Heat transfer is an interaction that occurs between materials by reason of the temperature difference between them. It is the most common type of inter-action in heat exchange equipment.

Heat transfer between the streams is usually effected indirectly. The streams are separated by a solid material, such as a metal tube wall or plate, or even a plastic membrane, and the heat passes from the first fluid through the solid material to the second fluid. The consequences of the heat transfer are often local increases in the temperature of the cooler fluid and decreases in that of the warmer fluid; they may also entail the change of phase of one or both fluids.

There are two common type of heat exchangers in oil and gas industries:

• Shell and tube heat exchangers
• Air cooled heat exchangers

The shell and tube exchanger is by far the most common type of heat-transfer equipment used in the oil and gas industries. The advantages of this type are:

• The configuration gives a large surface area in a small volume.
• Good mechanical layout: a good shape for pressure operation.
• Uses well-established fabrication techniques.
• Can be constructed from a wide range of materials.
• Easily cleaned.
• Well-established design procedures.

Essentially, a shell and tube exchanger consists of a bundle of tubes enclosed in a cylindrical shell. The ends of the tubes are fitted into tube sheets, which separate the shell-side and tube-side fluids. Baffles are provided in the shell to direct the fluid flow and support the tubes. The assembly of baffles and tubes is held together by support rods and spacers.

Air-cooled exchangers consist of banks of finned tubes over which air is blown or drawn by fans mounted below or above the tubes (forced or induced draft). Air-cooled exchangers should be considered when cooling water is in short supply or expensive. They can be competitive with water-cooled units even when water is plentiful.