Modes of heat transfer

2. 2
Heat and Mass Transfer
Module 1 Conduction Heat Transfer
Module 2 Convection Heat Transfer
Module 3 Boiling and Condensation
Module 4 Heat Exchanger
Module 5 Radiation Heat Transfer
Module 6 Mass Transfer

3. 3
Heat transfer – A Practical approach Y. A. Cengel
Fundamental of Heat and Mass transfer Incropera and Dewitt
Heat transfer - A Basic approach Osizik
Heat Transfer A. Bejan
Heat Transfer A. J.P. Holman

4. Thermodynamics does not answer the following
questions.
1. How does the heat transfer take place?
2. What is the rate of heat transfer?
3. How long the heat transfer process will continue?
Modes of heat transfer
1. Conduction heat transfer
2. Convection heat transfer
3. Radiation heat transfer
4

5. 5
Modes of
Heat Transfer

6. Conduction heat transfer
Conduction is the mode of heat transfer in which
heat is transferred from the high temperature
region to low temperature region in solids and
liquid at rest.
The energy is transferred from high energy
particles to low energy particles of the medium
due to interaction between them.
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7. 7
Fourier law of heat conduction
2
W/mfluxHeat
WferHeat trans
dx
dT
k
A
Q
q
dx
dT
kAQ


Where
k – thermal conductivity of the material W/mK
A – Area normal to heat transfer direction m2
dT/dx - temperature gradient in the direction of
heat flow K/m

8. L
X=0 X=L
 
L
TTk
A
Q
q
L
TT
k
A
Q
q
L
TT
dx
dT
21
12
12






8
Heat conduction in a slab
T1
T2

9. Material Thermal Conductivity W/mK
Aluminium 204.2
Copper 386
Zirconium 22.7
Glass wool 0.0372
Card board 0.064
Water 0.5978
Brass 111
Carbon steel 54
Lead 35
Saw dust 0.059
Asbestos-cement board 0.74
9

10. Convection heat transfer
Convection heat transfer occurs between the fluid in motion
and the bounding surface when there is temperature
difference exists between them.
Forced convection heat transfer the
fluid flow is assisted by a fan or
pump.
Free or natural convection heat
transfer, the flow of the fluid induced
by the buoyancy forces which arise
from the density difference caused
by the temperature variation within
the fluid.
10
The convection heat transfer is classified into two types:

11. Newton’s law of cooling
 
retemperatuFluid-T
retemperatuSurface-T
tcoefficienferheat trans-hwhere
W/mfluxHeat
s
2

 TTh
A
Q
q s
The value of heat transfer coefficient depends on the
type of flow, the geometry of the body and flow passage
area, physical properties of the fluid, the average
temperature and the mechanism of heat transfer.
11

12. Radiation heat transfer
Radiation is the mode of heat transfer in which the heat
may also be transferred in perfect vacuum.
Maxwell’s electromagnetic wave theory
Planck’s quantum theory
4
ATQ Stefan-Boltzman law
Radiation heat exchange between two black surfaces
 4
2
4
1112 TTAFQ   12

13. Reflection Spot
• What are the three modes of heat transfer?
• Write the Fourier law of heat conduction.
• Higher the thermal conductivity of material heat
conduction will be high. (True/False)
• What are the two types of convection heat transfer?
• Heat transfer coefficient in forced convection is
………….(more/less) than free convection
• Radiation mode does not require a medium for heat
transfer. (Yes/No)
13

14. Features of the book
 Lucid explanation of
subject content
 More solved problems
from Anna University
Question Papers
 Two mark questions with
answers
Publisher
Anuradha Publications
Chennai
14

15. Dr. K. Kannan
Professor Mechanical Engineering
Anjalai Ammal Mahalingam Engineering College
Kovilvenni – Tamil Nadu
k.kannan@aamec.edu.in
15