Heat Exchanger Glossary of Industry Terms

Baffle Plate. Also called support plate. Tubes pass through this plate for support. Provides a blocked path for the shell-side medium, forcing the medium across the tubes for better heat exchanger performance. 

Baffle Spacing. The space between baffle plates on a tube bundle. Baffle spacing is adjusted to achieve maximum heat exchanger performance.

Bonnet – Similar to a channel with straight tubes but without a removable cover. These do not have divider walls and are at each end of the heat exchanger.

Bonnet Assembly – Manages the tube side liquid for circulation through the tubes. This can also hold the tube side inlet and outlet connections and/or pass ribs.

End Plate. A cover that has been welded to the heat exchanger. Most end plates are used on bonnet assemblies.

Fixed Tube Sheet. A nonremovable tube sheet; the tube sheet on a core assembly; or any tube sheet that is an integral part of the shell assembly.

Floating Tube Sheet. The tube sheet at one end of a removable-tube bundle. The floating tube sheet always has a smaller diameter than does the stationary version. The floating tube sheet moves freely with the expansion and contraction of the tube bundle due to temperature changes in operation.

Gasket. A sealing device used between two parts to prevent leakage. Types include inside-the-bolt circle (no bolt holes) and full face (with bolt holes and the same diameter as the flange).

Impingement Plate. A small perforated- -plate or bar assembly placed inside the shell-side nozzle, usually a dome-type nozzle. The plate also can be attached directly to the bundle by being tack-welded to the tie rods. The impingement plate protects and prolongs tube life by breaking up and slowing down the shell side fluid, which otherwise would erode the tubing.

Nipple. A short piece of pipe threaded on both ends.

Design Pressure. Also called maximum allowable operating pressure. Used by engineers to calculate part thickness and heat exchanger design. Generally, it is slightly higher than the most severe condition or highest operating pressures seen by the heat exchanger.

One, Two, Four Pass. The number of times the fluid passes through the tube bundle. In a one-pass unit, the tube-side medium passes through all the tubes once. In a two-pass unit, it passes through one-half of the tubes and returns through the other half. A four-pass unit goes through approximately one-quarter of the tubes, down and back four times. Greater-than-one pass heat exchangers are referred to as multipass units.

Operating Pressure. The pressure a heat exchanger is actually operating at while in use.

Outer-Tube Limit (OTL). The diameter created by encircling the outermost tubes in a tube layout. Engineers use the design OTL to calculate clearances between bundle parts. The actual OTL is usually a few-thousandths less than the design OTL.

Test Pressure. Generally 1.5 times the design pressure. It is used during a hydrostatic test that detects leaks at any joint on the heat exchanger.

Removable Bundle. A type of heat exchanger in which the tube bundle can be removed from the shell pipe. This provides easy cleaning of the shell side and a less expensive way of replacing worn out tubes.

Shell Assembly. The assembly into which the tube bundle fits. The shell also contains the shell-side connections.

Shell Head. A formed plate welded to the shell, or bonnet, pipe. It can be many styles or shapes, including flanged and dished, elliptical, ellipsoidal and hemispherical. Generally, as a head gets flatter, it gets weaker; therefore, designers can use a flat-end plate or a thinner formed head to do the same job.

Shell Side. The side of a heat exchanger where the fluid circulates around the outside of the tubes.

Stationary Tube Sheet. The tube sheet at one end of a removable bundle. It has a larger diameter than the floating tube sheet and is held together in a permanent position between the bonnet and shell flanges.

Tube Sheet. A plate that secures both ends of the tube in a heat exchanger. Both the shell-side and tube-side mediums come in contact with it.

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1, 2, 4 Pass – The number of times, one, two or four, the liquid passes through the tube bundle. Anything greater than a one pass is considered a multi-pass unit.

Box Linear Style – Heat exchanger tubes parallel to each other from the inlet to the outlet manifold.

Bundle Assembly – The tubing assembly in removable bundle heat exchangers. This typically includes tubes, tube sheets, baffles, spacers and tie rods.

Capscrew – A threaded bolt that holds the bonnet onto the core of some types of heat exchangers.

Channel – A kind of front end with a removable cover from which the tube side flows in and out. A dividing wall separates the inlet and outlet flow.

Channel Assembly – Same function as a bonnet assembly, except that the cover is removable and provides access to the ends of the tubes.

Collector – What the tubes in a heat exchanger drain into.

Core Assembly – The shell and tube assembly in fixed tube sheet heat exchangers.

Coupling – The parts that connect the piping to the heat exchangers, come in many varieties.

Cover/Cover Assembly – Used to cover an opening on a heat exchanger. Covers are different from end plates because they can be removed to clean the interior of the tube side, without distressing any piping.

Cradle Assembly – The part used to support the heat exchanger and to secure it to the mounting surface when welded or strapped to the shell. Cradles may be fixed or moveable.

Design Pressure – Calculations of part thickness and heat exchanger design based on the most severe conditions or highest operating pressures seen by the heat exchanger, to make the pressure slightly higher.

Dome – A type of nozzle connection that provides a larger nozzle opening between the pipe size and heat exchanger tube bundle, typically to prevent tube erosion due to high inlet velocities.

End Plate – Covers welded to the heat exchanger. The majority of end plates are used on bonnet assemblies.

End Zone – The first baffle space on a tube bundle, occurring between the tube sheet and the first baffle plate. It is adjusted to maintain the baffle plates within the two shell side nozzles.

Ferrule – A small copper or stainless steel piece of tubing that is crimped or squeezed onto the tie tube, up against the last baffle, and locks the baffles into position.

Fixed Tube Sheet – A tube sheet that is an essential part of the core shell assembly.

Floating Tube Sheet – Placed at one end of a removable tube bundle and allowed to move freely with the expansion and contraction of the tube bundle due to temperature changes in operation. It always has a smaller diameter than the immobile tube sheets.

Gasket – A device used between two parts that helps prevent leakage.

Impingement Plate – A small perforated-plate or bar assembly in the shell-side nozzle that can also be attached directly to the bundle. This protects and prolongs tube life by breaking up and slowing down the shell side fluid, which slows the erosion of the tubing.

In and Out End – The side of the heat exchanger containing the tube side inlet and outlet connections in a multi-pass unit.

Lantern Ring – A metal or nylon ring on some packed joint heat exchangers that holds the packing rings in place.

Operating Pressure – The pressure a heat exchanger is operating at while in use.

Packed End – The end of a heat exchanger, which contains the packed joint and the packing rings.

Pass Lane – A lane in a tube layout where there are no tubes and where the pass ribs mate.

Pass Rib – A separator plate inside a bonnet or channel that merges with the pass lane surface, used to form multi-pass heat exchangers. By arranging the ribs, a designer can direct the flow of the tube side substance.

Protector Rod – Protects the heat exchanger parts (tubes, tube sheets and bonnets) from corrosion by acting as a sacrificial anode so that when water is flowing through the tube side it is consumed instead of the other heat exchanger parts.

Range Temperature – The temperature difference of a single fluid as it flows through the heat exchanger.

Removable Bundle – A heat exchanger that has a removable tube bundle from the shell casing. This provides easy cleaning of the shell side and also a more feasible way of replacing depleted tubes.

Reversing End – The end of a multi-pass heat exchanger where the tube side fluid reverses its flow. This usually contains only small vent and drain connections.

Shell – The container where the tube bundle is placed and is the conduit for one of the fluids in the heat exchanger.

Shell Assembly – The assembly into which the tube bundle is placed. It also houses the shell side connections.

Shell Head – A formed plate that is welded to the shell (or bonnet) pipe. It comes in many styles and shapes, including flanged and dished, elliptical, ellipsoidal and hemispherical.

Shell Side – The part of a heat exchanger where the fluid circulates around the tubes.

Spacer – Tubing that holds the baffle plate in place.

Stacking – Two or more heat exchangers connected together side by side or one on top of the other. Interconnecting piping hooks them together.

Stationary Tube Sheet – The tube sheet at one end of a removable bundle that has a larger diameter than the floating tube sheet. The stationary tube sheet is held in a permanent position between the bonnet and shell flanges.

Stuffing Box Flange – A flange used at a packed end joint. When a packed joint is tightened, the packing ring is forced into this by the lantern ring/lantern gland.

Support Foot – Bolted to the heat exchanger using bonnet to shell flange bolting.

Test Pressure – Test that detects leaks on the joints of a heat exchanger.

Tie Rods – Bars mounted between the tube sheets to support the baffles.

Tie Tube – A tie tube takes the place of the tie rod in a small diameter heat exchanger, and serves the same purpose.

Tube – A flow channel for one of the fluids in the heat exchanger. These are often parallel within the shell to provide a large surface area for heat transfer.

Tube Layout – Shows the positioning of the tubes inside the heat exchanger and the locations of the tie rods.

Tube Sheet – The apparatus that the tubes are affixed into that holds them in place. It also provides a seal between the tube-side and shell-side liquid.

Tube Side – The fluid that circulates through the inside of the tubes of the heat exchanger.