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Mechanical Engineering :: Heat and Mass Transfer

Heat and Mass Transfer - section-1
  1. The unit of overall coefficient of heat transfer is

    2. A.

     kcal/m²
    B.

     kcal/hr °C
    C.

     kcal/m² hr °C
    D.

     kcal/m hr °C

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

    3. A.

     J/m² sec
    B.

     J/m °K sec
    C.

     W/m °K
    D.

     Option (B) and (C) above

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  3. According to Wien's law, the wavelength corresponding to maximum energy is proportion to

    4. A.

     Absolute temperature (T)
    B.

     I²
    C.

     F
    D.

     T

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  4. Which of the following has least value of conductivity?

    5. A.

     Glass
    B.

     Water
    C.

     Plastic
    D.

     Air

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  5. According to Prevost theory of heat exchange

    6. A.

     It is impossible to transfer heat from low temperature source to t high temperature source
    B.

     Heat transfer by radiation requires no medium
    C.

     All bodies above absolute zero emit radiation
    D.

     Heat transfer in most of the cases takes place by combination of conduction, convection and radiation

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  6. Conduction is a process of heat transfer

    7. A.

     From one particle of the body to another without the actual motion of the particles
    B.

     From one particle of the body to another by the actual motion of the heated particles
    C.

     From a hot body to a cold body, in a straight line, without affecting the intervening medium
    D.

     None of the above

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  7. According to Dalton's law of partial pressures, (where pb = Barometric pressure, pa = Partial pressure of dry air, and pv = Partial pressure of water vapour)

    8. A.

     Pb = pa - pv
    B.

     Pb = pa + pv
    C.

     Pb = pa × pv
    D.

     Pb = pa/pv

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  8. A composite slab has two layers of different materials with thermal conductivities k₁ and k₂. If each layer has the same thickness, then the equivalent thermal conductivity of the slab will be

    9. A.

     k₁ k₂
    B.

     (k₁ + k₂)
    C.

     (k₁ + k₂)/ k₁ k₂
    D.

     2 k₁ k₂/ (k₁ + k₂)

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  9. Total emissivity of polished silver compared to black body is

    10. A.

     Same
    B.

     Higher
    C.

     More or less same
    D.

     Very much lower

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  10. Depending on the radiating properties, a body will be black when
    (Where a = absorptivity, p = reflectivity, X = transmissivity.)

    11. A.

     P = 0, x = 0 and a = 1
    B.

     P= 1, T = 0 and a = 0
    C.

     P = 0, x = 1 and a = 0
    D.

     X = 0, a + p = 0

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