Applications of heat transfer MCQs With Answer

Applications of heat transfer MCQs With Answer

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Applications of heat transfer MCQs With Answer provide B.Pharm students with targeted practice on how thermal processes affect pharmaceutical manufacturing, formulation stability, and product quality. This concise, keyword-rich introduction covers core areas such as heat exchangers, drying, sterilization, lyophilization, coating, and cold-chain management while emphasizing thermal conductivity, convective heat transfer, and process control. Designed for exam preparation and practical understanding, these questions link heat transfer principles to real-world pharmaceutical operations, scale-up, and safety considerations. Clear explanations improve problem-solving for unit operations and dosage form stability. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which mode of heat transfer is dominant in a fluidized bed dryer used in pharmaceutical drying?

  • Conduction through particle contacts
  • Convection between gas and particles
  • Radiation between hot surfaces
  • Mass diffusion without heat transfer

Correct Answer: Convection between gas and particles

Q2. Fourier’s law is primarily used to describe which phenomenon in pharmaceutical solids?

  • Convective heat transfer coefficient
  • Radiative heat flux between surfaces
  • Steady-state conductive heat transfer
  • Evaporative cooling rate

Correct Answer: Steady-state conductive heat transfer

Q3. In autoclave sterilization, which heat transfer concept is critical for ensuring rapid and uniform temperature rise in moist heat sterilization?

  • Surface emissivity
  • Convective heat transfer and steam condensation on surfaces
  • Thermal radiation from the chamber walls
  • Heat conduction through metal only

Correct Answer: Convective heat transfer and steam condensation on surfaces

Q4. The Biot number (Bi) helps determine whether a pharmaceutical tablet can be analyzed using lumped capacitance. What condition supports lumped system analysis?

  • Bi >> 10
  • Bi ≈ 1
  • Bi << 0.1
  • Bi between 5 and 10

Correct Answer: Bi << 0.1

Q5. Which dimensionless number correlates convective heat transfer to conductive transport in a fluid and is frequently used in heat exchanger design?

  • Reynolds number (Re)
  • Nusselt number (Nu)
  • Prandtl number (Pr)
  • Fourier number (Fo)

Correct Answer: Nusselt number (Nu)

Q6. During lyophilization (freeze-drying), which heat transfer mode supplies energy for sublimation of ice from the product?

  • Direct conduction through vial bottom
  • Radiation only
  • Conduction and radiation from shelf to product and gas phase transfer
  • Convective forced air within the chamber

Correct Answer: Conduction and radiation from shelf to product and gas phase transfer

Q7. Which property of a pharmaceutical material most directly affects its rate of conductive heat transfer?

  • Bulk density
  • Specific surface area
  • Thermal conductivity
  • Viscosity

Correct Answer: Thermal conductivity

Q8. In spray drying of pharmaceuticals, what is the primary benefit of increasing the convective heat transfer coefficient between droplets and drying air?

  • Reduced particle surface area
  • Faster moisture removal and shorter residence time
  • Increased crystallinity due to slow cooling
  • Higher solvent boiling point

Correct Answer: Faster moisture removal and shorter residence time

Q9. Which heat transfer mechanism is most important for heat loss from a hot tablet coating pan to the surrounding environment?

  • Conduction through air
  • Natural or forced convection and radiation
  • Evaporative mass transfer only
  • Steam condensation

Correct Answer: Natural or forced convection and radiation

Q10. When scaling up a heat exchanger for a pharmaceutical plant, which parameter is essential to maintain similar heat transfer performance?

  • Geometric similarity only
  • Same Reynolds and Prandtl numbers (dynamic similarity)
  • Same material composition regardless of flow
  • Identical absolute dimensions

Correct Answer: Same Reynolds and Prandtl numbers (dynamic similarity)

Q11. The rate of heat transfer by conduction through a wall is directly proportional to which of the following?

  • Thickness of the wall
  • Temperature difference across the wall
  • Square of thermal conductivity
  • Inverse of surface area

Correct Answer: Temperature difference across the wall

Q12. Which approach estimates transient temperature change in a small pharmaceutical particle where internal conduction is fast compared to surface convection?

  • Detailed PDE solution always required
  • Lumped capacitance model
  • Radiation-dominated model
  • Steady-state conduction model

Correct Answer: Lumped capacitance model

Q13. Fouling in pharmaceutical heat exchangers most commonly results in which effect?

  • Increased overall heat transfer coefficient
  • Decreased thermal resistance
  • Reduced heat transfer efficiency and increased pressure drop
  • Lower fluid viscosity uniformly

Correct Answer: Reduced heat transfer efficiency and increased pressure drop

Q14. For predicting freeze-thaw stability of biologics, which thermal property is most relevant?

  • Latent heat of fusion and freezing temperature profile
  • Optical refractive index
  • Surface tension of solvent
  • Magnetic susceptibility

Correct Answer: Latent heat of fusion and freezing temperature profile

Q15. In heat transfer calculations for a drying process, the driving potential for moisture removal is most directly related to:

  • Temperature gradient within solid only
  • Partial pressure or vapor pressure difference between surface and bulk air
  • Electrical conductivity of the solid
  • Color of the material

Correct Answer: Partial pressure or vapor pressure difference between surface and bulk air

Q16. Which correlation is commonly used to estimate convective heat transfer coefficient for external flow over a flat plate?

  • Fourier number correlation
  • Newton’s law of cooling only
  • Local Nusselt number correlations based on Reynolds and Prandtl numbers
  • Arrhenius-type correlation

Correct Answer: Local Nusselt number correlations based on Reynolds and Prandtl numbers

Q17. During hot-melt extrusion of a drug-polymer matrix, controlling heat transfer is critical to avoid:

  • Particle agglomeration in aqueous phase
  • Thermal degradation of drug or polymer
  • Loss of magnetic properties
  • Increased tablet porosity only

Correct Answer: Thermal degradation of drug or polymer

Q18. The overall heat transfer coefficient (U) in a double-pipe heat exchanger depends on:

  • Only the thermal conductivity of the tube material
  • Convective heat transfer coefficients on both sides, thermal resistance of wall, and fouling resistances
  • Chemical composition of fluids exclusively
  • Only flow rate on the hot side

Correct Answer: Convective heat transfer coefficients on both sides, thermal resistance of wall, and fouling resistances

Q19. In freeze-drying cycles, shelf temperature primarily controls which phase of primary drying?

  • Vacuum pump efficiency
  • Heat input to supply latent heat of sublimation
  • Final moisture content in secondary drying only
  • Radiation losses to chamber walls

Correct Answer: Heat input to supply latent heat of sublimation

Q20. Which dimensionless number relates momentum diffusivity to thermal diffusivity and influences convective heat transfer behavior?

  • Reynolds number (Re)
  • Prandtl number (Pr)
  • Biot number (Bi)
  • Nusselt number (Nu)

Correct Answer: Prandtl number (Pr)

Q21. A high Nusselt number for flow inside a pipe indicates:

  • Dominant conductive heat transfer within the fluid
  • Strong convective heat transfer relative to conduction
  • A very low fluid velocity
  • Negligible temperature gradients at the wall

Correct Answer: Strong convective heat transfer relative to conduction

Q22. In designing a pharmaceutical dryer, why is specific heat capacity of the product important?

  • It dictates the color change during drying
  • It determines how much sensible heat is needed to raise product temperature
  • It controls chemical reactivity only
  • It replaces the need for measuring moisture content

Correct Answer: It determines how much sensible heat is needed to raise product temperature

Q23. Which law describes convective heat transfer from a surface to a fluid in simple engineering approximations?

  • Fourier’s law
  • Newton’s law of cooling
  • Planck’s law
  • Fick’s law

Correct Answer: Newton’s law of cooling

Q24. In thermal processing of aseptic pharmaceuticals, cold spots in a sterilizer are usually due to inadequate:

  • Heat capacity of product
  • Steam penetration and convective mixing
  • Radiative heating from chamber walls
  • Electrical heating elements

Correct Answer: Steam penetration and convective mixing

Q25. Which parameter must be controlled to minimize heat-induced degradation during spray drying of thermolabile drugs?

  • Inlet air temperature and residence time
  • pH of feed only
  • Magnetic stirring speed
  • Electrical conductivity of feed

Correct Answer: Inlet air temperature and residence time

Q26. Radiative heat transfer becomes significant in pharmaceutical processing when:

  • Temperature differences are very small
  • High surface temperatures or long view factors exist between surfaces
  • Only solids at room temperature are involved
  • Vacuum conditions always prevail

Correct Answer: High surface temperatures or long view factors exist between surfaces

Q27. The latent heat of vaporization is crucial in which pharmaceutical unit operation?

  • Tablet compression
  • Spray drying and evaporation-based concentration
  • Granulation by dry mixing
  • Lyophilization primary drying

Correct Answer: Spray drying and evaporation-based concentration

Q28. In conduction through a multi-layered wall (e.g., jacketed vessel), the thermal resistance is analogous to:

  • Capacitance in series
  • Electrical resistance in series
  • Magnetic reluctance
  • Fluid pressure in parallel

Correct Answer: Electrical resistance in series

Q29. Which measurement is typically used to quantify how quickly a product reaches equilibrium temperature in a thermal study?

  • Heat flux only
  • Time constant or thermal time constant (tau)
  • Viscosity index
  • pH change over time

Correct Answer: Time constant or thermal time constant (tau)

Q30. For convective heat transfer inside a stirred tank, increasing agitator speed primarily affects heat transfer by:

  • Reducing thermal conductivity of fluid
  • Enhancing fluid mixing and increasing local convective coefficients
  • Changing radiative properties
  • Altering latent heat of solvent

Correct Answer: Enhancing fluid mixing and increasing local convective coefficients

Q31. Which factor most reduces the effective heat transfer coefficient in a plate heat exchanger used for sterile buffer preparation?

  • Clean, smooth surfaces
  • Deposition of protein and mineral fouling
  • Increased flow turbulence
  • Reduced plate spacing for better contact

Correct Answer: Deposition of protein and mineral fouling

Q32. The Arrhenius equation is used in thermal degradation studies to estimate:

  • Thermal conductivity at different temperatures
  • Rate constant dependence on temperature and activation energy
  • Viscosity change with shear
  • Diffusion coefficient of moisture only

Correct Answer: Rate constant dependence on temperature and activation energy

Q33. In cold chain management, which heat transfer aspect is most relevant to maintaining drug potency during transport?

  • Minimizing convective heat transfer from ambient to product using insulation and active cooling
  • Maximizing radiative heat gain
  • Increasing product thermal conductivity intentionally
  • Using steam injection

Correct Answer: Minimizing convective heat transfer from ambient to product using insulation and active cooling

Q34. Heat load calculation for a pharmaceutical cleanroom must include which components?

  • Only heat from HVAC fans
  • All sensible and latent heat gains: equipment, personnel, lighting, infiltration
  • Only latent loads from humidity
  • Only external solar radiation

Correct Answer: All sensible and latent heat gains: equipment, personnel, lighting, infiltration

Q35. Which concept explains why small particles heat or cool much faster than large ones?

  • Lower surface area-to-volume ratio for small particles
  • Higher thermal mass per unit area for small particles
  • Higher surface area-to-volume ratio leading to faster heat exchange
  • Smaller particles have no convective effects

Correct Answer: Higher surface area-to-volume ratio leading to faster heat exchange

Q36. In conduction-controlled drying, internal heat transfer limits drying rate; which property accelerates internal conduction?

  • Lower thermal conductivity
  • Higher thermal conductivity and higher temperature gradient
  • Lower specific heat
  • Decreased porosity always

Correct Answer: Higher thermal conductivity and higher temperature gradient

Q37. Which heat transfer consideration is most important when designing lyophilization vial arrangement on shelves?

  • Maximizing radiative view factors only
  • Uniform conduction contact and minimizing edge effects for equal heat supply
  • Random orientation for mixing
  • Using different shelf temperatures per row without control

Correct Answer: Uniform conduction contact and minimizing edge effects for equal heat supply

Q38. For a cylindrical core undergoing transient heat conduction, which analytical solution parameter indicates how quickly the center temperature responds?

  • Reynolds number
  • Fourier number (dimensionless time)
  • Nusselt number
  • Prandtl number

Correct Answer: Fourier number (dimensionless time)

Q39. When evaluating thermal stability of an API during processing, which experimental approach directly assesses heat-induced degradation kinetics?

  • Isothermal degradation studies at multiple temperatures and Arrhenius analysis
  • Single-run compression force test
  • Measuring only melting point once
  • Observing color change qualitatively

Correct Answer: Isothermal degradation studies at multiple temperatures and Arrhenius analysis

Q40. Which heat transfer mechanism can be exploited to rapidly cool liquids in pharmaceutical processing without direct contact with refrigerant?

  • Steam injection
  • Indirect conduction through a heat exchanger surface with a refrigerant on the other side
  • Direct exposure to sunlight
  • Magnetic stirring

Correct Answer: Indirect conduction through a heat exchanger surface with a refrigerant on the other side

Q41. In a shell-and-tube heat exchanger used for buffer preparation, increasing baffle spacing will generally:

  • Increase turbulence and reduce pressure drop
  • Reduce cross-flow mixing, potentially lowering heat transfer coefficient
  • Eliminate the need for tube-side flow control
  • Always improve heat transfer efficiency

Correct Answer: Reduce cross-flow mixing, potentially lowering heat transfer coefficient

Q42. The thermal conductivity of powders in a bed often increases with:

  • Decreased packing density
  • Increased packing density and contact between particles
  • Addition of air gaps
  • Reduced particle size only

Correct Answer: Increased packing density and contact between particles

Q43. In microwaving processes for drying, the primary heat generation mechanism within the product is:

  • Surface convection
  • Volumetric dielectric heating due to electromagnetic energy absorption
  • Radiative heat from lamp sources
  • Adiabatic compression

Correct Answer: Volumetric dielectric heating due to electromagnetic energy absorption

Q44. To minimize thermal gradients during tablet coating, process engineers commonly adjust:

  • Coating pan rotation speed, inlet air temperature, and spray rate
  • Tablet core API concentration only
  • Humidity control only without temperature changes
  • Use of metallic pigments exclusively

Correct Answer: Coating pan rotation speed, inlet air temperature, and spray rate

Q45. The concept of critical heat flux is most relevant to which pharmaceutical equipment/process?

  • Tablet die filling
  • Boiling heat transfer in evaporators and styrofoam heaters
  • Lyophilization vacuum control
  • Magnetic resonance imaging

Correct Answer: Boiling heat transfer in evaporators and styrofoam heaters

Q46. When modeling heat transfer in wet granulation, which coupled phenomena must be considered?

  • Only mechanical mixing
  • Conduction, convection, and moisture diffusion with changing thermal properties
  • Only electrical heating effects
  • Ignoring moisture completely

Correct Answer: Conduction, convection, and moisture diffusion with changing thermal properties

Q47. The emissivity of a surface affects which type of heat transfer in process equipment?

  • Conduction only
  • Radiation heat transfer between surfaces
  • Convective coefficient magnitude directly
  • Mass transfer coefficient

Correct Answer: Radiation heat transfer between surfaces

Q48. In designing freeze-drying cycles, control of chamber pressure affects primary drying because it changes:

  • Boiling point elevation of solutes only
  • Vapor removal resistance and sublimation driving force
  • Viscosity of ice
  • Electrical properties of vials

Correct Answer: Vapor removal resistance and sublimation driving force

Q49. Which statement about thermal diffusivity (alpha = k/(rho*cp)) is true for pharmaceutical solids?

  • High thermal diffusivity means a material responds quickly to temperature changes
  • Thermal diffusivity is independent of density and heat capacity
  • Low thermal diffusivity indicates rapid internal temperature equilibration
  • It increases when heat capacity increases, all else equal

Correct Answer: High thermal diffusivity means a material responds quickly to temperature changes

Q50. For energy-efficient thermal processing in a pharmaceutical plant, which strategy is most effective?

  • Operate all equipment at maximum temperature continuously
  • Recover waste heat via heat exchangers and optimize insulation to reduce losses
  • Disable insulation to allow equipment to cool naturally
  • Ignore process scheduling and run small batches randomly

Correct Answer: Recover waste heat via heat exchangers and optimize insulation to reduce losses

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