c documents and settings asim local settings temp ~hha9

Shell&Tube Thermal Design of Shell & Tube Heat Exchangers

Shell&Tube Input

Shell&Tube Results

Shell&Tube Getting Started Guide

Shell and Tube Heat Exchanger Geometry

Quick Guide to Geometry Selection

Shell&Tube Input Problem Definition

Headings/Remarks

Application Options – Calculation Mode, Fluid allocation, Application Types, Equipment Types

Process Data – Temperatures, Pressures, Flows, Quality, Pressure Drops, Fouling, Heat Load

Physical Property Data

Stream Composition

Stream Properties – Property Databanks, Stream Definition, Property Tables

Exchanger Geometry

Geometry Summary – Geometry, Tube Layout

Shell/Heads/Flanges/Tubesheets – Shell/Heads, Covers, Tubesheets, Flanges

of 47Shell&Tube Thermal Design of Shell & Tube Heat Exchangers

6/3/2010file://C:\Documents and Settings\Asim\Local Settings\Temp\~hhA90D.htm

Tubes – Tube, Low Fins, Longitudinal Fins, Inserts, KHT Twisted Tubes

Baffles/Supports – Baffles, Tube Supports, Longitudinal Baffles, Variable Baffle Pitches

Bundle Layout – Layout Parameters, Layout Limits/Pass Lanes, Tie Rods/Spacers, Tube Layout

Nozzles – Shell Side Nozzles, Tube Side Nozzles, Domes/Belts, Impingement

Thermosiphon Piping – Thermosiphon Piping, Inlet Piping Elements, Outlet Piping Elements

Construction Specifications

Materials of Construction – Vessel Materials, Cladding/Gasket Materials, Tube Properties

Design Specifications

Program Options

Design Options – Geometry Options, Geometry Limits, Process Limits, Optimization Options

Thermal Analysis – Heat Transfer, Pressure Drop, Delta T, Fouling

Methods/Correlations – General, Condensation, Vaporization, Enhancement Data

Calculation Options – Calculation Options

Shell&Tube Problem Definition The Problem Definition section includes the following screens:

Headings/Remarks

Application Options

Process Data

Shell&Tube Headings/Remarks The Headings/Remarks section includes the following screens:

TEMA Specification Sheet Descriptions



Shell&Tube Application Options The Application Options screen contains the following inputs:

General

Calculation Mode

Location of Hot Fluid

Select Geometry based on this Dimensional Standard

Calculation Method

Hot Side

Application

Condenser Type

Simulation Calculation

Cold Side

Application

Vaporizer Type

Simulation Calculation

Thermosiphon Circuit Calculation

Shell&Tube Process Data The Process Data screen contains the following inputs:



Fluid Name

Mass Flow Rate

Temperature

Vapor Mass Fraction

Operating Pressure

Pressure at Liquid Surface in Column

Heat Exchanged

Adjust if Over-Specified

Estimated Pressure Drop

Allowable Pressure Drop

Fouling Resistance

Physical Property Data Overview For each stream within the exchanger there are two input sections:

Composition

Properties

Within the Composition section, the Physical Property Package (Properties Data Source) can be selected.

The following property package options are available:

Aspen Properties

COMThermo

B-JAC Databank

User Specified Properties



Two other options are shown to indicate when the properties data have been generated by a process simulator. These are not facilities for generating properties with the stand-alone program:

Aspen Plus

HYSYS

The selection of the property package will dictate what subsequent inputs are requested and what screens may be displayed. The property package input will indicate where physical properties have come from or where they will be coming from.

The basic physical properties will consist of one to five data sets of stream properties at various temperature points which should encompass the operating temperatures of the exchanger. Each data set would represent a different operating pressure. It is recommended that multiple data sets at different pressure be used for applications involving changes of phase or gas only since the pressure change through an exchanger can significantly impact the properties and heat release curves for these applications. Data at two pressures are adequate for most exchangers, with more only needed when the pressure change in the exchanger is a significant fraction of the inlet pressure.

The Properties section includes the following screens:

Properties

Phase Composition

Component Properties

Properties Plots

See also:

Refrigerant Cross Referencing Table

Shell&Tube Exchanger Geometry The Exchanger Geometry section includes the following screens:

Geometry Summary



Shell/Heads/Flanges/Tubesheets

Tubes

Baffles/Supports

Bundle Layout

Nozzles

Thermosiphon Piping

Shell&Tube Geometry Summary The Geometry Summary section includes the following screens:

Geometry

Tube Layout

Shell&Tube Shell/Heads/Flanges/Tubesheets

The Shell/Heads/Flanges/Tubesheets section includes the following screens:

Shell/Heads

Covers

Tubesheets

Flanges

Shell&Tube Tubes The Tubes section includes the following screens:

Tube



Low Fins

Longitudinal Fins

Inserts

KHT Twisted Tubes

Shell&Tube Baffles/Supports The Baffles/Supports section includes the following screens:

Baffles

Tube Supports

Longitudinal Baffles

Variable Baffle Pitches

Shell&Tube Bundle Layout The Bundle Layout section includes the following screens:

Layout Parameters

Layout Limits/Pass Lanes

Tie Rods/Spacers

Tube Layout

Shell&Tube Nozzles The Nozzles section includes the following screens:



Shell Side Nozzles

Tube Side Nozzles

Domes/Belts

Impingement

Shell&Tube Thermosiphon Piping The Thermosiphon Piping section includes the following screens:

Thermosiphon Piping

Inlet Piping Elements

Outlet Piping Elements

Shell&Tube Construction Specifications The Construction Specifications section includes the following screens:

Materials of Construction


Shell&Tube Materials of Construction The Construction Specifications section includes the following screens:

Vessel Materials

Cladding/Gasket Materials

Tube Properties

Shell&Tube Design Specifications The Design Specifications section includes the following screens:


Shell&Tube Program Options



The Program Options section includes the following screens:

Design Options

Thermal Analysis

Methods/Correlations

Calculation Options

Shell&Tube Design Options The Design Options section includes the following screens:

Geometry Options

Geometry Limits

Process Limits

Optimization Options

Shell&Tube Thermal Analysis

The Thermal Analysis section includes the following screens:

Heat Transfer

Pressure Drop

Delta T

Fouling

Shell&Tube Methods/Correlations The Methods/Correlations section includes the following screens:

General

Condensation

Vaporization



Enhancement Data

Shell&Tube Calculation Options The items on this sheet let you specify whether to use the Standard or Advanced calculation method, and to select various options available with the Advanced method:

Calculation Method

Convergence Options

Maximum Number of Iterations

Convergence Tolerance - Heat Load

Convergence Tolerance - Pressure

Relaxation Parameter

Calculation Grid Resolution

Convergence Criterion

Calculation Step Size

Pressure Drop Options

Pressure drop calculations options - cold side

Pressure drop calculations options - hot side

Shell&Tube Results

Input Summary

Result Summary



Warnings & Messages

Optimization Path

Recap of Designs

TEMA Sheet

Shell&Tube Summary

Thermal / Hydraulic Summary

Performance – Overall Performance, Resistance Diagram

Heat Transfer – Heat Transfer Coefficients, MTD & Flux, Duty Distribution

Pressure Drop – Pressure Drop, Thermosiphon Piping, Thermosiphon Piping Elements

Flow Analysis – Flow Analysis, Thermosiphons and Kettles

Vibration & Resonance Analysis – Fluid-Elastic Instability, Resonance Analysis, TEMA Fluid Elastic Instability, TEMA Amplitude and Acoustic Analysis

Methods

Mechanical Summary

Exchanger Geometry

Setting Plan

Tubesheet Layout

Cost / Weights

Calculation Details

Analysis along Shell

Analysis along Tubes

Analysis for X and K shell



Shell&Tube Input Summary

This section provides you with a summary of the information specified in the input file.

It is recommended that you request the input data as part of your printed output so that it is easy to reconstruct the input, which led to the design.

Shell&Tube Result Summary

The Result Summary section includes the following screens:

Warnings & Messages

Optimization Path

Recap of Designs

TEMA Sheet

Shell&Tube Summary

Shell&Tube Warnings & Messages

Aspen Shell & Tube Exchanger provides an extensive system of errors, warnings and other messages to help you use the program. They are for the most part self explanatory, and contain information on the values of parameters which have led to the reported condition. There are several hundred messages built into the program, and these can be divided into number of types.

Range Checking Warning.

These relate to input values which are outside the range of what is normally expected. You should check that the input value referred to is correct. If so the message can usually be ignored, though for unusual exchanger geometries, or unusual fluid properties, it is likely that the uncertainty in the results is exacerbated.

Input Omission Error

These identify input parameters which are necessary for the program to run. Whether a particular parameter is necessary can depend on the values of other parameters. Required input is normally identified in the User interface, though there are occasionally instances where a required item is not highlighted in the Interface, or where an item is shown as required by the interface, does not lead to an



error when the program is run.

Range Checking Error

These identify input values which are beyond the range of what is permitted. They cause program execution to cease.

Results Warning

The run has completed, but problems have been identified with some part of the calculation, which indicate that some aspect of the results may be subject to more uncertainty than normal.

Results Error

The run has either failed to generate a significant part of the results, or failed to complete in some way that many of the results given should not be relied on.

Operation Warning

The run has completed, but is predicting operation which does not meet normal practice, or is in some other way inadvisable, or in extreme cases impracticable.

Advisory

There is some feature of the exchanger, or its operation which is unusual, and for which better alternatives may exist.

Notes

Any other information which may be useful.

Shell&Tube Optimization Path

This part of the output is the window into the logic of the program. It shows some of the heat exchangers the program has evaluated in trying to find one, which satisfies your design conditions. These intermediate designs can also point out the constraints that are controlling the design and point out what parameters you could change to further optimize the design.

To help you see which constraints are controlling the design, the conditions that do not satisfy your specifications are noted with an asterisk (*) next to the value. The asterisk will appear next to the required tube length if the exchanger is undersurfaced, or next to a pressure drop if it exceeds the maximum allowable.

In design mode, Shell&Tube will search for a heat exchanger configuration that will satisfy the desired process conditions. It will automatically change a number of the geometric parameters as it searches.



However Plate will not automatically evaluate all possible configurations, and therefore it may not necessarily find the true optimum by itself. It is up to the user to determine what possible changes to the construction could lead to a better design and then present these changes to the program.

Shell&Tube searches to find a design that satisfies the following:

(1) enough surface area to do the desired heat transfer

(2) pressure drops within the allowable

(3) physical size within acceptable limits

(4) velocities within an acceptable range

(5) mechanically sound and practical to construct

In addition to these criteria, Shell&Tube also determines a budget cost estimate for each design and in most cases performs a vibration analysis. However cost and vibration do not affect the program's logic for optimization.

There are over thirty mechanical parameters which directly or indirectly affect the thermal performance of a shell and tube heat exchanger. It is not practical for the program to evaluate all combinations of these parameters. In addition, the acceptable variations are often dependent upon process and cost considerations which are beyond the scope of the program (for example the cost and importance of cleaning). Therefore the program automatically varies only a number of parameters which are reasonably independent of other process, operating, maintenance, or fabrication considerations.

The parameters which are automatically optimized are:

shell diameter baffle spacing pass layout type

tube length number of baffles exchangers in parallel

number of tubes tube passes exchangers in series

The design engineer should optimize the other parameters, based on good engineering judgment. Some of the important parameters to consider are:

shell type tube outside diameter impingement protection

rear head type tube pitch tube pattern

nozzle sizes tube type exchanger orientation

tubesheet type baffle type materials

baffle cut fluid allocation tube wall thickness



Shell&Tube Recap of Designs

The recap of design cases summarizes the basic geometry and performance of all designs reviewed up to that point. The side by side comparison allows you to determine the effects of various design changes and to select the best exchanger for the application. As a default, the recap provides you with the same summary information that is shown in the Optimization Path. You can customize what information is shown in the Recap by selecting the Customize button. You can recall an earlier design case by selecting the design case you want from the Recap list and then select the Select Case button. The program will then regenerate the design results for the selected case.

Shell&Tube TEMA Sheet

The TEMA sheet displays the results from the thermal calculations using the standard datasheet detailed in TEMA standard and includes a basic Setting Plan.

Shell&Tube Summary

Shell&Tube Thermal / Hydraulic Summary The Thermal / Hydraulic Summary section includes the following screens:

Performance

Heat Transfer

Pressure Drop

Flow Analysis

Vibration & Resonance Analysis

Methods

Shell&Tube Performance



The Performance section includes the following screens:

Overall Performance

Resistance Distribution

Shell&Tube Heat Transfer The Heat Transfer section includes the following screens:

Heat Transfer Coefficients

MTD & Flux

Duty Distribution

Shell&Tube Pressure Drop The Pressure Drop section includes the following screens:

Pressure Drop

Thermosiphon Piping

Thermosiphon Piping Elements

Shell&Tube Flow Analysis The Flow Analysis section includes the following screens:

Flow Analysis

Thermosiphons and Kettles

Shell&Tube Vibration & Resonance Analysis The Vibration & Resonance Analysis section includes the following screens:

Fluid-Elastic Instability

Resonance Analysis



TEMA Fluid Elastic Instability

TEMA Amplitude and Acoustic Analysis

Shell&Tube Methods The Methods Summary screen lists all the models and methods that have been used by the program as part of the calculations.

Shell&Tube Mechanical Summary The Mechanical Summary section includes the following screens:

Exchanger Geometry

Setting Plan

Tubesheet Layout

Cost / Weights

Shell&Tube Exchanger Geometry The geometry used in the calculations is summarized in a series of screens:

Basic Geometry

Tubes

Baffles

Supports-Misc. Baffles

Bundle

Enhancements

Thermosiphon Piping



Shell&Tube Setting Plan The Setting Plan details a scaled drawing of the exchanger and includes the following data:

Overall length

Bundle/Tube Pulling Length

Location and orientation of Nozzles

Location and orientation of Supports

Location of Baffles

The following tables are also included:

Headings/Remarks

Design Codes and Standards

Design Data

Weight Summary

Nozzle Data

Click the left-hand mouse button to zoom in on an area of interest.

Click the right-hand mouse button to display a menu from which the following options can be selected:

Exchanger only

End Views only

Draw Internals

Draw Border

Inlet Channel on Left

Nozzle/Shell Intersection



Dimension to Tubesheet Face

Draw Complete Exchanger

Draw Dimensions

Nozzle Designations

The Setting Plan can be:

Printed

Copied to the clipboard

Saved as in file in the following formats: dxf, bmp, svg, wmf

Shell&Tube Tubesheet Layout The Tubesheet Layout details a scaled drawing of the Tube Layout as used as part of the thermal calculations. No editing of the drawing is permitted as this is an output view. To make changes to the Tube Layout refer to the ‘Exchanger Geometry – Geometry Summary – Tube Layout’ screen.

The tube layout diagram includes the following data:

Shell Side Inlet and Outlet Nozzles

Shell Cylinder (Shell Kettle Cylinder - if K Shell)

Tube Locations

Pass Partition Lanes

Baffles

Tie Rods

Impingement Plate

Sealing Strips

Bundle Runners

Longitudinal Baffle



Pass Partition Lane Sealing Strips

The following tables can be selected to view the data associated which each item:

Bundle Limits

Pass Regions

Nozzles

Baffles

Tie Rods

Tube Lines

Impingement Plate

Sealing Strips

Bundle Runners

Longitudinal Baffle

Pass Partition Lane Sealing Strips

Click the left-hand mouse button to zoom in on an area of interest.

Click the right-hand mouse button to display a menu from which the following options can be selected:

Draw tubes as circles

Draw tubes as crosses

Draw end tubes as circles

Draw border

Draw dimensions

Display titles



The Tubesheet Layout can be:

Printed

Copied to the clipboard

Saved as in file in the following formats: dxf, bmp, svg, wmf

Shell&Tube Cost / Weights This screen summarizes the weights calculated for the major components in the exchanger, and includes an empty weight and a weight flooded with water.

The total cost for the exchanger is also listed with a break down of the cost into total labor and material.

Shell&Tube Calculation Details The Calculation Details section includes the following screens:

Analysis along Shell

Analysis along Tubes

Analysis for X and K shell

Shell&Tube Analysis along Shell The Analysis along Shell section includes the following screens:

Interval Analysis

Physical Properties

Shell&Tube Analysis along Tubes The Analysis along Tubes section includes the following screens:

Interval Analysis

Physical Properties

Shell&Tube Analysis for X and K Shell



The Analysis for X and K shell section includes the following screens:

Interval Analysis

Overview

The purpose of this example is to guide you through the design a simple single-phase heat exchanger using Aspen Shell & Tube Exchanger (Shell&Tube).

Contents:

Process Overview

Building the Simulation

Viewing the results

Properties from COMThermo

Creating a Checking Case

The Design calculation will determine the shell length and diameter, the nozzle sizes, the number of tubes and passes, the number of baffles and baffle cut. Other details such as shell and header type, baffle type, tube type and layout will use program defaults.

The Shell&Tube design logic will optimise the heat transfer against the allowable pressure drop on both the shell and tube sides. The program has built in heuristic rules, which will stop it searching once it realizes that further calculations are pointless.

Help may be obtained at any time by placing the cursor on an item and pressing F1

Next step:

Process Overview

Process Overview



The details of the process data and some basic geometry are shown in the table below:

Note: Exchanger to be Horizontal

Next step:



Launch Aspen Exchanger Design & Rating (EDR) from either the shortcut or the AspenOneTool bar. Select Shell & Tube Exchanger (Shell&Tube) from the New tab and click OK.

Fluid Cold Side

Boiler Feedwater

Hot Side

Fuel Oil

Units

Total Flowrate 59100 284000 kg/h Temperature (In/Out) 50 / 165.3 213 / 168 °C Density (In/Out) 879.4 / 909.8 kg/m³ Specific Heat (In/Out) 2.34 / 2.18 kJ/kg*K Viscosity (In/Out) 1.94 / 3.37 mPa*s Thermal Conductivity (In/Out) 0.1 / 0.107 W/m*K Inlet Pressure 50 12 bar (abs) Allowable Pressure Drop 1 1.5 bar Fouling Resistance (min) 0.000088 0.0005 m2 °K/W



Shell&Tube will open where the screen as shown below will be displayed.



To change the units which data can be entered into the program there are a number of options;

Click on the drop down arrow by US and select SI units

From the menu bar, select Tools, then Program Settings. From the General tab set SI as the Default set of the units of measure. Click OK, where the next time Shell&Tube is started, SI units will be the default set of unit.



Highlight the Application Options from the tree menu structure on the left-hand side and then ether the data as follows;

Set the calculation mode to Design

Location of hot fluid to Tube side



Press the Next button to navigate to the next form where input data is required or highlight Process Data from the navigation tree. Enter the process data from the process overview table previously given.

The flowrate data has been specified as kg/h whereas the input screen by default shows kg/s. Therefore click on the scroll down arrow by the mass flowrate units and select kg/h then enter the data.

When sufficient data has been entered necessary for the program to run, the red cross will disappear from the menu tree.

(NOTE: Numbers in red are program defaults and are not entered by the user)



Enter the physical properties for the hot side fluid, where as property data is supplied at two temperature points. User Specified Properties is selected for the property package.



Enter the property data for the two temperature points.

By default, two pressure levels are available, where in this example data at only one pressure level is to be entered. To delete the second pressure level you have two options:

Enter 1 for the number of pressure levels

Highlight the second pressure level in the Pressures column then click on the Delete Set button.

(NOTE: The Overwrite properties box is checked for direct input of properties)



Use one of the physical property packages to retrieve the cold stream properties.



Either B-JAC Databank or COMThermo can be selected. Initially the B-JAC databank will be described below, but in the Continuation Exercise 2 the COMThermo method is used.

Select B-JAC databank as the Physical property package and then click on the Search Databank button.

Type in the first few letters of the fluid required, then highlight from the list and click on the Add button to enter in the selected components list. Click on OK.



Select the Cold Side Properties tab and click on the Get Properties button where the program will calculate the properties of water at the default pressure and temperature range.



Save your case – All the required data have been entered. It is important to save the dataset. This is achieved from the menu by File, then Save As. Now you can run by clicking on the Run button or from the menu, Run, then Run TASC.

Next step:

Viewing the results

Viewing the Results



Now the example has been run the Results screens can now be viewed

Next step:



The above example used B-JAC database to determine the physical properties for the cold stream. COMThermo can be used instead, where the method is described below.

Reload the Design case and re-run.

Select COMThermo as the Physical property package for the Cold side composition. Click on the Search Databank button.

Type in the first few letters of the fluid required, then highlight from the list and click on the Add button to enter in the selected components list. Click on OK.



Enter a composition fraction of 1 for water and then from the Property Methods tab select Ideal-Ideal as the property package



Select the Cold Side Properties tab and click on the Get Properties button where the program will calculate the properties of water at the default pressure and temperature range.



Run Shell&Tube and compare the areas with the Design generated with B-JAC Database.

Next step:





The Design mode of Shell&Tube will provide a number of designs that will achieve the required duty. These can be viewed on the ‘Results | Results Summary | Optimization Path’ tab. Here there will be a list of the different geometries evaluated by Shell&Tube indicating if they meet the duty and pressure drop requirements and also if they are a "near" miss. At the top of this table is the ‘Current selected case’ number that meets both the duty and pressure drops and has the lowest cost value.

In order to fine tune and fully optimize the design the Rating/Checking mode in Shell&Tube should be used.

Select ‘Run’ from the main menu and then ‘Update file with Geometry – Shell&Tube’. This will take the optimized heat exchanger geometry and create a Rating/Checking case.

The detailed geometry of the exchanger can now be changed if necessary from the Exchanger Geometry screens.

Return to:

Overview

Shell and Tube Heat Exchanger Overview

A shell and tube exchanger has a bundle of tubes within a shell. One stream flows through the tubes, the other in the shell, over the tubes. Many variants of this basic configuration exist. Further information on the various components of an exchanger, and on the reasons for selecting particular sizes or configurations, is available on the following key topics:

Shell and Head Types

TEMA Shell Types

Head Types

Shell/Head Combinations

Double Pipe and Multi-tube Exchangers

Shell Diameters

Pass Arrangements

Single Pass Exchangers



Allocation of Streams

Nozzles - Sizing

Nozzles - TEMA Standards

Nozzles - Achieving TEMA Standards

Tube Bundles

Tube Diameters

Tube Wall Thicknesses

Common Tube Diameters and Thicknesses

Standard Bare Tube Diameters and Gauges

Tube Pattern and Tube Pitch

Tube Length - Maximum Value

Tube Length / Number of Passes

Tube Counts

Baffle Types

Single Segmental Baffles

Double Segmental Baffles

Triple Segmental Baffles

Orifice Baffles

Disc and Doughnut Baffles



Rod Baffles

Baffle Cut Orientation

Baffle Spacing and Cut

Maximum Unsupported Tube Span Length

Sealing Strips

Expansion Joints

Quick Guide to Geometry Selection

TEMA

Shell&Tube Shell and Head Types

Shells and front and rear end heads for a shell and tube exchanger come in a range of types identified by a letter, designated by TEMA

There are also some shell and tube type exchangers, such as double pipe and multi-tube, which are not covered by TEMA

See also:

TEMA Shell Types

Shell&Tube Shell Diameters

Heat exchanger shells are normally manufactured from standard pipe for diameters up to 610 mm (24 inch) outside diameter, and from rolled plate thereafter. In theory, then, very large shell diameters are possible. In practice, however, most exchanger manufacturers cannot handle or drill tubesheets greater



than approximately 3 meters (120 inches) in diameter and engineers contemplating shell sizes of this order should always refer to prospective manufacturers for advice. At the other end of the scale heat exchangers as small as 51 mm (2 inches) diameter with 6.35 mm (1/4 inch) tubes have been manufactured. For exchangers with 19.05 mm (3/4 inch) tubes, 152 or 203 mm (6 or 8 inches) is usually the minimum size shell used.

The size of pipe shells is clearly determined by the nominal size of available pipe - normally 152, 203, 254, 305, 356, 406, 457, 508 and 610 mm nominal bore (6, 8, 10, 12, 14, 16, 18, 20 and 24 inch). It is, of course, the shell inside diameter (ID) that is of most interest to the thermal design engineer.

For standard wall pipe the IDs corresponding to the above nominal sizes are, respectively, 154, 203, 255, 305, 337, 387, 438, 489 and 591 mm (6.07, 7.98, 10.02, 12.00, 13.25, 15.25, 17.25, 19.25 and 23.25 inches).

For plate shells any diameter is possible but, in practice, design engineers tend to work in increments of 50 mm (e.g. 650, 700, 750 mm ID) or 2 inches (e.g. 26, 28, 30 inches ID).

See also:

Pass Arrangements

Shell&Tube Nozzles - Sizing

Generally speaking, heat exchanger design engineers will try to keep nozzle sizes as small as possible to keep down costs. Wherever possible, this means that making the nozzle the same diameter as the connecting pipework. It should be remembered, however, that any pressure loss in the nozzle can often be more effectively used in the shell or the tubes and engineers should always check each run to ensure that *P is not being 'wasted' in a nozzle when, for instance, it could be used to decrease the baffle pitch, or increase the number of tube-passes.

If possible, nozzles which are very large compared to the shell (greater than one-third shell diameter) should be avoided since these will require extensive re-enforcing and costly additional non-destructive examination of the shell.

Where pressure drop is not a problem the minimum nozzle size is usually limited by the maximum allowable fluid velocity. This is a metallurgical problem since excessive velocities can lead to erosion, especially if the fluid contains solids in suspension. Clearly, the velocities which can be tolerated will be much higher for gases than for liquids and it is more helpful to talk in terms of energy, or density times velocity squared (* v2) rather than velocity. On this basis a safe upper limit for most fluids is around 9000 kg/ms2 (6000 lb/ft s2) and tube side nozzles should be sized such that this value is not exceeded.

See also:

Nozzles - TEMA Standards



Shell&Tube Tube Bundles

Ideally a tube bundle will occupy as much of the inside of the shell as possible, but in practice tubes will be missing in a number of places.

1. Near the shell wall, particularly if there is a pull through floating head.

2. Next to the inlet nozzle, to give increased flow area (reduced velocity), or to give space for an impingement plate under the nozzle.

3. In pass-partition lanes, corresponding to the position of the pass partition plates between passes, in the front end or rear end heads.

In some positions tubes may be replaced by the tie rods that hold the baffles together.

The distance from the shell to the first tube row and to the last tube row define the size of the region adjacent to the nozzle where tubes are not present.

Where tubes are missing, there can be flow paths whereby the fluid could bypass the bundle, with adverse effects on the heat transfer. This can be particularly significant when the baffle cut is in line with the nozzle, so tubes removed under the nozzle give a large bypass area. Bypass flows are reduced by the use of sealing strips, between the bundle and the shell, and in any pass partition lanes which are in-line with the main cross-flow direction.

For segmentally baffled exchangers, the bundle can be divided into two regions, the baffle overlap region, where there is predominantly crossflow through the bundle, and the window flow region, where the flow changes direction between one baffle space and the next.

A normal bundle is one with tubes removed next to nozzles. A full bundle is one with no such tubes removed. In some exchangers, a reduced baffle cut is used, but there are No Tubes in the Window (NTIW). Such designs have the advantage that all tubes are supported by every baffle, so the maximum unsupported tube length is reduced, and with it the risk of vibration damage.

See also:

Tube Diameters

Shell&Tube Tube Diameters

TEMA section 'C lists nine standard tube outside diameters ranging from 6.35 to 50.8 mm (1/4 to 2 inch). Generally speaking tubes less than 12.7 mm (1/2 inch) are only used for small 'proprietary' type exchangers and tubes greater than 25.4 mm (1 inch) would only be required for severely pressure drop



limited designs. The standard diameters in general use are, therefore, 12.7, 15.88, 19.05 and 25.4 mm (1/2, 5/8, 3/4 and 1 inch).

The choice of diameter is usually based on established practice rather than the technical merits of any particular case. Thus 12.7 and 15.88 mm tend to be specified in smaller exchangers for general industrial use while, in the Process Industries it is established practice to use 19.05 mm tubes as standard with 25.4 mm being occasionally used for vertical thermosiphon reboilers and other services where tube side pressure drop presents a problem.

There are several reasons why 19.05 mm tubes are by far the most commonly used in the Process Industries:

19.05 mm is the smallest diameter recommended by section 'R' (the section applicable to petroleum refineries) of the TEMA code

Tubes smaller than 19.05 mm OD tend to have inside diameters which make mechanical cleaning difficult

Tube end welding of the smaller tubes is more difficult

The constraint imposed by the initial selection of a standard tube OD leads to a reduction in the man hours required for design and cost estimation.

See also:

Tube Wall Thicknesses

Shell&Tube Tube Pattern and Tube Pitch

Tubes may range in diameter from 12.7 mm (0.5 in) to 50.8 mm (2 in) but 19.05 mm (0.75 in) and 25.4 mm (1 in) are the more common sizes. The tubes are laid out in triangular or square patterns in the tube sheets.

There are four common patterns (sometimes called layouts).

Triangular: 30 degrees

Triangular: 60 degrees

Square: 45 degrees

Square: 90 degrees



The 90 degree pattern has tube rows ‘in-line’. The other layouts are ‘staggered’.

The square layouts permit access to tubes within the bundle for cleaning. Triangular layouts (with conventional tube pitches) do not. With multiple passes, access to all the tubes within the bundle may only be possible if the layouts within the various passes are aligned.

90 degree layouts are common in boiling applications such as kettles and flooded evaporators

30 degree layouts are more common than 60 degrees. The angles are usually defined relative to the flow direction, but are sometimes referred to the vertical. Clarification may be needed in exchangers with a vertical baffle cut, where the flow is side to side.

The triangular arrangement allows more tubes in a given space. The tube pitch is the shortest centre-to-centre distance between tubes. The tube spacing is given by the tube pitch minus the tube diameter. The tube pitch/tube diameter ratio is normally 1.25 or 1.33. Since a square layout is used for cleaning purposes a minimum gap of 6.35 mm (0.25in) is allowed between tubes.

For assembly reasons a gap must exist between the outer tubes forming the bundle and the inside surface of the shell (bundle to shell clearance). This gap depends upon the type of heat exchanger (fixed tube sheet, U-tube or floating head). A larger gap is usually needed adjacent to the shell nozzles to avoid excessive pressure drop (nozzle clearance). Tubes are either removed from the bundle opposite the nozzles or a greater shell diameter is used at the nozzles, the latter is known as a vapor belt.

A larger tube-to-tube spacing is needed between tubes in adjacent passes, when there is more than one pass. This is ‘pass partition gap’ is to allow for pass partition plates which are required to separate flows in the channels

See also:

Tube Length - Maximum Value

Shell&Tube Tube Counts

The tube count is the total number of tubes in an exchanger. For this purpose, a U-tube is counted as two-tubes, so the tube count still gives the total number of holes in the tubesheet.

Since tubes are laid out in a regular array, calculating the approximate number of tubes in an exchanger is relatively straightforward. Allowance can be made for tubes removed adjacent to nozzles, pass partition lanes etc. An exact tube count, however, can only be done when the position of every tube in the exchanger is fixed, and allowance has to be made for tubes removed to give space for tie-rods.

Shell&Tube uses an approximate tube count in Design mode, but does an exact tube count in all other modes.



The Tube Layout diagram in Shell&Tube shows you an exact tube count, and you can if you wish modify this to correspond exactly to an exchanger you are modeling. You can do this by making sure that all the Bundle Layout input items are set correctly, and then, if necessary, making additional revisions by editing the diagram, by adding or deleting tubes, or moving tube-pass regions.

Alternatively you can explicitly specify a tube count in the input, and this value will be used in the heat transfer and pressure drop calculations. If your specified value differs from the calculated value you will get a warning. As long as the Tube Layout calculated by Shell&Tube more or less matches your exchanger, using such a specified tube count should be a very good approximation, and will save you the trouble of detailed editing of the diagram.

See also:

Baffle Types

Shell&Tube Baffle Types

Baffles are installed on the shell side for two reasons. Firstly they cause crossflow over the tube bundle, and hence higher velocities and higher heat-transfer rates due to increased turbulence. Secondly they support the tubes thus reducing the chance of damage due to vibration. There are a number of different baffle types which give this turbulence due to crossflow:

Single Segmental Baffles

Double Segmental Baffles

Triple Segmental Baffles

Disc and Doughnut Baffles

The centre-to-centre distance between baffles is called the baffle-pitch or baffle spacing and this can be adjusted to vary the crossflow velocity. In practice the baffle spacing is not normally greater than a distance equal to the inside diameter of the shell or closer than a distance equal to one-fifth the diameter or 50.8 mm (2 in) whichever is greater. In order to allow the fluid to flow backwards and forwards across the tubes part of the baffle is cut away. The height of this part is referred to as the baffle-cut and is measured as a percentage of the shell diameter, e.g. 25 per cent baffle-cut. The size of the baffle-cut (or baffle window) needs to be considered along with the baffle spacing. It is normal to size the baffle-cut and baffle spacing to equalize the velocities through the window an in crossflow respectively.

There are two main types of baffle which give longitudinal flow:



Orifice Baffles

Rod Baffles

In these types of baffle the turbulence is generated as the flow crosses the baffle.

Shell&Tube Quick Guide to Geometry Selection

The following is a quick guide on how exchanger geometry is selected

Tube outside diameter - for the process industry 19.05mm (3/4") tends to be the most common.

Tube wall thickness - there is not short cut for deciding this. Reference must be made to a recognized pressure vessel code.

Tube length - for a given surface are the longer the tube length the cheaper the exchanger although a long thin exchanger may not be feasible.

Tube Pattern (layout) - 45 or 90 degree patterns are chosen if mechanical cleaning is required otherwise a 30 degree pattern is often selected because it provides a higher heat transfer and hence smaller exchanger.

Tube pitch - the smallest allowable pitch of 1.25 times the tube outside diameter id normally used unless there is a requirement to use a larger pitch due to mechanical cleaning or tube end welding.

Number of tube passes - is usually one or an even number (not normally greater than 16). Increasing the number of passes increases the heat transfer coefficient but care must be taken to ensure that the tube side rho-v2 is not greater than about 10 000 kg/m s2

Shell diameter - standard pipe is normally used for diameters up to 610mm (24"). Above this they are made from rolled plate. Typically shell diameters range from 152 mm to 3000 mm (6" to 120").

Baffle type - single segmental are used by default with other types being considered if pressure drop constraints or vibration is a problem.

Baffle spacing - this is decided after trying to balance the desire for increased crossflow velocity and tube support (smaller baffle pitch) and pressure drop constraints (larger baffle pitch). TEMA provides guidance on the maximum baffle pitch and the absolute minimum baffle pitch is about 50 mm (2").

Baffle cut - this depends on the baffle type but is typically 45% for single segmental baffles and 25% for double segmental baffles.

Nozzles and impingement protection - for shell side nozzles the rho-v2 should not be greater than about 9000 in kg/m s2. For tube side nozzles the maximum rho-v2 should not exceed 2230 kg/m s2 for non-corrosive, non-abrasive single phase fluids and 740 kg/m s2 for other fluids. Impingement protection is



always required for gases which are corrosive or abrasive, saturated vapors and two phase mixtures. Shell or bundle entrance or exit areas should be designed such that a rho-v2 of 5950 kg/m s2 is not exceeded.

Shell&Tube TEMA

TEMA is the U.S. Tubular Exchanger Manufacturers' Association, which produces a regularly updated set of standards, relating (primarily) to mechanical design considerations for shell and tube heat exchangers.

