Shell and tube heat exchangers are described along with basics, definition, parts, working principle, types, construction, application, advantages, disadvantages, etc.
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.
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.
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?
There are some essential parts of the shell and tube heat exchangers, without which you cannot imagine.
The following are the principal ones.
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.
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.
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 tube sheets are installed in order to fulfill the following purposes:
Hence, these two tube sheets act as anchor points at the two terminals of the shell.
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 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.
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.
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.
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.
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.
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.
The shell side fluid is among the essential parts of this exchanger that keeps on working around the baffles, which helps transfer energy.
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
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.
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.
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.
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.
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.
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:
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.
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”.
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.
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.
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.
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:
A comparison of both, the advantages and disadvantages of a 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,
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.
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
Let’s see, who are the manufacturers of shell and tube heat exchangers?
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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