This set of Heat Transfer Operations Multiple Choice Questions & Answers (MCQs) focuses on “Boilers – Overview of Boiling”.
1. The temperature of the liquid is below the saturation temperature and boiling takes place only in vicinity of the heated surface, then which type of boiling this?
a) Sub-cooled boiling
b) Superheated boiling
c) Saturated boiling
d) Pool boiling
View Answer
Explanation: Sub-cooled boiling is also known as bubble growth phase when the vapour bubbles travel a short path and then disappear into the bulk of the liquid which is at a temperature less than the boiling point, hence its name sub-cooled boiling.
2. The phenomenon of minimum heat flux in stable film boiling when heating a fluid with a tube is known as ___________
a) Nucleate effect
b) Bubbling effect
c) Leiden frost effect
d) Radiation effect
View Answer
Explanation: The Leiden frost effect can be represented as the point P on the curve which is the point of minimum heat flux for a given boiling regime.
3. In which type of boiling the temperature of steam is above its boiling point?
a) Superheated steam
b) Super-saturated steam
c) Leiden frost steam
d) Saturated steam
View Answer
Explanation: The superheated steam is the steam that is heated even further after evaporation to a much higher temperature, to serve as a heating medium without making surface wet by condensation.
4. What is the name of the point circled in the following boiling curve of water?
a) Critical heat flux
b) Bubbling effect
c) Leiden frost effect
d) Radiation effect
View Answer
Explanation: The stated point given above is the point of critical heat flux wherein the heat flux is maximum and intermediate between nucleate and stable film boiling.
5. What is the name of the phenomenon in the point circled in boiling curve of water?
a) Critical heat flux
b) Bubbling effect
c) Leiden frost effect
d) Radiation effect
View Answer
Explanation: This region of the boiling curve represents the region where bubbles start to form and popularly known as the nucleate boiling/ bubble effect region.
6. Which one of the following represents radiation heating region in the given boiling curve?
a)
b) 
c) 
d) 
View Answer
Explanation: The final region of heat flux growth/rise after the inefficient film boiling is called the radiation boiling region. Here the fluid is not in contact with the wall.
7. Which one of the following represents Stable film boiling region in the given boiling curve?
a)
b)
c)
d)
View Answer
Explanation: The region of minima of heat flux from the surface to the liquid after boiling the water/fluid is known as stable film boiling because here exists a film which does not allow heat transfer.
8. Which one of the following represents Nucleate boiling region in the given boiling curve?
a)
b)
c)
d)
View Answer
Explanation: This region of the boiling curve represents the region where bubbles start to form and popularly known as the nucleate boiling/ bubble effect region. This region can be further divided into three parts of evaporation, bubble formation and bubble rise phases.
9. Which one of the following represents partial nucleate and unstable film boiling region in the given boiling curve?
a)
b)
c)
d)
View Answer
Explanation: This region is called the unstable region because the film has not yet formed completely and flickers from place to place, the heat flux further drops on increasing temperature.
10. Which one of the following is the evaporation line in the given boiling curve?
a)
b) 
c)
d)
View Answer
Explanation: The onset of heating, that is the first and foremost region of the curve is known as the evaporation line of the boiling curve.
11. What is the meaning of burnout region/ critical heat flux in boiling, point the region?
a)
b)
c)
d)
View Answer
Explanation: The stated point given in the answer is the point of critical heat flux/burnout region wherein the heat flux is maximum and intermediate between nucleate and stable film boiling.
12. The burnout phenomenon for boiling of water occurs at a temperature at about ____________ degree Celsius.
a) 105
b) 115
c) 155
d) 301
View Answer
Explanation: The burnout phenomenon is visible when the excess temperature is around 50-100 degrees above the saturation point of the liquid, here water.
13. What is the name of the phenomenon in the point circled in boiling curve of water?
a) Critical heat flux
b) Bubbling effect
c) Evaporation region
d) Radiation effect
View Answer
Explanation: The onset of heating the fluid that is the first and foremost region of the curve is known as the evaporation line of the boiling curve. Here the liquid temperature rises firmly by convection.
14. What is the name of the phenomenon in the point circled in boiling curve of water?
a) Critical heat flux
b) Bubbling effect
c) Leiden frost effect
d) Radiation effect
View Answer
Explanation: The region of minima of heat flux from the surface to the liquid after boiling the water/fluid is known as Leiden Frost Effect of the stable film boiling region because here exists a film that does not allow heat transfer.
15. What is the name of the phenomenon in the point circled in boiling curve of water?
a) Critical heat flux
b) Bubbling effect
c) Leiden frost effect
d) Radiation effect
View Answer
Explanation: The final region of heat flux growth/rise after the inefficient film boiling is called the radiation boiling region. Here the fluid is not in contact with the wall rather it is the radiation from the heating surface that is causing the temperature rise.
Sanfoundry Global Education & Learning Series – Heat Transfer Operations.
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