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Mechanical Engineering :: Heat and Mass Transfer

  1. Unit of thermal diffusivity is

  2. A.

     m²/hr

    B.

     m²/hr °C

    C.

     kcal/m² hr

    D.

     kcal/m. hr °C

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  3. Temperature of steam at around 540°C can be measured by

  4. A.

     Thermometer

    B.

     Thermistor

    C.

     Thermocouple

    D.

     None of these

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  5. The total radiation from a black body per second per unit area is ________ fourth power of the absolute temperature. This statement is known as Stefan Boltzmann law.

  6. A.

     Equal to

    B.

     Directly proportional to

    C.

     Inversely proportional to

    D.

     None of these

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  7. The use of heat exchangers is made in

  8. A.

     Radiators in automobile

    B.

     Condensers and boilers in steam plants

    C.

     Condensers and evaporators in refrigeration and air conditioning units

    D.

     All of the above

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  9. The heat transfer from a hot body to a cold body is directly proportional to the surface area and difference of temperatures between the two bodies. This statement is called

  10. A.

     First law of thermodynamics

    B.

     Newton's law of cooling

    C.

     Newton's law of heating

    D.

     Stefan's law

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  11. Which of the following statement is wrong?

  12. A.

     The heat transfer in liquid and gases takes place according to convection

    B.

     The amount of heat flow through a body is dependent upon the material of the body

    C.

     The thermal conductivity of solid metals increases with rise in temperature

    D.

     Logarithmic mean temperature difference is not equal to the arithmetic mean temperature difference

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  13. When α is absorptivity, ρ is reflectivity and τ is transmissivity, then for a diathermanous body,

  14. A.

     α = 1, ρ = 0 and τ = 0

    B.

     α = 0, ρ = 1 and τ = 0

    C.

     α = 0, ρ = 0 and τ = 1

    D.

     α + ρ = 1 and τ = 0

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  15. Planck’s law holds good for

  16. A.

     black bodies

    B.

     polished bodies

    C.

     all coloured bodies

    D.

     all of the above

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  17. Thermal conductivity of a material may be defined as the

  18. A.

     Quantity of heat flowing in one second through one cm cube of material when opposite faces are maintained at a temperature difference of 1°C

    B.

     Quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C

    C.

     Heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces

    D.

     All of the above

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  19. A perfect black body is one which

  20. 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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