Desthex Manual

7/29/2019 Desthex Manual

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DESTHEx, Versin 1.0

DEsign ofShell-and-TubeHeatExchangers

Medardo Sernaa, Jos M. Poncea and Arturo Jimnezb

aFacultad de Ingeniera Qumica, Universidad Michoacana de San Nicols de Hidalgo,

58060, Morelia, Mich. MxicobDepartamento de Ingeniera Qumica, Instituto Tecnolgico de Celaya,

38010, Celaya, Gto. Mxico

Welcome to version 1.0 ofDESTHEx (DEsign ofShell-and-TubeHeat Exchangers).

This software package can be used to design shell-and-tube heat exchangers. The program has

been written in C++ and runs on a PC with Windows 2000. It uses important features supplied

by Windows, such as mouse control, pushbuttons and input boxes.

Design Problem

As indicated by Jegede and Polley (1992), it is convenient to formulate an algorithm

for designing shell and tube heat exchangers that ensures that the pressure drops within the

exchanger are equal to the specified values of the allowable pressure drops for both streams;

meeting this condition provides the smallest exchanger area for a given duty. Based on this

principle, Serna and Jimnez (2004) developed simple analytical expressions that relate the

fluid pressure drop, the exchanger area and the film heat transfer coefficient for both tube-side

and shell-side streams. The shell-side expression has been derived based on the Bell-

Delaware method (Taborek, 1983) and does not contain any simplification or approximation;

thus, this equation has the same accuracy as the full Bell-Delaware method and can be used

under the entire range of geometric parameters of interest. For the tube side of the exchanger,

the compact formulation for the pressure drop accounts for both straight pressure drop and

return losses in a simple manner. These formulations replace the use of the approximate Kern

method (1950) for the shell-side stream, and overcome certain simplifying assumptions made

in previous works (Jegede y Polley, 1992; Polley et al., 1990). The compact expressions

provide the basis for the simple and accurate design algorithm of single-phase shell-and-tube

heat exchangers in steady state described in the work by Serna and Jimnez (2004).


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The proposed design approach, nonetheless, still requires a significant amount of

numerical calculations to obtain the geometric parameters and the size of a shell and tube heat

exchanger for a given set of specifications. The computer code implements a design algorithm

that is independent of the nature of the hot and cold fluids to be processed and of the

geometric data for the system. With such package, students or practicing engineers should be

able to readily solve a shell-and-tube heat exchanger design problem, giving more attention to

the design problem instead of dealing themselves with extensive numerical calculations.

DESTHEx is the software package that implements the design algorithm developed by

Serna and Jimnez (2004). The package has been found simple to use and generally provides

fast and accurate results.

General Software Overview

Installing DESTHEx on a Hard Disk

The DESTHEX.ZIP program, which is downloaded through the Internet from the

website http://posgrado.fiq.umich.mx/~division/pag6.html, creates the DESTHEX

subdirectory on a hard disk when it is decompressed.

The DESTHEX subdirectory will contain:

DESTHEX.EXE Compiled program that performs shell-and-tube heat exchanger design

calculations

EX1.DAT Example file of a design problem reported by Serna and Jimnez

(2004)

Getting Started

The program can be run from Windows by double clicking from the File Manager or

Explorer.

As the DESTHEx program is initially executed, the main window shown in Figure 1

will appear. This is a simple user interface that aids the use of the program. The main window

is separated into three different sections as shown in Figure 1. In the top section, the user can

provide the input data for design. The medium section shows the data output or results. The

bottom section contains four pushbuttons: EXTRACT DATA, SAVE DATA,

EXECUTE PROGRAM, and EXIT.

The variables of the main window are listed in Table 1.


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Figure 1. User-friendly interface.

Table 1

Variables of DESTHEx window and description.

Variable Description

ASHELL Maximum allowable area per shell

BC Baffle cut as percent of inside shell diameterDI Inside tube diameter

DO Tube outside diameter

FTMIN The FTminimum correction factor for multipass heat exchangers. A lower

bound on the FT correction factor of 0.80 is considered by the program to

ensure practical designs, unless another value is set by the user (in that

case, a FTvalue grater than 0.75 is suggested)

IHAZ Integer in {1,,4} that specifies which type of tube bundle construction

is to be used: 1. Fixed tubesheet; 2. Packed floating-head bundle; 3. Split-

ring floating-head bundle; and4. Pull-through floating-head bundle.

LAYOUT Integer in {1,,3} which specifies which tube layout characteristic angleis to be used: 1. Triangular 30; 2. Square 90; 3. Square 45.


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LBB Inside shell-to-tube bundle bypass clearance (diametral)

LBS Inside shell-to-baffle clearance (diametral)

LPL Tube lane partition bypass width

LTB Tube outside diameter-to-baffle hole clearance (diametral)

LTP Tube layout pitch

LTS Tubesheet thicknessNPASS Number of tube passes

NSS Number of sealing strips (pairs)

RLI Ratio of inlet baffle spacing to central baffle spacing

RLO Ratio of outlet baffle spacing to central baffle spacing

Input Data

In the Input Data section the following parameters have to be set.

Process Data: mass flow rate, allowable pressure drop, inlet temperature, outlettemperature and fouling resistance for both fluids.

Geometric Data: inside tube diameter, tube outside diameter, tube layout pitch, tube layoutcharacteristic angle, number of tube passes, minimum value of the FT correction factor,

baffle cut, number of sealing strips, shell-side clearances (optional)*, tubesheet thickness

(optional)*, tube lane partition bypass width (optional)*, and type of tube bundle

construction.

Physical Properties: viscosity, heat capacity, thermal conductivity and density of bothfluids, as well as the tube wall material thermal conductivity.

The values for the input parameters can be typed directly in the corresponding boxes

or loaded from a data file created by DESTHEx. When this option is selected, the user should

type the name of the file to load in the left-top box, without including the file extension DAT;

then the EXTRACT DATA button must be used for loading the desired DESTHEx data file

from the disk.

If any existing Input Data has to be saved, the user must type a name to use for the

data file in the left-top box; then, by clicking the SAVE DATA button, the current Input

Data is saved in a DESTHEx file on disk.

*

These variables may be specified by the user or calculated by the program. The calculated values of tube-to-baffle clearance, shell-to-baffle clearance, shell-to-bundle clearance, tubesheet thickness, and tube lane partitionwidth are those recommended by Taborek (1983).


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Figure 2. Output Data screen.

Output Data

When the necessary input data are provided, the program can be run by clicking the

EXECUTE PROGRAM button. The summarized results from the program will then appear

in the medium section of the main window. A detailed output data for the EX1.DAT data file

is shown in Figure 2, which includes:

Geometric Data: inside shell diameter, overall nominal tube length, effective tube lengthfor heat transfer area, central baffle spacing, inlet baffle spacing, outlet baffle spacing, total

number of tubes, number of baffles, and total heat transfer area.

Process Information: heat duty, logarithmic mean temperature difference, corrected meantemperature difference, correction factor for logarithmic mean temperature difference for

non-countercurrent flow (optional), shell-side heat transfer coefficient, tube-side heattransfer coefficient, shell-side flow velocity, tube-side flow velocity, shell-side Reynolds


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number, tube-side Reynolds number, shell-side Prandtl number, and tube-side Prandtl

number

One can easily change some input parameters after each program execution. This is

done by filling out the corresponding boxes in the Input Data section with the desired values

of input parameters. Care must be taken, however, to supply data or changes that match the

energy balance for each stream of the exchanger.

References

Jegede, F.O. and Polley, G.T., 1992, Optimum heat exhanger design, Trans IChemE Part A,

70: 133.

Kern, D.Q., 1950, Process heat transfer, McGraw-Hill.

Polley, G.T., Panjeh Shahi, M.H. and Jegede, F.O., 1990, Pressure drop considerations in the

retrofit of heat exchanger networks, Trans IChemE Part A, 68: 211.

Serna, M. and Jimnez, A., 2005, A compact formulation of the Bell-Delaware method for

heat exchanger design and optimization, to appear inTrans IChemE Part A

.

Taborek, J., 1983, Shell-and-tube exchangers: Single-phase flow, in: E. U. Schlunder (Ed.),

Heat exchangers design handbook, Vol. 3, Section 3.3, Hemisphere Publishing Corp.

Documents

Desthex Manual