1. HEAT TRANSFER THROUGH EXTENDED
SURFACES
Presented by:-
Ashutosh pandey
M.E 3rd Year (0506me091008)
2. What is heat transfer ?
Heat transfer can be defined as the process by which energy
transport takes place. When two physical bodies (object or
fluid) are at different temperatures than transfer of thermal
energy is known as Heat Transfer.
MODE S OF HEAT TRANSFER:-
* CONDUCTION
* CONVECTION
* RADIATION
3. METHODS OF INCREASING HEAT TRANSFER RATE
FROM BODY:-
• By increasing the surface area in contact with air or
providing fins.
• By increasing the heat transfer coefficient for the
surface.
• By increasing the temp of the hot surface or by
increasing the temperature difference between hot and
cold bodies.
4. HEAT TRANSFER THROUGH FINS
INTRODUCTION:-
One of the way to increase the heat transfer from the hot
surface by increasing the surface area in contact with
environment. For this the surface area exposed to the
surroundings is frequently increased by the attachment of
protrusion to the surfaces, and the arrangement provides a
means by which heat transfer rate can be substantially
improved. These protrusions are called fines or spines.
5. Temperature distribution and heat transfer rate for
fins of uniform cross sectional area:-
Tip condition
Case Temperature distribution Fin heat transfer rate
(x=L)
Convection heat
A
transfer
B Adiabatic
Constant
C
Temperature
Infinite Fin
D
Length
6. Fin performance:-
Fin performance can be described in three different ways.
1:- The first is fin effectiveness. It is the ratio of the fin heat transfer rate to
the heat transfer rate of the object if it had no fin. The formula for this is
where is the fin cross-
sectional area at the base
2:- Fin performance can also be characterized by fin efficiency. This is the
ratio of the fin heat transfer rate to the heat transfer rate of the fin if the
entire fin were at the base temperature.
in this equation is equal to the surface area of the fin
Fin efficiency will always be less than one
7. 3:- The third way fin performance can be described is with overall surface
efficiency.
where is the total area and is the sum of the heat transfer rates of all
the fins.
8. comparison of the different types of extended
surfaces using heat transfer/pressure drop as the
figure of merit.
9. shows that, from a purely size standpoint, pin fins offer the
smallest design for the best heat transfer while straight fins are
the most inefficient from a heat transfer and smallest size
constraint.
10. USES OF FINS :-
1:- Fins are most commonly used in heat exchanging devices such
as radiators in cars and heat exchangers in power plants
2:- They are also used in newer technology such as hydrogen fuel cells.
3:- Nature has also taken advantage of the phenomena of fins.
4:- The ears of jackrabbits and Fennec Foxes act as fins to release heat
from the blood that flows through them.
11. Advantages:
By using the fins, heat transfer rate can be increased without
any preventive maintenance.
It is the cheapest way for increasing the heat transferring rate
from the hot bodies.
Disadvantages:
We know that the length of fins is directly proportional to the heat
transferring rate. But the larger length is may be cause of bending
in the fins and also increases the weight of engine. Therefore the
overall efficiency will goes to decrease.
