A shell and tube heat exchanger is a class of heat exchanger designs. It is the most common type of heat exchanger in oil refineries and other large chemical processes, and is suited for higher-pressure applications. As its name implies, this type of heat exchanger consists of a shell (a large pressure vessel) with a bundle of tubes inside it. One fluid runs through the tubes, and another fluid flows over the tubes (through the shell) to transfer heat between the two fluids. The set of tubes is called a tube bundle, and may be composed of several types of tubes: plain, longitudinally finned, etc.
Two fluids, of different starting temperatures, flow through the heat exchanger. One flows through the tubes (the tube side) and the other flows outside the tubes but inside the shell (the shell side). Heat is transferred from one fluid to the other through the tube walls, either from tube side to shell side or vice versa. The fluids can be either liquids or gases on either the shell or the tube side. In order to transfer heat efficiently, a large heat transfer area should be used, leading to the use of many tubes. In this way, waste heat can be put to use. This is an efficient way to conserve energy.
Shell and Tube heat exchangers are frequently used for:
Process or refrigerant vapor or steam condensing
Process liquid, steam or refrigerant evaporation
Process heat removal and preheating of feed water
Thermal energy conservation efforts, heat recovery
Process liquid or gas cooling
Compressor, turbine and engine cooling, oil and jacket water
Hydraulic and lube oil cooling
Many other industrial applications
Shell and tube Heat Exchangers can provide large amounts of effective tube surface while minimizing the requirements of floor space, liquid volume and weight. Shell and tube Heat Exchangers have the ability to transfer large amounts of heat in relatively low cost, servicable designs. Shell and tube exchangers are available in a wide range of sizes. Tube surfaces from standard to extraordinary metals with plain or upgraded surface characteristics are widely available. They can help leave the cost effective mechanical design for the flows, liquids and temperatures involved.
Fixed Tube Sheet, 2-Pass Heat Exchanger
There are two distinct types of shell and tube Heat Exchangers, based in part on shell diameter. Designs from 2" to around 12" in shell diameter are available that feature shell constructions of low cost welded steel, brazed pipe with hub forgings, cast end Bonnets and copper tubing rolled or brazed to the tube sheet.
The other major type of shell and tube Heat Exchanger generally is seen in shell diameters from 10" to over 100". Commonly available steel pipe is generally used up to 24" in diameter. Above 24", manufactures use rolled and welded steel plate, which is more costly and roundness can become an issue.
Heat Exchangers of this type are commonly manufactured to the standards set forth by TEMA, the Tubular Exchangers Manufacturers Association. TEMA, in cooperation with users and manufacturers, establishes a common set of guidelines for the construction methods, tolerances and practices to be employed. This allows industrial consumers to obtain more than one manufacturers offerings and know that they are generally of similar design and construction. Additionally, it allows manufactures to establish industry approved designs and offer state of the art equipment that help to assure competitiveness and overall product reliability.
Although there exists a wide variety of designs and materials available, there are components common to all designs. Tubes are mechanically attached to tube sheets, which are contained inside a shell with ports for inlet and outlet fluid or gas.
They are designed to prevent liquid flowing inside the tubes to mix with the fluid outside the tubes. Tube sheets can be fixed to the shell or allowed to expand and contract with thermal stresses by have one tube sheet float inside the shell or by using an expansion bellows in the shell. This design can also allow pulling the entire tube bundle assembly from the shell to clean the shell circuit of the exchanger.
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