It is not preferable to use superheated steam in evaporators, because of its very_________________?

Related Mcqs:

1. One kilogram of water at 0°C is changed to superheated steam of one atm pressure and 300° C. The major heat consumption in the process will be to________________?

   A. Heat the water from 0°C to 100°C
   B. Evaporate the water
   C. To superheat the steam
   D. Data insufficient, can’t be predicted

2. A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m2.°C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be__________________?

   A. Greater than that for un-insulated steam pipe
   B. Less than that of the un-insulated steam pipe
   C. Equal to that of the un-insulated steam pipe
   D. Less than the steam pipe with 5 cms insulation

3. Steam condensate is recovered by steam traps and recycled for use as boiler feed water, because of its low___________________?

   A. Hardness
   B. Dissolved solids content
   C. Suspended solids content
   D. All A., B. and C.

4. The film co-efficient is decreased due to the presence of non-condensing gases in the vapors. The film co-efficient of superheated vapor as compared to that of saturated vapor is___________________?

   A. More
   B. Less
   C. Some
   D. Either more or less; depends on the nature of vapor

5. The maximum heat transfer co-efficient from steam heating will be attained when the steam is_________________?

   A. Supersaturated
   B. Saturated
   C. Wet
   D. None of these

6. Steam traps are provided in steam carrying pipelines to_________________?

   A. Condense steam
   B. Release excess steam pressure by bleeding steam
   C. Remove condensate and inert gases
   D. None of these

7. 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__________________?

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

8. Forced circulation evaporators are normally used for concentrating liquids having ___________________?

   A. Scaling characteristics
   B. High viscosity
   C. Both A. & B.
   D. Neither A. nor B.

9. LMTD for evaporators & condensers for a given terminal parameters & set of conditions for counter-flow 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?

   A. Parallel
   B. Mixed
   C. Counter flow
   D. Same in either A , B. or C.

10. The advantage of backward feed multiple effect evaporators over forward feed units is that___________________?

    A. Heat sensitive material can be handled
    B. There is no additional cost of pumping
    C. Most concentrated liquid is at highest temperature
    D. Equal heat transfer co-efficients exist in various effects