It tells about heat transfer.

1. HEAT TRANSFER

2. Heat Transfer Methods
• Heat transfers in three ways:
–Conduction
–Convection
–Radiation

3. Conduction
When you heat a metal strip at one end, the heat travels to the
other end.
As you heat the metal, the particles vibrate, these vibrations make the
adjacent particles vibrate, and so on and so on, the vibrations are
passed along the metal and so is the heat. This IS KNOWN AS
Conduction

7. L1
L2 L3
K1 K2
K3
Ta Tb
ha
hb
T1
T4
T2 T3
Composite Plane Wall
Consider a multilayered wall.
1
( )
a a
Q Ah T T
 
2 1
1
1
( )
T T
Q K A
L

 
3 2
2
2
( )
T T
Q K A
L

 
4 3
3
3
( )
T T
Q K A
L

 
4
( )
b b
Q Ah T T
 

8. L1
L2 L3
K1 K2
K3
Ta Tb
ha
hb
T1
T4
T2 T3
Composite Plane Wall
Hence for a multilayered wall.
3
1 2
1 2 3
1 1
a b
a b
T T
Q
L
L L
h A k A k A k A h A


   

9. Heat Transfer: Extended Surfaces: Fins

10. Extended Surfaces: Fins cont..
General Solution of
above equation: 1 2
mx mx
C e C e
  
 

11. Extended Surfaces: Fins cont..
Case 1: Long Fins:
0
mx
T T
e
T T






 
0
Q hPkA T T
 
Case 2: Fins with insulated end:
 
 
0
cosh
cosh
m L x
T T
T T mL


 

  


   
0 tanh
Q hPkA T T mL

 
Case 3: Fins with Convection off the end:

12. The third method of heat transfer
How does heat energy get from the
Sun to the Earth?
There are no particles between
the Sun and the Earth so it
CANNOT travel by conduction
or by convection.
?
RADIATION

14. Thank You