The document contains information about different modes of heat transfer: conduction, convection, and radiation. It provides definitions and key details about each mode. For conduction, it describes how heat is transferred through collisions between particles in solids, liquids, and gases. It also explains Fourier's Law of Heat Conduction. For convection, it defines forced and natural convection and describes how fluid motion impacts heat transfer. Radiation is defined as the transfer of energy in the form of electromagnetic waves.

1. BIRLA VISHVAKARMA MAHAVIDYALAYA
vallabh vidyanagar
BIRLA VISHVAKARMA MAHAVIDYALAYA
vallabh vidyanagar
Div – 8 Nichay Agrawal 140080125001
group no : - 6 Ullas Bhalani
140080125002
Jaydeep Chaudhary 140080125003
Dobariya Yash 140080125004
Div – 8 Nichay Agrawal 140080125001
group no : - 6 Ullas Bhalani
140080125002
Jaydeep Chaudhary 140080125003
Dobariya Yash 140080125004

3. 3
 Heat:Heat: The form of energy that can be transferred from one system to
another as a result of temperature difference.
 ThermodynamicsThermodynamics is concerned with the amount of heat transfer as a
system undergoes a process from one equilibrium state to another.
 Heat TransferHeat Transfer deals with the determination of the rates of such energy
transfers as well as variation of temperature.
 The transfer of energy as heat is always from the higher-temperature
medium to the lower-temperature one.
 Heat transfer stops when the two mediums reach the same temperature.
 Heat can be transferred in three different modes:
conduction, convection,conduction, convection, radiationradiation

4.  HHeateat as the form of energy that can be transferred from one system to
another as a result of temperature difference.
 A thermodynamic analysis is concerned with the amountamount of heat transfer
as a system undergoes a process from one equilibrium state to another.
 The science that deals with the determination of the ratesrates of such energy
transfers is the heatheat transfertransfer..
 The transfer of energy as heat is always from the higher-temperature
medium to the lower-temperature one, and heat transfer stops when the
two mediums reach the same temperature.
 Heat can be transferred in three basic modes:
 conductionconduction
 convectionconvection
 radiationradiation
 All modes of heat transfer require the existence of a temperature
difference.

5. 5
ConductionConduction: The transfer of energy from the more energetic
particles of a substance to the adjacent less energetic ones as a
result of interactions between the particles.
In gases and liquidsIn gases and liquids,, conduction is due to the collisionscollisions and
diffusion of the molecules during their random motion.
In solidsIn solids, it is due to the combination of vibrationsvibrations of the
molecules in a lattice and the energy transport by free electrons.
The rate of heat conduction through a plane layer is proportional
to the temperature difference across the layer and the heat transfer
area, but is inversely proportional to the thickness of the layer.
ConductionConduction: The transfer of energy from the more energetic
particles of a substance to the adjacent less energetic ones as a
result of interactions between the particles.
In gases and liquidsIn gases and liquids,, conduction is due to the collisionscollisions and
diffusion of the molecules during their random motion.
In solidsIn solids, it is due to the combination of vibrationsvibrations of the
molecules in a lattice and the energy transport by free electrons.
The rate of heat conduction through a plane layer is proportional
to the temperature difference across the layer and the heat transfer
area, but is inversely proportional to the thickness of the layer.

6. 6
Fourier’s law of heat
conduction
Fourier’s law of heat
conduction
Thermal conductivity, k: A measure
of the ability of a material to conduct
heat.
Temperature gradient dT/dx: The
slope of the temperature curve on a T-
x diagram.
Heat is conducted in the direction of
decreasing temperature, and the
temperature gradient becomes
negative when temperature decreases
with increasing x. The negative sign
in the equation ensures that heat
transfer in the positive x direction is a
positive quantity.
Thermal conductivity, k: A measure
of the ability of a material to conduct
heat.
Temperature gradient dT/dx: The
slope of the temperature curve on a T-
x diagram.
Heat is conducted in the direction of
decreasing temperature, and the
temperature gradient becomes
negative when temperature decreases
with increasing x. The negative sign
in the equation ensures that heat
transfer in the positive x direction is a
positive quantity.
When x 0→When x 0→

7. Thermal conductivity: The rate of heat transfer through a unit thickness of the material
per unit area per unit temperature difference.
The thermal conductivity of a material is a measure of the ability of the material to
conduct heat.
A high value for thermal conductivity indicates that the material is a good heat
conductor, and a low value indicates that the material is a poor heat conductor or
insulator.
Thermal conductivity: The rate of heat transfer through a unit thickness of the material
per unit area per unit temperature difference.
The thermal conductivity of a material is a measure of the ability of the material to
conduct heat.
A high value for thermal conductivity indicates that the material is a good heat
conductor, and a low value indicates that the material is a poor heat conductor or
insulator.
A simple experimental setup
to determine the thermal
conductivity of a material.

8. 8
ConvectionConvection: The mode of
energy transfer between a solid
surface and the adjacent liquid
or gas that is in motion, and it
involves the combined effects
of conduction and fluid motion.
The faster the fluid motion, the
greater the convection heat
transfer.
In the absence of any bulk fluid
motion, heat transfer between a
solid surface and the adjacent
fluid is by pure conduction.
Heat transfer from a hot surface to air
by convection.

9. 9
•Forced convection: If the fluid
is forced to flow over the
surface by external means such
as a fan, pump, or the wind.
•Natural (or free) convection:
If the fluid motion is caused by
buoyancy forces that are
induced by density differences
due to the variation of
temperature in the fluid.
•Forced convection: If the fluid
is forced to flow over the
surface by external means such
as a fan, pump, or the wind.
•Natural (or free) convection:
If the fluid motion is caused by
buoyancy forces that are
induced by density differences
due to the variation of
temperature in the fluid.
The cooling of a boiled egg by
forced and natural convection.
Heat transfer processes that involve change of phase of a fluid
are also considered to be convection because of the fluid
motion induced during the process, such as the rise of the vapor
bubbles during boiling or the fall of the liquid droplets during
condensation.

10. 10
h convection heat transfer coefficient, W/m2
· °C
As the surface area through which convection heat transfer takes place
Ts the surface temperature
T∞ the temperature of the fluid sufficiently far from the surface.
•The convection heat transfer
coefficient h is not a property of
the fluid.
•It is an experimentally
determined parameter whose
value depends on all the variables
influencing convection such as
- the surface geometry
- the nature of fluid motion
- the properties of the fluid
- the bulk fluid velocity
•The convection heat transfer
coefficient h is not a property of
the fluid.
•It is an experimentally
determined parameter whose
value depends on all the variables
influencing convection such as
- the surface geometry
- the nature of fluid motion
- the properties of the fluid
- the bulk fluid velocity

11. •Energy transferred in the form of rays or waves
or particles.
•We will concentrate on the type of radiation that
travels as electromagnetic waves.

12. Heat transfer through the wall of a house can be
modeled as steady and one-dimensional.
The temperature of the wall in this case depends
on one direction only (say the x-direction) and
can be expressed as T(x).
Heat transfer through the wall of a house can be
modeled as steady and one-dimensional.
The temperature of the wall in this case depends
on one direction only (say the x-direction) and
can be expressed as T(x).
forfor steady operationsteady operation
Fourier’s law of heat conductionFourier’s law of heat conduction
In steady operation, the rate of heat transfer through the wallIn steady operation, the rate of heat transfer through the wall
is constant.is constant.
dEdEwall / dt = 0

13. •The rate of heat conduction
through a plane wall is proportional
to the average thermal conductivity,
the wall area, and the temperature
difference, but is inversely
proportional to the wall thickness.
•Once the rate of heat conduction is
available, the temperature T(x) at
any location x can be determined by
replacing T2 by T, and L by x.
•The rate of heat conduction
through a plane wall is proportional
to the average thermal conductivity,
the wall area, and the temperature
difference, but is inversely
proportional to the wall thickness.
•Once the rate of heat conduction is
available, the temperature T(x) at
any location x can be determined by
replacing T2 by T, and L by x.Under steady conditions, the temperature
distribution in a plane wall is a straight line:
dT/dx = const.

14. Analogy between thermal andAnalogy between thermal and
electrical resistance concepts.electrical resistance concepts.
rate of heat transfer -- electric currentrate of heat transfer -- electric current
thermal resistance -- electrical resistancethermal resistance -- electrical resistance
temperature difference -- voltagetemperature difference -- voltage
differencedifference
rate of heat transfer -- electric currentrate of heat transfer -- electric current
thermal resistance -- electrical resistancethermal resistance -- electrical resistance
temperature difference -- voltagetemperature difference -- voltage
differencedifference
Conduction resistance of the wall: Thermal
resistance of the wall against heat conduction.
Thermal resistance of a medium depends on the
geometry and the thermal properties of the
medium.
Conduction resistance of the wall: Thermal
resistance of the wall against heat conduction.
Thermal resistance of a medium depends on the
geometry and the thermal properties of the
medium.

15. •When the convection heat transfer coefficient is very large (h → ), the
convection resistance becomes zero and Ts  T.
•That is, the surface offers no resistance to convection, and thus it does not slow
down the heat transfer process.
•This situation is approached in practice at surfaces where boiling and
condensation occur.
•When the convection heat transfer coefficient is very large (h → ), the
convection resistance becomes zero and Ts  T.
•That is, the surface offers no resistance to convection, and thus it does not slow
down the heat transfer process.
•This situation is approached in practice at surfaces where boiling and
condensation occur.
•Schematic for convectionSchematic for convection
resistance at a surface.resistance at a surface.

18. The thermal resistance
network for heat transfer
through a two-layer plane
wall subjected to convection
on both sides.
The thermal resistance
network for heat transfer
through a two-layer plane
wall subjected to convection
on both sides.

19. Dr. Şaziye Balku 19
gapcontact QQQ
•••
+=
erfacec TAhQ int∆=
•
erface
c
T
AQ
h
int
/
∆
=
•
(W/m2 0
C)
(m2 0
C/ W)
AQ
T
h
R
erface
c
c
/
1 int
•
∆
==
hC: thermal contact conductance

20. Dr. Şaziye Balku 20
Thermal contact resistance is inverse of
thermal contact conduction,
Depends on
 Surface roughness,
 Material properties,
 Temperature and pressure at interface,
 Type of fluid trapped at interface

21. Dr. Şaziye Balku 21
Effect of metallic
coatings on thermal
contact conductance
For soft metals with
smoot surfaces at high
pressures
Thermal contact
conductance
Thermal contact
resistance

22. Dr. Şaziye Balku 22
)
11
)((
21
21
2
21
1
21
21
RR
TT
R
TT
R
TT
QQQ +−=
−
+
−
=+=
•••
totalR
TT
Q 21 −
=
•
21
111
RRRtotal
+=
21
21
RR
RR
Rtotal
+
=
Resistances are parallel

23. Dr. Şaziye Balku 23
totalR
TT
Q ∞
• −
= 1
convconvtotal RR
RR
RR
RRRR ++
+
=++= 3
21
21
312
11
1
1
Ak
L
R =
22
2
2
Ak
L
R =
33
3
3
Ak
L
R =
3
1
hA
Rconv =

24. Dr. Şaziye Balku 24
Steady-state heat conduction
Heat is lost from a hot-water
pipe to the air outside in the
radial direction.
Heat transfer from a long pipe
is one dimensional

25. Dr. Şaziye Balku 25
dr
dT
kAQ cylcond −=
•
,
Fourier’s law of conduction
=
•
cylcondQ , constant
∫∫ ==
•
−=
2
1
2
1
, T
TT
r
rr
cylcond
kdTdr
A
Q
rLA π2=
)/ln(
2
12
21
,
rr
TT
LkQ cylcond
−
=
•
π
cyl
cylcond
R
TT
Q 21
,
−
=
•
Lk
rr
Rcyl
π2
)/ln( 12
=

26. Dr. Şaziye Balku 26
2
4 rA π=
krr
rr
Rsph
21
12
4π
−
=
sph
sphcond
R
TT
Q 21
,
−
=
•
including convection
2
2
221
12
4
1
4 hrkrr
rr
Rtotal
ππ
+
−
=
totalR
TT
Q ∞
• −
= 1

27. Dr. Şaziye Balku 27
)2(
1
2
)/ln(
2
12
11
LrhLk
rr
TT
RR
TT
Q
convins
ππ
+
−
=
+
−
= ∞∞
•
0/ 2 =
•
drQd
h
k
r cylindercr =,
Thermal conductivity
External convection heat
transfer coefficient
show
CYLINDER

28. Dr. Şaziye Balku 28
cr
cr
cr
rr
rr
rr
>
=
<
2
2
2
max
Before insulation check for
critical radius
h
k
r spherecr
2
, =

29. Dr. Şaziye Balku 29
Two ways of increasing
- increase h
- increase As
By adding fins
(Car radiators)
•
Q
)( ∞
•
−= TThAQ SSconv

30. Dr. Şaziye Balku 30
rate of heat
conduction into
the element at x
rate of heat
conduction from
the element at
x+Δx
rate of heat
convection from
the element
+=
))(( ∞
•
−∆= TTxphQ Sconvconvxxcondxcond QQQ
•
∆+
••
+= ,,
0)(
,,
=−+
∆
−
∞
•
∆+
•
TThp
x
QQ xcondxxcond
0→∆x
0)( =−+ ∞
•
TThp
dx
dQcond

31. Dr. Şaziye Balku 31
dx
dT
kAQ ccond −=
•
0)( =−−





∞TThp
dx
dT
kA
dx
d
c
02
2
2
=− θ
θ
a
dx
d
axax
eCeCx −
+= 21)(θ
At constant AC and k
Solution is;
CkA
hp
a =2
∞−= TTbbθ
∞−= TTθ
(fin)
Boundary condition x = 0

32. Thank you…