Heat Transfer (Chemical Perspective) – Multiple Choice Questions (MCQs)

1. 49. For an opaque surface, what is the relationship between absorptivity, reflectivity, and transmissivity?

   • A. α + ρ + τ = 1
   • B. α + ρ = 1 (since τ = 0)
   • C. α + τ = 1
   • D. ρ + τ = 1

2. 50. What is 'thermal boundary layer'?

   • A. A thin region adjacent to a solid surface in a fluid flow where temperature gradients are significant
   • B. A region of uniform temperature
   • C. A region of stagnant fluid
   • D. A region of high velocity

3. 51. What is 'hydrodynamic boundary layer'?

   • A. A thin region adjacent to a solid surface in a fluid flow where velocity gradients are significant
   • B. A region of uniform velocity
   • C. A region of constant temperature
   • D. A region of high heat transfer

4. 52. What is the relationship between the thermal and hydrodynamic boundary layers?

   • A. The relative thickness depends on the Prandtl number
   • B. They are always of equal thickness
   • C. They are unrelated
   • D. One is always thicker than the other

5. 53. What is the 'critical heat flux' (CHF) in boiling?

   • A. The maximum heat flux that can be achieved in nucleate boiling before film boiling occurs
   • B. The minimum heat flux for boiling
   • C. The heat flux at which boiling stops
   • D. The heat flux for condensation

6. 54. What is 'quenching'?

   • A. Rapid cooling of a material
   • B. Rapid heating of a material
   • C. Slowing down heat transfer
   • D. Insulating a material

7. 55. What is 'regenerator' heat exchanger?

   • A. A heat exchanger where the same flow passages are alternately heated by a hot fluid and then cooled by a cold fluid
   • B. A heat exchanger where fluids flow continuously
   • C. A heat exchanger for boiling
   • D. A heat exchanger for condensation

8. 56. What is the 'overall energy balance' for a heat exchanger at steady state?

   • A. Rate of heat gained by cold fluid = Rate of heat lost by hot fluid
   • B. Rate of heat gained by hot fluid = Rate of heat lost by cold fluid
   • C. Heat input = Heat output + Work done
   • D. Mass input = Mass output

9. 57. What is 'thermal expansion'?

   • A. The tendency of matter to change in volume in response to a change in temperature
   • B. The tendency of matter to change phase
   • C. The tendency of matter to conduct heat
   • D. The tendency of matter to resist heat flow

10. 58. What is 'thermal stress'?

    • A. Stress caused by temperature changes
    • B. Stress caused by external forces
    • C. Stress caused by fluid flow
    • D. Stress caused by chemical reactions

11. 59. What is the 'heat generation rate' for a volumetric heat source?

    • A. q''' (heat generated per unit volume)
    • B. Q (total heat generated)
    • C. q'' (heat flux)
    • D. k (thermal conductivity)

12. 60. What is 'heat pipe'?

    • A. A heat transfer device that uses phase change (evaporation and condensation) to transfer heat with very high effective thermal conductivity
    • B. A device for insulation
    • C. A device for mixing fluids
    • D. A device for generating heat