A Shell and Tube Heat Exchanger is a mechanical device used to efficiently transfer heat between two separate fluids without mixing them. It consists of a bundle of tubes enclosed within a cylindrical shell—one fluid flows through the tubes (tube side), while the other circulates around the tubes inside the shell (shell side). As the fluids pass through their respective paths, heat is exchanged through the tube walls, allowing thermal energy to move from the hot fluid to the cold one. This design is widely used in industries such as oil and gas, power generation, chemical processing, and HVAC due to its durability, high pressure and temperature tolerance, and ease of maintenance.