Heat Transfer Multiple Choice Questions & Answers (MCQs) on “Bubble Growth”.
1. The bubble diameter at the time of detachment from the surface can be worked out from the relation proposed by
a) Stanton
b) Fritz
c) Fourier
d) Nusselt
Answer: b
Clarification: It is given by Fritz, an American scientist.
2. The nucleate pool boiling is influenced by the following factors
(1) Pressure
(2) Liquid properties
(3) Material
Identify the correct statements
a) i, ii and iii
b) ii only
c) i and ii
d) ii and iii
Answer: a
Clarification: It depends on pressure, material and liquid properties.
3. Consider the following phenomena
(i) Boiling
(ii) Free convection in air
(iii) Forced convection in air
(iv) Conduction in air
Identify the correct sequence (heat transfer coefficient)
a) iii – iv – i – ii
b) iv – i – iii – ii
c) iv – iii – ii – i
d) iv – ii – iii – i
Answer: d
Clarification: Heat transfer coefficient is maximum for conduction in air and is least for boiling.
4. The bubble diameter at the time of detachment from the surface can be worked out from the relation proposed by Fritz and is given by
a) C d β [2 σ/g (p t – p v)].
b) C d β [2 σ/g (p t – p v)] 3/2
c) C d β [2 σ/g (p t – p v)] 1/2
d) C d β [2 σ/g (p t – p v)] 5/2
Answer: c
Clarification: The constant C d has the value 0.0148 for water bubbles.
5. In spite of large heat transfer coefficient in boiling liquids, fins are used advantageously when the entire surface is exposed to
a) Film boiling
b) Transition boiling
c) Nucleate boiling
d) All modes of boiling
Answer: d
Clarification: Here all modes of boiling i.e. film, transition and nucleate are of great importance.
6. With increase in excess temperature, the heat flux in boiling
a) Increases continuously
b) Decreases and then increases
c) Decreases, then increases and again decreases
d) Increases, then decreases and again increases
Answer: d
Clarification: It first increases to 50% then decreases not to zero and again increases to its maximum value.
7. The excess temperature range 50 degree Celsius < d t < 200 degree Celsius is indicative of the region of
a) Interface evaporation
b) Nuclear boiling
c) Partial film boiling
d) Stable film boiling
Answer: c
Clarification: The physical phenomenon of pool boiling is generally divided into four different regions based on the excess temperature.
8. Heat flux increases with temperature excess beyond the Leiden-frost point due to
a) Radiation effect becomes predominant
b) Occurrence of subcooled boiling
c) Vapor space become large
d) Promotion of nucleate boiling
Answer: a
Clarification: Heat flux increases with temperature excess beyond the Leiden-frost point due to radiation effect becomes predominant.
9. Leiden-frost expansion is related to
a) Condensation of vapor on a cold surface
b) Exchange of heat between two solids
c) Evaporation of a solution
d) Boiling of liquid on a hot surface
Answer: d
Clarification: It is related to boiling of liquid on a hot surface.
10. Consider the following statements regarding nucleate boiling
(i) The temperature of the surface is greater than the saturation temperature of the liquid
(ii) Bubbles are created by the expansion of entrapped gas oil vapor at small cavities in the surface
(iii) The temperature is greater than that in film boiling
(iv) The heat transfer from the surface to the liquid is greater than that in the film boiling
Which of these statements are correct?
a) i and iii
b) i, ii and iv
c) ii, iii and iv
d) i, ii and iii