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Heat Transfer Terms
ASME to Zinc

American Society of Mechanical Engineers. The ASME Boiler and Pressure Vessel Code is a recognized and accepted standard throughout the world for the constructs of pressure vessels. The rules are formulated to provide minimum requirements for safety and serviceability and at the same time provide for reasonable and realistic costs.

Baffle Cut
Either 20%, 35%, or 45% of free area or percent of area cut off of the whole diameter baffle plate.

Baffle Plate
Also called support plate. A plate in which the tubes pass through for support. Also provides a blocked path for the shellside medium. This blocked path forces the shellside medium across the tubes providing better heat exchanger performance.

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

Bolt Circle
The circular dimension line on which bolt holes are drilled.

Bonnet Assembly
The name of a tube sheet exchanger part. It directs the tubeside medium for distribution through the tubes. It may also contain the tubeside inlet and outlet connections and/or pass ribs. It differs from a channel in the sense that it does not have a removable cover. See Channel Assembly and Waterbox.

Bundle Assembly
The name of the tubing assembly in removable bundle heat exchangers. It usually consist of tubes, tubesheets, baffles, spacers, and tierods. See Core Assembly.

The threaded bolt used to hold the bonnet onto the core of heat exchangers. Hex head capscrews may be used, but many different head types are available. Capscrews always have a head on one end with threads at the other.

Channel Assembly
See Bonnet Assembly and Waterbox. Performs same function as bonnet assembly. However, a removable cover permits access to the ends of the tubes.


Core Assembly
The name of the shell assembly and tube assembly in fixed tubesheet heat exchangers.

The name of a part which is used to connect customers's piping to heat exchangers. Couplings rarely exceed 3" sizes. Couplings come in many styles. The most used style are half couplings which we use for vent and drain pipe tap connections.

Cover/Cover Assembly
The name of the part which is used to cover an opening on a heat exchanger. Channel covers are used in conjunction with channels to seal off the tubeside of the heat exchanger. Nozzle covers can be used to cover nozzle openings to keep heat exchanger internals clean during shipping and storage. Covers are different from end plates in the sense that they can be removed from the heat exchanger to clean the interior of the tubeside, without disturbing any piping.

Cradle Assembly
The name of the part used to support the entire heat exchanger. Cradles may be fixed or moveable. Is also used to secure the heat exchanger to the customer's mounting surface, when they are welded or strapped to the shell.

Design Pressure
The pressure used by engineers to calculate part thickness and heat exchanger design. It is generally slightly higher than the most severe condition or highest operating pressures seen by the heat exchanger. Also called Maximum Allowable Operating Pressure.

The name of a type of nozzle connection. A dome provides a larger nozzle opening between the customer's pipe size and heat exchanger tube bundle, usually to prevent tube erosion due to high inlet velocities.

End Plate
End plates are covers which have been welded to the heat exchanger. Most end plates are used on bonnet assemblies.

End Zone
The first baffle space on a tube bundle. It is the space between the tubesheet and the first baffle plate. The end zone is adjusted to keep the baffle plates within the two shell side nozzles.

A small piece of tubing approximately 1 inch long made of copper or stainless steel. The ferrule is crimped or squeezed onto the tie tube, up against the last baffle, thus locking all the baffles into position.

Fixed Tubesheet
A non-removable tubesheet. The tubesheet on a core assembly. Any tubesheet that is an integral part of the shell assembly.

Floating Tubesheet
The tubesheet at one end of a removable tube bundle. The floating tubesheet will always have a smaller diameter than the stationary. The floating tubesheet is allowed to move freely with the expansion and contraction of the tube bundle due to temperature changes in operation.

A sealing device used in between two parts to prevent leakage. Types include inside the bolt circle, (no bolt holes) & full face, (has bolt holes, is as large as flange diameter).

The cast or forged part of a core assembly. The hub is made up of a tubesheet, shellside nozzle connection and vent/drain connections. The hub eliminates additional welding or brazing operations, therefore, making the exchanger less expensive.

Impingement Plate
A small perforated plate or bar assembly placed inside of the shellside nozzle, usually a dome type nozzle. They can also be attached directly to the bundle by being tack welded to the tierods. The impingement plate protects and prolongs the life of the tubes. The impingement plate breaks up and slows down the shellside fluid, which otherwise would erode the tubing.

In and Out End
The end of the heat exchanger which contains the tubeside inlet and outlet connections in a multi-pass unit.

Lantern Ring
A nylon or metal ring on some packed joint heat exchangers. The lantern ring fits over the outside diameter of the floating tubesheet between the packing rings. When the joint is tightened it holds the packing rings in place. The Lantern Ring also has small holes which act as leak detectors. The leak detectors let the customer know if one of the fluids is leaking around the packing rings. The fluids never mix.

Lap Joint Flange
These flanges are used to reduce the amount of an expensive material (S/S) required to make a flange. A steel ring is used in tandem with the more exotic material. The exotic material will be at the fluid contact surfaces or where the fluid touches the flanges. The steel ring contains the bolt holes.

A short piece of pipe threaded on both ends.

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

Outer Tube Limit
The O.T.L. is the diameter created by encircling the outer most tubes in a tube layout. The design O.T.L. is used by engineers to calculate clearances between bundle parts. The actual O.T.L. is usually a few thousandths less than the design O.T.L.

Packed End
The end of a heat exchanger which contains the packed joint. This packed joint contains the packing rings. It is also called the floating end of the unit, where the floating tubesheet is located.

Packing Ring
A fairly soft non-metallic ring which is used to seal the floating tubesheet or packed end of the heat exchanger. The packing ring slips over the floating tubesheet on either side of the lantern ring. It also fits into a groove in the shell and bonnet flange, or is held in place by retaining ring assembly.

Pass Lane
A lane in a tube layout where there are no tubes. The pass lane is the surface on the tubesheets where the pass ribs mate.

Pass Rib
A separator plate inside a bonnet or channel. This rib mates with the pass lane surface. It is used to create multi-pass heat exchangers. By arranging the ribs, a designer can control the flow of the tubeside medium.

Protector Rod
Also called a zinc. A sacrificial anode usually placed in the tubeside of a heat exchanger. The zinc protects the tubes, tubesheets and bonnets against corrosion. When water is flowing through the tubeside the zinc is consumed instead of the other heat exchanger parts.

Quad Layout
A quadrant type tube layout. Four separate quarters of a tube layout with pass lanes between them.

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

Retaining Ring Assembly
The retaining ring assembly performs the same job as a lantern ring. The retaining ring assembly eliminates the need for a stuffing box flange. See Lantern Ring.

Reversing End
The end of a heat exchanger where the tubeside fluid reverses its flow in a multi-pass unit. It usually contains only small vent and drain connections.

Ribbon Flow
A type of tube layout or pass rib pattern. Named because it creates an end to end flow which looks like a piece of ribbon candy.

Setting Drawing
The final assembly drawing of a heat exchanger.

Shell Assembly
The name of the assembly into which the tube bundle fits. The shell also contains the shellside connections.

Shell Head
A shell head is a formed plate which is welded to the shell (or bonnet) pipe. The shell head 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. See Tubeside.

Slip-On Flange
A type of nozzle flange. A slip-on flange slips over the nozzle pipe and is welded in place.

A piece of tubing that slides over the tie rod or tie tube between the baffle plates. The spacer holds the baffle plate in a permanent position.

Two or more heat exchangers which have been stacked together either side by side or one on top of the other. These units have interconnecting piping hooking them together.

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

Stub End
A stub end is the fluid contact surface used with a lap-joint flange.

Stud/Stud Bolt
A stud bolt is used to hold two or more pieces together. It is threaded the full length (T.F.L.) and fits through bolt holes which are not tapped. A hex nut is used on both ends. A stud is similar to studbolt except it threads into a tapped hole and a hex nut is used on one end only.

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

Support Foot
See Cradle Assembly. A support foot is usually bolted to the heat exchanger using the bonnet to shell flange bolting.

Tubular Exchange Manufacturer's Association. The TEMA Standards cover the design, manufacture, installation, operation, and maintenance of shell and tube heat exchangers. TEMA C is for generally moderate requirements of commercial and general process requirements. TEMA B is for chemical process services. TEMA R generally serves requirements of petroleum and related processing applications.

Test Pressure
Generally 1.5 times the design pressure. The pressure used during a hydrostatic test. The test is made to detect leaks at any joint on the heat exchanger.

Tie Rod
A small diameter rod which threads into the stationary end tubesheet. This rod ties the baffles and spacers together.

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

Tube Layout
The tube layout drawing shows the positioning of the tubes inside the heat exchanger. It also shows the locations of the tierods.

The tubesheet is a plate that secures both ends of the tube in a heat exchanger. Both the shellside and tubeside mediums come in contact with it.

Tube Side
The side of a heat exchanger where the fluid circulates through the inside of the tubes. See Shell Side.

Water Box
See Bonnet Assembly and Channel Assembly. Another name for bonnet or channel.

Weld Neck Flange
A type of nozzle flange. A weld neck flange is used when a butt weld is required. This means the end of the flange butts up against a piece of pipe, both the flange and the pipe are bevelled. The joint provides sound weld with no overlapping of parts.

See Protector Rod.

1,2,4 Pass
The number of times the fluid passed 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 1 Pass is referred to as a multi-pass unit.

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