deepen knowledge required for designing, optimizing and troubleshooting fluidized bed coating operations in industrial and lab settings.

Q1. What is the primary physical mechanism that keeps particles suspended in a fluidized bed coater?

• Surface tension between particles
• Buoyancy from the coating liquid
• Gas drag force exceeding particle weight
• Magnetic attraction between particles

Correct Answer: Gas drag force exceeding particle weight

Q2. In a Wurster (bottom-spray) fluidized bed coating, which region of the assembly is primarily responsible for particle conveyance through the spray zone?

• The outer annular downflow region
• The draft tube central riser
• The hopper cone
• The filter housing

Correct Answer: The draft tube central riser

Q3. Minimum fluidization velocity (Umf) is a critical design parameter. Which factor has the greatest influence on Umf for a given particle bed?

• Nozzle atomization pressure
• Particle size and density
• Coating solution viscosity
• Ambient humidity

Correct Answer: Particle size and density

Q4. Which nozzle type is most commonly used for producing fine droplets in fluidized bed coating with two-fluid atomization?

• Rotary disk nozzle
• Two-fluid pneumatic nozzle
• Pressure swirl (airless) nozzle
• Ultrasonic nozzle

Correct Answer: Two-fluid pneumatic nozzle

Q5. A common cause of particle agglomeration (sticking) during fluidized bed coating is:

• Too low coating solution solids content
• Excessive drying air temperature
• Insufficient droplet wetting and too high spray rate
• High atomization air pressure producing very small droplets

Correct Answer: Insufficient droplet wetting and too high spray rate

Q6. Which process parameter is most directly manipulated to control the size of spray droplets produced by a pneumatic nozzle?

• Inlet air temperature
• Atomization air pressure
• Bed height in the coater
• Nozzle-to-bed distance

Correct Answer: Atomization air pressure

Q7. During scale-up of a fluidized bed coating process, which dimensionless number is often used to maintain similar hydrodynamic behavior?

• Péclet number
• Reynolds number
• Mach number
• Sherwood number

Correct Answer: Reynolds number

Q8. Which coating defect is indicated by a rough, granular surface and is typically due to rapid solvent evaporation leading to polymer shell formation?

• Pitting
• Poor gloss
• Spray drying/film roughness (skin formation)
• Twinning

Correct Answer: Spray drying/film roughness (skin formation)

Q9. For an aqueous polymer coating, adding a plasticizer primarily affects which property of the dried film?

• Increases the minimum fluidization velocity
• Decreases film flexibility and increases brittleness
• Improves film flexibility and reduces cracking
• Precipitates the polymer during spraying

Correct Answer: Improves film flexibility and reduces cracking

Q10. Which process measurement is most useful for real-time endpoint determination of coating weight gain in a production fluidized bed?

• Off-line HPLC assay of active ingredient
• In-line near infrared (NIR) spectroscopy
• Periodic visual inspection through the sight glass
• Measuring atomization air pressure

Correct Answer: In-line near infrared (NIR) spectroscopy

Q11. What effect does increasing the inlet drying air temperature typically have on coating process performance, assuming other parameters constant?

• Decreases solvent evaporation rate and increases tackiness
• Increases solvent evaporation rate and can reduce product residence time
• Has no effect on droplet size
• Only affects particle density, not drying

Correct Answer: Increases solvent evaporation rate and can reduce product residence time

Q12. In top-spray fluidized bed coaters, where does most of the sprayed material deposit first?

• On the lower part of the bed near the air distributor
• Evenly on the filter bag
• On the uppermost layer of the fluidized particles
• Specifically inside the Wurster insert

Correct Answer: On the uppermost layer of the fluidized particles

Q13. High coating solution solids content (high % w/w solids) generally results in which of the following effects?

• Increased spray drying time per droplet
• Lower coating efficiency and longer drying time
• Higher coating efficiency and reduced solvent load on dryer
• Guaranteed elimination of agglomeration

Correct Answer: Higher coating efficiency and reduced solvent load on dryer

Q14. Which of these is a primary advantage of using a Wurster (bottom-spray) insert for tablet coating?

• Better mixing and uniform coating for multiparticulates due to continuous passage through a focused spray zone
• Lower equipment cost compared to top-spray
• Reduced risk of over-drying because there is no spray zone
• Increased throughput because coating is applied to the hopper walls

Correct Answer: Better mixing and uniform coating for multiparticulates due to continuous passage through a focused spray zone

Q15. Which property of the coating solution most directly affects droplet breakup and atomization behavior?

• Solid particle porosity
• Solution viscosity and surface tension
• Initial bed packing density
• Particle friability

Correct Answer: Solution viscosity and surface tension

Q16. What is the typical consequence of operating the fluidizing gas velocity significantly above the terminal velocity of fines in the bed?

• Improved product yield and less filter loading
• Increased entrainment and loss of fines to the filter
• Reduced atomization efficiency
• Lower evaporation rate of solvent

Correct Answer: Increased entrainment and loss of fines to the filter

Q17. Which corrective action is most appropriate to reduce tablet erosion during fluidized bed coating?

• Increase spray rate
• Decrease inlet air temperature drastically
• Lower atomization air pressure or adjust nozzle type to produce larger droplets
• Add more plasticizer to the coating solution

Correct Answer: Lower atomization air pressure or adjust nozzle type to produce larger droplets

Q18. Coating uniformity across dosage units is most influenced by which combination of factors?

• Spray rate, bed mixing dynamics, and droplet size distribution
• Only the polymer molecular weight
• Batch size alone
• Filter bag material selection

Correct Answer: Spray rate, bed mixing dynamics, and droplet size distribution

Q19. Which monitoring parameter would indicate that the product in the bed is too dry and risk of friability increases?

• Rising product outlet air temperature and very low relative humidity
• Decreasing atomization air pressure
• Increasing spray solution solids concentration
• Stable near infrared signal indicating constant coating mass

Correct Answer: Rising product outlet air temperature and very low relative humidity

Q20. During process troubleshooting, persistent mottling and color variation on coated beads most likely suggests a problem with:

• Particle density distribution only
• Non-uniform spray application or insufficient bed mixing
• Air filter pore size
• Excessive plasticizer concentration

Correct Answer: Non-uniform spray application or insufficient bed mixing

Download