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TEMA DESIGNATIONS OF HEAT EXCHANG ERS

Because of the number of variations in mechanical designs for front and rear heads and shells,

and for commercial reasons, TEMA has designated a system of notations that correspond to

each major type of front head, shell style and rear head.

The first letter identifies the front head, the second letter i dentifies the shell type and the third

letter identifies the rear head type.

REMOVABLE BUNDLE EXCHANGERS

Removable bundle exchangers give the customer the abili ty to replace the tube bundle without

replacing the shell or bonnets. They are generally less cost effective than non removable

designs.

BEU/AEU- U Bundle Exchangers are generally the most cost effective desi gn style of

removable bundle exchanger. Tubes may be water blasted, steam or chemically cl eaned.

These units must have an even number of tube passes, sometimes limiting their applicability

to a service(e.g. they generally can not be used wh en a temperature cross occurs).

CEU- This design has the tubesheet welded to the bonnet. You can remove the bundle from

the shell, however to replace the bundle, the inlet bonnet is included or you must cut off the

tubesheet. Tubes may be chemicall y cleaned, water blasted or steam cleaned.

BEW/AEW- These are strai ght tube units with one floating head and one stationary head. The

floating head is generally sealed with an O-Ring. These units are most often used as oil coolers

or air coolers. Cleaning can be performed either by chemical, mechanical method, water blast

or steam cleaning.

AEP/BEP- These are straight tube units with one inside packed fl oating head and one

stationary head. The floating head is generally sealed with packing. These units are most often

used as intercoolers and aftercoolers with the gas on the tube side. They are also the most

common style for oxygen service exchangers. These units have been used in services with

tube side design pressures in excess of 2000 PSIG.

AES/AET- These uni ts are the most expensive of the removable bundle designed units. The

floating head is internal to the shell. Tubes can be cleaned mechanically, chemi cally, water

blasted or steam cleaned. The design of these units forces an even number of tube side

passes therefore they suffer the same service restricti ons as U bundles. Al though i n theory

one pass unit can be designed, this is rarely done. These units are generally used in services

where U bundles are not desired and the service may be too corrosive/damaging to the

packing used in AEP/BEP units.

NON REMOVABLE BUNDLE EXCHANGERS

These types of units are often used in high pressure services and services where you wish to

avoid leakage problems at gasketed joints. Another advantage is that they are generally more

cost effective than removable bundle designs.

NEU- The most cost effective design available. The tubesheet is welded to both the shell and

bonnet. There is no access to the shell. Tubes may be chemically cleaned, water blasted or

steam cleaned from inside only. These units are commonly used in high pressure services

(such as feedwater heaters), where process conditi ons allow for even pass exchangers.

SOURCE: WWW.WERMAC.ORG/

Summary of content (6 pages)

PAGE 1
TEMA DESIGNATIONS OF HEAT EXCHANGERS Because of the number of variations in mechanical designs for front and rear heads and shells, and for commercial reasons, TEMA has designated a system of notations that correspond to each major type of front head, shell style and rear head. The first letter identifies the front head, the second letter identifies the shell type and the third letter identifies the rear head type.
PAGE 2
NEN- Tubesheets are welded to both the Shell & Bonnets. Access to the tubes is through covers on the channels. These units are favored in very high pressure designs as their construction minimizes the tubesheet thickness and number of high pressure retaining flanges. AEM/BEM/AEL-Shell side is completely welded up, however, the bonnets are removable. Chemical, mechanical, and water blast cleaning of the tubes is possible, however you do not have access to the shell.
PAGE 3
missing tubes result in larger annular spaces and can contribute to reduced flow across the effective tube surface, resulting in reduced thermal performance. Some designs include sealing strips installed in the shell to help block the bypass steam. Another floating head design that partially addresses the above disadvantages is a "split-ring floating head". Here the floating head bonnet is bolted to a split backing ring instead of the tubesheet.
PAGE 4
when the flow rate permits the use of one half of the shell at a time. In heat recovery applications, or where the application calls for increased thermal length to achieve effective overall heat transfer, shells can be installed with the flows in series. Up to six shorter shells in series is common and results in counter-current flow close to performance as if one long shell in a single pass design were used.
PAGE 5
TEMA J Shells are typically specified for phase change duties where significantly reduced shell side pressure drops are required. They are commonly used in stacked sets with the single nozzles used as the inlet and outlet. A special type of J-shell is used for flooded evaporation of shell side fluids. A separate vapor disengagement vessel without tubes is installed above the main J shell with the vapor outlet at the top of this vessel.
PAGE 6
The TEMA X shell, or crossflow shell is most commonly used in vapor condensing applications, though it can also be used effectively in low pressure gas cooling or heating. It produces a very low shell side pressure drop, and is therefore most suitable for vacuum service condensing. In order to assure adequate distribution of vapors, X-shell designs typically feature an area free of tubes along the top of the exchanger.