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A tube sheet is a plate, sheet, or bulkhead which is perforated with a pattern of holes designed to accept pipes or tubes. These sheets are used to support and isolate tubes in heat exchangers and boilers or to support filter elements. Depending on the application, a tube sheet may be made of various metals or of resin composites or plastic. A sheet tube may be covered in a cladding material which serves as a corrosion barrier and insulator and may also be fitted with a galvanic anode. Tube sheets may be used in pairs in heat exchange applications or singularly when supporting elements in a filter.
Perhaps the best known use of tube sheets are as supporting elements in heat exchangers and boilers. These devices consist of a dense arrangement of thin walled tubes situated inside an enclosed, tubular shell. Tubes are supported on either end by sheets which are drilled in a predetermined pattern to allow the tube ends to pass through the sheet. The ends of the tubes which penetrate the tube sheet are expanded to lock them in place and form a seal.
The tube arrangement forms a contained unit between the tube sheets. The tube sheets are then bolted to flanges inside the shell. The shell extends beyond each tube sheet and is sealed, thereby forming two closed chambers on the non-tube ends of the tube sheets. This creates an arrangement where the exchanger consists of two separate end chambers joined by tubes which pass through an isolated space between the tube sheets. Heated fluid is then passed from one end chamber to the other through the tubes where cold fluid in the cavity between the tube sheets absorbs the heat energy.
The design of tube sheets is a fairly precise and complex process; the exact number of tubes needs to be established and a pattern of holes calculated to spreads them evenly over the tube sheet surface. Large exchangers may have several thousand tubes running through them arranged into precisely calculated groups or bundles. Sheet design and production is largely automated these days with computer-aided design (CAD) software performing the calculations and the tube sheet drilling done on computer numerical control (CNC) machines.
The tube sheets used in heat exchangers and boilers are often clad with an insulating layer which also serves to protect against corrosion. To further protect the tube sheet from rust, a sacrificial or galvanic anode may also be attached to the surface of the sheet. Tube sheets are also used on cartridge-type filter devices to support the individual filter elements. They are similar in design to the high heat boiler varieties except they are typically made of resin composites or plastic and are generally used as single units. There are usually fewer tubes involved in a filter application although the tube sheet design still has to be carefully calculated to ensure optimal performance.