Air separator – principle, construction, working, uses, merits, demerits MCQs With Answer is an essential topic for B.Pharm students studying particulate processing and powder technology. This introduction explains the air separator principle, key construction features, working mechanism, pharmaceutical uses (e.g., powder classification, deagglomeration, and dust removal), and practical merits and demerits affecting product quality and process efficiency. Emphasis is on design parameters, performance factors, and troubleshooting to ensure regulatory compliance in drug manufacturing. The content is tailored for exam preparation and practical application in formulation labs. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the primary principle by which an air separator classifies particles?
- Electrostatic attraction of particles
- Difference in magnetic susceptibility
- Difference in aerodynamic diameter and settling velocity
- Centrifugal crushing of particles
Correct Answer: Difference in aerodynamic diameter and settling velocity
Q2. Which component of an air separator creates the primary air stream for classification?
- Static collector
- Air blower or fan
- Vibrating sieve
- Magnetic coil
Correct Answer: Air blower or fan
Q3. In pharmaceutical air separators, what is the typical purpose of the rotor or impeller?
- To cool the product
- To impart rotational airflow and centrifugal forces aiding classification
- To chemically treat the powder
- To electrically charge particles
Correct Answer: To impart rotational airflow and centrifugal forces aiding classification
Q4. Which of the following is a common advantage (merit) of using air separators in drug manufacturing?
- High chemical reactivity
- Energy-free operation
- Dry classification and reduced contamination risk
- Guaranteed sterilization
Correct Answer: Dry classification and reduced contamination risk
Q5. Which factor does NOT significantly influence the cut-size (d50) of an air separator?
- Airflow velocity
- Particle density
- Ambient humidity to an extreme extent if wet agglomeration occurs
- Color of the powder
Correct Answer: Color of the powder
Q6. The working of an air separator often relies on a balance between two forces acting on particles. Which are they?
- Gravitational and magnetic forces
- Electrostatic and van der Waals forces
- Inertial (centrifugal) forces and aerodynamic drag
- Thermal and osmotic forces
Correct Answer: Inertial (centrifugal) forces and aerodynamic drag
Q7. What is a common application of air separators in pharmaceutical powder processing?
- Liquid sterilization
- Particle size classification before tableting or capsule filling
- Granule coating
- Tablet dissolution testing
Correct Answer: Particle size classification before tableting or capsule filling
Q8. Which construction material is preferred for contact parts of air separators used with active pharmaceutical ingredients (APIs)?
- Plain carbon steel
- Untreated wood
- Stainless steel (e.g., SS316)
- Copper
Correct Answer: Stainless steel (e.g., SS316)
Q9. Which disadvantage (demerit) is commonly associated with air separators?
- Complete elimination of fines
- Generation of noise and potential particle attrition
- They are always sterile
- No need for maintenance
Correct Answer: Generation of noise and potential particle attrition
Q10. How does increasing the airflow velocity generally affect classification cut-size?
- Increases cut-size (coarser cut)
- Decreases cut-size (finer cut)
- No effect on cut-size
- Only affects temperature, not cut-size
Correct Answer: Decreases cut-size (finer cut)
Q11. A common performance metric for air separators is the sharpness of cut. What does sharpness of cut describe?
- How loud the machine operates
- How narrowly the separator distinguishes between retained and passed particle sizes
- How quickly the separator corrodes
- How much electrical energy it uses
Correct Answer: How narrowly the separator distinguishes between retained and passed particle sizes
Q12. Which design feature helps reduce particle agglomeration inside an air separator?
- Excessive humidity without controls
- Smooth internal surfaces and controlled airflow to minimize dead zones
- Sharp thermal gradients
- Use of sticky internal coatings
Correct Answer: Smooth internal surfaces and controlled airflow to minimize dead zones
Q13. In an air classifier, the term “cut-point” refers to:
- The time after which the machine must be cleaned
- The particle diameter at which 50% is classified to the fine fraction
- The temperature at which particles melt
- The rotational speed of the motor in rpm
Correct Answer: The particle diameter at which 50% is classified to the fine fraction
Q14. Why is controlling moisture important in air separation of pharmaceutical powders?
- Moisture enhances electrostatic levitation beneficially
- Moisture can cause agglomeration and change aerodynamic behavior
- Moisture increases the magnetic properties of powders
- Moisture has no effect on air classification
Correct Answer: Moisture can cause agglomeration and change aerodynamic behavior
Q15. Which maintenance activity is critical to maintain performance of air separators?
- Regular sharpening of blades
- Frequent lubrication and inspection of bearings, and cleaning of air passages
- Refilling chemical reagents
- Replacing glass filters daily regardless of use
Correct Answer: Frequent lubrication and inspection of bearings, and cleaning of air passages
Q16. How does particle density affect classification in an air separator?
- Denser particles behave like finer particles aerodynamically
- Denser particles have lower settling velocity for same size
- Denser particles have higher inertia and are more likely to be classified as coarse
- Particle density has no effect
Correct Answer: Denser particles have higher inertia and are more likely to be classified as coarse
Q17. Which equation is most relevant for estimating aerodynamic behavior of small spherical particles in a fluid?
- Arrhenius equation
- Stokes’ law
- Ideal gas law
- Beer-Lambert law
Correct Answer: Stokes’ law
Q18. What is the role of a classifier cage or multi-slot rotor in some air separators?
- To heat the particles before classification
- To provide adjustable passages controlling cut-size by changing flow paths
- To chemically modify particle surfaces
- To add liquid binders
Correct Answer: To provide adjustable passages controlling cut-size by changing flow paths
Q19. In pneumatic conveying combined with air classification, what is an important consideration?
- Channeling of liquids through the line
- Ensuring conveying velocity does not re-entrain separated fines unintentionally
- Making sure particles dissolve en route
- Minimizing magnetic interference
Correct Answer: Ensuring conveying velocity does not re-entrain separated fines unintentionally
Q20. Which parameter is commonly adjusted during operation to change the separation efficiency dynamically?
- Color of the housing
- Rotor speed or fan/blower speed
- Chemical composition of the powder
- Room lighting
Correct Answer: Rotor speed or fan/blower speed
Q21. Which type of air separator uses a stationary stator and rotating rotor to impart centrifugal forces?
- Cyclonic separator
- Electrostatic precipitator
- Rotor-stator air classifier
- Gravitational sifter
Correct Answer: Rotor-stator air classifier
Q22. Which safety concern is important when operating air separators with fine pharmaceutical powders?
- Electrical short-circuit in humid powders
- Dust explosion and occupational inhalation exposure
- Excessive biodegradation of powders
- Radioactive emissions
Correct Answer: Dust explosion and occupational inhalation exposure
Q23. How are fines typically collected downstream of an air separator?
- By magnetic traps only
- Using filters, cyclone collectors, or baghouses
- They are simply vented to the atmosphere
- By dissolving in solvents
Correct Answer: Using filters, cyclone collectors, or baghouses
Q24. When comparing an air separator and a screen sieve, what is a key advantage of the air separator?
- Air separators can classify based on aerodynamic properties, allowing easier separation of near-spherical vs. irregular particles
- Air separators are always cheaper
- Screen sieves have no moving parts
- Screen sieves can process liquids better
Correct Answer: Air separators can classify based on aerodynamic properties, allowing easier separation of near-spherical vs. irregular particles
Q25. What effect does particle shape have on air classification?
- Only particle color matters
- Irregular shapes change aerodynamic diameter and affect drag, changing classification behavior
- Shape has no impact; only mass matters
- Shape only affects magnetic properties
Correct Answer: Irregular shapes change aerodynamic diameter and affect drag, changing classification behavior
Q26. Which operational change would generally produce a coarser product from an air separator?
- Increasing airflow velocity
- Decreasing airflow velocity
- Decreasing feed rate drastically
- Increasing humidity to cause agglomeration
Correct Answer: Decreasing airflow velocity
Q27. Why might a pharmaceutical manufacturer prefer an air separator over wet classification?
- Air separators require solvents
- Dry classification avoids solvent residues and additional drying steps
- Wet classification is faster always
- Air separators always sterilize powders
Correct Answer: Dry classification avoids solvent residues and additional drying steps
Q28. What is an indicator of wear in an air separator that may alter classification performance?
- Change in paint color
- Increased clearances, damaged rotor vanes, and reduced sharpness of cut
- Increase in product potency
- Lower room humidity
Correct Answer: Increased clearances, damaged rotor vanes, and reduced sharpness of cut
Q29. In pharmaceutical practice, air separators are often integrated into which processing step?
- Final dissolution testing
- Pre-granulation and post-milling size classification
- Tablet coating drying
- Sterile filtration of liquids
Correct Answer: Pre-granulation and post-milling size classification
Q30. What is a common method to calibrate or verify cut-size of an air separator?
- Weighing the machine
- Using standard particle size reference materials and sieve or laser diffraction analysis
- Measuring electrical resistance
- Using smell test
Correct Answer: Using standard particle size reference materials and sieve or laser diffraction analysis
Q31. Which design modification can improve energy efficiency of an air separator?
- Using oversized motors without controls
- Optimizing airflow paths, using variable frequency drives, and minimizing pressure losses
- Running at max speed at all times
- Removing all sealing from ports
Correct Answer: Optimizing airflow paths, using variable frequency drives, and minimizing pressure losses
Q32. How does feed rate influence air separation performance?
- Higher feed rates never affect separation
- Too high feed rates can overload the separator and reduce classification efficiency
- Lower feed rates always produce coarser product
- Feed rate only affects color
Correct Answer: Too high feed rates can overload the separator and reduce classification efficiency
Q33. Which of the following is a typical demerit specific to pharmaceutical applications of air separators?
- Inability to handle dusts
- Possible cross-contamination if not properly contained
- Instant sterility of APIs
- Requires no validation
Correct Answer: Possible cross-contamination if not properly contained
Q34. What role does a feed distributor play in an air separator?
- Increases particle stickiness
- Ensures even distribution of material into the airflow for consistent classification
- Heats the feed
- Removes moisture chemically
Correct Answer: Ensures even distribution of material into the airflow for consistent classification
Q35. Which measurement technique is commonly used to evaluate separated fractions?
- Mass spectrometry of gases
- Particle size analysis by laser diffraction or sieve analysis
- UV-Vis spectroscopy of solids
- NMR of the bulk powder
Correct Answer: Particle size analysis by laser diffraction or sieve analysis
Q36. For very cohesive powders, which strategy improves separation in an air separator?
- Increasing humidity to promote clumping
- Pre-deagglomeration by milling or using ultrasonic or mechanical deagglomerators
- Reducing airflow to zero
- Mixing with sticky binders
Correct Answer: Pre-deagglomeration by milling or using ultrasonic or mechanical deagglomerators
Q37. Why is validation important for air separators used in pharmaceutical production?
- Validation is only for computers
- To ensure consistent performance, reproducible particle size distribution, and regulatory compliance
- Validation makes machines heavier
- It eliminates the need for cleaning
Correct Answer: To ensure consistent performance, reproducible particle size distribution, and regulatory compliance
Q38. Which parameter is often displayed on a control panel to monitor air separator performance?
- Number of operators in the room
- Airflow rate, rotor speed, and differential pressure
- Color of the powder
- Ambient music volume
Correct Answer: Airflow rate, rotor speed, and differential pressure
Q39. What is the likely effect of particle charging (electrostatic) inside an air separator?
- No impact at all
- It may cause particles to adhere to internal surfaces and reduce efficiency
- Always improves separation sharpness
- Makes particles magnetic
Correct Answer: It may cause particles to adhere to internal surfaces and reduce efficiency
Q40. Which type of pharmaceutical material is least suitable for dry air separation?
- Free-flowing, non-hygroscopic powders
- Highly hygroscopic and sticky powders prone to caking
- Granules requiring size classification
- Dry crystalline APIs
Correct Answer: Highly hygroscopic and sticky powders prone to caking
Q41. In an air separator, what is the effect of reducing the gap between rotor and stator?
- Reduces classification performance
- Generally increases centrifugal forces and sharpness of cut, influencing cut-size
- Makes the machine quieter but ineffective
- Has no mechanical impact
Correct Answer: Generally increases centrifugal forces and sharpness of cut, influencing cut-size
Q42. Which cleaning procedure is important between product changeovers to avoid cross-contamination?
- Only wipe with a dry cloth
- Validated clean-in-place (CIP) or thorough manual cleaning per SOPs
- Run the separator empty without cleaning
- Paint the interior
Correct Answer: Validated clean-in-place (CIP) or thorough manual cleaning per SOPs
Q43. What is a common method to reduce noise generated by air separators?
- Operate at higher speeds
- Use acoustic enclosures, dampers, and proper maintenance
- Leave the housing open
- Replace metal parts with glass
Correct Answer: Use acoustic enclosures, dampers, and proper maintenance
Q44. How can one quantify the efficiency of separation for a given size fraction?
- By measuring electrical consumption only
- By determining recovery percentage and grade (mass balance of target size in product vs feed)
- By the color change of the powder
- By the sound produced
Correct Answer: By determining recovery percentage and grade (mass balance of target size in product vs feed)
Q45. Which accessory is often used to control dust emissions from an air separator?
- Heat exchanger
- Bag filter or HEPA filter unit
- Open funnel
- Magnetic stirrer
Correct Answer: Bag filter or HEPA filter unit
Q46. What is the likely effect of temperature on air separation performance?
- Temperature changes density and viscosity of air, slightly altering drag and cut-size
- Temperature only affects magnetic powders
- Temperature has no physical effect
- Higher temperatures always make particles dissolve
Correct Answer: Temperature changes density and viscosity of air, slightly altering drag and cut-size
Q47. Which metric indicates the uniformity of particle size distribution after classification?
- Polydispersity index or span of the distribution
- Electrical conductivity
- Absolute humidity
- Color index
Correct Answer: Polydispersity index or span of the distribution
Q48. In regulatory contexts, documentation around an air separator must include:
- Only the paint supplier details
- Design specifications, validation data, cleaning procedures, and maintenance logs
- Operator phone numbers only
- Only the initial purchase invoice
Correct Answer: Design specifications, validation data, cleaning procedures, and maintenance logs
Q49. What modification can reduce particle attrition during air classification?
- Increasing impact zones and sharp edges
- Using gentler airflow profiles, smoother internal surfaces, and adjustable rotor speeds
- Adding abrasive inserts
- Increasing feed particle hardness chemically
Correct Answer: Using gentler airflow profiles, smoother internal surfaces, and adjustable rotor speeds
Q50. Which is a realistic performance goal when designing an air separation step for a tablet formulation?
- Achieve a precise, reproducible particle size distribution to ensure content uniformity and flowability
- Guarantee 0% variability in all cases
- Eliminate the need for granulation
- Allow uncontrolled fines in final blend
Correct Answer: Achieve a precise, reproducible particle size distribution to ensure content uniformity and flowability
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