Heat Transfer

61. As per Kirchoff‟s law, the ratio of the total radiating power to the absorptivity of a body depends on the

  1. Temperature of the body only
  2. Wavelength of monochromatic radiation
  3. Both (A) and (B)
  4. Nature of material of body
Correct answer: (A)
Temperature of the body only

62. As the difference between the wall temperature and bulk temperature increases, the boiling heat transfer co-efficient

  1. Continues to increase
  2. Continues to decrease
  3. Goes through a minimum
  4. Goes through a maximum
Correct answer: (C)
Goes through a minimum

63. Asymptotic conditions is reached, when for a fluid flowing in laminar flow through a long tube

  1. Exit-fluid temperature > wall temperature
  2. Exit fluid temperature < wall temperature
  3. Exit fluid temperature = wall temperature
  4. Graetz number > 100
Correct answer: (C)
Exit fluid temperature = wall temperature

64. At constant temperature, the thermal conductivities of gases _________ with rise in pressure.

  1. Decrease
  2. Increase
  3. Remain unchanged
  4. May increase or decrease; depends on the pressure
Correct answer: (A)
Decrease

65. At Pr > 1, conduction in an ordinary fluid flowing through a heated pipe is limited to the

  1. Buffer zone
  2. Turbulent core
  3. Both (A) and (B)
  4. Viscous sub-layer
Correct answer: (D)
Viscous sub-layer

66. At what value of Prandtl number, conduction is negligible in the turbulent core of a fluid flowing through a heated pipe?

  1. 0.5
  2. < 0.5
  3. > 0.6
  4. < 0.1
Correct answer: (C)
> 0.6

67. At what value of Prandtl number, the hydrodynamic and thermal boundary layers of a fluid flowing over a heated plate will be identical?

  1. 1
  2. < 1
  3. > 1
  4. None of these
Correct answer: (A)
1

68. Baffle spacing

  1. Is not the same as baffle pitch
  2. Should be less than one fifth the diameter of the shell
  3. Should be less than the inside diameter of the shell
  4. None of these
Correct answer: (C)
Should be less than the inside diameter of the shell

69. Baffles are provided in heat exchangers to increase the

  1. Fouling factor
  2. Heat transfer area
  3. Heat transfer co-efficient
  4. Heat transfer rate
Correct answer: (C)
Heat transfer co-efficient

70. Baffles in the shell side of a shell and tube heat exchanger

  1. Increase the cross-section of the shell side liquid
  2. Force the liquid to flow parallel to the bank
  3. Increase the shell side heat transfer co-efficient
  4. Decrease the shell side heat transfer co-efficient
Correct answer: (C)
Increase the shell side heat transfer co-efficient
Previous
Page 7 of 50
Next
Copyright © EngineeringMCQ.com