Spray dryer – principle, construction, working, uses, merits, demerits MCQs With Answer

Spray dryer – principle, construction, working, uses, merits, demerits MCQs With Answer

Spray drying is a vital unit operation in pharmaceutical manufacturing, converting liquid feeds into dry powders via rapid solvent evaporation. This introduction covers the spray dryer principle, construction (atomizer, drying chamber, cyclone, collectors), working mechanism (atomization, droplet drying, particle formation), key process parameters, uses in formulation of powders, merits like uniform particle size and scalability, and demerits such as thermal stress and product loss. Content is tailored for B.Pharm students to build practical understanding of pharmaceutical spray drying, process control, and quality considerations. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary principle behind spray drying?

• Condensation of vapor into liquid
• Rapid evaporation of solvent from atomized droplets
• Mechanical compression of powders
• Centrifugal separation of solids

Correct Answer: Rapid evaporation of solvent from atomized droplets

Q2. Which component of a spray dryer converts the feed into fine droplets?

• Drying chamber
• Nozzle or atomizer
• Bag filter

Correct Answer: Nozzle or atomizer

Q3. What type of atomizer uses high-speed rotation to produce droplets?

• Pressure nozzle
• Rotary cup atomizer
• Two-fluid nozzle
• Electrostatic atomizer

Correct Answer: Rotary cup atomizer

Q4. Which parameter directly affects droplet size in a two-fluid nozzle?

• Feed viscosity only
• Atomizing air pressure
• Drying chamber volume
• Collector design

Correct Answer: Atomizing air pressure

Q5. In spray drying, what does the term “inlet temperature” refer to?

• Temperature of the product powder
• Temperature of the air entering the drying chamber
• Temperature of the feed solution
• Temperature in the cyclone

Correct Answer: Temperature of the air entering the drying chamber

Q6. Which factor most influences particle morphology (porosity, surface) in spray drying?

• Solvent color
• Drying rate and solute concentration
• Room humidity only
• Collector type

Correct Answer: Drying rate and solute concentration

Q7. What is the main advantage of spray drying for heat-sensitive drugs?

• Extremely high residence time
• Rapid drying with short thermal exposure
• Complete elimination of solvent without energy
• Ability to compress directly without granulation

Correct Answer: Rapid drying with short thermal exposure

Q8. Which drying mode predominates when droplets rapidly form a solid shell and trap solvent inside?

• Constant-rate drying
• Falling-rate drying
• Instantaneous pyrolysis
• Glass transition drying

Correct Answer: Falling-rate drying

Q9. What is a common consequence of too high inlet temperature during spray drying?

• Improved solubility of product
• Thermal degradation of heat-sensitive APIs
• Reduced atomization efficiency
• Complete solvent condensation

Correct Answer: Thermal degradation of heat-sensitive APIs

Q10. Which of the following is a typical function of a cyclone separator in a spray dryer?

• To atomize the feed
• To separate fine particles from exhaust air by centrifugal forces
• To heat the inlet air
• To dissolve solids into the feed

Correct Answer: To separate fine particles from exhaust air by centrifugal forces

Q11. What does outlet air temperature indicate in spray drying process control?

• The temperature of air entering the dryer
• An indirect measure of residual moisture in the product
• The feed pump temperature
• The temperature of the cyclone interior

Correct Answer: An indirect measure of residual moisture in the product

Q12. Which feed property increases droplet size for a given atomizer?

• Lower viscosity
• Higher feed viscosity
• Lower solids content
• Higher atomizing air velocity

Correct Answer: Higher feed viscosity

Q13. What is the effect of increasing feed flow rate on spray dryer performance if other parameters are constant?

• Decreased particle moisture content
• Increased outlet temperature
• Higher residence time and possible wetter powder
• Lower production yield

Correct Answer: Higher residence time and possible wetter powder

Q14. Which solvent property is critical to spray drying evaporation rate?

• Color
• Boiling point and vapor pressure
• Electrical conductivity
• pH

Correct Answer: Boiling point and vapor pressure

Q15. Why is atomization energy important in spray drying?

• It determines powder taste
• It controls droplet size distribution and hence particle size
• It sterilizes the feed
• It removes residual solvent chemically

Correct Answer: It controls droplet size distribution and hence particle size

Q16. Which of the following is a major disadvantage of spray drying?

• Inability to produce uniform particle size
• High capital and operational costs and potential thermal degradation
• Requires extremely low temperatures only
• Cannot handle viscous feeds

Correct Answer: High capital and operational costs and potential thermal degradation

Q17. For hygroscopic products, which precaution is most important after spray drying?

• Immediate exposure to ambient humid air
• Controlled packaging and low-humidity storage
• Heating to remove more moisture
• Mixing with water to stabilize

Correct Answer: Controlled packaging and low-humidity storage

Q18. Which parameter is most directly used to control particle size in a rotary atomizer?

• Feed pH
• Rotational speed of the cup
• Type of cyclone
• Outlet air filter material

Correct Answer: Rotational speed of the cup

Q19. Which utility is commonly used as the heating medium in pharmaceutical spray dryers?

• Cold water
• Hot air
• Liquid nitrogen
• Compressed carbon dioxide

Correct Answer: Hot air

Q20. What is the role of excipients like polymers during spray drying of amorphous dispersions?

• They act as atomizers
• They stabilize the amorphous state and inhibit recrystallization
• They increase solvent boiling point
• They reduce drying chamber size

Correct Answer: They stabilize the amorphous state and inhibit recrystallization

Q21. Which spray drying configuration improves heat transfer by mixing hot air and droplets in opposite directions?

• Co-current flow
• Counter-current flow
• Static flow
• Vacuum flow

Correct Answer: Counter-current flow

Q22. Which flow pattern gives gentler thermal exposure to product but may increase residence time?

• Co-current flow
• Counter-current flow
• Cross-flow only
• Recirculating flow

Correct Answer: Co-current flow

Q23. What is the significance of the glass transition temperature (Tg) in spray-dried amorphous powders?

• Below Tg, material is sticky and more prone to collapse
• Above Tg, mobility increases and the product may become sticky leading to agglomeration
• Tg has no relevance to spray drying
• Tg determines atomizer type selection only

Correct Answer: Above Tg, mobility increases and the product may become sticky leading to agglomeration

Q24. Which technique can be used to reduce thermal degradation during spray drying?

• Increase inlet temperature drastically
• Use lower inlet temperature and higher air flow or use inert gases
• Increase feed concentration indefinitely
• Decrease atomization energy

Correct Answer: Use lower inlet temperature and higher air flow or use inert gases

Q25. What causes formation of hollow spherical particles in spray drying?

• Very slow solvent evaporation
• Rapid surface drying forming a shell while interior solvent vaporizes
• High feed solids that prevent drying
• Use of a rotary atomizer only

Correct Answer: Rapid surface drying forming a shell while interior solvent vaporizes

Q26. Which analytical technique is commonly used to determine moisture content of spray-dried powders?

• UV-Vis spectroscopy
• Thermogravimetric analysis (TGA) or loss on drying
• HPLC only
• Gel electrophoresis

Correct Answer: Thermogravimetric analysis (TGA) or loss on drying

Q27. What is a common purpose of spray drying in pharmaceuticals?

• To perform tablet compression
• To convert liquid formulations into stable powders for inhalation or oral use
• To sterilize syringes
• To perform coating of tablets

Correct Answer: To convert liquid formulations into stable powders for inhalation or oral use

Q28. Which type of spray dryer is often used for small-scale laboratory production?

• Industrial rotary atomizer dryer only
• Benchtop or lab-scale spray dryer with two-fluid nozzle
• Large continuous drum dryer
• Vacuum tray dryer

Correct Answer: Benchtop or lab-scale spray dryer with two-fluid nozzle

Q29. What is “secondary drying” in context of spray-dried powders?

• Removal of water by freezing
• Post-drying step to reduce residual moisture by drying under mild conditions
• Primary atomization repeated twice
• Mixing powder with excipients

Correct Answer: Post-drying step to reduce residual moisture by drying under mild conditions

Q30. Which operational problem is indicated by powder accumulating on the walls of the drying chamber?

• Too high atomization energy
• Formation of sticky particles due to high outlet temperature or low Tg
• Excessive feed pH
• Insufficient cyclone efficiency

Correct Answer: Formation of sticky particles due to high outlet temperature or low Tg

Q31. How does feed solids concentration influence the yield of spray drying?

• Lower solids generally decrease yield due to more gas-phase losses
• Feed solids concentration has no effect
• Higher solids always decrease yield
• Higher solids always eliminate fines

Correct Answer: Lower solids generally decrease yield due to more gas-phase losses

Q32. Which safety concern is particularly important for organic solvent-based spray drying?

• Low oxygen levels leading to oxidation
• Fire and explosion risk due to solvent vapors
• Excessive oxygenation of product
• Freezing hazard

Correct Answer: Fire and explosion risk due to solvent vapors

Q33. What is the effect of increased atomizer speed on particle size distribution?

• Shift to larger particle sizes
• Shift to smaller particle sizes and narrower distribution
• No change in particle size
• Only changes color of particles

Correct Answer: Shift to smaller particle sizes and narrower distribution

Q34. Which of the following helps reduce powder stickiness in spray drying?

• Operating above the material’s glass transition temperature
• Adding anti-caking agents or selecting carriers with higher Tg
• Increasing feed solvent volatility
• Reducing inlet air flow

Correct Answer: Adding anti-caking agents or selecting carriers with higher Tg

Q35. What does the term “encapsulation by spray drying” refer to?

• Coating tablets within the dryer
• Entrapping active ingredients within a carrier matrix during drying
• Using spray dryer as a reactor for chemical synthesis
• Sterilizing emulsion droplets only

Correct Answer: Entrapping active ingredients within a carrier matrix during drying

Q36. In which case is vacuum spray drying preferred?

• For highly volatile and oxygen-sensitive solvents to lower drying temperature
• For increasing oxygen exposure
• When very high inlet temperature is needed
• When atomizing very coarse suspensions only

Correct Answer: For highly volatile and oxygen-sensitive solvents to lower drying temperature

Q37. Which performance metric indicates how much product is collected versus what was fed?

• Throughput ratio
• Yield
• Residence index
• Drying constant

Correct Answer: Yield

Q38. How does increasing inlet air humidity affect spray drying?

• Enhances drying rate
• Reduces drying capacity and can increase residual moisture
• Has no effect
• Makes droplets smaller

Correct Answer: Reduces drying capacity and can increase residual moisture

Q39. Which cleaning concept is critical for GMP compliance of spray dryers?

• No cleaning between batches
• Cleaning validation and documented cleaning procedures
• Only visual cleaning is sufficient
• Cleaning after every year

Correct Answer: Cleaning validation and documented cleaning procedures

Q40. What is the main goal of process analytical technology (PAT) in spray drying?

• To eliminate quality checks
• To monitor and control critical process parameters in real time to ensure product quality
• To reduce operator training
• To increase solvent usage

Correct Answer: To monitor and control critical process parameters in real time to ensure product quality

Q41. Which property of the feed most affects the drying kinetics besides solvent volatility?

• Color of the solute
• Thermal conductivity and specific heat of the solution
• Brand of pump used
• Collector shape

Correct Answer: Thermal conductivity and specific heat of the solution

Q42. How can spray drying be used for taste masking of bitter drugs?

• By increasing particle hygroscopicity
• By encapsulating the drug in polymer matrix to control release in the mouth
• By forming larger crystals of the drug
• By heating the drug to degrade bitterness

Correct Answer: By encapsulating the drug in polymer matrix to control release in the mouth

Q43. Which downstream unit operation is commonly used after spray drying to improve flow properties?

• Granulation or milling and sieving
• Direct compression only
• Freeze-thaw cycling
• Chromatography

Correct Answer: Granulation or milling and sieving

Q44. Which characteristic indicates a powder suitable for inhalation after spray drying?

• Mean particle size > 100 microns
• Suitable aerodynamic diameter around 1–5 microns
• Very high moisture >15%
• Highly irregular coarse morphology only

Correct Answer: Suitable aerodynamic diameter around 1–5 microns

Q45. What is the likely effect of increasing drying air flow rate while keeping inlet temperature constant?

• Lower drying capacity
• Faster heat and mass transfer, potentially lower outlet temperature and lower residual moisture
• No change in process
• Instant product crystallization

Correct Answer: Faster heat and mass transfer, potentially lower outlet temperature and lower residual moisture

Q46. Which excipient is commonly used as a carrier for spray drying to enhance powder stability?

• Sodium chloride
• Polyvinylpyrrolidone (PVP) or lactose
• Hydrochloric acid
• Magnesium metal

Correct Answer: Polyvinylpyrrolidone (PVP) or lactose

Q47. Which measurement helps assess spray-dried particle size distribution?

• pH measurement
• Laser diffraction or microscopy
• IR spectroscopy only
• Electrical conductivity

Correct Answer: Laser diffraction or microscopy

Q48. What is “wall deposition” and how can it be minimized?

• Deposition of powders in the cyclone reduced by increasing feed pH
• Powder sticking to chamber walls; minimized by optimizing inlet/outlet temperatures and adding anti-sticking agents
• Formation of ice on the wall; minimized by heating walls
• Deposition of oils; minimized by vacuum only

Correct Answer: Powder sticking to chamber walls; minimized by optimizing inlet/outlet temperatures and adding anti-sticking agents

Q49. During scale-up of spray drying, which similarity criterion is most frequently considered?

• Geometric similarity only
• Maintaining similar droplet residence time and drying kinetics (e.g., constant volumetric heat load)
• Using the same brand of pump
• Keeping identical exhaust duct length

Correct Answer: Maintaining similar droplet residence time and drying kinetics (e.g., constant volumetric heat load)

Q50. What is the typical effect of using a higher molecular weight polymer as carrier in spray drying?

• Lower glass transition and more stickiness
• Higher Tg, improved stability but possibly higher viscosity of feed
• Decreased particle formation entirely
• Instant crystallization of API

Correct Answer: Higher Tg, improved stability but possibly higher viscosity of feed

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com