# Heat Transfer MCQ’s – Gaseous Radiations

1 - Question

Which of the following have a continuous spectrum?
a) Solids
b) Liquids
c) Gases
d) Solids and liquids
Explanation: They emit and absorb the radiant energy of all wavelength.

2 - Question

Which of the following is/are known as selective absorbers?
a) Solids
b) Liquids
c) Gases and vapors
d) Vapors
Explanation: They emit and absorb radiant energy in definite parts of the spectrum called bands.

3 - Question

Which layers participated in the process of thermal radiation through solids and liquids?
a) 1 micron to 1 mm thick
b) 2 micron to 2 mm thick
c) 1 micron to 0.5 mm thick
d) 2 micron to 4.57 mm thick
Explanation: Gases possess a much small radiating power and all their volumes participate in the radiation.

4 - Question

Some of the gases have low emissive power and absorptivity. They are considered practically diathermanous. Which of the following option is true?
a) Ammonia
b) Helium
c) Carbon-dioxide
d) Methane
Explanation: Helium is monoatomic gas and is extremely inert to thermal radiation.

5 - Question

Consider an enclosure formed by three surfaces having the following values of shape factors, emissivities and temperatures Surface 1 i.e. curved cylindrical has an emissivity 0.75 and temperature 800 K
Surface 2 i.e. closing disc has an emissivity 0.8 and temperature 700 K
Surface 3 i.e. closing disc has an emissivity 0.8 and temperature 700 K
The closing flat discs are 25 mm in diameter and they have interspacing distance equal to 100 mm. If the shape factor between these two identical discs is 0.05, calculate the net rate of radiant heat flow from the curve surface to each of the closing end surface

a) 1.561 W
b) 2.561 W
c) 3.561 W
d) 4.561 W
Explanation: F 21 + F 23 + 1 and A 1 = 0.00785 m2, A2 = 0.000491 m2. Then from reciprocity theorem, F 12 = 0.0594. Q12 = F 12 A 1 σ b (T 14 – T 2 4) = 3.561 W.

6 - Question

Consider a beam of monochromatic radiation at wavelength λ that enters a layer of absorbing gas. As the beam passes through the gas layer, its intensity
a) Decreases
b) Increases
c) Become twice
d) Remains same
Explanation: The decrease is given by d I λ X = – K λ I λ X d x.

7 - Question

When a gas or vapor is in the process of oxidation and combustion, it is called as
a) Oxidation
b) Flame
c) Reduction
d) Combustion
Explanation: It is known as a flame.

8 - Question

The monochromatic absorption coefficient depends upon (i) Temperature (ii) Time (iii) Pressure (iv) Wavelength Identify the correct option
a) i, ii and iv
b) ii, iii and iv
c) i and ii
d) i, iii and iv
Explanation: It depends upon the state of gas and the wavelength.

9 - Question

Which one of the following is not extremely inert to thermal radiation?
a) Orgon
b) Oxygen
c) Methane
d) Nitrogen
Explanation: Methane is a polyatomic gas.

10 - Question

Consider a beam of monochromatic radiation at wavelength λ that enters a layer of absorbing gas. As the beam passes through the gas layer, its intensity is given by
a) d I λ X = – K λ I λ X d x
b) d I λ X = – 2 K λ I λ X d x
c) d I λ X = – 3 K λ I λ X d x
d) d I λ X = – 4 K λ I λ X d x