Shell and tube heat exchangers are described along with basics, definition, parts, working principle, types, construction, application, advantages, disadvantages, etc.
What are Shell and Tube Heat Exchangers?
Shell and Tube Heat Exchange basics
A heat exchanger is a device which, as the name suggests, helps in the process of exchanging or transferring energy in the form of heat.
It is usually used for the transmission of heat energy from one working fluid to another, which can be either a liquid or a gas, and is one of the most efficient ways for the transfer of heat.
What is a Shell and Tube Heat Exchanger?
A shell and tube heat exchanger, in simple words, is a type of heat exchanger where the two working fluids exchange heat with the help of, as the name suggests, tubes and a shell.
- One of these is called the tube side fluid and the other is known as the shell side fluid.
- The tubes are encompassed in a cylindrical shell which exists at a temperature different from the network of tubes mounted inside it.
- Is is obvious by the basic laws of thermodynamics, a heat exchange will take place due to said temperature difference between the two parts.
It is most commonly used in massive chemical processes such as oil refineries because it is very well suited for applications that require a high-pressure environment.
This is because of the fact that they can be used for a wide range of temperature and pressure conditions, their uncomplicated design, and low maintenance requirements.
Now, what are the main important parts of shell and heat exchanger?
Parts of Shell and Tube Heat Exchanger
There are some essential parts of the shell and tube heat exchangers, without which you cannot imagine.
The following are the principal ones.
- Shell and Shell-Side Nozzles
- Tube-Side Channel and Nozzles
The shell, sometimes also known as the housing, is the main mass or body of the heat exchanger and it is built in the shape of a cylinder. It contains all the components of the heat exchanger.
It’s a pressure vessel, which means it’s going to be pressurized to match the fluid or the system pressure that’s flowing through it.
The shell acts as a container for the shell-side fluid. It has a circular cross-section and is manufactured by rolling a metal plate of desired dimensions. It specifically acquires a cylindrical shape.
- The attachments are obtained through welding the longitudinal joint, which provides strength to the whole shell.
- There are different kinds of sizes of these shells.
- If one wants to get a small diameter shell, it can be manufactured by cutting a circular pipe of the desired measurement.
- Here one of the factors that define the accuracy of the shell is its roundness.
- It helps in providing a maximum diameter of the baffles that can be inserted. As a result, it provides a shell to baffle leakage.
Tubes are the prominent part of shell and tube heat exchangers, which usually provide a heat transfer surface between the fluid flowing across the outer surface of the tube and the other fluid flowing inside the tube.
- These tubes are made up of copper or steel alloys which may be welded or seamless.
- Numerous other alloys can also be used for the desired tube, such as titanium, aluminum, and nickel.
- Material depends on the project requirements.
- The welded tubing is yielded by rolling a strip into a cylinder and welding the seam, while seamless tubing is produced with the help of the extrusion process.
- The most economical and efficient one that is used for tubes is the welded one.
- The tubes come with different enhancements, such as finned ones. These are effective when used for that fluid that has a lower heat transfer coefficient than the other ones.
- The normal tube measurement lies between 0.109 inches to 0.065 inches thick with tube diameters of 5/8″, ¾”, and 1″.
- Here thinner wall diameter tubes are also used where there is the inclusion of expensive materials such as nickel and titanium.
If offered a cross-sectional view, one can observe all the tubes in the main body, which are collectively known as the tube nest, tube bundle, tube stack, or tube system.
This tube system has two sections: the upper section or half and the lower section or half. The number of tube passes can either be odd or even.
These are the component of the shell and tube exchanger which holds the tube. Specifically, the tubes are inserted into the holes in tube sheets. These are either welded to the tube sheet or expanded into grooves that cut down into the holes.
- The core functionality of these tube sheets is to prevent the tube side fluid and shell side from mixing.
- It is usually a round plate of metal that has been given different shapes as per the desire.
- One of the most important factors that should be emphasized is its corrosion-resistant nature.
- These tube sheets should be selected based on the property that makes them withstand the corrosion attack by both the fluid in the heat exchanger.
- These should be compatible with tube-side material.
The tube sheets are installed in order to fulfill the following purposes:
- Holding the tube stack in place
- Sealing the inside of the shell (this helps in creating a pressure boundary for the shell side fluid and consequently, preventing the same from not staying in its designated space i.e., the shell.)
Hence, these two tube sheets act as anchor points at the two terminals of the shell.
- Glass shell and Tube heat exchangers can be used for condensation of vapours, vapourisation, cooling and heating of liquid, and have come out to be more advance and beneficial for its following advantages: Bigger Heat transfer are in one unit. Less pressure drop.Stuffing box sealing allows easy tube replacement./ Shell and tube condenser consists of a cylindrical shell which houses a glass tube bundle. Tubes are sealed with shell with the help of PTFE tube sheets./
- Each tube is individually sealed by Viton 'O' ring in tube sheets at both the ends. Baffles are provided in the shell to maintain state of turbulence of fluid as well as to hold the tubes./ Salient Features :/ 1.Universal corrosion resistance an excellent alternative to expensive MOCs like graphite, hastelloy, copper titanium, tantalum and other exotic metals./ 2. Excellent heat transfer as fouling does not occur on smooth glass surfaces./ 3. Flexibility of installation vertical/horizontal./
- 4. Easy replacement of tubes for repair and cleaning./ 5. Available in wide range of HTAs./ 6. Ease of installation due to light weight./ 7. Economical./ 8. Suitable for applications where large HTAs are required in limited space./ Advantages Over Conventional Coil Type condenser :/ 1. The overall heat transfer coefficient in shell and tube condenser is about 3 times higher than in coil type condenser./
- 2. The pressure drop in shell and tube condenser is minimal compared to 2-3 kg/cm2 in coil side of coil type condenser./ 3. Stuffing box sealing allows easy tube replacement./ Shell and tube condenser are of recent development ./ Shell and tube condenser can be operated within a temperature range of -40 to 200 on either side. /However, differential temperature should not exceed 120 at any point. /
- All the Shell and tube condenser can be used predominantly under full vacuum, provided differential pressure does not exceed 0.3Mpa./ It is generally used for horizontal installation.but also they can be installed vertically.PTFE per forated plates supports the glass tubes .shell and tube Exchanger are used for surface area . more details and dimensions can be sipplied on request./
Shell side nozzles
The shell side nozzles are specifically a part of the shell itself, the inlet and exit ports.
Tube side channel and nozzles
The flow of tube-side fluid in the shell and tube heat exchangers is controlled through the tube-side channel and nozzles. This helps in the flow of fluid into and out of the tubes.
- The nozzles of the tube side are made up of alloy materials as the fluid in the tube side is more corrosive.
- These channels are designed in a way that they will be compatible with the rubes and tube sheet as well.
- These are also manufactured with the help of clad also.
- The channels are equipped with channel covers which are the round plates tightened with the help of bolt to the channel flanges.
- This is movable and can be removed at the time of inspection.
The shell and tube heat exchangers, which have two tube side passes, effectively need pass dividers. These are needed in both bonnets and channels for an exchanger who is having two passes.
- A pass divider is needed in one channel or bonnet for an exchanger with two tube-side passes, and they are needed in both channels and bonnets for an exchanger with more than two passes.
- The divider is cast in line with the channel or we can say bonnets.
- Dividers need to have a smooth bearing surface.
- When the channels are manufactured from a plate or made up of a pipe, the dividers will be welded.
Baffles are the parts of shell and tube heat exchangers that have numerous functionalities. Baffles are used to provide a support structure for the tubes to lie in an accurate position.
- This is needed while it is being assembled.
- This also helps prevent the tubes’ vibration, which mainly comes due to the flow-induced working.
- Apart from this, the baffles also guide the shell side flow back and forth, which comes across the tube field.
- It specifically increases the heat transfer coefficient and velocity of the fluid.
- It also helps in maintaining the tube spacing.
While the two-terminal anchor points do help, it is not sufficient to provide a good enough balance for the tube stack. This is the reason why baffles are also required. They just add some extra support and ensure that the tubes are properly aligned. They also help
Sometimes, one can also observe tie rods which are used to connect the tube sheets and baffles together. Again, this adds further support to strengthen the structure.
There are a lot of connections or nozzles in the heat exchanger. This includes both inlets and outlets since we have two fluids flowing into and out of the device.
For the sake of a better and comprehensive understanding, the connections are labelled in the picture below.
It can be observed that within these tubes, turbulators or tube inserts can be embedded. These turbulators or tube inserts are pushed into every one of these tube holes in order to create a turbulent flow.
- This is much better than the laminar (or smooth) flow of fluids.
- This turbulent flow not only helps increase the heat transfer capacity of the shell and tube heat exchanger but also keeps the tubes clean by reducing the likelihood of the development of deposits on the inside.
With the brief introduction of the core parts of the shell and heat exchangers, now it is time to understand the core working of shell and tube heat exchangers.
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The next segment will provide a holistic idea about the working of the shell and tube heat exchanger.
Working Principle of Shell and Tube Heat Exchangers
Working Principle Basics
The principle on which a heat exchanger works is extremely simple. We have learned that as per the first law of thermodynamics, energy is always conserved from one form to another and no energy is added or removed.
As per the second law of thermodynamics, heat flows based on the temperature potentials and energy gained by fluid one is the exact amount of energy lost by fluid two.
Heat flows from a hotter body to a cooler body only.
Heat flow undergoes by below three processes,
Within these three heat transfer processes, conduction and convection are mainly used in shell and tube heat exchangers.
How does Shell and Tube heat Exchanger Work?
The specific idea behind the working of shell and tube heat exchangers revolves around the passing of hot fluid through a cold fluid without getting mixed so that their heat is being transferred.
- In the core structure of shell and tube heat exchangers, there are two inlets and two outlets where each of the fluids gets in motion at their respective inlet and get out of the device at their outlets.
- With the help of a tube bundle, the tube side flow passes and provides the desired mechanism.
- Turbulent flow exists in the tubes. It helps to cater down the sediment depositing and also helps in increasing the overall efficiency of the heat exchanger.
- These are secured by tube plates or tube sheets which act as a protective casing.
- When it comes to shell side flow, the liquid flow starts from the shell inlet and passes over the tubes.
- Another part of the heat exchanger known as baffles helps maximize the amount of thermal mixing that takes place in coolant pipes and shell-side fluid.
- After the whole process, it exits from the shell outlet.
- The presence of headers on both sides of the tube bundle helps construct a reservoir that helps the tube side flow to be continuous.
- This can also be split into different sections as per the specific heat exchanger types.
The shell side fluid is among the essential parts of this exchanger that keeps on working around the baffles, which helps transfer energy.
- The working of shell and tube heat exchangers also depends on the number of phases, whether single-phase or two phases.
- The single-phase exchangers are effective when there is a need for a constant fluid phase in the whole process.
- In accordance with that, the two-phase exchanger will work as a phase change while the process occurs.
Types of Shell and Tube Heat exchanger
Shell and tube heat exchangers are available in a variety of types with slight changes in the in the internal structure. They can be classified as
Single pass shell and tube heat exchanger
In this type of a heat exchanger, as the name suggests, neither the shell side fluid nor the tube side fluid passes through the body of the device more than once.
However, this design is not exactly very common because of the fact that it is quite inefficient and does not serve a great purpose anyway. Although, it is used in steam condensers and other devices where the state of something is being converted.
For example, when vapours have to be converted into a liquid.
Multiple pass shell and tube heat exchanger
In this type of a heat exchanger, at least one of the two fluids passes through the body of the device more than just once.
Types of Flows in Shell and Tube Heat Exchangers
When the two fluids are flowing in directions opposite to one another, it is known as counter flow.
It is the most efficient type of flow one can have for a shell and tube heat exchanger.
When the two fluids are flowing in exact same direction as one another, it is known as parallel flow.
When the two fluids are flowing in directions perpendicular to one another, it is known as cross flow. They are flowing at a 90 degree angle relative to each other.
For example, the shell side fluid entering from the top and coming out from the bottom without the baffles playing any role in this process while the tube side fluid is flowing in a horizontal direction (either left to right or right to left).
The type of flow being used depends on the usage of the heat exchanger the purpose or function it is intended for.
How Does Shell and Tube Heat Exchanger Built and How Does it Work?
The tube side fluid is named so because it flows through the tube nest which has two sections: the upper section and the lower section.
- Connection 1 (outlet): This offers an exit from the top section of the tube sack. The tube-side fluid exits from here.
- Connection 2 (inlet): This offers an entry to the shell. The shell-side fluid enters from here.
- Connection 3 (inlet): This offers an entry to the lower section of the tube sack. The tube-side fluid enters from here.
- Connection 4 (outlet): This offers an exit from the shell. The shell-side fluid exits from here.
The flow of the tube side fluid
The tube side fluid is going to enter the lower section through the connection number 3 which acts as an inlet (as labelled above).
It is going to flow through the tube system and get out on the other side, only to re-enter the tube system but this time, in the top section.
When the tube side fluid re-enters through the top section of the tubes, it is going to flow again in a straight line in the opposite direction towards the other end of the heat exchanger.
It is going to come out and get discharged or exit the heat exchanger through connection number 1 which acts as an outlet.
The flow of the shell side fluid
The shell side fluid is going to enter the shell of the heat exchanger through connection number 2 which acts as an inlet.
It is then going to come through and pass through a series of baffles. Since all the tubes in the tube stack are not directly next to each other, it allows the shell side fluid to flow through the spaces around the tubes.
Finally, it is going to be discharged with the help of connection number 4 which acts as an outlet.
The tube side fluid and the shell side fluid flow simultaneously but through different pathways. This allows them to come in indirect contact with each other for the heat exchange, which is the main goal of this device.
Modified Structures of Shell and Tube Heat Exchanger:
Sometime, a slight variation is introduced in the above described process to offer slight modifications in the path of the two fluids.
This is done in order to suit the device better for specific usage in certain factories and industrial processes.
This can be carried out by building the tube systems in a slightly different win the following ways:
U Type Tube Heat Exchanger
In this type of heat exchanger, the long straight tubes are modified by rounding them into a U type shape.
In this new design, the tube side fluid enters not from the connections described earlier but the right side of the shell and tube heat exchanger. It then proceeds to exit from the opposite (left) side.
It is interesting to note that, this time, the tube side fluid represents a single pass of the heat exchanger. It travels directly through the tube stack and exits the system.
The shell side fluid, on the other hand, has a multi pass design which means that it passes over the tubes more than just once.
If the tube side fluid would have entered the tube system from the right side, then come out from the left side and then go back around for another cycle to finally come out from the same side it entered from, it would be known as a multi pass design as well.
Since one of the two fluids passes through the more than just once, it acts as a suitable example of a multi pass shell and tube heat exchanger.
Alternately, if the shell side fluid had entered from the top and came out from the bottom without the baffles playing any role in this process, it would also be considered a single pass design, and the overall device would be considered a single pass heat exchanger.
Fixed Tube Sheet Heat Exchanger
In this type of shell and tube heat exchanger, the tubes are all passing straight through the shell. They are fixed at both the ends (to the respective tube sheets), hence the name “fixed tube exchanger”.
Floating Head Heat Exchanger
In this type of a heat exchanger, one of the ends of the tube system is fixed with the tube sheet. However, the other end is kept free to expand, which could be considered “floating” as the name suggests.
Applications of Shell and Tube Heat Exchanger
Heat exchangers are equipped with different functionalities which provide massive benefits. These kinds of heat exchangers are used in different sectors due to their ever-changing types and configurations.
The following are some of the areas that widely use the shell and tube type, heat exchangers.
- Marine applications
- Power generation
- Metals and mining
- Air processing and compressor cooling
- Removal of process heat and feed water preheating.
- Cooling of hydraulic and lube oil.
- Cooling of turbine, compressor, and engine.
- Condensing process vapour or steam.
- Evaporating process liquid or steam.
- Huge chemical processes in oil refineries.
The above sectors vividly use the shell and tube heat exchanger, though this depends upon the specific type of applications. It is mandatory to get on with the use and configuration to use it at par.
With the help of the appropriate design, we can select the appropriate type that can be highly efficient.
How to Select a good Shell and Tube Heat Exchanger?
These are the best-in-class heat exchangers used in different sectors, whether refrigerators, chemical plants, and power generators. When it comes to selecting an efficient shell and tube heat exchanger, some standards should be followed.
This is to be maintained by a regulatory body that regulates the design of this machine. As per TEMA standards, the parts of this machine are defined.
These are based upon some of the specifications that these points can follow:
- Flow rates and composition of the fluids
- Temperature change needed
- Fluid properties for examples density thermal conductivity, viscosity
- Needed operating pressure and temperature
A comparison of both, the advantages and disadvantages of a shell and tube heat exchanger:
Advantages of Shell and Tube Heat Exchanger
After getting all the information regarding these heat exchangers, it is now time to get on with some of the benefits and limitations of the shell and tube heat exchangers.
Here are some of them which can provide all the essential insights:
This is one of the prominent advantages of shell and tube heat exchangers as it is quite effectively resistant to scale formation. It entails that these are less frequent for cleaning as compared to other kinds of heat exchangers.
Regulation and calibration
These are pretty effective and provide a massive possibility of power regulation. We can quickly increase or decrease the power by calibrating some properties such as length, diameter, or several sections of the pipes.
These are made up of resistant material that makes them suitable to withstand corrosion or rust. This feature makes them suitable for less maintenance and cleaning.
Shell and tube heat exchangers are pretty redundant and provide maximum service life. Due to this, one can quickly get the maximum of this exchanger.
Other advantages are,
- A shell and tube heat exchanger is much cheaper when compared to a plate heat exchanger.
- In this device, it is quite simple to find and isolate leaking tubes since the entire tube stack does not act as a single entity.
- The tubes can also be ‘double walled’ to reduce the likelihood of the shell side fluid leaking into the tube side fluid (or vice versa).
- It can prove to be suitable even in higher pressure and temperature conditions, something that is not quite easy for a plate heat exchanger to execute.
- The pressure drop (delta P/ΔP) is less when compared to that of a plate heat exchanger.
Disadvantages of Shell and Tube Heat Exchanger
Bulky configuration and dimensions
The shell and tube heat exchangers typically weigh around 130-150 kilograms, and the overall length is up to 4 meters. Due to this, it does not get fitted to constrained spaces. Fitting and installing are quite complex.
Protection of the outer parts
The shell and tube heat exchangers are constructed of electric welded pipe. These welded pipes are prone to leaks, and outer coating gets worn along the seam after some time. There are numerous others also as sometimes leaks appear due to metal corrosion.
The coefficient of efficiency for shell and tube heat exchangers is only 65-70% which ultimately increases the energy losses that make it relatively ineffective.
- One of the biggest problems with a shell and tube heat exchanger is that its efficiency is not as high as that of a plate heat exchanger.
- Unlike a plate heat exchanger, the cooling capacity of this device can not be increased.
- It also requires much more space to open and remove tubes in case any problems occur and it needs some fixing
Standards for Shell and Tube Heat Exchangers
There are a few codes and standards for the design of Sheel and tube type heat exchangers, as follows
API 660 – Shell and Tube heat exchangers
ISO 16812 – Shell and Tube heat exchangers for Petroleum industry
TEMA – Tubular Exchanger Manufacturers Association
Manufacturers of Shell and Tube Type Heat Exchangers
Let’s see, who are the manufacturers of shell and tube heat exchangers?
- Johnson Controls
- Onda. etc.
High Rated Course
This article provides us a holistic idea about one of the efficient heat exchangers and its working with all the other information such as advantages, working and the components used for the making.
With this information, it is clear that these heat exchangers are primarily used for vivid industrial applications.
Apart from this, we have a plethora of information available that can provide all the insights about the heat exchanger process. For more information, we have to consider the broader aspect of the same.
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