Heat Transfer Objectives, applications & Heat transfer mechanisms. Fourier’s law. Heat transfer by conduction, convection & radiation. Heat interchangers & Heat exchangers.

1. Heat Transfer
Yogeshwary Bhongade
Assistant Professor
Gondia college of Pharmacy, Gondia

2. UNIT-II
1- Heat Transfer
• Objectives, applications & Heat transfer mechanisms.
• Fourier’s law.
• Heat transfer by conduction, convection & radiation.
• Heat interchangers &
• Heat exchangers.

3. Introduction
• Heat is a form of engery and transfer means movement
• Heat transfer is the movement of heat energy from one
substance to another.
A B

4. Objectives & Application
1. Model basic heat transfer processes and identify modes
2. Calculate thermal resistances
3. Perform an energy balance to determine temperature and heat
flux
4. Predict heat exchanger performance
5. Determine radiation heat transfer

5. Mechanism
Mechanism
Conduction Convection Radiation

7. CONDUCTION
• “When heat flow in a body is achieved by the transfer of the
momentum of individual atoms or molecules without mixing,
such process is known as conduction.”
• It takes place in solids and fluids whose movement is restricted.
• e.g. - iron rod such as metal wall of an evaporator.There is no
actual movement of molecules. On receiving energy from
surface of heat, molecules vibrates and pass on energy to
adjacent molecule.
• When both end have same temperature, heat transfer is stopped.
• Driving force: Difference of temperature between two end

8. CONVECTION
• “When heat flow is achieved by actual mixing of warmer portions
and cooler portions of the same material, the process is known as
convection.”
• There is actual physical movement of molecules.
• It takes place in some fluids (i.e. liquids and gases).
e.g. If hot and cold liquids are mixed, the heat can transfer from hot
liquid to cold liquid by physical movement of molecules. This
method of heat transfer is called as convection.

9. Convection is the transfer of thermal energy by the movement of
molecule fom one part of the material to another.
As the fluid motion increase, so dose the convective heat transfer.
The presence of bulk motion of the fluid enhances the heat transfer
between the solid surface and the fluid.
Convection heat transfer is mode of heat transfer between a surface
and fluid moving over it.
It is restricted to liquids and gases as movement of group of molecule
is not possible with solid.

10. • It involves two type of heat transfer.
1) Nature Convection
When movement of group molecule occurs due to change in density
resulting from temperature gradient it is known as natural convection.
2) Forced Convection
When a fluid is forced past a solid body and heate transferred between
the fluid and body, it is called forced convection heat transfer, heat
convection.'' Forced convection is involved during drying in ovens,
fluidised bed drier. etc
In Forced convection, fluid surrounding the surface is constantly
replaced; therefore rate of heat transfer is higher than for natural
convection

11. Application
• Dimenational analysis offers a rational approach to the
estimation of complex

12. RADIATION
• “When heat flows through space by means of electromagnetic
waves, such energy transfer is known as radiation.” E.g. Black
surface absorbs most of the radiation received by it &
simultaneously the absorbed energy is quantitatively transferred
into heat.
• In short The hot body emits radiant energy in all direction. If
this radiation strikes a receiver then part of it may be absorbed
and part of it may be refracted. This method of heat transfer is
called as radiation.

13. Fourier’s law
• Rate = Driving Force/ Resistance
i.e. dQ/dt = -KA.dt
where, dl
dQ/dt =Rate of heat transfer
K= constant
A= surface area
dt= Temperature difference
dl= length

14. Heat transfer through
• A Series
• A cylinder

15. Heat exchangers
• Heat exchangers ae devices that are used to transfer heat from
hot gas to liquid through metal wall.
• Heat exchange can be done by different flows,.

16. Heat exchangers
• Different types of heat exchangers are
a) Shell and tube heater
b) Multipass Heater
c)Two pass floating head heater

17. Shell and tube heater
It is single pass tubular heater
Construction:
It consist of number of parallel tube.
Both the end of tube are fitted into tube sheets, The tubes are enclose into
casing which is cylindrical in shape
Two distribution chembers are enclosed by cover.
Liquid inlet is provided to the distribution chember
There are also provision for steam inlet, condensate outlet and vent for non-
condensed gas.

18. Working
• Steam is introduced through inlet into space around tubes.
• Therefore tube get heated.
• Condense vapours and condensed gases are escap through
outlet.
• Liquid to be heated is pump to the first distribution chember.
• The fluid in tubes get heated due to heat transfer by conduction
through metal wal followed by Stagnant layer and finally by
convection.
• The hot liquid enters into second distrbution chember and
leaves through outlet.

19. Advantages
• Large heatig surface can be packed into small volume
• Simple Method
• Less time required
• Cross sectional area of tube are large but velocity of fluid in the
tube are low, hence heat transfer coefficient is also low.
• Slow Process.
• Limited amount of liquid can use
Disdvantages

20. Multipass Heater
• The main advantage of multipass heater is
to improve velocity of fluid.
Construction
It consist of number of parallel tubes.
The end of the tube are fitted into tube sheet.
The tubes are enclosed in the casing.
Baffles are placed into distribution head.
There are also provision for entrance and exit
of the fluid.

21. Working
• The feed is introduced into the compartment A of one of the
head.
• Then it is pass through tube into compartment B of the head.
• Then fluid back through other set of tube to compartment C of
the first head and finally leave through compartment 1. The
fluid is divered by using baffles.
• Since heater is multipass, so same liquid has to flow through
several tubes back and forth

22. Advantages
• The main advantage of multipass heater is to improve velocity
of fluid.
• Constuction is complicated.
• cost of pumping increases due to multiple number of entries
and exist.
• Friction loss
Disdvantages

23. Two pass floating heater

24. Construction
• It consist of bundle of parallel tubes which are enclosed in
casing.
• There are two distribution chembers and one of the distribution
chember is partitioned.
• The fluid inlet and outlet are also attached to the same chember
• Other distribution chember is like floating head. the end of tube
is embeded into floating head.
• There are also provision for steam inlet and outlet for
noncondensed vapours and condensate.

25. Working
• The steam is pass through the inlet as a result tube get heated.
• The non- condensed gases and condensed vapours pass throug
outlet.
• The fluid to be heated is introduced into one side of partition of
distribution chember.
• From there fluid reaches to floating head.
• The direction of fluid is changed and then fluid entered into
second side of partitif distribution chember.
• Due to head tube, The hot liquid leaves through oulet provided.

26. Advantages
• The floating head arrangement is advantageous because the
tube sheet is structurally independent of the shell.

27. Heat interchangers
• These divises are used to transfer heat fron one liquid to other
liquid or gas to other gas via metal wall
•

28. Double pipe heat interchanger
The double-pipe heat exchanger is one of the simplest types of heat
exchangers. It is called a double-pipe exchanger because one fluid
flows inside a pipe and the other fluid flows between that pipe and
another pipe that surrounds the first. This is a concentric tube
construction.

29. Construction
• This is usually consists of concentric pipes.
• One fluid flow in the inner pipe and the other fluid flow in the annulus
between pipes.
• The two fluid may flow concurrent (parallel) or in counter current flow
configuration;
• hence the heat exchanger are classified as: counter current double pipe
heat exchanger cocurrent double pipe heat exchanger

30. Advantages
• Its excellent capacity for thermal expansion
• It is easy to install and clean
• Its modular design makes it easy to add new sections
• Replacement parts are inexpensive and always in supply
Disadvantages
• It is not as cost effective as most shell and tube exchangers
• it requires special gaskets

31. THANK YOU