Mechanical Engineering - Heat and Mass Transfer - Radiation

Buy GATE - Mechanical Engineering Practice test pack

Question - 1

What is the basic equation of thermal radiation from which all other equations of radiation can be derived?

  • A Stefan-Boltzmann equation
  • B Planck's equation
  • C Wien's equation
  • D Rayleigh-Jeans formula

Question - 2

Match List I with List II and select the correct answer using the codes given below the lists.

List I List II
P. Infinite parallel planes 1. ε1
Q. Completely enclosed body large
compared to enclosing body
(subscript 1 for enclosed body)		 2. ε1ε2
R. Two rectangles with common
side perpendicular to each other		 3. \(\frac { 1 }{ \frac { 1 }{ { \varepsilon }_{ 1 } } +\frac { 1 }{ { \varepsilon }_{ 2 } } -1 } \)
S. Concentric cylinders 4. \(\frac { 1 }{ \frac { 1 }{ { \epsilon }_{ 1 } } +\frac { { A }_{ 1 } }{ { A }_{ 2 } } \left( \frac { 1 }{ { \epsilon }_{ 2 } } -1 \right) } \) ​​​
  • A P Q R S 1 2 4 3
  • B P Q R S 3 1 4 2
  • C P Q R S 2 1 3 4
  • D P Q R S 3 1 2 4

Question - 3

A large spherical enclosure has a small opening. The rate of emission of radiative flux through this opening is 7.35 kW/m2. The temperature at the inner surface of the sphere will be about (assume Stefan-Boltzmann constant a = 5.67 x  W/m2-K4)

  • A 6000C
  • B 3270C
  • C 373 K
  • D 1000 K

Question - 4

Heat transfer by radiation between two grey bodies of emissivity e is proportional to (notations have their usual meanings)

  • A \(\frac { ({ E }_{ b }-J) }{ (1-\varepsilon ) } \)
  • B \(\frac { ({ E }_{ b }-J) }{ (1-\varepsilon )/\epsilon } \)
  • C \(\frac { ({ E }_{ b }-J) }{ (1-\varepsilon )^{ 2 } } \)
  • D \(\frac { ({ E }_{ b }-J) }{ (1-\varepsilon ^{ 2 }) } \)

Question - 5

Solar radiation of 1200 W/m2 falls perpendicularly on a gray opaque surface of emissivity 0.5. If the surface temperature is 50°C and surface emissive power is 600 W/m2, the radiosity of that surface will be

  • A 600 W/m2
  • B 1000 W/m2
  • C 1200 W/m2
  • D 1800 W/m2

Question - 6

Sun's surface at 5800 K emits radiation at a wavelength of 0.5 μ, A furnace at 300°C will emit through a small opening, radiation at a wavelength of nearly

  • A 10 μ
  • B 5 μ
  • C 0.25 μ
  • D 0.025 μ

Question - 7

The spectral emissive power E⋋ for a diffusely emitting surface is
1. E⋋ =0 for ⋋≤3 μm
2. E⋋=150 W/m2-μm for 3 < ⋋ < 12 μm
3. E⋋=300 W/m2-μm for 12 < ⋋ < 25 μm
4. E⋋=0 for ⋋ < 25 μm
The total emissive power of the surface over the entire spectrum is

  • A 1250 W/m2
  • B 2500 W/m2
  • C 4000 W/m2
  • D 5250 W/m2

Question - 8

The shape factor of a hemispherical body placed on a flat surface with respect to itself is

  • A zero
  • B 0.25
  • C 0.5
  • D 1.0

Question - 9

An enclosure consists of four surfaces 1, 2, 3 and 4. The view factors for radiation heat transfer (where the subscripts 1, 2, 3, 4 refer to the respective surfaces) are F11 = 0.1, F12 = 0.4 and F13 = 0.25. The surface areas A1 and A4 are 4 m2 and 2 m2 respectively. The view factor F41 is

  • A 0.75
  • B 0.50
  • C 0.25
  • D 0.10

Question - 10

For an opaque plane surface, the irradiation radiosity and emissive power are respectively 20, 12 and 10 W/m2. What is the emissivity of the surface?

  • A 0.2
  • B 0.4
  • C 0.8
  • D 1.0
Previous Next
Previous Next
Previous Next
Previous Next
Previous Next
Previous Next
Previous Next
Previous Next
Previous Next
Previous Next
Previous Next
Previous Next
Previous Next
Previous Next
Previous Next