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Chemical Engineering :: Heat Transfer

  1. 1000 Kg of liquid at 30°C in a well stirred vessel has to be heated to 120°C, using immersed coils carrying condensing steam at 150°C. The area of the steam coils is 1.2 m2 and the overall heat transfer co-efficient to the liquid is 1500 W/m2.°C. Assuming negligible heat loss to the surrounding and specific heat capacity of the liquid to be 4 kJ/kg.°C, the time taken for the liquid to reach desired temperature will be

  2. A.
    15 min
    B.
    22 min
    C.
    44 min
    D.
    51 min

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  3. Overall thermal resistance for conductive heat transfer through a series of flat resistances is equal to the

  4. A.
    maximum resistance in the series.
    B.
    sum of all resistances.
    C.
    average of all resistances.
    D.
    minimum resistance presents in the series.

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  5. Double pipe heat exchangers are preferably useful, when

  6. A.
    high viscosity liquid is to be cooled.
    B.
    requirement of heat transfer area is low.
    C.
    overall heat transfer co-efficient is very high.
    D.
    a corrosive liquid is to be heated.

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  7. Removal of __________ heat is involved in the condensation of a vapor under saturated conditions.

  8. A.
    super
    B.
    sensible
    C.
    latent
    D.
    both(b) & (c)

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  9. The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (ΔT) between wall and outside bulk. The proportionality is given as

  10. A.
    (ΔT)1/4
    B.
    ΔT1/2
    C.
    (ΔT)5/4
    D.
    (ΔT)3/4

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  11. If air (a non-condensing gas) is present in a condensing vapor stream, it will __________ the condensation rate of vapor.

  12. A.
    increase
    B.
    decrease
    C.
    not affect
    D.
    increase the condensing film co-efficient as well as

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  13. The outlet temperature of cooling water in a heat exchanger is generally not allowed to exceed above 50°C in industrial practice mainly to avoid

  14. A.
    its evaporation loss
    B.
    excessive corrosion
    C.
    uneconomic LMTD
    D.
    decrease in heat exchanger efficiency

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  15. In evaporators, lowering the feed temperature

  16. A.
    increases the heating area required.
    B.
    reduces the economy.
    C.
    both (a) and (b).
    D.
    decreases the heating area required.

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