Cyclone separator – principle, construction, working, uses, merits, demerits is an essential topic for B. Pharm students studying air pollution control and powder handling in the pharmaceutical industry. A cyclone separator removes airborne particles from gas streams using centrifugal force and vortex flow; its basic construction includes an inlet, cylindrical body, cone, vortex finder and dust outlet. Understanding working principles, performance factors (cut-off diameter, pressure drop, efficiency), applications in dry powder processing, merits like no moving parts, and demerits such as low fine-particle capture is vital for GMP-compliant plant design and dust control. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the primary mechanism by which a cyclone separator removes particles from a gas stream?
- Electrostatic attraction
- Gravitational settling
- Centrifugal force created by a vortex
- Chemical absorption
Correct Answer: Centrifugal force created by a vortex
Q2. Which part of a cyclone directs the clean gas out of the unit?
- Inlet nozzle
- Vortex finder (dip tube)
- Cone section
- Dust hopper
Correct Answer: Vortex finder (dip tube)
Q3. Which inlet design is most commonly used to create the required swirl in a cyclone?
- Axial inlet
- Tangential inlet
- Perforated inlet
- Radial inlet
Correct Answer: Tangential inlet
Q4. The cone section of a cyclone mainly improves separation by:
- Reducing gas temperature
- Increasing residence time and centrifugal action
- Filtering particles chemically
- Providing electrical charge to particles
Correct Answer: Increasing residence time and centrifugal action
Q5. The term “cut-off diameter (d50)” in cyclone performance means:
- The maximum particle size that can pass through
- The diameter at which 50% of particles are collected
- The diameter of the vortex finder
- The smallest particle the cyclone can collect
Correct Answer: The diameter at which 50% of particles are collected
Q6. Which factor generally increases collection efficiency for a given cyclone?
- Lowering inlet velocity
- Increasing particle density
- Decreasing cyclone height
- Using an axial inlet
Correct Answer: Increasing particle density
Q7. For which particle size range are cyclones most efficient in typical practice?
- Sub-0.1 µm
- 0.1–1 µm
- 1–10 µm and above
- Only particles above 1 mm
Correct Answer: 1–10 µm and above
Q8. Which of the following is a major advantage of cyclone separators in pharmaceutical plants?
- High collection efficiency for ultrafine particles without add-ons
- No moving parts, low maintenance and robustness
- Wet scrubbing of toxic vapors
- Sterile filtration of aerosols
Correct Answer: No moving parts, low maintenance and robustness
Q9. A common limitation (demerit) of cyclone separators is:
- Excessive chemical reactivity with powders
- Inefficiency for very fine (submicron) particles
- Requirement for large rotating machinery inside
- Inability to handle abrasive dusts
Correct Answer: Inefficiency for very fine (submicron) particles
Q10. What phenomenon describes particles already collected that are drawn back into the gas stream?
- Compression
- Attrition
- Re-entrainment
- Agglomeration
Correct Answer: Re-entrainment
Q11. Which empirical or theoretical approach is commonly used to estimate cyclone performance?
- Lapple theory
- Michaelis-Menten kinetics
- Raoult’s law
- Beer-Lambert law
Correct Answer: Lapple theory
Q12. Increasing gas velocity in a cyclone typically affects cut-off diameter how?
- Increases d50 (worse for small particles)
- Decreases d50 (better capture of smaller particles)
- Has no effect on d50
- Only affects particle density, not d50
Correct Answer: Decreases d50 (better capture of smaller particles)
Q13. What is the inner upward flow in a cyclone called?
- Outer vortex
- Boundary layer
- Inner vortex or reverse flow
- Laminar core
Correct Answer: Inner vortex or reverse flow
Q14. Which design modification is used to improve fine particle collection without a full filter?
- Add a longer vortex finder and reduce velocity
- Use multi-cyclone arrays or add electrostatic enhancement
- Replace the cone with a flat plate
- Always use axial inlets
Correct Answer: Use multi-cyclone arrays or add electrostatic enhancement
Q15. In pharmaceutical applications, which material is commonly chosen for cyclone construction due to cleanliness and corrosion resistance?
- Cast iron
- Stainless steel
- Untreated carbon steel
- Wood-lined steel
Correct Answer: Stainless steel
Q16. What is the effect of increasing particle density on cyclone collection efficiency, all else equal?
- Efficiency decreases
- Efficiency increases
- No change in efficiency
- Efficiency becomes zero
Correct Answer: Efficiency increases
Q17. Short-circuiting in a cyclone occurs when:
- Particles settle too early in the hopper
- Gas exits quickly through the vortex finder without full swirl
- The inlet is too long
- The cone angle is too steep
Correct Answer: Gas exits quickly through the vortex finder without full swirl
Q18. Which performance curve is most informative when evaluating a cyclone?
- Pressure vs temperature curve
- Collection efficiency vs particle size curve
- Voltage vs current curve
- Absorbance vs concentration curve
Correct Answer: Collection efficiency vs particle size curve
Q19. Which operational change will generally increase cyclone pressure drop?
- Reducing gas velocity
- Increasing gas volumetric flow rate
- Making the vortex finder longer only
- Decreasing particle load
Correct Answer: Increasing gas volumetric flow rate
Q20. Why are cyclones often used as pre-separators upstream of bag filters in pharma plants?
- To remove all submicron particles
- To reduce dust load to downstream filters and extend filter life
- To sterilize the exhaust air
- To chemically neutralize particles
Correct Answer: To reduce dust load to downstream filters and extend filter life
Q21. Which shape of cyclone body commonly gives improved separation compared to a simple cylinder?
- Conical (cylinder-cone) body
- Triangular body
- Rectangular body
- Flat disc body
Correct Answer: Conical (cylinder-cone) body
Q22. Which cleaning/discharge device is typically used to remove collected powder from the hopper while maintaining isolation?
- Rotary valve (airlock)
- Open bucket
- Manual scooping during operation
- Venturi scrubber
Correct Answer: Rotary valve (airlock)
Q23. Which of the following best describes the vortex core inside a cyclone?
- High-pressure rotating solid column
- Low-pressure axial region where inner vortex rises
- Stationary central plug of particles
- Uniform laminar flow region
Correct Answer: Low-pressure axial region where inner vortex rises
Q24. According to basic theory, particle capture is favored when particle inertia is:
- Very low compared to gas inertia
- High enough to overcome the gas streamlines and move to the wall
- Equal to Brownian motion
- Negligible under all conditions
Correct Answer: High enough to overcome the gas streamlines and move to the wall
Q25. Which dimensionless parameter is useful for characterizing particle response to the flow in a cyclone?
- Prandtl number
- Stokes number
- Biot number
- Nusselt number
Correct Answer: Stokes number
Q26. Stairmand vortex design is known for:
- Worse performance than uncontrolled designs
- Providing geometry charts for high-efficiency cyclones
- Being used only for liquid separation
- Eliminating the need for a vortex finder
Correct Answer: Providing geometry charts for high-efficiency cyclones
Q27. Which operating condition will most likely lead to particle attrition and generation of fines within a cyclone?
- Low particle concentration
- High-velocity tangential inlet causing intense collisions
- Using a gentle axial flow
- Smooth particle surfaces and low turbulence
Correct Answer: High-velocity tangential inlet causing intense collisions
Q28. When designing cyclones for GMP pharmaceutical use, which consideration is especially important?
- Using porous materials for better filtration
- Sanitary design with smooth welds and cleanable surfaces
- Painting interior with rough coatings
- Open top for visual inspection during operation
Correct Answer: Sanitary design with smooth welds and cleanable surfaces
Q29. Multi-cyclone (parallel small cyclones) arrays are used primarily to:
- Increase pressure drop without improving efficiency
- Improve collection efficiency for fine particles and handle large gas volumes
- Remove gases instead of particles
- Create electrostatic charging
Correct Answer: Improve collection efficiency for fine particles and handle large gas volumes
Q30. Which operational parameter is most directly proportional to centrifugal force experienced by a particle in a cyclone?
- Particle surface area
- Square of tangential velocity
- Ambient humidity
- Length of the dust hopper
Correct Answer: Square of tangential velocity
Q31. Which condition would reduce a cyclone’s efficiency for a given particle size?
- Increasing particle density
- Lowering gas viscosity and density proportionally
- Operating at much lower Reynolds number leading to laminar flow
- Adding a conical extension
Correct Answer: Operating at much lower Reynolds number leading to laminar flow
Q32. Cyclones are especially suited for handling which type of dust in pharmaceutical plants?
- Sticky, wet agglomerates that clog easily
- Abrasive, dry particulate dusts where robustness is needed
- Sterile biological aerosols requiring HEPA-level capture only
- Highly soluble particulates in liquid streams
Correct Answer: Abrasive, dry particulate dusts where robustness is needed
Q33. Which factor does NOT directly influence cyclone efficiency?
- Particle size distribution
- Gas flow pattern and velocity
- Color of the cyclone exterior paint
- Cyclone geometry (vortex finder, cone angle)
Correct Answer: Color of the cyclone exterior paint
Q34. What is the primary reason cyclones are not considered sufficient as the only control device for ultra-fine pharmaceutical aerosols?
- They generate toxic by-products
- They have limited submicron capture efficiency
- They require electrical power to collect particles
- They are too expensive to install
Correct Answer: They have limited submicron capture efficiency
Q35. Which device is commonly combined with a cyclone to achieve high overall particulate removal in pharma exhausts?
- Baghouse (fabric filter) or HEPA filter downstream
- Gravity settling chamber only
- Electrolytic cell
- Absorption column for gases
Correct Answer: Baghouse (fabric filter) or HEPA filter downstream
Q36. What role do baffles or swirl vanes at the inlet sometimes play?
- Break the swirl to make flow axial
- Enhance vortex generation and distribute flow evenly
- Add electric charge to particles
- Decrease residence time intentionally
Correct Answer: Enhance vortex generation and distribute flow evenly
Q37. Which maintenance task is most critical to ensure consistent cyclone performance?
- Repainting the exterior every month
- Regular removal of accumulated dust from the hopper and checking discharge valves
- Changing the vortex finder weekly regardless of condition
- Replacing the entire body yearly
Correct Answer: Regular removal of accumulated dust from the hopper and checking discharge valves
Q38. In the Lapple model, cyclone efficiency depends on a parameter that includes which of the following?
- Particle electrical charge only
- Gas viscosity, particle size, and flow velocity
- Color and optical properties of dust
- Magnetic susceptibility of particles
Correct Answer: Gas viscosity, particle size, and flow velocity
Q39. Which operational safety consideration is crucial when a cyclone handles explosive pharmaceutical dust?
- Ensure ignition sources are eliminated and design is explosion-proof
- Use wooden blowers for electrical isolation
- Keep the cyclone open to atmosphere at all times
- Mix the dust with water inside the cyclone
Correct Answer: Ensure ignition sources are eliminated and design is explosion-proof
Q40. What happens to collection efficiency if the vortex finder is too short?
- Efficiency increases due to longer swirl
- Short-circuiting may occur and efficiency decreases
- No change in performance
- The cyclone becomes a bag filter
Correct Answer: Short-circuiting may occur and efficiency decreases
Q41. Which of the following best describes re-entrainment prevention strategies?
- Increase turbulence in the hopper
- Use smooth hopper slopes, reduce shear near wall, and ensure timely dust removal
- Remove the hopper entirely
- Intentionally vibrate the vortex finder
Correct Answer: Use smooth hopper slopes, reduce shear near wall, and ensure timely dust removal
Q42. How does increasing the number of parallel cyclones (smaller diameter each) affect overall performance for a fixed total flow?
- Decreases efficiency and increases pressure drop dramatically
- Can increase collection efficiency for fine particles while keeping manageable pressure drop
- Makes no difference to performance
- Only affects color of the dust
Correct Answer: Can increase collection efficiency for fine particles while keeping manageable pressure drop
Q43. Which particulate property most strongly influences separation in a cyclone when comparing two particles of equal size?
- Particle color
- Particle density
- Optical reflectivity
- Magnetic moment (unless magnetic)
Correct Answer: Particle density
Q44. Which of the following is a common indicator that a cyclone is overloaded with dust?
- Decrease in outlet gas clarity and increased pressure drop
- Complete elimination of pressure drop
- Appearance of liquid in the hopper only
- Noise stops entirely
Correct Answer: Decrease in outlet gas clarity and increased pressure drop
Q45. The main energy penalty of operating a cyclone is due to:
- Energy used to heat the gas
- Pressure drop across the cyclone that must be overcome by fans
- Energy lost in dust disposal
- Electricity used by internal motors
Correct Answer: Pressure drop across the cyclone that must be overcome by fans
Q46. Which improvement technique adds an electrical field to help cyclone performance for fine particles?
- Wet scrubbing
- Electrostatic enhancement (electrostatic precipitator combined design)
- Increasing hopper slope only
- Shortening the vortex finder
Correct Answer: Electrostatic enhancement (electrostatic precipitator combined design)
Q47. For hygienic pharmaceutical operations, which design feature helps avoid cross-contamination during maintenance?
- Hard-to-access service hatches
- Quick-release clamps and sanitary flanges for easy cleaning and inspection
- Open top design for manual access during operation
- Painted interior that flakes off for easy replacement
Correct Answer: Quick-release clamps and sanitary flanges for easy cleaning and inspection
Q48. Which statement about cyclone and bag filter comparison is true?
- Cyclones generally give higher capture of submicron particles than bag filters
- Bag filters achieve higher fine-particle efficiency, but cyclones are simpler and more robust
- Both are identical in cost and performance
- Cyclones operate only in liquid streams while bag filters are for gases
Correct Answer: Bag filters achieve higher fine-particle efficiency, but cyclones are simpler and more robust
Q49. Which maintenance-friendly discharge mechanism is often used for sticky or cohesive pharmaceutical powders?
- Open dump directly below cyclone
- Screw conveyor or pneumatic conveying discharge system
- Manual scooping while operating
- Forced washing with solvents during operation
Correct Answer: Screw conveyor or pneumatic conveying discharge system
Q50. To improve capture of very fine pharmaceutical aerosol (submicron), the most practical retrofit option is to:
- Paint the cyclone interior a lighter color
- Add a downstream HEPA or fabric filter or use electrostatic enhancement
- Shorten the vortex finder to increase speed
- Reduce the hopper slope to 10 degrees
Correct Answer: Add a downstream HEPA or fabric filter or use electrostatic enhancement
