Heat and Mass Transfer Objective Questions with Answers - ObjectiveBooks

Heat and Mass Transfer Objective Questions with Answers

Practice Test: Question Set - 11

1. An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m²). The critical thickness of insulation will be
    (A) 25 mm
    (B) 40 mm
    (C) 160 mm
    (D) 800 mm

2. Stefan Boltzmann law is applicable for heat transfer by
    (A) Conduction
    (B) Convection
    (C) Radiation
    (D) Conduction and radiation combined

3. A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is
    (A) h₁ + h₂ + h₃
    (B) (h₁.h₂.h₃)1/3
    (C) 1/h₁ + 1/h₂ + 1/h₃
    (D) None of these

4. The thermal diffusivities for gases are generally
    (A) More than those for liquids
    (B) Less than those for liquids
    (C) More than those for solids
    (D) Dependent on the viscosity

5. The process of heat transfer from one particle of the body to another is called conduction, when the particles of the body
    (A) Move actually
    (B) Do not move actually
    (C) Affect the intervening medium
    (D) Does not affect the intervening medium

6. The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit
    (A) Temperature
    (B) Thickness
    (C) Area
    (D) Time

7. The ratio of the energy absorbed by the body to total energy falling on it is called
    (A) Absorptive power
    (B) Emissive power
    (C) Absorptivity
    (D) Emissivity

8. 40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is
    (A) 0.45
    (B) 0.55
    (C) 0.40
    (D) 0.75

9. The amount of radiation mainly depends on
    (A) Nature of body
    (B) Temperature of body
    (C) Type of surface of body
    (D) All of the above

10. Depending on the radiating properties, a body will be opaque when
    (A) P = 0, x = 0 and a = 1
    (B) P=1, x = 0 and a = 0
    (C) P = 0, x = 1 and a = 0
    (D) X = 0, a + p = 1

11. The emissive power of a body depends upon its
    (A) Temperature
    (B) Wave length
    (C) Physical nature
    (D) All of the above

12. Absorptivity of a body will be equal to its emissivity
    (A) At all temperatures
    (B) At one particular temperature
    (C) When system is under thermal equilibrium
    (D) At critical temperature

13. Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by
    (A) Convection
    (B) Radiation
    (C) Forced convection
    (D) Free convection

14. In regenerator type heat exchanger, heat transfer takes place by
    (A) Direct mixing of hot and cold fluids
    (B) A complete separation between hot and cold fluids
    (C) Flow of hot and cold fluids alternately over a surface
    (D) Generation of heat again and again

15. A perfect black body is one which
    (A) Is black in colour
    (B) Reflects all heat
    (C) Transmits all heat radiations
    (D) Absorbs heat radiations of all wave lengths falling on it

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