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1. Find the heat flow rate through the composite wall as shown in figure. Assume one dimensional flow and take

k 1 = 150 W/m degree
k 2 = 30 W/m degree
k 3 = 65 W/m degree
k 4 = 50 W/m degree
AB = 3 cm, BC = 8 cm and CD = 5 cm.
The distance between middle horizontal line from the top is 3 cm and from the bottom is 7 cm
a. 1173.88 W
b. 1273.88 W
c. 1373.88 W
d. 1473.88 W
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Answer: (b).1273.88 W

2. A steel pipe of 20 mm inner diameter and 2 mm thickness is covered with 20 mm thick of fiber glass insulation (k = 0.05 W/m degree). If the inside and outside convective coefficients are 10 W/m² degree and 5 W/m² degree, calculate the overall heat transfer coefficient based on inside diameter of pipe. In the diagram, the diameter of small circle is 20 mm
a. 1.789 W/m² degree
b. 2.789 W/m² degree
c. 3.789 W/m² degree
d. 4.789 W/m² degree
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Answer: (b).2.789 W/m² degree

3. The oven of an electric store, of total outside surface area 2.9 m² dissipates electric energy at the rate of 600 W. The surrounding room air is at 20 degree Celsius and the surface coefficient of heat transfer between the room air and the surface of the oven is estimated to be 11.35 W/m² degree. Determine the average steady state temperature of the outside surface of the store
a. 38.22 degree Celsius
b. 48.22 degree Celsius
c. 58.22 degree Celsius
d. 68.22 degree Celsius
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Answer: (a).38.22 degree Celsius

4. The accompanying sketch shows the schematic arrangement for measuring the thermal conductivity by the guarded hot plate method. Two similar 1 cm thick specimens receive heat from a 6.5 cm by 6.5 cm guard heater. When the power dissipation by the wattmeter was 15 W, the thermocouples inserted at the hot and cold surfaces indicated temperatures as 325 K and 300 K. What is the thermal conductivity of the test specimen material?
a. 0.81 W/m K
b. 0.71 W/m k
c. 0.61 W/m K
d. 0.51 W/m K
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Answer: (b).0.71 W/m k

5. In Cartesian coordinates the heat conduction equation is given by
a. d²t/dx² + d²t/dy2 + d²t/dz2 + q g = (1/α) (d t/d T)
b. 2d²t/dx² + d²t/dy2 + d²t/dz2 + 34q g = (d t/d T)
c. d²t/dx² + 3d²t/dy2 + d²t/dz2 = (1/α) (d t/d T)
d. 4d²t/dx² + d²t/dy2 + d²t/dz2 + 1/2q g = (1/α) (d t/d T)
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Answer: (a).d²t/dx² + d²t/dy2 + d²t/dz2 + q g = (1/α) (d t/d T)

6. The temperature distribution in a large thin plate with uniform surface temperature will be
(Assume steady state condition)
a. Logarithmic
b. Hyperbolic
c. Parabolic
d. Linear
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Answer: (d).Linear

7. Let us assume two walls of same thickness and cross-sectional area having thermal conductivities in the ratio 1/2. Let us say there is same temperature difference across the wall faces, the ratio of heat flow will be
a. 1
b. 1/2
c. 2
d. 4
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Answer: (b).1/2

8. The interior of an oven is maintained at a temperature of 850 degree Celsius by means of a suitable control apparatus. The oven walls are 500 mm thick and are fabricated from a material of thermal conductivity 0.3 W/m degree. For an outside wall temperature of 250 degree Celsius, workout the resistance to heat flow
a. 0.667 degree/W
b. 1.667 degree/W
c. 2.667 degree/W
d. 3.667 degree/W
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Answer: (b).1.667 degree/W

9. A plane slab of thickness 60 cm is made of a material of thermal conductivity k = 17.45 W/m K. Let us assume that one side of the slab absorbs a net amount of radiant energy at the rate q = 530.5 watt/m². If the other face of the slab is at a constant temperature t₂ = 38 degree Celsius. Comment on the temperature with respect to the slab?
a. 87.5 degree Celsius
b. 32 degree Celsius
c. 47.08 degree Celsius
d. 32.87 degree Celsius
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Answer: (c).47.08 degree Celsius

10. The rate of heat transfer for a plane wall of homogenous material with constant thermal conductivity is given by
a. Q = kA (t₁-t₂)/δ
b. Q = 2kAx/ δ
c. Q = 2kAδx
d. Q = 2k/δ x
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Answer: (a).Q = kA (t₁-t₂)/δ

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