Heat exchangers transfer heat between two or more fluids that are at different temperatures. They work by bringing the fluids into thermal contact through a conducting surface while preventing mixing. There are several types of heat exchangers classified by their heat exchange process, fluid flow direction, mechanical design, and physical state. A common type is the shell and tube heat exchanger, which consists of a shell with a bundle of tubes inside. One fluid flows through the tubes while another flows over the tubes to transfer heat between the fluids. Double pipe heat exchangers are a simpler design with one pipe inside a larger pipe, allowing fluids to flow within and between the pipes.

1. HEAT EXCHANGERS
MADE BY :
RIMJHIM RAJ SINGH (13IME045)
SAKSHI SINGH (13IME051)

2. INTRODUCTION TO HEAT EXCHANGERS:
• A heat exchanger is a device in which two fluid streams, one hot and
another cold, are brought into 'thermal contact' in order to effect
transfer of heat from the hot fluid stream to the cold.
• It provides relatively large area of heat transfer for a given volume of
the equipment.
• They are widely used in space heating, refrigeration, air conditioning,
power plants, chemical plants, petrochemical plants , petrolium
refineries and sewage treatments.

3. PRINCIPLE OF HEAT EXCHANGERS
• Heat exchanger works because heat flows from higher tempreture to
lower temprature. therefore if a hot fluid and a cold fluid are
seperated by a conducting surface, heat can be transferred from hot
fluid to cold fluid.
• two fluids of different temperature are brought into close contact but
are prevented from mixingby a physical barrier. The temprerature of
the two fluids will tend to equalize. By arranginf counter current flow
it is possible for the temperature at the out let of each fluid to
approach the temperature at the inlet of the other. the heat contents
are simply exchanged from one fluid to the other and vice versa . No
energy is added or removed.

4. Heat transfer depends
upon following factors:
• Type of the material between
fluids.
• thickness of materials.
• surface area of materials
• type of fluids.
• flow rate of fluid.
Basic equation defining the
heat exchanger principle:
where,
Q= Rate of heat transfer between
the two fluids in the heat
exchanger .
U=overall heat transfer coefficient.
A= heat transfr surface area.
= log mean temp.
difference.
lmTUAQ 
lmT

5. CLASSIFICATION OF HEAT EXCHANGERS
• 1. Nature of heat exchange process
• 2. Relative direction of motion of fluids
• 3. Mechanical design of heat exchanger surface
• 4. Physical state of heat exchanging

6. NATURE OF HEAT EXCHANGE PROCESS
• Direct contact heat exchanger: this is done by complete physical mixing of
heat and mass transfer. Examples are water cooling towers and jet condensers
in steam power plants.
• Regenerator: here hot and cold fluids flows alternately when hot fluid passes,
the heat is transferred to the solid matrix and then stopped the flow of hot
fluid, next cold fluid is passed on the matrix which takes heat from solid
matrix. Examples are Open hearth and blast furnaces.
• Recuperator: the cold fluid flows simultaneously on either side of a
separating wall. Examples are super heaters, condensers, economizers and air
pre-heaters in steam power plants, automobile radiators.

7. Relative direction of motion of fluids
• Parallel flow heat exchangers: In parallel flow heat exchangers, both the tube
side fluid and the shell side fluid flow in same direction. In this case, the two
fluids enter the heat exchanger from the same end with a large temperature
difference.
• Counter flow heat exchangers: In counter flow heat exchangers, the two
fluids flow in opposite directions. Each of the fluids enter the heat exchanger
from opposite ends. Because the cooler fluid exists the counter flow heat
exchanger at the end where the hot fluid enters the heat exchanger, the
cooler fluid will approach the inlet temperature of the hot fluid.
• Cross flow heat exchangers: In cross flow heat exchangers, one fluid flows
through tubes and second fluid passes around the tubes perpendicularly.

8. Mechanical design of heat exchanger surface
• Shell and tube.
• Double pipe heat exchanger.
Physical state of heat exchanging
• Condenser
• Evaporator

9. DOUBLE PIPE HEAT EXCHANGER
• A double pipe heat exchanger, in its simplest form is just one pipe inside
another larger pipe. One fluid flows through the inside pipe and the other
flows through the annulus between the two pipes. The wall of the inner pipe
is the heat transfer surface. The pipes are usually doubled back multiple times
as shown in the diagram at the left, in order to make the overall unit more
compact.
• They are one of the simplest and cheapest types of heat exchanger.
• They can be used for high temperature, high pressure, and highly viscous
service.
• Some designs use inner tubes/pipes fitted with longitudinal fins to increase
the heat transfer area and improve heat transfer.

11. Shell and tube heat exchanger
• A shell and tube heat exchanger is a class of heat exchanger designs.
It is the most common type of heat exchanger in oil refineries and
other large chemical processes, and is suited for higher-pressure
applications. As its name implies, this type of heat exchanger consists
of a shell (a large pressure vessel) with a bundle of tubes inside it.
One fluid runs through the tubes, and another fluid flows over the
tubes (through the shell) to transfer heat between the two fluids. The
set of tubes is called a tube bundle, and may be composed of several
types of tubes: plain, longitudinally finned, etc.

13. ADVANTAGES OF SHELL AND TUBE
•Condensation or boiling heat transfer can be accommodated in either the tubes or the shell, and
the orientatioN can be horizontal or vertical. You may want to check out the orientation of the heat
exchanger in our laboratory. Of course, single phases can be handled as well.
• The pressures and pressure drops can be varied over a wide range.
• Thermal stresses can be accommodated inexpensively.
• There is substantial flexibility regarding materials of construction to accommodate corrosion and
other concerns. The shell and the tubes can be made of different materials.
• Extended heat transfer surfaces (fins) can be used to enhance heat transfer.
• Cleaning and repair are relatively straightforward, because the equipment can be dismantled for
this purpose