Heat Transfer Objective Questions Answers PDF

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Heat Transfer Objective Questions with Answers for Mechanical Engineers PDF

1. The emissive power of a body depends upon its
(a) temperature
(b) wavelength
(c) physical nature
(d) all of the above
(e) none of the above.
Ans: d

2. 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) free convection
(c) forced convection
(d) radiation
(e) radiation and convection.
Ans: d

3. Absorptivity of a body will be equal to its emissivity
(a) at all temperatures
(b) at one particular temperature
(c) when a system is under thermal equilibrium
(d) at the critical temperature
(e) for a polished body.
Ans: c

4. 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) the flow of hot and cold fluids alternately over a surface
(d) generation of heat again and again
(e) indirect transfer.
Ans: c

5. A perfect black body is one which
(a) is black in color
(b) reflects all heat
(c) transmits all heat radiations
(d) absorbs heat radiations of all wavelengths falling on it
(e) fully opaque.
Ans: d

6. Planck’s law holds good for
(a) black bodies
(b) polished bodies
(c) all colored bodies
(d) all of the above
(e) none of the above.
Ans: a

7. If the temperature of solid surface changes from 27°C to 627°C, then its emissive power changes in the ratio of
(a) 3
(b) 6
(c) 9
(d) 27
(e) 81.
Ans: e

8. Depending on the radiating properties, body will be transparent when
(a) p = 0, x = 0 and a = 1
(b) p=l,x = 0,anda = 0
(c) p = 0, T= l,anda = 0
(d) X = 0, a + p = 1
(e) a = 0,x + p= 1.
Ans: c

9. A grey body is one whose absorptivity
(a) varies with temperature
(b) varies with the wavelength of the incident ray
(c) varies with both
(d) does not vary with temperature and wavelength of the incident ray
(e) there is no such criterion.

10. Fourier’s law of heat conduction is valid for
(a) one dimensional case only
(b) two-dimensional cases only
(c) three-dimensional cases only
(d) regular surfaces having non-uniform temperature gradients
(e) irregular surfaces.
Ans: a

11. According to 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) the ratio of emissive power to absorptive power is maximum for perfectly black body
(e) the ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body.
Ans: e

12. All radiations in a black body are
(a) reflected
(b) refracted
(c) transmitted
(d) absorbed
(e) partly reflected and partly absorbed.
Ans: d

13. 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
(e) none of the above.
Ans: d

14. The concept of overall coefficient of heat transfer is used in case of heat transfer by
(a) conduction
(b) convection
(c) radiation
(d) conduction and convection
(e) convection and radiation.
Ans: d

15. According to Stefan-Boltzmann law, ideal radiators emit radiant energy at a rate proportional to
(a) absolute temperature
(b) square of temperature
(c) fourth power of absolute temperature
(d) fourth power of temperature
(e) cube of absolute temperature.
Ans: c

Part-2