Heat and Mass Transfer - Set 06 - ObjectiveBooks

# Practice Test: Question Set - 06

1. In counter flow heat exchangers
(A) Both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state
(B) Both the fluids at inlet are in their hottest state
(C) Both the fluids at exit are in their hottest state
(D) One fluid is in hottest state and other in coldest state at inlet

2. The ratio of surface convection resistance to the internal conduction resistance is known as
(A) Grashoff number
(B) Biot number
(C) Stanton number
(D) Prandtl number

3. A steam pipe is to be insulated by two insulating materials put over each other. For best results
(A) Better insulation should be put over pipe and better one over it
(B) Inferior insulation should be put over pipe and better one over it
(C) Both may be put in any order
(D) Whether to put inferior OIL over pipe or the better one would depend on steam temperature

4. Kirchhoff's law states that
(A) The total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature
(B) The wave length corresponding to the maximum energy is proportional to the absolute temperature
(C) The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body
(D) None of the above

5. Fourier's law of heat conduction is valid for
(A) One dimensional cases only
(B) Two dimensional cases only
(C) Three dimensional cases only
(D) Regular surfaces having non-uniform temperature gradients

6. The critical thickness of insulation for a sphere is
(A) k/h₀
(B) 2k/h₀
(C) h₀/k
(D) h₀/2k

7. According of Kirchhoff's law
(A) Radiant heat is proportional to fourth power of absolute temperature
(B) Emissive power depends on temperature
(C) Emissive power and absorptivity are constant for all bodies
(D) Ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body

8. Film coefficient is defined as the ratio of
(A) Thermal conductivity to the equivalent thickness of the film of fluid
(B) Temperature drop through the films of fluids to the thickness of film of fluids
(C) Thickness of film of fluid to the thermal conductivity
(D) Thickness of film of fluid to the temperature drop through the films of fluids

9. All radiations in a black body are
(A) Reflected
(B) Refracted
(C) Transmitted
(D) Absorbed

10. The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles caused by some mechanical means, is known as
(A) Conduction
(B) Free convection
(C) Forced convection

11. According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a
(A) Grey body
(B) Brilliant white polished body
(C) Red hot body
(D) Black body

12. When α is absorptivity, ρ is reflectivity and τ is transmissivity, then for a diathermanous body,
(A) α = 1, ρ = 0 and τ = 0
(B) α = 0, ρ = 1 and τ = 0
(C) α = 0, ρ = 0 and τ = 1
(D) α + ρ = 1 and τ = 0

13. The concept of overall coefficient of heat transfer is used in case of heat transfer by
(A) Conduction
(B) Convection
(D) Conduction and convection

14. The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as
(A) Wien's law
(B) Stefan's law
(C) Kirchhoff's law
(D) Planck's law

15. The unit of overall coefficient of heat transfer is
(A) kcal/m²
(B) kcal/hr °C
(C) kcal/m² hr °C
(D) kcal/m hr °C

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