Horizontal tube evaporator – principle, construction, working, uses, merits, demerits is a key unit operation in pharmaceutical processing for concentrating liquid formulations, syrups, and fermentation broths. This introduction explains the boiling principle, tube-and-shell construction, vapor–liquid separation, and operational controls in clear, student-friendly terms. Emphasis is placed on heat transfer, circulation, vacuum use for heat-sensitive materials, fouling issues, maintenance and safety considerations relevant to B.Pharm coursework and practicals. Keywords: horizontal tube evaporator, heat transfer, vapor separator, pharmaceutical concentration, fouling, vacuum evaporation, steam economy, construction, working, merits, demerits. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the primary principle by which a horizontal tube evaporator concentrates solutions?
- Chemical reaction to remove solvent
- Boiling and vaporization of solvent by heat transfer across tube surfaces
- Membrane filtration to separate solvent
- Adsorption of solvent onto packing material
Correct Answer: Boiling and vaporization of solvent by heat transfer across tube surfaces
Q2. In a typical horizontal tube evaporator, where does steam usually condense?
- Inside the tubes where product flows
- On the outer surface of the heating tubes (shell side)
- In the vapor outlet line
- In the feed inlet line
Correct Answer: On the outer surface of the heating tubes (shell side)
Q3. Which component separates vapor from the concentrated liquid in a horizontal tube evaporator?
- Vacuum pump
- Vapor-liquid separator (centrifugal or disengaging device)
- Steam trap
- Feed distributor
Correct Answer: Vapor-liquid separator (centrifugal or disengaging device)
Q4. Which of the following best describes the construction of a horizontal tube evaporator?
- A vertical shell with vertical tubes only
- A horizontal shell housing multiple horizontal tubes with inlet/outlet and steam chambers
- A single long tube coiled vertically
- A packed column with trays for liquid distribution
Correct Answer: A horizontal shell housing multiple horizontal tubes with inlet/outlet and steam chambers
Q5. Why is vacuum often applied in horizontal tube evaporators when processing pharmaceutical products?
- To increase boiling point of solvent
- To reduce boiling point and protect heat-sensitive drugs
- To raise pressure and speed up boiling
- To sterilize the product during evaporation
Correct Answer: To reduce boiling point and protect heat-sensitive drugs
Q6. Which material is commonly used for tubes in pharmaceutical horizontal tube evaporators due to corrosion resistance?
- Cast iron
- Stainless steel (e.g., SS316)
- Plain carbon steel
- Copper-nickel alloy exclusively
Correct Answer: Stainless steel (e.g., SS316)
Q7. Which flow pattern inside tubes reduces residence time and is often used for heat-sensitive liquids?
- Long residence time batch recirculation
- Single-pass high-velocity flow
- Stagnant hold-up
- Counter-current slow flow
Correct Answer: Single-pass high-velocity flow
Q8. What is the main disadvantage of severe fouling on tube surfaces in a horizontal tube evaporator?
- Improved heat transfer coefficient
- Reduced overall heat transfer and higher energy consumption
- Decreased product concentration capability
- No effect on operation
Correct Answer: Reduced overall heat transfer and higher energy consumption
Q9. For viscous pharmaceutical syrups, why are horizontal tube evaporators preferred?
- They have low heat transfer area
- They facilitate good circulation and handling of viscous and particulate-laden liquids
- They always operate at atmospheric pressure only
- They eliminate need for cleaning
Correct Answer: They facilitate good circulation and handling of viscous and particulate-laden liquids
Q10. What role do baffles play in the shell of a horizontal tube evaporator?
- They increase steam pressure
- They support tubes and direct shell-side flow for better heat transfer
- They separate vapor and liquid
- They function as vacuum pumps
Correct Answer: They support tubes and direct shell-side flow for better heat transfer
Q11. Which operational parameter is most critical to control to avoid bumping and foaming in pharmaceutical evaporation?
- Feed pH only
- Vacuum level, boil-up rate and vapor removal
- Ambient humidity
- Steam color
Correct Answer: Vacuum level, boil-up rate and vapor removal
Q12. What is steam economy in evaporator operation?
- Amount of heat lost to surroundings
- Ratio of mass of solvent evaporated to mass of steam used
- Volume of condensate returned per hour
- Number of tubes per shell
Correct Answer: Ratio of mass of solvent evaporated to mass of steam used
Q13. How does concentration increase affect viscosity and heat transfer in the evaporator?
- Viscosity decreases and heat transfer improves
- Viscosity increases and heat transfer deteriorates
- No effect on viscosity or heat transfer
- Viscosity becomes zero
Correct Answer: Viscosity increases and heat transfer deteriorates
Q14. Which cleaning method is commonly used for horizontal tube evaporators to remove scale and fouling?
- Dry ice blasting only
- Chemical cleaning (CIP) and mechanical brushing or hydroblasting
- Ignition inside shell
- Freezing the unit
Correct Answer: Chemical cleaning (CIP) and mechanical brushing or hydroblasting
Q15. In multi-effect evaporation systems, how does adding effects improve energy efficiency compared to a single horizontal tube evaporator?
- By increasing steam consumption per kg evaporated
- By reusing vapor as heating medium for subsequent effects, reducing steam per kg evaporated
- By increasing product residence time only
- By lowering product quality intentionally
Correct Answer: By reusing vapor as heating medium for subsequent effects, reducing steam per kg evaporated
Q16. Which parameter directly influences the overall heat transfer coefficient in a horizontal tube evaporator?
- Ambient room color
- Thickness of fouling layer, tube material, fluid velocities and temperature difference
- Number of operators present
- Length of product piping only
Correct Answer: Thickness of fouling layer, tube material, fluid velocities and temperature difference
Q17. What is the typical location of the feed entry in a horizontal tube evaporator?
- Into the vapor outlet
- Into the tube bundle or distributor to ensure even flow through tubes
- Directly onto the heating steam
- Into the condensate return line
Correct Answer: Into the tube bundle or distributor to ensure even flow through tubes
Q18. Which type of horizontal tube evaporator arrangement is best for handling solids or crystallizing products?
- Falling-film evaporator only
- Long residence tubular evaporator with scraper or agitated tubes
- Plate heat exchanger
- Membrane evaporator exclusively
Correct Answer: Long residence tubular evaporator with scraper or agitated tubes
Q19. What is a common method to control scale formation during evaporation of hard-water-based syrups?
- Ignoring it until failure
- Water softening, acid cleaning, and periodic CIP
- Increasing steam pressure only
- Using cast iron tubes
Correct Answer: Water softening, acid cleaning, and periodic CIP
Q20. Which safety device prevents overpressure in the steam chamber of a horizontal tube evaporator?
- Vacuum breaker only
- Pressure relief valve (safety valve)
- Sight glass
- Feed pump
Correct Answer: Pressure relief valve (safety valve)
Q21. Which advantage is specific to horizontal tube evaporators in pharmaceutical plants?
- They are maintenance-free
- Ease of inspection and maintenance due to horizontal tube access
- No requirement for condensate handling
- They operate without any heating medium
Correct Answer: Ease of inspection and maintenance due to horizontal tube access
Q22. What is the effect of increasing steam temperature on evaporation rate (assuming product stability)?
- Evaporation rate decreases
- Evaporation rate increases due to higher temperature difference
- No change in evaporation rate
- Evaporation stops completely
Correct Answer: Evaporation rate increases due to higher temperature difference
Q23. In pharmaceutical evaporation, why is gentle handling and short residence time important for some products?
- To intentionally degrade active ingredients
- To prevent thermal degradation and preserve potency
- To increase microbial load
- To change product color only
Correct Answer: To prevent thermal degradation and preserve potency
Q24. Which of the following is a common sign of poor vapor-liquid separation in the evaporator?
- Clear condensate with no foam
- Carryover of liquid into vapor line and foaming in the condenser
- Perfect vacuum and no noise
- Decreased product concentration only
Correct Answer: Carryover of liquid into vapor line and foaming in the condenser
Q25. What is the typical effect of vacuum leaks on evaporator performance?
- Improved control of boiling
- Loss of vacuum leads to higher boiling temperatures and risk of thermal damage
- Vacuum leaks are irrelevant
- They increase steam economy
Correct Answer: Loss of vacuum leads to higher boiling temperatures and risk of thermal damage
Q26. Which design choice minimizes dead zones and improves flow distribution in the tube bundle?
- Random placement of tubes
- Use of proper feed distributors and baffles to ensure uniform flow
- Sealing off alternate tubes
- Reducing tube diameter to zero
Correct Answer: Use of proper feed distributors and baffles to ensure uniform flow
Q27. When recovering heat-sensitive antibiotics, what operational change is commonly applied?
- Operate at higher temperatures with no vacuum
- Use lower temperature under vacuum and short residence time
- Use longer residence time at ambient pressure
- Remove vacuum and add more steam
Correct Answer: Use lower temperature under vacuum and short residence time
Q28. Which maintenance practice extends tube life and prevents leaks in horizontal tube evaporators?
- Never inspect tubes
- Regular inspection, nondestructive testing and timely replacement of corroded tubes
- Replacing all tubes daily
- Painting tubes externally only
Correct Answer: Regular inspection, nondestructive testing and timely replacement of corroded tubes
Q29. What is the likely cause if the evaporator is operating but product concentration is not increasing?
- Excessive steam condensing on tube surfaces
- Poor heat transfer due to fouling, low temperature difference or feed bypass
- Too low feed flow rate always increases concentration
- Product overflow into steam line always
Correct Answer: Poor heat transfer due to fouling, low temperature difference or feed bypass
Q30. Which advantage does a horizontal tube evaporator offer over a vertical tube evaporator in terms of solids handling?
- Worse solids handling
- Better accessibility for cleaning and ability to handle particulate and viscous feeds
- Cannot handle solids at all
- Requires more floor space always
Correct Answer: Better accessibility for cleaning and ability to handle particulate and viscous feeds
Q31. Which parameter is most useful to monitor for early detection of fouling?
- Color of steam
- Drop in overall heat transfer coefficient or increase in required steam flow for same output
- Operator count in the plant
- Brand of vacuum pump
Correct Answer: Drop in overall heat transfer coefficient or increase in required steam flow for same output
Q32. How does agitation or internal scrapers in certain horizontal tubular designs help?
- They reduce heat transfer area
- They remove fouling and maintain high heat transfer for viscous or crystallizing feeds
- They increase corrosion solely
- They reduce steam economy intentionally
Correct Answer: They remove fouling and maintain high heat transfer for viscous or crystallizing feeds
Q33. Which of the following is a demerit of horizontal tube evaporators?
- Low susceptibility to fouling
- Relatively large footprint and potential for uneven flow distribution
- They are always the most energy-efficient option
- They do not require condensate handling
Correct Answer: Relatively large footprint and potential for uneven flow distribution
Q34. In design, why is tube pitch important in a tube bundle?
- It determines tube color
- It affects flow distribution, heat transfer and cleaning accessibility
- It only affects weight but not performance
- It sets the vacuum level directly
Correct Answer: It affects flow distribution, heat transfer and cleaning accessibility
Q35. What is the effect of operating the evaporator at higher liquid velocities in the tubes?
- Increases fouling
- Generally enhances heat transfer and reduces fouling but increases pumping costs
- Stops evaporation completely
- Causes immediate corrosion only
Correct Answer: Generally enhances heat transfer and reduces fouling but increases pumping costs
Q36. Which control instrument is essential for maintaining desired concentration by adjusting evaporator operation?
- pH meter exclusively
- Level controller, temperature controller and vacuum controller
- Only a thermometer is sufficient
- Only a stopwatch
Correct Answer: Level controller, temperature controller and vacuum controller
Q37. What is entrainment in the context of evaporators?
- Solid deposition on tubes
- Carryover of liquid droplets with the vapor stream
- Intentional mixing of steam and feed
- Delayed condensation in condensers
Correct Answer: Carryover of liquid droplets with the vapor stream
Q38. How can entrainment be minimized in a horizontal tube evaporator?
- By increasing boiling intensity without separators
- By proper vapor-liquid separation, use of demisters and controlled boil-up
- By removing baffles
- By increasing feed solids only
Correct Answer: By proper vapor-liquid separation, use of demisters and controlled boil-up
Q39. In pharmaceutical applications, what is a typical use of horizontal tube evaporators?
- Solid tablet coating
- Concentration of syrups, extracts and fermentation broths under controlled conditions
- Freeze drying exclusively
- High-temperature incineration
Correct Answer: Concentration of syrups, extracts and fermentation broths under controlled conditions
Q40. What is the likely effect of prolonged operation with a thick fouling layer on tube surfaces?
- Improved product quality always
- Higher temperature differences needed, reduced capacity and possible hot spots causing product degradation
- No operational effect
- Automatic cleaning by steam
Correct Answer: Higher temperature differences needed, reduced capacity and possible hot spots causing product degradation
Q41. Which operational practice improves energy efficiency in evaporation processes?
- Working at the highest possible pressure only
- Using multi-effect systems or vapor recompression to reuse latent heat
- Removing condensate continuously to waste
- Using low-quality insulation only
Correct Answer: Using multi-effect systems or vapor recompression to reuse latent heat
Q42. What is mechanical vapor recompression (MVR) in evaporation?
- Using fresh steam for each kilogram evaporated
- Compressing vapor to a higher temperature and pressure to reuse as heating medium
- Pumping liquid vapor out to atmosphere
- Filtering the vapor through membranes
Correct Answer: Compressing vapor to a higher temperature and pressure to reuse as heating medium
Q43. Which operational hazard is associated with vacuum failure while processing heat-sensitive pharmaceuticals?
- Lower boiling point causing freezing
- Sudden increase in boiling temperature potentially degrading active components
- Instant sterilization
- Automatic cleaning of tubes
Correct Answer: Sudden increase in boiling temperature potentially degrading active components
Q44. During startup, why is controlled warm-up important for tube bundles?
- To cause thermal shock deliberately
- To avoid thermal stress, tube distortion and leakage by gradual heating
- Because tubes must remain cold always
- No reason; rapid heating is preferred
Correct Answer: To avoid thermal stress, tube distortion and leakage by gradual heating
Q45. How is product quality monitored during evaporation in pharmaceutical production?
- Only by tasting the product
- By sampling for concentration, potency, pH and microbial limits at intervals
- By checking only steam color
- By continuous visual inspection of tube surface only
Correct Answer: By sampling for concentration, potency, pH and microbial limits at intervals
Q46. Which evaporator configuration reduces hold-up volume and is preferred for very heat-sensitive materials?
- Long batch tanks with static heating
- Short residence time, single-pass tubular evaporator with vacuum
- Open pans at atmospheric pressure
- Large multi-pass slow-flow evaporators
Correct Answer: Short residence time, single-pass tubular evaporator with vacuum
Q47. What is the common consequence of inadequate condensate removal from the steam chest?
- Increased steam condensation efficiency
- Poor heat transfer due to condensate flooding and reduced effective heating area
- Improved vacuum automatically
- Lower fouling tendency always
Correct Answer: Poor heat transfer due to condensate flooding and reduced effective heating area
Q48. Which factor should be considered when specifying tube diameter for a horizontal tube evaporator handling viscous feed?
- Tube diameter only affects color of tubing
- Balance between sufficient hydraulic capacity to avoid high pressure drop and adequate heat transfer area
- Smaller diameter always better for viscous feeds
- Tube diameter is irrelevant
Correct Answer: Balance between sufficient hydraulic capacity to avoid high pressure drop and adequate heat transfer area
Q49. Why might a pharmaceutical plant choose single-effect horizontal tube evaporation despite lower energy efficiency?
- When capital cost, simplicity, batch flexibility and lower maintenance complexity are prioritized
- To maximize steam consumption intentionally
- Because single-effect is always better for all products
- There is no reason to choose single-effect ever
Correct Answer: When capital cost, simplicity, batch flexibility and lower maintenance complexity are prioritized
Q50. Which step is essential before performing chemical cleaning (CIP) of an evaporator?
- Igniting residues inside the evaporator
- Isolating steam and feed lines, draining product, and verifying permits and safety procedures
- Increasing steam pressure to maximum
- Removing all insulation only
Correct Answer: Isolating steam and feed lines, draining product, and verifying permits and safety procedures
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.
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