1. Pool boiling occurs when a heated surface transfers heat to a liquid through natural convection and the formation of bubbles at the surface. 2. There are four regimes of pool boiling as excess temperature increases: natural convection, nucleate boiling, transition boiling, and film boiling. In nucleate boiling, bubbles form rapidly at nucleation sites on the surface. 3. The pool boiling curve graphs heat flux against the temperature excess of a surface above the liquid's boiling point. It shows regions of unstable and stable boiling across the different boiling regimes.

1. ATMIYA INSTITUTE OF TECHNOLOGY &
SCIENCE
MECHANICAL DEPARTMENT
5th SEMESTER
Pool boiling curve
(HEAT TRANSFER– 2151909)
PREPARED BY:
Jay N. Katharotiya(130030119054)

2. CONTENTS
• What is the pool boiling ?
In occurs when heat transfer is due to natural
convection and mixing. (i.e. liquid is not moved
artificially)

3. Pool boiling
Four regimes/phases of pool boiling with change in
excess temperature :
1. Natural Convection Boiling
2. Nucleate Boiling
3. Transition Boiling
4. Film Boiling
unstable and stable

4. Pool boiling curve

5. 1.Natural Convection Boiling
• The liquid is slightly superheated in this case
(metastable state).
• The fluid motion in this mode of boiling is governed
by natural convection currents.
• at an excess temperature of about 5°C .(at point 1 to A)

7. 2.Nucleate Boiling
• The bubbles form at an increasing rate at an increasing
number of nucleation sites as we move along the boiling
curve toward point C.
• At starting part of nucleate boiling is unstable boiling
(point B-P).
• And other part is point (P-C) is higher high available at
time boiling is stable.
• For the entire nucleate boiling range, the heat transfer
coefficient ranges from about 2000 to 30,000 W/m2·K.

8. B-C
P
• Region A–B ─ isolated
bubbles.
• Region B–C ─ numerous
continuous columns of
vapor in the liquid.at
Temprature is

9. 3.Transition Boiling
• When Texcess is increased past point C, the heat flux decreases.
• This is because a large fraction of the heater surface is covered
by a vapor film, which acts as an insulation.
• In the transition boiling regime, both nucleate and film boiling
partially occur.
• Operation in the transition boiling regime, which is also called
the unstable film boiling regime, is avoided in practice.
• For water, transition boiling occurs over the excess temperature
range from about 30°C to about 120°C.

10. C-D

11. 4.Film Boiling
• Beyond point D the heater surface is completely
covered by a continuous stable vapor film.
• Point D, where the heat flux reaches a minimum is
called the Leidenfrost point.
• The presence of a vapor film between the heater
surface and the liquid is responsible for the low heat
transfer rates in the film boiling region.
• The heat transfer rate increases with increasing excess
temperature due to radiation to the liquid.

12. D-E

13. • Pool Boiling Heat Transfer - Dragonfly
Education.mp4

15. THANK YOU