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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.

77


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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.

COMPUTER-AIDED TOOL FOR HEAT EXCHANGER DESIGN 79


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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

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