A shell-and-tube heat exchanger is one of the most common and versatile types of heat exchangers, used to transfer heat between two fluids—typically a liquid or gas—without mixing them. It consists of a series of tubes enclosed within a cylindrical shell. One fluid flows through the tubes (tube side), while the other flows around the tubes inside the shell (shell side).

The heat is transferred through the walls of the tubes: the hot fluid transfers its heat to the cooler fluid via conduction, with convection aiding the process on both sides. This design allows for large surface areas and high-pressure operation, making it suitable for both cooling and heating applications.

Shell-and-tube heat exchangers are widely used in power plants, chemical processing, oil refineries, and HVAC systems. They are preferred for their robust construction, ability to handle high temperatures and pressures, and ease of maintenance. Variations in tube layout (such as U-tube or straight-tube) and flow arrangement (counterflow or parallel flow) help adapt the design to specific performance requirements.