Heat Transfer Practice Test 6

1. Which layers participated in the process of thermal radiation through solids and liquids?

2 micron to 4.57 mm thick

1 micron to 0.5 mm thick

2 micron to 2 mm thick

1 micron to 1 mm thick

2. The net heat exchange between the two grey surfaces may be written as

(Q ₁₂) _NET= E _{b 1}– E _{b 2}/ (1 – e ₁/A ₁ e₁ + 1/A ₁F ₁₂ + 1 – e ₂/A ₂ e₂)

(Q ₁₂) _NET= E _{b 1}– 2 E _{b 2}/ (1 – e ₁/A ₁ e₁ + 1/A ₁F ₁₂ + 1 – e ₂/A ₂ e₂)

(Q ₁₂) _NET= 2 E _{b 1}– 3 E _{b 2}/ (1 – e ₁/A ₁ e₁ + 1/A ₁F ₁₂ + 1 – e ₂/A ₂ e₂)

(Q ₁₂) _NET= 2 E _{b 1}– E _{b 2}/ (1 – e ₁/A ₁ e₁ + 1/A ₁F ₁₂ + 1 – e ₂/A ₂ e₂)

3. If an annulus has an inner diameter of d₁ and an outer diameter of d₂ then the equivalent diameter is

2 d₂- d₁

d₂- d₁

d₁- d₂

d₂- 2 d₁

4. Reynolds number is given by the quantity

2 p V l/δ

3 p V l/δ

4 p V l/δ

p V l/δ

5. 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

d I _{λ X}= - K _λI _{λ X} d x

d I _{λ X}= - 2 K _λI _{λ X} d x

d I _{λ X}= - 4 K _λI _{λ X} d x

d I _{λ X}= - 3 K _λI _{λ X} d x

6. Two black discs each of diameter 50 cm are placed parallel to each other concentrically at a distance of one meter. The discs are maintained at 1000 K and 500 K. Calculate the heat flow between the discs when no other surface is present

517.27 W

617.27 W

417.27 W

317.27 W

7. Two large parallel planes with emissivity 0.4 are maintained at different temperatures and exchange heat only by radiation. What percentage change in net radiative heat transfer would occur if two equally large radiation shields with surface emissivity 0.04 are introduced in parallel to the plates?

95.1%

85.1%

75.1%

65.1%

8. Which of the following heat flow situations pertains to free or natural convection?

Cooling of internal combustion engine

Cooling of billets in atmosphere

Air conditioning installations and nuclear reactors

Flow of water inside the condenser tubes

9. Heat exchange between two gray surfaces enclosed by an adiabatic surface is given by

Q ₁₂ = A σ _b (T₁⁴– T ₂⁴) / [1/E ₁ + 1/E₂ – 2].

Q ₁₂ = A σ _b (T₁⁴– T ₂⁴) / [1/E ₁ + 1/E₂ – 2 + 2/1 + F ₁₂].

Q ₁₂ = A (T₁⁴– T ₂⁴) / [1/E ₁ + 1/E₂ – 2 + 2/1 + F ₁₂].

Q ₁₂ = A σ _b (T₁⁴– T ₂⁴) / [1/E ₁ + 1/E₂ + 2/1 + F ₁₂].

10. Consider radiant heat exchange between two non-black parallel surfaces. The surface 1 emits radiant energy E ₁ which strikes the surface 2. Identify the correct option

The value of B is α E₁

The value of E is (1 – α₁) ² (1 - α₂)E ₁

The value of C is (1 – α₁) E ₁

The value of D is (1 – α₁) (1 - α₂) ²E ₁