Heat Transfer Questions and Answers – Adiabatic and Reradiating Surfaces

This set of Heat Transfer Questions for campus interviews focuses on “Adiabatic And Reradiating Surfaces”.

1. 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
a) 317.27 W
b) 417.27 W
c) 517.27 W
d) 617.27 W
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2. 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 the disks are connected by a cylindrical black no-flux surface
a) 2417.68 W
b) 3417.68 W
c) 4417.68 W
d) 5417.68 W
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3. Heat exchange between two black surfaces enclosed by an insulated surface is given by
a) Q ₁₂ = A ₁ σ _b (T ₁⁴ – T₂⁴) [A ₂ – A ₁ F ₁₂²/A ₁ + A ₂ – 2 A ₁ F ₁₂].
b) Q ₁₂ = 2 A ₁ σ _b (T ₁⁴ – T₂⁴) [A ₂ – A ₁ F ₁₂²/A ₁ + A ₂ – 2 A ₁ F ₁₂].
c) Q ₁₂ = 3 A ₁ σ _b (T ₁⁴ – T₂⁴) [A ₂ – A ₁ F ₁₂²/A ₁ + A ₂ – 2 A ₁ F ₁₂].
d) Q ₁₂ = 4 A ₁ σ _b (T ₁⁴ – T₂⁴) [A ₂ – A ₁ F ₁₂²/A ₁ + A ₂ – 2 A ₁ F ₁₂].
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4. Heat exchange between two gray surfaces enclosed by an adiabatic surface is given by
a) Q ₁₂ = A (T ₁⁴ – T ₂⁴) / [1/E ₁ + 1/E ₂ – 2 + 2/1 + F ₁₂].
b) Q ₁₂ = A σ _b (T ₁⁴ – T ₂⁴) / [1/E ₁ + 1/E ₂ + 2/1 + F ₁₂].
c) Q ₁₂ = A σ _b (T ₁⁴ – T ₂⁴) / [1/E ₁ + 1/E ₂ – 2 + 2/1 + F ₁₂].
d) Q ₁₂ = A σ _b (T ₁⁴ – T ₂⁴) / [1/E ₁ + 1/E ₂ – 2].
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5. A blind cylindrical hole of 2 cm diameter and 3 cm length is drilled into a metal slab having emissivity 0.7. If the metal slab is maintained at 650 K, make calculations for the radiation heat escape from the hole

a) 7 W
b) 3 W
c) 1 W
d) 9 W
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6. A cavity in the shape of a frustum of a cone has diameter 30 cm and 60 cm and the height is 80 cm. If the cavity is maintained at temperature of 800 K, determine the heat loss from the cavity when the smaller diameter is at the bottom
a) 6577 W
b) 2367 W
c) 8794 W
d) 3675 W
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7. How would the heat loss be affected if the cavity in the shape of a frustum of a cone, with diameters of 30 cm and 60 cm and height of 80 cm, is positioned with the larger diameter at the base instead of the smaller one?
a) 75.06 % (increase)
b) 55.06 % (decrease)
c) 65.06 % (increase)
d) 75.06 % (decrease)
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8. A conical cavity of base diameter 15 cm and height 20 cm has inside surface temperature 650 K. If emissivity of each surface is 0.85, determine the net radiative heat transfer from the cavity
a) 168.3 W
b) 158.3 W
c) 148.3 W
d) 138.3 W
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9. A cylindrical cavity of base diameter 15 cm and height 20 cm has inside surface temperature 650 K. If emissivity of each surface is 0.85, determine the net radiative heat transfer from the cavity
a) 194 W
b) 184 W
c) 174 W
d) 164 W
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10. What is the unit of coefficient of radiant heat transfer?
a) W/K
b) W/m² K
c) W/m²
d) W/m K
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Sanfoundry Global Education & Learning Series – Heat Transfer.

To practice all areas of Heat Transfer for campus interviews, here is complete set of 1000+ Multiple Choice Questions and Answers.