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· Shell-and-tube heat exchangers consist of basic components such as the shell, outer cover, heat exchange tubes, tube box, tube box cover, tube sheet, baffle plates, and connection pipes. Other components include； Pull rods, spacing tubes, partition plates, impact protection plates, longitudinal partitions, sealing strips, and supports, etc. 2. Classification based on structure 2.1 Fixed-tube-sheet heat exchangers In fixed-tube-sheet heat exchangers, the ends of the tubes are firmly connected to the tube sheet, which is welded to the shell. This structure comes in several forms, including detachable tube box covers, head-type tube boxes, and integral tube sheets. Fixed-tube-sheet heat exchangers have the advantage of low cost due to their simple structure. In fact, as long as no expansion joints are installed on the housing, it is the cheapest structural design available. There are also other advantages, such as the ability to mechanically clean the inside of the tubes by removing the tube box cover, and since there are no flange connections, the leakage of fluid in the shell side is minimized. The disadvantage of fixed-tube-sheet heat exchangers is that the tube bundle is fixed to the shell and cannot be removed, thus mechanical cleaning of the outside of the tubes is not possible. Therefore, its use is limited by the requirement that the medium outside the tube be clean. However, if a satisfactory chemical cleaning method is available, then this heat exchanger can also be used in situations where the shell side is contaminated. In the event that there is a large temperature difference between the tube and the shell, and the tube sheet is unable to absorb this difference, it becomes necessary to install an expansion joint, which will inevitably offset to a large extent the advantage of low cost. 2.2 U-tube heat exchangers: As the name implies, the tubes in a U-tube heat exchanger are bent into a U shape, and there is only one tube sheet. However, the advantage of lower cost for single-tube sheet design is offset by the additional expenses associated with bending the U-tubes and the need to increase the shell diameter (based on the minimum bending radius of the U-tubes); as a result, the cost of this type of heat exchanger is comparable to that of heat exchangers with fixed tube sheets. The advantage of a U-tube heat exchanger is that one end is unrestrained, allowing the tube bundle to expand and contract freely. Furthermore, since the tube bundle can be pulled out, the U-shaped tube bundle can be cleaned outside the tubes. Its drawback is that effective cleaning inside the tube is not possible; therefore, a telescopic rotating cleaning head must be used for cleaning. 2.3 Floating-head heat exchangers: Floating-head heat exchangers are the most widely used type of shell-and-tube heat exchanger, and they are also the most expensive ones. One tube sheet is fixed to the shell, while the other can move freely inside the shell. This structure not only enables cleaning inside and outside the tubes but also allows the tube bundle to expand and contract freely. Therefore, it can be used in situations where the media inside and outside the pipes are both dirty, such as in some units in refineries. There are many structural types of floating-head heat exchangers, among which the two most commonly used are the pull-out floating head with hook rings and the regular pull-out floating head. 3. Classification based on application: Generally, they can be divided into single-phase flow (heating or cooling of liquids or gases) and two-phase flow (condensation or vaporization). Shell-and-tube heat exchangers have a tube side and a shell side, so they can be classified according to several applications: · Single-phase (either on the shell side or the tube side) · Condensation (condensation on one side, single phase on the other) · Vaporization (vaporization on one side, single phase on the other) · Condensation/vaporization (vaporization on one side, condensation on the other). The following terms are also frequently used: Heat exchanger: Both sides are in single-phase and consist of process fluids (i.e., there is no common medium). Heater: One side contains the process fluid, while the other side contains a common heating medium such as steam or hot oil. Condenser: The flow on one side is condensed gas, while the other side has cooling water or air. Cryocooler: On one side, the fluid flow is the process fluid that is condensed at a temperature below atmospheric pressure; on the other side, it is the boiling refrigerant or process fluid. 4. Design data Before starting the design, let’s take a look at some of the data that process engineers should provide in actual heat transfer design. (1) The flow rates of the two streams. (2) Inlet and outlet temperatures of the two streams. (3) Operating pressure of the two fluids: It is essential for gaseous media, especially when the density of the gas is not provided; however, for liquid media, it is not necessarily required as their properties do not change with pressure. (4) Allowable pressure drop for the two flows. (5) Frictional drag. (6) Physical properties: including viscosity, thermal conductivity, density, specific heat, especially the properties at the inlet and outlet temperatures. (7) Heat load. (8) Type of heat exchanger. (9) Pipeline specifications. (10) Heat exchanger tube specifications. (11) Maximum diameter of the shell. (12) Structural materials. 5. Pipe side design 6. Heat transfer coefficient 7. Pressure drop