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Chemical Engineering :: Heat Transfer

  1. When does the heat generated by fluid friction becomes appreciable compared to the heat transferred between the fluids ?

  2. A.
    At high fluid velocity
    B.
    At low velocity
    C.
    When fluid flows past a smooth surface
    D.
    None of these

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  3. The Sieder-Tate correlation for heat transfer in turbulent flow in pipe gives Nu α Re0.8, where, Nu is the Nusselt number and Re is the Reynolds number for the flow. Assuming that this relation is valid, the heat transfer co-efficient varies with the pipe diameter (D) as

  4. A.
    (D)-1.8
    B.
    (D))-0.2
    C.
    (D)0.2
    D.
    (D)1.8

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  5. A long iron rod initially at a temperature of 20°C has one end dipped in boiling water (100°C) at time, t = 0. The curved surface of the rod is insulated so that heat conduction is one dimensional in the axial direction. The temperature at a distance 100 mm from the dipped end becomes 40°C at time, t = 200 s. The same temperature is achieved at a distance of 200 mm from the dipped end at time

  6. A.
    t = 283 s
    B.
    t = 356 s
    C.
    t = 400 s
    D.
    t = 800 s

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  7. LMTD for evaporators & condensers for a given terminal parameters & set of conditions for counterflow is equal to that for parallel flow. In such heat exchangers, with one of the fluids condensing or evaporating, the surface area required is the least in the __________ flow.

  8. A.
    parallel
    B.
    mixed
    C.
    counterflow
    D.
    same in either 'a', b' or 'c'

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  9. Thermal diffusivity of a material

  10. A.
    has the unit m2 /sec.
    B.
    is defined as K/ρ . Cp.
    C.
    is the ratio of thermal conductivity to thermal capacity.
    D.
    all (a), (b) and (c).

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  11. Viscosity of gases __________ with increase in temperature.

  12. A.
    increase very rapidly
    B.
    increase slowly
    C.
    decrease slowly
    D.
    remain unaffected

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  13. What is the emissivity of a black body ?

  14. A.
    1
    B.
    C.
    0.90
    D.
    0.5

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  15. Steam is routed through the tube in case of a __________ evaporator.

  16. A.
    basket type
    B.
    horizontal tube
    C.
    short tube vertical
    D.
    long tube vertical

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  17. Dropwise condensation of steam on cooling surface is promoted

  18. A.
    an oily surface.
    B.
    when both the steam and the tube are clean.
    C.
    only in presence of air.
    D.
    none of these.

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  19. Conduction occurs in the buffer zone for a fluid flowing through a heated pipe, only when Prandtl number is

  20. A.
    0.1
    B.
    >1
    C.
    < 1
    D.
    l

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