Basics of Shell and Tube Heat Exchangers (With PDF)

What is a Heat Exchanger?

A Heat exchanger is a device to transfer heat from one fluid (Liquid/Gas) to another. There are various types of heat exchangers used in process piping. Shell and tube heat exchanger is the most widely used heat exchanger and are among the most effective means of heat exchange. Shell and tube heat exchanger is a device where two working fluids exchange heats by thermal contact using tubes housed within a cylindrical shell. The fluid temperature inside the shell and tube are different and this temperature difference is the driving force for temperature exchange. Used for wide temperature and pressure range, Shell and tube heat exchangers are compact in design, easy in construction and maintenance and provide excellent heat exchange.

As the name specified, it consists of a shell and a number of tubes. Shell is the housing of the exchanger and tubes are mounted inside the cylindrical shell.

Working Principle of Shell and Tube Heat Exchanger

The working of a shell and tube heat exchanger is fairly simple. One fluid flows inside the tubes and the other through the shell. While flowing they exchange the heats which means the cold fluid gains the heat from the hot fluid. So one cold fluid enters the shell (or tube side or channel side) inlet nozzle and comes out of the outlet nozzle as hot fluid. Obviously, the other fluid will become cold in the outlet than in the inlet. The heat transfer in a shell and tube heat exchanger is determined by the exposed surface area that is decided by the number of thermally conductive metal tubes. The fluid flow inside the shell and tube heat exchanger can be parallel flow or crossflow.

Fig 1 shows the typical working principle of a shell and tube heat exchanger.

Working principle of Typical Shell and Tube Heat Exchanger
Fig. 1: Working principle of Typical Shell and Tube Heat Exchanger

The above figure shows both inlet and outlet nozzle in the front header of the channel side. That means this exchanger consists of even number of tube passes. However, there can be odd number of tube passes. On that situation, the channel side outlet nozzle will be on the read header. Increasing the number of tube passes increase the heat transfer co-efficient.

To increase the fluid turbulence in the tube and shell side flow, turbulator and baffles are installed inside tubes and shells respectively. This increase the heat transfer between the fluids.

Basic Components of Shell and Tube Heat Exchanger

Typically a Shell and Tube Heat Exchanger consists of two-compartment / section one is shell side and other is channel/tube side

  • Shell side section consists of the following components: Shell, Cover, Body Flange, Nozzles, Saddle support.
  • Channel / Tube side section consists of the following components: Channel, Cover, Body Flange, Nozzles, Tube Sheet and Tubes  (Tube Bundle)
Components of a Shell and Tube Heat Exchanger
Fig. 2: Components of a Shell and Tube Heat Exchanger

The heat exchanger is supported by saddles in the shell part.

Tube Bundle of Shell & Tube Heat Exchanger

Tube Bundle (Fig. 3) consists of the following components

  • Tube sheet
  • Tubes
  • Baffles
  • Tie rods and Spacers
  • Sliding strips

Tube bundles are removed during maintenance. Standard practice is to flow the corrosive fluid inside the tubes so that if corroded they can be easily replaced or repaired. Fig. 3 below shows a typical tube bundle.

Typical tube bundle of a shell and tube heat exchanger
Fig. 3: Typical tube bundle of a shell and tube heat exchanger

Tube Pattern inside Shell & Tube Heat exchanger

Normally tubes inside the exchanger are of 0.5″ to 2″ in sizes and arranged in triangular or square pattern as shown in Fig. 4

Typical tube patterns
Fig. 4: Typical tube patterns

Tube Pitch

The tube shall be placed with a minimum centre to centre distance of 1.25 times the tube outside diameter of the tube. When mechanical cleaning of the tube is specified then a minimum cleaning lane of 6.4 mm shall be provided.

Baffles

Baffles are installed in the shell of the shell and tube heat exchanger to create more turbulence and increase the flow time so that better heat exchange is possible. Baffles support the tubes so that damage and vibration of tubes are minimized.

Types of Shell and Tube Heat Exchanger

TEMA shell and tube heat exchanger types based on application

As per TEMA (Tubular Exchanger Manufacturers Association) Shell and Tube Heat Exchanger can be classified as

  • Class R Exchangers – Refinery and Petrochemical Application
  • Class C Exchangers – General Process Application
  • Class B Exchangers- Chemical Process Application

TEMA Shell and tube Heat Exchanger applicable Criteria

  • Inside diameter less than 2540 mm (100 inch)
  • Product of nominal diameter (mm) and design pressure (kPa) of   17.5 x 106
  • Design pressure of 3000 psig (20684 KPa)

The reason behind such limitation is to keep the maximum shell wall thickness below 3 in. (76 mm), and the maximum stud diameter to below 4 in. (102 mm).

Shell and Tube heat exchanger types based on construction

Depending on various construction and configuration parameters following types of shell and tube heat exchangers are widely used in industries.

Fixed Tube Sheet Heat Exchanger

The tubesheet is fixed in the shell by welding and hence the term fixed tube sheet exchanger applies. This simple and economical construction allows cleaning of the tube bores by mechanical or chemical means. An expansion bellow is installed in the shell when there is a large temperature differences between the shell and tube materials. Refer to Fig. 5 for an example of fixed tube heat exchanger.

Example of a typical fixed tube heat exchanger
Fig. 5: Example of a typical fixed tube heat exchanger

Floating Head Heat Exchanger

In floating head construction, the rear header can float or move as it is not welded to the shell. The tube bundle can easily be removed while maintenance. Fig. 6 shows an example of floating head heat exchanger.

Example of a typical Floating Head Removable bundle heat exchanger
Fig. 6:Example of a typical Floating Head Removable bundle heat exchanger

Stationary Tube sheet with removable tube bundle

Fig. 7 shows an example of stationary tube sheet with removable tube bundle.

Example of a typical stationary tube sheet type heat exchanger
Fig. 7: Example of a typical stationary tube sheet type heat exchanger

U-tube Heat exchanger

U-tube exchangers are a type of shell and tube heat exchanger whose tube bundle is made of continuous tubes bent into a “U” shape. The bend side is free-floating and this helps in thermal expansion without requiring expansion joints. However, such bends are difficult to clean.

Typical representation of U-tube Heat exchanger
Fig. 8: Typical representation of U-tube Heat exchanger

Based on the number of times the tube-side/shell-side flows pass through the exchanger, shell and tube heat exchanger is categorized as:

  • Single-Pass exchangers and
  • Multi-Pass exchangers

The full TEMA classification of shell and tube heat exchanger types are provided in Fig. 9 below:

TEMA Shell and Tube Heat Exchanger types
Fig. 9: TEMA Shell and Tube Heat Exchanger types

Depending on the application of shell and tube heat exchangers, they are known as various types as listed below:

  • Reboilers
  • Evaporators
  • Condensers
  • Aftercoolers
  • Preheaters, etc.

Stack Types of Configuration

In this, two or three heat exchangers placed one above other. This is termed as 1 shell in parallel and 2 or 3 Shells in series. Refer Fig. 10.

Figure showing stack arrangement of heat exchangers
Fig. 10: Figure showing stack arrangement of heat exchangers

Codes and Standards for Shell and Tube Heat Exchanger

The following codes and standards govern the design of shell and tube heat exchanger.

  • API 660 / ISO 16812 ( Shell and Tube heat exchangers for general refinery service )
  • ASME SECT.VIII Div.1 (UHX) or Div.2, PD 5500, EN 13445, AD 2000 Merkblatt.
  • TEMA -Tubular Exchanger Manufacturers Association
  • Shell DEP 31.22.20.31 and DEP 31.21.01.30

Design of Shell and Tube Heat exchangers

Process Design of Shell and tube Heat exchanger

Design of Shell and tube heat exchanger is a trial and error iterative process. In recent time, the thermal design is carried out by the process team using engineering software. However, the logic behind the calculations should be clearly understood. The shell and tube heat exchanger design calculations are based on initial selection of a preliminary exchanger configuration and certain initial decisions like

  • the front and rear header type,
  • shell type,
  • the sides the fluids are allocated,
  • baffle type and baffle pitch
  • tube diameter, length and tube layout
  • shell diameter, and
  • number of tube passes

Further steps for the shell and tube heat exchanger design consist of

  • Calculation of shell side flow distribution and heat transfer co-efficient
  • Estimation of tube side heat transfer coefficient and pressure drop
  • Determination of wall resistance and overall heat transfer coefficient
  • Calculation of Mean temperature difference (log mean temperature difference) from the inlet and outlet temperatures of the two fluids.
  • Estimation of required heat transfer area
  • Comparison of calculated area with the assumed geometry
  • Comparison of shell and tube-side pressure drop with allowable pressure drop
  • If the pressure drop is within the allowable pressure drop design is acceptable. Otherwise, adjust the assumed geometry and repeat the above steps.

Once the requirements are met, a process datasheet is developed indicating all process design parameters of shell and tube heat exchanger design.

General design Considerations for shell and tube heat exchanger

Fluid Allocation: Shell side vs Tube Side

The following table (Table-1) provides general guidelines for shell and tube side fluid allocation in a shell and tube heat exchanger:

Fluid ParametersFluid Allocation-Shell SideFluid Allocation-Tube Side
High Pressure Fluid Stream X
Corrosive Fluid X
High fouling fluid stream X
More Viscous fluidX 
Lower Flow Rate FluidX 
Fluid with low heat transfer co-efficientX 
Toxic Fluid X
Table 1: Shell and Tube-side Fluid Allocation

Fluid Velocity inside Shell and Tube

High fluid velocities increases heat transfer coefficients and reduces fouling but causes erosion and increases pressure drop. So velocity selected should be just enough to prevent settling of suspended soilds. Typical fluid velocities considered for the design of shell and tube heat exchangers are given the following table (Table-2):

Fluid TypesFluid Velocity-Shell SideFluid Velocity-Tube Side
Liquid0.3 to 1 m/s1 to 2 m/s
Gas /Vapor (Vacuum Pressure)50 to 70 m/s50 to 70 m/s
Gas /Vapor (Atmospheric Pressure)10 to 30 m/s10 to 30 m/s
Gas /Vapor (High Pressure)5 to 10 m/s5 to 10 m/s
Table 2: Typical fluid Velocities in Shell and Tube Heat Exchanger Design

Pressure Drop Consideration

Typical pressure drop values considered for shell and tube heat exchanger design are:

  • For Liquids with Viscosity<1 mN-s/m2, ΔP=35 kPa
  • For liquids with Viscosity=1 to 10 mN- s/m2, ΔP= 50-70 kPa
  • Liquids without phase change= 70 kPa
  • Condensing streams= 14 kPa
  • For Vapor and gas services:
    • High vacuum Pressure: 0.4-0.8 kPa
    • Medium vacuum Pressure: 0.1 x absolute pressure
    • Pressure 1 to 2 bar: 0.5 x system gauge pressure
    • Pressure above 10 bar: 0.1 x system gauge pressure
    • Vapors without phase change= 14 kPa
    • Boiling Streams = 7 kPa

Software used for Thermal Design

The most popular software used for thermal design of shell and tube heat exchanger are listed below

  • HTRI – Heat Transfer Research Institute
  • HTFS – Heat Transfer Research and fluid flow service

Mechanical design of Shell and Tube Heat exchanger

Mechanical design of shell and tube heat exchangers consist of calculation of shell thickness, flange thickness, etc. Various codes like ASME Sec VIII, PD 5500, TEMA, etc provides guidelines for mechanical design. The following design guidelines can be followed:

  • Minimum Shell Thickness (Fig. 11) as per TEMA for class – R
Minimum Shell thickness of shell and tube heat exchanger
Fig. 11: Minimum Shell thickness of shell and tube heat exchanger
  • Baffle clearance, Baffle spacing, and thickness as per TEMA table RCB -4.3
  • Tie rod size and nos. as per TEMA table R- 4.71  for class – R
  • Peripheral Gasket: The minimum width of the peripheral ring gasket for external joints shall be 10 mm for shell sizes up to 584 mm and 12 mm for all larger shell sizes.
  • Pass Partition Gasket: The min. width of the gasket web for pass partition of the channel shall not be less than 6.4 mm for shell sizes up to 584 mm and 9.5 mm for all larger shell sizes. Gasket  joint shall be confined type
  • Shell and Head design is done as per selected Pressure vessel Design Code  such as ASME, EN or AD
  • The most widely used design code across the world is ASME Sect. VIII Div.1 & 2
  • Body / Girth Flange Design as per Appendix -2 of ASME Sect. VIII Div.1
  • The tube sheet design is Mandatory as per UHX of ASME Sect. VIII Div.1
  • The tube sheet is designed for the following three cases.
    • Tube side pressure (Pt) acting and Shell side pressure (Ps) is Zero
    • Shell side pressure (Ps) acting and Tube side pressure (Pt) is Zero
    • Shell side pressure (Ps) acting and Tube side pressure (Pt) acting
  • Please consider the effect of Vacuum in above load cases
  • Tube sheet Design formula based on the theory of Flat Plates

Shell and tube Heat Exchanger Material of Construction

Following materials are the most common as Shell & Tube Heat Exchanger MOC.

  • Carbon steel and Cladding Plates
  • Stainless Steel
  • Duplex Stainless steel
  • Tubes –  Carbon steel, Stainless steel, Duplex stainless steel, Exotic material such as copper, Inconel, Titanium

Maintenance of Shell and Tube Heat exchangers

Depending on user experience and manufacturer guidelines, shell and tube heat exchangers should be inspected at regular intervals. A shell and tube heat exchanger can fail by one or more of the following factors:

  • Improper design.
  • Excessive fouling.
  • Air or gas binding resulting from improper piping installation or lack of suitable vents.
  • Excessive clearances between the baffles and shell and/or tubes, due to corrosion.
  • Operating conditions differing from design conditions.
  • Maldistribution of flow in the unit, etc

Following preventive maintenance steps at regular intervals can reduce the risk of equipment failure. Following maintenance steps can be followed to enhance shell and tube heat exchanger performance:

  • Cleaning periodically to avoid fouling
  • Inspection of tubes
  • Gasket replacement
  • Repairing leaks if detected during inspection.

Application of Shell and Tube Heat Exchangers

Shell & Tube Heat Exchangers find their application in the following Industries-

  • Refinery and Petrochemical
  • Fertilizer
  • Oil and Gas
  • Chemical
  • Power Plants

Few more resources for You..

Shell & Tube Heat Exchanger Piping: A brief Presentation
An article on Plate Heat Exchanger with Steam
A typical Check List for Reviewing of Shell & Tube Heat Exchanger Drawings
A brief presentation on Air Cooled Heat Exchangers
Basic Considerations for Equipment and Piping Layout of Air Cooled Heat Exchanger Piping
Reboiler Exchanger and System Type Selection

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Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

16 thoughts on “Basics of Shell and Tube Heat Exchangers (With PDF)

  1. What I like the most about the shell & tube design compare to other type like plate and frame or helicoil is that despite the fact they are built to last for a longer life is:
    1- The tube bundle is easy to replace because you have just one or 2 gaskets to replace
    2- They are easy to repair a tube temporary by plugging it for a fast restart of the process while waiting for the next shut down
    3- If you need to clean the tubes, you can easily see from your eyes if the tubes are clean enough.
    4- For high scale application their is the possibilty to add an automatic brush in each tube to avoid any scale or plug tube.

    In steam application I suggest to use a vertical shell & tube design to flood the heat exchanger.

  2. Congratulations
    Great presentation with very easy explanation to understand the fundamentals of heat exchanger
    Thank you

  3. Very Nice Presentation. Can we see any operation and maintenance guide for Shell & Tube type heat exchanger

  4. Thanks for a detailed information.
    Requesting you to also describe details related to its piping arrangement. Guidelines to be taken if the heat exchanger is located on the ground or on platforms above.

  5. Hi Anup. Very Good presentation.
    Do you have a presentation on maintenance of shell tube heat exchangers?

    I would like to strengthen aspects such as:
    – Recommended gaskets for service
    – recommended torque and / or tensioning
    – Hydrostatic tests on high pressure equipment on both sides.

    API 660, API 572 and ASME PCC-2 offer help, however I would like to know your opinion.

    Thank you
    best regards
    Norton

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