Heat Exchangers; Double Pipe, Shell & Tube Heat Exchanger

1. HEAT EXCHANGERS
Design & Construction

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Term Report
Topic
Heat Exchanger
Subject
CPC – 2
Subject Code
CHE – 204
Submitted To
Engineer Subhan Azeem

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Table of Contents
Topic Page Number
Cover Page
Term Report 01
Group Members 03
Abstract 04
Acknowledgements 05
Dedication 06
Heat Exchanger 07
DoublePipeHeat Exchanger 08
Shell & Tube Heat Exchanger 17

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Group Members:
Muhammad Usmaan Bin Khawer 2K15-CHE-05
Muhammad Ayyaz Tahir 2k15-CHE-04
Muhammad Junaid Afzal 2K15-CHE-06
Muhammad Aamush 2K15-CHE-12
Muhammad Idrees 2K15-CHE-17
Aqsa Ashfaq 2K15-CHE-02

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Abstract:
This term report deals with the construction, working
principles and design along with the industrial applications
of different types of heat exchangers such as double pipe
and shell and tube heat exchanger.

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Acknowledgements:
First of all, I would like to thanks my Allah, with whom
blessings I became able to do something. Secondly, our
parents whose efforts become fruitful and we become able to
compile this report. Thirdly, I would like to thanks my
friends; Mohammad Ayyaz Tahir, Muhammad Junaid,
Muhammad Aamush, Muhammad Ahtasham Nasir,
Muhammad Idrees and Aqsa Ishfaq who provided me with
relative material and innovative ideas to compile this term
report. I would also like to thanks to our respectable teacher,
Engineer Subhan Azeem whose guidance helped me to
conclude this term report.

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Dedication:
We dedicate this work to our beloved parents and respected
teachers with whom efforts, today I am able to do something.

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Heat Exchanger:
Introduction:
A heat exchangeris a device used to transfer heat between a solid object and
a fluid, or between two or more fluids. The fluids may be separated by a solid
wall to prevent mixing or they may be in direct contact. They are widely used
in spaceheating, refrigeration, air conditioning, power stations, chemical
plants, petrochemical plants, petroleum refineries, natural-gas processing,
sewage treatment, waste heat recovery, metallurgical industries.
The driving force for the operation of a heat exchanger is the temperature
difference between the fluids. The British standard for Heat Exchanger design
is BS 3274.
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 pastthe coils, which cools the coolant and
heats the incoming air. Another example is the heat sink, which is a passive heat
exchanger that transfers the heat generated by an electronic or a mechanical
device to a fluid medium, often air or a liquid coolant.

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Working Principle:
A heat exchanger is a special device that assists in heat transfer through one
channel to another usually by conduction. Basically, in almost all applications,
there is a solid barrier that prevents the media from mixing up with each other.
One side of the wall contains the hot fluid, while the other side has the cool
fluid flowing through the channels. Depending on the structure, the exchanger
can be more efficient in performing heat transfer. Fins or corrugations are often
included in the exchanger’s design in order to make this possible.
Types of Heat Exchanger:
There are many different types of Heat Exchanger depending upon their
construction and working. The types include
 Double pipe heat exchanger
 Shell & Tube heat exchanger
 Plate heat exchanger
 Plate & shell heat exchanger
 Waste heat recovery unit
1. Double Pipe Heat Exchanger:
A typical double pipe heat exchanger basically consists of a tube or pipe fixed
concentrically inside a larger pipe or tube. They are used when the flow rates of
the fluids and the heat duty are small (less than 500 kW). These are simple to
construct, but may require a lot of physical spaceto achieve the desired heat
transfer area.
Double pipe heat exchanger design is rather straightforward. It uses one heat
exchanger pipe inside another. After determining the required heat exchanger
surface area, for either counter flow or parallel flow, the pipe sizes and number
of bends for the double pipe heat exchanger can be selected.
In double pipe heat exchanger design, an important factor is the type of flow
pattern in the heat exchanger. A double pipe heat exchanger will typically be
either counter flow or parallel flow. Crossflow just doesn'twork for a double
pipe heat exchanger. The flow pattern and the required heat exchange duty
allows calculation of the log mean temperature difference. That together with an

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estimated overall heat transfer coefficient allows calculation of the required heat
transfer surface area. Then pipe sizes, pipe lengths and number of bends can be
determined.
Construction of double pipe:
Straight construction
 It has single sections of inner and outer pipes.
 It requires more space.

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Hairpin construction
 It has two sections each of the inner and outer pipes.
 It is more convenient because it requires less space.
 Several hairpins may be connected in series to obtain large heat transfer
area.
 All the return bends of the inner pipe are kept outside the jacket and do
not contribute to the heat transfer area.

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Figure 1: Hairpin Heat Exchanger
Components of Double Pipe Heat Exchangers:
❖Packing & gland
The packing and gland provides sealing to the annulus and supportthe inner
pipe.
❖Return bend
The opposite ends are joined by a U-bend through welded joints.
❖Support lugs
Supportlugs may be fitted at these ends to hold the inner pipe position.
❖Flange
The outer pipes are joined by flanges at the return ends in order that the
assembly may be opened or dismantled for cleaning and maintenance.
❖Union joint
For joining the inner tube with U-bend.

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Flow arrangementsin DoublePipeHeat Exchanger:
There are three primary classifications of heat exchangers according to their
flow arrangement.
 Co - Current (Parallel) Flow
 Counter current Flow
 Cross (Perpendicular) Flow
Co – Current Flow:
In parallel-flow heat exchangers, the two fluids enter the exchanger at the same
end, and travel in parallel to one another to the other side.

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Counter Current Flow:
In counter-flow heat exchangers the fluids enter the exchanger from opposite
ends. The counter current design is the most efficient, in that it can transfer the
most heat from the heat (transfer) medium per unit mass due to the fact that the
average temperature difference along any unit length is higher.
Cross Current Flow
In a cross-flow heat exchanger, the fluids travel roughly perpendicular to one
another through the exchanger.
For efficiency, heat exchangers are designed to maximize the surface area of the
wall between the two fluids, while minimizing resistance to fluid flow through
the exchanger. The exchanger's performance can also be affected by the
addition of fins or corrugations in one or both directions, which increase surface
area and may channel fluid flow or induce turbulence.
The driving temperature across the heat transfer surface varies with position, but
an appropriate mean temperature can be defined. In most simple systems this is
the "log mean temperature difference" (LMTD).
LMTD:
The logarithmic mean temperature difference (LMTD) is used to determine the
temperature driving force for heat transfer in flow systems, most notably in heat
exchangers. The LMTD is a logarithmic average of the temperature difference
between the hot and cold feeds at each end of the double pipe exchanger. The
larger the LMTD, the more heat is transferred. The use of the LMTD arises

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straightforwardly from the analysis of a heat exchanger with constant flow rate
and fluid thermal properties.
We assume that a generic heat exchanger has two ends (which we call "A" and
"B") at which the hot and cold streams enter or exit on either side; then, the
LMTD is defined by the logarithmic mean as follows:
Where ΔT1 is the temperature difference between the two streams at end A,
and ΔT2 is the temperature difference between the two streams at end B. With
this definition, the LMTD can be used to find the exchanged heat in a heat
exchanger:
Where Q is the exchanged heat duty (in watts), U is the heat transfer
coefficient (in watts per kelvin per square meter) and Ar is the exchange area.
Note that estimating the heat transfer coefficient may be quite complicated.
This holds both for co - current flow, where the streams enter from the same
end, and for counter-current flow, where they enter from different ends.
In a cross-flow, in which one system, usually the heat sink, has the same
nominal temperature at all points on the heat transfer surface, a similar relation
between exchanged heat and LMTD holds, but with a correction factor. A
correction factor is also required for other more complex geometries, such as a
shell and tube exchanger with baffles.

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Applications of Double Pipe Heat Exchangers:
Double Pipe Heat Exchangers have a wide variety of applications:
 Double pipe heat exchanger utilizes true counter-current flow to which
maximizes the temperature differences between the shell side and the
tube side fluids, resulting in less surface area required for a given duty.
 Double Pipe exchangers are especially suitable for extreme temperature
crossing, high pressure, high temperature, and low to moderate surface
area requirements. So when your process calls for a temperature cross
when the hot fluid outlet temperature is below the cold fluid outlet
temperature, a hairpin heat exchanger is the most efficient design and will
result in fewer sections and less surface area.
 Double-pipe heat exchangers use a single pipe within a pipe design and
are commonly used for high fouling services such as slurries, where
abrasive materials are present, and for smaller duties. Standard shell
diameters typically range from 2” to 6”.
 In commercial aircraft heat exchangers are used to take heat from the
engine's oil system to heat cold fuel. This improves fuel efficiency, as
well as reduces the possibility of water entrapped in the fuel freezing in
components.
 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 airflows past the coils, which cools the
coolant and heats the incoming air.
ADVANTAGES
 Easy to operate.
 Counter currents are obtained easily.
 It can withstand high pressure and temperature.
 Modular structure.
 Maintenance is easy and repairing also easy.
 Easily displace from one place to another if required.
 It can be adjusted according to the process need.
 Occupyless space.
 Structure is simple and heat transmission is large.
 Provides shorter deliveries than shell and tube due to standardization
of design and construction.
 Many suppliers are available worldwide.

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DISADVANTAGES
 Double pipe heat exchanger is expensive for heavy duties.
 The use of two single flow areas leads to relatively low flow rates and
moderate temperature differences.
 Can’t be used in handling dirty fluids.
 It is difficult to readily inspect the shell side of the tubes for scaling or
tube damage.
Conclusion:
As the consequences ofthe above mentioned detailed properties, applications
advantages and disadvantages the double pipe heat exchanger is used according
to the needs of the process in industry as well as other heat exchanging
processes.

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2.Shell & 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. It 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 ofseveral types of tubes: plain, longitudinally finned, etc.
They are the most versatile type of heat exchangers. They provide a large heat
transfer surface in a small space. They can operate at high pressures, are easy to
clean and can be made of a wide variety of materials.

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Working Principle:
Two fluids, of different starting temperatures, flow through the heat exchanger.
One flows through the tubes (the tube side) and the other flows outside the tubes
but inside the shell (the shell side). Heat is transferred from one fluid to the
other through the tube walls, either from tube side to shell side or vice versa.
The fluids can be either liquids or gases on either the shell or the tube side. In
order to transfer heat efficiently, a large heat transfer area should be used,
leading to the use of many tubes. In this way, waste heat can be put to use. This
is an efficient way to conserve energy.
Shell and tube heat exchangerdesign:
There can be many variations on the shell and tube design. Typically, the ends
of each tube are connected to plenums (sometimes called water boxes) through
holes in tube sheets. The tubes may be straight or bent in the shape of a U,
called U-tubes.
In nuclear power plants called pressurized water reactors, large heat exchangers
called steam generators are two-phase, shell-and-tube heat exchangers which
typically have U-tubes. They are used to boil water recycled from a surface
condenserinto steam to drive a turbine to producepower. Most shell-and-tube
heat exchangers are either 1, 2, or 4 pass designs on the tube side. This refers to
the number of times the fluid in the tubes passes through the fluid in the shell.
In a single pass heat exchanger, the fluid goes in one end of each tube and out
the other.

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Surface condensers in power plants are often 1-pass straight-tube heat
exchangers. Two and four pass designs are common becausethe fluid can enter
and exit on the same side. This makes construction much simpler.
There are often baffles directing flow through the shell side so the fluid does not
take a short cut through the shell side leaving ineffective low flow volumes.
These are generally attached to the tube bundle rather than the shell in order that
the bundle is still removable for maintenance.

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Counter current heat exchangers are most efficient because they allow the
highest log mean temperature difference between the hot and cold streams.
Many companies however do not use two pass heat exchangers with a u-tube
because they can break easily in addition to being more expensive to build.
Often multiple heat exchangers can be used to simulate the counter current flow
of a single large exchanger.
Selection of Tube Material:
To be able to transfer heat well, the tube material should have good thermal
conductivity. Because heat is transferred from a hot to a cold side through the
tubes, there is a temperature difference through the width of the tubes. Because
of the tendency of the tube material to thermally expand differently at various
temperatures, thermal stresses occurduring operation. This is in addition to
any stress from high pressures from the fluids themselves. The tube material
also should be compatible with both the shell and tube side fluids for long
periods under the operating conditions (temperatures, pressures, pH, etc.) to
minimize deterioration such as corrosion. All of these requirements call for
careful selection of strong, thermally-conductive, corrosion-resistant, high
quality tube materials, typically metals, including aluminium, copper
alloy, stainless steel, carbon steel, non-ferrous copper
alloy, Inconel, nickel, Hastelloy and titanium. Fluoropolymers such as
Perfluoroalkoxyalkanes (PFA)and Fluorinated ethylene propylene (FEP) are
also used to producethe tubing material due to their high resistance to extreme
temperatures. Poorchoice of tube material could result in a leak through a tube
between the shell and tube sides causing fluid cross-contamination and possibly
loss of pressure.
Construction of DoublePipeHeat Exchanger:
The main components are:

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1. Channel cover
2. Stationary head channel
3. Channel flange
4. Pass partition plate
5. Tube sheet
6. Shell flange
7. Tube
8. Shell
9. Baffles
10.Floating head backing device
11.Floating tube sheet
12.Floating head
13.Floating head flange
14.Stationary head bonnet
15.Heat exchanger support
16.Shell expansion joint
The shell
 The shell is the enclosure and passage of the shell-side fluid.
 It has a circular cross-section.
 The selection of the material depends upon the corrosiveness of the
fluid and the working temperature and pressure.
 Carbon steel is a common material for the shell under moderate working
conditions.
The tubes
 The tubes provide the heat transfer area in a shell and tube heat
exchanger.
 Tubes of 19mm and 25mm diameter are more commonly used.
 The tube wall thickness is designated in terms of BWG (Birmingham
wire gauge).
 Tubes are generally arranged in a triangular or square pitch.
 The tube sheets are circular, thick metal plates which hold the tubes at the
ends.
 The arrangement of tubes on a tube sheet in a suitable pitch is called tube-
sheet layout.
 Two common techniques of fixing the ends of a tube to the tube sheet are:
(i) expanded joints and (ii) welded joints.

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A few common joints between the tube and the tube sheet:
a) Grooved joint
b) Plain joint
c) Belled or beaded joint
d) Welded joint
The bonnet and the channel
 The closure of heat exchanger is called bonnet or channel depending
upon its shape and construction.
 A bonnet has an integral cover and a channel closure has a removable
cover.
 The bonnet closure consists of a short cylindrical section with a bonnet
welded at one end and a flange welded at the other end.
 The bonnet-type closure is replaced by a channel-type closure if a nozzle
is required to be fitted.
The pass partition plate
 The channel is divided into compartments by a pass partition plate.
 The number of tube and shell-side passes can be increased by using more
pass partition plates for both the sides.
 The number of passes in either the shell or the tube side indicates the
number of times the shell or the tube side fluid traverses the length of the
exchanger.
 For a given number of tubes, the area available for flow of the tube-side
fluid is inversely proportional to the number of passes.
 An even number of passes on any side is generally used (Forexample,1-
2,1-4,2-4,2-6 etc.; 1-3,2-5 etc. are not used).
Nozzles:
 Nozzles are small sections of pipes welded to the shell or the channel
which act as the inlet or outlet of the fluids.
 The shell-side inlet nozzle is often provided with an ‘impingement plate’.

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 The impingement plate prevents impact of the high velocity inlet fluid
stream on the tube bundle.
Figure 2: Two types of impingement plates:
a) The plates
b) Expanded nozzle
c) Nozzle flange
Baffles:
 A baffle is a metal plate usually in the form of the segment of a circle
having holes to accommodatetubes.
 Segmental baffle is the most popular type of baffle.
 Functions of shell-side baffles are:
(i) to cause changes in the flow pattern of the shell fluid creating
parallel or cross flow to the tube bundle and
(ii) To supportthe tubes.
Implementation of baffles is decided on the basis of size, costand their ability
to lend supportto the tube bundles and direct
A few types of baffles are
 Longitudinal Flow Baffles (used in a two-pass shell)
 Impingement Baffles (used for protecting bundle when entrance velocity
is high)
 Orifice Baffles
 Single segmental
 Double segmental
 Support/Blanking baffles
 DE resonating (detuning) baffles used to reduce tube vibration

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 Rod baffle
 Disc and doughnutbaffles
Tie rods and bafflespacers
 Tie rods having threaded ends are used to hold the baffles in position.
 The baffle spacers maintain the distance or spacing between successive
baffles.
Flangesand gaskets
 The flanges fixes the bonnet and the channel closures to the tube sheets.
 Gaskets are placed between two flanges to make the joint leak-free.
Expansion joint
 The expansion joint prevents the problem of thermal stress which may
occurwhen there is a substantial difference of expansion between the
shell and the tubes because of the temperature difference between the two
fluid streams.
Applications and uses of Shell & Tube Heat Exchangers:
The simple design of a shell and tube heat exchanger makes it an ideal cooling
solution for a wide variety of applications.
 One of the most common applications is the cooling of hydraulic
fluid and oil in engines, transmissions and hydraulic power packs. With
the right choice of materials they can also be used to coolor heat other
mediums, such as swimming poolwater or charge air. One of the big
advantages of using a shell and tube heat exchanger is that they are often
easy to service, particularly with models where a floating tube bundle
(where the tube plates are not welded to the outer shell) is available.
 In nuclear power plants called pressurized water reactors, large heat
exchangers called steam generators are two-phase, shell-and-tube heat
exchangers which typically have U-tubes. They are used to boil water
recycled from a surface condenser into steam to drive a turbine to

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producepower. Most shell-and-tube heat exchangers are either 1, 2, or 4
pass designs on the tube side. This refers to the number of times the fluid
in the tubes passes through the fluid in the shell. In a single pass heat
exchanger, the fluid goes in one end of each tube and out the other.
 A surface condenser is an example of heat-exchange system. It is a shell
and tube heat exchanger installed at the outlet of every steam
turbine in thermal power stations. Commonly, the cooling water flows
through the tube side and the steam enters the shell side where the
condensation occurs on the outside of the heat transfer tubes. The
condensate drips down and collects at the bottom, often in a built-in pan
called a hot well. The shell side often operates at a vacuum or partial
vacuum, produced by the difference in specific volume between the
steam and condensate. Conversely, the vapor can be fed through the tubes
with the coolant water or air flowing around the outside.
Advantages of shell & tube heat exchangers:
 Size - STHEs are capable of providing a larger surface area for heat
transfer to take place while having a shorter length overall due to
presence of multiple tubes.
 Heat duty - STHEs can handle higher temperatures and pressures and
hence higher heat duty. This is because besides providing a higher overall
heat transfer coefficient, additions can also be made to negate thermal
expansion effects and the thickness can also be varied (more in the next
point)
 Versatility - from the design point of view, STHEs are the most versatile
of all heat exchangers. Being tubular in shape, heads / closures of
required shape and thickness can be used. The number of tubes and tube
pitch can be selected according to operating conditions. Expansion
bellows can be used to negate thermal expansion effects, baffles if
different cuts and spacing can be used to influence the overall heat
transfer coefficients and there's even something called a floating head
which can be added to negate thermal expansion of the tubes. The
number of passes on shell side and tube side can be altered as well.

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Disadvantages:
 Size - yes. This can also be a disadvantage as at lower heat duty, there are
more compactheat exchangers such as plate type exchanger. Also, the
absence of hairpin bends causes STHEs to take up more spacethan
double pipe heat exchangers in some cases.
 Maintenance - cleaning of tubes is difficult and fouling is always an issue
when overall heat transfer coefficient is addressed. This requires periodic
cleaning of the shell as well as the tubes. Cleaning tubes may be
more difficult if the pitch is triangular.
Conclusion:
As the consequences ofthe above mentioned detailed properties,
applications advantages and disadvantages the shell & tube heat exchanger is
used according to the needs of the process in industry as well as other heat
exchanging processes.

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References:
https://en.wikipedia.org/wiki/Heat_exchanger
https://www.scribd.com/doc/93197671/Double-
Pipe-Heat-Exchanger
https://www.slideshare.net/rijumoniboro/heat-
exchangers-12606868
https://en.wikipedia.org/wiki/Shell_and_tube_heat
_exchanger
http://www.thermopedia.com/content/1121/
Kern, D. Q. (1950). Process Heat Transfer.

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