Heat Transfer Multiple Choice Questions & Answers (MCQs) on “Boiling”.
1. Boiling refers to a change from the
a) Solid to a liquid phase
b) Vapor to a liquid phase
c) Liquid to a solid phase
d) Liquid to a vapor phase
Answer: d
Clarification: Boiling is a convective heat transfer process that is associated with a change in the phase of a fluid.
2. The boiling process has wide-spread applications in
(i) Production of steam in nuclear and steam power plants for generation and for industrial processes and space heating
(ii) Absorption of heat in refrigeration and air-conditioning systems
(iii) Concentration, dehydration and drying of foods and materials
Identify the correct statements
a) i and ii
b) ii and iii
c) i, ii and iii
d) i and iii
Answer: c
Clarification: Boiling constitutes the convective heat transfer process that involves a phase change from liquid to vapor state.
3. Maximum heat transfer rate in a modern boiler is about
a) 2 * 10 5 W/m2
b) 3 * 10 5 W/m2
c) 4 * 10 5 W/m2
d) 5 * 10 5 W/m2
Answer: a
Clarification: Greater importance has recently been given to the boiling heat transfer.
4. Which type of boiling occurs in steam boilers employing natural convection?
a) Forced convection
b) Pool
c) Local
d) Saturated
Answer: b
Clarification: The liquid above the hot surface is essentially stagnant and the only motion near the surface is because of free convection.
5. In which type of boiling the fluid motion is induced by external means?
a) Pool
b) Local
c) Forced convection
d) Subcooled
Answer: c
Clarification: The liquid is pumped and forced across the surface in a controlled manner.
6. The temperature of the liquid is below the saturation temperature and boiling takes place only in vicinity of the heated surface. This type of boiling is known as
a) Subcooled
b) Forces
c) Saturated
d) Pool
Answer: a
Clarification: The vapor bubbles travel a short path and then vanish, apparently they condense in the bulk of the liquid which is at a temperature less than the boiling point.
7. In which type of boiling the temperature of the liquid exceeds the saturation temperature?
a) Forced
b) Saturated
c) Pool
d) Saturated
Answer: d
Clarification: The vapor bubbles generated at the solid surface are transported through the liquid by buoyancy effects and eventually escape from the surface.
8. The phenomenon of stable film boiling is referred to as
a) Nucleate effect
b) Boiling regimes
c) Leiden frost effect
d) Von karma effect
Answer: c
Clarification: This is the region of stable film boiling.
9. For water evaporating at atmospheric pressure, the burnout occurs at temperature excess slightly above
a) 25 K
b) 55 K
c) 75 K
d) 105 K
Answer: b
Clarification: The burnout point on the boiling curve represents the point of maximum heat flux at which transition occurs from nucleate to film boiling.
10. The boiling phenomenon is known to occur in how many forms?
a) 1
b) 2
c) 3
d) 4
Answer: d
Clarification: Pool, forced convection, subcooled and saturated boiling.