Heat Transfer

31. he unit of overall coefficient of heat transfer is

1. kcal/m2
2. kcal/hr °C
3. kcal/m2 hr °C
4. kacl/m hr °C
5. kcal/m3 hr °C.

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32. he unit of Stefan Boltzmann constant is

1. watt/cm2 °K
2. watt/cm4 °K
3. watt2/cm °K4
4. watt/cm2 °K4
5. watt/cm2 °K2.

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33. he value of Prandtl number for air is about

1. 0.1
2. 0.3
3. 0.7
4. 1.7
5. 10.5.

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34. he value of the wavelength for maximum emissive power is given by —

1. Wien's law
2. Planck's law
3. Stefan's law
4. Fourier's law
5. Kirchhoff's law.

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35. Heat conducted througfi unit area and unit thick face per unit time when temperature difference between opposite faces is unity,is called

1. thermal resistance
2. thermal coefficient
3. temperature gradient
4. thermal conductivity
5. heat-transfer.

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36. Heat flows from one body to other when they have

1. different heat contents
2. different specific heat
3. different atomic structure
4. different temperatures
5. none of the above.

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37. Heat is closely related with

1. liquids
2. energy
3. temperature
4. entropy
5. enthalpy.

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38. Heat is transferred by all three modes of transfer, viz, conduction, convection and radiation in

1. electric heater
2. steam condenser
3. melting of ice
4. refrigerator condenser coils
5. boiler.

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39. Heat transfer by radiation mainly depends upon

1. its temperature
2. nature of the body
3. kind and extent of its surface
4. all of the above
5. none of the above.

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40. Heat transfer in liquid and gases takes place by

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

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