Shell and tube heat exchangers are a type of heat exchanger. The most common type of heat exchanger in oil refineries and other large chemical processes, it can withstand higher pressures. Heat exchangers of this type consist of a shell (a large pressure vessel) with a bundle of tubes inside. One fluid flows through the tubes and another fluid flows over the tubes (through the shell) to transfer heat between the two fluids. Tube bundles are composed of several types of tubes, including plain tubes, longitudinally finned tubes, etc. The heat exchanger flows two fluids, each of which has a different starting temperature. Both flow through the tubes (the tube side) and one flows outside the tubes but inside the shell (the shell side). Through the tube walls, heat is transferred from one fluid to another, either from tube to shell or vice versa.
U-tube heat exchanger The typical layout of U-tube exchangers and how they got their name. The tube bundle is made of continuous tubes that bend into a U shape, and is secured to the shell using one tubeplate (shown above). A multi-pass design is created by the coolant flowing from the top half of the header, through the u-tubes, and then out of the bottom half of the header. As the bend side is free-floating within the shell and has room to expand/contract, no expansion joints are needed to allow for thermal expansion. They are excellent for high-temperature differences where expansion is expected. Their only major drawback is that they are hard to clean due to the bends.
Fixed tube sheet exchanger Two stationary tube sheets (labelled above) are welded directly to the shell of the fixed tube sheet exchanger. As they are the easiest to manufacture, they are the most cost-effective version of the shell and tube design. However, since the tubes are rigidly attached to the shell via the tube sheets, Expansion that is limited must be prevented. If there is a high temperature difference between the tube-side and shell-side flows, operators risk expansion and damage, so the temperature difference must be kept small. Another disadvantage of fixed tube sheet models is that the outside of their tubes cannot be accessed for cleaning. The shell-side fluid being used must not foul the outside of the tubes, or the heat exchanger’s efficiency will decrease.
Floating head exchanger The floating head exchanger combines the best features of both previous designs. A fixed tubesheet holds one end of the tubes stationary to the housing, while the other end is free to expand because of a floating tubesheet. This part allows the tubes to expand with increased temperatures, without having to bend the pipes. In addition to being able to clean the tubes easily, operators can also create a high temperature difference without fear of breaking the devices. Therefore, the floating head exchanger is the best heat exchanger in terms of efficiency and maintenance, but comes at a higher price.