heat transfer MCQs – Page 4

Practise focused heat transfer questions with marked answers for exam preparation and subject revision.

heat transfer Mcqs
61. Which of the following property of air does not increase with rise in temperature ________________?
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A. thermal conductivity

B. density

C. thermal diffusivity

D. dynamic viscosity

E. kuiematic viscosity

62. All radiations in a black body are___________________?
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A. reflected

B. transmitted

C. refracted

D. partly reflected and partly absorbed

E. absorbed
63. The unit of overall coefficient of heat transfer is___________________?
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A. kacl/m hr C

B. kcal/hr C

C. kcal/m3 hr C

D. kcal/m2 hr C

E. kcal/m2

64. The value of Prandtl number for air is about _______________________?
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A. 1.7

B. 10.5

C. 0.1

D. 0.7

E. 0.3

65. Stefan Boltzmann law is applicable for heat transfer by __________________?
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A. conduction

B. convection

C. convection and radiation combined

D. radiation

E. conduction and radiation combined

66. According to Stefan-Boltzmann law, ideal radiators emit radiant energy at a rate proportional to___________________?
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A. absolute temperature

B. fourth power of absolute temperature

C. cube of absolute temperature

D. square of temperature

E. fourth power of temperature

67. According to Kirchoffs law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a _________________?
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A. grey body

B. brilliant white polished body

C. none of the above

D. black body

E. red hot body

68. Depending on the radiating properties, a body will be opaque when _________________?
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A. p=l,x = 0anda = 0

B. x 0, a + p = 1

C. p = 0, x = 0 and a = 1

D. a=0,x + p= 1.

E. p = 0, x = 1 and a = 0

69. If the temperature of a solid surface changes form 27C to 627C, then its emissive power changes in the ratio of___________________?
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A. 3

B. 6

C. 9

D. 27

E. 81
70. The value of the wavelength for maximum emissive power is given by ___________________?
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A. Plancks law

B. Stefans law

C. Kirchhoffs law

D. Wiens law

E. Fouriers law

71. According to Wiens law, the wavelength corresponding to maximum energy is proportion to ________________?
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A. absolute temperature (T)

B. I2

C. t

D. f

E. 1/r

72. Two plates spaced 150 mm apart are maintained at 1000C and 70C. The heat transfer will take place mainly by ___________________?
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A. free convection

B. radiation and convection

C. convection

D. radiation

E. forced convection

73. The ratio of the energy absorbed by the body to total energy falling on it is called_________________?
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A. absorptive power

B. absorptivity

C. none of the above

D. emissive power

E. emissivity

74. Depending on the radiating properties, a body will be white when_________________?
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A. p=l,T = 0anda = 0

B. a = 0, x + p = 1.

C. p = 0, x = 1 and a = 0

D. p = 0, x = 0 and a = 1

E. x = 0, a + p = 1

75. According to Stefans law, the total radiation from a black body per second per unit area is proportional to____________________?
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A. T2

B. l/T

C. absolute temperature

D. T5

E. t
76. 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____________________?
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A. 0.75

B. 0.45

C. 0.6

D. 0.4

E. 0.55

77. A perfect black body is one which_______________?
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A. transmits all heat radiations

B. abslprbs heat radiations of all wave lengths falling on it

C. fully opaque

D. reflects all heat

E. is black in colour

78. In free con-vection heat transfer, Nusselt number is function of________________?
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A. Grashoff no and Prandtl no.

B. none of the above

C. Prandtl no. and Reynold no

D. Grashoff no. and Reynold no

E. Grashoff no., Prandtl no and Reynold no

79. The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit_______________?
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A. temperature

B. area and time

C. area

D. time

E. thickness

80. The thermal diffusivities for gases are generally_____________________?
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A. less than those for liquids

B. more than those for liquids

C. same as for the liquids

D. dependent on the viscosity

E. more than those for solids