Radiation Heat Exchange: Master the Fundamentals for Mechanical Engineers

Question 1

Which of the following properties is characteristic of black surfaces in radiation exchange?

Accepted Answer

Absorptivity equal to 1

Answer

Emissive power less than that of gray surfaces

Answer

Reflectivity of 1

Answer

Transmissivity equal to 1

Question 2

Which of the following does NOT influence the view factor between two surfaces?

Accepted Answer

Emissivity of the receiving surface

Answer

Surface area of the emitting surface

Answer

Orientation of the surfaces relative to each other

Answer

Distance between the surfaces

Question 3

Consider two parallel isothermal plates exchanging heat solely by radiation. Which of the following factors will NOT influence the net radiative heat exchange between the plates?

Accepted Answer

Shape of the plates

Answer

Emissivity of the plates

Answer

Surface areas of the plates

Answer

Distance between the plates

Question 4

Which of the following materials typically exhibits the highest emissivity?

Accepted Answer

Carbon black

Answer

Aluminum

Answer

Copper

Answer

Glass

Question 5

Which of the following is a factor that does NOT affect the view factor between two surfaces?

Accepted Answer

Emissivity of the surfaces

Answer

Surface area

Answer

Surface orientation

Answer

Distance between surfaces

Question 6

A black sphere with a diameter of 0.4 m is suspended in a large vacuum chamber at a temperature of 900 K. What is the total radiative heat transfer rate from the sphere?

Accepted Answer

7.54 kW

Answer

3.77 kW

Answer

11.31 kW

Answer

15.08 kW

Question 7

Between two infinite parallel plates, what is the view factor?

Accepted Answer

1

Answer

0

Answer

0.5

Answer

2

Question 8

Which surface type exhibits the highest emissivity?

Accepted Answer

Black paint

Answer

Polished aluminum

Answer

White paint

Answer

Glass

Question 9

How does increasing surface temperature affect the radiation heat transfer rate?

Accepted Answer

Exponential increase

Answer

Linear increase

Answer

Linear decrease

Answer

No effect

Question 10

What is the primary purpose of a radiation shield?

Accepted Answer

To minimize radiation heat transfer

Answer

To maximize radiation heat transfer

Answer

To prevent conduction heat transfer

Answer

To reflect radiation heat transfer

Question 11

What is the significance of the reciprocity theorem in radiation heat exchange?

Accepted Answer

It states that the view factor from surface 1 to surface 2 equals the view factor from surface 2 to surface 1.

Answer

It states that the radiation heat transfer rate is independent of surface areas.

Answer

It states that the emissivity of a surface is equal to its absorptivity.

Answer

It is not applicable to radiation heat exchange.

Question 12

For a black surface in a radiative heat transfer process, the net radiative heat flux absorbed by the surface is:

Accepted Answer

Equal to the emissive power of the surface

Answer

Less than the emissive power of the surface

Answer

Greater than the emissive power of the surface

Question 13

The reciprocity theorem for view factors states that for any two surfaces A and B, the view factor from surface A to surface B (F_AB) is equal to the view factor from surface B to surface A (F_BA). If the view factor from surface A to surface B is 0.4, what is the view factor from surface B to surface A?

Accepted Answer

0.4

Answer

1

Answer

2

Answer

0.25

Question 14

The emissivity of a surface is a measure of its ability to emit thermal radiation. Which of the following surfaces has the highest emissivity?

Accepted Answer

Black surface

Answer

Mirror-like surface

Answer

White surface

Answer

Gray surface

Question 15

Which of the following factors does NOT influence the radiative heat exchange between two surfaces?

Accepted Answer

Relative humidity between the surfaces

Answer

Shape and orientation of the surfaces

Answer

Emissivity of the surfaces

Question 16

The shape factor F12 between two surfaces is defined as:

Accepted Answer

The fraction of radiation emitted from surface 1 that is intercepted by surface 2

Answer

The ratio of the areas of surfaces 1 and 2

Answer

The fraction of radiation emitted from surface 2 that is intercepted by surface 1

Question 17

Which of the following materials exhibits the highest emissivity for thermal radiation?

Accepted Answer

Flat black paint

Answer

Clear glass

Answer

White ceramic

Answer

Polished aluminum

Question 18

Radiation heat transfer between two surfaces is primarily influenced by:

Accepted Answer

Surface temperature, emissivity, and view factor

Answer

Temperature difference alone

Answer

Surface area alone

Answer

Distance between surfaces alone

Question 19

The radiative heat flux emitted by a surface at temperature T is given by:

Accepted Answer

q = εσT^4

Answer

q = εσT^3

Answer

q = σT^3

Question 20

Which of the following accurately describes a non-gray surface?

Accepted Answer

A surface with wavelength-dependent emissivity

Answer

A white surface

Answer

A black surface

Answer

A surface with constant emissivity

Question 21

The net radiation exchange between two black surfaces is given by:

Accepted Answer

Q = σA(T1^4 - T2^4) / (1 - ε1ε2)

Answer

Q = σA(T1^4 + T2^4) / (1 + ε1ε2)

Answer

Q = σA(T1^4 - T2^4)

Answer

Q = σA(T2^4 - T1^4) / (1 - ε1ε2)