Drum dryer – principle, construction, working, uses, merits, demerits MCQs With Answer is an essential topic for B. Pharm students studying pharmaceutical drying technologies. This introduction explains the drum dryer (roller dryer) principle — heat transfer by conduction from a steam-heated rotating drum — along with construction features like drum shell, heating jacket, feed applicator, and scraper. You will learn working steps, operational parameters (drum speed, steam pressure, film thickness), pharmaceutical uses, advantages (high heat transfer, efficient for viscous pastes) and limitations (risk of local overheating, cleaning difficulty). Keywords: drum dryer, roller dryer, pharmaceutical drying, heat transfer, steam-heated drum, film drying. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the primary principle of drying in a drum dryer?
- Convective heat transfer from hot air
- Heat transfer by radiation from a source
- Direct contact evaporation inside the drum
- Conduction of heat through the heated drum surface
Correct Answer: Conduction of heat through the heated drum surface
Q2. Which component is essential in the construction of a drum dryer?
- Fluidized bed chamber
- Rotating heated drum
- Spray nozzle array
- Static heated plates
Correct Answer: Rotating heated drum
Q3. Heat transfer in a drum dryer is mainly by which mechanism?
- Conduction
- Convection
- Radiation
- Mass diffusion
Correct Answer: Conduction
Q4. How is the dried film typically removed from the drum surface?
- By washing with solvent
- By a scraper or knife
- By vacuum suction through pores
- By centrifugal force alone
Correct Answer: By a scraper or knife
Q5. Which feed form is most suitable for drum drying?
- Dry granules
- Large intact crystals
- Viscous pastes and slurries
- Gaseous reactants
Correct Answer: Viscous pastes and slurries
Q6. A major advantage of drum dryers in pharmaceutical processing is:
- Very long residence times required
- Extremely gentle drying for all materials
- High heat transfer rates and compact design
- No need for heating medium
Correct Answer: High heat transfer rates and compact design
Q7. A common demerit of drum drying is:
- Inability to handle viscous feeds
- Risk of local overheating and thermal degradation
- Extensive requirement for solvent addition
- Complete elimination of cleaning requirements
Correct Answer: Risk of local overheating and thermal degradation
Q8. Drum dryer is also commonly known as:
- Tray dryer
- Freeze dryer
- Roller dryer
- Fluid bed dryer
Correct Answer: Roller dryer
Q9. Which heating medium is most commonly used in drum dryers?
- Steam
- Direct hot air
- Microwave energy
- Liquid nitrogen
Correct Answer: Steam
Q10. The dried product from a drum dryer is usually obtained as:
- Fine aerosol
- Large monolithic blocks
- Flakes or thin sheets
- Granular pellets
Correct Answer: Flakes or thin sheets
Q11. Which parameter primarily controls residence time on the heated drum?
- Ambient humidity
- Drum rotation speed
- Color of the drum
- Type of scraper material
Correct Answer: Drum rotation speed
Q12. Film thickness on the drum surface is mainly affected by:
- Feed rate and applicator settings
- Drum external paint color
- Ambient noise level
- Type of motor coupling
Correct Answer: Feed rate and applicator settings
Q13. For drying heat-sensitive pharmaceutical extracts, which modification is commonly used?
- Increased drum temperature above decomposition point
- Vacuum drum drying to lower boiling point
- Using abrasive scrapers to speed removal
- Replacing steam with hot oil at high temperature
Correct Answer: Vacuum drum drying to lower boiling point
Q14. Drum dryers are predominantly which type of process?
- Batch process only
- Continuous process
- Intermittent freezing process
- Gas-phase polymerization process
Correct Answer: Continuous process
Q15. Heat reaches the product on the drum surface mainly by:
- Direct flame contact
- Conduction through the drum wall
- Ultraviolet radiation
- Induction heating through the product
Correct Answer: Conduction through the drum wall
Q16. For pharmaceutical applications, drum surfaces are often made from:
- Plain carbon steel with heavy rust
- Fragile glass
- Stainless steel with polished finish
- Uncoated cast iron with rough finish
Correct Answer: Stainless steel with polished finish
Q17. Which operating parameter most directly controls the maximum heating capacity of a steam-heated drum?
- Steam pressure
- Ambient room color
- Electrical supply frequency
- Type of floor material
Correct Answer: Steam pressure
Q18. The main function of the scraper knife in a drum dryer is to:
- Introduce the feed onto the drum
- Cool the drum surface
- Remove the dried film from the drum
- Polish the drum surface
Correct Answer: Remove the dried film from the drum
Q19. Increasing drum rotation speed generally causes:
- Increased residence time on the drum
- No change in residence time
- Decreased residence time and thinner product
- Formation of spherical granules
Correct Answer: Decreased residence time and thinner product
Q20. Which drum configuration increases the heat transfer area without increasing footprint?
- Single narrow drum
- Double drum arrangement
- Flat tray configuration
- Vertical tubular drums stacked
Correct Answer: Double drum arrangement
Q21. Are drum dryers suitable for highly abrasive solid particles?
- Yes, they are ideal for heavy abrasives
- No, abrasive particles can damage the drum
- Only if the drum is painted
- Only if feed is gaseous
Correct Answer: No, abrasive particles can damage the drum
Q22. Which pharmaceutical excipient is commonly processed using a drum dryer?
- Starch and modified starches
- Compressed tablets
- Coated capsule shells intact
- Metallic salts in solid block
Correct Answer: Starch and modified starches
Q23. Cleaning drum dryers between batches is generally:
- Extremely simple and instantaneous
- Not required at all
- Challenging and time-consuming
- Done by dissolving the drum in solvent
Correct Answer: Challenging and time-consuming
Q24. In terms of energy efficiency, drum dryers are generally:
- Very energy inefficient compared to all dryers
- Energy efficient due to high heat transfer coefficients
- Only efficient if operated at cryogenic temperatures
- Efficient because they use no heating medium
Correct Answer: Energy efficient due to high heat transfer coefficients
Q25. Drum dryers are particularly suited for feeds with:
- Very low solids content (nearly pure solvent)
- High solids content and viscous nature
- Large hard crystalline lumps
- Only gaseous components
Correct Answer: High solids content and viscous nature
Q26. Increasing the film thickness on the drum surface will generally:
- Decrease drying time
- Increase drying time
- Have no effect on drying time
- Instantly evaporate the solvent
Correct Answer: Increase drying time
Q27. If the drum speed is increased while other settings remain constant, the product moisture content will likely:
- Decrease due to longer drying
- Increase due to decreased residence time
- Stay exactly the same
- Be unaffected by residence time
Correct Answer: Increase due to decreased residence time
Q28. Increasing steam pressure in the drum jacket typically results in:
- Lower drum surface temperature
- Higher heat transfer and faster drying
- Complete condensation of the product
- Freezing of the feed
Correct Answer: Higher heat transfer and faster drying
Q29. Typical residence time for material on a drum dryer is usually on the order of:
- Seconds to a few minutes
- Days
- Several weeks
- Multiple months
Correct Answer: Seconds to a few minutes
Q30. If the feed slurry is too viscous to spread evenly, the likely result is:
- Perfect uniform thin film
- Uneven film formation and non-uniform drying
- Instant vaporization
- Formation of crystals by cooling
Correct Answer: Uneven film formation and non-uniform drying
Q31. Which device is commonly used to meter and spread the feed onto the drum surface?
- Doctor blade or feeder roll
- High-pressure spray dryer nozzle
- Fluidized bed distributor
- Centrifugal pelletizer
Correct Answer: Doctor blade or feeder roll
Q32. To protect heat-sensitive APIs during drum drying, which approach is preferred?
- Increase drum temperature above degradation point
- Use vacuum drum drying or lower steam temperature
- Expose product longer to air at high temperature
- Add reactive oxidants before drying
Correct Answer: Use vacuum drum drying or lower steam temperature
Q33. Exposure of product to ambient air during scraping can lead to:
- Improved sterility
- Oxidation of sensitive components
- Instant sterilization
- Reduction in product density
Correct Answer: Oxidation of sensitive components
Q34. Solvent removal in a drum dryer primarily occurs by:
- Filtration through the drum wall
- Evaporation from the thin film surface
- Magnetic separation
- Cryogenic distillation on the drum
Correct Answer: Evaporation from the thin film surface
Q35. Which factor is least likely to influence the drying rate in a drum dryer?
- Film thickness
- Drum surface temperature
- Ambient humidity far from the machine
- Drum color or paint
Correct Answer: Drum color or paint
Q36. Product stickiness during drum drying is commonly associated with:
- High glass transition temperature relative to operating temperature
- Low glass transition temperature making material sticky at operating temperature
- Excessive crystallinity preventing stickiness
- Complete dryness before scraping
Correct Answer: Low glass transition temperature making material sticky at operating temperature
Q37. Is CIP (clean-in-place) easy to implement for drum dryers?
- Yes, drum dryers are the easiest equipment for CIP
- No, CIP is often difficult and mechanical cleaning may be required
- No cleaning is ever required for drum dryers
- CIP is unnecessary because drums are disposable
Correct Answer: No, CIP is often difficult and mechanical cleaning may be required
Q38. Scaling up a drum dryer capacity is typically achieved by:
- Decreasing drum length and speed
- Increasing drum length, diameter, or adding additional drums
- Removing the scraper to allow thicker layers
- Reducing steam pressure to zero
Correct Answer: Increasing drum length, diameter, or adding additional drums
Q39. Compared to spray drying, drum drying is more suitable for:
- Producing fine free-flowing powders from dilute feed
- Drying highly viscous pastes and heat-stable concentrates
- Drying volatile gases into solids
- Lyophilizing biologicals at cryogenic temperatures
Correct Answer: Drying highly viscous pastes and heat-stable concentrates
Q40. A pharmaceutical advantage of drum drying is:
- Extensive product handling increasing contamination risks
- Minimal product handling reducing contamination risk
- Complete elimination of thermal exposure for all products
- Guaranteed sterility without validation
Correct Answer: Minimal product handling reducing contamination risk
Q41. The drum surface finish should ideally be:
- Very rough to hold the film tightly
- Coated with adhesive for better adhesion
- Smooth and polished for easy film release
- Perforated with large holes
Correct Answer: Smooth and polished for easy film release
Q42. A frequent maintenance concern in drum dryers involves:
- Leakage of seals at drum ends
- Excessive use of cryogens
- Corrosion due to liquid nitrogen
- Failure of ultrasonic evaporators
Correct Answer: Leakage of seals at drum ends
Q43. Can waste heat or condensate from the drum dryer be recovered?
- No, all heat is lost to the environment
- Yes, condensate and waste heat can be recovered and reused
- Only if the drum is made of gold
- Recovery is impossible due to product contamination
Correct Answer: Yes, condensate and waste heat can be recovered and reused
Q44. Drum drying is classified under which drying mechanism?
- Contact drying
- Convective spray drying
- Freeze drying
- Supercritical drying
Correct Answer: Contact drying
Q45. Compared to spray dryers, drum dryers are better for:
- Dilute solutions producing fine powders
- Highly viscous feedstocks and pastes
- Producing sterile injectable powders without further processing
- Drying very fine aerosols
Correct Answer: Highly viscous feedstocks and pastes
Q46. Which is a limitation of drum dryers regarding final product characteristics?
- Excellent control of narrow particle size distribution
- Limited control over particle size and morphology
- Always produces spherical granules
- Produces monodisperse nanoparticles
Correct Answer: Limited control over particle size and morphology
Q47. To reduce sticking and caking on the drum, formulators may add:
- Anti-caking or release agents
- Large metal shavings
- Reactive oxidants
- Excess free water
Correct Answer: Anti-caking or release agents
Q48. Which parameter is commonly adjusted to control the product final moisture content?
- Drum surface temperature
- Color of the feed container
- Time of day
- Drum external decorative plating
Correct Answer: Drum surface temperature
Q49. Drum dryers are widely used in which industries relevant to pharmacists?
- Only aerospace industry
- Food and pharmaceutical industries
- Only mining industry
- Only textile dyeing
Correct Answer: Food and pharmaceutical industries
Q50. A key safety hazard associated with steam-heated drum dryers is:
- Risk of steam burns and high-temperature surfaces
- Spontaneous cryogenic freezing
- Emission of large amounts of ozone
- Instant electrification of dried product
Correct Answer: Risk of steam burns and high-temperature surfaces
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