Forced circulation evaporator – principle, construction, working, uses, merits, demerits MCQs With Answer is a focused guide for B.Pharm students studying concentration techniques in pharmaceutical processing. This introduction explains the forced circulation evaporator principle, key constructional parts (pump, heat exchanger, vapour separator, condenser), working characteristics, typical uses for viscous and heat-sensitive drug solutions, and common merits and demerits. Emphasis is placed on design concepts such as circulation ratio, heat transfer, fouling control, and material compatibility for pharmaceutical applications. The content is ideal for exam preparation and practical lab understanding, with clear, keyword-rich coverage to improve search visibility and learning efficiency. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the primary principle behind a forced circulation evaporator?
- Maintaining high liquid velocity by external pumping to enhance heat transfer and avoid nucleate boiling inside tubes
- Allowing natural convective flow driven by density differences to circulate liquid
- Passing vapour through tubes and condensing it inside to heat the liquid
- Using rotating discs to spread liquid into thin films for evaporation
Correct Answer: Maintaining high liquid velocity by external pumping to enhance heat transfer and avoid nucleate boiling inside tubes
Q2. Which component is essential in a forced circulation evaporator to maintain high fluid velocity?
- Recirculation pump
- Demister pad
- Feed tray
- Rotary vane
Correct Answer: Recirculation pump
Q3. Why are forced circulation evaporators preferred for viscous pharmaceutical solutions?
- High circulation velocity reduces fouling and maintains uniform temperature in viscous fluids
- They operate at very high pressures, which evaporates viscous components instantly
- They require no heat input, which preserves viscosity
- Their small surface area concentrates viscous solutions faster
Correct Answer: High circulation velocity reduces fouling and maintains uniform temperature in viscous fluids
Q4. Which of the following is a typical advantage of forced circulation evaporators in pharmaceutical processing?
- Better control of temperature and reduced product degradation
- Lowest initial capital cost among all evaporators
- No need for condensers
- Complete removal of dissolved solids without crystallization
Correct Answer: Better control of temperature and reduced product degradation
Q5. What is the main disadvantage of forced circulation evaporators?
- Higher energy and mechanical costs due to pumps and recirculation
- Inability to handle heat-sensitive materials
- Excessive residence time that always causes product degradation
- No capacity to operate under vacuum
Correct Answer: Higher energy and mechanical costs due to pumps and recirculation
Q6. In a forced circulation evaporator, where does boiling primarily occur?
- In the vapour separator, not inside the heated tubes
- Directly inside the heating coils
- At the inlet feed point
- Inside the pump impeller
Correct Answer: In the vapour separator, not inside the heated tubes
Q7. Which design parameter is crucial to prevent scaling and deposition inside the heat exchanger tubes?
- High tube-side fluid velocity
- Very low feed concentration
- Using a larger tube diameter only
- Minimizing the number of passes regardless of velocity
Correct Answer: High tube-side fluid velocity
Q8. Forced circulation evaporators are particularly suitable for which pharmaceutical operation?
- Concentration of heat-sensitive plant extracts
- Primary sterilization of injectable solutions
- Tablet coating application
- Lyophilization of frozen products
Correct Answer: Concentration of heat-sensitive plant extracts
Q9. Which material is commonly chosen for construction to resist corrosion and adhere to pharmaceutical standards?
- Stainless steel (SS316)
- Plain carbon steel
- Aluminum alloy
- Polystyrene
Correct Answer: Stainless steel (SS316)
Q10. What role does the vapour-liquid separator play in a forced circulation evaporator?
- Separates generated vapour from the circulating liquid before recirculation
- Increases feed pressure for pumping
- Removes dissolved solids via filtration
- Provides additional heating to the liquid
Correct Answer: Separates generated vapour from the circulating liquid before recirculation
Q11. The circulation ratio in a forced circulation evaporator refers to:
- The ratio of recirculated liquid flow rate to evaporated vapour flow rate
- The ratio of feed flow to final concentrate flow
- The ratio of heat input to cooling capacity
- The ratio of tube length to diameter
Correct Answer: The ratio of recirculated liquid flow rate to evaporated vapour flow rate
Q12. How does operating under vacuum benefit pharmaceutical evaporation?
- Lower boiling temperature protects heat-sensitive compounds
- Increases the viscosity of the product for easier handling
- Removes the need for a pump
- Precipitates salts instantly
Correct Answer: Lower boiling temperature protects heat-sensitive compounds
Q13. What is a common method to control fouling in forced circulation evaporators?
- Maintaining turbulent flow and periodic cleaning-in-place (CIP)
- Reducing circulation velocity to laminar flow
- Removing the heat exchanger entirely
- Adding abrasive particles to the feed
Correct Answer: Maintaining turbulent flow and periodic cleaning-in-place (CIP)
Q14. Which heat transfer mode predominates inside the forced circulation evaporator tubes?
- Convective heat transfer from hot walls to flowing liquid
- Radiative heat transfer between fluid layers
- Pure conductive transfer across stagnant liquid
- Evaporative heat transfer at the tube surface only
Correct Answer: Convective heat transfer from hot walls to flowing liquid
Q15. Compared to natural circulation evaporators, forced circulation units typically:
- Handle higher viscosities and fouling-prone feeds more effectively
- Are simpler and require no moving parts
- Have lower power consumption in all cases
- Always achieve higher single-stage economy
Correct Answer: Handle higher viscosities and fouling-prone feeds more effectively
Q16. Which operational parameter directly increases heat transfer coefficient in a forced circulation evaporator?
- Increasing liquid flow velocity
- Decreasing tube material conductivity
- Lowering feed concentration only
- Reducing pump revolution speed
Correct Answer: Increasing liquid flow velocity
Q17. What is the typical sequence of units in a forced circulation evaporator system?
- Heater/evaporator tubes → Vapour-liquid separator → Condenser
- Condenser → Pump → Feed tank
- Separator → Heater → Distillation column
- Feed tray → Spray nozzle → Cooling coil
Correct Answer: Heater/evaporator tubes → Vapour-liquid separator → Condenser
Q18. Which type of pump is commonly used for forced circulation in evaporators?
- Centrifugal pump suitable for hot liquids
- Peristaltic pump exclusively for high pressure
- Screw pump that eliminates all shear
- Piston pump for constant vapour generation
Correct Answer: Centrifugal pump suitable for hot liquids
Q19. Which issue is minimized by preventing nucleate boiling inside heat exchanger tubes?
- Scale deposition and tube erosion due to localized hot spots
- Increase in feed concentration without evaporation
- Excessive condensation on exterior surfaces
- Overcooling of the vapour stream
Correct Answer: Scale deposition and tube erosion due to localized hot spots
Q20. For pharmaceutical applications, why is material compatibility important in evaporator design?
- To avoid contamination and chemical reaction with product
- To make the equipment transparent for inspection
- To reduce the boiling point of solvents
- To increase the rate of crystallization
Correct Answer: To avoid contamination and chemical reaction with product
Q21. What operational control is important to maintain product quality during forced circulation evaporation?
- Precise control of temperature and residence time
- Intermittent stopping of the pump every minute
- Use of open atmospheric conditions only
- Abrupt changes in circulation ratio frequently
Correct Answer: Precise control of temperature and residence time
Q22. Which product type is least suitable for forced circulation evaporation?
- Extremely shear-sensitive biological suspensions that degrade with pumping
- Viscous syrups requiring concentration
- Heat-sensitive herbal extracts under vacuum
- Solutions with moderate suspended solids designed for separator removal
Correct Answer: Extremely shear-sensitive biological suspensions that degrade with pumping
Q23. What is the main purpose of using an economizer or multiple-effect arrangement with forced circulation?
- To improve energy efficiency by reusing vapour heat
- To allow operation without a separator
- To increase the circulation ratio indefinitely
- To prevent any need for condensers
Correct Answer: To improve energy efficiency by reusing vapour heat
Q24. In terms of cleaning, what advantage do forced circulation evaporators offer?
- Easier CIP due to accessible tube bundles and controlled flow paths
- No need for cleaning because fouling never occurs
- They dissolve all solids automatically during operation
- CIP must be done offline for months at a time
Correct Answer: Easier CIP due to accessible tube bundles and controlled flow paths
Q25. Which parameter is NOT directly affected by increasing the heat transfer area?
- Feed chemical stability
- Overall heat transfer rate
- Evaporation capacity at given temperature difference
- Residence time for a fixed volume and flow
Correct Answer: Feed chemical stability
Q26. How does forced circulation help in handling feeds with suspended solids?
- High velocity keeps solids in suspension and prevents buildup on tube walls
- It filters out solids before heating
- It causes immediate coagulation and removal
- It dissolves solids chemically during circulation
Correct Answer: High velocity keeps solids in suspension and prevents buildup on tube walls
Q27. Which maintenance practice is critical for reliable forced circulation evaporator operation?
- Regular inspection and maintenance of the recirculation pump and seals
- Never checking pump bearings to save time
- Keeping the separator permanently sealed without inspection
- Using temporary piping to bypass the heater always
Correct Answer: Regular inspection and maintenance of the recirculation pump and seals
Q28. Which of the following best describes the working cycle of single-effect forced circulation evaporation?
- Single vaporization stage with external recirculation and vapour condensation
- Multiple cascaded stages sharing the same vapour
- Direct contact evaporation by spraying into a heated chamber
- Freezing and thawing cycles to remove water
Correct Answer: Single vaporization stage with external recirculation and vapour condensation
Q29. How does forced circulation influence residence time distribution?
- Promotes short and uniform residence time due to continuous recirculation
- Always causes infinite residence time
- Eliminates the need to consider residence time
- Creates very long tails in time distribution intentionally
Correct Answer: Promotes short and uniform residence time due to continuous recirculation
Q30. What is the effect of very high circulation ratio on evaporator performance?
- Improves heat transfer but increases pumping energy and operational cost
- Reduces heat transfer effectiveness dramatically
- Eliminates need for a condenser
- Decreases residence time to zero
Correct Answer: Improves heat transfer but increases pumping energy and operational cost
Q31. Which control parameter helps avoid bumping and carryover of liquid droplets into vapour?
- Proper vapour disengagement design and use of demisters
- Maximizing tube-side nucleate boiling
- Removing the separator altogether
- Adding surfactants to increase foaming
Correct Answer: Proper vapour disengagement design and use of demisters
Q32. In pharmaceutical contexts, why might vacuum operation be combined with forced circulation?
- To reduce thermal degradation while maintaining good circulation
- To increase the boiling point and speed up reactions
- To allow operation without heat exchangers
- To avoid using condensers altogether
Correct Answer: To reduce thermal degradation while maintaining good circulation
Q33. Which is a common sign that fouling is developing in the heat exchanger?
- Gradual drop in heat transfer rate and rise in wall temperature
- Instant increase in vapour quality without other changes
- Lower pump current with same flow
- Complete stoppage of separator operation without warning
Correct Answer: Gradual drop in heat transfer rate and rise in wall temperature
Q34. What is the main difference between falling-film and forced circulation evaporators?
- Falling-film forms thin film by gravity; forced circulation pumps liquid at high velocity through tubes
- Falling-film always uses boiling inside tubes while forced circulation never uses heat
- Forced circulation is gravity-driven, whereas falling-film uses pumps
- There is no difference; names are interchangeable
Correct Answer: Falling-film forms thin film by gravity; forced circulation pumps liquid at high velocity through tubes
Q35. Which operational hazard should be considered when designing a forced circulation evaporator for solvents?
- Flammability and proper ventilation/condensation of solvent vapours
- Complete incompatibility with stainless steel always
- Guaranteed polymerization of solvents at low temperature
- No special hazard beyond water evaporation
Correct Answer: Flammability and proper ventilation/condensation of solvent vapours
Q36. What is a common method to improve thermal economy of a forced circulation evaporator?
- Use multiple-effect arrangement or integrate with heat recovery
- Reduce the heat transfer area to minimum
- Operate at ambient pressure only
- Disable the condenser to save energy
Correct Answer: Use multiple-effect arrangement or integrate with heat recovery
Q37. Which testing parameter is important during commissioning of a forced circulation evaporator?
- Verification of circulation flow rate, temperature profiles, and separator efficiency
- Only checking external paint quality
- Operating solely with dry runs and no liquid
- Skipping leak tests to save time
Correct Answer: Verification of circulation flow rate, temperature profiles, and separator efficiency
Q38. In design, increasing the tube-side Reynolds number typically results in:
- Higher convective heat transfer coefficient
- Lower frictional pressure drop always
- Complete elimination of fouling
- A decrease in required heater area independent of duty
Correct Answer: Higher convective heat transfer coefficient
Q39. Which pharmaceutical product attribute can be preserved better using forced circulation evaporation?
- Active ingredient potency due to lower temperature exposure
- Sterility without additional steps
- Color change due to oxidation always stops
- Total removal of endotoxins automatically
Correct Answer: Active ingredient potency due to lower temperature exposure
Q40. What is the effect of dissolved solids concentration on evaporation performance?
- Higher concentration increases tendency for fouling and may reduce heat transfer
- It always increases heat transfer coefficient
- It has no effect whatsoever
- It prevents vapour formation completely
Correct Answer: Higher concentration increases tendency for fouling and may reduce heat transfer
Q41. Which feature makes forced circulation suitable for crystallization operations?
- Controlled supersaturation in the separator with good mixing and heat removal
- Complete elimination of nuclei formation
- Absence of any temperature gradients
- Guaranteed production of amorphous solids only
Correct Answer: Controlled supersaturation in the separator with good mixing and heat removal
Q42. Which of the following cleaning agents is commonly used in CIP of stainless steel evaporator surfaces?
- Caustic soda (NaOH) followed by acid rinse
- Hydrofluoric acid as sole cleaner for all residues
- Pure organic solvents without rinsing
- Saltwater for all types of fouling
Correct Answer: Caustic soda (NaOH) followed by acid rinse
Q43. What does vapour economy refer to in evaporator systems?
- The amount of water evaporated per unit of steam supplied or reused
- The cost of the evaporator divided by its weight
- The percentage of liquid recovered as condensate only
- The ratio of pump power to heater power
Correct Answer: The amount of water evaporated per unit of steam supplied or reused
Q44. How does scale formation influence heat transfer resistance?
- Scale adds thermal resistance, reducing overall heat transfer
- Scale improves conduction and increases heat transfer
- Scale only affects the vapour side and not heat transfer
- Scale formation always increases evaporation rate
Correct Answer: Scale adds thermal resistance, reducing overall heat transfer
Q45. In forced circulation evaporator operation, what is usually monitored to detect early fouling?
- Increase in temperature difference between heating medium and product or reduced heat transfer rate
- Decrease in product density only
- Color of outside paint
- Ambient humidity levels
Correct Answer: Increase in temperature difference between heating medium and product or reduced heat transfer rate
Q46. What is the role of a demister in the vapour path?
- To remove entrained liquid droplets from vapour before condensation
- To increase pressure in the vapour line
- To add chemicals to the vapour
- To cool the liquid feed before heating
Correct Answer: To remove entrained liquid droplets from vapour before condensation
Q47. For scale-prone feeds, which operational strategy helps extend run length between cleanings?
- Operate at higher flow velocities and control temperature to minimize local supersaturation
- Slow down flow to allow solids to settle in tubes
- Increase the tube wall temperature to burn off scales
- Close the separator vent to increase pressure
Correct Answer: Operate at higher flow velocities and control temperature to minimize local supersaturation
Q48. Which factor most influences selection of tube diameter in a forced circulation evaporator?
- Desired flow velocity to maintain turbulent conditions and acceptable pressure drop
- The color of the product
- The brand preference of the manufacturer
- The ambient wind conditions
Correct Answer: Desired flow velocity to maintain turbulent conditions and acceptable pressure drop
Q49. Which statement best describes energy consumption in forced circulation evaporators?
- They may have higher electrical energy usage for pumping but can be optimized with multiple effects for thermal efficiency
- They always use zero energy due to natural circulation
- Pumping energy is negligible compared to all other types
- They consume no steam when operated at atmospheric pressure
Correct Answer: They may have higher electrical energy usage for pumping but can be optimized with multiple effects for thermal efficiency
Q50. When preparing MCQs for exam practice on forced circulation evaporators, what is most important for B.Pharm students to focus on?
- Understanding principle, construction, working, operational parameters, pharmaceutical applications, merits and demerits
- Memorizing manufacturer names and logos only
- Learning unrelated distillation column internals exclusively
- Ignoring materials of construction and safety considerations
Correct Answer: Understanding principle, construction, working, operational parameters, pharmaceutical applications, merits and demerits
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