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An Educational
Computer-Aided Tool forHeat Exchanger Design
F. L. TAN,1 S. C. FOK2
1School of Mechanical and Aerospace Engineering, Nanyang Technological University,
50 Nanyang Avenue, Singapore 639798
2Department of Mechanical Engineering, The Petroleum Institute in Abu Dhabi, Abu Dhabi, United Arab Emirates
Received 5 November 2004; accepted 18 November 2005
ABSTRACT: This paper presents the development of an educational computer-aideddesign tool for the shell and tube heat exchanger. The software integrates the thermo-
hydraulics analysis based on Kern method with the mechanical design based on Tubular
Exchanger Manufacturing Association (TEMA) Class C standard. The software allows the
user to experiment with different design specifications and visualize the solutions in the form
of performance data and engineering drawings. Technical drawings on the parts of the heat
exchanger, like the shell, tube, front and rear header, tube sheet and baffle plate, are producedby the software to assist the user in appreciating issues relating to practical fabrication and
costing. Through the correlation of the thermo-hydraulic performance, configurations and
dimensions with respect to the technical specifications, it is hoped that the user could better
appreciate the fundamentals of heat exchanger design. 2006 Wiley Periodicals, Inc. Comput Appl
Eng Educ 14: 7789, 2006; Published online in Wiley InterScience (www.interscience.wiley.com); DOI10.1002/cae.20073
INTRODUCTION
Heat exchangers are found in a wide variety of
applications in the aeronautical, process, chemical,power, and electronics industries. They can be
classified based on the flow arrangements and
construction [1]. The parallel flow, center flow, and
cross flow are the three basic flow arrangements.
Figure 1 shows a shell and tube heat exchanger, one of
the most commonly used heat exchangers. A shell and
tube heat exchanger consists of two primary parts, the
shell and tube, along with other secondary compo-
nents including the inlet and outlet nozzles, the baffleplates, tube sheets, tie rods, guiding plates, and sealing
strip.
Due to the wide applications of heat exchangers
in industries, courses in the thermal design and
analysis of these systems can be found in many
engineering schools. The main motivation of
these courses is on the rating and sizing of the
system components [2] to meet the design thermal
specifications. Rating concerns the evaluation of theCorrespondence to F. L. Tan ([email protected])
2006 Wiley Periodicals Inc.
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thermo-hydraulics performance given the geometrical
dimensions of the heat exchanger. Sizing determines
the exchanger configuration given the specifications
including temperatures, fluid, flow rates, pressure
drop, etc. This focus is critical as an oversized
exchanger can lead to unnecessary and excessive
power consumption, while an undersized system may
not produce the thermal requirements.The conventional process of rating and sizing the
components in a heat exchanger involves tedious and
lengthy routine calculations that are not only time
consuming but also highly prone to human error.
Furthermore, an iterative procedure would often have
to be adopted to investigate different possible
configurations. To facilitate the development process
and minimize the problems as a result of human
errors, heat exchangers in industries are increasingly
designed and analyzed using computer-aided design
tools [35]. Many of these commercially availableprograms had included the heat exchanger design
standards from American Society of Mechanical
Engineers (ASME) and Tabular Exchangers Manu-
facturers Association (TEMA).
The industrial trend of using computer-aided
tools has compelled many universities to develop and
introduce computer software in courses for the design
and optimization of heat exchangers [6,7]. The
objective of using software in the education of heat
exchanger designs is not only to reinforce the student
understanding of the underlying principles of exchang-
er design, but also to allow students to bridge the gap
between theoretical consideration and engineering
practice. For example, the heat exchanger simulator(HES) [6] is developed for the training of chemical
engineers, the emphasis of which is in the analysis of
the real industrial heat exchanger problems. HES
allows students to concentrate on the analysis of the
solutions with respect to the practical problem but this
might not necessarily give students additional insight
into the fundamental theories. On the other hand, the
Shell and Tube Heat Exchanger Design Software
(STHEDS) [7] is an educational tool that caters for the
thermo-hydraulic design and flow-induced vibration
analysis of the shell and tube heat exchangers.
STHEDS allows students to better understand the
fundamentals in heat exchanger design but lacks the
mechanical design capabilities to enable students to
appreciate practical engineering considerations. In
industries, the thermal and hydraulic analysis of heat
exchangers cannot be viewed as a stand-alone process.The analysis must be integrated with other develop-
ment activities, including manufacturing, costing,
system life cycle support, etc. Otherwise, there is
the danger that the design is difficult to manufacture,
requires high-production cost, or contains flaws that
production engineers have to correct or send back for
redesign.
This paper describes an educational computer-
aided design tool for heat exchanger that integrates
thermo-hydraulics analysis with mechanical design.
This software focuses on the shell and tube heat
exchanger and aims to complement the theories
behind the thermo-hydraulics design analysis with
practical mechanical design details required for
costing and production. Program Description and
Development Consideration section gives an overall
description of the development consideration. Pro-
gram Implementation section covers the program
implementation. The verification of the program is
discussed in Validation With Benchmark Problem
section. Conclusions and future work can be found in
Conclusion section.
PROGRAM DESCRIPTION ANDDEVELOPMENT CONSIDERATION
The heat exchanger mechanical design software is
developed to educate users in heat exchanger design.
The aim is to allow users not only to better understand
the fundamentals associated with heat exchanger
designs through thermo-hydraulic analysis, but also
to appreciate the fabrication, costing, and mainte-
nance aspects through evaluation of the detailed
Figure 1 Shell and tube heat exchanger.
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mechanical drawings. The program is designed to
cater for both students and novice engineer to heat
exchanger design.
The program is developed in Java [8], a
programming language syntactically based on C and
C
. Java is not a procedural programming lan-
guage. It adopted an object-orientated programmingapproach and the code can be reused through
inheritance without sacrificing the functionality of
already implemented systems. This feature would
facilitate future expansion of the software. Figure 2
shows the flowchart of the logic behind the software
development. As in practical situations, the thermo-
hydraulics analysis should be initiated after the user
has input and selected the key parameters of the heat
exchanger requirements. Following the rating, the
results of the analysis and the input requirements
should be displayed for the user evaluation. The user
can modify the parameters until a satisfactory design
that meets the specifications (e.g., pressure drop) isobtained. This process will allow the users to reinforce
their understanding of the fundamentals by relating
the outcomes with input parameters. Once a satisfac-
tory design is obtained, the user can generate
the detailed mechanical drawings for the shell, tube
layout, headers, tube-sheets, and baffle plates.
These details will allow the user to further investigate
various issues associated with fabrication, costing and
maintenance.As an educational tool, the program must be user
friendly. GUI provides the key to making the program
easy to learn and simple to use. Figure 3 shows the
framework of the program structure. The program
structure allows the user the free choice of access to
whichever part of the program through menu bar,
which currently contains five main menus: design,
analysis, drawing, file and help. In the software
development, human-computer interaction has been
considered in the menu development. The number of
keystrokes required for user input has been kept to a
minimum. This will minimize the number of errors
and mistakes.Figure 4 shows the Design Menu, which is
automatically initiated at the start of program for the
SELECTION, INPUT DATA
& REQUIREMENT
OF
HE DESIGN PARAMETER
RATING OF THE DESIGNTHRU
THERMAL & HYDRULIC
ANALYSIS
MODIFICATION OF DESIGN
PARAMETER
EVALUATE THE DESIGN BY
THERMAL, HYDRAULIC &
DIMENSION CONSTRAINT
GENERATING HE
COMPONENT
DRAWINGS
PRINT OUT
UNACCEPTABLEACCEPTABLE
Figure 2 Design logic of heat exchanger design software.
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user to input and select key design parameters. These
include the type of exchanger, tube/shell profile, fluids
used, and temperature requirements. Some parameters
like mass flow rate and fluid inlet and outlet
temperature require user input. If this type of input
field is accidentally left blank, an error message will
be generated to prompt the user for input. Other
parameters like exchanger type can be selected by the
PROGRAM
Main Menu FILE HELP
THERMAL DESIGN
HYDRAULIC DESIGN
DATAENTRIES
ANALYSISDESIGN DRAWINGS
SHELL
TUBE/TUBE SHEETBAFFLE PLATE
FRONT HEADER
REAR HEADER
FULL ASSEMBLY
Figure 3 Program menu of heat exchanger design software.
Figure 4 Design menu.
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user. For these selections, default values will be used
if these are not specified by the user. Some parameters
like fluid density and fluid-specific heat are self-
generated when the type of fluid used is selected.
The Analysis menu contains two sub-menus:
thermal design and hydraulic design. Figure 5 shows
the results of a typical thermal design analysis. It givesboth the shell and tube fluid properties as well as the
tube profile. Figure 6 shows the results of a typical
hydraulic design analysis. It gives the calculated result
of fluid-related properties and vital information on
the pressure drop for both the shell-side fluid and the
tube-side fluid. A warning message is generated by the
software to advise the user to resize the heat
exchanger if the calculated pressure drop exceeded
that of the specified allowable pressure drop.
The Drawing Menu contains sub-menus to
generate the drawings and dimension details for the
shell, tube/tube sheet, baffle plate, front header, rear
header, and the fully assemble heat exchanger. Whena sub-menu is selected, the drawing of the selected
component will be displayed together with a pop-up
screen showing the dimensions (Fig. 7). Dimension
pop-up can be hidden by clicking X and be recalled
by clicking on the show button as shown in Figure 8.
The File Menu contains sub-menus for New,
Open, Save, and Exit: these are standard administra-
tion facilities in Widows based software. These allow
designs to be saved in .he format for later recall
using the OPEN sub-menu. The Help Menu
contains standard tutorial facilities to guide the user
not only on the use of the software but also on thedesign of the shell and tube heat exchanger. This
facility will further aid the user understanding on the
fundamentals and practice of heat exchanger design.
PROGRAM IMPLEMENTATION
Many methods of designing heat exchanger have been
developed in the past 50 years. The Kern method is
used in this work for the thermo-hydraulic design
analysis. The following sub-sections give the details
of the thermal analysis, hydraulic analysis, and the
fundamentals relationships in the mechanical design.
Thermal Analysis
Heat exchangers enable exchanges of thermal energy
among two or more fluids at different temperatures.
Figure 5 Thermal Analysis menu.
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Figure 6 Hydraulic Analysis menu.
Figure 7 Drawing with dimension pop-up screen.
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Thermal analysis of a heat exchanger is based on the
conservation of energy. Ideally, q the heat released by
the hot fluid should equal the heat gain by the cold
fluid:
_mcCpcTci Tco UAFDTm 1
_mhCphThi Tho UAFDTm 2where the subscripts c refers to cold, h refers to
hot, i refers to inlet, and o refers to outlet
conditions. Let DT1 be the temperature difference of
the two fluids at one end of the heat exchanger and
DT2 be the temperature difference of the two fluids at
the other end of the heat exchanger. Using the log
mean temperature difference (LMTD) approximation
DTm DT1 DT2ln DT1=DT2 3
the average overall heat transfer coefficient and the
heat transfer area that governs the size of the heat
exchanger can be determined as
U 1do
di
1
hi do
diRfi do ln do=di
2kmRfo 1
ho
4
The LMTD correction factor F, which varies with the
type of shell, the number of shell pass and the number
of tube pass, can be obtained from charts in the TEMA
standard handbook. The heat transfer coefficient for
inside flow is given by
hi Nudi
k 5
The Nusselt number Nu is determined using empirical
correlation based on the flow conditions governed by
the Reynolds number.
The heat transfer coefficient for outside flow, hocan be calculated using
ho 0:36kDe
Res0:55Pr1=3 bw
0:14 6
where
Res GsDe
7
Pr Cpk
8
Figure 8 Drawing without dimension pop-up screen.
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The shell-side mass velocity Gs is given by
Gs _mAs
9
where As, the bundle cross flow area at the center of
the shell, is given as
As DsCBPT
10
and C, the clearance between adjacent tubes, is
defined as
C PT do 11The equivalent diameter of the shell, De, is
dependent on the layout of the tube sheet. Generally
for any pitch layout, De can be assumed to be four
times the net flow area (as layout on the tube sheet)
divided by the wetted area. The tube layout is
characterized by the included angle between tubes,
such as 308, 458, 608, and 908. For a square pitch
layout, the equivalent diameter is given by
De 4P2T pd2o
4
pdo12
For a triangular pitch layout, the equivalent diameter
is given by
De 4 P2T
ffiffiffi3
p=4
pdo2=8 h ipdo=2 13
Hydraulic Analysis
The hydraulic analysis consists of the determination
of shell side and tube side pressure drop. The pressure
drop on the shell side is calculated using the following
expression:
Dps f DsNB 1G2s
2rsDeFs14
where Fs b=w 0:14
. The number of baffles NBcan be calculated by NB L=B. Note that (NB 1) isthe number of times the shell fluid passes the
tube bundle. The friction factor f can be determinedfrom
f exp0:576 0:19 lnRes 15for 400 < Res GsDes 1 10
6.
The pressure drop Dpi at tube side can be
calculated using
Dpt 4f LNpdi
4Np
tU2m
216
Equation (16) has taken into the account the sudden
expansion and contraction the tube fluid experiences.
For the laminar flow, Re Umditm
< 4; 000
f 16Re
17
For the turbulent flow, Re 4000