Shell and tube heat exchangers have a simple design, robust characteristics and relatively low purchase and maintenance costs. They also have a very high heat transfer rate although they require more space than a plate heat exchanger of similar thermal exchange capacity.
A shell and tube heat exchanger consists of a series of tubes housed within a cylindrical container known as a ‘shell’. All tubes within the shell are collectively termed a ‘tube bundle’ or 'tube nest'. Each tube passes through a series of baffles and tube sheets (also known as ‘tube stacks’). One of the tube sheets is fixed and one is free to move, this allows for thermal expansion as the heat exchanger is heated. Each medium has one entry and one discharge. The tube side medium is usually selected for the high pressure fluid as each tube can act as a small pressure vessel; it is also more cost effective to produce high pressure rated tubes than it is to produce a high pressure rated shell.
The shell and tube heat exchanger is split into two main systems, referred to as the shell side and tube side. Each system has one associated flowing medium. Turbulent flow increases the heat transfer rate of the heat exchanger and also reduces the likelihood of dissolved solids accumulating on the tube and shell walls (turbulent flow has a self-cleaning effect). Turbulent flow within the tubes is created by inserting tube inserts (also known as 'turbulators') into each of the tubes. Turbulent flow within the shell is created by baffles, which are used to direct the water across the tubes multiple times as it travels through the heat exchanger.
