Heat Transfer

71. Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of

1. 0.002
2. 0.02
3. 0.01
4. 0.1
5. 0.5.

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72. Thermal conductivity of air with rise in temperature

1. increases
2. decreases
3. remains constant
4. may increase or decrease depending on temperature
5. none of the above.

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73. Thermal conductivity of non-metallic amorphous solids with decrease in temperature

1. increases
2. decreases
3. remains constant
4. may increase or decrease depending on temperature
5. unpredictable.

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74. Thermal conductivity of solid metals with rise in temperature normally

1. increases
2. decreases
3. remains constant
4. may increase or decrease depending on temperature
5. unpredictable.

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75. Thermal conductivity of water at 20°C is of the order of

1. 0.1
2. 0.23
3. 0.42
4. 0.51
5. 0.64.

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76. Thermal conductivity of water in general with rise in temperature

1. increases
2. decreases
3. remains constant
4. may increase or decrease depending on temperature
5. none of the above.

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77. Thermal conductivity of wood depends on

1. moisture
2. density
3. temperature
4. all of the above
5. none of the above.

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78. Thermal diffusivity is

1. a dimensionless parameter
2. function of temperature
3. used as mathematical model
4. a physical property of the material
5. useful in case of heat transfer by radiation.

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79. Thermal diffusivity of a substance is .

1. proportional of thermal conductivity
2. inversely proportional to k
3. proportional to (k)
4. inversely proportional to k2
5. none of the above.

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80. Total heat is the heat required to

1. change vapour into liquid
2. change liquid into vapour
3. increase the temperature of a liquid or vapour
4. convert water into steam and superheat it
5. convert saturated steam into dry steam.

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