Heat Exchangers & its types & classifications

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HEAT EXCHANGERS
PRESENTED BY

CONTENTS
1. Introduction
2. Classification based on flow arrangement
3. Classification based on Construction
4. Advantages
5. Disadvantages
6. Applications

INTRODUCTION
1.Heat exchanger is a device which is used for transferring the heat from one
fluid to another through the separating wall.
2.The media may be separated by a solid wall to prevent mixing or they may
be in direct contact.
3.They are widely used in space heating, refrigeration, air conditioning,
power plants, chemical plants, petrochemical plants, petroleum
refineries, natural gas processing, and sewage treatment.
4.The classic example of a heat exchanger is found in an internal combustion
engine in which a circulating fluid known as engine coolant flows through
radiator coils and air flows past the coils, which cools the coolant and heats
the incoming air.

Classification of Heat Exchangers by
Flow Arrangement
There are four basic flow configurations:
1. Counter current Flow
2. Co-current Flow
3. Cross Flow
4. Hybrids such as Cross Counter Flow and Multi Pass Flow

Counter Flow Heat Exchangers
1. Figure-1 illustrates an idealized counter flow exchanger in which the
two fluids flow parallel to each other but in opposite directions.
2. This type of flow arrangement allows the largest change in
temperature of both fluids and is therefore most efficient (where
efficiency is the amount of actual heat transferred compared with the
theoretical maximum amount of heat that can be transferred).

Co-current Flow Heat Exchangers
1. In co-current flow heat exchangers, the stream flow parallel to each other
and in the same direction as shown in Figure.
2. This is less efficient than counter current flow but does provide more
uniform wall temperatures.

Cross Flow Heat Exchangers
1. Cross flow heat exchangers are intermediate in efficiency between
counter current flow and parallel flow exchangers.
2. In these units, the streams flow at right angles to each other as
shown in Fig.

Hybrid flow Flow Heat Exchangers
1. Hybrid flow heat exchangers are created by manufacturers to combine
the characteristics of the above-mentioned flow configurations.
2. Examples of hybrid flow patterns are shell-and-tube heat exchangers,
cross flow-counter flow, and multi-pass flow heat exchangers.

Classification of Heat Exchangers by
Construction

Recuperative Heat Exchangers
1. A Recuperative Heat Exchanger are designed to have separate flow paths for the two
fluids, wherein they exchange heat simultaneously.
2. They are further classified into two categories: indirect contact and direct contact heat
exchangers.
3. Indirect Contact Heat Exchangers utilize a conductive wall to separate the two
fluids. They are the most employed heat exchangers.
4. Direct Contact Heat Exchangers do not involve a conductive partition and rely on
direct contact for the heat exchange to take place.
5. They are suitable for two immiscible fluids, or if one of the fluids will undergo a
phase change. They are cheaper due to their simpler design.
6. It is commonly used in seawater desalination, refrigeration systems, and waste
heat recovery systems.
7. Examples of direct contact heat exchangers are direct contact condensers, natural
draft cooling towers, driers, and steam injection.

Double-pipe Heat Exchangers
1.The process fluid flows through the smaller inner pipe, and the utility fluid
flows through the annular space between the two pipes.
2.The wall of the inner pipe acts as the conductive barrier between the two fluids
wherein heat is transmitted.
3.The counter current flow pattern is the most utilized, though it may be
configured to co-current flow.
1.Double-pipe heat exchangers,
also known as a pipe in pipe or
hairpin or jacketed pipe
exchangers, are the simplest
type of heat transfer equipment.
2.They are made of two
concentric pipes with different
diameters.

Advantages & Dis-advantages
Advantages:
1. Double pipe heat exchangers are suitable
for heating or cooling small flow rates of
fluids.
2. They are cheap, have a flexible design,
and are easy to maintain.
3. They can be constructed from pipes of the
same lengths interconnected with fittings
at the ends to maximize floor space.
Dis-advantages:
1. They only operate at lower heating duties
compared to other heat exchanger
equipment.

Shell and Tube Heat Exchangers
1.Advantages:
2.Shell and tube heat exchangers are ideal for heating and cooling liquids with high
flow rates, temperatures, and pressures.
3. To increase operational efficiency, they can be designed to have multiple passes
wherein one fluid comes in contact with the other several times.
1.Shell and tube heat exchangers are
composed of tubes arranged in a
bundle that is housed in a large
cylindrical vessel called a shell.
2.Similar to the double pipe heat
exchanger, the wall of the inner
pipe acts as the conductive barrier.
3.The process fluid flows in the tube
side, and the utility fluid flows on
the shell side.

1.4.Baffles: They guide the shell fluid flow across the shell and increase its
turbulence.
2.They hold the tubes in proper position during operation since they are prone to sag
induced by the flow eddies.
3.Tie rods secure the baffle spacing and position.
Essential components of a shell and
tube heat exchanger are:
1.Tube Sheet: The tubes are held in
place by inserting them into the
holes of a plate called a tube sheet.
2.Plenums: Plenums are located in
both tube fluid inlet and outlet. It is
a container wherein the tube fluid is
gathered before loading and
discharge.

Plate Heat Exchangers
1.These types of heat exchangers utilize conductive plates (corrugated) to
transfer heat between two fluids.
2.They have a counter-current flow that allows for lower approach
temperature differences, high temperature exchanges, and improved
efficiency.

Plate and Frame Heat Exchangers
1.Plate and frame heat exchangers use
corrugated plates that are joined by a gasket,
weld, or braze to ensure that the fluids do not
mix.
2.The plates have inlet and outlet ports on the
corner to allow passage of the fluid streams.
3.The flow paths of the fluids are the spaces
between the plates that are arranged in
alternating hot-cold-hot-cold fluid streams.
4.Fluids flow in a countercurrent flow
configuration with the hot fluid flowing down
the plates while the cold fluid flows up the
plates.

Plate and Frame Heat Exchangers
Advantages of Plate Type Heat Exchanger :
1.Low cost of operation
2.Low cost of maintenance
3.Easy to clean
4.Highly efficient heat transfer
5.Future changes are possible by fitting extra
heat transfer plates
6.Less floor space required
Applications of Plate type Heat Exchanger:
1.Power generation applications
2.In food, Dairy and brewing industries
3.Refrigerants in cooling systems

Gasketed Plate Heat Exchangers
1.These type uses gaskets to connect and seal the plates together.
2.They are widely used in industries that require frequent sanitation, like food and
beverage processing.
3.Gasketed plates reduce maintenance costs since they are easy to clean, dismantle,
and assemble.
4.More plates may be added to increase the heat exchanger‘s capability and
throughput.
5.The disadvantage of this type is its potential for leakage.

Welded & Brazed Plate Heat Exchangers
Welded Plate Heat Exchangers:
1.Welded plate heat exchangers reduce the possibility of leakage.
2.They can handle higher temperatures, higher pressures, and more corrosive
fluids since the operating temperature is not limited by the gasket seals
Brazed Plate Heat Exchangers:
1.These heat exchangers have plates joined by a process called brazing, where two
pieces of metal are joined by a molten filter metal.
2.They are used in chillers, pumps, evaporators, and condensers.

Regenerative Heat Exchangers
1. Regenerative heat exchangers are also known as regenerators or
capacitive heat exchangers.
2. Regenerative heat exchangers are types of heat exchanger equipment
that utilize a heat storage medium that is made to contact with the hot
and cold fluids.
3. The two fluids are usually gasses.
4. They are used in power plants, glass and steel making, and heat
recovery systems.
5. There is potential contamination since the same medium is used to
interact with the hot and cold fluids.
6. There are two types of regenerative heat exchangers:
i. Static Regenerators
ii. Dynamic Regenerators

Static Regenerators
1.The hot fluid is made to flow first at a certain length of time. Once the heat
storage medium accumulates enough heat, the valve connecting the reservoir of
the hot fluid is switched off.
2.The cold fluid is then allowed to flow through the channel, which absorbs the
heat coming from the hot fluid.
1.Static regenerators, or fixed bed
regenerators, do not have
mechanical parts that facilitate the
flow of hot and cold fluids.
2.The fluids are made to pass through
the channel by a system of pipes
and ducts, fitted with valves that
act as a "switch" during the separate
release of the hot and cold fluids.

Dynamic Regenerators
1.Dynamic Regenerators are heat
exchangers that have a rotating
element which contains the heat
storage medium.
2.The hot and cold fluid streams flow
simultaneously and are placed on
opposite sides of the rotating wheel,
parallel to the axis of rotation.
3.Heat is transferred on the heat
storage medium as the wheel
rotates on the hot fluid stream, and
is released once it reaches the cold
fluid streams.

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Heat Exchangers & its types & classifications

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Heat Exchangers & its types & classifications