When vaporisation takes place through a blanketting film of gas, the phenomenon is termed as ___________________ boiling?

Related Mcqs:

1. In case of _______________ boiling, the liquid temperature is below the saturation temperature and the boiling takes place in the vicinity of the heated surface?

   A. Nucleate
   B. Local
   C. Pool
   D. Saturated

2. It is desired to concentrate a 20% salt solution (20 kg of salt in 100 kg of solution) to a 30% salt solution in an evaporator. Consider a feed of 300 kg/min at 30°C. The boiling point of the solution is 110°C, the latent heat of vaporisation is 2100 kJ/kg and the specific heat of the solution is 4 kJ/kg.K. The rate at which the heat has to be supplied in (kJ/min) to the evaporator is____________________?

   A. 3.06 × 105
   B. 6.12 × 105
   C. 7.24 × 105
   D. 9.08 × 105

3. When vaporisation takes place directly at the heating surface, it is called________________?

   A. Film boiling
   B. Nucleate boiling
   C. Vapour binding
   D. None of these

4. Boiling point elevation for a strong and concentrated solution is found by Duhring’s rule, which states that at the same pressure, the boiling point of a solution is a linear function of the _______________ of pure water?

   A. Boiling point
   B. Dynamic viscosity
   C. Kinematic viscosity
   D. Density

5. Boiling of milk in an open vessel is an example of ______________ boiling?

   A. Film
   B. Sub-cooled
   C. Saturated nucleate
   D. None of these

6. Film boiling is usually not desired in commercial equipments, because____________________?

   A. The heat transfer rate is low in view of the large temperature drop
   B. It is difficult to maintain
   C. It is not economic
   D. None of these

7. Film boiling occurs at ________________ pressure?

   A. Atmospheric
   B. Sub-atmospheric
   C. Negative
   D. Very high

8. 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

9. The local surface conductance for laminar film condensation on vertical surface is (where, t = film thickness) _________________?

   A. ∝ t
   B. ∝ 1/t
   C. ∝ √t
   D. Independent of ‘t’

10. The film thickness for laminar film condensation on vertical surface _____________ from top to bottom?

    A. Cumulatively increases
    B. Cumulatively decreases
    C. Remain constant
    D. And the surface conductance increase