Heat transfer by conduction MCQs With Answer

Heat transfer by conduction MCQs With Answer

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Mastering Heat transfer by conduction MCQs With Answer is essential for B. Pharm students involved in pharmaceutical engineering, formulation development, and process optimization. This concise, keyword-rich introduction covers core concepts such as Fourier’s law, thermal conductivity, steady and transient conduction, Biot number, thermal diffusivity, and conduction resistance in tablets, dryers, lyophilizers, and hot-melt extrusion. Practical relevance includes heat flow in tablet cores, drying kinetics, sterilization heating, and thermal property measurement methods. Clear explanations and application-focused MCQs help reinforce problem-solving for exams and laboratory work. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary physical mechanism described by Fourier’s law in heat conduction?

  • Heat transfer due to bulk fluid motion
  • Heat flow proportional to temperature gradient
  • Energy transfer by electromagnetic radiation
  • Heat transfer by phase change

Correct Answer: Heat flow proportional to temperature gradient

Q2. Thermal conductivity is a material property that indicates:

  • Rate of convective heat transfer at a surface
  • Amount of heat conducted per unit time per unit area per unit temperature gradient
  • Heat required to raise temperature by one degree
  • Thermal resistance per unit thickness

Correct Answer: Amount of heat conducted per unit time per unit area per unit temperature gradient

Q3. In one-dimensional steady-state conduction through a slab with constant thermal conductivity, temperature distribution is:

  • Exponential
  • Linear
  • Quadratic
  • Logarithmic

Correct Answer: Linear

Q4. Which of the following units corresponds to thermal conductivity?

  • J/(kg·K)
  • W/(m·K)
  • W/m²
  • m²/s

Correct Answer: W/(m·K)

Q5. The Biot number (Bi) compares which two resistances in heat transfer?

  • Radiative to convective resistance
  • Internal conductive resistance to external convective resistance
  • Convective resistance to mass transfer resistance
  • Viscous resistance to conductive resistance

Correct Answer: Internal conductive resistance to external convective resistance

Q6. For lumped capacitance method to be valid in transient conduction, the Biot number should be:

  • Much greater than 1
  • Approximately 1
  • Less than 0.1
  • Negative

Correct Answer: Less than 0.1

Q7. Thermal diffusivity (α) is defined as:

  • k/(ρ·c_p)
  • ρ·c_p/k
  • k·ρ·c_p
  • k·c_p/ρ

Correct Answer: k/(ρ·c_p)

Q8. In pharmaceutical drying, conduction primarily controls heat transfer when:

  • Drying occurs in turbulent gas flow
  • Product is pulverized with high porosity
  • Heat must penetrate deeply into solid tablets
  • Evaporation occurs at a free liquid surface only

Correct Answer: Heat must penetrate deeply into solid tablets

Q9. Contact thermal resistance between two solids in contact arises mainly from:

  • Radiative exchange across the gap
  • Microscopic surface roughness and air gaps
  • Bulk conduction through material
  • Convection in the contact zone

Correct Answer: Microscopic surface roughness and air gaps

Q10. In a composite wall made of layers in series, the overall thermal resistance is:

  • Sum of individual layer resistances
  • Product of individual layer resistances
  • Inverse of sum of conductances only for parallel layers
  • Equal to the highest single layer resistance

Correct Answer: Sum of individual layer resistances

Q11. Which equation governs transient heat conduction in solids?

  • Navier–Stokes equation
  • Time-dependent heat diffusion equation (heat equation)
  • Bernoulli’s equation
  • Clausius-Clapeyron equation

Correct Answer: Time-dependent heat diffusion equation (heat equation)

Q12. In steady-state conduction, which term in the heat equation becomes zero?

  • Conduction term
  • Time derivative term
  • Spatial derivative term
  • Source term

Correct Answer: Time derivative term

Q13. For a sphere undergoing unsteady conduction, a key nondimensional parameter governing behavior is:

  • Reynolds number
  • Sherwood number
  • Biot number
  • Péclet number

Correct Answer: Biot number

Q14. Which method is commonly used to measure thermal conductivity of powders and pharmaceutical excipients?

  • Hot-wire method
  • Chromatography
  • UV-Vis spectroscopy
  • Thermogravimetric analysis

Correct Answer: Hot-wire method

Q15. In a tablet during heating, thermal gradients can cause:

  • Uniform porosity throughout the tablet
  • Thermal stresses and possible cracking
  • No impact on mechanical properties
  • Only surface temperature changes

Correct Answer: Thermal stresses and possible cracking

Q16. Which of the following increases effective thermal conductivity of a porous powder bed?

  • Decreasing packing density
  • Introducing inert gas with lower conductivity
  • Compaction to increase solid contacts
  • Increasing void fraction

Correct Answer: Compaction to increase solid contacts

Q17. In heat conduction, heat flux (q”) is defined as:

  • Energy per unit mass
  • Heat transfer per unit area per unit time
  • Temperature difference across thickness
  • Thermal resistance times area

Correct Answer: Heat transfer per unit area per unit time

Q18. For a semi-infinite solid suddenly exposed to a constant surface temperature, temperature at depth x depends on which similarity variable?

  • x divided by time
  • x times thermal diffusivity
  • x divided by square root of (α·t)
  • Time divided by x squared

Correct Answer: x divided by square root of (α·t)

Q19. In hot-melt extrusion of pharmaceuticals, controlling conduction helps to:

  • Eliminate shear heating
  • Ensure uniform melt temperature and drug dispersion
  • Prevent mechanical mixing
  • Increase solvent evaporation

Correct Answer: Ensure uniform melt temperature and drug dispersion

Q20. Which boundary condition represents a surface insulated against heat transfer?

  • Constant temperature boundary
  • Convective boundary condition
  • Zero heat flux (adiabatic) boundary
  • Radiative boundary condition

Correct Answer: Zero heat flux (adiabatic) boundary

Q21. The unit of heat flux in SI is:

  • W
  • W/m
  • W/m²
  • J/kg

Correct Answer: W/m²

Q22. In conduction-dominated drying of a wet granule, the limiting step is often:

  • Convective mass transfer from the surface
  • Internal heat penetration to evaporate bound moisture
  • External radiation absorption
  • Vapor diffusion in ambient air only

Correct Answer: Internal heat penetration to evaporate bound moisture

Q23. Which approximation assumes uniform temperature within an object during transient heating?

  • Finite difference method
  • Lumped capacitance approximation
  • Separation of variables
  • Steady-state assumption

Correct Answer: Lumped capacitance approximation

Q24. Thermal resistance of a plane wall of thickness L and conductivity k is given by:

  • k·L/A
  • L/(k·A)
  • k/(L·A)
  • A·L/k

Correct Answer: L/(k·A)

Q25. For anisotropic materials, thermal conductivity is best described as:

  • A scalar constant same in all directions
  • A tensor varying with direction
  • Always zero in one direction
  • Independent of microstructure

Correct Answer: A tensor varying with direction

Q26. In the Fourier heat conduction equation, internal heat generation term represents:

  • Heat removed by convection
  • Heat produced per unit volume within material
  • Radiative heat loss only
  • Boundary heat input

Correct Answer: Heat produced per unit volume within material

Q27. Which of the following increases heat conduction in a solid cylinder?

  • Decreasing thermal conductivity
  • Increasing cross-sectional area
  • Adding insulating coating
  • Increasing thickness in radial direction

Correct Answer: Increasing cross-sectional area

Q28. During sterilization by dry heat, conduction is critical because:

  • Microbial death depends on surface radiation only
  • Heat must be conducted into the interior to inactivate microbes throughout product
  • Conduction is negligible at sterilization temperatures
  • Convective cooling dominates process

Correct Answer: Heat must be conducted into the interior to inactivate microbes throughout product

Q29. The concept of thermal penetration depth is most relevant to:

  • Rapid heating where only a surface layer heats in short time
  • Steady-state conduction problems only
  • Purely convective heat transfer
  • Radiative heat transfer in vacuum

Correct Answer: Rapid heating where only a surface layer heats in short time

Q30. In a planar wall with convection at one side and fixed temperature at the other, the solution requires:

  • Only algebraic equations
  • Application of mixed boundary conditions
  • No boundary conditions
  • Use of Navier–Stokes equations

Correct Answer: Application of mixed boundary conditions

Q31. Which nondimensional group characterizes transient conduction time scales?

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

Correct Answer: Fourier number (Fo)

Q32. Fourier number (Fo) is defined as:

  • α·t/L²
  • k·L/α
  • ρ·c_p·L/k
  • t/(α·L²)

Correct Answer: α·t/L²

Q33. In a pharmaceutical pellet, anisotropic conduction can arise from:

  • Uniform composition and isotropic packing
  • Layered coating or oriented crystal structure
  • Perfectly spherical homogeneous material
  • Absence of pores

Correct Answer: Layered coating or oriented crystal structure

Q34. Heat conduction in porous solids often involves contributions from:

  • Only solid conduction
  • Solid conduction, gas conduction, and radiation across pores
  • Only radiative transfer
  • Only convective flow within pores

Correct Answer: Solid conduction, gas conduction, and radiation across pores

Q35. The surface heat transfer coefficient (h) appears in conduction problems when:

  • There is a convective boundary at the surface
  • The material is perfectly insulating
  • Only conduction exists with no external environment
  • Thermal conductivity is infinite

Correct Answer: There is a convective boundary at the surface

Q36. Which technique helps reduce thermal gradients in a tablet during drying?

  • Increasing external air velocity to extreme turbulence without control
  • Optimizing heating rate and using step-wise temperature profiles
  • Applying very high temperature at start only
  • Removing all internal binder to increase conduction

Correct Answer: Optimizing heating rate and using step-wise temperature profiles

Q37. In solving conduction problems numerically, which method discretizes in time and space using control volumes?

  • Finite element method
  • Finite difference method
  • Finite volume method
  • Analytical separation of variables

Correct Answer: Finite volume method

Q38. For two materials in parallel thermal paths between same temperatures, the overall conductance is:

  • Sum of individual conductances
  • Average of resistances
  • Product of resistances
  • Difference of conductances

Correct Answer: Sum of individual conductances

Q39. Which property influences both heat storage and transient conduction behavior?

  • Thermal conductivity only
  • Density and specific heat (ρ·c_p)
  • Surface emissivity only
  • Viscosity

Correct Answer: Density and specific heat (ρ·c_p)

Q40. In a drying tray, conduction from tray to product is enhanced by:

  • Reducing contact area between product and tray
  • Using insulating tray material
  • Using thermally conductive tray and good contact
  • Removing tray and suspending product in air

Correct Answer: Using thermally conductive tray and good contact

Q41. The steady-state temperature profile in a hollow cylinder with inner and outer temperatures specified depends logarithmically on radius because:

  • Cylindrical coordinates produce radial dependence leading to a logarithmic solution
  • Conduction does not occur in cylinders
  • Temperature is linear with radius in cylinders
  • Biot number is always zero for cylinders

Correct Answer: Cylindrical coordinates produce radial dependence leading to a logarithmic solution

Q42. Which of the following reduces effective thermal conductivity of a composite by increasing phonon scattering?

  • Adding continuous metallic fibers aligned with heat flow
  • Introducing interfaces and nanostructured inclusions
  • Increasing crystallinity uniformly
  • Removing matrix material

Correct Answer: Introducing interfaces and nanostructured inclusions

Q43. Conduction is dominant over convection when:

  • Fluid flow is highly turbulent at the surface
  • Characteristic length is very small and Biot number is low
  • Surface area is extremely large only
  • Material is in a vacuum

Correct Answer: Characteristic length is very small and Biot number is low

Q44. In transient conduction analysis, boundary conditions of the third kind (Robin) represent:

  • Specified temperature at boundary
  • Specified heat flux at boundary
  • Convective heat exchange combining conduction and convection
  • No heat exchange allowed

Correct Answer: Convective heat exchange combining conduction and convection

Q45. Which pharmaceutical process can be limited by poor conduction through a coated pellet?

  • Surface photometry
  • Core temperature rise during coating cure
  • Gas chromatography analysis
  • pH measurement of dissolution media

Correct Answer: Core temperature rise during coating cure

Q46. The effect of moisture on thermal conductivity of many powders is:

  • Moisture always decreases thermal conductivity
  • Moisture can increase conductivity by creating liquid bridges between particles
  • Moisture has no effect on conduction
  • Moisture converts conduction to radiation only

Correct Answer: Moisture can increase conductivity by creating liquid bridges between particles

Q47. In Fourier’s law, negative sign indicates:

  • Heat flows from low to high temperature
  • Heat flows opposite to increasing temperature direction (from hot to cold)
  • Conservation of momentum
  • Energy generation within material

Correct Answer: Heat flows opposite to increasing temperature direction (from hot to cold)

Q48. Which analytical technique helps separate variables in conduction PDEs for simple geometries?

  • Laplace transform and separation of variables
  • Chromatographic separation
  • Mass spectrometry
  • Empirical correlations only

Correct Answer: Laplace transform and separation of variables

Q49. A higher Fourier number at given position and time implies:

  • Less progress of heat diffusion
  • More progress of heat diffusion and closer to thermal equilibrium
  • No change in transient behavior
  • Instantaneous steady state

Correct Answer: More progress of heat diffusion and closer to thermal equilibrium

Q50. When designing heat transfer for lyophilization (freeze-drying), conduction considerations include:

  • Only vapor diffusion, not conduction
  • Heat conduction through shelf and vial contact, and conductive resistance of frozen cake
  • Neglecting vial contact resistance always
  • Using convection coefficients inside vacuum chamber

Correct Answer: Heat conduction through shelf and vial contact, and conductive resistance of frozen cake

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