Shell-and-tube condensers, also known as tube-shell or longitudinal-tube condensers, are typical cross-flow heat exchangers with a long history of industrial application, holding a leading position among all types of heat exchangers to this day. The main components of shell-and-tube condensers include the shell, tube bundle, tube plate, and end caps. The shell is usually circular, internally fitted with parallel tube bundles, with the ends of the bundles securely fixed to the tube plate.

Two fluids are involved in heat exchange within a shell-and-tube heat exchanger: one flows inside the tubes, referred to as the tube side; the other flows outside the tubes, known as the shell side. The wall of the tube bundle constitutes the heat transfer surface. To enhance the heat transfer coefficient of the fluid on the shell side, a certain number of transverse baffle plates are typically installed within the shell. These baffles not only prevent short-circuiting of the fluid, increase fluid velocity, but also force the fluid to cross the tube bundle multiple times in a prescribed path, significantly increasing turbulence. The commonly used baffles are crescent-shaped and disc-shaped, with the former being more widely applied. 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 and cross the bundle multiple times, which is known as multi-tube passes. Similarly, to increase the fluid velocity on the shell side, longitudinal baffles can be installed within the shell to make the fluid pass through the shell space multiple times, referred to as multi-shell passes. Inside a tube-type 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.