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.
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Shell and tube Heat Exchangers represent the most widely used vehicle for the transfer of heat in industrial process applications. They are frequently selected for such duties as:
- Process liquid or gas cooling
- 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
- Compressor, turbine and engine cooling, oil and jacket water
- Hydraulic and lube oil cooling
- Many other industrial applications
Layouts
Shell and tube (a.k.a. multipass) heat exchangers are the most common industrial application for liquid/liquid heat exchange.
Inside the shell, baffles (dividers) are installed to direct the flow around the tubes, increase velocity, and promote crossflow. They also help support the tubes. The baffle cut is the ratio of the baffle window height to the shell diameter. Typically, baffle cut is about 20 percent. It effects both heat transfer and pressure drop. Designers also need to specify the baffle spacing; maximum spacing depends on how much support the tubes need.
A pass is when liquid flows all the way across from one end to the other of the exchanger. We will count shell passes and tube passes. An exchanger with one shell pass and two tube passes is a 1-2 exchanger (shown in the figure). Almost always, the tube passes will be in multiples of two (1-2, 1-4, 2-4, etc.), since odd numbers of tube passes have more complicated mechanical stresses, etc. An exception: 1-1 exchangers are sometimes used for vaporizers and condensers.
How do I decide whether the given shell and tube heat exchanger is a counter flow or parallel flow?
If the hot fluid is flowing in same direction as of cold fluid, then it is parallel heat exchanger.
Bur if the hot fluid is flowing in direction opposite to the cold fluid then it is counter flow heat exchanger.
2) If you have the information about the temperatures at inlet and outlet condition then you can find out the effectiveness. If the effectiveness is less than 50% it is mostly parallel flow heat exhanger. But if it has more than 50% than it is counterflow as effectiveness of parallel flow cannot be more than 50%. If both have effectiveness less than 50% then the greater one is counterflow heat exchanger.
3) If there are two heat exchangers in front of you with same parameters like inlet and outlet temperatures, mass flow rate. If you have to decide which one is parallel and counter flow,then the heat exchanger with larger area will be parallel flow while the one with less area will be counterflow heat exchanger.
4) If the outlet temperature of the hot fluid is less than outlet temperature of cold fluid it is definitely counterflow heat exchnager as it is possible only in counterflow heat exchanger
5) If you find out the LMTD of both heat exchangers for same mass flowrate, area then the one with higher LMTD will be counter flow heat exchanger.