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

1. 169. What is the 'Grashof number' (Gr)?

   • A. A dimensionless number that characterizes natural convection heat transfer
   • B. A dimensionless number for forced convection
   • C. A dimensionless number for conduction
   • D. A dimensionless number for radiation

2. 170. What is the 'critical thickness of insulation'?

   • A. The insulation thickness at which the heat loss from a pipe or sphere is maximized
   • B. The insulation thickness at which heat loss is minimized
   • C. The minimum thickness of insulation required
   • D. The maximum thickness of insulation allowed

3. 171. What is 'transient heat conduction'?

   • A. Heat conduction where the temperature within the body changes with time
   • B. Heat conduction where temperature is constant
   • C. Heat conduction in a steady state
   • D. Heat conduction without any medium

4. 172. What is 'steady-state heat conduction'?

   • A. Heat conduction where the temperature distribution within the body does not change with time
   • B. Heat conduction where temperature changes with time
   • C. Heat conduction in an unsteady state
   • D. Heat conduction with fluid motion

5. 173. What is the 'thermal resistance' concept in heat transfer?

   • A. The opposition a material offers to the flow of heat
   • B. The rate of heat flow
   • C. The temperature difference
   • D. The area for heat transfer

6. 174. What is 'thermal contact resistance'?

   • A. Resistance to heat transfer at the interface between two solid surfaces due to imperfect contact
   • B. Resistance within a single material
   • C. Resistance due to fluid flow
   • D. Resistance due to radiation

7. 175. What is the 'log mean area' used for in heat conduction through thick-walled cylinders?

   • A. To calculate the effective heat transfer area
   • B. To calculate the volume of the cylinder
   • C. To calculate the density of the material
   • D. To calculate the mass of the cylinder

8. 176. What is 'counter-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

9. 177. 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

10. 178. 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

11. 179. 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

12. 180. 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