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OPTIMIZATION OF SHELL AND TUBE HEAT EXCHANGER
Abhishek Arya1 , Dangar Sunilbhai Dhanjibhai 2
(Assistant professor Department of mechanical engineering, SCE Bhopal) (M.tech scholar department of Mechanical engineering, SCE Bhopal)
ABSTRACT A heat exchanger is a device, which
transfer internal thermal energy between two or
more fluids at different temperature. Without this
essential piece of equipment most industrial
process would be impossible. Heat exchangers are
widely used in refrigeration air conditioning, and
chemical plants. They can be employed in various
uses, for instance, to effectively transmit heat
from one fluid to the other. Shell-and-tube heat
exchangers (STHXs) are widely applied in various
industrial fields such as petroleum refining, power
generation and chemical process, etc. Tremendous
efforts have been made to improve the
performances on the tube side.
In this project experimental performance is done
on the fixed designed STHX and calculate the heat
transfer coefficient and effectiveness. Validation is
to be carried out using which gives the result
comparison with that of experimental result. Here
flow parameters are not varied but size and
number of tubes are varied and best efficient
model is selected as Optimized value. 3 different
number of tubes are used with same shell size
remaining same. 40 tubes , 32 tubes and 36 tubes
were tried . It's been observed for same input
temperatures and mass flow rates for three
different models one with 36 tubes , 32 tubes
model &other with 40 tubes, the temperature
variation in 36 tubes is more and also requires less
tubes compared to 40 tube model. so it is more
effective than tubes model.
1. INTRODUCTION Heat Exchanger:
heat exchanger is a device, which
transfer internal thermal energy between
two or more fluids at different
temperature. Without this essential piece of
equipment most industrial process would be
impossible.
Heat exchangers are widely used in refrigeration air
conditioning, and chemical plants. They can be
employed in various uses, for instance, to
effectively transmit heat from one fluid to the
other. Shell-and-tube heat exchangers (STHXs) are
widely applied in various industrial fields such as
petroleum refining, power generation and chemical
process, etc. Tremendous efforts have been made
to improve the performances on the tube side. For
the shell side, the velocity and temperature fields
are relatively complicated and the thermal
hydraulic performance depends on the baffle
elements to a great extent.
Shell-and-tube heat exchangers are fabricated with
round tubes mounted in cylindrical shells with their
axes coaxial with the shell axis. The differences
between the many variations of this basic type of
heat exchanger lie mainly in their construction
features and the provisions made for handling
differential thermal expansion between tubes and
shell. These are types of heat exchangers with the
outer area surrounding the tubes called shell side
and the inside of the tubes are called tube side
baffles are usually installed to increase the
A
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convective coefficient of the shell side fluid by
inducing turbulence.
1.1Classification of Shell-and-Tube Heat
Exchangers
Shell-and-tube heat exchangers can be classified
based on construction, or on service. Both
classifications are discussed in the paragraphs
below.
1.1.1 Classification based on construction:
Fixed Tube sheet:
A fixed tube sheet heat exchanger (Figure 1) has
straight tubes that are secured at both ends to tube
sheets welded to the shell. The principal advantage
of fixed tube sheet construction is its low cost
because of its simple construction. In fact, the fixed
tube sheet is the least expensive construction type,
as long as no expansion joint is required. Other
advantages are that the tubes can be cleaned
mechanically after removal of the channel cover or
bonnet, and that leakage of shell-side fluid is
minimized since there are no flanged joint.
A disadvantage of this design is that the since the
bundle is fixed to the shell and cannot be removed,
the outside of the tubes cannot be cleaned
mechanically. Thus, its application is limited to
clean services on the shell-side.
Figure 1.1 Fixed Tube sheet Heat Exchanger[B1]
U Tube Shell and heat Exchanger:
U Tube As the name implies, the tubes of a U-tube
heat exchanger (Figure 2.3) are bent in the shape of
a U. There is only one tube sheet in a U-tube heat
exchanger. However, the lower cost for a single
tube sheet is offset by the additional costs incurred
for the bending of the tubes and somewhat larger
shell diameter (due to the minimum U-bend
radius), making the cost of a U-tube heat exchanger
comparable to that of the fixed tube sheet heat
exchanger.
Figure 1.2 U-Tube Heat Exchanger[B1]
The advantage of a U-tube heat exchanger is that
because one end is free, the bundle can expand or
contract in response to stress differentials. In
addition, the outsides of tubes can be cleaned as
the tube bundle can be removed.
Floating Head:
The floating head heat exchanger is the most
versatile type of shell-and-tube heat exchanger,
and also is the costliest. In this design, one tube
sheet is fixed relative to the shell, and the other is
free to float within the shell.
Figure 1.3 Pull-through Floating Head Heat
Exchanger (TEMA S)[B1]
The TEMA S design is the most common
configuration in the chemical process industries.
The floating head cover is secured against the
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floating tube sheet by bolting it to an ingenious
split backing ring. This floating head closure is
located beyond the end of the shell and is
contained by a shell cover of a larger diameter.
1.1.2Classification based on service:
Basically, a service may be single phase (such as
cooling or heating of a liquid or gas) or two phase
(such as condensing or vaporizing). Since there are
two sides to shell-and-tube heat exchangers, this
can lead to several combinations of services.
Broadly services can be classified as follows:
• Single-phase (both shell-side and tube-side)
• Condensing (one side condensing and the other
single-phase)
• Vaporizing (one side vaporizing and the other
single-phase)
• Condensing/ vaporizing (one side condensing and
the other vaporizing)
The following nomenclature is normally used:
i. Heat Exchanger: Both sides single phase
and process streams (as opposed to
utility)
ii. Cooler: One stream a process fluid and
the other cooling water or air
iii. Heater: One stream a process fluid and
the other a hot utility such as steam or
hot oil
iv. Condenser: One stream a condensing
vapour and the other cooling water or air
v. Chiller: One stream a process fluid being
condensed at sub-atmospheric
temperature and the other a boiling
refrigerant or process stream.
vi. Reboilers: One stream a bottoms stream
from a distillation column and the other a
hot utility (steam or hot oil) or a process
stream.
1.1.3General TEMA exchanger classes-R, C and B.
There are three basic categories of shell and tube
type heat exchanger in heat exchanger in TEMA-
class R, class C, and class B. The difference I class is
the degree of severity of service the heat
exchanger will encounter. Descriptions of the three
classes are as follow:
i Class R – includes heat exchanger specified
for the most sever service in the
petrochemical processing industry. Safety
and durability are required for exchangers
designed for such rigorous conditions.
ii Class C – includes heat exchanged for the
generally moderate services and
requirements. Economy and overall
compactness are the two essential features
of this class.
iii Class B – are exchangers specified for
general process service. Maximum
economy and compactness are the main
criteria of design.
1.1.4 According to process requirement:
Process requirements dedicate the type of design
used. Figure shows some of the type of the major
construction. The standard TEMA classification of
exchanger is use the shell identification and
number with the exchanger designation type.
1.2 Introduction to Heat Exchanger Components
1. Shell 16. Tubes (U-type)
2. Shell cover 17. Tie rods and spacers
3. Shell flange
(channel end)
18. Transverse (or cross) baffles
or support plates
4. Shell flange (cover
end)
19. Longitudinal baffles
5. Shell nozzle or
branch
20. Impingement baffles
6. Floating tube
sheet
21. Floating head support
7. Floating head
cover
22. Pass partition
8. Floating head
flange
23. Vent connection
9. Floating head
gland
24. Drain connection
10. Floating head
backing ring
25. Instrument connection
11. Stationary tube 26. Expansion bellows
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sheet
12. Channel or
stationary head
27. Support saddles
13. Channel cover 28. Lifting lugs
14. Channel nozzle or
branch
29. Weir
15. Tube (straight) 30. Liquid level connection
1.3 Basic Component of Shell and Tube Heat
Exchanger Components:
Shell:
Shell is the container for the shell fluid and the tube
bundle is placed inside the shell. Shell diameter
should be selected in such a way to give a close fit
of the tube bundle.
Tube:
Tube OD of ¾’’ and 1’’ are very common to design
a compact heat exchanger. The most efficient
condition for heat transfer is to have the
maximum number of tubes in the shell to increase
turbulence. The tube thickness should be enough
to withstand the internal pressure along with the
adequate corrosion allowance.
2.1.1 Tube pitch, tube-layout and tube-count
Tube pitch is the shortest centre to centre
distance between the adjacent tubes. The tubes
are generally placed in square or triangular
patterns (pitch) as shown in the Figure 2.8.The
widely used tube layouts are illustrated in Table
1.1
Table 1.1 Common tube layouts
Tube OD, in Pitch type Tube pitch, in
¾ Square 1
1 - 1 ¼
¾ Triangular 15/16
¾ - 1
The number of tubes that can be accommodated in
a given shell ID is called tube count. The tube count
depends on the factors like shell ID, OD of tube,
tube pitch, tube layout, number of tube passes,
type of heat exchanger and design pressure.
Figure 1.7 Heat exchanger tube-layouts[B1]
2. LITERATURE REVIEW
Vindhya Vasiny Prasad Dubey, Raj Rajat Verma:[1]- This paper is concerned with the study of shell & tube type heat exchangers along with its applications and also refers to several scholars who have given the contribution in this regard. Moreover the constructional details, design methods and the reasons for the wide acceptance of shell and tube type heat exchangers has been described in details inside the paper.
M. M. El-Fawal, A. A. Fahmy and B. M. Taher:[2]- In this paper a computer program for economical design of shell and tube heat exchanger using specified pressure drop is established to minimize the cost of the equipment. The design procedure depends on using the acceptable pressure drops in order to minimize the thermal surface area for a certain service, involving discrete decision variables. Also the proposed method takes into account several geometric and operational constraints typically recommended by design codes, and provides global optimum solutions as opposed to local optimum solutions that are typically obtained with many other optimization methods.
M.Serna and A.Jimenez:[3]-They have presented a compact formulation to relate the shell-side pressure drop with the exchanger area and the film coefficient based on the full Bell–Delaware method. In addition to the derivation of the shell side compact expression, they have developed a compact pressure drop equation for the tube-side stream, which accounts for both straight pressure drops and return losses. They have shown how the compact formulations can be used within an efficient design algorithm. They have found a satisfactory performance of the proposed
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algorithms over the entire geometry range of single phase, shell and tube heat exchangers.
Andre L.H. Costa, Eduardo M. Queiroz:[4]-Studied that techniques were employed according to distinct problem formulations in relation to: (i) heat transfer area or total annualized costs, (ii) constraints: heat transfer and fluid flow equations, pressure drop and velocity bound; and (iii) decision variable: selection of different search variables and its characterization as integer or continuous. This paper approaches the optimization of the design of shell and tube heat exchangers. The formulation of the problem seeks the minimization of the thermal surfaces of the equipment, for certain minimum excess area and maximum pressure drops, considering discrete decision variables. Important additional constraints, usually ignored in previous optimization schemes, are included in order to approximate the solution to the design practice.
G.N. Xie, Q.W. Wang , M. Zeng, L.Q. Luo:[5]- carried out an experimental system for investigation on performance of shell-and-tube heat exchangers, and limited experimental data is obtained. The ANN is applied to predict temperature differences and heat transfer rate for heat exchangers. BP algorithm is used to train and test the network. It is shown that the predicted results are close to experimental data by ANN approach. Comparison with correlation for prediction heat transfer rate shows ANN is superior to correlation, indicating that ANN technique is a suitable tool for use in the prediction of heat transfer rates than empirical correlations. It is recommended that ANNs can be applied to simulate thermal systems, especially for engineers to model the complicated heat exchangers in engineering applications.
B.V. Babu, S.A. Munawarb:[6]- in the present study for the first time DE, an improved version of genetic algorithms (GAs), has been successfully applied with different strategies for 1,61,280 design configurations using Bell’s method to find the heat transfer area. In the application of DE, 9680 combinations of the key parameters are considered. For comparison, GAs are also applied for the same case study with 1080 combinations of its parameters. For this optimal design problem, it is found that DE, an exceptionally simple evolution strategy, is significantly faster compared to GA and yields the global optimum for a wide range of the key parameters.
Resat Selbas, Onder Kızılkan, Marcus Reppich:[7]- Applied genetic algorithms (GA) for the optimal design of shell-and-tube heat exchanger by varying the design variables: outer tube diameter, tube layout, number of tube passes, outer shell diameter, baffle spacing and baffle cut. From this study it was concluded that the combinatorial algorithms such as GA provide significant improvement in the optimal designs compared to the traditional designs. GA application for determining the global minimum heat exchanger cost is significantly faster and has an advantage over other methods in obtaining multiple solutions of same quality.
Zahid H. Ayub:[8]-A new chart method is presented to calculate single-phase shell side heat transfer coefficient in a typical TEMA style single segmental shell and tube heat exchanger. A case study of rating water-to-water exchanger is shown to indicate the result from this method with the more established procedures and software available in the market. The results show that this new method is reliable and comparable to the most widely known HTRI software.
Yusuf Ali Kara, Ozbilen Guraras:[9]-Prepared a computer based design model for preliminary design of shell and tube heat exchangers with single phase fluid flow both on shell and tube side. The program determines the overall dimensions of the shell, the tube bundle, and optimum heat transfer surface area required to meet the specified heat transfer duty by calculating minimum or allowable shell side pressure drop. He concluded that circulating cold fluid in shell-side has some advantages on hot fluid as shell stream since the former causes lower shell-side pressure drop and requires smaller heat transfer area than the latter and thus it is better to put the stream with lower mass flow rate on the shell side because of the baffled space.
Su Thet Mon Than, Khin Aung Lin, Mi Sandar Mon:[10]- In this paper data is evaluated for heat transfer area and pressure drop and checking whether the assumed design satisfies all requirement or not. The primary aim of this design is to obtain a high heat transfer rate without exceeding the allowable pressure drop.
3. PROBLEM IDENTIFICATION Problem definition:
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The most commonly used baffle is the segmental
baffle, which forces the shell-side fluid to go
through in a zigzag manner. But there are three
major drawbacks in the conventional shell-and-
tube heat exchangers with segmental baffles
(STHXSB):
(1) it causes a large shell-side pressure drop;
(2) it results in a dead zone in each compartment
between two adjacent segmental baffles, leading to
an increase of fouling resistance;
(3) the dramatic zigzag flow pattern also causes
high risk of vibration failure on tube bundle.
Thus, higher pumping power is often needed to
offset the higher pressure drop under the same
thermal load. Therefore, it is essential to develop a
new type of STHXs with improved baffles and
reduce pressure drop while maintaining and even
increasing shell side heat transfer performance.
Helical baffle heat exchangers have shown very
effective performance especially for the cases in
which the heat transfer coefficient in shell side is
controlled; or less pressure drop and less fouling
are expected. It can also be very effective, where
heat exchangers are predicted to be faced with
vibration condition.
From experimental performance, validation is to be
carried out. One design problem is taken from the
SAL STEEL, KANDLA as a case study and design
optimization of Heat exchanger and validate the
result with the software data.
Limitations:
1) Thermal and mechanical design should be
consider as basic aspects.
2) Design of shell and tube heat exchanger
has to be done in accordance to ASME
and TEMA standards.
3) The materials and size for the shell, tubes
and other components are to be selected
as available in Indian market.
Rating and sizing are the main problems related
with the STHX.
For Rating:
Experimental performance is done on the fixed
designed STHX and calculate the heat transfer
coefficient and effectiveness. Validation is to be
carried out which gives the result comparison with
that of experimental result. For the effective and
satisfactory solution of the given problem, a
systematic step by step procedure is required to be
followed as under: Calculation of heat transfer co
efficient and effectiveness of the experimental
data.
1) Validation of CFD code with experiment data.
2) Analytical calculation of mechanical design
data.
3) CFD analysis of shell and tube heat exchanger
for different number of tubes and optimising
result for greater effectiveness.
For sizing problem:
Design problem from a company has been taken as
a case study. For that purpose following steps are
required:
1. Thermal design and mechanical design is
calculated analytically.
2. Selection of the tube diameter, and other
data according from the different
standard.
3. Mass flow rates and inlet temperatures
are kept constant, no of tubes are to be
varied for effective heat transfer.
4. Calculation of the no of tubes required is
done by using CFD.
4. METHODOLOGY
Heat exchanger thermal design problems may be categorized primary as rating and sizing problems. The fluid outlet temperatures, total heat transfer capability, and pressure drops on each side of the heat exchanger are then determined in the rating problem. In contrast, in the sizing problem, the core lengths, surface areas and core dimensions are to be determined. Inputs to the sizing problems are surface geometries (including their heat transfer and pressure drop characteristics), fluid flow rates inlet and outlet fluid temperatures, fouling factors,
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and pressure drop on each side. The sizing problem is also sometimes referred to as the design problem Heat Exchanger design methodology for optimum design is illustrated in fig-4.1, which include various quantitative steps involved in arriving at the optimum heat exchanger design. These steps include thermal and hydraulic design, mechanical design, evaluation procedure and costing. Now mechanical design is done to ensure the mechanical integrity of the exchanger under steady and transient operating conditions.
A proper selection of the material and method of bonding fins thickness.
A proper selection of the material and method of bonding fins to plates or tubes is made depending upon the operating temperatures, pressure and fluids.
A proper selection of headers, tanks, manifolds, nozzles or pipes is made to ensure uniform flow distribution through the exchanger passages.
Several option solutions may be available when the thermal and mechanical designs are completed. The designer then considers the evaluation procedure (evaluation criteria and tread-off factors.) and cost estimating to arrive at an optimum solution.
4.1 Testing of the performance: Different types of tests are employed for the heat exchangers. For the evaluation of the heat transfer, pressure drop, temperature distribution and velocity by using small models to acceptance test of large full scale units. The selection and delineation of the test to be run, the design of the test set up, the conduct of the tests.
4.2 Heat transfer based performance test: a Heat Balances:- In the analysis of the heat
transfer test data is the heat balance obtained by comparing the heat given up by the hot fluids the heat absorbed by the cold fluid. The difference between these two quantities can be compared with the estimated heat losses.
b Temperature Stabilization:- For heat transfer performance tests, the test procedure should be worked out concurrently with the design of the test rig to facilitate the conduct of the test and the reduction of the test data. Depending on the size of unit, the heat capacity of various components m the test setup, and heat losses, it is usually necessary
to stabilize from several minutes to several hours for each point in order to obtain good equilibrium conditions and Constant. If room air is used care should be taken to avoid temperature irregularities arising from the opening and closing of door and windows
Correlation of data
It always important to correlated the experimentally evaluated performance of the heat exchanger with the analytically. This is desirable partly to check both the design and testing techniques and partly to provide the engineer to with a better background for future work of a similar nature. In reducing test data, first step in deciding how we organise •and reduce the data for finding out to which the physical properties of the fluid changes with the temperature covered in the test.
4.3 Flow Test: Tests of this sort may be carried out with simple models, since no provisions for heat addition or extraction need be employed. In these tests the only requirement is that the model be geometrically similar and that the Reynolds number be in the range of interest. Thus the tests may be carried out with water or air rather than with fluids that would be difficult to handle. Air is especially suited to tests of this sort, because the models can be inexpensive in construction and small leaks will not make a mess.
4.4 Structural tests:
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Structural tests on heat exchanger components such as pressure vessels or head can be carried out using any of a variety of techniques. Probably the most common approach is to build a fractional-or full-scale model of the structural element in question and determine the stress distribution with strain gauges. These can be applied in gauge lengths of as little as 6 mm. In one instance some 1300 strain gauges were installed on a 1/5-scale model of a complex pressure vessel; the cost of the test amounted to approximately 3% of the cost of the completed vessel, but it increased enormously the degree of confidence that could be placed in the design
4.5 Leak Test The problem related to the heat exchanger is to find out the location of the leakage and try to detect it. For that purpose various testing methods are applied.
I. Soap Bubble Test:
II. Rate of pressure rise:
III. Helium Leak Test
5. EXPERIMENTAL SET UP
5.1 Experimental Set up and Specification data of
Shell and tube heat exchanger:
Table 5.1Specification data
Tube Material: Stainless
steel
Tube side fluid: warm
water
Tube side pass number:
1
Tube Arrangement:
Triangular
Tube number: 24 Tube Effective Length:
750 mm
Tube Pitch: 16 mm Tube type: smooth
Tube inner diameter:
4.5 mm
Tube outer diameter:
6.35 mm
Shell inner
diameter:116 mm
Shell side Fluid: cool
water
Baffle No: 4 Baffle Type: 25% cut
Baffle Spacing: 300mm Baffle geometry Angle:
900
Figure 5.1 Dimension of the experimental set up
Table 5.2OBSERVATIONS
SR.no Hot water Cold water
INLET OUTLET INLET OUTLET
Parallel 42ᵒC 32ᵒC 24ᵒC 28ᵒC
Counter 53ᵒC 39ᵒC 26ᵒC 35ᵒC
Specifications:
Specific heat water = 4.174 kJ/kg k
Inside area of tube = 𝐴𝐴𝑖𝑖 = 𝜋𝜋 × 4.5 × 10−3 ×0.75 × 24 = 0.2544 𝑚𝑚2
Outside Area of tube = 𝐴𝐴0 = 𝜋𝜋 × 6.35 × 10−3 ×0.75 × 24 = 0.359 𝑚𝑚2
Density of Water = 1000 kg/m3
For Parallel Flow:
1. Hot mass flow rate of the hot fluid mh = 1/th = 1/43 = 0.023 Lit/sec
2. Heat transfer rate at hot side Qh = mhcp∆Th
=0.023 × 4.174 × (42 − 32) =1.34 kJ/sec
3. Mass flow rate of cold fluid mc=1/tc= 1/26 = 0.038 Lit/sec
4. Heat transfer rate at cold side Qc = mc
cp∆th
= 0.038× 4.178 × 4
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= 0.6429 kJ/sec
∆T𝑙𝑙𝑙𝑙 =∆T𝑖𝑖 − ∆Tℎ
log∆T𝑖𝑖∆Tℎ�
𝑖𝑖
Where,∆T𝑖𝑖 = Thi -Tci= 42 – 24 = 18ᵒC
∆Tℎ = Tho - Tco = 32 – 28 = 4ᵒC ……….For Parallel Condition
5. Heat Transfer Co efficient
i) Inside Heat Transfer Co efficient
𝑈𝑈ℎ =𝑄𝑄ℎ
𝐴𝐴𝑖𝑖 × ∆T𝑙𝑙𝑙𝑙=
1.34 0.2544 × 21.43= 0.2457 kW/𝑚𝑚2ᵒC
ii) Outside Heat Transfer Co efficient
Uc =Qc
Ao × ∆Tlm=
0.6429 0.359 × 21.43= 0.0835 kW/m2ᵒC
6. Effectiveness of heat Exchanger,
𝜀𝜀 = (Thi − Tho )(Thi − Tci)�
….………Because mh< R mc
𝜀𝜀 = 1018
= 0.55
6. REFERENCES
1. Vindhya Vasiny Prasad Dubey1, Raj Rajat Verma Shell & Tube Type Heat Exchangers: An Overview vol.2 issue 6 -2014 ISSN (ONLINE): 2321-3051 2. M. M. El-Fawal, A. A. Fahmy and B. M. Taher, “Modelling of Economical Design of Shell and tube heat exchanger Using Specified Pressure Drop”, 28 (2010) Journal of American Science. 3. M.Serna and A.Jimenez, “A compact formulation of the Bell Delaware method for Heat Exchanger design and optimization”, Chemical Engineering Research and Design, 83(A5) (2009): 539–550. 4. Andre L.H. Costa, Eduardo M. Queiroz, “Design optimization of shell-and-tube heat exchangers”, Applied Thermal Engineering 28 (2008) 1798–1805. 5. G.N. Xie, Q.W. Wang , M. Zeng, L.Q. Luo, “Heat transfer analysis for shell and tube heat exchanger with experimental data by artificial neural networks approach”, Applied Thermal Engineering 27 (2007) 1096–1104. 6. B.V. Babu, S.A. Munawarb, “Differential evolution strategies for optimal design of shell and
tube heat exchanger”, Chemical Engineering Science 62 (2007) 3720 – 3739. 7. Resat Selbas, Onder Kızılkan, Marcus Reppich, “A new design approach for shell and tube heat exchanger using genetic algorithms from economic point of view”, Chemical Engineering and Processing 45 (2006) 268–275. 8. Zahid H. Ayub, “A new chart method for evaluating singlephase shell side heat transfer coefficient in a single segmental Shell and tube heat exchanger”, Applied Thermal Engineering 25 (2005) 2412–2420. 9. Yusuf Ali Kara, Ozbilen Guraras, “A computer program for designing of Shell and tube heat exchanger”, Applied Thermal Engineering 24(2004) 1797–1805. 10.Sadik kakac, “Heat Exchangers Selection, Rating and Thermal Design”, 2002.
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