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

1. 109. What is 'parallel-current flow' (or co-current flow) in a heat exchanger?

   • A. The hot and cold fluids flow in opposite directions
   • B. The hot and cold fluids flow in the same direction
   • C. The fluids flow perpendicular to each other
   • D. One fluid is stagnant

2. 110. What is 'cross-flow' in a heat exchanger?

   • A. The hot and cold fluids flow perpendicular to each other
   • B. The hot and cold fluids flow in the same direction
   • C. The hot and cold fluids flow in opposite directions
   • D. One fluid is stagnant

3. 111. What is 'heat flux' (q'')?

   • A. The rate of heat transfer per unit area
   • B. The total rate of heat transfer
   • C. The temperature difference
   • D. The heat transfer coefficient

4. 112. What is the unit of heat flux (q'') in SI units?

   • A. W/(m·K)
   • B. J/(kg·K)
   • C. W/(m²·K)
   • D. W/m²

5. 113. What is 'thermal radiation'?

   • A. Energy emitted by matter as a result of changes in the electronic configurations of atoms or molecules
   • B. Energy transferred by molecular collisions
   • C. Energy transferred by fluid motion
   • D. Energy transferred by direct contact

6. 114. What is 'absorptivity' (α) in radiation?

   • A. The fraction of incident radiation that is absorbed by a surface
   • B. The fraction of incident radiation that is reflected
   • C. The fraction of incident radiation that is transmitted
   • D. The ability to emit radiation

7. 115. What is 'reflectivity' (ρ) in radiation?

   • A. The fraction of incident radiation that is absorbed
   • B. The fraction of incident radiation that is reflected by a surface
   • C. The fraction of incident radiation that is transmitted
   • D. The ability to emit radiation

8. 116. What is 'transmissivity' (τ) in radiation?

   • A. The fraction of incident radiation that is absorbed
   • B. The fraction of incident radiation that is reflected
   • C. The fraction of incident radiation that is transmitted through a medium
   • D. The ability to emit radiation

9. 117. 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

10. 118. 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

11. 119. 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

12. 120. 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