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Mechanical Engineering Objective Questions { Heat Transfer }

36. Thermal conductivity of water in general with rise in temperature
C.May increase or decrease depending on temperature
D.None of the above
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37. An electric furnace has a laminated wall composed of 0.2 m of refractory brick (k=2), 0.15 m of insulation (k =0.15), and 0.15 m of brick having (k= 1.5). Inner and outer temperatures of wall are 1027°C and 27°C respectively. Units of k are kcal-m/hr m2 °C. If surface area of the wall is 1.2 m2, heat transfer rate will be
A.10 kcal/hr
B.100 kcal/hr
C.1000 kcal/hr
D.10,000 kcal/hr
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38. A steam pipe is to be insulated by two insulating materials put over each other. For best results
A.Better insulation should be put over pipe and better one over it
B.Inferior insulation should be put over pipe and better one over it
C.Both may be put in any order
D.Whether to put inferior on over pipe or the better one would depend on steam temperature
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39. The ratio of emissive power of a body to the emissive power of a perfectly black body is called "
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40. Which of the following is expected to have highest thermal conductivity
B.Solid ice
C.Melting ice
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41. All radiations in a black body are
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42. A perfect black body is one which
A.Is black in colour
B.Reflects all heat
C.Transmits all heat radiations
D.Absorbs heat radiations of all wave lengths falling on it
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