This document outlines the content of a heat transfer course, including 8 topics: introduction to heat and mass transfer, 1D and 2D steady state conduction, unsteady state conduction, convection heat transfer, radiation heat transfer, heat exchangers, and boiling and condensation heat transfer. Evaluation of students includes continuous assessment, projects, mid-term and final exams. Attendance of 80% is required to sit for the final exam. Prerequisites include thermodynamics and applied mathematics courses. The document provides references and does not include any other content.

1. HEAT TRANSFER
MENG3121
1

2. 0. CONTENT
1. INTRODUCTION TO HEAT AND MASS TRANSFER
2. ONE-DIMENSIONAL STEADY STATE CONDUCTION
3. TWO-DIMENSIONAL STEADY STATE CONDUCTION
4. UNSTEADY STATE CONDUCTION
5. CONVECTION HEAT TRANSFER
6. RADIATION HEAT TRANSFER
7. HEAT EXCHANGERS
8. BOILING AND CONDENSATION HEAT TRANSFER
2

3. 0. CONTENT
REFERENCES
 FRANK P. INCROPERA, FUNDAMENTALS OF HEAT AND MASS TRANSFER, 5TH EDITION
 Y. A. CENGEL, HEAT TRANSFER-A PRACTICAL APPROACH, INTERNATIONAL EDITION
 J.P. HOLMAN, HEAT TRANSFER, 8TH EDITION
 A.F. MILLS, HEAT TRANSFER, 2ND EDITION
EVALUATION
 CONTINUOUS ASSESSMENT: 20%
 PROJECT: 20%
 MID-TERM EXAM: 20%
 FINAL EXAM: 40%
ATTENDANCE IS COMPULSORY (A STUDENT WITH ATTENDANCE LESS THAN 80% WILL NOT SIT
FOR FINAL EXAM).
PRE REQUISITES: THERMODYNAMICS II AND APPLIED MATHEMATICS III
3

4. 1. INTRODUCTION TO HEAT AND MASS TRANSFER
Fig.1.1 Interaction of a system with its surrounding
System
Surrounding
Heattransfer
Worktransfer
4

5. 1.1 WHAT IS HEAT TRANSFER?
 A system interacts with its surrounding through
heat and work transfer (Thermodynamics).
 Heat transfer is the energy in transit due to
temperature differences between system and
surrounding.
 Temperature difference is a driving force for
heat transfer.
5

6. 1.1 WHAT IS HEAT TRANSFER?…
 The energy change of a system is related to the
heat and work transfers according to equation (1.1)
(1.1)
 Where E includes all forms of the energy of the
system, Q is the heat transferred to the system and
W is the work done by the system.
 The heat transfer Q is what this course is concerned
with.
W
Q
dE 
 

6

7. 1.2 APPLICATION AREAS OF HEAT TRANSFER
Heat transfer analysis has a number of applications in
engineering and other aspects of life. Some
examples are:
 The human body.
7
On average, an adult male must lose heat at a
rate of about 90 watts as a result of his basal
metabolism. When the surrounding is at a
temperature below body temperature (370C), this
heat can be lost by the three standard heat
transfer mechanisms (conduction, convection and
radiation). But when the ambient temperature is
above 370C, all three heat transfer mechanisms
work against this heat loss by transferring heat
into the body. Our ability to exist in such
conditions comes from the efficiency of cooling
by the evaporation of perspiration.

8. 1.2 APPLICATION AREAS OF HEAT TRANSFER
 Many household equipment like heating and air-conditioning
system, the refrigerator and freezer, the water heater, the iron,
and even the computer.
8

9. 1.2 APPLICATION AREAS OF HEAT TRANSFER
 Energy-efficient home design- optimal
insulation thickness of walls and roofs.
 Recent buildings include hear transfer in their design analyses due to several reasons which include:
  Safety against thermal expansions and stresses,
  Effective use of air conditioning systems,
  Utilization of renewable energy systems, etc.
9

10. 1.2 APPLICATION AREAS OF HEAT TRANSFER
 Radiators and Engines of automotive.
10

11. 1.2 APPLICATION AREAS OF HEAT TRANSFER
 The design of solar collectors , various
components of power plants, and even
spacecrafts.
11

12. 1.2 APPLICATION AREAS OF HEAT TRANSFER
 Cooling of electronic equipment.
12

13. 1.2 APPLICATION AREAS OF HEAT TRANSFER
 Chemical processes where there is energy
(heat) generation.
13

14. 1.3 HEAT TRANSFER MODES
The modes of heat transfer between system and its
surrounding or between systems can be classified into
three:
 Conduction,
 Convection, and
 Radiation
In all the three modes the heat is transferred from a body
at higher temperature to one at lower temperature.
Except radiation, the other modes of heat transfer require
a medium for the heat to be transferred. Fig. 1.2 shows
an analogy for the three heat transfer modes.
14

15. 1.3 HEAT TRANSFER MODES …
15
Fig.1.2 Analogy for the Heat Transfer Modes

16. 1.3.1 Conduction Heat Transfer
Heat transfer by conduction is due to the interactions between
particles of a substance. More energetic particles transfer heat
to the less energetic ones.
 In solids conduction is due to vibration of molecules in a lattice
and motion of free electrons.
 In liquids and gases it is due to collision of molecules in their
random motion.
Experiments reveal that the rate of conduction heat transfer
through a medium is dependent on:
 Geometry of the medium (cross sectional area)
 Thickness of the medium
 Material property of the medium and
 Temperature difference across the medium
16

17. Fig. 1.3 One dimensional conduction heat transfer
1.3.1 Conduction Heat Transfer …
17

18. Conduction heat transfer rate can be expressed
mathematically by Fourier’s law.
(1.2)
Where = conduction heat transfer rate (W)
k= thermal conductivity of the material (W/mK)
A= cross-sectional area normal to direction of
heat flow ( )
The negative sign in equation (1.2) indicates that heat flow is in
the direction of temperature decrease.
The thermal conductivity k is the property of a material which
shows the ability of the material to conduct heat (Table 1.1)
L
T
T
kA
Q
)
( 1
2
. 


.
Q
1.3.1 Conduction Heat Transfer …
2
m
18

19. Materi
al
Diamo
nd
Silve
r
Coppe
r
Gold Alumi
num
Iron Mercu
ry
Glass Brick Water Air
K,(w/m
k)
2300 429 401 317 237 80.2 8.54 0.78 0.72 0.613 0.02
6
Table 1.1 Thermal conductivities of some materials at room temperature
1.3.1 Conduction Heat Transfer …
19

20. 1.3.1 Conduction Heat Transfer …
In the limiting case where the thickness , equation
(1.2) can be written as
(1.3)
Equation (1.3) is known as Fourier’s law of heat
conduction.
The heat transfer rate per unit area is known as heat flux,
q.
(1.4)
is temperature gradient or the slope of the curve on T-
x diagram.
0

L
dx
dT
kA
Q 

.
dx
dT
k
A
Q
q 


.
dx
dT
20

21. 1.3.1 Conduction Heat Transfer …
Example 1.1
A copper slab (k=372w/mK) is 3mm thick. It is
protected from corrosion on each side by a 2 mm
thick layer of stainless steel (k=17w/mK). The
temperature is 4000C on one side of this composite
wall and 1000C on the other. Find the temperature
distribution in the copper slab and the heat flux
conducted through the wall.
21

22. 1.3.1 Conduction Heat Transfer …
Fig. Example 1.1
22

23. 1.3.1 Conduction Heat Transfer …
Solution
From conservation of energy principle, heat flux
through stainless steel=heat flux through copper.
Solving this equation gives
T2=2550C and T3=2450C
The heat flux through the wall can be obtained as







 









 









 


















.
.
3
4
.
.
2
3
.
.
1
2
.
.
.
.
s
s
s
s
u
cu
s
s
s
s
cu
s
s
L
T
T
k
L
T
T
k
L
T
T
k
dx
dT
k
dx
dT
k
q
2
2
.
.
1
2
.
. /
5
.
1232
/
500
,
232
,
1
002
.
0
400
255
17 m
W
k
m
W
L
T
T
k
q
s
s
s
s 






 









 


23

24. 1.3.2 Convection Heat Transfer
Convection is a heat transfer mode that takes place
between a solid surface and a moving fluid when there
is a temperature difference between the surface of the
solid and the fluid. Convection occurs due to a
combination of two phenomena:
 Random motion of fluid molecules (conduction)and
 Bulk motion of the fluid
Convection heat transfer is classified in to two based on
the cause of motion of the fluid:
1. Forced convection- fluid motion is caused by pumps,
fans, blowers…
2. Natural convection-fluid moves due to density
variation caused by temperature variation.
24

25. 1.3.2 Convection Heat Transfer…
Fig. 1.4 Forced Convection Fig. 1.5 Free Convection
25

26. 1.3.2 Convection Heat Transfer…
The rate of convection heat transfer is given by the
Newton’s law of cooling
(1.5)
Where = convection heat transfer rate (w)
A= surface area through which convection
heat transfer takes place ( )
h= convection heat transfer coefficient ( )
= surface temperature (K)
= temperature of fluid far away from
surface (K)
)
(
.


 T
T
hA
Q s
2
m
K
m
W 2
/
s
T

T
26
.
Q

27. 1.3.2 Convection Heat Transfer…
Fig. 1.6 Velocity and thermal boundary layers
27

28. 1.3.2 Convection Heat Transfer…
Type of convection h, w/m2K
Free convection of
gases
2-25
Free convection of
liquids
10-1000
Forced convection of
gases
25-250
Forced convection of
liquids
50-20,000
Boiling and
condensation
2500-100,000
Table 1.2 typical values of convection heat transfer coefficient
28

29. 1.3.3 Radiation Heat Transfer
Thermal radiation is an energy emitted in the form of
photons (electromagnetic waves) from a body
because of its temperature. All objects at a
temperature above absolute zero emit thermal
radiation.
Fig. 1.7 Radiation heat transfer between a surface and its surrounding
Ts
A

Tsur
29

30. 1.3.3 Radiation Heat Transfer …
The maximum rate of radiation that can be emitted
from a surface at absolute temperature of Ts is
given by the Stefan-Boltzmann law
(1.6)
Where = radiation heat transfer rate (W)
= Stefan-Boltzmann constant ( )
A= surface area of the object ( )
= surface temperature (K)
4
max
.
s
AT
Q 

max
.
Q
s
T
4
2
8
/
10
67
.
5 K
m
W


2
m
30

31. 1.3.3 Radiation Heat Transfer …
An object that can emit is called Black body (ideal
thermal radiator). But real objects radiate thermal
energy less than given by:
(1.7)
Where is a property known as emissivity. The
value of emissivity is in the range .
When a surface is enclosed by a single or a number of
surfaces as shown in Fig. 1.7, the radiation heat transfer
is given by
(1.8)
max
.
Q
max
.
Q
4
.
s
AT
Q 

)
( 4
4
.
sur
s T
T
A
Q 
 
31


32. 1.3.3 Radiation Heat Transfer …
In general, these three basic mechanisms of heat transfer
occur simultaneously in real world problems (Fig. 1.8).
Fig. 1.8 Heat transfer mechanisms at the tube wall of a steam generator
32

33. 1.3.3 Radiation Heat Transfer …
Example 1.2
An insulated steam pipe passes through a room in
which the air and walls are at . The outside
diameter of the pipe is 70mm, and its surface
temperature and its emissivity are and 0.8,
respectively. What is the emissive power per unit
area of the pipe? If the coefficient associated with
free convection heat transfer from the surface to the
air is 15 , what is the rate of heat loss from the
surface per unit length of pipe?
33

34. 1.3.3 Radiation Heat Transfer …
Fig. Example 1.2
34

35. 1.3.3 Radiation Heat Transfer …
Solution
The surface emissive power per unit area is obtained by equation (1.7)
Heat is lost from the pipe through combination of convection to the
room air and radiation exchange with walls. From equations (1.5)
and (1.8),
The heat loss per unit length of the pipe will be
.
2
4
8
4
.
/
2270
473
*
10
*
67
.
5
*
8
.
0
m
W
T
A
Q
q s



 

)
)(
(
)
)(
(
)
(
)
(
4
4
4
4
.
su
s
s
su
s
s
T
T
DL
T
T
DL
h
T
T
A
T
T
hA
Q














m
W
T
T
D
T
T
D
h
L
Q
q su
s
s
/
998
421
577
)
298
473
(
10
*
67
.
5
*
)
07
.
0
*
(
*
8
.
0
)
25
200
)(
07
.
0
*
(
*
15
)
(
(
)
)(
(
'
4
4
8
4
4
.



















35

36. 1.4 MASS TRANSFER BY DEFUSION
 Mass transfer is the relative motion of
some chemical species with respect to
others driven by concentration
gradients.
 Heat transfer and mass transfer are
kinetic processes that may occur and
be studied separately or jointly.
 Heat and mass transfer are
mathematically modelled by similar
equations.
36

37. APPLICATION AREAS OF MASS TRANSFER
 commonly used to model
 Transport processes in foods,
 Neurons,
 Biopolymers,
 Pharmaceuticals,
 Porous soils,
 Population dynamics,
 Nuclear materials,
 Plasma physics, and
 Semiconductor doping processes.
37

38. END OF CHAPTER 1
38