Heat Exchanger World Magazine May 2023 | Page 29

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Tema Standards

This TEMA category , especially the NEN , is the lowest cost TEMA design per square foot of heat transfer surface .

Advantages

• Less costly than removable bundle designs

• Provides maximum amount of surface for a given shell and tube diameter

• Provides for single and multiple tube passes to ensure proper velocity

• May be interchangeable with other manufacturers of the same TEMA type limitations

Limitations

• Shell side can be cleaned only using chemical methods

• No provision to allow for differential thermal expansion ; an expansion joint on shell side must be used

Applications

• Oil coolers , liquid to liquid , vapor condensers , reboilers , gas coolers

• Generally , more viscous and warmer fluids flow through the shell

• Corrosive or high fouling fluids should flow inside the tubes

Removable bundle , externally sealed floating tubesheet - Type AEW , BEW This design allows for the removal , inspection and cleaning of the shell circuit and shell interior . A special floating tubesheet prevents intermixing of fluids . In most cases , a straight tube design is more economical than U-tube designs .

Advantages

• Floating tubesheet allows for differential thermal expansion between the shell and the tube bundle

• Shell circuit can be inspected and either steam- or mechanically cleaned

• The tube bundle can be repaired or replaced without disturbing the shell pipe

• Less costly than TEMA types BEP or BES which have an internal floating head

• Maximum surface for a given shell diameter for removable bundle design

• Tubes can be cleaned in AEW models without removing piping

Limitations

• Fluids in both the shell and tube circuits must be nonvolatile and non-toxic

• Tube side passes are limited to single or two-pass design

• All tubes are attached to two tubesheets . Tubes cannot expand independently , so large thermal shock applications should be avoided

• Packing materials produce limits on design pressure and temperature

Applications

• Intercoolers and aftercoolers , air inside the tubes

• Coolers with water inside the tubes

• Jacket water coolers or other high differential temperature duty

• Place hot side fluid through the shell with entry nearest the front end

Removable bundle , outside packed head - Type BEP , AEP This design allows for the easy removal , inspection , and cleaning of the shell circuit and shell interior without removing the floating head cover . A special floating tubesheet prevents intermixing of fluids . In most cases , a straight tube removable design is more costly than U-tube designs .

Advantages

• A floating tubesheet allows for differential thermal expansion between the shell and the tube bundle

• The shell circuit can be inspected and steam-cleaned . If the tube bundle has a square tube pitch , tubes can be mechanically cleaned by passing a brush between rows of tubes

• The tube bundle can be repaired or replaced without disturbing shell piping

• On AEP design , tubes can be serviced without disturbing tube-side piping

• Less costly than TEMA type BES or BET designs

• Only shell fluids are exposed to packing . Toxic or volatile fluids can be cooled in the tube-side circuit

• Provides large bundle entrance area , reducing the need for entrance domes for proper fluid distribution

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Heat exchanger types

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Typical floating head

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Typical kettle-type reboiler

Typical fixed tube sheet

Fig 2 : Parts identification in most common shell & tube exchanger types ( Source : Mihir ’ s Handbook of Chemical Process Engineering ).

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