Shell-and-tube condensers, also known as tube-and-shell or longitudinal-tube condensers, are typical wall-type heat exchangers with a long history of industrial application and continue to dominate among all heat exchangers today. The main components of a shell-and-tube condenser include the shell, tube bundle, tube plate, and end caps. The shell is typically circular, housing parallel tube bundles that are fixed at both ends to the tube plate.

Two fluids are involved in the heat exchange within a shell-and-tube heat exchanger: one flows inside the tubes, known as the tube side; the other flows outside the tubes, referred to as the shell side. The wall of the tube bundle serves as the heat transfer surface. To enhance the heat transfer coefficient of the fluid outside the tubes, a certain number of transverse baffle plates are typically installed inside the shell. These baffles not only prevent short-circuiting and increase fluid velocity but also force the fluid to pass through the tube bundle multiple times in a specified path, significantly increasing turbulence. Common baffles include crescent and disk shapes, with the former being more widely used. Each time the fluid passes through the tube bundle is called a tube pass, and each time it passes through the shell is called a shell pass. To increase the fluid velocity inside the tubes, appropriate baffles can be set in the end caps to evenly divide all the tubes into several groups. This allows the fluid to pass through only a portion of the tubes each time, repeatedly traversing the bundle, which is referred to as multi-tube passes. Similarly, to increase the fluid velocity outside the shell, longitudinal baffles can be installed inside the shell to make the fluid pass through the shell space multiple times, known as multi-shell passes. Within a tubular heat exchanger, due to the different temperatures of the fluids inside and outside the tubes, the temperatures of the shell and the tube bundle are also different.