Heat Exchanger
A heat exchanger is a system designed for the transfer of heat between two or more fluids that are at different temperatures.
 
 
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Applications of Heat Exchangers
Heat exchangers have wide applications in various industries, including oil refineries, pharmaceuticals, food production, metal smelting, air conditioning, refrigeration systems, aerospace, and power plants.
 
Key Considerations When Selecting a Heat Exchanger
Choosing the appropriate heat exchanger should be done by an engineer or expert. Factors to consider include:

Determining the phase of the two fluids
Operating pressure and temperature
Cleanability
Manufacturing and design processes
Choosing between plate or shell-and-tube heat exchangers
Fluid corrosiveness
Material (e.g., copper, stainless steel, carbon steel, aluminum)
Installation and maintenance costs

 
 
Plate Heat Exchanger
A plate heat exchanger consists of multiple plates in parallel, which may be either smooth or corrugated. These plates not only separate the fluids but also create channels for fluid flow. The design facilitates a higher heat transfer rate as the fluids spread across the metal plates, improving heat exchange efficiency. Compared to shell-and-tube heat exchangers, plate heat exchangers are more compact and can achieve substantial thermal exchange within a smaller size.
 
Design of Plate Heat Exchanger
Unlike the design, where the heat exchange occurs inside a tube, the plate heat exchanger uses sequential chambers formed by stainless steel plates due to their strength and high-temperature resistance.
 
Shell-and-Tube Heat Exchanger
Shell-and-tube heat exchangers are used in various industrial sectors because they are highly adaptable to high-pressure and high-temperature conditions. These exchangers consist of a series of tubes placed within a shell or cylinder.
 
In fact, one fluid flows through the tubes, while the other fluid circulates around the tubes within the shell. Heat is transferred between the fluids as a result of the temperature difference. The heat exchangers come in a variety of applications and are classified based on different features.
 
The shell-and-tube heat exchanger is used in industries, utilities, water structures, paper manufacturing factories, refrigeration systems, pharmaceuticals, painting, mining, and metallurgy.
 
Therefore, shell-and-tube heat exchangers are the most widely used exchangers.
 
The mechanism of this type of heat exchanger works by having the hot fluid flow through the cold fluid and then transferring heat without mixing. In essence, a shell-and-tube heat exchanger is designed with a series of tubes and shells. One fluid moves through the tubes, while the second fluid moves around the tubes. In this process, the heat is transferred, with the cold fluid absorbing the heat from the hot fluid.
 
In shell-and-tube heat exchangers, the efficiency of heat transfer depends directly on how much the fluids contact the surface around the tubes. In fact, this factor is directly related to the quantity of tubes within the heat exchanger. Therefore, increasing the number of tubes or pathways improves the heat transfer rate.
 
 
It should be noted that shell-and-tube heat exchangers should be cleaned regularly because the flow of various fluids can lead to deposits. The cleaning of shell-and-tube heat exchangers can be conducted through a variety of chemical or mechanical techniques.
 
There are numerous benefits to using shell-and-tube heat exchangers. The most significant advantage is their affordability. Additionally, identifying leaks in the tubes is relatively simple, and different cleaning methods can be used. These heat exchangers are known for their high resistance to heat, withstanding temperatures above 260°C.
 
Shell-and-tube heat exchangers are available in a wide range of designs. One of these variants is the U-tube heat exchanger. This particular type is more cost-effective than others. The use of the U-shape maximizes the contact between the shell and the tubes.
 
 
A different kind of heat exchanger is the fixed tube sheet model, which has a very simple design and is relatively inexpensive. This type includes N, M, and L variations. It contains a fixed tube sheet, and the tubes within it are mechanically cleaned without any leakage.
 
Another version of the shell-and-tube heat exchanger is the floating sheet heat exchanger. These heat exchangers have high resistance to thermal expansion and are very easy to clean. Floating sheet heat exchangers come in P, T, W, and S classes. The end of the heat exchanger is not welded to the shell. The components of the shell-and-tube heat exchanger are the partition plate, gaskets, baffles, tubes, covering plate, and bolts and nuts.
 
 
Gasketed Heat Exchanger
In gasketed heat exchangers, rubber seals are placed around the edges of metal plates and prevent leakage and direct the flow of fluids.
 
Factors Influencing Heat Transfer in Heat Exchangers
One of the most important elements that significantly affect heat transfer in a heat exchanger is the area separating the two fluids. Furthermore, the material of the heat exchanger is extremely important. For example, when a heat exchanger is made from copper, the heat transfer coefficient increases, but with steel, the rate of heat transfer considerably decreases. The velocity and the heat transfer coefficient are also key factors in the heat transfer of heat exchangers because they cause turbulent flow, which increases the heat transfer.
 
However, it is worth noting that extremely high flow speeds can lead to the corrosion of the heat exchanger. The fluid must first be heated before entering the tubes. Therefore, it notably increases the total heat transfer coefficient.
 
Moreover, the type of fluid affects the heat transfer process. For example, heat transfer differs between oil and water. Chemical and thermal properties are also effective such as temperature, pressure, and flow speed. The heat exchanger design and surface area are also important factors in heat transfer; for example, plate heat exchangers are able to transfer more heat than shell-and-tube types due to their larger surface area.