Shell and tube heat exchangers are elongated steel cylindrical vessels containing bundles of parallel tubes. Liquid passes through the inside of the shell over the exterior side of the tubes, with another liquid passing through the interior of the tubes, causing the
necessary interchange of heat between the two liquids.
The heads at the ends of the exchanger can be designed to accommodate several passes of the tube side. Multiple passes on the shell side can be achieved by installing baffles parallel to the tubes.
Baffles may also be installed inside the shell, perpendicular to the tubes, do direct the liquid in the shell against the tubes. Multiple passes are used to increase the fluid velocity or to improve the flow
path, causing increased heat recovery.
Following figure shows an exchanger with two passes on the tube side and one on the shell side. The shells of most heat exchangers are constructed of seamless pipe for small diameters and shaped welded steel plates for larger sizes.
Tube bundle sizes can vary from 8 to 96 inch (200 mm to 2400 mm) in diameter and from 6 to 50 ft (1800 mm to 15000 mm) in length. The ends of the shell can be designed to accommodate, welded, dished or flanged shell covers as well as flanged or welded heads.
Both the tube side and shell side of the exchangers have inlet and outlet nozzles positioned to provide the required flow through the exchanger. The unit is supported at the shell by attached saddles for horizontal installations and by lugs for vertical arrangements.
Tube bundles are made up of many small diameter tubes that are expanded into tube sheets at each end of the bundle. One end is usually fixed, the other is allowed to float for expansion. For the more simplified U-tube arrangement, only one tube sheet is used, which is integrated with the channel head.
Following drawing shows a typical shell and tube heat exchanger identifying the key items of construction. With many shells, shell covers and head covers available, exchangers can be arranged in various combinations to provide a wide range of services.
The U-tube, fixed tube and kettle arrangements are shown below.