E-PolyLearning

1. A very long copper rod 20 mm in diameter extends horizontally from a plane heated wall maintained at 100 degree Celsius. The surface of the rod is exposed to an air environment at 20 degree Celsius with convective heat transfer coefficient of 8.5 W/m² degree. Workout the heat loss if the thermal conductivity of copper is 400 W/m degree
a. 10.71 W
b. 20.71 W
c. 30.71 W
d. 40.71 W
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Answer: (b).20.71 W

2. Common applications of finned surfaces are with

(i) Electrical motors

(ii) Economizers for steam power plant

(iii) Convectors for steam and cold water heating systems

(iv) Cooling coils

Identify the correct option
a. 1, 2 and 4
b. 1, 2 and 3
c. 1, 2, 3 and 4
d. 1 and 2
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Answer: (a).1, 2 and 4

3. The extended surface used for the enhancement of heat dissipation is
a. Convective coefficient
b. Fourier number
c. Fin
d. No finned surface
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Answer: (c).Fin

4. It is said that fins can take a variety of forms

(i) Longitudinal fins of rectangular cross section attached to a wall

(ii) Cylindrical tubes with radial fins

(iii) Conical rod protruding from a wall

Identify the correct statement
a. 1 only
b. 1 and 2
c. 2 and 3
d. 1, 2 and 3
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Answer: (d).1, 2 and 3

5. A steel rod (k = 30 W/m degree) 1 cm in diameter and 5 cm long protrudes from a wall which is maintained at 10 degree Celsius. The rod is insulated at its tip and is exposed to an environment with h = 50 W/m² degree and t a = 30 degree Celsius. Calculate the fin efficiency
a. 56.57%
b. 66.57%
c. 76.57%
d. 86.57%
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Answer: (b).66.57%

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