Test: Radiation Heat Transfer - 3 - Mechanical Engineering MCQ

The ratio of total emissive power of body to the total emissive power of a black body at the same temperature is called

Which one of the following is true for black body

Which one of the following is true for white body?

A surface is called Grey surface. If

The unit of Stefan-Botlzmann constant is

When metallic surfaces are oxidized, the emissivity

The solar energy falling on the earth’s surface is called

The shape factor F₁₂ in case of a conical cavity having a semi vertex angle a and height h is given by

If the temperature of a solid surface changes from 27°C to 627°C. Its emissive power will increase in the ratio of

The radiative heat transfer rate per unit area (W/m²) between two plane parallel grey surface (emissivity = 0.9) maintained at 400 K and 300 K is (StefanBoltzmann constant s = 5.67 x 10^-8 W/m²K⁴)

Two long parallel surfaces each of emissivity 07 are maintained at different temperature and accordingly have radiation heat exchange between them. It is desirable to reduce 75% of this radiant heat transfer by inserting thin parallel shields of equal emissivity on both sides. The number of shields should be

Heat transfer by radiation between two gre bodies of emissivity ∈ is proportional to (Notations have their usual meanings)

The shape factor of a hemispherical body place on a flat surface with respect to it self is

The shape factor of a cylindrical cavity with respect to it self is

A spherical body with surface A₁ is completely enclosed by another hollow body with inner surface A₂. The shape factor of A₂ with respect to A₁ is

For a circular tube of equal length and diameter shown below, the view factor F₁₃ = 0.17. The view factor F₁₂ in this case will be

For a hemisphere, the solid angle is measured

Two spheres A and B of same material have radii 1m and 4m and temperature 1000 K and 2000 K respectively. Which one of the following statement is correct.
The energy radiated by sphere A is

A plate having 10 cm² area each side is hanging in the middle of a room of 100 m² total surface area, the plate temperature and emissivity are respectively 800 K and 0.6. The temperature and emissivity values for the surface of the room are 300 K and 0.3 respectively. Boltzman’ constant σ = 5.67 x 10^-8 W/m²K⁴. The total heat loss from the two surface of the plate is

Match List-I (surface with orientations) with List-lI (equivalent emissivity) and select the correct answer using the codes given below:
List-I
A. Infinite parallel planes
B. Body 1 completely enclosed by body 2 but body 1 is very small
C. Radiation exchange between two small Grey bodies
D. Two concentric cylinders with large lengths
List-II
1. ∈₁

4. ∈₁∈₂
Codes:
      A  B  C  D
(a)  3  1  4   2
(b)  2  4  1   3
(c)  2  1  4   3
(d)  3  4  1   2

For the two long concentric cylinders with surface areas A₁, and A₂, the view factor F₂₂ is given by

For a thin steel sheet, total emissive power is given as 32 W/m², insolation as 93 W/m². If thin sheet has reflectivity = 0,6, absorbtivity = 0.1 and transmissivity = 0.3. Then radiosity in W/m²

The thermal radiative flux from a surface of emissivity = 0 .4 is 22.68 kW /m². The approximate surface temperature (K) is
Stefan Boltzmann's constant = 5.67x10^-8 W/m²K⁴

A solid cylinder (surface 2) is located at the centre of a hollow sphere (surface 1). The diameter of the sphere is 1 m, while the cylinder has a diameter and length of 0.5 m each. The radiation configuration factor F₁₁ is

Match List-I (Thermal spectrum) with List-l! (Wavelength mm) and select the correct aswer using the code given below the lists:
List-I
A. Cosmic rays
B. Radio waves
C. Visible light
D. UVrays
List-II
1. λ < 10^-8
2. 10² < λ < 10¹⁰ 
3. 0.38 < λ< 0.78 
4. 10^-2 < λ < 0.38
Codes:
     A  B  C  D
(a) 4  2  3  1
(b) 2  1  3  4
(c) 4  3  2  1
(d) 1  2  3  4

Match List-I with List-ll and select the correct answer using the code given below the lists:
List-I
A. Window glass
B. Grey surface
C. Carbon dioxide
D. Radiosity
List-ll
1. Emissivity
2. Kinematic viscosity
3. Diffusion coefficient
Codes:
     A  B  C
(a) 2  3  1
(b) 3  2  1
(c) 1  3  2
(d) 1  2  3

The radiation heat flux from a heating element at a temperature of 800°C, in a furnace maintained at 300°C is kW/m². The flux when the element temperature is increased to 1000°C for the same furnace temperature is