Heat Transfer

481. Which of the following situations can be approximated to a steady state heat transfer system?

  1. A red hot steel slab (having outside surface temperature as 1300°C) exposed to the atmospheric air at 35°C
  2. 10 kg of dry saturated steam at 8 kgf/cm2 flowing through a short length of stainless steel pipe exposed to atmospheric air at 35°C
  3. Boiling brine kept in open vessel when the bottom surface temperature of the vessel is maintained constant at 180°C
  4. A sub-cooled refrigerant liquid at 8°C flowing at the rate of 6 Kg/minute through a copper pipe exposed to atmospheric air at 35°C
Correct answer: (B)

10 kg of dry saturated steam at 8 kgf/cm2 flowing through a short length of stainless steel pipe exposed to atmospheric air at 35°C

482. Which one gives the monochromatic emissive power for black body radiation?

  1. Planck's law
  2. Kirchhoff’s law
  3. Wien's law
  4. Stefan-Boltzmann law
Correct answer: (A)
Planck's law

483. Which type of heat exchanger is preferred for heavy heat loads?

  1. Double pipe
  2. Plate fine
  3. Series and parallel set of shell and tube
  4. None of these
Correct answer: (C)
Series and parallel set of shell and tube

484. While the total emissivity of a perfect black body is unity, the same for a real body is

  1. 0
  2. 1
  3. > 1
  4. Between 0 and 1
Correct answer: (D)
Between 0 and 1

485. With increase in porosity, the thermal conductivity of a solid substance

  1. Increases
  2. Decreases
  3. Remains unchanged
  4. May increase or decrease; depends on the solid
Correct answer: (B)
Decreases

486. With increase in temperature, the thermal conductivity of a gas

  1. Increases
  2. Decreases
  3. Remain same
  4. May increase or decrease depending on the type of gas
Correct answer: (A)
Increases

487. With increase in temperature, the thermal conductivity of fresh lubricating oil

  1. Increases
  2. Decreases
  3. Remains unchanged
  4. May increase or decrease; depends on its composition
Correct answer: (B)
Decreases

488. With increase in temperature, the thermal conductivity of most liquids

  1. Increases
  2. Decreases
  3. Remain same
  4. First increases upto a certain temperature and then becomes constant
Correct answer: (B)
Decreases

489. With increase in temperature, the thermal conductivity of non-metallic amorphous solids

  1. Decreases
  2. Increases
  3. Remain constant
  4. First decreases upto certain temperature and then increases
Correct answer: (B)
Increases

490. With increase in temperature, the thermal conductivity of steel

  1. Increases
  2. Decreases
  3. Remains unchanged
  4. Increases exponentially
Correct answer: (B)
Decreases
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