Heat and Mass Transfer Objective Questions with Answers - Set 09 - ObjectiveBooks

# Practice Test: Question Set - 09

1. The total radiation from a black body per second per unit area is ________ fourth power of the absolute temperature. This statement is known as Stefan Boltzmann law.
(A) Equal to
(B) Directly proportional to
(C) Inversely proportional to
(D) None of these

2. The insulation ability of an insulator with the presence of moisture would
(A) Increase
(B) Decrease
(C) Remain unaffected
(D) May increase/decrease depending on temperature and thickness of insulation

3. The amount of radiation mainly depends upon the
(A) Nature of the body
(B) Temperature of the body
(C) Type of surface of the body
(D) All of these

4. When heat is transferred by molecular collision, it is referred to as heat transfer by
(A) Conduction
(B) Convection
(D) Scattering

5. The highest thermal diffusivity is of
(A) Iron
(C) Concrete
(D) Wood

6. Conduction is a process of heat transfer
(A) From one particle of the body to another without the actual motion of the particles
(B) From one particle of the body to another by the actual motion of the heated particles
(C) From a hot body to a cold body, in a straight line, without affecting the intervening medium
(D) None of the above

7. Thermal conductivity of water in general with rise in temperature
(A) Increases
(B) Decreases
(C) Remain constant
(D) May increase or decrease depending on temperature

8. The emissivity for a black body is
(A) 0
(B) 0.5
(C) 0.75
(D) 1

9. Thermal conductivity of water at 20°C is of the order of
(A) 0.1
(B) 0.23
(C) 0.42
(D) 0.51

10. Free convection flow depends on
(A) Density
(B) Coefficient of viscosity
(C) Gravitational force
(D) All of these

11. Which of the following statement is correct?
(A) A grey body is one which absorbs all radiations incident on it.
(B) At thermal equilibrium, the emissivity and absorptivity are same.
(C) The energy absorbed by a body to the total energy falling on it, is called emissivity.
(D) A perfect body is one which is black in colour.

12. Which of the following has least value of conductivity?
(A) Glass
(B) Water
(C) Plastic
(D) Air

13. Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be
(A) One
(B) Two
(C) Three
(D) Four

14. Which of the following is expected to have highest thermal conductivity?
(A) Steam
(B) Solid ice
(C) Melting ice
(D) Water

15. The ratio of Nusselt number and the product of Reynold's number and Prandtl number is equal to
(A) Stanton number
(B) Biot number
(C) Peclet number
(D) Grashoff number

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