Heat exchangers transfer heat from one medium to another. They are classified by flow configuration and construction. Key flow configurations are parallel, counter, and cross flow. Main construction types are shell and tube, and plate heat exchangers. Heat transfer is calculated using methods like log mean temperature difference (LMTD) and number of transfer units (NTU). Standards like TEMA provide guidelines for shell and tube heat exchanger design and components.

1. Assignments Contents :
Heat exchanger basic concept
Working principle
LMDT Method
NTU Method
Types of heat Exchanger based on;
 Working Principle
 Construction Configuration
 Construction Material
Standards use for H.E..(i.e TEMA…)
Refernces

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HEAT EXCHANGER
A heat exchanger is a piece of equipment built for efficient heat
transfer from one medium to another. The media may be separated by a solid wall, so
that they never mix, or they may be in direct contact.
They are widely used in space heating, refrigeration, air conditioning, power plants,
chemical plants, petrochemical plants, petroleum refineries, natural gas processing,
and sewage treatment.
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.
Principle Of Heat Exchanger
Heat exchangers work because heat naturally flows
from higher temperature to lower temperatures. Therefore if a hot fluid and a cold fluid
are separated by a heat conducting surface heat can be transferred from the hot fluid
to the cold fluid.
Two fluids of different temperatures are brought into close contact but are prevented
from mixing by a physical barrier. The temperature of the two fluids will tend to
equalize. By arranging counter-current flow it is possible for the temperature at the
outlet 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.
Heat transfer depends upon following
factors:
Type of the material between fluids
Thickness of material
Surface Area of material
Type of fluid
Gravity of fluid
Flow rate of fluid

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Basic Equation defining the Heat Exchanger Principle:
Heat exchanger theory leads to the basic heat exchanger
design equation: Q = U A ΔTlm, where
Q is the rate of heat transfer between the two fluids in the heat exchanger in But/hr,
U is the overall heat transfer coefficient in Btu/hr-ft2-oF,
A is the heat transfer surface area in ft2,
ΔTlm is the log mean temperature difference in oF, calculated from the inlet and
outlet temperatures of both fluids.
Log mean temperature difference
(LMDT):
The log 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 streams at each
end of the exchanger. The larger the LMTD, the more heat is transferred. The use of the
LMTD arises 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 ΔTA is the temperature difference between the two streams at end A, and ΔTB is the
temperature difference beween the two streams at end B.
This equation is valid both for parallel flow, where the streams enter from the same end, and
for counter-current flow, where they enter from different ends.
Once calculated, the LMTD is usually applied to calculate the heat transfer in an exchanger
according to the simple equation:
Where Q = Heat transfer

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Once calculated, the LMTD is usually applied to calculate the heat transfer in an exchanger
according to the simple equation:
Where Q is the exchanged heat duty (in watts), U is the heat transfer coefficient (in watts per kelvin
per square meter) and A is the exchange area. Note that estimating the heat transfer coefficient may
be quite complicated.
Number of Transfer Units (NTU) method:
The Number of Transfer Units (NTU) Method is used to calculate the rate of heat transfer in
heat exchangers (especially counter current exchangers) when there is insufficient
information to calculate the Log-Mean Temperature Difference (LMTD). In heat exchanger
analysis, if the fluid inlet and outlet temperatures are specified or can be determined by
simple energy balance, the LMTD method can be used; but when these temperatures are not
available The NTU or The Effectiveness method is used.
U = Overall heat transfer co-efficient
A= surface area
C min =specific heat capacity of cold fluid
Effectiveness of heat exchanger is calculated as;
Classification of Heat Exchangers:
Types w.r.t Flow:
There are two primary classifications of heat exchangers according to their flow arrangement.
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.
Counter-flow heat exchangers:
The fluids enter the exchanger from
opposite ends. The counter current design is

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most efficient, in that it can transfer the most heat
from the heat (transfer) medium.
Cross-flow heat exchangers:
In a cross-flow heat exchanger, the fluids travel
roughly perpendicular to one another through the
exchanger.
Single and Multi-pass Heat Exchanger
In actuality, most large heat exchangers are not purely parallel flow, counter flow, or cross
flow; they are usually a combination of the two or all three types of heat exchangers. This is
due to the fact that actual heat exchangers are more complex than the simple components
shown in the idealized figures used
below to depict each type of heat
exchanger. The reason for the
combination of the various types is to
maximize the efficiency of the heat
exchanger within the restrictions placed
on the design. That is, size, cost, weight,
required efficiency, type of fluids,
operating pressures, and temperatures,
all help determine the complexity of a
specific heat exchanger.
One method that combines the characteristics of two or more heat exchangers and improves
the performance of a heat exchanger is to have the two fluids pass each other several times
within a single heat exchanger. When a heat exchanger’s fluids pass each other more than
once, a heat exchanger is called a multi-pass heat exchanger. If the fluids pass each other
only once, the heat exchanger is called a single-pass heat exchanger. Commonly, the multi-
pass heat exchanger reverses the flow in the tubes by use of one or more sets of “U” bends in
the tubes. The “U” bends allow the fluid to flow back and forth across the length of the heat
exchanger. A second method to achieve multiple passes is to insert baffles on the shell side
of the heat exchanger. These direct the shell side fluid back and forth across the tubes to
achieve the multi-pass effect.

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Types of H.E w.r.t Construction
Shell and tube heat exchanger:
Shell and tube heat exchangers consist of a series of tubes. One set of these tubes contains
the fluid that must be either heated or cooled. The second fluid runs over the tubes that are
being heated or cooled so that it can either provide the heat or absorb the heat required. A set
of tubes is called the tube bundle and can be made up of several types of tubes: plain,
longitudinally finned, etc. Shell and tube heat exchangers are typically used for high-pressure
applications (with pressures greater than 30 bar and temperatures greater than 260°C).This is
because the shell and tube heat exchangers are robust due to their shape.
Plate heat exchanger:
Another type of heat exchanger is the plate heat exchanger. One is composed of multiple,
thin, slightly-separated plates that have very large surface areas and fluid flow passages for
heat transfer. This stacked-plate arrangement can be more effective, in a given space, than
the shell and tube heat exchanger. Advances in gasket and brazing technology have made
the plate-type heat exchanger increasingly practical. In
HVAC applications, large heat exchangers of this type
are called plate-and-frame; when used in open loops,
these heat exchangers are normally of the gasket type
to allow periodic disassembly, cleaning, and inspection.
There are many types of permanently-bonded plate heat
exchangers, such as dip-brazed and vacuum-brazed
plate varieties, and they are often specified for closed-

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loop applications such as refrigeration. Plate heat exchangers also differ in the types of plates
that are used, and in the configurations of those plates. Some plates may be stamped with
"chevron" or other patterns, where others may have machined fins and/or grooves.
Materials of construction:
The materials of construction used in heat exchangers depend on the fluids or vapor being
handled, process conditions, such as pressures, temperatures, etc., and a balance of initial
cost against expected life and maintenance requirements. Any component or the entire unit
can be made of materials such as carbon steel, stainless steel, nickel, nickel alloys or other
special alloys. Selection of materials involves careful evaluation of factors other than the basic
cost of possible metals compatible with the application.
Main Components
1- Channel Cover 2- Channel 3- Channel Flange
4- Pass Partition 5- Stationary Tube 6- Shell Flang
7- Tube 8- Shell 9- Baffles
10- Floating Head backing Devi 11- Floating Tubesheet
12- Floating Head 13- Floating Head Flange 14 –Shell Cover
TEMA STANDARDS:
The Tubular Exchanger Manufacturers' Association (TEMA) produces the most widely known
standard in the heat transfer business, which is on shell-and-tube heat exchangers. They

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currently update the standards every 10 years with "TEMA 98" having been published slightly
late, in 1999. This latest version includes the following main additions and changes
Design of floating head split rings
Design of double tube sheets
Modifications to the design of flexible shell elements (expansion joints)
Two-phase flow added to vibration section
Information on the design of supports, lifting lugs and the reaction on foundations
TEMA(Tubular Exchanger Manufactures Association) Heat Exchanger
Front Head Type
Shell Types

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Rear End Head Types
Floating Head Floating
Head Pull-Through Floating Head
TEMA DESIGNATIONS
The TEMA designations for shell and tube heat exchangers are a series of three
letters. The first letter represents the front head of the tube side of the exchanger. The
second letter represents the shell type, and the third letter indicates the rear head type
of the tube side of the exchanger. Knowledge of the TEMA designations can provide
an engineer with a quick glimpse to the design and configuration of the shell and tube
heat exchanger.
FRONT AND REAR HEAD TYPE
Different front and rear heads offer varying advantages, depending on the application,
process conditions, and ease of maintenance. Tubes are connected to the heads in a
tube sheet. The front and rear heads distribute process flow into and out of the tubes.
Some head types are flat with removable covers that allow the tubes to be cleaned
without disconnecting the exchanger from the system. Other head types have a
bonnet and single flange to lower cost.

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SHELL TYPES AND EXAMPLES
Shell types in TEMA shell and tube heat exchangers can offer a variety of flow and
heat transfer options. Some shells have a one-pass fluid flow that only contacts the
tubes one time before exiting. Others have multiple or divided flow paths that offer
higher heat transfer rates. Internal baffles are used to segregate the flows through the
shell. A typical example of a TEMA heat exchanger configuration would be BEM. The
"B" indicates a stationary bonnet with one flange. The "E" designates a standard one-
pass shell, and the "M" indicates a fixed tube sheet and bonnet head similar to "B."
Reference
I. http://en.wikipedia.org/wiki/Heat_exchanger
II. http://www.vesma.com/tutorial/hr_principles.htm
III. http://www.thomasnet.com/articles/process-
equipment/heat-exchanger-types
IV. http://www.engineeringpage.com/heat_exchangers/tema.
html
V. http://www.hcheattransfer.com/shell_and_tube.html
VI. http://en.wikipedia.org/wiki/NTU_method