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Mechanical Engineering :: Heat and Mass Transfer

Heat and Mass Transfer - section-1
  1. Absorptivity of a body will be equal to its emissivity

    2. A.

     At all temperatures
    B.

     At one particular temperature
    C.

     When system is under thermal equilibrium
    D.

     At critical temperature

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  2. In a heat exchanger with one fluid evaporating or condensing, the surface area required is least in

    3. A.

     Parallel flow
    B.

     Counter flow
    C.

     Cross flow
    D.

     All of these

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  3. A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,

    4. A.

     The better insulation must be put inside
    B.

     The better insulation must be put outside
    C.

     One could place either insulation on either side
    D.

     One should take into account the steam temperature before deciding as to which insulation is put where

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  4. The ratio of Nusselt number and the product of Reynold's number and Prandtl number is equal to

    5. A.

     Stanton number
    B.

     Biot number
    C.

     Peclet number
    D.

     Grashoff number

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  5. The product of Reynolds number and Prandtl number is known as

    6. A.

     Stanton number
    B.

     Biot number
    C.

     Peclet number
    D.

     Grashoff number

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  6. Upto the critical radius of insulation,

    7. A.

     Added insulation will increase heat loss
    B.

     Added insulation will decrease heat loss
    C.

     Convective heat loss will be less than conductive heat loss
    D.

     Heat flux will decrease

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  7. Fourier's law of heat conduction is (where Q = Amount of heat flow through the body in unit time, A = Surface area of heat flow, taken at right angles to the direction of heat flow, dT = Temperature difference on the two faces of the body, dx = Thickness of the body, through which the heat flows, taken along the direction of heat flow, and k = Thermal conductivity of the body)

    8. A.

     k. A. (dT/dx)
    B.

     k. A. (dx/dT)
    C.

     k. (dT/dx)
    D.

     k. (dx/dT)

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  8. In counter current flow heat exchanger, the logarithmic temperature difference between the fluids is ________ as compared to parallel flow heat exchanger.

    9. A.

     Same
    B.

     Less
    C.

     Greater
    D.

     None of these

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  9. In counter flow heat exchangers

    10. A.

     Both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state
    B.

     Both the fluids at inlet are in their hottest state
    C.

     Both the fluids at exit are in their hottest state
    D.

     One fluid is in hottest state and other in coldest state at inlet

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  10. The energy distribution of an ideal reflector at higher temperatures is largely in the range of

    11. A.

     Shorter wavelength
    B.

     Longer wavelength
    C.

     Remain same at all wavelengths
    D.

     Wavelength has nothing to do with it

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