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Chemical Engineering :: Heat Transfer

  1. Nusselt number is the ratio of the temperature gradient at the wall to

  2. A.
    temperature difference
    B.
    heat flux
    C.
    that across the entire pipe
    D.
    none of these

  3. The Stefan-Boltzman constant depends on the

  4. A.
    medium
    B.
    temperature
    C.
    surface
    D.
    none of these

  5. The units of resistance to heat transfer is

  6. A.
    J.m-2.K-1
    B.
    J.m-1.K-1
    C.
    W.m-2.K-1
    D.
    W-1m2K

  7. Thermal conductivity of a gas at low density, __________ with increase in temperature.

  8. A.
    decreases
    B.
    increases
    C.
    remains unchanged
    D.
    may increase or decrease; depends on the gas

  9. Nusselt number is a function of Prandtl number and __________ number of fluid in natural convection heat transfer.

  10. A.
    Grashoff
    B.
    Biot
    C.
    Stantan
    D.
    Reynolds

  11. __________ heat exchanger is used for chilling oil to be dewaxed.

  12. A.
    U-tube
    B.
    Double pipe
    C.
    Fixed tube
    D.
    Floating head

  13. It is not recommended to use a 1-2 shell and tube heat exchanger for a particular heat duty, whenever the LMTD correction factor is

  14. A.
    > 0.75
    B.
    < 0.75
    C.
    < 0.50
    D.
    < 0.25

  15. Pick out the wrong statement.

  16. A.
    Economy of a multiple effect evaporator is not influenced by the boiling point elevation.
    B.
    Two identical cubes of iron and copper will have the same heat content under the same conditions of temperature.
    C.
    Double pipe heat exchangers are mostly used in the field of refrigeration.
    D.
    Finned tube heat exchangers are suitable for heating air by steam.

  17. In sub-cooled boiling,

  18. A.
    temperature of the heating surface is less than the boiling point of the liquid.
    B.
    temperature of the heating surface is more than the boiling point of the liquid.
    C.
    bubbles from heating surface are absorbed by the mass of the liquid.
    D.
    very large vapour space is necessary.

  19. With increase in temperature, the thermal conductivity of a gas

  20. A.
    increases.
    B.
    decreases.
    C.
    remains same.
    D.
    may increase or decrease depending on the type of gas.