The term heat exchanger encompasses all devices used to transfer energy from one fluid to another. Some examples of this group are: radiators, water heaters, refrigeration batteries, evaporators, steam generators, etc.
Direct contact heat exchangers, also known as mix exchangers, are devices where both fluids undergo a complete physical mixture. On the other hand, devices in which heat transfer takes place through a flat or cylindrical surface are called indirect contact exchangers. There is a barrier that physically separates the two fluid flows, thus there being no possibility of direct contact or contamination between such fluids, except in case of damage of the separation barrier.
A Shell & Tube heat exchanger is a device in which two fluids, one through the tube side and the other through the shell side, circulating at different temperature conditions, exchange heat through the walls of the tubes, without direct contact between them. These equipment are widely used in chemical process industries, especially in refineries, because of the numerous advantages they offer over other types of heat exchangers, for example:
- The pressures and pressure drops can be varied over a wide range.
- Thermal stresses can be accommodated inexpensively
- There is substantial flexibility regarding materials of construction to accommodate corrosion and other concerns.
- Cleaning and repair are relatively straightforward (easily dismantled)
- It is essential for the designer to have a good working knowledge of the mechanical features of S&T heat exchangers, and how they influence the thermal design.