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1. HEAT
TRANSFER

2. INTRODUCTION
 Heat always moves from a warmer place to a cooler place.
 Hot objects in a cooler room will cool to room temperature.
 Cold objects in a warmer room will heat up to room
temperature.

3. HEAT TRANSFER
METHODS
Heat transfers in three ways:
• Conduction
Process by which heat is transmitted through a substance
when there is a difference of temperature between
adjoining regions without material movement.
• Convection
Movement caused in fluids by tendency of hotter and
therefore less denser material to sink under the influence
of gravity which consequently results in heat transfer
• Radiation
Heat transmitted by radiation

4. 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. We call this? Conduction

5. Metals are different
The outer e______ of metal atoms
drift, and are free to move.
When the metal is heated, this
‘sea of electrons’ gain kinetic
energy and transfer it
throughout the metal.
Insulators, such as wood and plastic do not have this ‘sea of
electrons’ which is why they do not conduct heat.
lectrons

6. Why does metal feel colder than wood, if they
are both at the same temperature?
Metal is a conductor, wood is an insulator. Metal
conducts the heat away from your hands. Wood
does not conduct the heat away from your hands as
well as the metal, so the wood feels warmer than
the metal.

7. Convection
What happens to the particles in a liquid or a
gas when you heat them?
The particles spread out and
become less dense.
This effects fluid movement.

8. Fluid movement
Cooler, more d____, fluids
sink through w_____, less
dense fluids.
In effect, warmer liquids and gases rise
up.
Cooler liquids and gases sink.
ense
armer

9. Why is it windy at the seaside?

10. 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

11. HEAT TRANSFER BY RADIATION
 Radiation travels in straight lines
 Radiation can travel through a vacuum
 Radiation travels at the speed of light

12. CONVECTION QUESTIONS
QUESTIONS
Why does hot air rise and cold air sink?
Why are boilers placed beneath hot water tanks in people’s
homes?
Why are houses painted white in hot countries?

13. HEATING OF FLUIDS
Fluids are mainly heated in steam jacketed pan which is double
walled.
Steam circulated inside the double wall for heating purpose.
Apparently in between steam and water wall of the pan is the
barrier but actually there are many layers involved through which
heat is transferred.

14. HEATING OF FLUIDS
These seven layers are:
1. Steam
2. Air
3. Condensate layer
4. Scales (inorganic salts)
5. Wall of the container
6. Bound layer of water
7. Bulk of water
1 2 3 4 5 6 7

15. STEAM
The vapor into which water is converted when heated, forming a
white mist of minute water droplets in the air.
Practical aspects:
In practice there are various steps from generation of steam up to
its use.
1. Generation of steam
2. Distribution
3. Pressure reduction
4. Uses in plant
5. Condensate removal
6. Removal of air from steam

16. GENERATION OF
STEAM
Generated centrally in boiler which is then distributed to all parts
of plant where ever it is needed.
Central generation of steam has following advantages.
1. Central production is economical
2. Steam is generated at very high pressure in boiler and is then
used in generation of electricity.
3. The increased pressure of steam provides the driving force for
distribution.
4. Low pressure steam is used for heating purposes.

18. DISTRIBUTION OF
STEAM
Steam is distributed from boiler to the various sections of the plant
with the help of close system pipes.
Piping should be of suitable size to supply the required quantity of
steam to desired area. Moreover pipes are covered with insulating
material such as asbestos, glass and wool etc.
These insulating material prevent the loss of heat.
In some cases pipes are covered with multiple layers of
aluminium foils. Air is entrapped with in these layers so as to
prevent the loss of heat by conduction.

19. PRESSURE REDUCTION
Steam generated is at very high pressure of 1.7-2.0 bars, therefore
pressure reduction valves are used for its safe use.
These valves maintains the pressure of steam at required levels.
Mechanism:
pressure reduction valve is in b/w low pressure & high pressure. the
increased pressure of the spring tends to open the valve.so steam
will come from high too low pressure &will accumulate. pressure will
develop which tends to compress the spring &close the values.so in
this way equilibrium is setup in which the value is open slightly.in this
way desired pressure steam is achieved which is carried to the
consumption area.

21. USES OF STEAM IN THE PLANT
Steam produced in the generator is used in two ways for heating
purpose.
1,Direct Method:
in this way steam is directly blown over the material to be
heated.it is efficient method bcz the steam has direct contact with
the material to be heated this method is mostly used for
sterilization purpose
2,In direct Methods:
In this way steam is circulated in external jackets or close pipes.
There is no direct contact of steam with product. The barrier
between steam and the product is the wall of tube or pan.

22. CONDENSATE
REMOVAL
Accumulation of vapors is called condensate. When steam loses its
latent heat, then it will condense. Removal of this condensate is
necessary to prevent the stoppage or lugging of the process. devices
used for removal of this condensate is called steam trappers. These
steam traps differentiate b/w steam and condensate.
Types Of Steam Traps:
There are two types of steam traps,
1. Mechanical steam traps
2. Thermostatic steam traps

23. MECHANICAL TRAPS
It works on the basis of physical differences between steam and
condensate.
a. Float traps
b. Bucket traps
Float traps:
This consist of a floating ball or
Balloon which is attached to the
Valve, as the condensate accumu-
lates its level rises and the ball
also rises, that causes opening

24. MECHANICAL TRAPS
Of the valve.
When the valve is opened the condensate is discharged.
When level falls the valve is closed and the cycle is repeated.
Bucket Traps:
the mechanism consists of an inverted bucket which is attached
by a lever to a valve. An essential part of the trap is the small air
vent hole in the top of the bucket. Figure shows the method of
operation. In (i) the bucket hangs down, pulling the valve off its
seat. Condensate flows under the bottom of the bucket filling the
body and flowing away through the outlet. In (ii) the arrival of
steam causes the bucket to become buoyant, it then rises and
shuts the outlet.

25. In (iii) the trap remains shut until the steam in the bucket has
condensed or bubbled through the vent hole to the top of the trap body.
It will then sink, pulling the main valve off its seat. Accumulated
condensate is released and the cycle is repeated

26. THERMOSTATIC
STEAM TRAPS
The thermostatic steam trap contains a thermostatic element
which opens and closes a valve in response to fluid temperature.
Condensate collected upstream of the valve is sub-
cooled cooling the thermostat, which, in turn, exposes the
discharge port. When the cooler condensate is discharged and
the incoming condensate temperature approaches the saturation
temperature, the thermostat closes the discharge port. Because of
its principle of operations, the thermostatic trap operates
intermittently under all but maximum condensate loads.

28. HEAT EXCHANGERS
Technically speaking ……
A heat exchanger is a device that is used to transfer thermal energy between two
or more fluids, between a solid surface and a fluid, or between solid particulates
and a fluid, at different temperatures and in thermal contact.

29. TYPES OF HEAT
EXCHANGERS
1. Tube and shell heat exchangers
2. Fin type heat exchangers
3. Plate type heat exchangers
4. Spiral blade heat exchangers
5. Graphite heat exchangers

30. TUBE AND SHELL
HEAT EXCHANGERS
It causes turbulent flow of fluids (to be heated) to produce
increased heat transfer.
 Two types of fluids are used, fluid I (for heating purposes) and
fluid II (to be heated).
 Moreover strips are used in the way of fluid to be heated so as
to increase the rate of heat transfer.

32. FIN TYPE HEAT
EXCHANGERS
 Structure is same as of tube and shell heat exchangers.
 Used when co-efficient of heat transfer is low.
 To increase the rate of heat transfer, fins or strips are used
internally or externally in the tube and shells.
 These strips or fins are used to increase surface area and to
produce turbulence flow.

34. PLATE TYPE HEAT
EXCHANGERS
In this type the plates are easily
demountable for cleaning purposes and
used in the sterilization like pasteurization of
milk etc.
In this type Plates hung vertically and
clamped in a press or frame.
Plates made of stainless steel or higher
quality material.
Many points of contact and a tortuous flow
path.

35. GRAPHITE HEAT
EXCHANGERS
Used for highly corrosive fluids such as strong acids and alkalis.
Its having sets of tubes located at right angle to each other,
Where the two fluids i.e. fluid I and fluid II circulates alternatively.

36. APPLICATIONS
Heat transfer is an essential process throughout a number of
residential, industrial and commercial facilities. Within these
locations, heat must efficiently and effectively be added, removed
or transferred from one process to another in order to maintain the
status quo