Heat Transfer

81. Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by

1. convection
2. free convection
3. forced convection
4. radiation
5. radiation and convection.

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82. Unit of thermal conductivity in M.K.S. units is

1. kcal/kg m2 °C
2. kcal-m/hr m2 °C
3. kcal/hr m2 °C
4. kcal-m/hr °C
5. kcal-m/m2 °C.

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83. Unit of thermal conductivity in S.I. units is

1. J/m2 sec
2. J/m °K sec
3. W/m °K
4. (a) and (c) above
5. (b) and (c) above.

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84. Unit of thermal diffusivity is

1. m2/hr
2. m2/hr°C
3. kcal/m2 hr
4. kcal/m.hr°C
5. kcal/m2 hr°C.

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85. When heat is Transferred by molecular collision, it is referred to as heat transfer by

1. conduction
2. convection
3. radiation
4. scattering
5. convection and radiation.

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86. When heat is transferred form hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by

1. conduction
2. convection
3. radiation
4. conduction and convection
5. convection and radiation.

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87. When heat is transferred from one particle of hot body to another by actual motion of the heated particles, it is referred to as heat transfer by

1. conduction
2. convection
3. radiation
4. conduction and convection
5. convection and radiation.

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88. Which of the following has least value of conductivity

1. glass
2. water
3. plastic
4. rubber
5. air.

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89. Which of the following has maximum value of thermal conductivity

1. aluminium
2. steel
3. brass
4. copper
5. lead.

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90. Which of the following is a case of steady state heat transfer

1. I.C. engine
2. air preheaters
3. heating of building in winter
4. all of the above
5. none of the above.

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