Shell and tube heat exchangers consist of tubes housed inside a large shell vessel. Fluids of different temperatures are circulated through the tubes and shell without mixing. Common types include U-tube, straight tube single pass, and straight tube double pass configurations. Heat is transferred between the fluids through the tubes and baffles direct the shell-side fluid flow across the tubes. Shell and tube heat exchangers are widely used due to their design flexibility, reliability, and ability to operate at a wide range of pressures and temperatures.