Multiple effect evaporator – principle, construction, working, uses, merits, demerits MCQs With Answer

Multiple effect evaporator – principle, construction, working, uses, merits, demerits MCQs With Answer is an essential topic for B. Pharm students studying pharmaceutical engineering and unit operations. This guide explains the multiple effect evaporator principle, detailed construction, working mechanisms, operational uses, merits and demerits with focus on steam economy, boiling point elevation, types (forward, backward, rising/falling film, forced circulation), heat transfer and scale control. Ideal for exam preparation and practical understanding, the content emphasizes design considerations, process parameters, troubleshooting and material selection relevant to pharmaceutical concentrates and solvents. Clear explanations and focused MCQs help reinforce concepts and improve problem-solving skills. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary principle behind a multiple effect evaporator?

• Using multiple heating sources to raise temperature
• Sequential use of vapor from one effect to heat the next
• Compressing vapor to increase boiling point
• Adding vacuum to each effect separately

Correct Answer: Sequential use of vapor from one effect to heat the next

Q2. What is “steam economy” in a multiple effect evaporator?

• The ratio of feed flow to steam flow
• The amount of steam condensed per unit of evaporation
• The mass of vapor produced per unit mass of steam supplied
• The heat transfer coefficient multiplied by area

Correct Answer: The mass of vapor produced per unit mass of steam supplied

Q3. In an n-effect evaporator running at similar temperature drops per effect, the theoretical steam economy is approximately:

• n/2
• n
• 2n
• √n

Correct Answer: n

Q4. Boiling point elevation (BPE) in evaporators refers to:

• Increase in boiling point due to dissolved non-volatile solutes
• Decrease in boiling point caused by vacuum
• Temperature difference between steam and condensate
• Temperature rise in heating steam under pressure

Correct Answer: Increase in boiling point due to dissolved non-volatile solutes

Q5. Which feed arrangement minimizes thermal degradation for heat-sensitive pharmaceutical solutions?

• Forward feed
• Backward feed
• Cross feed
• Single pass feed

Correct Answer: Backward feed

Q6. Which type of evaporator is best suited for viscous or fouling-prone pharmaceutical feeds?

• Rising film evaporator
• Falling film evaporator
• Forced circulation evaporator
• Natural circulation evaporator

Correct Answer: Forced circulation evaporator

Q7. What is the main advantage of falling film evaporators in pharmaceuticals?

• High residence time for slow reactions
• Low liquid hold-up and gentle heating
• Very high circulation ratios
• Operates only under high pressure

Correct Answer: Low liquid hold-up and gentle heating

Q8. In a forward-feed multiple effect evaporator, feed enters:

• The last effect and moves to the first
• Each effect at the same point simultaneously
• The first effect and moves to successive effects of lower temperature
• Only the middle effect

Correct Answer: The first effect and moves to successive effects of lower temperature

Q9. The main purpose of a condenser in a multiple effect evaporator system is to:

• Increase feed concentration
• Condense final vapor to maintain vacuum and recover condensate
• Preheat incoming steam
• Filter solids from vapor

Correct Answer: Condense final vapor to maintain vacuum and recover condensate

Q10. Which operating parameter most directly affects evaporation rate in an effect?

• Surface roughness of tubes
• Temperature difference between heating steam and boiling liquid
• Color of the vessel
• Ambient humidity outside the plant

Correct Answer: Temperature difference between heating steam and boiling liquid

Q11. Entrainment in evaporators refers to:

• Solid particles settling at the bottom
• Liquid droplets carried away with vapor
• Condensate flowing back into feed
• Steam leaking to atmosphere

Correct Answer: Liquid droplets carried away with vapor

Q12. Which device is commonly used to reduce entrainment before vapor enters the condenser?

• Thermocompressor
• Demister or vapor separator
• Feed heater
• Plate heat exchanger

Correct Answer: Demister or vapor separator

Q13. Rising film evaporators rely on which driving force to create the film?

• Forced pumping by external pump
• Vapor-lift created by vapor generation
• Gravity exclusively
• Magnetic stirring

Correct Answer: Vapor-lift created by vapor generation

Q14. Which material is commonly used for heat transfer surfaces in pharmaceutical evaporators to resist corrosion and meet GMP?

• Plain carbon steel with no lining
• Stainless steel (SS 316)
• Cast iron
• Brass

Correct Answer: Stainless steel (SS 316)

Q15. Boiling point elevation affects multiple effect evaporators by:

• Reducing the steam economy and requiring larger heat transfer area
• Increasing vapor velocity and improving economy
• Lowering feed viscosity drastically
• Enhancing nucleate boiling uniformly

Correct Answer: Reducing the steam economy and requiring larger heat transfer area

Q16. Thermocompression in evaporators is primarily used to:

• Reduce feed volume
• Compress and reuse vapor to improve economy
• Cool the product quickly
• Separate solids from liquid

Correct Answer: Compress and reuse vapor to improve economy

Q17. For a multiple effect evaporator, “overall heat transfer coefficient (Uo)” depends on:

• Only the temperature of steam
• Fouling resistances, film coefficients, and thermal conductivity of tube wall
• Ambient air temperature
• Only the tube length

Correct Answer: Fouling resistances, film coefficients, and thermal conductivity of tube wall

Q18. Which cleaning method is preferred for internal scale removal in pharmaceutical evaporators?

• High pressure abrasive blasting
• CIP (clean-in-place) using appropriate acidic/alkaline solutions
• Manual scraping while hot
• Burning residues with open flame

Correct Answer: CIP (clean-in-place) using appropriate acidic/alkaline solutions

Q19. The term “circulation ratio” in forced circulation evaporators is defined as:

• Mass of vapor produced per unit time
• Ratio of recirculated liquid to feed in the evaporator
• Feed temperature divided by steam temperature
• Number of effects divided by heat transfer area

Correct Answer: Ratio of recirculated liquid to feed in the evaporator

Q20. Cross-flow or parallel feed arrangement is typically used when:

• Feed is highly heat-sensitive and requires minimal temperature rise
• Feed requires equal residence time in all effects and simple hardware
• Maximum steam economy is desired
• Product must be cooled rather than concentrated

Correct Answer: Feed requires equal residence time in all effects and simple hardware

Q21. Which effect in a multiple effect evaporator usually operates at the highest temperature?

• Final effect
• Middle effect
• First effect
• All effects operate at same absolute temperature

Correct Answer: First effect

Q22. A falling film evaporator is most appropriate when the product is:

• Very viscous and requires long residence time
• Heat-sensitive and requires short residence time
• Solid slurry with high particulate content
• Non-volatile gaseous mixture

Correct Answer: Heat-sensitive and requires short residence time

Q23. What is the primary disadvantage of increasing the number of effects indefinitely?

• Unlimited improvement in economy without downsides
• Higher capital cost, complexity, and diminishing returns
• Reduced product quality always
• Failure to concentrate feed at all

Correct Answer: Higher capital cost, complexity, and diminishing returns

Q24. In backward-feed arrangement, concentration increases in the direction of:

• Decreasing temperature
• Increasing temperature
• Random order
• Only within the first effect

Correct Answer: Increasing temperature

Q25. Which of the following is a common operational problem causing reduced heat transfer in evaporators?

• Excessive vacuum
• Scaling and fouling on heat transfer surfaces
• Too much demisting
• High feed humidity

Correct Answer: Scaling and fouling on heat transfer surfaces

Q26. Mechanical vapor recompression (MVR) differs from thermocompression by:

• Using steam ejectors only
• Using mechanical compressors to raise vapor pressure and temperature
• Eliminating the need for condensers
• Reducing the boiling point elevation

Correct Answer: Using mechanical compressors to raise vapor pressure and temperature

Q27. What is the effect of operating under vacuum in an evaporator?

• Increases boiling temperature of the liquid
• Lowers boiling temperature, useful for heat-sensitive materials
• Has no effect on boiling point
• Causes solids to precipitate immediately

Correct Answer: Lowers boiling temperature, useful for heat-sensitive materials

Q28. In pharmaceutical evaporations, why is minimizing residence time often important?

• To maximize color formation
• To prevent thermal degradation of active pharmaceutical ingredients
• To promote crystallization at high temperature
• To allow more scaling to form

Correct Answer: To prevent thermal degradation of active pharmaceutical ingredients

Q29. Which effect receives the steam directly from the boiler in a conventional multiple effect evaporator?

• Last effect
• Second effect
• First effect
• No effect receives boiler steam directly

Correct Answer: First effect

Q30. Heat transfer area required in an evaporator is inversely proportional to:

• Overall heat transfer coefficient and log mean temperature difference
• Mass flow of feed only
• Boiling point elevation only
• Number of operators

Correct Answer: Overall heat transfer coefficient and log mean temperature difference

Q31. Which multiple effect feed arrangement provides the best thermal efficiency but may increase product degradation?

• Forward feed
• Backward feed
• Cross feed
• Recirculation feed

Correct Answer: Forward feed

Q32. If feed contains volatile solvents (e.g., ethanol), what precaution is essential during evaporation?

• Increase steam pressure only
• Control temperature to avoid solvent loss and handle flammability, use condensation recovery
• Use open heating to vent vapors freely
• Avoid condensers to reduce contamination

Correct Answer: Control temperature to avoid solvent loss and handle flammability, use condensation recovery

Q33. Which parameter measures how much heat is transferred per unit area per degree temperature difference?

• Steam economy
• Overall heat transfer coefficient (U)
• Boiling point elevation
• Circulation ratio

Correct Answer: Overall heat transfer coefficient (U)

Q34. What is the main merit of multiple effect evaporators in pharmaceutical production?

• Higher capital cost but lower energy usage per unit evaporated
• Lower steam economy compared to single effect
• Unlimited scaling prevention
• They are single-use only

Correct Answer: Higher capital cost but lower energy usage per unit evaporated

Q35. Which factor is least likely to influence the choice between falling film and forced circulation evaporators?

• Viscosity of feed
• Heat sensitivity of product
• Particle loading in feed
• Color of the evaporator paint

Correct Answer: Color of the evaporator paint

Q36. In a multiple effect evaporator, vapour bleed is sometimes used to:

• Increase entrainment
• Provide vapor to a downstream dryer or crystallizer and control pressure
• Cool the first effect
• Replace condensers entirely

Correct Answer: Provide vapor to a downstream dryer or crystallizer and control pressure

Q37. Scaling in evaporators reduces performance primarily by:

• Increasing effective heat transfer coefficient
• Adding thermal resistance and reducing heat transfer rate
• Decreasing feed concentration automatically
• Enhancing nucleate boiling uniformly

Correct Answer: Adding thermal resistance and reducing heat transfer rate

Q38. What is the effect of high liquid viscosity on film-type evaporators?

• Improves film formation and heat transfer
• Causes thicker films, reduced heat transfer and may require forced circulation
• Has no effect at all
• Enhances vapor quality dramatically

Correct Answer: Causes thicker films, reduced heat transfer and may require forced circulation

Q39. The “log mean temperature difference (LMTD)” in evaporator design is used to:

• Estimate vapor velocity
• Calculate driving temperature difference for heat transfer across an effect
• Measure condenser pressure
• Determine steam purity

Correct Answer: Calculate driving temperature difference for heat transfer across an effect

Q40. Which method is commonly used to determine the number of effects required for a desired steam economy?

• Trial and error with no calculations
• Energy balance and steam economy equations considering boiling point elevations and ΔT per effect
• Counting the number of tanks available
• Using ambient temperature alone

Correct Answer: Energy balance and steam economy equations considering boiling point elevations and ΔT per effect

Q41. Which of the following is a demerit of multiple effect evaporators?

• High energy consumption per unit evaporated
• Complexity, higher initial capital cost and larger floor space
• Impossible to scale-up
• Cannot handle heat-sensitive materials

Correct Answer: Complexity, higher initial capital cost and larger floor space

Q42. When designing evaporators for sterile pharmaceutical products, which consideration is critical?

• Use of flammable materials for better economy
• Material selection (304/316 SS), sanitary design, and CIP compatibility
• Open-top vessels without seals
• Using unregulated condensers

Correct Answer: Material selection (304/316 SS), sanitary design, and CIP compatibility

Q43. Which control strategy helps maintain product concentration in continuous evaporators?

• Open-loop control without sensors
• Level control in effects and concentration monitoring with feedback to feed rate
• Random manual adjustments by operator only
• Shutting down half of the effects periodically

Correct Answer: Level control in effects and concentration monitoring with feedback to feed rate

Q44. Flash steam loss in evaporators can be minimized by:

• Increasing pressure drop in pipes
• Using condensers or vapor recompression and careful pressure control
• Removing demisters
• Reducing heat transfer area

Correct Answer: Using condensers or vapor recompression and careful pressure control

Q45. Which statement about thermocompressor (steam ejector) in evaporator systems is true?

• It uses motive steam to entrain and compress vapors but reduces overall steam quality
• It cools vapor without compression
• It increases the number of effects automatically
• It acts as a chemical additive to reduce scaling

Correct Answer: It uses motive steam to entrain and compress vapors but reduces overall steam quality

Q46. Why is preheating feed often practiced before entering the first effect?

• To cool the feed to ambient
• To reduce steam consumption and improve economy by using available heat
• To increase boiling point elevation unexpectedly
• To increase entrainment losses

Correct Answer: To reduce steam consumption and improve economy by using available heat

Q47. In heat-sensitive botanical extracts, which evaporator configuration is preferred?

• High temperature single effect only
• Multiple effect with backward or falling film design under vacuum
• Open kettle boiling
• Direct flame heating

Correct Answer: Multiple effect with backward or falling film design under vacuum

Q48. Which operational parameter should be monitored to avoid product foaming in evaporators?

• Feed pH, surfactant content, and vapor velocity; use antifoam if needed
• Only ambient light intensity
• Paint color of the vessel
• Time of day

Correct Answer: Feed pH, surfactant content, and vapor velocity; use antifoam if needed

Q49. In a pharmaceutical plant, the condensate from evaporators is often:

• Disposed without treatment regardless of content
• Recovered, tested and either reused as process water or sent to treatment depending on purity
• Ignited immediately
• Mixed with feed to increase yield

Correct Answer: Recovered, tested and either reused as process water or sent to treatment depending on purity

Q50. Which design approach helps reduce fouling and maintain high U in evaporators?

• Design for low shear and stagnant films
• Allow uncontrolled scale formation for protection
• High turbulence on heating surfaces, appropriate materials and regular CIP schedules
• Use narrow tubes with no access for cleaning

Correct Answer: High turbulence on heating surfaces, appropriate materials and regular CIP schedules

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