The shell and tube type heat exchanger is widely used on board ships due to the flexibility it offers in order to allow a wide range of pressures and temperatures. A shell and tube heat exchanger consists of a number of tubes mounted inside a cylindrical shell. Two fluids can exchange heat. One fluid flows over the outside of the tubes, while the other fluid flows through the tubes. The fluids can flow in a parallel or cross / counter flow management, and the fluids can be single or double phase.
This type of heat exchanger is by far the most common heat exchanger used in various industries. These heat exchangers can be used in almost all process heat transfer applications. They are more rugged than the other types of heat exchangers, as they can withstand more physical as well as process abuse.
A shell and tube type heat exchanger consists of various components such as tubes, tubesheets, baffles, tie rods and spacers, pass partition plates and expansion joints. The shell and tube type heat exchanger is generally divided into four major parts – Front Header, Rear Header, Tube Bundle, and Shell.
Front header is where the fluid enters the tubeside of the exchanger. It is also referred to as ‘Stationary Header’. The tubeside fluid leaves the exchanger from the Rear Header. In exchangers having multiple tubeside passes, the fluid returns to the Front Header after completing the cycle. Tube bundle consists of tubes, tubesheets, baffles and tie rods, etc. to hold the bundle together. The shell contains the tube bundle.
Tubesheets are used to provide holes through which tubes are inserted. These tubesheets are generally referred to as plates or forgings. The tubes are appropriately secured to the tubesheet so that the fluid on the shell is prevented from mixing with the fluid on the tube side. Holes are drilled on the tubesheet, in either triangular or square pattern.
A tube pitch is the distance between the centers of the tube hole. They are used to reduce the shell side pressure drop and control the velocity of the shell side fluid as it flows across the tube bundle. The triangular pitch provides higher heat transfer and compactness. On the other hand, the square pitch facilitates mechanical cleaning of the outside of the tubes. Generally, there are two tubesheets fitted on both the ends, however, for the U-tube bundles only one tubesheet is required.
Tie Rods and Spacers:
To handle the baffle assembly together and maintain the selected baffle spacing, tie rods and spacers are made use of. The tie rods are secured at one end to the tubesheet. The spacers are placed over the tie rods between each baffle to maintain the selected baffle pitch. Depending on the diameter of the shell and size of the tie rod and spacers, the minimum number of tie rod and spacers can be used.
To contain the tube side fluid and to provide the desired flow path, channels or heads are required for shell and tube type heat exchangers. Usually, the channel type is selected on the basis of its application. Most channels can be removed for access to the tubes. The most commonly used channel type is the bonnet. It is generally used for services which do not require frequent removal of the channel for inspection or cleaning. In other type of channels, the removable cover channel can be either flanged or welded to the tubesheet. The removable cover enables access to the channel and tubes for inspection or cleaning without having to remove the tube side piping. When frequent access to the tubes is required, removable cover channels are equipped.
These are some essential parts of the shell and tube type heat exchanger. It’s better to get in touch with our professionals if you wish to know more about our world-class heat exchangers. We at Kainon also manufacture marine boilers which are used on board ships for various purposes.